Measurement of the pretilt angle and the cell gap of nematic liquid crystal cells by heterodyne interferometry
TL;DR: This work proposes a simple method, based on the crystal rotation technique and heterodyne interferometry, to simultaneously determine the pretilt angle and cell gap of nematic liquid crystal cells, characterized by the advantages of simplicity of installation, ease of operation, high stability, high accuracy, and high resolution.
Abstract: This work proposes a simple method, based on the crystal rotation technique and heterodyne interferometry, to simultaneously determine the pretilt angle and cell gap of nematic liquid crystal cells. When heterodyne light passes through a nematic liquid crystal cell, the phase retardation given by the characteristic parameters of the cell can be measured accurately by heterodyne interferometry. This phase retardation relates to the pretilt angle, cell gap, and angle of incidence on the cell. By using the measured phase retardations at two incident angles, the pretilt angle and cell gap of the nematic liquid crystal cell can be estimated by numerical analysis. This method is feasible, requiring only two incident angles and prior knowledge of two characteristic parameters—extraordinary and ordinary refractive indices of the liquid crystal. It is characterized by the advantages of simplicity of installation, ease of operation, high stability, high accuracy, and high resolution.
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TL;DR: The results show that the pretilt angle of LCs can be tuned continuously from ∼0 to ∼90° as the contact angle of water on ZnO NPAs changes from 33 to 108°, and the wettability of ZnOs fabricated by the solution-based hydrothermal method can be controlled by changing the annealing temperature.
Abstract: The control of the liquid crystal (LC) alignment is very important for both academic research and practical applications. LC molecules aligned on the ZnO nanoparticle arrays (ZnO NPAs) are demonstrated and the pretilt angles of LCs can be controlled by using ZnO NPAs with different surface wettability. The wettability of ZnO NPAs fabricated by the solution-based hydrothermal method can be controlled by changing the annealing temperature of the as-prepared ZnO NPAs. The measurements of the energy-dispersive spectra and photoluminescence have shown that the chemical properties of ZnO NPAs have been changed with the annealing temperature. Our results show that the pretilt angle of LCs can be tuned continuously from ∼0 to ∼90° as the contact angle of water on ZnO NPAs changes from 33 to 108°.
36 citations
TL;DR: In this paper, physical dispersion of polyhedral oligomeric silsesquioxane (POSS) nanoparticles in commercial homogenous PIs decreases the surface energy of the PI alignment films and generates a controllable θ p in the range 0°
28 citations
TL;DR: In this article, anisotropic waveguide theory is developed for electrically tunable distributed feedback (DFB) laser from dye-doped holographic polymer dispersed liquid crystal (HPDLC) grating.
Abstract: Anisotropic waveguide theory is developed for electrically tunable distributed feedback (DFB) laser from dye-doped holographic polymer dispersed liquid crystal (HPDLC) grating. The period grating structure, optical anisotropy of the liquid crystal (LC) and practical light propagation path in the HPDLC have been considered. The emitted lasing wavelength is deduced on basis of the dielectric anisotropy of the LC, transverse-magnetic (TM) light wave propagation in the core layer and DFB laser theory. An experimental method to determine the tilt angle of the LC and the lasing behaviours under different electric fields are used to verify the validity of the anisotropic numerical analysis. The results show that a more accurate agreement between the theoretical calculations and the experimental data is achieved. The anisotropic numerical analysis presented here is very useful when designing and optimising tunable lasers for optical communications and integrated optics.
17 citations
Cites methods from "Measurement of the pretilt angle an..."
...A characterisation method, which was always applied to measure the pretilt angle of LC [41], is used here to determine the LC tilt angle under different electric fields, as shown in Figure 2....
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TL;DR: A novel phase measurement method composed of the rising-edge locked signal processing and the digital frequency mixing is proposed for laser heterodyne interferometer and a series of experiments verified the feasibility of the method in large displacement measurement with high speed and nanometer resolution.
Abstract: A novel phase measurement method composed of the rising-edge locked signal processing and the digital frequency mixing is proposed for laser heterodyne interferometer. The rising-edge locked signal processing, which employs a high frequency clock signal to lock the rising-edges of the reference and measurement signals, not only can improve the steepness of the rising-edge, but also can eliminate the error counting caused by multi-rising-edge phenomenon in fringe counting. The digital frequency mixing is realized by mixing the digital interference signal with a digital base signal that is different from conventional frequency mixing with analogue signals. These signal processing can improve the measurement accuracy and enhance anti-interference and measurement stability. The principle and implementation of the method are described in detail. An experimental setup was constructed and a series of experiments verified the feasibility of the method in large displacement measurement with high speed and nanometer resolution.
14 citations
TL;DR: Based on the Doppler effect and heterodyne technology, the information is loaded of length variation to the frequency difference of the multi-beam laser heter-odyne signal by the frequency modulation of the oscillating mirror as discussed by the authors.
