The diffractive optical element (DOE) has the transformation function of wavefront, and its applications are forming or
homogenization of beam, and aberration correction, and so on. In this study, we evaluate possibility as storage
application of the DOE. The optical data storage using the DOE is thought of as a kind of holographic data storage
(HDS). In the HDS, digital data is recorded and read out as modulated 2-dimensional page data, instead of bit-by-bit
recording in conventional optical storages. Therefore, HDS actualize high data transfer rate. We design and optimize
phase distribution of the DOE using the iterative method with regularization. In the optimization process, we use
iterative Fourier transform algorithm (IFTA) that is known as Gerchberg–Saxton (GS) algorithm. At this time, the
regularization method is adopted to suppress minute oscillation of the diffraction pattern. Designed and optimized DOE
is fabricated by ultraviolet (UV) nanoimprinting technology. High productivity can be expected by adopting
nanoimprinting technology. DOEs are duplicated on the silicon (Si) substrate as reflection-type elements. Fabricated
DOE is evaluated in the experiment. We verify that DOE for optical data storage can be actualized through our approach.
The research and development of the holographic data storage (HDS) is advanced, as one of the high-speed, mass storage systems of the next generation. Recently, along the development of the write-once system that uses photopolymer media, large capacity ROM type HDS which can replace conventional optical discs becomes important. In this study, we develop the ROM type HDS using a diffractive optical element (DOE), and verify the effectiveness of our approach. In order to design DOE, iterative Fourier transform algorithm was adopted, and DOE is fabricated with electron beam (EB) cutting and nanoimprint lithography. We optimize the phase distribution of the hologram by iterative Fourier transform algorithm known as Gerchberg–Saxton (GS) algorithm with the angular spectrum method. In the fabrication process, the phase distribution of the hologram is implicated as the concavity and convexity structure by the EB cutting and transcribed with nanoimprint lithography. At this time, the mold is formed as multiple-stage concavity and convexity. The purpose of multiple-stage concavity and convexity is to obtain high diffraction efficiency and signal-to-noise ratio (SNR). Fabricated trial model DOE is evaluated by the experiment.
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