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Resonant electro-optic frequency comb
摘要： High-speed optical telecommunication is enabled by wavelength-division multiplexing, whereby hundreds of individually stabilized lasers encode information within a single-mode optical fibre. Higher bandwidths require higher total optical power, but the power sent into the fibre is limited by optical nonlinearities within the fibre, and energy consumption by the light sources starts to become a substantial cost factor. Optical frequency combs have been suggested to remedy this problem by generating numerous discrete, equidistant laser lines within a monolithic device; however, at present their stability and coherence allow them to operate only within small parameter ranges. Here we show that a broadband frequency comb realized through the electro-optic effect within a high-quality whispering-gallery-mode resonator can operate at low microwave and optical powers. Unlike the usual third-order Kerr nonlinear optical frequency combs, our combs rely on the second-order nonlinear effect, which is much more efficient. Our result uses a fixed microwave signal that is mixed with an optical-pump signal to generate a coherent frequency comb with a precisely determined carrier separation. The resonant enhancement enables us to work with microwave powers that are three orders of magnitude lower than those in commercially available devices. We emphasize the practical relevance of our results to high rates of data communication. To circumvent the limitations imposed by nonlinear effects in optical communication fibres, one has to solve two problems: to provide a compact and fully integrated, yet high-quality and coherent, frequency comb generator; and to calculate nonlinear signal propagation in real time. We report a solution to the first problem.
关键词： optical telecommunication,electro-optic effect,optical frequency combs,wavelength-division multiplexing,whispering-gallery-mode resonator
更新于2025-11-28 14:23:57
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Broadband molecular spectroscopy with optical frequency combs
摘要： Over the past dozen years, optical frequency combs have evolved into valuable tools for broadband molecular spectroscopy. They have already enabled remarkable advances for the measurement of complicated molecular spectra by improving the resolution, accuracy, sensitivity, and measurement times of spectrometric approaches. In this featured article, we trace some recent developments relevant to high-resolution spectroscopy of molecules, especially in the mid-infrared spectral region. We discuss examples that harness the emerging techniques of cavity-enhanced frequency comb spectroscopy and dual-comb spectroscopy and we conclude with a perspective of forthcoming opportunities and challenges.
关键词： optical frequency combs,molecular spectroscopy,dual-comb spectroscopy,cavity-enhanced frequency comb spectroscopy
更新于2025-09-23 15:21:21
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Passive coherent dual-comb spectroscopy based on optical-optical modulation with free running lasers
摘要： Dual-comb spectroscopy is a powerful spectroscopic tool with ultrahigh-resolution, high-sensitivity properties, which opens up opportunities for the parallel detection of multi-species molecules. However, in its conventional form, highly stable laser combs with sophisticated control systems are required to perform dual-comb spectroscopy. Here, a passive mutually coherent dual-comb spectroscopy system via an optical-optical modulation method is addressed, where all fast phase-locking electronics are retired. Without post computer-based phase-correction, a high degree of mutual coherence between the two combs with a relative comb-tooth linewidth of 10 mHz is achieved, corresponding to a coherent time of 100 s. To demonstrate the performance and versatility of the system, the dual comb spectrometer is applied to record the mode-resolved single molecular spectra as well as parallel detected spectra of mixed gases including CO2, CO and C2H2 that well agree with the established spectral parameters. Our technique exhibits flexible wavelength tuning capability in the near-infrared region and can be potentially extended to the mid-infrared region for more applications.
关键词： Optical frequency combs,Molecular spectroscopy,Comb spectroscopy,Optical-optical modulation
更新于2025-09-23 15:19:57
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Accurate laser frequency locking to optical frequency combs under low-signal-to-noise-ratio conditions
摘要： We demonstrate a method for accurately locking the frequency of a continuous-wave laser to an optical frequency comb under conditions where the signal-to-noise ratio is low, too low to accommodate other methods. Our method is typically orders of magnitude more accurate than conventional wavemeters and can considerably extend the usable wavelength range of a given optical frequency comb. We illustrate our method by applying it to the frequency control of a dipole lattice trap for an optical lattice clock, a representative case where our method provides significantly better accuracy than other methods.
关键词： optical lattice clock,optical frequency combs,laser frequency locking,low-signal-to-noise-ratio
更新于2025-09-19 17:13:59
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Observation of Arnold Tongues in Coupled Soliton Kerr Frequency Combs
摘要： We demonstrate various regimes of synchronization in systems of two coupled cavity soliton-based Kerr frequency combs. We show subharmonic, harmonic, and harmonic-ratio synchronization of coupled microresonators, and reveal their dynamics in the form of Arnold tongues, structures that are ubiquitous in nonlinear dynamical systems. Our experimental results are well corroborated by numerical simulations based on coupled Lugiato-Lefever equations. This Letter illustrates the newfound degree of flexibility in synchronizing Kerr combs across a wide range of comb spacings and could find applications in time and frequency metrology, spectroscopy, microwave photonics, optical communications, and astronomy.
