| 1. |
- Valyukh, Iryna, 1971-, et al.
(författare)
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Characteristic functions for uniformly twisted birefringent media
- 2007
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 102:6, s. 063110-1-063110-7
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Tidskriftsartikel (refereegranskat)abstract
- We present two functions for characterization of birefringent media with application to twisted nematic liquid crystal (LC) cells in the field off state. The first function is for reflective LC cells and the second is for transmissive LC cells. Based on the Stockes formalism, it is shown that these functions describe the ability of a layer of the twisted birefringent medium to change polarization of the output light and are invariant to the layer orientation. The characteristic functions are found in simple procedures and can be used for simultaneous determination of retardation, its wavelength dispersion, and twist angle, as well as for solving optimization problems.
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| 2. |
- Valyukh, Iryna, 1972-, et al.
(författare)
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Characterization of the Photo-Alignment Material SD-1/SDA-2 with Spectroscopic Ellipsometry
- 2007
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Ingår i: Proceedings of the IDW'07, Japan. ; , s. 391-394, s. 391-394, s. 391-394
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Konferensbidrag (refereegranskat)abstract
- Variable angle spectroscopic ellipsometry (VASE) is applied for investigation of the azo-dye SD-1/SD-2 which are used for photoalignment of liquid crystals. The azo-dye was spin coated on silicon substrates. Samples as prepared as well as samples illuminated with polarized UV light were studied. The measured optical constants were modelled with an ensample of the Lorentz oscillators. The results confirm the reorientation mechanism of the photo-induced order formation in the azo-dye films under the action of polarized light, and also show that there exist some photochemical processes.
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| 3. |
- Valyukh, Iryna, et al.
(författare)
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Monochromatic bistable reflective and transfiective ferroelectric LCDs
- 2005
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Ingår i: Proceedings of the 25th International Display Research Conference, Eurodisplay 2005. ; , s. 305-308
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Konferensbidrag (refereegranskat)abstract
- We study single and double polarizer monochromatic bistable reflective and transfective direct view ferroelectric liquid crystal displays (FLCDs). Three types of monochromatic displays are considered Black & White, Black & Yellow, Black & Green. Theoretical approach for finding optimal parameters of an FLCD is presented.
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| 4. |
- Valyukh, Iryna, et al.
(författare)
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Optical properties of thin films of mixed Ni-W oxide made by reactive DC magnetron sputtering
- 2011
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Ingår i: Thin Solid Films. - : Elsevier BV. - 0040-6090 .- 1879-2731. ; 519:9, s. 2914-2918
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Tidskriftsartikel (refereegranskat)abstract
- Thin films of NixW1-x oxides with x = 0.05, 0.19, 0.43 and 0.90 were studied. Films with thicknesses in the range 125-250 nm were deposited on silicon wafers at room temperature by reactive DC magnetron co-sputtering from targets of Ni and W. The films were characterized with X-ray diffraction (XRD), scanning electron microscopy (SEM), and spectroscopic ellipsometry (SE). XRD spectra and SEM micrographs showed that all films were amorphous and possessed a columnar structure. The ellipsometric angles psi and Delta of as-deposited films were measured by a rotating analyzer ellipsometer in the UV-visible-near infrared range (0.63-6.18 eV) and by an infrared Fourier transform rotating compensator ellipsometer in the 500-5200 cm(-1) wavenumber range. SE measurements were performed at angles of incidence of from 50 degrees to 70 degrees. Parametric models were used to extract thicknesses of the thin films and overlayers of NixW1-x oxide at different compositions, band gaps and optical constants. Features in the optical spectra of the NixW1-x oxides were compared with previous data on tungsten oxide, nickel oxide and nickel tungstate.
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| 5. |
- Valyukh, Iryna, 1972-, et al.
(författare)
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Theoretical study of the optical properties of low voltage stacked cholesteric liquid-crystal displays
- 2004
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Ingår i: Asia Display/IMID'04, South Korea. ; , s. 202-204
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Konferensbidrag (refereegranskat)abstract
- We study theoretically optical properties of thin layered stacked monochrome cholesteric liquid-crystal displays. Thin thickness of the layers (~1 µm) allows us appreciably to reduce driving voltage and use such displays in smart cards. Good selective reflection is achieved due to stacked structure. Dependence of the reflectivity of this type of displays on the quality of the layers, their thickness, and liquid crystal birefringence is investigated.
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| 6. |
- Valyukh, Iryna, et al.
(författare)
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UV-induced in-plane anisotropy in layers of mixture of the azo-dyes SD-1/SDA-2 characterized by spectroscopic ellipsometry
- 2008
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Ingår i: Physica Status Solidi. C, Current topics in solid state physics. - Weinheim, Germany : Wiley-VCH Verlagsgesellschaft. ; , s. 1274-1277, s. 1274-1277
-
Konferensbidrag (refereegranskat)abstract
- The optical properties of the azo-dyes SD-1/SDA-2, which are used for photoaligning of liquid crystals (LCs), are investigated with Variable Angle Spectroscopic Ellipsometry (VASE). Films of mixture of SD-1/SDA-2 are deposited by spin coating on silicon wafers. The estimated thickness is approximately 10 nm. To achieve photo-induced anisotropy, one of the samples is illuminated during 15 minutes with linearly polarized UV light followed by thermal stabilization during 1 hour at 150 °C. VASE measurements are performed in the wavelength range 200–1350 nm at several angles of incidence and at different sample orientations. Dielectric functions of azo-dye films without/with polarized UV light illumination were modelled using an ensemble of Lorentz oscillators. The results confirm the diffusion model proposed recently for explanation of the formation of the photo-induced order in azo-dye films under the action of polarized light. Refractive indices, their wavelength dispersion and thicknesses of films of SD-1/SDA-2 are reported here.
