Optical element with variable transmission

Abstract

Optical element, comprehensive, - an essentially plate-shaped substrate with a first large surface designed as a light entry surface (3) and a second large surface designed as a light exit surface (4), - a plurality of fluid chambers (R) embedded in the substrate, each with one or more surfaces, wherein the fluid chambers (R) are honeycomb, cylindrical or rectangular and fill part or all of the substrate, - a liquid (F) with which the fluid chambers (R) are filled, wherein the liquid (F) contains up to 20 volume percent electrophoretically or magnetophoretically movable particles (P) which absorb light of one or more wavelengths or wavelength ranges, and which are designed as nanoparticles, quantum dots and / or dyes and have a spatial extent of at most 100 nm, preferably at most 50 nm, particularly preferably at most 20 nm, - Electromagnetic switching means (2) formed in a planar manner on one or more surfaces of the fluid chambers (R) in the substrate, which in a switched-on state generate an electromagnetic field effective within the fluid chambers (R), causing the particles (P) to move in the liquid (F) so that the transmission of the optical element changes for light of wavelengths or wavelength ranges absorbed by the particles (P), wherein in a first operating state B1 the transmission is greater than 50% and in a second operating state B2 it is less than 50%, with respect to the direction of the surface normal of the second large surface of the substrate.

Description

Field of the invention

[0001] In recent years, great strides have been made in widening the viewing angle of LCDs. However, there are often situations where the very large viewing area of ​​a screen can be a disadvantage. Information, such as banking details and other personal and sensitive data, is becoming increasingly available on mobile devices such as notebooks and tablet PCs. Accordingly, people need control over who can see this sensitive data; they need to be able to choose between a wide viewing angle in order to share information on their display with others, e.g. when looking at holiday photos or for advertising purposes. On the other hand, they need a narrow viewing angle if they want to keep the image information confidential.

[0002] A similar problem arises in vehicle construction: The driver must not be distracted by image content, such as digital entertainment programs, when the engine is running, while the passenger also wants to consume the same content while driving. Therefore, a screen that can switch between the corresponding display modes is required. State of the art

[0003] US 2015 / 0346578 A1 discloses a method for controlling an electrophoretic display. This method utilizes dielectrophoretic particle motion.

[0004] WO 2018 / 232099 A1 describes an electro-optical medium with encapsulated pigments in a gelatin binder.

[0005] US 2018 / 0173073A1 describes an electrophoretic privacy display.

[0006] A reflective display is known from US Pat. No. 9740075 B2. For this purpose, electrophoretic particles are moved in front of or behind a reflector layer / electrode. Depending on whether the particles are in front of or behind the electrode, the respective location reflects light or not. Such a location corresponds to a pixel. This pursues the creation of an improved electronic paper. No design allows for variable transmission of the entire structure. Rather, it is exclusively concerned with the modulation of reflected light for information display.

[0007] WO 2006 / 108285 A1 also describes a reflective display. Opaque electrophoretic particles are used to selectively disrupt the total internal reflection of hemibeads (e.g., lenticulars) or to selectively suppress reflection on a reflective surface. Depending on the location of the particles (on the hemibead or on a reflector), the respective location reflects light or not. Each such location corresponds to a pixel. However, this does not allow for variable transmission of the entire structure. Rather, it is again solely concerned with the modulation of reflected light to display information.

[0008] None of the above-mentioned documents describes an inexpensively implementable optical element which can influence the transmission at least vertically and which can switch between at least two operating states in order to achieve either complete or partial dimming, for example of windows in a car, or to allow a view through.

[0009] Additional films based on micro-louvres have already been used for mobile displays to achieve visual privacy. However, these films were not switchable; they always had to be applied and removed manually. They also had to be transported separately from the display when not in use. A major disadvantage of using such louvre films is the associated light loss.

[0010] US Pat. No. 6,765,550 A describes such a privacy screen using micro-louvres. The biggest disadvantage here is the mechanical removal or installation of the filter, as well as the loss of light in protected mode.

[0011] US Pat. No. 5,993,940 A describes the use of a film with evenly spaced, small prism strips on its surface to achieve a privacy mode. Development and production are quite complex.

[0012] In WO 2012 / 033583 A1, switching between unobstructed and restricted view is achieved by controlling liquid crystals between so-called "chromonic" layers. This results in a loss of light and is quite complex.

