Abstract
Nonlinear one-dimensional metallo-dielectric photonic crystals (NMPhC) has been shown to be highly efficient sources of photon pairs. An NMPhC consisting of 5 Gallium-Nitride (GaN) and 6 silver (Ag) layers has been numerically designed to provide the highest possible photon-pair emission rate. The pump beam has been assumed to be a monochromatic plane wave with central wavelength λ = 400 nm propagating along the z axis of the structure. The generated signal and idler quantum fields have been decomposed into plane waves. Spatial, temporal and spectral properties of the generated photon pairs have been investigated. In the analyzed structure, photons are emitted at the radial angles θ = 47.7° (TE polarized) and θ = 61.1° (TM polarized, see Fig. 1a). They form two concentric rings. The photons emitted at angle θ = 47.7° are spectrally positioned at wavelength λ = 737.8 nm, while the other emission maximum (at radial angle θ = 61.1°) is centred at wavelength λ = 873.6 nm. The emission peaks are narrow both in the spatial and spectral domain as a consequence of strong selective interference of TM polarized plane waves in the structure. This interference originates in high reflectivity of metallic surfaces and their high refractive indices in the red region of visible spectrum. Spectral width of the TM-polarized photon equals Δλ = 4.45 × 10−4 nm (FWHM, see Fig 1b). Such a narrow spectrum implies long temporal correlations of the signal and idler photons, on the time scale of nanoseconds. Correlated areas of the TE- and TM-polarized photons in the transverse plane differ. Radial width of the correlated area of the TM-polarized photon is considerably narrower than that of the TE-polarized photon. Also photon losses inside the structure have been evaluated in the model. The number of noise photons is comparable to that of photon pairs. Therefore, NMPhCs as sources of photon pairs are suitable especially for experimental schemes involving coincidence-count measurements.
© 2015 IEEE
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