Coherent multi-mode dynamics in a quantum cascade laser: amplitude- and frequency-modulated optical frequency combs

Area of Science:

• Semiconductor physics
• Quantum optics
• Laser dynamics

Background:

• Quantum cascade lasers (QCLs) are crucial for mid-infrared applications.
• Optical frequency combs (OFCs) have diverse applications in spectroscopy and metrology.
• Understanding OFC generation in semiconductor lasers is key for device development.

Purpose of the Study:

• To theoretically investigate the spontaneous generation of optical frequency combs in multi-mode mid-infrared quantum cascade lasers.
• To model the complex dynamics governing OFC formation within a Fabry-Perot resonator.

Main Methods:

• Development of a theoretical model based on effective semiconductor Maxwell-Bloch equations.
• Inclusion of key semiconductor active medium features: asymmetric, frequency-dependent gain and refractive index.
• Incorporation of resonator features like spatial hole burning and phase-amplitude coupling via the linewidth enhancement factor.

Main Results:

• Numerical simulations accurately replicate recent experimental findings on OFC generation.
• Broad ranges of comb formation observed in locked regimes, interspersed with chaotic dynamics.
• Identification of self-confined traveling structures and linear chirp behavior in the instantaneous frequency during OFC generation.

Conclusions:

• The theoretical model successfully captures the dynamics of OFC generation in QCLs.
• OFCs in locked regimes exhibit distinct characteristics, including amplitude and frequency modulation.
• The study provides insights into controlling and optimizing OFC formation in semiconductor lasers.