Real-time measurement of optical fiber length with chaotic ring laser

摘要

A measurement method of optical fiber length based on the adjacent-frame similarity of chaos from a fiber ring laser is proposed. The test fiber is acted as a part of the ring laser. By calculating the autocorrelation function of multi-frame chaotic data the frame length, namely, time of light running a cycle in the laser, ring length and test fiber length can be obtained. A real-time processing program of the measurement system is designed. The program is based on a PicoScope PC oscilloscope in hardware, LabVIEW and Matlab joint programming in software. When optical fibers with different lengths are connected into the laser respectively, the LabVIEW front panel shows the length measurement results in real time. A semiconductor optical amplifier fiber ring laser is built to measure the fiber length. The measurement range is from less than 1 m to a few tens km depending on the sample rate and amplifier gain in the ring. Due to the limit of the sample rate of the oscilloscope, the longer the test fibers, the bigger the errors compared with the length measured by an optical time domain reflectometry (OTDR). At the maximum sample rate of 1 GS/s, the minimum and maximum errors are 1.075 m for 150 m length fiber and 175.973 m for 25 km one respectively. The measurement results of four different optical fiber patch cords whose lengths can't be measured by the OTDR are consistent with the lengths labeled by the manufacturer. The measuring method is simple and fast, no dead zone.