Spatially dispersive scheme for transmission and synthesis of femtosecond pulses through a multicore fiber.

A new scheme is presented for fiber transmission of ultrashort laser pulses. A dispersive device divides the input pulses into spatially separated spectral components which are individually launched in the different channels of a multicore fiber before being recombined at the output by a second dispersive device. The parallel transmission of narrow spectral bands avoids self-phase modulation and could be appropriate to deliver high peak power pulses. Phase management of the spectral bands by an active element offers recovery of the seed pulse duration at the fiber output as well as pulse shaping capabilities. Both are reported in a proof of concept experiment using 190 fs input pulses and a 5 cores polarization maintaining fiber. Extension of the concept to femtosecond pulses amplification is suggested.

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.

Control of supercontinuum generation and soliton self-frequency shift in solid-core photonic bandgap fibers.

We experimentally investigate the nonlinear propagation of subnanosecond pulses in solid-core photonic bandgap fibers. By launching pulses with a few kilowatts peak power, a flat supercontinuum is generated. The long-wavelength edge of the supercontinuum can be controlled thanks to the original linear properties inherent to solid-core photonic bandgap fibers. This allows one to tailor the generated supercontinuum radiation and to keep it over a given spectral range of interest without any significant power loss.

White-light cw-pumped supercontinuum generation in highly GeO(2)-doped-core photonic crystal fibers.

GeO(2)-doped-core photonic crystal fibers show greatly enhanced Kerr and Raman responses with respect to pure silica without any significant modification of the group-velocity dispersion curve. We show that such fibers allow a significant improvement of cw-pumped supercontinuum generation. We report for the first time to our knowledge the generation of a white-light cw-pumped supercontinuum spanning from 470 nm to more than 1750 nm.

Design of a photonic crystal fiber for phase-matched frequency doubling or tripling.

We report on a possible phase matching between two fundamental modes guided in an appropriately designed photonic crystal fiber. The phase index matching condition can be perfectly fulfilled for second or third harmonic generation and for wavelengths over a large spectral range, simply by tuning the lattice pitch. This can be achieved in such a structure thanks to the coexistence of total internal reflection and photonic bandgap guidance, leading to two different dispersive behaviours for the fundamental and the harmonic waves.

Solid photonic bandgap fiber assisted by an extra air-clad structure for low-loss operation around 1.5 microm.

We demonstrate that our previous loss results [1] in an all-solid photonic bandgap fiber were in fact limited by bend loss. A new design, based on the addition of an extra ring of air holes on the outside of the all solid photonic bandgap structure, is then proposed, realized and characterized. We demonstrate that it significantly reduces both the fiber diameter and its sensitivity to bend loss.

Time evolution of the second-order nonlinear distribution of poled Infrasil samples during annealing experiments.

The spatial distribution of the second-order nonlinearity induced in thermally poled Infrasil silica samples is recorded after thermal annealing experiments. Two regimes have been studied: short and long poling durations. For short poling durations, the observations are in good agreement with a model where only one ion type recombines inside the depletion region. The nonlinear distribution and erasure observed for the other case are well explained by considering the addition of another positive-charged ion injected during the poling process. This second ion acts as a barrier during thermal annealing and reduces the mobility of the first one.

Modeling of the chi(2) susceptibility time-evolution in thermally poled fused silica.

The dynamics of the second-order nonlinearity induced in a thermally poled Infrasil silica glass is experimentally and theoretically studied. 200 mum and 500 mum-thick samples have been poled for different durations varying from 1 minute to 100 minutes. After the poling process, the magnitude and the spatial distribution of the induced chi((2)) susceptibility have been characterized accurately with the "layer peeling" method. A two-charge carrier model with an electric field dependant charge injection is used to explain the experimental time-evolution of the chi((2)) profiles. A good agreement between experimental results and simulations is reported.

Second-harmonic generation of thermally poled chalcogenide glass.

Second harmonic generation (SHG) has been obtained in a sample of Ga5Ge20Sb10S65 glass submitted to a thermal poling treatment. An original characterization method is used for the determination of the induced second-order nonlinear profile. A reproducible chi(2) susceptibility of 4.4 +/- 0.4 pm/Volt was achieved for specific poling conditions.

Fabrication and characterization of an all-solid 2D photonic bandgap fiber with a low-loss region (< 20 dB/km) around 1550 nm.

The fabrication and characterization of an all-solid photonic bandgap fiber is reported. The fiber presents a low-loss region (< 20 dB/km) around 1550 nm and can be used as single-mode even for a fiber core diameter as large as 20 microm. The fiber presents a zero dispersion at the short wavelength edge of the bandgap. The measured polarisation mode dispersion is wavelength dependent but remains small (few ps/km1/2). This fiber opens the possibility to realize low-loss large mode area bandgap fiber with a doped core and or Bragg gratings.

Influence of electrode composition on the second-order nonlinearity profile in thermally poled silica glass.

Silica glass plates (Infrasil from Heraeus) have been thermally poled with different types of electrodes (evaporated or pressed-on) having different chemical compositions (Au, Al, n-doped Si or p-doped Si). We show for the first time to our best knowledge that the profile of the induced second-order nonlinearity strongly depends on the composition of electrodes used for the thermal poling process.

Improvements of solid-core photonic bandgap fibers by means of interstitial air holes.

We report the fabrication, characterization and modeling of a solid-core photonic bandgap fiber with interstitial air holes between the cladding rods. The presence of these interstitial air holes leads to a great improvement of optical properties for this kind of fiber. Particularly, we demonstrate that confinement losses and bend sensitivity are substantially reduced. Our experimental results for this new solution are well supported by numerical results.

Efficient Bragg gratings in phosphosilicate and germanosilicate photonic crystal fiber.

We present ArF laser-induced dynamics of Bragg grating (BG) growths in phosphosilicate-doped or germanosilicate-doped core photonic crystal fibers (PCFs). To this end, we have adapted the technique of H2 loading, usually used in conventional fiber, to the case of microstructured fiber, allowing both the concentration of hydrogen in the PCFs to be kept nearly constant for the time of the exposure and the BG spectra to be easily recorded. We compared the characteristics of BG growths in the two types of PCF to those in conventional step-index fibers. We then conducted a study of the thermal stability of the BGs in PCFs through 30 min of isochronal annealing. At the same time we discuss the role played by the microstructuration and the doping with regard to the grating contrast and the Bragg wavelength stability.

Photoinscription of Bragg gratings within a germanosilicate fiber subjected to a high static electric field.

The kinetics of Bragg grating growth in germanosilicate fibers subjected to a high static electric field are compared with those obtained without any electric field. The gratings were written by exposure of the fiber core to laser light at 244 or 193 nm. These experiments gave some clues about the mechanisms responsible for both the photosensitivity in germanosilicate fibers and the nonlinear second-order UV-induced susceptibility in silica glasses. The refractive-index modulation proved to be significantly higher in the fibers subjected to an electric field. Furthermore, the change in the fiber's mean effective refractive index as a function of exposure time was not monotonic. This evolution can be explained by the assumption that some electric-field-induced diffusion of electron trapped centers [Ge(1) and Ge(2)] from the fiber core is involved.