Visibility control of phase fiber optic sensors in passive optical networks

Abstract

Integrating sensors into existing high-speed data networks delivers an intelligent hybrid network that is able to communicate and deliver a plethora of information about its surroundings. The use of existing fiber optic passive optical networks (PONs) is economically and technically advantageous in the future. Existing networks are often conveniently located, and the measured quantities maybe diagnostics of the network itself but, for example, monitoring of traffic, critical infrastructures, security, construction work, and others. These sensors can have unique features such as long-range interrogation, immunity to electromagnetic interference (EMI), high sensitivity, or, for example, distributed measurements, and their spatial resolution. The techniques of embedding a phase sensor into a PON are discussed in the article, and how the data and sensor part of the network will be affected and the balancing between the two. The measured quantity is the vibration acting on the interferometric fiber optic sensor (IFOS) and the visibility of its phase response (interference). In the case of a data network, it is the stability of the data transmission. Five different methods of sensor insertion have been investigated, simulated, and experimentally tested, showing functional and non-functional ways of integration. For the security of the network data part, the best configurations are those that influence visibility using asymmetric or WDM couplers. Changes in the difference in arm lengths are also a potentially promising method, but the coherent length of the source affects data security. These findings show how sensors can be operated on existing networks but also in what ways data services will be disrupted or completely disrupted.