The article presents the method of encoding a laser beam for control systems. The experiments were performed using a red laser emitting source with a wavelength of <i>λ</i> = 650 nm and a power of <i>P</i> ≈ 3 mW. The aim of the study was to develop methods of modulation and demodulation of the laser beam. Results of research, in which we determined the effect of selected camera parameters, such as image resolution, number of frames per second on the result of demodulation of optical signal, is also shown in the paper. The experiments showed that the adopted coding method provides sufficient information encoded in a single laser beam (36 codes with the effectiveness of decoding at 99.9%).
A new kind of waveguide and waveguide coupler formed in a nematic liquid crystal (lc) cell is created by means of a weak-intensity laser beam that propagates along the flat boundary between layers of lc and photoconductive polymer. To obtain a waveguide, the connection between the lc and polymer must be driven by the properly polarized voltage. The examined lc cells were of a common kind with indium-tin-oxide (ITO) uniform electrodes on both inner sides of a glass plate. The planar homogeneous alignment of the lc layer was confined by a poly (N-vinyl carbazole) (PVC) layer on one side and a polyimide layer on the opposite side. We applied the PVC doped with a photosensitizer as the photoconductive polymer and a nematic lc mixture of high birefringence. A waveguide was created along a light beam propagation path, and coupling between the waveguides was fabricated in the same way. The energy transfer between the waveguides was proved in properly prepared experiments for laser beam wavelengths equal to 532 nm and 632.8 nm. For both wavelengths, the outcomes of the experiments were of the same quality.
Remote controlled spatial light modulator (SLM) has been applied to design tuned "pin-hole" filter. The name "hole" means transparent area in the spatial light modulator (SLM) window. Transparent area in the SLM is remote controlled in the presented filter in accordance with the imposed "holes" distribution. As a result desired optical field diffraction has been obtained in the SLM window. Finally, one produces controlled movement of the focus in a resulting "pin-hole" filter. Proper optical field simulation has been described as well as presentation of the filter.
The liquid crystal (lc) filter, which produces distributed form of light transmission, has been described. Distribution of the transmitted intensity may be altered in filter window by means of an incident light polarization.
To obtain such polarization sensitive transmission the special alignment of a liquid crystal layer is arranged in such a way, that on the one side, inside the filter, the lc layer has been aligned as planar or homeotropic, while on the opposite side of the filter it stay aligned in form of circles. Such liquid crystal cell may be called circular - homogeneous or circular homeotropic (CH LC). The filter transmission basis is adiabatic following in a twisted nematic lc layer (Mauguin regime).
As Mauguin regime is fulfilled then CH alignment causes polarization sensitive transmission. Such filter provides new possibilities in a polarisation difference image analysis so may be convenient tool for a polarimetric image processing.
Numerical simulation of the transmission has been presented as well as the experimental results. Even if Maugin regime is fulfil the examined filter transmission depends on the transmitted spectrum to some extent. It has been analyzed and potential application of this property of the filter has been discussed too.
Dispersion of the refraction indices n (λ) as well as dispersion of the imaginary part of the refection coefficient r = r0*exp(-iφ<sub>R</sub>(λ)) have to be determined to design band-pass Fabry-Perot filter. In the case when liquid crystal is placed in the filter gap then both ordinary and extraordinary indices have to be determined. Consequently one must find imaginary part of the coefficient r for ordinary and extraordinary waves transmitted by the filter. Imaginary part of the refraction coefficient is called also phase of reflection. Proposed method exploits a Fabry-Perot filter to obtain examined values. It has been proved that both values, phase of reflection, and refraction indices must be determined in the same procedure from data obtained in the same measurement. The procedure consists of: determination of the transmission peaks position in the Fabry-Perot filter spectrum; nonlinear fit procedure which optimize dispersions of the n(λ), and φ<sub>R</sub>(λ) to minimize the differences between theoretical and experimental transmissions of the filter; simulation of the free spectral range (FSR), and finesse of the filter spectrum in dependence on dispersions of n(λ), and φ<sub>R</sub>(λ). Results have been presented in the case of four different liquid crystal substances and two different mirrors applied in the filter. The way for determination of the φ<sub>R</sub> (λ) seems to be interesting as this value is really hard to measure. Presented data for the examined liquid crystals are also new.
