Features of single-mode emission in 7.5–8.0 $\mu$m range quantum-cascade lasers with a short cavity length

The possibility of realizing single-mode emission in quantum-cascade lasers due to modulation of output optical losses in a Fabry–Perot cavity is demonstrated. For the active region of the 7.5–8.0 $\mu$m spectral range, the two-phonon resonance design was used, thus, 50 stages and waveguide layers based on indium phosphide made it possible to realize single-mode 7.765 $\mu$m lasing at the temperature of 292 K. Side-mode suppression ratio was about 24 dB and remained the same with an increase in the current pumping up to 1.2 of the threshold current values. The coefficient of wavelength shift with temperature (temperature tuning) in the single-mode lasing regime was 0.56 nm/K.