KR20090058558A - Controllable light guide - Google Patents

Abstract

A controllable light guide (101; 405) comprising a light guide (103) configured to guide in-coupled light through reflections of the light against a guiding boundary (109) of the light guide (103), and at least one light-modifying member (102; 201-202; 303-304; 414-416) arranged adjacent to the guiding boundary (109) of the light guide (103). The light-modifying member (102; 201-202; 303-304; 414-416) comprises a fluid (104) and a plurality of particles (105) distributed in the fluid. The light-modifying member is controllable between at least a first state having a first particle distribution resulting in at least a portion (106; 209, 210) of the light-modifying member (102; 201-202; 303-304; 414-416) having a first compound refractive index (rid), and a second state having a second particle distribution resulting in the portion (106; 209, 210) of the light-modifying member having a second compound refractive index (n^). At least the second compound refractive index (nc2) is sufficiently high in relation to the refractive index of the light guide (103) at the guiding boundary (109) so as to allow at least partial outcoupling of light through a corresponding portion of the guiding boundary of the light guide.

Description

Controllable light guide, controllable lighting device, and display device {CONTROLLABLE LIGHT GUIDE}

The present invention relates to controllable light guides, lighting devices and display devices comprising such controllable light guides.

Today, various types of flat panel displays are used in a wide range of applications, from mobile phone displays to large screen television receivers. Some types of flat panel displays, such as plasma displays, include an array of light emitting pixels, but most flat panel displays have an array of pixels that can switch between states but cannot emit light independently. Such flat panel displays include universal LCD displays. In order for such a flat panel display to display an image to a user, the pixel array is either backlit in the case of transmissive pixel arrays or ambient light or frontlight (in the case of reflective pixel arrays). should be illuminated by a frontlight.

Conventional backlights (and frontlights) include planar light guides into which light from a light source is coupled. One side of the planar light guide is typically modified through structuring or modification, such as surface roughening, to allow outcoupling of light through that side. The outcoupled light then passes through the pixels in the pixel array that are in a transmissive state, and the corresponding image is visible to the viewer.

However, when only a very small percentage of the pixels are bright (in their transmissive state), as is often the case, a relatively large proportion of the light emitted by the backlight will not reach the viewer, so valuable energy is wasted.

To overcome this problem, a backlight has been proposed in which the outcoupling of light is spatially controllable. For example, WO 2004079437 discloses an illumination system comprising an optical waveguide and a matrix-addressable light-management member. Outcoupling of light from the optical waveguide can be controlled by modulating a portion of the light management member between the transparent state and the scattering state.

The illumination system disclosed in WO 2004079437, for example, provides controllable illumination of a liquid crystal panel, but the outcoupling efficiency is limited because the light management member is sensitive to only one polarization state.

Therefore, there is a need for an improved controllable light guide that allows for outcoupling of more energy efficient light.

It is an object of the present invention to provide an improved controllable light guide.

Another object of the present invention is to provide energy efficient controlled illumination of pixel arrays in flat panel displays.

According to the present invention, these and other objects are achieved by a controllable light guide, the controllable light guide being configured to include light coupled into the light guide and through the reflection of light to the guide boundary of the light guide. A light guide configured to guide light along a principal extension of the light guide, the light guide having a first refractive index at the guide boundary; And at least one light modifying member arranged adjacent to a guide boundary of the light guide and comprising a fluid having a second index of refraction and a plurality of particles having a third index of refraction different from the second index of refraction, the plurality of particles being fluid Distributed within, the light modifying member being controllable between at least a first state and a second state, the first state having a first particle distribution such that at least a portion of the light modifying member has a first compound refractive index, and a second The state has a second particle distribution that causes at least a portion of the light modification member to have a second compound refractive index, the at least second compound refractive index allowing at least partial outcoupling of light through the corresponding portion of the guide boundary of the light guide. In order to be sufficiently high compared to the first refractive index.

The light guide may be, for example, a planar optical waveguide or an optical fiber.

In the case where the light guide is a planar optical waveguide, the light guide may, for example, consist of a single dielectric material or a slab of a compound of dielectric materials. Suitable dielectric materials include different transparent materials such as various types of glass, polymethyl methacrylate (PMMA), and the like. Such planar waveguides may be flat or curved. Slab-type planar waveguides typically rely on total internal reflection (TIR) to include light coupled into the waveguide.

