Surface-emitting distributed feedback terahertz quantum-cascade lasers in metal-metal waveguides

Area of Science:

• Optics and Photonics
• Semiconductor Devices
• Terahertz Technology

Background:

• Terahertz (THz) quantum-cascade lasers (QCLs) are crucial for THz applications.
• Achieving robust single-mode operation in surface-emitting THz QCLs remains a challenge.
• Metal-metal waveguides offer high confinement but can support multimode operation.

Purpose of the Study:

• To develop single-mode surface-emitting distributed feedback (DFB) THz QCLs.
• To achieve a single-lobed far-field radiation pattern.
• To investigate the operational characteristics and temperature performance of these devices.

Main Methods:

• Fabrication of DFB THz QCLs in metal-metal waveguides.
• Implementation of precise facet phase control and sidewall metallization to suppress higher-order lateral modes.
• Design of a second-order Bragg grating with a central pi phase-shift for beam shaping.

Main Results:

• Robust single-mode operation achieved over a 0.35 THz range.
• Single-lobed far-field pattern demonstrated.
• Pulsed operation up to 149 K at 2.93 THz with 19.7 GHz temperature tuning (5 K–147 K).
• Continuous-wave (cw) operation up to 78 K, emitting over 6 mW of cw power at 5 K.

Conclusions:

• The developed DFB THz QCLs exhibit robust single-mode operation and desirable beam characteristics.
• Performance is comparable to multi-mode Fabry-Perot lasers in terms of maximum operating temperature.
• These devices represent a significant advancement for THz sensing, imaging, and spectroscopy.