Metasurface based chromatic confocal endoscope

Pennsylvania State University, The, University Park PA

Investigators

Abstract

Metasurface based chromatic confocal endoscope Endoscopy is an indispensable diagnostic tool for imaging hard-to-reach regions inside the body. Confocal endo- microscopy, with its capability of cellular imaging resolution, optical sectioning, and three-dimensional imaging, has proved to be a valuable tool in health diagnosis, including cancer screening. However, the traditional design approach used in current confocal endo-microscopes, which involves using multiple discrete optical elements such as objective lenses and prisms, leads to bulky size and high cost. Moreover, the lateral mechanical scanning in the distal end presents a significant challenge, limiting the imaging speed and hindering its broader applicability. To overcome these challenges, we propose a meta-photonic design approach that empolys a metasurface, an artificial ultrathin metamaterial consisting of subwavelength nanostructures, to realize spectral encoding for wavelength division multiplexed confocal imaging and to integrate all necessary functionalities, including high-numerical-aperture focusing, into a single ultracompact device. This new type of metasurface- based chromatic confocal endo-microscope will have a miniature distal end that can be integrated with a conventional endoscope, and it will have a low cost potential for mass production. Importantly, the proposed confocal endo-microscope has high imaging speed by eliminating one lateral scanning (Aim 1) or both lateral scannings (Aim 2). We will develop a metasurface that integrates the dual functions of an objective lens and a grating. The metasurface will be directly fabricated on a silica coreless fiber spacer that is epoxied to a cantilevered single-mode fiber, resulting in a miniature confocal endo-microscope probe of just 400 μm in diameter. Different wavelengths of broadband illumination light delivered through the single-mode fiber (which also behaves as a confocal pinhole) will be focused by the metasurface linearly along a selected lateral direction, enabling parallel confocal imaging of multiple lateral points simultaneously. The other lateral direction will be scanned by using a piezotube to achieve real-time imaging speed (30 frames per second). We will also design a spatial-spectral encoding metasurface that focuses each wavelength to form a random array of focal spots across a two-dimensional (2D) area. Different wavelengths sample the 2D image with different random sampling focal spots. The proposed strategy is thus an analogue of the compressive single-pixel camera, in which each wavelength is an effective single-pixel detector, and a spectrum represents a series of multiplexed measurements. The proposed metasurface will enable 2D compressive confocal imaging and eliminate lateral scanning, leading to a detector-limited imaging speed (up to KHz). The proposed metasurfaces will be fabricated and characterized. Lateral and axial resolutions of the proposed confocal endo-microscope will be quantified. Imaging speed and field of view will also be characterized. We will also demonstrate and validate the proposed systems by imaging tissue phantoms.