Accurate elasto-optic probe method for measurement of coupling length in twin-core optical fiber.

The theoretical principle and experimental procedure of a new method of measuring the coupling length of a twin-core fiber are presented. This method is simple, nondestructive, and gives direct results without extensive data processing. It is based on the elasto-optic technique and had a very good spatial resolution so that coupling lengths of the order of a few millimeters can be measured. We show how this method can be applied to the measurement of the polarization coupling of birefringent noncircular twin-core fibers.