We demonstrate the possibility of photodimerizable chromophores attached to a short alkyl chain as a potential medium for high capacity digital optical storage. A large increase in transmission from 4% to 70% is obtained in 20 s when irradiated with a 5 mW unfocused laser beam at 257 nm in a thin film of 1-(6-Bromohexyl)uracil. Through theoretical simulations, we show that the interaction cross-section is 6 10-18 cm2 at a photon dose of 9 1016 photons cm-2 s-1. We also
investigate the formation of holographic diffraction grating in a film, obtaining an efficiency of 16%, mainly due to a surface relief grating.
We demonstrate the possibility of photodimerizable chromophores attached to a short peptide chain as potential media for high capacity optical storage. The chromophores used in the present case are bromo-, chloro and fluorouracil.
We describe a photodimerization process in organic thin films, for high capacity optical storage in the blue and UV. Neighboring molecules attached through a short peptide chain can be made to undergo cycloaddition. Preliminary experiments performed with anthracene and thymine dipeptides at 360 and 257 nm respectively show that the photo-induced change in absorption is stable both at room temperature, and at elevated temperatures. Very good optical quality films of the monomers can be fabricated.
Polarization holographic read/write and read only demonstrator systems have been developed using ~2 µm thick azobenzene polyester on a card form media. The thin-film holographic system has practical advantages, e.g. high diffraction efficiency, no cross talk between the holograms, reading in reflection mode, no hardware servo, different wavelengths for writing and reading (non-volatile storage), data encryption possibility, no problem with material shrinkage, etc. The candidate azobenzene polyester has good thermal, room temperature and ambient light stability and good optical properties for the purpose of thin film application. Using thin-film holography the possibilities of multiplexing are limited, however, raw data density as high as 2.77 bit/µm2 has been achieved in an optimized Fourier holographic system using high numerical aperture (NA³ 0.74) objective in a 8f arrangement with sparse code modulation and Fourier-filtering at 532 nm. High density polarization holographic demonstrator systems have been developed using ~2μm thick azobenzene polyesters on reflective card form media. FFT computer simulation of the system including saturation model of the material allows optimization of system components including data density and capacity. A raw density as high as 2.77 bit/μm2 has been achieved without multiplexing in a compact, portable read/write sytem at 532 nm allowing more than 1000 readout without data loss. A separate read only system working at 635 nm realizes non-volatile readout and allows card exchange at a data density of 1.3 bit/μm2. Security level of the presents holographic optical card systems can be further increased by using phase encoded reference beam. Advantageous applications of the proposed encrypted holographic card system are also outlined.
We present the improved demonstrator of our rewritable holographic memory card system. High density optical storage is realized in a non-commercial optical set-up. Fourier transformed recording is used in a polarization holographic arrangement realizing reading and writing from the same side of the data carrier which is a modified plastic card. Holograms containing binary information of 300 x 220 bits are as small as 0.0484 square mm. The storage layer is amorphous polyester providing repeated writing and erasure cycles and thousandfold readouts without loss of information. Alternate read only system providing non-volatile storage can be realized using 635 nm laser diode.
Optical storage properties of thin azobenzene side-chain polyester films were examined by polarization holographic measurements. The new amorphous polyester film is the candidate material for the purpose of rewritable holographic memory system. Temporal formation of anisotropic and topographic gratings was studied in case of films with and without a hard protective layer. We showed that the dominant contribution to the diffraction efficiency comes from the anisotropy in case of expositions below 1 sec even for high incident intensity. The usage of the same wavelength for writing, reading and erasing was tested. The ability of azobenzene polyester for rewriting was found satisfactory after many writing-erasing cycles.
Our goal is to develop a re-writable holographic memory card system based on thin film polymer media on credit card size plastic carriers. Data is stored in our system in form of polarization holograms that present high efficiency and excellent suppression of higher orders even for thin material. Data is written on the card in a parallel way using spatial light modulators to encode the object beam that is Fourier transformed by a custom objective lens and interferes with the reference beam (of orthogonal polarization) on the card. We use reflective carrier in order to read out the data from the same side of the card. This allows us to have a compact system and standard ID 1 type carrier card. The optical system and the data organization are optimized to have a data density higher than 1bit/micrometers 2. We expect to pass the limit of 10 bit/micrometers 2 with the introduction of phase coded multiplexing that would provide more than 2Gbyte capacity if using half the card area as active surface.
We present a novel solution for high-density optical storage of data in thin media. The holographic memory card of Optilink provides sixty-fold data density enhancement compared to present commercial LaserCard devices. The 1 - 2 micrometers thin amorphous polyester storage film is capable of rewritable storage using a single laser source for writing and erasing. The polarization holographic principle used in reflection mode requires demanding optical solutions. Successful data evaluations prove applicability of the new system. Density enhancement up to 16 bit/micrometers 2 with the use of 20 - 30 micrometers thick layer is also outlined.
