Extended Source of Indistinguishable Polarization-entangled Photons over Wide Angles of Emission

TL;DR

This paper presents an experimental scheme to generate polarization-entangled photon pairs with high fidelity over wide emission angles, using a phase-only spatial light modulator to compensate for phase variations across the SPDC cone.

Contribution

The authors introduce a tunable phase compensation method employing a 2D SLM to extend indistinguishability of entangled photons over wide angles, covering the entire SPDC cone.

Findings

Achieved 97% polarization visibility across wide emission angles.

Demonstrated effective phase compensation over the entire SPDC cone.

Extended the spatial and temporal indistinguishability of entangled photons.

Abstract

The generation of high-fidelity polarization-entangled photon pairs, to date, has been demonstrated on specific spatial modes or over relatively narrow apertures. We put forward and demonstrate an experimental scheme to extend the temporal and spatial indistinguishability of polarization-entangled photons over wide emission angles, which can be applied to cover the whole SPDC cone. Over such wide angular extent, while the time-delay map is almost flat which renders the conventional compensation via a birefringent element an appropriate approach, the relative-phase map -- verified as a quadratic function -- necessitates a tunable compensation paradigm. Here, to do so, we employ a phase-only two-dimensional spatial light modulator (2D SLM) loaded by the complementary of the relative phase map to equalize the phase variations for one third of the noncollinear spontaneous parametric down conversion (SPDC) emission. After eliminating the temporal and spatial distinguishability over the 2D SLM area, a 97% polarization visibility is verified for the entangled photon pairs scattered widely across the SPDC cone.