Abstract
Multi-mode fiber (MMF) endoscopes are extremely thin and have higher spatial resolution than conventional endoscopes; however, all current MMF endoscope designs require either that the MMF remain rigid during insertion and imaging or that the orientation of the MMF be known. This limits their possible medical applications. We describe an MMF endoscope design that allows the MMF to be arbitrarily bent as it is maneuvered to the target site prior to imaging. This is achieved by the addition of a partial reflector to the distal end of the MMF, which allows measurement of the mode coupling in the MMF using the reflected light arriving at the proximal end of the MMF. This measurement can be performed while the distal end of the endoscope is not directly accessible, as when the endoscope is being maneuvered. We simulate imaging through such a flexible MMF endoscope, where the MMF is step-index with 1588 spatial modes, and obtain an image even after the mode coupling matrix of the MMF is altered randomly, corresponding to an unknown bending of the MMF.
Highlights
Multi-mode fiber (MMF) endoscopes are a class of endoscope that can be made much thinner than endoscopes of other designs [1], while maintaining a high resolution [2], opening up new medical applications [3]
This is achieved by attaching a partial reflector to the distal end of the MMF, which reflects light back to the proximal end of the MMF, allowing calibration of the MMF endoscope to be performed
Common components in both configurations are a single-longitudinal-mode laser, a polarization-maintaining single mode fiber (PMF), a polarizing beamsplitter (PBS), a halfwave plate (HWP), and a phase-only spatial light modulator (SLM), which are together used to excite an arbitrary superposition of modes in an MMF
Summary
Multi-mode fiber (MMF) endoscopes are a class of endoscope that can be made much thinner than endoscopes of other designs [1], while maintaining a high resolution [2], opening up new medical applications [3]. All MMF endoscopes require a calibration procedure to measure the mode coupling in the MMF before they can be used for imaging This calibration requires placing an apparatus of substantial size at the distal end of the endoscope. We propose a design for an MMF endoscope that can be bent arbitrarily while it is maneuvered to the imaging site This is achieved by attaching a partial reflector to the distal end of the MMF, which reflects light back to the proximal end of the MMF, allowing calibration of the MMF endoscope to be performed. The MMF endoscope can be calibrated after any bending occurs, ensuring accuracy during subsequent imaging We describe this calibration procedure in detail in this paper.
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