We have been investigating wavelength multiplexed holograms in persistent spectral hole burning (PHB) materials. We have examined PHB hologram characteristics in some organic PHB materials to show guides to produce more suitable PHB materials for wavelength multiplexed holograms. The examined characteristics were diffraction efficiency, sensitivity and the capability of wavelength-multiplexing and the distribution of diffraction efficiency at the temperature of 4.2 K. Typical characteristics in the examined materials at 4.2 K were as follows: (1) sensitivity of > 0.1 mJ/cm2, (2) diffraction efficiency of < 0.3%, and (3) the holograms' intervals of > 15 GHz where adjacent holograms could be formed most closely without cross talk. Hundreds of holograms can be stored without crosstalk with each other in calculation. Furthermore, we showed that wavelength multiplexed holographic storage of tens of 2- and 3-D images could be performed at the different laser frequencies at the temperature of 4.2 K. The continuous 3D retrieval of the images of a moving object could be performed by scanning laser frequency continuously.
The capacity of optical memories can be enhanced by using extra dimensions to store the signals besides the spatial dimension. We have investigated the photochemical persistent hole burning (PHB) reaction in a series of quinone derivatives as the guest molecules. In wavelength dimension, we showed that 600 ultra-high multiple spectral holes can be recorded in a double layered system. To increase the multiplicity of spectral holes, we intended to use electric field as another dimension. We have investigated the influence of electric field effect (Stark effect) in the PHB reaction characteristics. We observed for the first time with the quinone derivative systems that the burnt holes were broadened and then diminished when the applied electric field was changed, and that they reappeared when the applied electric field was changed again to the initial value. Multiple hole formation in the electric field dimension and optical modulation by electric field were also achieved.
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