The coherent Ising machine (CIM) is designed to solve the NP-hard Ising problem quickly and energy efficiently. Boolean satisfiability (SAT) and maximum satisfiability (Max-SAT) are classes of NP-complete and NP-hard problems that are equally important and more practically relevant combinatorial optimization problems. Many approaches exist for solving Boolean SAT, such as quantum annealing and classical stochastic local search (SLS) solvers; however, they all are expected to require many steps to solve hard SAT problems and, thus, require large amounts of time and energy. In addition, a SAT problem can be converted into an Ising problem and solved by an Ising machine; however, we have found that this approach has drawbacks. As well as reviewing existing approaches to solving the SAT problem, we have extended the CIM algorithm and architecture to solve SAT and Max-SAT problems directly. This new technique is termed a coherent SAT solver (CSS). We have studied three implementations of the CSS, all-optical, hybrid optical–digital and all digital (cyber-CSS), and have compared the time-to-solution and energy-to-solution of three machines. The cyber-CSS, which is already implemented using a graphics processing unit (GPU), demonstrates competitive performance against existing SLS solvers such as probSAT. The CSS is also compared with another continuous-time SAT solver known as the CTDS, and the scaling behavior is evaluated for random 3-SAT problems. The hybrid optical–digital CSS is a more performant and practical machine that can be realized in a short term. Finally, the all-optical CSS promises the best energy-to-solution cost; however various technical challenges in nonlinear optics await us in order to build this machine.

Starting with a historical account of evolution in Raman spectroscopy, in this review we provide details of the advancements that have pushed detection limits to single molecules and enabled non-invasive molecular characterization of distinct organelles to provide next-generation bioanalytical assays and ultrasensitive molecular and cellular diagnostics. Amidst a growing number of publications in recent years, there is an unmet need for a consolidated review that discusses salient aspects of Raman spectroscopy that are broadly applicable in biosensing ranging from fundamental biology to disease identification and staging, to drug screening and food and agriculture quality control. This review offers a discussion across this range of applications and focuses on the convergent use of Raman spectroscopy, coupling it to bioanalysis, agriculture, and food quality control, which can affect human life through biomedical research, drug discovery, and disease diagnostics. We also highlight how the potent combination of advanced spectroscopy and machine-learning algorithms can further advance Raman data analysis, leading to the emergence of an optical Omics discipline, coined “Ramanomics.” Finally, we present our perspectives on future needs and opportunities.

The commercial success of radio-frequency acoustic filters in wireless communication systems has launched aluminum nitride (AlN) as one of the most widely used semiconductors across the globe. Over recent years, AlN has also been investigated as an attractive photonic integrated platform due to its excellent characteristics, such as enormous bandgaps (∼6.2 eV), quadratic and cubic optical nonlinearities, Pockels electro-optic effects, and compatibility with the complementary metal-oxide semiconductor technology. In parallel, AlN possesses outstanding piezoelectric and mechanical performances, which can provide new aspects for controlling phonons and photons at the wavelength scale using nanophotonic architectures. These characteristics pose AlN as a promising candidate to address the drawbacks in conventional silicon and silicon nitride platforms. In this review, we aim to present recent advances achieved in AlN photonic integrated circuits ranging from material processing and passive optical routing to active functionality implementation such as electro-optics, piezo-optomechanics, and all-optical nonlinear frequency conversion. Finally, we highlight the challenges and future prospects existing in AlN nanophotonic chips.

This tutorial provides an overview of the local description of polarization for nonparaxial light, for which all Cartesian components of the electric field are significant. The polarization of light at each point is characterized by a three-component complex vector in the case of full polarization and by a 3 × 3 polarization matrix for partial polarization. Standard concepts for paraxial polarization such as the degree of polarization, the Stokes parameters, and the Poincaré sphere then have generalizations for nonparaxial light that are not unique and/or not trivial. This work aims to clarify some of these discrepancies, present some new concepts, and provide a framework that highlights the similarities and differences with the description for the paraxial regimes. Particular emphasis is placed on geometric interpretations.

Optical microcombs represent a new paradigm for generating laser frequency combs based on compact chip-scale devices, which have underpinned many modern technological advances for both fundamental science and industrial applications. Along with the surge in activity related to optical microcombs in the past decade, their applications have also experienced rapid progress: not only in traditional fields such as frequency synthesis, signal processing, and optical communications but also in new interdisciplinary fields spanning the frontiers of light detection and ranging (LiDAR), astronomical detection, neuromorphic computing, and quantum optics. This paper reviews the applications of optical microcombs. First, an overview of the devices and methods for generating optical microcombs is provided, which are categorized into material platforms, device architectures, soliton classes, and driving mechanisms. Second, the broad applications of optical microcombs are systematically reviewed, which are categorized into microwave photonics, optical communications, precision measurements, neuromorphic computing, and quantum optics. Finally, the current challenges and future perspectives are discussed.

