High Quality Erbium-Doped Bismuth Based Oxide Film for Planar Waveguide Amplifier Prepared by Sputtering
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High Quality Erbium-Doped Bismuth Based Oxide Film for Planar Waveguide Amplifier Prepared by Sputtering S. Suzuki, Y. Kondo, T. Nagashima, N. Sugimoto, J. Ebisawa, S. Ito Research Center, Asahi Glass Co., Ltd. 1150 Hazawa-cho, Kanagawa-ku, Yokohama 221-8755, Japan ABSTRACT High quality Bi2O3 based Er-doped films for planar waveguide amplifier have been deposited by sputtering from sintered targets. It was found that both the amount of residual water and the Er concentration in films mainly affected a lifetime of the fluorescence at 1530nm. By optimizing these parameters, we have obtained films with a lifetime over 3msec, as the same as that of bulk glass prepared by the melting method.
INTRODUCTION In optical telecommunication, Er-doped amplifier is one of key components for wavelength division multiplexing (WDM). We have already reported that Bi2O3 based Er-doped fiber and waveguide are advantageous in higher amplification efficiency due to higher Er concentration without concentration quenching and in broader amplification band width [1-5]. Figure 1 shows the energy level of Er3+, which concerns the fluorescence at 1530nm by 980 nm pumping. The pumping light excites the state from 4I15/2 to 4I11/2, followed by a rapid relaxation to 4I13/2. The fluorescence at 1530nm is yielded with relaxation from 4I13/2 to 4I15/2. The lifetime of the fluorescence is an important factor for amplification efficiency and longer lifetime is required. It is well known that sputter deposition is a non-equilibrium process and is useful to form amorphous metal oxide, i.e., glass, films with complicated component at low temperatures. The purpose of the present study is to prepare high quality (i.e., longer lifetime of the fluorescence) Bi2O3 based Er-doped films for planer waveguide amplifier by sputtering. 4
I11/2
4
I13/2
hν 980nm
hν
1530nm 4
I15/2
Figure 1. Energy level of Er3+. Pumping light at 980nm causes the excitation from 4I15/2 to 4 I11/2, followed by a rapid relaxation to 4I13/2. The 1530nm fluorescence is yielded by the relaxation from 4I13/2 to 4I15/2.
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EXPERIMENTAL Bi2O3 based Er-doped films were sputtered onto soda lime silicate glasses at 200°C by RF sputtering from sintered targets consisting of Bi2O3, SiO2, Ga2O3, Al2O3, Er2O3 and Yb2O3, where Bi2O3, SiO2, Ga2O3 composed a glass matrix and Er2O3, Yb2O3 were dopants. Er2O3 was doped from 0.5 to 3.0 mol%. Al2O3 and Yb2O3 were added up to 3.5 and 2.0 mol%, respectively, to enhance the fluorescence from Er3+ when pumping at 980 nm. A mixture of Ar/O2 was introduced and the pressure inside the vacuum chamber was maintained at about 0.3 Pa. The input power was 1.0 ∼ 3.0 W/cm2. Some of the as-deposited films were annealed at over 400°C at a pressure less than 133 Pa for several hours. The lifetime of the fluorescence at 1530 nm was measured using a pulsed pumping at 980 nm using a semiconductor laser diode. The pumping light was incident on the cross section of film of about 3 µm in thickness. The fluorescent light was detected in a direction
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