arXiv subjects

Nicolas Englebert

Publications and source records attributed to Nicolas Englebert.

At least 19 recordsLinked to original sources

arXiv2026

Laser electro-optic frequency comb in lithium niobate nanophotonics

Optical frequency combs have revolutionized precision science and technology, yet their nanophotonic implementations have failed to simultaneously achieve high efficiency, power, and coherence. Optically driven microcombs provide broad and stable spectra but low usable power, whereas active comb generators, including mode-locked lasers, can be efficient yet offer less control over coherence. We introduce the laser electro-optic (LEO) frequency comb, a comb-generation mechanism in which coherent continuous-wave injection drives a phase-modulated laser cavity above threshold into a distinct operating regime. Unlike other coherently driven integrated comb sources, the LEO comb generates comb powers that exceed the injected continuous-wave power by an order of magnitude. We realize the LEO comb in a hybrid lithium niobate/III-V nanophotonic circuit and demonstrate milliwatt-level power per comb line, 1.76-ps pulses, a 4.7-nm background-free spectrum, and linewidths as narrow as 19.6 kHz. By unifying high efficiency, power, and coherence, this architecture establishes a definitive route to chip-scale frequency comb sources that deliver on the promise of scalable, high-performance coherent optical technologies.

physics.optics↗

arXiv2026

Temporal soliton generation in an ultra-high-effective-Q Kerr resonator enabled by Raman gain

We demonstrate temporal pattern formation in a coherently driven fiber ring cavity whose effective finesse is continuously reconfigured using distributed Raman amplification. We achieve an effective finesse of up to $\mathcal{F}_{\mathrm{eff}}\approx800$, corresponding to a linewidth of approximately 725 Hz ($Q\approx2.7\times10^{11}$) at 1555 nm. By exploiting the resulting increase in effective photon lifetime, we excite stable temporal cavity solitons and generate a low-repetition-rate frequency comb with a spacing of 580~kHz. Finally, we analyze the impact of the Raman loss-compensation mechanism, particularly its associated noise and show that a trade-off exists between soliton excitation threshold and stability.

physics.optics↗

arXiv2025

Topological Soliton Frequency Comb in Nanophotonic Lithium Niobate

Frequency combs have revolutionized metrology, ranging, and optical clocks, which have motivated substantial efforts on the development of chip-scale comb sources. The on-chip comb sources are currently based on electro-optic modulation, mode-locked lasers, quantum cascade lasers, or soliton formation via Kerr nonlinearity. However, the widespread deployment of on-chip comb sources has remained elusive as they still require RF sources, high-Q resonators, or complex stabilization schemes while facing efficiency challenges. Here, we demonstrate an on-chip source of frequency comb based on the integration of a lithium niobate nanophotonic circuit with a semiconductor laser that can alleviate these challenges. For the first time, we show the formation of temporal topological solitons in a on-chip nanophotonic parametric oscillator with quadratic nonlinearity and low finesse. These solitons, independent of the dispersion regime, consist of phase defects separating two $\pi$-out-of-phase continuous wave solutions at the signal frequency, which is at half the input pump frequency. We use on-chip cross-correlation for temporal measurements and confirm formation of topological solitons as short as 60 fs around 2 $\mu$m, in agreement with a generalized parametrically forced Ginzburg-Landau theory. Moreover, we demonstrate a proof-of-concept turn-key operation of a hybrid-integrated source of topological frequency comb. Topological solitons offer a new paradigm for integrated comb sources, which are dispersion-sign agnostic and do not require high-Q resonators or high-speed modulators and can provide access to hard-to-access spectral regions, including mid-infrared.

physics.optics↗

arXiv2025

Quadratic Supercontinuum Generation from UV to Mid-IR in Lithium Niobate Nanophotonics

