T. Ujvari

A secure data storage system based on phase-encoded thin polarization holograms

A novel secure data storage architecture based on phase-encoded, thin film, Fourier-type polarization holograms is reported. Efficient data encryption and verification can be obtained by phase modulation of the reference wave introduced by a phase-type spatial light modulator that is imaged onto the hologram plane. A physical model is formulated including phase-encoding, non-linear storage medium behaviour and features of the proposed optical system. A method is proposed and implemented in the form of a custom modelling tool for generating code sets optimal in terms of code number and security level. The utility of the architecture and the achievable security level are experimentally demonstrated.

Polarization holographic data storage using azobenzene polyster as storage material

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.

Holographic data storage in thin polymer films

We present our results on polarization holographic data storage in thin azobenzene side chain polymers. Two different systems have been demonstrated: a read only system with red diode laser and a read&write system with green frequency doubled solid state lasers. Error free operation have been proved at 2.77 bit/µm2 data density. We have also demonstrated enhanced security holographic storage by applying phase coded reference waves imaged onto the hololographic storage material. We also present the concept of extending the principle to multilayer holographic storage.

Data storage on holographic memory card

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.

New results in holographic data storage with organic polymer films

High density polarization holographic demonstrator system has been developed using ~2 µm thick azobenzene polyesters on reflective card form media. One possible development of the system is the introduction of phase encoding into the reference arm that provides enhanced security applications. Simulations were carried out with a custom computer program based on mathematical model of the system to generate code sets optimal in terms of code number and security level. The model is suitable also for the prediction of expected tolerances necessary before the definition of a working system. Performed experiments proved applicability of the model for possible system considerations. We also present our concept of extending thin-film holographic principle to multilayered holographic storage of increased capacity.

Holographic Data Storage with Organic Polymer Films

Up to this date only limited attempts has been made to employ the benefits of optical data storage on credit card sized information carriers, although cards represent a rapidly growing part of the market. Applications like personal medical data carrier cards, ID cards, catalogues, service cards, public documentation services etc. demand higher data capacities and device performances that are probably not within the reach of today’s magnetic and IC cards. For these applications we are developing a new Holographic Memory Card (HMC) system [1] that provides the advantages of optical storage in a card format in order to largely exceed the performances of present cards. Compared to bit-serial optical data storage (employes in CD, DVD and existing optical cards), our page organised holographic storage technology presents a number of advantages that can further increase the robustness, cost effectiveness, data density and transfer rates. Holographic data carriers have higher immunity to local defects, lower card positioning and fabrication tolerances, eliminate the problems related to focus and track servo mechanisms and naturally fit to parallel access read and write systems.

Storage Density Enhancement in Holographic Memory Card System

Our goal is increase the storage density of our rewritable holographic memory card system based on thin film polymer media on credit card size plastic carriers. We use computer simulation to optimize the illumination and the Fourier filtering in order to have optimal trade-off between bit error rate and data density.We also investigate the possibility of using gray scale data coding.

Phase-coded recording in polarization holograms for data multiplexing and encryption

We introduce a new physical model for description of thin polarization holograms recorded and reconstructed with complex reference beams. Next we apply this model for two fundamentally different arrangements supposed to be used in a data storage system based on phase coded thin polarization holograms. On the basis of the model, we construct some computer programs for simulation of the storage system and optimization of the phase codes. We investigate the feasibility of multiplexed and security encrypted data storage in the form of thin polarization holograms based on the phase encoding method.