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Optics Letters

Polarization entanglement generation at 15 μm based on walk-off effect due to fiber birefringence

Qiang Zhou, Wei Zhang, Pengxiang Wang, Yidong Huang, Jiangde Peng

Published May 9, 2012• 17 citations
Publisher

Abstract

In this Letter, a linear scheme to generate polarization entanglement at 1.5 μm based on commercial polarization maintained dispersion shifted fiber (PM-DSF) is proposed. The birefringent walk-off effect of the pulsed pump light in the PM-DSF provides an effective way to suppress the vector scattering processes of spontaneous four-wave mixing. A 90 deg offset of fiber polarization axes is introduced at the midpoint of the fiber to realize the quantum superposition of the two correlated photon states generated by the two scalar processes on different fiber polarization axes, leading to polarization entanglement generation. Experiments of the indistinguishable property on single-side and two-photon interference in two nonorthogonal polarization bases are demonstrated. A two-photon interference fringe visibility of 89±3% is achieved without subtracting the background counts, demonstrating its great potential in developing highly a efficient and stable fiber based polarization-entangled quantum light source at the optical communication band.

DOI
10.1364/ol.37.001679

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Polarization entanglement generation at 1.5 um based on walk-off effect due to fiber birefringence

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In this Letter, a linear scheme to generate polarization entanglement at 1.5 um based on commercial polarization maintained dispersion shifted fiber (PM-DSF) is proposed. The birefringent walk-off effect of the pulsed pump light in the PM-DSF provides an effective way to suppress the vector scattering processes of spontaneous four wave mixing. A 90 degree offset of fiber polarization axes is introduced at the midpoint of the fiber to realize the quantum superposition of the two correlated photon states generated by the two scalar processes on different fiber polarization axes, leading to polarization entanglement generation. Experiments of the indistinguishable property on single side and two-photon interference in two non-orthogonal polarization bases are demonstrated. A two photon interference fringe visibility of 89\pm3% is achieved without subtracting the background counts, demonstrating its great potential in developing highly efficient and stable fiber based polarization-entangled quantum light source at optical communication band.

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Spontaneous four-wave mixing (SFWM) in optical fibers is an important way to generate correlated/entangled photon pairs. When the pulsed pump light passes through the optical fiber, two kinds of SFWM will take place simultaneously. One is scalar scattering processes, in which two annihilated pump photons and generated photon pair are all polarized along the same fiber polarization axis. The other is vector scattering processes, in which two annihilated pump photons are polarized along different fiber polarization axes, either to the two photons of the generated pair. If the fiber has large group birefringence, the intensity of vector scattering processes will be suppressed at the phase matching frequencies of the scalar scattering processes. On the other hand, the walk-off effect of the pump pulse components polarized along the two fiber polarization axes also suppresses the vector scattering processes. Hence, by proper pump polarization and signal/idle frequency selection, photon pairs can be generated only by the two independent scalar scattering processes in optical fibers with birefringence, which provide a simple way to realize polarization entangled photon pair generation. In this paper, related experiments based on the high nonlinearity microstructure fiber (HN-MSF) with group birefringence and polarization maintained dispersion shifted fiber (PM-DSF) are introduced, showing their potential on developing practical quantum light sources.

