I. Bányász

Ion beam irradiated channel waveguides in Er3+-doped tellurite glass

Erbium-doped tellurite glasses are of great interest for the fabrication of active integrated circuits because of their unique properties in terms of bandwidth and rare earth solubility. The fabrication of multimode channel waveguides in a glass of this family, namely, a sodium-tungsten-tellurite glass, is demonstrated using a high-energy ion beam irradiation technique. Nitrogen ions with dose of 1.0×1016ions∕cm2 and 1.5MeV energy were used for this aim. The waveguiding effect was investigated using the end-fire coupling technique.

Recording of transmission phase gratings in glass by ion implantation

Transmission phase gratings of grating constants of 4–12 μm have been designed and fabricated in glass via implantation of helium and nitrogen ions of energies in the 500 keV–1.6 MeV range, through photoresist masks of thickness of 3.3 μm. Multienergy implantations were applied, too. Phase profiles of the gratings were measured via interference and phase contrast microscopy and scanning electron microscopy. Quasisinusoidal profiles were obtained for the finest gratings. The highest first order diffraction efficiencies were around 20%. Dependence of the efficiencies of the gratings on the energy and dose of the implantation have been determined.

Method for the evaluation of the effects of film nonlinearities on the holographic image.

An exact method for the evaluation of the images reconstructed from holograms recorded in nonlinear media is reported for what is to the author’s knowledge the first time. The method is based on the use of the nonlinear holographic characteristics of the recording material without any limitation on the range of bias exposures and visibilities. These characteristics have been obtained by fitting analytical functions to experimental data describing practical recording materials. Numerical calculations have been carried out for high-numerical-aperture thin amplitude holograms of a five-element Ronchi ruling. The contrast of the reconstructed image as a function of the bias exposure and beam ratio is computed.

Laser irradiation, ion implantation and e-beam writing of integrated optical structures

Much attention is currently being paid to the materials and processes that allow one to directly write or to imprint waveguiding structures and/or diffractive elements for optical integrated circuits by exposure from a source of photons, electrons or ions. Here a brief overview of the results achieved in our laboratories is presented, concerning the fabrication and characterization of optical guiding structures based on different materials and exposure techniques. These approaches include: electron and ion beam writing of waveguides in (poly)-crystalline lithium fluoride, uv-laser printing of waveguides and gratings in photorefractive glass thin films, and fs-laser writing in tellurite glasses. Properties and perspectives of these approaches are also discussed.

On the semi-physical developing effect of the AAC developer on holograms recorded in Agfa-Gevaert 8E75HD emulsions

Abstract In the course of experiments on measurement of the effects of processing on nonlinear characteristics of transmission-type silver halide holograms recorded in Agfa-Gevaert 8E75HD emulsions we found that, under certain circumstances, the AAC developer acted as a semi-physical developer instead of the normal chemical developing action. The developed and fixed holograms were of low optical density (

Hologram build-up in a near infrared sensitive photopolymer

A self-processing photopolymer material suitable for holographic recording in the near infrared region (at 780 nm) has been studied. It has been shown that the amount of the pre-polymerizing exposure plays a crucial role in the build-up of the holographic grating. By a proper choice of the pre-exposure it is possible to reduce the inhibition period and to optimize holographic sensitivity and maximum diffraction efficiency. Maximum diffraction efficiencies above 70% have been measured. Significant differences have been found between gratings recorded with s and p polarised beams.

Method for the characterization of hologram processing

Abstract A novel method for the characterization of the processing of both absorption and phase holograms is proposed. Differently from the previous models, the square root of the diffraction efficiency of the processed hologram was directly related to the amplitude of the optical density modulation obtained at the developed step. This characteristic is a good indicator of the degree of nonlinearity of the hologram processing. While the Lin functions of phase holograms are similar to those of absorption holograms, the shape of the proposed function is completely different. The optical density and diffraction efficiency of holograms recorded using Agfa–Geveart 8E75HD plates and processed with AAC developer and a solvent bleach without a fixation step were measured and used to demonstrate the method.

Model of holographic recording in thermoplastic materials

A method for the evaluation of images reconstructed from holograms recorded in thermoplastic materials is reported. The method is based on the use of the experimental modulation transfer function and nonlinear holographic characteristics of the recording material. Calculations have been carried out for high-numerical-aperture holograms of a five-element Ronchi ruling. The quality of the reconstructed image as a function of the recording parameters has been computed. The model predicts that it is possible to optimize holographic recording in these materials.

Comparison of nonlinear characteristics of phase holograms processed by various combinations of developers and bleaching agents

Abstract Optical densities before bleaching and final Lin curves of planewave phase holograms recorded in Agfa—Gevaert 8E75HD emulsions were measured for various combinations of developers (AAC, Pyrogallol and Catechol) and bleaching agents (R-9 and EDTA). To characterize the processing, the square root of the diffraction efficiency of the processed holograms was related to the amplitude of the optical density modulation obtained at the development step. Characteristics of similar forms were obtained for all the processings, with significant differences in the slope and extent of the curves, so that sensitivity, linearity and dynamic range of the processes could be compared directly.

Slab optical waveguides in Er3-doped tellurite glass by N + ion implantation at 1.5 MeV

Slab optical waveguides were fabricated in tung-sten-tellurite glass doped with Er3 + ions by means of nitrogen ion implantation at 1.5 MeV. A wide range of ion doses (from 5·1012 to 8·1016 ions/cm2) was used. Optical characterization, performed by dark-line spectroscopy, revealed that the waveguides were of optical barrier type: the implanted layer exhibited a decrease of the refractive index with respect to the virgin bulk glass, while the region comprised between the sample surface and the end of the ion track acted as an optical guiding structure. It was also demonstrated that a post-implantation annealing process, performed at various temperatures on the samples implanted at higher doses, contributes to the reduction of the barrier region.