WO2020072732A1

WO2020072732A1 - Fast-switched optical components with dye-doped dual-frequency liquid crystal

Info

Publication number: WO2020072732A1
Application number: PCT/US2019/054423
Authority: WO
Inventors: Oleg D. Lavrentovich; Sergij V. Shiyanovskii; Bingxiang LI; Ruilin XIAO
Original assignee: Kent State University
Priority date: 2018-10-04
Filing date: 2019-10-03
Publication date: 2020-04-09

Abstract

An electro-optic shutter includes a pair of dual frequency dye-doped nematic cells with orthogonal alignments driven by an electric field of low and high frequency between transparent and light-absorbing states. The shutter is polarization-independent, with sub- millisecond switching time and contrast ratio in the range from 10:1 to 1000:1, or higher. The shutter may be used in dimmable eyewear or in devices for multispectral imaging.

Description

FAST-SWITCHED OPTICAL COMPONENTS WITH DYE-DOPED

DUAL-FREQUENCY LIQUID CRYSTAL

[0001] This application claims the priority benefit of U.S. Provisional Application No. 62/740,987 filed October 4, 2018 and titled “FAST-SWITCHED OPTICAL

COMPONENTS WITH DYE-DOPED DUAL-FREQUENCY LIQUID CRYSTAL”, which is incorporated by reference in its entirety.

BACKGROUND

[0002] The present exemplary embodiment relates to fast-switching optical components.

[0003] Anisotropic dielectric and optical properties of nematic liquid crystals (NLCs) enable a large number of electro-optic applications. The dielectric anisotropy of NLCs determines the effect of an applied electric field E on the orientation of the director n (which is also an optical axis) of the NLCs. When this anisotropy is positive, Ae = e^ -e_± > 0

(here ^ and e_± are the dielectric permittivities parallel and perpendicular to the director), the director tends to align parallel to the field, ή || E , while for Ae < 0 , the orientation is orthogonal, ή ΐ E . The main problem of the nematic electro-optic effects is a very long relaxation time t_{0 o//} = gά ² / p²K when the field is switched off, typically on the order of milliseconds; here y is the rotational viscosity, K is the elastic constant, d is the cell thickness. To achieve a sub-millisecond switching time, Yin et al and Golovin et al proposed an approach based on a high-pretilt cell containing a dual frequency NLC (DFLC) in which Ae > 0 below some critical frequency f < f_c and Ae < 0 above it. The cross-over frequency f_c depends on the material and temperature; it is usually in the range between l kHz and 100 kHz ; the most frequently met values are on the order of tens of kHz . In the absence of the electric field, the director makes an angle Q , e.g., about 45 degrees with the normal to the substrates. When the electric field is applied, this large pretilt angle ensures a substantial realigning torque proportional to sin Q cos Q and thus a faster response time as compared to cells with either planar, q = p / 2 , or homeotropic, <9 = 0 , alignment.

[0004] It would be desirable to develop new optical components with fast response time.

BRIEF DESCRIPTION

[0005] The present disclosure relates to optical components with fast switching times. Devices containing the optical components, methods for making the optical components, and method for using the optical components are also disclosed.

[0006] Disclosed in some embodiments is a method for switching an optical component from a first state to a second state. The method includes applying a high- frequency electric field (f _> f_{c ,} e.g., tens of kHz ). The optical component includes: a first cell located between a first transparent end plate and a transparent divider plate and having a first alignment direction. The first cell includes: a first dual-frequency liquid crystal; and a first dichroic dye. The optical component further includes a second cell located between a second transparent end plate and the transparent divider plate and having a second alignment direction approximately orthogonal to the first alignment direction. The second cell includes a second dual-frequency liquid crystal; and a second dichroic dye.

[0007] About 0.1 wt% to about 5 wt % of dichroic dye in the DFLC may be used. Non- dual frequency nematic liquid crystals can be add into the mixture to adjust the dielectric anisotropy and the cross over frequency f_{c .} A mixture of dichroic dyes can be add into the system to fulfill different needs of the absorption spectrum. The amount of dichroic dye (in the range 0.1 wt%~ 5 wt %) is determined by the required optical characteristics and by its solubility in DFLC. The dynamic characteristics can be modified by adding to the commercial DFLC mixture other nematic liquid crystals to adjust the dielectric anisotropy and the cross-over frequency f_c , and/or polymerizable monomers to create a polymer network that would stabilize the director structure in one of the desired states, either field-off or field-on.

