Ji-deog Kim

Compensation for pixel-mismatch errors in shift- multiplexed holographic data storage

To read out correct data from shift-multiplexed holographic data storage, we propose a novel method of pixel matching by use of a tiny plane-parallel refraction plate placed in the path of converging readout beams. Tilting the refraction plate produces a shift in the lateral position of the readout beam incident upon the holographic storage disk, leading to compensation for pixel-mismatch errors by an improvement in bit-error rate of 3 orders of magnitude.

Metamorphosis of photonic bandgaps

We found a nontrivial metamorphosis of photonic band gaps during interpolation between two photonic crystals with two different length scales. The interpolation is parametrized by a dielectric constant of the columns inserted at the positions that are appropriately chosen in each unit cell of the starting photonic crystal. For an instance of the metamorphosis, the first band gap that is present at the beginning gradually shortens and disappears during the interpolation, while the second band gap which is initially absent begins to appear and eventually becomes a first band gap. This mechanism of opening and closing of the photonic band gaps can be used when designing tunable photonic crystals.

Cross talk in holographic memories with lensless phase-conjugate holograms

Recently holographic memory with lensless phase-conjugate holograms has attracted much attention because it opens up the possibility of compact holographic memories. We investigate cross-talk noise in compact holographic memories with angular multiplexing. It turns out that the optimum angular separation is the same as that for the Fourier plane hologram in the leading order and that the noise-to-signal ratio is independent of the positions in the output plane, similar to the case of the image plane hologram.

A Multiplexing Method using HOE`s for Bit-Type Holographic Data Storages

The bit type holographic data storage is known to have many advantages in instrumentation for its compactness and simplicity, when compared to the 2-D page type holographic data storage. But it requires various multiplexing method for one bit hologram to achieve high storage densities. We propose an optical architecture for bit type holographic data storage which utilizes peristrophic and angular multiplexing simultaneously. Selectivity and characterization are analyzed for the proposed architecture. The possible number of multiplexing(72 bit holograms) and maximum storage densities calculation is confirmed experimentally.

On-axis servo control in pickup actuator for disk type holographic data storage

In order to read correct data from a disk-type holographic storage medium, it is very important to implement a servo-control in the pick-up module, as in a conventional CD-ROM. We propose a novel servo-control method using a glass plate on the optical axis, which is able to compensate the mechanical errors coming from wobbling of holographic disk and spindle motor. By rotating the glass plate within 10 degrees, we can reduce the reading errors of 200 to 15 .

Servo control with a flat glass tilt in pickup actuator for holographic data storage

In order to read out correct data from a disk-type holographic storage system, it is very important to implement a servo control in pickup modules, like as in conventional CD-ROM and DVD-ROM. We propose a novel servo-control method by use of a glass-plate on optical axis, which is able to compensate readout errors mainly coming from mechanical wobbling of the holographic disk. By rotating the glass-plate within ± 10 degrees, we can reduce the readout position-errors of ± 200 μm to ± 15 μm.

A new structure of photonic bandgaps: metamorphosis

Photonic crystals with two different length scales are known to have a simple scaling property under the interpolation parametrized by a length scale s that the frequencies of eigenmodes scale by the inverse of s. We found that photonic crystals can have a nontrivial transformation property of metamorphosis under a certain interpolation. During the metamorphosis, the first bandgap that is present at the beginning gradually shortens and disappears, while the second bandgap which is initially absent begins to appear and eventually becomes a new first bandgap.

From optical MEMS to photonic crystal

This paper presents the emergence of photonic crystals as significant optomechatronics components, following optical MEMS. It is predicted that, in the coming years, optical MEMS and photonic crystals may go through dynamic interactions leading to synergy as well as competition. First, we present the Structured Defect Photonic Crystal (SDPCTM) devised by the authors for providing the freedom of designing photonic bandgap structures, such that the application of photonic crystals be greatly extended. Then, we present the applications of optical MEMS and photonic crystals to displays and telecommunications. It is shown that many of the applications that optical MEMS can contribute to telecommunications and displays may be implemented by photonic crystals.

Effects of storing defocused Fourier plane holograms in three-dimensional holographic disk memories

We show that, when defocused Fourier plane holograms are stored in threedimensional holographic disk memories, there exists an optimal pixel pitch that makes the area storage density per hologram maximize.