A small optical device which has low power consumption and which is excellent
for
integration, and which has a variable optical attenuation function which features
proper polarization dependence over the entire wide variable optical attenuation
range is provided. In the optical device, an optical circuit including a core and
a cladding that covers the core is formed on a substrate. An optical element is
movably disposed inside a groove provided in the substrate so as to traverse the
core, and includes a plurality of optical attenuation elements having different
light attenuation amounts. By moving the optical element by an actuation function
portion provided on the optical circuit, the attenuation amount of signal light
that propagates through the optical circuit is changed.
