TEST LIGHT CUTOFF FILTER AND IN-SERVICE TESTING METHOD APPLYING THE SAME

摘要

PROBLEM TO BE SOLVED: To allow an in-service test of a test object optical line to be performed by reducing an impact which test light has on communication light in the test object optical line.SOLUTION: An in-service testing method according to the present invention uses a test light cutoff filter 14 that gives loss to light with the wavelength of test light and lets light with the wavelength of communication light propagated by test object optical fiber penetrate. The test light cutoff filter 14 comprises: a mode conversion unit 31 that converts the mode of light with the wavelength of the test light that propagates in a fundamental mode in the test object optical fiber into a higher order mode; and a loss inflicting unit 32 that inflicts only little loss to the communication light propagating in the fundamental mode in the test object optical fiber and inflicts loss to the test light propagating in the higher mode in the test object optical fiber.SELECTED DRAWING: Figure 2