Since last decade, microresonator-based optical frequency combs (i.e. microcombs) have attracted significant attentions due to their unprecedented advantages of ultrahigh repetition rates, wide bandwidth and high compactness
Opto-Electronic Advances, Volume. 8, Issue 3, 240257-1(2025)
Soliton microcombs in optical microresonators with perfect spectral envelopes
We theoretically and experimentally investigate thermal dynamics involved soliton microcomb generation in silicon oxynitride microresonators. Importantly, auxiliary laser heat balance scheme with flexible thermal manipulation is introduced to circumvent thermal instability and the intra-cavity temperature can be tuned from 60 °C to 41.5 °C via the commercial thermoelectric controller. As a result, various perfect soliton states with ultra-smooth spectral envelopes are observed on a well-designed and fabricated microresonator with homogeneous sidewall and thickness where spatial modes interaction and distortion are eliminated. The pre-reported spectral abrupt jumps due to mode hybridization are completely avoided and solitons tail oscillation vanishes simultaneously. This reported ideal coherent comb source without residual temporal and spectral noise will facilitate practical applications such as spectroscopy, ranging and astrocomb calibration.
Introduction
Since last decade, microresonator-based optical frequency combs (i.e. microcombs) have attracted significant attentions due to their unprecedented advantages of ultrahigh repetition rates, wide bandwidth and high compactness
However, during the transition into a steady soliton state, the dramatic intracavity power drop can result in the pump frequency shifting out of cavity resonance through the thermo-optical effect, thus introducing the difficulties to deterministically capture solitons in experiments. The specific technical approaches are required according to distinct thermal and nonlinear properties for different platforms. To date, the rapid forward frequency-tuning
Beyond these encouraging progresses, certain challenges to further improve the performance of soliton microcombs still remain, especially for those with high thermal constant considering the continuously emerging new platforms. For instance, researchers quench thermorefractive effects of AlGaAs by cryogenic cooling temperatures to 4–20 K for soliton microcomb generation. Its thermorefractive value in room-temperature is an order of magnitude larger than that of Si3N4 and SiO2, and AlN by more than two orders of magnitude
Here, we explore the thermal influence on soliton microcomb generation in silicon oxynitride materials platform. We found that the strong thermal effect prohibits the soliton microcomb generation under single pump frequency scanning scheme. Therefore, we employ a novel auxiliary-laser-assisted tuning method combined with precise and flexible thermal regulation via a thermoelectric controller (TEC), applied to a sophisticated design and processing silicon oxynitride microresonator with smooth sidewall and uniform thickness, thereby generate stable Kerr solitons. Eliminating the influences of other modes or mode distortion and sustaining the pure fundamental mode field, various perfect soliton states with favored smooth spectral envelope are accessible promptly by adjusting auxiliary light. Our perfect soliton state features the completely vanishing spectral discontinuities caused by avoided-mode-crossing (AMX) effects
Theory and simulation
The Lugiato-Lefever equation (LLE) including second-order dispersion, Raman and thermal effects is used to describe the spectral-temporal dynamics of frequency comb generation
where E(t, τ) is the envelope of field within the resonator, t and τ correspond to the slow time and the fast time, respectively, TR is the round-trip time, Ein is the pump field, δ0 is the laser detuning and δT is the thermal detuning.
In the first stage, relatively stronger thermal effects with ζ = −1 × 104 (Ws)−1 is used for simulation. The laser detuning is linearly tuned from −0.004 to 0.056 in 0–1600 ns and held at 0.056 in 1600–3500 ns. It is found that stochastic solitons annihilate or survive in all 30 scans as seen from
Figure 1.The influences of thermal effects on soliton formation and auxiliary laser assisted tuning method. (
Experimental setup and principle
The experimental setup is built as shown in
Figure 2.Experimental setup and single perfect soliton. (
In this system, the auxiliary laser operating in the blue detuning regime at one cavity mode is to balance the intracavity heat flow and actively stabilize different soliton states. In detail, the c.w. pump laser counter-propagates in the microcavity and works at a different cavity mode, thus heats the cavity and red-shifts all cavity resonances. While the red-shifted resonances displace the auxiliary laser from its own cavity mode, in turn cooling the cavity. By properly setting the pump power and temperature of TEC (equally to varying the detuning of pump and auxiliary lasers), the heat flow induced by dual pump tends to balance out each other. Therefore, the pump laser can scan across the entire cavity resonance linewidth without thermal dragging. Furthermore, adjusting injection power of auxiliary laser or precise temperature control through TEC can be used to suppress the minimal power fluctuations and maintain power stability during stable solitons. Stable soliton states can be generated with high repeatability by implementing the auxiliary laser heating scheme.
