Optical alignment of dual-axis MEMS based scanning optical probe for Optical Coherence Tomography (OCT) application

In this paper we present the alignment process for a dual-axis electro-thermal actuated MEMS mirror, silicon optical bench (SiOB)-based probe for endoscopic optical coherence tomography (BOCT). The proposed optical design of the endoscope consists of the propagation of broadband low coherence light source from a 1310 nm laser source thru optical fiber, graded index (GRIN) lens, MEMS scanning mirror to the sample and back. The alignment approach undertaken consists of both passive and active elements. The passive element involves mounting and passively aligning the GRIN lens and MEMS scanning mirror onto trenches etched on separate SiOBs. This is followed by an active alignment of the two optical elements by first mounting each bench onto a five-axis stage rigged with a customized aluminum jig and a goniometer. An average double-pass coupling efficiency of 63.3% was achieved experimentally which was in line with optical simulation results. A fully functional probe was assembled and the cross-sectional images obtained are then presented within the paper. The difference in coupling efficiency resulting from the experiment/simulation and actual assembled probe is then reported and commented upon.