Silicon Mach–Zehnder modulators (MZMs) have become indispensable in optical interconnects for data centers and AI clusters due to their robustness and scalability. However, its working principle makes it challenging for silicon MZMs to simultaneously achieve the bandwidth necessary to support 400 Gbps/lambda PAM-4 transmission while maintaining practical modulation efficiency. Here, we present an O-band slow-light silicon MZM leveraging photonic crystal (PhC) waveguides, fabricated on a 300 mm silicon photonics platform. By exploiting the slow-light effect to enhance light–matter interaction, the device achieves a compact footprint of 500 µm, a low half-wave voltage-length product (V π ⋅L) of 0.65V⋅cm, and a high median electro-optic bandwidth of 94.7 GHz. Operated with a 2.7V pp driving voltage, the modulator demonstrates its potential for high-speed, high-density optical interconnects by supporting optical transmission rates of 300Gbps/ λ (135 Gbaud PAM-4) and 400Gbps/ λ (135 Gbaud PAM-8) with a low power consumption of 15.0 fJ/bit.

Visible-light photonic integrated circuits (PICs) with self-powered and high-sensitivity waveguide photodetectors (PDs) are essential for advancing next-generation biosensing, optogenetics, and DNA sequencing technologies. Conventional bulk-material-based visible PDs integrated on silicon nitride (SiN) platforms have limitations, including complex fabrication, lattice mismatch, and the need for high bias voltages in avalanche detection, which hinder low-cost manufacturing and energy-efficient scalability. Here, we present a self-powered 2D perovskite/InSe van der Waals (vdWs) heterostructure waveguide PD integrated onto a SiN photonic platform for on-chip visible-light biosensing. Leveraging the strong light-matter interaction of 2D perovskite and the built-in electric field at the perovskite/InSe interface, the device achieves an ultralow dark current of 2.6 & times; 10-13 A at zero bias and exceptional sensitivities, with normalized photocurrent-to-dark-current ratios (NPDRs) of up to 5.0 & times; 107 mW-1. The PD exhibits fast temporal response (similar to 20 ms) and excellent self-powered operation, enabling energy-efficient visible-light detection. We further demonstrate visible SiN slot waveguides monolithically integrated with 2D vdWs PDs for fluorescence-labeled DNA detection, yielding a sensitivity of 30.6 pA mu M-1 and a detection limit of 100 nM at zero bias. Our results establish a scalable route to energy-saving, high-performance visible-light biosensing PICs based on 2D vdWs heterostructure PDs.

Photonic computing offers a compelling route towards high-throughput and energy-efficient information processing by exploiting ultrahigh bandwidth and intrinsic parallelism. However, its scalability is fundamentally limited by the electronic overhead at the optical–electrical interface, particularly the power-hungry digital-to-analog converters (DACs) required for multibit weight programming. Here, we report a silicon photonic multiplier that eliminates electronic DACs by introducing an electro-optic digital-to-analog converter (EO-DAC), implemented with a Mach–Zehnder interferometer (MZI) incorporating segmented carrier-injection phase shifters. Driven solely by binary electrical signals, the EO-DAC directly synthesizes multibit optical weight states, enabling 4-bit-resolved analogue modulation without analogue electrical circuitry. By monolithically integrating on-chip input encoding and differential electrical readout, we further minimize external interface overhead and realize a compact photonic computing unit. The proposed architecture is experimentally validated through image convolution and MNIST handwritten digit recognition tasks, demonstrating accurate and energy-efficient operation. Our results establish a scalable paradigm for energy-efficient optical weight synthesis and highlight a viable path towards large-scale photonic computing systems with reduced electronic bottlenecks.

We demonstrate a novel polarization multiplexing silicon vector optical phased array for 100 Gbps inter-satellite coherent communication, featuring wavelength-selective capability and enables coherent beam combining through independent control of phase and polarization.

With the surge of data-intensive AI and cloud workloads, optical interconnects have become a key enabler for high-speed, low-latency, energy-efficient, and scalable compute-node interconnection. However, current inter-rack optical interconnects still rely on Ethernet protocol incurring microsecond-level latency, which constrain the scaling of compute-nodes across racks. To mitigate this issue, we propose a novel architecture that enables direct rack-to-rack communication through a PCIe-compatible optical I/O, leveraging the inherent nanosecond-level latency of the PCIe protocol. Furthermore, leveraging a 95 GHz bias- and electrical amplification-free silicon microring modulator (MRM) and a 85 GHz Ge/Si photodetector, this optical I/O is demonstrated supporting PCIe 6.0 transmission and 64 Gbps NRZ transmission over 2 km fiber with $< 0.8$ $V_{pp}$ drive. The link achieves sub-pJ/bit energy consumption in the optical domain, confirming the feasibility of low-power, high-speed optical interconnects for next-generation scalable computing systems.

