Coupling characteristics measurements between curved waveguides using a two-core fiber coupler.

Coupling characteristics between two curved waveguides are studied using a two-core fiber. A tunable monochromatic light source is used to measure the wavelength dependence of the coupling efficiency. Measured values of the coupling efficiency agree well with theory. It is found that (1) the coupling efficiency can be changed from 0 to 1 by changing the radius of curvature, for example, from 100 mm to infinity in the measured coupler; and (2) when phase shift due to curvature sbeta/2R exceeds the coupling coefficient K, where s is the center-to-center core separation, beta the propagation constant, and R the radius of curvature, coupling between the curved cores does not occur, and there is only the phase shift between the cores.