Design and fabrication of low-loss hydrogenated amorphous silicon overlay DBR for glass waveguide devices

We report a methodology for the design of low-loss, high-reflectivity, amorphous silicon, overlay DBRs for glass waveguide devices. In order to improve the DBR reflectivity while minimizing the DBR-induced loss, we theoretically determine the optimum overlay thickness and establish an iterative deposition procedure to achieve this value. Details of the design criteria, measurement of the design parameters, and a numerical analysis of the resulting overlay DBR structure are presented. The deposition and characterization methods for low-loss overlay materials are also discussed. We apply the procedures to implement a multiple-wavelength source consisting of an array of overlay DBR waveguide lasers on a single Er/Yb-doped glass substrate. The lasing wavelengths of the laser array are linearly related to the width of the mask openings used to fabricate the waveguides. One laser with an 8.5-mm-long gain section and a 1.5-mm-long overlay DBR had a launched pump power threshold of 29 mW and an 8.5% slope efficiency. Good agreement is observed between theory and measurement results.