Supercontinuum light sources are widely used for applications ranging from imaging to sensing and frequency comb stabilization. The most common mechanisms for their generation rely on cubic nonlinearities, for instance in crystals, optical fibers, and integrated photonics. However, quadratic supercontinuum generation (QSCG) offers potential for enhanced energy efficiency and broader spectral coverage because of the typically much stronger nonlinearity and ability to achieve both coherent up- and down-conversion via three-wave mixing processes. Despite such potentials, demonstrations of QSCG in integrated photonic waveguides have been sparse and have barely surpassed their cubic counterparts in terms of spectral coverage and energy-efficiency. Here, we introduce a new dispersion engineering principle and experimentally demonstrate purely quadratic supercontinuum generation in lithium niobate nano-waveguides substantially outperforming previous demonstrations in integrated photonics. In one device, by engineering a near-zero dispersion profile and using a single poling period for quasi-phase matched saturated second-harmonic generation, we achieve robust and energy efficient multi-octave QSCG with only femtojoules of pump pulse energy. In another device, we use a flat dispersion profile with two distant zero crossings of group velocity dispersion (GVD) to achieve broadband difference-frequency generation (DFG) for extending the spectral coverage further into the mid-IR and cover the entire transparency window of lithium niobate from 350 nm to 5000 nm. Our results showcase how DFG-assisted QSCG can access hard-to-access spectral regions in an energy-efficient fashion by properly utilizing dispersion engineering and quasi-phase matching.

physics.optics↗

arXiv2025

Modulation instability and frequency-comb generation in hybrid quadratic-cubic resonators with spectral filtering

We present an analytical and numerical investigation into the phenomenon of filter-induced modulation instability in passive hybrid optical resonators exhibiting quadratic and cubic nonlinearity. We show that asymmetric spectral losses, with respect to the continuous-wave solution frequency, can trigger sideband amplification in the normal dispersion regime. We calculate the parametric gain and demonstrate the associated pattern formation process. We furthermore show how this parametric process can be exploited to generate optical frequency combs with tunable repetition rate.

physics.optics↗

arXiv2025

Two-optical-cycle pulses from nanophotonic two-color soliton compression

Few- and single-cycle optical pulses and their associated ultra-broadband spectra have been crucial in the progress of ultrafast science and technology. Moreover, multi-color waveforms composed of independently manipulable ultrashort pulses in distinct spectral bands offer unique advantages in pulse synthesis and attosecond science. However, the generation and control of ultrashort pulses has required bulky and expensive optical systems at the tabletop scale and has so far been beyond the reach of integrated photonics. Here, we break these limitations and demonstrate two-optical-cycle pulse compression using quadratic two-color soliton dynamics in lithium niobate nanophotonics. By leveraging dispersion engineering and operation near phase matching, we achieve extreme compression, energy-efficient operation, and strong conversion of pump to the second harmonic. We experimentally demonstrate generation of $\sim$13-fs pulses at 2 $\mu$m using only $\sim$3 pJ of input energy. We further illustrate how the demonstrated scheme can be readily extended to on-chip single-cycle pulse synthesis with sub-cycle control. Our results provide a path towards realization of single-cycle ultrafast systems in nanophotonic circuits.

physics.optics↗

arXiv2025

All-optical computing with beyond 100-GHz clock rates

A computer's clock rate ultimately determines the minimum time between sequential operations or instructions. Despite exponential advances in electronic computer performance owing to Moore's Law and increasingly parallel system architectures, computer clock rates have remained stagnant at $\sim5~\mathrm{GHz}$ for almost two decades. This poses an intractable problem for applications requiring real-time processing or control of ultrafast information systems. Here we break this barrier by proposing and experimentally demonstrating computing based on an end-to-end and all-optical recurrent neural network harnessing the ultrafast nature of linear and nonlinear optical operations while avoiding electronic operations. The all-optical computer realizes linear operations, nonlinear functions, and memory entirely in the optical domain with $>100~\mathrm{GHz}$ clock rates. We experimentally demonstrate a prototypical task of noisy waveform classification as well as perform ultrafast in-situ analysis of the soliton states from integrated optical microresonators. We further illustrate the application of the architecture for generative artificial intelligence based on quantum fluctuations to generate images even in the absence of input optical signals. Our results highlight the potential of all-optical computing beyond what can be achieved with digital electronics by utilizing ultrafast linear, nonlinear, and memory functions and quantum fluctuations.

