A. Saïssy

Diffusion Raman stimulée à trois ondes dans une fibre optique

Three-wave stimulated Raman scattering in optical fibers has been studied theoretically in connection with the characteristics of the fiber (core diameter, core-cladding refractive-index difference) and excitation conditions. We observe experimentally this type of scattering in a silica fiber, from which we can estimate the nonlinearity of silica and the index difference of the fiber.

Absolute measurement of the 1.06 μm two-photon absorption coefficient in GaAs

Comparing the recombination light intensity produced in GaAs by a 1.06 μm pulse inducing two-photon absorption, with the intensity produced by a 0.53 μm pulse, we obtain directly the two-photon absorption cross-section. This method can be generalized to other materials.

Laser Raman à fibre émettant dans un très large domaine spectral.

A very broad stimulated emission of light covering almost the entire visible spectrum is provided by a fused silica fiber Raman laser. The fiber is 3.5-50 m long with a 50-microm diameter, and the exciting light at 5320 A has a power of about 60 kW.

Guided‐wave measurement of the 1.06‐μm two‐photon absorption coefficient in GaAs epitaxial layers

The optical perturbation of an infrared wave guided in a GaAs epitaxial layer allows us to measure the two‐photon absorption coefficient β for the wavelength λ=1.06 μm. The use of optical properties of free carriers induced by the two‐photon effect and of guided optical wave techniques strongly enhances method accuracy. The result (β=0.06 cm MW−1) is in good agreement with the most recent bulk measurements and the theoretical values.

Optical determination of free carriers parameters in an epitaxial GaAs layer

The optical perturbation of an infrared wave guided in a GaAs epitaxial layer allows to measure characteristic parameters of free carriers: collision frequency (2·1013 rad·sec−1), depth penetration of induced photopairs (∼2.5μm), relaxation times of free carriers.

Fluorescence and superfluorescence line narrowing and tunability of Nd/sup 3+/ doped fibers

The inhomogeneous behavior of the 1.06 /spl mu/m-neodymium transitions in doped optical fibers have been investigated, using the fluorescence line narrowing technique, pumping on the /sup 4/F/sub 3/2/ and /sup 4/F/sub 5/2/ sublevels at 4 K. Each observed transition has been identified. As the pump wavelength varies, the shift of the main fluorescence line is 40 nm, with the two pumping levels. We have studied the spectral behavior of the superfluorescence as a function of the pump wavelength, the temperature, and the absorbed power. The spectral evolution depends on /spl lambda//sub p/ with 19 nm-tuning range at low temperature. At 300 K, the quasihomogeneous behavior of the transition decreases the tunability to 14 nm. Based on these results, we present a simple technique permitting precise prediction of gain and spectral line shapes of superfluorescent Nd-doped fiber sources. >

Effet Kerr optique dans une fibre optique biréfringente multimode

In this paper, we study the optical Kerr effect theoretically in multimode birefringent optical fibers in connection with the characteristics of the fiber and excitation conditions. We observe experimentally, for a pump power 2 W in the fundamental mode, 70% modulation depth for the probe light with multimodal coupling.

Q-switched operation of a 810 nm thulium-doped fluorozirconate fibre laser

Pulsed emission (350 ns, 810 nm) has been obtained in a 790 nm-pumped thulium doped fluorozirconate ring cavity fibre laser. Calculations of the pump power laser threshold and pulse duration are consistent with experimental measurements. Optimization of this laser is analysed.

Simultaneous measurements of lifetime, gain and emission cross section in a neodymium-doped fiber

A method for measuring the gain and the emission cross section of the four-level neodymium system in doped waveguides is presented. The method is based on a temporal analysis of the fluorescence decay occurring when the pump is switched off, after establishing a steady-state with high levels of absorbed power. For the case of doped fibers, results obtained using this method are compared with the usual low signal amplification technique, using a launched signal in the fiber, and the agreement is good. It is shown that the technique allows a rapid, simple method of determining low signal gain.<<ETX>>

Near infrared emission in Ho3+ fluorozirconate fibres

Near infrared absorption and emission of Ho3+ in fluorozirconate fibres are studied at room and nitrogen temperature. Stimulated emission cross sections are deduced, sigma (1.19 mu m)=0.7*10-20 cm2, sigma (2.06 mu m)=1.45*10-20 cm2, and self-consistency with stimulated spectra is verified and discussed.