[0013] US patent application 2013 / 0308185 A1 describes a special light guide with steps that emits light across a large surface in different directions depending on the direction from which it is illuminated from a narrow side. In conjunction with a transmissive image display device, e.g. an LCD, this can create a screen that can be switched between free and restricted view modes. A disadvantage of this is that the restricted view effect can only be created for left / right or up / down, but not for left / right / up / down simultaneously, as is necessary for certain payment transactions, for example. In addition, even in restricted view mode, residual light is still visible from blocked viewing angles.

[0014] WO2015 / 121398 A1 by the applicant describes a screen of the type described above. In this case, scattering particles are present in the volume of the corresponding light guide, which are essential for switching between operating modes. However, the polymer scattering particles selected there generally have the disadvantage that light is coupled out of both large surfaces, causing approximately half of the useful light to be emitted in the wrong direction, namely toward the backlight, where it cannot be adequately recycled due to the design. Furthermore, the polymer scattering particles distributed throughout the volume of the light guide can, under certain circumstances, particularly at higher concentrations, lead to scattering effects that reduce the privacy effect in the protected operating mode.

[0015] The aforementioned methods and arrangements generally have the disadvantage that they significantly reduce the brightness of the basic screen and / or require a complex and expensive optical element for mode switching and / or reduce the resolution in the freely viewable mode. Description of the invention

[0016] The object of the invention is therefore to describe an optical element that can influence the transmission at least vertically and that can switch between at least two operating states. The optical element should be inexpensive to implement, either to fully or partially dim car windows or to allow a view through them.

[0017] This object is achieved according to the invention by an optical element comprising - a substantially plate-shaped substrate with a first large surface designed as a light entry surface and a second large surface designed as a light exit surface, - a plurality of fluid chambers embedded in the substrate, each having one or more surfaces, wherein the fluid chambers are honeycomb-shaped, cylindrical, or rectangular and fill part or all of the substrate, - a liquid F with which the fluid chambers are filled, wherein the liquid contains up to 20 volume percent of electrophoretically or magnetophoretically movable particles which absorb light of one or more wavelengths or wavelength ranges and which are formed as nanoparticles, quantum dots and / or dyes and have a spatial extent of a maximum of 100 nm, preferably a maximum of 50 nm, particularly preferably a maximum of 20 nm, - electromagnetic switching means formed in a planar manner on one or more sides of the fluid chambers in the substrate, which, when switched on, generate an electromagnetic field effective in the fluid chambers, whereby the particles are moved in the liquid, so that an angle-dependent transmission of the optical element for light of the wavelengths or wavelength ranges which are absorbed by the particles, which light enters the substrate via the light entry surface at such angles that it strikes the fluid chambers, changes, wherein in a first operating state B1 the transmission is more than 50% and in a second operating state B2 it is less than 50%, based on the direction of the surface normal of the second large surface of the substrate.

[0018] The first and second large surfaces of the plate-shaped substrate are preferably arranged parallel to each other. However, in special configurations, for example, when special angle-dependent transmissions of the optical element are to be achieved, they can also be arranged non-parallel, e.g., wedge-shaped at a defined angle of up to 20 degrees to each other.

[0019] The first large surface of the plate-shaped substrate, designed as a light entry surface, is usually located on the back of the substrate from the observer's perspective and, depending on the application of the optical element, borders, for example, an image display device, a light source, or an air volume. Light then enters the substrate from the latter through said light entry surface.

[0020] The lamellar fluid chambers with longitudinal and narrow sides, which extend between the first large surface and the second large surface, can, for example, be aligned parallel to the large surfaces and have a cuboid shape. However, it is also possible for the narrow sides to be trapezoidal or curved, such as arched.

[0021] In the case of the (non-cubic) cuboid shape, the narrow sides are the elongated sides, which have a smaller surface area, i.e., the long sides, which in turn usually have the largest surface area of ​​all six surfaces of a fluid chamber. Typically, the narrow sides are arranged parallel or—except for a tilt angle described below—parallel to the large surfaces of the substrate, while the long sides are arranged perpendicular or—except for a tilt angle described below—perpendicular to the large surfaces of the substrate.

[0022] In contrast, the remaining end faces are those two surfaces which do not represent any narrow sides or long sides.

[0023] It is also explicitly possible that the fluid chambers protrude at least partially from one or both large surfaces of the substrate.

