The Design And Implementation Of Control Scheme For SU(2)-type Polarization State Generator

Continuous variables coherent optical communication is a noval communication which uses coherent optical signal as the information carrier. It has the advantages of coherent optical communication and continuous variable quantum cryptography communication, includes the characteristics of low cost, stable communication quality. It has become the current research hotspot. But the technology of continuous variables coherent optical communication is not yet mature, and there are still some key technologies have not been very solved very well. One of the important points is high speed encoding/decoding, namely fast generate target polarization, realize polarization encoding and transmit the information. Therefore, the study of the polarization state generator has the theoretical and practical significance.In this thesis, we focus on the design and implementation of control scheme for SU(2)-type polarization state generator which has existed in the laboratory. Using ST’s STM32f103RFT6 chip and TI’s product TMS320F2812, an ARM+DSP polarization control system is designed. A random number (each one, corresponds to a state of polarization) is sent to DSP by ARM through the SPI interface. DSP transfers a group of voltage control signals producted by the tabu search algorithm and the random number which corresponding to the voltages to ARM internal buffer through the SPI interface. Finally, the voltage control signals are sent to the high-voltage power supply by ARM. Amplifying the voltage, we load the volatage into two ends of the crystal of to realize the polarization conversion.Tabu search algorithm is a meta heuristic intelligent optimization algorithms. A new polarization control algorithm based on tabu search theory is proposed in this thesis. We verify the polarization control algorithm through MATLAB software programming. The simulation results show that, by using this polarization control algorithm, SU(2)-type polarization state generator can transform the linear polarization into arbitrary polarization. If the Stokes parameter S2 and S3 are restricted to specific region on the Poincare sphere:region 1 or region 2, the desired polarization state is generated by this control algorithm and the control voltage size is ensured within 120V. It will reduce the requirements of the high-voltage power supply.We set up the experimental light path and solidfy the polarization control algorithm which has been converted to DSP code to DSP internal flash. We use single beam transmission mode. This mode adopts two quadrature Stokes components S2 and S3 as the operable physical quantities instead of the amplitude and phase. The Stokes parameters are obtained by measuring the polarization intensity. We takes the S2 and S3 components analogous to the eigen light and signal light in double beams continuous variables coherent optical communication, so the eigen light and signal light transmit in a light beam at the same time. It not only has the advantages of simple structure and high degree of coherence, but also simplifies the control process of information encoding. According to the characteristic of SU(2)-type polarization state generator, when the input polarization light is -45° linearly polarized light, SU(2)-type polarization state generator is able to realize the encoding of S2 and S3 components in Alice, while another SU(2)-type polarization state generator combined with one half wave plate and homodyne detection circuit is applied to decode. The experimental results showed that, the polarization control algorithm could better realize the polarization conversion and complete the random encoding of the polarization component. Moreover, the random selection and measurement of S2 and S3 components are also achieved perfectly. The single beam continuous variables coherent optical communication is futherly implemented.