We demonstrate robust turnkey soliton frequency combs using a fiber Fabry-Pérot cavity laser. This believed to be novel linear fiber-laser-based approach leverages Rayleigh scattering from a microresonator to serve as a partial reflector to facilitate both lasing and soliton generation. Numerical simulations are used to optimize the gain-maximum wavelength of the fiber cavity to match the target wavelength, at which the microresonator exhibits strong backscattering. A fused silica microrod resonator with an intrinsic Q-factor of 2 × 108 simultaneously acts as partial reflector and filter for the laser cavity. Based on this fiber cavity laser, we successfully generate soliton crystal frequency combs in a fused silica microresonator with a mode spacing of approximately 109 GHz. We also validate soliton comb generation using different microresonators with varying dimensions. Our laser system exhibits self-injection locking to one of the microresonator modes. Turnkey performance is evaluated through laser current switching tests. The laser power conversion efficiency from 980 nm to 1550 nm is 25%. As a complement to chip-based systems, our work provides insights into soliton generation using extremely low-loss laser cavities and narrow linewidth fused silica microresonators. Our soliton frequency combs are expected to advance various microwave photonic applications that demand long-term stability and turnkey performance.
Monolithic electric field control of a grating coupler for finely tuning wavelength, efficiency, and bandwidth
Yifan Zhang,
Yongyong Zhuang,
Liu Yang,
Xin Liu,
Qingyuan Hu,
Haochen Yan,
Hao Zhang,
Yaojing Zhang,
Shuangyou Zhang, et al.
In this Letter, we propose a Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3-On-Insulator (PIN-PMN-PTOI) based apodized grating coupler through finite-difference time-domain (FDTD) simulations. By leveraging the ultrahigh electro-optic coefficient of PIN-PMN-PT single crystal, we demonstrate precise control over the effective refractive index, thereby fine-tuning the central wavelength, enhancing coupling efficiency (CE) and 3-dB bandwidth. Simulation results reveal that, under an external electric field, the center wavelength can be tuned from 1544.84 nm to 1553.36 nm, while the CE remains above 80%. The CE can be improved by 5.9%; the 3-dB bandwidth can be increased by 2.1 nm at 1550 nm. Our results show that PIN-PMN-PTOI-based gratings are promising for large-scale photonic chip integration with high CE and large bandwidth.
Microresonator soliton frequency combs via cascaded Brillouin scattering
Hao Zhang,
Shuangyou Zhang,
Toby Bi,
George N. Ghalanos,
Yaojing Zhang,
Haochen Yan,
Arghadeep Pal,
Jijun He,
Shilong Pan, et al.
Communications Physics
8
216
(2025)
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Microresonator frequency combs are vital for advancing optical communications and sensing, but current methods face challenges in achieving low phase noise and flexible repetition rates simultaneously. Here, we demonstrate forward-propagating soliton frequency combs using cascaded Brillouin scattering in a silica resonator. This method bridges distinct resonator modes and decouples soliton repetition rates from the Brillouin frequency shift (~10 GHz in silica). By generating soliton pulses at 107 GHz, we show that the repetition rates can be tailored through resonator geometry without compromising low noise. This integration of Brillouin lasing with microcombs unites stability and design flexibility, overcoming prior limitations. The results can enable scalable photonic platforms for applications such as LiDAR, high-capacity optical networks, and precision microwave generation. This technique is of interest for technologies that demand both ultra-stable and customizable light sources.
Inverse-Designed Silicon Nitride Nanophotonics
Toby Bi,
Shuangyou Zhang,
Egemen Bostan,
Danxian Liu,
Aditya Paul,
Olga Ohletz,
Irina Harder,
Yaojing Zhang,
Alekhya Ghosh, et al.
Silicon nitride photonics has enabled integration of a variety of components for applications in linear and nonlinear optics, including telecommunications, optical clocks, astrocombs, bio-sensing, and LiDAR. With the advent of inverse design – where desired device performance is specified and closely achieved through iterative, gradient-based optimization – and the increasing availability of silicon nitride photonics via foundries, it is now feasible to expand the photonic design library beyond the limits of traditional approaches and unlock new functionalities. In this work, we present inverse-designed photonics on a silicon nitride platform and demonstrate both the design capabilities and experimental verification by realising precisely tailored wavelength-division multiplexers, mode-division multiplexers, and high-Q resonators with controllable wavelength range and dispersion. This demonstrates inverse-designed enhanced manipulation of orthogonal bases of light. Furthermore, we use these inverse-designed structures to form optical cavities that hold promise for on-chip nonlinear and quantum optics experiments.
Exceptional, but Separate: Precursors to Spontaneous Symmetry Breaking
Lewis Hill,
Julius Gohsrich,
Alekhya Ghosh,
Jacob Fauman,
Pascal Del'Haye,
Flore K. Kunst
Spontaneous symmetry breaking (SSB) and exceptional points (EPs) are often assumed to be inherently linked. Here we investigate the intricate relationship between SSB and specific classes of EPs across three distinct, real-world scenarios in nonlinear optics. In these systems, the two phenomena do not<br>coincide for all classes of EPs; they can occur at dislocated points in parameter space. This recurring behavior across disparate platforms implies that such decoupling is not unique to these optical systems, but likely reflects a more general principle. Our results highlight the need for careful analysis of assumed correlations between SSB and EPs in both theoretical and applied contexts. They deepen our understanding of nonlinear dynamics in<br>optical systems and prompt a broader reconsideration of contexts where EPs and<br>SSB are thought to be interdependent.
