EFFECTS OF RADIATION LOSS ON THE PERFORMANCE OF 2ND-ORDER DFB SEMICONDUCTOR-LASERS

The effects of radiation loss on the performance of second-order distributed-feedback (DFB) semiconductor lasers with a symmetrical grating are analyzed systematically. The threshold gains of the two lowest modes, the differential quantum efficiency, and the spectral linewidth are calculated as a function of the complex coupling coefficient. The comparison is also made between a conventional DFB and a quarter-wave phase-shifted DFB laser. It is shown that the effects of radiaion loss are different in these two laser types. In addition, a simple approximate expression for threshold gain is derived. By way of example, a DFB laser with a rectangular grating is analyzed. It is shown that the performance of a second-order DFB laser is not sensitive to the grating pitch over a fairly wide range, provided that it is close to the pitch which gives the maximum coupling coefficient.