Large-area broad band saturable Bragg reflectors using oxidized AlAs in the circular and inverted mesa geometries

Abstract

A semiconductor Saturable Bragg Reflector (SBR) is a mirror structure comprising alternating layers of high and low refractive index materials with an incorporated saturable absorber. SBRs can be used to initiate and sustain ultra-short pulses in various laser systems. In order to form ultra-short pulses, SBRs with high reflectivity over a broad wavelength range are required. Furthermore, large-area SBRs facilitate easy integration in a laser cavity. One of the key elements for the realization of broad band SBRs is the development of the thermal oxidation process that creates buried low-index AlxOy layers over large areas. The design, fabrication, characterization, and implementation of broad band, high index contrast III-V/AlxOy SBRs in the form of circular mesas, as well as inverted mesa structures, is presented.

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“…Other authors have tackled the oxidation of large area devices for laser applications. 11,12 Among the different approaches explored, the inverted-mesa geometry has been proven to allow the oxidation of virtually any device area. 12 A hexagonal array of holes are etched to gain access to the AlAs layer throughout the device area, thus drastically decreasing the total oxidation length required to fully oxidize the layer.…”

“…11,12 Among the different approaches explored, the inverted-mesa geometry has been proven to allow the oxidation of virtually any device area. 12 A hexagonal array of holes are etched to gain access to the AlAs layer throughout the device area, thus drastically decreasing the total oxidation length required to fully oxidize the layer. The time required for the lateral oxidation depends on the hole spacing and an optimum is usually found in the tradeoff between oxidation time and hole density.…”

“…The inset of Figure 3 shows two Nomarski images of the surface of the structure after oxidizing it for less than 120 min (incomplete oxidation) and for 120 min (complete oxidation). In both cases, the oxidation front can be observed, thanks to the fact that the AlAs layer shrinks during oxidation 12 and creates a topographic feature that can be resolved under the Nomarski microscope.…”