Abstract: This paper proposes a novel method of multi-beam laser heterodyne measurement for metal linear expansion coefficient. Based on the Doppler effect and heterodyne technology, the information is loaded of length variation to the frequency difference of the multi-beam laser heterodyne signal by the frequency modulation of the oscillating mirror, this method can obtain many values of length variation caused by temperature variation after the multi-beam laser heterodyne signal demodulation simultaneously. Processing these values by weighted-average, it can obtain length variation accurately, and eventually obtain the value of linear expansion coefficient of metal by the calculation. This novel method is used to simulate measurement for linear expansion coefficient of metal rod under different temperatures by MATLAB, the obtained result shows that the relative measurement error of this method is just 0.4%.
13 citations
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TL;DR: In this article, a detailed analysis is given for three techniques used to determine the tilt bias angle of a nematic liquid crystal in contact with a boundary surface, including crystal rotation, capacitive and magnetic null methods.
Abstract: A detailed analysis is given for three techniques used to determine the tilt bias angle of a nematic liquid crystal in contact with a boundary surface. Two of these methods, the crystal rotation and capacitive methods, have severe disadvantages, such as a restricted range of application, an insufficient accuracy, and sometimes require knowledge of nematic material constants which have to be determined by separate experiments. A third and more useful method, a magnetic null method, makes it possible to determine the tilt bias angle directly with only one measurement to an accuracy of 0.1°, regardless of the size of the angle or the nature of the nematic liquid crystal. Using the magnetic null method we have investigated the tilt bias angles of nematics in contact with glass substrates onto which a coating of SiO had been obliquely evaporated. We find that the tilt bias angle decreases with increasing evaporation angle (both angles measured from sample plane) until a critical evaporation angle of ?14° is reached, whereupon the director reorients out of the plane of incidence of the evaporation beam and assumes a direction normal to this plane with a 0° tilt bias. We also find that the tilt bias angle varies from compound to compound for the same evaporation parameters and is influenced by temperature and trace impurities.
321 citations
TL;DR: Conoscopy as an optical method for accurate measurement of crystal tilt angles from interference figures is analyzed for the special case of uniaxial crystals to derive equations developed that are approximations with a limited range of applicability.
Abstract: Conoscopy as an optical method for accurate measurement of crystal
tilt angles from interference figures is analyzed for the special case
of uniaxial crystals. The displacement of interference figures is
related to the crystal tilt angle in an explicit, noniterative manner
that is accurate to within ∼2%. The analysis applies to uniaxial
nematic liquid-crystal monodomains and homogeneous crystals when a
symmetrical center of the conoscopic interference figure is
visible. The equations developed are also used to derive other
previously reported expressions that are approximations with a limited
range of applicability.
47 citations
Patent•
09 Jun 2006
TL;DR: In this paper, a model of the polarization properties of an LCD cell is developed based on estimations of what the physical parameters of the LCD cell (30) are believed to be.
Abstract: Method and apparatus for testing of LCD panels is disclosed. An LCD panel under lest (30) may be mounted to a translatable table (40) between polarization state generator (10) and polarization state analyzer (16). For each location on cell (30) to be tested, a variety of known polarization states (22) are launched through the LCD cell (30) and detected by the polarization state analyzer (16). Electrical signals representative of polarization states are acquired by a computer. Within the computer, a model of polarization properties of the LCD cell (30) is developed based on estimations of what the physical parameters of the LCD cell (30) are believed to be. RMS differences between simulated polarization properties and measured polarization properties are minimized by iteratively refining the modeled physical cell properties, at which point cell thickness and other physical parameters of the LCD cell may be deduced.
30 citations
TL;DR: In this paper, a Mueller-matrix spectrometer was constructed to perform fast, dynamic measurements of the Mueller matrix of small areas of liquid-crystal cells throughout the visible range, which can be used for comparison with theoretical calculations, the determination of material parameters and modelling of the cell as an optical building block for technological use.
Abstract: The Mueller matrix is the transfer matrix in the Stokes algebra that describes the polarization of natural light. This matrix is very versatile for the task of characterizing the optical properties of liquid-crystal cells, since it can be used for comparison with theoretical calculations, the determination of material parameters and the modelling of the cell as an optical building block for technological use. We have constructed a Mueller-matrix spectrometer, with the ability to perform fast, dynamic measurements of the Mueller matrix of small areas of liquid-crystal cells throughout the visible range. To illustrate the potential of the instrument, dynamic measurements on a ferroelectric-liquid-crystal cell are presented and analysed. The optical measurements indicate that there is an asymmetry between the up and the down state, tilted smectic layers and polarization reversal initiated at the boundaries.
25 citations
TL;DR: In this article, a method for phase retardation measurement of a reflective liquid crystal cell is presented, which is based on the heterodyne interferometer theory for probing cell parameters.
10 citations