ALBERT

Description: Gold nanorods (GNRs) with surface plasmon resonance peak at 1063.8 nm were fabricated and experimentally exploited as the single and combined saturable absorber (SA) in a $Q$ -switched Nd:YAG laser for the first time. In the situation using GNRs as a single SA, the maximum pulse energy of 19 $muhbox{J} $ was achieved at a pulse repetition rate of 20 kHz. However, due to the small effective modulation depth of the GNRs, microsecond pulses were generated in such a GNRs-based passively $Q$ -switched laser. A novel configuration using GNRs as a combined SA in an acoustooptic $Q$ -switched Nd:YAG laser was proposed. The small nonlinear loss modulation induced by the GNRs played a distinctive role in flexibly manipulating the nanosecond pulse waveforms. Our study demonstrated the feasibility of generating high-energy pulses by singly using GNRs-based SA in all solid-state lasers. Meanwhile, a new application mode incorporating GNRs as a combined SA was studied, providing an alternative method to take advantage of the nanomaterial-based SA with a relatively small modulation depth.

Description: This paper proposes the improved design of an ultraviolet (UV)- and-blue-light-inhibited white light-emitting diode for use as a safe and practical light source. Covered with a glass substrate coated with a photocatalyst resin on one side and a reflectance film on the other side, wavelengths below 400 nm are reflected back to re-excite the red–green–blue phosphors and, consequently, enhance luminous efficiency. The absorption spectrum of bismuth oxide photocatalysts is below 521 nm, and the leaked UV and blue light can be absorbed, thereby exciting electron–hole pairs and producing the photocatalytic effect. Thus, blue light and UV leakage can be suppressed appreciably, and the luminous efficiency can be increased markedly. Experimental results showed a UV suppression ratio of 88.43% and a visible light increasing ratio of 21.66%. The Commission International de L'Eclairage chromaticity coordinates $(x,y)$ were (0.343, 0.404), the correlated color temperature and the deviation from de Blackbody locus were (5201 K, 0.0250), and the color rendering index was 93.16. In addition, the photocatalyst coating layer can act as a diffuser to provide a comfortable visual experience and facilitate environmental purification.

Description: Metamaterial-based perfect absorbers have attracted considerable attention due to their potential for practical applications. The existing absorbers, however, are mostly polarization insensitive or only sensitive to one direction, which is inapplicable in some areas. Polarization tunable or high absorption in two orthogonal directions is very useful and necessary. Herein, we present a polarization tunable absorber formed by an asymmetric patch and a dielectric layer on top of a metallic board. With this structure, the frequency of the absorber can be tuned by merely changing the polarization of the incident. The tunable mechanism originates from the different length of the patch along the two orthogonal directions. The concept is rather general and applicable to various absorbers, as long as the asymmetric design is valid. The absorber can find practical applications in manipulation of the polarization of the light and detecting waves with specific polarization.

Description: We demonstrate low-voltage waveguide-coupled germanium avalanche photodetectors (APDs) with a (wafer-scale mean) gain $times$ bandwidth product of 140 GHz at $-$ 5 V by utilizing a 185-nm-thick Ge layer. An optical receiver based on such an APD operating up to 25 Gb/s is demonstrated.

Description: We report a fast and efficient method for permanently correcting fabrication-induced phase errors in silicon photonic circuits. The method uses femtosecond laser pulses at 400-nm wavelength to amorphize a thin layer of crystalline silicon near the waveguide surface, thereby inducing a change in the effective index of the waveguide. Using a single femtosecond laser pulse, we reduced the polarization-dependent frequency shift between the two interferometers of a polarization diversity differential phase shift keying silicon demodulator from 11 GHz to less than 0.5 GHz, thereby restoring the polarization diversity operation of the circuit with little degradation to the circuit performance.

Description: A refined model of a mid-IR amplifier, constituted by a tapered chalcogenide fiber coupled to an erbium-doped chalcogenide microsphere, is integrated with a global solution search procedure based on particle swarm optimization approach. It is implemented in a computer code in order to obtain an inversion algorithm useful to evaluate the spectroscopic parameters of rare-earth-doped glass microspheres. The rare earth parameters can be recovered by means of the optical gain measurement. The error in evaluation of the erbium lifetime $tau _{41}$ is <3.5%. It is <0.5% for the other lifetimes and ion–ion interaction parameters. These excellent results are obtained since whispering gallery mode electromagnetic field interacts with rare earth for long effective distances.

Description: We demonstrate an integrated spectral shaper based on a Sagnac loop incorporating a chirped Bragg grating in silicon photonics for the photonic generation of chirped microwave pulses. The technique is based on optical spectral shaping combined with linear frequency-to-time mapping. By tuning the central wavelength of the input optical pulse, we obtain chirped microwave pulses with central frequencies ranging from $sim 10$ GHz to $sim 30$ GHz and an RF chirp rate of $sim 20$ GHz/ns with both positive and negative signs.

Description: A system based on phase-sensitive optical time domain reflectometry is proposed for simultaneously strain and vibration sensing. The strain of fiber is detected by comparing the patterns of signal for different laser frequencies, and the vibration of fiber is detected simultaneously from the signals for any certain laser frequency. During the measurement, frequencies of the probe optical pulses are modulated sequentially in ascending or descending order. Using the signals generated by optical pulses with the same frequency, the vibration of fiber is detected with fast response speed; using that with different frequencies, the strain of fiber is detected with high resolution. In our experiment, a sensing system with 2-m spatial resolution, up to 1-kHz frequency measurement range and 10- $text{n}{{varepsilon }}$ strain resolution is realized for a 9-km sensing fiber length.

Description: We report on the design, fabrication, and optical characterization of InN-based optical waveguides aiming at their application as all-optical limiters at 1.55 $mu text{m}$ . The InN guiding layers are grown by radio frequency (RF) sputtering on sapphire substrates. Experimental cutback method and nonlinear optical transmittance measurements were performed for the developed devices. The waveguides present nonlinear behavior associated with two photon absorption process. A nonlinear absorption coefficient ranging from $sim 43$ to 114 cm/GW is estimated from optical measurements. These results open the possibility of using RF sputtering as a low cost and thermally harmless technique for the development and overgrowth of InN-based optical waveguides in future III-nitride all-optical integrated circuits working at telecom wavelengths.

Description: A new simple structure of ultrahigh birefringent and ultrahigh nonlinear slot silicon microfiber with highly efficient dispersion reduction is proposed and numerically simulated using the full-vector finite-element method with anisotropic perfectly matched layers. Benefiting from the slot effect-induced sub-wavelength mode confinement, ultrahigh birefringence up to the order of $10^{mathrm {{-1}}}$ can be realized within a wide wavelength range from 1.4 to 1.7 $mu text{m}$ , which is comparable with the results in these ultrahigh birefringent photonic crystal fibers, but cannot be achieved in traditional microfibers. Meanwhile, the nonlinear coefficients of quasi-TE mode and quasi-TM mode at the wavelength of 1.55 $mu text{m}$ are as high as 969.58 $text{W}^{mathrm {{-1}}}text{m}^{mathrm {{-1}}}$ and 156.74 $text{W}^{mathrm {{-1}}}text{m}^{mathrm {{-1}}}$ , respectively. Furthermore, the dispersion value of quasi-TE mode at 1.55 $mu text{m}$ can be decreased from $1.2358times 10^{mathrm {{3}}}$ ps/(nm $cdot $ km) to 0 ps/(nm $cdot $ km) simply by modifying the slot size. Owing to its excellent performance, the proposed slot silicon microfiber will have great potential for polarization maintaining nonlinear signal processing applications.

Description: The two-, three-, and four-channel mapping multiplexing technique (MMT) is demonstrated to increase the data capacity of multilevel intensity-modulated transmission formats to 2, 3, and 4 bits/symbol with a substantial reduction in power penalty. This paper outlines the $N$ -channel MMT design metric consideration influence on the performance enhancement of higher order amplitude modulated systems in terms of power penalty, receiver sensitivity, and spectral efficiency. The signal space model has been developed for $N$ -channel MMT, where the average electrical and optical power expressions are derived. Transmission of 2, 3, and 4 bits/symbol using MMT system shows better performance in terms of the average optical power penalty, in comparison with pulse amplitude modulation (M-PAM) formats, with respect to the information capacity. The proposed scheme can be considered as an alternative to M-PAM systems with enhanced power efficiency.

Description: Optical networks-on-chips (ONoCs) are burgeoning structures of communication that can give a solution to the bandwidth and latency for multiprocessor systems-on-chips. Furthermore, photonic devices are widely used in ONoCs but suffer from crosstalk noise. Therefore, crosstalk noise is the critical factor that affects signal transmission and limits the network scale of ONoCs. To reduce the crosstalk noise sharply, an angle optimization that uses the cross angle of 60 $^{circ}$ or 120 $^{circ}$ instead of the conventional angle of 90 $^{circ} $ is proposed to optimize the Crux router. Furthermore, we present a signal transmission system simulation model for the mesh-based ONoC. For different routers applied to the mesh-based ONoC, the simulation model can present the time-domain waveform, eye diagram, and bit-error-rate (BER) curve clearly. On the basis of the analytical model, the results show that the minimum signal-to-noise ratio (SNR) of a 7 $times$ 7 mesh-based ONoC is 20.9 dB when using optimized Crux routers, and the injection power is equal to 0 dBm, which is 2.1 dB better than using Crux routers. Therefore, the application of angle optimization to the Crux router and mesh network can minimize crosstalk noise and improve the scalability of mesh-based ONoCs.

