Self-referencing turns pulsed laser systems into self-referenced frequency combs.Such frequency combs allow counting of optical frequencies and have a wide range of applications.The required optical bandwidth to imple...Self-referencing turns pulsed laser systems into self-referenced frequency combs.Such frequency combs allow counting of optical frequencies and have a wide range of applications.The required optical bandwidth to implement self-referencing is typically obtained via nonlinear broadening in optical fibers.Recent advances in the field of Kerr frequency combs have provided a path toward the development of compact frequency comb sources that provide broadband frequency combs,exhibit microwave repetition rates and are compatible with on-chip photonic integration.These devices have the potential to significantly expand the use of frequency combs.Yet to date,self-referencing of such Kerr frequency combs has only been attained by applying conventional,fiber-based broadening techniques.Here we demonstrate external broadening-free self-referencing of a Kerr frequency comb.An optical spectrum spanning two-thirds of an octave is directly synthesized from a continuous wave laser-driven silicon nitride microresonator using temporal dissipative Kerr soliton formation and soliton Cherenkov radiation.Using this coherent bandwidth and two continuous wave transfer lasers in a 2f–3f self-referencing scheme,we are able to detect the offset frequency of the soliton Kerr frequency comb.By stabilizing the repetition rate to a radio frequency reference,the self-referenced frequency comb is used to count and track the continuous wave pump laser’s frequency.This work demonstrates the principal ability of soliton Kerr frequency combs to provide microwave-to-optical clockworks on a chip.展开更多
Kerr frequency combs have been attracting significant interest due to their rich physics and broad applications in metrology,microwave photonics,and telecommunications.In this review,we first introduce the fundamental...Kerr frequency combs have been attracting significant interest due to their rich physics and broad applications in metrology,microwave photonics,and telecommunications.In this review,we first introduce the fundamental physics,master equations,simulation methods,and dynamic process of Kerr frequency combs.We then analyze the most promising material platform for realizing Kerr frequency combs—silicon nitride on insulator(SNOI)in comparison with other material platforms.Moreover,we discuss the fabrication methods,process optimization as well as tuning and measurement schemes of SNOI-based Kerr frequency combs.Furthermore,we highlight several emerging applications of Kerr frequency combs in metrology,including spectroscopy,ranging,and timing.Finally,we summarize this review and envision the future development of chip-scale Kerr frequency combs from the viewpoint of theory,material platforms,and tuning methods.展开更多
By overcoming fabrication limitations, we have successfully fabricated silica toroid microcavities with both large diameter(of 1.88 mm) and ultra-high-Q factor(of 3.3 × 10~8) for the first time, to the best of ou...By overcoming fabrication limitations, we have successfully fabricated silica toroid microcavities with both large diameter(of 1.88 mm) and ultra-high-Q factor(of 3.3 × 10~8) for the first time, to the best of our knowledge. By employing these resonators, we have further demonstrated low-threshold Kerr frequency combs on a silicon chip,which allow us to obtain a repetition rate as low as 36 GHz. Such a low repetition rate frequency comb can now bedirectly measured through a commercialized optical-electronic detector.展开更多
The optical frequency comb has attracted considerable interest due to its diverse applications in optical atomic clocks,ultra-low-noise microwave generation,dual-comb spectroscopy,and optical communications.The merits...The optical frequency comb has attracted considerable interest due to its diverse applications in optical atomic clocks,ultra-low-noise microwave generation,dual-comb spectroscopy,and optical communications.The merits of large frequency spacing,high integration,and low power consumption have shown that microresonator-based Kerr optical frequency combs will become mainstream in the future.Two methods of pump frequency tuning and self-injection locking were used to obtain Kerr combs in the same silicon nitride microresonators with free spectral ranges of 50 GHz and 100 GHz.Singlesoliton combs are realized with both methods.Simplicity,pump power,spectrum bandwidth,conversion efficiency,and linewidth are compared and analyzed.Our results show that the advantages of pump frequency tuning are a wider spectrum and higher soliton power while the advantages of self-injection locking are simplicity,compactness,low cost,significant linewidth narrowing,and high conversion efficiency.展开更多
