Polarized Light in Liquid Crystals and Polymers
Equation 1 represents the fact that the V th decreases with the increase [decrease] of UV light intensity [LC droplet size, D ] as shown in Figure 8. Decreasing concentration of NOA65 to increase LC droplet size can further decrease V th orange curve , but the initial transmission might increase to decrease the contrast ratio, which can refer to Figure 4 [ 1 , 2 ]. It is well-known that the surface anchoring of NOA65 is weak [ 1 ].
The experimental setup for the following experiments was identical with that shown in Figure 3 , except for the addition of the polarizer, which was placed between the NDF and the beam splitter. The scattering performances of the PSMLS when various electric potentials were applied onto the blue and light-yellow interdigital electrode stripes Figure 2 a are discussed in the following paragraph. The orange and blue curves in Figure 11 a show the T-V curves of the PSMLS when the polarization directions of the incident lights were parallel and perpendicular to the direction of the interdigital electrode stripes, respectively.
The experimental results show that the lights with a polarization direction parallel to the direction of the interdigital electrode stripes can pass through the PSMLS, whereas the lights with a polarization direction perpendicular to the interdigital electrode stripes are scattered.
Polarized Light in Liquid Crystals and Polymers | Wiley Online Books
Figure 11 b shows the observation of the PSMLS in the initial scattering condition without any application of an external voltage. Figure 11 c,d shows the experimental results, where the PSMLS was transparent opaque when the polarization direction of the incident lights was parallel perpendicular to the direction of the interdigital electrode stripes when applied voltage is This result indicates that the LCs in all LC droplets in the bulk of the cell orient at the same time through the application of an external field.
By contrast, the applied field strength is reduced gradually from the bottom interdigital electrode to the top substrate in the PSMLS Figure 2 a.
Moreover, the blue curve Figure 11 a shows that the transmission of the PSMLS applied with approximately 16 V rms for the case of incident lights with the polarization direction perpendicular to the direction of the interdigital electrode stripes was higher than the initial transmission. This result indicates that the scattering strength is stronger when the LCs in LC droplets point to random directions than that when the LCs in LC droplets are rotated to be the configuration of Figure 2 a via the applied voltage 16 V rms.
The cause can be understood because the corresponding refractive index mismatches were different. Photos of c transparent and d opaque PSMLS when the polarization direction of the incident lights is parallel and perpendicular to the direction of the interdigital electrode stripes when the applied voltage is The applied electric field is an AC square wave.
The scattering performances of the PSMLS driven by the applied vertical fields, as shown in Figure 2 b, are discussed in the following paragraph. Figure 12 a shows the T-V curve when the polarization direction of the incident lights is perpendicular to the interdigital electrode stripes. The highest transmission in Figure 12 a was also lower than that in Figure 8 , which was elucidated in Section 2.
Briefly, on the basis of Figure 2 b, the fringing electric fields close to the electrode stripe edges were not completely perpendicular to the substrates, so light-scattering occurred there because of a small refractive index mismatch between LCs and polymers to reduce the transmission. A small amount of LCs in LC droplets close to the dead zones orange region in Figure 2 b , which cannot be electrically oriented, also caused the reduction of transmittance. Moreover, the V op in Figure 12 a is higher than that in Figure 8 , which is reasonable because a high applied voltage was required to reorient LCs closer to the edges of the electrode stripes.
Polarized Light in Liquid Crystals and Polymers
The LPA is defined as the angle between the absorption axis of the polarizer and the direction of the interdigital electrode stripes. The incident lights with the polarization direction perpendicular to the interdigital electrode stripes should be slightly scattered. The clarity of the words background in Figure 12 c,d is approximately the same. Based on the results in Figure 11 c,d, we proposed the method to approach a fast switch between a polarization-selective scattering state and polarization-independent transparent state. The potentials of V a , V b , and V c to obtain the transparent state, as shown in Figure 13 a, are V op , V op , and 0, respectively.
Because the switch from transparent to scattering states of x -LPLs in PSMLS is driven by the applied electric fields rather than the weak surface anchoring in each LC droplet, the switch time can be further shortened [ 1 , 22 , 23 ]. By contrast, the required time of switch from transparent to scattering states in a common PDLC device depends only on surface anchoring in each LC droplet; therefore, its switch time is relatively long [ 1 , 2 ].
To simplify the design to approach this method, the interdigital electrode stripes can be replaced by using a configuration consisting of grid electrodes located on top of a common electrode [ 22 , 23 ]. In addition to the optimized conditions for fabrication processes, the electro-optical properties, including scattering performance, V th , initial transmission, surface anchoring, and droplet size, of the -PDLCs NBA were investigated.
Accordingly, the -PDLCs NBA with low power consumption has considerable potential to be applied in the various areas of optics [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 ]. The PSMLS mainly driven by the in-plane field can scatter lights with the polarization direction perpendicular to the direction of the interdigital electrode stripes, whereas the scattering of the PSMLS driven by the vertical field is insensitive to the polarization direction of incident lights.
