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Volume 5 Issue ，2025
Research Article
Abstract：Chip-scale integration of optical frequency combs, particularly soliton microcombs, enables miniaturized instrumentation for timekeeping, ranging, and spectroscopy. Although soliton microcombs have been demonstrated on various material platforms, realizing complete comb functionality on photonic chips requires the co-integration of high-speed modulators and efficient frequency doublers, features that are available in a monolithic form on X-cut thin-film lithium niobate (TFLN). However, the pronounced Raman nonlinearity associated with extraordinary light in this platform has so far precluded soliton microcomb generation. Here, we report the generation of transverse-electric-polarized soliton microcombs with a 25 GHz repetition rate in high-Q microresonators on X-cut TFLN chips. By precisely orienting the racetrack microresonator relative to the optical axis, we mitigate Raman nonlinearity and enable soliton formation under continuous-wave laser pumping. Moreover, the soliton microcomb spectra are extended to 350 nm with pulsed laser pumping. This work expands the capabilities of TFLN photonics and paves the way for the monolithic integration of fast-tunable, self-referenced microcombs.Keywords：Thin film lithium niobate;Optical frequency comb;Optical microresonator;Nonlinear photonics29|21|0Updated：2025-07-25- Abstract：Microresonator-based Kerr frequency combs (“Kerr microcombs”) constitute chip-scale frequency combs of broad spectral bandwidth and repetition rate ranging from gigahertz to terahertz. A critical application that exploits the coherence and high repetition rate of microcombs is microwave and millimeter-wave generation. Latest endeavor applying two-point optical frequency division (OFD) to photonic-chip-based microcombs has created microwaves with remarkably low phase noise. Nevertheless, existing approaches to achieve exceptionally coherent microcombs still require extensive active locking, additional lasers, and external RF or microwave sources, as well as sophisticated initiation. Here we demonstrate a simple and entirely passive (no active locking) architecture, which incorporates an optoelectronic oscillator (OEO) and symphonizes a coherent microcomb and a low-noise microwave spontaneously. Our OEO microcomb leverages state-of-the-art integrated chip devices, including a high-power DFB laser, a broadband silicon Mach–Zehnder modulator, an ultralow-loss silicon nitride microresonator, and a high-speed photodetector. Each can be manufactured in large volume with low cost and high yield using established CMOS and III-V foundries. Our system synergizes a microcomb of 10.7 GHz repetition rate and an X-band microwave with phase noise of − 97/ − 126/ − 130 dBc/Hz at 1/10/100 kHz Fourier frequency offset, yet does not demand active locking, additional lasers, and external RF or microwave sources. With potential to be fully integrated, our OEO microcomb can become an invaluable technology and building block for microwave photonics, radio-over-fiber, and optical communication.15|13|0Updated：2025-07-22
- Abstract：Spatio-spectral selectivity, the capability to select a single mode with a specific wavevector (angle) and wavelength, is imperative for light emission and imaging. Continuous band dispersion of a conventional periodic structure, however, sets up an intrinsic locking between wavevectors and wavelengths of photonic modes, making it difficult to single out just one mode. Here, we show that the radiation asymmetry of a photonic mode can be explored to tailor the transmission/reflection properties of a photonic structure, based on Fano interferences between the mode and the background. In particular, we find that a photonic system supporting a band dispersion with certain angle-dependent radiation-directionality can exhibit Fano-like perfect reflection at a single frequency and a single incident angle, thus overcoming the dispersion locking and enabling the desired spatio-spectral selectivity. We present a phase diagram to guide designing angle-controlled radiation-directionality and experimentally demonstrate double narrow Fano-like reflection in angular (±5°) and wavelength (14 nm) bandwidths, along with high-contrast spatio-spectral selective imaging, using a misaligned bilayer metagrating with tens-of-nanometer-scale thin spacer. Our scheme promises new opportunities in applications in directional thermal emission, nonlocal beam shaping, augmented reality, precision bilayer nanofabrication, and biological spectroscopy.Keywords：Spatio-spectral selectivity;Metagratings;Fano resonance;Mode coupling;Bilayer nanofabrication;AR/VR20|11|0Updated：2025-07-08
- Abstract：Neuromorphic computing offers a promising approach to artificial intelligence by mimicking biological neural networks to perform complex tasks efficiently. While software-based simulations have demonstrated the potential of neuromorphic architectures, a physical platform is crucial to fully realize its computational advantages. Herein, we present the first demonstration of perovskite microcavity exciton polaritons as a platform for reservoir computing-based artificial neural networks. By leveraging the nonlinear response properties of exciton polaritons, we developed a neuromorphic computing architecture capable of performing classification tasks with single-step training, eliminating the need for iterative algorithms like backpropagation. Applying this system to a handwritten digit recognition task, we achieve 92% classification accuracy at room temperature. Notably, we also show that the system is dynamically nonlinear, further enhancing the potential to improve classification efficiency and address more complex tasks. Our findings advocate the promising capabilities of perovskite exciton polaritons as energy-efficient, ultrafast response platforms for artificial intelligence, paving the way for next-generation computational technologies.Keywords：Perovskite microcavity;Exciton polaritons;Neuromorphic computing;Dynamical nonlinear;Image classification16|11|0Updated：2025-06-02
