Near-field Meta-optics

TL;DR

This paper introduces near-field meta-optics, demonstrating how integrating metasurfaces directly within the near field of a terahertz antenna enables unprecedented control of emission, resulting in ultra-compact, high-efficiency photonic devices.

Contribution

It experimentally demonstrates near-field meta-optics with integrated metasurfaces inside the near field, enabling simultaneous emission control and significant device miniaturization.

Findings

Collapse emission divergence from ~60° to <10°

Enhance on-axis intensity 50-fold

Achieve 10% higher outcoupling efficiency than bulky lenses

Abstract

Metasurfaces have revolutionized compact wavefront control using planar, subwavelength structures. However, conventional meta-optical devices predominantly operate within a far-field paradigm, assuming electromagnetic decoupling between the source and metasurface, which limits control to post-emission wavefront shaping. Here, we define and experimentally demonstrate near-field meta-optics - a regime where strong source - structure coupling enables simultaneous control of emission and radiation. By integrating an inverse-designed dielectric metasurface directly within the near field of a terahertz photoconductive antenna (PCA), we show that the metasurface co-defines the emission process itself. Our meta-PCA, incorporating a 50-um-high metasurface - one-third the thickness required by reciprocal far-field designs - collapses emission from ~60deg divergence to a sharp < 10deg forward beam, while enhancing on-axis intensity 50-fold compared to bare GaAs. Unlike far-field metasurfaces that typically trade efficiency for thinness while remaining laterally large, our device achieves extreme compactness in both dimensions. Remarkably, it exceeds the outcoupling efficiency of a bulky, millimeter-scale silicon lens by 10%, despite a volume reduction of over three orders of magnitude. These results establish near-field meta-optics as a transformative paradigm for developing high-efficiency, ultra-compact on-chip photonic systems across the electromagnetic spectrum.