ALBERT

Description: We propose mode couplers and converters based on dual-core hollow-core photonic bandgap fiber (HC-PBGF) structures, which might be potential solutions for integrated all-fiber multiplexers or demultiplexers of a mode-division multiplexed (MDM) transmission system using HC-PBGFs. Coupling properties of ${text{LP}}_{01}$ and ${text{LP}}_{11}$ mode in the mode coupler are investigated and applied to mode separators and polarization separators. Mode transition from ${text{LP}}_{01}$ to ${text{LP}}_{11}$ and ${text{LP}}_{21}$ mode are demonstrated in the mode converter whose smaller core is expected as input end and matched with single-mode fiber. The coupling between fundamental mode and high-order modes is accomplished through the resonant effect, which is fulfilled by modifying the structure parameter of the smaller core. Such mode converters based on dual-core HC-PBGF could be a promising substitute for the free-space coupling device, which is costly and not suitable for integration design in MDM systems and other hollow-core fiber experiments and applications.

Description: Interferometric lithography with curved wavefronts produces chirped gratings. The chirp can be longitudinal, with the periodicity changing along the grating wavevector, or transverse, with the periodicity changing in the perpendicular direction. The chirp is investigated for a range of configurations, and specific optical systems to generate a wide range of grating chirp parameters are analyzed.

Description: We demonstrate a Gb/s real-time visible light communication (VLC) system based on NRZ-OOK by a phosphorescent white light-emitting diode (LED). We propose an equalizer employed by an RC series-parallel connection cascade circuit based on the T-bridge structure. With the proposed circuit, the 3-dB bandwidth of the VLC system can be extended from 1 to 520 MHz. The Bit Error Ratio (BER) of the system was $7.36 times 10^{-4}$ , and the data rate was 1 Gb/s at a distance of 1.5 m. To the best of our knowledge, this is the highest real-time data rate and 3-dB bandwidth achieved based on a white LED.

Description: We present electroabsorption modulators integrated with distributed feedback lasers (EMLs) fabricated by a simple method, which combines the advantages of the selective area growth and double stack active layer techniques. The obtained EML device has a threshold current as low as 16 mA and optical power of larger than 10 mW at 85 mA laser current. Quite low chirp parameter of the fabricated EMLs is obtained. Negative chirp parameters can be obtained at only about 0.5 V reverse bias voltage. Open eye diagrams are demonstrated from the EML at both 10 and 20 Gb/s modulations with the driving voltage of only 0.65 V while securing high dynamic extinction ratio. The exhibited performance makes our device a very promising candidate as a simple light source in long distance and cost sensitive applications.

Description: In this paper, a broadband wireless optical nanolink with plasmonic optical nanoantennas is theoretically proposed and analyzed. The nanolink is formed by linear dipole-loop nanoantennas for transmitter and receiver. The analysis is performed using the linear method of moments with equivalent surface impedance, where we apply a voltage source in the transmitting antenna and connect a load in the receiving antenna. The power received in the load is investigated as a function of frequency and distance between transmitter and receiver. In addition, a comparison is made between this wireless nanolink with a bifilar optical transmission line. The results show that the proposed nanolink, with dipole-loop nanoantenna, can increase the operating bandwidth in the range of 179.1–202.5 THz, when compared with conventional nanolink based only on dipole antennas. In addition, wireless nanolinks, based on dipole or dipole-loop antennas, are more suitable than wired nanolink for distances above approximately 22 μm.

Description: One of the main challenges in establishing a robust visible light communication (VLC) link is to prevent optical interference produced by other light sources from corrupting the signal. Previous solutions catering for this issue assume that optical interference and the signal operate in nonoverlapping frequency bands. This paper presents an innovative transceiver architecture for establishing a frequency-independent interference-tolerant VLC link. The transmitter exploits the polarization property of light to transmit differential signals over adjacent channels, and the receiver utilizes differential amplification in conjunction with polarization to implement a common noise rejection technique. The implemented system demonstrated a 32.6% more robust VLC link compared to the conventional transceiver under severe optical interference.

Description: We experimentally demonstrate a thermally induced reflective optical limiter using Ge $_2$ Sb $_2$ Te $_5$ (GST) and SiO $_2$ in a multilayer photonic bandgap edge-filter configuration. In the PASS state, greater than 80% transmission was achieved at $lambda sim 1500$  nm over a 300 nm spectral bandwidth and $pm 45^{circ }$ angles of incidence. In the BLOCK state, extinction ratios higher than 30 dB were achieved. By comparison, all previous optical limiters based on nonlinear photonic crystals have severe spectral bandwidth and/or angle of incidence limitations in either the PASS or BLOCK states. A nine-layer implementation of this device was fabricated and tested in this paper. Numerical modeling results show reasonable agreement with measured values. To the best of our knowledge, this is the first demonstration of optical limiting over a broad spectral band using phase change materials with this level of performance. However, it should be noted that although GST can be switched in both directions, the experimental results demonstrated in this paper are limited to PASS-to-BLOCK switching only.

Description: Families of vortex-like and Gaussian-like localized Airy wave packets, propagating in a self-defocusing Kerr medium, are discovered. Their propagation is described by the cylindrical Korteweg–de Vries (CKdV) equation, reduced from the nonlinear Schrödinger equation by utilizing the reductive perturbation technique. The CKdV equation is solved using the Hirota bilinear method to obtain analytical Airy wave packet families of different order. In particular, we focus on the distribution of optical intensity via numerical simulations of the Airy wave packet solutions, obtained for different initial phases and amplitudes, at given propagation distances. In distinction to the usual ring solitons, the Airy wave packets display a novel internal structure, which reveals novel nonlinear phenomena during the propagation of packets.

Description: Complementary metal-oxide-semiconductor (CMOS) sensor based visible light positioning (VLP) has been widely studied in recent years due to its high robustness and high precision. In most researches about CMOS sensor based VLP, researchers always focus on the high-precision positioning algorithm but ignore that the accuracy of LED-ID detection and recognition plays a more important role in a VLP system. Without the correct recognition of LED-ID, the positioning algorithm would be meaningless no matter how effective it is. In addition, high-precision positioning is not required in most applications since it is enough for people to know just the approximate location. To solve these problems, in this paper, an LED-ID detection and recognition method based on visible light positioning using proximity method is propose. Different from the traditional LED-ID coding and decoding method, we create different features for different LED-ID, and use a machine learning method to identify the LED-ID once the feature extraction and selection of the LED image is achieved with an image processing method. It is the first time the machine learning method is used for LED-ID recognition in VLP. Moreover, we use a proximity-based positioning method to get the approximate location since it is easy to obtain once the LED-ID is recognized. The studies we have demonstrated shows that the proposed method can achieve high LED-ID recognition rate, and provide enough unique LED-ID for variable large-scale indoor VLP system. Furthermore, with the development of camera technology, the number of the unique LED-ID and the maximum recognizable distance would increase. Therefore, this scheme may be considered as one of the useful LED-ID detection and recognition method for visible light positioning in the future.

Description: Precise time-difference detections among different radars in uplink radar arrays require ultrastable phase transfer in bidirectional analog optical fiber links. We propose and demonstrate a scheme based on passive frequency mixing to satisfy this requirement in which two continue wave (CW) radio frequency (RF) signals after passing through double-path of the transport fiber are utilized for dynamic phase fluctuation cancellation in uplink and downlink, respectively. Our scheme has the capabilities on stable phase transfers for both CW and pulsed RF signals. Experimental results show that the phase stability improvements in uplink and downlink are greater than a factor of 30 and a factor of 20 for 2.4-GHz RF signals over a 2-h measurement period along 25-km single mode fiber.

Description: We numerically report designs of color filters comprising of 2-D photonic crystal (2D-PhC) slabs of square lattice of air holes. The filter principle is based on excited Fano-like guided-mode resonances (GMRs) in the visible regime with high-quality factor ( Q -factor) and low reflection sidebands. The 2D-PhC slab architecture influence on its spectroscopic property is comprehensively investigated. We introduce an alternative PhC lattice, which is formed by introducing an additional hole in each unit cell to enhance the light confinement in the waveguide slab, as such the induced Fano-like GMRs’ Q -factor is significantly increased about two orders of magnitude compared to the traditional PhC without additional holes. At Fano-like GMRs, two in-plane waves oscillate toward the opposite directions with a phase difference of π . The radiated fields of these waves strongly cancel each other in the far field, and the coupling between the waveguiding slab and the incident light is dramatically reduced resulting in the high Q -factor of the Fano-like GMR in the introduced PhC slab. As a result, the 2D-PhC slab excited Fano-like GMRs in this work may find fascinating applications in optical filters, optical imaging, optical switching, and so on.

Description: The improved performance of Si quantum dot-based silicon nitride light-emitting devices with the inserted hole-blocking nc-Si layer was investigated. An enhanced electroluminescence (EL) efficiency of 200% from the SiN x -based LEDs is demonstrated through H 2 plasma treatment of the inserted nc-Si layer. The enhancement of an EL efficiency is depended on time for plasma treatment. Moreover, the injected current of the devices with H 2 plasma treatment is significantly higher than that of the device without H 2 plasma treatment under the same driving voltage. The Z-parameter of the devices increases from 1.25 to 1.41 after H 2 plasma treatment of inserted nc-Si layer. The inserted nc-Si layers with and without H 2 plasma treatment were further investigated by the Raman spectroscopy and the Fourier transform infrared absorption spectroscopy, respectively. It is suggested that the improved EL efficiency is due to the suppression of nonradiative recombination, which resulted from the hydrogen passivation that effectively reducing Si-related defect states of the inserted nc-Si layer.

Description: A 128 Gbit/s free-space laser link demonstration has been presented. We use a simulated atmosphere system with a tunable 1 km equivalent weak turbulence channel. Eye diagrams and constellation diagrams were observed. Bit error rate curves of back to back transmission and that in a simulated atmospheric channel are measured. The results show that the receiving sensitivities can be better than –37.3 dBm at the rate of 128 Gbit/s in a turbulence channel. To the best of our knowledge, it is the first time that the transmission performance of high speed space laser in a tunable atmospheric channel is studied.