Description: Pulse-amplitude-modulated discrete multitone (PAM-DMT) modulation is an optical orthogonal frequency division multiplexing scheme, which is compatible with intensity modulation and direct detection channel. In the conventional receiver for PAM-DMT, only the imaginary parts of subcarriers are detected, while the real parts are considered as clipping noise and simply discarded, causing insufficient usage of the received power. This letter proposes a new receiver characterizing temporal and spectral diversity combining for PAM-DMT, which extracts the effective information in clipping noise to recover the data. The proposed receiver achieves a better performance than the conventional receiver with a gain of at least 2.3 dB in ${E_{b}}/{N_{0}}$ at the system bit error rate of $10^{-5}$ in additive white Gaussian noise channel by simulation when using 4-PAM modulation.

Description: Sample preparation plays an essential role in most biochemical reactions. Raw reactants are diluted to solutions with desirable concentration values in this process. Since the reactants, like infant’s blood, DNA evidence collected from crime scenes, or costly reagents, are extremely valuable, their usage should be minimized whenever possible. In this paper, we propose a two-phased reactant minimization algorithm (REMIA), for sample preparation on digital microfluidic biochips. In the former phase, REMIA builds a reactant-minimized interpolated dilution tree with specific leaf nodes for a target concentration. Two approaches are developed for tree construction; one is based on integer linear programming (ILP) and the other is heuristic. The ILP one guarantees to produce an optimal dilution tree with minimal reactant consumption, whereas the heuristic one ensures runtime efficiency. Then, REMIA constructs a forest consisting of exponential dilution trees to produce those aforementioned specific leaf nodes with minimal reactant consumption in the latter phase. Experimental results show that REMIA achieves a reduction of reactant usage by 32%–52% as compared with three existing state-of-the-art sample preparation approaches. Besides, REMIA can be easily extended to solve the sample preparation problem with multiple target concentrations, and the extended version also effectively lowers the reactant consumption further.

Description: The 3-D integrated dynamic random-access memory (DRAM) structure with a processor is being widely studied due to advantages, such as a large band-width and data communication power reduction. In these structures, the massive heat generation of the processor results in a high operating temperature and a high refresh rate of the DRAM. Thus, in the 3-D DRAM over processor architecture, temperature-aware refresh management is necessary. However, temperature determination is difficult, because in the 3-D DRAM, the temperature changes dynamically and temperature variation in a DRAM die is complicated. In this paper, a thermal guard-band set-up method for 3-D stacked DRAM is proposed. It considers the latency of the temperature data and the position difference between the temperature sensor and the DRAM cell. With this method, the data reliability of the on-chip temperature sensor-dependent adaptive refresh control is guaranteed. In addition, an efficient temperature sensor built-in and refresh control method is analyzed. The expected refresh power reduction is examined through a simulation.

Description: A novel low cost and simple temperature sensor based on multimode interference (MMI) is formed by a successive singlemode fiber (SMF)-bent multimode fiber (MMF)-SMF structure. Due to the small curvature radius of bent MMF section mimicking a balloon shape, MMI effect from the core is spreading into coating. The high temperature sensitivity is mainly due to the large thermo-optical coefficient of the existing acrylate coating of the MMF fiber. A temperature sensitivity of up to −2060 pm/°C and −25.1 nW/°C for wavelength- and intensity-based interrogation, respectively, have been achieved in the range between 27 °C and 31 °C. This sensor is most suitable in high sensitivity and low-temperature application such as the measurement of human body temperature.

Description: We reported the observation of whispering gallery modes (WGMs) from silicon microspheres in $C$ -band with a biconical tapered fiber-microsphere coupled system. We experimentally studied the resonant transmission spectra with broadband light source and optical spectrum analyzer, and measured the X-ray diffraction pattern of silicon microspheres. We analyzed the WGMs of silicon microspheres, the full-width at half-maximum was 0.12 nm, and the dip of the transmission spectra was 3.5 dB (55% of the incident power). The $Q$ factor of the silicon microsphere was $1.3 times 10 ^{4}$ . The Raman gain coefficient in silicon is rather strong and the energy density of microsphere resonator is rather high, so the silicon microsphere resonator possesses broad application prospect in optical communication fields, including filter, modulator, switch, wavelength converter, amplifier, Raman laser source, and so on.

Description: A working small-footprint asymmetrically and vertically coupled hybrid Si/GaN microring resonator (HMR) was demonstrated. The HMR of a minimum radius of 20 $muhbox{m}$ was fabricated in a high-yield ( $sim$ 90%) hybrid nanophotonic platform that allowed interactions between the GaN microring and the underlying Si waveguide circuit. The HMR's spectral response across the telecommunication C- and L-bands was measured. The high extinction ratio of up to 17 dB, the resonance linewidth as narrow as 40 pm, and the intrinsic quality factor of up to 70 000, which was the highest value for GaN microring reported so far, were achieved. The explicit analytical model for the high-index-contrast HMR was developed. Our basic study opened new possibilities for exploring GaN–Si nonlinear phenomena and for developing complex on-chip optical interconnects.

Description: It is difficult to manipulate the pulse distribution of a multipulse passively mode-locked fiber laser, and an effective solution is yet to be demonstrated. Here, we all-optically manipulate the pulsing of a mode-locked fiber ring laser at a telecommunication window (1.5 $mu text{m}$ ) by an optical pattern at 1 $mu text{m}$ . It can be demonstrated as an effective solution by examining different optical patterns modulated on an external laser source. In particular, the minimum pulse separation being manipulated by the external optical pattern can be shorter than 20 ps. It is noted that, with such a large wavelength separation between the cavity and the external sources, i.e., $sim 1550$ and 1060 nm, respectively, our scheme can simultaneously serve as an ultra-wideband wavelength convertor.

Description: AlGaN multiple quantum well lasers for optical pumping have been grown by metal-organic vapor phase epitaxy on high and low dislocation density AlN/sapphire templates. Lasers on planar templates exhibited high dislocation densities and high V-pit densities, but a smooth surface morphology leading to inefficient, but laterally very homogeneous optical emission. Lasing was not observed when optically pumped with up to 50 MW/cm 2 . Epitaxially laterally overgrown templates on patterned sapphire showed much lower dislocation densities, but also step bunching on the surface. This resulted in good photoluminescence efficiencies of up to 20%, but also in a higher lateral inhomogeneity of the emission. Lasers on these templates exhibited lasing at $sim 240$ nm with low full-width at half-maximum of 1 nm and threshold power densities of 11–15 MW/cm 2 .

Description: In the light-emitting-diode (LED) industry, it is a great challenge to simultaneously achieve high efficiency values and excellent light quality in practical applications. In this paper, we have designed microscale-roughness-controlled-surface modules to optimize rectified mellowness index, quantum efficiency, correlated color temperature, and color rendering index; we have also discovered a mechanism that reduces the total internal reflection trapped within the diffuser, maximizes phosphor fluorescence probabilities, and randomizes photon emissions. The first effect subsequently leads to the photon-propagation-direction rectification, such that incident photons are allowed to escape from the top but are discouraged to reversely exit from the bottom. In addition to the discovery of this mechanism, we have proposed a previously undefined criterion that evaluates the uniformity of various optical parameters exemplified by wavelengths, solid angles, and spatial distributions. Current findings offer a guide on future research for human-eye-comfort-related uniformities.

Description: We experimentally investigate the wavelength-division multiplexing (WDM) transmission of single-carrier 400G based on an orthogonal optical time-division multiplexed (orth-OTDM) 80-GBd polarization-division multiplexed (PDM) 8 quadrature-amplitude modulation (QAM) signal. The 80-GBd 8QAM signal is generated using the OTDM method based on two tributaries of time-domain orthogonal pulses with 40-GBd 8QAM signals. Full-band coherent detection is utilized with digital signal processing based on a single broadband receiver for the 80-GBd signals. The WDM transmission performance of single-carrier 400G signals within different channel grids and carrier spacing is also investigated. Finally, four 400G channels, each carrying an 80-GBd PDM-8QAM signal within 100-, 80-, and 75-GHz grids, are successfully transmitted over 1600-, 800-, and 400-km standard single-mode fibers with Erbium-doped fiber amplifier (EDFA)-only amplification below a pre-Forward error correction (FEC) bit-error rate (BER) of $2.4times10^{-2} $ (20% soft-decision FEC) , respectively. The achieved spectral efficiency for the 400G channel can be 4, 5, and 5.33 bit/s/Hz, respectively.

Description: This letter presents a multiplexed fiber-optic sensor array suitable for detection of liquid intrusions, spills, and leaks. The proposed detection systems is based on active heating and observation of temperature changes in short sections of optically absorbing (vanadium-doped) optical fibers that were interconnected into a sensing array by a standard single-mode optical fiber. The heating of the vanadium-doped fiber sections was achieved by application of a common 980-nm pump laser source. The associated signal processing and integration utilizes a simple, custom-designed optical time domain reflectometry that relies on only a few low-cost standard telecom components.

Description: A method for mitigating local oscillator (LO) phase noise-induced impairment, also known as equalization-enhanced phase noise, in coherent optical systems is discussed. The method is suitable for real-time implementation and requires hardware with a bandwidth much lower than the signal baud rate, even for a system utilizing conventional semiconductor laser as LO. We evaluate the required parameters like interpolation technique, electrical signal-to-noise ratio at digital coherence enhancement (DCE) front end, for long haul transmission links having quadrature phase shift keying and 16-quadrature amplitude modulation formats. We show that the method can be implemented using a low-speed DCE front end and a simple digital linear interpolator with small (<1 dB) implementation penalty even in cases that would otherwise result in error floor.

