Low threshold current GaInAsP/InP DFB lasers

Low threshold current GaInAsP/InP distributed feedback lasers emitting at 1.55 μm were investigated experimentally and theoretically. A low threshold current as low as 5.7 mA was obtained in anti-reflection/high-reflection coated DFB lasers with a short cavity and submicron width of the active layer. The differential efficiency was as high as 0.44 W/A. The stable single longitudinal mode operation was obtained over a wide range of driving current and under high-speed direct modulation whereas a product of coupling coefficient and laser length L was kept around 1. The lowest threshold current of 5 mA was obtained around L = 100 \mu m under pulsed operation. When the laser length was shorter than 50 μm, the threshold current increased rapidly. The laser length dependence of the threshold current was in agreement with the calculated results taking Auger recombination process into account.