Phase demodulation method for stable long-haul frequency transmission based on the Michelson interferometer.

Area of Science:

• Optoelectronics
• Fiber optics communication
• Radio frequency engineering

Background:

• Accurate radio frequency (RF) transmission over long distances is crucial for modern communication networks.
• Existing fiber-optic systems often face challenges with noise and instability.
• Phase modulation techniques offer potential for improved signal fidelity.

Purpose of the Study:

• To present a novel fiber-optic RF transmission scheme utilizing phase modulation and interferometric detection.
• To demonstrate the effectiveness of a Michelson interferometer (MI) for demodulating frequency signals.
• To improve the fractional frequency instability compared to intensity modulation methods.

Main Methods:

• A self-developed Michelson interferometer (MI) with an electrically controlled optical shifter was employed for signal demodulation.
• Balanced detection was used to suppress common-mode noise in the fiber link.
• The system was tested using a frequency transfer setup over a 560 km fiber link.

Main Results:

• Stable 2.4 GHz frequency transmission was achieved.
• A fractional frequency instability of 3.9 × 10^-14 at 1 s and 6.2 × 10^-17 at 10,000 s was obtained.
• Frequency instability at 1 s was improved from 7.3 × 10^-14 to 3.9 × 10^-14 compared to intensity modulation.

Conclusions:

• The proposed phase modulation scheme with interferometric detection offers superior performance for RF signal transmission.
• The use of a Michelson interferometer and balanced detection effectively reduces noise and enhances stability.
• This method is promising for building robust time-frequency synchronous fiber networks.