Werner F. Frank

Field dependent soft and goldstone mode in a ferroelectric liquid crystal as studied by dielectric spectroscopy

Abstract Broadband dielectric spectroscopy (frequency range 10 -1 –10 7 Hz and temperature range 100 to 450 K) was used to analyze in detail the frequency and temperature dependence of the soft and the Goldstone mode in a ferroelectric liquid crystal.

Ionizing radiation for fabrication of optical waveguides in polymers

Ionizing radiation (light ions up to 200 keV and UV radiation with λ < 280 nm) is used to structure the surfaces of transparent polymers like Poly-(methyl-methacrylate) and related materials. Areas with an index increase up to 1% suitable for waveguiding are obtained. Compaction of the irradiated areas leads to diffractive structures. Changes in the chemical structures of the irradiated samples are reported. The physical properties like mode spectra and attenuation were measured. Passive components with fibers coupled to the devices were fabricated.

Optical components in polymers

Samples of PMMA [Poly-(Methyl-Meth-Acrylate)] were modified by ionizing radiation (especially UV-radiation) in order to generate regions of increased refractive index. These waveguiding structures were used to build optical power splitters and optical polarizers simply by varying the exposure time. The refractive index profile and the variation in thickness of the waveguides for different exposure times were observed. Also the cut-off- wavelength and the spectral absorption behavior for different exposure times were measured. The compaction at the surface was used to build up diffraction gratings with grating constants of 4 micrometer to 20 micrometer. By annealing the samples the diffraction efficiency was increased.

Optical properties of waveguiding structures in polymers

Optical waveguides have been produced in poly-(methyl-meth-acrylate) (PMMA) by ionizing radiation of the surface of polymer solid blocks. Planar and strip structures have been obtained. Dispersion curves of refractive indices have been measured between 458 nm and 1523 nm. Mechanical changes of the surface geometry have been studied by surface profilometry. Chemical reactions within the irradiated volumes have been investigated by ATR-FT-IR spectroscopy. Light guiding properties of the waveguides are reported.

Optical waveguides in polymer materials by ion implantation

Poly-(methyl-methacrylate) (PMMA) on different substrates was implanted by He+ ions of energies between 50 keV and 250 keV as well as 1 MeV and 2 MeV. The ion doses varied between 1012/cm2 and 1015/cm2. We have studied the increase of the refractive index in the implanted surface layer, which acts as an optical waveguide, by measuring the effective index of refraction neff for different optical modes. According to the range of ions in the polymer, surface waveguides and buried waveguides can be generated. The number of modes a waveguide is carrying depends on the ion doses. For single mode waveguides low doses must be used. Waveguides with losses below 1 dB/cm were obtained. The chemical effects caused by the implantation are measured by IR spectroscopy and residual gas analysis (RGA), physical modifications of the surface were studied by scanning electron microscopy (SEM). The refractive index profiles are discussed using simulation calculations.

Spectroscopic study of surface effects in polymer waveguides generated by ionizing radiation related to guiding properties

Samples of PMMA have been modified by ionizing radiation in order to generate regions of increased refractive index for the use as optical waveguides in a surface layer. To get a better understanding of the formation of these guides the chemical processes which are responsible for the increase of the refractive index were studied using different spectroscopic methods. It is shown that the thickness as well as the refractive index profile of the layer at the surface depends on the irradiation dose. In this paper also the guiding properties of the waveguides in dependence of these parameters are discussed. The waveguiding structures were used to build optical polarizers simply by varying the exposure time. The spectral absorption behavior of different strip waveguides for different exposure doses were studied.

Photoinduced phase modulation in PMMA lightguides doped with an azo dye

Polymer lightguides ofPMMA, doped with azo dyes are investigated with respect to their opto-optical or all optical properties. The TRANS-CIS photoisomerisation of the azo dyes leads to reasonable polarization dependent optically induced refractive index changes. These are studied in planar lightguides and in leaky guides. With light at the absorption edge all optical properties are studied leading to a possible application as bistable device.

Fiber chip coupling and refractive index profile of UV-generated waveguides in PMMA

As an example for a new technology for the fabrication of passive components in polymers a 1:2 splitter has been made in PMMA bulk material. The geometrical structure of the waveguides has been preembossed by a Ni-shim together with precision grooves to hold the silica fibers. The waveguides have been formed by UV-exposure. The refractive index profile has been studied to optimize the depth of the grooves in order to fit the fiber core to the strip waveguide without any further alignment. Insertion loss of the component has been measured.

Polymer optical fibers in Germany: reliability test for use in premises wiring

Progresses in fiber technology - low NA fibers, graded index fibers, perfluorinated fibers of extremely low attenuation - let expect that polymer fibers find their way from in-house wiring outside to the premise and moreover to the access network. In order to study the application range of these fibers a long term reliability test at different temperatures and humidity conditions has been initialized. This contains an accelerated lifetime test in order to separate thermal activated processes from those of different origin. Different environmental conditions will be simulated, especially adverse ones.The experiments are planned as a round robin test and can possibly contribute to a new concept of standard specification.

Patterning polymer surfaces with laser radiation for fiber chip coupling

Computer controlled laser beam recording techniques are used for the fabrication of V-shaped grooves in polymers. With a CO2-laser patterns are recorded which are suitable for the embedding of multimode polymer fibers with core diameters above 300 micrometers . Using a KrF excimer laser in a cylindric lens configuration V-grooves in PMMA are produced, where shape, width and depth of the grooves are highly reproducible and the parameters may be controlled by pulse energy and number of pulses with an accuracy of less than a micrometer. This method appears attractive for mounting monomode fibers.