[0008] In some embodiments, the first dual frequency liquid crystal, the first dichroic dye, the second dual-frequency liquid crystal, and the second dichroic dye are oriented in an initial direction that makes an angle Q with the normal to the first transparent end plate and the second transparent end plate prior to the application of the high-frequency electric field. The value of the angle Q can be in a broad range from 1 to 89 degree, to yield a substantial torque (proportional to sin Q cos Q ) on the molecular alignment when the electric field is applied.

[0009] The optical component may have a sub-millisecond response time (e.g., less than 0.3 milliseconds).

[0010] In some embodiments, the optical component has a polarization-independent contrast in the range from 10: 1 to 1000:1 or higher. The optimized contrast ratio can be 10: 1 for a transmission 60%; 100: 1 for 36%; 1000:1 for 21 %. Thus, the contrast ratio is in the range from 10: 1 to 1000: 1 .

[0011] The first dual-frequency liquid crystal and the second dual-frequency liquid crystal may be the same or different. Similarly, the first dichroic dye and the second dichroic dye may be the same or different.

[0012] In some embodiments, the first transparent end plate, the divider plate, and the second transparent end plate comprise glass.

[0013] The method may further include: rubbing the first cell to generate the first alignment direction; and rubbing the second cell to achieve the second alignment direction.

[0014] In some embodiments, the high-frequency electric field is applied via at least one electrode deposited onto at least one of the first transparent end plate, the divider plate, and the second transparent end plate.

[0015] The high-frequency electric field may be applied as an initial special short pulse of high amplitude and high frequency and a subsequent high-frequency holding voltage.

[0016] In some embodiments, the method further includes switching the optical component from the second state back to the first state by applying a second special short pulse.

[0017] Disclosed in other embodiments is a fast-switching optical component. The optical component includes a first cell and a second cell. The first cell is located between a first transparent end plate and a transparent divider plate and has a first alignment direction. The first cell includes a first dual-frequency liquid crystal; and a first dichroic dye. The second cell is located between a second transparent end plate and the transparent divider plate and has a second alignment direction approximately orthogonal to the first alignment direction. The second cell includes a second dual-frequency liquid crystal; and a second dichroic dye.

[0018] In some embodiments, first dual-frequency liquid crystal and the second dual- frequency liquid crystal are the same.

[0019] In some embodiments, the first dichroic dye and the second dichroic dye are the same.

[0020] The first transparent end plate, the divider plate, and the second transparent end plate may comprise glass.

[0021] In some embodiments, at least one of the first transparent end plate, the divider plate, and the second transparent end plate comprises an electrode. The electrode may comprise indium tin oxide (ITO).

[0022] In some embodiments, the optical component further includes a voltage source connected to the electrode.

[0023] The first dual-frequency liquid crystal, the first dichroic dye, the second dual- frequency liquid crystal, and the second dichroic dye may be oriented approximately orthogonal to the first transparent end plate and the second transparent end plate in the absence of a high-frequency electric field.

[0024] In some embodiments, the first dual-frequency liquid crystal and the first dichroic dye are oriented in the first alignment direction when a high-frequency electric field is applied; and the second dual-frequency liquid crystal and the second dichroic dye are oriented in the second alignment direction when the high-frequency electric field is applied.

[0025] Disclosed in further embodiments are devices including the fast-switching optical component. The device may be an eyewear or a color filter.

BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The following is a brief description of the drawings, which are presented for the purposes of illustrating the exemplary embodiments disclosed herein and not for the purposes of limiting the same.

[0027] FIG. 1 illustrates an electro-optic shutter comprised of a pair of cells for polarization-independent light absorption.

[0028] FIG. 2 is a graph of the light transmittance of the cell at different incident angles in the crystal rotation method at 23°C .

