# Total angular momentum sorting in the telecom infrared with silicon Pancharatnam-Berry transformation optics

## TL;DR

This paper introduces a silicon-based Pancharatnam-Berry optical element that efficiently sorts orbital angular momentum and polarization states of light at 1310 nm, advancing integrated structured light processing for telecommunications.

## Contribution

It presents the design, fabrication, and testing of a hybrid metasurface device combining geometric and dynamic phase control for simultaneous OAM and polarization sorting.

## Key findings

- Successfully demonstrated OAM and polarization sorting at 1310 nm
- High-resolution phase pattern achieved with subwavelength gratings
- Device integrates geometric and dynamic phase manipulation

## Abstract

Parallel sorting of orbital angular momentum (OAM) and polarization has recently acquired paramount importance and interest in a wide range of fields ranging from telecommunications to high-dimensional quantum cryptography. Due to their inherently polarization-sensitive optical response, optical elements acting on the geometric phase prove to be useful for processing structured light beams with orthogonal polarization states by means of a single optical platform. In this work, we present the design, fabrication and test of a Pancharatnam-Berry optical element in silicon implementing a log-pol optical transformation at 1310 nm for the realization of an OAM sorter based on the conformal mapping between angular and linear momentum states. The metasurface is realized in the form of continuously-variant subwavelength gratings, providing high-resolution in the definition of the phase pattern. A hybrid device is fabricated assembling the metasurface for the geometric phase control with multi-level diffractive optics for the polarization-independent manipulation of the dynamic phase. The optical characterization confirms the capability to sort orbital angular momentum and circular polarization at the same time.

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Source: https://tomesphere.com/paper/1902.01325