Qing-Xin Ji

We demonstrate a chip-scale ring-laser gyroscope on a CMOS-ready Si ₃ N ₄ platform, achieving sensed rotation approaching the Earth’s rotation rate. The device is based on counter-propagating Brillouin lasers that convert rotation into a Sagnac-induced frequency shift. To our knowledge, this is the first demonstration of an actual measurement near the Earth’s rotation rate on a photonic-chip-integrated platform, marking a significant step toward fully integrated optical gyroscopes.

A computer’s clock rate ultimately determines the minimum time between sequential operations or instructions. Despite exponential advances in electronic computer performance due to Moore’s Law and increasingly parallel system architectures, clock rates of conventional processors have remained stagnant at ~5 GHz for nearly two decades. This creates a significant challenge for applications requiring real-time processing or control of ultrafast information systems. Here, we break this barrier by proposing and experimentally demonstrating computing based on an all-optical recurrent neural network leveraging the ultrafast characteristics of linear and nonlinear optical operations while circumventing electronic bottlenecks. The all-optical computer realizes linear operations, nonlinear functions, and memory entirely in the optical domain with accuracy surpassing a purely linear model up to 80 GHz clock rates depending on the task. We experimentally demonstrate a prototypical task of noisy waveform classification as well as perform ultrafast in-situ analysis of the soliton states from integrated optical microresonators. We further illustrate the application of the architecture for generative artificial intelligence based on quantum fluctuations to generate images even in the absence of input optical signals. Our results highlight the potential of all-optical computing beyond what can be achieved with digital electronics by utilizing ultrafast linear, nonlinear, and memory functions and quantum fluctuations.

Recent experiments have demonstrated impressive performance in AlGaAs on insulator waveguides due to their dual advantages of very large Kerr nonlinearity and low loss. Here, we study the acoustic properties of these waveguides, adding stimulated Brillouin scattering (SBS) to the already impressive library of nonlinear effects available within this platform. We observe SBS mediated by both shear and pressure acoustic waves in AlGaAs-on-insulator integrated photonic waveguides, with Brillouin gain coefficients of up to 150m ⁻¹ W ⁻¹ . We also discuss competing non-linear processes that interfere with the formation of an SBS laser.

In microcombs, solitons can drive non-soliton-forming modes to induce optical gain. Under specific conditions, a regenerative secondary temporal pulse coinciding in time and space with the exciting soliton pulse will form at a new spectral location. A mechanism involving Kerr-induced pulse interactions has been proposed theoretically, leading to multicolor solitons containing constituent phase-locked pulses. However, the occurrence of this phenomenon requires dispersion conditions that are not naturally satisfied in conventional optical microresonators. Here, we report the experimental observation of multicolor pulses from a single optical pump in a way that is closely related to the concept of multicolor solitons. The individual soliton pulses share the same repetition rate and could potentially be fully phase-locked. They are generated using interband coupling in a compound resonator.

Over the past decades, remarkable progress has been made in reducing the loss of photonic integrated circuits (PICs) within the telecom band^1,2,3,4, facilitating on-chip applications spanning low-noise optical⁵ and microwave synthesis⁶, to lidar⁷ and photonic artificial intelligence engines⁸. However, several obstacles arise from the marked increase in material absorption and scattering losses at shorter wavelengths^9,10, which prominently elevate power requirements and limit performance in the visible and near-visible spectrum. Here we present an ultralow-loss PIC platform based on germano-silicate—the material underlying the extraordinary performance of optical fibre—but realized by a fully CMOS-foundry-compatible process. These PICs achieve resonator Q factors surpassing 180 million from violet to telecom wavelengths. They also attain a 10-dB higher quality factor without thermal treatment in the telecom band, expanding opportunities for heterogeneous integration with active components¹¹. Other features of this platform include readily engineered waveguide dispersion, acoustic mode confinement and large-mode-area-induced thermal stability—each demonstrated by soliton microcomb generation, stimulated Brillouin lasing and low-frequency-noise self-injection locking, respectively. The success of these germano-silicate PICs can ultimately enable fibre-like loss onto a chip, leading to an additional 20-dB improvement in waveguide loss over the current highest performance photonic platforms. Moreover, the performance abilities demonstrated here bridge ultralow-loss PIC technology to optical clocks¹², precision navigation systems¹³ and quantum sensors¹⁴.

Optically generated microwave signals exhibit some of the lowest phase noise and timing jitter of any microwave-generating technology to date. The success of octave-spanning optical frequency combs in down-converting ultrastable optical frequency references has motivated the development of compact, robust and highly manufacturable optical systems that maintain the ultralow microwave phase noise of their tabletop counterparts. Two-point optical frequency division using chip-scale components and ~1 THz-spanning microcombs has been quite successful, but with stringent requirements on the comb source’s free-running noise and feedback control dynamics. Here we introduce a major simplification of this architecture that replaces feedback control of the frequency comb in favor of electronic feedforward noise cancelation that significantly relaxes the comb requirements. Demonstrated with both a high repetition rate solid-state mode-locked laser and a microcomb, feedforward on a 10 GHz carrier results in more robust operation with phase noise as low as -153 dBc/Hz at offsets ≥10 kHz, femtosecond timing jitter, and elimination of the large “servo bump” noise increase at high offset frequency. The system’s compatibility with a variety of highly manufacturable mode-locked laser designs and its resilience and straightforward implementation represents an important step forward towards a fully chip-scale implementation of optically generated microwaves, with applications in radar, sensing, and position, navigation and timing.

The revolutionary impact of optical frequency combs in fields as diverse as timekeeping and spectroscopy hinges on a way to independently control comb line spacing and spectral position. However, achieving such control in microcombs remains challenging. In this work, we demonstrate separable control of these parameters in a microcomb using a single integrated actuation mechanism. As a proof of concept, we fully frequency-lock a microcomb to a high-stability reference cavity and apply it to spectroscopy and microwave generation. This approach significantly simplifies the implementation of frequency-stabilized microcombs across a broad range of applications.

The remarkable frequency stability of resonant systems in the optical domain (optical cavities and atomic transitions) can be harnessed at frequency scales accessible by electronics using optical frequency division. This capability is revolutionizing technologies spanning time keeping to high-performance electrical signal sources. A version of the technique called two-point optical frequency division (2P-OFD) is proving advantageous for application to high-performance signal sources. In 2P-OFD, an optical cavity anchors two spectral endpoints defined by lines of a frequency comb. The comb need not be self-referenced, which greatly simplifies the system architecture and reduces power requirements. Here, a 2P-OFD microwave signal source is demonstrated with record-low phase noise using a microcomb. Key to this advance is a spectral endpoint defined by a frequency-agile single-mode dispersive wave that is emitted by the microcomb soliton. Moreover, the system frequency reference is a compact all-solid-state optical cavity with a record Q factor. A hybridly packaged version of the system offers excellent longer term stability. The results advance integrable microcomb-based signal sources into the performance realm of much larger microwave sources.