| CPC G02B 5/1814 (2013.01) [G02B 5/1852 (2013.01); G02B 2005/1804 (2013.01)] | 8 Claims |

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1. A grating part comprising:
a first transparent substrate having an optical grating on a surface thereof;
a second transparent substrate having an optical grating on a surface thereof; and
a spacer positioned between the first transparent substrate and the second transparent substrate, the spacer bonding the first transparent substrate and the second transparent substrate,
wherein the optical grating on the surface of the first transparent substrate, and the optical grating on the surface of the second transparent substrate are provided in non-overlapping regions in a plan view,
wherein a cavity is formed by the first substrate, the second substrate, and the spacer, and
wherein the optical grating on the surface of the first transparent substrate, and the optical grating on the surface of the second transparent substrate are provided in the cavity.
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