Apparatus and method for determining the optical power passing through

Abstract

An apparatus and method for determining the optical power transmitted through an optical fiber. The invention is based on measuring the intensity of the fluorescence produced by a doped segment of an optical fiber. The dopant is selected so that it emits light at a different wavelength than that responsible for producing the fluorescence. The doped segment is of sufficient length and dopant concentration to provide a detectable signal, but short enough to prevent the doped segment from serving as a gain medium, resulting in amplified spontaneous emission and excess fluorescence traveling along the optical fiber. The dopant material is excited by the optical signal carried by the fiber, causing a fluorescence. In the preferred embodiment the intensity of the fluorescence is proportional to the intensity of the propagating light. The signal power is then determined from the intensity of the fluorescence. The intensity of the fluorescent signal is measured by a photodetector placed so as to detect the light emitted through the side of the doped segment. The detector may wrap around the circumference of the fiber, or be placed to one side and used in conjunction with a reflector placed on the opposing side of the fiber. Filters may be used to shield the detector from other light sources and assist with accurately determining the optical power of the signal propagating within the fiber.