A current sensor based on optical sensing in a fiber coil, comprising:
- a light source that produces probe light;
- a first polarization splitting device coupled to receive the probe light from the light source and produces light in a first polarization only as a first polarized light beam and light in a second, different polarization only as a second polarized light beam;
- a first Faraday rotator placed to receive only the first polarized light beam from the first polarization splitting device, without receiving the second polarized light beam, to produce an output light beam with a rotated polarization;
- a second polarization splitting device coupled to receive the output light beam from the first Faraday rotator to produce light in a third polarization only as a third polarized light beam and light in a fourth polarization different from the third polarization as a fourth polarized light beam;
- a second Faraday rotator placed to receive the third polarized light beam from the second polarization splitting device to produce a second output light beam;
- a fiber line coupled to receive the second output light beam from the Faraday rotator and configured to include a sensing fiber coil that is wrapped around a segment of a conductor carrying a current to be measured to sense a magnetic field produced by the current in the conductor;
- a Faraday reflector coupled to receive light from the sensing fiber coil and to reflect the received light back into the sensing fiber coil to return to the second Faraday rotator which transmits the returned light to the second polarization splitting device which splits the returned light into light in the third polarization and light in the fourth polarization;
- a first optical detector coupled to receive and detect the returned light in the fourth polarization from the second polarization splitting device which directs the returned light in the third polarization to transmit through the first Faraday rotator to reach the first polarization splitting device;
- a second optical detector coupled to receive and detect the returned light in the second polarization from the first polarization splitting device;
- a measurement module that receives detector outputs from the first and second optical detectors to obtain information of the current.