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.
We describe two novel modulation techniques for collinear holographic data encoding, employing a spatial light
modulator (SLM) based on twisted nematic LCD. In the Fourier transform holographic storage system, the reference
beam in the outside part and the object beam in the inside part are simultaneously modulated by one single SLM, with
different modulation techniques. In one of the modulation methods, the reference beam is phase modulated with a
circular blazed grating pattern, and then diffracted into the central part to interfere with the amplitude modulated object
beam. Multiple holograms can be recorded on the same location with reference beams of different grating period.
Another modulation method is to modulate both the reference beam and the object beam with pure phase modulation by
the SLM. The binary ones are encoded with random phase shift from 0 to 2π, while the binary zeroes are encoded with a
constant phase of 0. When the dc component of the spatial frequency generated by the binary zeroes is blocked, a
homogeneous hologram will be obtained, and the amplitude object will be reconstructed directly. In this paper, both of
the two modulation methods are performed theoretically and experimentally. From the experimental results, it can be
seen that the blazed-grating modulation technique gets a higher efficiency, while pure phase modulation method can
reconstruct the images with more uniform intensity. These techniques are demonstrated to be attractive for applications
in data storage and encryption systems.
A novel approach for optical beam distribution into a 2-dimensional (2-D) packaged fiber arrays using 2-D Dammann gratings is investigated. This paper focuses on the design and fabrication of the diffractive optical element (DOE) and investigates the coupling efficiencies of the beamlets into a packaged V-grooved 2x2 fibre array. We report for the first time experimental results of a 2-D optical signal distribution into a packaged 2x2 fibre array using Dammann grating. This grating may be applicable to the FTTH network as it can support sufficient channels with good output uniformity together with low polarization dependent loss (PDL) and acceptable insertion loss. Using an appropriate optimization algorithm (the steepest descent algorithm in this case), the optimum profile for the gratings can be calculated. The gratings are then fabricated on ITO glass using electron-beam lithography. The overall performance of the design shows an output uniformity of around 0.14 dB and an insertion loss of about 12.63 dB, including the DOE, focusing lens and the packaged fiber array.