Application of the fast-Fourier-transform-based volume integral equation method to model volume diffraction in shift-multiplexed holographic data storage.

Numerical simulation of diffraction on thick holographic gratings in shift-multiplexed optical data storage application is presented. The grating is generated by the interference of a spherical reference wave and a plane signal wave corresponding to a single pixel of the input data page. To describe diffraction on this weak-index-modulated grating, we use the volume integral equation in the first Born approximation. This description yields a convolution integral that can be efficiently evaluated by a 3D fast Fourier transform (FFT) technique. For a 51.2 microm recording layer thickness, a serial-divided single personal computer code was built based on parallel FFT coding principles. Diffracted electric field and Poynting-vector distributions are calculated for probe beams spatially shifted with respect to the reference beams. The shift selectivity curves show significant differences from previous analytical calculations based on paraxial propagation and infinite gratings, as they have monotonic decrease in all three directions instead of sinclike functions with Bragg nulls. With the chosen numerical aperture of 0.6 and linear polarization, both the scalar and vector calculations provided similar results within 5%.

Difference displacement measurement by digital holography by use of simulated wave fronts.

A concept called fringe compensation was first presented in phase-shifting electronic speckle-pattern interferometry. We apply a similar principle to digital holographic interferometry; here the phase of a wave front is known and can be manipulated. The basic mathematical formulation of fringe compensation and some experimental results are shown with relatively large, simple rigid-body rotation and circular membrane deformation.