Design and fabrication of low-cost tunable semiconductor swept-source lasers at 850 nm

Abstract

Swept-source lasers are key components of the modern spectral-domain Optical Coherence Tomography (OCT) systems. Further progress of OCT technology requires swept-source lasers working at specific, application dependent, wavelength, which are also compact and low-cost. In this work, we report the development of a low cost, compact, semiconductor swept-source laser based on slots etched along the ridge. The laser consists of a central gain section, phase section, semiconductor-optical-amplifier (SOA) sections and mirror sections employing higher-order gratings. The design and optimization of different parameters of the laser structure such as ridge width/depth, slot width/depth, no. of slots and so on are performed before the fabrication process. The main aim in the design step was to ensure single mode operation while maximizing the tuning range. The above optimization is performed keeping in mind the narrow linewidth of the emission spectra and minimum laser length. Due to the nature of the surface gratings, this type of laser does not require any complex regrowth and expensive e-beam lithography steps during fabrication. The slot and ridge sections of the laser are etched in a single wafer process step and the laser is also monolithically integrable with other system components. Initial measurements have indicated the high quality of the slot geometry and stable single mode operation with high side mode suppression ratio (SMSR) of 25 dB. The full-scale development of this laser will allow increasing resolution and imaging depth of OCT systems.