Description: Organic light-emitting diodes (OLEDs) show several attractive features superior to traditional semiconductor LEDs for visible light communication (VLC). This paper experimentally tests and models the radiation pattern of a bent OLED panel for the first time. Different from a Lambertian radiation pattern, we propose an improved analytic mixed Gaussian model to describe the rotational radiation asymmetry, whose parameter values are found by applying an expectation-maximization algorithm for curve fitting with measurements. The OLED radiation pattern is observed to show strong directionality along the bent axes. Its impact on VLC channel characteristics is further studied. Compared with the Lambertian source, the OLED source is more flexible in radiation pattern control and shows advantages in smaller root mean square delay spread and optical path loss.

Description: A new design of radially polarized surface-emitting laser (RPSEL) is presented for the first time. RPSEL which has a second-order grating shallowly etched on top of a microcylinder cavity is easy to fabricate. The grating selects a specific whispering-gallery mode with the proper emission pattern (radially polarized emission) to lase and simultaneously scatters the mode vertically to form the surface emission. Through numerical simulations, RPSEL is predicted to be a single-mode laser with radially polarized surface emission. RPSEL can be rather easily realized at different wavelengths such as the near infrared 1310 and 1550 nm wavelength bands. Furthermore, it can be fabricated with microcylinder cavities with very small radii even down to wavelength-scale, therefore it has the potential to realize very high modulation bandwidth and very low threshold current.

Description: An approach based on a comprehensive, unified model for fiber laser and amplifier systems is used in the design of high-power, high-energy systems. With guidance from the model, a chirally coupled-core Yb-doped fiber amplifier system is constructed. We use a two-stage system comprised of a 2.5-m long fiber preamplifier and a 3.0-m long fiber booster amplifier to illustrate the method. This compact system is capable of generating outputs of up to 1.2 mJ for 25-ns pulses at a repetition rate of 100 kHz, with average power of up to 121 W, and a slope efficiency of 82%.

Description: A distributed Bragg reflector (DBR) composed of Y 2 O 3 -doped HfO 2 (YDH)/SiO 2 layers with high reflectivity spectrum centered at a wavelength of ∼240 nm is fabricated using radio-frequency magnetron sputtering. Before the DBR deposition, optical properties for a single layer of YDH, SiO 2 , and HfO 2 thin films were studied using spectroscopic ellipsometry and spectrophotometry. To investigate the performance of YDH as a material for the high refractive index layer in the DBR, a comparison of its optical properties was made with HfO 2 thin films. Due to larger optical bandgap, the YDH thin films demonstrated higher transparency, lower extinction coefficient, and lower absorption coefficient in the UV-C regime (especially for wavelengths below 250 nm) compared to the HfO 2 thin films. The fabricated YDH/SiO 2 DBR consisting of 15 periods achieved a reflectivity higher than 99.9% at the wavelength of ∼240 nm with a stopband of ∼50 nm. The high reflectivity and broad stopband of YDH/SiO 2 DBRs will enable further advancement of various photonic devices such as vertical-cavity surface-emitting lasers, resonant-cavity light-emitting diodes, and resonant-cavity photodetectors operating in the UV-C wavelength regime.

Description: In this paper, with the aids of the Monte Carlo simulations, we have investigated the depolarization performances of circularly polarized light (CPL) and linearly polarized light (LPL) transmitted in homogeneous scattering media systems. The depolarization performances depend on the number density, refractive index, and the concrete size distributions of scattering particles. Here, we mainly investigate the mixed ratio and distribution effect of scattering particles on the depolarization performances of CPL and LPL, respectively. The simulation results show that there exist larger mismatches in the depolarization performances between monodisperse and polydisperse scattering systems, and with increasing small particles’ proportion the degree of linear polarization decreases slightly, but the degree of circular polarization decreases drastically. When the size distribution of scattering particles obey the logarithmic normal distribution, the simulated results show that the propagation behavior of the incident light in a polydisperse medium system with standard deviation of $sigma = text{0.1} mu{rm {m}}$ can be modeled very well by the corresponding monodisperse medium system with the mean value, however, the approximation will fail for a scattering medium with larger standard deviation of $sigma = text{0.5} mu{rm {m}}$ . These results demonstrated that the depolarization behavior of light was sensitive to the mixed ratio or the distribution state of particles, which was significant to the polarization engineering, such as polarization imaging and polarization based communications.

Description: We present a detailed study of the effect of large optical cavity (LOC) waveguide design on the laser's kink performance and it was found that a multimode waveguide in the epi growth direction could lead to the occurrence of the power kink in the light–current ( L–I ) curve, and the occurrence of the power kink was accompanied with the broadening of the beam divergence in the wafer growth direction. In order to eliminate the kink issue that is associated with the lasing of the higher-order modes, a new type of waveguide, which is called higher-order-mode tunneling waveguide, was proposed in our design. The new type of waveguide can strongly promote the leakage of higher-order modes, and in this way, the LOC waveguide becomes single-moded. Test of the fabricated devices based on the new design showed that the devices indeed exhibited perfect L–I linearity without kinks.

Description: We present data transmission using a directly modulated distributed Bragg reflector (DBR) laser having an integrated Ti thin film heater in the DBR section and butt-jointed InGaAsP as DBR material. By combining DBR current tuning and thermal tuning effects, an over 16 nm wavelength tuning range is obtained. 5 Gb/s data transmissions are conducted at up to 25 km distance and different wavelengths. In the fabricated device, the butt-jointed InGaAsP material is also used for the formation of an integrated photodiode for monitoring the light power of the device.

Description: We demonstrate a compressive normalized ghost imaging system with entangled photons employing complementary compressive imaging (CCI) technique. The quantum ghost image reconstruction was achieved with 19.53% sampling ratio of raster scanning and average 0.78 photons/pixel of each measurement. Using the special +1/−1 type sensing matrix and appropriate optimal algorithm, the photon utilization efficiency, and robustness of the imaging system is enhanced significantly. Our results reveal the great potential of CCI technique applied in quantum imaging and other quantum optics field such as quantum characterizing and quantum state tomography to use the information loaded in each photon with high efficiency.

Description: The generation of optical beams with multiple, mutually coherent orbital-angular-momentum (OAM) modes using phase gratings is analyzed from the perspective of energy distribution and radial mode composition. We show that phase gratings designed with equally weighted Laguerre–Gauss (LG) modes will generate beams with uneven energy distribution among OAM components. This unwanted outcome cannot be corrected by adjusting the width of the illuminating beam. We propose a way to design phase gratings that will produce a uniform energy distribution among the constituent OAM states after illumination while minimizing the content of high radial modes. This method is based on a generalized definition for the LG modes that take advantage of the freedom to select their radial scales.

Description: In this paper, we propose a microdisk resonator with negative thermal optical coefficient (TOC) polymer for refractive index (RI) sensing with thermal stability. The transmission characteristics and sensing performances by using quasi-TE 01 and quasi-TM 01 modes are simulated by a three-dimensional finite element method. The influences of the TOC, RI, and thickness of the polymer on the sensing performances are also investigated. The simulation results show that the RI sensitivity S n and temperature sensitivity S T with different polymers are in the ranges of 25.1–26 nm/RIU and 67.3–75.2 pm/K for the quasi-TE 01 mode, and 94.5–110.6 nm/RIU and 1.2–51.3 pm/K for the quasi-TM 01 mode, respectively. Moreover, figure-of-merit of the temperature sensing for the quasi-TM 01 mode is in the range of 2 × 10 −4 –8 × 10 –3 , which can find important application in the implementation of the adiabatic devices.

Description: Geiger-mode avalanche photodiode (Gm-APD) offers 3D imaging lidar much better capability in terms of detection sensitivity. However, a range walk error (RWE) exists in Gm-APDs which refers to the fluctuation of the measured distance as a function of the intensity of echo pulses. In this paper, we present a real-time restraint method for RWE implemented by unequally intensity-dividing the echo pulses into two Gm-APDs. The difference image of two depth images measured by the divided beams is a matrix of RWE distribution and the intensity image is used to censor the anomalous pixels in the matrix. Combined with the matrix of RWE distribution, an accurate depth image with low RWE can be obtained. Experimental results demonstrate that the proposed method reduces approximately 86% RWE of the conventional method in real time.

Description: We report on the lasing action in weakly modulated parity-time (PT) symmetric lattices. At the exceptional point in PT-symmetric lattices, the amplitude and phase of unidirectionally scattered waves are independently and flexibly determined by the PT modulations, thus, providing a distinctive route to construct a lasing mode in finite systems with weakly modulated structures. It is revealed that the resonant feedback mechanism plays a crucial role in building up the lasing action. Our finding would enrich the singularity dynamics in the weakly modulated PT systems.

Description: The paper introduces a 24-channel air-trench isolated Silica-based VOA array. The air trenches thermally insulate the VOAs with etched-free waveguide technologies. Reactive ion etching and wet etching were used at different channel locations to suppress thermal crosstalk and reduce power consumption. When thermal crosstalk is declined by 3 dB for the straight waveguide, the power consumption was decreased from 195 to 95 mW because the lightwave radiation can be scattered by the air trench in the dark state. This crosstalk is improved by 9 dB for the curved waveguide. The polarization dependent loss falls down to 0.28 dB at 15 dB attenuation since the air trench and etched-free waveguide also releases the stress.

