Abstract

In coherent lightwave communication systems, a narrow line width single frequency laser is required for phase shift keying and homodyne schemes. To obtain sub-MHz linewidth, distributed-feedback (DFB) lasers have been made with a cavity length longer than one millimeter.^1,2 Even with multiple-quantum well (MQW) active layer, the threshold current of these lasers is 20 mA or higher. By incorporating compressive strain into the quantum well, both the threshold current³ and the line width enhancement factor⁴ are expected to be reduced theoretically. Recently, we have reported sub-milliampere- threshold compressive-strained MQW Fabry- Perot lasers at 1.5 μm wavelength.⁵ In this work, we are reporting the sub-MHz (600 kHz) DFB lasers with a low threshold current of 5.5 mA by the use of the compressive-strained MQW active layer and the strong grating.

© 1991 Optical Society of America