DSP-based Optical Coherence Tomography System And Its Applications

The research was supported by the grants from National Natural Science Foundation of China (NSFC) for the project "Nondestructive testing and quantitative evaluation for creep and microcrack propagation behavior of multilayed structures", and Fujian provincial outstanding young scientist fund for the project "Nondestructive testing and quantitative evaluation of aircraft composite materials using optical coherence tomography and terahertz pulsed imaging techniques". An optical coherence tomography system, and characterization of thin films and glass fiber reinformced polymer (GFRP) using Fourier domain optical coherence tomography were investigated in the thesis.Optical Coherence Tomography (OCT) is a new technique allowing high-resolution cross-sectional images from within scattering media to be obtained non-destructively. OCT is a nondestructive, noncontact, and high-resolution technique, which is first used in biomedical field, such as ophthalmology and cardiovascular imaging. Recently, there is a trend that OCT is employed in non-medical non-destructive testing (NDT) applications. Generally, a spectral interferogram is captured from a spectrometer and is sent to computer for subsequent signal and imaging processing to reconstruct an OCT imaging. Therefore, the speed of spectrum acaqusition and transmission will affect the speed of OCT imaging. One of the objectives of the thesis is to develop a spectrometer based on digital signal processor (DSP) and to apply the new spectrometer in Fourier domain optical coherence tomography system.Based on Czerny Turne optical structure, two theoretical functions on image characteristics for concave mirrors were derived in the thesis. With the two functions, the collimation, dispersion and imaging parts of spectrometer were designed and finally a Czerny Turne structure spectrometer was obtained. In addition, the ZEMAX optical system design software was used for the simulation of the spectrometer. The thesis provides the necessary theoretical foundation for the development of Czerny Turne spectrometer. A spectrometer was developed based on the Czerny Turne optical structure. In the spectrometer, a TMS320VC5509 DSP was used as core control unit, a SONY ILX511 CCD was used as detector, and a CCD Signal Processor AD80066 was employed as AD converter. The system software developed by Microsoft Visual C++, was responsible for hardware control, communication, data acaqusition and data transimission. The data was transimited to computer via high speed USB 2.0. The spectrum obtained by the home-mode spectrometer was compared with the one, obtained by comencial spectrometer HR2000 (Ocean Optics). It can be seen from the experimental results, the performace of the two spectrometers was similar. Therefore, it has been demonstrated the feasibility of the developed spectrometer. In the mean while, the developed spectrometer was embeded in an OCT system, it was also demonstrated that the developed OCT has the capacity in the characterization of thin film structures.Aimed at the high-resolution testing of GFRP, a Fourier domain optical coherence tomography system was build and optimized in the thesis. The experimental results showed that the developed OCT system could be used in the high-resolution nondestructive testing of GFRP. The achieved axial resolution is 0.7 um, one of the best ever reported. The thesis provides a new technique for GFRP characterization and it has great potential in real applications for defect detection of GFRP.