[0029] FIG. 3 shows the temperature dependence of crossover frequency for several materials (a), dielectric anisotropy at different frequencies for DP 002-026 (b), and dielectric anisotropy at different frequencies for MCC-2048 (c).

[0030] FIG. 4 is a graph showing the dependence of the minimum order parameter S on the required transmission T_transparent at the transparent state and contrast ratio C .

[0031] FIG. 5 is a graph showing the dependence of the required transmission T_tranSparent ^at the transparent state on the minimum order parameter S and contrast ratio

C .

[0032] FIG. 6 illustrates (a) the voltage waveform, (b) the electro-optical response in a single cell filled with the mixture (2 wt% dye G-472 in DP002-026) corresponding to the applied voltages in (a), (c) the first SSP, and (d) the second SSP.

[0033] FIG. 7 illustrates (a) the voltage waveform and (b) the electro-optical response in a single cell filled with the mixture in (2 wt%) AB4 in DP002-026 corresponding to the applied voltages in (a).

[0034] FIG. 8 illustrates (a) the voltage waveform and (b) the electro-optical response of the mixture DP002-026 with 2 wt% of G-472 dye in two orthogonal cells and corresponding to the applied voltages in (a).

[0035] FIG. 9 illustrates the frequency dependences of the amplitude (a) and the phase (b) of the impedance of the experimental circuit.

DETAILED DESCRIPTION

[0036] The present disclosure may be understood more readily by reference to the following detailed description of desired embodiments included therein and the appended materials. In the following specification and the claims which follow, reference will be made to a number of terms which shall be defined to have the following meanings.

[0037] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. In case of conflict, the present document, including definitions, will control. Preferred methods and materials are described below, although methods and materials similar or equivalent can be used in practice or testing of the present disclosure. All publications, patent applications, patents, and other references mentioned herein are incorporated by reference in their entirety. The materials, methods, and articles disclosed herein are illustrative only and not intended to be limiting.

[0038] The singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise.

[0039] As used in the specification and in the claims, the term “comprising” may include the embodiments “consisting of” and “consisting essentially of.” The terms “comprise(s),”“include(s),”“having,”“has,”“can,”“contain(s),” and variants thereof, as used herein, are intended to be open-ended transitional phrases that require the presence of the named ingredients/steps and permit the presence of other ingredients/steps. However, such description should be construed as also describing compositions, mixtures, or processes as“consisting of and“consisting essentially of” the enumerated ingredients/steps, which allows the presence of only the named ingredients/steps, along with any impurities that might result therefrom, and excludes other ingredients/steps.

[0040] Unless indicated to the contrary, the numerical values in the specification should be understood to include numerical values which are the same when reduced to the same number of significant figures and numerical values which differ from the stated value by less than the experimental error of the conventional measurement technique of the type used to determine the particular value.

[0041] All ranges disclosed herein are inclusive of the recited endpoint and independently combinable (for example, the range of “from 2 to 10” is inclusive of the endpoints, 2 and 10, and all the intermediate values). The endpoints of the ranges and any values disclosed herein are not limited to the precise range or value; they are sufficiently imprecise to include values approximating these ranges and/or values.

[0042] As used herein, approximating language may be applied to modify any quantitative representation that may vary without resulting in a change in the basic function to which it is related. Accordingly, a value modified by a term or terms, such as “about” and“substantially,” may not be limited to the precise value specified, in some cases. The modifier“about” should also be considered as disclosing the range defined by the absolute values of the two endpoints. For example, the expression“from about 2 to about 4” also discloses the range“from 2 to 4.” The term“about” may refer to plus or minus 10% of the indicated number. For example,“about 10%” may indicate a range of 9% to 1 1 %, and“about 1” may mean from 0.9-1 .1 .

[0043] For the recitation of numeric ranges herein, each intervening number there between with the same degree of precision is explicitly contemplated. For example, for the range of 6-9, the numbers 7 and 8 are contemplated in addition to 6 and 9, and for the range 6.0-7.0, the number 6.0, 6.1 , 6.2, 6.3, 6.4, 6.5, 6.6, 6.7, 6.8, 6.9, and 7.0 are explicitly contemplated.

