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1. Efficient generation of optical bottle beams

   https://doi.org/10.1515/nanoph-2021-0243  

   Xiao, Yuzhe; Yu, Zhaoning; Wambold, Raymond A.; Mei, Hongyan; Hickman, Garrett; Goldsmith, Randall H.; Saffman, Mark; Kats, Mikhail A. (August 2021, Nanophotonics)

   null (Ed.)

   Abstract Optical bottle beams can be used to trap atoms and small low-index particles. We introduce a figure of merit (FoM) for optical bottle beams, specifically in the context of optical traps, and use it to compare optical bottle-beam traps obtained by three different methods. Using this FoM and an optimization algorithm, we identified the optical bottle-beam traps based on a Gaussian beam illuminating a metasurface that are superior in terms of power efficiency than existing approaches. We numerically demonstrate a silicon metasurface for creating an optical bottle-beam trap. 

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2. Optical Transformers

   Anderson, M; Ma, S-Y; Wang, T; Wright, L; McMahon, PL (May 2024, Transactions on machine learning research)

   The rapidly increasing size of deep-learning models has renewed interest in alternatives to digital-electronic computers as a means to dramatically reduce the energy cost of running state-of-the-art neural networks. Optical matrix-vector multipliers are best suited to performing computations with very large operands, which suggests that large Transformer models could be a good target for them. In this paper, we investigate---through a combination of simulations and experiments on prototype optical hardware---the feasibility and potential energy benefits of running Transformer models on future optical accelerators that perform matrix-vector multiplication. We use simulations, with noise models validated by small-scale optical experiments, to show that optical accelerators for matrix-vector multiplication should be able to accurately run a typical Transformer architecture model for language processing. We demonstrate that optical accelerators can achieve the same (or better) perplexity as digital-electronic processors at 8-bit precision, provided that the optical hardware uses sufficiently many photons per inference, which translates directly to a requirement on optical energy per inference. We studied numerically how the requirement on optical energy per inference changes as a function of the Transformer width $$d$$ and found that the optical energy per multiply--accumulate (MAC) scales approximately as $$\frac{1}{d}$$, giving an asymptotic advantage over digital systems. We also analyze the total system energy costs for optical accelerators running Transformers, including both optical and electronic costs, as a function of model size. We predict that well-engineered, large-scale optical hardware should be able to achieve a $$100 \times$$ energy-efficiency advantage over current digital-electronic processors in running some of the largest current Transformer models, and if both the models and the optical hardware are scaled to the quadrillion-parameter regime, optical accelerators could have a $$>8,000\times$$ energy-efficiency advantage. Under plausible assumptions about future improvements to electronics and Transformer quantization techniques (5× cheaper memory access, double the digital--analog conversion efficiency, and 4-bit precision), we estimate that the energy advantage for optical processors versus electronic processors operating at 300~fJ/MAC could grow to $$>100,000\times$$. 

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3. A Hybrid Optical-Electrical Analog Deep Learning Accelerator Using Incoherent Optical Signals

   https://doi.org/10.1145/3453688.3461531  

   Yang, Mingdai; Jokar, Mohammad Reza; Qiu, Junyi; Lou, Qiuwen; Liu, Yuming; Udupa, Aditi; Chong, Frederic T.; Dallesasse, John M.; Feng, Milton; Goddard, Lynford L.; et al (July 2021, GLSVLSI '21: Proceedings of the 2021 on Great Lakes Symposium on VLSI)

   null (Ed.)

   We present a hybrid optical-electrical analog deep learning (DL) accelerator, the first work to use incoherent optical signals for DL workloads. Incoherent optical designs are more attractive than coherent ones as the former can be more easily realized in practice. However, a significant challenge in analog DL accelerators, where multiply-accumulate operations are dominant, is that there is no known solution to perform accumulation using incoherent optical signals. We overcome this challenge by devising a hybrid approach: accumulation is done in the electrical domain, while multiplication is performed in the optical domain. The key technology enabler of our design is the transistor laser, which performs electrical-to-optical and optical-to-electrical conversions efficiently to tightly integrate electrical and optical devices into compact circuits. As such, our design fully realizes the ultra high-speed and high-energy-efficiency advantages of analog and optical computing. Our evaluation results using the MNIST benchmark show that our design achieves 2214× and 65× improvements in latency and energy, respectively, compared to a state-of-the-art memristor-based analog design. 