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| 7. |
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| 8. |
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| 9. |
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| 10. |
- Valyukh, Sergiy, et al.
(författare)
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Liquid-crystal based light steering optical elements
- 2011
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Ingår i: Photonics Letters of Poland. - : Photonics Society of Poland. - 2080-2242. ; 3:2, s. 88-90
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Tidskriftsartikel (refereegranskat)abstract
- Potential abilities of active optical elements based onliquid crystals are investigated. We consider liquid crystal cells in whicha desired distribution of the liquid crystal director is achieved by a non-uniform electric field and by inhomogeneous boundary conditions. Theoptical elements built on principles of diffractive optics are discussed.
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| 11. |
- Valyukh, Sergiy, et al.
(författare)
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Liquid crystal light deflecting devices based on nonuniform anchoring
- 2010
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Ingår i: APPLIED PHYSICS LETTERS. - : American Institute of Physics. - 0003-6951 .- 1077-3118. ; 97:23, s. 231120-
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Tidskriftsartikel (refereegranskat)abstract
- Tunable liquid crystal light deflecting devices based on nonuniform anchoring energy are proposed. These devices have uniform thicknesses of the layers they are composed of, and beam deviation is controlled with a uniform electrical field. Potential applicability of such an approach in beam deflectors and active lenses is investigated. It is shown that the approach is a competitive alternative to liquid crystal light deflecting devices, in which the needed spatial distribution of liquid crystal molecules is achieved either due to nonuniform thickness or due to generation of nonuniform electrical field.
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| 12. |
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| 13. |
- Valyukh, Sergiy, et al.
(författare)
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Spectrophotometric determination of reflective liquid crystal cell parameters
- 2006
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550 .- 8750-7587 .- 1522-1601. ; 99, s. 053102-1-053102-6
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Tidskriftsartikel (refereegranskat)abstract
- We introduce a method for determination of the optical retardation, its wavelength dispersion, the cell twist angle, and the orientation of the input director in a reflective liquid crystal (LC) cell. These parameters are found from the extremes of a characteristic function defined as a sum of two spectral reflectivities of the LC cell placed between a pair of linear polarizers. The reflectivities are measured for two cell orientations, one of which is arbitrary and the other one is turned through 45°. Both theoretical analysis and experimental procedures are presented. Excellent agreement between the experiment and our theory has been found. The proposed method can be applied to the measurements of reflective LC cells with small and large cell gaps, as well as with small and large twist angles.
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| 14. |
- Valyukh, Sergiy, et al.
(författare)
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Study on Birefringent Color Generation for a Reflective Ferroelectric Liquid Crystal Display
- 2006
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Ingår i: Japanese Journal of Applied Physics. - 0021-4922 .- 1347-4065. ; 45:10A, s. 7819-7826
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Tidskriftsartikel (refereegranskat)abstract
- We study the possibility of a layer of a surface stabilized ferroelectric liquid crystal coupled with several retardation plates for birefringent color generation. Double and single polarizer reflective bistable dichromatic ferroelectric liquid crystal displays are considered. We demonstrate that one or two retardation plates are sufficient for a display having good color characteristics and high brightness. Optimal parameters for green/red and blue/yellow ferroelectric liquid crystal displays are found.
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| 15. |
- Valyukh, Vladimir, et al.
(författare)
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Mobile multifunctional system for characterization of LC cells and LC materials
- 2011
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Ingår i: SID Symposium Digest of Technical Papers. - : John Wiley & Sons. - 0097-966X .- 2168-0159. ; 42:1, s. 1241-1244
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Tidskriftsartikel (refereegranskat)abstract
- A compact measuring system for determination of electoro-optical time resolved characteristics of LC cells, as well as optical retardation and twist angle, has been developed. Moreover, the system enables one to measure anchoring energy, elastic and dielectric constants of LC materials. Software of the system contains functions for simulation and optimization of LC devices.
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| 16. |
-
Advanced Energy Materials
- 2014
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Samlingsverk (redaktörskap) (övrigt vetenskapligt/konstnärligt)abstract
- An essential resource for scientists designing new energy materials for the vast landscape of solar energy conversion as well as materials processing and characterizatio.Based on the new and fundamental research on novel energy materials with tailor-made photonic properties, the role of materials engineering has been to provide much needed support in the development of photovoltaic devices. Advanced Energy Materials offers a unique, state-of-the-art look at the new world of novel energy materials science, shedding light on the subject's vast multi-disciplinary approach.The book focuses particularly on photovoltaics, efficient light sources, fuel cells, energy-saving technologies, energy storage technologies, nanostructured materials as well as innovating materials and techniques for future nanoscale electronics. Pathways to future development are also discussed.Critical, cutting-edge subjects are addressed, including:Non-imaging focusing heliostat; state-of-the-art of nanostructuresMetal oxide semiconductors and their nanocompositesSuperionic solids; polymer nanocomposites; solid electrolytes; advanced electronicsElectronic and optical properties of lead sulfideHigh-electron mobility transistors and light-emitting diodesAnti-ferroelectric liquid crystals; PEEK membrane for fuel cellsAdvanced phosphors for energy-efficient lightingMolecular computation photovoltaics and photocatalystsPhotovoltaic device technology and non-conventional energy applicationsReadershipThe book is written for a large and broad readership including researchers and university graduate students from diverse backgrounds such as chemistry, materials science, physics, and engineering working in the fields of nanotechnology, photovoltaic device technology, and non-conventional energy.
