Design of a multimode interference waveguide semiconductor laser combining gain coupled distributed feedback grating

Abstract

Semiconductor laser is one of the most critical components in the field of modern communication. Research and development of single-mode semiconductor laser with high stability, high power, high beam quality and narrow line width is an important research area in this field. In this paper, A novel edge-emitting semiconductor laser diode structure is proposed. In the structure an active multimode interference waveguide structure serves as a main gain region. To modulate the longitudinal mode of the laser, a gain-coupled distributed feedback(DFB) laser based on high order surface gain coupled grating is introduced into the structure as well. The novel structure is then fabricated and compared with an conventional DFB laser. The experimental results show that higher slope efficiency and output power are achieved with the proposed structure than those with the conventional distributed feedback semiconductor lasers. The novel structure is also compared with conventional MMI laser with only Fabry-Parot(FP) cavity. The result shows that the proposed structure has higher beam quality and better stability than the FP cavity multimode interference waveguide lasers. To enhance the gain contrast in the quantum wells without introducing the effective index-coupled effect, the groove length and depth are well designed. Our device provides a single longitudinal mode with the maximum CW output power up to 53.8 mW/facet at 981.21 nm and 400 mA without facet coating, 3 dB linewidth < 13.6 pm, and SMSR > 32 dB. Optical bistable characteristic is observed with a threshold current difference. Meanwhile, by using high-order distribution feedback grating formed by shallow surface etching in the process of chip design and fabrication, the proposed structure of laser diode can realize regrowth freely and only micron-scale precision i-line lithography is required. Such a structure with simple fabrication process and low manufacturing cost has great potential for commercial mass production.