Selection of transverse oscillation modes in tilted ridge DFB lasers

In this paper, the effects of tilt angle on multi-transverse moded ridge-waveguide DFB lasers is presented. A small tilt angle is introduced between the waveguide orientation and the gratings to control the lasing wavelength. The authors find that although each transverse mode experiences a wavelength shift that approximately varies as 1/cos θ, the accompanying variation in κ dictates which transverse mode will oscillate. At small tilt angles the fundamental E _x,0 mode has the lowest threshold gain; at larger angles the higher order transverse modes will be sequentially selected while all other modes are attenuated. As a result, the wavelength versus tilt angle exhibits sudden jumps due to this transverse mode selection in addition to the 1/cos θ dependence. For the analysis, the authors develop a two-dimensional finite-difference method for modeling the multilayered ridge waveguide modes. The effect of tilt angle on the intramode coupling coefficient is derived and the behavior of lasing wavelength, threshold gain and stop-band width are studied