arXiv subjects

Camille-Sophie Brès

Publications and source records attributed to Camille-Sophie Brès.

At least 19 recordsLinked to original sources

arXiv2026

Thermo-optic dynamics of effective epsilon-near-zero media

Epsilon-near-zero (ENZ) photonic media exhibit extreme optical dispersion that enables unconventional light-matter interactions and enhanced optical nonlinearities. Recent studies suggested that thermo-optic effects, traditionally regarded as slow and secondary, can be strongly modified under the ENZ condition. Here we establish thermo-optic reconfiguration of effective media as a unified physical framework to describe both static and transient thermo-optic phenomena in ENZ systems. Using a CMOS-compatible effective medium operating in the visible spectral range, we experimentally demonstrate that temperature variation, whether under thermal equilibrium or transient excitation, reconfigures the constitutive parameters defining the ENZ condition, giving rise to pronounced linear and nonlinear optical responses. At thermal equilibrium, this reconfiguration manifests itself as static ENZ wavelength shift with an unprecedentedly large thermal-spectral modulation rate and an effective thermo-optic coefficient on the order of $10^{-1}$ K$^{-1}$. Under ultrafast excitation, we observe a picosecond-scale thermo-optic nonlinear response induced by transient heating. This response can be consistently interpreted as a time-dependent reconfiguration of the effective ENZ medium, corresponding to a transient evolution of its optical parameters. By reframing thermo-optic effects as a process of static and dynamic reconfiguration of effective media, this work provides a unified perspective that bridges thermo-optic physics, effective-medium theory, and time-varying photonics.

physics.optics↗

arXiv2026

Backward-Wave Difference-Frequency Generation in Thin-Film Lithium Niobate

Second-order nonlinear processes involving counter-propagating light generation have been explored for quantum applications and optical parametric oscillators. However, realizing these processes on integrated photonic platforms such as thin-film lithium niobate (TFLN) remains challenging because of the extremely short quasi-phase matching (QPM) periods required, which are difficult to achieve with standard fabrication workflows. In this work, we achieve 1425 nm periodicity on 800 nm-thick X-cut TFLN via poling prior to etching. We present the first integrated demonstration of backward-wave difference-frequency generation (BWDFG), using a pump near 775 nm and a counter-propagating signal near 1980 nm, and thereby combine the high nonlinear efficiency of QPM with favorable dispersion characteristics. Within the same waveguide, we demonstrate backward-wave second-harmonic generation (BWSHG), where the pump and second-harmonic are counter-propagating, together with BWDFG. Idler generation spans from 1244 nm to 1290 nm and simulations predict extended coverage up to ~2200 nm. This process provides broad spectral tunability while remaining tolerant of fabrication-induced dimensional offsets, addressing a key challenge for the TFLN platform.

physics.optics↗

arXiv2026

Enhancing broadband second harmonic generation in a thin film lithium niobate racetrack resonator with tunable-coupling

Second harmonic generation in thin film periodically poled lithium niobate (PPLN) is constrained by an efficiency-bandwidth trade-off and fabrication-sensitive scaling. We demonstrate a racetrack resonator incorporating a short PPLN section and a tunable Mach-Zehnder interferometer coupler that enables in situ control of the coupling condition, compensating fabrication tolerances and stabilizing operation near critical coupling. The telecom pump is resonantly enhanced, while the near-infrared second harmonic is generated in single pass, eliminating dual-resonance requirements. The device achieves a 35 times efficiency enhancement over a non-resonant structure while maintaining a 7 nm bandwidth. This architecture provides a robust platform for broadband integrated frequency doubling.

physics.optics↗

arXiv2026

Reconfigurable Resonant Multimode Nonlinear Coupling for UV-to-infrared Frequency Generation

