Non-paraxial design and fabrication of a compact OAM sorter in the telecom infrared

TL;DR

This paper presents a novel, compact, and non-paraxial optical OAM sorter designed for telecom infrared, improving alignment, miniaturization, and performance for mode-division multiplexing in optical communications.

Contribution

It introduces a non-paraxial transformation optics design and a miniaturized fabrication process for efficient OAM beam demultiplexing at telecom wavelengths.

Findings

Successfully fabricated a 256-level phase-only diffractive optic

Achieved effective demultiplexing of OAM beams at 1310 nm

Enhanced compactness and alignment simplicity of the OAM sorter

Abstract

A novel optical device is designed and fabricated in order to overcome the limits of the traditional sorter based on log-pol optical transformation for the demultiplexing of optical beams carrying orbital angular momentum (OAM). The proposed configuration simplifies the alignment procedure and significantly improves the compactness and miniaturization level of the optical architecture. Since the device requires to operate beyond the paraxial approximation, a rigorous formulation of transformation optics in the non-paraxial regime has been developed and applied. The sample has been fabricated as 256-level phase-only diffractive optics with high-resolution electron-beam lithography, and tested for the demultiplexing of OAM beams at the telecom wavelength of 1310 nm. The designed sorter can find promising applications in next-generation optical platforms for mode-division multiplexing based on OAM modes both for free-space and multi-mode fiber transmission.