Description: Group-III nitride-based ultraviolet (UV) quantum-disks (Qdisks) nanowires (NWs) light-emitting diodes grown on silicon substrates offer a scalable, environment-friendly, compact, and low-cost solution for numerous applications in solid-state lighting, spectroscopy, and biomedical. However, the internal quantum efficiency, injection efficiency, and extraction efficiency need to be further improved. The focus of this paper encompasses investigations based on structural optimization, device simulation, and device reliability. To optimize a UV-A (320–400 nm) device structure, we utilize the self-assembled Qdisks NWs with varying Qdisks thickness to study carrier separation in active-region and implement an improved p-contact-layer to increase the output power. By simulation, we found a 100× improvement in the direct recombination rate for samples with thicker Qdisks thickness of ∼5 monolayers (MLs) compared to the sample with ∼2 MLs-thick Qdisks. Moreover, the sample with graded top Mg-doped AlGaN layer in conjunction with thin Mg-doped GaN layer shows 10× improvement in the output power compared to the samples with thicker top Mg-doped GaN absorbing contact layer.  A fitting with ABC model revealed the increase in nonradiative recombination centers in the active region after a soft stress test.  This paper aims to shed light on the research efforts required for furthering the UV NWs LED research for practical applications.

Description: Nano-groove arrays incorporated into a freestanding GaN membrane are proposed for coupling with visible light. The coupling of transverse electric mode light over the entire visible wavelength region into and out of the planar membrane is thoroughly investigated herein by performing a finite element method analysis. Coupling can be regulated by device parameters such as groove depth, membrane thickness, grating period, and duty cycle. Single-band coupling featuring tunable coupling bands can be realized, with the peak dual coupling efficiency reaching 0.55. This study paves the way for realizing planar photonics devices at specific single wavelengths. The proposed device is a suitable candidate for use in optical filters, de-multiplexers, planar photonic sensors, and other devices.

Description: A novel method of pixel reassignment (PRA) is proposed to achieve transverse superresolution in the confocal microscopy. Inspired by it, for the first time, we report a pixel-reassigned spectral-domain optical coherence tomography (OCT) with $sim$ 1.5 times transverse resolution improvement both in numerical simulations and imaging experiments. PRA is implemented by transversely shifting the detection fiber from the on-axis position to five off-axis positions, capturing cross-sectional images at each shifting step of the detection fiber and digitally reassigning them together to give a sharper image with moderately extended depth of focus and enhanced intensity. So, we believe that the PRA technique will improve the imaging performance and be beneficial to the development of the OCT community.

Description: A three-dimensional dual-band perfect absorber in the THz range (3–10 THz) is theoretically investigated. The absorber is composed of periodically placed cross- and disk-shaped graphene arrays on the top of a gold layer separated by a thick SiO $_{2}$ dielectric spacer. The simulated results show two absorption peaks with near-unity absorbance ( $99.923%$ and $99.601%$ ) at wavelengths 43.747  $mu$ m and 69.94  $mu$ m, respectively. Also, the absorber is insensitive to the polarization of the incident light and has a good tolerance to the incident angle whether it is TE or TM waves. Moreover, the peak wavelengths of the absorber can be flexibly modulated by varying the Fermi level $mu _{C}$ of graphene while no need to refabricate the structure. This paper provides a new perspective for the design of graphene-based tunable multiband perfect THz absorbers, but not limited to THz absorbers, and may also be used in other THz graphene-based photonic devices.

Description: We reported on the soliton booting dynamics of an ultrafast fiber laser operating in an anomalous dispersion regime. Based on the advanced experimental methodologies of spatio-temporal reconstruction and dispersive Fourier transform (DFT), the soliton booting dynamics are analyzed in the time and spectral domains. The spectral interference pattern with strong intensity oscillation behavior was observed near the mode-locking transition. It was found that the spectral pattern distributions are induced by the transient structured soliton formation during the pulse shaping from the noise background. The experimental results were further verified by the theoretical simulations. The obtained results would provide a general guideline for understanding the soliton booting dynamics in the ultrafast fiber lasers, and will prove to be fruitful to the various communities interested in solitons and fiber lasers.

Description: We propose a method of computational temporal ghost imaging over a single optical fiber using simple optical intensity detection instead of coherent detection. The transfer function of a temporal ghost imaging system over a single optical fiber is derived, which is a function of the total fiber dispersion and the power density spectrum of the light source. In the simulations, we find that the bandwidth of the transfer function will decrease rapidly along with the increase of fiber length or light source bandwidth, resulting in a significantly distorted ghost image. To improve the image quality, we first calculate the transfer function by approximating the optical spectrum of the light source based on intensity detection as its power density spectrum. Then, we use an optimized Fourier deconvolution to compute a high-quality image by deconvoluting the measured transfer function from the spectrum of the distorted image. Our experiments achieve single-arm ghost images of a 5-Gb/s nonreturn-to-zero pulse object over a 200-km fiber, which have almost the same quality as the two-arm ones.

Description: A secure key distribution scheme for orthogonal frequency division multiplexing (OFDM) passive optical network system is proposed and experimentally demonstrated. The training symbol (TS), which is used for time synchronization and channel estimation, is formed by adopting a noise-like chaotic sequence. The redundancy of the TS is utilized to embed secure keys. An experiment is performed, in which 7.64 Gb/s 16-quadrature-amplitude-modulation OFDM data and 28.4 Mb/s keys embedded in are successfully transmitted over 25 km standard single mode fiber. The results indicate a promising key distribution method for physical layer secure optical communication.

Description: An indium phosphide-based monolithic integrated chip with semiconductor optical amplifiers and a tunable delay interferometer (DI) is developed. Because of the comb filtering characteristics of DI, this chip has the potential to be used for multichannel all-optical signal processing functions in dense wavelength-division-multiplexed networks. In this paper, four-channel all-optical format conversion simultaneously from nonreturn-to-zero to return-to-zero at 40 Gb/s with a power penalty of less than 0.5 dB is demonstrated as a validation based on this chip.

Description: This paper presents an experimental demonstration of bidirectional 4-PAM transmission for intra-datacenter links using a pair of SMF fibers. In the proposed architecture, each transceiver laser feeds both fibers, which are thus used bidirectionally to double the capacity per used fiber, wavelength, and laser. Besides the experimental demonstration, we also report a theoretical and simulative investigation on the penalty induced in this architecture by spurious connector back-reflections. We show that the resulting penalty can be kept under control for typical realistic connector reflection values, provided that each pair of lasers in both directions are separated by at least twice the system symbol rate.

Description: Delay-division-multiplexing (DDM) involves the use of signal preprocessing for the detection of data via sub-Nyquist analog-to-digital sampling, based on preallocated relative sampling delays among optical network users (ONUs) in an orthogonal frequency-division multiplexing (OFDM) passive optical network (PON). If a DDM-PON consists of $M$ virtual groups, the sampling rate at the receivers is only $1/M$ of the Nyquist rate, but the maximum capacity of each ONU is fixed at $1/M$ of the total capacity. In this study, we developed a novel DDM scheme that uses hybrid sub-Nyquist sampling rates to accommodate heterogeneous services of different capacities in an OFDM-PON. To equalize the transmission performances using hybrid sub-Nyquist sampling rates, the modification of preprocessing was proposed, and its necessity was demonstrated. Without loss of generality, we experimentally demonstrated a 25-Gbps DDM-OFDM-PON using hybrid sampling at 1/2, 1/8, and 1/32 (or 1/8, 1/16, and 1/32) of the Nyquist rate. Compared to a DDM-PON with a fixed sub-Nyquist rate, the received signals based on hybrid sub-Nyquist sampling rates show similar sensitivities. A loss budget of 26 dB was experimentally achieved using all sub-Nyquist sampling rates after employing the modified preprocessing.

Description: We report a self-injection-locked InAs/InP quantum-dash tunable laser with ∼11 nm (∼1602–1613 nm) tuning window for next generation multiuser ultrahigh capacity fiber/free-space optics (FSO)/hybrid fiber-FSO-based optical networks. A tunability of >18 independently locked subcarriers with ∼28 dB side mode suppression ratio (SMSR) and stable (±0.1 dBm) mode power is exhibited, and an estimated small injection ratio of ∼–22 dBm is found to sustain locking and SMSR. Error free transmission of 100 and 128 Gb/s externally modulated dual-polarization quadrature phase shift keying (DP-QPSK) signals over 20 km single mode fiber (SMF) and 16 m indoor FSO links are demonstrated across 8 and 4 individual subcarriers, respectively, thus covering the entire tuning range. Moreover, up to 168 (192) Gb/s successful transmission over 10 km SMF (BTB) and 176 Gb/s over 16 m FSO link is achieved on a ∼1610 nm subcarrier. Finally, a 128 Gb/s DP-QPSK transmission over 11 km SMF–8 m FSO–11 km SMF hybrid system is accomplished, thus paving the potential deployment of this single-chip, cost-effective, and energy efficient tunable light source in terabits/s next-generation passive optical networks.

Description: An efficient method based on a hybrid approach that combines extreme learning machine (ELM) technique and differential evolution (DE) algorithm is proposed to optimize the multipumped Raman fiber amplifier (RFA). The proposed method takes advantage of the fast learning speed and high generalization of the ELM as well as the strong global search capability of DE. From a novel perspective, we utilize ELM as a powerful learning tool to construct the nonlinear mapping between the pump parameters and gains of RFA. Instead of time-consuming integration of Raman coupled equations, the gains can be directly and accurately determined by the ELM model. To obtain a flat gain spectrum, DE algorithm is employed to find the optimal wavelengths and powers of pumps. The well-trained ELM model is incorporated into the evolution of DE to accelerate the search process. The results show that the designed RFAs with the optimized pump parameters achieve the desired gain performance and meanwhile maintain very low level of gain ripple. In comparison to other related methods, the proposed method significantly shortens the computation time and enhances the overall optimization efficiency, which offers potential for real-time adjustment and flexibility of RFA design.

