Polarization Purity and Dispersion Characteristics of Nested Antiresonant Nodeless Hollow-Core Optical Fiber at Near- and Short-wave-IR Wavelengths for Quantum Communications

TL;DR

This study demonstrates that nested antiresonant nodeless hollow-core fibers (NANF) exhibit exceptional polarization purity and low dispersion at near- and short-wave IR wavelengths, making them promising for quantum communication and sensing applications.

Contribution

The paper provides the first detailed analysis of polarization and dispersion characteristics of NANF at 2 μm, including pulsed regime insights relevant for quantum information protocols.

Findings

Achieved polarization extinction ratios between -30 dB and -70 dB across 1520-1620 nm.

Peak polarization extinction ratio of -60 dB at 2 μm wavelength.

Demonstrated broadband propagation of quantum states with low quantum bit error rates.

Abstract

Advancements in quantum communication and sensing require improved optical transmission that ensures excellent state purity and reduced losses. While free-space optical communication is often preferred, its use becomes challenging over long distances due to beam divergence, atmospheric absorption, scattering, and turbulence, among other factors. In the case of polarization encoding, traditional silica-core optical fibers, though commonly used, struggle with maintaining state purity due to stress-induced birefringence. Hollow core fibers, and in particular nested antiresonant nodeless fibers (NANF), have recently been shown to possess unparalleled polarization purity with minimal birefringence in the telecom wavelength range using continuous-wave (CW) laser light. Here, we investigate a 1-km NANF designed for wavelengths up to the 2-$\mu$m waveband. Our results show a polarization extinction ratio between ~-30 dB and ~-70 dB across the 1520 to 1620 nm range in CW operation, peaking at ~-60 dB at the 2-$\mu$m design wavelength. Our study also includes the pulsed regime, providing insights beyond previous CW studies, e.g., on the propagation of broadband quantum states of light in NANF at 2 $\mu$m, and corresponding extinction-ratio-limited quantum bit error rates (QBER) for prepare-measure and entanglement-based quantum key distribution (QKD) protocols. Our findings highlight the potential of these fibers in emerging applications such as QKD, pointing towards a new standard in optical quantum technologies.