Abstract

We present a mid-IR semiconductor optical amplifier based on a quantum cascade (QC) active region, which has been used to attain high output powers from distributed-feedback (DFB) QC lasers without affecting their single mode behavior. The QC layer structure is the same as outlined in ref [1]. The device was realized as schematically shown in the inset of Fig. 1, i.e. in a master oscillator—power amplifier (MOPA) configuration. The oscillator is a 16 μm wide, 2 mm long ridge waveguide where the single mode laser action is achieved by wet-etching a first-order Bragg grating in the topmost layer of the waveguide.² The power amplifier is a linearly tapered structure with no grating on top, 0.5 mm long and with a final width of 100 μm. Selective current injection in the different sections is achieved by separate contact areas. In order to keep a high (>30 dB) side mode suppression ratio and to avoid the use of low-reflectivity (R < 0.1%) coatings on the amplifier facet, the MOPA structure is tilted at a 7° angle to the crystal lattice, so that the light reflected by the cleaved facets does not couple back into the waveguide.'

© 2002 Optical Society of America