Longitudinal spatial hole burning in a gain clamped semiconductor optical amplifier

Abstract

Summary form only given. A microscope objective mounted on a computerized two-axis translation stage allows us to measure spontaneous emission (SE) spectra along the InGaAsP active layer of a gain clamped semiconductor optical amplifier (GC-SOA) with a 1510 nm internal lasing mode selected by two DBRs of different reflectivity (0% and 98%). From a careful fitting of the SE spectra we can obtain the carrier density (n), the carrier temperature (T) and the band gap energy (E). The measurements have been performed with and without injection of a 0.3 mW CW beam at 1540 nm into the low reflectivity DBR facet. The density variations and the carrier heating in the amplifier are shown. For 50 and 100 mA, the carrier density continuously decreases along the direction where the injected cw beam is amplified via stimulated recombination, therefore consuming carriers as it is amplified. The temperature reported is the carrier temperature. The increase that we observe may however have two separate origins linked with the temperature of the lattice or to the heating of the carriers above the lattice temperature. We get information on this contribution from the variations of the band gap of the active layer under operation. As for the carrier temperature three main sources may account for this heating: Auger recombination, Joule heating and stimulated recombination. Carrier clamping above threshold prevents Auger recombination from playing an important role even at the highest current. The observed inhomogeneous heating might be caused by stimulated recombination which removes carriers with energies below the average energy. However, the computed difference is very small and should not account for the large changes observed. Joule heating should be proportional to the square of the driving current and indeed our data roughly follow this variation. We presently favor this last mechanism.