Low-threshold 1.55-μm InGaAsP/InP buried heterostructure distributed feedback lasers

Abstract
An extremely low‐threshold current of 6 mA in cw mode at 22 °C was achieved in 1.55‐μm InGaAsP/InP buried heterostructure distributed feedback lasers with a first‐order grating and a normal cavity length of 300 μm. These lasers exhibited an average differential efficiency of 30% total at 4 mW without any coating on the facets, and a T0 (25–70 °C) value of 55 K. A spectral linewidth as low as 8 MHz at cw mode was obtained. The lasers showed high‐speed pulse modulation response to 2.4 Gb/s (NRZ).