Common-path optical coherence tomography using a conical-frustum-tip fiber probe

We demonstrated an in-fiber common-path optical coherence tomography (OCT) system using a conical-frustum-tip fiber probe. The probe had a circularly truncated conical shape to increase reflection of reference light while preserving focus without additional lens components. We analyzed the intensity of reference light back-reflected from the probe using a ZEMAX simulation, and the optimal height of the conical-frustum lens was 1.0 μm. Compared to various other types of conical-frustum-tip fiber probes, the probe in this paper showed the best lateral resolution with a relatively high reflectivity. Experimental results are compared to simulations. This conical-frustum-tip probe provided a 3.7 times larger reflectivity than a conventional conical lens. Due to the increased reflection, the signal-to-noise ratio (SNR) of an OCT image was enhanced by up to 5.6 dB. Furthermore, the lateral resolution was less than 4.4 μm as verified by B-scan profiles of a resolution target card. This probe can be utilized as a forward-viewing endoscopic probe to enhance OCT image quality through an increase in SNR, sensitivity, a small size, and effective focusing without additional lens components.