Design of scanning fiber micro-cantilever based catheter for ultra-small endoscopes

During the past few decades, optical devices are frequently being used in medical applications to image lesions and malignancies, and to assist with surgical procedures. An endoscopic procedure requires the distal end of the scope to be placed close to the imageable target area through an opening such as nose, mouth, etc. Thus, the size of an endoscopic device dictates the area of the body that can be imaged using that device. The continuous evolution of micro-electro-mechanical systems (MEMSs) along with the development in optics enable the fabrication of flexible endoscopes having diameters just over a millimeter. As a result, medical users are able to image smaller areas of the body that were inaccessible in the past. Thus, lesions and tumors can be detected at preliminary cancerous stages permitting more accurate diagnoses and supporting an increased life expectancy of the patients. The overarching goal of this work has been to develop a sub-millimeter sized optical scanner that sets the bases for a miniaturized endoscope able to image previously inaccessible luminal organs in real time, at high resolution, in a minimally invasive manner without compromising the comfort of the subject, nor introduce additional risk. Thus, an initial diagnosis can be made, or a small precancerous lesion may be detected, in a small-diameter luminal organ that would not have otherwise been possible. This work sets out to present an optical-fiber scanner for a scanning fiber endoscope design that has an insertion tube diameter in the sub-millimeter range; small enough to potentially be inserted into the smallest airways of the lung and other small diameter tubes, which may include narrow sections of the pancreatic duct, and the narrowest section at the openings of the fallopian tubes. To attain this goal, a novel approach based on exciting a single mode optical fiber at resonance with the help of an electro-thermal actuator is proposed where an asymmetric conducting element expands due to the Joule effect in presence of an electric current. The actuator provides base excitation motion to a cantilevered based optical fiber whose free end follows a closed line pattern. It has been seen experimentally that the area inside the circle can be scanned by offsetting the excitation frequency from the resonant value to achieve the bi-dimensional scanning. The backscattered reflected light from the target sample is set to be captured using multiple multimode fibers placed at the periphery of the device in a ring shape.