Oskar Krumpholz

Smart sensing of aviation structures with fiber optic Bragg grating sensors

We developed a surface mounting technique where fiber-optic Bragg grating (FBG) sensors are glued to the surface of structures and tested the technique on the surface of a CFRP- wing at the DASA Airbus test center Hamburg for over one year. The FBG sensors were interrogated with a measurement system capable of determining the Bragg wavelength in a few seconds over a spectral range of 60 nm (around 1.53 μm) with an absolute accuracy better than 1 pm. A polarization scrambler was used to account for polarization effects. Excellent consistence between the values of electrical strain gauges and the FBG sensors were found during all measurements. However because this method shows drawbacks in a harsher environment such as a flight test, we are currently investigating the possibilities of integrating FBG sensors into the varnish of the structures. For reasons of their better mechanical performance we use FBG sensors produced on the fiber draw-tower with a special UV-curable coating. The sensors are integrated into an original Airbus varnish build- up. We observed linear strain sensitivities in a temperature range between -50 and +100 °C. Furthermore, at negative temperatures we found a vanish- induced polarization dependence which could be used to differentiate between strain and temperature effects.

Tunable laser-based hybrid WDM/TDM sensor system for the interrogation of low-reflective fiber bragg gratings

This paper describes a novel, patented wavelength- and time-division multiplexing sensor system based on a tunable laser source with an additional optical modulator geared for intenogating a large number of low-reflective Bragg grating sensors with high accuracy.

Optical backplane in planar technology

Optical interconnects are expected to overcome the limitations imposed by electrical interconnects. For board- to-board and board-to-multiboard communication we have developed an optical backplane for applications in mobile systems. Compared to existing realizations it is compact, rugged and has the potential to be fabricated at low cost. The main features of the optical backplane in planar technology are free space expanded beam transmission between boards and backplane and guided wave transmission within the backplane. No optical connectors are required. Due to the expanded beams and highly multimode waveguides large coupling tolerances of several 100 micrometers are achieved. Low loss polymer backplane waveguides allow transmission length of more than 19 inches. Demonstrators for board-to-board interconnections and for ring and star networks have been realized. Transmission experiments at 1GBit/s have been successfully performed. First environmental test with respect to dust, moisture, temperature and vibrations showed the feasibility of the concept.