| http://www.w3.org/ns/prov#value | - and having a lower refractive index than that of the waveguide layer; wherein the undercladding layer is a substrate and the waveguide layer is formed from an optical functional material K.sub.1-vLi.sub.vTa.sub.xNb.sub.1-xO.sub.3 (0<x<1,
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