In recent years, optical phased arrays (OPAs) have attracted great interest for their potential applications in light detection and ranging (LiDAR), free-space optical communications (FSOs), holography, and so on. Photonic integrated circuits (PICs) provide solutions for further reducing the size, weight, power, and cost of OPAs. In this paper, we review the recent development of photonic integrated OPAs. We summarize the typical architecture of the integrated OPAs and their performance. We analyze the key components of OPAs and evaluate the figure of merit for OPAs. Various applications in LiDAR, FSO, imaging, biomedical sensing, and specialized beam generation are introduced.

随着全球数据流量的不断增长，硅基光子集成电路已经成为高性能芯片内/芯片间光通信领域中一个极具发展潜力的研究方向。然而，由于本征硅的发光效率极低，硅基片上光源成为光子集成电路中最具挑战性的元器件。为了解决缺乏原生光源的问题，硅基集成的Ⅲ?Ⅴ族半导体激光器已经得到了广泛研究，该激光器提供了优越的光学和电学性能。值得注意的是，在Ⅲ?Ⅴ族半导体激光器中使用量子点作为增益介质已经引起了诸多关注，因为它具有多种优点，如对晶体缺陷的容忍度高、温度敏感度低、阈值电流密度低和反射灵敏度低等。使用量子点的激光增益区在光子集成方面相比量子阱有许多改进。增益带宽可以根据需要进行设计优化，并在整个近红外光范围内实现激射。量子态与周围材料的大能级分离使其获得了优异的高温性能和亚皮秒时间尺度的增益恢复。本文从量子点材料及量子点激光器、基于晶圆键合技术、基于倒装键合技术、基于直接外延生长技术等多个角度，综述了硅基Ⅲ?Ⅴ族半导体量子点激光器的最新研究进展，并对其未来前景和挑战进行了探讨。

压电效应是一种实现电能与机械能之间相互转换的重要物理现象。随着集成光电子技术和压电薄膜材料制备技术的日益成熟，压电效应在光电子集成芯片领域引起广泛的研究。在压电效应的作用下，外部电场可以操控薄膜材料的形变，从而改变折射率，实现光电调谐和声光调制。本文首先介绍常见压电薄膜材料及其研究进展，随后回顾和探讨基于压电效应的光电子集成器件的研究进展。最后，对压电调谐器件和声光调制器的应用进行介绍和展望，分析其大规模应用面临的挑战和问题。

A silicon-based digitally tunable positive/negative dispersion controller (DC) is proposed and realized for the first time using the cascaded bidirectional chirped multimode waveguide gratings (CMWGs), achieving positive and negative dispersion by switching the light propagation direction. A 1 × 2 Mach–Zehnder switch (MZS) and a 2 × 1 MZS are placed before and after to route the light path for realizing positive/negative switching. The device has Q stages of identical bidirectional CMWGs with a binary sequence. Thus the digital tuning is convenient and scalable, and the total dispersion accumulated by all the stages can be tuned digitally from - ( 2^Q - 1 ) D₀ to ( 2^Q - 1 ) D₀ with a step of D₀ by controlling the switching states of all 2 × 2 MZSs, where D₀ is the dispersion provided by a single bidirectional CMWG unit. Finally, a digitally tunable positive/negative DC with Q = 4 is designed and fabricated. These CMWGs are designed with a 4-mm-long grating section, enabling the dispersion D₀ of about 4.16 ps / nm in a 20-nm-wide bandwidth. The dispersion is tuned from -61.53 to 63.77 ps / nm by switching all MZSs appropriately, and the corresponding group delay is varied from -1021 to 1037 ps.

