Abstract
Terahertz quantum cascade laser sources based on intra-cavity frequency mixing are currently the only monolithic electrically pumped semiconductor devices that can operate in the 1–6 THz spectral range at room temperature. The introduction of the Cherenkov waveguide scheme in these devices grown on semi-insulating InP substrates enabled generation of tens of microwatts of average terahertz power output and wide spectral tunability. However, terahertz radiation outcoupling in these sources is still highly inefficient. Here we demonstrate that an application of the III–V-on-silicon hybrid laser concept to terahertz quantum cascade laser sources based on Cherenkov intra-cavity difference-frequency generation dramatically improves their output power and mid-infrared-to-terahertz conversion efficiency. The best-performing device transfer-printed on a float-zone high-resistivity silicon substrate produced 270 μW of peak power output at 3.5 THz at room temperature, a factor of 5 improvement over the best reference devices on a native semi-insulating InP substrate.
Highlights
The terahertz (THz) spectral region, spanning from 0.3 to 10 THz, hosts numerous applications including chemical and biomedical sensing, non-invasive imaging and security screening, radio astronomy, and spectroscopy [1,2]
To produce THz quantum cascade lasers (QCLs) sources operable at room temperature, a technology based on intra-cavity difference-frequency generation (DFG) in mid-infrared QCLs has been proposed and developed [7]
Cherenkov emission occurs in THz DFG-QCLs when the propagation vector of the THz radiation in the device substrate is larger than the propagation vector of the nonlinear polarization wave in the laser active region
Summary
The terahertz (THz) spectral region, spanning from 0.3 to 10 THz, hosts numerous applications including chemical and biomedical sensing, non-invasive imaging and security screening, radio astronomy, and spectroscopy [1,2]. To produce THz QCL sources operable at room temperature, a technology based on intra-cavity difference-frequency generation (DFG) in mid-infrared (mid-IR) QCLs has been proposed and developed [7] These THz DFG-QCL devices have active regions designed to provide both gain for mid-IR pump waves and giant second-order nonlinearity (χ 2) for THz DFG inside of the laser cavity [8]. Cherenkov THz DFG-QCLs on SI InP demonstrated broadly tunable THz emission in the 1–6 THz range [11,12,13,14,15], up to 2 mW of THz peak power output in pulsed mode [16], and over 10 μW of THz power output in CW operation [17] at room temperature. The THz peak power was 5 times higher and the mid-IR-toTHz conversion efficiency was 8 times higher than those of the best reference devices with the same dimensions on the SI InP substrate
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