Description: This letter presents a low-power, 40-Gb/s optical receiver front-end fabricated in a 65-nm CMOS technology. Using an inverter-based topology for both the transimpedance amplifier and the post amplifier, high energy efficiency has been obtained. Cascaded amplifiers with transconductance and transimpedance combinations are utilized to acquire a bandwidth of 29.6 GHz. A low-dropout voltage regulator is applied to reduce the supply noise of the single-ended amplifiers. The prototype chip excluding output buffer consumes only 12.4 mW (310 fJ/b) at a 1.2 V single supply, and the integrated input referred noise is 9.2 $mu text{A}_{mathrm { {rms}}}$ .

Description: Design of power delivery system has great influence on the power management in many-core processor systems. Moving voltage regulators from off-chip to on-chip gains more and more interest in the power delivery system design, because it is able to provide fine-grained dynamic voltage scaling. Previous works are proposed to implement power efficient on-chip voltage regulators. It is important to analyze the characteristics of the entire power delivery system to explore the tradeoff between the promising properties and costs of employing on-chip voltage regulators, especially the on-chip buck converters. In this paper, we present a novel analysis and design optimization platform of power delivery system called power supply on-chip (PowerSoC). It employs an analytical model to provide an accurate and fast evaluation of important characteristics, e.g., power efficiency, output stability, and dynamic voltage scaling, for the entire power delivery system consisting of on-chip/off-chip buck converters and power delivery network. Based on our model, geometric programming is utilized to find the optimal design for different power delivery systems and explore the tradeoff of using on-chip converters. Compared with SPICE simulations, our model achieves a simulation time reduction of six to seven orders of magnitude within 5% model error for the characteristic evaluation of different power delivery systems. By using PowerSoC, various architectures of power delivery systems are optimized for power efficiency under constraints of output stability, area, etc. Simulation results show that the hybrid architecture, consisting of both on-chip and off-chip converters, achieves 1.0% power efficiency improvement and 66.4% area reduction of converters, compared to the conventional design. We conclude the hybrid architecture has potential for efficient dynamic voltage scaling, small area, and the adaptability of the change of power delivery network parasitic, but ca- eful account for the overhead of on-chip converters is needed.

Description: As the technology sizes of integrated circuits (ICs) scale down rapidly, current transistor densities on chips dramatically increase. While nanometer feature sizes allow denser chip designs in each technology generation, fabricated ICs become more susceptible to wear-outs, causing operation failure. Even a single link failure within an on-chip fabric can halt communication between application blocks, which makes the entire chip useless. In this paper, we aim to make faulty chips designed with network-on-chip (NoC) communication usable. Specifically, we present fault-tolerant irregular topology-generation method for application-specific NoC designs. Designed NoC topology allows different routing path if there is a link failure on the default routing path. Additionally, we present a simulated annealing-based application mapping algorithm aiming to minimize total energy consumption of the NoC design. We compare fault-tolerant topologies with nonfault-tolerant application-specific irregular topologies on energy consumption, performance, and area using multimedia benchmarks and custom-generated graphs. Our results demonstrate that our method is able to determine fault-tolerant topologies with negligible area increase and better energy values.

Description: Three-dimensional (3-D) integration is an attractive technology platform for next-generation ICs. Despite the benefits offered by 3-D integration, test cost remains a major concern, and analysis and tools are needed to understand test flows and minimize test cost. We propose a generic cost model to account for various test costs involved in 3-D integration and present a formal representation of the solution space to minimize the overall cost. We present an algorithm based on A*—a best-first search technique—to obtain an optimal solution. An approximation algorithm with provable bounds on optimality is proposed to further reduce the search space. In contrast to prior work, which is based on explicit enumeration of test flows, we adopt a formal optimization approach, which allows us to select an effective test flow by systematically exploring an exponentially large number of candidate test flows. Experimental results highlight the effectiveness of the proposed method. Adopting a formal approach to solving the cost-minimization problem provides useful insights that cannot be derived via selective enumeration of a smaller number of candidate test flows.

Description: We design a series of plasmonic bowtie antennas with broadly varying resonant wavelengths from 1.34 to 3.36 $muhbox{m}$ under the same antenna footprint size. Based on the prototype of contour bowtie antennas (CBAs), we modify the geometry of CBAs with extensive resonant paths and, therefore, redshift resonances and maintain the gap enhancement factors, at least at the same level with that of the solid bowtie antenna.

Description: As data centers evolve to sustain the economic scale in network traffic, optical interconnections are adapted to support the vast amount of capacity requirements. Among emerging solutions is the incorporation of digital-signal-processing (DSP) functionalities at the receiver to compensate for the optical fiber and optoelectronic components impairments. The bottleneck in such architecture is often implementing a high-resolution and high-speed analog-to-digital-converter (ADC) device, which usually leads to massive power consumption and high costs. In this paper, we propose novel transmission schemes based on low-resolution ADCs, termed DSP-enhanced analog-to-digital conversion. The proposed methods are based on the mathematical principle of predictive quantization, combined with linear equalization theory. Mathematical analysis and performance bounds associated with common channel impairments are derived. Simulation results demonstrate that the DSP-enhanced ADC provides a significant signal-to-noise-ratio (SNR) gain and, subsequently, may enable heavy digital compensation with reduced-resolution ADCs.

Description: A frequency-doubling optoelectronic oscillator (OEO) has been proposed. In the proposed device, several passive components are introduced into the traditional OEO to handle the polarization state of the laser in the feedback loop. Making use of the polarization dependence of the LiNbO 3 intensity modulator, a special double sidebands modulation is implemented where the polarization direction of the optical carrier is orthogonal with that of the first-order sidebands. Two polarizers are used to choose the specific optical components from the modulated light, which ensures that a microwave signal at the second-harmonic frequency outputs from the OEO when the fundamental frequency signal is self-oscillating in the loop. In the experiment, a 20-GHz frequency-doubled signal was generated, whose phase noise performance and immunity to the polarization drift were measured and evaluated.

Description: A simple and low cost analog photonic link with the compensation of dispersion-induced power fading is proposed and demonstrated using a dual-electrode Mach–Zehnder modulator. In the proposed link, the modulator is single-electrode driven to realize a novel double-sideband (DSB) modulation. By adjusting the dc bias of the modulator, the frequency response of a dispersive link can be controlled to compensate the power fading at any working frequency. Experimental results show that the power fading in a conventional DSB modulated link after fiber transmission over 25 and 50 km can be both successfully compensated in the proposed link, and the spurious-free dynamic range at 12 GHz of a link with 25 km of single-mode fiber is improved by 11.6 dB.

Description: We demonstrated that silicon (Si) microsphere resonators, which exhibited high quality factor ( $Q$ ) whispering-gallery-modes (WGMs), could be rapidly fabricated from Si-cored fibers using CO 2 laser reformation. WGMs were excited using the tapered silica fiber coupling technique, and a record resonant $Q$ as high as $4 times 10^{mathrm {mathbf {5}}}$ was obtained from a Si microsphere with a diameter of $25.4~mu text{m}$ . The shift of resonant wavelength caused by thermooptic effect of Si material was also observed.

Description: We present a CMOS integrated optical receiver having under-damped transimpedance amplifier (TIA) and CMOS avalanche photodetector (APD) realized in 65-nm CMOS technology. The under-damped TIA compensates the bandwidth limitation of CMOS APD and provides enhanced receiver bandwidth performance with reduced power consumption and better sensitivity compared with previously reported techniques. We successfully demonstrate 10-Gb/s $2^{31}-1$ PRBS and 12.5-Gb/s $2^{7}-1$ PRBS operation with the bit-error rate less than $10^{-12}$ at the incident optical power of −6 and −2 dBm, respectively. The receiver has core size of 0.24 mm $times 0.1$ mm and power consumption excluding output buffer of $sim 13.7$ mW with 1.2 V supply voltage.

Description: The performance of dual-carrier 400G solutions based on three high-order quadrature amplitude modulation (QAM) formats (8/16/32-QAM) is investigated on the same platform. We first study the benefit and penalty differences of gray and differential coding, and then experimentally compare OSNR sensitivities and transmission performance using flexible transceiver configuration and the same erbium-doped fiber amplifiers-only standard single-mode fiber link. Experimental results show the implementation penalties are 1.85 dB for 42-GBd polarization multiplexed (PM)-8QAM, which is 1 and 1.5 dB better than 32-GBd PM-16QAM and 25-GBd PM-32QAM at 5.92-dB $text{Q}^{2}$ -factor (corresponding to a bit error rate of 2.4E-2), respectively. It is also found that maximum reaches of 2460 km for 42.6-GBd PM-8QAM, 1640 km for 32-GBd 16QAM, and 820 km for 25-GBd PM-32QAM are achieved. Furthermore, the performances of cascaded multimodulus algorithm and decision-directed least mean square (DD-LMS) algorithms are also compared. The improvement by addition of one sample-/symbol-based DD-LMS digital filter is investigated as well.

