Adaptive Phase Stabilization System for Microwave Signals Transmitted via Fiber Optic Line

The article provides a description and results of an experimental study of an adaptive system for stable phase microwave signal transmission over long-haul analog fiber optic link operating in the IM-DD mode - intensity modulation of the laser radiation and direct detection at the photodetector. To ensure the phase stability of microwave signals at the output of the link, it includes a fiber stretcher with piezoelectric control, which allows adjusting the electrical length of the link. The regulator of the developed closed-loop automatic control system includes a three-channel radio system made of technology software defined radio with frequency range up to 6 GHz and PID controller, the output of which is fed to the fiber stretcher driver. The basic parameters of volt-degree characteristic of piezoelectric stretcher which determine how it should work in the channel of signal phase control have been experimentally investigated. The results of measuring the statistical characteristics of the microwave signal phase fluctuations during its transmission over a fiber-optic communication link with a length of up to 1 km with the developed closed-loop automatic control system are presented.