We identify the physical mechanism responsible for the generation of clustered frequency combs in optical microresonators. This theory is validated by experimentally measuring the coherence of such clustered combs in a MgF2 monolithic microresonator.

Temporal cavity solitons (CSs) are pulses of light that can persist in an optical cavity without any change to their shape or energy, and in the spectral domain correspond to highly coherent frequency combs. Cavity solitons were recently demonstrated for the first time in crystalline microresonators [1], and have subsequently been reported in a number of other resonator platforms [2-4], further establishing microresonators as a viable alternative to commercial mode-locked laser sources of ultrashort pulses and frequency combs. Cavity solitons arise from a noisy and unstable background; as a result, the number of cavity solitons generated each time the state is accessed is expected to be random, with a distribution determined solely by the resonator and driving parameters.

We experimentally demonstrate a ring geometry all-fiber cavity system for cavity quantum electrodynamics with an ensemble of cold atoms. The fiber cavity contains a nanofiber section which mediates atom-light interactions through an evanescent field. We observe well-resolved, vacuum Rabi splitting of the cavity transmission spectrum in the weak driving limit due to a collective enhancement of the coupling rate by the ensemble of atoms within the evanescent field, and we present a simple theoretical model to describe this. In addition, we demonstrate a method to control and stabilize the resonant frequency of the cavity by utilizing the thermal properties of the nanofiber.

We present a widely-tunable microresonator optical parametric oscillator based on a high-finesse MgF2 microdisk. The oscillator operates at low-power with output parametric sidebands discretely tunable from 1166 nm to 2226 nm.

We experimentally investigate the spectral coherence of microresonator optical frequency combs. Specifically, we use a spectral interference method, typically used in the context of supercontinuum generation, to explore the variation of the magnitude of the complex degree of first-order coherence across the full comb bandwidth. We measure the coherence of two different frequency combs and observe wholly different coherence characteristics. In particular, we find that the observed dynamical regimes are similar to the stable and unstable modulation instability regimes reported in previous theoretical studies. Results from numerical simulations are found to be in good agreement with experimental observations. In addition to demonstrating a new technique to assess comb stability, our results provide strong experimental support for previous theoretical analyses.

We report on experimental observations of coherent cavity soliton frequency combs in silica microspheres. By careful alignment of the sphere relative to the coupling fiber taper, we can reduce mode interactions and enable soliton formation.

We use spectral interferometry to experimentally measure the degree of coherence across the full bandwidth of microresonator-based frequency combs. Our results show distinct coherence characteristics for two different frequency combs, supporting previous theoretical findings.

We report on the experimental observation of coherent cavity soliton frequency combs in silica microspheres. Specifically, we demonstrate that careful alignment of the microsphere relative to the coupling fiber taper allows for the suppression of higher-order spatial modes, reducing mode interactions and enabling soliton formation. Our measurements show that the temporal cavity solitons have sub-100-fs durations, exhibit considerable Raman self-frequency shift, and generally come in groups of three or four, occasionally with equidistant spacing in the time domain. RF amplitude noise measurements and spectral interferometry confirm the high coherence of the observed soliton frequency combs, and numerical simulations show good agreement with experiments.

We review recent experimental and theoretical work on temporal cavity solitons in macroscopic fibre cavities and monolithic microresonators. In addition to reviewing basic characteristics of cavity solitons, we will discuss their role in optical memories and microresonator frequency combs.

We show experimentally and theoretically that fiberoptic analogues of event horizons can be explained by cascaded four-wave mixing between two continuous waves. Excellent agreement is obtained between experiments using pulsed and continuous wave lasers.

The emission of dispersive waves (DWs) by temporal solitons can be described as a cascaded four-wave mixing process triggered by a pair of monochromatic continuous waves (CWs). We report experimental and numerical results demonstrating that the efficiency of this process is strongly and nontrivially affected by the frequency detuning of the CW pump lasers. We explain our results by showing that individual cycles of the input dual-frequency beat signal can evolve as higher-order solitons whose temporal compression and soliton fission govern the DW efficiency. Analytical predictions based on the detuning dependence of the soliton order are shown to be in excellent agreement with experimental and numerical observations.

We experimentally show that the efficiency of dispersive wave generation by a four-wave mixing cascade is strongly affected by pump frequency detuning. Results are explained using both time and frequency domain descriptions.

The nonlinear interaction of light in an optical fibre can mimic the physics at an event horizon. This analogue arises when a weak probe wave is unable to pass through an intense soliton, despite propagating at a different velocity. To date, these dynamics have been described in the time domain in terms of a soliton-induced refractive index barrier that modifies the velocity of the probe. Here we complete the physical description of fibre-optic event horizons by presenting a full frequency-domain description in terms of cascaded four-wave mixing between discrete single-frequency fields, and experimentally demonstrate signature frequency shifts using continuous wave lasers. Our description is confirmed by the remarkable agreement with experiments performed in the continuum limit, reached using ultrafast lasers. We anticipate that clarifying the description of fibre event horizons will significantly impact on the description of horizon dynamics and soliton interactions in photonics and other systems.

We show that the emission of dispersive waves in nonlinear fiber optics is not limited to soliton-like pulses propagating in the anomalous dispersion regime. We demonstrate, both numerically and experimentally, that pulses propagating in the normal dispersion regime can excite resonant dispersive radiation across the zero-dispersion wavelength into the anomalous regime.