Description: An amplitude-division Fourier transform spectroscopy system has been constructed. The system design hinges on an electrothermally actuated micromirror with large piston motion. The micromirror is composed of electrothermal mesh actuators and can generate up to $95~mu text{m}$ usable linear optical path difference of the system at only $0.8~V_{rm dc}$ . A custom electrical system is developed to control the micromirror and data processing is implemented to extract the spectrum from interferograms. The system can achieve a spectral resolution of 5 nm at 532 nm.

Description: A new technique is presented to reconfigure the dispersion-induced RF fading in a spectrum-sliced microwave photonic filter to an arbitrary spectral shape, including the flat-top response with rectangular shape and operating frequencies beyond conventional baseband. The technique is based on the Fourier transform of the modified optical source power spectrum, which is realized by applying a designed optical amplitude and phase manipulation using a diffraction-based spectral pulse shaper to the ports of a dual-output Mach–Zehnder electro-optic modulator in combination with a broadband light source. This scheme is fundamentally different from earlier finite-impulse-response-based spectrum-sliced microwave-photonic filters that require specific slicing elements for optical taps, but offers the same flexibility in realizing various filter passband characteristics with the added benefit of widely shape-invariant tuning and a single passband response. Experimental results verify the technique and demonstrate a continuously tunable dispersion-induced RF fading up to 20 GHz, exhibiting shape invariance and a flat-top response.

Description: In this letter, a light-emitting heterostructure is designed and manufactured using vertically aligned n-type zinc oxide nanorods (ZnO NRs) on n + -GaAs wafers. The chemically grown ZnO NRs were also converted to nanotubes (NTs) using 2 molar KCl solution and the device fabrication was repeated using them. Both types exhibited a significant visible light at a forward bias of 1 V but with different brightness. Photoluminescence $sim 390$ nm from NRs and NTs was obtained and the current injection in these devices is explained by a tunneling phenomenon.

Description: We have numerically demonstrated the significant impacts on the resonance mode characteristics of subwavelength grating structures due to tapered sidewall profile and high aspect ratio, which is normally obtained due to the practical CMOS-compatible fabrication and etching processes. Our simulation results have revealed that the tapered sidewall profile with high aspect ratio plays important roles on the resonance mode behavior of subwavelength grating photonic devices. The coupling mechanism between the guided mode resonance and the grating cavity is also emphasized. Our numerical studies can be utilized for a series of integrated photonic devices applications, such as compact optical filter, photonic amplifier, and lasers, while considering realistic subwavelength grating structures due to current nanoelectronics fabrication process.

Description: A photonic approach to generating a dual-chirp microwave waveform using a single dual-parallel Mach-Zehnder modulator (DPMZM) is proposed and experimentally demonstrated. A dual-chirp microwave waveform can be used in a radar system to improve its range-Doppler resolution. In the proposed approach, a baseband single-chirp waveform is applied to one sub-Mach-Zehnder modulator (sub-MZM) in the DPMZM and a microwave carrier is applied to the other sub-MZM. By biasing the two sub-MZMs at the minimum transmission point to suppress the optical carrier, a dual-chirp microwave waveform with a central frequency upconverted to the frequency of the microwave carrier is generated. A theoretical analysis is performed, which is then verified by a proof-of-concept experiment. A dual-chirp microwave waveform at 6 GHz with a tunable bandwidth at 200 MHz and 2 GHz is generated.

Description: The basic properties of a thermal memory effect of polymer optical fibers (POFs) are experimentally investigated. We measure the thermally induced loss as a function of time at several high temperatures, and find that the loss becomes almost constant after heating for $sim 200$ s. The loss remains unchanged even after the heated section is cooled to room temperature. We subsequently measure the optical time-domain reflectometry traces under three different conditions: 1) before a POF section is heated; 2) shortly after the POF section is heated at high temperature; and 3) after the heated section is cooled to room temperature. The traces measured under 2) and 3) are moderately identical, which indicates that the thermal memory effect can be exploited in developing excess-heat detecting system in future.

Description: A monolithically integrated silicon coherent receiver based on a novel scheme with a crossing-free 90 $^{circ}$ hybrid optical coupler and two balanced germanium photodetectors is reported. The integrated receiver is compact (footprint is $0.8times 1.0 hbox{mm}^{2}$ ), and it is demonstrated by working with single-polarization 56-Gb/s quadrature phase-shift keying (QPSK) and 80-Gb/s 16-quadrature amplitude modulation (16-QAM) signals. In particular, QPSK transmission that is back-to-back at 28 Gbaud shows a bit-error rate (BER) below $10^{-4}$ for an optical signal-to-noise ratio (OSNR) lower than 17 dB, whereas 16-QAM at 20 Gbaud shows a BER not better than $3^{ast}10^{-2}$ because of the nonideal behavior of the device. Reasons for the performance limitations are discussed.

Description: We demonstrate a 56 Gb/s four-level pulse-amplitude modulation (PAM-4) transmission using direct detection and a long-wavelength 18-GHz bandwidth vertical-cavity surface-emitting laser as directly modulated light source for short-reach inter- and intra-connects in datacenters and short-reach networks. Error-free transmission over 2 km at 7% hard-decision forward-error correction threshold is achieved by applying powerful equalization schemes at the receiver side. Three equalization schemes, i.e., a maximum likelihood estimation (MLSE), a feed-forward equalizer (FFE), and a combination of the FFE and the MLSE are thoroughly investigated, and the performance comparison between them is carried out.

Description: We investigate lifetime (induced dipole–dipole interaction) of spontaneous parametric four-wave mixing (SP-FWM) and multiorder fluorescence (FL) signals controlled by polarization dressing in a heteronuclear-like molecule system of Pr $^{3+} $ :YSO. The comparisons between a lifetime of SP-FWM and multiorder FL controlled by single dressing, double dressing, and triple dressing polarization have been investigated. It is observed that FLs have a stronger dressing effect than SP-FWM. The polarization dressing is more obvious in the intensity signal in the spectral domain than that in the time domain. Such results have potential applications in quantum communication such as optical information storage, routing, and processing on a photonic chip.

Description: The limited band of optical and electrical devices in an intensity-modulation direct detection (IM/DD) system is considered to be a major bottleneck that hinders the increase in transmission capacity. Spectrally efficient modulation formats and advanced digital signal processing are key technologies to improving the performance of IM/DD for high-speed short-reach optical systems. In this paper, we propose and experimentally demonstrate a novel Nyquist eight-level, pulse-amplitude, single-carrier modulation with frequency-domain equalization (PAM8-SCFDE). In addition, 40-GBd Nyquist PAM8-SCFDE signals can be successfully transmitted over 2-km standard single-mode fiber or 20-km large effective area fiber based on 10-G-class DAC and photodiode. Therefore, the achieved aggregate data rate is 120 Gb/s, and the measured bit error rate (BER) is under 7% pre-forward-error-correction (FEC) threshold of $3.8times 10^{-3} $ . Compared with conventional PAM8, this scheme can provide double spectral efficiency and 6-dB receiver sensitivity improvement.

Description: An eight-channel integrated optical add-drop multiplexer with cascaded parent-sub microring resonators is experimentally demonstrated on a silicon-on-insulator (SOI) substrate. Through thermal tuning, each channel can be independently switched between the adding and dropping states. The measured thermal tuning efficiency is 0.15 nm/mW. Typically, all eight channels can be multiplexed and demultiplexed with a 2.6-dB drop loss, a 0.36-nm bandwidth ( $〉$ 40 GHz), and a $-$ 20-dB channel crosstalk. Moreover, the scheme to increase the number of operating channels is also discussed.

Description: We apply the principle of master-slave (MS) interferometry to a full-field swept source optical coherence tomography (OCT) setup equipped with a fast 2-D camera. MS interferometry does not involve Fourier transformations and, therefore, eliminates the need for spectrum data resampling required by the conventional spectral domain OCT. Using this method in a full-field OCT setup, en face images are acquired in vivo from finger skin, Drosophila melanogaster larvae, and pupae, with no spectrum resampling and no mechanical scanning. The signal processing is based on a comparison operation of the shapes of channeled spectra for each camera pixel, with a set of reference signals (masks). In this way, en face OCT images can be obtained with no need for the volumetric assembly and software cutting the en face images from an image volume, which are required by the conventional spectral domain OCT method. We demonstrate that the sensitivity and axial resolution of the MS method in a full-field swept source OCT setup are similar to the values obtained using the conventional Fourier-transformation-based swept source OCT method in a full-field setup. Multiple en face images can be produced in parallel by using multiple stored shapes of channeled spectra for the depths of interest. The full-field MS-OCT method presented here opens the possibility of parallel processing for all image points in a 3-D volume of the object.

Description: We report the fabrication of amorphous (In x Ga 1− x ) 2 O 3 metal–semiconductor–metal ultraviolet (UV) photodetectors on glass substrate by co-sputtering. It was found that, we could change the cutoff wavelength of the fabricated photodetectors by changing the RF sputtering power of the In 2 O 3 target. With 5 V applied bias, it was found that the measured dark currents were $2times 10^{-12}$ , $1times 10^{-11}$ , and $2.3,times , 10^{-11}$ A for sample A prepared with 40 W In 2 O 3 sputtering power, sample B prepared with 50 W In 2 O 3 sputtering power, and sample C prepared with 60 W In 2 O 3 sputtering power, respectively. It was also found that the UV-to-visible rejection ratios were $3times 10^{3}$ , $5times 10^{3}$ , and $1.5times 10^{4}$ for samples A, B, and C, respectively. Furthermore, it was found that the response speeds of the fabricated devices were good.

