Sub-wavelength grating structures made in an isotropic medium induce form birefringence effects with the induced optical axis parallel to the grating vector. The phase shift between the two orthogonal electric field components exiting this grating varies linearly with the thickness of the grating. When a grating with sub-wavelength period is formed on a uniaxial birefringent material with the grating vector aligned parallel to is natural optical axis, the total effect is enhanced birefringence for the material. Smaller thickness of the material is required to achieve the same phase shift. If the natural optical axis and the induced optical axis lie within the surface plane and have an angle between them, the phase shift varies nonlinearly with the thickness of the grating.
The rigorous coupled-wave model is used to determine the polarization of diffracted waves from two superimposed volume gratings with their grating vectors in the same plane. The phase relations used in computing the phase shift of diffracted beams are derived. The relative phase difference between orthogonal components of the + 1 diffracted order is computed for a single grating and two superimposed gratings. The level of induced ellipticity in polarization is greater for light diffracted from a multiplexed grating than from a single grating. Experimental and theoretical results show that the phase shift of a beam diffracted from two superimposed gratings has both positive and negative values.
Magneto-optic data storage is an emerging read/write storage technology with many potential applications in consumer computer systems. One of the limitations to this development is the cost of the read/write head. This device must provide high optical power during the write phase, and sense a small change in the polarization of the beam reflected from an MO disk during the read operation. Typically the head consists of many individual optical components which must be aligned and accurately assembled, and contributes significantly to system cost. Two important elements in the head are a leaky beamsplitter and a polarization beamsplitter. In this presentation we discuss the design parameters and performance characteristics for these beamsplitters formed in dichromated gelatin. Experimental grating performance is also given.