arXiv subjects

Stuart G. Murdoch

Publications and source records attributed to Stuart G. Murdoch.

At least 37 records · Page 2Linked to original sources

arXiv2020

Dissipative polarization domain walls in a passive driven Kerr resonator

Using a passive driven nonlinear optical fiber ring resonator, we report the experimental realization of dissipative polarization domain walls. The domain walls arise through a symmetry breaking bifurcation and consist of temporally localized structures where the amplitudes of the two polarization modes of the resonator interchange, segregating domains of orthogonal polarization states. We show that dissipative polarization domain walls can persist in the resonator without changing shape. We also demonstrate on-demand excitation, as well as pinning of domain walls at specific positions for arbitrary long times. Our results could prove useful for the analog simulation of ubiquitous domain-wall related phenomena, and pave the way to an all-optical buffer adapted to the transmission of topological bits.

physics.optics↗

arXiv2020

Experimental observations of bright dissipative Kerr cavity solitons and their collapsed snaking in a driven resonator with normal dispersion

Driven Kerr nonlinear optical resonators can sustain localized structures known as dissipative Kerr cavity solitons, which have recently attracted significant attention as the temporal counterparts of microresonator optical frequency combs. Whilst conventional wisdom asserts that bright cavity solitons can only exist in the region of anomalous dispersion, recent theoretical studies have predicted that higher-order dispersion can fundamentally alter the situation, enabling bright localized structures even under conditions of normal dispersion driving. Here we demonstrate a flexible optical fibre ring resonator platform that offers unprecedented control over dispersion conditions, and we report on the first experimental observations of bright localized structures that are fundamentally enabled by higher-order dispersion. In broad agreement with past theoretical predictions, we find that several distinct bright structures can co-exist for the same parameters, and we observe experimental evidence of their collapsed snaking bifurcation structure. In addition to enabling direct experimental verifications of a number of theoretical predictions, we show that the ability to judiciously control the dispersion conditions offers a novel route for ultrashort pulse generation: the bright structures observed in our work correspond to pulses of light as short as 220~fs -- the record for a passive all-fibre ring resonator. We envisage that our work will stimulate further fundamental studies on the impact of higher-order dispersion on Kerr cavity dynamics, as well as guide the development of novel ultrashort pulse sources and dispersion-engineered microresonator frequency combs.

physics.optics↗

arXiv2020

Asymmetric balance in symmetry breaking

Spontaneous symmetry breaking is central to our understanding of physics and explains many natural phenomena, from cosmic scales to subatomic particles. Its use for applications requires devices with a high level of symmetry, but engineered systems are always imperfect. Surprisingly, the impact of such imperfections has barely been studied, and restricted to a single asymmetry. Here, we experimentally study spontaneous symmetry breaking with two controllable asymmetries. We remarkably find that features typical of spontaneous symmetry breaking, while destroyed by one asymmetry, can be restored by introducing a second asymmetry. In essence, asymmetries are found to balance each other. Our study illustrates aspects of the universal unfolding of the pitchfork bifurcation, and provides new insights into a key fundamental process. It also has practical implications, showing that asymmetry can be exploited as an additional degree of freedom. In particular, it would enable sensors based on symmetry breaking or exceptional points to reach divergent sensitivity even in presence of imperfections. Our experimental implementation built around an optical fiber ring additionally constitutes the first observation of the polarization symmetry breaking of passive driven nonlinear resonators.

physics.optics↗

arXiv2020

Harmonic and rational harmonic driving of microresonator soliton frequency combs

With demonstrated applications ranging from metrology to telecommunications, soliton microresonator frequency combs have emerged over the past decade as a remarkable new technology. However, standard implementations only allow for the generation of combs whose repetition rate is tied close to the fundamental resonator free-spectral range (FSR), offering little or no dynamic control over the comb line spacing. Here we propose and experimentally demonstrate harmonic and rational harmonic driving as novel techniques that allow for the robust generation of soliton frequency combs with discretely adjustable frequency spacing. By driving an integrated Kerr microresonator with a periodic train of picosecond pulses whose repetition rate is set close to an integer harmonic of the 3.23 GHz cavity FSR, we deterministically generate soliton frequency combs with frequency spacings discretely adjustable between 3.23 GHz and 19.38 GHz. More remarkably, we also demonstrate that driving the resonator at rational fractions of the FSR allows for the generation of combs whose frequency spacing corresponds to an integer harmonic of the pump repetition rate. By measuring the combs' radio-frequency spectrum, we confirm operation in the low-noise soliton regime with no supermode noise. The novel techniques demonstrated in our work provide new degrees of freedom for the design of synchronously pumped soliton frequency combs.

