Lateral-Current-Injection Distributed Feedback Laser With Surface Grating Structure

As a step toward the realization of injection-type membrane distributed feedback (DFB) lasers, which are expected to be important components of optical interconnections, we realized lateral-current-injection DFB (LCI-DFB) lasers with surface grating structures prepared on semiinsulating InP substrates. First, we designed the surface grating structure to have a high index-coupling coefficient together with a high optical confinement in the quantum wells. Then, we investigated the surface grating structure formed on an amorphous-Si (a-Si) layer deposited on the GaInAsP/InP initial wafer containing five quantum wells. A moderately low threshold current of 7.0 mA and a high differential quantum efficiency of 43% from the front facet were obtained under a continuous-wave operating condition at room temperature for a uniform grating LCI-DFB laser with a stripe width of 2.0 μm and a cavity length of 300 μm. A threshold current of 5.8 mA was obtained with a λ/4 phase-shifted LCI-DFB laser with a-Si surface grating. Furthermore, a small-signal modulation bandwidth of 4.8 GHz was obtained at a bias current of 30 mA with a modulation current efficiency factor of 1.0 GHz/mA
^1/2
.