Photo-elastic correction factor for fiber strain measurements in a cable under tensile load

There has been a large variation among reported values for photo-elastic correction factor (K). The nonlinearity of group index versus strain plot was demonstrated to be the cause of the inconsistency. Based on this finding, it is concluded that the K value should be in the range of 1.26-1.30 when the fiber strain is less than 0.6% and 1.22-1.24 when the strain is in the range of 2-3% regardless of fiber types and measurement wavelengths. As a practical example of strain measurements, a test result for an OPGW was described.<
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