A coupler can be used as a splitter to couple out some portion of the light circulating in the resonator of fiber laser, for example. Directional 2 × 2 couplers (see Figure 1) are usually used for such purposes. The same kind of device is useful in fiber interferometers . What happens when light is injected into both input ports of a directional fiber coupler? How do high-power fiber couplers differ from standard couplers? What principles are used in high-power fiber couplers to minimize power losses? More questions. This is part 8 of a tutorial on passive fiber. Detailed measurements of fiber parameters like e. Note that the term fiber coupler is used with two different meanings: It can be an optical fiber device with one or more input fibers and one or more output fibers. Light from an input fiber can. How measured fiber parameters help to choose the best coupling and collimation optics. A stable measurement setup is fundamental for any successful measurement.