Full-depth Optical Coherence Tomography System Based On Double Beam Splitters

Optical Coherence Tomography(OCT)is a new optical imaging technology with the advantages of non-contact and high resolution,which has been rapidly used in medical fields such as ophthalmology.It has also been applied in engineering field in recent years.Frequency-domain OCT technology has developed from Time-domain OCT(TD-OCT).FD-OCT greatly improves the imaging speed without the axial scanning device comparing to TD-OCT.However,in traditional FD-OCT system,complex conjugate mirror image will appear in positive and negative optical space because of doing FFT of real number signal which results in a half loss of the system detection ability.How to eliminate the complex conjugate mirror image to achieve full depth imaging system,is always been a hot research topic of OCT technology.This dissertation is focused on a new full-depth FD-OCT system based on double beam splitter structure.The detailed works are as follows:A segmentation modified phase shift method was proposed to reconstruct the complex interference signal in this dissertation which has better performance in complex conjugate mirror image reduction compared with the traditional multiple phase shift method.In the present work,a full-depth FD-OCT system was designed based on double beam splitter interference structure.The path of reference light is single way which is different from traditional return-way light path in the reference arm.After tilting the mirror in the reference light arm,a series of interference signal with difference phase delay distributions in the height direction.In this way,the imaging speed of the OCT system is greatly increased comparing with the speed of the traditional FD-OCT system which requires moving the reference mirror.To receive these interference signals simultaneously,a home-made line-spectrometer system was developed.A self-calibration based on interference fringes was proposed to calibrate the line-spectrometer and it greatly improve the axial resolution and imaging sensitivity of the OCT system.Together with the process of phase choosing and interference intensity normalization of the interference image,the segmentation modified phase shift method was employed to achieve the full-depth imaging.At the same time,analysis and optimization of the system parameters was carried out theoretically,including lateral and axial resolution,detecting depth and sensitivity,and mirror imaging suppression performance.The additional optical path error lead by sample place off the focal plane and its related affect to image noise suppression performance,were analyzed.The problem that system imaging sensitivity will gradually reduce from zero optical path,was investigated.It further proves the necessity of research about full-depth FD-OCT,which making full use of the area near zero optical path.The home-made double beam-splitter full-depth FD-OCT system was used to detect the inner structure of the pharmaceutical capsule and anterior segment of eye.The experimental results demonstrated the excellent performance of system in the field of inner structure imaging.In addition,a full-depth FD-OCT distance measurement system was developed with spectrum correction theory.The system was proved that it could reach a large dynamic range of 16.74 mm with an ultrahigh resolution of 0.627 nm.Subsequently,the system performance was verified by measuring the piezoelectric properties of PZT actuators.Furthermore,the distance measurement system was extended to a full-depth FD-OCT vibration measurement system as well.The imaging blurring problem was studied when the instantaneous speed of vibrating object is too fast.The relationships were investigated for the measurable fastest vibration speed,highest vibration frequency,amplitude and the exposure time of the full-depth FD-OCT vibration measurement system.It provided theoretical support and experimental basis for vibration measurement.This dissertation expand the potential applications of the existing OCT technology and it can actively promote the innovation and development of OCT technology.