Fig. 1. Device structure of the DFB QCL integrated with a DBR.

Fig. 2. (a) Transmission spectrum of the uniform grating. The inset shows the detail near the Bragg wavelength. (b) The transmission spectrum of the uniform sampled grating. (c) The transmission spectrum of the uniform sampled grating with the EPS of the λ/4. The inset displays the detail of the positive first-order mode. (d) The blue line is the transmission spectrum of the uniform sampled grating with the EPS of the λ/4, and the red line is the reflection spectrum of the DBR section of the DFB QCL integrated with a DBR.

Fig. 3. (a) Emission spectra of the laser without DBR section at 20°C for different currents of 500–580 mA in a step of 40 mA. (b) The emission spectra of the laser with the DBR section at 1.1Ith and 1.25Ith current. (c) The emission spectra of the laser with the DBR section at 20°C for different currents of 500–700 mA in a step of 40 mA. (d) The emission spectra of the laser with the DBR section at 1.1Ith for different heat-sink temperatures of 10–40°C in a step of 10°C. The inset shows the linear tuning characteristics of the wavelength with temperature.

Fig. 4. P-I characteristics of the lasers as a function of the injection current at pulsed operation at 20°C. The red line shows the P‐I characteristic of the laser without DBR section. The black line displays the P‐I characteristic of the laser with DBR section.