physics.optics↗

arXiv2024

Manipulation and control of temporal cavity solitons with trapping potential

Temporal cavity solitons (CSs) are stable, localized particle-like objects in the form of optical pulses that circulate indefinitely in coherently driven nonlinear resonators. In the spectral domain, they form highly coherent frequency combs. Owing to their remarkable stability, they are attracting attention for applications in sensing, metrology, or optical signal synthesis. In this work, we report on the dynamics of CSs interacting with a trapping potential. We demonstrate that this interaction provides a powerful means to control their properties such as position, speed, and central frequency. Our theoretical analysis predicts fundamental limitations on the spectral shift of CSs relative to the driving frequency. Specifically, it reveals that within a broad range of detunings, frequency-shifted CSs encounter destabilization through a Hopf bifurcation. Moreover, we find that with periodic potentials, the Kelly sidebands emitted by trapped solitons undergo Bloch oscillations. In our experiments, we use an intracavity phase modulator to create the equivalent of an external real potential. We observe stable blue- and red- shifted solitons up to a limit close to our theoretical predictions. We then show theoretically and experimentally that this unprecedented level of control over the CS spectrum can be leveraged to cancel the Raman-induced self-frequency shift and even to stabilize CSs beyond the limitation imposed by stimulated Raman scattering. Our results provide valuable insights for applications requiring robust and potentially rapid tunable control over the cavity soliton properties.

physics.optics↗

arXiv2023

Cavity Soliton-Induced Topological Edge States

Over the past decade, cavity solitons have attracted substantial attention for their rich dynamics and their myriad potential applications. Recently, there has been growing interest in understanding cavity solitons in systems of coupled resonators, where both new physics and applications can emerge. While numerous works have theoretically studied the interplay between cavity solitons and lattice topology, experimental demonstrations of cavity solitons in topological lattices remain elusive. Here, we experimentally realize cavity solitons in a Su-Schrieffer-Heeger (SSH) lattice and illustrate that the synergy between topology and soliton formation dynamics can induce soliton formation at the boundaries of a topological SSH lattice. Our work illustrates the rich physics of cavity solitons in topological lattices and demonstrates a flexible approach to study solitons in large-scale coupled resonator arrays.

physics.optics↗

arXiv2023

Sideband Injection Locking in Microresonator Frequency Combs

Frequency combs from continuous-wave-driven Kerr-nonlinear microresonators have evolved into a key photonic technology with applications from optical communication to precision spectroscopy. Essential to many of these applications is the control of the comb's defining parameters, i.e., carrier-envelope offset frequency and repetition rate. An elegant and all-optical approach to controlling both degrees of freedom is the suitable injection of a secondary continuous-wave laser into the resonator onto which one of the comb lines locks. Here, we study experimentally such sideband injection locking in microresonator soliton combs across a wide optical bandwidth and derive analytic scaling laws for the locking range and repetition rate control. As an application example, we demonstrate optical frequency division and repetition rate phase-noise reduction to three orders of magnitude below the noise of a free-running system. The presented results can guide the design of sideband injection-locked, parametrically generated frequency combs with opportunities for low-noise microwave generation, compact optical clocks with simplified locking schemes and more generally, all-optically stabilized frequency combs from Kerr-nonlinear resonators.