[0044] The present disclosure relates to optical components (e.g., shutters) with fast switching times.

[0045] A dual-frequency approach to the construction of polarization-independent sub- millisecond shutters is disclosed. The dual-frequency liquid crystal (DFLC) is doped with a dichroic dye that shows a strongly anisotropic light absorption. The dual-frequency liquid crystal may be a nematic dual-frequency liquid crystal. Rod-like molecules of dichroic dyes may align along the director; their director-mediated reorientation in the applied electric field is known as the guest-host effect. To achieve a polarization- independent switching, a sandwich structure including two identical cells in which the in- plane director projections are orthogonal to each other, as shown in FIG. 1 , may be used. The director orientation itself can be designed in a variety of ways, depending on whether the field-off state is desired to be transparent, dark, or semitransparent. If the field-off state is needed to be transparent, than the value of polar angle Q should be small, with the director being almost perpendicular to the bounding plates, e.g., Q « 35° . In this field off state with a small Q , light absorption by the dichroic dye is negligibly small, since the axis of molecular absorption is aligned closely to the direction of observation. To create a dark state, a high-frequency voltage ( f > f_c ) is applied so that the director and dye molecules realign mostly parallel to the bounding plates along two orthogonal directions. In this state, the two-cell system absorbs light strongly for all polarizations of light. To accelerate the switching between the transparent and light-absorbing states, a special short pulse of high amplitude and high frequency is used prior to high-frequency holding voltage. To switch quickly from the absorbing state to a transparent state, another special short pulse is used, this time of a direct current (DC) type or of a low-frequency AC type ( / < f_c ) The scheme presented in FIG. 1 may achieve high contrast ratios (e.g., in the range from 10: 1 to 1000: 1 or higher), with the transmittance changing, e.g., from 48% ± 1% in the transparent state to 5% ± l% in the dark state. By designing the special short pulses, the response time may be reduced to less than 0.3 ms . If the device is desired to be non-transparent in the field-off state, then the angle Q should be close to 89 degrees. To switch the device to a transparent state, one should apply a low-frequency AC electric field ( / < f_c ) to realign the director and dye molecules parallel to the direction of light propagation. The transparent state can be switched back to the nontransparent state by a high frequency electric field ( / > /_c ). If the field-off state is desired to be semitransparent, then the angle Q should be in the range 30 - 60 degrees. A high- frequency electric field ( / > f_c ) would make it non-transparent, while a low-frequency electric field ( / < f_c ) would make it transparent.

[0046] FIG. 1 shows an electro-optic shutter comprised of a pair of cells for polarization-independent light absorption. It is designed for the case when the initial field- off state is transparent. In the field-free state (a), the nearly homeotropic alignment of the dual frequency nematic doped with a dye make the cells transparent to normally impinging light. The rubbing direction of two cells are perpendicular to each other. A light- absorbing state (b) is formed when a high-frequency electric field ( / > f_c ) is applied and realigns the director and dye molecules parallel to the bounding plates. Since the two alignment directions are orthogonal, the state is light-absorbing for all polarizations of light. The open and closed symbols denote dual frequency nematic liquid crystals and dichroic dyes, respectively.

[0047] The polarization-independent fast electro-optic switching of dichroic dye doped dual frequency nematic liquid crystals was demonstrated. The response time is less than 0.3 milliseconds for both switching-on and switching-off processes. The electro-optic effect can be used in shutters, eyewear, and color filters. Among three studied dual frequency nematics, DP002-026 shows the fastest response. It exhibits (1 ) low viscosity, (2) small and weak temperature dependent crossover frequency and (3) almost constant dielectric anisotropy. Power consumption was not significant. The typical power for the holding voltage is on the order of 0.01 W . The energy consumed by special DC and AC pulses (that are very short in duration, ~ 0.3 ms ) used to accelerate the switching, is less than 1 mJ . Note that the power consumption of the display of a smart phone is typically 0.5 W .

[0048] The shutter may be used in electrically switchable eyewear that is polarization independent and has a response time of less than 0.3 milliseconds. It may be used to quickly block undesired light in order to protect human eyes.

