KEYWORDS: Signal to noise ratio, Binary data, Digital holography, Holography, Data storage, Error analysis, Algorithm development, Computer programming, Forward error correction, Detection and tracking algorithms
We present a new class of modulation codes based on permutation coding which satisfy the channel coding constraint
suitable for the digital holographic data storage, and which simultaneously provide strong error correction at high code
rates. The channel decoding scheme is based on the true maximum likelihood detection realized using a newly
developed efficient algorithm. The sparse permutation codes of large block sizes closely approach the information
theoretic limits for the binary channel data capacity.
Aluminum oxide single crystals doped with magnesium and carbon and having aggregate vacancy defects are proposed
for volumetric fluorescent bit-wise data storage. A unique optical recording technique, which utilizes sequential two-photon
absorption and incoherent confocal fluorescence detection, is utilized for nondestructive readout. The new
medium is exceptionally environmentally and temporally stable and can be recorded with diode lasers. Recent static and
dynamic test stand results are reported, including demonstration of 20 layers of data and random mark-length recording
with a clear "eye pattern" and satisfactory carrier-to-noise ratio.
A single meniscus aspherical lens and air-spaced spherical lenses having negative and positive
powers are identified as minimum aberration configurations for page-based holographic recording
systems. Further correction of pupil aberrations makes the lens system usable both for holographic and
for surface recording, and the lens is realizable by using two air-spaced apsherics. Two air-spaced
apsherics can attain high an imaging NA of 0.7 for holographic recording only, and an NA of 0.45 for a
combination of holographic and surface recording.
By using a direct-write e-beam technique with liquid phase epitaxy LiNbO3 thin films, we have successfully produced sub-micron domain structures for achieving dynamically switchable filters in a periodically poled lithium niobate (PPLN) waveguide. Sub-micron domain (~200 nm) structures with a period ~1.2 um are realized in liquid phase epitaxy LiNbO3 films on congruent LiNbO3 substrates by using the direct-write e-beam domain engineering method. In comparison with single crystal congruent LiNbO3 (CLN) and stoichiometric LiNbO3 (SLN), we show that LPE LiNbO3 is the most promising material for producing superior domain regularities and finer domain sizes than single crystals. A physical model is presented to qualitatively explain the observed differences in structure and regularity of the induced periodic domains among the three different materials we studied. We postulate that the higher Li/Nb ratio in LPE LN than in CLN enhances domain inversion initiation. Also, we believe that the vanadium incorporation and distortion due to the lattice mismatch between films and substrates enhance electron localization, domain wall pinning and domain nucleation in LPE materials, giving rise to better structures.
Recording and readout in two-photon absorbing Al2O3:C,Mg optical data storage media was investigated for crystals having different concentrations of color centers and for two orientations of the crystal optical c-axis. The writing and reading efficiency of the media was increased by taking into account the anisotropy of optical absorption and by rotating the laser light polarization vector synchronously with the disk rotation. The parameters for writing and non-destructive reading of the bits in the volume of a single crystal disk are reported.
We present theoretical calculations and experimental measurements of silicon micromachining rates, efficiency of laser pulse utilization, and morphology changes under UV nanosecond pulses with intensities ranging from 0.5 GW/cm2 to 150 GW/cm2. Three distinct irradiance regimes are identified based on laser intensity. At low intensity, proper gas dynamics and ablation vapor plume kinetics are taken into account in our theoretical modeling. At medium high intensity, we incorporate the proper plasma dynamics, and predict the effects of the laser generated vapor plasma and the electron hole plasma on the laser-matter interaction. At even higher intensity, we attribute the observed increased ablation rate to energy re-radiation from the laser heated hot plasma, the strong shock wave, and the accompanied strong shock wave heating effects. Experimentally measured data in these regimes agree well with our calculations, without changing parameters in the calculations used for the three regimes. Our results can be applied toward quantitatively characterize the behavior of ablation results under different laser parameters to achieve optimal results for micromachining of slots and vias on silicon wafers.
Two-photon absorption in new aluminum oxide single crystals is used for recording single bits in multiple layers while one-photon absorption and a confocal fluorescence detection scheme is applied for data readout.
Spectroscopic properties of new aluminum oxide crystals for volumetric optical data storage are investigated. Magnesium impurity and double oxygen vacancy defects are responsible for the main optical properties of the new material. Sequential two-photon absorption and ionization of color centers followed by capture of a free electron on a deep trap is a suggested mechanism for writing information. One-photon absorption and non-destructive readout using reconstruction of recorded holograms or a confocal fluorescence detection scheme are proposed.
Periodic copying and electrical fixing are presented as two practical methods for controlling the decay rate of volume photorefractive holograms in the implementation of optical image processing systems.