Mid-infrared optical frequency combs: Progress and applications (Invited)
-
摘要: 光学频率梳是一种宽谱的相干光源,由一系列等频率间隔的离散谱线组成,具有超高的时频精度。自诞生以来,光学频率梳为精密光谱学、光学测量、相干光通信、光时钟等多种应用的发展带来了革命性的变化。近年来,研究人员通过新型激光增益介质、非线性频率转换和微谐振腔等技术将频率梳扩展到中红外光谱区域(2~20 μm),进一步扩大了光频梳的应用范围。文中全面介绍了中红外光频率梳的产生机制、最新进展及应用。Abstract: Optical frequency comb is a kind of broad spectrum coherent light source, which is composed of a series of discrete spectral lines with equal frequency interval and has ultrahigh time-frequency accuracy. Since its birth, optical frequency comb has brought revolutionary changes to the development of precision spectroscopy, optical measurement, coherent optical communication, optical clock and other applications. In recent years, researchers have extended the frequency comb to the mid-infrared spectrum region (2-20 μm) by using novel laser gain media, nonlinear frequency conversion and micro-resonator techniques, and further expand the application range of optical frequency comb. In this paper, the generation mechanism, latest development and application of mid-infrared frequency comb are introduced.
-
Key words:
- mid-infrared /
- optical frequency comb /
- precision measurement /
- nonlinear /
- molecular fingerprint
-
图 2 基于锁模激光器的MIR-OFC:(a) 利用强光泵浦中红外激光增益介质实现粒子数反转和激光激射,通过可饱和吸收体实现锁模脉冲输出;(b) 环形光纤锁模中红外激光器的典型系统图;(c)~(e) 中红外锁模激光器的典型光谱、脉冲自相关轨迹和重复频率信号[3, 28]
Figure 2. Mode-locked laser-based mid-infrared optical frequency comb: (a) Particle number inversion and laser emission are realized by using strong light pumped mid-infrared laser gain medium, and mode-locked pulse output is realized by saturable absorber; (b) Typical setup of ring fiber mode-locked lasers in mid-infrared band; (c)-(e) Typical optical spectrum, pulse autocorrelation traces and repetition rate signal of the mid infrared mode-locked laser[3, 28]
图 3 基于差频产生MIR-OFC:(a) 在具有二阶非线性χ(2)的介质中,泵浦光和信号梳的不同纵模混频产生不同的差频,从而形成中红外的闲频梳。其中泵浦也可以是光频梳;(b) 差频产生MIR-OFC的典型系统;(c) 逆转差频过程和梳激发过程的MIR-OFC非线性过程,和(d)相应的器件结构[3, 7, 36]
Figure 3. Difference-frequency based mid-infrared optical frequency comb: (a) Longitudinal mode mixing frequency of pump light and signal comb produces different difference frequencies in the middle wave with second order nonlinear χ(2), thus forming a mid-infrared idle frequency comb. The pump can also be an optical frequency comb; (b) A typical system for a difference generation based mid-infrared optical frequency comb; (c) A mid-infrared optical frequency comb nonlinear process that reverses the difference frequency process and the comb excitation process, and (d) the corresponding device structure[3, 7, 36]
图 4 基于光参量振荡产生MIR-OFC:(a) 在强泵浦光的作用下,具有χ(2)非线性介质的光学谐振腔中信号光获得增益,当该增益超过的损耗时,信号光就会产生相干振荡。由于能量守恒,中红外闲频光同时产生;(b) OPOs产生MIR-OFC的典型系统;(c) 基于连续种子光方案的OPO MIR-OFC激发系统。(d) 利用连续波种子光参量生成信号和闲频梳光谱(上图)和对应的激光模式示意图(下图)[3, 11, 45]
Figure 4. Optical parametric oscillation based mid-infrared optical frequency comb: (a) Under the action of strong pump light, the signal light in the optical resonant cavity with χ(2) nonlinear medium obtains gain, and when the gain exceeds the loss, the signal light will produce coherent oscillation. Due to the conservation of energy, the mid-infrared idle frequency comb is generated at the same time; (b) Typical system of mid-infrared frequency comb generated by optical parametric oscillation; (c) Mid-infrared optical frequency comb excitation system of OPO based on continuous seed light scheme; (d) Signal and idle frequency comb spectrum based on CW seeded OPO (top) and the schematic diagram of corresponding laser mode (bottom)[3, 11, 45]
