Decades ago tomographic interferometry was successfully applied to the measurement of phase objects in a large scale.
Recently the application field was extended to nearly micro scale, for example optical fibers. Nevertheless, the geometry
of tested objects was usually relatively simple and the spatial resolution at the level of several microns was always a
barrier. In this paper we investigate the possibility of tomographic reconstruction of complex phase objects by means of
tomographic interferometry. The analyses have been performed on the photonic crystal fiber, which is not only a high-resolution
object, but additionally contains periodic structures. The influences of the following factors are investigated:
proper matching of the immersion liquid, mechanical imperfections of the rotation, geometry of the fiber, polarization of
the illumination beam and type of reconstruction algorithm. In addition to experimental results, the numerical simulation
of wavefront propagation through the fiber is performed. According to the results, the high - resolution reconstruction of
the three-dimensional refractive index distribution in the object containing a periodic structure is possible, however
limited by several conditions, as described in the paper.
The paper, the method of three-dimensional refractive index measurement in optical fibers. The emphasis is put on experimental technique and instrumentation; however, important theoretical topics are briefly described (e.g., diffraction influence on measurement results). The experimental setup and measurement algorithm are presented in detail. Experimental results include measurement of the following objects: multimode optical fiber; optical fiber splice; and single-mode optical fiber. Sources of errors and accuracy of the method are analyzed. As a conclusion, we discuss the limitations and possible other applications of tomographic microinterferometry.
In biological micromanipulation image aberrations are introduced not
only by the optical system, but also by the immersion liquid. Whereas
optical system aberrations are constant and it is relatively easy to
measure and correct for them, the immersion caused aberrations are
variable in time and space. In this paper a method using a spherical
microparticle as an artificial point source for aberration control is
presented. The particle is positioned by optical tweezers at the
location of the biological sample. In the experiment holographic
tweezers are used. They are based on computer generated holograms,
written into spatial light modulators, which create light traps for
the microparticle in the object plane. The light traps can be moved
without any mechanically moving parts, just by changing the
hologram. The particle strongly focuses the light, therefore an
artificial point source in the object space is created. The
illumination light is filtered, so that only the signal corresponding
to a spherical wave is analyzed by the wavefront detection system. The
information about the wavefront distortion is used to dynamically
correct for it. This can be done by using spatial light modulators.
The method is suitable for biophotonic imaging systems, where
refractive index variations in the sample plane are significant. The
integration with holographic tweezers is advantageous since it offers
flexibility in positioning and imaging the particles.
This paper presents tomographic microinterferometry as a tool for determination of 3D refractive index distribution in optically transparent elements. Principles of method and exemplary results are obtained in laboratory system are given. Concept of insensitive for ambient influence field tomograph dedicated for fast determination of refractive index distribution is given. Decreasing of acquisition and computing time is achieved by reduction of number of views, for which measurements are taken. The influence of decreasing number of projection is analyzed in order to determine a certain compromise between the quality of n(x,y,z) reconstruction and time of measurement.
Microinterferometric tomography method for determination of 3D refractive index distribution in phase elements is described. Applications of this method to measurement of gradient index fibers, fiber splices and single mode fiber are presented. Initial results of holey fiber testing are given and future trends in development of this method (applications to photonic structures) are discussed.
The paper presents a new approach to structural investigations of elliptical-core liquid crystal fibers (ECLCFs) by using the interferometric method. The method enables to confirm envisaged molecular distribution within the elliptical core previously observed in polarimetric configuration.
In this paper we discuss the problems connected with analysis of mechanical properties of silicon microelements being basic parts of MEMS (e.g. micromembranes, microbeams). The quality of these microproducts (the reliability and the lifetime) is strongly dependent on the material properties and the mechanical design. There is also strong influence of the technology process on their performance. The best suited methods for their testing are optical full-field measuring methods. They provide data (displacements, strains, distribution of material constants) which may be easily used in the hybrid experimental-numerical methods for microelements analysis and optimization of their design.