Yunxiang Song

Thin-film lithium niobate (TFLN) has emerged as a versatile integrated photonics platform, combining strong electro-optic and nonlinear effects. Among TFLN devices, ring resonators play a central role in filtering, modulation, and nonlinear optical processes. However, intrinsic loss—which ultimately limits ring performance—is most often summarized by single-valued metrics, and its statistical variability across resonances has received limited attention. Here, we show that intrinsic loss rates in monolithic TFLN ring resonators follow a statistical distribution, comprising a baseline loss and a tail arising from discrete loss events. This behavior is revealed by characterizing 2233 resonances, using an adiabatic waveguide-ring coupling architecture that selectively excites the fundamental mode and yields clean spectra in the ultrahigh-Qi regime. We find the most probable intrinsic loss rate κi = 2π × 10.4 MHz, indicating operation in a low-loss regime comparable to state-of-the-art thick silicon nitride platforms.

The ability to generate efficient and coherent frequency combs using photonic integrated circuits offers tremendous potential for a range of applications. X-cut thin-film lithium niobate (TFLN) is promising for developing next-generation microcomb-driven photonic systems, providing a diversity of functionalities through combined χ ( 3 ) and electro-optic effects. Normal-dispersion Kerr combs are critically needed because of their standout advantages, yet this dispersion regime remains unexplored on x-cut TFLN. Here, we design and demonstrate microresonators suitable for the robust generation of normal-dispersion Kerr combs. We show Kerr combs that substantially surpass state-of-the-art microcombs on x-cut TFLN in key performance metrics and an ultrabroad frequency comb whose existence is underpinned by both normal-dispersion Kerr dynamics and stimulated Raman scattering. Our work will unlock high-speed and low-energy-consumption photonic circuits for communications and signal processing enabled by a monolithic microcomb technology while also stimulating investigations of previously unknown nonlinear states that may synergize hybrid material nonlinearities.

Cavity electro-optic (EO) modulation plays a pivotal role in optical pulse and frequency comb synthesis, supporting a wide range of applications including communication, computing, ranging, and quantum information. The ever-growing demand for these applications has driven efforts in enhancing modulation coupling strength and bandwidth towards advanced pulse-comb synthesis. However, the effects of strong-coupling and high-bandwidth cavity EO modulation remain underexplored, due to the lack of a general, unified model that captures this extreme condition. In this work, we present a universal framework for pulse-comb synthesis under cavity EO modulation, where coupling strength and modulation bandwidth far exceed the cavity’s free spectral range (FSR). We show that, under such intense and ultrafast driving conditions, EO-driven frequency combs and pulses exhibit rich higher-order nonlinear dynamics, including temporal pulse compression and comb generation with arbitrary pump detuning. Leveraging this framework, we reveal a direct link between the higher-order dynamics of EO pulse-comb generation and the band structure of synthetic dimension. Furthermore, we demonstrate arbitrary comb shaping via machine-learning-based inverse microwave drive design, achieving a tenfold enhancement in cavity EO comb flatness by exploring the synergistic effects of high-bandwidth driving and detuning-induced frequency boundaries. Our findings push cavity EO modulation into a new frontier, unlocking significant potential for universal and machine-learning-programmable EO frequency combs, topological photonics, as well as photonic quantum computing in the strong-coupling and high-bandwidth regimes.

The surge in artificial intelligence applications calls for scalable, high-speed, and low-energy computation methods. Computing with photons is promising due to the intrinsic parallelism, high bandwidth, and low latency of photons. However, current photonic computing architectures are limited by the speed and energy consumption associated with electronic-to-optical data transfer, i.e., electro-optic conversion. Here, we demonstrate a thin-film lithium niobate (TFLN) computing circuit that addresses this challenge, leveraging both highly efficient electro-optic modulation and the spatial scalability of TFLN photonics. Our circuit is capable of computing at 43.8 GOPS/channel while consuming 0.0576 pJ/OP, and we demonstrate various inference tasks with high accuracy, including the classification of binary data and complex images. Heightening the integration level, we show another TFLN computing circuit that is combined with a hybrid-integrated distributed-feedback laser and heterogeneous-integrated modified uni-traveling carrier photodiode. Our results show that the TFLN photonic platform holds promise to complement silicon photonics and diffractive optics for photonic computing, with extensions to ultrafast signal processing and ranging.