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Optics Letters•Jul 27, 2013•21 citations
In this Letter, a linear scheme to generate polarization entanglement at 1.5 μm based on commercial polarization maintained dispersion shifted fiber (PM-DSF) is proposed. The birefringent walk-off effect of the pulsed pump light in the PM-DSF provides an effective way to suppress the vector scattering processes of spontaneous four-wave mixing. A 90 deg offset of fiber polarization axes is introduced at the midpoint of the fiber to realize the quantum superposition of the two correlated photon states generated by the two scalar processes on different fiber polarization axes, leading to polarization entanglement generation. Experiments of the indistinguishable property on single-side and two-photon interference in two nonorthogonal polarization bases are demonstrated. A two-photon interference fringe visibility of 89±3% is achieved without subtracting the background counts, demonstrating its great potential in developing highly a efficient and stable fiber based polarization-entangled quantum light source at the optical communication band.
In this Letter, a linear scheme to generate polarization entanglement at 1.5 um based on commercial polarization maintained dispersion shifted fiber (PM-DSF) is proposed. The birefringent walk-off effect of the pulsed pump light in the PM-DSF provides an effective way to suppress the vector scattering processes of spontaneous four wave mixing. A 90 degree offset of fiber polarization axes is introduced at the midpoint of the fiber to realize the quantum superposition of the two correlated photon states generated by the two scalar processes on different fiber polarization axes, leading to polarization entanglement generation. Experiments of the indistinguishable property on single side and two-photon interference in two non-orthogonal polarization bases are demonstrated. A two photon interference fringe visibility of 89\pm3% is achieved without subtracting the background counts, demonstrating its great potential in developing highly efficient and stable fiber based polarization-entangled quantum light source at optical communication band.
Spontaneous four-wave mixing (SFWM) in optical fibers is an important way to generate correlated/entangled photon pairs. When the pulsed pump light passes through the optical fiber, two kinds of SFWM will take place simultaneously. One is scalar scattering processes, in which two annihilated pump photons and generated photon pair are all polarized along the same fiber polarization axis. The other is vector scattering processes, in which two annihilated pump photons are polarized along different fiber polarization axes, either to the two photons of the generated pair. If the fiber has large group birefringence, the intensity of vector scattering processes will be suppressed at the phase matching frequencies of the scalar scattering processes. On the other hand, the walk-off effect of the pump pulse components polarized along the two fiber polarization axes also suppresses the vector scattering processes. Hence, by proper pump polarization and signal/idle frequency selection, photon pairs can be generated only by the two independent scalar scattering processes in optical fibers with birefringence, which provide a simple way to realize polarization entangled photon pair generation. In this paper, related experiments based on the high nonlinearity microstructure fiber (HN-MSF) with group birefringence and polarization maintained dispersion shifted fiber (PM-DSF) are introduced, showing their potential on developing practical quantum light sources.
In this Letter, the generation of a 1.5 μm discrete frequency-entangled two-photon state is realized based on a piece of commercial polarization-maintaining fiber (PMF). It is connected with a polarization beam splitter to realize a modified Sagnac fiber loop (MSFL). Correlated two-photon states are generated through a spontaneous four-wave-mixing process along the two propagation directions of the MSFL, and output from the MSFL with orthogonal polarizations. Their quantum interference is realized through a 45° polarization collimation between polarization axes of PMFs inside and outside the MSFL, while their phase difference is controlled by the polarization state of the pump light. The frequency-entangled property of the two-photon state is demonstrated by a spatial quantum beating experiment with a fringe visibility of 98.2±1.3%, without subtracting the accidental coincidence counts. The proposed scheme generates a 1.5 μm discrete frequency-entangled two-photon state in a polarization-maintaining way, which is desired in practical quantum light sources.
We demonstrate an optical-fiber-based source of polarization-entangled photon pairs with improved quality and efficiency, which has been integrated with off-the-shelf telecom components and is, therefore, well suited for quantum communication applications in the 1550-nm telecom band. Polarization entanglement is produced by simultaneously pumping a loop of standard dispersion-shifted fiber with two orthogonally polarized pump pulses, one propagating in the clockwise and the other in the counterclockwise direction. We characterize this source by investigating two-photon interference between the generated signal-idler photon pairs under various conditions. The experimental parameters are carefully optimized to maximize the generated photon-pair correlation and to minimize contamination of the entangled photon pairs from extraneously scattered background photons that are produced by the pump pulses for two reasons: (i) spontaneous Raman scattering causes uncorrelated photons to be emitted in the signal and idler bands and (ii) broadening of the pump-pulse spectrum due to self-phase modulation causes pump photons to leak into the signal and idler bands. We obtain two-photon interference with visibility >90>90%>90 without subtracting counts caused by the background photons (only dark counts of the detectors are subtracted), when the mean photon number in the signal (idler) channel is about 0.02/pulse, while no interference is observed in direct detection of either the signal or idler photons.
In this Letter, the 1.5 μm polarization entanglement generation is realized in a silicon wire waveguide utilizing its birefringence. In this scheme, two orthogonal polarized correlated states are generated by scalar processes of spontaneous four-wave mixing (SFWM) in the quasi-transverse electrical and quasi-transverse magnetic modes, respectively. Meanwhile, the vector processes of SFWM are suppressed by the group birefringence in the waveguide. The maximum polarization entangled state is generated by optimizing the pump polarization, which is demonstrated by the experiments of two-photon interference and polarization indistinguishability at one side. The fringe visibilities of two-photon interferences are 96.8±4.7% and 86.0±3.7% under two nonorthogonal polarization detection settings, respectively. This scheme provides a simple way to realize silicon integrated sources for 1.5 μm polarization entanglement generation.