Optical information processing is a very important branch of optics research nowadays. One interesting application is the comparison of two images. These techniques are of interest in many applications such as automatic inspection, remote sensing or in communication processing. Such a comparison by means of optical methods is a well established technique both for coherent and incoherent illumination and various methods are known. But especially the use of incoherent light is often connected with complex setups. We describe a simple method for a correlation technique based on optically induced anisotropy which allows the use of white light or of two mutually incoherent laser beams. The element based on the specific feature of photoanisotropic media. These materials response on the intensity of a linearly polarized light wave only.
A Two-dimensional holographic memory for archival storage is described. Assuming a coherent transfer function, an A4 page can be stored at high resolution in an area of 1 mm2. Recently developed side-chain liquid crystalline azobenzene polyesters are found to be suitable media for holographic storage. They exhibit high resolution, high diffraction efficiency, have long storage life, are fully erasable and are mechanically stable.
Bacteriorhodopsin, a natural occuring photochromic protein present in the purple membrane of certain halophilic bacteria has been shown to posses unique optical properties. The ground state has a broad absorption band (bR) centred at 570 nm (light adapted bacteriorhodopsin) and a metastable state (M) centred at 412 nm with a thermal relaxtion time of 10 ms. The metastable can be stimulated to decay to the ground state through light in 200 ns. The thermal relaxation time can, however, be extended by five orders of magnitude through suitable chemical treatment of the purple membrane, without compromising the stimulated decay of 200 ns. At the same time, there is a concomitant change in the dipole moment accompanying trans to cis isomerization and. charge translocation across the purple membrane. Bacteriorhodopsin is also a highly nonlinear optical material with a large third-order nonlinearity. A nonlinear Kerr coefficient of 10-4 cm2 /W has been reported for this material, and new mutants are reported to possess even higher nonlinearities. This high nonlinerity enables the use of even fairly low- powered lasers to investigate nonlinear optical propagation. The time constant of the nonlinearity is on the order of a few milliseconds. We report in this talk applications of bacteriorhodopsin thin films for holographic storage, coherent-to- incoherent conversion, incoherent-to-coherent conversion, and contrast reversal of images.
We describe novel organic compounds based on polyester and peptide backbones with azobenzenes in the side chain for erasable holographic storage. These materials exhibit high diffraction efficiency, high resolution and long storage life and can be used for holographic storage in a broad spectra window of 415 - 530 nm. In polyester thin film systems with a chiral azobenzene, diffraction efficiencies of about 50% have been achieved with just 300 ms exposure. Through atomic force and near-field optical microscopic investigations, we have found an aggregation process encompassing both the main and side chains to be responsible for the permanent storage in the case of polyesters. The stored information can be erased globally in this case with heat. On the contrary, holograms written in peptide films are not totally erased even after exposure to 250 degree(s)C for one month. However, the information can be locally erased using circularly polarized light. A strong polarization dependent surface relief is observed both for the polyesters and peptides. Through FTIR and surface profile measurements, we further show that irradiation of the films with p- polarized light results in a large surface roughness. We show that in the case of the polyesters the storage is mostly due to optical anisotropy and in the case of the peptide oligomers, both the anisotropy and surface relief are large.
Bacteriorhodopsin (bR) originating from the purple membrane of the bacterium Halobacterium Halobium has been extensively studied during the last few years for a number of optical applications. Extending the lifetime of the intermediate M-state in bR chemically, has been found to improve the sensitometric properties of bR. In this paper, a new method of extending the lifetime of the M-state in the bacteriorhodopsin photocycle is presented. The method pertains to the use of 18- crown-6 ether as an agent to extend the M-state lifetime.
It has been demonstrated that the photo-induced orientation or reorientation of dye-containing liquid-crystalline side-chain (LCSC) polymers can be used for reversible optical data storage. A method which enables the determination of this orientational behavior in addition to the order parameter is infrared dichroism. The present experimental approach uses Fourier- Transform infrared (FTIR) spectroscopy with polarized radiation to determine the orientation of the main chain and side chains in a LCSC polyester with a dodecamethylene spacing of the ester groups in the main chain and six methylene groups in the spacer, after irradiation with an Argon ion laser beam.
We describe a modification of a nonlinear
Mach-Zehnder interferorneter to produce
a sub-Poissonian photon distribution and
an experimental set-up to realize it.
It is shown that it is possible to achieve
a substantial reduction in the photon
number uncertainty with a high power