Description: In this letter, a direct current (DC) bias optimization scheme is proposed for the low-density parity-check (LDPC) coded DC-biased optical orthogonal frequency division multiplexing (DCO-OFDM) systems from consideration of power efficiency and dimming control. The DC bias can be optimized subject to the decoding convergence threshold, which is calculated by the extrinsic information transfer (EXIT) chart analysis for the LDPC coded DCO-OFDM systems. The simulations demonstrate that the decoding performance with different DC bias is quite consistent with the numerical results after the EXIT chart analysis.

Description: In this letter, a novel pressure sensor using an SU-8 structure and angle polished fiber is proposed. There are two different Fabry–Pérot cavities in the design, and the cavity lengths can be demodulated at the same time to realize temperature compensation. SU-8 photoresist is suited for forming a high-aspect-ratio structure and the thickness can be controlled precisely. The fabrication process is described and the lithography technology is employed. The characteristics of both pressure and temperature are tested. Experimental results show that the sensor has a good linearity over the pressure range of 0–0.1 MPa. The R-square is 0.998. The sensitivity (change in cavity/loaded pressure) is 60.9 $mu text{m}$ /MPa.

Description: In this letter, we present what we believe to be a new design for simultaneously coherent and spectral beam combinations by active phasing and bandwidth-controlled dichromatic mirror. A principle of concept experiment is demonstrated by employing eight 20-W power-level polarization-maintained all fiber amplifiers, which generate a 142.1-W near diffraction limited ( $M^{2}_{x}sim 1.1$ and $M^{2}_{y}sim 1.1$ ) output power with the whole combining efficiency of $>90$ %. The new designed beam combining system is competent for both narrow-band and broadband gain elements with full linewidth of $〈4$ nm. Along with the near-diffraction-limited power scaling progress on monolithic polarization-maintained amplifier, we believe that the approach demonstrated has great potential for remarkable power boosting in both continuous- and pulsed-wave operations.

Description: In this letter, we demonstrate a liquid optical switch based on total internal reflection. A conductive liquid (Liquid-1) is filled in the chamber and surrounded by a nonconducting liquid (Liquid-2). The refractive index of the transparent cube ( $n_{c})$ , Liquid-1 ( $n_{1}$ ), and Liquid-2 ( $n_{2}$ ) meet the relations of $n_{c}>n_{1}$ , and $n_{2}>n_{1}$ . In initial state, the cube is totally immerged in Liquid-1. The incident light is adjusted to just meet the condition of total internal reflection when it illuminates the solid-liquid interface. The light is totally reflected by the cube, and the device shows light-OFF state. When we apply a voltage to sidewall electrodes, Liquid-1 stretches toward to the sidewalls. The cube’ top surface comes out from Liquid-1. The interface of solid/liquid changes. The light is refracted by Liquid-2. The device shows light-ON state. So the device can achieve the functions of optical switch. Because the light can be totally reflected by the cube, the device can attain 100% intensity attenuation. Our experiments show that the device has a fast switch time of 49 and 53 ms from light-OFF (ON) to light-ON (OFF), respectively. The proposed optical switch has potential applications in variable optical attenuators, information displays, and light shutters.

Description: A monolithic integrated amplified feedback laser is experimentally demonstrated as a new solution to generate dual-mode lasing with a wide frequency tuning range covering the entire 60-GHz band. This laser consists of a complex-coupled distributed feedback laser and an integrated feedback cavity formed by a phase section and an amplifier section. Different laser sections are integrated by a simple quantum well intermixing technique. By tuning the injection currents of the laser sections, the beating-frequency can be continuously tuned from 46.8 to 72 GHz with a 3-dB linewidth below 5 MHz. Benefit from the simple fabrication process and wide tuning range, the device will be a potential candidate for hybrid fiber-wireless access network and high frequency optical microwave generation.

Description: We reported a gas pressure sensor based on CO 2 -laser-induced long-period fiber grating (LPFG) in an air-core photonic bandgap fiber (PBF). The LPFG was inscribed in an air-core PBF by the use of an improved CO 2 laser system with an ultraprecision 2-D scanning technique, which induced periodic collapses of air holes along the axis of the PBF. Such an LPFG could be used to develop a promising gas pressure sensor with a sensitivity of −137 pm/MPa. Moreover, a simplified fiber model with a relatively similar elastic response was developed to qualitatively study the gas pressure response of the LPFG inscribed in the air-core PBF. A simulated stress distribution along the LPFG revealed that the gas pressure leads to a stress concentration at the collapsed area of the air holes in the fiber cladding, which finally results in a resonant wavelength shift of the LPFG through an elastooptical effect.

Description: In optical burst/packet switched (OBS/OPS) networks, bursts/packets may be dropped because of equipment failures. A widely used mechanism to protect a connection from a single-trunk-failure event is 1 + 1 path protection. We consider a bufferless OBS/OPS network with two types of users: 1) premium (that receive 1 + 1 protection service) and 2) regular (that do not receive such a service). We propose a fast and accurate approximation to evaluate the performance of such OBS/OPS network. The accuracy and scalability of the approximation and the effect of the proportion of the premium users in the network are discussed.

Description: Influences of external optical injection on the nonlinear dynamics of a three-section monolithically integrated semiconductor laser (MISL) are investigated experimentally. The results show that, for the solitary three-section MISL, diversely dynamical states including the stable state as well as the so-called period-one, period-two, multi-period, and chaotic states can be observed through adjusting the currents of the gain section ( $I_{G}$ ) and the phase section ( $I_{P}$ ). However, the chaotic operation region of the solitary MISL in the parameter space of $I_{G}$ and $I_{P}$ is very small and found to exist when $21.28~textrm {mA}〈 I_{G}〈 26.40$ mA and $31~textrm {mA}〈I_{P}〈 37$ mA. After introducing an external optical injection, the MISL originally operating at other dynamical states can always be driven into chaotic state under suitable injection strength and frequency detuning, and a relatively large $I_{G}$ will be helpful for obtaining broad and continuous chaotic regions in the parameter space of injection strength and frequency detuning.

Description: We demonstrate a high refractive index (RI) liquid level sensor based on coreless multimode fiber (CMF) which is capable of measuring the liquid level and discriminating the high RI. The direct exposure of the CMF enables a strong interaction between the high-order modes guided in it and the surrounding medium through evanescent wave. Part of the energy leak out at the fiber/liquid interface when the RI of the liquid exceeds that of the CMF. The transmission of the single-mode fiber (SMF)-CMF-SMF structure is a function of both the liquid level and RI which experiences leakage loss with the increasing liquid level. Liquid level information can be determined by simply selecting a wavelength range with linear power variation. The proposed sensor with 4.1-cm CMF has approximately linear responses of −0.223, −0.253, −0.316, −0.392, and −0.461 dB/mm for glycerol solution concentrations of 98%, 96%, 92%, 88%, and 84% in a 2-nm wavelength range, respectively. Such a simple and low-cost sensor may be integrated as biochemical probes, indicating preferable sensing performance and practicability.

Description: Visible light communication (VLC) is attractive as a supplementary method for future fifth-generation (5G) wireless communication owing to the shortage of radio-frequency bandwidth in conventional wireless communications. The VLC systems reported in the literature are mainly based on PIN receivers (Rxs). It is highly desirable if these VLC signals can be detected by using built-in complementary metal–oxide–semiconductor (CMOS) cameras as Rxs to provide flexible and low-cost wireless communications. However, using the CMOS camera is challenging. In this paper, we propose and demonstrate a VLC link using a CMOS mobile phone camera as Rx. By using the rolling shutter effect of the CMOS sensor, the VLC data rate can be significantly enhanced. We first use a second-order polynomial fitting to mitigate the “blooming effect” (saturation of pixels) of the CMOS sensor. In order to extend the VLC transmission distance and mitigate the influence of the background noise, we also propose and demonstrate using histogram equalization and Sobel filter to enhance VLC signal performance. Finally, a third-order polynomial fitting is used to define the threshold. The experimental results show that significant improvement of bit error rate (BER) for about an order of magnitude under different illuminances can be achieved.

Description: An optical fiber humidity sensor with porous anodic alumina (PAA) film on single-mode fiber tip is proposed and experimentally demonstrated. Relative-humidity (RH) sensing is correlated with the shift of interference fringe due to capillary condensation, which results in the change of effective refractive index of PAA film when exposed to different RH environments. Experimental result shows that sensitivity of 0.31 nm/%RH can be realized with very good repeatability in range of 20%RH–90%RH. It can be concluded that fiber-optic RH sensors with PAA film of thinner thickness, smaller aperture size, and aspect ratio would present promising sensing performance.

Description: A novel efficient and air-stable electron injection layer (EIL) of cesium azide (CsN 3 ) was compared with conventional ones including CsF, Cs 2 CO 3 , LiF and without EIL in type-II quantum dot light-emitting diodes (QLEDs) with both organic electron and hole transport layers. Via directly decomposing to pristine cesium (Cs), the low-temperature evaporated CsN 3 provided a better interfacial energy level alignment without damaging the underneath organic layer. Consequently, the current efficiencies of 7.45 cd/A was achieved in the CsN 3 -based green QLEDs consisting of giant CdSe@ZnS/ZnS quantum dots at 544 nm, which was 310% (at 10 mA/cm 2 ) improvement over the LiF-based QLEDs. Moreover, the light turn-on voltage in CsN 3 -devices significantly decreased $sim 5.5$ V in comparison with LiF-devices.