[0024] The one or more wavelengths or wavelength ranges in which the electrophoretically or magnetophoretically movable particles absorb light are preferably in the visible spectrum and, particularly preferably, cover this spectrum essentially completely. However, they can also be outside the visible spectrum for special purposes, such as when UV or IR light is to be influenced, e.g., for metrology purposes.

[0025] The electromagnetic switching means formed in a planar manner on one or more sides of the fluid chambers in the substrate are arranged, for example, on the narrow sides of the respective fluid chambers.

[0026] The particles are, for example, nanoparticles, quantum dots, and / or dyes. These have a spatial dimension of a maximum of 100 nm, preferably a maximum of 50 nm, and particularly preferably a maximum of 20 nm.

[0027] Spatial extent here means the maximum extent in three-dimensional space or the hydrodynamic radius, whichever is larger.

[0028] For spherical particles, this is the diameter. For string-shaped particles, this is the greatest possible distance between two points on the particle's surface.

[0029] The liquid can be polar or non-polar. It can also consist of water, oil, toluene, or formaldehyde, for example, or mixed with a 10 vol.% ferrofluid and / or electrolyte.

[0030] Furthermore, either the particles are electrically charged and the electromagnetic switching means are designed as electrodes for generating a static or dynamic electric field, or the particles are magnetic and the electromagnetic switching means are designed as electromagnetic layers for generating a static or dynamic magnetic field, so that the electromagnetic particles move in the electric or magnetic field within the fluid. The corresponding electric field lines would then, for example, be parallel in the center of a fluid chamber and tend to deviate from parallelism at the edges. However, other configurations are also possible.

[0031] The leading physical effects for the movement of particles when an electromagnetic field, especially a static field, is applied are (di-)electrophoresis or magnetophoresis.

[0032] In the absence of an electric or magnetic field, the particles move through the fluid chambers, primarily due to diffusion, and thus spread homogeneously over time. For particles smaller than 50 nm, gravity plays no role; they therefore do not settle.

[0033] By means of the electromagnetic switching means and a control circuit, at least two operating states are defined, with the angle-dependent transmission being more than 50% in a first operating state B1 and less than 50% in a second operating state B2. This applies in an angular range of more than 30° (this angle can also be varied, e.g., 10°, 20°, or 25°) relative to a surface normal of the second large surface of the substrate and measured in a direction perpendicular to a longitudinal extent of the lamellar fluid chambers. The longitudinal extent is defined here as the straight line connecting the surface centers of the two end faces of each fluid chamber.

[0034] In a preferred development of this embodiment, in the first operating state B1, more than 70% of the particles are located in regions on the sides of the fluid chambers where the electromagnetic switching means are formed, and in the second operating state B2, in which the switching means are configured such that there is no static electromagnetic field or an alternating electromagnetic field, more than 50% of the particles (primarily due to diffusion and / or the alternating electromagnetic field) are predominantly evenly distributed in the fluid chambers, so that the angle-dependent transmission in the first operating state B1 is more than 60% and in the second operating state B2 less than 5%. This again applies in an angular range of more than 30° (this angle can also be varied, e.g.10°, 20° or 25°) relative to a surface normal of the second large surface of the substrate and measured in a direction perpendicular to a longitudinal extension of the lamellar fluid chambers.

[0035] In other words, the different operating states B1, B2, .. differ in particular in that the local concentration and location of the particles in the fluid chambers is changed in order to change the transmission properties due to the absorption by the particles.

[0036] Advantageously, the electromagnetic switching means are at least 50% transparent to light in the visible wavelength range entering the substrate perpendicularly via the light entry surface.

[0037] The electromagnetic switching means (as well as the fluid chambers) can further be divided into several separately switchable segments, enabling local switching between the first operating state B1 and the second operating state B2. Local switchability here means that the operating state B1 and B2 is not switched simultaneously in all fluid chambers, but rather that areas with both operating states B1 and B2 are present on the optical element simultaneously. This is advantageous, for example, when using the optical element in front of a screen from a viewing angle of more than 30 degrees to the side, where parts of the displayed image content should be visible and others invisible.

[0038] In a further advantageous embodiment, the liquid contains several types of particles that differ in their absorption properties and / or their transport properties in the electromagnetic field. "Transport properties" refers in particular to the behavior of the particles during the respective phoresis (transport in the field).

