Fiber endoscope design utilizing metalens for illumination and collection

Abstract

Endoscopes are medical inspection devices allowing doctors to examine internal organs without the need for large incisions. Made of optical fibers and an imaging lens at the tip, one of their most critical parameters is the size of the imaging optical system, limiting the agility and accessibility for clinical applications. Metalens-based fiber-optic endoscopes offer a promising alternative to conventional devices to reduce the size while maintaining the image quality. However, the accurate modelling and analysis required to design these devices can be challenging as they combine nanoscopic elements in a macroscopic optical system. In this work, we present a new multiscale metalens design solution for fiber-optic endoscopes, utilizing full-wave electromagnetic simulations and ray-tracing techniques.The metalens consists of subwavelength scatterers (meta-atoms) characterized individually using Rigorous Coupling Wave Analysis (RCWA). By controlling their distribution in size according to a target phase profile optimized in ray-tracing optics software, one can manipulate the phase, amplitude and polarization of the transmitted light. Smaller scale metalens (~100λ),can be directly simulated and their near-/far-field results can be obtained with the Finite Difference Time Domain (FDTD) method. For larger metalens (≫ 100 𝜆) stitching the near field or summing up the farfield from individual metaatoms to obtain the overall response of the metalens is more efficient than the direct simulationFinally, we can perform ray-tracing simulations to characterize the full system in a macro-scale environment, utilizing the response of the metalens.