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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) - 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