Methods and apparatus for optically measuring polarization rotation of optical wavefronts using rare earth iron garnets

A magneto-optic sensor element comprising:

• a crystal substrate which is optically transparent with respect to the wavelength of an incident polarized wavefront from a sensor light source, said crystal substrate further comprising a rare-earth iron garnet crystal;
• a dielectric thin-film mirror deposited one side of said rare-earth iron garnet crystal;
• and,
• an anti-reflection coating of thickness 0<=t<=N*.lambda./4, where lambda is the primary wavelength of an incident polarized wavefront and N is an odd-integer multiple such that 1<N<=∞, deposited on the opposite end of the rare-earth iron garnet substrate.

A magneto-optic sensor probe comprising:

• a crystal substrate;
• a thin-film reflective surface on a first face of said crystal substrate;
• a rare-earth iron garnet thin-film on a second face of said crystal substrate, said second face opposing said first face;
• a graded-index lens for coupling optical energy into said crystal substrate;
• and,
• a optical fiber coupled with said graded-index lens.

A fiber optic sensor system, comprising:

• a light source for emitting a light beam;
• a polarizing means for polarizing said light beam;
• fiber optic coupler;
• crystal substrate having a rare-earth iron garnet thin-film on a face thereof;
• graded index lens assembly optically coupled to said fiber optic coupler;
• beamsplitter optically coupled to said graded index lens assembly;
• and,
• detector means for converting optical energy into electrical energy.