Coupling coefficients for partially meltback trapezoidal gratings

In distributed-feedback or distributed Bragg reflector lasers, the coupling coefficient K describing the grating feedback strength is an important parameter which must be optimized. The author presents a simple way to take into account the grating deformation likely to occur during regrowth and computes corresponding coupling coefficients for optimum first- and second-order, dry- and wet-etched gratings. He shows that meltback has little effect on K as long as the grating depth remains unchanged. Because of their V-groove-like shape, wet etched gratings are very meltback-sensitive. Therefore, it is concluded that dry-etched gratings must be preferred to avoid coupling coefficient degradation during regrowth