DFB Semiconductor Laser With Discrete Coupling Coefficient Based on the Equivalent Technique

An equivalently discrete coupling coefficient (EDCC) distributed feedback (DFB) semiconductor laser with EDCC grating is numerically investigated and experimentally demonstrated; the EDCC grating structure is designed by discretizing the duty cycle of sampled Bragg grating along the laser cavity, i.e., the cavity is divided into some subsections, and the duty cycle is constant in each subsection while it is different between two adjacent subsections, instead of the truly discrete coupling coefficient grating profile realized by discontinuously varying the duty cycle and/or etching depth of the uniform gating pitch. Moreover, the EDCC grating is fabricated by combining the conventional holographic exposure with a micrometer-level photolithography, which will simplify the fabrication process and reduce the fabrication cost. Based on experimental data, the analysis of spectral behavior as a function of injection current shows that the stable single-longitudinal-mode operation has been realized, even at large injection current and high temperature.