Ultra-long-distance distribution of low-phase-noise two-tone lightwave for THz seeding

Area of Science:

• Optoelectronics
• Terahertz (THz) Technology
• Optical Communications

Background:

• Advanced THz transmission requires high-quality optical reference signals.
• Distributing these signals over long distances while maintaining signal integrity is challenging.
• The method of generating two-tone optical THz signals impacts transmission quality over distance.

Purpose of the Study:

• To investigate the generation and long-distance distribution of high-quality two-tone optical THz reference signals.
• To evaluate the impact of different tone generation methods on THz signal quality over fiber links.
• To demonstrate the feasibility of distributing THz references for advanced wireless transmission.

Main Methods:

• Generation of two-tone optical THz reference signals at 300 GHz.
• Long-distance fiber optic distribution of the THz reference signals.
• Utilized narrowband fiber Bragg grating (FBG) filters to suppress noise.
• Compared THz signal quality using optical comb versus two frequency-locked lasers for tone generation.
• Performed numerical simulations to assess THz wireless transmission capabilities.

Main Results:

• Achieved excellent reference signal quality (0.034 degrees integrated phase error) over 12,000 km fiber distribution.
• Narrowband FBG filters effectively suppressed high-frequency noise, irrespective of the tone generation method.
• THz signal quality degraded significantly with distance when using an optical comb for tone generation.
• THz signal quality showed weak dependence on distribution distance when using two frequency-locked lasers.
• Simulations indicated potential for 32 GBaud, 32-64 QAM THz wireless transmission without complex digital signal processing.

Conclusions:

• Two frequency-locked lasers offer superior performance for long-distance THz reference signal distribution compared to optical combs.
• High-quality THz reference signals can be distributed over extended fiber links, enabling widespread access for users.
• The findings support the development of robust THz wireless communication systems with simplified signal processing requirements.