CSIC has developed a device that determine and corrects the inclination of the polarization received from an emitter towards a receiver between which a quantum key distribution is taking place. Said device allows the reorientation of the received polarization to a predetermined state of optimal alignment between the axes of the emitter and the receiver without prior information from the receiver.
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An answer to the current challenge in quantum key distribution
The device allows continuous automatic polarization tracking for a QKD system between emitter and receiver where at least one of them is mobile Quantum Key Distribution (QKD) is a communication protocol that provides a secure way to transmit an encryption key over an insecure channel between two users. However, when it comes to links between transmitter and receiver in free space in which at least one of them is mobile, the challenge is to correct the relative mismatch that can occur between the two, to compensate for the angular difference between the coordinates axes of both reference systems and thus keep them aligned throughout the QKD transmission.
CSIC scientists have managed to respond to this challenge by developing an active device that allows maintaining the alignment between emitter and receiver in terms of polarization so that the relative orientation between both platforms always coincides throughout the entire QKD transmission.
The device consists of a dichroic mirror configured to separate the reference signal from the sending signal, a detector block configured to analyze the polarization of the reference signal and an electro-mechanical module that rotates the polarization of the incident beam, both from the reference signal as of the sent signal.
Main innovations and advantages
· Unlike other technologies based on two alternating polarization states,the device developed does not require that a polarization modulatorbe mounted on the emitter
· Unlike other technologies based on two alternating polarization states,the device developed does not require the polarization modulator tobe mounted on the emitter, thus minimizing the complexity of theplatform while not affecting its weight. This is especially relevant whenit comes to a mobile platform (satellite, drone, etc.)
· Its main application is as an automatic polarization tracking device for aquantum key distribution system between an emitter and a receiver inwhich at least one of them is mobile.