Description: The transverse focal shift (TFS) is a phenomenon that the maximum of a focused field does not occur at the geometrical focus, but is moved a short distance transversely in the focal plane. In this paper, the TFS of vortex beams in a high numerical aperture system is investigated. Four typical types of incident vortex beams are selected and the intensity distributions and the vortices behaviors in the focal region are discussed analytically and numerically. It is found that there are three main parameters, the topological charge, the initial positions of the vortices, and the semiaperture angle influencing the TFS in different ways, and the TFS even can be observed when the vortices annihilate in the focal plane. Our results also show that the intensity maximum can move from the $y$ -axis, $x$ -axis to the geometrical focus, or move from $+y$ -axis to $-y$ -axis in different cases, which may have implications in optical trapping.

Description: Generally, the plasmonic Fano resonances can be divided into two types: the electric and the magnetic Fano resonance. Compared to pure electric or magnetic multiple Fano resonances, the mixed electric/magnetic multiple Fano resonances provide more flexibility for their application in multiwavelength surface enhanced Raman scattering and biosensing. Whereas, the dramatic difference between the two Fano resonances makes it difficult to realize magnetic and electric Fano resonances together in the same structure. In this paper, magnetic-octupole mode based Fano resonance and electric-quadrupole mode based Fano resonances in optical frequency were together achieved in a combined square-shaped split-ring resonator with an internal square nanoantenna nanocavities. The two Fano resonances are switchable by adjusting the polarization of the incident light. The lineshape modulated by the geometry and the environment of the two Fano resonances was investigated. Both the Fano resonances show high sensitivity to the environment. This study reveals a new multiple Fano resonance constitution and the proposed structure, which are expected with benefit application in multiwavelength polarization modulated chemistry and biological sensing.

Description: A distributed vibration-sensing system based on phase-sensitive optical time-domain reflectometry (Φ-OTDR) and distributed feedback interferometer (DFI) with broadband frequency response and high spatial resolution has been proposed and demonstrated. A couple of narrow line-width lasers with different wavelengths were used to form the light source, which were consistent with two channels of dense wavelength division multiplexer. Both functions of Φ-OTDR and DFI could work synchronously without influence between each other. The characteristic of broadband frequency disturbance event could be fully captured and identified by the DFI, while the corresponding location could be determined by the Φ-OTDR scheme. Unlike ordinary interferometer, the proposed DFI scheme could make single-end monitoring without the installation of extra accessories. Furthermore, broadband frequency response range and precise locating of the disturbance event could be achieved at the same time. Experimental results have shown that spatial resolution of 10 m and frequency response up to 1 MHz have been obtained over 2.16-km-sensing fiber, which have proved the validity of the proposed method.

Description: We demonstrate the design, fabrication, and the experimental characterization of gold-based plasmonic stripes butt-coupled with low-pressure-chemical-vapor-deposition (LPCVD)-based Si 3 N 4 waveguides for the excitation of surface-plasmon-polariton (SPP) modes in aqueous environment. Plasmonic gold stripes, in aqueous environment, with cross-sectional dimensions of 100 nm × 7  μ m were interfaced with 360 nm × 800 nm Si 3 N 4 waveguides cladded with low-temperature-oxide, exploiting linear photonic tapers with appropriate vertical (VO) and longitudinal (LO) offsets between the plasmonic and photonic waveguide facets. An interface insertion loss of 2.3 ± 0.3 dB and a plasmonic propagation length ( $L_{{rm{spp}}}$ ) of 75  μ m have been experimentally measured at 1.55  μ m for a VO of 400 nm and an LO of 500 nm, with simulation results suggesting high tolerance to VO and LO misalignment errors. The proposed integration approach enables seamless co-integration of plasmonic stripes, in aqueous environment, with a low-loss and low-cost LPCVD-based Si 3 N 4 waveguide platform, revealing its strong potential for future employment in biochemical sensing applications.

Description: A microcavity laser is reported using dye-doped cholesteric liquid crystals (CLCs) filled in a glass capillary with photo-alignment polyimide films. This laser runs based on the properties that a CLC has a refractive index much higher than that of glass, so whispering-gallery-mode (WGM) laser and distributed-feedback-mode lasers are included in the emission spectrum. We obtain a low threshold energy of $4.5;mu {rm{J}} cdot {rm{puls}}{{rm{e}}^{ - 1}} cdot {rm{m}}{{rm{m}}^{ - 2}}$ , establish the shift of 3.04 nm of the WGMs in the temperature range 43–48 °C, and investigate electric field tunability.

Description: We report on a passively mode-locked thulium-doped fiber laser (TDFL) with dual operation regimes and applications in cascaded Raman light and supercontinuum generation. The mode-locking is initiated by using a semiconductor saturable absorber mirror (SESAM) and can operate at both fundamental mode-locking and noise-like twin-pulse regimes. Output power can be scaled up through two-stage amplifications, and then was further fed into a segment of ultrahigh numerical aperture (NA) single-mode fiber with a length of ∼30 m. At the fundamental mode-locking regime, two orders of stokes lights can be generated, centered at 2.13 and 2.35 μ m, respectively, with a maximum total power of 3.75 W. At the noise-like twin-pulse regime, a near-infrared supercontinuum from 1.93 to 2.46 μ m was generated with a maximum average output power of 2.5 W. It is, to the best of our knowledge, the first demonstration of both cascaded Raman light and supercontinuum generation with the same system.

Description: In this study, a two-layer polarization-maintaining solid-core photonic crystal fiber (SC-PCF) is proposed. The cladding has two large holes both in the first and second layers for high birefringence and confinement loss reduction, respectively. The structural parameters are determined from the confinement loss, birefringence, and mode fields, based on which the two-layer polarization-maintaining SC-PCF is fabricated. The experimental results indicate that the loss and birefringence are 1.25 dB/km and 5.2 × 10 –4 , respectively.

Description: We propose and demonstrate a novel WDM-based Brillouin optical time domain analysis (BOTDA) sensor using Brillouin loss configuration, and theoretically analyze channel capacity of WDM-based brillouin optical time domain reflectometry (BOTDR) and BOTDA sensors by considering the fiber dispersion and nonlinear effects in sensing fibers. A three-wavelength WDM-based BOTDA senor is experimentally validated in the distributed temperature measurement of a 23-km-long standard telecom fiber (SMF-28), demonstrating an electrical signal-to-noise ratio enhancement of 9.2 dB. The numerical calculation results of the channel capacity of WDM-based Brillouin optical time domain sensors show that, when compared with the conventional single-wavelength BOTDR and BOTDA sensors, 11-wavelength BOTDR and BOTDA sensor using large effective area fiber can respectively achieve 8.4 and 20.8 dB signal-noise-ratio improvement (SNRI), and 7-wavelength BOTDR and BOTDA sensor using SMF-28 can respectively achieve 7.2 B and 16.9 dB SNRI without evident spatial resolution degradation and nonlinear impairment.

Description: Y 2 O 3 :Eu 3+ nanomaterials were obtained using a low-cost, large-scale, solution-based hydrothermal method followed by a thermal annealing process. The morphology of the Y 2 O 3 :Eu 3+ nanomaterials can be controlled by tuning the aging time, aging temperature, and the pH values of the suspension. The optical properties of Y 2 O 3 :Eu 3+ nanosheets and nanotubes were investigated with the goal of improving the material's functionalities. Synchrotron X-ray diffraction patterns, field emission scanning electron microscopy images, high-resolution transmission electron microscopy images, emission spectra, excitation spectra, and fluorescence decay curves were measured and compared. The results showed that a novel Eu 3+ environment exists in Y 2 O 3 :Eu 3+ nanosheets, which led to rapid decay of emission at 611 nm. The unique properties of Y 2 O 3 :Eu 3+ nanosheets could lead to potential applications in white light-emitting diodes (LEDs) based on GaAlN deep UV LEDs.

Description: We propose a noise adaptive Kalman filter for joint polarization tracking and channel equalization using cascaded covariance matching. With the process noise covariance ( Q ) and the measurement noise covariance ( R ) estimated in a cascaded manner, the proposed Kalman filter scheme can be implemented in adaptive mode. The experimental results demonstrate that in wide range of OSNR and polarization rotation, the scheme can adaptively configure noise covariance parameters and consequently can achieve optimal performance even in long transmission cases. Besides, the scheme is more robust against the initial errors in Q and R compared to nonadaptive filter and R / Q -adaptive algorithms with the allowable initial values of Q and R within 6 and 9 magnitudes, respectively.

Description: A perfect absorber based on plasmonic resonance for a variety of remarkable properties has motivated vivid research during the last few decades. However, most of the perfect absorbers had been focused on polarization-insensitive and narrow-band absorption, due to the existence of a theoretical limit. It is urgent to extend the optical properties of absorbers with omnidirectional and broadband performances to satisfy the requirements for practical application. Hence, we adopt a new convenient, energy-saving, and environmentally friendly silk mediated layer nanoimprint technology to obtain biomimetic moth eye structures with omnidirectional and broadband perfect absorption. Experimental and simulation results show that the absorbers can realize the absorption efficiency to a maximum of 99% over the entire visible spectrum for angles up to 70° from normal. In addition, it also exhibits excellent bidirectional absorptive characteristic of this design. We anticipate that this absorber may have greatly potential application in the photovoltaic and thermal imaging area.

Description: In this paper, two classes of multiparticle entangled states are constructed to resist against the collective-dephasing noise and collective-rotation noise, respectively. Based on it, two new multipartite quantum key agreement protocols over the collective noise are presented. In each protocol, only one user needs to prepare the multiparticle quantum entangled state. Then, the user keeps the first qubit, and distributes each two qubits of the state to other users. In this case, all users can perform the security test and derive the shared key from the measurement outcomes of the qubits in their hands. From the security analysis, it is evident that the presented protocols are secure against the inside attack and some common outside attacks.

Description: Combination of the classical effect of light self-focusing and recently emerged multicore fiber technology offers new opportunities for the spatio-temporal control and manipulation of high-power light radiation. Here, we apply genetic algorithm to design a system enabling self-focusing of light in various fiber cores on demand. The proposed concept is general and can be applied and adapted to any multicore fiber or two-dimensional array of coupled waveguides paving a way for numerous applications.