Description: By solving the two-dimensional Poisson equation for fibers with circular internal electrodes, we show that the parallel-plate approximation incurs significant error in the determination of the electric field applied to the fiber core. This also affects the value of $chi ^{mathrm {mathbf {(3)}}}$ measured in electro-optical fibers. The exact solution of Poisson’s equation is used to solve the field applied to the core of a photonic crystal fiber, where the many holes screen the field. A universal curve is derived to allow using the simplifying parallel plate approximation and correcting for the error in symmetric fibers with round holes.

Description: In this letter, we propose and experimentally demonstrate a compact, flexible, and scalable ultrawideband (UWB) generator based on the merge of phase-to-intensity conversion and pulse shaping employing an fiber Bragg Grating-based superstructure. Our approach offers the capacity for generating high-order UWB pulses by means of the combination of various low-order derivatives. Moreover, the scheme permits the implementation of binary and multilevel modulation formats. Experimental measurements of the generated UWB pulses, in both time and frequency domain, are presented revealing efficiency and a proper fit in terms of Federal Communications Commission settled standards.

Description: We present a long-period fiber grating sensor composed of a tapered optical fiber embedded in a polymeric grating. The fabrication process is based on a mold-replica approach, thus yielding low-cost reproducible structures. We evaluate the sensitivity to temperature and refractive index changes showing that the proposed structures could render useful for developing sensors with biocompatible polymers.

Description: A new evanescent-field-based coupler that achieves high coupling efficiency between a single-mode fiber (SMF) and a photonic crystal fiber (PCF) is proposed. The coupling equations are presented and a numerical solution is obtained in this letter. Optimization of the refractive index, the effective radius of PCF, and the coupling length can enhance the coupling efficiency. It is shown that a maximum coupling ratio of 93% can be achieved for a coupling length of 1.72 mm for commercially available SMFs and PCFs. The proposed PCF-SMF fiber coupler opens a path for the development of unique modalities for fiber-optic chemical sensors where the light ingress and egress paths can be via SMF, but the light interaction with analytes of interest occurs in the PCF where enhanced evanescent interactions can be obtained at the multiple air holes.

Description: A series of slot Si-on-SiO 2 photonic crystal heterostructure cavities with resonant wavelengths ranging from 1.28 to $1.6~mu text{m}$ is reported. These cavities, presenting $Q/V$ factors typically around 800 000, can be used for the hybrid integration of various active materials within the silicon photonics platform.

Description: An algorithm based on Karhunen–Loeve transform (KLT) for accurate tracking of fiber Bragg grating (FBG) sensors is presented. The routine is based on main eigenvalue analysis of the KLT applied to the Fourier transform of the FBG spectrum. The algorithm achieves sub-picometer accuracy, down to 4.9 fm, when applied to coarse (156 pm) wavelength sampling, providing accuracy superior to correlation-based algorithms. Experimental validation has been carried out in a climatic chamber. The proposed algorithm can be applied to any off-the-shelf white-light setup for FBG interrogation, and is compatible with 100–1-kHz operation.

Description: Nd(TTA) 3 (TPPO) 2 complex (HTTA: 2-thenoyltrifluoroacetone, TPPO: triphenylphosphine oxide) doped SU-8 polymer waveguide amplifiers were demonstrated. The absorption and photoluminescence spectra were observed on a 100- $mutextrm{m}$ -thick film of the Nd(TTA) 3 (TPPO) 2 complex doped SU-8 polymer. Under excitation at 808 nm, the fluorescence was obtained at 904 nm, 1068 nm, and 1346 nm wavelengths. The full-width at half-maximum bandwidth was about 25 nm wide around 1068 nm. Using reactive ion etching technology, optical waveguides were fabricated by taking the Nd(TTA) 3 (TPPO) 2 complex doped SU-8 polymer and polymethylmethacrylate (PMMA) material as the core and cladding layers, respectively. According to fundamental rate equations and optical power propagation equations, the gain characteristic of the polymer waveguide amplifier was simulated to be 5.1 dB/cm. An experimental setup for the optical gain measurement was established. A relative optical gain of about 2.4 dB/cm at 1064 nm was obtained in a 20-mm-long multimode waveguide for an input signal power value of 0.1 mW and pump power of 140 mW.

Description: The nonlinearity of a light-emitting diode (LED) limits the system performance of a visible light communications (VLC) system. Many nonlinearity mitigation methods have been studied. Recent technology advances in the micro-LED array have provided a simple alternative to deal with the system nonlinearity. In this paper, we study the approach of providing multiple access for the VLC system with the micro-LED array. A code-division multiple-access (CDMA) scheme that enables multiple access with variable data rate is proposed. In addition, the proposed system architecture is immune to the nonlinearity of the micro-LED array, thus providing optimal system performance. Simulations and laboratory experiments show the robustness and consistency of the proposed scheme.

Description: A high-index-contrast grating (HCG) reflector is implemented in the polysilicon gate of a standard bulk CMOS for the first time. A transverse-electric (TE) preferred CMOS HCG reflector allows a >90% peak reflectivity, a 100-nm reflection bandwidth, and a 1.64:1 TE/transverse-magnetic polarization ratio, which is limited by the thin field oxide layer between the HCG and the silicon substrate, resulting in optical leakage to the substrate. Remarkable improvements in peak reflectivity (close to 100%) and polarization ratio (10:1) are achieved by removing the substrate of HCG devices. Guided-mode resonance reflection in HCGs is further verified by the corresponding transmission dips and is predicted by the rigorous coupled-wave analysis simulations.

Description: An external laser cavity was constructed that utilizes polarization multiplexing to combine the emission from two gallium nitride blue laser diodes. A polarization-dependent narrow-band resonant mirror was designed to be the output coupler of this cavity, which locked both laser diodes at a fixed wavelength of 445.5 nm with a line-width of <0.5 nm. Output powers from this system approached 0.7 W while maintaining complete spectral control.

Description: Thermoelectric devices integrated with optical resonance absorbers are demonstrated. We design the absorbers with rigorous numerical methods and fashion experimental prototypes by thin-film deposition, patterning, and etching. A $sim 2.5$ - $mu text{m}$ -thick p-type heavily doped polysilicon film on a $sim 2$ - $mu text{m}$ layer of thermally grown SiO 2 enables guided-mode resonance. The SiO 2 layer additionally serves to thermally insulate the polysilicon layer from the Si substrate. A grating layer is etched into the polysilicon film to form the absorber. Thus, the polysilicon film works as functional material for both the absorber and the thermoelectric converter itself. Numerical simulations show that the resonance segment enhances absorption by $sim 30$ % in the visible spectral range and by $sim 40$ % in the infrared (IR) range relative to unpatterned devices. Moreover, the experimental results demonstrate significantly increased electrical output over reference devices. These simple devices can be applied as compact voltage generators and IR sensors.

Description: A low-cost and real-time frequency division multiplexing system is proposed based on multi-longitudinal mode fiber laser sensor array and beat signal demodulation technology. The lasers have staggered cavity lengths with corresponding mode spacing. Beat signals of the longitudinal modes of each laser in the array are detected by a common detector. A relationship is worked out between the maximum multiplexing number of the sensors and maximum detectable frequency. A multiplexing array with four laser sensors is investigated experimentally and its potential application for strain measurement is also demonstrated. In the proposed multiplexing system, only one common photodetector and a commercial frequency analyzer are used to monitor all sensors simultaneously, which greatly decreases the cost of the system and makes it more competitive in large-scale monitoring field.

Description: As optical transport networks become more configurable, the need for reconfigurable optical add/drop multiplexers (ROADMs) that are colorless, directionless, and contentionless (CDC) increases. Either of the two major classes of ROADM architectures, i.e., broadcast-and-select and wavelength-selective, can provide the CDC properties. With broadcast-and-select ROADMs, this is generally accomplished by employing more costly or complex configurations or adding adjunct equipment. In contrast, the wavelength-selective class of ROADMs, where the central component is an optical cross-connect (OXC), inherently provides the CDC properties. However, this architecture is limited by the achievable size (i.e., port count) of the OXC. We present alternative wavelength-selective ROADM designs that require smaller OXCs while providing equivalent functionality.

Description: The new era of cognitive computing brings forth the grand challenge of developing systems capable of processing massive amounts of noisy multisensory data. This type of intelligent computing poses a set of constraints, including real-time operation, low-power consumption and scalability, which require a radical departure from conventional system design. Brain-inspired architectures offer tremendous promise in this area. To this end, we developed TrueNorth, a 65 mW real-time neurosynaptic processor that implements a non-von Neumann, low-power, highly-parallel, scalable, and defect-tolerant architecture. With 4096 neurosynaptic cores, the TrueNorth chip contains 1 million digital neurons and 256 million synapses tightly interconnected by an event-driven routing infrastructure. The fully digital 5.4 billion transistor implementation leverages existing CMOS scaling trends, while ensuring one-to-one correspondence between hardware and software. With such aggressive design metrics and the TrueNorth architecture breaking path with prevailing architectures, it is clear that conventional computer-aided design (CAD) tools could not be used for the design. As a result, we developed a novel design methodology that includes mixed asynchronous–synchronous circuits and a complete tool flow for building an event-driven, low-power neurosynaptic chip. The TrueNorth chip is fully configurable in terms of connectivity and neural parameters to allow custom configurations for a wide range of cognitive and sensory perception applications. To reduce the system’s communication energy, we have adapted existing application-agnostic very large-scale integration CAD placement tools for mapping logical neural networks to the physical neurosynaptic core locations on the TrueNorth chips. With that, we have successfully demonstrated the use of TrueNorth-based systems in multiple applications, including visual object recognition, with higher performance and orders of magnitude lower- power consumption than the same algorithms run on von Neumann architectures. The TrueNorth chip and its tool flow serve as building blocks for future cognitive systems, and give designers an opportunity to develop novel brain-inspired architectures and systems based on the knowledge obtained from this paper.