[0049] Non-limiting examples of other applications include multispectral imaging, in which different wavelengths are used to image the same objects. The shutter may be used in switchable color filters.

[0050] Electrically-operated optical shutter switches between a transparent state and a light-absorbing state within a short time (e.g., less than 0.3 milliseconds). The shutter may show a polarization-independent contrast in the range from 10: 1 to 1000: 1 or higher.

[0051] The shutter has a fast response time of 0.3 milliseconds or less, which is faster than the typical switching time of current liquid crystal displays used in television screens, smartphones, and monitors.

[0052] The shutter may be switched between transparent and dark states within 0.3 milliseconds.

[0053] The methods of the present disclosure generally switch an optical component from a first state to a second state. In some embodiments, the first state is an opaque state and the second state is a transparent state. In other embodiments, the first state is a transparent state and the second state is an opaque state. Either or both of the first state and the second state may be semi-transparent in other embodiments.

[0054] The first state may permit a first optical transmittance and the second state may permit a second optical transmittance. In some embodiments, the first optical transmittance exceeds the second optical transmittance. In other embodiments, the second optical transmittance exceeds the first optical transmittance.

[0055] The systems of the present disclosure generally include at least two liquid crystal cells. Each cell contains a dual-frequency liquid crystal and a dichroic dye. The orientation of these materials impact the optical transmittance. In some embodiments, one of the optical states is characterized by the dichroic dyes in both cells being oriented approximately orthogonal to end plates. In some embodiments, one of the optical states is characterized by the dichroic dyes being oriented approximately parallel to the end plates but in approximately orthogonal orientation with respect to each other.

[0056] In some embodiments, at least one of the first state and the second state is characterized by at least one of the cells exhibiting a pre-tilt angle. In some embodiments, both cells exhibit a different pre-tilt angle.

[0057] The following examples are provided to illustrate the devices and methods of the present disclosure. The examples are merely illustrative and are not intended to limit the disclosure to the materials, conditions, or process parameters set forth therein.

EXAMPLES

[0058] The cells were filled with the commercial dual-frequency nematic mixtures (DP 002-016, DP 002-026, MCC-2048, etc.) doped with commercial dichroic dyes (Sudan III, AB4, G-472, etc.), whose elongated molecules align parallel to the molecules of the liquid crystal and absorb light in the required optical range.

[0059] ITO electrodes were deposited onto glass substrates and patterned by a photolithographic method. The active area of electrode was 5 x 5 mm² and 2.5 x 2.5 cm² . The layers of homeotropic alignment agent SE121 1 (Merck) were rubbed unidirectionally in order to provide a directional tilt of the director when the electric field is not applied or applied at frequencies f < f_{c .} The cells were assembled from pairs of plates rubbed in an antiparallel fashion. The pretilt angle is about 3.5 degrees, as determined by the crystal rotation method. The thicknesses of the cells were fixed by the spherical glass spacers in the range 2 - 6 mih .

[0060] FIG. 2 is a graph showing the light transmittance of the cell at different incident angles in the crystal rotation method at 23°C . The cell thickness is 50 mih . The used NLC is 5CB. The cell was placed between two crossed polarizers in such a way that the rubbing direction makes 45 degrees with them. The light intensity changes when the cell was rotated about the axis which is parallel to the substrates and perpendicular to the rubbing direction. The fitting suggests that the pretilt angle is about 3.5 degrees.

[0061] The dielectric properties of three DFLCs (DP002-016, DP002-026 from Jiangsu Hecheng Display technology, and MLC-2048 from EM Industries) were characterized by using an LCR meter 4284A (Hewlett-Packard). The temperature of cell was controlled with a Linkam LTS350 hot stage to investigate the temperature dependence of dielectric properties of three materials. At room temperature, DP002-026 and MLC-2048 show crossover frequency f_c ~ 20 kHz . It increases by a factor of about 3 when the temperature is raised from 26°C to 38°C , as shown in FIG. 3(a). The temperature dependences of dielectric anisotropy at different frequencies for DP002-026 and MLC-2048 are shown in FIG. 3(b) and (c), respectively. DP002-026 exhibits weak temperature dependence and exhibits De « +4 in entire temperature range at 6 kHz and De « -4 ίqG frequencies 120 kHz and above. MLC-2048 exhibit a strong temperature dependence of As .

