Abstract
We present a method to accurately measure the birefringence properties of spun fibers using binary polarization rotators. By taking the advantages of binary polarization rotator in polarization analysis, we are able to simultaneously measure both the circular and linear birefringences in a spun fiber with high accuracy. We obtain the circular and the residual linear birefringences of the spun fiber as a function of temperature T to be 3.34 × 10-5-5.11 × 10-8T and 8.1 × 10-6-1.19 × 10-8T, respectively, with the residual linear birefringence about 4 times less than the circular birefringence. We find, for the first time with the best of authors' knowledge, that the circular and the residual linear birefringences in a spun fiber are highly linear with the temperature, with thermal coefficients of -5.11 × 10-8 °C-1 and -1.19 × 10-8°C-1, respectively, and that the relative changes per °C of the circular and residual linear birefringence are almost identical, with values of -0.152% and -0.147% respectively. We believe that the method and data presented in this paper will be beneficial for making high quality spun fibers, as well as high accuracy fiber optic current sensors.
Highlights
Fiber optic current sensors (FOCS) based on Faraday effects for measuring the electric current in power systems have the advantages of inherent insulation, immunity to electromagnetic interference and light weight
The main objective of our work is to develop a measurement technique capable of accurately measuring the circular and residual linear birefringences of spun fibers which is critical to FOCS applications, especially for meeting the demanding requirement of accuracy on the order of 0.2% or less over the temperature range between −40 °C to + 80 °C [10, 11]
In our previous publications [20,21,22], we presented using binary polarization rotators made of magneto-optic crystals for polarization related analysis and achieved exceptionally high accuracy and sensitivity for linear birefringence measurement of optical fibers, an order of magnitude more sensitive than those relying on the analog techniques
Summary
Fiber optic current sensors (FOCS) based on Faraday effects for measuring the electric current in power systems have the advantages of inherent insulation, immunity to electromagnetic interference and light weight. In a commercial spun fiber’s data sheet (e.g. Spun HiBi Fiber of Fibercore Ltd.) [9], a parameter called elliptical beat length (circular beat-length in [9]) is generally used to describe its birefringence characteristics, which is estimated using the linear beat length of the un-spun fiber made with the same perform and spin pitch of the spinning process [4]. Previous methods for the birefringence measurements include those of using rotating-wave plate and polarizer [12,13,14,15,16], wavelength scanning [17], and the photo-elastic modulators [18, 19] Such analog techniques relying on using analog signals to obtain birefringences usually have the disadvantages of low repeatability and require complicated methods to compensate for imperfections in the optical components and in moving mechanical parts. We believe that the method and data presented in this paper will be beneficial for making high quality spun fibers, as well as high accuracy fiber optic current sensors
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