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Tunable diffractive optical elements on various electro active polymers

: Döring, S.; Hildebrandt, N.; Stumpe, J.; Kollosche, M.; Kofod, G.


Thienpont, H. ; Society of Photo-Optical Instrumentation Engineers -SPIE-, Bellingham/Wash.:
Micro-Optics 2010 : 12.-16.4.2010, Brussels, Belgium
Bellingham, WA: SPIE, 2010 (Proceedings of SPIE 7716)
ISBN: 978-0-8194-8189-4
Paper 77160F
Conferecne "Micro-Optics" <2010, Brussels>
Fraunhofer IAP ()

An innovative approach for voltage-tunable optical gratings based on dielectric elastomer actuators (DEAs) using electro active polymers is presented. Sinusoidal surface gratings, holographically written into azobenzene containing films, are transferred via nanoimprinting to DEAs of different carrier materials. We demonstrate that the surface relief deformation depends on the mechanical and geometrical properties of the actuators. The tested DEAs were made using commercially available elastomers, including a tri-block copolymer poly-styrene-ethylene-butadiene-styrene (SEBS), a silicone polydimethylsiloxane rubber (PDMS) and commonly used polyacrylic glue. The polyacrylic glue is ready to use, whereas the SEBS and the PDMS precursors have to be processed into thin films via different casting methods. The DEA material was pre-stretched, fixed to a stiff frame and coated with stretchable electrodes in appropriate designs. Since the actuation strain of the DEA depends strongly upon the conditions such as material properties, pre-stretch and geometry, the desired voltage-controllable deformations can be optimized during manufacturing of the DEA and also in the choice of materials in the grating transfer process. A full characterization of the grating deformation includes measurements of the grating pitch and depth modulation, plus the change of the diffraction angle and efficiency. The structural surface distortion was characterized by measuring the shape of the transmitted and diffracted laser beam with a beam profiling system while applying an electro-mechanical stress to the grating. Such surface distortions may lead to decreasing diffraction efficiency and lower beam quality. With properly chosen manufacturing parameters, we found a period shift of up to 9 % in a grating with 1 ?m pitch. To describe the optical behavior, a model based on independently measured material parameters is presented.