Long-working-distance fiber optics probes with large diameter GRIN fibers for OCT imaging

Fiber-optic probes used in medical Optical Coherence Tomography (OCT) imaging usually utilize short pieces of graded-index (GRIN) fiber to focus the output beam from the single mode (SM) fiber to achieve the desired beam size and working distance. For applications involving large organ imaging, longer working distances of a few mm are required. However, such long working distances are not achievable with standard 125μm diameter GRIN fiber lens and larger diameter GRIN lens are required. Fabricating a fiber optics probe using a large-diameter GRIN fiber lens presents some unique challenges. We present both theoretical simulations and experimental measured results of the output beam profiles of probes made with 500μm diameter GRIN fiber to investigate and understand those challenges.