An optical device that measures and dynamically compensates power loss variations in an optical fiber based on supervisory signals. An injector injects supervisory signals having a predefined optical power downstream of the fiber entry end and a detector extracts the supervisory signals at the exit end of the fiber to detect their optical power. Based on the detected optical power and the predefined optical power, the optical power loss of the supervisory signals in the fiber is determined. The optical power loss and the nominal power loss in the fiber are compared to determine a variation in the power loss in the optical fiber. A controller coupled to the detector and to the exit end of the fiber modifies the power of primary signals delivered by the exit end of the fiber as a function of the detected variation in power loss.