Design And Implementation Of Automatic Feedback Polarization Controller Based On STM32

In distributed phase stabilized transmission system,the polarization states of optical signals are vulnerable to be distorted during the transmission in optical fiber link,resulting in the unstable polarization state of optical signals in remote end.The LiNb03 modulator in remote end requires high stability of polarization state of the received optical signals.Moreover,if the polarization state of received optical signals has not been corrected before entering the modulator,the efficiency of LiNb03 modulator and the received signal-to-noise ratio(SNR)will be significantly degraded,resulting in poor performance of the optical fiber link.Hence,the stability of polarization state for the received optical signals,which directly affect the transmission effects of stable phase,is vital for the implementation of phase stabilized transmission system.There are mainly two kinds of methods available to control the optical signal polarization in remote end in the phase stabilized transmission system,which are polarization tracking and polarization scrambler,respectively.In the center polarization scrambler scheme,the power of the radio frequency(RF)signal will be reduced after polarization scrambler,resulting in the degradation of the link SNR.While the polarization tracking scheme would not cause too much power consumption,and has little effects on the link SNR.Based on the above analysis,a polarization tracking and control scheme is proposed for the phase stabilized transmission system in this paper.Moreover,an automatic feedback polarization controller(Auto-PC)is designed,and it has been applied in the phase stabilized transmission system center to realize the polarization tracking control of optical signals in remote end.In this paper,the automatic feedback polarization controller(Auto-PC)have been designed to achieve the polarization control of optical signals in the center end.The functional parts of the Auto-PC feedback power supply system,including O/E photoelectric module,STM32-A/D module,SPI-D/A module,V&C-Adjust module,have been introduced in detail.The Auto-PC has been also successfully applied to control the polarization state in the central end of phase stabilized transmission system.In experiments,the 1.21 GHz optical signal is transmitted to the remote end via 5 km optical fiber,and the OSC is used to record link phase jitter.Under the stable link delay,the phase jitter of the received RF signal is between 0.002 DEG.The stability of the RF signal in remote end is recorded using a frequency counter.The link stability is 8.1 ×10-11 in the phase stabilized transmission system by applying Auto-PC.The waveform of the RF signal in remote end is recorded by OSC.When adding the Auto-PC to the phase stabilized transmission system,the jitter amplitude of the RF signal in remote end is reduced to one-sixth of original one after 20 minutes.Three experiments presented above have verified that the polarization state of the optical signal can be stabilized by the automatic feedback polarization controller and the link stability in the remote end is not reduced due to the addition of the Auto-PC.