Single-path Sagnac interferometer with Dove prism for orbital-angular-momentum photon manipulation

Area of Science:

• Quantum Optics
• Quantum Information Processing

Background:

• Orbital angular momentum (OAM) is a key resource for high-dimensional quantum information processing due to its potentially infinite quantum number.
• Dove prisms (DPs) are commonly used for OAM manipulation but alter photon polarization and reduce interferometer sorting fidelity.

Purpose of the Study:

• To analyze the polarization-dependent effects of Dove prisms on OAM light manipulation in single-path Sagnac interferometers (SPSIs).
• To propose and experimentally realize a modified BS Sagnac interferometer with improved fidelity and polarization independence.

Main Methods:

• Analysis of OAM light manipulation in normal beam splitter (BS) and polarizing beam splitter (PBS) SPSIs.
• Experimental implementation of a modified BS Sagnac interferometer incorporating additional half-wave plates.

Main Results:

• The BS Sagnac interferometer shows high sensitivity to input polarization and DP parameters.
• The modified BS Sagnac interferometer achieves theoretically 100% sorting fidelity, independent of input polarization and DP transmission matrix.
• Experimental fidelity of the modified Sagnac interferometer is 5%–10% higher than the normal one.

Conclusions:

• The modified BS Sagnac interferometer offers superior performance and robustness for OAM manipulation.
• The proposed design is stable, easy to implement, and suitable for critical quantum information processing tasks like quantum cryptography.