Fiber optic current sensor and method for sensing current using the same

A fiber optic current sensor comprising:

• a substrate;
• first and second tunable light sources on the substrate and operable to emit respective first and second beams of light;
• a recirculator on the substrate and configured such that the first and second beams of light are transmitted therethrough;
• an optical fiber having first and second opposing ends and a hollow passageway therethrough, at least one end of the optical fiber being connected to the substrate and the optical fiber being arranged such that, after being transmitted by the recirculator, the first beam of light enters the first end of the optical fiber and is emitted from the second end of the optical fiber onto the recirculator and the second beam of light enters the second end of the optical fiber and is emitted from the first end of the optical fiber onto the recirculator, a portion of the first beam being reflected by the recirculator into the first end of the optical fiber and a portion of the second beam being reflected by the recirculator into the second end of the optical fiber such that the optical fiber and the recirculator jointly form a resonant optical loop with an opening therethrough, the first beam propagating around the resonant optical loop in a clockwise direction and the second beam propagating around the resonant optical loop in a counterclockwise direction, and at least some of the first beam and at least some of the second beam being transmitted by the recirculator;
• a Faraday sensitive material positioned in the hollow passageway, an index of refraction of the Faraday sensitive material changing from a first value to a second value in the clockwise direction of light propagation and from a third value to a fourth value in the counterclockwise direction when a current flows through the opening of the optical loop;
• first and second photo-detectors on the substrate arranged to capture the respective at least some of the first and second beams of light;
• and
• a processor on the substrate and in operable communication with the first and second light sources and the first and second photo-detectors and configured to:
• tune the first and second tunable light sources;
• calculate a difference between resonance frequencies for the clockwise and counterclockwise directions around the optical loop;
• and
• determine a current flowing through the opening in the optical loop based on the difference between the resonance frequencies.

A method for sensing current comprising:

• arranging a recirculator and an optical fiber having first and second opposing ends such that a first beam of light that is transmitted by the recirculator enters the first end of the optical fiber and is emitted from the second end of the optical fiber onto the recirculator and a second beam of light transmitted by the recirculator enters the second end of the optical fiber and is emitted from the first end of the optical fiber onto the recirculator, wherein a portion of the first beam is reflected by the recirculator into the first end of the optical fiber and a portion of the second beam is reflected by the recirculator into the second end of the optical fiber such that the optical fiber and the recirculator jointly form a resonant optical path loop with an opening therethrough, the first and second beams of light propagating around the resonant optical path loop in respective first and second directions;
• positioning a Faraday sensitive material, having an index of refraction and a Verdet Constant, within the optical path loop such that the first and second beams of light pass therethrough;
• conducting a current through the opening in the optical path loop, said current conduction causing the index of refraction of the Faraday sensitive material to change from a first value to a second value for light propagation in the first direction and from the first value to a third value for light propagation in the second direction;
• determining first and second resonance frequencies for the respective first and second directions of propagation;
• and
• calculating the current based on a difference between the first and second resonance frequencies.