基于拉锥结构的全光纤型内窥光学相干层析成像探针研究

Tapered structure based all-fiber probe for endoscopic optical coherence tomography

本文报道了一种基于拉锥结构的全光纤型内窥光学相干层析成像探针.基于大纤芯多模光纤的低光束发散特性,使用大纤芯多模光纤代替透镜作为成像元件,并在单模光纤与大纤芯多模光纤之间引入过渡拉锥段以减少插入损耗.首先利用光学仿真软件(Rsoft)确定探针的最佳结构,然后通过拉锥、切割以及熔接工艺实现探针制作,并对探针的出射光束特性与插入损耗进行测量,最后将该探针与扫频光学相干层析成像主系统联机,对人体指尖皮肤及鸡气管壁组织进行成像.该探针直径为250μm,不锈钢保护管外径为325μm,硬端长度1 cm,插入损耗约为0.3 d B,空气中有效成像范围达800μm.该探针为内窥光学相干层析成像技术在心血管疾病的应用提供了高紧凑度、高传输效率与高灵活性的选择.

A tapered structure based all-fiber endoscopic probe for endoscopic optical coherence tomography （OCT） is pre- sented in this paper. The designation and fabrication of a miniaturized high-performance probe are critical in endoscopic OCT. Compared to the conventional fiber-lens structure based endoscopic probe, the all-fiber probe has a prominent edge in size and flexibility. Due to its lower beam-divergence, the large core multi-mode fiber makes a better fit than a general single mode fiber does when utilized to replace the micro lens in a conventional endoscopic probe as the imaging component. Furthermore, a tapered fiber is introduced as a transition section between the single mode fiber and the large core multi-mode fiber in order to enhance the light transmission efficiency and reduce the rigid length of the probe simultaneously. First, in order to obtain an optimal performance, optical simulation software （Rsoft） is adopted to determine the probe＇s proper lengths of the tapered section and the large core multi-mode fiber. Second, the all-fiber structure based endoscopic probe is fabricated by means of large core multi-mode fiber tapering, cutting and fusing processes. The beam characterization and insertion loss of the fabricated probe are measured experimentally. The probe itself is 250 μm, and after covering with a stainless steel protective tube, its outer diameter becomes 325 μm. The rigid length of the probe is about 1 cm, which is more flexible and easier for inserting into curved blood vessels. The insertion loss of the probe is measured to be about 0.3 dB. To the best of our knowledge, it is the lowest among all of the all-fiber endoscopic probes. Finally, the probe is integrated with a custom-built swept-source optical coher- ence tomography system. Imaging of human fingertip and ex-vivo chicken trachea is conducted to demonstrate the key performance parameters of our probe. The effective imaging range of the probe is up to 800 microns in air without the help of any extra mechanism to expand its depth of focus. The probe offers a compact, efficient and flexible candidate for endoscopic optical coherence tomography, which is promising in cardiovascular investigations.