A curved surface constituting a convex surface or a concave surface of each of a plurality of lenses includes at least a silicon nitride layer and another silicon nitride layer. An interlayer having a composition different from a composition of the silicon nitride layer and a composition of the other silicon nitride layer is arranged between the silicon nitride layer and the other silicon nitride layer, and a thickness of the interlayer is less than a thickness of the silicon nitride layer and a thickness of the other silicon nitride layer.