[0062] The viscosity of MLC-2048 ( h = 200 mPa -s ) is four times larger than DP002- 016 ( ?7 = 48 mPa · s ) and DP002-026 (^ = 5l mPa -s ) at 25°C . Thus, the electro-optic response of MLC-2048 is expected to be slower than in the other two materials at the same conditions.

[0063] An important performance parameter of the shutter is the contrast ratio, which is calculated as the ratio of the transmitted light intensities for the transparent and absorbing states, C = T_tmnsparent / T_ahsorhjng ⁼ T I T_a . Here T_transparent = T ³ and T_absorbmg = T _a refer to the system comprised of two crossed cells. T_n and T_L are the transmittance of one single cell for the polarizations of light are parallel and perpendicular to the director of DFLC, respectively.

[0064] The transmittance of dye doped DFLC is determined by the concentration of dyes c, cell thickness d , absorption in the isotropic phase a_lS0 , and the order parameter of the dichroic dye. From the relationship

where

T_{c «} 0.9 is the transmittance of the single cell filled with non-doped DFLC, one can obtain the order parameter of dichroic dye

. Thus,

Tr_ansparent = ^T _c C^{2(s l)lis} . However, the transmittance of two cells at the transparent state is Transparent = T_cC^{2(s 1)/3}* when a matching liquid is applied into the gap of two orthogonal cells. For two cells, the relationship T_transparent = T²C^{2 s X)ns} suggests that the minimum order parameter of dye molecules needs to be at the level of S 0.79 or higher, in order to achieve T_transparent = 0.55 and C = l0 : l . FIG. 4 shows how the order parameter S depends on the required transmission T_transparent of the transparent state for different values of the contrast ratio C .

[0065] FIG. 5 shows the dependence of the required transmission T_transparent at the transparent state on the order parameter S and contrast ratio C .

[0066] The contrast ratio is determined by the order parameter of dye molecules S . To determine S , single planar cells were coated with PI-2555 and the transmittance of the cells 7j_| and T_L were measured.

[0067] Several dichroic dyes, Sudan III (from Sigma-Aldrich), AB4 (from Nematel GmbH), and G-472 (from Mitsui Fine Chemicals) were used. In order to characterize the order parameter of the dyes, the dye doped DP002-026 in planar cells were coated with PI-2555. Each cell was probed with a normally incident light beam, produced by a He-Ne laser (543 nm for Sudan III, 632 nm for AB4 and G-472) and linearly polarized by a polarizer. Order parameter of dyes are calculated from the transmittance of the cells and T_L at two different polarization of normal incident laser beams. G-472 shows the largest order parameter 0.80, Table 1.

[0068] Table 1. Order parameter of three dichroic dyes (2 wt%) in DP002-026.

[0069] To test the electro-optic performance, the orthogonal cells were probed with a normally incident light beam, produced by a laser (632 nm). The Alternating current (AC) voltage was generated by a waveform generator (Stanford Research Systems, Model DS345) and an amplifier (Krohn-hite Corporation, Model 7602).

[0070] In order to speed up the electro-optic switching, a specific voltage waveform (FIG. 6) was designed. The response time for the field-induced reorientation of the nematic director is proportional to H E² . Thus, two short special pulse (SSP) with high voltage amplitude were introduced. The first SSP of 40 V was applied for 1.1 ms to achieve the dark planar state. This SSP is comprised of a DC pulse of duration 0.1 ms , followed by the AC pulse of frequency 60 kHz , (FIG. 6(c)). To hold this dark state, a holding voltage of 10 V at 60 kHz is applied after the first SSP for 20 ms . To switch from the dark planar to bright homeotropic state, the second SSP of 40 V of a DC type was applied for 1.0 ms , after which the voltage is switched off. FIG. 6(b) shows that the response in optical performance is very fast, ~ 0.2 ms , where we take into account 0.1 ms delay caused by 0.1 ms DC pulse in the first SSP.

