Fabrication and characterization of implanted polymer waveguides

Abstract

Polymeric materials such as poly[diethylene glycol bis(allyl carbonate)], simply called CR-39, subjected to (gamma) -rays or ion beams (H, He, Li...) undergo structural, physical and chemical modifications. In the case of ion beam, these modifications lead to a sufficient and localized increase of the polymer refractive index to achieve optical waveguides. The first CR-39 polymer studied at the laboratory was a commercial one, we recently fabricated our own material dedicated to our work, thanks to a collaboration with the Polymer Group (University of Bristol, U.K.). Consequently, its composition is mastered, notably by the concentration of the initiator used during the polymerization process. Then we showed that the refractive index of the substrate can be controlled by the curing conditions. The losses of the waveguide fabricated by irradiation have been systematically measured in order to apply this technique to integrated optics (microstructure fabrication). The device used has been recently improved and it is based on a CCD camera related to an image analysis system and an exponential regression calculation program. The values are obtained with an accuracy of +/- 0.5 dB/cm and they remain too high (2 to 4 dB/cm) for a lot of applications. That is the reason why we studied the behavior of the waveguide under thermal treatments with temperature around the glass transition temperature (Tg) of the unirradiated CR-39 polymer. These experiments showed that, on the range of Tg - 10 degree(s)C, Tg + 10 degree(s)C, the attenuation after the annealing treatment remains equal to its original value. They also pointed out the thermal stability of the refractive index, then we can conclude that the radiation induced modifications have stable structural consequences.