Ultralow-power-consumption continuous-wave terahertz quantum cascade lasers enabled by few-period patch-antenna arrays

We demonstrate terahertz quantum cascade lasers (THz-QCLs) employing a few-period patch-antenna array as the resonant cavity, enabling a drastic reduction of the active-region area while preserving a high cavity quality factor Qcav. By designing the antenna period in the deep-subwavelength regime, an infinite array supports a photonic band located well below the light cone with theoretically infinite Qcav. Reducing the number of antenna periods progressively broadens the mode in momentum space and couples it to radiative channels, allowing controlled tuning of Qcav. Experimentally, a four-antenna THz-QCL exhibits continuous-wave (CW) lasing with an ultralow electrical power consumption of 56 mW, delivering 0.8 mW output power at 20 K and operating up to 76.6 K. Increasing the cavity size to eight antennas extends the CW operating temperature to 97.3 K with a power dissipation of only 100 mW. These results establish few-period patch-antenna resonators as an effective strategy for low-power-consumption, high-temperature CW THz-QCLs.