Coupling loss

Coupling loss, also known as connection loss, is the loss that occurs when energy is transferred from one circuit, circuit element, or medium to another. Coupling loss is usually expressed in the same units—such as watts or decibels—as in the originating circuit element or medium. Coupling loss in fiber optics refers to the power loss that occurs when coupling light from one optical device or medium to another. (See also Optical return loss.) Coupling losses can result from a number of factors. In electronics, impedance mismatch between coupled components results in a reflection of a portion of the energy at the interface. Likewise, in optical systems, where there is a change in index of refraction (most commonly at a fiber/air interface), a portion of the energy is reflected back into the source component.