Hilmar Franke

Ion implantation, a method for fabricating light guides in polymers

Li+ and N+ ions were implanted into aliphatic polymethylmethacrylate (PMMA), polyvinylalcohol (PVA), and aromatic polyimide (PI) polycarbonate (PC) polymers in the energy range of 100–130 keV. Planar optical waveguides guiding between one and three modes were formed. For low implantation doses (≤ 1014 ions/cm2), total waveguide loss values at λ=633 nm were found to be less than 2 dB/cm. The changes in the refractive index were found to be very large (Δn≥0.05) in the case of PMMA and PVA. We interpret this change in refractive index as being due to the formation of aromatic compounds in the regions of electronic scattering.

Optical gas sensing by evaluating ATR leaky mode spectra

Abstract The angular reflectivity spectrum of a glass-silver-polymer-air multilayer structure is investigated for gas-sensor applications. Minima of reflectance are caused by surface plasmon polariton (SPP) excitation at the silver-polymer interface and by attenuated total reflection (ATR) leaky modes coupled into the polymer film. Changes in refractive index of the polymer (here Teflon®AF) due to absorption of vapour molecules in the surrounding atmosphere lead to line shifts of the resonances in the reflectivity spectrum. For several vapours (benzene, toluene, xylene, etc.) maximum index changes of about Δn = 0.02 are observed with an accuracy better than 0.0001. A dynamic and more accurate measurement is obtained by recording the reflected intensity as a function of time at a fixed observation angle, the angle of the SPP resonance. The recorded intensity is then a measure for the refractive-index changes of the Teflon®AF coating. In a modified set-up for application purposes, a divergent reflected beam is recorded by a CCD camera and the line shifts of two leaky modes are monitored simultaneously with a time resolution of a few microseconds. On-line evaluation of these shifts allows the time-resolved observation of the refractive-index changes. A first miniaturization step is achieved by laser-beam patterning of PMMA substrates.

Physical analysis of teflon coated capillary waveguides

Abstract A theoretical analysis of the properties of a liquid core waveguide (LCW) formed by a water filled, teflon AF2400 inner coated glass tube is presented. The theoretical analysis is based on numerical FD-BPM simulations and reflectivity calculations of the layer system in the LCW. The improvements due to this inner coating compared to other capillary cells are shown. A teflon AF2400 layer thickness of about 5 μm is sufficient to confine the optical intensity to the liquid core and thus avoid any absorption or scattering by the capillary material or any influence of the outside environment.

Liquid core waveguide with fiber optic coupling for remote pollution monitoring in the deep ultraviolet

A new combination of silica fibres, highly transparent in the ultraviolet (UV) and showing long term stability, combined with a teflon-coated liquid-core waveguide (LCW) is presented for remote sensing in the deep UV, for monitoring one of the major pollutants, nitrates, in water, but with potentially wider applicability. The arrangement exhibits low spectral loss in the range between wavelengths of 200 nm and 400 nm and can be used for analytical investigations to determine small concentrations of such impurities in water. The operation of the optical system to achieve guidance of UV light below a wavelength of 250 nm for fibre optic sensors is discussed. With an optical pathlength of 203 mm, nitrate concentrations as low as 22 μg/l could be detected.

Patterning polymer surfaces by laser ablation for integrated optics

Polymers may be ablated photochemically and photothermally. We restrict here on the photothermal laser beam ablation technique in order to produce patterns for integrated optics. The edges of the ablated material have to be smooth in order to avoid additional optical scattering. For poly-(methylmethacrylate) (PMMA) optical waveguide patterns are recorded forming multimode lightguides. Three different types of lightguides are discussed. Smooth edges for the use as total internal reflection mirrors have been made. With the CO/sub 2/ laser multimode patterns have been produced. They appear useful for applications with polymer optical fibres. For the recording of smaller patterns fitting to optical monomode fibres 248 nm excimer laser radiation was used. We report on the production of V-type grooves in PMMA suitable for the mount of optical single mode fibres for fibre-chip coupling. Those grooves can be controlled in their form, in their depth and their width with a resolution of better than 0.1 /spl mu/m/pulse.<<ETX>>

Monitoring the diffusion of vapour molecules in polymer films using SP-leaky-mode spectroscopy

Abstract Vapour molecules that diffuse into a polymer film cause refractive index changes that lead to a signal in an optical sensor device. In a gas-sensor based on surface-plasmon-leaky-mode spectroscopy refractive index changes induce measurable resonance shifts in the reflectivity spectrum depending on the present vapour concentration. The measurement of the whole angular spectrum of a glass/metal/polymer multilayer system provides detailed information about the optical properties of the layers. Recording the resonance shifts with time leads to the dynamic behaviour of the diffusion process, i.e. the diffusion coefficient of the vapour molecule in the particular polymer can be determined.

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.

Optical Waveguiding In Polyimide II

Planar optical waveguides were fabricated on glass substrates using soluble polyimides. A fast curing treatment leads to nearly isotropic products with improved waveguiding properties. The stability of these films is discussed. Strip waveguides were recorded in doped polyimide films and the optical constants of the doped material were investigated.

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.

Gratings in nonlinear optical polymers for integrated optical device applications

The polymer poly(methyl methacrylate) (PMMA) doped with the active photoinitiator dimethoxyphenalacetophenon (DMPA) is a well known material to form permanent gratings by uv-holographie. An additional doping with the photochromic material E-(alpha) (2,5- dimethyl-3-furyl)ethylidene(adamantylidene)succinic anhydride (Aberchrome 670) leads to a one step fabrication of a nonlinear optical grating. After the permanent grating is fixed, the refractive index of the grating can be tuned by a homogenous illumination. The diffraction efficiency of the grating can be tuned because the fulgide Aberchrome 670 undergoes a reversible transition from its bleached to its colored form by homogeneous uv illumination and back again by irradiating the film with a wavelength near the absorption maximum (here (lambda) equals 514.5 nm).