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arXiv:1907.05477 · Optics Express

Spectrally pure single photons at telecommunications wavelengths using commercial birefringent optical fiber

Jasleen Lugani, Robert J. A. Francis-Jones, Joelle Boutari, Ian A. Walmsley

Published Jan 25, 2020• 36 citations
arXivHTMLPDF

Abstract

We report a bright and tunable source of spectrally pure heralded single photons in the telecom O-Band, based on cross-polarized four wave mixing in a commercial birefringent optical fiber. The source can achieve a purity of 85%, heralding efficiency of 30% and a coincidence-to-accidentals ratio of 108. Furthermore, through the measurements of joint spectral intensities, we find that the fiber is homogeneous over at least 45 centimeters and thus can potentially realize 4 sources that can produce identical quantum states of light. This paves the way for a cost-effective fiber-optic approach to implement multi-photon quantum optics experiments.

DOI
10.1364/oe.383704

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We report a bright and tunable source of spectrally pure heralded single photons in the telecom O-Band, based on cross-polarized four wave mixing in a commercial birefringent optical fiber. The source can achieve a purity of 85%, heralding efficiency of 30% and a coincidence-to-accidentals ratio of 108. Furthermore, through the measurements of joint spectral intensities, we find that the fiber is homogeneous over at least 45 centimeters and thus can potentially realize 4 sources that can produce identical quantum states of light. This paves the way for a cost-effective fiber-optic approach to implement multi-photon quantum optics experiments.
High-quality quantum sources are of paramount importance for the implementation of quantum technologies. We present here a heralded single-photon source based on commercial-grade polarization-maintaining optical fiber. The heralded photons exhibit a purity of at least 0.84 and an unprecedented heralding efficiency into a single-mode fiber of 8585%85. The birefringent phase-matching condition of the underlying four-wave mixing process can be controlled mechanically to optimize the wavelength tuning needed for interfacing multiple sources, as is required for large-scale entanglement generation.
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We demonstrate theoretically the direct (filter-free) generation of spectrally uncorrelated photon pairs, and consequently high-purity heralded single photons at telecommunication wavelengths, in SOI (silicon-on-insulator) nanowaveguides via spontaneous four-wave mixing (SFWM). The inherent strong waveguide dispersion in such high-index contrast structures is employed for discrete-band phase-matching in order to suppress the pair spectral correlations, and to produce photons in the fundamental spatial mode for easy in-out coupling to single-mode optical fibers. Additionally, by optimizing the source parameters like waveguide length, dispersion and pump bandwidth, the group-velocity of generated photons is also engineered to further eliminate spectral correlations. Extensive numerical mode simulations for various waveguide widths are used to design intrinsically pure photon sources via joint spectral amplitude (JSA) engineering. Purity$>9595% is shown to be achievable in a silica-clad SOI waveguide with a cross-section 220 × 600 nm95^{2}fortypicalvaluesoflengthandpumpbandwidth.Thewavelengthoftheseheraldedsinglephotonscanbetunedintherangeof1266–1363nm(for typical values of length and pump bandwidth. The wavelength of these heralded single photons can be tuned in the range of 1266–1363 nm (fortypicalvaluesoflengthandpumpbandwidth.Thewavelengthoftheseheraldedsinglephotonscanbetunedintherangeof1266–1363nm(\sim$O-band) by varying the pump wavelength. Considering the high accuracy provided by silicon nanofabrication techniques, the feasibility of generating single photons across the wavelength range 1333–1425 nm (E-band) and 1437–1510 nm (S-band) for slightly different waveguide widths (625 nm & 650 nm) is also demonstrated. These filter-free integrated photon sources could be important for large-scale linear optical quantum computation (LOQC) and long-distance fiber-optic quantum key distribution (QKD) networks.
Single photons are at the heart of optical quantum technologies such as quantum cryptography, quantum computing and quantum metrology. In this paper we report on the creation of photon pairs via four-wave-mixing (FWM) in birefringent photonic crystal fibres (PCF). It has recently been suggested that for thoroughly engineering the phase matching condition of a birefringent PCF, photon pairs can by created in an intrinsically pure state and narrow band. This can be achieved for cross-polarized phase matching, where two pump photons in the slow axis are converted into a pair of photons, polarized in the orthogonal fast axis. The aim is to produce such intrinsically pure and narrow-band photons and hence to achieve high non-classical interference visibility without any requirement for spectral filtering. In order to experimentally test the purity of our heralded single photons we performed a Hong-Ou-Mandel experiment using heralded signal photons generated in separate PCF sources.
An actual task of quantum communications over long distances is the creation of a bright source of photon pairs operating at standard wavelengths of fiber optic communication lines. In this work, we experimentally investigated the spectral and correlation characteristics of photon pairs generated on the phenomenon of spontaneous four-wave mixing in a highly nonlinear photonic-crystal fiber with a wavelength of one of the photons near 1.5 μm. The demonstrated source can be used as an efficient single photon generator at a telecommunications wavelength with prediction and tuning over a wide spectral range.