Qi-Fan Yang

Electrostrictive Brillouin scattering provides a ubiquitous mechanism to optically excite high-frequency (> 10 GHz), bulk acoustic phonons that are robust to surface-induced losses. Resonantly enhancing such photon-phonon interactions in high-Q microresonators has spawned diverse applications spanning microwave to optical domains. However, tuning both the pump and scattered waves into resonance usually comes with the cost of photon confinement or modal overlap, leading to limited optomechanical coupling. Here, we introduce Bragg scattering to realize strong bulk optomechanical coupling in the same spatial modes of a micron-sized supermode microresonator. A single-photon optomechanical coupling rate up to 12.5 kHz is demonstrated, showing more than 10 times improvement than other devices. Low-threshold phonon lasing and optomechanical strong coupling are also observed for the 10.2-GHz …

Optical frequency division relies on optical frequency combs to coherently translate ultra-stable optical frequency references to the microwave domain. This technology has enabled microwave synthesis with ultralow timing noise, but the required instruments are too bulky for real-world applications. Here, we develop a compact optical frequency division system using microresonator-based frequency references and comb generators. The soliton microcomb formed in an integrated SiN microresonator is stabilized to two lasers referenced to an ultrahigh- MgF microresonator. Photodetection of the soliton pulse train produces 25 GHz microwaves with absolute phase noise of -141 dBc/Hz (547 zs Hz) at 10 kHz offset frequency. The synthesized microwaves are tested as local oscillators in jammed communication channels, resulting in improved fidelity compared with those derived from electronic oscillators. Our work demonstrates unprecedented coherence in miniature microwave oscillators, providing key building blocks for next-generation timekeeping, navigation, and satellite communication systems.

Synergistic control of the frequency and orbital angular momentum (OAM) of light offers new opportunities for the generation of spatio-temporal optical waveforms and optical metrology. However, their physical realizations are typically bulky and complex owing to challenges in creating, manipulating and detecting mutually coherent, high-dimensional OAM states. Here we achieve combined control over the frequency and the OAM of a comb structure on a photonic chip. Dissipative optical solitons are formed in a nonlinear ring microresonator and emitted owing to engraved angular gratings, with each comb line carrying a distinct OAM. The beam of such a vortex soliton microcomb manifests dynamically revolving, double-helical intensity profiles. The one-to-one correspondence between the OAM and frequencies features a high extinction ratio of over 18.5 dB, enabling precision spectroscopy of optical vortices. Our …

Microcombs are revolutionizing optoelectronics by providing parallel, mutually coherent wavelength channels for time-frequency metrology and information processing. To implement this essential function in integrated photonic systems, it is desirable to drive microcombs directly with an on-chip laser in a simple and flexible way. However, two major difficulties have prevented this goal: (1) generating mode-locked comb states usually requires a significant amount of pump power and (2) the requirement to align laser and resonator frequency significantly complicates operation and limits the tunability of the comb lines. Here, we address these problems by using microresonators on an AlGaAs on-insulator platform to generate dark-pulse microcombs. This highly nonlinear platform dramatically relaxes fabrication requirements and leads to a record-low pump power of <1  mW for coherent comb generation. Dark-pulse …

Quantum diffusion of soliton microcombs has long been recognized as their fundamental noise limit. Here we surpass such limit by utilizing dispersive wave dynamics in multimode microresonators. Through the recoil force provided by these dispersive waves, the quantum diffusion can be suppressed to a much lower level that forms the ultimate fundamental noise limit of soliton microcombs. Our findings enable coherence engineering of soliton microcombs in the quantum-limited regime, providing critical guidelines for using soliton microcombs to synthesize ultralow-noise microwave and optical signals.

