An all‐fiber ring laser geometry in the form of a nonreciprocal S‐ring is presented and demonstrated. Its operation is demonstrated to allow unidirectional laser oscillation. The intensity ratio for laser oscillation in each of the two directions were measured, and found to be larger than 150. This value is the largest such ratio obtained for a ring laser without Faraday isolators.

A multipoint fiber-optic temperature sensor network integrated inside a power transformer for continuous monitoring of hot-spots on windings, cellulose insulations, and oil, is demon- strated and tested. The temperature sensors are based on propri- etary encapsulated fiber Bragg grating (FBG) sensors and the op- tical interrogation unit uses a special designed narrowband high power broadband fiber source. The fiber-optic sensing network is integrated into a 20MVA, 345/ kV kV power transformer (CORE type) having 12 temperature sensing points, distributed over several physical locations inside the transformer (windings, cellulose insulators, magnetic circuit, and cooling oil entrance and exit).