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| 17. |
- Arwin, Hans, et al.
(författare)
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On the polarization of light reflected from beetle cuticle
- 2017
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Ingår i: MATERIALS TODAY-PROCEEDINGS. - : ELSEVIER SCIENCE BV. ; , s. 4933-4941
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Konferensbidrag (refereegranskat)abstract
- The use of Mueller matrices for studies of polarizing properties and cuticle structure of scarab beetles are partly reviewed. Specifically we show how the polarization of the reflected light can be quantified in terms of degree of polarization and ellipticity. It is also shown that sum decomposition of Mueller matrices reveals cuticle reflection characteristics in different spectral regions, e.g. in terms of mirrors and circular polarizers. With a differential decomposition of cuticle transmission Mueller matrices, we determine the spectral variation in the fundamental optical properties circular birefringence and dichroism. (C) 2017 Elsevier Ltd. All rights reserved.
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| 18. |
- Bi, Shubo, et al.
(författare)
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Influence of no-core fiber on the focusing performance of an ultra-small gradient-index fiber probe
- 2018
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Ingår i: Optics and lasers in engineering. - : ELSEVIER SCI LTD. - 0143-8166 .- 1873-0302. ; 107, s. 46-53
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Tidskriftsartikel (refereegranskat)abstract
- The light-beam expansion effect of a no-core fiber on the focusing performance of an ultra-small gradient-index fiber probe is investigated with a view to optimizing the optical performance of such probes. By taking the variable relationship between the focusing performance (including the working distance and the focusing spot size) of the probe and the length of the no-core fiber as the criterion, the effective beam expansion length of the no-core fiber in the ultra-small gradient-index fiber probe is calculated based on the basic properties of the Gaussian beam. Verification and analysis are done by numerical calculations and experimental measurements, respectively. The obtained results show that the working distance of an ultra-small gradient-index fiber probe can be increased effectively by adding a no-core fiber; however, this will lead to increasing the focusing spot size. For the parameters of the fiber probe studied here, the effective beam expansion length of the no-core fiber spacer is less than 0.357 mm. (C) 2018 Elsevier Ltd. All rights reserved.
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| 19. |
- Chang, Lin, et al.
(författare)
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Multi-surface phase-shifting algorithm using the window function fitted by the nonlinear least squares method
- 2022
-
Ingår i: Journal of Modern Optics. - : TAYLOR & FRANCIS LTD. - 0950-0340 .- 1362-3044. ; 69:3, s. 160-171
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Tidskriftsartikel (refereegranskat)abstract
- A multi-surface phase demodulation algorithm is proposed to measure surfaces of the transparent plate simultaneously. A non-linear least-squares method based on the trust region is utilized to fit the window function derived from the characteristic polynomials. The fitted window function requires fewer parameters and has a flexible form, which means the window length can be stretched freely and used flexibly. Then, a multi-surface phase demodulation technique combining the discrete Fourier principle and the fitted window function is investigated, allowing simultaneous reconstruction of the measured front surface, rear surface, and thickness variation. During the implementation of our algorithm, the processing time for the interferograms with 850x850 pixels is around 5.1s. Measurement errors caused by several factors are analyzed, including wavelength-tuning error, frequency order error, cavity length error, and average thickness error. The experimental result on a rectangular transparent plate further verifies the effectiveness of our algorithm.
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| 20. |
- Chang, Lin, et al.
(författare)
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Multisurface Interferometric Algorithm and Error Analysis With Adaptive Phase Shift Matching
- 2022
-
Ingår i: IEEE Transactions on Instrumentation and Measurement. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 0018-9456 .- 1557-9662. ; 71
-
Tidskriftsartikel (refereegranskat)abstract
- To simultaneously measure topographies of both surfaces of a transparent plate through wavelength-tuning interferometry at arbitrary cavity lengths, a flexible phase shift matching algorithm (FPSMA) is proposed. The FPSMA includes two parts: 1) taking the four-term third-order Nuttall window as an example, a phase demodulation approach is designed and analyzed for extracting the harmonic phases of the front surface, rear surface, and thickness variation of the measured plate and 2) based on the residual error analysis of the developed 5N-Nuttall algorithm for different cavity length coefficients M and the phase-shifting parameters N , a parameter-change technique that allows the developed phase demodulation approach is applied to arbitrary cavity lengths by adaptively changing the phase shifts and frames of the captured interferograms. By this technique, the algorithm failures due to the spectral aliasing of harmonics can be avoided effectively and conveniently, and then the correct phase demodulation can be ensured. Besides, using the developed method, when the values of N or M are chosen in advance, the corresponding available measurement ranges can be given. Besides, the relationship between the window length and the measurement limitation of the measurable thinnest optical thickness is investigated. Considering the common linear and nonlinear errors in the wavelength-shifting process, the error analysis of FPSMA is performed and discussed for situations close to reality. The comparative studies and the experimental results of two transparent parallel plates also support the performance of the developed FPSMA.
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| 21. |
- Chen, Dingfu, et al.
