Characterization of spectral gain alignment in high-power DBR-MOPA lasers

Achieving spectral alignment between the distributed Bragg reflector (DBR) and the gain spectra of the master oscillator and power amplifier (MOPA) sections is essential for high-performance monolithic DBR-MOPA lasers. Directly probing this internal alignment, however, remains challenging. This work presents a systematic study by using epitaxial wafers with deliberately varied photoluminescence (PL) wavelengths to introduce a controllable initial spectral offset. Through high-resolution spectral analysis and temperature-dependent measurements, we quantitatively correlate the extent of this initial offset with device performance. Our results demonstrate that even minor deviations from the optimal PL wavelength lead to measurable degradation in threshold current, slope efficiency, and spectral linewidth. The temperature-dependent spectral shifts further reveal the dynamic interplay between the fixed DBR feedback and the tunable material gain.