DESIGN STUDIES FOR DISTRIBUTED BRAGG REFLECTORS FOR SHORT-CAVITY EDGE-EMITTING LASERS

In conventional edge-emitting lasers, mirror reflectivity is similar t o 0.3-0.4 so that very short cavities have an unacceptable loss, To de crease the mirror losses, one can conceive of an external distributed Bragg reflector (DBR) structure produced by etching, We examine the de sign considerations for such mirrors. Using a finite-difference time-d omain (FDTD) scheme, we numerically simulate the propagation of a Gaus sian wave packet in a laser cavity with an external DBR structure on o ne end, We find that despite the divergence of light at the semiconduc tor-air interface, high reflectivities (>90%) can be obtained using on ly a few mirrors, provided a low refractive index material (such as ai r) is one of the components of the DBR period. In our modeling, we inc lude fluctations based on factors such as lithographical error, etch e rror, and off-design wavelength lasing, Our results indicate that the external DBR is highly tolerant of such factors. In addition, simulati ons done using material with higher refractive index than air in the D BR structure indicate that it is possible for insulators to be deposit ed in the DBR structure, yet allow high reflectivity.