Stable single-mode distributed feedback quantum cascade lasers at λ ∼ 4.25 μm with low power consumption

• Room temperature CW operation of short-wavelength (4.25 μm) DFB-QCL was demonstrated.
• Stable single-mode operation was maintained by gain coupling mechanism.
• Very low threshold power consumption of 1.45 W was achieved by strong coupling buried grating.

Short-wavelength (4.25 μm) distributed-feedback quantum cascade laser operating in continuous wave (cw) mode at room temperature with low power consumption was presented. Stable single-mode operation with a side-mode-suppression-ratio above 25 dB was maintained for the whole measured current and temperature range by enlarging gain difference and strong grating coupling. Because of the strong coupling, very low threshold current and power consumption were achieved. For a device of 9-μm-wide and 2-mm-long, the cw threshold current and power consumption at 293 K were as low as 126 mA and 1.45 W, respectively. All results above were from the device without using buried heterostructure geometry.