Hence, the fast switch between a polarization-selective scattering state Figure 11 d and polarization-independent transparent state Figure 12 c in the PSMLS is feasible with a suitable electrode design [ 22 , 23 , 24 , 25 ]. Also, the response time of a switch between polarization-independent light scattering and transparency based on PDLCs can be reduced according to the similar method, with two substrates having orthogonally interdigital electrode stripes [ 34 ].
We also sincerely thank the reviewers for their valuable comments and great suggestions. All authors reviewed the manuscript. National Center for Biotechnology Information , U. Journal List Polymers Basel v. Polymers Basel. Published online Dec 6. Author information Article notes Copyright and License information Disclaimer. Received Oct 12; Accepted Nov Abstract Low-threshold-voltage V th and electrically switchable, polarization-selective scattering mode light shutters PSMLSs using polymer-dispersed liquid crystals PDLCs are demonstrated in this work.
Keywords: liquid crystals, polarization, scattering, polymers. Introduction Optical devices based on polymer-dispersed liquid crystals PDLCs have been studied worldwide for several decades because of their electrically switchable light-scattering properties [ 1 , 2 ]. Open in a separate window. Figure 1. Figure 2. Results and Discussion 4. Figure 3. Figure 4. Figure 5. Figure 6. Figure 7.
Properties of Liquid Crystals
Figure 8. Figure 9. Figure Electrically Switchable Dual-Polarization Scattering Shutter The experimental setup for the following experiments was identical with that shown in Figure 3 , except for the addition of the polarizer, which was placed between the NDF and the beam splitter. Author Contributions C. Conflicts of Interest The authors declare no conflict of interest. References 1. Fundamentals of Liquid Crystal Devices. Wiley; Chichester, UK: The latest advances in the optics of small birefringent structures With the proliferation of liquid crystal technologies such as flat panel displays, understanding the polarization of light in liquid crystals has become a vital concern of optics, biology, communication, and numerous other areas in research and industry.
Polarized Light in Liquid Crystals and Polymers deals with the linear optics of birefringent materials, such as liquid crystals and polymers, and surveys light propagation in such media with special attention to applications. It is unique in treating light propagation in micro- and nanostructured birefringent optical elements, such as lenses and gratings composed of birefringent materials, as well as the spatial varying anisotropic structures often found in miniaturized liquid crystal devices. Presenting a comprehensive treatment of an exciting and rapidly developing field, Polarized Light in Liquid Crystals and Polymers provides both students and practitioners with a superlative resource for learning and reference.
Read more Read less. Amazon Global Store US International products have separate terms, are sold from abroad and may differ from local products, including fit, age ratings, and language of product, labeling or instructions. Manufacturer warranty may not apply Learn more about Amazon Global Store. When increasing the applied voltage, the inclined electric fields become stronger, but this does not cause more LC molecules to be aligned perpendicular to the substrates.
The residual birefringence caused by the reoriented LC molecules leads to a certain polarization dependency of the transmission curves. That is the reason why the transmission variation of the H states is almost unchanged even with higher applied voltages. It is expected that with the conductive layer below the grating structures, the slanted electric field could be relieved to some extent due to the electric field redistribution caused by the dielectric polymer layers, thus improving the polarization independence of the H state for Ch-LC beam steering components.
We have indeed verified this experimentally and Fig. It is seen that the transmission variation 2.
Hither, it can be concluded that the beam steering component with the combination of DFCh-LCs and polymer gratings based on Scheme 4, i. In order to get the optimized condition for the dual frequency driving, the transmission versus applied frequency curve of the DFCh-LC-grating beam steering device based on Scheme 4 has been characterized, the results are shown in Fig.
The net torque exerted by the two electric field components which are respectively parallel and perpendicular to the long LC molecule axis, results in the LC directors reorienting along the direction of the electric field. The helical structure is unwound and the device enters the H state. When increasing the applied frequency, the positive dielectric anisotropy starts decreasing. Hence, the net torque for realigning the LCs into the H state becomes weaker and some scattering FC domains appear among the dominant H textures. This phenomenon indicates that the dielectric anisotropy of the DFCh-LC has been transformed into a negative value and the LC directors try to reorient perpendicularly to the electric field, which contributes to the formation of the P texture.
The response time of the DFCh-LC—grating beam steering components are characterized between different states, the results are illustrated in Fig. Cholesteric liquid crystal was combined with micro grating structures to build polarization independent beam steering devices. Dual frequency cholesteric liquid crystal is adopted to accelerate the switching from the homeotropic state back to the initial planar state. The polarization dependence of the transmission is as low as 4. This kind of polarization independent beam steering components could be used in many novel optical applications such as highly efficient solar cell concentrators, micro beam deflector arrays for autostereoscopic displays, polarization independent auto-focus contact lenses and so forth.
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To get the desired refractive index of the micro gratings, another replication process with polydimethylsiloxane PDMS molds and UV curable resins was developed. KG , with 0.
A polyimide layer is subsequently spin coated on the flat ITO glass substrate and thermally cured. The grating substrate and the ITO counterpart are assembled to form empty LC cells, which are filled with liquid crystals by vacuum filling.
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The linearly polarized light beam is incident onto the sample and deflected by the device, which is driven by an arbitrary waveform generator with applying the required voltage signals.