Debanuj Chatterjee

Etude théorique des amplificateurs sensibles à la phase des fibres pourles applications: Les amplificateurs paramétriques à fibre optique (FOPA) sont prometteurs pour les systèmes de communication de demain. En particulier, les amplificateurs sensibles à la phase des fibres offrent des fonctionnalités intéressantes comme un faible bruit et un gain élevé, ce qui en fait des candidats potentiels pour des applications dans les liaisons photoniques micro-ondes. Cette thèse propose une étude théorique de tels amplificateurs sensibles à la phase destinés à certaines applications.La première partie de la thèse est consacrée au développement d'un modèle analytique pour la propagation de sept ondes continues à travers un FOPA. Le système est résolu lorsque les effets non linéaires de la fibre ne sont pas trop forts. Le modèle développé révèle le rôle important des ondes d'ordre supérieur dans la détermination des performances d'amplification du FOPA. Des stratégies sont formulées pour améliorer l'amplification. La possibilité d'une conversion de fréquence sensible à la phase avec seulement deux ondes de pompe est également prédite.Dans la deuxième partie de cette thèse, la possibilité d'introduire un amplificateur sensible à la phase dans une liaison photonique hyperfréquence pour la distribution de signaux analogiques est étudiée. Un modèle numérique est utilisé pour simuler comment les non-linéarités RF dans une liaison photonique hyperfréquence sont amplifiées par le FOPA. Les performances de la liaison lorsque le FOPA atteint la saturation du gain sont également étudiées. L'étude révèle la possibilité d'une atténuation de la non-linéarité RF en utilisant la non-linéarité de la fibre. La mise en œuvre de telles techniques pourrait conduire à la réalisation de liaisons photoniques hyperfréquences à longue portée et hautement linéaires pour les applications de déport d'antenne.

We demonstrate a polarization-maintaining, all-fiber electro-optic modulation comb source delivering 27.5 fs pulses at 10 GHz and 13 kW peak power. A novel architecture based on cascaded normal- and anomalous-dispersion fibers, with minimal splice loss, enables multi-stage spectral broadening and compression leading to 100 compression factor, with 65% conversion efficiency from the amplifier. These results set a new benchmark for high-repetition-rate ultra-fast comb sources suitable for nonlinear spectroscopy and dual-comb metrology.

High-resolution ultrasound based imaging techniques like photoacoustic (PA) imaging that require fast detection of acoustic waves, are often coupled with an opto-mechanical sensor like a Fabry–Pérot cavity (FPC) for enhanced sensitivity at high frequency. Due to the inherent inhomogeneity of the FPC thickness, the resonance of the cavity can exhibit a spatial distribution, requiring dynamic adjustment of the interrogation wavelength when raster-scanning the sensor with a probe beam. To avoid this, we propose in this work the use of an electro-optically modulated dual-comb light source for rapid acoustic wave sensing within a specified bandwidth. Utilizing a dual-comb vibrometry approach, we demonstrated a proof-of-principle of the technique, with real-time detection of 10 MHz acoustic waves simultaneously with three different teeth (separated by 10 GHz) of the dual-frequency comb, achieving a 20 ns temporal resolution. We also investigated the system’s sensitivity limit in terms of the strength of the detected acoustic waves, opening new possibilities for ultrafast PA imaging modalities.

We make a comparative study of the impact of fiber configuration on relative phase noise of a nonlinearly broadened electro-optic dual-comb light source. In particular, we considered two all-fiber platforms for the comb broadening, where the two combs were broadened (a) in the same core (counter-propagation configuration) and (b) in different cores of a multicore fiber (same facet input). Although far from the comb center, the RF synthesizer noise is dominant, leading to the same relative phase noise for different configurations, near the comb center, using two distinct cores in a multicore fiber allows a significant reduction of the residual phase noise compared to a counter-propagation in the same core. These results are also verified using a continuous wave in a simple traditional interferometric setup, where better mutual coherence is obtained when propagating through two different cores of a multicore fiber compared to two different single core fibers, or same core with counter-propagation. These results highlight the advantage of multicore fibers for nonlinear broadening of two mutually coherent frequency combs, essential for dual-comb or multi-comb spectroscopic techniques.

