arXiv subjects

Linjie Zhou

Publications and source records attributed to Linjie Zhou.

11 recordsLinked to original sources

arXiv2026

Fully integrated continuous-variable quantum key distribution with composable security over 100 km

Quantum key distribution (QKD) guarantees information-theoretic security by the laws of physics, but deployment at scale requires compact, manufacturable photonic terminals. Continuous-variable QKD (CV-QKD) is well suited for this transition through telecom-compatible, room-temperature coherent detection. However, unifying full on-chip core terminal integration, room-temperature operation, high loss tolerance, and composable end-to-end security in long-distance QKD remains a key bottleneck. Here we report a fully integrated CV-QKD platform in which two hybrid III--V/Si$_3$N$_4$ integrated lasers, a silicon transmitter, and a silicon coherent receiver implement the core terminal functions, operating with a local local oscillator (LLO) over fibre links of 25--150 km. A Bayesian machine-learning algorithm maintains robust phase lock throughout the long records required for composable security, consistently outperforming the conventional unscented Kalman filter, while rate-matched multidimensional reconciliation approaches the Shannon limit. The system certifies a composable finite-size secret-key rate of 29.3 kbps at 100 km from a 140-billion-symbol block, with 12.9 kbps at 125 km under finite-size analysis and 9.17 kbps at 150 km under asymptotic analysis. By establishing the longest finite-size and asymptotic reaches and the highest secret-key rate per symbol reported for integrated CV-QKD, this work advances the development of practical chip-based quantum networks.

quant-ph↗

arXiv2026

Noise-resilient nanophotonic gyroscope with sub-prad phase resolution

Optical gyroscopes based on the Sagnac effect are the cornerstone of precision orientation and navigation. However, their bulky form factors prevent deployment in emerging mobile and autonomous systems. On nanophotonic platforms, the Sagnac signal plummets under aggressive miniaturization. Consequently, the signal is easily swamped by refractive-index fluctuations, rendering navigation-grade sensitivity within just a few square millimeters a notoriously elusive goal. Here, we demonstrate a noise-resilient nanophotonic optical gyroscope by exploiting a two-chain decoupling architecture to effectively isolate the rotation signal from channel noise. Implemented on a 3 mm^2 passive silicon nitride chip, the proof-of-concept device achieves a bias instability of 1.42 deg/h and an angle random walk of 0.001 deg/\sqrt{h}, representing improvements of 4 and 6 orders of magnitude, respectively, over the representative nanophotonic gyroscope of similar footprint (ref. 27). In the broader context of integrated optical gyroscopes, our approach bridges the long-standing size-performance gap by two to three orders of magnitude, moving chip-scale devices into a previously inaccessible regime and pointing toward navigation-relevant precision for monolithic microsystems. This architecture further enables sub-prad phase resolution with general applicability, establishing a foundational framework for the next generation of robust, monolithically integrated photonic sensing systems.

physics.optics↗

arXiv2025

Electrically switchable photonic diode empowered by chiral resonance

The on-chip integration of nonreciprocal optical devices remains a critical challenge for modern optoelectronics, as conventional magneto-optic approaches suffer from material incompatibility and excessive optical losses. Nonlinear photonic diodes have emerged as a promising magnet-free alternative, yet their widespread adoption has been constrained by inherent limitations in reconfigurability. Here, we present an all-silicon, electrically tunable photonic diode leveraging engineered chiral resonances in an ultra-compact microring architecture. The pronounced asymmetric modal coupling enables nonreciprocal transmission with two distinct operation modes at threshold powers down to -5 dBm. The chirality further enables unprecedented control over self-pulsation dynamics, manifesting in propagation-direction-dependent oscillation thresholds and temporal signatures. Crucially, post-fabrication electrical reconfigurability allows dynamic switching between forward, backward, and disabled states. This work represents a significant advancement in integrated nonreciprocal photonics, offering a CMOS-compatible solution with transformative potential for optical interconnects, photonic neural networks, and signal processing systems.

