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arXiv:1407.3207

Correlated Photon-Pair Generation in a Highly Nonlinear Fiber Using Spontaneous FWM

Álvaro J. Almeida, L. M. P. P. Martins, Nuno A. Silva, Nelson Jesus Muga, Armando N. Pinto

Published Jul 11, 2014• 1 citation
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Abstract

We generate 1550 nm correlated photon pairs through the spontaneous four-wave mixing (SpFWM) process in a highly nonlinear fiber (HNLF). The pair source quality generation is evaluated by the coincidence-to-accidental ratio (CAR) parameter. It is verified that the spontaneous Raman scattering (SpRS) photons generated inside the fiber contribute to the degradation of the source. Nevertheless, a CAR value of 2.77 is found for a pump power at the input of the fiber of 1.1 mW.

DOI
10.48550/arxiv.1407.3207

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We generate 1550 nm correlated photon pairs through the spontaneous four-wave mixing (SpFWM) process in a highly nonlinear fiber (HNLF). The pair source quality generation is evaluated by the coincidence-to-accidental ratio (CAR) parameter. It is verified that the spontaneous Raman scattering (SpRS) photons generated inside the fiber contribute to the degradation of the source. Nevertheless, a CAR value of 2.77 is found for a pump power at the input of the fiber of 1.1 mW.
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We report on a spontaneous four-wave mixing (SFWM) based broadband correlated photon pair generation using a dispersion flattened highly-nonlinear fiber (DF-HNLF). The DF-HNLF is pumped by a stable mode-locked laser (MLL) which generates pump pulses of 250 ps FWHM at a repetition rate of 94.509 MHz. The joint spectral intensity (JSI) data indicates photon pair generation across entire S, C, and L bands. The intrinsic photon pair generation rate, after accounting for spontaneous Raman scattering (SpRS), system loss, and detector dark counts, is ≈ 100kHz although due to detection gating limit we measured the rate to be 1 kHz at peak pump power of 70 mW. The use of an arbitrary waveform generator for establishing pump MLL and gating of the single-photon detectors (SPDs) allows for precise synchronization of generation and detection of photon pairs.
Single photon sources are a key element for quantum computing, quantum key distribution (QKD) and quantum communications. In particular, producing single photons at telecommunications wavelengths is valuable for QKD protocols and would enable realizing the quantum internet. The preferred method for their generation has long been spontaneous down conversion in bulk crystals, which suffers from connection loss to fiber networks. In-fiber spontaneous four-wave mixing provides a viable alternative as a photon pair source due to being compatible with existing fiber networks. We present an all-fiber photon pair source based on degenerate four-wave mixing in a 400 m Highly-Nonlinear fiber, with signal and idler wavelengths generated at 1552.5 nm and 1557 nm respectively. The source consists of CW pump laser operating at 1554.75 nm, which is slightly detuned from the zero group velocity dispersion wavelength into the normal dispersion regime. After pair generation in the highly-nonlinear fiber, three arrayed waveguide gratings are employed to spatially separate signal and idler, and provides a 120 dB pump power reduction. Firstly the source is modelled and experimentally characterized in the well known classical regime of stimulated four-wave mixing. The effect of fiber cooling on spontaneous Raman scattering is modelled and characterized, and a 30% reduction in spontaneous emission is found when cooling the fiber to -77°C. In the low power regime the coincidence to accidental count ratio is simulated and measured. An increase in the coincidence to accidental count ratio is observed when cooling the fiber.
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We experimentally demonstrate, for the first time to our knowledge, the generation of correlated photon pairs in a liquid-core photonic crystal fiber. Moreover, we show that, thanks to the specific Raman properties of liquids, the Raman noise (which is the main limitation of the performance of silica-core fiber-based correlated photon pair sources) is highly reduced. With a demonstrated coincident-to-accidental ratio equal to 63 and a pair generation efficiency of about 10 −4 per pump pulse, this work contributes to the development of high-quality correlated photon pair sources for quantum communications.