A first diffractive optical element pattern with a pattern pitch that is no greater
than a wavelength of incident light is formed on a first main surface of substrate
such as a glass plate. Second diffractive optical element patterns are formed at
positions that are respectively incident to positive first-order diffracted light
and negative first-order diffracted light produced by the first diffractive optical
element pattern. Negative first-order diffracted light produced by each second
diffractive optical element pattern is incident upon a boundary face of the substrate
at an angle that is smaller than the critical angle, and so exits the substrate.