A resonant fiber optic gyroscope (RFOG) comprising: a ring resonator including a fiber coil fabricated from a first type of hollow core fiber; at least one light source to produce at least two light beams, wherein a first light beam of the at least two light beams is configured to travel in a clockwise direction in the ring resonator and a second light beam of the at least two light beams is configured to travel in a counterclockwise direction in the ring resonator; a filter resonator assembly coupled between the at least one light source and the ring resonator, the filter resonator assembly further including: at least two short pieces of optical fiber, wherein the at least two short pieces of optical fiber are shorter in length than the fiber coil, and wherein the at least two short pieces of optical fiber are fabricated from the first type of hollow core fiber; and a plurality of reflective devices, wherein prior to the first light beam and the second light beam entering the ring resonator, the first light beam and the second light beam propagate between the plurality of reflective devices until they excite a fundamental mode of the hollow core fiber within the ring resonator; and a tuning device configured to change a distance between pairs of reflective devices in the plurality of reflective devices to tune the filter resonator assembly to the fundamental mode, the pairs of reflective devices respectively associated with one of the at least two short pieces of optical fiber. a ring resonator including a fiber coil fabricated from a first type of hollow core fiber; at least one light source to produce at least two light beams, wherein a first light beam of the at least two light beams is configured to travel in a clockwise direction in the ring resonator and a second light beam of the at least two light beams is configured to travel in a counterclockwise direction in the ring resonator; a filter resonator assembly coupled between the at least one light source and the ring resonator, the filter resonator assembly further including: at least two short pieces of optical fiber, wherein the at least two short pieces of optical fiber are shorter in length than the fiber coil, and wherein the at least two short pieces of optical fiber are fabricated from the first type of hollow core fiber; and a plurality of reflective devices, wherein prior to the first light beam and the second light beam entering the ring resonator, the first light beam and the second light beam propagate between the plurality of reflective devices until they excite a fundamental mode of the hollow core fiber within the ring resonator; and a tuning device configured to change a distance between pairs of reflective devices in the plurality of reflective devices to tune the filter resonator assembly to the fundamental mode, the pairs of reflective devices respectively associated with one of the at least two short pieces of optical fiber. at least two short pieces of optical fiber, wherein the at least two short pieces of optical fiber are shorter in length than the fiber coil, and wherein the at least two short pieces of optical fiber are fabricated from the first type of hollow core fiber; and a plurality of reflective devices, wherein prior to the first light beam and the second light beam entering the ring resonator, the first light beam and the second light beam propagate between the plurality of reflective devices until they excite a fundamental mode of the hollow core fiber within the ring resonator; and a tuning device configured to change a distance between pairs of reflective devices in the plurality of reflective devices to tune the filter resonator assembly to the fundamental mode, the pairs of reflective devices respectively associated with one of the at least two short pieces of optical fiber.