In an optical element, a first mirror stack layer is formed on a
substrate, and a spacer layer made of a paraelectric material having a
secondary electrooptic effect is formed thereon through a first
conductive thin film. Further, a second mirror stack layer is formed
thereon through a second conductive thin film, and a coupling layer is
formed thereon; thus, a basic structure of the optical element is formed.
By changing a voltage to be applied between the first and second
conductive thin films, it becomes possible to switch wavelengths of light
to be transmitted through the optical element at a high speed.