Abstract: A beam splitter includes a substrate unit, and first and second prisms disposed on surfaces at two opposite sides of the substrate unit, respectively. The substrate unit includes a substrate member, and a beam splitter film disposed at the substrate member and capable of beam splitting. The beam splitter film includes a plurality of thin film layers arranged in a stack. Each of the thin film layers is made of an inorganic material.

Abstract: An optical device includes a first prism unit, a second prism unit spaced apart from the first prism unit, and a spacer unit disposed between the first and second prism units. Each of the first and second prism units includes a substrate, an anti-reflection coating, and a prism. The substrate has a first surface disposed to face the other one of the first and second prism units, and a second surface opposite to the first surface. The anti-reflection coating is disposed on the first surface of the substrate. The prism is disposed adjacent to the second surface of the substrate. The spacer unit is disposed between the anti-reflection coatings of the first and second prism units.