Removal of back-reflection noise at ultrathin imaging probes by the single-core illumination and wide-field detection (Conference Presentation)

Research trends in endoscopy have been to reduce the dimension of the system for minimally invasive diagnostics and to improve spatial resolution to the microscopic level for the detailed investigation of specimens. In developing endoscopes that meet these needs, ultrathin imaging probes such as graded index lenses and fiber bundles have been widely used. And a single imaging probe is used for both illumination and detection to maintain the small diameter of the probe unit. However, this causes a fundamental problem, that is the back-reflection noise from the surface of the imaging probes. This back-reflection noise can overwhelm signals from target objects with weak contrast, which is the case for biological tissues, and degrade image contrast to such an extent that the objects remain unresolved. Here, we present an endomicroscope free from back-reflection noise generated at an ultrathin imaging probe and yet guaranteeing microscopic spatial resolution. In our method, we send illumination through single individual core fibers in the image fiber bundle, and detect signal light by the other core fibers. By blocking the back-reflection occurring only at the core used for the illumination, we remove the back-reflection noise before it reaches the detector sensor. The transmission matrix of the fiber bundle is measured and used to reconstruct a pixelation-free and high-resolution image from the raw images captured by the other fibers, which are blurred and pixelated. We demonstrated that the proposed imaging method improved 3.2 times on the signal to noise ratio produced by the conventional illumination-detection scheme.