In the present application, the term "fluid" is understood to be a material that changes shape in response to a force and tends to flow in or follow the shape of the chamber in which the material may be contained. Thus, the term "fluid" includes gases, liquids, vapors, and mixtures of solids and liquids (where these mixtures can flow).

The term "particle" is not limited to solid particles, but also includes liquid droplets and fluid filled capsules.

The present invention recognizes that the outcoupling of light from the light guide can be altered by changing the refractive index of the light modifying member located adjacent to the guide boundary of the light guide, and such a change in the refractive index can be achieved by a predetermined amount of fluid having a different refractive index. It is based on the recognition that it can be achieved by controlling the distribution of particles by refractive index.

Since the controllable light guide according to the invention relies on outcoupling due to refraction, it is ensured that all the light actually intended to outcoupling can actually leave the light guide regardless of the polarization state.

The particles distributed in the fluid are preferably small enough to limit scattering to the level at which the particle-fluid suspension mainly acts as a fluid having a variable refractive index.

Particles with a median diameter of about 100 nm or less and a size distribution that is not too wide are suitably used because when the particles are significantly larger than 100 nm, i.e. when the size of the particles is at wavelengths above visible light (scattering) Because it prevails.

The light modification member may be controllable between two states or between multiple states. In the first case mentioned, the light modifying member can function as an optical switch to locally allow or prevent outcoupling of light from the light guide, and in the last case, the light in the light guide is partially outcoupled. Ring, in which case gray scale can be achieved. At this point, which light is outcoupled and which light remains in the light guide depends on the angle of incidence at the guide boundary, where the light rays with small incidence angles are outcoupled while the light rays with large incidence angles are fully reflected.

Advantageously, the first compound refractive index may be low enough to allow total internal reflection at the guide boundary of the light guide, thereby preventing outcoupling of light through the corresponding portion of the guide boundary.

In order for the light guide to fully reflect internally the light entering the light guide at all angles, the refractive index of any element adjacent to the boundary of the light guide must satisfy the following relationship:

Where n _1g is the refractive index of the light guide at the guide boundary of the light guide, and n _cl is for example a light guide core or center slab portion, air, and / or a controllable light modifying member in the case of the present invention. Indicative of the refractive index of adjacent elements, which may be cladding layers arranged to enclose.

For example, if the light guide has a refractive index of 1.67, the first compound refractive index may be less than 1.34 to achieve internal total reflection (TIR) for all coupled incohered light.

In this way, light coupled into the light guide is effectively prevented from being coupled out of the light guide through a portion of the guide boundary that corresponds to the portion of the adjacent light modifying member in the first state.

The second refractive index (fluid) may be lower than the third refractive index (particle).

In this case, for a given portion of the light modification member containing a fluid having an essentially uniform particle distribution, higher particle concentration means higher compound refractive index of that portion. Thus, TIR can be achieved at low particle concentration in that portion of the light modification member, and outcoupling can be obtained at higher particle concentration.

Alternatively, the third refractive index may be lower than the second refractive index, in which case, apparently, higher particle concentrations result in lower compound refractive index in the above-described given portion of the light modification member.

According to one embodiment of the invention, the particles may be subject to an electric field, the light modifying member being controllable at least between the first and second states by changing the electric field in the above-mentioned part of the light modifying member. As a result, the particle distribution can be controlled.

In this embodiment, the particles may or may not be charged. In the case of uncharged particles, the particles may be H.A. Pohl's "Dielectrophoresis; the behavior of neutral matter in non-uniform electric fields", dielectrophoresis, described in detail in University Press, Cambridge, 1978, moves in response to the application of an electric field.

In the case of charged particles, most of the particles advantageously have a charge of the same sign to prevent the aggregation of charged particles. (The electrical neutral state of the fluid is ensured by the presence of ions of opposite charge.)

