Kerstin Schroeder

A fibre Bragg grating sensor system monitors operational load in a wind turbine rotor blade

A fibre Bragg grating sensor system has been installed and successfully operated in a horizontal-axis wind turbine since February 2004. We herewith report the requirements, design and construction parameters of the sensor system for continuous on-line monitoring of bending loads of the rotor blades and provide examples of the monitoring results.

Optical switch based on a fluid-filled photonic crystal fiber Bragg grating

We report the implementation of an in-fiber optical switch by means of filling a fluid into the air holes of a photonic crystal fiber with a fiber Bragg grating. Such a switch can turn on/off light transmission with an extinction ratio of up to 33 dB within a narrow wavelength range (Bragg wavelength) via a small temperature adjustment of +/-5 degrees C. The switching function is based on the temperature-dependent coupling between the fundamental core mode and the rod modes in the fluid-filled holes resulting from the thermo-optic effect of the filled fluid.

Thermo-Optic Switching Effect Based on Fluid-Filled Photonic Crystal Fiber

We report a thermo-optic switching effect with a high extinction ratio of 30 dB by means of filling a fluid into air holes of a solid-core photonic crystal fiber (PCF). Such an effect can perform a turn on-off operation of the transmitted light via a small temperature adjustment of ±10°C. The switching function attributes to the absorption of the filled fluid in combination with the interaction between the core mode and the excited ¿fluid rod¿ modes, resulting from the thermo-optic effect of the filled fluid.

Fibre Bragg grating sensor system monitors operational load in a wind turbine rotor blade

A fibre Bragg grating sensor system has been installed in a horizontal axis wind turbine and was successfully tested for already more than one year. We report the requirements, system design and realisation of the sensor system for continuous on-line load monitoring of the rotor blades, and provide examples of strain measurement results.

On-line characterization of impacts on electrical train current collectors using integrated optical fiber grating sensor network

A sensor network consisting of unified fiber grating based temperature and strain sensor pads has been developed for integration in carbon/aluminum composite current collector strips, and has been tested in electrical trains on commercial railways. The fiber optic sensor network measures value and position of both con-tact forces and impacts under real-time conditions, immediately at the high voltage location of the interface between overhead contact line and current collector.

Investigating Transverse Loading Characteristics of Microstructured Fiber Bragg Gratings With an Active Fiber Depolarizer

In this letter, the transverse loading characteristics of Bragg gratings in microstructured optical fibers were investigated by use of an active fiber depolarizer. Increasing transverse load shifts the Bragg wavelength to longer wavelengths; its sensitivity to transverse load decreases with increasing volume of air holes around the fiber core. Such transverse loading characteristics were found to be dependent on the fiber orientations.

Separation of refractive index and temperature measurements using surface plasmon-coupled fiber grating

A new fiber optic sensor based on Bragg reflection influenced by a surface plasmon is presented. This arrangement allows for self-referencing due to its highly polarization-resolved response.

Fiber optical sensor network embedded in a current collector for defect monitoring on railway catenary

In order to identify defects of the electrical infrastructure during train operation, a fiber Bragg grating based sensor system performs measurements of the distribution of short time force changes in vertical and horizontal (driving) direction between current collector and overhead contact line. The actual model calculations and the practical design of a 2-dimensionally arranged strain sensor network have been especially enhanced to the calculation of impact directions. The well-known advantages of fiber-optic sensors - embedding capability in the composite carbon/aluminum collector strip, multiplexing of distributed sensor networks, electrical isolation - are of particular importance for detection and characterization of fast impacts immediately at the position of incidence. Tests under everyday operating conditions with trains on high-speed tracks as well as under high load in mountain regions proved the application of this sensing technology. Problems and solutions for the sensor network embedment, the fast Bragg sensor interrogation algorithms, and actual lab test results with their application-orientated analysis will be presented.

Optical fiber grating sensor network for monitoring refractive index and temperature distributions in fluids

In a fiber-optic multi-point sensor network basing on optical fiber Bragg gratings, simultaneous measurements of refractive indices and of temperature are performed. The Bragg wavelength of a side-polished fiber grating is determined by the refractive index of the surrounding fluid, and is measured using a high-resolving low-cost compact spectrometer. The influence of temperature is separated considering the temperature-induced Bragg wavelength shift in an adjacent non-polished part of the fiber grating. The sensor network can be applied for on-line process control in chemical, biochemical and petrol technologies, and for environmental and geotechnical monitoring, especially in flammable or corrosive surroundings, and in electromagnetic fields. A buffer layer between fiber core and analyte allows to adjust the sensor characteristic to appear with high sensitivity in the refractive index range of the interesting fluids.

Fiber Bragg grating optochemical sensor basing on evanescent-field interaction with surface plasmon waves

Fiber Bragg grating sensors in side-polished optical fiber are sensitive to an external analyte by evanescent field interaction. Deposition of sensor-specific transducer layers can advance such fiber Bragg grating refractometer to the optochemical monitoring of specific substances: absorbed gases, vapors, and adsorbed biomolecules as well. Refractive index range of highest sensitivity can be adjusted to the analyte medium of interest by proper construction of the multilayer waveguide. A specific application example aims at hydrogen detection using a palladium thin film transducer.