Cascaded Metasurface Interferometer for Multipath Interference with Classical and Quantum Light

TL;DR

This paper presents a scalable, reconfigurable metasurface-based multimode interferometer that works with both classical and quantum light, overcoming limitations of traditional bulk beamsplitters in optical networks.

Contribution

The authors design and experimentally demonstrate a metasurface multiport beamsplitter and cascaded interferometer capable of controlling classical and quantum light interference.

Findings

Controllable splitting ratios via tunable phase relations.

Successful demonstration of quantum interference with single photons.

Scalable and reconfigurable platform for classical and quantum photonics.

Abstract

Beamsplitters represent fundamental components in both classical and quantum optical systems, enabling the distribution of light, as well as the generation of interference, superposition and entanglement. However, optical networks constructed from conventional bulk 2x2-beamsplitters encounter inherent scalability issues, as the number of required beamsplitters scales quadratically with the number of optical modes for a fully connected network. Metasurfaces offer a promising route to overcome these constraints. By manipulating light at the wavelength scale compact optical components with advanced functionalities can be constructed, which address several modes simultaneously. In this work, we design and experimentally utilize a metasurface as a multiport beamsplitter. Furthermore, we realize a multimode interferometer composed of two cascaded metasurfaces. We characterize the individual and cascaded metasurfaces using classical light, showing controllable splitting ratios through tunable phase relations. We then expand the approach to quantum light, employing single photons to demonstrate second- and third-order photon correlations, as well as single photon interference across multiple spatial paths. These results establish metasurface-based multiport beamsplitters as a scalable and reconfigurable platform bridging classical and quantum photonics.