Fail-Safe Nodes for Lightguide Digital Networks

The use of regenerators at the nodes of a lightwave network introduces a reliability problem when the power at one node fails. Optical passive couplers solve this problem, but the number of passive couplers in a network is limited by the maximum insertion loss that can be tolerated between a transmitter and the receiver farthest away from it.1 This paper describes a new arrangement for a lightguide digital network built with fail-safe nodes and with the characteristics that the number of stations is independent of the coupler insertion loss, and that the network keeps functioning when the power at one or more nodes fails. A fail-safe node consists of a lightguide receiver and a lightguide transmitter electrically connected by a regenerator and optically connected by a directional coupler. Figure 1 shows a configuration for a fail-safe node consisting of a lightwave receiver and transmitter pair connected by a regenerator and a directional coupler that provides optical continuity when the power at the node fails. The feasibility of the network was tested using lightwave transmitters