Optical biosensors have exhibited worthwhile performance in detecting biological systems and promoting significant advances in clinical diagnostics, drug discovery, food process control, and environmental monitoring. Without complexity in their pretreatment and probable influence on the nature of target molecules, these biosensors have additional advantages such as high sensitivity, robustness, reliability, and potential to be integrated on a single chip. In this review, the state of the art optical biosensor technologies, including those based on surface plasmon resonance (SPR), optical waveguides, optical resonators, photonic crystals, and optical fibers, are presented. The principles for each type of biosensor are concisely introduced and particular emphasis has been placed on recent achievements. The strengths and weaknesses of each type of biosensor have been outlined as well. Concluding remarks regarding the perspectives of future developments are discussed.

Optical biosensors: an exhaustive and comprehensive review.

Environmental monitoring has become essential in order to deal with environmental resources efficiently and safely in the realm of green technology. Environmental monitoring sensors are required for detection of environmental changes in industrial facilities under harsh conditions, (e.g. underground or subsea pipelines) in both the temporal and spatial domains. The utilization of optical fiber sensors is a promising scheme for environmental monitoring of this kind, owing to advantages including resistance to electromagnetic interference, durability under extreme temperatures and pressures, high transmission rate, light weight, small size, and flexibility. In this paper, the optical fiber sensors employed in environmental monitoring are summarized for understanding of their sensing principles and fabrication processes. Numerous specific applications in petroleum engineering, civil engineering, and agricultural engineering are explored, followed by discussion on the potentials of OFS in manufacturing.

A review on optical fiber sensors for environmental monitoring

2D materials are considered to be the most promising materials for photodetectors due to their unique optical and electrical properties. Since the discovery of graphene, many photodetectors based on 2D materials have been reported. However, the low quantum efficiency, large noise, and slow response caused by the thinness of 2D materials limit their application in photodetectors. Here, recent progress on 2D material photodetectors is reviewed, covering the spectrum from ultraviolet to terahertz waves. First the interaction of 2D materials with light is analyzed in terms of optical physics. Then the present methods to improve the performance of 2D material photodetectors are summarized, such as defect engineering, p-n junctions and hybrid detectors, and the issue of serious overestimation of the performance in reported photodetectors based on 2D materials is discussed. Next, a comparison of 2D material photodetectors with traditional commercially available detectors shows that it is difficult to balance the current 2D material photodetectors with regard to having simultaneously both high sensitivity and fast response. Finally, a possible novel EIW mechanism is suggested to advance the performance of 2D material photodetectors in the future.

Photodetectors of 2D Materials from Ultraviolet to Terahertz Waves

X.G., X.Y., and D.P. contributed equally to this work. The authors thank the support from Singapore National Research Foundation, Competitive Research Program (NRF-CRP18-2017-02 and NRF–CRP19–2017–01), A*Star AME Programmatic Grant under Grant A18A7b0058, Singapore Ministry of Education Tier 2 Program (MOE2016-T2-1-128), and National Natural Science Foundation of China (61704082) and Natural Science Foundation of Jiangsu Province (BK20170851).

Recent Progress in Short- to Long-Wave Infrared Photodetection Using 2D Materials and Heterostructures

Nonlinear optics has undergone dramatic developments in the past 60 years, which has revolutionized the photonic and optoelectronic fields with many essential applications such as electro-optic switching, frequency mixing, optical parametric oscillation, optical phase conjugation, and so forth. As one of the new and promising candidates for both next-generation photovoltaic and optoelectronic devices, halide perovskite semiconductors have attracted extensive research attention because of their excellent electrical and optical properties demonstrated in the linear optical regime. In the past five years, halide perovskites have become a new research frontier of nonlinear optical materials because their highly tunable chemical components and multiple structures provide a variety of outstanding nonlinear optical properties, which support a broad scope of nonlinear optical applications. In this review, we have summarized the nonlinear optical properties of halide perovskites categorized according to the second-, third-, and high-order processes. Aside from the more conventional nonlinear effects, such as sum and difference frequency generation, this review also pays attention to the lesser known but important nonlinear phenomena, such as linear and circular photogalvanic effects, the high-order shift current effect, and the multi-photon pumped photoluminescence. We have also reviewed and summarized the nonlinear applications of halide perovskites, including multi-photon pumped photoluminescence imaging, multi-photon pumped amplified spontaneous emission and lasing, sub-bandgap and self-powered photodetection, all-optical and electro-optic modulation, saturable absorption, optical limiting, and so on. It is our belief that halide perovskites have proven to be excellent candidates for promoting the upgrading and updating of nonlinear optical devices with greatly improved performance and novel functionalities.

