Fabrication and testing of lensed fiber-optic probes for distance sensing using common-path low-coherence interferometry

Common-path low-coherence interferometry enables high-resolution distance measurements to be made via thin fiber-optic probes. This is particularly advantageous for applications such as ophthalmic vitreoretinal microsurgery, where the probes can be used to precisely locate the position of surgical tools relative to the retinal surface, but could also have a wide range of other medical and industrial applications. The performance of the fiber probes depends critically on the fabrication of a focusing lens at the distal tip and on creating a medium-independent partial reflection that is used for common-path interferometry. These are complex multi-step procedures that are not fully described in the literature. In this note, we detail a procedure to manufacture probes by fusing coreless and gradient index sections of fiber to single-mode fiber and to apply a thin gold coating to act as a partial reflector. We also explain how quality control of the fabrication can be performed, demonstrate how the probes can be coupled to a common-path swept-source interferometer, and describe algorithms to convert raw data to distance measurements. These procedures are intended to aid researchers in developing their own customized probes and develop new applications for distance sensors.