Buried grating distributed feedback laser at λ=1.51 μm

The growth of a distributed feedback (DFB) laser by two steps of organometallic chemical vapor deposition (OMCVD) epitaxy in which the feedback grating is a series of higher index of refraction InGaAsP segments (first growth) completely embedded in lower index InP (second growth) is reported. In the buried grating DFB (BG-DFB) laser, the coupling coefficient (Kl) of the laser optical mode to the feedback grating can be reproducibly and accurately adjusted by changing the thickness of the grating layer or the distance of the grating from the active region. The coupling coefficient can be adjusted over a large range without altering the waveguide parameters of the laser. The duty cycle (ratio of InGaAsP grating segment width to grating period) of the grating can be changed by adjusting the grating etch parameters. This provides another means to optimize the reflectivity and output coupling of second order gratings for grating surface emitter lasers