The Fpga-based Dual-detector Polarization-sensitive Optical Coherence Tomography Signal Processing

Polirization-sensitive Optical Coherence Tomography is a new optical imaging technology.using the polarized light to detect the biological tissue and obtain the information of tissue. It inherits the general OCT features of no damage, non-invasive, high-resolution. PS-OCT, using the polarized light to image, can obtain not only the reflectivity information, but also the birefringence of the biological tissue. The birefringence index can be changed, when the tissue is pathological, so it is an indicator to Diagnose the tissue.In this paper, the output signal of PS-OCT photodetector are analyzed, and a singal processing system based on FPGA is designed according to the characteristics of the signal. Photoelectric detector transform the interfere signals to electrical signals. The electrical signals , amplified and filtered, are sampled by ADC, and then sent into FPGA. After quadrature demodulation of the signals, CORDIC arithmetic operations, the median intercept and RAM cache are usd to achieve the demodulation of the signal.The main work is finished by this paper as follows:1. Based upon the introduction of PS-OCT theory and frame, the paper propose the main scheme to obtain and process signal. The system use FPGA as core controlling and processing unit. This make hardware part of system simple and efficient.2. The paper uses the singlechip to communicate with the Stepper motor and implement the the horizontal scanning on the control of interrupt signal generated by the FPGA.3. The paper design all kind of the control signals like the ADC, USB, horizontal scanning and so on. It demodulates the signal from the carrier wave with the quadrature demodulation. And the CORDIC algorithm is brought in the system, obtaining the reflectivity and birefringence information. Complete the main chip digital circuit PCB of FPGA-base system design.4. The paper designs the verification experiment, to obtain two dimensional image of glass and biological tissue. After analyzing the result of experiment, the correctness of system is verified. The resolution of this system is about 10μm and this system can detect birefringence accurately.