Ciyuan Qiu

We propose and experimentally demonstrate a compact optical switch based on a one-dimensional (1D) silicon nitride (Si ₃ N ₄ ) photonic crystal nanobeam cavity (PCNC) integrated with a graphene microheater. The PCNC exhibits a small optical mode volume of approximately 3.2 μm ³ , which enhances light-matter interaction and improves thermo-optic (TO) tuning efficiency. Graphene is positioned at the center of the cavity, and heat generation is induced by applying a bias voltage across it. The refractive index of the underlying PCNC is then changed due to the TO effect, thereby enabling resonance wavelength tuning. Additionally, fast thermal response is achieved owing to the high thermal conductivity of graphene. Measurements show a TO tuning efficiency of 0.21 nm/mW and an extinction ratio (ER) of 7 dB at an applied heating power of 5.2 mW. The thermal rise and fall time constants are 4.55 μs and 1.55 μs, respectively. This work achieves a microsecond-level Si ₃ N ₄ -based optical switch with a compact device footprint, offering a promising solution for high-density on-chip optical interconnects and routing systems.

Narrow-linewidth, frequency-modulated continuous-wave (FMCW) lasers are indispensable components in modern sensing and measurement systems. Toward their integrated photonic implementations, self-injection-locked lasers stand out for the ultralow noise and operational simplicity. However, their tuning range remains limited, primarily due to the restricted locking range imposed by the long-delay external cavities. In this work, we address this limitation by demonstrating a widely tunable FMCW integrated laser through self-injection locking to a strongly reflective multimode micro-ring resonator (MRR). This MRR adopts a tailored over-coupled design with negligible intermodal crosstalk, unifying large free spectral range and high-Q strong reflection, substantially extending the laser self-injection locking range. Experimental results reveal that the multimode MRR presents a high intrinsic Q value of 1.45×107 together with a reflectivity of −0.92 dB. The demonstrated hybrid integrated laser leverages a combination of exhibits, a static mode-hop-free tuning range up to 37.84 GHz, a side-mode suppression ratio exceeding 65 dB, and an intrinsic linewidth of 1.55 kHz. Furthermore, it achieves FMCW generation with a record-high chirp bandwidth of 25.42 GHz at a 100 Hz repetition rate. These results highlight the promising application prospects and practical value of the proposed laser in cutting-edge fields, including light detection and ranging, microwave photonics, and optical fiber sensing.

A broadband silicon polarization beam splitter (PBS) is proposed and experimentally demonstrated based on Floquet-engineered directional couplers. The total length of the coupling structure is 20 μm. By periodically modulating the waveguide widths of the directional couplers, the power exchange between the two waveguides for the transverse-electric (TE) mode is suppressed, while the power coupling for the transverse-magnetic (TM) mode is enhanced. The fabricated PBS exhibits polarization extinction ratios (PERs) >20 dB for both polarizations over a broad wavelength range of 1483–1620 nm. Additionally, the measured insertion losses (ILs) are 0.15 dB and 1.2 dB at 1550 nm for TE and TM polarizations, respectively.

In this work, we propose and demonstrate a compact low-crosstalk silicon waveguide array for dense integration of passive photonic devices. In this device, the waveguide pitch of the array is set to half of the working wavelength. To achieve low crosstalk, the widths of the waveguides in the array are modulated, and the modulation phase difference between adjacent waveguides is set to ${\bm{\pi}}$. Based on Floquet theory, quasi-energy collapse would occur and a zero-crosstalk transmission can then be achieved. Simulation results show that, for a 104.5-μm-length array, the insertion loss is as low as 0.09 dB and the crosstalk is below −23 dB in 1500 nm–1580 nm. In the experiments, an insertion loss of 0.6 dB and crosstalk lower than −23 dB are obtained at a wavelength range from 1530 nm to 1570 nm. Our device exhibits the ability to suppress transmission crosstalk while maintaining low propagation loss, revealing its potential in enhancing the integration density of CMOS-compatible passive optical components.

This paper demonstrates a Verilog-A compact photonic model based on coupled-mode theory for nonlinear interactions, including four-wave mixing (FWM) and cross-phase modulation (XPM), to present a general framework and methodology for modeling nonlinear interactions in electronic-photonic co-simulation. The model is compatible with existing electronic design automation (EDA) platforms and can support rapid electronic-photonic co-simulation. It avoids describing the complicated physical process of the FWM and provides an easy way for system designers to monitor the dynamics of the critical optical parameters, thus accelerating the co-design and co-optimization of the electronic-photonic hybrid systems incorporating FWM. Meanwhile, the model is not tailored for a particular photonic device but can be applied to different photonic devices as a fundamental component. The model framework and modeling methodology presented in this paper are expected to be further applied to the modeling of other optical nonlinear interactions. The simulation results of the proposed model agree well with both numerical and experimental results. A closed-loop electronic-photonic co-simulation example using the proposed model is also carried out successfully.

