Holographic lensless fiber endoscope with needle size using self-calibration

Abstract

Abstract Endoscopes enable optical keyhole access in many applications for instance in biomedicine. In general, coherent fiber bundles (CFB) are used in conjunction with rigid lens systems which determine a fixed image plane. However, the lens system limits the minimum diameter of the endoscope typically to several millimeters. Additionally, only pixelated two-dimensional amplitude patterns can be transferred due to phase scrambling between adjacent cores. These limitations can be overcome by digital optical elements. Thus, in principle thinner, lensless, holographic endoscopes with a three-dimensional adjustable focus for imaging and illumination can be realized. So far, several techniques based on single mode CFB and multi mode fibers (MMF) have been presented. However, these techniques require access to both sides of the fiber, in order to calibrate the bending and temperature sensitive phase distortion, which is not possible in a real application. We present the feasibility of an in-situ calibration and compensation of a CFB with single sided access. A lensless endoscope with a diameter of only 500 µm, a spatial resolution around 1 µm and video rate capability is realized.