图 5 基于超连续产生MIR-OFC:(a) 孤子诱导色散波(DW)产生的示意图;(b) 超连续产生MIR-OFC的典型系统;(c) 典型的超连续MIR-OFC光谱;(d) 在非线性介质中泵浦梳的超连续光谱演变过程[12, 54]
Figure 5. Supercontinuous generation based mid-infrared optical frequency comb:(a) Schematic diagram of soliton induced dispersion wave (DW) generation; (b) Typical systems for supercontinuous generation of mid-infrared optical frequency combs; (c) Typical supercontinuous mid-infrared optical frequency-comb spectrum; (d) Supercontinuous spectral evolution of pump combs in nonlinear media[12, 54]
图 6 基于量子级联激光器产生MIR-OFC: (a) QCLs的工作原理示意图;(b) QCLs对FP腔内分散的谐振模式通过注入锁定产生MIR-OFC;(c) 通过电注入锁定产生中红外相干稳定光频梳器件;(d) 相干注入锁定后的强度谱(蓝线)、SWIFTS谱(红线)、完全相干的预期SWIFTS幅度(蓝点)及相邻梳齿间的相位差(绿线)[58-59]
Figure 6. Quantum cascade laser based MIR-OFC: (a) Working principle of QCLs; (b) QCLs generates MIR-OFC by injection locking the resonant modes dispersed in the FP cavity; (c) Mid-infrared coherent and stable optical frequency comb device produced by electrical injection locking; (d) Intensity spectrum (blue line) after coherent injection locking, SWIFTS spectrum (red line), fully coherent expected SWIFTS amplitude (blue dot) and phase difference between adjacent comb teeth (green line)[58-59]
图 7 基于微腔克尔效应产生中红外光频梳:(a)孤子诱导DW产生的示意图;(b)微腔产生中红外频率梳光谱的典型系统;(c) 当扫描泵浦激光经过谐振腔时的传输和有效泵浦腔失谐;(d) 扫描中不同位置(i-vi)的光谱和腔内时间行为[3, 16, 75]
Figure 7. Microcavity Kerr effect based mid-infrared optical frequency comb: (a) Schematic diagram of soliton induced dispersion wave (DW) generation; (b) Typical system of microcavity generating mid-infrared frequency comb spectrum; (c) Transmission and effective pump-cavity detuning when scanning pump laser over a resonance cavity; (d) Optical spectra and intracavity temporal behavior at different positions (i–vi) in the scanning[3, 16, 75]
8b 基于中红外光频梳的典型应用:(a) 基于双梳的吸收光谱测试原理图。通过一个连续波光学参量振荡器泵入两个单独的硅微谐振器,产生两个锁模梳状结构;(b) 双梳源的表征。两个锁模梳的光谱(红色,黑色)和基于迈克尔逊的傅里叶变换红外光谱(蓝色);(c) 吸收光谱;(d) GHz中红外DCS系统的实验装置。在硅微腔中产生两个1.55 μm的反向传播孤子,对这些孤子进行光探测,并对产生的信号进行处理,以1.06 μm的电光调制产生另外两个梳状信号。这些近红外梳状体成对结合后进入泵浦PPLN晶体,通过交错差频产生GHz线间距中红外频率梳;(e) 1.55 μm孤子梳(上)和1.06 μm EO梳(下)的光谱;(f) 甲烷P(3)分支在ν3波段的吸收光谱以及乙烷在ν7波段的振动跃迁。由于乙烷的吸收线宽度较窄,使用N = 16的iDFG进一步提高光谱分辨率[9, 17]
8b. Typical application based on mid-infrared optical frequency combs: (a) Schematic of dual-comb absorption spectroscopy test. A continuous-wave optical parametric oscillator pumps two separate silicon microresonators, which generates two mode locked comb structure; (b) Characterization of dual-comb source. Spectra for each mode locked comb (red, black) combined Michelson-FT spectrum (blue); (c) Absorption spectra; (d) Experimental setup of the GHz-mid-IR DCS system. Two counter-propagating (CP) solitons at 1.55 μm are generated in a silica microcavity to provide two comb signals. These solitons are photo-detected and the resulting signals are processed by electro-optic modulation at 1.06 μm. These near-IR