Planar integrated metasurfaces for highly-collimated terahertz quantum cascade lasers.

Area of Science:

• Optoelectronics
• Metamaterials
• Terahertz (THz) Technology

Background:

• Quantum cascade lasers (QCLs) are crucial for THz generation.
• Efficiently coupling THz radiation from QCLs to integrated photonic structures remains a challenge.
• Metasurfaces offer novel ways to manipulate electromagnetic waves at the nanoscale.

Purpose of the Study:

• To demonstrate planar integration of THz QCLs with metasurface waveguides.
• To achieve efficient out-coupling and beam shaping of THz radiation.
• To explore the potential for integrated THz photonic circuits.

Main Methods:

• Fabrication of tapered THz quantum cascade lasers (QCLs).
• Design and integration of metasurface waveguides with spoof surface plasmon (SSP) scatterers.
• Characterization of the emitted THz beam profile and coupling efficiency.

Main Results:

• Achieved a highly collimated surface-emitting THz beam with narrow divergence (~4° × 10°).
• Demonstrated good waveguiding properties of the metasurface waveguide.
• Observed low background THz power, indicating high coupling efficiency.

Conclusions:

• The planar integration scheme provides a versatile platform for engineering THz QCL emission.
• Metasurface waveguides act as efficient spoof surface plasmon (SSP) out-couplers.
• This work paves the way for active THz photonic circuits for sensing and communication.