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arXiv2023

Parametrically driven pure-Kerr temporal solitons in a chip-integrated microcavity

The discovery that externally-driven nonlinear optical resonators can sustain ultrashort pulses corresponding to coherent optical frequency combs has enabled landmark advances in applications from telecommunications to sensing. The main research focus has hitherto been on resonators with purely cubic (Kerr-type) nonlinearity that are externally-driven with a monochromatic continuous wave laser -- in such systems, the solitons manifest themselves as unique attractors whose carrier frequency coincides with that of the external driving field. Recent experiments have, however, shown that a qualitatively different type of temporal soliton can arise via parametric down-conversion in resonators with simultaneous quadratic and cubic nonlinearity. In contrast to conventional solitons in pure-Kerr resonators, these parametrically driven solitons come in two different flavours with opposite phases, and they are spectrally centred at half of the frequency of the driving field. Here, we theoretically predict and experimentally demonstrate that parametrically driven solitons can also arise in resonators with pure Kerr nonlinearity under conditions of bichromatic driving. In this case, the solitons arise through four-wave mixing mediated phase-sensitive amplification, come with two distinct phases, and have a carrier frequency in between the two external driving fields. Our experiments are performed in an integrated silicon nitride microcavity, and we observe frequency comb spectra in good agreement with theoretical predictions. In addition to representing a fundamental discovery of a new type of temporal dissipative soliton, our results constitute the first unequivocal realisation of parametrically driven soliton frequency combs in a microcavity platform compatible with foundry-ready mass fabrication.

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arXiv2022

Depletion-limited Kerr solitons in singly-resonant optical parametric oscillators

We analyze the impact of pump depletion in the generation of cavity solitons in a singly-resonant parametrical oscillator that includes a $\chi^{(3)}$ nonlinear section. We find an analytical expression that provides the soliton existence region using variational methods, study the efficiency of energy conversion, and compare it to a driven Kerr resonator modeled by the Lugiato-Lefever equation. At high walk-off, solitons in singly-resonant optical parametric oscillators are more efficient than those formed in a Kerr resonator driven through a linear coupler.

physics.optics↗

arXiv2022

Parametrically-driven temporal cavity solitons in a bichromatically-driven pure Kerr resonator

Temporal cavity solitons (CSs) are pulses of light that can persist endlessly in dispersive, nonlinear optical resonators. They have been extensively studied in the context of resonators with purely cubic (Kerr-type) nonlinearity that are externally-driven with a monochromatic continuous wave laser -- in such systems, the solitons manifest themselves as unique attractors whose carrier frequency coincides with that of the external driving field. Recent experiments have, however, shown that a qualitatively different type of temporal CS can arise via parametric down-conversion in resonators with simultaneous quadratic and cubic nonlinearity. In contrast to conventional CSs in pure-Kerr resonators, these \emph{parametrically-driven cavity solitons} come in two different flavours with opposite phases, and they are spectrally centred at half of the frequency of the driving field. Here, we theoretically and numerically show that, under conditions of bichromatic driving, such parametrically-driven CSs can also arise in dispersive resonators with pure Kerr nonlinearity. In this case, the solitons arise through parametric four-wave mixing, come with two distinct phases, and have a carrier frequency in between the two external driving fields. We show that, when all waves are resonant, the solitons can experience long-range interactions due to their back-action on the intracavity fields at the pump frequencies, and we discuss the parameter requirements for the solitons' existence. Besides underlining the possibility of exciting a new type of cavity soliton in dispersive Kerr cavities, our work advances the theoretical modeling of resonators that are coherently-driven with polychromatic fields.

physics.optics↗

arXiv2022

High peak-to-background-ratio solitons in a coherently-driven active fiber cavity

We demonstrate that the peak-to-background ratio of driven solitons can be greatly improved by harnessing the cavity detuning. We use a driven fiber laser pumped below the lasing threshold to increase the finesse and excite solitons in a very wide region of detunings. When driving a 50 m long fiber cavity close to the anti-resonance condition, we excite sub-800 fs solitons with a peak-to-background ratio over 30000. The experimental results are in good agreement with simple theoretical models describing the soliton peak power and the background power.

