BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a fragmentary cross-sectional view of an optical device according to a first embodiment of the present invention;
FIG. 2 is an enlarged cross-sectional view of the optical device taken along line II-II of FIG. 1;
FIG. 3A is a fragmentary cross-sectional view of an optical device according to a first specific example;
FIG. 3B is a fragmentary cross-sectional view of an optical device according to a second specific example;
FIG. 4A is a fragmentary cross-sectional view of an optical device according to a third specific example;
FIG. 4B is a fragmentary cross-sectional view of an optical device according to a fourth specific example;
FIG. 5 is a diagram showing the results of an experiment which was conducted to observe attenuated levels of reflected light at different angles θ3 of inclination of a filter;
FIG. 6 is a fragmentary cross-sectional view of an optical device according to a second embodiment of the present invention;
FIG. 7 is a fragmentary cross-sectional view of an optical device according to a third embodiment of the present invention; and
FIG. 8 is a fragmentary cross-sectional view of an optical device according to a fourth embodiment of the present invention.