Design studies for distributed Bragg reflectors for short-cavity edge-emitting lasers

In conventional edge-emitting lasers, mirror reflectivity is ~0.3-0.4 so that very short cavities have an unacceptable loss. To decrease the mirror losses, one can conceive of an external distributed Bragg reflector (DBR) structure produced by etching. We examine the design considerations for such mirrors. Using a finite-difference time-domain (FDTD) scheme, we numerically simulate the propagation of a Gaussian wave packet in a laser cavity with an external DBR structure on one end. We find that despite the divergence of light at the semiconductor-air interface, high reflectivities (>90%) can be obtained using only a few mirrors, provided a low refractive index material (such as air) is one of the components of the DBR period. In our modeling, we include fluctuations based on factors such as lithographical error, etch error, and off-design wavelength lasing. Our results indicate that the external DBR is highly tolerant of such factors. In addition, simulations done using material with higher refractive index than air in the DBR structure indicate that it is possible for insulators to be deposited in the DBR structure, yet allow high reflectivity