关键词： synchronization,nonlinear dynamics,Arnold tongues,Kerr frequency combs,microresonators
更新于2025-09-19 17:13:59
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Observation of Laser-Cavity Solitons in Micro-Resonators
摘要： Optical frequency combs based on micro-cavity resonators, also known as ‘micro-combs’, are ready to achieve the full capability of their bulk counterparts but on an integrated footprint [1]. They have enabled major breakthroughs in spectroscopy, communications, microwave photonics, frequency synthesis, optical ranging, quantum sources and metrology. Of particular relevance was the recent experimental implementation of temporal cavity-solitons [2,3]. Temporal cavity-solitons in micro-resonators are described by the well-known Lugiato-Lefever equation. Currently, these self-localised waves form on top of a strong background of radiation, usually containing 95% of the total power [4] and require active control of an external driving laser – a complex process which limits the choice of fundamental parameters such as the repetition-rate. Developing simple methods for controlling and generating highly efficient, self-localised pulses is one of the most compelling challenges to overcome, in anticipation of the widespread use of micro-combs outside of laboratory environments. Here we report the discovery of micro-comb laser cavity-solitons, which are the most efficient class of cavity-solitons because they are intrinsically background-free. Laser cavity-solitons have previously underpinned major breakthroughs in other systems, e.g. for the realisation of efficient semiconductor lasers [5]. By merging their properties with the physics of both micro-resonators and multi-mode systems, we provide a fundamentally new paradigm for the generation, stabilisation and control of self-localised optical pulses in micro-cavities. Our design is inspired to the filter-driven four-wave mixing scheme [6], which is based on a nonlinear micro-cavity nested in a larger fibre-cavity loop. We demonstrate 50 nm wide soliton combs induced with average powers more than one order of magnitude lower than those typically used in state-of-the-art soliton micro-combs [1]. Very importantly, in stark contrast to temporal cavity-solitons based on passive Lugiato-Lefever systems, our bright laser cavity solitons are background-free, and we achieve a mode-efficiency [4] above 75%, compared to typical 1% - 5% for bright solitons realised with standard approaches. Furthermore, we can tune the repetition-rate to well over a megahertz with no-active control.
关键词： Lugiato-Lefever equation,optical frequency combs,micro-combs,micro-resonators,laser cavity-solitons
更新于2025-09-16 10:30:52
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Scrutinizing the Equidistance of Frequency Comb Sources
摘要： Frequency combs have revolutionized frequency metrology, enabling optical clockworks with unprecedended precisions approaching the 10-18 range. Early frequency comb measurements exclusively relied on mode-locked lasers, which provide a periodic waveform as a matter of working principle. In turn, the resulting frequency comb is guaranteed to be absolutely equidistant. While this expectation is ultimately based on theoretical mode-locking models, experimental tests have scrutinized deviations from equidistance of mode-locked laser combs down to the 10-15 level. Experimental tests of equidistance are rather elaborate and typically require beating of different spectral parts of the comb with a reference comb. Such tests have also been performed with microresonator combs, which are not a priori guaranteed to be equidistant from theoretical considerations. Finally, there are rather recent reports of quantum cascade laser combs; yet careful investigations of the equidistance of such sources still appear to be outstanding. Here we propose and demonstrate a novel experimental test for the equidistance of frequency combs.
关键词： metrology,frequency combs,mode-locked lasers,equidistance
更新于2025-09-16 10:30:52
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[IEEE 2019 18th International Conference on Optical Communications and Networks (ICOCN) - Huangshan, China (2019.8.5-2019.8.8)] 2019 18th International Conference on Optical Communications and Networks (ICOCN) - Fast high-resolution spectral sensing with a single frequency comb
摘要： Transmission spectra of a phase-shift fiber Bragg grating and H13CN gas at comb-line-defined resolution of 54.5 MHz are measured within 2 μs using heterodyne detection of a broadband comb and a continuous wave laser.