On-chip coherent visible and near-infrared (NIR) light generation has broad applications in metrology, bio-sensing, and quantum information. High-Q microresonators are ideal candidates for generating light across such broad wavelength ranges via efficient second- ($χ^{(2)}$) and third-order ($χ^{(3)}$) nonlinear optical processes. However, harnessing these diverse nonlinearities simultaneously in a single microresonator remains elusive yet highly attractive both fundamentally and technologically. Here, we demonstrate coherent light generation from the ultraviolet to NIR in a silicon nitride microresonator pumped by a single continuous-wave telecom laser. This broad frequency generation arises from the interplay of $χ^{(2)}$ and $χ^{(3)}$ nonlinear processes. A cascade of nonlinear processes, including harmonic generation and optical parametric oscillation (OPO), is initiated by the photoinduced second harmonic generation enabled by all-optical poling. The dynamic reconfigurability of this $χ^{(2)}$ nonlinearity enables access to different transverse spatial modes at the second harmonic, enabling highly tunable OPO processes triggered by hybrid modal phase matching conditions and yielding milliwatt-level NIR light. This work sheds new insights into the fundamental physics of cooperative nonlinear multimode interactions in resonant systems and provides a versatile approach for reconfigurable OPOs, highlighting their potential to generate light at wavelengths beyond the reach of photonic integrated lasers.

physics.optics↗

arXiv2025

High-purity frequency-degenerate photon pair generation via cascaded SFG/SPDC in thin film lithium niobate

Frequency-degenerate photon pairs generated using nonlinear photonic integrated devices are a crucial resource for scalable quantum information processing and metrology. However, their realization is hindered by unwanted parametric processes occurring within the same phase matching band, which degrade the signal-to-noise ratio and reduce the purity of the associated quantum states. Here, we propose a dual-pump scheme to produce frequency-degenerate photon pairs, based on cascaded sum-frequency generation and spontaneous parametric down-conversion occurring within a single waveguide, while strongly suppressing parasitic photon pair generation from single-pump processes. This approach significantly simplifies the design compared to microresonator-based methods and enables both pumping and collection of photon pairs entirely in the telecom band. We experimentally validate the concept in a layer-poled thin film lithium niobate waveguide, achieving frequency-degenerate photon pair generation with a brightness of \SI{1.0(3)e5}{\hertz \per \nm \per \square \milli \watt } and a 40 dB suppression of unwanted single-pump processes.

quant-ph↗

arXiv2025

Three-Octave Supercontinuum Generation in Thick Crystalline Aluminum Nitride Waveguides

We report an efficient extension of supercontinuum generation through dispersion engineering of crystalline aluminum nitride (AlN)-on-sapphire waveguides. Using a tailored epitaxial regrowth of AlN epilayers and an optimized fabrication protocol, the dispersion sensitivity to the waveguide cross-section was enhanced allowing for a significant reach extension of both short and long dispersive wave with optimized pumping conditions, reaching down to 550 nm in the visible and up to 4.5 μm in the mid-infrared.

physics.optics↗

arXiv2025

Roadmap: Emerging Platforms and Applications of Optical Frequency Combs and Dissipative Solitons

The discovery of optical frequency combs (OFCs) has revolutionised science and technology by bridging electronics and photonics, driving major advances in precision measurements, atomic clocks, spectroscopy, telecommunications, and astronomy. However, current OFC systems still require further development to enable broader adoption in fields such as communication, aerospace, defence, and healthcare. There is a growing need for compact, portable OFCs that deliver high output power, robust self-referencing, and application-specific spectral coverage. On the conceptual side, progress toward such systems is hindered by an incomplete understanding of the fundamental principles governing OFC generation in emerging devices and materials, as well as evolving insights into the interplay between soliton and mode-locking effects. This roadmap presents the vision of a diverse group of academic and industry researchers and educators from Europe, along with their collaborators, on the current status and future directions of OFC science. It highlights a multidisciplinary approach that integrates novel physics, engineering innovation, and advanced researcher training. Topics include advances in soliton science as it relates to OFCs, the extension of OFC spectra into the visible and mid-infrared ranges, metrology applications and noise performance of integrated OFC sources, new fibre-based OFC modules, OFC lasers and OFC applications in astronomy.

physics.optics↗

arXiv2025

Sputtered AlN buffer layer for low-loss crystalline AlN-on-sapphire integrated photonics