In an arrangement according to this embodiment of the invention, the particles may be distributed essentially non-uniformly in the absence of an electric field. When an electric field is applied, the particles can be redistributed. The particles travel until the electric field is removed or through equilibrium between the applied electric field and the force applied to the particles through the charge (for electrophoresis) or dipole (for electrophoresis) of the particles. For a more detailed description of electrophoresis, the following documents are referenced:

"Principles of Colloid and Surface Chemistry" by PC Hiemenze and R. Rajagopalan, 3 ^rd edition, Marcel Dekker Inc., New York, 1997, pp. 534-574.

According to another embodiment, the particles are susceptible to magnetic fields, and the light modifying members are controllable in at least the first and second states by applying a magnetic field in the above-mentioned part of the light modifying members, thereby distributing the particles. Control (magnetophoresis).

In this embodiment, the particles can be magnetized, for example, and have properties such that magnetic dipoles can be induced in the particles. At this time, the particle distribution can be controlled through the application of a magnetic field.

As an alternative or supplement to the two above-mentioned embodiments of the present invention, the distribution of particles in the fluid may also result in a spatially variable density of the fluid, and thus a variable concentration of particles in the fluid-particle suspension (in a MEMS device). Such as by mechanical means).

For example, in order to realize control of the particle distribution according to any of the above-mentioned mechanisms, the controllable light guide may further comprise control means.

These control means can be provided in the form of a pattern, for example an electrode pattern, a coil pattern or a mechanical actuator, which can be located adjacent to the light modifying member or elsewhere in the controllable light guide. To prevent unnecessary blocking of outcoupled light, these patterns can be advantageously formed by using one or several transparent materials, such as Indium-Tin-Oxide (ITO) or similar well known materials, depending on their location. have. In locations where outcoupling should be prevented, electrodes which reflect light (for example made of aluminum or silver) are advantageously used.

Control means may be provided opposite the light modifying member, in which case the particle distribution is controlled by causing the particles to selectively move toward either side of the light modifying member (in a direction substantially perpendicular to the light guide).

Alternatively, control means can be provided to achieve what is called "in-plane switching". In this case, particle distribution is controlled by causing the particles to selectively move laterally within the light modifying member. Combinations of plane alignment and vertical switching are also possible.

As an alternative to the control means included in the controllable light guide, an electric field and / or a magnetic field may be generated outside of the controllable light guide.

The controllable light guide according to the invention may advantageously comprise a plurality of light modifying members, each light modifying member being individually controllable.

More or less complex patterns of the outcoupling and light containing portions of the controllable light guide can be thus formed.

According to yet another embodiment, the controllable light guide is arranged adjacent to the light modification member on a remote side of the light modification member with respect to the light guide and adapted to change at least one property of the at least partially outcoupled light. It may further include a light changing member.

This light changing member may be, for example, a layer added to the controllable light guide at the light exit face of the light modifying member, the light changing member being, for example, in the angular distribution, spatial distribution and polarization state of the outcoupled light. You can change at least one.

In order to direct the outcoupled light in a direction perpendicular to the outcoupling surface of the controllable light guide, a light modifying member that can be provided in the form of a layer having a higher refractive index than the light modifying element can be used.

Moreover, the light changing member may have an outcoupling structure to enhance the directing effect. This outcoupling structure can be provided separately or in combination with the higher refractive index mentioned above.

These outcoupling structures can be advantageously formed by generally parallel grooves.

To outcouple the polarized light, the light modifying member may be made of a birefringent material.

In particular, the light modifying member may be birefringent and may have generally parallel grooves. These grooves may be provided in such a manner that the refractive index component of the birefringent light changing member is perpendicular to the grooves. These refractive index components may be about the same as the refractive index component of a fluid having a low concentration of floating particles, or alternatively may be approximately the same as the refractive index component of a fluid having a high concentration of floating particles.

Moreover, a controllable light guide according to the invention can advantageously be included in a controllable lighting device, which controllable light device is arranged to allow incoupling of light emitted by the light source into the controllable light guide. It includes more.

The controllable illumination device described above may advantageously be included in a display device further comprising an image forming member having at least partially controllable transmittance, the controllable lighting device being located behind the image forming member at the viewer's point of view, And to illuminate the image forming member to act as a controllable backlight.