physics.optics↗

arXiv2019

Experimental observation of internally-pumped parametric oscillation and quadratic comb generation in a $χ^{(2)}$ whispering-gallery-mode microresonator

We report on the experimental observation of internally-pumped parametric oscillation in a high-Q lithium niobate microresonator under conditions of natural phase-matching. Specifically, launching near-infrared pump light around 1060 nm into a $z$-cut congruent lithium niobate microresonator, we observe the generation of optical sidebands around the input pump under conditions where second-harmonic generation is close to natural phase-matching. We find that a wide range of different sideband frequency shifts can be generated by varying the experimental parameters. Under particular conditions, we observe the cascaded generation of several equally-spaced sidebands around the pump -- the first steps of optical frequency comb generation via cavity-enhanced second-harmonic generation.

physics.optics↗

arXiv2019

Engineered discreteness enables observation and control of chimera-like states in a system with local coupling

Chimera states -- named after the mythical beast with a lion's head, a goat's body, and a dragon's tail -- correspond to spatiotemporal patterns characterised by the coexistence of coherent and incoherent domains in coupled systems. They were first identified in 2002 in theoretical studies of spatially extended networks of Stuart-Landau oscillators, and have been subject to extensive theoretical and experimental research ever since. While initially considered peculiar to networks with weak nonlocal coupling, recent theoretical studies have predicted that chimera-like states can emerge even in systems with purely local coupling. Here we report on the first experimental observations of chimera-like states in a system with local coupling -- a coherently-driven Kerr nonlinear optical resonator. We show that artificially engineered discreteness -- realised by suitably modulating the coherent driving field -- allows for the nonlinear localisation of spatiotemporal complexity, and we demonstrate unprecedented control over the existence, characteristics, and dynamics of the resulting chimera-like states. Moreover, using ultrafast time lens imaging, we resolve the chimeras' picosecond-scale internal structure in real time.

physics.optics↗

arXiv2019

Impact of de-synchronization and drift on soliton-based Kerr frequency combs in the presence of pulsed driving fields

Pulsed driving of Kerr microresonators represents a promising avenue for the efficient generation of soliton states associated with coherent optical frequency combs. The underlying physics has not, however, yet been comprehensively investigated. Here, we report on a numerical and theoretical study of the impact of de-synchronization between the periodic pump field and the train of solitons circulating in the cavity. We show that de-synchronization can affect the soliton configurations that can be sustained for given parameters, and that it can be leveraged to guarantee operation in the attractive single-soliton regime. We also reveal that the interplay between pump-resonator de-synchronization and stimulated Raman scattering can give rise to rich dynamics that explain salient features observed in recent experiments. Our work elucidates the dynamics of Kerr cavity solitons in the presence of pulsed driving fields, and could facilitate the development of efficient microresonator frequency comb systems.

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arXiv2019

Real-time spectral analysis of ultrafast pulses using a free-space angular chirp enhanced delay

Frequency to time mapping is a powerful technique for observing ultrafast phenomena and non-repetitive events in optics. However, many optical sources operate in wavelength regions, or at power levels, that are not compatible with standard frequency to time mapping implementations. The recently developed free-space angular chirp enhanced delay (FACED) removes many of these limitations, and offers a linear frequency to time mapping in any wavelength region where high-reflectivity mirrors and diffractive optics are available. In this work, we present a detailed formulation of the optical transfer function of a FACED device. Experimentally, we verify the properties of this transfer function, and then present simple guidelines to guarantee the correct operation of a FACED frequency to time measurement. We also experimentally demonstrate the real-time spectral analysis of femtosecond and picosecond pulses using this system.

physics.optics↗

arXiv2019

Octave-spanning tunable parametric oscillation in crystalline Kerr microresonators

