Spatial Data Encryption Using Phase Conjugating Lenses

Spatial encryption of a BPSK modulated signal radiated by a dipole-like antenna and transmitted through a phase conjugating lens (PCL) or through a system of PC lenses in free space is theoretically studied using a time domain electromagnetic (EM) formulation. The PC lenses are composed of antenna elements interconnected via phase conjugating circuitry. It is shown that when the PCLs are modulated with a phase encoded pump sequence at the same rate as the BPSK information signal, spatial encryption in the space between the two PCLs is possible, while the signal can only be decoded in well defined spatial regions after passing a second PCL. The effect that phase offset between PCL modulation signals has on viable spatial demodulation regions is also discussed. We show also that the signal detection area can be further confined using a third phase encoded pumped PCL located behind the second lens and modulated by an arbitrary BPSK pump sequence. The considered spatial encryption mechanism can find applications in secure communications.