A long-haul and high-accuracy fiber length measurement technology based on Mach–Zehnder and Sagnac hybrid interferometer

Abstract

In this paper, an optical fiber length measurement system based on phase-modulated pulse time of flight method is proposed. The fiber length is calculated by measuring the flight time of the phase-modulated pulse in the fiber under test. The measurement system is based on the interference structure of Mach–Zehnder hybrid Sagnac to obtain stable interference effects. To improve the signal-to-noise ratio of the system, the phase-generated carrier technique is utilized to effectively eliminate the parasitic Rayleigh scattering noise along the optical fiber. Finally, a balance of long measurement distance and high measurement precision is achieved in the system, and a measurement resolution of 0.2 m is realized within the measurement range of 100 km.