Accessing different soliton states in experiment
In experiments, the microresonator with a loaded Q-factor of 1.7 × 106 and dispersion of −37 ps2 km−1 is used for soliton generation. The platform is well established and used in large-scale integrated photonic circuits as well as on-chip soliton crystal generation
Figure 3.(
Interestingly, it is further demonstrated that this scheme can suppress the thermal effect well and sequentially access stable different two soliton states flexibly through control the wavelength and power of auxiliary light as shown in
Figure 4.(
Figure 5.(
Conclusions
In summary, this work theoretically investigates thermal effect in silicon oxynitride microresonators based on the LLE model that incorporates thermal parameters. Simulations show that the generated solitons can either survive or annihilate due to thermal dynamics when the continuous pump laser is scanned from the blue to red detuning region. Therefore, the counter-propagating pump-auxiliary scheme possessing flexible thermal regulation is adopted to generate single soliton with favored smooth and standard sech2 spectral profile. Furthermore, different multi-soliton states can be obtained easily by adjusting the TEC and auxiliary laser to balance the intracavity thermal instability. Thanks to our elaborate design and processing technology introducing uniform waveguide thickness and sidewall, the observed smooth spectra profile of solitons without any spike related to mode interaction as reported before paves the way for further frequency domain applications in spectroscopy, astronomy and telecommunications. The concomitant tail-oscillation-free temporal pulse in absence of absorption background can also accelerate soliton-based precision measurement like ranging and imaging. In future work, we will also investigate the generation of soliton microcombs with perfect spectral envelopes using auxiliary laser heat balance scheme in other material platforms.
[1] Y Sun, JY Wu, MX Tan et al. Applications of optical microcombs. Adv Opt Photonics, 15, 86-175(2023).
[2] SA Diddams, K Vahala, T Udem. Optical frequency combs: coherently uniting the electromagnetic spectrum. Science, 369, eaay3676(2020).
[3] TE Drake, TC Briles, JR Stone et al. Terahertz-rate Kerr-microresonator optical clockwork. Phys Rev X, 9, 031023(2019).
[4] Y Geng, H Zhou, XJ Han et al. Coherent optical communications using coherence-cloned Kerr soliton microcombs. Nat Commun, 13, 1070(2022).
[5] L Stern, JR Stone, SB Kang et al. Direct Kerr frequency comb atomic spectroscopy and stabilization. Sci Adv, 6, eaax6230(2020).
[6] CY Bao, ZQ Yuan, L Wu et al. Architecture for microcomb-based GHz-mid-infrared dual-comb spectroscopy. Nat Commun, 12, 6573(2021).
[7] LY Dang, LG Huang, LL Shi et al. Ultra-high spectral purity laser derived from weak external distributed perturbation. Opto-Electron Adv, 6, 210149(2023).
[8] P Trocha, M Karpov, D Ganin et al. Ultrafast optical ranging using microresonator soliton frequency combs. Science, 359, 887-891(2018).
[9] JD Wang, ZZ Lu, WQ Wang et al. Long-distance ranging with high precision using a soliton microcomb. Photonics Res, 8, 1964-1972(2020).
[10] SL Camenzind, JF Fricke, J Kellner et al. Dynamic and precise long-distance ranging using a free-running dual-comb laser. Opt Express, 30, 37245-37260(2022).
[11] MA Guidry, DM Lukin, KY Yang et al. Quantum optics of soliton microcombs. Nat Photonics, 16, 52-58(2022).
[12] LW Chen, Y Zhou, Y Li et al. Microsphere enhanced optical imaging and patterning: from physics to applications. Appl Phys Rev, 6, 021304(2019).
[13] CY Bao, Y Xuan, DE Leaird et al. Spatial mode-interaction induced single soliton generation in microresonators. Optica, 4, 1011-1015(2017).
[14] YR Zhai, JC Liu, LH Jia et al. Dissipative Kerr soliton formation in dual-mode interaction Si3N4 microresonators. APL Photonics, 9, 101304(2024).
[15] KW Liu, SY Yao, CX Yang. Raman pure quartic solitons in Kerr microresonators. Opt Lett, 46, 993-996(2021).
[16] C Xiang, JQ Liu, J Guo et al. Laser soliton microcombs heterogeneously integrated on silicon. Science, 373, 99-103(2021).
