Arne Røyset

Measurement of laser parameters for simulation of high-speed fiberoptic systems

The semiconductor laser rate equations are rewritten using a new set of parameters which can all be found from steady state and small signal measurements on the laser. Procedures for finding these parameters are described. Parameters have been measured on three 1550 mm lasers from different manufacturers. Comparison between large signal measurements and simulations using the measured parameters shows in general good agreement for modulation currents sufficiently above threshold.

Optimizing the performance of phase-change materials in personal protective clothing systems.

Phase-change materials (PCM) can be used to reduce thermal stress and improve thermal comfort for workers wearing protective clothing. The aim of this study was to investigate the effect of PCM in protective clothing used in simulated work situations. We hypothesized that it would be possible to optimize cooling performance with a design that focuses on careful positioning of PCM, minimizing total insulation and facilitating moisture transport. Thermal stress and thermal comfort were estimated through measurement of body heat production, body temperatures, sweat production, relative humidity in clothing and subjective ratings of thermal comfort, thermal sensitivity and perception of wetness. Experiments were carried out using 2 types of PCM, the crystalline dehydrate of sodium sulphate and microcapsules in fabrics. The results of 1 field and 2 laboratory experimental series were conclusive in that reduced thermal stress and improved thermal comfort were related to the amount and distribution of PCM, reduced sweat production and adequate transport of moisture.

Optical properties of single diatom frustules revealed by confocal microspectroscopy.

Optical properties of single diatom frustule valves from two different Coscinodiscus species (C. wailesii and C. centralis) are studied by transmission confocal hyperspectral imaging and numerical calculations. Light convergence, concentration, and trapping effects are observed and depend on both the wavelength and the valve orientation. These effects seem to occur independently of the incident light angle. From our results, a wavelength-dependent multifocal lens behavior can be explained by light diffraction related to the radial symmetry of the multiscaled 3D nanostructure.

Comparison of speckle reduction using polarization diversity and frequency compounding in optical coherence tomography

We present a novel OCT (Optical Coherence Tomography) instrument which enables us to detect two orthogonal polarization states at two different wavelengths simultaneously. We have used this instrument to demonstrate, study, and compare the properties of speckle averaging using frequency compounding and polarization diversity separately and in combination. Reductions in speckle contrast obtained by measurements are compared to theoretical values and results from computer simulations of OCT signals.

Functional imaging of dye concentration in tissue phantoms by spectroscopic optical coherence tomography

We present functional imaging of the concentration of a photodynamic therapy (PDT)-related dye in scattering tissue phantoms based on spatially resolved measurements of optical properties through spectroscopic optical coherence tomography (OCT). Expressions for the OCT signal are developed, enabling estimation of depth-resolved sample optical properties. Based on these expressions, we discuss speckle statistics and speckle correlations of the OCT signal. Speckle noise reduction is performed by spatial filtering and is used to improve accuracy in the estimated optical properties at the expense of spatial resolution. An analytic expression for the precision in the estimated optical properties is derived. This expression shows that axial filtering, and thereby a reduction of axial resolution, gives a larger improvement in precision compared to the same filtering and reduction in the transversal resolution. It also shows that imaging with a shorter coherence length, or a larger numerical aperture, improves precision when the filter length determines the spatial resolution. Good agreement is obtained between experimentally determined and theoretically predicted variance in the estimated attenuation coefficients and dye concentration. Finally, we present guidelines for spectroscopic OCT systems for concentration imaging and discuss application of the method to more realistic phantoms and tissue.

Quantitative measurements of flow velocity and direction using transversal Doppler optical coherence tomography

We present the first demonstration of measurements of velocity and direction of flow using Transversal Doppler Optical Coherence Tomography. The experiments are carried out using a four-channel quadrant detector at the output of a freespace Michelson interferometer. This allows real three dimensional mapping of both flow and velocity with no limitation on the Doppler angle.

Measurement of dye diffusion in agar gel by use of low-coherence interferometry.

