Generalized angle-orbital-angular-momentum Talbot effect and modulo mode sorting

TL;DR

This paper introduces a generalized angle-OAM Talbot effect linking azimuthal angle and orbital angular momentum domains, enabling advanced mode sorting with high fidelity and potential applications in optical information processing.

Contribution

It reveals the missing connection between azimuthal angle and OAM Talbot effects, demonstrating a unified self-imaging principle and novel modulo mode sorting techniques.

Findings

Experimental demonstration of the generalized angle-OAM Talbot effect.

Development of high-performance, crosstalk-free OAM mode sorters.

Unconventional mapping of neighboring OAM modes to distant positions.

Abstract

The Talbot effect describes periodic revivals of field patterns and is ubiquitous across wave systems. In optics, it is mostly known for its manifestations in space and time, but is also observed in the wavevector and frequency spectra owing to the Fourier duality. Recently, the Talbot self-imaging has been shown separately in the azimuthal angle and orbital angular momentum (OAM) domains. Here, we unveil the missing link between them and demonstrate the generalized angle-OAM Talbot effect. Versatile transformations of petal fields and OAM spectra are experimentally showcased, based on the synergy of angular Talbot phase modulation and light propagation in a ring-core fiber. Moreover, the generalized self-imaging concept leads to new realizations in mode sorting, which separate OAM modes in a modulo manner, theoretically free from any crosstalk within the congruence classes of OAM modes. We design and experimentally construct various mode sorters with excellent performance, and show the unconventional behavior of Talbot-based sorters where neighboring OAM modes can be mapped to positions far apart. Besides its fundamental interest, our work finds applications in OAM-based information processing, and implies that the physical phenomena in time-frequency and angle-OAM domains are broadly connected as well as their processing techniques may be borrowed interchangeably.