(författare)
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Bayesian uncertainty evaluation of stitching interferometry for cylindrical surface
- 2020
-
Ingår i: Measurement. - : ELSEVIER SCI LTD. - 0263-2241 .- 1873-412X. ; 157
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Tidskriftsartikel (refereegranskat)abstract
- Uncertainty evaluation is one of the most important concepts in metrological characterizations. This paper proposes a method for uncertainty evaluation of measurements of cylindrical surfaces by means of stitching interferometry. The proposed method is based on the Bayesian statistical analysis. The prior deviation for a tested surface is determined by both calculation of standard deviation through multiple measurements of a single sub-aperture and calibration of the optical system error. The probability distribution functions (PDF) of the prior and real misalignment error and measured data of the aperture are derived according to the stitching model. Simulated observations are approximated with the Gibbs Sampler using the Markov Chain Monte Carlo (MCMC) method. Our proposed method is a promising alternative to the ordinary least square technique (LST) with the maximum likelihood estimation (MLE) for obtaining the uncertainty of the misalignment and measurement error in the stitching results. Moreover, it can take the inevitable environment errors into account. The prediction of the uncertainty interval makes our method more attractive in industrial applications. (C) 2020 Elsevier Ltd. All rights reserved.
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| 22. |
- Chen, Dingfu, et al.
(författare)
-
Measurement of High Numerical Aperture Cylindrical Surface with Iterative Stitching Algorithm
- 2018
-
Ingår i: Applied Sciences. - : MDPI. - 2076-3417. ; 8:11
-
Tidskriftsartikel (refereegranskat)abstract
- There are some limitations in null test measurements in stitching interferometry. In order to meet the null test conditions, the moving distance between the sub-apertures often deviates from the theoretical preset distance, which leads to a position deviation of sub-apertures when measured. To overcome this problem, an algorithm for data processing is proposed in this paper. An optimal estimation of the deviation between sub-apertures is used to update their positions, and then a new overlapped region is obtained and again optimized. This process is repeated until the algorithm converges to an acceptable tolerance, and finally exact stitching is realized. A cylindrical lens was taken as an object for experimental examination of the proposed method. The obtained results demonstrate the validity, reliability, and feasibility of our iterative stitching algorithm.
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| 23. |
- Chen, Dingfu, et al.
(författare)
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Stitching interferometry of cylindrical surface
- 2022
-
Ingår i: Optics and lasers in engineering. - : ELSEVIER SCI LTD. - 0143-8166 .- 1873-0302. ; 157
-
Tidskriftsartikel (refereegranskat)abstract
- High resolution and high precision are advantages of measuring cylindrical objects employing stitching interferometry. However, due to errors in the cylinder position in a measurement procedure, it is difficult to ensure the accuracy of a macroscopic shape contour and surface waviness contour of the workpiece of the stitching results. To overcome this problem, we proposed a new strategy of stitching interferometry for cylindricity calibration. The measuring process is divided into two parts to measure the macroscopic shape and waviness contour, respectively. Finally, the two measurement results are merged to produce an accurate and complete 360 degrees form map. Besides, we build a two-dimensional Gaussian filter weighting function for a cylindrical profile according to its special shape characteristic. To express the stitching results more precisely, we provide the uncertainty map and power spectral density of the stitching results. An experiment is carried out by taking a ceramic plug gage as the workpiece. The results demonstrate the excellent performance of our method in analyzing the characteristic of the cylindrical profile and show good agreement with such by using cylindricity measuring instruments.
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| 24. |
- Fernandes, Rui D. V., et al.
(författare)
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Iridescence Mimicking in Fabrics: A Ultraviolet/Visible Spectroscopy Study
- 2024
-
Ingår i: BIOMIMETICS. - : MDPI. - 2313-7673. ; 9:2
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Tidskriftsartikel (refereegranskat)abstract
- Poly(styrene-methyl methacrylate-acrylic acid) photonic crystals (PCs), with five different sizes (170, 190, 210, 230 and 250 nm), were applied onto three plain fabrics, namely polyamide, polyester and cotton. The PC-coated fabrics were analyzed using scanning electronic microscopy and two UV/Vis reflectance spectrophotometric techniques (integrating sphere and scatterometry) to evaluate the PCs' self-assembly along with the obtained spectral and colors characteristics. Results showed that surface roughness of the fabrics had a major influence on the color produced by PCs. Polyamide-coated fabrics were the only samples having an iridescent effect, producing more vivid and brilliant colors than polyester and cotton samples. It was observed that as the angle of incident light increases, a hypsochromic shift in the reflection peak occurs along with the formation of new reflection peaks. Furthermore, color behavior simulations were performed with an illuminant A light source on polyamide samples. The illuminant A simulation showed greener and yellower structural colors than those illuminated with D50. The polyester and cotton samples were analyzed using scatterometry to check for iridescence, which was unseen upon ocular inspection and then proven to be present in these samples. This work allowed a better comprehension of how structural colors and their iridescence are affected by the textile substrate morphology and fiber type.
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| 25. |
- Hsiao, Ching-Lien, et al.
(författare)
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Curved-lattice epitaxial growth of chiral AlInN twisted nanorods for optical applications
- 2012
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Despite of using chiral metamaterials to manipulate light polarization states has been demonstrated their great potential for applications such as invisible cloaks, broadband or wavelength-tunable circular polarizers, microreflectors, etc. in the past decade [1-6], operating wavelength in ultraviolet-visible range is still a challenge issue. Since these chiral structures often consist of metallic materials, their operation is designed for the infrared and microwave regions [2-4]. Here, we show how a controlled curved-lattice epitaxial growth (CLEG) of wide-bandgap AlInN semiconductor curved nanocrystals [7] can be exploited as a novel route for tailoring chiral nanostructures in the form of twisted nanorods (TNRs). The fabricated TNRs are shown to reflect light with a high degree of polarization as well as a high degree of circular polarization (that is, nearly circularly polarized light) in the ultravioletvisible region. The obtained polarization is shown to be dependent on the handedness of the TNRs.
