Georg M. Müller

Inherent temperature compensation of fiber-optic current sensors employing spun highly birefringent fiber.

We investigate the various contributions to the temperature dependence of an interferometric fiber-optic current sensor employing spun highly-birefringent sensing fiber, in particular, the contributions from the fiber retarder at the fiber coil entrance, the spun fibers birefringence, and the Faraday effect. We theoretically and experimentally demonstrate that an appropriately designed retarder inherently compensates the temperature dependence of the fiber birefringence and the Faraday effect. We demonstrate insensitivity to temperature to within ± 0.2% between -40 and + 85 °C. Furthermore, we analyze the influence of the retarder parameters on the linearity of the recovered magneto-optic phase shift vs. current and determine a set of parameters that results in a perfectly linear relationship.

Temperature compensation of fiber-optic current sensors

We report the first fabrication of polarization rocking filters in a highly birefringent elliptical microfiber. The rocking filters are made by periodically heating/twisting a microfiber with an ellipticity of ~0.7 and a diameter of ~2.8 μm along its major axis. Strong input polarization suppression of ~20 dB is achieved at a resonant wavelength of ~1556.4 nm with a device length of ~3.12 mm. High-order polarization rocking filter was used to measure the refractive index with sensitivity of 32036 nm/RIU.

Interferometric fiber-optic current sensor with inherent source wavelength shift compensation

Fiber-optic current sensors utilize the Faraday effect in fused silica fiber to measure electric current. Since the effect is wavelength dependent, high sensor accuracy requires a stable source wavelength. Commonly used semiconductor sources require temperature stabilization within ≈0.1°C for adequate wavelength stability that adds extra cost. Here, we theoretically and experimentally demonstrate a novel method for inherent (passive) compensation of source wavelength shifts in interferometric fiber-optic current sensors. The method is based on an appropriately detuned fiber-optic half-wave retarder that generates wavelength dependent cross-coupling between the two orthogonal polarization modes of the sensor which compensates the change of the Faraday effect with wavelength. It is shown that at a wavelength shift over 14 nm (near 1305 nm), which corresponds to a source temperature change of 24°C, the scale factor variation is reduced from 2% to <;0.2%.

A Study on Different Types of Fiber Coils for Fiber Optic Current Sensors

We consider an interferometric fiber optic current sensor with a fiber coil operated in reflection and compare three different techniques to prepare the coil: thermally annealed coils, stress-free packaging of a bare low birefringent fiber in a fused silica capillary, and coils from highly birefringent spun fiber. In particular we theoretically and experimentally investigate how the fiber retarder that generates the near left and right circular light waves in the sensing fiber must be prepared for temperature compensation of the Faraday effect in the three cases. All three methods can achieve accuracy within ±<0.2% over an extended temperature range but they considerably differ in their practical challenges.

Simple Fiber-Optic Current Sensor with Integrated-Optics Polarization Splitter for Interrogation

A simplified fiber-optic current sensor configuration is presented. Key component is an assembly of a 1x3 integrated-optics splitter with retarder and polarizer platelets that transforms the magneto-optic phase shift into anti-phase signals proportional to current.