[0039] This variant is particularly important in the case of nanoparticles: the difference between the particle types lies, for example, in the particle size and / or the surface function, ie in the zeta potential.

[0040] When using quantum dots or dyes as particles and if these are fluorescent, a so-called “quencher” material is preferably used to prevent fluorescence.

[0041] The fluid chambers can be aligned either parallel to each other or in a grid pattern with intersecting regions. The angle-dependent transmission properties of the optical element with respect to one or two mutually perpendicular planes are then determined accordingly.

[0042] As a rule, the fluid chambers (especially their long sides) will each be aligned essentially parallel to the perpendicular bisector of the substrate S.

[0043] In contrast, it is also possible for the fluid chambers to be tilted relative to the perpendicular bisector of the substrate within an angular range ("tilt angle") of -10° to +10°, possibly even between -30° and +30°. This configuration also influences the angle dependence of the transmission of the optical element, particularly in operating state B2. The aforementioned tilt angle tilts the angle-dependent absorption caused by the particle absorption and the particle positions within the fluid chambers by a fixed offset angle, for example, when low transmission at a particularly steep angle is desired.

[0044] For example, the lamellar fluid chambers can be between 2µm and 30µm wide (distance from long side to long side of a fluid chamber) in a plane PL1 parallel to the main propagation direction of the substrate and can be spaced from each other by a minimum of 10µm and a maximum of 150µm (distance from long side to next adjacent long side of the next adjacent fluid chamber).

[0045] Finally, the lamellar fluid chambers can have a height (distance from narrow side to narrow side) of a minimum of 10µm and a maximum of 300µm, measured in a plane PL2 perpendicular to the plane PL1.

[0046] However, deviations from these typical dimensions are possible and are also within the scope of the invention.

[0047] It is also within the scope of the invention that more than two operating states B1, B2, B3, etc. can be set. For this purpose, for example, compared to the variants described above for operating states B1 and B2, a different type of electromagnetic field would be applied in a third (fourth, fifth, etc.) operating state. This results in the degree of particle or particle type output being different between the operating modes, so that a total of three or more different angle-dependent transmittances are achieved. This can be of interest, for example, for angle-dependent dimming applications.

[0048] Furthermore, it should be noted that if electromagnetic switching means are formed in the substrate in a planar manner only on one surface of the fluid chambers, these can then generate an electromagnetic field effective within the fluid chambers in a switched-on state, which is similar to an electromagnetic field as used in so-called IPS (“In Plane Switching”) LCD panels.

[0049] The optical element according to the invention is particularly suitable for controlling the transmission of vertical (but also, in combination, non-vertical) light passage. One application for this would be, for example, the complete or partial dimming of car windows to prevent glare for the driver. Furthermore, the additional optical element can be used to create, for example, switchable mirrors.

[0050] The design variants and means-effect relationships given above apply here, which will not be repeated here for reasons of redundancy.

[0051] In principle, the performance of the invention is maintained if the parameters described above are varied within certain limits.

[0052] It is understood that the features mentioned above and those to be explained below can be used not only in the combinations indicated, but also in other combinations or in isolation, without departing from the scope of the present invention.

[0053] The invention is explained in more detail below with reference to drawings which also show features essential to the invention. Fig. 1 the schematic diagram of an optical element in sectional view, Fig. 2 the schematic diagram of an optical element in plan view, wherein this is in operating state B1, and Fig. 3 the schematic diagram of an optical element in plan view, wherein this is in operating state B2.

[0054] The drawings are not to scale and only represent schematic diagrams.

[0055] An optical element is first identified by Fig. 1, which shows a schematic diagram of such an optical element in sectional view in operating state B1. This includes - a substantially plate-shaped substrate S with a first large surface designed as a light entry surface 3 and a second large surface designed as a light exit surface 4, - a plurality of fluid chambers R embedded in the substrate S, each having one or more surfaces, wherein the fluid chambers R are honeycomb-shaped, cylindrical, or rectangular and fill part of the substrate S or the entire substrate S, - a liquid F with which the fluid chambers R are filled, wherein the liquid contains up to 20 volume percent of electrophoretically or magnetophoretically movable particles P which absorb light of one or more wavelengths or wavelength ranges and which are formed as nanoparticles, quantum dots and / or dyes and have a spatial extent of a maximum of 100 nm, preferably a maximum of 50 nm, particularly preferably a maximum of 20 nm, - electromagnetic switching means 2 formed in a planar manner on one or more surfaces of the fluid chambers R in the substrate S, which, when switched on, generate an electromagnetic field effective within the fluid chambers R, whereby the particles P are moved in the liquid, so that the transmission of the optical element for light of the wavelengths or wavelength ranges absorbed by the particles P changes, wherein in a first operating state B1 the transmission is more than 50% and in a second operating state B2 it is less than 50%, based on the direction of the surface normal of the second large surface of the substrate S.

