Spatial hole burning suppression for the distributed feedback laser diode with an asymmetric grating Gap structure

We propose and design an asymmetric grating distributed feedback (DFB) laser with a grating gap at its center. The below and above threshold analyses show that this kind of laser will be lasing at the Bragg wavelength independent of the grating gap length with an output spectrum similar to those of λ/ 4 phase-shifted DFB lasers. However, the proposed structure shows a uniform photon and carrier distribution in the grating gap region, and therefore, spatial hole burning, which is the bottle-neck for the phase-shifted DFB laser design, is greatly suppressed. By simulation, it is demonstrated that with the same grating coupling efficiency, the proposed laser will share similar threshold current and efficiency as those of λ/ 4 phase-shifted DFB lasers, but as the biased current increases, reaching 100 mA the former keeps the single mode operation with more than 30 dB side mode suppression ratio while the λ/ 4 phase-shifted laser becomes multi-mode. Fabrication of the proposed laser structure does not involve extra complexity. It is much easier to implement compared to the other techniques used to suppress the spatial hole burning effect.