In recent years, aluminum nitride (AlN) has emerged as an attractive material for integrated photonics due to its low propagation losses, wide transparency window, and presence of both second- and third-order optical nonlinearities. However, most of the research led on this platform has primarily focused on applications, rather than material optimization, although the latter is equally important to ensure its technological maturity. In this work, we show that voids, which are commonly found in crystalline AlN-on-sapphire epilayers, have a detrimental role in related photonic structures, as they can lead to propagation losses exceeding 30 dB cm$^{-1}$ at 1550 nm. Their impact on light propagation is further quantified through finite-difference time-domain simulations that reveal that void-related scattering losses are strongly dependent on their size and density in the layer. As a possible solution, we demonstrate that when introducing a thin sputtered AlN buffer layer prior to initiating AlN epitaxial growth, void-free layers are obtained. They exhibit intrinsic quality factors in microring resonators as high as $2.0\times 10^6$, corresponding to propagation losses lower than 0.2 dB cm$^{-1}$ at 1550 nm. These void-free layers are further benchmarked for high-power applications through second-harmonic and supercontinuum generation in dispersion-engineered waveguides. Such layers are highly promising candidates for short-wavelength photonic integrated circuit applications, particularly given the strong potential of AlN for visible photonics. Given that volumetric scattering losses scale as $λ^{-4}$, the platform quality becomes increasingly critical in the visible and ultraviolet range, where our improved layers are expected to deliver enhanced performance.

physics.optics↗

arXiv2025

Broadband spectral mapping of photo-induced second-harmonic generation in silicon nitride microresonators

By employing a pump-probe technique for enhanced spectral mapping of the dynamics in nonlinear frequency conversion, we demonstrate that photo-induced second-harmonic generation (SHG) in silicon nitride (Si3N4) microresonators can persist when transitioning from the preferred doubly resonant condition--where the resonances of the optical harmonics are required to be matched--to a highly detuned state where the generated second harmonic is significantly shifted away from its corresponding resonance. This results in an unconventionally broad conversion bandwidth. Other intriguing phenomena, such as detuning-dependent all-optical poling and nonlinear multi-mode interaction, are also presented for the first time with direct experimental evidence. Our findings provide new insights into the physics of photo-induced second-order (χ^{(2)}) nonlinearity, highlighting its potential applications for nonlinear χ^{(2)} photonics in integrated Si3N4 platform

physics.optics↗

arXiv2025

Ultrabroadband Milliwatt-Level Resonant Frequency Doubling on a Chip

Microresonators are powerful tools to enhance the efficiency of second-order nonlinear optical processes, such as second-harmonic generation, which can coherently bridge octave-spaced spectral bands. However, dispersion constraints such as phase-matching and doubly resonant conditions have so far limited demonstrations to narrowband operation. In this work, we overcome these limitations showing ultrabroadband resonant frequency doubling in a novel integrated device, wherein the resonant enhancement of pump and second harmonic are individually addressed in two distinct and linearly uncoupled microring resonators, each adjusted to target the respective spectral band. The two microresonators are designed and tuned independently, yet share a common interaction region that grants nonlinear coupling over a quasi-phase-matching bandwidth exceeding 200 nm, enabled by the inscription of a photoinduced $χ^{(2)}$ grating. The system allows to not only conveniently disentangle the design parameters of the two microresonators but also to reconfigure the doubly resonant condition electrically, and the phase-matching condition optically. We demonstrate milliwatt-level addressable second-harmonic generation over the entire telecom band and then configure the device to internally generate and upconvert a Kerr frequency comb with bandwidth exceeding 100 nm and upconverted power up to 10 mW.

physics.optics↗

arXiv2025

Integrated tunable green light source on silicon nitride

Integrated green light sources are essential for telecommunications and quantum applications, while the performance of current on-chip green light generation is still limited in power and tunability. In this work, we demonstrate green light generation in silicon nitride microresonators using photo-induced second-order nonlinearities, achieving up to 3.5 mW green power via second-harmonic generation and densely tunable over a 29 nm range. In addition, we report milliwatt-level all-optical poling (AOP) threshold, allowing for amplifier-free continuous-wave AOP. Furthermore, we demonstrate non-cascaded sum-frequency generation, leveraging the combination of AOP and simultaneous coherent frequency combs generation at 1 $μ$m. Such comb-assisted AOP enables switching of the green light generation over an 11 nm range while maintaining the pump within a single resonance. The combination of such highly efficient photo-induced nonlinearity and multi-wavelength AOP enables the realization of low-threshold, high-power, widely-tunable on-chip green sources.