[17] JY Ma, LF Xiao, JX Gu et al. Visible Kerr comb generation in a high-Q silica microdisk resonator with a large wedge angle. Photonics Res, 7, 573-578(2019).
[18] FJ Shu, PJ Zhang, YJ Qian et al. A mechanically tuned Kerr comb in a dispersion-engineered silica microbubble resonator. Sci China Phys Mech Astron, 63, 254211(2020).
[19] DY Chen, A Kovach, XQ Shen et al. On-chip ultra-high-Q silicon oxynitride optical resonators. ACS Photonics, 4, 2376-2381(2017).
[20] MF Qu, CH Li, KQ Liu et al. Dynamic process of soliton generation in CaF2 crystalline whispering gallery mode resonators with negative TO effects. Opt Express, 32, 42846-42855(2024).
[21] H Wang, B Duan, K Wang et al. Direct tuning of soliton detuning in an ultrahigh-Q MgF2 crystalline resonator. Nanophotonics, 12, 3757-3765(2023).
[22] XW Liu, CZ Sun, B Xiong et al. Integrated high-Q crystalline ALN microresonators for broadband Kerr and Raman frequency combs. ACS Photonics, 5, 1943-1950(2018).
[23] SY Yao, KW Liu, CX Yang. Pure quartic solitons in dispersion-engineered aluminum nitride micro-cavities. Opt Express, 29, 8312-8322(2021).
[24] L Chang, WQ Xie, HW Shu et al. Ultra-efficient frequency comb generation in AlGaAs-on-insulator microresonators. Nat Commun, 11, 1331(2020).
[25] O Melchert, S Kinnewig, F Dencker et al. Soliton compression and supercontinuum spectra in nonlinear diamond photonics. Diam Relat Mater, 136, 109939(2023).
[26] RL Miao, CX Zhang, X Zheng et al. Repetition rate locked single-soliton microcomb generation via rapid frequency sweep and sideband thermal compensation. Photonics Res, 10, 1859-1867(2022).
[27] HR Guo, M Karpov, E Lucas et al. Universal dynamics and deterministic switching of dissipative Kerr solitons in optical microresonators. Nat Phys, 13, 94-102(2017).
[28] V Brasch, M Geiselmann, MHP Pfeiffer et al. Bringing short-lived dissipative Kerr soliton states in microresonators into a steady state. Opt Express, 24, 29312-29320(2016).
[29] J Li, S Wan, JL Peng et al. Thermal tuning of mode crossing and the perfect soliton crystal in a Si3N4 microresonator. Opt Express, 30, 13690-13698(2022).
[30] XR Ji, JQ Liu, JJ He et al. Compact, spatial-mode-interaction-free, ultralow-loss, nonlinear photonic integrated circuits. Commun Phys, 5, 84(2022).
[31] H Zhou, Y Geng, WW Cui et al. Soliton bursts and deterministic dissipative Kerr soliton generation in auxiliary-assisted microcavities. Light Sci Appl, 8, 50(2019).
[32] XY Wang, XK Qiu, ML Liu et al. Flat soliton microcomb source. Opto-Electron Sci, 2, 230024(2023).
[33] T Herr, V Brasch, JD Jost et al. Temporal solitons in optical microresonators. Nat Photonics, 8, 145-152(2014).
[34] SS Jiang, CL Guo, HY Fu et al. Mid-infrared Raman lasers and Kerr-frequency combs from an all-silica narrow-linewidth microresonator/fiber laser system. Opt Express, 28, 38304-38316(2020).
[35] MJ Yu, Y Okawachi, R Cheng et al. Raman lasing and soliton mode-locking in lithium niobate microresonators. Light Sci Appl, 9, 9(2020).
[36] V Brasch, M Geiselmann, T Herr et al. Photonic chip–based optical frequency comb using soliton Cherenkov radiation. Science, 351, 357-360(2016).
[37] Z Gong, XW Liu, YT Xu et al. Near-octave lithium niobate soliton microcomb. Optica, 7, 1275-1278(2020).
[38] CL Wang, J Li, AL Yi et al. Soliton formation and spectral translation into visible on CMOS-compatible 4H-silicon-carbide-on-insulator platform. Light Sci Appl, 11, 341(2022).
[39] W Wu, QB Sun, Y Wang et al. Mid-infrared broadband optical frequency comb generated in MgF2 resonators. Photonics Res, 10, 1931-1936(2022).
[40] FX Wang, WQ Wang, R Niu et al. Quantum key distribution with on-chip dissipative Kerr soliton. Laser Photon Rev, 14, 1900190(2020).
