Novel multiplexed coaxial holographic storage technique

We propose a novel multiplexed holographic storage technique in a coaxial alignment based on dually modulated spatial light modulator (SLM). In this paper, a spatial light modulator based on a high-resolution twisted nematic liquid crystal display is used to record both reference and object beams. We have programmed the active region of the SLM, so that some part will work in the phase modulation mode and some part will work in the amplitude modulation mode. In our coaxial holography design, the central ring area is reserved for amplitude modulation of the object beam while the outer rings/annuli will cater for various phase modulation of the reference beams for multiplexed storage. A number of objects can then be stored/encoded in the same location of the hologram and later be reconstructed using the appropriate reference beams. Three different methods of phase modulating the reference beam are investigated, viz. the diffraction of blaze grating, the diffusion of random speckle and beam shaping. The coaxial multiplexing holographic data encoding and reconstruction are carried out experimentally in a single-beam 4-f setup using He-Ne laser with a wavelength of 632.8nm. A 2-D holographic medium is used for recording and the reconstructed images are captured by a camera on the image plane. From the results of simulation and experiment, it can be seen that all the images are reconstructed clearly and separately, demonstrating the feasibility of our proposed novel technique of coaxial multiplexed storage/encoding.