Polarization properties of gratings made in uniaxial birefringent materials

The diffraction characteristics of light from gratings formed in anisotropic volume and surface-relief gratings are examined. The rigorous coupled-wave equations for computing diffraction efficiencies and polarization of light from a volume grating formed in anisotropic substrates are derived. A grating made in a uniaxial birefringent material with its grating vector within the plane of incidence has the unique property that the incident and diffracted light may have different polarization. A holographic polarization selective grating was designed and made in dichromated gelatin and experimentally tested in a magneto-optic head tester. The performance of the grating was compared to that of a polarization beamsplitter cube. The coupled-wave equations for anisotropic volume gratings are modified to compute efficiencies from surface relief gratings. The method involves applying the Fourier series expansion on the nine permittivity elements in a tensor and subtracting the corresponding elements in the tensor describing the adjacent medium The enhanced birefringence effects which result from sub-wavelength period gratings made in a uniaxial material are theoretically investigated. When the natural optical axis and the induced optical axis are parallel or perpendicular to each other within the surface plane, the phase shift varies linearly with the thickness of the grating. When the two axes have an angular separation between them and lie within the surface plane, the phase shift varies nonlinearly with the thickness of the grating.