| CPC G02B 5/26 (2013.01) [G02B 5/0816 (2013.01); H10F 39/024 (2025.01); H10F 39/8067 (2025.01)] | 20 Claims |

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1. A filter comprising:
a substrate;
a first mirror comprising a stepped surface of the first mirror;
a monolithic spacer disposed on the stepped surface of the first mirror; and
a second mirror disposed on a flat surface of the monolithic spacer,
wherein the first mirror and the second mirror sandwich at least a portion of the monolithic spacer, and
wherein the stepped surface of the first mirror is between the substrate and the second mirror.
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