Most commonly,this is used for OTDR testing at 1650 nm.Testing loss on single mode fiber at 1625 nm.This extra wavelength is used to check that the fiber is unstressed, since this wavelength is more sensitive to bending loss.
1625nm DFB Laser Pigtail for COTDR. A Coherent Optical Time Domain Reflectometer (COTDR) provides dB vs. km attenuation traces of amplified (repeatered) line systems over the entire length of the submarine cable. A submarine optical Fiber Pair (FP) is tested by launching a test signal in transmit (Tx) direction fiber.