The development of efficient O-band light sources on silicon is crucial for next-generation short-reach optical interconnects. While significant progress has been made in the C-band, the integration of III-V/Si lasers for the O-band presents distinct challenges, including the optimization of material gain and the implementation of robust single-mode selection mechanisms. In this work, we address these challenges by implementing a multi-cavity Vernier-effect III-V/Si laser architecture that requires neither fine-pitch Bragg gratings nor complex ring structures. By precisely controlling the longitudinal cavity lengths, the device achieves single-mode lasing with a side-mode suppression ratio (SMSR) exceeding 45 dB.

Silicon-based microring modulators (MRMs) are emerging as essential components in wavelength-division multiplexing (WDM) systems due to their compact footprint, low power consumption, and inherent wavelength selectivity. However, conventional add-drop MRMs face challenges such as limited modulation efficiency and a trade-off between electro-optic (EO) bandwidth and efficiency. Here, we present a high-performance 4 & times; 400 Gbps WDM transmitter operating in both the O-band and C-band, fabricated on a 300 mm CMOS silicon photonics platform. By optimizing the doping profile across the microring, the bus waveguides, and the coupling sections, the MRMs achieve 3 dB EO bandwidths exceeding 67 GHz and modulation efficiencies as low as 0.57 V & centerdot;cm for the O-band and 0.65 V & centerdot;cm for the C-band. At 400 Gbps using PAM-6 modulation, the power consumption is reduced to similar to 0.40 fJ/bit for both bands. The demonstrated four-channel transmitter achieves an aggregate data rate of 1.6 Tbps within a compact footprint of 1 & times; 0.27 mm2, corresponding to a data-rate density of approximately 5.9 Tbps/mm2. These results highlight the potential of our silicon photonic transmitter for high-capacity optical interconnects in data centers and AI-driven architectures.

We demonstrate simultaneous distance and velocity measurement in spectral-scanning FMCW LiDAR using a unidirectional nonlinear frequency sweep, enabling simplified 4D coherent imaging without requiring bidirectional modulation.

The escalating demands of compute-intensive applications urgently necessitate the adoption of optical interconnect technologies to overcome bottlenecks in scaling computing systems. This requires fully exploiting the inherent parallelism of light across scalable dimensions for data loading. Here we experimentally demonstrate a synergy of wavelength- and mode- multiplexing combined with high-order modulation formats to achieve multi-tens-of-terabits-per-second optical interconnects using foundry-compatible silicon photonic circuits. Implementing an edge-guided analog-and-digital optimization method that integrates high efficiency with fabrication robustness, we achieve the inverse design of mode multiplexers based on digital metamaterial waveguides. Furthermore, we employ a packaged five-mode multiplexing chip, achieving a single-wavelength interconnect capacity of 1.62 Tbit s-1 and a record-setting multi-dimensional interconnect capacity of 38.2 Tbit s-1 across 5 modes and 88 wavelength channels, with high-order formats up to 8-ary pulse-amplitude-modulation (PAM). This study highlights the transformative potential of optical interconnect technologies to surmount the constraints of electronic links, thus setting the stage for next-generation datacenter and optical compute interconnects.

A three-section grating coupler is proposed and numerically demonstrated on a 300-nm-thick silicon nitride (SiN) platform for O-band fiber-to-chip vertical coupling. The device comprises a refractive-index-graded SiN subwavelength grating for index smoothing and reflection suppression, a fully etched amorphous-silicon interlayer enabling near-vertical radiation, and SiN Bragg gratings for recycling residual guided power. With a minimum feature size of 130 nm, 2D Finite-Difference Time-Domain(FDTD) simulations indicate a coupling efficiency of -0.37 dB at 1309 nm under near-vertical incidence, with 99.2% mode overlap and 93.1% upward-radiated power, without requiring a bottom reflector. Furthermore, 3D-FDTD verification confirms a coupling efficiency of -0.38 dB with a 33-nm 3-dB bandwidth. Even under perfectly vertical incidence, the device achieves -0.9 dB performance. To the best of our knowledge, this represents one of the highest simulated efficiency reported for SiN grating couplers without bottom reflectors. Tolerance analysis further confirms robust performance over a wide fabrication window, highlighting the design's promise for SiN photonic interfaces.

We demonstrate a lateral waveguide coupled Ge-Si photodetector enabling uniform absorption with 67 GHz bandwidth under 4 mA photocurrent, in which 112 Gbps NRZ and 224 Gbps PAM4 clear openings of eye diagrams are experimentally attained.