Wavelet transformation localizes all irregularities in the scene. It is most effective in the case when intensities in the scene have no sharp details. It is the case often present in a medical imaging. To identify the shape one has to extract it from the scene as typical irregularity. When the scene does not contain sharp changes then common differential filters are not efficient tool for a shape extraction. The new 2-D wavelet for such task has been proposed. Described wavelet transform is axially symmetric and has varied scale in dependence on the distance from the centre of the wavelet symmetry. The analytical form of the wavelet has been presented as well as its application for details extraction in the scene. Most important feature of the wavelet transform is that it gives a multi-scale transformation, and if zoom is on the wavelet selectivity varies proportionally to the zoom step. As a result, the extracted shape does not change during zoom operation. What is more the wavelet selectivity can be fit to the local intensity gradient properly to obtain best extraction of the irregularities.
The way for designing and analysis of the tuned Fabry-Perot Interferometer (FPI) for monochromatic wave filtering has been established and presented. The filter is filled with liquid crystal for achieving the tuneable optical axis orientation. The meaning of the refractive index dispersion on the designing and spectral characteristics of the tuned FPI has been explained in detail. The phase of reflection for the electromagnetic waves in the mirroring layers of the filter has been experimentally determined. It allows one to obtain real effective optical thickness of the filter and successfully applied 4x4-matrix method for transmission calculations. The conditions for lc substance parameters to design the FPI filter have been verified.
The particular family of liquid crystalline filters is presented. Their basis application is multiresolution image analysis (wavelet transform). That filter creates polarized beam of light, which constitutes the Haar wavelet. Simulation of such a filter by means of 4 X 4 matrix is presented as well as experimental results. The picture of the filter in polarized light is shown below in Fig. 2. In cooperation with phase shifter the polarization of the light beam may be rotated in the filter to extract image's features.
The direct measurement of the refraction index profile in the nematic layer (NL) creates possibility to verify and exploit the non-linear solution of the Ericksen-Leslie equation (E-L). It has been done for NL of 6 CHBT tuned in wide range of external voltage. The symmetrical case of the director field distribution has been analyzed. The way for local values of the electric field estimation inside the lc layer is discussed.
The analysis of the tuned, liquid crystalline Fabry-Perot interferometer (FPTI) has been done by means of 4 X 4 matrix. Wide-angle incidence has been analyzed in terms of Trollinger-Chipman correction for extraordinary wave. Results have been applied to determine constraints in the design of the monochromatic tuned FPTI. Main features of the FPTI device and liquid crystal determining FPTI parameters has been described in detail. Especially attention has been paid on dispersion of the LC' refraction indices as a factor of spectral FPFI' properties.
We report the method of the refractive dispersion determination in the anisotropic refractive indices in a planar liquid crystal layers. The experimental data have been obtained from transmission spectra of a plane parallel Fabry-Perot Filter (FPF) filled with the investigated liquid crystal (LC). Physical basis, experimental techniques and math procedures have been described. We assumed the perpendicular light incidence and the absence of absorption and scattering. The dispersion of both refractive indices has been determined over the visible spectrum. During the test measurement similarity of refraction index for 5 CB (K15 MERCK) with literature values has been obtained. Results for no.602 and no.1292 liquid crystalline mixtures made in Institute of Chemistry MUT are given.
Orientation of director field can be obtained by liquid crystalline (lc) waveguide application. The method has been described earlier. As it is new approach verification of the results in an independent experiment is presented here. The retardation measured in tunable lc retarder has been used to do such verification. Calculations of the retardation made with director field profile measured in the lc waveguide has been compared with measurement results obtained in the lc retarder.
