Abstract: An optical device includes a light transmitting non-linear optical material having a first face and a second face. The first and second faces oppose each other. The first face has a plurality of first reflecting portions provided thereon, and the second face has a plurality of second reflecting portions provided thereon. Each of the second reflecting portions corresponds to one of the first reflecting portions. Furthermore, the first and second faces are substantially flat except for at least one convex arcuate portion being formed on at least one of the first and second faces. Additionally, at least one of the first and second reflecting portions is obtained by coating a reflective material on the convex arcuate portion.