Parametric nonlinear optical processes allow for the generation of new wavelengths of coherent electromagnetic radiation. Their ability to create radiation that is widely tunable in wavelength is particularly appealing, with applications ranging from spectroscopy to quantum information processing. Unfortunately, existing tunable parametric sources are marred by deficiencies that obstruct their widespread adoption. Here we show that ultrahigh-Q crystalline microresonators made of magnesium fluoride can overcome these limitations, enabling compact and power-efficient devices capable of generating clean and widely-tunable sidebands. We consider several different resonators with carefully engineered dispersion profiles, achieving hundreds of nanometers of sideband tunability in each device when driven with a standard low-power laser at 1550 nm. In addition to direct observations of discrete tunability over an entire optical octave from 1083 nm to 2670 nm, we record signatures of mid-infrared sidebands at almost 4000 nm. The simplicity of the devices considered -- compounded by their remarkable tunability -- paves the way for low-cost, widely-tunable sources of electromagnetic radiation.

physics.optics↗

arXiv2019

Coexistence and interactions between nonlinear states with different polarizations in a monochromatically driven passive Kerr resonator

We report on experimental observations of coexistence and interactions between nonlinear states with different polarizations in a passive Kerr resonator driven at a single carrier frequency. Using a fiber ring resonator with adjustable birefringence, we partially overlap nonlinear resonances of two orthogonal polarization modes, achieving coexistence between different nonlinear states by locking the driving laser frequency at various points within the overlap region. In particular, we observe coexistence between temporal cavity solitons and modulation instability patterns, as well as coexistence between two nonidentical cavity solitons with different polarizations. We also observe interactions between the distinctly polarized cavity solitons, as well as spontaneous excitation and annihilation of solitons by a near-orthogonally polarized unstable modulation instability pattern. By demonstrating that a single frequency driving field can support coexistence between differentially polarized solitons and complex modulation instability patterns, our work sheds light on the rich dissipative dynamics of multimode Kerr resonators. Our findings could also be of relevance to the generation of multiplexed microresonator frequency combs.

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arXiv2018

Emission of intense resonant radiation by dispersion-managed Kerr cavity solitons

We report on an experimental and numerical study of temporal Kerr cavity soliton dynamics in dispersion-managed fiber ring resonators. We find that dispersion management can significantly magnify the Kelly-like resonant radiation sidebands emitted by the solitons. Because of the underlying phase-matching conditions, the sideband amplitudes tend to increase with increasing pump-cavity detuning, ultimately limiting the range of detunings over which the solitons can exist. Our experimental findings show excellent agreement with numerical simulations.

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arXiv2018

Origins of clustered frequency combs in Kerr microresonators

Recent experiments have demonstrated the generation of widely-spaced parametric sidebands that can evolve into "clustered" optical frequency combs in Kerr microresonators. Here we describe the physics that underpins the formation of such clustered comb states. In particular, we show that the phase-matching required for the initial sideband generation is such that (at least) one of the sidebands experiences anomalous dispersion, enabling that sideband to drive frequency comb formation via degenerate and non-degenerate four-wave mixing. We validate our proposal through a combination of experimental observations made in a magnesium-fluoride microresonator and corresponding numerical simulations. We also investigate the coherence properties of the resulting clustered frequency combs. Our findings provide valuable insights on the generation and dynamics of widely-spaced parametric sidebands and clustered frequency combs in Kerr microresonators.

physics.optics↗

arXiv2018

Spontaneous symmetry breaking and trapping of temporal Kerr cavity solitons by pulsed or amplitude modulated driving fields

We report on a systematic study of temporal Kerr cavity soliton dynamics in the presence of pulsed or amplitude modulated driving fields. In stark contrast to the more extensively studied case of phase modulations, we find that Kerr cavity solitons are not always attracted to maxima or minima of driving field amplitude inhomogeneities. Instead, we find that the solitons are attracted to temporal positions associated with specific driving field values that depend only on the cavity detuning. We describe our findings in light of a spontaneous symmetry breaking instability that physically ensues from a competition between coherent driving and nonlinear propagation effects. In addition to identifying a new type of Kerr cavity soliton behaviour, our results provide valuable insights to practical cavity configurations employing pulsed or amplitude modulated driving fields.

physics.optics↗

arXiv2018

Writing and Erasing of Temporal Kerr Cavity Solitons via Intensity Modulation of the Cavity Driving Field