Hybrid Nonlinear Effects in Photonic Integrated Circuits
Nonlinear optics in photonic integrated circuits is usually limited to utilizing the nonlinearity of a single material. In this work, we demonstrate the use of hybrid optical nonlinearities that occur in two different materials. This approach allows us to observe combined Raman scattering and Kerr frequency comb generation using silicon nitride (Si3N4) microresonators with fused silica cladding. Here, the fused silica cladding provides Raman gain, while the silicon nitride core provides the Kerr nonlinearity for frequency comb generation. This way we can add Raman scattering to an integrated photonic silicon nitride platform, in which Raman scattering has not been observed so far because of insufficient Raman gain. The Raman lasing is observed in the silica-clad silicon nitride resonators at an on-chip optical power of 143 mW, which agrees with theoretical simulations. This can be reduced to mw-level with improved optical quality factor. Broadband Raman-Kerr frequency comb generation is realized through dispersion engineering of the waveguides. The use of hybrid optical nonlinearities in multiple materials opens up new functionalities for integrated photonic devices, e.g. by combining second and third-order nonlinear materials for combined supercontinuum generation and self-referencing of frequency combs. Combining materials with low threshold powers for different nonlinearities can be the key to highly efficient nonlinear photonic circuits for compact laser sources, high-resolution spectroscopy, frequency synthesis in the infrared and UV, telecommunications and quantum information processing.
Near‐Infrared Dual‐Band Frequency Comb Generation from a Silicon Resonator
Keyi Zhong,
Yaojing Zhang,
Shuangyou Zhang,
Yuanfei Zhang,
Yuan Li,
Yue Qin,
Yi Wang,
Jose M. Chavez Boggio,
Xiankai Sun, et al.
Benefitting from the mature, cost-effective, and scalable manufacturing capabilities of complementary metal-oxide-semiconductor (CMOS) technology, silicon photonics has facilitated the seamless and monolithic integration of diverse functionalities, including optical sources, modulators, and photodetectors. Microresonators can generate multiple coherent optical frequency comb lines and serve as optical sources. However, at the telecom band, silicon suffers from two-photon absorption and free-carrier absorption, which severely hampers the realization of microcombs from a single silicon chip at telecom wavelengths until now. In this paper, a novel approach is presented and demonstrated with near-infrared dual-band frequency combs from a multimode silicon resonator. With a single pumping configuration, dual-band combs are generated from the interaction between the pump and Raman Stokes fields by involving two different optical mode families but with similar group velocities. It is observed that the pump power required to generate dual-band combs is as low as 0.7 mW. The work in bringing telecom microcombs to the silicon platform will advance silicon photonics for the next generation of monolithically integrated technology based on a single silicon chip, enabling new possibilities for further exploring silicon photonics-based applications in optical telecommunications, sensing, and quantum metrology in the telecom band using a monolithic single silicon chip.
Integrated optical switches based on Kerr symmetry breaking in microresonators
Yaojing Zhang,
Shuangyou Zhang,
Alekhya Ghosh,
Arghadeep Pal,
George N. Ghalanos,
Toby Bi,
Haochen Yan,
Hao Zhang,
Yongyong Zhuang, et al.
Photonics Research
13
360-366
(2025)
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With the rapid development of the Internet of Things and big data, integrated optical switches are gaining prominence for applications in on-chip optical computing, optical memories, and optical communications. Here, we propose a novel approach for on-chip optical switches by utilizing the nonlinear optical Kerr effect induced spontaneous symmetry breaking (SSB), which leads to two distinct states of counterpropagating light in ring resonators. This technique is based on our first experimental observation of on-chip symmetry breaking in a high-Q (9.4 × 106) silicon nitride resonator with a measured SSB threshold power of approximately 3.9 mW. We further explore the influence of varying pump powers and frequency detunings on the performance of SSB-induced optical switches. Our work provides insights into the development of new types of photonic data processing devices and provides an innovative approach for the future implementation of on-chip optical memories.
On-chip microresonator dispersion engineering via segmented sidewall modulation
Masoud Kheyri,
Shuangyou Zhang,
Toby Bi,
Arghadeep Pal,
Hao Zhang,
Yaojing Zhang,
Abdullah Alabbadi,
Haochen Yan,
Alekhya Ghosh, et al.
Photonics Research
13
367-372
(2025)
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Microresonator dispersion plays a crucial role in shaping the nonlinear dynamics of microcavity solitons. Here, we introduce and validate a method for dispersion engineering through modulating a portion of the inner edge of ring waveguides. We demonstrate that such partial modulation has a broadband effect on the dispersion profile, whereas modulation on the entire resonator’s inner circumference leads to mode splitting primarily affecting one optical mode. The impact of spatial modulation amplitude, period, and number of modulations on the mode splitting profile is also investigated. Through the integration of four modulated sections with different modulation amplitudes and periods, we achieve mode splitting across more than 50 modes over a spectral range exceeding 100 nm in silicon nitride resonators. These results highlight both the simplicity and efficacy of our method in achieving flatter dispersion profiles.
Contact
Research GroupPascal Del'Haye
Max Planck Institute for the Science of Light Staudtstr. 2 91058 Erlangen, Germany
