Double-channel Signal Processing System Based PS-OCT

Optical Coherence Tomography (OCT) is an imaging technology, which uses thebasic principles of the interference of weak coherent light to detect the light scatteringmedium such as biological tissue and to obtain the micro-sized3-dimensionalstructure images. OCT imaging system is a biological micro imaging system with thefeatures of non-contact, non-invasive and high-resolution. Polarization-sensitiveOptical Coherence Tomography (PS-OCT), a kind of functional OCT using thepolarized light to image, can obtain reflectivity information and the birefringence ofthe biological tissue simultaneously. It can be regarded as an indicator for diagnosisthrough detecting the change of birefringence of the biological tissue using PS-OCT.In this paper, based on the study of the imaging principle of the PS-OCT and thecorresponding theoretical analysis, a double-channel signal processing system basedPS-OCT is designed. The PS-OCT imaging system includes all fiber beam path,analog circuit of amplification module, gain compensation module, band-pass filter,the FPGA used for data processing and synchronization control module, USB moduleapplied for data transmission module and the software platform for real-time displayon the computer.The main work is finished by this paper as follows:1. Establishing the all fiber beam path PS-OCT system and obtaining the signalof the coherent light.2. Designing the amplification circuit to amplify the weak signal by a factor of100; Designing the gain compensation circuit to realize the differentamplification of information at different depth; Designing band-pass filter toeliminate direct current component and noise, and improve thesignal-to-noise ratio (SNR).3. Designing the AD conversion circuit to convert analog signal to digital signal;Designing FPGA based circuit and using Verilog program to realize theband-pass filtering, orthogonal demodulation, amplitude and phasedemodulation, median filtering and RAM cache; Designing the USB moduleto upload data to the computer; Designing the image software to display thereflectivity information and the birefringence image in real time. 4. Designing the retardation comparator to realize the synchronous operation bythe synchronous control signal in FPGA after the input of two referencesignals generated by the rapid scanning delay line. Designing a state machinein FPGA to complete the cyclic transformation of null state, writing state andreading state during the longitudinal scan.5. Obtaining the reflectivity image and birefringence image of the samples suchas slices, mica plates and biological tissues; the shape and internal structurecan be available in these images, which proves that the PS-OCT system inthe paper has the ability the detect the reflectivity and the birefringence atdifferent depth of the biological tissue.