  In this work, the concept of optical identification (OI) based on physical
unclonable functions is introduced for the first time, to our knowledge, in
optical communication systems and networks. The OI assigns an optical
fingerprint and the corresponding digital representation to each sub-system of
the network and estimates its reliability in different measures. We highlight
the large potential applications of OI as a physical layer approach for
security, identification, authentication, and monitoring purposes. To identify
most of the sub-systems of a network, we propose to use the Rayleigh
backscattering pattern, which is an optical physical unclonable function and
allows to achieve OI with a simple procedure and without additional devices.
The applications of OI to fiber and path identification in a network and to the
authentication of users in a quantum key distribution system are described.
