Patent ID: 7684701

Claim:
A photon emitter comprising: a photon generator configured to generate randomly polarized photons separable into a first polarisation state and a second polarisation state, the first polarisation state being orthogonal to the second polarisation state; and time delay means receiving said randomly polarized photons and being configured to delay photons having the second polarisation state with respect to those having the first polarisation state such that photons which enter the time delay means with the first polarisation exit the time delay means at a different time to photons which enter the time delay means with the second polarization; encoding means, wherein photons which have passed through the time delay means are passed into an encoding means, wherein said encoding means are configured to encode the phase of a photon and comprise a first interferometer, said first interferometer comprising an entrance coupler connected to a long arm and a short arm, said long arm and short arm being joined at their other ends by an exit coupler, one of said arms having first phase variation means which allows the phase of a photon passing through that arm to be set to one of at least two values, wherein the photons are received by a receiver, and the receiver comprises a second interferometer, the second interferometer comprising an entrance coupler connected to a long arm and a short arm, said long arm and short arm being joined at their other ends by an exit coupler, one of said arms having second phase variation means which allows the phase of a photon passing through that arm to be set to one of at least two values; and further comprising directing means configured to ensure that photons which have passed through the short arm of the first interferometer are directed down the long arm of the second interferometer and photons which have passed through the long arm of the first interferometer pass through the short arm of the second interferometer, wherein the directing means comprises first polarising means configured to allow photons which have traveled through different arms of the first interferometer different polarisations and second polarising means which distinguish between the photons having different polarisations and direct them down the appropriate arm of the second interferometer.