[41] J Riemensberger, A Lukashchuk, M Karpov et al. Massively parallel coherent laser ranging using a soliton microcomb. Nature, 581, 164-170(2020).
[42] JR Stone, TC Briles, TE Drake et al. Thermal and nonlinear dissipative-soliton dynamics in Kerr-microresonator frequency combs. Phys Rev Lett, 121, 063902(2018).
[43] HM Zheng, W Sun, XX Ding et al. Programmable access to microresonator solitons with modulational sideband heating. APL Photonics, 8, 126110(2023).
[44] G Moille, L Chang, WQ Xie et al. Dissipative Kerr solitons in a III-V microresonator. Laser Photon Rev, 14, 2000022(2020).
[45] BL Zhao, LR Wang, QB Sun et al. Repetition-rate multiplicable soliton microcomb generation and stabilization via phase-modulated pumping scheme. Appl Phys Express, 13, 032009(2020).
[46] WC Fan, ZZ Lu, W Li et al. Low-threshold 4/5 octave-spanning mid-infrared frequency comb in a LiNbO3 microresonator. IEEE Photonics J, 11, 6603407(2019).
[47] M Karpov, MHP Pfeiffer, HR Guo et al. Dynamics of soliton crystals in optical microresonators. Nat Phys, 15, 1071-1077(2019).
[48] Y He, JW Ling, MX Li et al. Perfect soliton crystals on demand. Laser Photon Rev, 14, 1900339(2020).
[49] MG Suh, X Yi, YH Lai et al. Searching for exoplanets using a microresonator astrocomb. Nat Photonics, 13, 25-30(2019).
[50] C Kim, CC Ye, Y Zheng et al. Design and fabrication of AlGaAs-on-insulator microring resonators for nonlinear photonics. IEEE J Sel Top Quantum Electron, 29, 5900214(2023).
[51] H Liu, WT Wang, JH Yang et al. Observation of deterministic double dissipative-Kerr-soliton generation with avoided mode crossing. Phys Rev Res, 5, 013172(2023).
[52] CY Bao, Y Xuan, JA Jaramillo-Villegas et al. Direct soliton generation in microresonators. Opt Lett, 42, 2519-2522(2017).
[53] ZZ Lu, WQ Wang, WF Zhang et al. Raman self-frequency-shift of soliton crystal in a high index doped silica micro-ring resonator [Invited]. Opt Mater Express, 8, 2662-2669(2018).
[54] I Coddington, N Newbury, W Swann. Dual-comb spectroscopy. Optica, 3, 414-426(2016).
[55] G Piccoli, M Sanna, M Borghi et al. Silicon oxynitride platform for linear and nonlinear photonics at NIR wavelengths. Opt Mater Express, 12, 3551-3562(2022).
[56] ZZ Lu, WQ Wang, WF Zhang et al. Deterministic generation and switching of dissipative Kerr soliton in a thermally controlled micro-resonator. AIP Adv, 9, 025314(2019).
[57] WQ Wang, WF Zhang, ST Chu et al. Repetition rate multiplication pulsed laser source based on a microring resonator. ACS Photonics, 4, 1677-1683(2017).
[58] LK Chen, YF Xiao. On-chip lithium niobate microresonators for photonics applications. Sci China Phys Mech Astron, 63, 224231(2020).
[59] M Zhang, B Buscaino, C Wang et al. Broadband electro-optic frequency comb generation in a lithium niobate microring resonator. Nature, 568, 373-377(2019).
[60] WQ Wang, ZZ Lu, WF Zhang et al. Robust soliton crystals in a thermally controlled microresonator. Opt Lett, 43, 2002-2005(2018).
[61] ZD Li, YQ Xu, S Shamailov et al. Ultrashort dissipative Raman solitons in Kerr resonators driven with phase-coherent optical pulses. Nat Photonics, 18, 46-53(2024).
Get Citation
Copy Citation Text
Mulong Liu, Ziqi Wei, Haotong Zhu, Hongwei Wang, Xiao Yu, Xilin Han, Wei Zhao, Guangwei Hu, Peng Xie. Soliton microcombs in optical microresonators with perfect spectral envelopes[J]. Opto-Electronic Advances, 2025, 8(3): 240257-1
Category: Research Articles
Received: Oct. 29, 2024
Accepted: Feb. 10, 2025
Published Online: May. 28, 2025
The Author Email: Wei Zhao (WZhao), Guangwei Hu (GWHu), Peng Xie (PXie)