Control of the absorption recovery time in GaSb SESAMs

GaSb-based semiconductor saturable absorber mirrors (SESAM) are instrumental for extending mode-locking to new types of gain media operable in the 2-3 μm wavelength range [1,2]. Suitable SESAMs favorably incorporate lattice-matched GaSb/AlAsSb distributed Bragg reflectors (DBRs), which already provide a high reflectivity with a small amount of pairs while simultaneously exhibiting exceptionally broadband (≈300 nm) reflection. Moreover, GaSb-based quantum-well (QW) heterostructures were recently reported to exhibit sub-ps absorption recovery times, which, in turn, enables straightforward generation of mode-locked pulses with sub-ps duration [2,3]. Indeed, the ultrafast recovery dynamics of high-quality GaInSb QWs are intriguing. These dynamics are probably ruled by the much higher Auger recombination rates compared to standard InP and GaAs materials used at shorter wavelengths. Here we report a study aimed at investigating the interplay between fabrication and design parameters of GaSb-based QWs and their associated absorption recovery time characteristics. In particular, we report on the absorption recovery characteristics of SESAMs grown at different temperatures, incorporating GaInAsSb with different composition and strain, as well as employing different optical designs to control the intensity of the optical field in the QW region.