Plasmon-enhanced waveguide for dispersion compensation in mid-infrared quantum cascade laser frequency combs

Area of Science:

• Optics and Photonics
• Quantum Engineering

Background:

• Quantum cascade lasers (QCLs) are crucial for mid-infrared (mid-IR) applications.
• Frequency combs (FCs) generated from QCLs offer precise frequency standards.
• Dispersion management is critical for stable FC operation.

Purpose of the Study:

• To demonstrate dispersion compensation in mid-infrared QCL frequency combs.
• To enhance the stability and output power of QCL-based FCs.
• To explore the use of engineered waveguides for improved FC performance.

Main Methods:

• Coupling a dielectric waveguide to a plasmonic resonance in the top cladding layer.
• Fabricating devices with engineered group velocity dispersion.
• Measuring beatnotes, optical output power, optical spectrum, and multi-heterodyne beating spectrum.

Main Results:

• Achieved group velocity dispersion below 110 fs²/mm.
• Measured narrow beatnotes with FWHM linewidths below 1 kHz.
• Obtained optical output power of 275 mW at -20°C.
• Demonstrated an optical spectrum spanning 60 cm⁻¹ and multi-heterodyne beating of 46 cm⁻¹.

Conclusions:

• Dispersion-engineered waveguides enable highly stable and reliable mid-infrared QCL FCs.
• The developed devices show potential for high output power applications.
• This work advances the development of advanced photonic sources in the mid-infrared region.