An optical device includes a first waveguide layer in which multiple-beam
interference occurs, a second wavelength layer which includes a back
surface facing the first waveguide layer and a front surface as a light
output surface, and an outcoupling layer which is disposed on a back side
of the second waveguide layer and faces the first wave guide layer,
wherein the outcoupling layer includes a first portion as a layer with
light transmission property and second portions which are dispersed in
the first portion and differ in optical property from the first portion,
and wherein an array of the second portions forms a triangular lattice.