Ghost polarization communication

Abstract

Ghost metrology is a measurement modality exploiting correlation of photons. Recently, we have demonstrated ghost imaging and ghost spectroscopy by exploiting spatial and spectral photon correlations of amplified spontaneous emission light emitted by optoelectronic superluminescent diodes and erbium-doped fiber amplifiers. Here, we now exploit polarization correlations of so-called unpolarized light. We conceive and realize a novel communication scheme, - Ghost Polarization Communication (GPC) -, between two parties, Alice and Bob, which is based on the ultra-fast correlations of the polarization state of unpolarized classical light emitted by an erbium-doped fiber amplifier (EDFA) and which provides a measure of security directly on the physical layer. The light emitted by the EDFA is divided in to a reference arm which remains solely on Bob’s side and an object arm which is sent to Alice, who encodes a message onto the unpolarized light via a half-wave plate and sends it back to Bob. By determining the second-order correlation coefficient g(2) on femtosecond timescale and using an agreed encoding table or keypad he uniquely extracts the message which has been camouflaged within the infinite number of polarization states on the Poincaré sphere. The investigated polarization correlation results are modelled within a theoretical approach based on the Stokes vectors dynamics and a Glauber protocol for g(2) and the experimental results are in excellent agreement with this theory. We conclude with a proof-of-principle demonstration of a message transmitted by GPC and discuss real-world implementation and security issues of the proof-of-principle demonstration.