Resonance-shifted DFB-LD for asymmetric light output from front/rear facets

To obtain asymmetric light output from front/rear facets in a semiconductor laser maintaining single longitudinal mode (SLM) operation, a resonance-shifted DFB-LD is proposed and its lasing characteristics are simulated. The laser cavity of the resonance-shifted DFB-LD is divided into two regions. Each region has uniform diffraction gratings, and the corrugation pitch of region 1 is different from that of region 2. By adjusting the corrugation pitches of the two regions, a resonance mode in region 1 and that in region 2 are overlapped. At the overlapped resonance mode, SLM operation is obtained. When the corrugation pitch difference is 0.3 nm with κL1 = κL2 = 3 where κ is the grating coupling coefficient; length L1 of region 1 and length L2 of region 2 are about 560 μm, the normalized threshold gain difference was 0.509, which is large enough for SLM operation. Under this condition, the light output ratio from the front/rear facets is 5.69. This light output ratio is larger than the highest value of 2.6, which was achieved in a phase-shifted DFB-LD with asymmetrically-pitch-modulated gratings.