Lensless Fiber Imaging With Long Working Distance Based on Active Depth Measurement

Abstract

Lensless fiber endoscopes allow noncontact imaging in narrow spaces without lenses or scanning devices at the distal tip. In this work, an active depth measurement module based on a Fabry–Perot interferometer is integrated onto the imaging fiber bundles. An accurate depth-dependent point spread function can be constructed for <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$a$ </tex-math></inline-formula> <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">priori</i> deconvolution in image deblurring. We have demonstrated that the working distance of a lensless fiber endoscope can be increased from the end face to several tens of micrometers, or even up to more than double for certain spatial frequencies. The contrast of the reconstructed image is also significantly improved. Furthermore, the proposed device can be implemented rapidly without precalibration and is resilient to fiber bending; thus, it can be used for real-time monitoring applications.