Phase-conjugation-based fast RF phase stabilization for fiber delivery.

Area of Science:

• Optical Communications
• Signal Processing
• Physics

Background:

• Long-distance fiber optic delivery of radio frequency (RF) signals faces challenges with phase instability due to environmental factors and transmission delays.
• Existing phase stabilization techniques, often based on phase-locking loops, can be slow and require complex, tunable components.

Purpose of the Study:

• To propose and validate a novel, fast, and open-loop phase auto-stabilization technique for RF signals transmitted over long-distance optical fibers.
• To overcome the limitations of traditional phase-locking loop methods by eliminating the need for dynamic phase tracking and tunable parts.

Main Methods:

• A phase-conjugation-based scheme is employed where the RF signal is pre-phase-promoted at the center site.
• The pre-promotion shift is determined by a round-trip transmission of an RF signal at half the target frequency.
• This pre-promoted signal counteracts the phase retard introduced during one-way fiber delivery.

Main Results:

• Theoretical analysis confirms the efficacy of the proposed open-loop design.
• Experimental validation using a 2.42 GHz signal over a 30-km fiber link demonstrated significant phase drift compression.
• Rapid phase stabilization was confirmed by introducing sudden time delay changes, with a recovery time shorter than traditional methods.

Conclusions:

• The proposed phase-conjugation technique provides a fast and effective solution for RF phase auto stabilization in long-distance fiber delivery.
• The open-loop, non-tunable design offers advantages in speed and simplicity compared to existing phase-locking loop systems.
• The technique achieves endless compensation capacity and demonstrates robust performance against dynamic link changes.