High-resolution optical measurement of fiber optics transmission line length

This paper studies a frame-loss-free shunt system for broadband optical fiber transmission lines. This system switches transmitting optical pulses between duplicated optical fibers to avoid any interruption to communication. A high-resolution measurement technique is necessary to evaluate the optical fiber length. We applied an interferometry technique to adjust 15 km duplicated optical lines at a resolution of 10 mm. An optical line switching system and procedure are designed for use in replacing in-service optical lines. A free space optics (FSO) system adjusts the length of an in-service optical line by up to 100 m. A gigabit ether-passive optical network (GE-PON) line is successfully replaced with an extended line while maintaining transmission.