With its unique and exclusive linear and nonlinear optical characteristics, epsilon-near-zero (ENZ) photonics has drawn a tremendous amount of attention in the recent decade in the fields of nanophotonics, nonlinear optics, plasmonics, light-matter interactions, material science, applied optical science, etc. The extraordinary optical properties, relatively high tuning flexibility, and CMOS compatibility of ENZ materials make them popular and competitive candidates for nanophotonic devices and on-chip integration in all-optical and electro-optical platforms. With exclusive features and high performance, ENZ photonics can play a big role in optical communications and optical data processing. In this review, we give a focused discussion on recent advances of the theoretical and experimental studies on ENZ photonics, especially in the regime of nonlinear ENZ nanophotonics and its applications. First, we overview the basics of the ENZ concepts, mechanisms, and nonlinear ENZ nanophotonics. Then the new advancements in theoretical and experimental optical physics are reviewed. For nanophotonic applications, the recent decades saw rapid developments in various kinds of different ENZ-based devices and systems, which are discussed and analyzed in detail. Finally, we give our perspectives on where future endeavors can be made.

The survey focuses on the most significant contributions in the field of fiber optic plasmonic sensors (FOPS) in recent years. FOPSs are plasmonic sensor-based fiber optic probes that use an optical field to measure the biological agents. Owing to their high sensitivity, high resolution, and low cost, FOPS turn out to be potential alternatives to conventional biological fiber optic sensors. FOPS use optical transduction mechanisms to enhance sensitivity and resolution. The optical transduction mechanisms of FOPS with different geometrical structures and the photonic properties of the geometries are discussed in detail. The studies of optical properties with a combination of suitable materials for testing the biosamples allow for diagnosing diseases in the medical field.

Light detection and ranging (LiDAR), as a hot imaging technology in both industry and academia, has undergone rapid innovation and evolution. The current mainstream direction is towards system miniaturization and integration. There are many metrics that can be used to evaluate the performance of a LiDAR system, such as lateral resolution, ranging accuracy, stability, size, and price. Until recently, with the continuous enrichment of LiDAR application scenarios, the pursuit of imaging speed has attracted tremendous research interest. Particularly, for autonomous vehicles running on motorways or industrial automation applications, the imaging speed of LiDAR systems is a critical bottleneck. In this review, we will focus on discussing the upper speed limit of the LiDAR system. Based on the working mechanism, the limitation of optical parts on the maximum imaging speed is analyzed. The beam scanner has the greatest impact on imaging speed. We provide the working principle of current popular beam scanners used in LiDAR systems and summarize the main constraints on the scanning speed. Especially, we highlight the spectral scanning LiDAR as a new paradigm of ultrafast LiDAR. Additionally, to further improve the imaging speed, we then review the parallel detection methods, which include multiple-detector schemes and multiplexing technologies. Furthermore, we summarize the LiDAR systems with the fastest point acquisition rate reported nowadays. In the outlook, we address the current technical challenges for ultrafast LiDAR systems from different aspects and give a brief analysis of the feasibility of different approaches.

Silicon photonics is a low-cost and versatile platform for various applications. For design of silicon photonic devices, the light-material interaction within its complex subwavelength geometry is difficult to investigate analytically and therefore numerical simulations are majorly adopted. To make the design process more time-efficient and to improve the device performance to its physical limits, various methods have been proposed over the past few years to manipulate the geometries of silicon platform for specific applications. In this review paper, we summarize the design methodologies for silicon photonics including iterative optimization algorithms and deep neural networks. In case of iterative optimization methods, we discuss them in different scenarios in the sequence of increased degrees of freedom: empirical structure, QR-code like structure and irregular structure. We also review inverse design approaches assisted by deep neural networks, which generate multiple devices with similar structure much faster than iterative optimization methods and are thus suitable in situations where piles of optical components are needed. Finally, the applications of inverse design methodology in optical neural networks are also discussed. This review intends to provide the readers with the suggestion for the most suitable design methodology for a specific scenario.

Compact, high repetition rate ( ∼ G H z level) femtosecond fiber lasers are attractive for high-precision, high-speed scientific and engineering fields. However, the noise of such a laser seems far higher than low repetition rate ones, which limits its application. Motivated by this challenge, we combined the solid state and the fiber laser into a novel and highly stable “solid-state fiber laser” operating at 840 MHz repetition rate. Benefitting from the robust architecture of “optical cubes,” the laser shows an ultralow timing jitter (130 as) in free-running operation. This is the first time the timing jitter of a high repetition rate fiber laser has been brought to the attosecond level, to the best of our knowledge. This breakthrough makes an impact on the concept that the high repetition rate is associated with high timing jitter in fiber lasers and opens the way for real-world applications of these lasers.

The low coherence of the supercontinuum (SC) generated using picosecond pump pulses is a major drawback of such SC generation scheme. In this paper, we propose to first self-similarly compress a high power picosecond pump pulse by injecting it into a nonlinearity increasing fiber. The compressed pulse is then injected into a non-zero dispersion-shifted fiber (NZ-DSF) for SC generation. The nonlinearity increasing fiber can be obtained by tapering a large mode area photonic crystal fiber. The fiber nonlinearity is varied by varying the pitch sizes of the air holes. By using the generalized nonlinear Schrödinger equation, we show that a 1 ps pump pulse with random noise can be compressed self-similarly down to a pulse width of 53.6 fs with negligible pedestal. The noise level of the compressed pulse is reduced at the same time. The 53.6 fs pulse can then be used to generate highly coherent SC in an NZ-DSF. By using the proposed scheme, the tolerance of noise level for highly coherent SC generation with picosecond pump pulses can be improved by 5 order of magnitude.