Apparatus for electronically measuring the angle of rotation of the polarization plane of a linearly polarized light beam produced by passage of the beam through a magneto-optical element subjected to a magnetic field to be measured

Claim 1

Apparatus for measuring the current flowing through a conductor comprising a magneto-optical element including a coil through which the current is passed to produce a corresponding magnetic field, means for passing a beam of linearly polarized light through said magneto-optical element which effects a rotation of the polarization plane proportional to the magnetic field, an optical divider into which said light beam is directed after leaving said magneto-optical element, said divider serving to split said light beam into two partial light beams, means directing one of said partial beams through a first polarizer to a first photo-detector, means directing the other partial beam through a second polarizer to a second photo-detector, said second polarizer transmitting light polarized in a direction rotated by about 45* relative to that of said first polarizer, multipliers individual to and receiving the respective outputs from said first and second photo-detectors, a local oscillator having its output connected into said multipliers to mix the respective detector signals with a sinusoidal oscillation signal from said oscillator, an adding member to which the outputs from said multipliers are connected, and a frequency demodulating device to which the output from said adding member is connected.