Modeling optical fiber dynamics for increased efficiencies in scanning fiber applications

Abstract

A cantilevered singlemode optical fiber is base-excited to create 2D amplitude-modulated resonant motion as a basis for a scanning fiber endoscope (SFE). Over the past few years, prototype SFEs have been developed with smaller sizes of the distal rigid tip which houses the fiber scanner. Our current prototype is 2 mm in diameter with 15 mm rigid length at the tip of a highly flexible shaft. A spiral scan pattern at 40 degrees field of view generates 250 rings (500 lines) at greater than 10 frames per second with negligible distortion at 10 micron resolution. Future SFEs will use microfabrication techniques to sculpt the optical fiber cantilever to form tapered and microlensed tips for the purpose of increasing field of view without increasing electrical power. Microfabrication of complex optical fiber geometries is guided by linear and nonlinear dynamic models of the resonant motion of these fiberoptic scanners. Linear finite element analysis (FEA) is used to match low amplitude motions of tapered and notched fiber geometries, indicating that more flexible regions or hinges can be designed into future fiber scanners for increased amplitude of motion without sacrificing frequency. Nonlinear models of the fiber dynamics are developed and the results help predict the more complex behavior of microfabricated fiber scanners at wider fields of view. Thus, sophisticated fiber dynamics models are used to guide the development of more efficient scanning fiber image acquisition sensors and systems, such as ultrathin flexible SFEs and low-cost sensors.