Analysis and structure design of Distributed Feedback laser (DFB) and Distributed Bragg Reflector (DBR) laser using regrowth-free surface grating technology

The realization of single-mode Distributed Feedback (DFB) and Distributed Bragg Reflector (DBR) lasers, based on surface grating structures is of considerable interest. Such devices offer a relatively simple grating fabrication process without complicated multistep-epitaxial growth or regrowth, as required in more conventional devices. This simplified processing could potentially reduce the fabrication cost for these lasers. A key concern for the surface grating lasers is designing the structure to provide sufficient feedback to achieve single mode operation with high yield and high quality as compared to conventional buried-grating DFB and DBR lasers. This paper reports numerical modelling of surface grating DFB and DBR lasers based on 1.55 pm wavelength InGaAs/InGaAsP/InP with graded-index separate confinement heterostructure multiple quantum well (GRINSCH-MQW) structures. Bragg wavelength operation of the DFB and DBR lasers may be satisfied by deeply etching fine surface gratings on both side portions and along top of the ridge stripe respectively. Sufficiently strong optical coupling between the corrugated structure and evanescent field can be achieved by controlling various parameters such as ridge width, etch depth, and grating width. The numerical results obtained allow optimum grating geometries to be developed to provide the desired feedback effect. Furthermore, the model has been used to investigate the influence on the device performance of fabrication errors and processing effects on the grating structures, prior to fabrication.