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1. Diagnostic Applications of Lasers

   Fried, Nathaniel ; Seeber, Fred ; MacGregor, Tom ( January 2021 , Diagnostic Applications of Lasers)

   Panayiotou, Chrysanthos ; Pedrotti, Leno (Ed.)

   About the LASER-TEC Laser and Fiber Optics Educational Series This series was created for use in engineering technology programs such as electronics, photonics, laser-electro-optics, and related programs. This series of publications has three goals in mind:1) to create educational materials for areas of laser electro-optics technology in which no materials exist 2) work with industry to use, adapt and enhance available industry-created material, 3) make these materials available to technicians at no cost to them making education in these areas more accessible to everyone. The Laser and Fiber Optics Educational Series is available for free online at www.laser-tec.org. About Diagnostic Applications of Lasers Diagnostic Applications of Lasers was created to provide a fundamental background for technicians on the theory of optical imaging, microscopy, and spectroscopy, as well as other major imaging modalities in medicine, (e.g. ultrasound, nuclear imaging, x-rays, and computed tomography). There are numerous examples of successful optical diagnostic technologies, such as the pulsed oximeter for the measurement of blood oxygenation levels and optical coherence tomography for diagnosis of ophthalmic diseases. Promising emerging fields are also briefly covered, such as super-resolution microscopy and photoacoustic tomography. 

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2. Photonic advantage of optical encoders

   https://doi.org/10.1515/nanoph-2023-0579  

   Huang, Luocheng ; Tanguy, Quentin A. ; Fröch, Johannes E. ; Mukherjee, Saswata ; Böhringer, Karl F. ; Majumdar, Arka ( November 2023 , Nanophotonics)

   Light’s ability to perform massive linear operations in parallel has recently inspired numerous demonstrations of optics-assisted artificial neural networks (ANN). However, a clear system-level advantage of optics over purely digital ANN has not yet been established. While linear operations can indeed be optically performed very efficiently, the lack of nonlinearity and signal regeneration require high-power, low-latency signal transduction between optics and electronics. Additionally, a large power is needed for lasers and photodetectors, which are often neglected in the calculation of the total energy consumption. Here, instead of mapping traditional digital operations to optics, we co-designed a hybrid optical-digital ANN, that operates on incoherent light, and is thus amenable to operations under ambient light. Keeping the latency and power constant between a purely digital ANN and a hybrid optical-digital ANN, we identified a low-power/latency regime, where an optical encoder provides higher classification accuracy than a purely digital ANN. We estimate our optical encoder enables ∼10 kHz rate operation of a hybrid ANN with a power of only 23 mW. However, in that regime, the overall classification accuracy is lower than what is achievable with higher power and latency. Our results indicate that optics can be advantageous over digital ANN in applications, where the overall performance of the ANN can be relaxed to prioritize lower power and latency.

    

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3. Active optical metasurfaces: comprehensive review on physics, mechanisms, and prospective applications

   https://doi.org/10.1088/1361-6633/ac2aaf  

   Yang, Jingyi ; Gurung, Sudip ; Bej, Subhajit ; Ni, Peinan ; Howard Lee, Ho Wai ( March 2022 , Reports on Progress in Physics)

   Abstract Optical metasurfaces with subwavelength thickness hold considerable promise for future advances in fundamental optics and novel optical applications due to their unprecedented ability to control the phase, amplitude, and polarization of transmitted, reflected, and diffracted light. Introducing active functionalities to optical metasurfaces is an essential step to the development of next-generation flat optical components and devices. During the last few years, many attempts have been made to develop tunable optical metasurfaces with dynamic control of optical properties (e.g., amplitude, phase, polarization, spatial/spectral/temporal responses) and early-stage device functions (e.g., beam steering, tunable focusing, tunable color filters/absorber, dynamic hologram, etc) based on a variety of novel active materials and tunable mechanisms. These recently-developed active metasurfaces show significant promise for practical applications, but significant challenges still remain. In this review, a comprehensive overview of recently-reported tunable metasurfaces is provided which focuses on the ten major tunable metasurface mechanisms. For each type of mechanism, the performance metrics on the reported tunable metasurface are outlined, and the capabilities/limitations of each mechanism and its potential for various photonic applications are compared and summarized. This review concludes with discussion of several prospective applications, emerging technologies, and research directions based on the use of tunable optical metasurfaces. We anticipate significant new advances when the tunable mechanisms are further developed in the coming years. 

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4. Software-defined meta-optics

   https://doi.org/10.1063/5.0164387  

   Audhkhasi, Romil ; Fröch, Johannes E. ; Zhan, Alan ; Colburn, Shane ; Majumdar, Arka ( October 2023 , Applied Physics Letters)

   Rapid advancements in autonomous systems and the Internet of Things have necessitated the development of compact and low-power image sensors to bridge the gap between the digital and physical world. To that end, sub-wavelength diffractive optics, commonly known as meta-optics, have garnered significant interest from the optics and photonics community due to their ability to achieve multiple functionalities within a small form factor. Despite years of research, however, the performance of meta-optics has often remained inferior compared to that of traditional refractive optics. In parallel, computational imaging techniques have emerged as a promising path to miniaturize optical systems, albeit often at the expense of higher power and latency. The lack of desired performance from either meta-optical or computational solutions has motivated researchers to look into a jointly optimized meta-optical–digital solution. While the meta-optical front end can preprocess the scene to reduce the computational load on the digital back end, the computational back end can in turn relax requirements on the meta-optics. In this Perspective, we provide an overview of this up-and-coming field, termed here as “software-defined meta-optics.” We highlight recent contributions that have advanced the current state of the art and point out directions toward which future research efforts should be directed to leverage the full potential of subwavelength photonic platforms in imaging and sensing applications. Synergistic technology transfer and commercialization of meta-optic technologies will pave the way for highly efficient, compact, and low-power imaging systems of the future.

    

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5. Non-Hermitian optics and photonics: from classical to quantum

   https://doi.org/10.1364/AOP.475477  

   Wang, Changqing ; Fu, Zhoutian ; Mao, Wenbo ; Qie, Jinran ; Stone, A_Douglas ; Yang, Lan ( June 2023 , Advances in Optics and Photonics)

   Non-Hermitian optics is a burgeoning field at the intersection of quantum physics, electrodynamics, and nanophotonics. It provides a new perspective of the role of gain and loss in optical systems. Leveraging the advanced designs inspired by non-Hermitian physics, classical optical platforms have been widely investigated to unveil novel physical concepts, such as parity-time symmetry and exceptional points, which have no counterparts in the conventional Hermitian settings. These investigations have yielded a plethora of new phenomena in optical wave scattering, optical sensing, and nonlinear optical processes. Non-Hermitian effects also have a profound impact on the lasing behaviors in the semiclassical framework of lasers, allowing for novel ways to engineer single-mode lasers, chiral laser emission, laser noise, linewidth, etc. Furthermore, over recent years, there has been increasing interest in the explorations of non-Hermitian physics in quantum optics, which addresses photon statistics, entanglement, decoherence, and quantum sensing in non-Hermitian systems. In this review, we review the most recent theoretical and experimental advances in non-Hermitian optics and photonics, covering the significant progress in both classical and quantum optics regimes.

    

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