physics.optics↗

arXiv2024

Ultrabroadband tunable difference frequency generation in standardized thin-film lithium niobate platform

Thin-film lithium niobate (TFLN) on insulator is a promising platform for nonlinear photonic integrated circuits (PICs) due to its strong light confinement, high second-order nonlinearity, and flexible quasi-phase matching for three-wave mixing processes via periodic poling. Among the three-wave mixing processes of interest, difference frequency generation (DFG) can produce long wave infrared (IR) light from readily available near IR inputs. While broadband DFG is well studied for mid-IR frequencies, achieving broadband idler generation within the telecom window (near C-band) and the short-wave infrared (near 2 micron) is more challenging due to stringent dispersion profile requirements, especially when using standardized TFLN thicknesses. In this paper, we investigate various standard waveguide designs to pinpoint favorable conditions for broadband DFG operation covering several telecom bands. Our simulations identify viable designs with a possible 3-dB conversion efficiency bandwidth (CE-BW) of 300 nm and our measurements show idler generation from 1418 nm to 1740 nm, limited by our available sources, experimentally confirming our design approach. Furthermore, temperature tuning allows further shift of the idler towards the mid-IR, up to 1819 nm. We also achieve a stretched wavelength range of idler generation by leveraging the longitudinal variation of the waveguide in addition to poling. Finally, our numerical simulations show the possibility of extending the CE-BW up to 780 nm while focusing on waveguide cross-sections that are available for fabrication within a foundry. Our work provides a methodology that bridges the deviations between fabricated and designed cross-sections, paving a way for standardized broadband DFG building blocks.

physics.optics↗

arXiv2024

Monolithic silicon nitride electro-optic modulator enabled by optically-assisted poling

Electro-optic (EO) modulation is a key functionality to have on-chip. However, achieving a notable linear EO effect in stoichiometric silicon nitride has been a persistent challenge due to the material's intrinsic properties. Recent advancements revealed that the displacement of thermally excited charge carriers under a high electric field induces a second-order nonlinearity in silicon nitride, thus enabling the linear EO effect in this platform regardless of the material's inversion symmetry. In this work, we show for the first time optically-assisted poling of a silicon nitride microring resonator, removing the need for high-temperature processing of the device. The optical stimulation of charges avoids the technical constraints due to elevated temperature. By optimizing the poling process, we experimentally obtain a long-term effective second-order nonlinearity of 1.2 pm/V. Additionally, we measure the high-speed EO response of the modulator, showing a bandwidth of 4 GHz, only limited by the quality factor of the microring resonator. This work goes towards the implementation of monolithic, compact silicon nitride EO modulators, a necessary component for high-density integrated optical signal processing.

physics.optics↗

arXiv2024

Self-organized spatiotemporal quasi-phase-matching in microresonators

Quasi-phase-matching (QPM) is a widely adopted technique for mitigating stringent momentum conservation in nonlinear optical processes such as second-harmonic generation (SHG). It effectively compensates for the phase velocity mismatch between optical harmonics by introducing a periodic spatial modulation to the nonlinear optical medium. Such a mechanism has been further generalized to the spatiotemporal domain, where a non-stationary spatial QPM can induce a frequency shift of the generated light. Here we demonstrate how a spatiotemporal QPM grating, consisting in a concurrent spatial and temporal modulation of the nonlinear response, naturally emerges through all-optical poling in silicon nitride microresonators. Mediated by the coherent photogalvanic effect, a traveling space-charge grating is self-organized, affecting momentum and energy conservation, resulting in a quasi-phase-matched and Doppler-shifted second harmonic. Our observation of the photoinduced spatiotemporal QPM expands the scope of phase matching conditions in nonlinear photonics.