Description: The optical, color, electrical, and thermal properties of an LED devices are highly dependent on one another. The luminous flux variation and correlated color temperature (CCT) shifting of white LED sources is attributed to luminous efficacy and emission spectrum shifting with the electrical power and heat-dissipation power. An analysis model that includes the luminous flux, CCT, electrical power, and junction temperature of the white LED sources with bilevel driver is proposed in this paper. The proposed model can descript that the stablized luminous flux and CCT of the white LED system with bilevel driver is a result of the complex interactions among the given electrical power of bilevel, duty cycle, thermal resistances, junction temperature, and the physical parameters of the LED sources. Reduction variation of CCT and luminous flux of the white LED device with bilevel driver over a dimming range has been practically achieved. The proposed method can be easily adopted for improving the CCT and luminous flux stabilization of the white LED device with a bilevel driver.

Description: We report the numerical demonstration of the transformation from dissipative solitons to amplifier similaritons in an all-normal dispersion ultrafast fiber laser for the first time. Different from the strong spectral filtering as well as large spectral and temporal breathing ratios for the typical amplifier similariton fiber lasers, our case has relatively weak spectral filtering and small spectral and temporal breath ratios (〈6) for amplifier similaritons. An intermediate state between the dissipative soliton and amplifier similariton is discovered, which we call “dissipative similariton” considering its shaping mechanism and characteristics. Pulse regime dynamics is thoroughly explored. The chirp evolution together with pulse structures in time and frequency domains can be used to distinguish the three pulse regimes. This paper can enrich the pulse dynamics in all-normal dispersion fiber lasers and help one to properly design high-energy ultrafast laser configurations.

Description: This paper introduces a new multicarrier system, named sparse orthogonal circulant transform multiplexing (S-OCTM), for optical fiber communication. This technique uses an inverse sparse orthogonal circulant transform (S-OCT) matrix, which is simple and contains only two nonzero elements in each column, to multiplex information of different subcarriers. We compared the proposed scheme with conventional orthogonal frequency division multiplexing (OFDM), orthogonal chirp division multiplexing (OCDM), and discrete-Fourier-transform spreading OFDM (DFT-S-OFDM) in a coherent optical communication system. It is shown that S-OCTM, while exhibiting the complexity among the least, avoids the performance disadvantages of all investigated conventional schemes. It is theoretically proved that the S-OCT matrix equalizes the bandwidth limitation effect that degrades the performance of conventional OFDM. It also shows a greatly reduced peak-to-average power ratio and higher tolerance to fiber nonlinearity than OFDM and OCDM. On the other hand, compared to DFT-S-OFDM, S-OCTM shows a better dispersion tolerance under insufficient length of cyclic prefix and is more tolerable to strong optical filtering. The performance advantages and low complexity enable the proposed scheme to be a promising multicarrier solution for optical communications.

Description: Numerical and experimental investigations are carried out on the performance of parallelized Kalman filters applied for mitigation of the excess phase noise of fast tunable lasers. Based on the characterization of the phase noise of a sampled grating distributed Bragg reflector (SG-DBR) laser, the proposed carrier phase recovery (CPR) scheme using Kalman filters is introduced. By performing simulations of data transmission with various advanced modulation formats in the presence of the excess phase noise, the Kalman filter based CPR scheme shows its ability to overcome the excess phase noise and this method is suitable for parallel processing. Then the results are further demonstrated by 12.5 Gbaud QPSK and 16-QAM transmission experiments employing the SG-DBR laser. We find that the Kalman filters have better performance than the 2nd-order phase-locked loop in parallel systems due to a better phase noise tolerance. The bit error rate performance is also examined in the whole tuning range (∼30 nm) of the tunable laser, which further proves the feasibility of the proposed scheme.

Description: Most street lights currently deployed have constant illumination levels or vary based on a predetermined schedule. However, with advances in lighting controls, intelligent transportation systems, and the efforts of transportation agencies at regional and national levels to better sustain and manage the transportation system by monitoring the roadway network, many different types of real-time traffic data are available; which enables the implementation of a traffic responsive outdoor light system. The International Commission on Illumination (CIE) has proposed a class-based lighting control model based on a number of roadway parameters, some of which are traffic related. However, the adaptation of the available traffic data to the existing model is not obvious. In addition, the CIE model can be improved to better reflect traffic characteristics to increase energy efficiency of the overall street lighting system. The intention of this research is to quantify the relationship between real-time traffic, and roadway lighting and to develop a control strategy based on real-time traffic data in order to reduce light energy consumption, enhance safety, and maximize throughput of the roadway. Significant energy savings were observed when the proposed control strategy was implemented in two case studies using available lighting and traffic data for Washington, DC, and Montgomery County, MD, representing urban and rural roadway networks, respectively.

Description: The energy efficiency of silicon modulators can be enhanced by increasing the doping level. As an alternative solution, slow light modulators based on corrugated waveguides can also be used for improving the energy efficiency. Using numerical and analytical tools, we show that for the same level of energy consumption reduction, the loss coefficient and the loss-modulation efficiency for the slow-light modulators are smaller than those for the modulators with an increased doping level. It is shown that the slow light structures with medium slow down factors (specifically slowdown factors of less than 6) can be reasonable candidates for enhancing the modulator's energy efficiency. For example, an energy consumption of less than 100 fJ/bit can be achieved at a slow-down factor of 6, using a doping level of 5 × 10 17 cm -3 for acceptors and 1 × 10 18 cm -3 for donors.

Description: An electro-optic modulator (EOM) based on a racetrack resonator coupled to a waveguide using butterfly multi-mode interference (MMI) coupler is fabricated on Y-cut lithium niobate (LN) thin film. This is the first demonstration of a LN EOM in which the thin film of LN is etched in a Y-cut substrate using chlorine-based inductively coupled plasma reactive ion etching, a process, which is readily compatible with semiconductor fabrication facility. The Y-cut LNOI platform is interesting for the integration of electro-optic and acousto-optic components, since differently from any other LN cut it facilitates taking advantage of the maximum electro-optic and piezoelectric coefficients of LN. Coupling to the racetrack was enabled using a butterfly MMI coupler, which offered operation near the critical coupling condition, hence increasing the extinction ratio (ER) of the modulator. An unloaded quality factor of 1.3 × 10 5 was extracted for this device, which is equivalent to a propagation loss of 2.3 dB/cm. Modulation bandwidth of 4 GHz, wavelength tuning rate of 0.32 pm/V, and an ER of more than 10 dB were experimentally measured for the EOM.

Description: This paper reports a reconstruction method to determine a 3-D space curve from the distributed strain by using the parallel transport frame. Parallel transport frame can efficiently eliminate the singularities and discontinuous point which appear in another existing commonly used reconstruction method Frenet Frame and thus improve the accuracy and stability of the shape sensing. To validate this method, a simulation method based on the rotation minimizing frame is proposed and used. It provides a general procedure to numerically obtain the strain distribution with a certain configuration of the shape sensor and spatial shape. Some typical space curves whose space position is analytically given are reconstructed by two reconstruction methods and the results are compared. The error sources of the reconstruction method are also analyzed.

Description: This paper reports a compact spectrometer based on a guided-mode resonance (GMR) filter mounted on a linear charge-coupled device (CCD). The GMR is specially designed to exhibit gradient grating periods (GPPs) laterally to ensure that the GMR functions as a linear-variable bandstop filter. Each period corresponds to a resonant wavelength such that this wavelength is reflected back at its corresponding resonant period and transmitted to all other periods. Consequently, when a resonant wavelength is incident on the GGP-GMR attached to a linear CCD, the CCD pixel underneath its resonant period receives the minimum intensity, and the other pixels receive higher intensities. In terms of the wavelength range of interest, by scanning a single wavelength at a time, a transmission efficiency matrix that contains the transmission efficiency of each wavelength at each pixel can be established. An unknown incident spectrum can be reconstructed using the established transmission efficiency matrix and the intensity measured using the CCD. In this study, a GGP-GMR spectrometer less than 3 mm long that can achieve a wavelength detection range of 200 nm was demonstrated to reconstruct various incident spectra, including a single wavelength of light with a resolution of 0.5 nm, a single wavelength of light with varying intensity levels, and dual incident light sources.

Description: We propose a silicon strip waveguide structure with alumina thin-film coating in-between the core and the cladding for group-velocity dispersion tailoring. By carefully designing the core dimension and the coating thickness, a spectrally-flattened near-zero anomalous group-velocity dispersion within the telecom spectral range is obtained, which is predicted to significantly broaden the bandwidth of four-wave mixing. We validate this by characterizing the wavelength conversion in a waveguide sample by atomic layer deposition technology, which to our best knowledge is the first experimental demonstration of the proposed structure. Due to the alumina thin-film coating, the wavelength conversion bandwidth reaches $58,mathrm{nm}$ , an increase by a factor of 1.3 compared to the corresponding structure without coating. This method can also be applied to other material platforms and applications requiring accurate group-velocity dispersion control.

Description: A dual photonic-delay line cross-correlation method for phase noise measurement of microwave signal based on dense wavelength division multiplexing (DWDM) is proposed and experimentally demonstrated. The kilometer-long delay fiber is used together by the two mutually independent channels through the DWDM technology, which makes it easier to get the same delay between two channels. And it reduces the cost of the system by reducing the use of several kilometers of fiber and a Mach–Zendher modulator. Then, it uses variable optical fiber delay lines to replace the electronic phase shifters and a broader operation bandwidth can be obtained. A lower phase noise floor has been obtained by more averaging of the cross-correlation spectrum. In the experiments, the phase noise of a 10-GHz microwave signal has been measured accurately. A large operation bandwidth of 4–11 GHz is achieved and a measurement phase noise floor of –152.6 dBc/Hz at 10 kHz offset at 10 GHz in a 20 μ s delay measurement system is realized by averaging 100 times.

