B. Barviau

Parabolic pulse generation with active or passive dispersion decreasing optical fibers

We experimentally demonstrate the possibility to generate parabolic pulses via a single dispersion decreasing optical fiber with normal dispersion. We numerically and experimentally investigate the influence of the dispersion profile, and we show that a hybrid configuration combining dispersion decrease and gain has several benefits on the parabolic generated pulses.

Spectral broadening of a multimode continuous- wave optical field propagating in the normal dispersion regime of a fiber

We investigate experimentally and theoretically the broadening of the optical spectrum of a multimode cw field propagating in the normal dispersion regime of a single-mode fiber. The width of the optical spectrum is not a monotonic function of propagation length. This behavior arising from the interplay between the Kerr effect and group-velocity dispersion contrasts with spectral broadening of mode-locked pulses.

Control of pulse-to-pulse fluctuations in visible supercontinuum

Long-pulse supercontinuum sources are initiated by modulation instability and consequently suffer from stochastic shot-to-shot variations of their spectral power density. In this paper, we provide a measurement of pulse-to-pulse fluctuations over the whole supercontinuum spectrum, and we show that their spectral dependence follows the group index curve of the fiber. Then, we demonstrate a significant reduction of supercontinuum pulse-to-pulse fluctuations in the visible by using a photonic crystal fiber with longitudinally tailored guidance properties. We finally show numerically that this new source would allow a significant improvement of the signal-to-noise ratio in fluorescence microscopy.

Experimental signature of optical wave thermalization through supercontinuum generation in photonic crystal fiber

We report an experimental, numerical and theoretical study of the incoherent regime of supercontinuum generation in a two zero-dispersion wavelengths fiber. By using a simple experimental setup, we show that the phenomenon of spectral broadening inherent to supercontinuum generation can be described as a thermalization process, which is characterized by an irreversible evolution of the optical field towards a thermal equilibrium state. In particular, the thermodynamic equilibrium spectrum predicted by the kinetic wave theory is characterized by a double peak structure, which has been found in quantitative agreement with the numerical simulations without adjustable parameters. We also confirm that stimulated Raman scattering leads to the generation of an incoherent structure in the normal dispersion regime which is reminiscent of a spectral incoherent soliton.

Efficient blue conversion from a 1064 nm microchip laser in long photonic crystal fiber tapers for fluorescence microscopy.

Using a low-cost microchip laser and a long photonic crystal fiber taper, we report a supercontinuum source with a very efficient visible conversion, especially in the blue region (around 420 nm). About 30 % of the total average output power is located in the 350-600 nm band, which is of primary importance in a number of biophotonics applications such as flow cytometry or fluorescence imaging microscopy for instance. We successfully demonstrate the use of this visible-enhanced source for a three-color imaging of HeLa cells in wide-field microscopy.

Toward a thermodynamic description of supercontinuum generation.

Based on the kinetic wave theory, we describe continuous-wave supercontinuum generation as a thermalization process, i.e., an irreversible evolution of the optical field towards a state of maximum nonequilibrium entropy.

Black-light continuum generation in a silica-core photonic crystal fiber

We report the observation of a broadband continuum spanning from 350 to 470 nm in the black-light region of the electromagnetic spectrum as a result of picosecond pumping a solid-core silica photonic crystal fiber at 355 nm. This was achieved despite strong absorption and a large normal dispersion of silica glass in the UV. Further investigations reveal that the continuum generation results from the interplay of intermodally phase-matched four-wave mixing and cascaded Raman scattering. We also discuss the main limitations in terms of bandwidth and power due to temporal walk-off, fiber absorption, and the photo darkening effect, and we suggest simple solutions.

Significant reduction of power fluctuations at the long-wavelength edge of a supercontinuum generated in solid-core photonic bandgap fibers

We show that the infrared edge of supercontinua generated in solid core photonic bandgap fibers is characterized by a very different temporal behavior than the one obtained in standard fibers. In particular, pulse-to-pulse spectral power fluctuations are significantly reduced near the bandgap edge, and the statistical distribution is quasi-gaussian. The spectral dynamics of this process and statistical properties are investigated experimentally and confirmed by numerical simulations. The reduction of power fluctuations originates from the cancellation of the soliton self-frequency shift near the bandgap edge.

Simple Method for Measuring the Zero-Dispersion Wavelength in Optical Fibers

Group velocity dispersion (GVD) is one of the key characteristics of optical fibers. It is thus important to be able to accurately measure this parameter. Several techniques have been developed to reach this goal [1] including methods based on nonlinear effects (mainly the four wave mixing (FWM) process [2,3]) valid for fiber samples ranging from a few meters up to hundred of meters. However, these methods require an important number of measurements as well as an accurate knowledge of the fiber nonlinear coefficient and of the launched pump peak power. In this work, we propose an extremely simple nonlinear method, free of these constraints, and that requires the measurement of only two optical spectra (Fig.1) to retrieve the zero-dispersion wavelength (ZDW) of an optical fiber. Moreover, this technique enables us also to determine the ratio between the third- and fourth-order dispersion terms expressed at the ZDW.

Towards a thermodynamic description of supercontinuum generation

Based on the kinetic wave theory, we describe continuous-wave supercontinuum generation as a thermalization process, i.e., an irreversible evolution of the optical field towards a state of maximum nonequilibrium entropy.