Truncated Conical-Tip Fiber Probe for Common-Path Optical Coherence Tomography With Optimal Sensitivity

A truncated conical-tip fiber probe was developed for common-path (CP) swept-source optical coherence tomography (SSOCT) with optimized sensitivity. The probe was fabricated by mechanically polishing a conical no-core fiber (NCF) spliced to a section of gradient-index (GRIN) fiber. The GRIN fiber expanded the sample light at the entrance of the conical tip, and the conical tip generated the Bessel beam with a spot size of ∼2.2 μm over a depth of focus (DOF) of 90 μm. Improvement in the DOF was experimentally verified by measuring the axial profile of the output beam from the probe tip. Moreover, the truncated fiber tip with a flat surface significantly increased the reflectivity of the reference light compared with an untreated conical tip. A 6.6 dB sensitivity improvement was achieved by increasing the diameter of the flat surface from 2.8 μm to 5.8 μm. The performance of the probe was further examined by imaging a multi-layer translucent tape as well as a mouse lung tissue. The designed fiber probe with a high resolution and optimized sensitivity is attractive to common-path OCT imaging in biomedical and clinical applications.