Optical Source

An integrated optical device and method for generating photons by manipulating path (quantum) entanglement is provided. An integrated optical splitter 10 splits pump light 60 between two interferometer arms 6, 8 wherein each arm comprises a substantially identical photon pair source 12 configured to be able to convert at least one pump light photon into a signal and idler photon pair. An integrated optical combiner device 14 in optical communication with a first 18 and a second 20 optical output path interferes light from the first and second arms and outputs the signal and idler photons by bunching the signal and idler photons together in one of the optical output paths, or anti-bunching the signal photon in one output path and the corresponding idler photon in the other optical output path. The device may be used in optical communication such as quantum cryptography.