A behavioral model for optically powered OCT endoscope with a micro electrostatic vertical-comb optical scanner

Abstract

This paper presents a novel device architecture for optically actuated microelectromechanical systems (MEMS) endoscopes for optical coherence tomography (OCT) measurement. A 10-mW infrared light beam at a wavelength of 1.5 μm is transferred through the single-mode fiber to provide a scanning MEMS mirror with the drive voltage (maximum 11 V) by exciting a photovoltaic cell, while also providing with a secondary light beam at a wavelength of 1.3 μm for the OCT measurement. An electrostatic vertical comb-drive optical scanner (1.5 mm × 2.0 mm × 0.5 mm) has been developed by using the deep reactive ion etching (DRIE) of a silicon-on-insulator (SOI) wafer. The design of the scanner module is discussed, along with the experimental results of electrostatic operation. An equivalent circuit model for the optical scanner is developed to explain the behavior of the optically powered actuation mechanism, including the hysteresis loop in the frequency response and the voltage dependence of oscillating angle (mechanical peak ±3.2• /7 V around the resonance frequency of 250 Hz). OCT measurement of a tissue is demonstrated to reconstruct the cross-sectional image of a fingerprint at a resolution of lateral 40 μm × vertical 8 μm and penetration depth of 2.5 mm.

New Endoscopic Imaging Technology Based on MEMS Sensors and Actuators

“…On the distal end of OCT imaging probe, MEMS scanners and actuators play a crucial role in the miniaturization of the endomicroscope. After the first introduction of the electro-thermal scanner based OCT system by Xie et al [ 43 ], researchers have made significant progress on the MEMS based OCT imaging system [ 44 , 45 , 46 , 47 , 48 , 49 , 50 , 51 , 52 , 53 , 54 , 55 , 56 , 57 , 58 , 59 , 60 , 61 , 62 , 63 , 64 , 65 , 66 , 67 , 68 , 69 ]. The in vivo endomicroscopic imaging with angled vertical comb-drive (AVC) actuated MEMS scanner ( Figure 5 a) based OCT endomicroscope was demonstrated for the first time by Piyawattanametha and colleagues at MIT [ 46 , 47 ].…”

“…Different from the AVC actuated MEMS scanners that are fabricated by surface machining approaches, staggered or in-plane configured vertical comb-drive actuated MEMS scanners are usually realized by bulk machining MEMS fabrication technology [ 48 , 49 , 50 , 51 , 52 ]. As shown in Figure 6 , bulk-micromachined MEMS scanner based OCT endomicroscope has been developed by Toshiyoshi et al [ 51 ].…”

“…OCT measurement is performed with another source of wavelength 1.3 μm. ( c ) Photograph of the endomicroscope head (Reproduced with permission from IEEJ [ 52 ]).…”