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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) - Dynamics of Kerr-Like Optical Frequency Combs Generated via Phase-Mismatched Second-Harmonic Generation
摘要： The ability to generate optical frequency combs in nonlinear resonators has attracted significant attention over the last decade. While the majority of studies have considered resonators dominated by the third-order Kerr nonlinearity, more recent investigations have shown that comb generation is also possible through second order nonlinear effects. Experimental works have in particular demonstrated that combs can arise in driven resonators via second-harmonic generation (SHG), both in the presence and absence of a phase-mismatch. Theoretical works have so far focussed almost exclusively on the case of perfect phase-matching. This is somewhat surprising, for it is well-known that phase-mismatched SHG can give rise to a strong effective Kerr nonlinearity coefficient whose sign can be controlled with the phase-mismatch. Here, we theoretically and numerically investigate the generation of Kerr-like frequency combs in resonators under conditions of phase-mismatched SHG. We show that the equations describing intracavity SHG tend towards the Lugiato-Lefever equation of Kerr nonlinear resonators when the phase-mismatch is very large. The resulting effective Kerr nonlinearity coefficient can still exceed that of typical fused silica microcavities. Importantly, the Kerr coefficient is negative if the phase-mismatch is negative, alluding to the possibility of Kerr-like combs in the regime of normal dispersion. In conclusion, we have shown that a cavity subject to phase-mismatched SHG can display pure Kerr cavity dynamics in the regime of very large phase-mismatch. Moreover, we find that localised soliton states can manifest themselves even for intermediate values of phase-mismatch.
关键词： Kerr nonlinearity,optical frequency combs,second-harmonic generation,phase-mismatch,solitons
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) - Femtosecond-Driven Up-Conversion in a Radially Poled LiNbO <sub/>3</sub> Microresonator
摘要： Nowadays, there are plenty of different techniques developed for the generation of Optical Frequency Combs (OFCs), but Mode Locked Laser (MLL) OFC is still the most commonly used and commercially available one [1]. Although MLLs are capable of producing very high-peak power OFCs with femtosecond pulse durations, it is sometimes challenging to apply them directly for a number of reasons. First, MLLs typically produce OFCs with repetition frequencies (fr) below 1 GHz, so additional filtering of the unwanted modes is required for the applications in telecommunications, astrocombs etc. Second, many spectral regions – namely mid-infrared, visible and ultraviolet – are difficult to access by MLLs, which implies the use of external parametric up- and down-conversion. One promising platform for such spectral transfer is high Q-factor optical microresonators based on second order (χ(2)) nonlinear crystals, since not only do they provide the desired spectral transfer, but also open up opportunities for the miniaturization of the system. In addition, such microresonators support whispering gallery modes that possess very low mode volumes, making it possible to enhance nonlinear (χ(2)) processes. This is a significant advantage over the already existing bulk analogs.