The collected results of the refraction index profile measurement in highly anisotropic, tunable liquid crystalline waveguides are presented. The three different liquid crystal substances have been examined. Initial orientation of the liquid crystal layer is deformed by an external electric field. The initial orientations have been prepared as twisted and planar for liquid crystal material with positive dielectric anisotropy. In the liquid crystal material with negative dielectric anisotropy as initial has been examined hybrid orientation.
The refractive index profile (RIP) is measured to provide data for obtaining local optical axis arrangement in the waveguide cross-section. Measurements have been made in the electric field applied perpendicularly across the layer in a liquid crystalline waveguide. New approach is proposed to accomplish RIP measurement in a direct way. The m - line method is presented as a tool that allows one to do it and to improve the attenuated total reflection disadvantages as well. Obtained results maintain applicability of the m - line method for a direct RIP measurement. Nematic LC layer has been examined as well described in the literature to verify observations. Most interesting seems those results illustrating the presence and the deformation of the boundary layer in homogeneous LC layer alignment.
Optical measurements of the retardation between ordinary and extraordinary wave in the liquid crystalline retarder suggest that an interfacial layer between substrate and liquid crystal (LC) exists. The theoretical model that allows one to describe the presence of such a layer has been constructed and illustrated, for simplicity, in model with neglected elastic anistropy. It turns out to be quite enough to fit an experimental data of phase retardation to obtain values of the pretilt angle and anchoring energy. Experimental results confirm that near threshold voltage value the homogeneous LC layer is deformed in more complicated way that his one describe in one elastic constant model. For higher voltages such a model seems to be proper one because of the LC layer deformation is mostly bend like kind.
The investigation results of the propagation loss due to light scattering in electrically induced channel in planar waveguides are presented. The channel structure was obtained by means of electric driven stripe electrode made by photolithographic process. Planar waveguiding cell has been fabricated using ITO/SiO<SUB>2</SUB>/polyimide-coated glass plates and LC film 20 micrometers thick. A nematic liquid crystal layer with 90 degrees-twisted nematic orientation was studied. The He-Ne light beam was endfire coupled into an input edge of a waveguide using an objective lens. The propagation loss have been evaluated from the spatial variation intensity of light scattered out perpendicularly to the waveguide surface along the light propagation direction measured with CCD camera. Loss measurements have been made in room temperature. Waveguiding channel effect has been observed above 2.5 V<SUB>rms</SUB> of applied voltage with the loss of about 17 +/- 1 dB. Increased driving voltage up to 100 V<SUB>rms</SUB> reduces the loss to minimum value of 12 +/- 1 dB/cm. As a result of the experiments one may conclude that transmission loss in thick nematic waveguide have bulk character caused by imperfection of molecular alignment.
The particular diffraction on periodic orientation deformation of liquid crystal (LC) layer was investigated. The deformation was introduced by means of alternative electric field applied across the LC film using electrodes on both substrates plates, or along the one side of the sandwich, using interdigital electrodes patterned on one of the plates. Diffraction pattern was dependent on the frequency and amplitude of driving voltage and the thickness of the LC layer. For the first configuration, diffraction spots correspond to the diffraction period of electrodes. In the second configuration diffraction spots were observed as if the diffraction grating constant is two times smaller. Specific oscillations of intensity with their frequency minimum near 25 and 47 Hz of driving frequency were observed for the spots corresponding to greater period. Achieving this is possible with the increasing driving voltage. The theoretical description of the diffraction process based on earlier results has been shown. Presented formulae illustrate the possibility for twofold deformation maximum appearance in LC layer in dependence of the driving electric field frequency and such parameters as the LC viscosity, and the other mechanisms of dissipation. The computer simulation of the diffraction pattern is made herein.
The acoustic waves on the interface surface between elastic medium and liquid crystal (LC) were examined. When the elastic body is Bi<SUB>12</SUB>SiO<SUB>20</SUB> and liquid crystal is smectic A (DEADB) then Rayleigh type and leaky waves are present in the considered case. For leaky waves final results are similar to those reported for Langmuir-Blodget films. Calculations were made in the case without dispersion of elasticity in liquid crystal medium.