Optimal coupling of entangled photons into single-mode optical fibers
ABSTRACT We present a consistent multimode theory that describes the coupling of single photons generated by collinear Type-I parametric downconversion into single-mode optical fibers. We have calculated an analytic expression for the fiber diameter which maximizes the pair photon count rate. For a given focal length and wavelength, a lower limit of the fiber diameter for satisfactory coupling is obtained.
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ABSTRACT: We develop a theoretical analysis of four-wave mixing used to generate photon pairs useful for quantum information processing. The analysis applies to a single mode microstructured fibre pumped by an ultra-short coherent pulse in the normal dispersion region. Given the values of the optical propagation constant inside the fibre, we can estimate the created number of photon pairs per pulse, their central wavelength and their respective bandwidth. We use the experimental results from a picosecond source of correlated photon pairs using a micro-structured fibre to validate the model. The fibre is pumped in the normal dispersion regime at 708nm and phase matching is satisfied for widely spaced parametric wavelengths of 586nm and 894nm. We measure the number of photons per pulse using a loss-independent coincidence scheme and compare the results with the theoretical expectation. We show a good agreement between the theoretical expectations and the experimental results for various fibre lengths and pump powers. Comment: 23 pages, 9 figuresNew Journal of Physics 01/2006; DOI:10.1088/1367-2630/8/5/067 · 3.67 Impact Factor
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ABSTRACT: We address the problem of efficient modeling of photon pairs generated in spontaneous parametric down-conversion and coupled into single-mode fibers. It is shown that when the range of relevant transverse wave vectors is restricted by the pump and fiber modes, the computational complexity can be reduced substantially with the help of the paraxial approximation, while retaining the full spectral characteristics of the source. This approach can serve as a basis for efficient numerical calculations or can be combined with analytically tractable approximations of the phase-matching function. We introduce here a cosine-Gaussian approximation of the phase-matching function that works for a broader range of parameters than the Gaussian model used previously. The developed modeling tools are used to evaluate characteristics of the photon pair sources such as the pair production rate and the spectral purity quantifying frequency correlations. Strategies to generate spectrally uncorrelated photons, necessary in multiphoton interference experiments, are analyzed with respect to trade-offs between parameters of the source.Physical Review A 07/2009; 80(1):013811-013811. DOI:10.1103/PHYSREVA.80.013811 · 2.99 Impact Factor
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ABSTRACT: We report a series of experimental studies on single-mode fiber coupling of entangled photon pairs in type-II spontaneous parametric down-conversion. We experimentally compare the single-mode coupling efficiencies for three different phase matching regimes of bulk type-II spontaneous parametric down-conversion: collinear, noncollinear, and beamlike. Our experiment shows that the beamlike scheme provides the best single-mode coupling efficiency.Physical Review A 11/2008; 78:053825. DOI:10.1103/PhysRevA.78.053825 · 2.99 Impact Factor