Description: Provides a listing of board members, committee members and society officers.

Description: Many commercial systems in the embedded space have shown weakness against power analysis-based side-channel attacks in recent years. Random masking is a commonly used technique for removing the statistical dependency between the sensitive data and the side-channel information. However, the process of designing masking countermeasures is both labor intensive and error prone. Furthermore, there is a lack of formal methods for quantifying the actual strength of a countermeasure implementation. Security design errors may therefore go undetected until the side-channel leakage is physically measured and evaluated. We show a better solution based on static analysis of C source code. We introduce the new notion of quantitative masking strength (QMS) to estimate the amount of information leakage from software through side channels. Once the user has identified the sensitive variables, the QMS can be automatically computed from the source code of a countermeasure implementation. Our experiments, based on measurement on real devices, show that the QMS accurately reflects the side-channel resistance of the software implementation.

Description: Currently available electronic design automation tools for design space exploration of solid state drives (SSDs) are not able to assess: 1) the device architecture inefficiencies; 2) architecture overdesign for a target performance; and 3) performance degradation caused by the disk usage. These tools feature either an overly high abstraction modeling strategy or lack the required flexibility to perform design exploration. To overcome these problems, this paper proposes SSDExplorer, a tool for fine-grained yet reasonably fast design space exploration of different SSD architectures highlighting possible bottlenecks. To prove its accuracy SSDExplorer has been validated with two real SSDs. SSDExplorer efficiency has been assessed by evaluating the impact of the NAND flash read retry algorithm impact on the SSD performance as a function of its internal architecture.

Description: Radiation-induced soft errors have become a key challenge in advanced commercial electronic components and systems. We present the results of a soft error rate (SER) analysis of an embedded processor. Our SER analysis platform accurately models generation, propagation, and masking effects starting from a technology response model derived using TCAD simulations at the device level all the way to application masking. The platform employs a combination of accurate models at the device level, analytical error propagation at gate level, and fault emulation at the architecture/application level to provide the detailed contribution of each component (flip-flops, combinational gates, and SRAMs) to the overall SER. At each stage in the modeling hierarchy, an appropriate level of abstraction is used to propagate the effect of errors to the next higher level. Unlike previous studies which are based on very simple test chips, analyzing the entire processor gives more insight into the relative contributions of combinational and sequential SER. The results of this analysis can assist circuit designers to adopt effective hardening techniques to reduce the overall SER while meeting the required power and performance constraints.

Description: To improve the efficiency of direct solution methods in SPICE-accurate integrated circuit (IC) simulations, preconditioned iterative solution techniques have been widely studied in the past decades. However, it is still an extremely challenging task to develop robust yet efficient general-purpose preconditioning methods that can deal with various types of large-scale IC problems. In this paper, based on recent graph sparsification research we propose circuit-oriented general-purpose support-circuit preconditioning (GPSCP) methods to dramatically improve the sparse matrix solution time and reduce the memory cost during SPICE-accurate IC simulations. By sparsifying the Laplacian matrix extracted from the original circuit network using graph sparsification techniques, general-purpose support circuits can be efficiently leveraged as preconditioners for solving large Jacobian matrices through Krylov-subspace iterations. Additionally, a performance model-guided graph sparsification framework is proposed to help automatically build nearly-optimal GPSCP solvers. Our experiment results for a variety of large-scale IC designs show that the proposed preconditioning techniques can achieve up to $18 {times }$ runtime speedups and $7 {times }$ memory reduction in DC and transient simulations when compared to state-of-the-art direct solution methods.

Description: Electron-beam (e-beam) lithography has long been employed for mask writing but the write time is increasing due to the escalating mask pattern complexity. Besides, e-beam direct write is being pursued as an alternative solution for chip production in the sub-22 nm regime. To improve the throughput of e-beam lithography, character projection method is commonly employed and a critical problem is to pack as many useful characters as possible onto the stencil. In this paper, we consider three enhancements in packed stencil design over previous works. First, the fact that the pattern of a character can be located anywhere within its enclosing projection region is exploited to facilitate flexible blank space sharing. Second, the use of multiple shaping apertures with different sizes is explored. Third, the use of overlapping shots for printing some characters is investigated. For the packed stencil design problem with flexible blank space sharing and multiple shaping apertures, two dynamic programming-based algorithms are proposed, one allows overlapping shots and the other does not. Experimental results show that the proposed enhancement and the associated algorithms can significantly reduce the total shot count and hence improve the throughput of e-beam lithography.

Description: This paper proposes an efficient algorithm that maximizes performance under power constraints and is applicable in the general context of traditional dynamic voltage/frequency (V/P) scaling, or core heterogeneity and emerging dynamic micro-architectural adaptation. Performance maximization in these scenarios can be essentially viewed as mapping application threads to appropriate core states that have various power/performance characteristics. Such problems are formulated as a generic 0-1 integer linear program (ILP). The proposed algorithm is an iterative heuristic-based solution. Compared with an optimal solution generated by commercial ILP solver, the proposed algorithm produces results less than 1% away from optimum on average, with more than two orders of magnitude improvement in runtime. The algorithm can be brought online for hundred-core heterogeneous systems as it scales to systems comprised of 256 cores with less than 1 ms in overhead in worst cases. The intrinsic history awareness also provides flexibility to control cost induced by switching V/F pairs, migrating threads across cores, or tuning on/off micro-architectural resources. 1 A villainous son of Poseidon in Greek mythology who forces travelers to fit into his bed by stretching their bodies or cutting off their legs (adapted from Merriam-Webster).

Description: Graphics processing units (GPUs) have become ubiquitous for general purpose applications due to their tremendous computing power. Initially, GPUs only employ scratchpad memory as on-chip memory. Though scratchpad memory benefits many applications, it is not ideal for those general purpose applications with irregular memory accesses. Hence, GPU vendors have introduced caches in conjunction with scratchpad memory in the recent generations of GPUs. The caches on GPUs are highly configurable. The programmer or compiler can explicitly control cache access or bypass for global load instructions. This highly configurable feature of GPU caches opens up the opportunities for optimizing the cache performance. In this paper, we propose an efficient compiler framework for cache bypassing on GPUs. Our objective is to efficiently utilize the configurable cache and improve the overall performance for general purpose GPU applications. In order to achieve this goal, we first characterize GPU cache utilization and develop performance metrics to estimate the cache reuses and memory traffic. Next, we present efficient algorithms that judiciously select global load instructions for cache access or bypass. Finally, we present techniques to explore the unified cache and shared memory design space. We integrate our techniques into an automatic compiler framework that leverages parallel thread execution instruction set architecture to enable cache bypassing for GPUs. Experiments evaluation on NVIDIA GTX680 using a variety of applications demonstrates that compared to cache-all and bypass-all solutions, our techniques improve the performance from 4.6% to 13.1% for 16 KB L1 cache.

Description: Nonvolatile memory (NVM) has many benefits compared to the traditional static RAM, such as improved reliability and reduced power consumption, but it has long write latency and limited write endurance. Scratchpad memory (SPM) is software-managed small on-chip memory for improving system performance and predicability. We consider SPM based on spin-transfer torque RAM, a type of NVM with high performance and good endurance. We present algorithms for allocating data variables to SPM and distribute write activity evenly in the SPM address space, in order to achieve wear-leveling and prolong the lifetime of NVM. We present two optimization algorithms for minimizing system CPU utilization subject to NVM lifetime constraints: 1) an optimal algorithm based on ILP and 2) an efficient heuristic algorithm that can obtain close-to-optimal solutions.

Description: Finite field arithmetic operations have been traditionally used in different applications ranging from error control coding to cryptographic computations. Among these computations are normal basis multiplications and exponentiations which are utilized in efficient applications due to their advantageous characteristics and the fact that squaring (and subsequent powering by two) of elements can be obtained with no hardware complexity. In this paper, we present 2-D decomposition systolic-oriented algorithms to develop systolic structures for digit-level Gaussian normal basis multiplication and exponentiation over $ {GF}({2}^{m})$ . The proposed high-performance architectures are suitable for a number of applications, e.g., architectures for elliptic curve Diffie–Hellman key agreement scheme in cryptography. The results of the benchmark of efficiency, performance, and implementation metrics of such architectures through a 65-nm application-specific integrated circuit platform confirm high-performance structures for the multiplication and exponentiation architectures presented in this paper are suitable for high-speed architectures, including cryptographic applications.

Description: This paper introduces a new methodology for pipeline synthesis with applications to data flow high-level system design. The pipeline synthesis is applied to dataflow programs whose operators are translated into graphs and dependencies relations that are then processed for the pipeline architecture optimization. For each pipeline-stage time, a minimal number of pipeline stages are first determined and then an optimal assignment of operators to stages is generated with the objective of minimizing the total pipeline register size. The obtained “optimal” pipeline schedule is automatically transformed back into a dataflow program that can be synthesized to efficient hardware implementations. Two new pipeline scheduling: “least cost search branch and bound” and a heuristic technique have been developed. The first algorithm yields global optimum solutions for middle size designs, whereas the second one generates close-to-optimal solutions for large designs. Experimental results on FPGA designs show that the total pipeline register size gain in a range up to $4.68 {times } $ can be achieved. The new algorithms overcome the known downward and upward direction dataflow graph traversal algorithms concerning the amount of pipeline register size by up to 100% on average.

