Guanghui Ren

The electrostatic functionality of barrier heterostructures relies on the fidelity of buried dopant profiles, particularly across nominally undoped layers. Here, a nonabrupt Si concentration profile near the functional barrier is identified as an important factor affecting barrier electrostatics in 14 μm-cutoff InAs/GaSb type-II superlattice (T2SL) nBn photodetectors. Secondary ion mass spectrometry (SIMS) resolves a nonabrupt Si concentration profile extending from the doped contact region toward the nominally undoped barrier. Numerical simulations show that a donor-like perturbation representative of such a nonideal doping profile can localize the barrier potential and enhance the local electric field, disrupting carrier-selective transport and promoting tunneling-related leakage. Introducing an undoped contact-layer spacer spatially separates the measured Si concentration transition from the functional barrier, preserves the intended barrier electrostatics, and improves peak specific detectivity by a factor of 2.24. The apparently earlier spectral turn-on is therefore attributed to barrier degradation rather than enhanced carrier extraction.

Microwave photonic (MWP) all-pass filters (APFs), which enable phase manipulation without altering signal amplitudes, are essential for phase engineering in high-bandwidth microwave signal processing. However, achieving a high degree of reconfigurability in the filter order and characteristic parameters of APFs remains challenging for conventional methods. Here, we propose and experimentally demonstrate MWP APFs based on a microcomb-driven finite-impulse-response (FIR) transversal filter system, enabling high reconfigurability and sharp phase transitions with high group delays. We experimentally demonstrate both first- and second-order APFs, achieving maximum amplitude variations (MAVs) down to ∼1.95 dB and maximum group delays (MGDs) up to ∼580 ps for the former, and MAVs down to ∼2.01 dB and MGDs up to ∼1740 ps for the latter. In addition, by simply programming the tap coefficients without changing any hardware, we experimentally demonstrate a high degree of filter reconfigurability with respect to filter order, group delay, center frequency, and independent control of multiple APF parameters. These results highlight the potential of our approach for implementing MWP APFs with both high performance and reconfigurability for practical applications requiring dynamic and versatile phase control.

Mode-division multiplexing is a common technology in photonic integrated circuits, which can combine various optical mode signals into a single channel, such as a multimode waveguide, to improve the communication system’s capacity. The optical mode (de)multiplexer plays a critical role in mode-division multiplexing by converting multiple single-mode signals from different channels into corresponding multimode signals, respectively, and then combining them into the same physical channel and vice versa. Here, we propose an ultra-broadband optical mode (de)multiplexer based on modal-field redistribution assisted by subwavelength grating (SWG) structures in lithium niobate on insulator. As a proof of concept, we design and fabricate a three-channel mode (de)multiplexer. The simulation results show an operating bandwidth of 800 nm (from 1.2 to 2.0 μm) with an insertion loss of less than 1 dB, and the experimental results show that the insertion loss and crosstalk of all devices are less than 1.0 dB and −15.9 dB in the wavelength range of 1500–1600 nm, which is basically consistent with the simulation results. This work holds significant promise for the future implementation of high-performance photonic integrated circuits (PICs) on the LNOI platform.

Electro-optic modulators (EOMs) are pivotal for optical communication systems, converting electrical signals to the optical domain. To further maximize spectral efficiency and boost transmission capacity, endowing EOMs with dual-band operation capability has become imperative. Here, we demonstrate a dual-band silicon nitride-loaded thin-film lithium niobate modulator that supports energy-efficient operation in both the O- and C-band using a unified photonic-electronic architecture. The device integrates dual-band grating couplers and bidirectional dual-band multiplexers with capacitively loaded traveling-wave electrodes engineered for high-speed modulation. By tailoring the waveguide geometry to minimize inter-band group-index disparity, the modulator achieves simultaneous velocity matching across widely separated wavelengths. The proposed EOM achieves PAM-8 transmission at a raw line rate of 600 Gbps before FEC overhead at both 1310 and 1550 nm, with corresponding power consumption of 0.82 and 0.89 fJ/bit, respectively. Our results establish a scalable route toward multi-band thin-film lithium niobate photonic interconnects for future high-capacity optical communication systems.

