Wolfgang Schippers

Femtosecond laser-inscribed fiber Bragg gratings for strain monitoring in power cables of offshore wind turbines

A fiber Bragg grating sensor system used for monitoring the effects of strain on the power cable of an offshore wind turbine is presented. The Bragg grating structure was inscribed into coated nonphotosensitive standard telecommunication fibers using an IR femtosecond laser and the point-by-point writing technique. Because of the presence of the protective coating of the fiber, the mechanical stability of the resultant sensor device is better than that of a sensor consisting of a bare fiber. A system containing this sensing element was to our knowledge for the first time successfully installed and tested in an offshore wind turbine prototype (REpower 6M, REpower Systems, AG, Germany) in February 2010, near Ellhöft (Germany). The fabrication process of the fiber Bragg gratings, measurement results of the online monitoring, and a comparison between the sensor signal and commonly used sensing techniques are presented.

Fiber optic sensor system for stress monitoring in power cables

Monitoring of stress in power cables is of great interest to determine the cable lifetime, especially under rough environmental conditions like in offshore wind energy plants. Standard single mode fibers are generally included in power cables for data transfer. In our approach we developed a sensor device which uses single mode fibers already included in the cables and a short pulse broadband light source. This allows measuring temperature and pressure via time resolved Raman backscattering photon counting as well as monitoring bending and torsion via fiber bragg gratings.

Synchronised Pulsed Pumped Fiber Amplifiers

An Yb fiber amplifier is seeded by a Cr⁴⁺Nd³⁺:YAG microchip laser. Due to improvement of the slope efficiency and suppression of ASE a pulsed diode laser is used as pump source of the active fiber.

LT-GaAsSb photomixer for THz generation with a two-color Nd:LSB microchiplaser

Photomixing is performed with a novel two-color Nd:LSB laser that simultaneously emits at 1061.3 nm and 1063.9 nm in LT-GaAsSb antennas.

Photomixing with LT-GaAsSb Antennas and a Two -Color Nd: LSB Microchiplaser

We present a new cost-effective two-colour Nd: LaSc₃(BO₃)₄ microchip laser for photomixing in a low temperature grown (LT) GaAsSb antennas. The generated 700 GHz radiation is detected with a bolometer.