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arXiv2022

Mode-locking induced by coherent driving in fiber lasers

The generation of stable short optical pulses in mode-locked lasers is of tremendous importance for many applications. Mode-locking is a broad concept that encompasses different processes enabling short pulse formation. It typically requires an intracavity mechanism that discriminates between single and collective mode lasing, which can be complex and sometimes adds noise. Moreover, known mode-locking schemes do not guarantee phase stability of the carrier wave. Here we theoretically propose that injecting a detuned signal seamlessly leads to mode-locking in fiber lasers. We show that phase-locked pulses, akin to cavity solitons, exist in a wide range of parameters. In that regime the laser behaves as a passive resonator due to the non-instantaneous gain saturation.

physics.optics↗

arXiv2021

Bloch Oscillations of Driven Dissipative Solitons in a Synthetic Dimension

The engineering of synthetic dimensions allows for the construction of fictitious lattice structures by coupling the discrete degrees of freedom of a physical system, such as the quantized modes of an electromagnetic cavity or the internal states of an atom. This method enables the study of static and dynamical Bloch band properties in the absence of a real periodic lattice structure. So far, the vast majority of implementations have focused on linear and conservative processes, with the potentially rich physics and opportunities offered by nonlinearities and dissipation remaining largely unexplored. Here, we theoretically and experimentally investigate the complex interplay between Bloch band transport, nonlinearity, and dissipation, exploring how a synthetic dimension realised in the frequency space of a coherently-driven optical resonator influences the dynamics of nonlinear waves of the system. In particular, we observe and study nonlinear dissipative Bloch oscillations occurring along the synthetic frequency dimension, sustained by localized dissipative structures (solitons) that persist endlessly in the resonator. The unique properties of the dissipative soliton states can extend the effective size of the synthetic dimension far beyond that achieved in the linear regime, as well as enable long-lived Bloch oscillations and high-resolution probing of the underlying band structure. Besides representing the first experimental study of the interplay between Bloch oscillations and dissipative solitons, our work establishes Kerr resonators as an ideal platform for the study of nonlinear dynamics in long-scale synthetic dimensions, with promising applications in topological photonics.

physics.optics↗

arXiv2021

Self-Pulsing in driven-dissipative photonic Bose-Hubbard dimers

We experimentally investigate the nonlinear dynamics of two coupled fiber ring resonators, coherently driven by a single laser beam. We comprehensively explore the optical switching arising when scanning the detuning of the undriven cavity, and show how the driven cavity detuning dramatically changes the resulting hysteresis cycle. By driving the photonic dimer out-of-equilibrium, we observe the occurrence of stable self-switching oscillations near avoided resonance crossings. All results agree well with the driven-dissipative Bose-Hubbard dimer model in the weakly coupled regime.

physics.optics↗

arXiv2021

Parametrically driven Kerr cavity solitons

Temporal cavity solitons are optical pulses that propagate indefinitely in nonlinear resonators. They are currently attracting a lot of attention, both for their many potential applications and for their connection to other fields of science. Cavity solitons are phase locked to a driving laser. This is what distinguishes them from laser dissipative solitons and the main reason why they are excellent candidates for precision applications such as optical atomic clocks. To date, the focus has been on driving Kerr solitons close to their carrier frequency, in which case a single stable localised solution exists for fixed parameters. Here we experimentally demonstrate, for the first time, Kerr cavity solitons excitation around twice their carrier frequency. In that configuration, called parametric driving, two solitons of opposite phase may coexist. We use a fibre resonator that incorporates a quadratically nonlinear section and excite stable solitons by scanning the driving frequency. Our experimental results are in excellent agreement with a seminal amplitude equation, highlighting connections to hydrodynamic and mechanical systems, amongst others. Furthermore, we experimentally confirm that two different phase-locked solitons may be simultaneously excited and harness this multiplicity to generate a string of random bits, thereby extending the pool of applications of Kerr resonators to random number generators and Ising machines.

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