combs are combined in pairs to pump PPLN crystals for generation of GHz line spacing mid-IR frequency combs by interleaved difference frequency generation; (e) Optical spectra of 1.55 μm soliton comb (top) and 1.06 μm EO-comb(bottom); (f) Absorbance spectrum of the methane P(3) branch in the ν3 band together with the ethane rovibrational transitions in the ν7 band. Since ethane has a narrower absorption linewidth, iDFG with N = 16 was also used to further improve the spectral resolution[9, 17]
-
[1] Cundiff S T, Ye J. Colloquium: Femtosecond optical frequency combs [J]. Reviews of Modern Physics, 2003, 75(1): 325-342. doi: 10.1103/RevModPhys.75.325 [2] Fortier T, Baumann E. 20 years of developments in optical frequency comb technology and applications [J]. Communica-tions Physics, 2019, 2(1): 153. doi: 10.1038/s42005-019-0249-y [3] Schliesser A, Picqué N, Hänsch T W. Mid-infrared frequency combs [J]. Nature Photonics, 2012, 6(7): 440-449. doi: 10.1038/nphoton.2012.142 [4] Qin Z, Hai T, Xie G, et al. Black phosphorus Q-switched and mode-locked mid-infrared Er: ZBLAN fiber laser at 3.5 μm wavelength [J]. Optics Express, 2018, 26(7): 8224. doi: 10.1364/OE.26.008224 [5] Wei C, Lyu Y, Shi H, et al. Mid-infrared Q-switched and mode-locked fiber lasers at 2.87 μm based on carbon nanotube [J]. IEEE Journal of Selected Topics in Quantum Electronics, 2019, 25(4): 1-6. [6] Cruz F C, Maser D L, Johnson T, et al. Mid-infrared optical frequency combs based on difference frequency generation for molecular spectroscopy [J]. Optics Express, 2015, 23(20): 26814. doi: 10.1364/OE.23.026814 [7] Soboń G, Martynkien T, Mergo P, et al. High-power frequency comb source tunable from 2.7 to 4.2 μm based on difference frequency generation pumped by an Yb-doped fiber laser [J]. Optics Letters, 2017, 42(9): 1748. doi: 10.1364/OL.42.001748 [8] Ycas G, Giorgetta F R, Baumann E, et al. High-coherence mid-infrared dual-comb spectroscopy spanning 2.6 to 5.2 μm [J]. Nature Photonics, 2018, 12(4): 202-208. doi: 10.1038/s41566-018-0114-7 [9] Bao C, Yuan Z, Wu L, et al. Architecture for microcomb-based GHz-mid-infrared dual-comb spectroscopy [J]. Nature Communi-cations, 2021, 12(1): 6573. doi: 10.1038/s41467-021-26958-6 [10] Jin Y, Cristescu S M, Harren F J M, et al. Femtosecond optical parametric oscillators toward real-time dual-comb spectroscopy [J]. Applied Physics B, 2015, 119(1): 65-74. doi: 10.1007/s00340-015-6035-y [11] Muraviev A V, Smolski V O, Loparo Z E, et al. Massively parallel sensing of trace molecules and their isotopologues with broadband subharmonic mid-infrared frequency combs [J]. Nature Photonics, 2018, 12(4): 209-214. doi: 10.1038/s41566-018-0135-2 [12] Grassani D, Tagkoudi E, Guo H, et al. Mid infrared gas spectroscopy using efficient fiber laser driven photonic chip-based supercontinuum [J]. Nature Communications, 2019, 10(1): 1553. doi: 10.1038/s41467-019-09590-3 [13] Guo H, Weng W, Liu J, et al. Nanophotonic supercontinuum-based mid-infrared dual-comb spectroscopy [J]. Optica, 2020, 7(9): 1181. doi: 10.1364/OPTICA.396542 [14] Borri S, Insero G, Santambrogio G, et al. High-precision molecular spectroscopy in the mid-infrared using quantum cascade lasers [J]. Applied