An optical waveguide capable of having various characteristics and a method
of manufacture thereof as well as a method of manufacturing a crystal film
are provided. An optical functional material KTa.sub.x Nb.sub.1-x O.sub.3
is used as an optical waveguide. The input optical signal is transmitted
to the KTa.sub.x Nb.sub.1-x O.sub.3 film. The KTa.sub.x Nb.sub.1-x O.sub.3
film undergoes changes in optical property when an external voltage signal
is applied to the electrode. Therefore, as it passes through the KTa.sub.x
Nb.sub.1-x O.sub.3 film, the input optical signal is modulated by the
characteristic change. The modulated optical signal is taken out as an
output optical signal.
