Resolution-enhanced imaging for endoscopy using diffractive optics

Abstract

Optical endoscopy is indispensable for minimally-invasive medical diagnostics and therapeutics, whereby visualization of subtle changes in the structure of tissue can be used to identify disease. Adaptive real-time zoom functionality is highly desirable for resolving mucosal microvasculature, which when visualized can be used to improve diagnostic accuracy. Realizing this functionality in state-of-the-art miniaturized endoscopic imaging, such as chip-on-tip endoscopes, is challenging: conventional zoom objectives are bulky and existing chip-on-tip systems still have far from diffraction-limited performance. Point-scanning illumination approaches have been shown to improve imaging resolution by reducing the focused spot size. Typically, this higher resolution comes at the cost of low optical throughput (efficiency) and long acquisition times due to mechanical scanning requirements, thereby limiting applicability in clinical settings. In this work, we demonstrate an innovative Diffractive Optical Element (DOE) based optical imaging system for spatial resolution enhancement without mechanical scanning. Our imaging system is based on simultaneous utilization of a custom DOE and high-speed Digital Micromirror Device (DMD). The multi-level phase-only DOE produces a single super-resolution spot in the far-field while the DMD laterally scans the spot in the object plane at kHz rates. To demonstrate resolution enhancement with high-speed acquisition, we image a resolution test target and fluorescently labelled cells. In the future, through envisioned DOE-array integration in an endoscopic module, resolution enhancement (in an adaptive zoom-mode) can be achieved through illumination modulation alone without the need for separate systems.