Alternatively, the controllable illumination device may be included in a display device further comprising an image forming member having at least partially controllable reflectance, wherein the controllable lighting device is positioned in front of the image forming member at the viewer's point of view and is controllable. And to illuminate the image forming member to act as a frontlight.

These and other aspects of the invention are now described in more detail with reference to the accompanying drawings, which show presently preferred embodiments of the invention.

1a to 1c schematically show part of a controllable light guide according to the invention in three different states;

2 schematically illustrates a portion of a controllable light guide according to a first embodiment of the invention;

3 schematically illustrates a portion of a controllable light guide according to a second embodiment of the present invention, including a light changing member arranged adjacent to the light modifying member;

4A-4B schematically illustrate an example of a display device according to the present invention.

The present invention is hereinafter described primarily with reference to a planar controllable light guide comprising a light guide and a light modification member, wherein the light modification member is a plurality of suspended particles in a fluid having a refractive index lower than the refractive index of the light guide as well as the refractive index of the particles. Have positively charged particles. It will be appreciated that this is in no way intended to limit the scope of the invention, but may equally be applied to other configurations of controllable light guides such as optical fibers and curved planar light guides. Moreover, particles suspended in a fluid may be negatively charged, uncharged, magnetic or non-magnetic. Of course, the fluid may have a higher refractive index than the light guide and the particles. In addition, an application of an embodiment of a controllable light guide according to the invention is shown in which the controllable light guide is included in a backlight for a transmissive flat panel display. In this regard, a lighting device comprising a controllable light guide according to the invention can equally be applied as an ambient-generating lighting device, or can be a reflective liquid crystal display, an electrowetting display, an electrophoretic display or an electrochromic The same may be applied as frontlights for various types of reflective displays such as (electrochromic) displays.

1A-1C illustrate a portion of a controllable light guide 101 that includes a light modification member 102 arranged adjacent to the light guide 103. The light modification member 102 is provided here in the form of a compartment containing the fluid 104 and a plurality of particles, collectively indicated at 105. In this case, the light guide 103 has a single refractive index n _lg , the fluid 104 has a refractive index n _fl which is lower than the refractive index n _lg of the light guide 103, and the particle 105 of the light guide 103. The refractive index n _p is higher than the refractive index n _lg . In each of FIGS. 1A-1C, a portion 106 of the light modification member 102 is shown, in which the concentration of particles 105 in the fluid 104 is illustrated by the three examples shown in FIGS. 1A-1C. Change between normal states. Light is coupled into the light guide by a suitably positioned light source (not shown).

1A shows a controllable light guide 101 having a light modifying member 102 in a first state, in which the particle 105 is the central portion 106 of the light modifying member 102. Is distributed in the fluid 104 such that the particle concentration of is very low. This results in a low compound refractive index n _c1 of the fluid-particle suspension present in the central portion 106. In the example shown, the compound refractive index n _cl in this first state is low enough to meet the requirements for total internal reflection (TIR) in the light guide, as represented by light ray 107.

Note that the central portion 106 of the light modification member 102 is preferably as large as possible (in the art currently available, the central portion 106 is for example 90 of the surface of the light modification member 102). May account for more than%). In order to make the light guide 103 as efficient as possible, the area of the light modification member 102 outside the central portion 106 can be made well reflective, which can be achieved by covering this area with a mirror. Alternatively, reflective particles can be used when densely packed.

1B shows a controllable light guide 101 having a light modifying member 102 in a second state, in which the particles 105 are essentially non-uniformly distributed in the fluid 104. This results in a high compound refractive index n _c2 of the central portion 106. In the example shown, the compound index of refraction n _c2 is approximately equal to the index of refraction of the light guide, which results in an essentially complete coupling of the light in the light guide that has passed through the central portion 106, as represented by light ray 108. The state of FIG. 1B is preferably a zero output state.

FIG. 1C shows a controllable light guide 101 having a light modifying member 102 in a third state that is intermediate between the first state and the second state. In this third state, the particles 105 are distributed in the fluid 104 such that the concentration of the particles 105 in the central portion 106 is higher than in the first state and lower than in the second state. This results in an intermediate compound index of refraction n _c3 of the central portion 106. In the example shown, the compound refractive index n _c3 is the rate of incidence on the guide boundary 109 between the light guide 103 and the light modification member 102, as represented by transmitted and reflected light rays 110a and 110b, respectively. Allow outcoupling of the light.