Physics B, 2019, 125(1): 18. doi: 10.1007/s00340-018-7119-2 [15] Meng B, Singleton M, Shahmohammadi M, et al. Mid-infrared frequency comb from a ring quantum cascade laser [J]. Optica, 2020, 7(2): 162. doi: 10.1364/OPTICA.377755 [16] Wang C Y, Herr T, Del’haye P, et al. Mid-infrared optical frequency combs at 2.5 μm based on crystalline microresonators [J]. Nature Communications, 2013, 4(1): 1345. doi: 10.1038/ncomms2335 [17] Yu M, Okawachi Y, Griffith A G, et al. Silicon-chip-based mid-infrared dual-comb spectroscopy [J]. Nature Communications, 2018, 9(1): 1869. doi: 10.1038/s41467-018-04350-1 [18] Haus H A. Mode-locking of lasers [J]. IEEE Journal of Selected Topics in Quantum Electronics, 2000, 6(6): 1173-1185. doi: 10.1109/2944.902165 [19] Chen G, Li W, Wang G, et al. Generation of coexisting high-energy pulses in a mode-locked all-fiber laser with a nonlinear multimodal interference technique [J]. Photonics Research, 2019, 7(2): 187. doi: 10.1364/PRJ.7.000187 [20] Qin C, Jia K, Li Q, et al. Electrically controllable laser frequency combs in graphene-fibre microresonators [J]. Light: Science & Applications, 2020, 9(1): 185. [21] Kivisto S, Okhotnikov O G. 600-fs mode-locked Tm–Ho-doped fiber laser synchronized to optical clock with optically driven semiconductor saturable absorber [J]. IEEE Photonics Technology Letters, 2011, 23(8): 477-479. doi: 10.1109/LPT.2011.2109945 [22] Wang Q, Geng J, Luo T, et al. Mode-locked 2 μm laser with highly thulium-doped silicate fiber [J]. Optics Letters, 2009, 34(23): 3616. doi: 10.1364/OL.34.003616 [23] Kivisto S, Hakulinen T, Guina M, et al. Tunable Raman soliton source using mode-locked Tm–Ho fiber laser [J]. IEEE Photonics Technology Letters, 2007, 19(12): 934-936. doi: 10.1109/LPT.2007.898877 [24] Antipov S, Hudson D D, Fuerbach A, et al. High-power mid-infrared femtosecond fiber laser in the water vapor transmission window [J]. Optica, 2016, 3(12): 1373. doi: 10.1364/OPTICA.3.001373 [25] Woodward R I, Majewski M R, Jackson S D. Mode-locked dysprosium fiber laser: Picosecond pulse generation from 2.97 to 3.30 μm [J]. APL Photonics, 2018, 3(11): 116106. doi: 10.1063/1.5045799 [26] Li J, Hudson D D, Liu Y, et al. Efficient 2.87 μm fiber laser passively switched using a semiconductor saturable absorber mirror [J]. Optics Letters, 2012, 37(18): 3747. doi: 10.1364/OL.37.003747 [27] Ma J, Qin Z, Xie G, et al. Review of mid-infrared mode-locked laser sources in the 2.0 μm–3.5 μm spectral region [J]. Applied Physics Reviews, 2019, 6(2): 021317. doi: 10.1063/1.5037274 [28] Wang Y, Jobin F, Duval S, et al. Ultrafast Dy3+: fluoride fiber laser beyond 3 μm [J]. Optics Letters, 2019, 44(2): 395-398. doi: 10.1364/OL.44.000395 [29] Mirov S B, Fedorov V V, Martyshkin D V, et al. Progress in mid-IR Cr2+ and Fe2+ doped Ⅱ-Ⅵ materials and lasers [Invited] [J]. Optical Materials Express, 2011, 1(5): 898. doi: 10.1364/OME.1.000898 [30] Nagl N, Gröbmeyer S, Pervak V, et al. Directly diode-pumped, Kerr-lens mode-locked, few-cycle Cr: ZnSe oscillator [J]. Optics Express, 2019, 27(17): 24445. doi: 10.1364/OE.27.024445 [31] Pushkin A V, Migal E A, Tokita S, et al. Femtosecond graphene mode-locked Fe: ZnSe laser at 4.4 µm [J]. Optics Letters, 