Th.J.A. Popma

Experimental study of integrated-optics microcavity resonators: Toward an all-optical switching device

An integrated all-optical switch based on a high-Q nonlinear cylindrical microcavity resonator is proposed. The switch consists of single mode planar waveguides that allow coupling light in and out to a microresonator, exhibiting whispering gallery modes. Due to the high Q factor and the small dimensions, fast switching at low power is feasible for devices based on presently available nonlinear polymers as the active material. In this approach, the transmission of an integrated optical waveguide close to a microcavity has been measured and related to the resonances of the cylindrical microcavity.

R.F. planar magnetron sputtered ZnO films I: structural properties

The structural properties of r.f. planar magnetron sputtered ZnO films are studied as a function of deposition parameters: substrate type, substrate temperature, sputter gas pressure, growth rate and sputtering power. These films are applied as piezoelectric transducers in micromechanical sensors and actuators. The electric properties, and consequently the piezoelectric behaviour, depend strongly on the structural properties of the layers. All films are polycrystalline. The individual grains are highly oriented with their crystallographic c axis perpendicular to the substrate. Crystalline substrates such as silicon or SiO2 induce a growth of small grains, a few hundredths of a micron wide and long. Amorphous substrates such as metals or amorphous SiO2 induce a growth of broad columnar grains extending through the film thickness and a few tenths of a micron wide. Trends in density and grain size are in agreement with Thorntons structure zone model.

R.F. planar magnetron sputtered ZnO films II: Electrical properties

The electrical properties of r.f. planar magnetron sputtered ZnO films are studied by means of current-voltage, capacitance-voltage and Van der Pauw measurements. These films are applied as piezoelectric transducers in micromechanical sensors and actuators. Their piezoelectric behaviour strongly depends on the electric properties. A conduction model for the polycrystalline ZnO layers is presented. This model gives a good description of the electrical behaviour, and is useful in understanding the piezoelectric properties of the films studied.

Photoluminescence and attenuation of spray-pyrolysis-deposited erbium-doped Y2O3 planar optical waveguides

Erbium-doped Y20 3 planar optical waveguides have been fabricated by spray-pyrolysis deposition. The attenuation spectrum of the waveguide shows peaks that are due to absorption of the erbium ions. The as-deposited layers also show photoluminescence sharply peaking at 1540 nm with additional Stark splitting. The thin layers of Er 3:Y 203 obtained are promising for the realization of integrated-optic amplifiers and lasers.

Surface Plasmon Dispersion And Luminescence Quenching Applied To Planar Waveguide Sensors For The Measurement Of Chemical Concentrations.

Two novel types of planar waveguide sensors for the chemical domain are introduced. Both are realized by thin film technologies. They consist of multilayered structures coated by a very thin organic overlayer that is able to absorb the species to be measured out of the environment. This absorbtion results in a change in its dielectric function. In the first sensor to be demonstrated this change is measured using a surface plasmon mode as a probe. In the second one the radiationless energy transfer from luminescent centres incorporated in one of the layers to the overlayer serves as a probe.

Third harmonic generation as a rapid selection tool for organic materials for nonlinear integrated optics devices

In the long trajectory from the synthesis of organic nonlinear optical materials to the completed all-optical device it is highly desirable to be able to concentrate already in an early state on only a few promising materials. Third harmonic generation (THG) is a very convenient method as it allows measurements of the third order nonlinear coefficient of very small samples in the liquid and solid state and also of thin films. For our application in all-optical switching devices the relevant parameter is the intensity dependent refractive index (IDRI). Assuming a simple two-level model for the polymeric materials we can estimate the IDRI on the basis of THG measurements and linear absorption measurements of the materials. We have measured the THG of several polymers in the liquid state and as thin film. The nonlinear coefficients and the IDRI are derived and compared with those obtained from other methods by ourselves and from the literature.

Effects of Pt seed layer and Ar pressure on magnetic and structural properties of sputtered CoNi/Pt multilayers

CoNi/Pt multilayers were prepared by magnetron sputtering using Ar gas. The effects of the Pt seed layer and the Ar sputtering pressure on magnetic and structural properties are investigated. Microstructures of the multilayers were analysed using XRD and TEM. It was found that perpendicular magnetic anisotropy and coercivity increase with an increase in either the thickness of the Pt seed layer or Ar pressure. The causes of the increases in perpendicular anisotropy and coercivity are discussed in relation to the interface roughness, the curvature of layers and the columnar structures.

Nonlinear refractive index of erbium-doped Y2O3 integrated-optical waveguides

Self-induced phase modulation in erbium-doped polycrystalline Y(2)O(3) integrated-optic waveguides is studied by use of a Mach-Zehnder interferometric setup. We determined the wavelength dispersion of the nonlinear refractive index near the (4)F(9/2) absorption band and show that it corresponds qualitatively with a Kramers-Krönig analysis. The nonlinear coefficient at 670 nm was determined to be 1.4 x 10(-14) m(2)/W and has an electronic origin with a slow relaxation time of 6 ms.

Curie temperature dependence of magnetic properties of CoNi/Pt multilayer films

The Curie temperature of Co1?xNix/Pt multilayer films (x = 0.5 and 0.6) has been studied as a function of CoNi and Pt layer thicknesses. Magnetic properties at room temperature are dominated by the Curie temperature. Interlayer coupling and interdiffusion are discussed as possible contributions to the thickness dependence of the Curie temperature and magnetic properties.

3D analysis of magnetic anisotropies in OI and CVI films

In this paper a general model is presented to describe torque curves for a thin magnetic film with two anisotropy axes. One axis is assumed to lie in the plane of the film, having first-order anisotropy only, whereas the other one, having first- and second-order anisotropy, makes an arbitrary angle with the normal to the film. Given the parameters of the model, explicit expressions can be derived for both in-plane as well as perpendicular torque measurements with an infinite magnetic field. With some restrictions analytical expressions are derived to obtain the model parameters from the Fourier coefficients of experimentally obtained torque curves. Furthermore several methods are discussed to obtain finite-field corrections, including a power series expansion in the inverse magnetic field of the Fourier coefficients. An analytical expression was also derived to determine the direction of the easy axis. The applicability of the model is tested on a metal evaporated tape and we found it gave a consistent and quite accurate description of the torque curves of such a film. With this three-dimensional model the accuracy of the determination of the material parameters increases considerably, especially for the relatively weak transverse anisotropy of the film.