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| 26. |
- Hsiao, Ching-Lien, et al.
(författare)
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Curved-Lattice Epitaxial Growth of InxAl1-xN Nanospirals with Tailored Chirality
- 2015
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Ingår i: Nano letters (Print). - : American Chemical Society (ACS). - 1530-6984 .- 1530-6992. ; 15:1, s. 294-300
-
Tidskriftsartikel (refereegranskat)abstract
- Chirality, tailored by external morphology and internal composition, has been realized by controlled curved-lattice epitaxial growth (CLEG) of uniform coatings of single-crystalline InxAl1-xN nanospirals. The nanospirals are formed by sequentially stacking segments of curved nanorods on top of each other, where each segment is incrementally rotated around the spiral axis. By controlling the growth rate, segment length, rotation direction, and incremental rotation angle, spirals are tailored to predetermined handedness, pitch, and height. The curved morphology of the segments is a result of a lateral compositional gradient across the segments while maintaining a preferred crystallographic growth direction, implying a lateral gradient in optical properties as well. Left- and right-handed nanospirals, tailored with 5 periods of 200 nm pitch, as confirmed by scanning electron microscopy, exhibit uniform spiral diameters of ~80 nm (local segment diameters of ~60 nm) with tapered hexagonal tips. High resolution electron microscopy, in combination with nanoprobe energy dispersive X-ray spectroscopy and valence electron energy loss spectroscopy, show that individual nanospirals consist of an In-rich core with ~15 nm-diameter hexagonal cross-section, comprised of curved basal planes. The core is surrounded by an Al-rich shell with a thickness asymmetry spiraling along the core. The ensemble nanospirals, across the 1 cm2 wafers, show high in-plane ordering with respect to shape, crystalline orientation, and direction of compositional gradient. Mueller matrix spectroscopic ellipsometry shows that the tailored chirality is manifested in the polarization state of light reflected off the CLEG nanospiral-coated wafers. In that, the polarization state is shown to be dependent on the handedness of the nanospirals and the wavelength of the incident light in the ultraviolet-visible region.
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| 27. |
- Kalustova, Daria, et al.
(författare)
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Color temperature tunable RGBW cluster with optimize color rendering and efficacy
- 2023
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Ingår i: Optical Engineering. - : SPIE-SOC PHOTO-OPTICAL INSTRUMENTATION ENGINEERS. - 0091-3286 .- 1560-2303. ; 62:4
-
Tidskriftsartikel (refereegranskat)abstract
- Our work is devoted to the optimization of 4-component RGBW smart lighting systems that are able to obtain the resulting white light with a combination of high color rendering and luminous efficacy for a certain fixed correlated color temperature. Three approaches for the determination of the optimal brightness contributions of the light emitting diodes (LEDs) are studied. They are accordingly based on: (1) maximization of the color rendering, (2) prioritizing to reduce the color rendering maximum by 1 to 6 units to increase luminous efficacy, and (3) getting a constant value of RGB contribution and luminous efficacy while maintaining high color rendering. A comparison of the three systems with different base white LEDs is demonstrated. The obtained theoretical results are verified experimentally.
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| 28. |
- Kalustova, Darla, et al.
(författare)
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Color temperature tunable RGBW clusters with 3 control channels
- 2020
-
Ingår i: Photonics Letters of Poland. - Warsaw, Poland : PHOTONICS SOC POLAND. - 2080-2242. ; 12:1, s. 10-12
-
Tidskriftsartikel (refereegranskat)abstract
- The work is devoted to the development of a smart lighting system that is able to change correlated colour temperature and consists of tunable 4-components RGBW clusters controlled via three channels. It is shown that fixing a ratio between the intensities of white and red LEDs at a level of 100:9 enables obtaining high values of colour rendering in a wide range of correlated colour temperatures. The control of 3 from 4 channels simplifies the system. The influence of the red LED on CRI and luminous efficiency is analysed.
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| 29. |
- Kalustova, D. O., et al.
(författare)
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RGBW lighting systems : Influence of the white LED
- 2022
-
Ingår i: Semiconductor Physics, Quantum Electronics & Optoelectronics. - : National Academy of Sciences Ukraine ; Institute of Semiconductor Physics. - 1560-8034 .- 1605-6582. ; 25:1, s. 76-82
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Tidskriftsartikel (refereegranskat)abstract
- People spend most of the time under artificial light sources, so it is important to create a comfortable lighting environment for work and rest. Four-component RGBW systems are the most effective for this. It is needed to create methods for obtaining white light with the specified parameters and choose the most optimal LED components. In this work, the influence of the white LEDs parameters on the resulting white light of the RGBW systems is studied. Two different methods proposed by us earlier for obtaining white light are applied for three RGBW systems with different warm white LEDs. It is shown that the use of white LEDs with a colour rendering index close to 80 is more optimal for most applications. In this case, they provide the resulting white light with the colour rendering index above 90 and luminous efficacy above 130 lm/W.
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| 30. |
- Kalustova, Daria, et al.
