OPTICAL PHYSICALLY UNCLONABLE FUNCTION DEVICE

A physically unclonable function (PUF) device comprises a plurality of optical fibres, at least some of which are arranged such that they are optically coupled. A media surround at least a portion of the optical fibres and at least one light source is configured to transmit light through one or more of the optical fibres. There is provided at least one light sensor configured to receive the transmitted light from one or more of the optical fibres and provide an output. Circuitry applies a challenge signal to at least one of the fibres using at least one light source and receives the output from the at least one light sensor, using the output to generate an identifying response to the challenge signal. The fibres are arranged such that the identifying response is unique to the device.