Several Key Techniques And Applications Of Fourier-domain Optical Coherence Tomography

Optical Coherence Tomography(OCT)is a new optical nondestructive testing and imaging technology.Low-coherence light is employed and the basic core of the system is Michelson interferometer.It's a high-resolution imaging technology which obtained the surface or internal microstructure information of the samples by detecting the backscattered or reflected lights from the detected samples.OCT has advantages of non-contact,non-destructive and high-resolution.It was rapidly used in medical field,such as ophthalmology,endoscopy and cardiovascular imaging.Recently,OCT was introduced into non-medical field.Aiming at the low imaging speed of Time-domain OCT(TD-OCT)which needs vertical mechanical scanning,two-dimensional Fourier-domain OCT(2D FD-OCT)system that based on basic principles of OCT was developed.The hardware of the independent development system include light source,light splitter,lens,area CCD camera,piezoelectric ceramic transducer(PZT)and reference mirror and so on.The system is based on free space Michelson interferometer.Halogen lamp and near infrared Superluminescent Diode(SLD)were used as the light sources to meet different testing purpose.A cylindrical lens was attached in order to let the light focus into a line when the light arrives at the sample so that two-dimensional structure information of the sample could be acquired at single detection.An array CCD camera was applied to acquire the interference signal and a computer was used to process the data get by CCD and to reconstruct the image.Meanwhile,in order to facilitate 2D FD-OCT research,VC++ and MATLAB mixed programming technology was employed to develop the FD-OCT system software.The developed software was multiple functions with a friendly interface and it was convenient for software maintenance and upgrade.Effects of some parameters on the imaging performance of the developed 2D FD-OCT system had been carried out.The research of light influence on the axial resolution and lens impact on transverse resolution had been done by adopting lights with different central wavelength and lens with different numerical aperture respectively.Also,the effect of pixels of area CCD camera on detection depth was investigated.FD-OCT system has superiority in dynamic range and sensitivity comparing with TD-OCT system.However,FD-OCT has its disadvantages.The FD-OCT images is acquired by Fast Fourier transform(FFT)of the real component of the interference spectrum,so not only the information of sample is got,but also a complex conjugate image mirror symmetrical about zero optical path difference position is contained.This complex conjugate image may overlap with the structure information of sample and make it hard to read the structure information of sample.Aiming at resolving the problem,the method of removing complex conjugate image was employed on developed 2D FD-OCT system.In the real applications,2D and 3D images of thin pieces of scratched and cracked glasses had been achieved by using the developed system.Measurement of the radius of curvature of lens and joint bearing inner ring were done.This expended the application fields of 2D FD-OCT system.The experimental results demonstrate accuracy and reliability of the developed 2D FD-OCT system and it could be recommended to be employed in real engineering applications.