(författare)
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Red, green, blue, and white clusters for daylight reproduction
- 2020
-
Ingår i: Optical Engineering. - : SPIE-SOC PHOTO-OPTICAL INSTRUMENTATION ENGINEERS. - 0091-3286 .- 1560-2303. ; 59:5
-
Tidskriftsartikel (refereegranskat)abstract
- Daylight is an inherent attribute of a sustainable building. Artificial reproduction of natural illumination under varying needs and environmental conditions has been made possible after the appearance of the new wave of solid-state light sources. Our work is devoted to the development of white light-emitting diode (LED) clusters consisting of red, green, blue, and white (RGBW) LEDs for implementation in a smart lighting system that is able to reproduce light with correlated color temperature (CCT) similar to daylight, high values of color rendering index, and luminous efficacy. A method for determination of the optimal contribution of each of the four LEDs is demonstrated and discussed. We show that only three LEDs-green, blue, and white (no red) can be used in many cases for reproducing daylight. Both luminous efficacy of radiation and actual luminous efficacy of the considered RGBW clusters as functions of the CCT are analyzed. (C) 2020 Society of Photo-Optical Instrumentation Engineers (SPIE).
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| 31. |
- Patra, Hirak Kumar, et al.
(författare)
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Switchable label free apta-nanosensor: In situ biopsy?
- 2016
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Ingår i: <em>Biosensors 2016 – The World Congress on Biosensors</em>, Gothenburg, Sweden, 25-27 May 2016. - : Elsevier.
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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| 32. |
- Pranovich, Alina, 1993-, et al.
(författare)
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Angular dependent reflectance spectroscopy of RGBW pigments
- 2022
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Traditional printing relies primarily on subtractive color mixing techniques. In this case, optical color mixing is achieved by one of the established halftoning methods that use Cyan, Magenta, Yellow and Black (CMYK) primaries on a reflective white substrate. The reason behind the subtractive color mixing in printing is the high absorbance of available pigments used in inks. A new type of mica-based pigments that exhibit high reflectivity at Red, Green, Blue and White (RGBW) spectral bands was recently introduced by Merck (SpectravalTM). Printing with RGBW primaries on black background allows additive color mixing in prints. While offering excellent color depth, the reflected spectra of such pigments vary with the angles of incidence and observation. As a result, new approaches in modelling the appearance of prints as well as strategies for color separation and halftoning are needed. The prior optical characterization of the reflective inks is an essential first step. For this purpose, we have used SpectravalTM pigments to prepare acrylic based inks, which we applied on glass slides by screen printing. In this work, we measured the relative spectral bidirectional reflection distribution of Red, Green, Blue and White reflective inks. The measurements were conducted on an experimental set up consisting of a goniometer, spectrometer, and a xenon light source. Based on the measurements, we simulate the reflectance spectra under diffuse illumination and demonstrate ratios of red, green, and blue spectral components for different observation angles of individual inks and their combinations.
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| 33. |
- Pranovich, Alina, 1993-, et al.
(författare)
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Dot Off Dot Screen Printing with RGBW Reflective Inks
- 2023
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Ingår i: Journal of Imaging Science and Technology. - : The Society for Imaging Science and Technology. - 1062-3701 .- 1943-3522. ; 67:3
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Tidskriftsartikel (refereegranskat)abstract
- Recent advances in pigment production resulted in the possibility to print with RGBW primaries instead of CMYK and performing additive color mixing in printing. The RGBW pigments studied in this work have the properties of structural colors, as the primary colors are a result of interference in a thin film coating of mica pigments. In this work, we investigate the angle-dependent gamut of RGBW primaries. We have elucidated optimal angles of illumination and observation for each primary ink and found the optimal angle of observation under diffuse illumination. We investigated dot off dot halftoned screen printing with RGBW inks on black paper and in terms of angle-dependent dot gain. Based on our observations, optimal viewing condition for the given RGBW inks is in a direction of around 30◦ to the surface normal. Here, the appearance of the resulting halftoned prints can be estimated well by Neugebauer formula (weighted averaging of the individual reflected spectra). Despite the negative physical dot gain during the dot off dot printing, we observe angularly dependent positive optical dot gain for halftoned prints. Application of interference RGBW pigments in 2.5D and 3D printing is not fully explored due to the technological limitations. In this work, we provide colorimetric data for efficient application of the angle-dependent properties of such pigments in practical applications.
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| 34. |
- Pranovich, Alina, 1993-, et al.
(författare)
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Empirical BRDF model for goniochromatic materials and soft proofing with reflective inks.
- 2024
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Ingår i: IEEE Computer Graphics and Applications. - 0272-1716 .- 1558-1756.
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Tidskriftsartikel (refereegranskat)abstract
- The commonly used analytic bidirectional reflectance distribution functions (BRDFs) do not model goniochromatism, that is, angle-dependent material color. The material color is usually defined by a diffuse reflectance spectrum or RGB vector and a specular part based on a spectral complex index of refraction. Extension of the commonly used BRDFs based on wave theory can help model goniochromatism, but this comes at the cost of significant added model complexity. We measured the goniochromatism of structual color pigments used for additive color printing and found that we can fit the observed spectral angular dependence of the bidirectional reflectance using a simple modification of the standard microfacet BRDF model. All we need to describe the goniochromatism is an empirically-based spectral parameter, which we use in our model together with a specular reflectance spectrum instead of the spectral complex index of refraction. We demonstrate the ability of our model to fit the measured reflectance of red, green, and blue commercial structural color pigments. Our BRDF model enables straightforward implementation of a shader for interactive preview of 3D objects with printed spatially and angularly varying texture.
