To assess the suitability of bismuth germanate as an electro-optic material for high precision applications, we have confirmed and extended previous data on its refractive index, electro-optic tensor element r(41), and thermal expansion coefficient. In addition, we have measured the thermo-optic coefficient dn/dT, the temperature dependence of the electro-optic coefficient, and the stress-optic tensor elements. From the stress-optic tensor elements and previously published data, we have computed the strain-optic tensor elements. The index of refraction is given, to a good approximation, by the single-term Sellmeier equation, n(2) - 1 = S(0)λ(0)(2)/[1 - (λ(0)/λ)(2)], with S(0) = 95.608 µm(-2) and λ(0) = 0.1807 µm. The thermo-optic coefficient is 3.9 × 10(-5)/°C at 632.8 nm and 3.5 × 10(-5)/°C at 1152.3 nm. The electro-optic tensor element varies between approximately 1.05 and 1.11 pm/V over the spectral range of 550-1000 nm; its normalized effective change with temperature is approximately 1.54 × 10(-4)/°C. The thermal expansion coefficient is 6.3 × 10(-6)/°C over the range 15-125 °C. Values of the stress-optic tensor elements are q(11) - q(12) = -2.995 × 10(-13) m(2)/N and q(44) = -0.1365 × 10(-12) m(2)/N. The strain-optic tensor elements are p(11) - p(12) = -0.0266 and p(44) = -0.0595.

Abstract-Annealing procedures that greatly reduce linear birefringence in single-mode fiber coils are described in detail. These procedures have been successfully applied to coils ranging from 5 mm to 10 cm in diameter and up to 200

Measured temperature dependences of the Verdet constants of SiO(2), SF-57, and BK-7 are approximately 10(-4)/K within 3-20% of Becquerel formula estimates.

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Abstract-The Verdet constant in annealed optical fiber current sensors has been measured at wavelengths from 636 to1320 nm. The measurements are fitted to two models, one classical and the other an expansion of the classical model that includes a nonlinear term. These measurements and models are compared to previous measurements made in optical fiber and bulk SiO 2.Our measurements have an average accuracy of 60.6% and an average measurement uncertainty of 60.5% over the 636 to 1320 nm range.

Abstract-The decrease in transmittance of annealed optical fiber has been measured versus temperature and time. The annealing loss is due to the devitrification of the glass and OH absorption in the 1200 to 1500 nm wavelength region. Both loss mechanisms propagate primarily from the surface into the core. However, to increase the OH absorption significantly, annealing times greater than 10 h are required. Fibers heated from 1000 to 1300 C in an air atmosphere quickly devitrify and their transmittance approaches zero. Also, the current sensitivity of annealed fiber current sensors versus annealing time at 850 C has been measured. A decrease in the current sensitivity is attributed to devitrification in the fiber.

The Faraday effect is becoming widely used as an optical method of measuring electric current or magnetic field. It is particularly advantageous where the measurements must be made at high voltage or in the presence of electromagnetic interference, and where speed or stability are considerations. In this paper we review the development of the technology over the last twenty years, with an emphasis on the basic principles, design considerations, and performance capabilities of sensors that represent the latest achievements. Faraday effect current sensors are now used routinely in the measurement of large current pulses, and are starting to become available for ac current measurements in the power industry. Recent developments include their extension to the measurement of currents in the milliampere range and substantial reductions in size. Similar devices, in slightly different configurations, can be used for magnetic field measurements. Further improvements, based on new fiber types and new materials, are projected.

We demonstrate that twisting a fiber a few turns per meter before it is annealed largely eliminates the residual linear birefringence. This dramatically improves the yield of annealed coils used for current sensing and makes it possible to use fibers that previously had large residual linear birefringence. Twisting the fiber is effective because the residual birefringence, associated with core ellipticity, is reduced to near zero by twisting. A theoretical model of the twisted and annealed fiber current sensor is compared to experimental data. We also show good temperature stability for a sensor made with this new technique.