Alain Villeneuve

The nonlinear optical properties of AlGaAs at the half band gap

We report experimental values for the nonlinear optical coefficients of AlGaAs, in the half-band-gap spectral region. The dispersion of the nonlinear refractive-index coefficient, n/sub 2/, is measured for both TE- and TM-polarized light. We observe n/sub 2/(TE)>n/sub 2/(TM) and a ratio of cross-phase modulation to self-phase modulation (TE) of /spl sim/0.95, as predicted from band structure calculations. The spectral dependence of the two- and three-photon absorption coefficients are also measured. Finally, the implications for all-optical switching and spatial soliton propagation are discussed.

Fabrication and characterization of integrated optical waveguides in sulfide chalcogenide glasses

This paper reports on the fabrication process of As-S-(Se)-based chalcogenide glass optical waveguides using three techniques: photolithography, laser beam writing, and ion implantation. The fabrication method of the bulk sulfide glasses and the processing of integrated devices are described and assessed in light of the propagation characteristics and optical losses in each case.

Ultrafast all‐optical switching in semiconductor nonlinear directional couplers at half the band gap

Efficient ultrafast all‐optical switching in nonlinear directional couplers made of AlGaAs and AlGaAs/GaAs quantum wells near half the band gap is reported. The switching is limited by multiphoton absorption which is dominated by three‐photon absorption in this spectral range. The three‐photon absorption in the quantum well nonlinear directional coupler is stronger than that of bulk AlGaAs. Autocorrelations of the output pulses in the bar and cross states confirm pulse breakup through nonlinear coupling, and illustrate the effects of multiphoton absorption. All sets of experimental data are fitted well by a theoretical model.

Compensating for dispersion and the nonlinear Kerr effect without phase conjugation.

We propose the use of a dispersive medium with a negative nonlinear refractive-index coefficient as a way to compensate for the dispersion and the nonlinear effects resulting from pulse propagation in an optical fiber. The undoing of pulse interaction might allow for increased bit rates.

As 2 S 3 photosensitivity by two-photon absorption: holographic gratings and self-written channel waveguides

We observed two-photon-induced refractive-index changes in As2S3 by exposure in the 800-nm region. We studied this photosensitivity by writing interference gratings on a 2-μm As2S3 thin film. This property is the key to creating self-written channel waveguides in a planar As2S3 slab.

First- and second-order Bragg gratings in single-mode planar waveguides of chalcogenide glasses

First- and second order Bragg reflectors at telecommunication wavelength (1.5 /spl mu/m) were fabricated in single-mode monolayer (As/sub 2/S/sub 3/) and multilayer (AsSSe-AsS) chalcogenide glass (ChG) planar waveguides with near bandgap illumination using an interferometric technique. Reflectivities as high as 90% near 1555 nm, and index modulations up to 3/spl times/10/sup -4/ were achieved. The volume photodarkening effect is the principal mechanism involved in the formation of the Bragg gratings.

High photoluminescence in erbium-doped chalcogenide thin films

Abstract The spectral properties of the chalcogenide glasses As2S3 and As24S38Se38-doped with Er3+ are presented and discussed. Thin films were formed by thermal evaporation and the erbium doping was obtained by subsequent ion implantation. Strong Er3+ emission at 1.54 μm has been observed. The high refractive index of these chalcogenide glasses lead to Er3+ emission cross-sections (15×10 −21 cm 2 ) which are two times higher than for doped silica glass. The lifetime of the Er3+ metastable 4I13/2 energy level was measured to be 2.3 ms. This short lifetime is consistent with the high emission cross-section. Furthermore, the very low phonon energies of chalcogenide glasses lead to relatively long lifetimes of the Er3+ 4I11/2 pump level, which have been measured to be of the order of 0.25 ms. These spectral properties make this glass a good candidate for applications in the field of integrated optics.

Nonlinear refractive‐index and two photon‐absorption near half the band gap in AlGaAs

The wavelength dependence of the nonlinear refractive index and two‐photon absorption coefficient near half the band gap was measured in an AlGaAs waveguide. The two photon figure of merit for efficient nonlinear optics in AlGaAs is shown to be quite favorable for photon energies less than one half the band gap.

Coherent anti-Stokes Raman scattering hyperspectral tissue imaging with a wavelength-swept system

We present a wavelength-swept coherent anti-Stokes Raman scattering (WS-CARS) spectroscopy system for hyperspectral imaging in thick tissue. We use a strategy where the Raman lines are excited sequentially, circumventing the need for a spectrometer. This fibre laser system, consisting of a pump laser synchronized with a rapidly tunable programmable laser (PL), can access Raman lines over a significant fraction of the high wavenumber region (2700–2950 cm−1) at rates of up to 10,000 spectral points per second. To demonstrate its capabilities, we have acquired WS-CARS spectra of several samples as well as images and hyperspectral images (HSI) of thick tissue both in forward and epi-detection. This instrument should be especially useful in providing local biochemical information with surrounding context supplied by imaging.

Limitation due to three‐photon absorption on the useful spectral range for nonlinear optics in AlGaAs below half band gap

We report measurements of the spectral dispersion and the magnitude of three‐photon absorption in Al0.18Ga0.82As for photon energies between one half and one third the band gap and show that a two‐parabolic‐band model is valid in this material. These results indicate that there is a limited spectral range below half the band gap in AlGaAs (and presumably all semiconductors) in which the bound electronic optical nonlinearity can be used without significant multiphoton absorption.