A polarisation encryption/decryption module comprising at least two array based modulating devices, preferably spatial light modulators (SLMs), at least one array based intensity detector, and at least one source of electromagnetic radiation. A local region of information displayed on a first of the modulating devices has corresponding local regions on each of the other modulating devices and on each of the detectors. Preferably uses XOR operations. The module is compact in size and capable of performing encryption as well as decryption. Provides fast encryption/decryption because the key may be changed rapidly. May be used for real time encryption/decryption of motion pictures. Further, a method of polarisation encrypting and decrypting information. The encryption/decryption is performed optically while the communication is performed electronically.