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| 35. |
- Pranovich, Alina, 1993-
(författare)
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Modelling appearance printing : Acquisition and digital reproduction of translucent and goniochromatic materials
- 2024
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Colour perception is fundamental to our everyday experiences, allowing us to communicate and interpret visual information effectively. Yet, replicating these experiences accurately poses a significant challenge, particularly in the context of full-colour 3D printing. Advances in this field have revolutionised the fabrication of customised prosthetic body parts, such as eyes, teeth, and skin features, with profound implications for medical and aesthetic applications.The key to successful 3D printing lies in the digital preview of objects before fabrication, enabling users to assess colour reproduction and quality. However, accurately representing colour in a digital environment is complex, as it depends on numerous factors, including illumination, object shape, surface properties, scene context, and observer characteristics. Traditional methods of previewing conventional 2D prints overlook this complexity.This thesis addresses this challenge by focusing on two types of materials: semitransparent polymers commonly used in 3D printing, and goniochromatic colorants employed in printing to introduce unique effects unattainable with conventional inks for 2D printing. For semitransparent materials, we developed an empirical function to represent colour based on sample thickness, enabling efficient digital representation. Additionally, we adapted a colour measuring device to identify two key material parameters, absorption and scattering coefficients, essential for accurate colour reproduction.Goniochromatic materials, such as thin film-coated mica particles, are slightly more complicated and less predictive in terms of their final colour appearance. Although not yet used in 3D printing, these particles used in conventional printing introduce colour variation while rotating the print. We found that goniochromatic properties can be expressed with an empirically found function after collecting angle-dependent light reflecting properties of the sample. We used this function and showed how prints with goniochromatic materials can be efficiently previewed on a computer monitor.
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| 36. |
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| 37. |
- Sun, Tao, et al.
(författare)
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Algorithm for Surfaces Profiles and Thickness Variation Measurement of a Transparent Plate Using a Fizeau Interferometer with Wavelength Tuning
- 2019
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Ingår i: Applied Sciences. - : MDPI. - 2076-3417. ; 9:11
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Tidskriftsartikel (refereegranskat)abstract
- An interferogram obtained from a transparent plate contains information on the profiles of both surfaces and on the thickness variation. The present work is devoted to the processing of interferograms of this type. The processing technique is based on a 36-step algorithm developed by the authors for characterization of transparent plates having approximately equal reflections from both sides. The algorithm utilizes weighted multi-step phase shifting that enables one not only separately to extract the front and rear surface profiles together with the thickness variation of the tested plate but also to suppress the coupling errors between the higher harmonics and phase-shift deviation. The proposed measuring method was studied on a wavelength tunable Fizeau interferometer. The tested sample had an optical thickness and surface profile deviations equal to 0.51 µm, 1.38 µm and 0.89 µm, respectively. According to the results obtained using 10 repeated measurements, the root mean square (RMS) errors for determining both surface profiles did not exceed 1.5 nm. Experimental results show that the setup and presented 36-step algorithm are suitable for the measurement of a transparent plate of arbitrary thickness.
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| 38. |
- Sun, Tao, et al.
(författare)
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Calibration of Tunable Diode Laser Wavelength Based on Energy Centrobaric Correction Method for Discrete Spectrum
- 2018
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Ingår i: SIXTH INTERNATIONAL CONFERENCE ON OPTICAL AND PHOTONIC ENGINEERING (ICOPEN 2018). - : SPIE-INT SOC OPTICAL ENGINEERING. - 9781510622579
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Konferensbidrag (refereegranskat)abstract
- The resolution of wavelength scanning of diode laser can influence the performance of interferometer mostly. In this article, we propose a method to improve the precision of wavelength calibration by using the theory of energy centrobaric correction for discrete spectrum. An optical wedge whose angle of tilt was known has been set in the optical system to measure the series of wavelength on time using a 2D Fourier Transfer (FT) of the interferograms generated by both surfaces of optical wedge. An energy centrobaric correction method is also put forward to evaluate the distribution of frequency and phase of fringe pattern generated by front and rear surface of optical wedge. The results of simulation and experiment show that the error of wavelength calibration reach to 0.01pm by correlating the distribution of frequency and phase of interferograms. The benefit is that the precision of wavelength of diode laser is improved significantly with a higher signal-to-noise ratio. This method can used to any tunable diode laser wavelength to improve the precision of measurement due to its simplicity and practicability.
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| 39. |
- Sun, Tao, et al.
(författare)
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Determination of surface profiles of transparent plates by means of laser interferometry with wavelength tuning
- 2019
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Ingår i: Optics and lasers in engineering. - : ELSEVIER SCI LTD. - 0143-8166 .- 1873-0302. ; 115, s. 59-66
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Tidskriftsartikel (refereegranskat)abstract
- An interferogram obtained from a transparent plate contains information about the profiles of both surfaces of the plate. This information can be extracted by processing fringe patterns measured at different wavelengths. The conventional Fourier analysis applied to solve such problems for a set of a restricted number of the fringe patterns is quite sensitive to the error of detuning the wavelength shifting and suffers from fringe patterns interference noise. This study proposes a method for finding surface profiles of a transparent plate using a series of fringe patterns obtained at different phase shifts caused by wavelength changes. The data treatment is based on the analytical approach for describing spatial distributions of irradiance in interference patterns. The results show that the proposed method is feasible. The experimental setup used herein was a Fizeau interferometer with tunable wavelength laser. A glass plate approximately 1 cm thick was as the test sample. According to the obtained results, the root mean square (RMS) errors for determining both surface profiles did not exceed 2.3 nm.