Quantum fluctuations disrupt the cyclic motions of dissipative Kerr solitons (DKSs) in nonlinear optical microresonators and consequently cause timing jitter of the emitted pulse trains. This problem is translated to the performance of several applications that employ DKSs as compact frequency comb sources. Recently, device manufacturing and noise reduction technologies have advanced to unveil the quantum properties of DKSs. Here we investigate the quantum decoherence of DKSs existing in normal-dispersion microresonators known as dark pulses. By virtue of the very large material nonlinearity, we directly observe the quantum decoherence of dark pulses in an AlGaAs-on-insulator microresonator, and the underlying dynamical processes are resolved by injecting stochastic photons into the microresonators. Moreover, phase correlation measurements show that the uniformity of comb spacing of quantum …

Vibrational spectroscopy is a ubiquitous technology that derives the species, constituents and morphology of an object from its natural vibrations. However, natural vibrations of mesoscopic particles—including most biological cells—have remained hidden from existing technologies. These particles are expected to vibrate faintly at megahertz to gigahertz rates, requiring a sensitivity and resolution that are impractical for current optical and piezoelectric spectroscopies. Here we demonstrate the real-time measurement of natural vibrations of single mesoscopic particles using an optical microresonator, extending the reach of vibrational spectroscopy to a different spectral window. Conceptually, a spectrum of vibrational modes of the particles is stimulated photoacoustically by the absorption of laser pulses and acoustically coupled to a high-quality-factor optical resonance for ultrasensitive readout. Experimentally, this …

Colloidal nanoplatelets (NPLs), a class of semiconductor nanocrystals, have attracted considerable attention as a promising gain material for their ultralow amplified spontaneous emission (ASE) and lasing thresholds. However, there exist spectral gaps, especially in the green-color range, that NPLs cannot fully cover. The recently developed CdSe/CdSeS core/alloyed-crown NPLs with excellent tunability across the green-color range offer the possibility to remedy this deficiency. Here, the ASE and lasing characteristics of this new type of NPL are investigated. A remarkably low ASE threshold of 16 μJ/cm2 at 522 nm is measured, the lowest among core/crown NPLs. Microlasers are fabricated by spin-coating them on second-order distributed feedback (DFB) cavities developed in silicon nitride (SiN) substrates. The microlasers exhibit an ultralow lasing threshold of 9 μJ/cm2 at 522 nm. Moreover, they can cover a …

Micro‐optical frequency combs are miniaturized coherent light sources exhibiting a tremendous influence on precision spectroscopy, optical clocks, and high‐speed optical communications. The rare‐earth‐doped lithium niobate (LN) is a promising platform to integrate the lasers and comb sources on the same chip of single material. However, microcombs generated in rare‐earth‐doped LN thin film (LNTF) have not yet been fully explored. To explore the protocols of generating optical combs in ytterbium‐doped LNTF, the comb‐like laser is studied in the 1060 nm band, and the dissipative Kerr soliton is experimentally demonstrated in the telecom band in a Z‐cut wafer. The over‐coupled fundamental transverse electric mode with anomalous dispersion is excited at an on‐chip pump power of 75.7 mW to generate the robust bright soliton. The broadband spectrum of the Kerr soliton ranges from 1480 to 1660 nm with …

In the past decade, photonic integrated circuits (PICs) based on thin-film lithium niobate (TFLN) have made substantial progress in various fields, including optical communication, nonlinear photonics, and quantum optics. A critical component is an efficient edge coupler facilitating the connection between PICs and light sources or detectors. Here, we propose an innovative edge coupler design with a wedge-shaped TFLN waveguide and a silicon oxynitride cladding. Experimental results show a low coupling loss between the TFLN PIC and a 3-lm mode field diameter (MFD) lensed fiber, measuring at 1.52 dB/facet, with theoretical potential for improvement to 0.43 dB/facet. Additionally, the coupling loss between the edge coupler and a UHNA7 fiber with an MFD of 3.2 lm is reduced to 0.92 dB/facet. This design exhibits robust fabrication and alignment tolerances. Notably, the minimum linewidth of the TFLN …

We theoretically investigate the quantum-induced Brownian motion of dissipative Kerr solitons in multi-mode microresonators. The dispersive-wave radiation is found to modify the effective viscosity, reducing the diffusion rate by up to 19 dB.

