Patent ID: 6831749
Filing Date: 2004-12-14
Classification: G01R

Abstract:
A current sensor using a Sagnac interferometer comprisinga light source, a first optical branch unit on which light from the light source impinges, a first depolarizer on which light from the first optical branch unit impinges and which emits non-polarized light, a first polarization filter on which light emitted from the first depolarizer impinges and which emits a given linearly polarized light, a second optical branch unit for branching light emitted from the first polarization filter into two beams, an optical phase modulator connected to one branch end of the second optical branch unit, a current sensing coil on which light from the other branch end of the second optical branch unit and light from the optical phase modulator impinge as levorotatory light and dextrorotatory light, a first quarter-wave plate inserted between the optical phase modulator and the current sensing coil, a second quarter-wave plate inserted between the other branch end of the second optical branch unit and the current sensing coil, a light detector connected to said first optical branch unit, a second depolarizer and a second polarization filter connected in series between the optical phase modulator and the first quarter-wave plate; and a third depolarizer and a third polarization filter connected in series between the other branch end of the second optical branch unit and the second quarter-wave plate, the second depolarizer being connected to the optical phase modulator side and the third depolarizer being connected to the second optical branch unit side.