Design Of MEMS-OCT Endoscopic Microscopic Imaging Probe And Research On Field Of View Enhancement Technology

Proposed at the end of the 20th,Optical coherence tomography(OCT)is a novel medical imaging technology century with micron-level resolution and imaging depth of several millimeters.OCT has a wide range of applications in noninvasive living tissue examination and real-time imaging,which can be used for pre-cancer detection potentially.Early cancer mainly occurs in the intracorporal organ,especially the depth of 1-3mm below the epidermis of the mucosal layer of the inner wall of tubular organs in the body.Therefore,to achieve in vivo high-resolution depth imaging,the OCT imaging probe needs to be miniaturized(outer diameter ?5 mm).Based on the electrothermal driven MEMS mirror,a 5 mm diameter endoscopic OCT probe is designed,and the field of view(FOV)of the MEMS-OCT endoscopic probe is enhanced by Snell Window Effect.The main work and achievements of this paper are as follows:(1)Designed and fabricated a miniaturized OCT probe.On the basis of the transfer matrix theory,the optical path of the endoscopic probe was simulated using Zemax software.The mechanical structure of the probe was designed by Solidworks.To provide the driving signal to MEMS,the flexible printed circuit board(FPCB)was designed using Altium Designer.After assembled,the probe was tested to evaluate performance,such as FOV and the lateral resolution.(2)The Snell window effect was used to increase the FOV of the MEMS-OCT endoscopic probe by immersing the electrothermal driven MEMS mirror into the liquid with a high refractive index.As a preliminary test,a transistor out-line packaging MEMS was made to observe the variation of optical scanning angle when the MEMS mirror was encapsulated in air,white mineral oil,methyl pyruvate-silicone oil or liquid paraffin.The test results showed that the FOV of the MEMS mirror can be increased by using the Snell window effect when the MEMS mirror was encapsulated in higher refractive index liquid at the same driving temperature as the MEMS mirror in air.The resonance frequency and response time of the MEMS mirror sealed in the liquid had been tested.Compared with the air environment,the viscosity coefficient and thermal conductivity of the filled liquid are increased,so it has a stronger damping effect on the MEMS mirror,which makes the immersed MEMS mirror unable to achieve resonance scanning and increases the response time of the MEMS mirror.To analysis the influence of the liquid absorption on the intensity of OCT imaging,the absorption spectrum of liquid was tested.(3)White mineral oil was selected and sealed in the MEMS-OCT endoscopic probe.The parameters of the probe such as FOV and the lateral resolution were tested.The test results showed that the FOV of the MEMS-OCT endoscopic microscopic imaging probe can be enhanced by using white oil as the filling liquid at the cost of reducing the lateral resolution.