We demonstrate low-coherence interferometry for diffusion measurements. We have measured the diffusion coefficient of a phthalocyanine dye in 1.5% agar gel with a two-wavelength interferometer; one wavelength was matched to the absorption peak of the dye at 675 nm, while the other, 805 nm, was not affected by the dye. The diffusion coefficient of the dye was found by fitting a mathematical model for the interferometer signal to the measured low-coherence interferometry amplitude. A 95% confidence interval for the diffusion coefficient was found to be D = (2.5 +/- 0.2) x 10(-10) m2/s. The influence of speckle averaging and experiment time on the determination of the diffusion coefficient has been studied. The presented technique allows in situ characterization of diffusion in semitransparent media.

Measurement of dye diffusion in scattering tissue phantoms using dual-wavelength low-coherence interferometry.

We demonstrate low-coherence interferometry (LCI) for dye diffusion measurements in scattering tissue phantoms. The diffusion coefficient of a phthalocyanine dye in 1.5% agar gel containing scattering Intralipid was measured using a dual-wavelength interfero-meter. One wavelength was matched to the absorption peak of the dye at 675 nm. The other, 805 nm, was not affected by the dye, and was used to correct for varying sample scattering as a function of depth, assuming a constant ratio between scattering at the two wavelengths. The same wavelength dependence of scattering is assumed for the entire sample, but no a priori knowledge about the amount of scattering is needed. The dye diffusion coefficient was estimated by fitting a mathematical model of the interferometer signal to the measured LCI envelope. We compare results obtained using both a constant-scattering and a depth-resolved-scattering approach to determine the sample scattering. The presented method provides robust estimation of the diffusion coefficient when spatial resolution in determining the depth-resolved scattering is varied. Results indicate that the method is valid for samples having continuous spatial variations in the scattering coefficient over lengths as short as the coherence length of the probing light. The method allows in situ characterization of diffusion in scattering media.

Printed organic conductive polymers thermocouples in textile and smart clothing applications

This work reports on an experimental investigation of the potential of using selected commercially available organic conductive polymers as active ingredients in thermocouples printed on textiles. Poly(3, 4-ethylenedioxythiophene): poly(4 styrenesulfonate) (PEDOT:PSS) and polyaniline (PANI) were screen printed onto woven cotton textile. The influence of multiple thermocycles between 235 K (−38°C) and 350 K (+77°C) on resistivity and thermoelectric properties was examined. The Seebeck coefficients of PEDOT:PSS and PANI were found to be about +18 μV/K and +15 uV/K, respectively, when “metal-polymer” thermocouples were realized by combining the polymer with copper. When “polymer-polymer” thermocouples were formed by combining PEDOT:PSS and PANI, a thermoelectric voltage of about +10 μV/K was observed. A challenge recognized in the experiments is that the generated voltage exhibited drift and fluctuations.

Sputter-deposited (Pb,La)(Zr,Ti)O3 thin films: Effect of substrate and optical properties

Optically transparent (Pb,La)(Zr,Ti)O3 (PLZT) thin films were sputter-deposited on SrTiO3(001) and MgO(001) substrates with a SrRuO3(110) bottom electrode. X-ray diffraction analysis showed epitaxial growth of monocrystalline PLZT, with (001) rocking curve full width at half maxima of ∼0.03° and ∼0.3° for films deposited on SrTiO3 and MgO, respectively. In-plane epitaxial alignment of the SrRuO3 and PLZT epilayers was verified from φ-scans. It was established from atomic force microscopy measurements that the PLZT surface roughness meets the requirement for optical waveguide applications. Recorded P-E loops for films grown on both substrates showed a remanent polarization of ∼36 μC/cm2. The refractive index of the PLZT layer was estimated from rutile prism coupling measurements at ∼2.56 for λ=633 nm, consistent with data obtained by spectroscopic ellipsometry. The ferroelectric and optical characteristics of the films, as well as their surface roughness, were not appreciably different for the two substrat...