A three dimensional finite element method is used to model the forces acting on red blood cells trapped on
an optical waveguide surface. The parameters are chosen to correspond to strip waveguides made of tantalum
pentoxide (Ta2O5). A wavelength of 1070 nm is used and the cells are taken to be spherical. Gradient and
scattering forces experienced by the cells are studied and found to be highly dependent on the refractive index
of the cells. Gradient forces are found to be one order of magnitude larger than scattering forces. Only the lower
part of the cells is in contact with the evanescent field of the waveguide. For low refractive indices, we find that
the lower 0.5-1 μm of the cells is sufficient to determine the optical forces. For the cell sizes considered, all forces
increase with the size.
Three dimensional finite element method is employed to determine optical trapping forces on hollow glass spheres on
an optical waveguide. The evanescent field from the waveguide interacts mostly with the shell of the hollow glass
sphere. We describe how the optical forces vary with shell thickness and particle size, and find the minimum shell
thickness allowing trapping and propulsion of hollow glass spheres. Hollow glass spheres with shell thickness less than
the minimum are repelled away from the optical waveguide. The simulation results are compared with analytical Mie
calculations and experimental data.
Interferometry is a powerful and versatile tool for active MEMS characterisation. The high accuracy measurement of
deformations and vibrations of MEMS structures is an important application and well described by classical
interferometry. Deformation measurements in multi-layered structures requires a more sophisticated approach. All
phase changes along the optical path of the object light influence the measurements. Thus the shape and the
displacement of obstacles (like glass cover plates) must be included to quantify the measurement results.
The paper presents numerical simulations of the light path in an interferometric deformation measurement. A ray
tracing program is developed that keeps track of the optical path length and can thus be used to analyse disturbances
along the optical path. The simulations show how the deformation of more than one interface influences the phase
measurement. The phase errors are quantified and the reliability of the deformation measurements is evaluated.
Different interface geometries are examined. The simulations are compared to measurements on a MEMS pressure
MEMS characterisation is an important application area for interferometry. In this paper a Mach-Zehnder
interferometer configuration is presented that combines both coherent and low coherent techniques in one setup. It
incorporates the application of classical Laser Interferometry (LI) and Electronic Speckle Pattern Interferometry as well
as classical Low Coherence Interferometry (LCI), full-field Optical Coherence Tomography and Low Coherence
Speckle Interferometry. Digital Holography can be applied by minor modifications of the setup.
The setup, working principle, and applications of the interferometer will be described. Measurements on a MEMS-based
pressure sensor are presented. The sensor consists of a glass wafer attached to a silicon membrane. A cavity is
etched into the glass wafer. The wafers are bonded and form a vacuum cavity. Membrane deformations are measured
through the window using LI and LCI. LCI provides information about the shape of the glass window. Results from
speckle techniques are compared with similar results from plane wave techniques. The influence of the glass window
and the illumination of the object are investigated.