- Abstract：Coherent frequency microcombs, generated in nonlinear high-Q microresonators and driven by a single continuous-wave laser, have enabled several scientific breakthroughs in the past decade, thanks to their high intrinsic phase coherence and individual comb line powers. Here, we report terabit-per-second-scale coherent data communications over a free-space atmospheric link, using a platicon frequency microcomb, employing wavelength- and polarization-division multiplexing for next-generation optical wireless networks. Spanning more than 55 optical carriers with 115 GHz channel spacing, we report the first free-space coherent communication link using a frequency microcomb, achieving up to 8.21 Tbit/s aggregate data transmission at a 20 Gbaud symbol rate per carrier over 160 m, even under log-normal turbulent conditions. Utilizing 16-state quadrature amplitude modulation, we demonstrate retrieved constellation maps across the broad microcomb spectrum, achieving bit-error rates below both hard- and soft-decision thresholds for forward-error correction. Next, we examine a wavelength-division multiplexing free-space passive optical network as a baseline for free-space fronthaul, achieving an aggregate data rate of up to 5.21 Tbit/s and a field-tested spectral efficiency of 1.29 bit/s/Hz in the microcomb-based atmospheric link. We also quantify experimental power penalties of ≈ 3.8 dB at the error-correction threshold, relative to the theoretical additive white Gaussian noise limit. Furthermore, we introduce the first-ever demonstration of master–slave free-space carrier phase retrieval with frequency microcombs, and the compensation for turbulence-induced intensity scintillation and pointing error fluctuations, to improve end-to-end symbol error rates. This work provides a foundational platform for broadband vertical heterogeneous connectivity, terrestrial backbone links, and ground-satellite communication.7|8|0Updated：2025-05-20
- Abstract：Computing with light is widely recognized as a promising paradigm for overcoming the energy and latency limitations of electronic computing. However, the energy consumption and latency in current optical computing hardware predominantly arise in the electrical domain rather than the optical domain, primarily due to frequent signal conversions between optical (analog) and electrical (digital) formats. Furthermore, as the operating frequency of optical computing surpasses the GHz range, the synchronization of parallel electrical signals and the management of optical delays become increasingly critical. These challenges exacerbate energy consumption and latency, particularly in recurrent optical operations. To address these limitations, we propose a novel asynchronous computing paradigm for on-chip optical recurrent accelerators based on wavelength encoding, effectively mitigating synchronization challenges. By leveraging the intrinsic causality of wavelength relay, our approach eliminates the need for rigorous temporal alignment. To demonstrate the flexibility and efficacy of this asynchronous paradigm, we present two advanced recurrent models—an optical hidden Markov model and an optical recurrent neural network—monolithically integrated for the first time. These models incorporate hundreds of linear and nonlinear computing units densely packed into a compact footprint of just 10 mm2. Experimental evaluations on various benchmark tasks underscore the superior energy efficiency and low latency of the proposed asynchronous optical accelerators. This innovation enables the efficient processing of large-scale parallel signals and positions optical processors as a pivotal technology for applications such as autonomous driving and intelligent robotics.13|11|0Updated：2025-05-06
- Abstract：Lasers with the gain medium of gas, liquid, semiconductor, and solid could generate coherent light with rather narrow spectral linewidth, which play an important role in the fields of communication, measurement, sensing, and so on. Although free electron lasers have been realized with their unique advantages, they face challenges in narrowing the spectral linewidth, owing to electron energy fluctuation, Coulomb effect, and other mechanism. Here we demonstrate the superradiant Smith-Purcell radiation (S-SPR) in terahertz frequency band with ultra-narrow and continuously tunable linewidth in a compact device. By proposing a new effect of pump-induced stimulated S-SPR (PIS-SPR), the spectral linewidth could be reduced to 0.3 kHz @ 291.7 GHz, which is about two–six orders of magnitude narrower compared with those obtained by accelerators and other electron devices. Meanwhile, the wide range of continuously tunable spectral linewidth spanning 0.3–900 kHz is observed for the first time. This work provides a way to greatly narrow the spectral linewidth of free electron radiation and to achieve high-order harmonic of S-SPR in a compact device, and offers a platform to study the interaction between free electron bunches and different micro-&nano-structures.10|2|0Updated：2025-04-17
Editorial
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Letter
Abstract：In the era of artificial intelligence, the computing hardware is of critical importance, with various new modalities explored. Information processing using photons, with abundant intrinsic degrees of freedom, as the carrier could embrace low loss, high speed, low latency, low power consumption, and high parallelism. Here, harvesting the intrinsic frequency channels, we propose and demonstrate a parallel optical computing architecture powered by a soliton microcomb source, a broadband Mach–Zehnder interferometer (MZI) mesh and a parallel MZI mesh computing model. The examinations validate the system's capability to perform over 100-frequency channel multiplexed parallel optical information processing. Both spectral consistency and matrix consistency exceed 0.9. This achievement enables a 100-fold increase (and even beyond) in optical computility through ultra-high parallelism without scaling up the chip size, offering a novel technological pathway for future optical computers.Keywords：Photonic chip;Parallel optical computing;100-wavelength multiplexing20|72|0Updated：2025-06-17
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