The heterogeneous integration of photonic integrated circuits (PICs) with a diverse range of optoelectronic materials has emerged as a transformative approach, propelling photonic chips toward larger scales, superior performance, and advanced integration levels. Notably, two-dimensional (2D) materials, such as graphene, transition metal dichalcogenides (TMDCs), black phosphorus (BP), and hexagonal boron nitride (hBN), exhibit remarkable device performance and integration capabilities, offering promising potential for large-scale implementation in PICs. In this paper, we first present a comprehensive review of recent progress, systematically categorizing the integration of photonic circuits with 2D materials based on their types while also emphasizing their unique advantages. Then, we discuss the integration approaches of 2D materials with PICs. We also summarize the technical challenges in the heterogeneous integration of 2D materials in photonics and envision their immense potential for future applications in PICs.

Dealing with the increase in data workloads and network complexity requires efficient selective manipulation of any channels in hybrid mode-/wavelength-division multiplexing (MDM/WDM) systems. A reconfigurable optical add-drop multiplexer (ROADM) using special modal field redistribution is proposed and demonstrated to enable the selective access of any mode-/wavelength-channels. With the assistance of the subwavelength grating structures, the launched modes are redistributed to be the supermodes localized at different regions of the multimode bus waveguide. Microring resonators are placed at the corresponding side of the bus waveguide to have specific evanescent coupling of the redistributed supermodes, so that any mode-/wavelength-channel can be added/dropped by thermally tuning the resonant wavelength. As an example, a ROADM for the case with three mode-channels is designed with low excess losses of <0.6, 0.7, and 1.3 dB as well as low cross talks of < - 26.3, -28.5, and -39.3 dB for the TE₀, TE₁, and TE₂ modes, respectively, around the central wavelength of 1550 nm. The data transmission of 30 Gbps / channel is also demonstrated successfully. The present ROADM provides a promising route for data switching/routing in hybrid MDM/WDM systems.

The photosensitivity of silicon is inherently very low in the visible electromagnetic spectrum, and it drops rapidly beyond 800 nm in near-infrared wavelengths. We have experimentally demonstrated a technique utilizing photon-trapping surface structures to show a prodigious improvement of photoabsorption in 1-μm-thin silicon, surpassing the inherent absorption efficiency of gallium arsenide for a broad spectrum. The photon-trapping structures allow the bending of normally incident light by almost 90 deg to transform into laterally propagating modes along the silicon plane. Consequently, the propagation length of light increases, contributing to more than one order of magnitude improvement in absorption efficiency in photodetectors. This high-absorption phenomenon is explained by finite-difference time-domain analysis, where we show an enhanced photon density of states while substantially reducing the optical group velocity of light compared to silicon without photon-trapping structures, leading to significantly enhanced light–matter interactions. Our simulations also predict an enhanced absorption efficiency of photodetectors designed using 30- and 100-nm silicon thin films that are compatible with CMOS electronics. Despite a very thin absorption layer, such photon-trapping structures can enable high-efficiency and high-speed photodetectors needed in ultrafast computer networks, data communication, and imaging systems, with the potential to revolutionize on-chip logic and optoelectronic integration.

Optical neural networks (ONNs), enabling low latency and high parallel data processing without electromagnetic interference, have become a viable player for fast and energy-efficient processing and calculation to meet the increasing demand for hash rate. Photonic memories employing nonvolatile phase-change materials could achieve zero static power consumption, low thermal cross talk, large-scale, and high-energy-efficient photonic neural networks. Nevertheless, the switching speed and dynamic energy consumption of phase-change material-based photonic memories make them inapplicable for in situ training. Here, by integrating a patch of phase change thin film with a PIN-diode-embedded microring resonator, a bifunctional photonic memory enabling both 5-bit storage and nanoseconds volatile modulation was demonstrated. For the first time, a concept is presented for electrically programmable phase-change material-driven photonic memory integrated with nanosecond modulation to allow fast in situ training and zero static power consumption data processing in ONNs. ONNs with an optical convolution kernel constructed by our photonic memory theoretically achieved an accuracy of predictions higher than 95% when tested by the MNIST handwritten digit database. This provides a feasible solution to constructing large-scale nonvolatile ONNs with high-speed in situ training capability.