Advancing microwave photonics: metalens integration for enhanced optical fiber expanders

Metalens, a novel class of optical devices based on metasurfaces, exhibit exceptional optical properties and superior wavefront control capabilities. These characteristics have enabled the development of ultra-thin devices with broad applications in imaging, spectroscopy, optical communications, and photodetection. This paper presents the realization of a near-infrared (IR) metalens used as a beam expander. Our approach effectively achieves optical beam expansion functionality. Initially, we designed the geometric structure of the metalens on a silicon platform, leveraging its design principles. Numerical simulations confirmed that the proposed structure can achieve effective lens focusing. Subsequently, we fabricated the metalens using micro-nanofabrication techniques and validated its performance with a customized testing system. The results demonstrate that the near-IR metalens exhibits excellent focusing performance at a working wavelength of 1550 nm. It can expand and collimate the output beam of a single-mode fiber, thereby verifying the effectiveness and practicality of our design. This design can replace traditional lenses in fiber beam expansion, achieving a thinner profile. Additionally, arrayed metalenses can provide a solution for beam expansion in multi-core fibers, reducing alignment workload and enhancing alignment precision.