[0071] FIG. 7 shows (a) the voltage waveform, (b) the electro-optical response in a single cell filled with the mixture (2 wt% dye G-472 in DP002-026) corresponding to the applied voltages in (a), (c) the First SSP, and (d) the second SSP. The polarization of incident light is along the rubbing direction of the cell. The holding voltage at 60 kHz is 7 V .

[0072] Using the same voltage scheme, a fast response ( ~ 0.2 ms ) was also achieved in the mixture of DP002-026 doped with 2 wt% of AB4 dye.

[0073] FIG. 7 shows (a) the voltage waveform and (b) the electro-optical response in a single cell filled with the mixture in (2 wt%) AB4 in DP002-026 corresponding to the applied voltages in (a). The polarization of incident light is along the rubbing direction of the cell. The holding voltage is 10 V at 60 kHz .

[0074] FIG. 8 shows (a) the voltage waveform and (b) the electro-optical response of the mixture DP002-026 with 2 wt% of G-472 dye in two orthogonal cells and corresponding to the applied voltages in (a). The holding voltage is 5 V at 60 kHz .

[0075] The previous experimental data was collected for single cells. To demonstrate the approach for the intended scheme with two cells assembled as shown in FIG. 1 , cells of thickness 4.5 mih filled with the same dye doped nematic, representing DP002-026 with 2 wt% of G-472 dye were used. The cells were assembled with the rubbing directions being perpendicular to each other. The waveform was similar to the previous experiments in FIGS. 6 and 7, but with that difference that the holding voltage that keeps the planar dark state was of the smaller amplitude, 5 V instead of 10 V . During the switching, the transmittance changes from 48% ± 1% (Bright state) to 5% ± l% (Dark state) for different polarization of light. The switching times are less than 0.3 ms .

[0076] Another important parameters of fast switching shutters is their power consumption. To explore the issue, the liquid crystal cell as a series of a resistor R (10 W/m) and a dielectric capacitor C were considered. The frequency dependence of the impedance in a cell of thickness ~ 4 mih and the active area 2.5 cm x 2.5 cm filled with dye (G472) doped DFLC (DP002-026) (FIG. 9). The results show that the magnitude and the phase of the impedance of the mixture at 60 kHz are Z « 450 W and f 70° , respectively. One can estimate the power for the holding voltage and the special short pulse at 60 kHz , i.e. P_h = U_h ² cos^ / Z « 0.02 W and P_s = f/_s ² cos ^ / Z « 1.2 W , where the typical holding voltage is ¾ 5 V and the voltage of the special pulse is U_P ~ 40 V . The power consumption for the special short pulse is high, however, the short pulse is only applied for a very short duration ~ 0.3 ms . The power consumption of the display of a smart phone is typically ~ 0.5 W . Thus, the power consumption should not be a problem for the practical application.

[0077] FIG. 9 shows the frequency dependences of (a) the amplitude and (b) the phase (b) of the impedance of the experimental circuit.

[0078] These examples demonstrate the polarization-independent fast electro-optic switching of dichroic dye doped dual frequency nematic liquid crystals. The response time is less than 0.3 milliseconds for both switching-on and switching-off processes. The electro-optic effect can be used in shutters, eyewear, and color filters. Among three studied dual frequency nematics, DP002-026 shows the fastest response. It exhibits (1 ) low viscosity, (2) small and weak temperature dependent crossover frequency and (3) almost constant dielectric anisotropy. It was also determined that the power consumption is not significant.

[0079] It will be appreciated that variants of the above-disclosed and other features and functions, or alternatives thereof, may be combined into many other different systems or applications. Various presently unforeseen or unanticipated alternatives, modifications, variations or improvements therein may be subsequently made by those skilled in the art which are also intended to be encompassed by the following claims.

Claims

CLAIMS:

1 . A method for switching an optical component from a first state to a second state, comprising:

applying an electric field of a high frequency;

wherein the optical component comprises:

a first cell located between a first transparent end plate and a transparent divider plate, wherein the first cell has a first alignment direction, and wherein the first cell comprises:

a first dual-frequency liquid crystal; and

a first dichroic dye; and

a second cell located between a second transparent end plate and the transparent divider plate, wherein the second cell has a second in-plane projection of the alignment direction approximately orthogonal to the first in-plane projection of the alignment direction, and wherein the second cell comprises:

a second dual-frequency liquid crystal; and

a second dichroic dye.

