Research On OCT Probes For Biomedical Imaging Applications

Optical coherence tomography(OCT)is a novel imaging technique that is based on the principle of low-coherence light interference.This technique has been widely used in biology medical imaging because of its advantages of non-invasive,non-radiative,high resolution and high imaging speed.Currently,OCT is clinically limited to diagnose ophthalmology and skin due to the limitation of the imaging depth.OCT combined with endoscopic technology can perform high-resolution imaging of internal organs and tissues,providing an effective means for early diagnosis and treatment of diseases.Based on the swept-source OCT technology and the development of OCT endoscopic probes,this dissertation has achieved breakthrough research results.Specific research content and innovative research results are as follows:1.A swept-source OCT system with a center wavelength of 1300 nm based on fiber-optic Mach-Zehnder interferometer was designed and built.This system has an axial resolution of 12 ?m and a lateral resolution of 14.81 ?m.We respectively performed imaging on mirrors,coverslips and onion tissue,showing good imaging performance.2.A novel capillary ball lens-based probe for common-path optical coherence tomography(CP-OCT)has been proposed,which is flexible and compact.By adjusting the distance between the fiber end and the ball lens,the working distance of the probe output beam is freely tuned from 878.2?m to 444.7?m and the corresponding lateral resolution is changed from 11.4 ?m to 26.1 ?m,which meets the requirements of OCT imaging.The flexibly adjustable of the working distance can effectively solve trade-off between lateral resolution and depth of focus that encountered in traditional OCT probes.In addition,the intensity of reference power derived from single-mode fiber(SMF)tip could be flexibly adjusted by choosing appropriate polishing angle so as to optimize the OCT system sensitivity.3.A miniature all-fiber axicon probe with an extended depth of focus(DOF)for forward-viewing OCT imaging has been developed.First,we theoretically proved that the DOF of the Bessel beam can be effectively expanded by increasing the diameterof incident light field on the axicon lens without sacrificing the spot size.And then,we introduced a 1/4 pitch GRIN fiber into the designed fiber probe to generate a Bessel beam with a 155 ?m DOF and a 2 ?m FWHM beam diameter.This design effectively alleviated the contradiction of traditional optical lenses between DOF and lateral resolution.Finally,we performed OCT imaging experiments on multilayer translucent tape to verify that the improvement of image depth mainly comes from the enhancement of DOF.