Farey tree locking of terahertz quantum cascade laser frequency combs

Area of Science:

• Optics and Photonics
• Quantum Electronics
• Spectroscopy

Background:

• Terahertz (THz) frequency combs are crucial for applications like molecular fingerprinting and communications.
• Semiconductor-based quantum cascade lasers (QCLs) are promising for THz frequency comb generation.
• Existing active locking methods for THz QCL combs, such as microwave injection and femtosecond laser locking, often introduce phase noise and complexity.

Purpose of the Study:

• To demonstrate a novel and simpler method for stabilizing terahertz quantum cascade laser frequency combs.
• To reduce phase noise in terahertz QCL frequency combs.
• To enable the development of compact and low phase noise terahertz comb sources.

Main Methods:

• Demonstration of Farey tree locking for terahertz QCL frequency combs under microwave injection.
• Utilizing the frequency competition between Farey fraction frequencies and cavity round-trip frequencies for locking.
• Accurate prediction of Farey fraction frequencies using the Farey tree hierarchy.

Main Results:

• Successful implementation of Farey tree locking in terahertz QCL frequency combs.
• Significant reduction in phase noise for dual-comb spectral lines.
• Demonstration of predictable frequency locking based on Farey tree principles.

Conclusions:

• Farey tree locking offers a promising alternative to traditional methods for stabilizing terahertz QCL frequency combs.
• The method leads to significantly reduced phase noise, enhancing comb performance.
• This technique facilitates the creation of compact, low phase noise terahertz frequency comb sources for various applications.