Lensless wide-field 3D fiber endoscopy through scattering media using synthetic wavelength holography

Abstract

Minimally invasive imaging with fiber optic endoscopes is crucial for in vivo visualization of tissue morphology, as it supports applications such as early detection of tumors. However, imaging performance of conventional fiber endoscopes is limited when scattering layers are present between target and the distal end of endoscope. This limitation is particularly relevant in biomedicine, where targets such as early stage lesions or blood clots can be obscured by scattering tissue. To address this challenge, we present a lensless endoscopic imaging approach based on synthetic wavelength holography (SWH). SWH is a computational imaging technique in which two optical fields acquired at closely spaced wavelengths are combined to synthesize a field at a longer synthetic wavelength. As the field at longer wavelengths is less sensitive to path length perturbations, this approach can enable endoscopic recovery of holographic information despite scattering in the intervening tissue. In addition, because the synthetic field is assembled from scattered optical fields with larger optical \'etendue, our approach can extend the field of view (FoV) beyond the numerical aperture of the fiber. In this paper, we present the first demonstration of an SWH-based lensless endoscope using a multicore multimode fiber. We experimentally recover three-dimensional images of objects hidden behind scattering layers and through real biological tissue, with a spatial resolution of $\approx 500~\mu m$. We further demonstrate recovery of object information over an extended FoV of 46{\deg} without any distal optics. These results suggest a practical path toward extending fiber endoscopy for wide-field, three-dimensional imaging through scattering media.