Simultaneous Kerr comb formation and second-harmonic generation with on-chip microresonators can greatly facilitate comb self-referencing for optical clocks and frequency metrology.Moreover,the presence of both second...Simultaneous Kerr comb formation and second-harmonic generation with on-chip microresonators can greatly facilitate comb self-referencing for optical clocks and frequency metrology.Moreover,the presence of both second-and third-order nonlinearities results in complex cavity dynamics that is of high scientific interest but is still far from being well-understood.Here,we demonstrate that the interaction between the fundamental and the second-harmonic waves can provide an entirely new way of phase matching for four-wave mixing in optical microresonators,enabling the generation of optical frequency combs in the normal dispersion regime under conditions where comb creation is ordinarily prohibited.We derive new coupled time-domain mean-field equations and obtain simulation results showing good qualitative agreement with our experimental observations.Our findings provide a novel way of overcoming the dispersion limit for simultaneous Kerr comb formation and second-harmonic generation,which might prove to be especially important in the near-visible to visible range where several atomic transitions commonly used for the stabilization of optical clocks are located and where the large normal material dispersion is likely to dominate.展开更多
Chip-based frequency combs have attracted increasing attention in recent years due to the advantages of small size,integrability, low power consumption, and large re-frequency range. Continuous and deterministic gener...Chip-based frequency combs have attracted increasing attention in recent years due to the advantages of small size,integrability, low power consumption, and large re-frequency range. Continuous and deterministic generation of optical frequency combs is critical for the development of diverse applications. In this work, an integrated design of a computer-program-controlled optical frequency comb generation scheme is developed, whereby the optical frequency comb generation and monitoring units are housed inside an aluminum box. Through this improvement, an optical frequency comb with a free spectral range(FSR) of 100.3 GHz can be generated and maintained continuously for a duration of >48 h.It is varied that the control method is highly effective during 1000 startup tests. With statistical analysis, the startup probability and mean time of the single-soliton state is 100% and as short as 1.5 s, respectively. Besides, chaotic states with a startup probability of 100% and a mean time of 0.31 s are also generated with the same program. The self-injection-locked generation method is still less stable and shorter in duration, and it requires a different state for each generation, which is capable of generating the Kerr optical frequency comb more consistently and more rapidly.展开更多
Low-noise microwave oscillators are cornerstones for wireless communication,radar and clocks.The employment and optimization of optical frequency combs have enabled photonic microwave synthesizers with unrivalled nois...Low-noise microwave oscillators are cornerstones for wireless communication,radar and clocks.The employment and optimization of optical frequency combs have enabled photonic microwave synthesizers with unrivalled noise performance and bandwidth breaking the bottleneck of those electronic counterparts.Emerging interest is to use chip-based Kerr frequency combs,namely microcombs.Today microcombs built on photonic integrated circuits feature small size,weight and power consumption,and can be manufactured to oscillate at any frequency ranging from microwave to millimeter-wave band.A monolithic microcomb-based microwave oscillator requires integration of lasers,photodetectors and nonlinear microresonators on a common substrate,which however has still remained elusive.Here,we demonstrate the first,fully hybrid-integrated,microcomb-based microwave oscillator at 10.7 GHz.The chip device,powered by a customized microelectronic circuit,leverages hybrid integration of a high-power DFB laser,a silicon nitride microresonator of a quality factor exceeding 25× 10^(6),and a high-speed photodetector chip of 110 GHz bandwidth(3 dB)and 0.3 A/W responsivity.Each component represents the state of the art of its own class,yet also allows large-volume manufacturing with low cost using established CMOS and Ⅲ-Ⅴ foundries.The hybrid chip outputs an ultralow-noise laser of 6.9 Hz intrinsic linewidth,a coherent microcomb of 10.7 GHz repetition rate,and a 10.7 GHz microwave carrier of 6.3 mHz linewidth-all the three functions in one entity occupying a footprint of only 76 mm^(2).Furthermore,harnessing the nonlinear laser-microresonator interaction,we observe and maneuver a unique noise-quenching dynamics within discrete microcomb states,which offers immunity to laser current noise,suppression of microwave phase noise by more than 20 dB,and improvement of microwave power by up to 10 dB.The ultimate microwave phase noise reaches-75/-105/-130dBc/Hz at 1/10/100 kHz Fourier offset frequency.Our results can reinvigorate our information society for communication,sensing,imaging,timing and precision measurement.展开更多
