Optical fiber length measurement system and measurement method

Abstract

The invention discloses an optical fiber length measuring system and a measuring method for measuring the optical fiber length by using the measuring system. The measurement system uses frequency counting and graphic analysis to judge the superposition state of the two optical signal pulses, which can avoid the measurement error introduced by directly reading the time delay difference through the oscilloscope, and is conducive to improving the measurement accuracy of the optical fiber length; In the invention, the light source adopts the internal modulation method, which is beneficial to eliminate the dependence of the optical fiber length measurement system on the polarization state of the optical signal, and then eliminates the influence on the measurement uncertainty due to the use of polarization and reflection components to measure the length of the optical fiber. Since the present invention is not affected by the polarization of the light source Due to the influence of the state, the invention can not only measure the length of single-mode optical fiber but also the length of multi-mode optical fiber, which solves the problems of accurate calibration of multi-mode optical fiber length and traceability of multi-mode optical time domain reflectometer length value.

Description

technical field [0001] The invention relates to an optical fiber length measuring system and a measuring method for measuring the optical fiber length by using the measuring system. Background technique [0002] With the continuous development of optical fiber technology in civil and military fields, accurate measurement of optical fiber length plays an increasingly important role in optical fiber communication and optical fiber sensing systems. At present, the instruments for measuring the length of optical fiber mainly include low coherent optical reflectometer (OLCR), optical time domain reflectometer (OTDR), optical frequency domain reflectometer (OFDR), optical coherent domain reflectometer (OCDR) and frequency-based Shift asymmetric Sagnac interferometer. The above-mentioned instruments for measuring the length of optical fibers have the following defects: (1) Although the measurement accuracy of the low-coherence light reflection measuring instrument is very high, it...

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Problems solved by technology

The above-mentioned instruments for measuring the length of optical fibers have the following defects: (1) Although the measurement accuracy of the low-coherence light reflection measuring instrument is very high, it can reach 10 microns, but the measurement dynamic range of the measuring instrument is small, only a few centimeters; (2) Although the measurement dynamic range of the optical time domain reflectometer is very large, the measurement accuracy is limited. The accuracy of the commonly used optical time domain reflectometer can only reach about 1 meter; A monochromatic light source with a line width, and a high-frequency modulation signal of more than a dozen GHz is required, resulting in high cost; (4) The measurement accuracy of the optical coherence domain reflectometer can reach 10 microns, and the measurement dynamic range can reach several thousand meters, but it requires good stability and coherence of the light source; (5) The frequency of the minimum value point of the interference signal in the asymmetric Sagnac interferometer based on frequency shift is not easy to read

[0004] Although the measurement accuracy of the above-mentioned measurement system can reach the centimeter level, there are still the following defects: (1) reading the time difference of the two signals directly through the oscilloscope will cause a large measurement uncertainty; (2) by measuring the measured optical fiber The reflected signal obtains the length value of the measured fiber, which is easy to reduce the measurement dynamic range of the measurement system; (3) in the above measurement system, a polarization controller needs to be added before the output light of the light source enters the electro-optical modulator to control the polarization state, and it is also necessary to Adding a Faraday rotator behind the optical fiber to stabilize the polarization state of light will, on the one hand, cause the measurement system to be unstable due to the influence of the polarization state, and on the other hand will increase the uncertain influencing factors and system cost of the measurement system; (4) In addition The above measurement system is only suitable for measuring the length of G.652 single-mode fiber at 1310nm and 1550nm wavelength points, but not suitable for accurate measurement of the length of 850nm and 1300nm multimode fiber. accurate calibration

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