Spectroscopic Aspects of Polydimethylsiloxane (PDMS) Used for Optical Waveguides
Polydimethylsiloxane polymers were studied for their suitability in optical waveguides. Optical constants of core and clad materials have been measured within the visible and near-infrared spectral range. The absorption loss of PDMS in the datacom region of 600–1600 nm is mainly caused by scattering loss and attenuation by overtone and combination band vibrations of CH containing groups. Based on observed positions of those fundamental, overtone and combination bands and their vibrational assignment, normal vibration frequencies and anharmonicity constants were determined. An empirical correlation between integral band strength and intrinsic absorption loss was derived based on the vibrational spectra of the two materials, providing also estimates for deuterated and halogenated PDMS materials with even lower absorption losses. Besides intrinsic material attenuation, also extrinsic losses from waveguide fabrication have been investigated. Furthermore, multimode waveguides were fabricated with an insertion loss of 0.05 dB/cm at the most frequently applied data communication wavelength of 850 nm. Effects of accelerated ageing have been assessed for the optical characteristics of PDMS materials.
The authors gratefully acknowledge the continued support by Dipl.-Ing. Rüdiger Kuckuk (Leibniz-Institut für Analytische Wissenschaften—ISAS) and Prof. Andreas Neyer (TU Dortmund University). The fruitful cooperation with Wacker Chemie, Burghausen (Germany), is also acknowledged.
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