Figure 2 schematically shows a first embodiment of a controllable light guide according to the invention, in which two light modification members 201 and 202 are shown, with one light modification member 201 being non-outcoupling. State, and the other light modification member 202 is in an outcoupling state.

Each light modifying member 201, 202 shown is formed by a region containing an insulator fluid 203 and a plurality of electrically charged particles 204. In this example, the particles carry a positive charge. Each light modifying member 201, 202 further comprises three electrodes 207a-207c and 208a-208c, at least some of which are preferably optically transparent and electrically conductive materials, such as ITO or the like. It is formed of equivalent material. Peripheral electrodes 207a, 207c and 208a, 208c may advantageously be reflective to prevent outcoupling of light through the densely packed particles in a non-outcoupling state by light modifying member 201 in FIG. 2. In order to limit the angular spread of outcoupled light, each light modifying member 201, 202 further has structural outcoupling faces 205, 206.

As shown in FIG. 2, the light modifying member 201 applies the first non-outcoupling by applying a negative voltage to the two peripheral electrodes 207a and 207c and a positive voltage to the center electrode 207b. Controlled by state. By selecting a suitable voltage, the particles 204 are concentrated in the vicinity of the peripheral electrodes 207a and 20c, while the concentration of particles in the central portion 209 of the light modification member 201 is very low. Due to this, the compound refractive index at this portion 209 is low enough to prevent outcoupling of the light as described in connection with FIG. 1A.

Also, as shown in FIG. 2, the light modifying member 202 is controlled in a second outcoupling state by applying no voltage to the electrodes or by connecting all three electrodes 208a-208c to the same potential. In this case, the charged particles form an essentially uniform suspension to minimize system energy. As a result, the concentration of particles in the central portion 210 of the light modifying member 202 is high, and outcoupling is allowed as indicated by the outcoupled light rays 211.

It should be emphasized that, for the sake of simplicity, for the sake of simplicity, this is a schematic drawing which does not involve any measures for preventing cross-talk between adjacent light modifying members. Measures to prevent or at least reduce crosstalk include spacing the areas filled with adjacent fluid-particles and / or introducing shielding electrodes between adjacent light modifying members.

3 schematically shows a second embodiment of a controllable light guide according to the invention. Here, control electrodes 301a-301c and 302a-302c are formed on two adjacent light modifying members 303 and 304, respectively. Furthermore, a light modifying member 305 in the form of a structural layer is added to the light modifying members 303 and 304 facing away from the light guide 103.

The operation of the controllable light guide shown in FIG. 3 is the same as described above in connection with FIG. 2, with the main difference between the two illustrated embodiments being out from the light guide 103 by the light modifying member 304. The various properties of the coupled light are changeable by the light changing member 305. In the example shown, the light modifying member 305 is a structural layer having a refractive index higher than the compound refractive index of the outcoupling light modifying member 304. As shown by the outcoupled light ray 306, the outcoupled light is directed in the normal direction of the light guide 103.

4A-4B are controllable light guides in accordance with the present invention in the form of a flat panel display 401 that includes a backlight 404 and a 3x3 pixel array 402 of pixels 403a-403i that are controllably transmitted. An application example of the embodiment is schematically shown.

In FIG. 4A, the backlight 404 is located behind the pixel array 402 at the viewer's point of view of the flat panel display. In this example, one pixel 403e of the pixels in the pixel array 402 is in a transmissive state, and the remaining pixels 403a-403d and 403f-403i are in a non-transmissive state.

4B shows the backlight 404 not hidden by the pixel array 402. As shown, the backlight includes a controllable light guide 405, and the outcoupling of light is controllable in three segments 406, 407, and 408. The backlight 404 further includes at least one light source (not shown) arranged to achieve incoupling of light into the controllable light guide 405.

In order to enable more efficient energy use and / or to achieve local highlighting of the transmissive pixel 403e, the segments 406 and 408 are controlled out of coupling, while the segments corresponding to the transmissive pixel 403e 407 is controlled in an outcoupling state as indicated by light rays 409 and 410 in FIG. 4B.

