Quantum cryptography system for a secure transmission of random keys using a polarization setting method

摘要

A quantum cryptography system using electrooptical liquid crystal modulators which change the polarization and which are designed as electrically rotatable retardation plates whose two birefringent axes are rotated by the applied electrical field around an angle theta which depends on the strength of this field. A lambda/2 retardation plate rotates the elliptically polarized light striking the plate around an angle 2theta at speeds in the microsecond range. The quantum cryptography system can be used for interception-proof data transmission over transmission links that are accessible to the public.