Fig. 1. (Color online) Structure illustration of the DFB array device. (a) Three-dimension (3D) structure diagram of the DFB array device consisting of a ridge array with first-order buried DFB grating and a Talbot cavity. (b) Enlarged view of the ridge array region. (c, d) 3D microscope images of the buried DFB grating that has not yet been covered by metal, with a grating depth of around 600 nm. (e) Scanning electron microscope image of the DFB array device.

Fig. 2. (Color online) FEM simulation results of the first-order buried DFB grating. The red line represents the relationship between the frequency of the two band edge modes and the grating etching depth, and the blue line represents the contribution of waveguide loss to threshold gain versus grating etching depth. The solid circle represents high-frequency (H_f) band edge mode, and the hollow circle represents low-frequency (L_f) band edge mode.

Fig. 3. (Color online) Performance of the DFB array device. (a) Measured P–I–V curves at 13 K of the array device. (b−d) Measured emission spectra of the array device. Duty cycle σ = 50% and etching depth d_etch = 600 nm for the grating. The robustness and capability for lithographic tuning was verified by three different grating periods Λ = 9.36/9.40/9.44 μm. Stable single-mode operation is achieved under all bias conditions, and the side mode suppression ratio is above 20 dB.

Fig. 4. (Color online) Far-field patterns of the array device. (a) One-dimensional far-field distribution in the ridge width direction (x direction) of the five-elements array device (red line) and simulated far-field distribution of the array device (blue dotted line) and single-ridge (purple dotted line). (b, c) Far-field patterns of a representative array device measured at maximum peak power and at half peak power, respectively. (d) Calculated far-field pattern obtained by a two-dimensional Fourier transform of the near-field distribution.