一种微米分辨率全光纤OCT内窥探头设计与仿真研究

Design and Simulation Study of a Micrometer-Resolution OCT Endoscopic Probe

摘要: 为了让光学相干层析成像(Optical coherence tomography，简称OCT)内窥探头在保持高分辨率的情况下拓展景深，研究设计了一种微米分辨率的全光纤OCT内窥探头，首次在全光纤结构下实现了高分辨和景深的增加。本文所设计的全光纤内窥探头直径为140 µm，共有三个部分组成，依次为阶跃多模光纤，无芯光纤和渐变折射率光纤。基于光束传播法模拟了波长为0.83 µm的高斯光束分别在该探头、常规OCT内窥探头和梯式变芯全光纤内窥探头中的传输情况，并对比分析了三种内窥探头输出光场的景深和横向分辨率。仿真结果显示，常规OCT内窥探头分辨率约为5 µm，景深为50 µm，大纤芯多模全光纤内窥探头的约有17 µm分辨率以及500 µm的景深，而所设探头横向分辨率约为2.4 µm，景深约为200 µm。所设计内窥探头能在外径几百微米的小尺寸下，兼具~2 µm的高分辨率和~200 µm的扩展景深，与大芯多模全光纤内窥探头(17 µm分辨)相比，其分辨率提高了约3倍，与常规OCT内窥探头(50 µm)相比，其景深扩展了约3倍。本文所设计的高性能全光纤内窥结构可以为狭窄腔体组织内壁病变观察技术的开发提供理论依据。

Abstract: In order to expand the depth of field of Optical coherence tomography (OCT) endoscopic probes while maintaining high resolution, a micrometer-resolution all-fiber optic OCT endoscopic probe was designed to achieve high resolution and increased depth of field for the first time in an all-fiber optic structure. The all-fiber endoscopic probe designed in this paper has a diameter of 140 µm and consists of three parts, which are step multimode fiber, coreless fiber and gradient refractive index fiber in that order. The transmission of a Gaussian beam with a wavelength of 0.83 µm in this probe, a conventional OCT endoscopic probe, and a ladder-type variable-core all-fiber endoscopic probe, respectively, was simulated based on the beam propagation method, and the depth of field and lateral resolution of the output light fields of the three types of endoscopic probes were analyzed comparatively. The simulation results show that the conventional OCT endoscopic probe has a resolution of about 5 µm and a depth of field of 50 µm, the large-core multimode all-fiber endoscopic probe has a resolution of about 17 µm as well as a depth of field of 500 µm, and the setup probe has a lateral resolution of about 2.4 µm and a depth of field of about 200 µm. The designed endoscopic probe can combine high resolution of ~2 µm and extended depth of field of ~200 µm in a small size of several hundred micrometers in outer diameter, which improves the resolution by ~3 times compared with the large-core multimode all-fiber endoscopic probe (17 µm resolution), and extends the depth of field by ~3 times compared with the conventional OCT endoscopic probe (50 µm). The high-performance all-fiber-optic endoscopic structure designed in this paper can provide a theoretical basis for the development of observation techniques for lesions in the inner wall of narrow luminal tissues.