Germanium photodetectors (Ge-PDs) are key components in silicon photonics (SiPh) to enable high-speed optical communications for various applications. Several works have been reported to improve the bandwidth, quantum efficiency, and manufacturing process of Ge-PDs. However, a significant trade-off between bandwidth and responsivity remains a major challenge in developing high-performance Ge-PDs for large-scale silicon photonic integrated circuits. Here, by co-optimizing the chemical mechanical polishing (CMP) process and device structure, ultra-thin Ge-PDs with high 3 dB bandwidth have been achieved. The dimensions of the Ge region and doping areas have also been optimized to attain a high-bandwidth, high-quantum-efficiency product. Consequently, we demonstrate lateral-PIN Ge-PDs with a high bandwidth of up to 100 GHz, 1.05 A/W responsivity at 1550 nm and <20nA dark current on 300 mm CMOS silicon-photonic process. Our work demonstrates that high-performance Ge-PDs with a simple fabrication process are feasible, which paves the way for developing next-generation 200 Gbaud intensity-modulated direct-detection (IMDD) and coherent optical systems.

We demonstrate a 280 Gbps optical link using a silicon depletion-type microring modulator and a germanium photodetector, both with 3dB bandwidth over 110 GHz and fabricated on 300 mm silicon photonic platform.

We propose a Multi-Path EKF algorithm for polarization demultiplexing in multi-path coherent optical systems. This algorithm handles high-rate RSOP without per-path polarization controllers, reducing chip area and ensuring robust BER performance.

Significance High-coherence and widely tunable laser sources are key enabling components in modern silicon photonic systems, playing a critical role in coherent optical communications, frequency-modulated continuous-wave (FMCW) LiDAR, precision metrology, and distributed fiber-optic sensing. With the rapid growth of data traffic, increasing demands on sensing accuracy, and the continuous evolution toward system-level integration, laser sources are no longer required to merely provide stable emission, but must instead support precise phase and frequency control with high stability, wide tuning range, and low noise. Different applications impose distinct and often competing performance requirements on laser sources. In coherent communication systems, narrow linewidth and low phase noise directly determine achievable modulation formats, transmission capacity, and bit error rate, while precise wavelength locking to standardized channels is essential for dense wavelength division multiplexing. In LiDAR and three-dimensional imaging, high output power and broadband linear frequency sweeping are required to enhance detection range and spatial resolution. In fiber-optic sensing and precision metrology, long-term frequency stability and low drift are critical for achieving high sensitivity and measurement accuracy. Conventional semiconductor lasers are fundamentally limited by short cavity length and intrinsic noise mechanisms, which restrict their linewidth and frequency stability. Although discrete external-cavity lasers can achieve excellent coherence and tunability, they are not compatible with large-scale integration. Silicon-based integrated external-cavity lasers, realized through integration of III-V gain media with low-loss silicon photonic circuits, have therefore emerged as a promising solution, offering both high performance and scalability. This review focuses on precise phase-frequency control technologies for silicon-based integrated external-cavity lasers and their applications. Progress This paper systematically reviews the working principles, key phase-frequency control techniques, recent research advances, and representative applications of silicon-based integrated external-cavity lasers. We first introduce the fundamental configurations and physical mechanisms of two mainstream device architectures (Figs. 1-3). Subsequently, three core phase-frequency control techniques are discussed in detail. For wavelength tuning and locking, implementations based on Fabry-P & eacute;rot (FP) etalons combined with servo feedback circuits are introduced (Fig. 4), enabling precise alignment with International Telecommunication Union (ITU) channels. For frequency stabilization, the widely adopted Pound-Drever-Hall (PDH) technique is described (Fig. 5), which locks the laser to a high-stability optical reference to enhance long-term stability. For linear frequency sweeping in FMCW applications, two representative linearization approaches, namely iterative pre-distortion and electro-optic phase-locked loops, are comparatively analyzed (Fig. 6), both of which effectively suppress chirp nonlinearity. Furthermore, recent representative research progress is comprehensively summarized. Advances in narrow-linewidth tunable lasers are reviewed, including linewidth reduction to the Hz level enabled by low-loss extended cavities and high-Q resonators (Fig. 7), wide-range mode-hop-free tuning and high-linearity frequency sweeping (Fig. 8), as well as power scaling strategies (Fig. 9). A comparative analysis of material platforms, including Si, Si3N4, and lithium niobate on insulator (LNOI), is also provided. In addition, wavelength-locking technologies based on discrete FP etalons (Fig. 10) and integrated wavelength-locked lasers (Fig. 11) are discussed. Progress in integrated frequency stabilization is reviewed, covering miniaturized optical frequency references (Fig. 12), on-chip reference cavities (Fig. 13), and dual-polarization self-referenced stabilization schemes (Fig. 14). Finally, the application potential of silicon-based external-cavity lasers is validated through system-level demonstrations in space coherent optical communication (Figs. 15-17), FMCW LiDAR (Fig. 18), and distributed fiber-optic sensing (Figs. 19-23). Conclusions and Prospects Silicon-based integrated external-cavity lasers have achieved significant progress in linewidth reduction, wavelength tuning, frequency stabilization, and power scaling, demonstrating strong potential for next-generation coherent photonic systems. By leveraging the integration of III-V gain media with low-loss photonic circuits, these devices effectively combine their respective advantages, enabling high-performance and scalable on-chip laser sources. Despite these advances, several challenges remain for practical deployment. A key limitation is the lack of high-stability on-chip optical frequency references, which constrains long-term absolute frequency stability. Future efforts should focus on complementary metal oxide semiconductor (CMOS) compatible materials with improved thermal stability and hybrid stabilization schemes combining self-injection locking with integrated absorption-based references. In parallel, advances in multi-material integration and optoelectronic co-design, enabled by wafer-scale bonding and advanced integration technologies, will be essential for achieving compact, low-power, and system-level solutions. Furthermore, intelligent control strategies such as machine-learning-assisted optimization are expected to enhance real-time phase and frequency stabilization in complex environments. Overall, these developments will drive highly integrated, high-performance laser sources for applications in communication, sensing, and precision metrology.

