Liquid crystal metalens with extended depth of focus spot for deep sample optical imaging

With the expanding clinical applications of optical coherence tomography, the inherent tradeoff between high transverse resolution and insufficient depth of focus has become increasingly pronounced. Improved lateral resolution drastically reduces the usable focal depth, compromising consistent image quality across the axial imaging range. To address this core limitation, we propose a liquid crystal metalens incorporating geometric phase corrected by an inverse-quartic axicon phase. Then, the proposed metalens was fabricated by a polarization-exposure system based on a spatial light modulator, where the calculated phase was transformed into the polarization-sensitive geometric phase. The experimental results demonstrate that the developed metalens achieves a 0.5 mm focal depth with left-handed circularly polarized illumination at an incident wavelength of 1550 nm. Within this axial range, the measured focal spots maintain a full-width at half-maximum of around 9 µm. Therefore, the proposed metalens has both high lateral resolution and a large depth of focus, providing a practical solution for optical coherence tomography systems and demonstrating great promise for compact endoscopic imaging platforms.