A shunted ring fiber optic network topology providing fault detection, isolation and circumvention

This paper describes an electro-optic and all optical implementation of a novel “shunted ring” network topology which uses optical waveguide shunts to bypass faults in ring networks. This technique eliminates the need for costly bypass switches and their related deficiencies. “One-by-N” tree couplers are used as the fanout mechanism from an LED or laser to send optical signals to a primary fiber and “N” shunt fibers. These shunt fiber waveguides can be “switched” into the active network when the optical signal in the primary fiber drops below a prescribed level. This permits rapid reconfiguration around a failed node or primary fiber path and minimizes or eliminates the loss of data. In a near term implementation of the concept, the signals from the input primary and shunt fibers are converted to electrical form with standard PIN photodiodes and the signal level is analyzed. If the signal falls below the preset threshold, the output from the shunt fiber(s) is electronically switched into the network node to restore robust network operation. The power budget to determine the number of successive nodes which can be bypassed is identically that of a “1×N” tree network permitting any number of bypasses within the link margin