Research On A Novel Swept-source Optical Coherence Tomography System

Optical Coherence Tomography(OCT)is a noninvasive,high-resolution,new technology for microscopic imaging of medical biological tissues.Swept OCT(SS-OCT)is an evolution of spectral domain OCT(SD-OCT)technology and is superior to SD-OCT in terms of imaging speed and imaging depth.Therefore,it is of great significance to further study the SS-OCT system with fast imaging speed,large imaging depth,high resolution and practical probe micro-probes.In this paper,a novel swept optical coherence tomography system is constructed and its optical properties are studied.This paper proposes new ideas and methods for improving OCT imaging speed,resolution and probe miniaturization.The main contents of this paper are as follows:(1)In order to improve the imaging speed,a high-speed swept source for optical coherence tomography system was prepared.The tunable FP filter and QW-SOA were used to improve the sweep rate by Fourier mode-locking method.The swept source has a bandwidth of 100 nm,an output optical power of 14.8 mW,a bidirectional scanning frequency of 101 kHz,and a duty cycle of 70.4%.(2)The OCT probe is large in size and cannot imaging for the narrow position of human internal cavity,a microsphere-type all-fiber lens probe is designed.According to the transmission characteristics,the mathematical relationship between focal length and spherical diameter was constructed.Then,microsphere-type all-fiber lens probes with diameters of 250,300,and 350 ?m were prepared,and the characteristic parameters of the probes were tested.The results show that the lateral resolution of the probe is high and the good transmission characteristics.(3)Eccentric fiber(ECF)is proposed instead of the traditional single mode fiber(SMF)fiber delay line as the reference arm of the OCT interference.Since the core of the ECF is offset from the central axis,the core is stretched and contracted during the bending process,thereby causing a continuous change of the optical path transmitted in the ECF,further changing the optical path difference between the two interference arms,Making the optical path matching to improve interference fringe contrast(4)Uniformly sampling the interferometer in the time domain creates a discrepancy,leading to the sampled signal being nonuniform in wavenumber,“k”.The optical k-clock spectral resampling method of MZI-assisted interferometer is studied.Nearest neighbor algorithm was used to spectrally resample the original OCT signal.Through spectral shaping and DC denoising of SS-OCT resampled signals,two-dimensional grayscale reconstruction of tissue structure is realized by Fourier transform and standard gray level mapping method.(5)The SS-OCT system and experiments were carried out.The axial resolution of the system was 15.64 ?m and horizontal resolution was 5.6 ?m,the A-scan speed was 101 kHz,and the imaging depth in air was 1.25 mm.The feasibility of the imaging probe and the effectiveness of the signal processing method were verified by imaging experiments on multiple slides.