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.

Project Narrative Confocal endo-microscopy is a powerful tool for high-resolution imaging of cells and tissues inside the body, allowing for high-sensitivity and high-specificity diagnosis of diseases, including cancer. However, current confocal endo-microscope probes are made of discrete bulky optical elements and require scanning, resulting in slow imaging speed and large size and thus hindering their broader utility. The goal of the proposed research is to overcome these limitations by developing a metasurface based chromatic confocal endo-microscope, which promises to enhance medical imaging and enable fast, minimally invasive diagnosis of diseases deep within the body.