Fibre imaging bundles for full-field optical coherence tomography

Abstract

An imaging fibre bundle is incorporated into a full-field imaging optical coherence tomography system, with the aim of eliminating the mechanical scanning currently required at the probe tip in endoscopic systems. Each fibre within the imaging bundle addresses a Fizeau interferometer formed between the bundle end and the sample, a configuration which ensures down-lead insensitivity of the probe fibres, preventing variations in sensitivity due to polarization changes in the many thousand constituent fibres. The technique allows acquisition of information across a planar region with single-shot measurement, in the form of a 2D image detected using a digital CCD camera. Depth scanning components are now confined within a processing interferometer external to the completely passive endoscopic probe. The technique has been evaluated in our laboratory for test samples, and images acquired using the bundle-based system are presented. Data are displayed either as en-face scans, parallel to the sample surface, or as slices through the depth of the sample, with a spatial resolution of about 30 µm. The minimum detectable reflectivity at present is estimated to be about 10−3, which is satisfactory for many inorganic samples. Methods of improving the signal-to-noise ratio for imaging of lower reflectivity samples are discussed.