We make a comparative study of the impact of fiber configuration on relative phase noise of a nonlinearly broadened electro-optic dual-comb light source. In particular, we considered two all-fiber platforms for the comb broadening, where the two combs were broadened (a) in the same core (counter-propagation configuration) and (b) in different cores of a multicore fiber (same facet input). Although far from the comb center, the RF synthesizer noise is dominant, leading to the same relative phase noise for different configurations, near the comb center, using two distinct cores in a multicore fiber allows a significant reduction of the residual phase noise compared to a counter-propagation in the same core. These results are also verified using a continuous wave in a simple traditional interferometric setup, where better mutual coherence is obtained when propagating through two different cores of a multicore fiber compared to two different single core fibers, or same core with counter-propagation. These results highlight the advantage of multicore fibers for nonlinear broadening of two mutually coherent frequency combs, essential for dual-comb or multi-comb spectroscopic techniques.

We report recent results on frequency comb generation in high-quality factor fiber Fabry-Perot resonators in our laboratory. These platforms not only facilitate a plug-and-play integration into photonic systems via FC/PC connectors but also enable the generation of broadband and powerful frequency combs in the GHz range. Specifically, we will demonstrate the generation of modulation instability, cavity solitons, switching waves, and novel interactions between Kerr and Brillouin effects, resulting in a stable frequency comb at a few GHz repetition rate.

We report an all-fiber-based experimental setup to generate a correlated photon-pair comb using Four Wave Mixing (FWM) in Highly non-linear fiber (HNLF). Temporal correlations of the generated photons were confirmed through coincidence measurements. We observed a maximum of 32 kcps, with a coincidence to accidental ratio of $17 \pm 1$. To further understand the underlying processes, we also simulated a generalized FWM event involving the interaction between an arbitrary frequency comb and a Continuous Wave (CW) pump. non-linear dynamics through the HNLF were modelled using Schrödinger propagation equations, with numerical predictions agreeing with our experimental results.

This paper presents a novel approach to dual-frequency comb generation utilizing a single fiber Fabry–Perot resonator, advancing the implementation of these sources in fiber-based systems. Dual-comb applications such as spectroscopy, ranging, and imaging, known for their high-resolution and rapid data acquisition capabilities, benefit significantly from the stability and coherence of optical frequency comb sources. Our method leverages the birefringent property of the resonator induced by the optical fiber to generate two orthogonally polarized optical frequency combs in a monolithic resonator. This approach allows for the generation of two different frequency combs with slightly different repetition rates, exhibiting excellent mutual coherence, making it highly relevant for dual-comb applications. The 40 nm bandwidth generated combs are induced by switching-waves in a normal dispersion fiber Fabry-Perot resonator. These comb types have the advantage of being easily generated by a pulse pumping scheme, which is employed in this study. Finally, the potential of the source is demonstrated by a proof-of-concept spectroscopy measurement.

We demonstrate the signal-to-noise ratio (SNR) and/or the recording speed improvement of dual comb spectroscopy (DCS) with time- programmed electro-optically modulated (EOM) frequency combs, in a simple all-fiber architecture. Unlike mode-locked laser based combs, where time-programming requires complex locking mechanisms, time-programming in EOM combs is simple and robust. Thus by directly engineering time-shifts into the pulse train of an EOM comb, the dead time of the interferogram signal in DCS is reduced. The utilized time-shifting technique is theoretically analyzed and the results are experimentally verified. A SNR improvement of 11.6 dB or a 12 times reduction in recording speed is demonstrated experimentally with this simple method. These results open new possibilities for improvement of SNR and/or recording speed of EOM-based multi-comb spectroscopic techniques.

Using electro-optic dual-comb light source, we demonstrate rapid ultrasound sensing with a Fabry-Pérot cavity. We perform real-time 10 MHz acoustic wave detection with 20 ns temporal resolution, suggesting potential applications in photoacoustic imaging technologies.