With the rapid development of coherent optical communication systems, lasers are required to have higher power and narrower linewidths. In this paper, a process method using buried heterojunction is proposed. By comparing the optoelectronic properties of lasers with different mesa widths and different cavity lengths, the laser with a 1000 µm cavity length and a mesa width of 2.4 µm can reach 133.7 mW at 25°C at 300 mA, and a side mode suppression ratio (SMSR) greater than 50 dB. This laser also exhibits low relative intensity noise (<-150d B/H z at 260 mA) and narrow linewidth (<200k H z).