Butterfly Packaged Ultra-Narrow Linewidth Single Frequency Teardrop Laser Diode

In this letter, an InP-based single facet teardrop laser which integrates a $1\times 2$ multi-mode interferometer and a linear curvature loop reflector deep-etched by inductively coupled plasma is demonstrated. The teardrop lasers which have the loop reflectors with different radius of curvature values (25, 50, 75, 100, and $150~\mu \text{m}$ ) have been successfully designed and fabricated, and the one with 75- $\mu \text{m}$ radius loop shows the lowest lasing threshold and highest slope efficiency. The butterfly packaged teardrop laser with 150- $\mu \text{m}$ radius loop reflector shows a single frequency emission at 1562.5 nm with 30-dB side mode suppression ratio and 75-kHz ultra-narrow linewidth at room temperature with 100-mA current injection on the MMI and 60 mA on the ring.