Fig. 1. EL spectrum and the calculated transmission spectrum. The inset displays the enlarged −2nd order mode in the transmission spectrum. The defect mode introduced by EPS can ensure stable single-mode emission.

Fig. 2. (a) Optical microscope image of SBG-QCL array bonded on patterned AlN submount; (b) magnified view of the front facet of the array; (c) SEM image of the sampled grating.

Fig. 3. Measured spectra of the 18 SBG-QCLs from an array with different sampling periods ranging from 8 to 32 μm (from bottom to top).

Fig. 4. (a) Measured spectra of laser #6 in the array at different heat sink temperatures from 20°C to 55°C. The inset shows the tuning of the peak wavenumber with temperature. (b) The P-I-V characteristics of laser #6 in the array.

Fig. 5. Calculated transmission spectrum with a sampling period of 19 μm and base grating period of 1.38 μm. The inset illustrates the breakdown of the translational symmetry.

Fig. 6. Calculated effective refractive index coupling |Δn| versus duty cycle for the (a) zero-, (b) first-, (c) second-, and (d) third-order modes, respectively.