Analysis of optical crosstalk in flexible imaging endoscopes based on multicore fibers

Imaging endoscopes have enabled the development of minimally invasive procedures in a wide range of medical applications. Flexible endoscopes have additional advantages over rigid endoscopes. Remarkably, they have an enhanced capability of being guided through the internal conduits of the human body. The development of imaging endoscopes based on coherent optical fiber bundles have made high resolution fiber endoscopy possible. In the last years, multicore fibers have been proposed as an alternative to coherent fiber bundles for high resolution applications. Both types of structures entail several limiting factors. Among them, the most critical one is the optical crosstalk that takes place between the parallel contiguous fibers of the device, which provokes a worsening in the contrast of the images. Therefore it imposes a limit to the quality of the endoscopic system that must be avoided. In this work, we present a theoretical model for the study of optical coupling in multicore fibers, which is based on an electromagnetic optics approach. This model is applied to the analysis of crosstalk within fiber imaging endoscopes. It includes the effect of core non-homogeneities and bendings. The essential equations of the model will be shown. These equations provide us with a theoretical basis that is subsequently applied to fiber endoscopes design. Therefore, we present a robust method for the adjustment of opto-geometrical parameters of the fiber in order to fulfil the quality requirements for a certain application. The key role of core diameter variations in the quality of the image will be specially highlighted.This work has been partially carried out under the project TEC2006-06548/TCM of the Spanish Ministry of Science and Innovation