The rapid growth in artificial intelligence and modern communication systems demands innovative solutions for increased computational power and advanced signalling capabilities. Integrated photonics, leveraging the analogue nature of electromagnetic waves at the chip scale, offers a promising complement to approaches based on digital electronics. To fully unlock their potential as analogue processors, establishing a common technological base between conventional digital electronics and analogue photonics is imperative for building next-generation computing and communications systems. However, the absence of an efficient interface has thus far critically challenged a comprehensive demonstration of the advantages of analogue photonic hardware, with the scalability, speed and energy consumption as primary bottlenecks. Here we address this challenge and demonstrate a general electro-optic digital-to-analogue link enabled using foundry-based lithium niobate nanophotonics. Using purely digital electronic inputs, we achieve the on-demand generation of both analogue optical and electronic waveforms at information rates of up to 186 Gb s⁻¹. The optical waveforms address the digital-to-analogue electro-optic conversion challenge in photonic computing, showcasing high-fidelity Modified National Institute of Standards and Technology image encoding with an ultralow power consumption of 0.058 pJ b⁻¹. The electronic waveforms enable a pulse-shaping-free microwave arbitrary waveform generation method with ultrabroadband tunable delay and gain. Our results pave the way for efficient and compact digital-to-analogue conversion paradigms enabled by integrated photonics, and underscore the transformative impact that analogue photonic hardware may have on various applications, such as computing, optical interconnects and high-speed ranging.

Optical frequency combs are indispensable links between the optical and microwave domains. Chip-scale integration promises compact, scalable, and power-efficient frequency comb sources, enabled by the resonantly-enhanced Kerr effect or the electro-optic effect. While combs utilizing the former can reach octave-spanning bandwidths, and combs based on the latter can feature microwave-rate spacings, achieving both features at the same time has been challenging. Here, we simultaneously leverage the strong Kerr and electro-optic effects on thin-film lithium niobate, where dissipative Kerr soliton generation is followed by electro-optic phase modulation, to realize an integrated frequency comb reference with 2,589 lines spaced by 29.308 GHz and spanning 75.9 THz (588 nm). Further, we demonstrate electronic stabilization and control of the comb spacing, naturally facilitated by this approach. The broadband, microwave-rate frequency comb in our work overcomes the spacing-span tradeoff that exists in nonlinear integrated frequency comb sources, paving the way towards chip-scale solutions for next-generation laser spectroscopy, microwave and millimeter wave synthesis, as well as optical communications.

Soliton microcombs are a cornerstone of integrated frequency comb technologies, with applications spanning photonic computing, ranging, microwave synthesis, optical communications, and quantum light generation. In nearly all such applications, electro-optic (EO) components play a critical role in generating, monitoring, stabilizing, and modulating solitons. Toward building photonic integrated circuits for next-generation applications that will simultaneously maximize system performance and minimize size, weight, and power consumption metrics, achieving soliton microcombs and efficient EO modulation on a chip is essential. X-cut thin-film lithium niobate (TFLN) has emerged as a leading photonic platform for the realization of high-performance integrated EO devices and systems. However, despite extensive research, soliton microcombs have remained elusive to X-cut TFLN due to its multiple strong Raman-active modes, in-plane refractive index anisotropy, and photorefractive effects. Here, we address this long-standing challenge and demonstrate versatile soliton microcombs on X-cut TFLN, with repetition rates spanning from the gigahertz (∼26GHz, single soliton) up to the millimeter-wave (∼0.156THz, soliton crystal) regime. The combs feature exceptional long-term stability, maintaining a direct injection-locked state for over 90 min (manually terminated), with repetition-rate phase noise closely tracking that of a high-quality electronic microwave synthesizer. Our finding broadly advances both the fundamental science and practical applications of integrated comb sources by enabling efficient EO modulation and broadband coherent solitons to be monolithically combined on the same chip.