关键词： frequency combs,spectroscopy,sensing
更新于2025-09-16 10:30:52
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Self-Healing Dynamically Controllable Micro-Comb
摘要： Micro-resonator-based frequency combs, or micro-combs, have gained considerable interest in recent years due to their many potential applications such as high-speed communication systems, spectroscopy and ultrafast optical clocks. Most micro-combs systems are based on laser pumped optical parametric oscillation and are typically non-self-starting, requiring a well-defined warm-up strategy involving smart control. An alternative approach to micro-combs is represented by the Filter-Driven Four-Wave Mixing (FD-FWM) laser, based on a nonlinear micro-resonator nested in a main amplifying fibre cavity. Although this system has demonstrated self-starting regimes, stable operation typically imposes a strict relation between the minimum free-spectral range (FSR) of the main-cavity and the Q-factor of the micro-resonator. The use of longer main-cavity fibre lengths (highly desirable for several positive features, such as a larger gain) results in unrecoverable unstable regimes, i.e. in super-mode instability, which arises from the existence of many oscillating main-cavity modes within each micro-resonator resonance. Here, we report a novel micro-comb scheme based on a three-cavitiy design shown in Fig. 1 (a). Our scheme exhibits the ability to spontaneously recover a set of unstable regimes in the FD-FWM laser. The basic concept is to introduce an intracavity periodic phase change via an additional short-loop fibre cavity, which effectively works as a low-Q, all-pass linear filter. Such a filter creates an irregular frequency-spacing among adjacent modes of the main-cavity loop, weakening the typical four-wave-mixing coupling between them. In sharp contrast to standard FD-FWM scheme, the system is tolerant to a significantly narrower spacing of the main-cavity modes. In the example, the total fibre length of the main-cavity is fixed to 20 metres, corresponding to a main-cavity FSR of 7.5 MHz - more than an order of magnitude lower than the micro-resonator bandwidth (~120MHz). This main-cavity FSR is generally very unstable at any pumping regime in the absence of the additional short-loop fibre cavity. An example of a stable mode-locking state with the properly chosen parameters is shown in Fig. 1(b)-(j). The experimental optical spectrum along with the corresponding intensity autocorrelation traces and RF spectrum are shown in Fig. 1 (b)-(d). A low background in the autocorrelation (AC) trace and a flat RF spectrum indicate the high stability of the generated micro-combs. A frequency comb-assisted spectroscopy is performed to accurately characterize resonances in the micro-cavity and the additional all-pass resonator filter, as well as the position of the oscillating comb lines (Fig. 1 (e)-(g)). The intra-cavity spectrum reveals that there is only a single longitudinal mode lasing within each micro-cavity resonance, regardless of the high modal density of the main cavity. Our analysis reveals that the introduced periodical spectral-phase modulation dominates the emergence of the oscillating modes.
关键词： Filter-Driven Four-Wave Mixing,micro-combs,frequency combs,optical parametric oscillation,micro-resonator
更新于2025-09-12 10:27:22
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Frequency Comb Generation and Conversion in Non-Centrosymmetric Optical Microresonators
摘要： Optical frequency combs have become the key technology in optical precision measurements [1], bear a high potential for broadband, high-resolution molecular spectroscopy [2] and are promising to advance future optical clocks [3]. For low-power, compact and mobile applications, high-repetition-rate combs such as continuous-wave-pumped Kerr combs [4] and soliton frequency combs based on a third-order nonlinearity [5] have turned out to be especially useful. Thus far, most of these frequency combs operate in the near-infrared (NIR) spectral regime around 1550 nm for reasons such as chromatic material dispersion. Many applications ranging from astronomical spectroscopy, optical clocks and quantum physics all the way to molecular sensing, however, require the frequency combs to be centered in the ultraviolet (UV), visible (VIS) and mid-infrared (MIR) spectral regimes [3,6-8]. In this contribution, we present pathways towards achieving this goal. In a first approach [9], synchronously pumped high-Q whispering gallery-mode resonators with a second-order nonlinearity are employed to convert a high-repetition-rate (21 GHz) NIR comb into the VIS and UV wavelength regimes at the same time (see Fig. 1(a)), using an engineered quasi-phase-matching structure. Furthermore, via degenerate optical parametric oscillation (OPO) the sub-harmonic of the initial comb in the MIR can be generated; non-degenerate OPO even allows for wavelength-tunable signal and idler combs. These results pave the way towards a phase-coherent link of frequency combs across the UV, VIS, NIR and MIR spectral regions in a single microresonator. This could allow for low-power self-referenced frequency combs without the need for octave-spanning spectra (e.g. via 3f-4f-interferometry). Additionally, we show first results towards achieving frequency combs purely based on second-order nonlinearities in few-mode optical microresonators (see Fig. 1(b)). This type of combs not only allows to potentially access wavelength regimes different from the NIR, but they also come with the opportunity to use fast electro-optic tuning, a method that is very weak for Kerr microcombs.
关键词： optical frequency combs,nonlinear optics,microresonators,frequency conversion
更新于2025-09-12 10:27:22