Abstract: In many fields, such as electronic countermeasure system, radar system, satellite navigation and deep space exploration, microwave signal is modulated by laser and loaded on the optical signal. After transmitted by optical fiber, its phase is affected by the external environment, so it can not achieve stable phase transmission. In this paper, a two-way homologous coherent microwave optical fiber stable phase transmission system is proposed, which can realize microwave signal's stable phase transmission in optical fiber. In this technique, the constant temperature crystal oscillator is used to generate multi-channel reference signals with stable phase. One signal is used as the phase change identification signal for optical fiber transmission. The signal is modulated into an optical signal by the laser, and then the multi-channel optical reference signal is separated by the optical splitter and the signal to be stabilized is transmitted with the optical fiber. In addition, the same reference signal is used as the reference signal to identify the phase with the phase identification signal transmitted through the optical fiber, and the reference signal and the reference signal are coherent. Two kinds of signal coherence mechanisms are constructed to realize the phase identification system with the phase change as the parameter. The phase change of the reference signal is used to identify the phase change of the transmitted broadband RF microwave signal. In the realization process of phase detection, a double balanced mixer is used to complete the real-time phase detection of the reference signal phase change. The MCU samples the real-time change of the reference signal phase, and controls the adjustable electric delay line (VODL) in real time to track and compensate the optical path difference of the optical transmission link, so as to complete the active phase compensation of the required stable phase signal and the reference signal. It can realize the stable phase transmission of wideband RF microwave signal through optical fiber.

Key words: optical fiber phase stabilized transmission, phase discrimination, phase stability, double balanced mixer, VODL