High-density silicon waveguide arrays manufactured on a complementary metal-oxide-semiconductor (CMOS)-foundry platform hold great promise for optical information processing and photonic integration. However, evanescent waves arising from nanoscale confinement would cause significant optical crosstalk in waveguide arrays, which remains a vital issue in various applications. Here, by utilizing silicon photonic nanohole metamaterials, we propose a scheme to greatly suppress the crosstalk in the devices and then demonstrate ultra-compact low-crosstalk waveguide arrays. For a 100-µm-long waveguide array at a half-wavelength pitch, low crosstalk of −19 dB can be obtained in a wide range of wavelengths (1500 nm–1580 nm). In the experimental demonstrations, our approach exhibits the ability to suppress the crosstalk over a broad bandwidth without substantially increasing the propagation loss as well as the promising design flexibility, which shall pave the way for metamaterials enabled high-density waveguide arrays.

This paper presents general SPICE photonic models for closed-loop electronic-photonic co-simulation. SPICE models are originally intended for electronic devices, which have significantly different physics compared to photonic devices. Most existing SPICE photonic models are specialized and fail to capture important features like multi-dimensional signals. It remains a key challenge to represent general photonic devices using SPICE models that include their essential features. To address the above challenge, we separate the signal meaning from its numerical result and adopt a numerically-equivalent approach to construct photonic models using native SPICE primitives. And the designer is left to interpret the meaning of the numerically-equivalent electronic signals, such as wavelength and polarization. Our models encompass the features of existing SPICE models, including wavelength dependence and bi-directional transmission, as well as new features beyond those. Specifically, polarization, optical Kerr effect, two-photon absorption, free carrier absorption, and free carrier dispersion are included in our SPICE models. Closed-loop polarization simulation is realized for the first time. We can quickly achieve frequency-domain simulation by DC sweep instead of stepped frequency transient simulations or frequency chirp-based methods. Our SPICE photonic models show excellent agreement with the simulation results of Verilog-A models and Lumerical models. Our SPICE photonic models are more efficient in co-simulation with SPICE electronic models than Verilog-A photonic models due to less compiling time and better compatibility. Our general models make the circuit design of electronics-photonics convergence (EPC) as convenient as that of traditional integrated circuits, paving the way for the circuit-level convergence of electronics and photonics.

Due to the rise of 5G, IoT, AI, and high-performance computing applications, datacenter traffic has grown at a compound annual growth rate of nearly 30%. Furthermore, nearly three-fourths of the datacenter traffic resides within datacenters. The conventional pluggable optics increases at a much slower rate than that of datacenter traffic. The gap between application requirements and the capability of conventional pluggable optics keeps increasing, a trend that is unsustainable. Co-packaged optics (CPO) is a disruptive approach to increasing the interconnecting bandwidth density and energy efficiency by dramatically shortening the electrical link length through advanced packaging and co-optimization of electronics and photonics. CPO is widely regarded as a promising solution for future datacenter interconnections, and silicon platform is the most promising platform for large-scale integration. Leading international companies (e.g., Intel, Broadcom and IBM) have heavily investigated in CPO technology, an inter-disciplinary research field that involves photonic devices, integrated circuits design, packaging, photonic device modeling, electronic-photonic co-simulation, applications, and standardization. This review aims to provide the readers a comprehensive overview of the state-of-the-art progress of CPO in silicon platform, identify the key challenges, and point out the potential solutions, hoping to encourage collaboration between different research fields to accelerate the development of CPO technology. Graphical Abstract

Micro-ring resonator (MRR) is a key photonic device that has a wide range of applications but suffers from wavelength uncertainties. For almost all practical applications, a wavelength controller is required for each MRR. The wavelength controller is usually much larger than the MRR. With more complicated control algorithms, the controller size becomes even larger. Equipping each MRR with a wavelength controller will not be scalable. We propose a pipelined time-division-multiplexing (PTDM) control scheme that achieves high scalability while maintaining good loop bandwidth by exploiting the speed mismatch between the heater and the controller. To verify this proposed scheme, a hybrid integrated controller supporting four MRRs is designed. Measurement results show that it achieves a sine tracking speed of about 15 nm/s while achieving a locking accuracy of 7 pm and a tuning range of 9 nm.

Terahertz (THz) diffractive optical neural networks (DONNs) highlight a new route toward intelligent THz imaging, where the image capture and classification happen simultaneously. However, the state-of-the-art implementation mostly relies on passive components and thus the functionalities are limited. The reconfigurability can be achieved through spatial light modulators (SLMs), while it is not clear what device specifications are required and how challenging the associated device implementation is. Here, we show that a complex-valued modulation with a π/2 phase modulation in an active reflective graphene-plasmonics-based SLM can be employed for realizing the reconfigurability in THz DONNs. By coupling the plasmonic resonance in graphene nanoribbons with the reflected Fabry-Pérot (F-P) mode from a back reflector, we achieve a minor amplitude modulation of large reflection and a substantial π/2 phase modulation. Furthermore, the constructed reconfigurable reflective THz DONNs consisting of designed SLMs demonstrate >94.0% validation accuracy of the MNIST dataset. The results suggest that the relaxation of requirements on the specifications of SLMs should significantly simplify and enable varieties of SLM designs for versatile DONN functionalities.