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Platinum Metals Rev., 1988, 32, (1), 10

Fabricating Lithium Niobate Optical Wavelengths

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One of the earliest uses of platinum was for the fabrication of crucibles to be used during chemical analysis, and over the years it has found application as a reliable containment material during many specialised processes, often under the most arduous conditions.

A recent communication from workers at the Universität Dortmund, West Germany, describes a new diffusion technique which is regarded as an important step towards the reproducible fabrication of low-loss titanium-diffused LiNbO3 waveguides (A. Neyer and T. Pohlmann, Electron. Lett., 1987, 23, (22), 1187–1188).

During the fabrication of such waveguides precise control of substrate material stoichiometry, amount of deposited titanium and the diffusion conditions is required. The last are of paramount importance since the in-diffusion of titanium may be accompanied by an outdiffusion of LiO2 from the LiNbO3 crystal, resulting in an unwanted surface waveguide. This can now be avoided by containing the LiNbO3 in a platinum box loosely closed with a platinum lid, during diffusion at a temperature of 1050°C.

The partial pressure of Li2O built up in the small enclosed container is thought to prevent strong outdiffusion of Li2O, but the main advantages of the platinum box are that it does not have to be stabilised by LiNbO3 powder, it is not affected by Li2O and it provides excellent temperature homogeneity.

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