Emoke Lorincz

Amplitude, phase, and hybrid ternary modulation modes of a twisted-nematic liquid-crystal display at ∼400 nm

Applicability of a commercial twisted-nematic liquid-crystal display is examined at ∼400 nm. Different modulation modes predicted by Jones-matrix calculus are experimentally tested. High contrast amplitude modulation with negligible loss, high contrast and low loss hybrid ternary modulation, and 1.5π continuous phase delay without intensity modulation and with low loss are presented. Simulation results of a 4f holographic system prove the usefulness of the high contrast for amplitude modulation, and the importance of π phase difference between high transmission white levels in a hybrid ternary modulation.

Physics and technology of optical storage in polymer thin films

Abstract We discuss different strategies for optical storage of information in polymeric films. An outline of the existing trends is given. The synthesis and characterization of side-chain azobenzene polyester films for holographic storage of information is described. A compact holographic memory card system based on polarization holography is described. A storage density of greater than 10MB/cm 2 has been achieved so far, with a potential increase to 100MB/cm 2 using multiplexing techniques and software correction. Finally the role of surface relief in azobenzene polymers on irradiation with polarized light is mentioned.

Modeling of multilayer microholographic data storage

We focus on the investigation of multilayer recording in microholographic data storage. We have developed a numerical model for calculating the electromagnetic scattering from thick microholographic gratings using the Born approximation and the direct volume integral. The signal-to-noise ratio and bit error rate were calculated to estimate the noise arising from interlayer and interhologram cross talk. Measurements were done to prove the validity of the model. The results of our calculations and the measurements show good agreement. We present the application of the model to the investigation of confocal filtering at the image plane and to the evaluation of positioning and wavelength tolerances.

Hybrid multinary modulation using a phase modulating spatial light modulator and a low-pass spatial filter.

We propose a method for performing binary intensity and continuous phase modulation of beams with a spatial light modulator (SLM) and a low-pass spatial filtering 4-f system. With our method it is possible to avoid the use of phase masks in holographic data storage systems or to enhance the phase encoding of the SLM by making it capable of binary amplitude modulation. The data storage capabilities and the limitations of the method are studied.

Modeling and Optimization of Scintillator Arrays for PET Detectors

A new Zemax model has been developed, which reliably predicts the light output of scintillator crystal pins for positron emission tomography. Different configurations, including pin shape, surface finish and reflector types are investigated. The simulations use the actual measured wavelength-dependent parameters of the scintillator crystal, of the reflector and of the PMTs components. Good agreement is demonstrated between simulated and measured light output figures for 33 different pin configurations. The highest light output was found by both simulation and experiment for the pins with polished superficies (either polished or diffuse ¿-side) with a non-coupled high reflectivity specular reflector around the superficies and an optically coupled high reflectivity diffuse reflector on the ¿ -side. We also present the measured light output homogeneity of a scintillator array fabricated according to one of the best pin configurations.

System modeling and optimization of Fourier holographic memory

A new fast-Fourier-transform-based model of a page-oriented holographic data-storage system is presented. The model accounts for essential system and storage material features (e.g. diffraction, noises, and saturation) and provides reliable results in the form of output images, histograms, or bit-error rates. The model is built on a modular basis and provides the possibility of working with different system versions, key components, and storage materials. Applications of the method are presented through examples of optimization of the data density, reference beam size at Gaussian beam illumination, and calculation of the storage mediums positioning tolerances in accordance with the results of test measurements.

Computer simulation of reflective volume grating holographic data storage

The shift selectivity of a reflective-type spherical reference wave volume hologram is investigated using a nonparaxial numerical modeling based on a multiple-thin-layer implementation of a volume integral equation. The method can be easily parallelized on multiple computers. According to the results, the falloff of the diffraction efficiency due to the readout shift shows neither Bragg zeros nor oscillation with our parameter set. This agrees with our earlier study of smaller and transmissive holograms. Interhologram cross talk of shift-multiplexed holograms is also modeled using the same method, together with sparse modulation block coding and correlation decoding of data. Signal-to-noise ratio and raw bit error rate values are calculated.

Light scattering of thin azobenzene side-chain polyester layers

Light scattering properties of liquid crystalline and amorphous azobenzene side-chain polyester layers used for optical data storage were examined by means of transmissive scatterometry. Comparative experiments show that the amorphous polyester has significantly lower light scattering characteristics than the liquid crystalline polyester. The amorphous samples have negligible polarization part orthogonal to the incident beam, the liquid crystalline samples have relative high orthogonal polarization part in light scattering. The light scattering results can be used to give a lower limit for the domain size in thin liquid crystalline polyester layers being responsible for the dominant light scattering. The characteristic domain sizes obtained from the Fourier transformation of polarization microscopic pictures confirm these values.

SPADnet: A fully digital, networked approach to MRI compatible PET systems based on deep-submicron CMOS technology

This paper is the first comprehensive presentation of the SPADnet concept. SPADnet is a fully digital, networked MRI compatible time-of-flight PET system, exploiting the speed and integration density of deep-submicron CMOS technologies. The core enabling technologies of SPADnet are a sensor device comprising an array of 8×16 pixels, each composed of 4 mini-SiPMs with in situ time-to-digital conversion, a multi-ring network to filter, carry, and process data produced by the sensor devices at 2Gbps, and a 130nm CMOS process enabling mass-production of photonic modules that are optically interfaced to scintillator crystals. The SPADnet photonic modules comprise a matrix of tightly packed sensor devices; each module is networked in multiple rings, where coincidence pairs are identified and readily used in reconstruction algorithms, enabling scalable, MRI compatible pre-clinical PET systems for multi-modal imaging.

Tolerancing surface accuracy of aspheric lenses used for imaging purposes

Tolerancing aspheres and preparing the corresponding drawing indications significantly differ from techniques used at spherical lenses due mainly to surface waviness, an error caused by most asphere fabrication technologies. Standard (ISO) regulations proved to be adequate for several kinds of aspheric lenses (e.g. laser focusing/collimation) made by the traditional diamond turning method, but sometimes are not general enough for recent fabrication techniques (such as CNC polishing of glass aspheres), and today’s more demanding lenses (eyepieces, Fourier objectives, relays etc.). A new, generalized tolerancing technique has been developed to accurately constrain surface waviness, quite independently of fabrication technology, and to provide easy verification of the results. Operation of the method is demonstrated on a Fourier-type objective comprising a glass aspheric lens, by computer simulation and testing of the fabricated prototypes.