ALBERT

Description: We propose a method to use artificial neural networks to approximate light scattering by multilayer nanoparticles. We find that the network needs to be trained on only a small sampling of the data to approximate the simulation to high precision. Once the neural network is trained, it can simulate such optical processes orders of magnitude faster than conventional simulations. Furthermore, the trained neural network can be used to solve nanophotonic inverse design problems by using back propagation, where the gradient is analytical, not numerical.

Description: Author(s): M. Ghebrebrhan, P. Bermel, Y. X. Yeng, I. Celanovic, M. Soljačić, and J. D. Joannopoulos We develop a model for predicting the thermal emission spectrum of a two-dimensional metallic photonic crystal for arbitrary angles based on coupled-mode theory. Calculating the appropriate coupled-mode parameters over a range of geometrical parameters allows one to tailor the emissivity spectrum to... [Phys. Rev. A 83, 033810] Published Wed Mar 09, 2011

Description: Author(s): O. D. Miller, C. W. Hsu, M. T. H. Reid, W. Qiu, B. G. DeLacy, J. D. Joannopoulos, M. Soljačić, and S. G. Johnson We show that there are shape-independent upper bounds to the extinction cross section per unit volume of dilute, randomly arranged nanoparticles, given only material permittivity. Underlying the limits are restrictive sum rules that constrain the distribution of quasistatic eigenvalues. Surprisingly... [Phys. Rev. Lett. 112, 123903] Published Wed Mar 26, 2014

Description: We report on the experimental observation of modulation instability of partially spatially incoherent light beams in noninstantaneous nonlinear media and show that in such systems patterns can form spontaneously from noise. Incoherent modulation instability occurs above a specific threshold that depends on the coherence properties (correlation distance) of the wave packet and leads to a periodic train of one-dimensional filaments. At a higher value of nonlinearity, the incoherent one-dimensional filaments display a two-dimensional instability and break up into self-ordered arrays of light spots. This discovery of incoherent pattern formation reflects on many other nonlinear systems beyond optics. It implies that patterns can form spontaneously (from noise) in diverse nonlinear many-body systems involving weakly correlated particles, such as atomic gases at (or near) Bose-Einstein condensation temperatures and electrons in semiconductors at the vicinity of the quantum Hall regime.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Kip, D -- Soljacic, M -- Segev, M -- Eugenieva, E -- Christodoulides, D N -- New York, N.Y. -- Science. 2000 Oct 20;290(5491):495-8.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Physics Department and Solid State Institute, Technion, Haifa 32000, Israel.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/11039925" target="_blank"〉PubMed〈/a〉

Description: One of the most striking phenomena in condensed-matter physics is the quantum Hall effect, which arises in two-dimensional electron systems subject to a large magnetic field applied perpendicular to the plane in which the electrons reside. In such circumstances, current is carried by electrons along the edges of the system, in so-called chiral edge states (CESs). These are states that, as a consequence of nontrivial topological properties of the bulk electronic band structure, have a unique directionality and are robust against scattering from disorder. Recently, it was theoretically predicted that electromagnetic analogues of such electronic edge states could be observed in photonic crystals, which are materials having refractive-index variations with a periodicity comparable to the wavelength of the light passing through them. Here we report the experimental realization and observation of such electromagnetic CESs in a magneto-optical photonic crystal fabricated in the microwave regime. We demonstrate that, like their electronic counterparts, electromagnetic CESs can travel in only one direction and are very robust against scattering from disorder; we find that even large metallic scatterers placed in the path of the propagating edge modes do not induce reflections. These modes may enable the production of new classes of electromagnetic device and experiments that would be impossible using conventional reciprocal photonic states alone. Furthermore, our experimental demonstration and study of photonic CESs provides strong support for the generalization and application of topological band theories to classical and bosonic systems, and may lead to the realization and observation of topological phenomena in a generally much more controlled and customizable fashion than is typically possible with electronic systems.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Wang, Zheng -- Chong, Yidong -- Joannopoulos, J D -- Soljacic, Marin -- England -- Nature. 2009 Oct 8;461(7265):772-5. doi: 10.1038/nature08293.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA. zhwang@mit.edu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/19812669" target="_blank"〉PubMed〈/a〉

