Terahertz photonic crystal quantum cascade lasers.

Area of Science:

• Optoelectronics
• Solid-state physics
• Nanotechnology

Background:

• Terahertz (THz) quantum cascade lasers (QCLs) face challenges in performance metrics like threshold current, waveguide losses, and operational temperature.
• Existing THz laser technologies lack efficient mode selection and broad tunability.

Purpose of the Study:

• To engineer an in-plane laser operating at terahertz frequencies by integrating photonic crystals with quantum cascade band engineering.
• To demonstrate significant performance improvements in THz QCLs using this novel approach.

Main Methods:

• Fabrication of an in-plane laser by combining photonic crystal structures with quantum cascade gain material.
• Operation in a slow-light regime within the photonic crystal's band structure.
• Lithographic tuning of the photonic crystal period for coarse frequency control.
• Utilizing field-assisted gain shift and cavity pulling for fine-tuning.

Main Results:

• Achieved substantial improvements in threshold current, waveguide losses, and maximum operation temperature for THz QCLs.
• Demonstrated precise emission mode selection and enhanced laser tunability.
• Obtained coarse frequency control of 0.5 THz by adjusting the photonic crystal period.
• Achieved continuous single-mode tuning over 30 GHz via field-assisted gain shift and cavity pulling.

Conclusions:

• The integration of photonic crystals with quantum cascade band engineering offers a powerful route to high-performance in-plane terahertz lasers.
• This approach overcomes key limitations of current THz QCLs, paving the way for advanced THz applications.
• The demonstrated tunability and improved performance metrics represent a significant advancement in terahertz optoelectronics.