SYSTEMS AND METHODS FOR A HOLLOW CORE RESONANT FILTER

Systems and methods for a hollow core resonant filter are provided. In one embodiment, a hollow-core fiber resonant cavity comprises: a hollow-core fiber having a first and second ends; a first and a second pigtail fiber each of solid core fiber material. A tip of the first pigtail is optically aligned with the first-end to couple light from the first pigtail to the hollow core fiber across a first free-space gap. A tip of the second pigtail is optically aligned with the second-end to couple light from the second pigtail to the hollow-core fiber across a second free-space gap. The tip of the second pigtail is coated to reflect light received from the second-end back across the second free-space gap into the second-end. The tip of the first pigtail is coated to reflect light received from the first-end back across the first free-space gap into the first-end.