Michaël Delqué

Frequency-selective excitation of guided acoustic modes in a photonic crystal fiber.

We present experimental and numerical results demonstrating the simultaneous frequency-selective excitation of several guided acoustic Brillouin modes in a photonic crystal fiber with a multi-scale structure design. These guided acoustic modes are identified by using a full vector finite-element model to result from elastic radial vibrations confined by the wavelength-scale air-silica microstructure. We further show the strong impact of structural irregularities of the fiber on the frequency and modal shape of these acoustic resonances.

Photonic crystal fiber mapping using Brillouin echoes distributed sensing

In this paper we investigate the effect of microstructure irregularities and applied strain on backward Brillouin scattering by comparing two photonic crystal fibers drawn with different parameters in order to minimize diameter and microstructure fluctuations. We fully characterize their Brillouin properties including the gain spectrum and the critical power. Using Brillouin echoes distributed sensing with a high spatial resolution of 30 cm we are able to map the Brillouin frequency shift along the fiber and get an accurate estimation of the microstructure longitudinal fluctuations. Our results reveal a clear-cut difference of longitudinal homogeneity between the two fibers.

Generation of multicolor vector Kerr solitons by cross-phase modulation, four-wave mixing, and stimulated Raman scattering

We numerically and experimentally show the existence of multicolor vector spatial solitons in a Kerr planar waveguide through the combined effects of cross-phase modulation, four-wave mixing, and stimulated Raman scattering. Mutual spatial guiding of the Raman-Stokes, anti-Stokes, and pump waves is achieved in the high-conversion regime mainly by cross-phase modulation and phase-matched four-wave mixing induced by a power imbalance between Stokes and anti-Stokes components, leading to the generation of a clear-cut sech-shape three-frequency spatial soliton.

SBS Mitigation in a Microstructured Optical Fiber by Periodically Varying the Core Diameter

In this letter, we experimentally demonstrate a 4-dB increase of the stimulated Brillouin scattering threshold in a microstructured optical fiber. This result is obtained by periodically varying the size of the air-hole structure by only 7% amplitude, while keeping a low attenuation coefficient. The efficiency of this passive technique is verified by use of the Brillouin echoes-distributed sensing technique where the Brillouin frequency-shift oscillation is clearly observed.

Suppression of SBS in a photonic crystal fiber with periodically-varied core diameter

We experimentally demonstrate 7 dB improvement in Brillouin suppression in a photonic crystal fiber by periodically varying the size of the air-hole-structure by only 7% amplitude while keeping a low attenuation coefficient.

Experimental observation of Brillouin linewidth broadening and decay time in photonic crystal fiber

We present a novel distributed sensing technique that makes possible the observation of Brillouin gain spectral distribution and acoustic decay time in photonic crystal fiber as well as in standard single-mode fiber.

Effect of inhomogeneities on backward and forward Brillouin scattering in Photonic Crystal Fibers

Photonic Crystal Fibers (PCF) play a crucial role for fundamental investigations such as acousto-optical interactions as well as for applications, such as distributed sensors. One limiting factor for these experiments is the fiber inhomogeneity owing to the drawing process. In this paper we study the effect of structural irregularities on both the backward and forward Brillouin scattering by comparing two PCFs drawn with different parameters, in order to minimize diameter fluctuations. We fully characterize their Brillouin properties including the backward Brillouin spectrum, the Brillouin threshold, a distributed measurement along the fibers and polarized Guided Acoustic Wave Brillouin Scattering (GAWBS). In the Brillouin spectrum we observe a single peak as in a singlemode fiber whereas former investigations have often shown a multiple peak spectrum in PCFs with small core. The theoretical and experimental values for the Brillouin threshold are in good agreement, which results from the single peak spectrum. By using a Brillouin echoes distributed sensing system (BEDS), we also investigate the Brillouin spectrum along the fiber with a high spatial resolution of 30 cm. Our results reveal a clear-cut difference between the distributed measurements in the two fibers and confirm the previous experiments. In the same way the GAWBS allows us to estimate the uniformity of the fibers. The spectra show a main peak at about 750 MHz, in accordance with theoretical simulations of the acoustic mode and of the elasto-optical coefficient. The fiber inhomogeneity impacts on the stability and the quality factor of the measured GAWBS spectra. We finally show that the peak frequency of the trapped acoustic mode is more related to the optical effective area rather than the core diameter of the PCF. Thus measuring the main GAWBS peak can be applied for the precise measurement of the effective area of PCFs.

Opto-acoustic coupling and Brillouin phenomena in microstructure optical fibers

Like photonic crystals have revolutionized the way of manipulating optical waves at the sub-micron scale, phononic crystals have more recently played similar decisive role for sound waves, or more generally elastic waves. Then, the idea of coupling light and sound in purposely designed microstructures is now emerging. In this respect, the periodic, wavelength-scale (for both optic and high-frequency acoustic waves) transverse air-hole microstructure of photonic crystal fibers (PCFs) provides additional degrees of freedom for light-sound interactions. PCFs can indeed exhibit photonic and phononic bandgap effects, allowing for tight confinement and joint waveguiding of both types of waves [1]. Electrostriction-driven Brillouin phenomena, namely backward Stimulated Brillouin Scattering (SBS) and forward Guided Acoustic Wave Brillouin Scattering (GAWBS), constitute an important category of such opto-acoustic coupling. The geometry of PCFs can dramatically modify the Brillouin spectrum, the gain and the stimulated Brillouin threshold, globally yielding much richer opto-acoustic dynamics and spectral features than in conventional fibers [2-11]. Specific transverse or longitudinal guided acoustics modes in the 100 MHz-10 GHz range can thus be selectively excited, resonantly enhanced and tightly confined within the microstructure, with an intimate dependence on its μm or sub-μm geometry. All these specific features have great potential for developing novel PCF-based distributed Brillouin sensors [6,7,12-14], for high-resolution longitudinal mapping of the intrinsic fluctuations of the fiber microstructure [15], and more generally for developing original tools of optical signal processing [1-4,9,16,17]. This talk will give a comprehensive overview of these original behaviors in a range of PCFs.

Observation of brillouin linewidth broadening and decay time in photonic crystal fiber

We present a novel distributed sensing technique that allows for the observation of Brillouin gain spectral distribution and acoustic decay time in photonic crystal fiber as well as in standard single-mode fiber.

All-fiber optical parametric amplifier at 1 μm using a microstructured fiber

We demonstrate experimentally an all-fiber optical parametric amplifier and wavelength converter at 1μm using a microstructured fiber and an electro-optical intensity modulator. A gain of 40dB is obtained for a signal at 1053nm. The experimental gain bandwidth agrees well with the theoretical one including Raman gain.