Patent ID: 7554733

Claim:
A diffractive optical element having, within its outer bounds, only a single diffraction grating and comprising: a first transparent member made of a material on which grooves of the diffraction grating are formed; a second transparent member devoid of grooves and having a smooth plane or curved surface; and an adhesive agent made of ultraviolet-curable resin, different from the material of the grooves, directly contacting the material of the grooves and cementing the grooves with the plane or curved surface of the second transparent member, wherein the material of the grooves and the ultraviolet-curable resin have different refractive indices and different Abbe numbers, wherein the grooves form a sawtooth pattern, in which each tooth has a ramp of predetermined length and a height, with the height being less length than the predetermined length of the ramp, wherein the following conditional expression is satisfied: h≦16.0 μm where h denotes the groove height, wherein a pitch of the grooves is 80 μm or more, wherein the adhesive agent is cured by the steps of: dripping the adhesive agent onto the grooves; attaching the smooth plane or curved surface of the second transparent member to the adhesive agent; and irradiating the adhesive agent with ultraviolet light, and wherein the following conditional expressions are satisfied: 1.55≦ndG≦1.70 50≦νdG≦65 1.50≦ndR≦1.65 νdR≦45 where ndG denotes refractive index at d-line of the first transparent member and νdG denotes Abbe number of the first transparent member, ndR denotes refractive index at d-line of the adhesive agent, and νdR denotes Abbe number of the adhesive agent.