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4. Optical Dispersion Data Analysis of Single Crystal CH3NH3PbBr3 for Optimized Perovskite Solar Cell Active Layer Absorptance

   https://doi.org/10.26434/chemrxiv-2023-05fw9  

   McCleese, Christopher; Brennan, Michael; Episcopo, Nathan; Sun, Lirong; Hong, Nina; Ramana, Chintalapalle; Grusenmeyer, Tod; Stevenson, Peter (November 2023, Wiley-VCH GmbH)

   Proper derivation of CH3NH3PbX3 (CH3NH3+ = methyl ammonium or MA+; X- = Cl-, Br-, I-) optical constants is a critical step toward the development of high-performance electronic and optoelectronic perovskite devices. To date, the optical dispersion regimes at, above, and below the band gap of these materials have been inconsistently characterized by omitting or under-approximating anomalous spectral features (from ultraviolet to infrared wavelengths). In this report, we present the rigorous optical dispersion data analysis of single crystal MAPbBr3 involving variable angle spectroscopic ellipsometry data appended with transmission intensity data. This approach yields a more robust derivation of MAPbBr3 optical constants (refractive index, n, and extinction coefficient, k) for both anomalous (absorptance) and normal (no absorptance) optical dispersion regimes. Using the derived optical constants for our MAPbBr3 single crystals, illustrative modeled solar cell device designs are presented in relation to non-realistic designs prepared using representative optical constants reported in the literature to date. In comparison, our derived optical dispersion data enables the modeled design of realistic planar perovskite solar cell (PSC) optical performance where the active layer (MAPbBr3) is optimized for maximum solar radiation absorption. We further demonstrate optimized modeled planar PSC designs with minimal parasitic optical absorptance in non-active PSC device layers resulting in improved performance at broad angles of incidence (approximately 0-70°). Our robust derivation of MAPbBr3 optical properties is expected to impact the optical dispersion data analysis of all perovskite analogs and expedite targeted development of, for example, solar cell, light-emitting diode, photo and X-ray/γ-ray detector, and laser system technologies. 

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5. Testing the relativistic Doppler boost hypothesis for the binary candidate quasar PG1302-102 with multiband Swift data

   https://doi.org/10.1093/mnras/staa1643  

   Xin, Chengcheng; Charisi, Maria; Haiman, Zoltán; Schiminovich, David; Graham, Matthew J; Stern, Daniel; D’Orazio, Daniel J (August 2020, Monthly Notices of the Royal Astronomical Society)

   null (Ed.)

   ABSTRACT The bright quasar PG1302-102 has been identified as a candidate supermassive black hole binary from its near-sinusoidal optical variability. While the significance of its optical periodicity has been debated due to the stochastic variability of quasars, its multiwavelength variability in the ultraviolet (UV) and optical bands is consistent with relativistic Doppler boost caused by the orbital motion in a binary. However, this conclusion was based previously on sparse UV data that were not taken simultaneously with the optical data. Here, we report simultaneous follow-up observations of PG1302-102 with the Ultraviolet Optical Telescope on the Neil Gehrels Swift Observatory in six optical + UV bands. The additional nine Swift observations produce light curves roughly consistent with the trend under the Doppler boost hypothesis, which predicts that UV variability should track the optical, but with a ∼2.2 times higher amplitude. We perform a statistical analysis to quantitatively test this hypothesis. We find that the data are consistent with the Doppler boost hypothesis when we compare the the amplitudes in optical B-band and UV light curves. However, the ratio of UV to V-band variability is larger than expected and is consistent with the Doppler model, only if either the UV/optical spectral slopes vary, the stochastic variability makes a large contribution in the UV, or the sparse new optical data underestimate the true optical variability. We have evidence for the latter from comparison with the optical light curve from All-Sky Automated Survey for Supernovae. Additionally, the simultaneous analysis of all four bands strongly disfavours the Doppler boost model whenever Swift V band is involved. Additional, simultaneous optical + UV observations tracing out another cycle of the 5.2-yr proposed periodicity should lead to a definitive conclusion. 

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