Over the past few years, progress in hollow-core optical fiber technology has reduced the attenuation of these fibers to levels comparable to those of all-solid silica-core single-mode fibers. The sustained pace of progress in the field has sparked renewed interest in the technology and created the expectation that it will one day enable realization of the most transparent light-propagating waveguides ever produced, across all spectral regions of interest. In this work we review and analyze the various physical mechanisms that drive attenuation in hollow-core optical fibers. We consider both the somewhat legacy hollow-core photonic bandgap technology as well as the more recent antiresonant hollow-core fibers. As both fiber types exploit different guidance mechanisms from that of conventional solid-core fibers to confine light to the central core, their attenuation is also dominated by a different set of physical processes, which we analyze here in detail. First, we discuss intrinsic loss mechanisms in perfect and idealized fibers. These include leakage loss, absorption, and scattering within the gas filling the core or from the glass microstructure surrounding it, and roughness scattering from the air–glass interfaces within the fibers. The latter contribution is analyzed rigorously, clarifying inaccuracies in the literature that often led to the use of inadequate scaling rules. We then explore the extrinsic contributions to loss and discuss the effect of random microbends as well as that of other perturbations and non-uniformities that may result from imperfections in the fabrication process. These effects impact the loss of the fiber predominantly by scattering light from the fundamental mode into lossier higher-order modes and cladding modes. Although these contributions have often been neglected, their role becomes increasingly important in the context of producing, one day, hollow-core fibers with sub-0.1-dB/km loss and a pure single-mode guidance. Finally, we present general scaling rules for all the loss mechanisms mentioned previously and combine them to examine the performance of recently reported fibers. We lay some general guidelines for the design of low-loss hollow-core fibers operating at different spectral regions and conclude the paper with a brief outlook on the future of this potentially transformative technology.

Dielectric laser accelerators (DLAs) are fundamentally based on the interaction of photons with free electrons, where energy and momentum conservation are satisfied by mediation of a nanostructure. In this scheme, the photonic nanostructure induces near-fields which transfer energy from the photon to the electron, similar to the inverse-Smith–Purcell effect described in metallic gratings. This, in turn, may provide ground-breaking applications, as it is a technology promising to miniaturize particle accelerators down to the chip scale. This fundamental interaction can also be used to study and demonstrate quantum photon-electron phenomena. The spontaneous and stimulated Smith–Purcell effect and the photon-induced near-field electron-microscopy (PINEM) effect have evolved to be a fruitful ground for observing quantum effects. In particular, the energy spectrum of the free electron has been shown to have discrete energy peaks, spaced with the interacting photon energy. This energy spectrum is correlated to the photon statistics and number of photon exchanges that took place during the interaction. We give an overview of DLA and PINEM physics with a focus on electron phase-space manipulation.

Augmented reality (AR) and virtual reality (VR) have the potential to revolutionize the interface between our physical and digital worlds. Recent advances in digital processing, data transmission, optics, and display technologies offer new opportunities for ubiquitous AR/VR applications. The foundation of this revolution is based on AR/VR display systems with high image fidelity, compact formfactor, and high optical efficiency. In this review paper, we start by analyzing the human vision system and the architectures of AR/VR display systems and then manifest the main requirements for the light engines. Next, the working principles of six display light engines, namely transmissive liquid crystal display, reflective liquid-crystal-on-silicon microdisplay, digital light processing microdisplay, micro light-emitting-diode microdisplay, organic light-emitting-diode microdisplay, and laser beam scanning displays, are introduced. According to the characteristics of these light engines, the perspectives and challenges of each display technology are analyzed through five performance metrics, namely resolution density, response time, efficiency/brightness/lifetime, dynamic range, and compactness. Finally, potential solutions to overcoming these challenges are discussed.

The advent of chirped-pulse amplification in the 1980s and femtosecond Ti:sapphire lasers in the 1990s enabled transformative advances in intense laser–matter interaction physics. Whereas most of experiments have been conducted in the limited near-infrared range of 0.8–1 μm, theories predict that many physical phenomena such as high harmonic generation in gases favor long laser wavelengths in terms of extending the high-energy cutoff. Significant progress has been made in developing few-cycle, carrier-envelope phase-stabilized, high-peak-power lasers in the 1.6–2 μm range that has laid the foundation for attosecond X ray sources in the water window. Even longer wavelength lasers are becoming available that are suitable to study light filamentation, high harmonic generation, and laser–plasma interaction in the relativistic regime. Long-wavelength lasers are suitable for sub-bandgap strong-field excitation of a wide range of solid materials, including semiconductors. In the strong-field limit, bulk crystals also produce high-order harmonics. In this review, we first introduce several important wavelength scaling laws in strong-field physics, then describe recent breakthroughs in short- (1.4–3 μm), mid- (3–8 μm), and long-wave (8–15 μm) infrared laser technology, and finally provide examples of strong-field applications of these novel lasers. Some of the broadband ultrafast infrared lasers will have profound effects on medicine, environmental protection, and national defense, because their wavelengths cover the water absorption band, the molecular fingerprint region, as well as the atmospheric infrared transparent window.

Owing to advances in fabrication technology and device design, semiconductor optical amplifiers (SOAs) are evolving as a promising candidate for future optical coherent communication links. This review article focuses on the fundamentals and broad applications of SOAs, specifically for optical channels with advanced modulation formats, as an integrable broadband amplifier in commercial transponders and as a nonlinear medium for optical signal processing. We discuss the basic functioning of an SOA and distortions of coherent signals when SOAs are used as amplifiers. We first focus on the techniques used for low-distortion amplification of phase-modulated signals using SOAs. Then we discuss optical signal processing techniques enabled by SOAs with an emphasis on all-optical wavelength conversion, optical phase conjugation, and phase quantization of coherent optical signals.