The dissipative Kerr soliton(DKS)frequency comb exhibits broad and narrow-linewidth frequency modes,which make it suitable for quantum communication.However,a scalable quantum network based on multiple independent com...The dissipative Kerr soliton(DKS)frequency comb exhibits broad and narrow-linewidth frequency modes,which make it suitable for quantum communication.However,a scalable quantum network based on multiple independent combs is still a challenge due to fabrication-induced frequency mismatches.This limitation becomes critical in measurement-deviceindependent quantum key distribution,which requires high visibility of Hong–Ou–Mandel interference between multiple frequency channels.Here,we experimentally demonstrate two independent DKS combs with 10 spectrally aligned lines without any frequency locking system.The visibility for individual comb-line pairs reaches up to 46.72%±0.63%via precision frequency translation,establishing a foundation for deploying DKS combs in multi-user quantum networks.展开更多
Dissipative Kerr solitons(DKS) have long been suffering from poor power conversion efficiency when driven by continuous-wave lasers. By deriving the critical coupling condition of a multimode nonlinear optics system i...Dissipative Kerr solitons(DKS) have long been suffering from poor power conversion efficiency when driven by continuous-wave lasers. By deriving the critical coupling condition of a multimode nonlinear optics system in a generalized theoretical framework,two efficiency limitations of the conventional pump method of DKS are revealed: the effective coupling rate is too small and is also power-dependent. A general approach is provided to resolve this challenge by introducing two types of nonlinear couplers to couple the soliton cavity and CW input through nonlinear processes. The collective coupler opens multiple coupling channels and the self-adaptive coupler builds a power-independent effective external coupling rate to the DKS for approaching the generalized critical coupling condition, which promises near-unity power conversion efficiencies. For instance, a conversion efficiency exceeding 90% is predicted for aluminum nitride microrings with a nonlinear coupler utilizing second-harmonic generation. The mechanism applies to various nonlinear processes, including Raman and Brillouin scattering, and thus paves the way for micro-solitons toward practical applications.展开更多
基金supported by the European Space Agency(ESA)contract ESTEC CN 4000108280/12/NL/PAthe Defense Advanced Research Projects Agency(DARPA)contract W911NF-11-1-0202(QuASAR)+4 种基金the Swiss National Science Foundationsupported by the Air Force Office of Scientific Research,Air Force Material Command,under award FA9550-15-1-0099support from the ESA via contract ESTEC CN 4000105962/12/NL/PAsupport by the Marie Curie IIF Fellowshipsupport from the Hasler foundation and support from the‘EPFL Fellows’fellowship program co-funded by Marie Curie,FP7 Grant agreement no.291771。
文摘Self-referencing turns pulsed laser systems into self-referenced frequency combs.Such frequency combs allow counting of optical frequencies and have a wide range of applications.The required optical bandwidth to implement self-referencing is typically obtained via nonlinear broadening in optical fibers.Recent advances in the field of Kerr frequency combs have provided a path toward the development of compact frequency comb sources that provide broadband frequency combs,exhibit microwave repetition rates and are compatible with on-chip photonic integration.These devices have the potential to significantly expand the use of frequency combs.Yet to date,self-referencing of such Kerr frequency combs has only been attained by applying conventional,fiber-based broadening techniques.Here we demonstrate external broadening-free self-referencing of a Kerr frequency comb.An optical spectrum spanning two-thirds of an octave is directly synthesized from a continuous wave laser-driven silicon nitride microresonator using temporal dissipative Kerr soliton formation and soliton Cherenkov radiation.Using this coherent bandwidth and two continuous wave transfer lasers in a 2f–3f self-referencing scheme,we are able to detect the offset frequency of the soliton Kerr frequency comb.By stabilizing the repetition rate to a radio frequency reference,the self-referenced frequency comb is used to count and track the continuous wave pump laser’s frequency.This work demonstrates the principal ability of soliton Kerr frequency combs to provide microwave-to-optical clockworks on a chip.
基金the National Key Research and Development Program of China(2021YFA1401000,2021YFB2801600,and 2017YFF0206104)National Natural Science Foundation of China(62075114 and 62175121)the Beijing Natural Science Foundation(4212050)。
文摘Kerr frequency combs have been attracting significant interest due to their rich physics and broad applications in metrology,microwave photonics,and telecommunications.In this review,we first introduce the fundamental physics,master equations,simulation methods,and dynamic process of Kerr frequency combs.We then analyze the most promising material platform for realizing Kerr frequency combs—silicon nitride on insulator(SNOI)in comparison with other material platforms.Moreover,we discuss the fabrication methods,process optimization as well as tuning and measurement schemes of SNOI-based Kerr frequency combs.Furthermore,we highlight several emerging applications of Kerr frequency combs in metrology,including spectroscopy,ranging,and timing.Finally,we summarize this review and envision the future development of chip-scale Kerr frequency combs from the viewpoint of theory,material platforms,and tuning methods.
