Fig. 1. (a) Longitude mode distribution and (c) the transmission spectrum of a λ/4 shifted DFB cavity for different values of κL, (b) flatness of the longitude mode profile versus κL, and (d) the linewidth of the resonance mode versus κL.

Fig. 2. 2D-FDTD simulation result of λ/4 shifted DFB cavity: the mode profile of the three cavities with lengths of 25, 50, and 75 μm.

Fig. 3. (a) Coupling coefficient of the rib and strip waveguide as a function of the corrugation length and field distribution of the fundamental TE mode for (b) the rib and (c) the strip waveguide, where the dashed line indicates the sidewall corrugation.

Fig. 4. (a) SEM image of the phase-shift region and the sidewall corrugation (inset) of the DFB cavity and (b) optical microscope micrographs of the whole cavity C.

Fig. 5. (a) Illustration of the measurement experiment setup and (b) the measured transmission spectrum of cavities A, B, and C. The inset is a Lorentz fit of the resonance peak for cavity C.

Fig. 6. Coupling coefficient as a function of the corrugation length on the rib waveguides.