DFB lasers for sensing applications in the 3.0-3.5 um wavelength range

Abstract

There are two particularly promising approaches to reach laser emission in the 3.0 - 3.5 μm wavelength range with application grade performance; GaSb based laser structures using GaInAsSb / AlGaInAsSb type-I quantum well (QW) active region, as well as type-II interband cascade (IC) material have been investigated and corresponding results are discussed in this paper. We also present different techniques for the fabrication of spectrally monomode distributed feedback (DFB) lasers for sensing applications in the targeted wavelength range. Based on the different waveguide designs of the two material approaches, different concepts to achieve monomode emission were applied: lateral metal gratings were used for type-I laser structures, vertical sidewall gratings for ICL designs. The fabrication procedure, including growth of the laser structures by molecular beam epitaxy, device processing and characterization, are described in the following. DFB emission under continuous wave (cw) operation was achieved up to room temperature (RT) in the target wavelength range. Sidemode suppression ratios (SMSRs) exceed 30dB for the fabricated devices and mode-hop free monomode tuning ranges of several nanometers are demonstrated.