Performance of digital servos in an optical frequency transfer network

Area of Science:

• Physics
• Optical Engineering
• Control Systems

Background:

• Optical frequency transfer is crucial for metrology and communication.
• Existing analog systems face limitations in cost, complexity, and reliability.
• Stabilization of optical fiber links, temperature, and polarization is essential for precision.

Purpose of the Study:

• To demonstrate the efficacy of flexible digital servos for stabilizing key parameters in optical frequency transfer.
• To evaluate the performance of a fully digital optical frequency transfer system.
• To provide a pathway for developing cost-effective and reliable optical frequency transfer solutions.

Main Methods:

• Utilized three types of flexible digital servos for distinct stabilization tasks.
• Implemented a digital servo with an acousto-optic modulator and voltage-controlled oscillator for fiber noise cancellation.
• Employed digital servos for precise interferometer temperature control and polarization stabilization.

Main Results:

• Achieved high phase detection range (∼2^10π radians) and low cycle-slip rate in a 62 km fiber link.
• Stabilized interferometer temperature to within 0.01 K.
• Enhanced data uptime from 85.5% to 99.9% through polarization control.
• Demonstrated performance comparable to existing analog systems.

Conclusions:

• The digital servos are sufficient for high-precision optical frequency transfer.
• The fully digital approach offers a low-cost, low-complexity, and high-reliability alternative.
• This method provides guidance for future optical frequency transfer system development.