Description: In analog designs, the most widely adopted layout practice to improve matching is the symmetrical common-centroid placement. However, this arrangement cannot be obtained in general. In this paper, it is shown that there are asymmetrical placements with a common centroid which are also immune to process gradients and suitable for designs where a symmetrical layout is not possible. In addition, this paper proposes an automated method, based on a standard simulated annealing framework, to arrange fully-integrated capacitors in a layout to improve their matching.

Description: With the steady growth of chip complexity and shrinking feature size, multiple challenges are emerging for transistor level circuit simulation. Compact SPICE models are a fundamental part of circuit verification, serving as a bridge between the semiconductor design and foundry. It is also an integral part of SPICE simulators, which directly affects tool performance and therefore design schedule. While the advanced 3-D technology nodes deliver superior level of scalability, simulation cost is rapidly increasing due to the computational complexity introduced by device model equations and the number of iterations required for numerical methods. In this paper, an efficient solution is proposed to reduce the computational cost associated with UC Berkeley BSIM-CMG device model evaluation, by applying robust Verilog compiler and computer algebra techniques to the device model equations. As a result of this implementation, simulation time reduction is up to 72% for complex blocks of the latest generation processor design.

Description: The hardware Trojan threat has motivated development of Trojan detection schemes at all stages of the integrated circuit (IC) lifecycle. While the majority of existing schemes focus on ICs at test-time, there are many unique advantages offered by post-deployment/run-time Trojan detection. However, run-time approaches have been underutilized with prior work highlighting the challenges of implementing them with limited hardware resources. In this paper, we propose three innovative low-overhead approaches for run-time Trojan detection which exploit the thermal sensors already available in many modern systems to detect deviations in power/thermal profiles caused by Trojan activation. The first one is a local sensor-based approach that uses information from thermal sensors together with hypothesis testing to make a decision. The second one is a global approach that exploits correlation between sensors and maintains track of the ICs thermal profile using a Kalman filter (KF). The third approach incorporates leakage power into the system dynamic model and apply extended KF (EKF) to track ICs thermal profile. Simulation results using state-of-the-art tools on ten publicly available Trojan benchmarks verify that all three proposed approaches can detect active Trojans quickly and with few false positives. Among three approaches, EKF is flawless in terms of the ten benchmarks tested but would require the most overhead.

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Description: We describe a compact Yb:YAG laser Q-switched by a graphene-based saturable absorber and pumped by a laser diode at 932 or 969 nm. The compact laser generates a maximum average output power value of 185 mW at 1032 nm with a slope efficiency value of 12%. The shortest duration of the Q-switched pulse achieved is 228 ns at a repetition frequency of 285 kHz. The maximum pulse energy amounts to 0.65 $mumathrm{J}$ .

Description: Orthogonal frequency-division multiplexing (OFDM) has been widely studied and adopted in visible-light communication (VLC) systems because of its high spectral efficiency and low-complexity implementation. However, OFDM-based VLC systems suffer from a high peak-to-average power ratio (PAPR), along with the nonlinear transfer characteristics of light-emitting diodes (LEDs). In this paper, a subcarrier grouping scheme for an OFDM-based VLC system is proposed. This scheme exploits the property that one LED lamp usually contains multiple independent LED chips. In the proposed scheme, all OFDM signal subcarriers are divided into groups, and each group is transmitted by an individual LED chip while the same receiver structure is maintained. The PAPR is reduced significantly because only some of the subcarriers are located on each LED chip. Hence, the achievable input power can be increased, leading to a higher signal-to-noise ratio (SNR) and a lower bit error rate (BER). Simulated and experimental results demonstrate that the BER performance can be improved by over two orders of magnitude. Moreover, an adaptive switching mechanism is also proposed in this paper, in which a subcarrier grouping scheme is employed adaptively when the required input power is high. Simulation results validate that the proposed mechanism can enhance system robustness significantly.

Description: Distributed fiber sensing technology based on a Brillouin optical time domain reflectometer is widely applied for health monitoring in engineering. However, it cannot perceive quick external interference. In this paper, we propose to use polynomial fitting on the inverse of an incomplete Brillouin spectrum and find the peak frequency by statistical analysis. Simulation results show that the peak frequency obtained by our method is only 1.096 MHz higher than that by using the Lorenz fitting method on a whole discrete Brillouin spectrum. The method has high accuracy, good repetitiveness, and high stability and is helpful in health monitoring for situations with interference that lasts for a short time.

Description: Optical frequency combs (OFCs) generated by an InP-based semiconductor Mach-Zehnder modulator (MZM) are numerically investigated. Nonlinear phase modulation induced by drive voltages applied to the MZM prove to be useful in obtaining a flat OFC. The experimentally measured intensity deviations of OFCs reported previously are quantitatively reproduced using a numerical model considering nonlinear change of refractive index and optical absorption induced by the drive voltages applied to the MZM. It is found that such nonlinearities generate a flat nine-channel (9-ch) OFC with an intensity deviation of <1 dB when a moderate RF drive voltage of <5 V is used. This flat 9-ch OFC is sustained regardless of the ratio of RF drive voltages of two arms in the MZM. Conversion efficiency is reasonably high (27%), but it is decreased by optical absorption and extinction losses in the MZM.

Description: We analyze the performance and the complexity of a real-time digital signal processing (DSP)-based optical network unit architecture for the digital detection of Nyquist-shaped signals in ultra-dense wavelength-division multiplexing passive optical network (UDWDM-PON) scenarios. Using field-programmable gate array-based 8-bit DSP, we experimentally demonstrate in a real-time mode operation the receiver performance in terms of Nyquist filter roll-off factor for $8times 2.5$ Gb/s quadrature phase-shift keying (QPSK) with 2.5 GHz of channel spacing. We analyze the performance of the linear and cubic interpolation for the clock recovery as well as the Gardner algorithm for the timing-error estimation, considering the amplitude and power formulations. The experimental evaluation shows that the linear interpolation along with the power formulation is an attractive solution for the QPSK-based UDWDM-PON, considering the tradeoff between the performance and the complexity.

Description: We present a thorough numerical analysis of a highly birefringent slotted porous-core circular photonic crystal fiber (PCF) for terahertz (THz) wave guidance. The slot shaped air-holes break the symmetry of the porous-core which offers a very high birefringence whereas the compact geometry of the circular cladding confines most of the power in the fiber-core. The fiber structure reported in this letter exhibits simultaneously ultrahigh modal birefringence of $7.5 times 10^{-2}$ and a very low effective absorption loss of 0.07 cm $^{-1}$ for $y$ -polarization mode at an operating frequency of 1 THz. It is highly anticipated that the slotted-core waveguide would be of very much convenience in many polarization maintaining THz appliances.

Description: We propose a direct-detection receiver capable of detecting polarization-division-multiplexed (PDM) ON-OFF keying (OOK) signals without using a dynamic polarization controller. The proposed receiver, consisted of a polarization-beam splitter, three $1times 2$ directional couplers, three photodetectors, three analog-to-digital converters, and a digital signal processing unit, can discriminate among the four symbol combinations of the PDM-OOK signal with the help of a short training sequence. For a demonstration, we show that the proposed receiver can detect a 20-Gb/s PDM-OOK signal even when its polarization is scrambled at the speed of 3 Mrad/s.

Description: This letter reports a multiplexed optical oil level meter using a thin core fiber (TCF) cladding mode exciter. Weak cladding mode reflection (<−75 dB) was employed to probe external refractive index discontinuity at an air-oil boundary. The insertion loss of one sensor is <3 dB. A linear relationship was evaluated between the measurement position and the absolute position during the oil-level test. System-level multiplexing capability was demonstrated and no crosstalk was found between the sensors. The system accuracy was 0.16 mm.

Description: (Pb,La)(Zr,Ti)O 3 (PLZT) has a high electro-optical coefficient and is very attractive for optical waveguide switches with high speed, low driving voltage, and compact size. The $1times 2$ PLZT optical switch using ridge type Mach–Zehnder interference structure has been designed and fabricated. By introducing offset upper electrodes instead of the conventional top electrodes, the insertion loss of the fabricated $1times 2$ PLZT optical switch was decreased 9.8 dB significantly with a crosstalk of −25.3 dB and the driving voltage <10 V.

Description: A novel approach to achieving ultrafast three-dimensional (3-D) imaging based on space-to-wavelength-to-time mapping and short-time Fourier transform (STFT) is proposed and experimentally demonstrated. The fundamental concept to achieve 3-D imaging is to encode the depth information of a sample by interfering two delayed pulses that are reflected from the surface of the sample and an additional reference plane on the top of the sample. The interference pattern that contains the depth information in the frequency domain is converted into the time domain based on dispersive Fourier transform and then analyzed based on STFT. Thus, ultrafast 3-D imaging is achieved. The proposed approach is experimentally evaluated. The imaging of a sample with a depth of 1.5 mm using an ultrafast pulse laser source with a beam width of $sim 2$ mm at a repetition rate of 48.8 MHz is demonstrated.