Reconfigurable unitary transformations of optical beam arrays

TL;DR

This paper demonstrates a reconfigurable multi-plane light converter (MPLC) capable of implementing arbitrary high-fidelity unitary transformations on optical beam arrays, advancing photonic information processing capabilities.

Contribution

It introduces a dynamically reconfigurable MPLC system that can perform any unitary transformation on optical beam superpositions, with experimental validation of high fidelity.

Findings

Achieved an average transformation fidelity of 0.85 ± 0.03.

Demonstrated the ability to perform the full range of unitary transformations on two-beam arrays.

Showcased potential for quantum and classical information processing applications.

Abstract

Spatial transformations of light are ubiquitous in optics, with examples ranging from simple imaging with a lens to quantum and classical information processing in waveguide meshes. Multi-plane light converter (MPLC) systems have emerged as a platform that promises completely general spatial transformations, i.e., a universal unitary. However until now, MPLC systems have demonstrated transformations that are far from general, e.g., converting from a Gaussian to Laguerre-Gauss mode. Here, we demonstrate the promise of an MLPC, the ability to impose an arbitrary unitary transformation that can be reconfigured dynamically. Specifically, we consider transformations on superpositions of parallel free-space beams arranged in an array, which is a common information encoding in photonics. We experimentally test the full gamut of unitary transformations for a system of two parallel beams and make a map of their fidelity. We obtain an average transformation fidelity of $0.85 \pm 0.03$. This high-fidelity suggests MPLCs are a useful tool implementing the unitary transformations that comprise quantum and classical information processing.