Faraday Rotation Angle Measurement Based on Coupled Optoelectronic Oscillator with Temperature Compensation

We have proposed and experimentally demonstrated a high-precision and temperature-compensated Faraday rotation angle measurement based on Coupled Optoelectronic Oscillator (COEO). The COEO contains two positive feedback loops. The magnetic-optics crystal is positioned outside the laser loop and in the OEO loop, where the Faraday Effect occurs. The polarization of the light from the laser loop will be rotated. Combined with the polarizer, the intensity of the photocurrent, which is the driving signal of the MZM, fluctuates according to the Faraday rotation angle. The variation of the active mode-locked modulation signal will change the loss of the laser loop, as well as the oscillation optical mode and the laser wavelength. Serving as the optical source of the OEO loop, the wavelength shift will induce the oscillation frequency shift. The oscillation frequency has a linear relationship with the Faraday rotation angle. Benefitting from the matching of two loops, the system can mitigate temperature disturbances, making it suitable for dual-parameter sensing applications. The experimental results show that the sensitivities of the Faraday rotation angle and temperature are 375.73 Hz/deg and 1.6 kHz/°C. The max errors for rotation angle and temperature are 0.29 ° and 0.39 °C, respectively.