A prism optimally separating and synthesizing a light beam of a wide angle
of incidence. A diffraction prism 15 of the present invention is so
constructed that a diffraction grid 21 is sandwiched between a pair of
diffraction grid substrates 22, a pair of prism substrates 24 are bonded
to the surfaces of the prism substrates 22 facing the diffraction grid 21
with interposition of adhesive layers 23, and a diffraction grid medium 25
having a refractive index substantially equal to that of the prism
substrates 24 is charged in a gap defined by the diffraction grid 21 and
the prism substrates 24, with the respective component members being
optically combined together. An incident light is led to the diffraction
grid 21 and separated on transmission or reflection by the operation of
diffraction by the diffraction grid 21.