physics.optics↗

arXiv2024

Integrated adaptive coherent LiDAR for 4D bionic vision

Light detection and ranging (LiDAR) is a ubiquitous tool to provide precise spatial awareness in various perception environments. A bionic LiDAR that can mimic human-like vision by adaptively gazing at selected regions of interest within a broad field of view is crucial to achieve high-resolution imaging in an energy-saving and cost-effective manner. However, current LiDARs based on stacking fixed-wavelength laser arrays and inertial scanning have not been able to achieve the desired dynamic focusing patterns and agile scalability simultaneously. Moreover, the ability to synchronously acquire multi-dimensional physical parameters, including distance, direction, Doppler, and color, through seamless fusion between multiple sensors, still remains elusive in LiDAR. Here, we overcome these limitations and demonstrate a bio-inspired frequency-modulated continuous wave (FMCW) LiDAR system with dynamic and scalable gazing capability. Our chip-scale LiDAR system is built using hybrid integrated photonic solutions, where a frequency-chirped external cavity laser provides broad spectral tunability, while on-chip electro-optic combs with elastic channel spacing allow customizable imaging granularity. Using the dynamic zoom-in capability and the coherent FMCW scheme, we achieve a state-of-the-art resolution of 0.012 degrees, providing up to 15 times the resolution of conventional 3D LiDAR sensors, with 115 equivalent scanning lines and 4D parallel imaging. We further demonstrate cooperative sensing between our adaptive coherent LiDAR and a camera to enable high-resolution color-enhanced machine vision.

physics.optics↗

arXiv2024

Ultra-compact beam steering nanolasers

The miniaturization and integration of beam steering devices have consistently been the focus of the field. Conventional methods alter the eigenmode of the optical cavity by regulating the refractive index. Due to the weak nonlinear effect of the optical system, the device must be sufficiently large to achieve sufficient light modulation. The effective method for miniaturizing beam steering devices currently in use is based on metasurfaces. However, this type of device necessitates the input of a laser source, which precludes the simultaneous generation and control of light in a single device. Here we propose a miniaturized beam steering device that employs mode selection between different bound states in the continuum (BIC) states through phase change material. The device is capable of simultaneously achieving both light generation and beam steering (33{\deg}) in a single device with a size of only 25 {\mu}m and with a low threshold of 8.9 kW cm-2. Furthermore,it is possible to achieve a significant degree of dynamic wavelength tunability, with a range extending up to 296 nm. This method achieves high-efficient regulation of light properties by dynamically controlling the system's topological charge, circumventing the problem of weak nonlinearity in traditional methods. Furthermore, the integration of phase change materials with nanolasers enables the direct alteration of lasing properties, which provides a novel idea for dynamic light control. The device process scheme based on phase change materials is straightforward, direct, and highly compatible, which will be advantageous for its intended application.

physics.optics↗

arXiv2021

NTIRE 2021 Challenge on Quality Enhancement of Compressed Video: Methods and Results

This paper reviews the first NTIRE challenge on quality enhancement of compressed video, with a focus on the proposed methods and results. In this challenge, the new Large-scale Diverse Video (LDV) dataset is employed. The challenge has three tracks. Tracks 1 and 2 aim at enhancing the videos compressed by HEVC at a fixed QP, while Track 3 is designed for enhancing the videos compressed by x265 at a fixed bit-rate. Besides, the quality enhancement of Tracks 1 and 3 targets at improving the fidelity (PSNR), and Track 2 targets at enhancing the perceptual quality. The three tracks totally attract 482 registrations. In the test phase, 12 teams, 8 teams and 11 teams submitted the final results of Tracks 1, 2 and 3, respectively. The proposed methods and solutions gauge the state-of-the-art of video quality enhancement. The homepage of the challenge: https://github.com/RenYang-home/NTIRE21_VEnh

eess.IV↗

arXiv2021

High-speed silicon microring modulator at 2-um waveband

We demonstrated a silicon integrated microring modulator working at the 2-um waveband with an L-shaped PN junction. 15-GHz 3-dB electro-optic bandwidth and <1 Vcm modulation efficiency for 45-Gbps NRZ-OOK signaling is achieved at 1960 nm.

physics.app-ph↗

arXiv2020

Comparison of phase change process in Si-GST hybrid integrated waveguide and MMI devices

