Fig. 1. (Color online) (a) The near-field distribution of the fundamental supermode and high-order supermode. (b) The dependence of loss difference of the modal waveguide between the high-order and fundamental supermode on ridge width with a fixed etching depth at 3.5 µm and array period 9 µm. (c) The dependence of loss difference on the etching depth with a fixed ridge width at 6 µm and period of array at 9 µm. (d) The dependence of loss difference on period of array with a fixed ridge width at 6 µm and etching depth at 3.5 µm.

Fig. 2. (Color online) (a) The image of the buried grating from SEM. (b) The cross-section photography of the device. (c) A 3-D sketch of the structure.

Fig. 3. (Color online) (a) The devices’ far-field distribution from the substrate emitting windows in the ridge-width direction at different operating current. (b) The far-field distribution from the substrate emitting windows of the QCL array in the cavity direction at the current of 6 A.

Fig. 4. (Color online) The power–current characteristics of the device at 25 °C. The red line and blue line represent the output power from the edge and the substrate, respectively.

Fig. 5. (Color online) The emitting spectra of the QCL array at different temperatures of the heatsink. The inset shows the dependence of wavelength on heatsink temperature.