Erbium doping into lithium niobate and sapphire single crystal wafers

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J. Schro¨fel Department of Microelectronics, Faculty of Electrical Engineering, Czech Technical University, Technicka 3, 166 27 Prague, Czech Republic

V. Perina Department of Neutron Physics, Nuclear Physics Institute, Czech Academy of Sciences, 250 68 Rez, Czech Republic (Received 5 October 2000; accepted 13 November 2000)

The possibility of localized doping by Er3+ diffusion at moderate (less than 500 °C) temperature was for the first time demonstrated for sapphire single crystal wafers. The doping was achieved by immersing the substrate wafers into reaction melt containing small amounts of erbium salt. The crucial point of the presented technology was a crystallographic orientation of the used wafers. The most suitable orientation of the cuts was the “X-cut” with orientation (11–20). The strong anisotropy of the moderate temperature Er3+ doping into lithium niobate and sapphire was explained on the basis of the crystal structure of particular cuts.

Rare earth doped optical materials have attracted much attention in fabrication of planar waveguide amplifiers and waveguide lasers for numerous applications in optical communication systems and signal processing systems. The most extensively studied material is single crystalline lithium niobate1 as it is a widely used compound for fabrication of very sophisticated integrated optics structures. The most popular laser active dopant is erbium (Er3+), of which 4I13/2 → 4I15/2 transition1 emits in the third low loss telecommunication window (around 1.5 ␮m). Several techniques for incorporation of Er3+ ions into lithium niobate have been investigated recently. The most common technique is the bulk doping of substrates which is done during the crystal growth. For many reasons, however, the localized doping with the laser active particles, which occurs in the well-defined area in substrates surfaces, is a much more suitable alternative. A possibility of localized doping of Er3+ ions into lithium niobate has been studied using pulsed laser deposition, in-diffusion of erbium from metal erbium layer evaporated onto the substrate surface, and ion implantation. Integrated optics amplifiers and waveguide lasers have already been realized in erbium doped lithium niobate (see e.g., Ref. 6). Positions and site-symmetry of the incorporated erbium ions in lithium niobate have also been studied,3,4 as well as other aspects of this subject.5–7 As far as we know nothing was reported on localized diffusion of laser active ions into sapphire. J. Mater. Res., Vol. 16, No. 2, Feb 2001

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In this article we are presenting results of our study of moderate temperature localized diffusion of erbium into sapphire. The study is based on the results of our experiments with low (or moderate-temperature) diffusion of erbium ions into lithium niobate which had already been reported8–10 and some of which were later confirmed by Sada et al.11 During our study of moderate temperature diffusion processes we have understood the importance of different

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