Microring modulators are the most fundamental and crucial building blocks for next-generation big data applications, including optical interconnect, photonic computing, and optical wireless communication. However, achieving exceptionally fast modulation rates for microring modulator remains a formidable challenge due to the photon lifetime limitations and lumped electrode architectures. In this work, we propose and experimentally demonstrate an ultra-high-speed microring modulator on a silicon nitride-loaded lithium niobate on insulator platform. By integrating low-loss Euler-bend waveguides with fully symmetrical capacitively loaded traveling-wave electrodes reinforced by a dummy waveguide, the device achieves a record-breaking modulation rate of 517 Gbps (200 GBaud PAM6). This exceptional performance is accompanied by an electro-optic bandwidth exceeding 110 GHz and an ultra-low energy consumption of merely 1.5 fJ/bit. To demonstrate the performance and application prospects of this modulator, we successfully verify its capability to accelerate feature extraction at a modulation rate of 40 GBaud in photonic computing and support breakthrough wireless multi-target communication with a single-channel capacity of 360 Gbps (180 GBaud PAM4), highlights its transformative potential across a broad spectrum of next-generation photonic systems.

Synthetic dimensions provide a powerful tool that uses comparatively simple structures to probe high‐dimensional topological physics, in which edge states emerging at lattice boundaries are of great importance. However, the demonstration of lattice boundaries in synthetic dimensions is relatively nascent. In this work, we realize an integrated coupled ring system in a thin‐film lithium niobate photonic platform that enables the simulation of one‐dimensional frequency crystal lattice with sharp boundaries, attaining suppression for two coupling terms with a single auxiliary cavity. Their effect on tight‐binding lattice dynamics was verified by acquiring discretized band structures of an site lattice. The ability to create robust frequency‐space boundaries is a key step toward the realization of topological systems that harness bulk‐edge correspondence as well as optical information processing in a photonic chip.

Photonic designs based on conventional transformation optics (TO) techniques often assume isotropic materials, which makes them incompatible with the anisotropic nature of emerging photonic platforms such as lithium niobate on insulator (LNOI), impeding advances in high-density and multi-functional photonic integration. In this work, we extend the application of TO to the design of anisotropic photonic devices. By incorporating topology optimization in the virtual space, our approach effectively suppresses anisotropic scattering loss and mode crosstalk, thereby reducing the constraints imposed by specific material properties. As an example, we realize a 90° fundamental transverse electric (TE) mode waveguide bend with an effective radius of 40 µm, exhibiting a low insertion loss (IL) of 0.15 dB at 1550 nm, based on the silicon nitride loaded LNOI platform. Furthermore, a 90° multimode waveguide bend with an effective radius of 60 µm, supporting TE ₀ and TE ₁ , is also demonstrated using the proposed scheme. Experimental results for the two modes show crosstalk below -19.7 dB, and IL below 0.14 dB at 1550 nm. Both devices exhibit an ultra-broad bandwidth beyond 400 nm. Importantly, this work establishes a general TO-based design paradigm applicable to diverse material platforms and provides avenues for anisotropic device design.

Integrated photonics-based coexistence systems enable classical data channels and quantum channels to share the same optical waveguide by integrating quantum key distribution (QKD) into existing telecommunications infrastructure, reducing the costs and complexities of deploying quantum-secure links. Achieving this requires photonic components that efficiently reject intense classical light while preserving the integrity of ultra-weak single-photon quantum signals. Here, we demonstrate the first on-chip quantum-classical coexistence platform based on thin-film lithium niobate (TFLN). The chip integrates a polarization splitter-rotator (PSR) with two four-channel wavelength-division multiplexers, creating eight distinct channels encoded by wavelength and polarization in a highly compact millimeter-scale footprint. The device features ultra-low on-chip insertion loss ( IL ), high polarization isolation, and robust suppression of nonlinear noise, minimizing crosstalk from classical to quantum channels. Single-photon experiments verify its compatibility with QKD operations under realistic scenarios of simultaneous classical and quantum transmission. Its fabrication-robust design eases lithography constraints, enabling scalable and cost-effective manufacturing. Overall, this chip offers a viable path to integrate QKD into dense optical networks and advances the development of scalable quantum-secure communications.