Description: In this paper, an alternative implementation for the hybrid free-space optical (FSO)/radio frequency (RF) wireless communication system without requiring channel state information is presented. The proposed hybrid system transmits the same data with the same data rate over both links simultaneously. The well-known diversity selection combining scheme is implemented to combine the received signals in the electrical domain. New closed-form expressions for the average bit error rate and outage probability are derived in order to trace the system's performance over various channel turbulence conditions. The analysis of the proposed system's performance clearly indicates that the proposed system is advantageous as it exploits the complementary properties of the FSO and RF channels, even in strong turbulence conditions. In addition, the performance comparison demonstrates the proposed system's superior performance compared with the FSO-only system.

Description: The physical model of polarized light scattered from oil film had been analyzed, which helped us to derive the Mueller matrix of uniform scattering. The parameter, uniform scattering power (USP), has been proposed to analyze the scattering intensity of regular, smooth, and raised surfaces in the observation direction. USP could overcome the influence of angles in oil spill detection and provide us with better monitoring signals. The actual spilled oil had been measured by this model, and the oil film could been accurately identified at various angles.

Description: In certain applications, modal wavefront sensors (MWFSs) can outperform zonal wavefront sensors, which are widely used due to their high flexibility. In this paper, a holography-based MWFS as described is developed for the fast position control of a light emitter in a deep parabolic mirror. The light source is located in the vicinity of the focal point. Instead of Zernike polynomials, more complex phase functions, which are related to certain dislocations of the light source are used as detector modes. The performance of the sensor is verified with a test setup, where the test wavefront is generated by a spatial light modulator instead of a real parabolic mirror. The design and fabrication of the required high-resolution holographic element is described and an easy way of multiplexing several single mode sensors is demonstrated.

Description: Color converting films of colloidal quantum dots (CQDs) encapsulated with flexible glass are integrated with microsize GaN LEDs (μLEDs) in order to form optical sources for high-speed visible light communications (VLC). VLC is an emerging technology that uses white and/or colored light from LEDs to combine illumination and display functions with the transmission of data. The flexible glass/CQD format addresses the issue of limited modulation speed of typical phosphor-converted LEDs while enhancing the photostability of the color converters and facilitating their integration with the μLEDs. These structures are less than 70 μm in total thickness and are directly placed in contact with the polished sapphire substrate of 450-nm-emitting μLEDs. Blue-to-green, blue-to-orange, and blue-to-red conversion with respective forward optical power conversion efficiencies of 13%, 12%, and 5.5% are reported. In turn, free-space optical communications up to 1.4 Gb/s VLC is demonstrated. Results show that CQD-converted LEDs pave the way for practical digital lighting/displays with multi-Gb/s capability.

Description: We proposed and experimentally demonstrated an approach of dispersion-free arbitrary waveform generation based on a wavelength-swept laser, for the first time to the best of our knowledge. The system has been proven to generate a variety of waveforms, such as Gaussian pulses, rectangular pulses, and a chirped pulse with a large time-bandwidth product of 273.6. Thanks to the linear relationship of frequency to the time of the wavelength-swept laser, time-domain optical signal exhibits the user-defined shape of the optical spectrum without any dispersive element. Furthermore, the proposed method features simple structure, full reconfiguration, and, especially, the high potential for integration.

Description: A novel photonic approach to generate high-speed and wideband frequency-hopping microwave signal via switching the bias point of a dual-drive Mach-Zehnder modulator (DD-MZM) is proposed and experimentally demonstrated. The core component of the system is a DD-MZM. By switching the bias point of the DD-MZM between the quadrature transmission point and the minimum transmission point, frequency hopping between two frequencies can be realized with an ultra-high frequency-hopping speed and a very wide bandwidth. The proposed approach has a compact structure and good tunability. A proof-of-concept experiment is performed to verify the principle of the proposed technique. Tunable frequency-hopping microwave signals between two frequencies of 4 and 8 GHz, 9 and 18 GHz, or 12 and 24 GHz are generated with a frequency-hopping speed up to 1 GHz.

Description: We theoretically investigate a Dy 3+ -doped chalcogenide fiber lasers operating at 4.3 μ m based on the rate equations and propagation equations. The two main pump bands for 1319 and 1707 nm corresponding to the 6 H 15/2 → 6 H 9/2 and 6 H 15/2 → 6 H 13/2 transitions are discussed in detail. The predicted maximum slope efficiencies are determined to be ∼7.8% and ∼15.1% for the two pumping wavelength, respectively. Besides, the variety of laser performance has been systematically analyzed when the pump configurations, fiber length, fiber loss are varied. This numerical analysis might be useful to explore the 4.3 μ m lasing operation for the mid-infrared chalcogenide fiber lasers in future.

Description: In order to obtain high peak power RF intensity-modulated pulses for long-distance applications, a Q-switched Nd:YAG laser is injection seeded by a dual-frequency laser signal. The beat note frequency of the dual-frequency laser signal is adjusted to the frequency spacing of two adjacent longitudinal modes of the Q-switched laser. When the dual-frequency signal is injected into the Q-switched slave resonator, simultaneously two cavity axial modes are tuned to allow the injected wave frequencies within the axial modes selection range, the two selected slave cavity modes will oscillate due to phase-pulling effect. The Interference of the two modes results in intensity modulated pulses. The modulation frequency equals to a free spectral range of the Q-switched cavity, which is 225 MHz in our experiment. Maximum intensity-modulated pulse energy of 7 mJ and pulsewidth of 16 ns are measured. The dependence of locking bandwidth to the injected power is also studied experimentally, it is confirmed that the locking bandwidth increases with respect to the injected power of the seed signal. The high peak power RF intensity-modulated pulsed light source is a promising candidate for long-distance lidar-radar applications.

Description: A microwave photonic system that can realize frequency up- and down-conversion, multichannel phase shift, high conversion gain, and elimination of dispersion-induced power fading is proposed and experimentally demonstrated. The scheme is based on an integrated dual-polarization quadrature phase shift keying modulator that contains two dual parallel Mach–Zehnder modulators (X-DPMZM and Y-DPMZM). The X-DPMZM implements dual side band carrier suppression (DSB-CS) modulation of radio frequency signal, and the Y-DPMZM implements frequency shift of an optical carrier. They are combined in orthogonal polarizations to implement frequency up- and down-conversion. The polarization multiplexed signal will go through polarization controllers and polarizers to implement multichannel phase shift. In the experiment, the phase shift can be tuned independently over 360° in each channel. By suppressing the optical carrier, the conversion gain and LO isolation are improved by 20.5 dB and 51.26 dB, respectively, compared with conventional dual side band modulation scheme. In addition, the proposed scheme can achieve a spurious-free dynamic range (SFDR) of 103.6 dB·Hz 2/3 .

Description: An ultrafast high-sensitivity refractive index (RI) and temperature-sensing system based on an optoelectronic oscillator (OEO) is proposed and demonstrated in this paper. A Fabry–Perot fiber Bragg grating (FP-FBG), which combines a gap with two FBGs in a silica V-shaped slot and characterizes a narrow notch in the reflection spectrum, is incorporated in the OEO to implement a microwave photonic filter and perform oscillating frequency selection. A microwave signal is generated by the OEO, whose oscillating frequency is determined by the center frequency of the FP-FBG notch, which varies with the surrounding environments. The RI or the temperature change can be accordingly measured by monitoring the frequency shift of the microwave signal using an electrical spectrum analyzer or a digital signal processor. An experiment is performed to verify the proposal. An RI sensitivity of 413.8 MHz/0.001RIU and a temperature sensitivity of 2516 MHz/°C are successively demonstrated.

Description: We present a silicon dual-coupled-ring resonator modulator with push–pull coupling tunings. The basic idea of this scheme is to construct a dual-coupled-ring resonator structure in which the coupling coefficients of all coupling regions are tunable through Mach–Zehnder interferometers operated in push–pull modes. Two coupling coefficients are tuned jointly for optical bandwidth shaping and tuning while another coupling coefficient is tuned for high speed and chirp-free modulation. The fundamental analytical expressions for the intensity transmittance, the critical and the resonance conditions of the proposed dual-coupled-ring resonator modulator are derived. In addition, the performance simulations and optimization are presented and compared with those of the single-ring resonator modulator. The proposed dual-coupled-ring resonator modulator is more likely to achieve wide optical bandwidth tuning range and narrow channel spacing simultaneously, which are suitable for future optical processing and interconnects.

Description: Hyperlens consisted by period plasmonic metamaterials is an interesting technology for the optical imaging of arbitrary objects beyond the diffraction limit in the far field, which has great potential applications in nanophotonics. However, the functionality of previously presented hyperlens is limited to image two-dimensional (2-D) objects and work at a certain wavelength due to the dispersion of metal, dramatically impose restrictions on its practical application. In this paper, we proposed and theoretically demonstrated a multiwavelength tunable hyperlens, with the ability of 3-D imaging by focal plane tuning achieved by electro-optical modulation. The simulation results indicate that full-width half-maximum (FWHM) of minimum imaging spot can be reduced down to the level of less than half-wavelength of the incident in a wide wavelength range real-timely, down to the level of ∼200 nm using visible light illumination. In addition, the focal position of the hyperlens can also be tuned in large spatial scope, which greatly facilitates the application of the hyperlens in optical signal acquisition and processing.

Description: The need for ever faster and more efficient computation and communication devices has spurred interest in the field of all-optical modulators. Here a small-size hybrid plasmonic-photonic all-optical waveguide modulator utilizing a subwavelength Au/VO 2 nanostructure is proposed as a high-modulation optically actuatable modulator. Using finite-difference-time-domain simulations, a nanoscale (320 nm × 300 nm cross-section) optimized modulator is designed. The modulator design has an extinction ratio as high as 26.85 dB/μm, and a length of only 550 nm.