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| 40. |
- Valyukh, Sergiy, et al.
(författare)
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A Liquid Crystal Lens Array-Based Projection System for NearEye Displays
- 2012
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Ingår i: The 19th International Display Workshops in conjunction with Asia Display, 2012. - Kyoto, 2012. ; , s. 1305-1308
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- A projection optical system for hypothetic near eyedisplays that can be built into a contact lens or glasses isconsidered. The system parameters are evaluated.Aspects of practical usage of the displays and possibleembodiments of the optical system are discussed.
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| 41. |
- Valyukh, Sergiy, et al.
(författare)
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A Liquid Crystal Lens with Non-uniform Anchoring Energy
- 2008
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Ingår i: SID Digest, 2008. ; , s. 659-662
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Konferensbidrag (refereegranskat)abstract
- The study of a tunable liquid crystal lens having a uniform cell gap, uniform applied voltage and non-uniform anchoring energy was done. Optimal parameters of such a lens were found and discussed. We demonstrated that producing a desired director gradient profile with non-uniform spatial distribution of the anchoring energy is a good alternative for other known methods applied for liquid crystal lenses.
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| 42. |
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| 43. |
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| 44. |
- Valyukh, Sergiy
(författare)
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Adaptive liquid crystal lenses for display applications
- 2012
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Ingår i: SID-ME Spring Meeting 2012.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- This work is devoted to study of adaptive liquid (LC) lens arrays utilized as a switcher between 2D and 3D autostereoscopic displays. In addition, the adaptive lens array can set and control viewing zones of an autostereoscopic display. The needed spatial distribution of LC director caused the lens effect can be achieved due to a non-uniform electric field or inhomogeneous alignment. In order to obtain a non-uniform electric field, it is necessary a pattered structure of electrodes or a specific design, e.g. non-uniform thickness of a dielectric layer sandwiched between the electrodes and LC. The inhomogeneous alignment is achieved due to a non-uniform distribution of the pre-tilt angle or anchoring energy. Analysis of adaptive LC lenses based on a non-uniform electric field and inhomogeneous alignment is done.
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| 45. |
- Valyukh, Sergiy, et al.
(författare)
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Assessment of minimum permissible geometrical parameters of a near-to-eye display
- 2015
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Ingår i: Applied Optics. - : Optical Society of America. - 1559-128X .- 2155-3165. ; 54:21, s. 6526-6533
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Tidskriftsartikel (refereegranskat)abstract
- Light weight and small dimensions are some of the most important characteristics of near-to-eye displays (NEDs). These displays consist of two basic parts: a microdisplay for generating an image and supplementary optics in order to see the image. Nowadays, the pixel size of microdisplays may be less than 4 mu m, which makes the supplementary optics the major factor in defining restrictions on a NED dimensions or at least on the distance between the microdisplay and the eye. The goal of the present work is to find answers to the following two questions: how small this distance can be in principle and what is the microdisplay maximum resolution that stays effective to see through the supplementary optics placed in immediate vicinity of the eye. To explore the first question, we consider an aberration-free magnifier, which is the initial stage in elaboration of a real optical system. In this case, the paraxial approximation and the transfer matrix method are ideal tools for simulation of light propagation from the microdisplay through the magnifier and the human eyes optical system to the retina. The human eye is considered according to the Gullstrand model. Parameters of the magnifier, its location with respect to the eye and the microdisplay, and the depth of field, which can be interpreted as the tolerance of the microdisplay position, are determined and discussed. The second question related to the microdisplay maximum resolution is investigated by using the principles of wave optics. (C) 2015 Optical Society of America
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| 46. |
- Valyukh, Sergiy, et al.
(författare)
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Bragg reflection from periodic helicoidal media with laterally graded refractive index
- 2017
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Ingår i: Optical materials (Amsterdam). - : ELSEVIER SCIENCE BV. - 0925-3467 .- 1873-1252. ; 72, s. 334-340
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Tidskriftsartikel (refereegranskat)abstract
- Light interaction with a columnar structure of InxAl1-xN where each column is a layered periodic helical medium with laterally graded refractive index is considered. It is demonstrated that such a columnar structure can be presented as a stack of layers with a gradient of the refractive index. To calculate reflectance in the proposed model, the 2 x 2 characteristic matrix method adopted for a gradient index medium was applied. The influence of the refractive indices (including absorption), parameters of the twisting, and thickness of the periodic structure on reflectance is studied. Cases of normal and oblique incident light are considered. The presented medium is a one-dimensional photonic crystal that can be utilized in many devices for light manipulation. (C) 2017 Published by Elsevier B.V.
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| 47. |
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| 48. |
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| 49. |
- Valyukh, Sergiy, et al.
(författare)
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Characterization of flexible reflective liquid crystal cells
- 2005
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Ingår i: Journal of the Society for Information Display. - : Wiley. - 1071-0922 .- 1938-3657. ; 13:6, s. 501-506
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Tidskriftsartikel (refereegranskat)abstract
- We consider peculiarities in testing flexible reflective liquid-crystal (LC) cells. Several new methods for measuring optical retardation of filled reflective LC cells on plastic substrates are proposed. Cases when the plastic is anisotropic and the LC cell consists of either one or two internal polarizers are studied. The majority of proposed methods can be applied for transmissive LC cells as well as for measuring twist angle.
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| 50. |
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