Single-mode distributed feedback lasing using photonic bandgaps to suppress degenerate modes

We present a method for achieving single-mode distributed feedback lasing, using photonic bandgaps (PBGs) to suppress degenerate lasing modes. These PBGs arise from direct-Bragg coupling and exchange-Bragg coupling due to a passive waveguide placed in proximity to a uniform-grating-active-waveguide lasing structure. Analytic solutions at lasing threshold for this dual-waveguide, four-port structure reveal a high normalized gain margin (e.g., ΔαL = 0.86) accompanied by a low power flatness (e.g., F = 0.001) along the active region, outperforming the λ/4-shifted DFB laser structure. This single-mode lasing mechanism is compelling for both III/V and III/V-on-silicon platforms.