We present a silicon dual-ring modulator (DMRM) that integrates the direct current (DC) Kerr effect with a dual-ring coupled resonance architecture, achieving high linearity, broad optical bandwidth, and a high extinction ratio. The DC Kerr effect complements the plasma dispersion effect to suppress high-order nonlinear distortions, while the dual-ring design extends the operational wavelength range and enhances the extinction ratio. Experimental results demonstrate a spurious-free dynamic range (SFDR) of 107 dB·Hz²/³ at a carrier frequency of 1 GHz, a 58 GHz electro-optic bandwidth, and a static extinction ratio exceeding 30 dB. These results highlight the potential of the proposed DMRM for high-speed, high-linearity optical interconnects in microwave photonic systems.

In this paper, a high signal-to-noise ratio (SNR) phase-sensitive optical time-domain reflectometer (Φ-OTDR) system based on the 1440-level diversity merging technique is proposed, aiming to solve the problem of SNR degradation in long-distance detection of the conventional Φ-OTDR. The 1440-level diversity merging scheme is realized by combining 4-level wavelength diversity, 3-level frequency diversity, 30-level space diversity, and 4-level time diversity techniques, which can significantly improve the detection capability and the system SNR without triggering the nonlinear effect of the fiber. The experimental results show that the system achieves the fading suppression over the whole-line 20 km fiber, the mean noise floor reaches -77.4 dB (re 1rad2/Hz)@500 Hz, and the SNR is improved by 28.5 dB compared with the conventional Φ-OTDR system, and the external disturbance signal is successfully reconstructed. Furthermore, the system is verified to achieve the long-distance detection up to 70 km, which noise performance rivals that of commercial long-distance system. This study provides effective technical support for the application of Φ-OTDR in long-distance and high-SNR detection scenarios such as geophysical prospecting and marine acoustics.

Wavelength division multiplexing (WDM) optical interconnect technology offers an effective solution for addressing the ever-increasing data traffic. Microring modulators (MRMs), owing to their high bandwidth, compact footprint, and inherent wavelength selectivity, have become key building blocks in WDM systems. However, the limited free spectral range (FSR) of MRMs restricts the number of available wavelength channels and the corresponding overall data rate capacity in WDM systems. In this study, we propose an optimized Bezier-bent MRM, in which the device radius is reduced to 3 mu m to significantly enhance the FSR. The proposed MRM operates without the need for a DC bias voltage and an RF amplifier, exhibiting a low insertion loss of 0.4 dB, an ultrawide FSR exceeding 4 THz, and a high electro-optic bandwidth of over 110 GHz. Back-to-back (BtB) transmission experiments demonstrate that the modulator supports 400 Gbps PAM-8 data transmission under a driving voltage of only 1 V, satisfying the 7% hard-decision forward error correction (HD-FEC) bit-error-rate (BER) threshold of 3.8 & times; 10-3. Owing to the compact-radius design, the junction capacitance is substantially reduced, enabling an exceptionally low modulation power consumption of 0.2 fJ/bit. The proposed MRM presents significant potential for dense integration in future optical communication systems.