2020, 45(3): 738. doi: 10.1364/OL.384300 [32] Frolov M P, Gordienko V M, Korostelin Y V, et al. Fe 2+ -doped CdSe single crystal: Growth, spectroscopic and laser properties, potential use as a 6 µm broadband amplifier [J]. Laser Physics Letters, 2017, 14(2): 025001. doi: 10.1088/1612-202X/aa5130 [33] Frolov M P, Korostelin Y V, Kozlovsky V I, et al. 2 mJ room temperature Fe: CdTe laser tunable from 5.1 to 6.3 μm [J]. Optics Letters, 2019, 44(22): 5453. doi: 10.1364/OL.44.005453 [34] Silva de Oliveira V, Ruehl A, Masłowski P, et al. Intensity noise optimization of a mid-infrared frequency comb difference-frequency generation source [J]. Optics Letters, 2020, 45(7): 1914. doi: 10.1364/OL.391195 [35] Foreman S M, Jones D J, Ye J. Flexible and rapidly configurable femtosecond pulse generation in the mid-IR [J]. Optics Letters, 2003, 28(5): 370. doi: 10.1364/OL.28.000370 [36] He J, Li Y. Design of on-chip mid-IR frequency comb with ultra-low power pump in near-IR [J]. Optics Express, 2020, 28(21): 30771. doi: 10.1364/OE.401881 [37] Lu J, Surya J B, Liu X, et al. Periodically poled thin-film lithium niobate microring resonators with a second-harmonic generation efficiency of 250, 000%/W [J]. Optica, 2019, 6(12): 1455. doi: 10.1364/OPTICA.6.001455 [38] Chang L, Li Y, Volet N, et al. Thin film wavelength converters for photonic integrated circuits [J]. Optica, 2016, 3(5): 531. doi: 10.1364/OPTICA.3.000531 [39] Yan M, Luo P L, Iwakuni K, et al. Mid-infrared dual-comb spectroscopy with electro-optic modulators [J]. Light: Science & Applications, 2017, 6(10): 1-8. [40] Lind A J, Kowligy A, Timmers H, et al. Mid-infrared frequency comb generation and spectroscopy with few-cycle pulses and χ(2) nonlinear optics [J]. Physical Review Letters, 2020, 124(13): 133904. doi: 10.1103/PhysRevLett.124.133904 [41] Reid D T, Gale B J S, Sun J. Frequency comb generation and carrier-envelope phase control in femtosecond optical parametric oscillators [J]. Laser Physics, 2008, 18(2): 87-103. doi: 10.1134/S1054660X08020011 [42] Iwakuni K, Porat G, Bui T Q, et al. Phase-stabilized 100 mW frequency comb near 10 μm [J]. Applied Physics B, 2018, 124(7): 128. doi: 10.1007/s00340-018-6996-8 [43] Adler F, Cossel K C, Thorpe M J, et al. Phase-stabilized, 15 W frequency comb at 2.8–4.8 μm [J]. Optics Letters, 2009, 34(9): 1330. doi: 10.1364/OL.34.001330 [44] Leindecker N, Marandi A, Byer R L, et al. Octave-spanning ultrafast OPO with 2.6-6.1 µm instantaneous bandwidth pumped by femtosecond Tm-fiber laser [J]. Optics Express, 2012, 20(7): 7046. doi: 10.1364/OE.20.007046 [45] Roiz M, Kumar K, Karhu J, et al. Simple method for mid-infrared optical frequency comb generation with dynamic offset frequency tuning [J]. APL Photonics, 2021, 6(2): 026103. doi: 10.1063/5.0038496 [46] Erny C, Moutzouris K, Biegert J, et al. Mid-infrared difference-frequency generation of ultrashort pulses tunable between 3.2 and 4.8 μm from a compact fiber source [J]. Optics Letters, 2007, 32(9): 1138. doi: 10.1364/OL.32.001138 [47] Maidment L, Schunemann P G, Reid D T. Molecular fingerprint-region spectroscopy from 5 to 12 μm using an orientation-patterned gallium phosphide optical parametric oscillator [J]. Optics