Design Optimization for Semiconductor Lasers With High-Order Surface Gratings Having Multiple Periods

Semiconductor lasers that use high-order surface gratings formed with etched slots have simple fabrication. Such gratings however increase loss and have a small free-spectral range that can increase threshold, lower slope efficiency, and limit SMSR. In this paper, we look at the design of a grating and use 2, 3, and 4 period structures within a 37th order grating. At fixed temperature, a single period device should work best while temperature tuning requires a multiperiod device. We found that the two period grating structure works best among the multiperiod devices. A follow-on study with the scattering matrix model shows that the slope efficiency which is quite low in this study (about 0.1 mW/mA at best) can be improved to a value of upto 0.17 mW/mA by reducing the number of slots used to form the grating from the present design that has 24 slots to 18.