Description: We demonstrate a phase-shifted fiber Bragg grating with a taper induced by femtosecond laser micromachining. In this configuration, a fiber taper fabricated by an arc discharge in a fiber splicer was sandwiched between two fiber Bragg grating sections, which were formed using femtosecond laser line-by-line inscription. The degree of phase shift produced by this device can be adjusted by introducing axial strain, with a sensitivity of 4.59 pm/μϵ. A theoretical study was also conducted by modeling the taper under axial strain. The relative deviation between simulated and measured sensitivities is less than 10%.

Description: Spectral and polarimetric contents of the light reflected from an object contain useful information on material type and surface characteristics of the object. Jointly exploiting spatial, spectral, and polarimetric information helps detect camouflage targets. Motivated by the vision mechanism of some known aquatic insects, we construct a bioinspired multiband polarimetric imaging system using a camera array, which simultaneously captures multiple images of different spectral bands and polarimetric angles. But the disparity between the fixed positions of each component camera leads to the loss of information in the boundary region and a reduction in the field of view (FOV). In order to overcome the limits, this paper presents a deep learning method for FOV expansion, incorporating the gradient prior of the image into a nine-dimensional convolutional neural network's framework to learn end-to-end mapping between the incomplete images and the FOV-expanded images. With FOV expansion, the proposed model recovers significant missing information. For the problem of insufficient training data, we construct the training dataset and propose the corresponding training methods to achieve good convergence of the network. We also provide some experimental results to validate its state-of-the-art performance of FOV expansion.

Description: We investigate the decay properties of the quantumness including quantum entanglement, quantum discord, and quantum coherence for two photonic qubits, which are partially entangled in their orbital angular momenta, through Kolmogorov turbulent atmosphere. It is found that the decay of quantum coherence and quantum discord may be qualitatively different from that of quantum entanglement when the initial state of two photons is not maximally entangled. We also derive two universal decay laws for quantum coherence and quantum discord, respectively, and show that the decay of quantum coherence is more robust than nonclassical correlations.

Description: A new phase retrieval technique in digital holographic microscopy (DHM) with three defocused holograms is proposed. Given the defocusing distance, the phase distributions of tested specimen can be reconstructed with a simple algebraic equation. We have deduced this equation in detail. To avoid the manual operation, the defocused holograms can be flexibly and precisely obtained by introducing an electronically tunable lens based 4f system. This method is suitable for an on-axis hologram as well as the off-axis one but avoids the requirements for not only the iterative process, complex spectrum selection in off-axis DHM or additional phase-shifting devices in on-axis DHM but also the assumption of tested specimen or previous knowledge of the system. A series of simulations and the experimental results of the microlens array and water drop demonstrate the feasibility and effectiveness of the proposed method.

Description: Binocular stereo vision (BSV) system has been widely used in various fields, such as intelligent manufacture, smart robot, and so on. However, the location accuracy of the current BSV still cannot fully satisfy industry requirements due to lack of a parameters optimization BSV system. In this paper, a high accuracy BSV system is proposed. This is achieved through analyzing the seven parameters of the BSV system, which are classified into two groups: system structure parameters (SSPs) and camera calibration parameters (CCPs). For the SSPs, an improved analysis model is designed to expose the possible errors caused by three parameters. Furthermore, a new correlation model among them is also proposed to analyze the errors caused by their correlation. On the other hand, for the CCPs, the orthogonal experiment model is employed for selecting the optimal combination of the four calibration parameters. Meanwhile, the weight among the four parameters is also analyzed for reducing errors. Finally, the effectiveness of our proposed method is demonstrated by a large number of experiments. It gives a useful reference to the BSV system used in applied optics research and application fields.

Description: We propose an all-optical virtual private network (VPN) supporting dynamic bandwidth allocation (DBA) in an orthogonal frequency division multiple access-based passive optical network. A microwave photonic bandpass filter (MP-BPF) is used to transmit the VPN signal without electrical conversion. The DBA is implemented by adjusting a free spectral range of the MP-BPF with corresponding subcarrier allocation. A RF clipping-tone (CT) is used to stabilize the optical channel suffered from phase induced-intensity noise and Rayleigh back-scattering noise. The DBA is experimentally verified at different two DBA scenarios in 20-km single-fiber loopback link in terms of channel error vector magnitude, spectral efficiency after adaptive modulation. Due to the CT-based channel stabilization, achievable spectral efficiency could be improved, and the feasibility of the proposed system is successfully demonstrated.

Description: The exponential growth of network traffic within data centers and high-performance computing generates a growing volume of fiber cabling. This raises the need for spectrally efficient communication scheme, which allows easy integration of optics and electronics. In this paper, we suggest a mode group division multiplexing scheme based upon intensity-modulated silicon photonics (SiP) Mach–Zehnder modulators (MZMs) coupled to standard graded-index multi-mode fiber directly detected using multi-segment concentric photo-detector. In addition, we have theoretically derived the bit and power loading of such a system in a closed-loop multiple-input multiple-output (MIMO) formation using convex optimization with two possible types of architectures: the vertical Bell Labs layered space-time architecture (V-BLAST) with minimum mean square error and successive interference cancellation (MMSE-SIC); and singular value decomposition (SVD). Our optimization problem maximizes the system's capacity under peak amplitude, power consumption, and BER constraints. Simulation results have shown the superiority of a V-BLAST MMSE-SIC over the SVD architecture in terms of total spectral efficiency for a 4 × 4 MIMO short reach low driving voltage conventional SiP-based MZM system.

Description: A novel multichannel free-space optical (FSO) communication system based on orbital angular momentum (OAM) carried by frozen waves with different longitudinal patterns is studied in this paper. The longitudinal OAM multiplexing (LOAMM) system is simulated under atmospheric turbulence, which is based on the split-step Fourier transform method and includes multiple random phase screens. The influences of system parameters on the average OAM mode probability densities are analyzed and discussed, such as propagation distance, strength of turbulence, sizes of finite aperture function, OAM mode numbers, and source parameters. It is found that in the limited apertures, the detection probability spectrum of the LOAMM system is inversely proportional to OAM mode numbers, strength of turbulence, and propagation distance. The bit-error rate and aggregate capacities are compared between the traditional OAM-based space-division-multiplexing (OAM-SDM) system with Bessel beams and our proposed LOAMM system. Our work should contribute to proving that the LOAMM system has a number of advantages over the OAM-SDM system in FSO communication.

Description: In this letter, we propose a strategy to enhance absorption in the black phosphorus absorber based on a nanocavity structure. By introducing a porous silver layer, an enhanced broadband light absorption can be obtained in the spectral range of 520–820 nm. The optical characteristics of the black phosphorus absorptive layer are thoroughly analyzed by absorption spectra, electric intensity distribution, and power flow distribution. Numerical and analytical analysis revealed that the optical absorption of the black phosphorus layer with a porous silver layer can be enhanced by 50% and 396% at the resonant wavelength of 690 nm for p-polarized and s-polarized incidences, respectively, when compared to that without a silver layer. Furthermore, the short-circuit current density ( $J_{{rm{SC}}}$ ) was calculated for the proposed architecture. The peak value of $J_{{rm{SC}}}$ was more than 18 mA/cm 2 . It is demonstrated that this super absorption structure could find important applications on plasmonic-assisted photovoltaic devices or other opto-electronic devices, which will promote the development of ultrathin on-chip energy harvesting and new thin-film active devices.

Description: We proposed an improved phase-based method by using a filtering window on the low-coherence interferogram. Through theoretical derivation and numerical simulation, we prove the correction of our proposed method that the fringe phase can be demodulated nondestructively after applying a symmetrical filtering window nearby the envelope peak, and our method can enhance system SNR. Since fringe overlap phenomenon arising from narrow bandwidth occurs frequently in single-mode sensing system, this method is especially applicable to remote sensing wherein the localization of interference fringe is difficult using traditional phase-based methods. To verify this method, an experiment with a single-mode fiber Fabry-Perot air pressure sensing system was carried out. The experiment results showed that the precision using our method decreased to less than 0.053 $%$ in full 280 kPa pressure scale and the sensing distance extended to 20 km, which were apparently superior to traditional phase-based methods.

Description: One of the most important applications of THz frequencies is biomedical sensing. However, in a THz range, surface plasmon waves on flat metals are not confined and therefore cannot be used for subwavelength sensing. But, it has been shown that graphene can support surface waves at THz frequencies, which has similar properties as plasmonic waves in an optical range. In this paper, a highly sensitive gas sensor in the terahertz frequencies by exciting surface plasmon resonance (SPR) of graphene is proposed. The results show that the proposed SPR gas sensor has high stability and high sensitivity ( S ), and the highest S max (∼147°/RIU) has been obtained by optimizing the Fermi energy, the thickness of the dielectric layer, and the incident light frequency. Moreover, the S of the proposed THz sensor for different refractive index (RI) of gas sensing medium ( n 1 ) is also discussed.

Description: Distributed optical fiber strain sensing significantly increases the number of sensing points compared with fiber Bragg grating sensor, which makes it an excellent candidate for shape sensing. Theoretical analysis indicates that the spatial resolution of strain measurement is crucial to the performance of shape sensing, so a shape sensor based on differential pulse-width-pair Brillouin optical time-domain analysis is proposed to improve the spatial resolution and shape sensing performance. The sensing fiber is attached on the both sides of a steel strip substrate, which enables the measurement of Brillouin frequency shifts (BFSs) of both the sides to suppress temperature crosstalk. In the experiment, first, the dependence of BFS variation on the curvature of the fiber is measured, the result of which agrees well with theory. Then the reconstruction of three shapes are demonstrated, the spatial resolution of which is 10 cm.

