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- 摘要
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- 实验方案
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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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[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) - 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
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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) - Electro-Optic Frequency Comb Generation in Lithium Niobate Whispering Gallery Mode Resonators
摘要： Optical frequency combs (OFCs) are light sources whose spectra consists of equally spaced frequency lines in the optical domain [1]. They have great potential for improving high-capacity data transfer, all-optical atomic clocks, spectroscopy, and high-precision measurements [2]. In contrast to the traditional third-order nonlinearity based OFC generation methods, we present a new approach which is based on second-order non-linear effects in a whispering gallery mode (WGM) resonator made of lithium niobate (LN) [3,4]. Our system is composed of a resonant hybrid structure comprising an optical LN disk resonator and a microwave copper cavity. The hybrid structure enables highly efficient nonlinear mixing of photons. In this scheme, two continuous waves, one in the optical domain ((cid:2033) = 193 THz) and another in the microwave region (Ω = 8.9 GHz) couple within a LN WGM resonator [5]. The second-order non-linearity of LN leads to frequency comb generation via cascaded symmetric sum and difference frequency generation [6]. In our experiment, the optical pump power is coupled into the WGM by using a standard prism coupling method that is based on frustrated total internal reflection (Fig. 1 (a)). The microwave power is coupled using a coaxial probe coupled attached to the 3-D copper cavity specifically designed to have the microwave cavity resonance to be equal to the optical free spectral range of the LN resonator, required for efficient phase matching. In addition, the cavity design also provides a very good spatial overlap between the microwave and optical modes by confining the microwave field to the rim of the LN disk. In our proof-of-concept experimental demonstration we observe a 1.6 THz long frequency comb centred around 193.5 THz more than180 comb lines by using only 20 dBm of microwave power. Compared to previously reported OFCs generation schemes, this method has two major advantages: inherent phase stability, and better power efficiency. The power efficiency when measured in terms of pi-voltage of the modulator is 25 times better than a commercial Thorlabs modulator.
关键词： second-order non-linearity,whispering gallery mode resonators,electro-optic frequency comb generation,Optical frequency combs,lithium niobate
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) - Highly Flat Optical Frequency Comb Based on the Time Lens Principle
摘要： Broad bandwidth optical frequency combs (OFCs) have received much attention in recent years due to a dramatic growth of their applications, such as spectroscopy measurements, microwave photonics applications, and optical communications. There are several advanced optical superchannel systems, which have been practically implemented by OFCs, such as a Tbit/s coherent optical orthogonal frequency division multiplexing (OFDM) system [1] and Tbit/s single-channel coherent Nyquist pulse transmission systems with high spectral efficiency [2], etc. Those systems require the OFC with a high degree of flatness and broad bandwidth that are difficult to achieve with conventional methods based on sinusoidal phase modulation (SPM).
关键词： microwave photonics,optical frequency combs,Nyquist pulse transmission,OFDM,spectroscopy measurements,optical communications
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) - Dual-Comb Spectroscopy of Acetylene with a Single, Free-Running MIXSEL Generating two Frequency Combs
摘要： Dual-comb spectroscopy combines the advantages of conventional Fourier transform infrared spectroscopy (FTIR) with the measurement speed, stability and accuracy of multiheterodyne beat note detection. Two optical frequency combs (OFCs) with slightly different line spacing beat on a photodetector and convert the optical spectra down to the more accessible radio frequency (RF) domain. This enables an accurate broadband spectrometer without moving parts featuring short measurement time, however, it also requires two mutually locked OFCs with good noise performance which is challenging. Dual-comb modelocked optically pumped semiconductor disk lasers (SDLs) provide a great simplification. The modelocked integrated external-cavity surface emitting laser (MIXSEL) is a special type of ultrafast SDLs which integrates a semiconductor gain and a saturable absorber in a single epitaxial structure and allows for modelocking in a simple and straight cavity. Most recently we increased the modelocked optical bandwidth above 10 nm with pulse durations below 150 fs. With two intracavity birefringent crystals, the initially unpolarized beam is separated onto two spots on the MIXSEL chip, which can be individually pumped. The dual-comb MIXSEL is a straight linear cavity formed by the two end mirrors (i.e. MIXSEL chip and output coupler (OC) and emits two orthogonally polarized OFCs with a slight difference in line spacing from the same cavity with an intrinsically high mutual coherence. Here, we present dual-comb spectroscopy of acetylene with a single, free-running dual-comb MIXSEL at 1030 nm (290 THz). The laser provides more than 10 nm of optical bandwidth usable for spectroscopic interrogations and with a resolution of 2.73 GHz, we can clearly resolve the individual absorption lines with great precision. Without active stabilization and locking electronics, the overlay of the experimentally acquired dual-comb transmission follows line-by-line the characteristic acetylene transmission envelope as computed from the HITRAN 2016 database after an a posteriori wavelength calibration. Furthermore, the residuals between the observed traces and the HITRAN reference spectrum and its standard deviation of 0.028 attests good transmission intensity precision to our dual-comb spectrometer.
关键词： optical frequency combs,MIXSEL,acetylene,Dual-comb spectroscopy,HITRAN database
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) - A Single Free-Running Dual-Comb MIXSEL for Fast and Precise Distance Measurements
摘要： Multiheterodyne techniques in science and technology promise unsurpassed precision in many fields of application such as dual-comb spectroscopy or light detection and ranging (LIDAR). Complexity, performance and cost can be greatly improved with dual-comb semiconductor disk lasers (SDL). Integration of the active semiconductor gain of a vertical external-cavity surface emitting laser (VECSEL) with the saturable absorber of a semiconductor saturable absorber mirror (SESAM) in the same epitaxial structure leads to the modelocked integrated external-cavity surface emitting laser (MIXSEL). The MIXSEL allows modelocking in a simple straight cavity. With two intracavity birefringent crystals, the initially unpolarized cavity beam is separated by polarization. When optically pumping two spots on the semiconductor chip, the dual-comb MIXSEL emits two orthogonally polarized optical frequency combs (OFCs) with a slight difference in pulse repetition rate which can be freely adjusted. The common cavity leads to an intrinsically high mutual coherence between the two OFCs, making the dual-comb MIXSEL the ideal source for dual-comb spectroscopy and other field-deployable multiheterodyne beatnote techniques.
关键词： semiconductor disk lasers,optical frequency combs,Multiheterodyne techniques,dual-comb spectroscopy,MIXSEL,SESAM,VECSEL,LIDAR
更新于2025-09-12 10:27:22