A Horn Ridge Waveguide DFB Laser for High Single Longitudinal Mode Yield

In this paper, we propose a novel approach to enhance the single longitudinal mode (SLM) yield for uniform grating distributed feedback (DFB) laser diode by breaking the dual-mode degeneracy. By introducing a horn ridged waveguide (HRW) in replace of the conventional straight ridge waveguide (RW), we create an effectively chirped grating as well as a longitudinally varying modal gain. As such, the field distribution along the laser cavity is different for the two possibly lasing longitudinal modes on each side of the Bragg stopband, and the field having a larger overlap with the gain becomes the only dominant lasing mode. We have optimized the ridge width of HRW-DFB lasers with different normalized coupling coefficients (L) in terms of the SLM yield. Our experimental results show that the SLM yield of the HRW-DFB laser with L of 2.9 can reach 65 as opposed to 19 obtained by the conventional RW-DFB lasers fabricated on the same wafer.