Optical materials such as semiconductors, glass and optical crystals doped with Er offer prospects for optical sources or amplifiers operating at 1.55μm but doping these materials with erbium means rather complex problem. Therefore new materials such as polymers have been investigated in the last decade as well. Erbium ions are the most interest dopants because of the Er3+ emission at 1.55μm, which corresponds to wavelengths where for the absorption of silica optical fibers is minimal. Despite its potential usefulness, one drawback of the Er3+ system is that it lacks absorption bands where low cost pump sources can emit. One way to overcome this problem is using co-doping with Er sensitizer, which has a broad absorption band. Ytterbium is especially attractive for this purpose.
In this paper we report about fabrication and properties of Er3+ and Yb3+ ions doped with Polymethylmethacrylate (PMMA). The reported layers were fabricated by spin coating onto Si, Si/SiO2 or onto glass substrates. For the Er and Yb doping were used ErCl3 and YbCl3 or ErF3 and YbF3 dissolved in C5H9NO. Optimization of the doping and the influence of the amount of the dopants on the photoluminescence spectra at 1.55μm were studied as well.
Properties of the fabricated layers were analyzed by various methods. Refractive indices of the samples were determined using refractometer at wavelength range from 250 to 750nm and by prism coupling method at 632.8nm. The absorption spectra were taken at wavelength range from 300 to 900nm. The photoluminescence measurement was carried out at excitation wavelengths at 980nm.
We found that the samples deposited onto the Si/SiO2 substrate had waveguiding properties. The number of propagating modes varied from 1 to 6 depending on the thickness of the deposited layers. The PMMA refractive indices varied from 1.489 to 1.386 and the Er3+ and Yb3+ doping caused decrease of the refractive indices values. We observed photoluminescence emission at 1.55μm due to the transition 4I13/2 → 4I15/2. Co-doping with ytterbium ions increased the intensity of the luminescence. Best results we obtained with the samples containing 1 at. % of Er and 10 at. % of Yb. This research has been supported by GAER grant No. GA102/06/0424.