Nonlinear optical properties of halide perovskites and their applications

Mode‐Locking of All‐Fiber Lasers Operating at Both Anomalous and Normal Dispersion Regimes in the C‐ and L‐Bands Using Thin Film of 2D Perovskite Crystallites

Quantum correlation is a fundamental resource for various quantum information tasks. It is thus of importance to share the correlation to utilize it for many parties, but sharing quantum correlation among multiple parties is strictly restricted by the well-known monogamy relations. Nonetheless, this restriction can be relaxed when weak measurements are employed. Here, we experimentally demonstrate multiple-observer quantum steering by exploiting sequential weak measurements. Specifically, we observe simultaneous triple violations of the quantum steering inequality among four observers for a bipartite entangled system. Our results not only provide fundamental insights into the relation between quantum steering and measurement disturbance, but also suggest that quantum steering might be repeatably exploited to find applications to, for example, unbounded randomness certification and sharing secret keys among multiple parties simultaneously.

Demonstration of simultaneous quantum steering by multiple observers via sequential weak measurements

We propose a new hollow ring core silica photonic crystal fiber that can support 101 orbital angular momentum (OAM) modes, maintaining a high mode quality without phase distortion, a low confinement loss, and a large effective index difference between the adjacent modes, which could open a new avenue of OAM mode multiplexing applications. The fiber consists of three layers: the circular central air hole, silica ring core, and circumferencing silica-air hole porous inner cladding. Using the full-vectorial finite element method (FEM), the modal characteristics of individual OAM modes in the proposed fiber were thoroughly analyzed by varying the number of air-holes in the circularly symmetric cladding. We found a general selection rule for the number of air-holes in the first layer and the topological charge to cause the phase distortion of OAM modes, for the first time. The phase distribution of the guided OAM modes was thoroughly investigated to select usable modes for mode division multiplexing. Parametric analyses of the proposed PCF are reported to optimize optical properties of the OAM modes.

Hollow Silica Photonic Crystal Fiber Guiding 101 Orbital Angular Momentum Modes Without Phase Distortion in C+L Band

We report unique thermo-optical characteristics of DNA-Cetyl tri-methyl ammonium (DNA-CTMA) thin solid film with a large negative thermo-optical coefficient of -3.4×10-4/°C in the temperature range from 20°C to 70°C without any observable thermal hysteresis. By combining this thermo-optic DNA film and fiber optic multimode interference (MMI) device, we experimentally demonstrated a highly sensitive compact temperature sensor with a large spectral shift of 0.15 nm/°C. The fiber optic MMI device was a concatenated structure with single-mode fiber (SMF)-coreless silica fiber (CSF)-single mode fiber (SMF) and the DNA-CTMA film was deposited on the CSF. The spectral shifts of the device in experiments were compared with the beam propagation method, which showed a good agreement.

Seongjin Hong

Papers

Mode‐Locking of All‐Fiber Lasers Operating at Both Anomalous and Normal Dispersion Regimes in the C‐ and L‐Bands Using Thin Film of 2D Perovskite Crystallites

Demonstration of simultaneous quantum steering by multiple observers via sequential weak measurements

Hollow Silica Photonic Crystal Fiber Guiding 101 Orbital Angular Momentum Modes Without Phase Distortion in C+L Band

Thermo-optic characteristic of DNA thin solid film and its application as a biocompatible optical fiber temperature sensor

Seamless MoTe2 Homojunction PIN Diode toward 1300 nm Short-Wave Infrared Detection