The advantages of digital holographic microscopy to record not only the intensity but also the optical phase are
employed. The experimental arrangement comprises a Mach-Zehnder type interferometer with a microscopic objective
of magnification 100x. The used camera is a 5 Mpixels Allied Vision Guppy Pro F-503 with a pixel pitch of 2.2 μm. The lateral magnification is set to about 200x based on the standard MIL-STD-150A 1951 USAF resolution test target.
The dimensions of the aggregated natural cellulose nanowhisker fibers used are in the range of some hundreds of
nanometers, which are positioned in the front of the microscopic objective using a 3D translation stage in the object arm of the holographic setup. The recorded off-axis holograms are refocused using the angular spectrum method. The
reconstructed complex field is used to calculate optical phase and intensity distributions of the object at different
reconstructions depths. The dimensions and orientation of the fibers can be evaluated from the optical field at different depths. Then, the shape and textures along the aggregated natural cellulose nanowhisker fiber can be presented in 3D space. The nano fiber found to have the dimensions of mean width 223 nm, depth 308 nm and length of 8.1 μm. Further, the mean local refractive index of the nano fibers can be calculated (n=1.501).
Digital holographic interferometric phase shifting method is used to calculate the refractive index profile of
graded index (GRIN) optical fibre and the 3D refractive index distribution across the GRIN fibre. GRIN optical fibre
sample is immersed in a suitable liquid and then Mach-Zehnder-like arrangement phase shifting digital holographic
system is used. The optical phase difference due to the graded index optical fibre can be extracted by digital holographic
interferometric phase shifting technique. The problem of the tilted GRIN optical fibre with respect to the reference axis
is solved, since the fibre must be perpendicular to the reference axis according to symmetry considerations. The optical
phase difference map along the GRIN optical fibre is used to calculate the mean values of the optical phase difference
across the fibre. The refractive index profile of GRIN optical fibre is calculated using the multilayer mathematical
model, where the refraction of the incident rays through the fibre layers is considered. The shape parameter of the
investigated optical fibre is determined. The mode field distributions can be analyzed for the used GRIN optical fibre.
The calculated refractive index profile is used to reconstruct the 3D refractive index distribution across the fibre sample.
The optical- functional properties of an integrated-optical strip-waveguide in a planar polymer chip are presented in this
article. The waveguide was directly written into the surface of a planar polymer chip by UV-laser irradiation. Digital
holographic interferometric phase shifting method is used to calculate the refractive index profile of the waveguide. This
profile contains one or two zones according to the parameters of UV-laser. The mode field distribution and the effective
mode indices for each zone are obtained. The study shows that the optical-functional properties strongly depend on the
UV-irradiation parameters. Several mostly independently occurring photochemical processes competing with one
another are proposed to explain the formation and shape of the refractive index distribution.
The refractive index distribution over a cross-section of an optical fiber can differ between core and cladding, can
vary over the core in graded index fibers, or may even have a more complicated form in polarization preserving
fibers. Besides this intended variations the refractive index may vary due to a loading of the fiber like pressure
or bending or due to a faulty production. Digital holographic interferometry is a suitable means for measuring
the refractive index distribution. In the experiments reported here the fiber is embedded into an index matching
fluid, which is mixed so as to match the index of the cladding. Phase-shifted digital holograms are recorded
and the interference phase distribution is calculated. From a single demodulated interference phase distribution
the refractive index field is determined by an algorithm based on a model which takes into account the known
symmetry of the fiber. It can be shown that the obtained accuracy is better than that of classical two-beam
interferometry. Results of experiments with step-index, with graded index, and with polarization preserving
fibers are demonstrated.
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