We experimentally and numerically study the use of intensity modulation for the controlled addressing of temporal Kerr cavity solitons. Using a coherently driven fiber ring resonator, we demonstrate that a single temporally broad intensity modulation pulse applied on the cavity driving field permits systematic and efficient writing and erasing of ultrashort cavity solitons. We use numerical simulations based on the mean-field Lugiato-Lefever model to investigate the addressing dynamics, and present a simple physical description of the underlying physics.

physics.optics↗

arXiv2017

Widely tunable optical parametric oscillation in a Kerr microresonator

We report on the first experimental demonstration of widely-tunable parametric sideband generation in a Kerr microresonator. Specifically, by pumping a silica microsphere in the normal dispersion regime, we achieve the generation of phase-matched four-wave mixing sidebands at large frequency detunings from the pump. Thanks to the role of higher-order dispersion in enabling phase matching, small variations of the pump wavelength translate into very large and controllable changes in the wavelengths of the generated sidebands: we experimentally demonstrate over 720 nm of tunability using a low-power continuous-wave pump laser in the C-band. We also derive simple theoretical predictions for the phase-matched sideband frequencies, and discuss the predictions in light of the discrete cavity resonance frequencies. Our experimentally measured sideband wavelengths are in very good agreement with theoretical predictions obtained from our simple phase matching analysis.

physics.optics↗

arXiv2017

Stimulated Raman Scattering Imposes Fundamental Limits to the Duration and Bandwidth of Temporal Cavity Solitons

Temporal cavity solitons (CS) are optical pulses that can persist in passive resonators, and they play a key role in the generation of coherent microresonator frequency combs. In resonators made of amorphous materials, such as fused silica, they can exhibit a spectral red-shift due to stimulated Raman scattering. Here we show that this Raman-induced self-frequency-shift imposes a fundamental limit on the duration and bandwidth of temporal CSs. Specifically, we theoretically predict that stimulated Raman scattering introduces a previously unidentified Hopf bifurcation that leads to destabilization of CSs at large pump-cavity detunings, limiting the range of detunings over which they can exist. We have confirmed our theoretical predictions by performing extensive experiments in several different synchronously-driven fiber ring resonators, obtaining results in excellent agreement with numerical simulations. Our results could have significant implications for the future design of Kerr frequency comb systems based on amorphous microresonators.

physics.optics↗

arXiv2017

Universal mechanism for the binding of temporal cavity solitons

We present theoretical and experimental evidence of a universal mechanism through which temporal cavity solitons of externally-driven, passive, Kerr resonators can form robust long-range bound states. These bound states, sometime also referred to as multi-soliton states or soliton crystals in microresonators, require perturbations to the strict Lugiato-Lefever mean field description of temporal cavity solitons. Binding occurs when the perturbation excites a narrowband resonance in the soliton spectrum, which gives long oscillatory tails to the solitons. Those tails can then interlock for a discrete set of temporal separations between the solitons. The universality of this mechanism is demonstrated in fiber ring cavities by providing experimental observations of long-range bound states ensuing from three different perturbations: third-order dispersion (dispersive wave generation), the periodic nature of the cavity (Kelly sidebands), and the random birefringence of the resonator. Sub-picosecond resolution of bound state separations and their dynamics are obtained by using the dispersive Fourier transform technique. Good agreement with theoretical models, including a new vector mean-field model, is also reported.

physics.optics↗

arXiv2017

Experimental and numerical investigations of switching wave dynamics in a normally dispersive fiber ring resonator

Optical frequency combs generated in normally dispersive Kerr microresonators have been observed to correspond to dark temporal structures, and theoretically explained as interlocked switching waves (also known as domain walls or fronts). The time-domain dynamics that underpin the formation of this type of frequency combs has however so far eluded direct experimental observation. Here we use a closely related system - a synchronously driven optical fibre ring resonator - to experimentally study the dynamics of deterministically excited switching waves. We measure the switching wave velocities across broad parameter regions, and observe clear signatures of interlocking behaviour leading to the formation of persisting dark pulses. Our experimental findings are in good agreement with simulations of the mean-field Lugiato-Lefever equation, and strongly support the nature of normal-dispersion microresonator frequency combs suggested in the literature.

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