2. The method of claim 1 , wherein the first dual-frequency liquid crystal, the first dichroic dye, the second dual-frequency liquid crystal, and the second dichroic dye are oriented in an initial direction approximately orthogonal to the first transparent end plate and the second transparent end plate prior to the application of the high-frequency electric field.

3. The method of claim 1 , wherein the optical component has a response time in the sub-millisecond range and less than 0.3 milliseconds.

4. The method of claim 1 , wherein the optical component has a polarization- independent contrast of from 10: 1 to 1000: 1 .

5. The method of claim 1 , wherein the first dual-frequency liquid crystal and the second dual-frequency liquid crystal are the same; and wherein the first dichroic dye and the second dichroic dye are the same.

6. The method of claim 1 , wherein the first transparent end plate, the divider plate, and the second transparent end plate comprise glass.

7. The method of claim 1 , further comprising:

rubbing the first cell to generate the first alignment direction; and

rubbing the second cell to achieve the second alignment direction.

8. The method of claim 1 , wherein the high-frequency electric field is applied via at least one electrode deposited onto at least one of the first transparent end plate, the divider plate, and the second transparent end plate.

9. The method of claim 1 , wherein the high-frequency electric field is applied as an initial special short pulse of high amplitude (e.g., tens of volts) and high frequency (e.g., tens of kHz or higher) and a subsequent high-frequency holding voltage (e.g., several volts and tens of kHz or higher).

10. The method of claim 9, further comprising:

switching the optical component from the second state back to the first state by applying a second special short DC pulse of an amplitude of tens of volts with duration less than 1 miilisecond.

1 1 . A fast-switching optical component comprising:

a first dual-frequency liquid crystal; and

a first dichroic dye; and

a second dual-frequency liquid crystal; and

a second dichroic dye.

12. The fast-switching optical component of claim 1 1 , wherein the first dual- frequency liquid crystal and the second dual-frequency liquid crystal are the same.

13. The fast-switching optical component of claim 1 1 , wherein the first dichroic dye and the second dichroic dye are the same.

14. The fast-switching optical component of claim 1 1 , wherein the first transparent end plate, the divider plate, and the second transparent end plate comprise glass.

15. The fast-switching optical component of claim 1 1 , wherein at least one of the first transparent end plate, the divider plate, and the second transparent end plate comprises an electrode.

16. The fast-switching optical component of claim 15, wherein the electrode comprises indium tin oxide (ITO).

17. The fast-switching optical component of claim 15, further comprising:

a voltage source connected to the electrode.

18. The fast-switching optical component of claim 1 1 , wherein the first dual- frequency liquid crystal, the first dichroic dye, the second dual-frequency liquid crystal, and the second dichroic dye are oriented approximately orthogonal to the first transparent end plate and the second transparent end plate in the absence of a high-frequency electric field.

19. The fast-switching optical component of claim 1 1 , wherein the first dual- frequency liquid crystal and the first dichroic dye and are oriented in the first alignment direction when a high-frequency electric field is applied; and wherein the second dual- frequency liquid crystal and the second dichroic dye are oriented in the second alignment direction when the high-frequency electric field is applied.

20. A device comprising the fast-switching optical component of claim 1 1 ; wherein the device is eyewear or a color filter.

21. A method for switching an optical component from a first state to a second state, comprising:

applying an electric field of a high frequency;

wherein the optical component comprises:

a first cell located between a first transparent end plate and a transparent divider plate, wherein the first cell has a first in-plane projection of an alignment direction, and wherein the first cell comprises:

a first dual-frequency liquid crystal; and

a first dichroic dye; and

a second cell located between a second transparent end plate and the transparent divider plate, wherein the second cell has a second in-plane projection of the alignment direction which differs from the first in-plane projection of the alignment direction, and wherein the second cell comprises:

a second dual-frequency liquid crystal; and

a second dichroic dye.