Quantum cascade laser frequency comb at λ ≃ 5.3 µm via a double-plasmon waveguide architecture.

Area of Science:

• Optics and Photonics
• Semiconductor Lasers
• Quantum Cascade Lasers

Background:

• Quantum cascade lasers (QCLs) are crucial for mid-infrared applications.
• Achieving stable frequency comb operation in short-wavelength QCLs is challenging due to dispersion.
• Dispersion management is key to enhancing QCL frequency comb performance.

Purpose of the Study:

• To introduce a novel dispersion compensation technique for short-wavelength QCLs.
• To enable efficient frequency comb generation in the 4-6 µm range.
• To improve the operating temperature and power of QCL frequency combs.

Main Methods:

• Engineered waveguide structures with two highly doped InP plasmon layers.
• Precisely controlled layer dimensions and distances for dispersion management.
• Integrated plasmon layers above and below the active QCL region.

Main Results:

• Achieved small group velocity dispersion between 4 and 6 µm with low optical losses.
• Demonstrated highly efficient frequency comb operation at 5.3 µm.
• Obtained up to 350 mW output power in coherent comb mode.
• Maintained coherent comb operation up to 50°C.

Conclusions:

• The novel dispersion compensation method is effective for short-wavelength QCLs.
• This design facilitates robust fabrication of efficient QCL frequency combs.
• The results pave the way for practical applications of QCL frequency combs at higher temperatures.