基金National Key R&D Program of China(2017YFA0303703,2016YFA0302500)National Natural Science Foundation of China(NSFC)(61435007,11574144,61475099)+1 种基金Natural Science Foundation of Jiangsu Province,China(BK20150015)Fundamental Research Funds for the Central Universities(021314380086)
文摘By overcoming fabrication limitations, we have successfully fabricated silica toroid microcavities with both large diameter(of 1.88 mm) and ultra-high-Q factor(of 3.3 × 10~8) for the first time, to the best of our knowledge. By employing these resonators, we have further demonstrated low-threshold Kerr frequency combs on a silicon chip,which allow us to obtain a repetition rate as low as 36 GHz. Such a low repetition rate frequency comb can now bedirectly measured through a commercialized optical-electronic detector.
基金supported by the National Key R&D Program of China(No.2020YFB2205804)the National Natural Science Foundation of China(No.62075240)。
文摘The optical frequency comb has attracted considerable interest due to its diverse applications in optical atomic clocks,ultra-low-noise microwave generation,dual-comb spectroscopy,and optical communications.The merits of large frequency spacing,high integration,and low power consumption have shown that microresonator-based Kerr optical frequency combs will become mainstream in the future.Two methods of pump frequency tuning and self-injection locking were used to obtain Kerr combs in the same silicon nitride microresonators with free spectral ranges of 50 GHz and 100 GHz.Singlesoliton combs are realized with both methods.Simplicity,pump power,spectrum bandwidth,conversion efficiency,and linewidth are compared and analyzed.Our results show that the advantages of pump frequency tuning are a wider spectrum and higher soliton power while the advantages of self-injection locking are simplicity,compactness,low cost,significant linewidth narrowing,and high conversion efficiency.
基金supported in part by the National Science Foundation under grant ECCS-1509578the Air Force Office of Scientific Research under grant FA9550-15-1-0211+3 种基金the DARPA PULSE program through grant W31P40-13-1-0018 from AMRDECfunding from the National Natural Science Foundation of China under grant 6169190011/12,61420106003the Beijing Natural Science Foundation under grant 4172029funding from the Marsden Fund and the Rutherford Discovery Fellowships of the Royal Society of New Zealand.
文摘Simultaneous Kerr comb formation and second-harmonic generation with on-chip microresonators can greatly facilitate comb self-referencing for optical clocks and frequency metrology.Moreover,the presence of both second-and third-order nonlinearities results in complex cavity dynamics that is of high scientific interest but is still far from being well-understood.Here,we demonstrate that the interaction between the fundamental and the second-harmonic waves can provide an entirely new way of phase matching for four-wave mixing in optical microresonators,enabling the generation of optical frequency combs in the normal dispersion regime under conditions where comb creation is ordinarily prohibited.We derive new coupled time-domain mean-field equations and obtain simulation results showing good qualitative agreement with our experimental observations.Our findings provide a novel way of overcoming the dispersion limit for simultaneous Kerr comb formation and second-harmonic generation,which might prove to be especially important in the near-visible to visible range where several atomic transitions commonly used for the stabilization of optical clocks are located and where the large normal material dispersion is likely to dominate.
基金supported by the National Key R&D Program of China (No.2020YFB2205804)the National Natural Science Foundation of China (No.62075240)。
文摘Chip-based frequency combs have attracted increasing attention in recent years due to the advantages of small size,integrability, low power consumption, and large re-frequency range. Continuous and deterministic generation of optical frequency combs is critical for the development of diverse applications. In this work, an integrated design of a computer-program-controlled optical frequency comb generation scheme is developed, whereby the optical frequency comb generation and monitoring units are housed inside an aluminum box. Through this improvement, an optical frequency comb with a free spectral range(FSR) of 100.3 GHz can be generated and maintained continuously for a duration of >48 h.It is varied that the control method is highly effective during 1000 startup tests. With statistical analysis, the startup probability and mean time of the single-soliton state is 100% and as short as 1.5 s, respectively. Besides, chaotic states with a startup probability of 100% and a mean time of 0.31 s are also generated with the same program. The self-injection-locked generation method is still less stable and shorter in duration, and it requires a different state for each generation, which is capable of generating the Kerr optical frequency comb more consistently and more rapidly.
基金support from the National Natural Science Foundation of China(Grant No.12261131503,No.12404436,No.61975121,and No.12404417)Innovation Program for Quantum Science and Technology(2023ZD0301500)+2 种基金National Key R&D Program of China(Grant No.2024YFA1409300),Shenzhen-Hong Kong Cooperation Zone for Technology and Innovation(HZQB-KCZYB2020050)Shenzhen Science and Technology Program(Grant No.RCJC20231211090042078)Guangdong-Hong Kong Technology Cooperation Funding Scheme(Grant No.2024A0505040008).
