Laszlo Domjan

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.

Ternary phase-amplitude modulation with twisted nematic liquid crystal displays for Fourier-plane light homogenization in holographic data storage

Summary Holographic data storage applications often use liquid crystal displays as spatial light-amplitude modulators for writing data images. The hologram created in the Fourier plane is usually applied to store the information, since this plane supplies optimal data density. A well known technique for homogenizing the light distribution in the Fourier plane is the application of external random phase modulating masks. The requirement for pixel by pixel matched positioning of the phase modulating mask and the pixels of the spatial light-amplitude modulator is hard to solve in the optical systems and any positioning error leads to significant signal degradations. The article analyses the possibilities of realizing the required simultaneous amplitude and phase modulation of light with the application of a single LCD. Twisted nematic LCDs with different maximal birefringence are numerically investigated using the Jones matrix method. Elliptical incident and exit polarizations are proposed, by which ternary phase-amplitude modulation (+1,–1,0) can be realized. Test measurements are also presented that demonstrate the validity of the calculated results.

Phase modulation configuration of a liquid crystal display

Phase-mostly modulation mode of a Sony LCX016AL-6 liquid crystal display has been found for appropriate elliptical polarization states of the input and output light with calculation using Jones matrices. Phase delay measurement with an accuracy of 2° were performed using a simple diffractive technique at different gray levels. Our measured results agree well with the theoretical calculation with Jones matrices. Both gave about 10% intensity variation and more than 200° phase modulation in the whole range.

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.