The core working principle of polarization-maintaining fiber coupler is based on the evanescent field coupling effect between optical fibers. This tab provides a brief explanation of how we determine several key specifications for our 1x2 couplers. 1x2 couplers are manufactured using the same process as our 2x2 fiber optic couplers, except the second input port is internally terminated using a proprietary method that minimizes back. When using fiber optics, one often needs to use fiber couplers for various purposes. A stable measurement setup is fundamental for any successful measurement.