文摘Low-noise microwave oscillators are cornerstones for wireless communication,radar and clocks.The employment and optimization of optical frequency combs have enabled photonic microwave synthesizers with unrivalled noise performance and bandwidth breaking the bottleneck of those electronic counterparts.Emerging interest is to use chip-based Kerr frequency combs,namely microcombs.Today microcombs built on photonic integrated circuits feature small size,weight and power consumption,and can be manufactured to oscillate at any frequency ranging from microwave to millimeter-wave band.A monolithic microcomb-based microwave oscillator requires integration of lasers,photodetectors and nonlinear microresonators on a common substrate,which however has still remained elusive.Here,we demonstrate the first,fully hybrid-integrated,microcomb-based microwave oscillator at 10.7 GHz.The chip device,powered by a customized microelectronic circuit,leverages hybrid integration of a high-power DFB laser,a silicon nitride microresonator of a quality factor exceeding 25× 10^(6),and a high-speed photodetector chip of 110 GHz bandwidth(3 dB)and 0.3 A/W responsivity.Each component represents the state of the art of its own class,yet also allows large-volume manufacturing with low cost using established CMOS and Ⅲ-Ⅴ foundries.The hybrid chip outputs an ultralow-noise laser of 6.9 Hz intrinsic linewidth,a coherent microcomb of 10.7 GHz repetition rate,and a 10.7 GHz microwave carrier of 6.3 mHz linewidth-all the three functions in one entity occupying a footprint of only 76 mm^(2).Furthermore,harnessing the nonlinear laser-microresonator interaction,we observe and maneuver a unique noise-quenching dynamics within discrete microcomb states,which offers immunity to laser current noise,suppression of microwave phase noise by more than 20 dB,and improvement of microwave power by up to 10 dB.The ultimate microwave phase noise reaches-75/-105/-130dBc/Hz at 1/10/100 kHz Fourier offset frequency.Our results can reinvigorate our information society for communication,sensing,imaging,timing and precision measurement.
基金supported by the National Key Research and Development Program of China(No.2022YFE0137000)the Natural Science Foundation of Jiangsu Province(Nos.BK20240006 and BK20233001)+2 种基金the Leading-Edge Technology Program of Jiangsu Natural Science Foundation(No.BK20192001)the Fundamental Research Funds for the Central Universities,and the Innovation Program for Quantum Science and Technology(Nos.2021ZD0300700 and 2021ZD0301500)the Fundamental Research Funds for the Central Universities(No.2024300324)。
文摘The dissipative Kerr soliton(DKS)frequency comb exhibits broad and narrow-linewidth frequency modes,which make it suitable for quantum communication.However,a scalable quantum network based on multiple independent combs is still a challenge due to fabrication-induced frequency mismatches.This limitation becomes critical in measurement-deviceindependent quantum key distribution,which requires high visibility of Hong–Ou–Mandel interference between multiple frequency channels.Here,we experimentally demonstrate two independent DKS combs with 10 spectrally aligned lines without any frequency locking system.The visibility for individual comb-line pairs reaches up to 46.72%±0.63%via precision frequency translation,establishing a foundation for deploying DKS combs in multi-user quantum networks.
基金supported by the National Natural Science Foundation of China (Grant Nos. 11934012, 12293053, 12374361, 11904316, 61690192, U21A20433, 12104441, 12293052, and U21A6006)the Anhui Provincial Natural Science Foundation (Grant Nos. 2008085QA34, and 2108085MA22)+2 种基金the Major Scientific Project of Zhejiang Laboratory (Grant No. 2020LC0AD01)supported by the Fundamental Research Funds for the Central Universities and University of Science and Technology of China (USTC) Research Funds of the Double First-Class Initiativesupported by the Supercomputing System in the Supercomputing Center of USTC and the USTC Center for Micro and Nanoscale Research and Fabrication。
文摘Dissipative Kerr solitons(DKS) have long been suffering from poor power conversion efficiency when driven by continuous-wave lasers. By deriving the critical coupling condition of a multimode nonlinear optics system in a generalized theoretical framework,two efficiency limitations of the conventional pump method of DKS are revealed: the effective coupling rate is too small and is also power-dependent. A general approach is provided to resolve this challenge by introducing two types of nonlinear couplers to couple the soliton cavity and CW input through nonlinear processes. The collective coupler opens multiple coupling channels and the self-adaptive coupler builds a power-independent effective external coupling rate to the DKS for approaching the generalized critical coupling condition, which promises near-unity power conversion efficiencies. For instance, a conversion efficiency exceeding 90% is predicted for aluminum nitride microrings with a nonlinear coupler utilizing second-harmonic generation. The mechanism applies to various nonlinear processes, including Raman and Brillouin scattering, and thus paves the way for micro-solitons toward practical applications.
