Photonics Insights, Volume. 3, Issue 4, R09(2024)
Microcomb technology: from principles to applications Story Video
Fig. 1. Timeline of the microcomb technology development. The four columns from left to right are developments of the application, the design, the principle, and the fabrication, respectively. Abbreviations: DCS, dual-comb spectroscopy; OCT, optical coherence tomography; MIR, mid-infrared; FSO, free-space optical communication; PhCR, photonic crystal ring; SIL, self-injection locked;
Fig. 3. Dynamic evolution of mode-locked soliton formation in a microresonator[11,92] (a) Numerical simulation results. Average intracavity power trace during the laser scan. The colored region shows the existing area of different comb states: soliton state (green), breather solitons with time-variable envelop (yellow), and solitons cannot exist (red). (b) Experimental observation of soliton steps, Top: pump power transmission of a silica microresonator as the pump tunes, exhibiting multiple steps indicative of soliton formation. Middle: imaging of soliton formation corresponding to the scan where the
Fig. 4. Numerical simulation of the microcomb evolution. (a) The evolution process of intracavity optical spectra (top), pulse shapes (middle), and total powers (bottom). (b) Optical spectra under different states marked in (a). (c) Pulse shapes under different states marked in (a).
Fig. 8. Illustration of self-injection microcombs. (a) Concept and principle of self-injection locking and turnkey operation[77]. (b) Self-injection locking of a laser diode to a bulk cavity for microcomb generation[145]. (c) Self-injection locking of a laser diode chip to an integrated SiN microcavity chip for microcomb generation[138]. (d) Bright soliton generated by self-injection locking[86]. (e) The dark pulse is generated by self-injection locking[140]. (f) Suppressed frequency noise[140].
Fig. 9. Optical comb wavelength ranges and
Fig. 17. Electro-optical crystal platforms. (a)
Fig. 22. Recent advances in packaging and integration technologies for microcombs. (a) Hybrid integrated amplifiers with microcavities for microcomb generation[62]. (b) Direct butt-coupling of the laser diode with the microcavity chip for self-injection locking[138]. (c) Photonics wire bonging[226]. (d) Packaged microcomb module with a laser diode butt-coupled with a microcavity chip[77]. (e) The integrated Er-doped amplifier chip[227]. (f) The schematic (left) and the packaged (right) Er-doped laser chip[228]. (g) Single-chip microcomb generators[86].
Fig. 23. Microcombs under different dispersion conditions. (a) Bright soliton under anomalous dispersion[11]. (b) Dark pulse under normal dispersion[72]. (c) Dispersion wave due to high-order dispersion[73]. (d) Quartic soliton supported by fourth dispersion[64]. (e) Bright pulse under near-zero dispersion[252].
Fig. 24. Different dispersion engineering methods. (a) Concentric microring[61]. (b) Coupled rings for single-point dispersion changing[78]. (c) Coupled rings for wideband dispersion changing[68]. (d) PhCR for single-point dispersion changing[65]. (e) PhCR for multiple-point dispersion changing[265].
Fig. 25. Schemes for high-efficiency microcombs. (a) The comparison between the soliton and the dark pulse[277]. (b) The pulse pumped soliton[130]. (c) Pump recycling for high efficiency with dual rings[63]. (d) Interferometric back-coupling for high-efficiency solitons[278]. (e) Interferometric back-coupling for high-efficiency dark pulses[279]. (f) Dispersion engineering for high-efficiency solitons[67]. (g) Soliton laser for high-efficiency microcombs. (h) The electrically empowered microcomb laser[81].
Fig. 26. Noise sources and suppression methods. (a) Different noise sources for the intrinsic linewidth of comb lines[288]. (b) The influence of thermal noise[289]. (c) Intrinsic (top) and effective (bottom) linewidth distribution of comb lines[288]. (d) Self-injection locking for high-coherence lasers[140]. (e) Reduced thermal-optical effect under low temperature[290]. (f) Suppressed thermal noise with laser cooling[289]. (g) Low-noise soliton microcomb operating at the quiet point[176]. Top: spectrum; bottom: phase noise of the repetition rate. (h) KIS for reducing the repetition rate fluctuation[80].
Fig. 27. Microcomb-based frequency standard. The stabilization of the microcomb could be achieved by locking (a) one optical mode and repetition frequency[67], (b) two separate optical modes[42], and (c) repetition frequency and CEO frequency via the f-2f technique[304]. First demonstrations of octave-spanning microcomb on (d) SiN[225], (e) AlN[206], and (f) 4H-SiC[305] platforms. The highly integrated (g) optical clock[34] and (h) optical frequency synthesizer[46] based on dual-comb frequency clockwork.
Fig. 28. Microcomb-based spectroscopy. The direct frequency comb spectroscopy (DFCS) utilizes a single frequency comb for molecular fingerprint recognition, which can measure (a) atomic transition[311] and (b) gas phase[312]. (c) The plasmonic-enhanced DFCS systems[313]. Dual-frequency spectroscopy (DCS) is enabled by a pair of microcombs, which can be generated simultaneously by (d) separately pumping[36], (e) counterpropagating stimulation, and (f) single-pump driving[314]. (g) The microcomb densification via iDFG scheme[50].
Fig. 29. Microcomb based LiDAR. Two kinds of LiDAR schemes, ToF and FMCW, are implemented in microcomb-based LiDAR systems. (a) A pair of separated microcombs[35] and (b) a pair of counter-propagating microcombs[323] are employed for ToF schemes. (c) Microcomb-based dispersive interferometry[324] for accurate ranging under long distances. (d) Principle of parallel FMCW LiDAR[49].
Fig. 32. Microcomb-based optical computing. (a) A SiN soliton microcomb combined with a phase-change material attached to an on-chip waveguide array for tensor core operation[345]. (b) A time-stretch strategy for both the convolution layer and fully connected layer in the optical neural network[51]. (c) Silicon-photonic-assisted highly integrated optical computing processor based on a microcomb[346].
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Haowen Shu, Bitao Shen, Huajin Chang, Junhao Han, Jiong Xiao, Xingjun Wang, "Microcomb technology: from principles to applications," Photon. Insights 3, R09 (2024)
Category: Review Articles
Received: Oct. 31, 2024
Accepted: Dec. 17, 2024
Published Online: Jan. 2, 2025
The Author Email: Haowen Shu (haowenshu@pku.edu.cn), Xingjun Wang (xjwang@pku.edu.cn)
CSTR:32396.14.PI.2024.R09