# Dove prism in single-path Sagnac interferometer for orbital-angular-momentum photon states

## TL;DR

This paper investigates the polarization effects of Dove prisms in Sagnac interferometers for orbital angular momentum photons and proposes a modified interferometer design with polarization-independent, high-fidelity sorting capabilities.

## Contribution

It analyzes the polarization-dependent effects of Dove prisms and introduces a modified single-path beam splitter Sagnac interferometer with polarization-independent, near-perfect sorting fidelity.

## Key findings

- Dove prism effects depend on photon polarization.
- Modified interferometer achieves near 100% sorting fidelity.
- Design is stable and suitable for quantum information applications.

## Abstract

The degree of freedom of orbital angular momentum (OAM) is an important resource in high-dimensional quantum information processing, as the quantum number of OAM can be infinite. The Dove prism (DP) is a most common tool to manipulate the OAM light, such as in interferometers. However, the Dove prism does not preserve the polarization of the photon states and decreases the sorting fidelity of the interferometer. In this work, we analyze the polarization-dependent effect of the DP on single-path Sagnac interferometers. The results are instructive to quantum information processing with OAM light. We also proposed a modified single-path beam splitter Sagnac interferometer (BSSI), of which the sorting fidelity is independent on input polarization and can be 100\% in principle. The single-path BSSI is stable for free running. These merits are crucial in quantum information processing, such as quantum cryptography.