Many key functionalities of optical frequency combs such as self-referencing and broad spectral access rely on coherent supercontinuum generation (SCG). While nanophotonic waveguides have emerged as a compact and power-efficient platform for SCG, their geometric degrees of freedom have not been fully utilized due to the underlying nonlinear and stochastic physics. Here, we introduce inverse design to unlock free-form waveguides for coherent SCG. The efficacy of our design is numerically and experimentally demonstrated on Si3N4 waveguides, producing flat and coherent spectra from visible to mid-infrared wavelengths. Our work has direct applications in developing chip-based broadband light sources for spectroscopy, metrology, and sensing across multiple spectral regimes.

We experimentally investigate the dynamics of dissipative chaotic modulational instability in Kerr microresonators. Correlations of these waveforms are revealed in both temporal and spectral domain.

Optical frequency comb (OFC) has coherently bridged the gap between light and microwave. Its advent has brought revolutionary progress to the accurate measurements of optical frequency and time, and profoundly promoted the technological development of technology of the contemporary world. The earliest optical frequency combs are generated from mode-locked laser systems. However, optical frequency combs based on mode-locked lasers have typically been limited to laboratory applications, due to their complexity, large size, and high cost. In recent years, a new type of optical frequency comb has emerged to address these problems. It is excited by continuous-wave laser coupling into a high-quality optical microresonator, generating equidistant sidebands in the frequency domain through four-wave mixing, and achieving mode locking in the time domain by using nonlinear effects to balance dispersion …

A time-of-flight LiDAR is demonstrated using a single soliton frequency comb generated in an ultrahigh-Q silica microresonator. Utilizing an electro-optic sampling Sagnac interferometer, distance measurement with 8-nm precision at 1-km range is achieved.

We investigate the fundamental timing jitter of dark pulse microcombs generated in an AlGaAs microresonator, where the quantum-limited frequency noise of the 91-GHz repetition rate is measured to be 0.5 Hz 2/Hz.

We demonstrate coherent microcomb generation based on an AlGaAs-on-insulator microresonator operating at sub-milliwatt pump power regime, that can be directly driven by on-chip laser.

A single pump generates counter-propagating Brillouin laser, enabling dual-soliton excitation in an over-modal microresonator. Via tuning the pump detuning, the dual-soliton demonstrates tunable repetition offset ranging from 8.4 MHz to 367 MHz.

Optical microresonators with high quality (Q) factors are essential to a wide range of integrated photonic devices. Steady efforts have been directed towards increasing microresonator Q factors across a variety of platforms. With success in reducing microfabrication process-related optical loss as a limitation of Q, the ultimate attainable Q, as determined solely by the constituent microresonator material absorption, has come into focus. Here, we report measurements of the material-limited Q factors in several photonic material platforms. High-Q microresonators are fabricated from thin films of SiO2, Si3N4, Al0.2Ga0.8As, and Ta2O5. By using cavity-enhanced photothermal spectroscopy, the material-limited Q is determined. The method simultaneously measures the Kerr nonlinearity in each material and reveals how material nonlinearity and ultimate Q vary in a complementary fashion across photonic materials. Besides …

Microresonator soliton frequency combs offer unique flexibility in synthesizing microwaves over a wide range of frequencies, while their phase noise is currently limited by thermal noise. Enlarging the mode volume would mitigate thermal noise but also raise power consumption. Here, we fabricate optical microresonators with large mode volumes by lathe machining high-purity fiber preforms. Quality factors greater than 4 billion result in a record-low threshold power of 110 µW to initiate comb operation in millimeter-sized devices. The synthesized X-band microwaves with an absolute phase noise level of −107(−133)dBc/Hz at 1(10) kHz offset frequency feature considerable noise reduction compared to other silica-microresonator-based oscillators, which are further used to cope with high-speed data links as carrier waves. Our work illuminates a pathway toward low-noise photonic microwave generation as well as …