Suppression of longitudinal spatial hole-burning effect in λ/4-shifted DFB lasers by nonuniform current distribution

The mode and the output properties of an asymmetric λ/4-shifted DFB (distributed-feedback) laser with a distributed injection current density along the cavity are investigated theoretically and experimentally. Coupled wave equations that describe the longitudinal spatial hole-burning phenomenon due to both distributions of a stimulated recombination carrier density and an injection current density are developed. The calculations show that an appropriate distribution of the injection current similar to the intensity profile can be effectively suppress the longitudinal spatial hole-burning effect from the aspect of threshold gai difference Δα_th. A 1.55-μm InGaAsP/InP asymmetric λ/4-shifted DFB laser was fabricated with three divided electrodes. Improvement of the linearity of the output characteristics, decrease of threshold current, stability of the single-mode property, and narrowing of the spectral linewidth by injection current and distribution along the cavity were observed