Letters, 2016, 41(18): 4261. doi: 10.1364/OL.41.004261 [48] Vainio M, Karhu J. Fully stabilized mid-infrared frequency comb for high-precision molecular spectroscopy [J]. Optics Express, 2017, 25(4): 4190. doi: 10.1364/OE.25.004190 [49] Gale B J S, Sun J H, Reid D T. Composite frequency comb spanning 0.4-2.4 μm from a femtosecond Ti: Sapphire laser and synchronously pumped optical parametric oscillator[C]//2007 European Conference on Lasers and Electro-Optics and the International Quantum Electronics Conference, 2007. [50] Alfano R R, Shapiro S L. Emission in the region 4000 to 7000 Å via four-photon coupling in glass [J]. Physical Review Letters, 1970, 24(11): 584. [51] Lesko D M B, Timmers H, Xing S, et al. A six-octave optical frequency comb from a scalable few-cycle erbium fibre laser [J]. Nature Photonics, 2021, 15(4): 281-286. doi: 10.1038/s41566-021-00778-y [52] Yuan J, Kang Z, Li F, et al. Mid-infrared octave-spanning supercontinuum and frequency comb generation in a suspended germanium-membrane ridge waveguide [J]. Journal of Lightwave Technology, IEEE, 2017, 35(14): 2994-3002. doi: 10.1109/JLT.2017.2703644 [53] Kowligy A S, Lind A, Hickstein D D, et al. Mid-infrared frequency comb generation via cascaded quadratic nonlinearities in quasi-phase-matched waveguides [J]. Optics Letters, 2018, 43(8): 1678. doi: 10.1364/OL.43.001678 [54] Guo H, Herkommer C, Billat A, et al. Mid-infrared frequency comb via coherent dispersive wave generation in silicon nitride nanophotonic waveguides [J]. Nature Photonics, 2018, 12(6): 330-335. doi: 10.1038/s41566-018-0144-1 [55] Faist J, Villares G, Scalari G, et al. Quantum cascade laser frequency combs [J]. Nanophotonics, 2016, 5(2): 272-291. doi: 10.1515/nanoph-2016-0015 [56] Tatham M C, Ryan J F, Foxon C T. Time-resolved Raman measurements of intersubband relaxation in GaAs quantum wells [J]. Physical Review Letters, 1989, 63(15): 1637-1640. doi: 10.1103/PhysRevLett.63.1637 [57] Wang C Y, Kuznetsova L, Gkortsas V M, et al. Mode-locked pulses from mid-infrared quantum cascade lasers [J]. Optics Express, 2009, 17(15): 12929. doi: 10.1364/OE.17.012929 [58] Hugi A, Villares G, Blaser S, et al. Mid-infrared frequency comb based on a quantum cascade laser [J]. Nature, 2012, 492(7428): 229-233. doi: 10.1038/nature11620 [59] Hillbrand J, Andrews A M, Detz H, et al. Coherent injection locking of quantum cascade laser frequency combs [J]. Nature Photonics, 2019, 13(2): 101-104. doi: 10.1038/s41566-018-0320-3 [60] Consolino L, Nafa M, Cappelli F, et al. Fully phase-stabilized quantum cascade laser frequency comb [J]. Nature Communications, 2019, 10(1): 2938. doi: 10.1038/s41467-019-10913-7 [61] Villares G, Faist J. Quantum cascade laser combs: effects of modulation and dispersion [J]. Optics Express, 2015, 23(2): 1651. doi: 10.1364/OE.23.001651 [62] Henry N, Burghoff D, Hu Q, et al. Temporal characteristics of quantum cascade laser frequency modulated combs in long wave infrared and THz regions [J]. Optics Express, 2018, 26(11): 14201. doi: 10.1364/OE.26.014201 [63] Opačak N, Schwarz B. Theory of frequency-modulated combs in lasers with spatial hole burning, dispersion, and Kerr nonlinearity [J]. Physical Review Letters, 2019, 