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

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. To improve the signal-to-noise ratio of the system, the interference structure of Mach-Zehnder hybrid Sagnac assisted by phase-generated carrier(PGC) technique is utilized to effectively eliminate the parasitic Rayleigh scattering noise along the optical fiber. Finally, the balance of long measurement distance and high measurement precision is achieved in the system, and the measurement resolution of 0.2 meter is realized within the measurement range of 100 kilometers.