Description: The Dirac cone underlies many unique electronic properties of graphene and topological insulators, and its band structure--two conical bands touching at a single point--has also been realized for photons in waveguide arrays, atoms in optical lattices, and through accidental degeneracy. Deformation of the Dirac cone often reveals intriguing properties; an example is the quantum Hall effect, where a constant magnetic field breaks the Dirac cone into isolated Landau levels. A seemingly unrelated phenomenon is the exceptional point, also known as the parity-time symmetry breaking point, where two resonances coincide in both their positions and widths. Exceptional points lead to counter-intuitive phenomena such as loss-induced transparency, unidirectional transmission or reflection, and lasers with reversed pump dependence or single-mode operation. Dirac cones and exceptional points are connected: it was theoretically suggested that certain non-Hermitian perturbations can deform a Dirac cone and spawn a ring of exceptional points. Here we experimentally demonstrate such an 'exceptional ring' in a photonic crystal slab. Angle-resolved reflection measurements of the photonic crystal slab reveal that the peaks of reflectivity follow the conical band structure of a Dirac cone resulting from accidental degeneracy, whereas the complex eigenvalues of the system are deformed into a two-dimensional flat band enclosed by an exceptional ring. This deformation arises from the dissimilar radiation rates of dipole and quadrupole resonances, which play a role analogous to the loss and gain in parity-time symmetric systems. Our results indicate that the radiation existing in any open system can fundamentally alter its physical properties in ways previously expected only in the presence of material loss and gain.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Zhen, Bo -- Hsu, Chia Wei -- Igarashi, Yuichi -- Lu, Ling -- Kaminer, Ido -- Pick, Adi -- Chua, Song-Liang -- Joannopoulos, John D -- Soljacic, Marin -- England -- Nature. 2015 Sep 17;525(7569):354-8. doi: 10.1038/nature14889. Epub 2015 Sep 9.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Research Laboratory of Electronics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA. ; Department of Applied Physics, Yale University, New Haven, Connecticut 06520, USA. ; Smart Energy Research Laboratories, NEC Corporation, 34 Miyuiga-ka, Tsukuba, Ibaraki 305-8501, Japan. ; Department of Physics, Harvard University, Cambridge, Massachusetts 02138, USA. ; DSO National Laboratories, 20 Science Park Drive, Singapore 118230, Singapore.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/26352476" target="_blank"〉PubMed〈/a〉

Description: Using self-resonant coils in a strongly coupled regime, we experimentally demonstrated efficient nonradiative power transfer over distances up to 8 times the radius of the coils. We were able to transfer 60 watts with approximately 40% efficiency over distances in excess of 2 meters. We present a quantitative model describing the power transfer, which matches the experimental results to within 5%. We discuss the practical applicability of this system and suggest directions for further study.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Kurs, Andre -- Karalis, Aristeidis -- Moffatt, Robert -- Joannopoulos, J D -- Fisher, Peter -- Soljacic, Marin -- New York, N.Y. -- Science. 2007 Jul 6;317(5834):83-6. Epub 2007 Jun 7.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Physics, Massachusetts Institute of Technology, Cambridge, MA 02139, USA. akurs@mit.edu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/17556549" target="_blank"〉PubMed〈/a〉

Description: 〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Bravo-Abad, Jorge -- Soljacic, Marin -- New York, N.Y. -- Science. 2008 May 2;320(5876):623-4. doi: 10.1126/science.1157494.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Physics and Research Laboratory of Electronics, Massachusetts Institute of Technology, Cambridge, MA 02139, USA. jbravo@mit.edu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/18451291" target="_blank"〉PubMed〈/a〉

Description: 〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Reed, Evan J -- Soljacic, Marin -- Ibanescu, Mihai -- Joannopoulos, John D -- New York, N.Y. -- Science. 2004 Aug 6;305(5685):778; author reply 778.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Physics, Massachusetts Institute of Technology, Cambridge, MA 02139, USA. evan@mit.edu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/15297649" target="_blank"〉PubMed〈/a〉

Description: The ability to confine light is important both scientifically and technologically. Many light confinement methods exist, but they all achieve confinement with materials or systems that forbid outgoing waves. These systems can be implemented by metallic mirrors, by photonic band-gap materials, by highly disordered media (Anderson localization) and, for a subset of outgoing waves, by translational symmetry (total internal reflection) or by rotational or reflection symmetry. Exceptions to these examples exist only in theoretical proposals. Here we predict and show experimentally that light can be perfectly confined in a patterned dielectric slab, even though outgoing waves are allowed in the surrounding medium. Technically, this is an observation of an 'embedded eigenvalue'--namely, a bound state in a continuum of radiation modes--that is not due to symmetry incompatibility. Such a bound state can exist stably in a general class of geometries in which all of its radiation amplitudes vanish simultaneously as a result of destructive interference. This method to trap electromagnetic waves is also applicable to electronic and mechanical waves.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Hsu, Chia Wei -- Zhen, Bo -- Lee, Jeongwon -- Chua, Song-Liang -- Johnson, Steven G -- Joannopoulos, John D -- Soljacic, Marin -- England -- Nature. 2013 Jul 11;499(7457):188-91. doi: 10.1038/nature12289.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Research Laboratory of Electronics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA. cwhsu@mit.edu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/23846657" target="_blank"〉PubMed〈/a〉