123(24): 1-5. [64] Piccardo M, Schwarz B, Kazakov D, et al. Frequency combs induced by phase turbulence [J]. Nature, 2020, 582(7812): 360-364. doi: 10.1038/s41586-020-2386-6 [65] Komagata K, Shehzad A, Hamrouni M, et al. All-mid-infrared stabilized quantum cascade laser frequency comb with 30-kHz frequency stability at 7.7 μm[C]//CLEO: Science and Innovations 2021: STu1H.3. [66] Zhou H, Geng Y, Cui W, et al. Soliton bursts and deterministic dissipative Kerr soliton generation in auxiliary-assisted microcavities [J]. Light: Science & Applications, 2019, 8(1): 50. [67] Wang W, Chu S T, Little B E, et al. Dual-pump Kerr micro-cavity optical frequency comb with varying FSR spacing [J]. Scientific Reports, 2016, 6(1): 28501. doi: 10.1038/srep28501 [68] Lu Z, Chen H J, Wang W, et al. Synthesized soliton crystals [J]. Nature Communications, 2021, 12(1): 3179. doi: 10.1038/s41467-021-23172-2 [69] Del’haye P, Schliesser A, Arcizet O, et al. Optical frequency comb generation from a monolithic microresonator [J]. Nature, 2007, 450(7173): 1214-1217. doi: 10.1038/nature06401 [70] Herr T, Hartinger K, Riemensberger J, et al. Universal formation dynamics and noise of Kerr-frequency combs in microresonators [J]. Nature Photonics, 2012, 6(7): 480-487. doi: 10.1038/nphoton.2012.127 [71] Zhang X, Zhao Y. Research progress of microresonator-based optical frequency combs [J]. Acta Optica Sinica, 2021, 41(8): 0823014. (in Chinese) doi: 10.3788/AOS202141.0823014 [72] Yao B, Liu Y, Huang S, et al. Broadband gate-tunable terahertz plasmons in graphene heterostructures [J]. Nature Photon, 2018, 12: 22-28. doi: https://doi.org/10.1038/s41566-017-0054-7 [73] Del’haye P, Herr T, Gavartin E, et al. Octave spanning tunable frequency comb from a microresonator [J]. Physical Review Letters, 2011, 107(6): 063901. doi: 10.1103/PhysRevLett.107.063901 [74] Chen H J, Ji Q X, Wang H, et al. Chaos-assisted two-octave-spanning microcombs [J]. Nature Communications, 2020, 11(1): 2336. doi: 10.1038/s41467-020-15914-5 [75] Yu M, Okawachi Y, Griffith A G, et al. Mode-locked mid-infrared frequency combs in a silicon microresonator [J]. Optica, 2016, 3(8): 854. doi: 10.1364/OPTICA.3.000854 [76] Xuan Y, Liu Y, Varghese L T, et al. High-Q silicon nitride microresonators exhibiting low-power frequency comb initiation [J]. Optica, 2016, 3(11): 1171. doi: 10.1364/OPTICA.3.001171 [77] Luke K, Okawachi Y, Lamont M R E, et al. Broadband mid-infrared frequency comb generation in a Si(3)N(4) microresonator [J]. Optics Letters, 2015, 40(21): 4823. doi: 10.1364/OL.40.004823 [78] Guo Y, Wang J, Han Z, et al. Power-efficient generation of two-octave mid-IR frequency combs in a germanium microresonator [J]. Nanophotonics, 2018, 7(8): 1461-1467. doi: 10.1515/nanoph-2017-0131 [79] Jiang S, Guo C, Fu H, et al. Mid-infrared Raman lasers and Kerr-frequency combs from an all-silica narrow-linewidth microresonator/fiber laser system [J]. Optics Express, 2020, 28(25): 38304. doi: 10.1364/OE.412157 [80] Suh M G, Yang Q F, Yang K Y, et al. Microresonator soliton dual-comb spectroscopy [J]. Science, 2016, 354(6312): 600-603. doi: 10.1126/science.aah6516 [81] Su P, Han Z, Kita D, et al. Monolithic on-chip mid-IR methane gas sensor