In the past decades, silicon photonic integrated circuits (PICs) have been considered as a promising approach to solve the bandwidth bottleneck in optical communications and interconnections. Despite significant advances, large-scale PICs still face a series of technical challenges, such as footprint, power consumption, and routing state storage, resulting from the active tuning methods used to control the optical waves. These challenges can be partially addressed by combining chalcogenide phase change materials (PCMs) such as Ge2Sb2Te5 (GST) with silicon photonics, especially applicable in switching applications due to the nonvolatile nature of the GST. Although GST phase transitions between amorphous and crystalline states actuated by optical and electrical pulses heating have been experimentally demonstrated, there is no direct comparison between them. We carried out simulations and experiments to systematically investigate the difference in the phase change process induced by optical and electrical pulses for two types of Si-GST hybrid waveguides. For the phase transition induced by optical pulses, the device has a clear advantage in terms of power consumption and operation speed. For the phase transition induced by electrical pulses, the device is suitable for large-scale integration because it does not require complex light routing. It helps us better understand the phase change process and push forward the further development of Si-GST hybrid integration platform, bringing in new potential applications.

physics.optics↗

arXiv2020

A silicon integrated microwave photonic beamformer

Optical beamforming networks (OBFNs) based on optical true time delay lines (OTTDLs) are well-known as the promising candidate to solve the bandwidth limitation of traditional electronic phased array antennas (PAAs) due to beam squinting. Here we report the first monolithic 1x8 microwave photonic beamformer based on switchable OTTDLs on the silicon-on-insulator platform. The chip consists of a modulator, an eight-channel OBFN, and 8 photodetectors, which includes hundreds of active and passive components in total. It has a wide operating bandwidth from 8 to 18 GHz, which is almost two orders larger than that of electronic PAAs. The beam can be steered to 31 distinguishable angles in the range of -75.51° to 75.64° based on the beam pattern calculation with the measured RF response. The response time for beam steering is 56 μs. These results represent a significant step towards the realization of integrated microwave photonic beamformers that can satisfy compact size and low power consumption requirements for the future radar and wireless communication systems.

physics.optics↗

arXiv2019

Miniature Multi-Level Optical Memristive Switch Using Phase Change Material

The optical memristive switches are electrically activated optical switches that can memorize the current state. They can be used as optical latching switches in which the switching state is changed only by applying an electrical Write/Erase pulse and maintained without external power supply. We demonstrate an optical memristive switch based on a silicon MMI structure covered with nanoscale-size Ge2Sb2Te5 (GST) material on top. The phase change of GST is triggered by resistive heating of the silicon layer beneath GST with an electrical pulse. Experimental results reveal that the optical transmissivity can be tuned in a controllable and repeatable manner with the maximum transmission contrast exceeding 20 dB. Partial crystallization of GST is obtained by controlling the width and amplitude of the electric pulses. Crucially, we also demonstrate that both Erase and Write operations, to and from any intermediate level, are possible with accurate control of the electrical pulses. Our work marks a significant step forward towards realizing photonic memristive switches without static power consumption, which are highly demanded in high-density large-scale integrated photonics.

physics.optics↗

arXiv2016

Six-wave mixing induced by free-carrier plasma in silicon nanowire waveguides

Nonlinear wave mixing in mesoscopic silicon structures is a fundamental nonlinear process with broad impact and applications. Silicon nanowire waveguides, in particular, have large third-order Kerr nonlinearity, enabling salient and abundant four-wave-mixing dynamics and functionalities. Besides the Kerr effect, in silicon waveguides two-photon absorption generates high free-carrier densities, with corresponding fifth-order nonlinearity in the forms of free-carrier dispersion and free-carrier absorption. However, whether these fifth-order free-carrier nonlinear effects can lead to six-wave-mixing dynamics still remains an open question until now. Here we report the demonstration of free-carrier-induced six-wave mixing in silicon nanowires. Unique features, including inverse detuning dependence of six-wave-mixing efficiency and its higher sensitivity to pump power, are originally observed and verfied by analytical prediction and numerical modeling. Additionally, asymmetric sideband generation is observed for different laser detunings, resulting from the phase-sensitive interactions between free-carrier six-wave-mixing and Kerr four-wave-mixing dynamics. These discoveries provide a new path for nonlinear multi-wave interactions in nanoscale platforms.

physics.optics↗