Effective Rabi frequency in ultrafast semiconductor lasers: self-starting harmonic frequency combs

Area of Science:

• Optics and Photonics
• Semiconductor Lasers
• Quantum Cascade Lasers (QCLs)

Background:

• Optical frequency combs are crucial in optics and photonics research.
• Harmonic Frequency Combs (HFCs) exhibit optical lines spaced by multiples of the free spectral range.
• Spontaneous HFC formation in Quantum Cascade Lasers (QCLs) lacks a clear physical explanation.

Purpose of the Study:

• To provide a physical interpretation for HFC formation in QCLs.
• To elucidate the underlying mechanism of spontaneous HFC generation.
• To connect HFC formation to specific laser dynamics.

Main Methods:

• Developed a physical interpretation based on resonance phenomena.
• Utilized numerical integration of Effective Semiconductor Maxwell-Bloch Equations (ESMBEs).
• Performed linear stability analysis of continuous-wave emission.

Main Results:

• Identified a resonance between effective Rabi frequency and cavity modes as the HFC formation mechanism.
• Numerical simulations corroborated the proposed resonance theory.
• Linear stability analysis supported the findings regarding laser dynamics.

Conclusions:

• The study clarifies the physical mechanism behind HFC formation in QCLs.
• Resonance between Rabi frequency and cavity modes is key to HFC generation.
• Findings advance understanding of nonlinear dynamics in semiconductor lasers.