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1. Electrically empowered microcomb laser

   https://doi.org/10.1038/s41467-024-48544-2  

   Ling, Jingwei; Gao, Zhengdong; Xue, Shixin; Hu, Qili; Li, Mingxiao; Zhang, Kaibo; Javid, Usman A; Lopez-Rios, Raymond; Staffa, Jeremy; Lin, Qiang (December 2024, Nature Communications)

   Abstract Optical microcomb underpins a wide range of applications from communication, metrology, to sensing. Although extensively explored in recent years, challenges remain in key aspects of microcomb such as complex soliton initialization, low power efficiency, and limited comb reconfigurability. Here we present an on-chip microcomb laser to address these key challenges. Realized with integration between III and V gain chip and a thin-film lithium niobate (TFLN) photonic integrated circuit (PIC), the laser directly emits mode-locked microcomb on demand with robust turnkey operation inherently built in, with individual comb linewidth down to 600 Hz, whole-comb frequency tuning rate exceeding 2.4 × 10¹⁷ Hz/s, and 100% utilization of optical power fully contributing to comb generation. The demonstrated approach unifies architecture and operation simplicity, electro-optic reconfigurability, high-speed tunability, and multifunctional capability enabled by TFLN PIC, opening up a great avenue towards on-demand generation of mode-locked microcomb that is of great potential for broad applications. 

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2. Chaos-assisted two-octave-spanning microcombs

   https://doi.org/10.1038/s41467-020-15914-5  

   Chen, Hao-Jing; Ji, Qing-Xin; Wang, Heming; Yang, Qi-Fan; Cao, Qi-Tao; Gong, Qihuang; Yi, Xu; Xiao, Yun-Feng (May 2020, Nature Communications)

   Abstract Since its invention, optical frequency comb has revolutionized a broad range of subjects from metrology to spectroscopy. The recent development of microresonator-based frequency combs (microcombs) provides a unique pathway to create frequency comb systems on a chip. Indeed, microcomb-based spectroscopy, ranging, optical synthesizer, telecommunications and astronomical calibrations have been reported recently. Critical to many of the integrated comb systems is the broad coverage of comb spectra. Here, microcombs of more than two-octave span (450 nm to 2,008 nm) is demonstrated throughχ⁽²⁾andχ⁽³⁾nonlinearities in a deformed silica microcavity. The deformation lifts the circular symmetry and creates chaotic tunneling channels that enable broadband collection of intracavity emission with a single waveguide. Our demonstration introduces a new degree of freedom, cavity deformation, to the microcomb studies, and our microcomb spectral range is useful for applications in optical clock, astronomical calibration and biological imaging. 

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3. A squeezed quantum microcomb on a chip

   https://doi.org/10.1038/s41467-021-25054-z  

   Yang, Zijiao; Jahanbozorgi, Mandana; Jeong, Dongin; Sun, Shuman; Pfister, Olivier; Lee, Hansuek; Yi, Xu (August 2021, Nature Communications)

   Abstract The optical microresonator-based frequency comb (microcomb) provides a versatile platform for nonlinear physics studies and has wide applications ranging from metrology to spectroscopy. The deterministic quantum regime is an unexplored aspect of microcombs, in which unconditional entanglements among hundreds of equidistant frequency modes can serve as critical ingredients to scalable universal quantum computing and quantum networking. Here, we demonstrate a deterministic quantum microcomb in a silica microresonator on a silicon chip. 40 continuous-variable quantum modes, in the form of 20 simultaneously two-mode squeezed comb pairs, are observed within 1 THz optical span at telecommunication wavelengths. A maximum raw squeezing of 1.6 dB is attained. A high-resolution spectroscopy measurement is developed to characterize the frequency equidistance of quantum microcombs. Our demonstration offers the possibility to leverage deterministically generated, frequency multiplexed quantum states and integrated photonics to open up new avenues in fields of spectroscopy, quantum metrology, and scalable, continuous-variable-based quantum information processing. 

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4. Vernier microcombs for integrated optical atomic clocks

   https://doi.org/10.1038/s41566-025-01617-0  

   Wu, Kaiyi; O’Malley, Nathan P; Fatema, Saleha; Wang, Cong; Girardi, Marcello; Alshaykh, Mohammed S; Ye, Zhichao; Leaird, Daniel E; Qi, Minghao; Torres-Company, Victor; et al (April 2025, Nature Photonics)

   Abstract Kerr microcombs have drawn substantial interest as mass-manufacturable, compact alternatives to bulk frequency combs. This could enable the deployment of many comb-reliant applications previously confined to laboratories. Particularly enticing is the prospect of microcombs performing optical frequency division in compact optical atomic clocks. Unfortunately, it is difficult to meet the self-referencing requirement of microcombs in these systems owing to the approximately terahertz repetition rates typically required for octave-spanning comb generation. In addition, it is challenging to spectrally engineer a microcomb system to align a comb mode with an atomic clock transition with a sufficient signal-to-noise ratio. Here we adopt a Vernier dual-microcomb scheme for optical frequency division of a stabilized ultranarrow-linewidth continuous-wave laser at 871 nm to an ~235 MHz output frequency. This scheme enables shifting an ultrahigh-frequency (~100 GHz) carrier-envelope offset beat down to frequencies where detection is possible and simultaneously placing a comb line close to the 871 nm laser—tuned so that, if frequency doubled, it would fall close to the clock transition in¹⁷¹Yb⁺. Our dual-comb system can potentially combine with an integrated ion trap towards future chip-scale optical atomic clocks. 

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5. Interdisciplinary advances in microcombs: bridging physics and information technology

   https://doi.org/10.1186/s43593-024-00071-9  

   Yao, Bai-Cheng; Wang, Wen-Ting; Xie, Zhen-Da; Zhou, Qiang; Tan, Teng; Zhou, Heng; Guo, Guang-Can; Zhu, Shi-Ning; Zhu, Ning-Hua; Wong, Chee_Wei (October 2024, eLight)

   Abstract The advancement of microcomb sources, which serve as a versatile and powerful platform for various time–frequency measurements, have spurred widespread interest across disciplines. Their uses span coherent optical and microwave communications, atomic clocks, high-precision LiDARs, spectrometers, and frequency synthesizers. Recent breakthroughs in fabricating optical micro-cavities, along with the excitation and control of microcombs, have broadened their applications, bridging the gap between physical exploration and practical engineering systems. These developments pave the way for pioneering approaches in both classical and quantum information sciences. In this review article, we conduct a thorough examination of the latest strategies related to microcombs, their enhancement and functionalization schemes, and cutting-edge applications that cover signal generation, data transmission, quantum analysis, and information gathering, processing and computation. Additionally, we provide in-depth evaluations of microcomb-based methodologies tailored for a variety of applications. To conclude, we consider the current state of research and suggest a prospective roadmap that could transition microcomb technology from laboratory settings to broader real-world applications. 

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