FREQUENCY AND PHASE SWEPT HOLOGRAMS IN SPECTRAL HOLE-BURNING MATERIALS

A new hologram type in spectral hole-burning systems is presented. Dur ing exposure, the frequency of narrow-band laser light is swept over a spectral range that corresponds to a few homogeneous linewidths of th e spectrally selective recording material. Simultaneously the phase of the hologram is adjusted as a function of frequency-the phase sweep f unction. Because of the phase-reconstructing properties of holography, this recording technique programs the sample as a spectral amplitude and phase filter. We call this hologram type frequency and phase swept (FPS) holograms. Their properties and applications are summarized, an d a straightforward theory is presented that describes all the diffrac tion phenomena observed to date. Thin FPS holograms show strongly asym metric diffraction into conjugated diffraction orders, which is an unu sual behavior for thin transmission holograms. Investigations demonstr ate the advantages of FPS holograms with respect to conventional cw re cording techniques in frequency-multiplexed data storage. By choosing appropriate phase sweep functions, various features of holographic dat a storage can be optimized. Examples for cross-talk reduction, highest diffraction efficiency, and maximal readout stability are demonstrate d. The properties of these FPS hologram types are deduced from theoret ical considerations and confirmed by experiments.