with waveguide-integrated detector [J]. Applied Physics Letters, 2019, 114(5): 051103. doi: 10.1063/1.5053599 [82] Bailey D M, Zhao G, Fleisher A J. Precision spectroscopy of nitrous oxide isotopocules with a cross-dispersed spectrometer and a mid-Infrared frequency comb [J]. Analytical Chemistry, 2020, 92(20): 13759-13766. doi: 10.1021/acs.analchem.0c01868 [83] Abbas M A, Pan Q, Mandon J, et al. Time-resolved mid-infrared dual-comb spectroscopy [J]. Scientific Reports, 2019, 9(1): 17247. doi: https://doi.org/10.1038/s41598-019-53825-8 [84] Liang Q, Chan Y C, Changala P B, et al. Ultrasensitive multispecies spectroscopic breath analysis for real-time health monitoring and diagnostics [J]. Proceedings of the National Academy of Sciences, 2021, 118(40): e2105063118. doi: 10.1073/pnas.2105063118 [85] Lin H, Luo Z, Gu T, et al. Mid-infrared integrated photonics on silicon: a perspective [J]. Nanophotonics, 2017, 7(2): 393-420. doi: 10.1515/nanoph-2017-0085 [86] Sterczewski L A, Bagheri M, Frez C, et al. Mid-infrared dual-comb spectroscopy with room-temperature bi-functional interband cascade lasers and detectors [J]. Applied Physics Letters, 2020, 116(14): 141102. doi: 10.1063/1.5143954 [87] Yao B, Huang S W, Liu Y, et al. Gate-tunable frequency combs in graphene–nitride microresonators [J]. Nature, 2018, 558(7710): 410-414. doi: 10.1038/s41586-018-0216-x [88] Tan T, Yuan Z, Zhang H, et al. Multispecies and individual gas molecule detection using Stokes solitons in a graphene over-modal microresonator [J]. Nature Communications, 2021, 12(1): 6716. doi: 10.1038/s41467-021-26740-8 [89] Zhang L, Ding J, Zheng H, et al. Ultra-thin high-efficiency mid-infrared transmissive Huygens meta-optics [J]. Nature Communications, 2018, 9(1): 1481. doi: 10.1038/s41467-018-03831-7 [90] Zhang X, Cao Q T, Wang Z, et al. Symmetry-breaking-induced nonlinear optics at a microcavity surface [J]. Nature Photonics, 2019, 13(1): 21-24. doi: 10.1038/s41566-018-0297-y [91] Jiang X, Shao L, Zhang S X, et al. Chaos-assisted broadband momentum transformation in optical microresonators [J]. Science, 2017, 358(6361): 344-347. doi: 10.1126/science.aao0763 [92] Diddams S A, Vahala K, Udem T. Optical frequency combs: Coherently uniting the electromagnetic spectrum. [J]. Science, 2020, 369(6501): eaay3676. doi: 10.1126/science.aay3676 [93] Stern B, Ji X, Okawachi Y, et al. Battery-operated integrated frequency comb generator [J]. Nature, 2018, 562(7727): 401-405. doi: 10.1038/s41586-018-0598-9 [94] Shen B, Chang L, Liu J, et al. Integrated turnkey soliton microcombs [J]. Nature, 2020, 582(7812): 365-369. doi: 10.1038/s41586-020-2358-x [95] Tan T, Peng C, Yuan Z, et al. Predicting Kerr soliton combs in microresonators via deep neural networks [J]. Journal of Lightwave Technology, 2020, 38(23): 6591-6599. doi: 10.1109/JLT.2020.3015586 [96] Xu X, Tan M, Corcoran B, et al. 11 TOPS photonic convolutional accelerator for optical neural networks [J]. Nature, 2021, 589(7840): 44-51. doi: 10.1038/s41586-020-03063-0 [97] Feldmann J, Youngblood N, Karpov M, et al. Parallel convolutional processing using an integrated photonic tensor core [J]. Nature, 2021, 589(7840): 52-58. doi: 10.1038/s41586-020-03070-1