Figure 7
From: Orthogonal quasi-phase-matched superlattice for generation of hyperentangled photons
Comparison of the temporal characteristics of biphotons emitted by three LiNbO3 structures—cascaded (top), double-nonlinearity (middle), and superlattice (bottom)—of 5-mm overall length, excited by a 532-nm, 133-fs pulsed pump focused to a 50-μm waist. The emitted light is collected through two Gaussian apertures placed in the focal planes of two identical 2-f systems of 15-cm focal lengths and with \({\sigma }_{{q}_{1}}={\sigma }_{{q}_{2}}=60\) mm−1, corresponding to apertures widths of 1.2 mm (16-mrad collection angle) and 2.2 mm (29-mrad collection angle) for the signal and idler, respectively. Due to the phase-matching condition, the signal and idler bandwidth set by the apertures is ~750 nm. (a) The biphoton probability distribution P H(t 1, t 2) for the HH component. (b) Same as (a) but for the VV component. (c) Projections of P H(t 1, t 2) and P V(t 1, t 2) along the diagonal and off-diagonal directions as functions of the average arrival time (t 1 + t 2)/2 and the relative delay (t 1 − t 2) between the signal and idler, normalized to their respective maximum values. The relative time delay is due to first-order dispersion, while dispersion of higher order contribute to the biphoton wavepacket distortion. (d) Normalized coincidence rate C(τ), after HOM interferometer, expected for a monochromatic (gray line) and a 133-fs pulsed (red line) pump beam. Here, the apertures are pinholes placed in the central emission directions. The sinusoidal oscillation within the dip envelope is at frequency (ω 1 − ω 2).