Description: We propose and numerically study a novel type of hollow core antiresonant fiber with a single layer of nodeless radially asymmetric cladding tubes, i.e., the cladding tube presents a bulb-like shape, that the local cladding curvature radius at the core/cladding boundary is larger than the other side. Compared with counterparts with conventionally used radially symmetric nodeless claddings, e.g., circular and elliptical tubes, numerical analysis shows that such structure can provide excellent broadband low-loss property and robust single-mode guidance. By tuning the local cladding tube curvature radius, the confinement loss characteristic can be less sensitive but the phase matching between core high-order modes (HOMs) and resonant cladding modes can be significantly enhanced than that of the elliptical structure. Since the cladding modal fields are moved closer to those of the core HOMs, the HOM extinction ratio can reach above 10 4 and maintain over an octave of bandwidth.

Description: We numerically demonstrate a scheme of optofluidic sorting of nanoparticles on a silicon-based lab-on-a-chip system, with reconfigurable and multilevel sorting size thresholds. Size-dependent sorting of nanoparticles originates from the size-dependent distribution of trapping potential wells, which determines whether a nanoparticle can jump back and forth between parallel waveguides in weakly coupling condition. In numerical modeling, we find that it is easier for larger ones to transfer and the size threshold is power ratio dependent. By setting a thermal tuning ring-assisted Mach–Zehnder interferometer ahead, we can adjust effectively the input power ratio of the parallel waveguides as well as the potential well distribution across them, working as a thermal tuning reconfigurable sorting unit. Consequently, a tree cascaded unit with different thresholds is also presented to be a reconfigurable multilevel sorting unit. The proposed design offers a simple and ultracompact scheme for the reconfigurable and multilevel optofluidic sorting of nanoparticles on thermo-optofluidics chip for the first time.

Description: In this paper, we report polarization-locked vector soliton (PLVS) generation in a linear thulium-doped fiber laser. The fiber laser was composed of all-anomalous-dispersion fibers, passively mode-locked with a semiconductor saturable absorber mirror. Approximately 1.2-ps single vector soliton pulses centered at 2023.7 nm were generated. Extra “peak-dip” spectral sidebands were clearly visible in the polarization-resolved optical spectra, indicating coherent energy exchange between the two polarization components of the vector solitons. In addition, multiple-PLVS operation modes were experimentally investigated, and our experimental results were confirmed by numerical simulations. To the best of our knowledge, this is the first observation of polarization-locked single vector soliton generation operating in the 2-μm spectral range.

Description: A fast gain-switched Tm-doped fiber laser and amplifier system providing stable 17-ns pulses with a 0.64-mJ energy and 35.6-kW peak power at 25 kHz is demonstrated. Then, self-starting mode-locked resembling pulses with duration of 〈200 ps, recorded within the gain-switched pulse envelope, were achieved in the same laser cavity. By amplifying the pulse train in a Tm-doped fiber amplifier, an average output power of 6.8 W at a ∼15-ns full width at half maximum gain-switch envelope and a ∼36.9-μJ subpulse with a peak power of up to 115.6 kW were demonstrated. To the best of our knowledge, this is the shortest gain-switched and mode-locked-like pulse as well as the highest peak-power that has been demonstrated in this type of laser system. A mid-infrared supercontinuum generation with a total output power of 2.45 W and a cutoff wavelength at 4.4 μm is also reported.

Description: A two-segment regrowth-free gain-coupled distributed feedback (DFB) laser monolithically integrated different gain contrast segments was proposed, realizing both wavelength-tunable (5 nm) and wavelength stabilization characteristics, controlled by a single electrode only. At current larger than 320 mA, side mode suppression ratio reached >30 dB with 3 dB linewidth 〈80 pm. The CW power reached up to 159 mW/facet at single-mode operation. Considering both uncoated facets all together, it is at the same power level as index-coupled DFB lasers. Periodic surface grooves and 4- μ m-width ridge were patterned merely by one-step i-line lithography. It provides a novel method for low-cost practical gain-coupled DFB laser fabrication, which can be used in either/both wavelength-tunable applications such as sensing and detection, or/and wavelength stabilization fields such as pumping fiber lasers.

Description: We present a photo-excited switchable broadband reflective linear polarization conversion metasurface for terahertz waves. The unit-cell structure of the switchable polarization conversion metasurface is composed of metallic disk and split-ring resonator (together named as DSRR) integrated with semiconductor photoconductive silicon (Si) placed over the continuous films. The electric response of the photoconductive Si filled in the gap of the DSRR can be tunable through a pump beam with different optical power. The simulation results indicate that the polarization conversion ratio (PCR) of the compound metasurface without pump beam is greater than 80% in the frequency range of 0.65–1.58 THz, and the PCR is up to 99% at resonances frequencies of 0.69 THz, 1.01 THz and 1.42 THz, respectively. The numerical simulation results are in good agreement with the theoretical predictions based on the interference theory. Furthermore, the broadband PCR can be tunable continuously with the changes of Si conductivity by adjusting the pump optical power. Moreover, the surface current distributions of the unit-cell structure with different Si conductivity at the resonance frequency are discussed to illustrate its physics mechanism. Thus, our design can find potential applications in many areas, such as remote sensors, reflector antennas, and radiometers in terahertz region.

Description: Tunable surface plasmon polariton launchers are highly demanded in various applications of nanophotonics for achieving controllable plasmonic signals coupling and multiplexing. Here, a tunable-focusing device with simplified structure is suggested. It consists of an array of nanofootprints. This device allows us polarization-controlled tunable plasmonic directing and focusing on the two-dimensional metallic surface. The simulation and experimental results indicate that the focal position of the excited plasmon field can be flexibly tuned between two distinct positions just by manipulating the incident polarization state. Hence, this nanofootprints structure can serve effectively as controllable plasmonic routers and demultiplexers. It also has promising application prospects in many other fields of optics.

Description: A tensile-strained GeSn/SiGeSn multiple quantum well (MQW) laser wrapped in Si 3 N 4 liner stressor is designed and characterized theoretically. A biaxial tensile strain is introduced into the GeSn/SiGeSn MQW laser by the Si 3 N 4 liner stressor. The boosting effects of tensile strain on the threshold current density J th and optical gain in GeSn/SiGeSn lasers are attributed to the modulation of energy band structure and carrier distribution in the GeSn wells. Tensile-strained Ge 0.90 Sn 0.10 /Si 0.161 Ge 0.695 Sn 0.144 MQW laser wrapped in 500 nm Si 3 N 4 liner stressor achieves a J th reduction from 476 to 168 A/cm 2 and a significant enhancement of optical gain, as compared to the relaxed control device without Si 3 N 4 . The design of GeSn/SiGeSn MQW structure wrapped in Si 3 N 4 liner stressor provides a practical way to realize high performance GeSn based mid-infrared laser.

Description: Drude's equation, a classical equation, can be used to express the properties of optic polarization. In the paper, an optimized two-term Drude's equation is introduced for expressing the specific rotation. The optical rotation angle for each wavelength is measured by a charge-coupled device. In order to verify the precision and versatility of the equation, we compare the obtained specific rotation with published analysis at a wavelength of 589.3 nm. Moreover, the two-term Drude's equation is translated into calculate the approximatively individual concentration of the molecules in aqueous solution. The calculation is based on the linear functional relation and fitting parameters of total rotation without knowing the ranges of concentrations and setting constraints. The viability and flexibility of this method demonstrate the potential applications in optics.

Description: A method (ion-implantation) that can control surface carrier density of silicon wafer in silicon fabrication industry is combined with metamaterial to demonstrate a new way to control response of metamaterial transmission operating at terahertz frequency. Ion-implantation which is the most exact and easy way to control carriers of silicon wafer is used to fabricate a stable response of transmission metamaterial. Therefore, a split-ring resonators (SRRs) metamaterial is designed and fabricated to investigate the relationship between carrier density, power of pumping light, and transmission. Meanwhile, the numerical simulation was carried out to verify the experimental results. The relationship between the simulation results and experiments results was confirmed. This method could be a potential way to make stable response of metamaterial, which could be switcher, filter, and terahertz detectors.

Description: We propose the generation of high-purity perfect cylindrical vector beams (PCVB) using the Fourier transformation of Bessel–Gauss vector beams. The demonstration of PCVBs is implemented via an interferometric method employing a spatial light modulator that allows a fully independent control of the ring diameter ( $R_D$ ) and ring width ( $R_W$ ) of the PCVB. The proposed scheme enables to generate different types of cylindrical vector beams with precise user-defined transverse dimensions. The dynamic control of the ring width, ring diameter, and the specific type of PCVBs desired is theoretically as well as experimentally demonstrated. The proposed experimental setup can not only be employed in the generation of arbitrary PCVB, but also in perfect vortex beams. The ability to generate fully tailorable cylindrical vector beams and vortex beams has implications for the efficient launch of exotic optical modes in specialty fibers, in the field of optical tweezers as well as for superresolution microscopy.

Description: We construct a family of optical ring lattices that manifest the quasi-nondiffracting property via superposition of high-radial-order Laguerre-Gaussian beams. A theoretical derivation of the optical ring lattice along with the validity condition is presented, and its evolution behaviors are investigated in comparison with the diffraction-free Bessel beams. Moreover, multiple ultralong bright channels or optical tubes with various transverse profiles can be formed with the ring optical lattices. As a proof of concept, flexible generation of the lattice beams was demonstrated by complex wavefront engineering using a binary digital micromirror device. We anticipate that the quasi-nondiffracting ring lattices and the ultralong optical channels might motivate novel applications in optical trapping and high-resolution microscopy.

Description: The underwater imaging could be severely degraded by the scattering media due the backscatter veiling and signal attenuation. Image recovery based on polarization information has shown its efficiency in improving the quality of image in scattering medium, but few of them considered the effect of nonuniform optical field on the image recovery. In this paper, we consider the condition of nonuniform optical field, and we propose a method of retrieving the objects radiance based on estimating the degree of polarization (DOP) and the intensity of backscatter at different positions of the image. The experimental results demonstrate that the quality of the underwater image can be effectively enhanced by this method. In addition, compared with the previous methods, the method proposed in this paper can maintain a better performance at different positions of the image, thanks to considering the DOP and intensity of backscatter as spatial variables instead of constants.