Optical loop back and line test apparatus

摘要

A testing apparatus is presented which evaluates the performance of optical signal transmissions in the 1.3 mu m wavelength region, independently or simultaneously with signal transmission. An optical signal is transmitted in the network->user direction in a thermo-optic (TO) switch 11, and the signal is also looped in the direction A of an optical directional coupler 3. An optical time domain reflectometer (OTDR) 10 Generates a test beam at 1.55 mu m wavelength region, which is reflected by a wavelength selective filter 8 back to the OTDR 10 in the user-network direction. The apparatus is thus able to perform testing of the transmission cable 7 simultaneously with the signal transmission. When an operating problem is to be pinpointed in the system, the optical switch 11 is switched so as to permit the signal from a line terminal LT 1 to transmit in the network->user direction. The signal is attenuated by the same magnitude as the loss budget between the terminals NT 9 and LT1, and is looped back to LT 1, thereby enabling Loop 1 testing at the same signal strength level as in the actual signal transmission.