Fibre-optical analogue of the event horizon

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Black holes are like space-time rivers: their curved geometry can be viewed as if space where a moving medium rushing towards the singularities of the holes. Horizons are formed where the flow speed of the space-time river exceeds the speed of light such that nothing can escape anymore. We plan to create a similar situation for light in optical fibres where we will be capable of probing the quantum effects of horizons, in particular the generation of pairs of photons from their virtual existence as the quantum vacuum. Such virtual photons are separated at the horizons and hence forced to materialize in a radiative process first predicted by Stephen Hawking. Our proposal, ambitious and adventurous, but we believe feasible, is to use pulses of light as the moving medium, because light can easily catch up with light and light can act upon light in the regime of nonlinear optics. In particular, we will exploit the fact that in modern photonic-crystal fibres light pulses of one polarization interact sufficiently strongly with light of the other polarization, establishing a moving medium, the optical analogue of the space-time river.