Enhancement of asymmetry in light output from front/rear facets in resonance-shifted DFB-LDs

To enhance asymmetry in light output from front/rear facets in a resonance-shifted DFB-LD maintaining single longitudinal mode (SLM) operation, lasing characteristics of resonance-shifted DFB-LDs with asymmetric regions are simulated. The laser cavity of the resonance-shifted DFB-LD is divided into two regions. Each region has uniform diffraction gratings; a corrugation pitch in Region 1 is different from a corrugation pitch in Region 2; length L1 of Region 1 is different from length L2 of Region 2. By adjusting the corrugation pitches of the two regions, a resonance mode in Region 1 and a resonance mode in Region 2 are overlapped. At the overlapped resonance mode, SLM operation is obtained. When a corrugation pitch difference is 0.2 nm with κL1 = 2κL2 = 3 where κ is a grating coupling coefficient, a normalized threshold gain difference is 0.413, which is large enough for SLM operation. Under this condition, the light output ratio from the front/rear facets is 67.6, which is larger than the reported highest value of 51 with SLM operations.