The impact of chromatic dispersion on frequency scanning COTDR and its compensation

Frequency Scanning Coherent Optical Time Domain Reflectometry (COTDR) is a promising technology for the maintenance and management of social infrastructures because of its capability to measure strain with high accuracy over a long distance. In Frequency Scanning COTDR, Rayleigh scattering intensity for each optical frequency is measured while the light source frequency is discretely varied. However, group velocity in optical fiber depends on the optical frequency, which is called chromatic dispersion. Therefore, as the measurement distance increases and the optical frequency range widens, the effect of chromatic dispersion is expected to become significant and degrade the measurement accuracy. However, to the best of our knowledge, this issue has not been thoroughly investigated. In this paper, this is the first time we theoretically derived the impact of chromatic dispersion on Frequency Scanning COTDR and proposed its compensation method. We also experimentally demonstrated the impact of chromatic dispersion and the effectiveness of the proposed method through the Fresnel reflection from the far end of the optical fiber and strain measurement accuracy. The experimental results presented here show that the proposed method effectively compensates for chromatic dispersion and improves the measurement accuracy.