Abstract: Compact and minimally invasive optical imaging probes are of growing importance for high-resolution tis-sue interrogation and early disease diagnosis. In particular, scanning fiber endoscopy for confocal imaging at visible wavelengths offers micron-scale resolution in a compact form factor suitable for in vivo appli-cations. However, the optical performance of such probes is fundamentally limited by aberrations in the micro-objective, which is typically implemented using refractive lens assemblies or gradient-index (GRIN) lenses. Among these limitations, off-axis aberrations significantly degrade resolution toward the edges of the imaging field, restricting overall image quality.

This work addresses these challenges by designing and implementing a hybrid lens system that integrates a metasurface with a GRIN micro-objective to correct aberrations in scanning fiber microendoscopy. In the first part of this work, a metasurface is introduced as an aberration-correcting element in a fiber-scanning confocal reflectance imaging system, where a single optical fiber is used for both excitation and collec-tion. Modeling hybrid refractive-metasurface designs requires the coupling of simulation techniques across macroscale and nanoscale optics, for which an Ansys simulation workflow platform is used. The metaoptical element serves as a thin and compact aberration correction surface, ensuring uniform resolution across the entire imaging field. Experimental results from our scanning fiber endoscopy system demonstrate a notable enhancement in optical performance both on-axis and off-axis. Impressively, the resolution experiences only a modest degradation by a factor of 0.13 at the edge of the field of view compared to the center.

Building on this foundation that metasurfaces correct aberrations in reflectance imaging, further inves-tigated the role of metasurfaces in fluorescence imaging, where chromatic aberration presents an additional constraint. Typically, color correction is achieved by implementing multiple refractive lenses that complicate lens assembly and alignment. The effectiveness of a single metasurface with a gradient refractive index (GRIN) lens for confocal fluorescence imaging is demonstrated, showing significant improvement in image quality. It is shown that it is not necessary to correct explicitly for chromatic aberration, as the system is designed such that the excitation and emission wavelengths focus at different planes. This relaxes the need for conventional achromatic correction, as each wavelength is optimised for its respective function.

Finally, the practical utility of the proposed hybrid meta-GRIN optical system is demonstrated through its implementation in a confocal endoscopy platform with a compact and portable detection unit. Experimen-tal validation shows substantial improvements in imaging performance. The results of reflectance imaging on resolution targets show a 3.5-fold contrast improvement, and fluorescence imaging on biological tissue (mammalian brain) shows a 2-fold increase in the contrast-to-noise ratio at the intermediate to extreme fields (without compromising on-axis performance). Overall, the work establishes metasurface-integrated micro-optics as a powerful approach for overcoming key limitations in scanning fiber endoscopy, enabling improved resolution and simplified optical design. All are cordially invited.

Event Details
Title: Meta-optics Beam Shaping for Improved Bessel Light SheetsAberration correction in microendoscopic imaging using metaoptics (PhD viva voce)
Date: June 26, 2026 at 11:30 AM
Venue: Google Meet (https://meet.google.com/yqq-xbym-wuz)
Speaker: Ms. Susan Thomas (EE20D751)
Guide: Dr. Shanti Bhattacharya
Type: PHD seminar

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