Concave tapered grating design of DFB laser at high power operation for reduced spatial hole-burning effect

Distributed feedback laser with concave tapered grating (CTG-DFB) is introduced and theoretical analysis of λ/4 phase-shifted CTC-DFB laser is presented. It is shown that, this structure has flat infra-cavity optical field and effectively reduces the spatial hole burning at high injection current. In addition, in this investigation the output power, linewidth and gain margin of the quarter wavelength phase-shifted distributed feedback (QWS-DFB) laser is compared with CTG-DFB laser. While the output power of proposed CTG structure is approximately equal to output power of QWS-DFB laser it has a smaller linewidth. The variation of lasing wavelength of CTG structure is very stable against the increase of injected current density.