physics.optics↗

arXiv2023

A chip-scale second-harmonic source via injection-locked all-optical poling

Second-harmonic generation allows for coherently bridging distant regions of the optical spectrum, with applications ranging from laser technology to self-referencing of frequency combs. However, accessing the nonlinear response of a medium typically requires high-power bulk sources, specific nonlinear crystals, and complex optical setups, hindering the path toward large-scale integration. Here we address all of these issues by engineering a chip-scale second-harmonic (SH) source based on the frequency doubling of a semiconductor laser self-injection-locked to a silicon nitride microresonator. The injection-locking mechanism, combined with a high-Q microresonator, results in an ultra-narrow intrinsic linewidth at the fundamental harmonic frequency as small as 57 Hz. Owing to the extreme resonant field enhancement, quasi-phase-matched second-order nonlinearity is photoinduced through the coherent photogalvanic effect and the high coherence is mapped on the generated SH field. We show how such optical poling technique can be engineered to provide efficient SH generation across the whole C and L telecom bands, in a reconfigurable fashion, overcoming the need for poling electrodes. Our device operates with milliwatt-level pumping and outputs SH power exceeding 2 mW, for an efficiency as high as 280%/W under electrical driving. Our findings suggest that standalone, highly-coherent, and efficient SH sources can be integrated in current silicon nitride photonics, unlocking the potential of $χ^{(2)}$ processes in the next generation of integrated photonic devices.

physics.optics↗

arXiv2023

Integrated Backward Second-Harmonic Generation Through Optically Induced Quasi-Phase Matching

Quasi-phase-matching for efficient backward second-harmonic generation (BSHG) requires sub-$\rmμ$m poling periods, a non-trivial fabrication feat. For the first time, we report integrated first-order quasi-phase-matched BSHG enabled by seeded all-optical poling. The self-organized grating inscription circumvents all fabrication challenges. We compare backward and forward processes and explain how grating period influences the conversion efficiency. These results showcase unique properties of the coherent photogalvanic effect and how it can bring new nonlinear functionalities to integrated photonics.

physics.optics↗

arXiv2022

Observation of SQUID-like behavior in fiber laser with intra-cavity epsilon-near-zero effect

Establishing relations between fundamental effects in far-flung areas of physics is a subject of great interest in the current research. We here report realization of a novel photonic system akin to the radio-frequency superconducting quantum interference device (RF-SQUID), in a fiber laser cavity with epsilon-near-zero (ENZ) nanolayers as intra-cavity components. Emulating the RF-SQUID scheme, the photonic counterpart of the supercurrent, represented by the optical wave, circulates in the cavity, passing through effective optical potential barriers. Different ENZ wavelengths translate into distinct spectral outputs through the variation of cavity resonances, emulating the situation with a frequency-varying tank circuit in the RF-SQUID. Due to the presence of the ENZ element, the optical potential barrier is far lower for selected frequency components, granting them advantage in the gain-resource competition. The findings reported in this work provide a deeper insight into the ultrafast ENZ photonics, revealing a new path towards the design of nanophotonic on-chip devices with various operational functions, and offer a new approach to study superconducting and quantum-mechanical systems.

physics.optics↗

arXiv2022

Single-shot Kramers-Kronig complex orbital angular momentum spectrum retrieval

Orbital angular momentum (OAM) spectrum diagnosis is a fundamental building block for diverse OAM-based systems. Among others, the simple on-axis interferometric measurement can retrieve the amplitude and phase information of complex OAM spectra in a few shots. Yet, its single-shot retrieval remains illusive, due to the signal-signal beat interference inherent in the measurement. Here, we introduce the concept of Kramers-Kronig (KK) receiver in coherent communications to the OAM domain, enabling rigorous, single-shot OAM spectrum measurement. We explain in detail the working principle and the requirement of the KK method, and then apply the technique to precisely measure various characteristic OAM states. In addition, we discuss the effects of the carrier-to-signal power ratio and the number of sampling points essential for rigorous retrieval, and evaluate the performance on a large set of random OAM spectra and high-dimensional spaces. Single-shot KK interferometry shows enormous potential for characterizing complex OAM states in real-time.

physics.optics↗