关键词： Mode Locked Laser,microresonators,second harmonic generation,femtosecond pulses,Optical Frequency Combs
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) - Thermally Stabilized, Energy Efficient, All-Fiber Optical Frequency Comb
摘要： In recent years, optical frequency combs are gaining attention in many fields of science, e.g. frequency metrology, optical clocks, and high-resolution spectroscopy. Most sophisticated comb sources can be repetition rate stabilized down to 10-16 uncertainty in 1 s averaging time [1] (bounded by the stability of the reference clock). Therefore compact, low-cost and energy efficient fiber-based sources are highly demanded on the market [2]. Accurate thermal stabilization of the fiber laser cavity is the first step to obtain stable repetition frequency, which is critical for optical frequency comb spectroscopy schemes [3]. Moreover, cavity-enhanced spectroscopic techniques like Vernier spectroscopy requires additional detuning of the comb repetition rate from the cavity mode-spacing [4]. We report an experimental investigation of the performance of a Er-doped, low power, thermally stabilized, mode locked laser, utilizing graphene as a saturable absorber. The oscillator, depicted in Figure 1(a), consists of: a hybrid component comprising an output coupler, wavelength division multiplexer and isolator (TIWDM), saturable absorber, and a piezo-electric transducer (PZT). The laser based only on polarization maintaining (PM) fibers, without any free space components. The entire resonator and all components are placed on a custom-made heating plate with uniformly spread heating traces, which equally cover the entire board surface, ensuring perfectly homogenous heat distribution. For efficient thermal stabilization, the fibers are attached to the plate by acrylic adhesive thermopads. The resonator is placed in a 3D-printed enclosure. A custom-made thermal controller is responsible for thermalization of all oscillator components with long term stability better than 0.05°C. Additional tuning of the repetition rate in the range of 0 – 2.79 kHz is performed by means of a piezo stretcher driven with voltages from 0 to 150 V. The stretcher is based on a miniature, monolithic, multilayer piezo stack (5x5x50 mm), which stretches the Er-doped fiber by approximately 36 μm. The fundamental repetition rate (fc), resulting from the cavity length is equal to 124.6539196 MHz at 30°C (without any voltage applied to the PZT). The signal to noise ratio (SNR) in the radio frequency (RF) spectrum measured with 2.7 Hz resolution bandwidth (RBW) is at the level of 70 dB. The repetition rate of the laser can be detuned by 17 kHz via heating the resonator from 30 to 50°C. We believe that such compact, simple frequency combs with low power consumption are suitable for field applications. The presented work was funded by the Foundation for Polish Science (First TEAM/2017-4/39) co-financed by the European Union under the European Regional Development Fund. A.G. acknowledges the support of the Faculty of Electronics (grant “M?oda Kadra”).
关键词： optical frequency combs,fiber stretcher,thermal stabilization,graphene saturable absorber,mode locked laser
更新于2025-09-12 10:27:22
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Numerical and Experimental Analysis of Optical Frequency Comb Generation in Gain-Switched Semiconductor Lasers
摘要： We have performed a systematic experimental and simulation analysis of the optical frequency combs generated by gain-switching single mode laser diodes, either free-running or subjected to optical injection. The simulations have been produced with a dynamical model consisting of three rate equations that include stochastic noise terms. The model parameters have been extracted from experiments. An exhaustive comparison between the simulated and the experimental temporal profiles and optical spectra generated under a wide range of switching and optical injection conditions has been performed. The excellent quantitative agreement found in the entire range of the explored operating conditions supports the validity of the model for the analysis of the comb generation mechanisms. The detailed maps generated provide guidelines for selecting suitable operating conditions for specific comb characteristics.
关键词： optical frequency combs,Semiconductor lasers,rate equations,optical injection,gain switching
更新于2025-09-11 14:15:04
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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) - Kerr Optical Frequency Combs Generated Around 2-μm in a Dual-Pumped Brillouin Fiber Ring Resonator
摘要： Broadband coherent light sources consisting of equally-spaced discrete lines in the frequency domain, also called optical frequency combs (OFCs), constitute a very powerful tool in a vast number of applications such as optical frequency metrology, biology, and astronomical spectrograph calibration, optical fiber wavelength division multiplexing (WDM), microwave generation and molecular spectroscopy [1–4]. The latter application has attracted significant interest especially in the mid-infrared range (from 2-μm to 16-μm) where various relevant molecules, such as carbon dioxide and ammonia, exhibit vibration fingerprints. Various OFCs generated at 2-μm wavelengths have recently been reported based on different configurations [3,5]. In this communication, we demonstrate a simple and reconfigurable all-fibered system that generates symmetric optical frequency combs based on a dual-wavelength-pumped fiber ring cavity. More specifically, more than 20 symmetrical and stable optical frequency comb lines, with tunable frequency spacing and center wavelength, have been generated by exploiting both stimulated Brillouin scattering (SBS) and cascaded four-wave-mixing (FWM) in the 2-μm wavelength region.
关键词： 2-μm wavelength,optical frequency combs,Brillouin scattering,four-wave-mixing
更新于2025-09-11 14:15:04