[0056] Preferably, the said transmission in operating state B1 changes from over 80% to less than 10% in operating state B2, which is easily possible by appropriate selection of the parameters within the scope of the invention.

[0057] The fluid chambers R in this case are, for example, honeycomb-shaped and they essentially fill the entire substrate S. In Fig. In the operating state B1 shown in Figure 1, the particles P are concentrated at an electrode of the switching means 2 due to an applied static electric field, so that the transmission of the optical element reaches a maximum in the vertical direction.

[0058] Fig. 2 shows the schematic diagram of such an optical element in plan view, with this being in operating state B1, and Fig. Figure 3 shows the operating state B2 as a schematic diagram.

[0059] This optical element is particularly suitable for controlling the transmission of vertical (and, in combination, non-vertical) light. One application for this is, for example, the complete or partial dimming of car windows to prevent glare for the driver.

[0060] The design variants and means-effect relationships specified above apply accordingly, and will not be repeated here for reasons of redundancy.

[0061] The optical element according to the invention described above solves the stated problem: An optical element has been disclosed that influences the transmission at least vertically and that can switch between at least two operating states. The optical element is inexpensive and allows for optionally fully or partially dimming car windows or allowing a view through them.

[0062] The invention described above can be used, for example, in a car, as described above.

Claims

[1] Optical element comprising, - a substantially plate-shaped substrate with a first large surface designed as a light entry surface (3) and a second large surface designed as a light exit surface (4), - a plurality of fluid chambers (R) embedded in the substrate, each having one or more surfaces, wherein the fluid chambers (R) are honeycomb-shaped, cylindrical, or rectangular and fill part or all of the substrate, - a liquid (F) with which the fluid chambers (R) are filled, wherein the liquid (F) contains up to 20 volume percent of electrophoretically or magnetophoretically movable particles (P) which absorb light of one or more wavelengths or wavelength ranges and which are formed as nanoparticles, quantum dots and / or dyes and have a spatial extent of a maximum of 100 nm, preferably a maximum of 50 nm, particularly preferably a maximum of 20 nm, - electromagnetic switching means (2) formed in the substrate in a planar manner on one or more surfaces of the fluid chambers (R), which, when switched on, generate an electromagnetic field effective within the fluid chambers (R), whereby the particles (P) are moved in the liquid (F) so that the transmission of the optical element for light of the wavelengths or wavelength ranges absorbed by the particles (P) changes, wherein in a first operating state B1 the transmission is more than 50% and in a second operating state B2 it is less than 50%, based on the direction of the surface normal of the second large surface of the substrate. [2] Optical element according to claim 1, characterized bythat the electromagnetic switching means (2) are at least 50% transparent to light in the visible wavelength range incident perpendicularly into the substrate via the light entry surface (3). [3] Optical element according to one of the preceding claims, characterized by that the electromagnetic switching means (2) are divided into several separately switchable segments, so that a local switchability between the first operating state B1 and the second operating state B2 is possible. [4] Optical element according to one of the preceding claims, characterized by that in the liquid (F) there are several types of particles which differ in their absorption properties and / or their transport properties in the electromagnetic field. [5] Optical element according to one of the preceding claims, characterized bythat the said transmission changes from over 80% in operating condition B1 to less than 10% in operating condition B2. [6] Optical element according to one of the preceding claims, characterized by that in the operating state B1 the particles (P) are concentrated at the electrodes of the switching means (2) due to an applied static electric field, so that the transmission of the optical element in the vertical direction reaches a maximum. [7] Optical element according to one of the preceding claims, characterized bythat more than two operating states B1, B2, etc. can be set by applying a different type of electromagnetic field in at least one further operating state compared to the operating states B1 and B2, which leads to the degree of output of the particles (P) or particle types being different between the operating states, so that a total of three or more different degrees of transmission are achieved.

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