High performance quantum cascade laser frequency combs at λ ∼ 6 μm based on plasmon-enhanced dispersion compensation

Area of Science:

• Optoelectronics
• Quantum Optics
• Semiconductor Lasers

Background:

• Quantum cascade lasers (QCLs) are semiconductor lasers with unique properties.
• Optical frequency combs are crucial for precise frequency measurements and applications.
• Dispersion compensation is essential for stable frequency comb generation.

Purpose of the Study:

• To demonstrate QCL optical frequency combs emitting at approximately 6 μm.
• To investigate the operational temperature range and output power of these combs.
• To develop and validate a novel dispersion compensation technique for QCLs.

Main Methods:

• Utilized a plasmonic-waveguide approach for dispersion compensation.
• Integrated a highly-doped indium phosphide (InP) layer into the QCL design.
• Fabricated and characterized QCLs with varying ridge widths (2.8–5.5 μm).

Main Results:

• Achieved stable frequency comb operation from -20 °C to 50 °C.
• Obtained a maximum output power of 300 mW at 50 °C.
• Demonstrated a spectral width of ~80 cm^-1 with 240 modes, each averaging 0.8 mW.

Conclusions:

• The plasmonic-waveguide approach provides robust dispersion compensation for QCLs.
• This method enables reliable optical frequency comb generation in semiconductor lasers.
• The technique is adaptable for designing QCL combs at shorter wavelengths, down to 4 μm.