The outcoupling states of the segments 406-408 are controlled by applying a voltage to the electrodes 411a-411c, 412a-412c and 413a-413c included in the light modification members 414, 415 and 416, respectively. By applying a voltage to these electrodes, the particle distribution in the light modifying members 414-416 and thus the compound refractive index are controlled in the manner described above with respect to FIGS.

It will be apparent to those skilled in the art that the present invention is by no means limited to the preferred embodiments described above. For example, various configurations of electrodes or control means other than those described above are possible, such as electrodes or other control means may be formed at the boundary between adjacent light modifying members and / or protrude into the light modifying member. Can be. Moreover, any electrode or other control means can be made of a non-transparent material, especially if their extension is very small compared to the rest of the light modifying member.

Claims (13)

As controllable light guide 101 (405), Configured to include light coupled into the light guide and configured to guide the light along a principal extension of the light guide through reflection of the light to a guiding boundary of the light guide 103. A light guide 103, the light guide having a first index of refraction at the guide boundary 109; And At least one light-modifying member 102; 201-202; 303-304; 414-416 arranged adjacent to the guide boundary 109 of the light guide 103 Including, The light correction member, A fluid 104 having a second refractive index; And A plurality of particles 105 having a third refractive index different from the second refractive index and distributed in the fluid Including; The light modifying members 102; 201-202; 303-304; 414-416 are controllable between at least a first state and a second state, the first state being the light modifying members 102; 201-202; 303 At least a portion 106 (209, 210) of -304; 414-416 has a first particle distribution such that it has a first compound refractive index n _c1 , the second state being the portion 106 of the light modifying member. 209, 210 have a second particle distribution that causes a second compound refractive index n _c2 , at least the second compound refractive index being equal to the light through the corresponding portion of the guide boundary 109 of the light guide 103; High enough relative to the first refractive index to allow at least partial outcoupling Controllable light guide 101 (405). The method of claim 1, The first compound refractive index n _c1 is low enough to allow total internal reflection at the guide boundary 109 of the light guide 103, thereby preventing outcoupling of light through the corresponding portion of the guide boundary. Controllable light guide 101 (405). The method according to claim 1 or 2, Wherein the third refractive index is higher than the second refractive index. The method according to any one of claims 1 to 3, The particles 105 are susceptible to electric fields; The light modifying members 102; 201-202; 303-304; 414-416 are at least between the first state and the second state by varying the electric field in the portions 106; 209, 210 of the light modifying members. A controllable light guide (101; 405), which is controllable, thereby controlling the distribution of the particles. The method according to any one of claims 1 to 3, The particles are susceptible to magnetic fields; The light modifying members 102; 201-202; 303-304; 414-416 are at least between the first state and the second state by changing the magnetic field in the portions 106; 209, 210 of the light modifying members. A controllable light guide (101; 405) in which it is controllable, thereby controlling the distribution of the particles. The method according to any one of claims 1 to 5, Further control means 207a-207c, 208a-208c; 301a-301c, 302a-302c; 411a-411c, 412a-412c, 413a-413c to control the distribution of the particles 105 in the fluid 104 Controllable light guide (101; 405) comprising; The method according to any one of claims 1 to 6, A plurality of said light modifying members (201-202; 303-304; 414-416), each light modifying member being individually controllable controllable light guide (101; 405). The method according to any one of claims 1 to 7, Arranged adjacent to the light modifying members 303-304 on the far side of the light modifying member with respect to the light guide 103 and adapted to change at least one property of the at least partially outcoupled light. Controllable light guide 101 (405) further comprising a light changing member (305). The method of claim 8, The light modulating member (305) is a controllable light guide (101; 405) which is a structural element having a refractive index higher than the first refractive index. The method according to claim 8 or 9, The light changing member (305) is birefringent and the outcoupled light passing through the light changing member is polarized controllable light guide (101; 405). As a controllable lighting device, A controllable light guide (101; 405) according to any one of claims 1 to 10; And A light source arranged to allow incoupling of light emitted by the light source into the controllable light guide 101 (405) Controllable lighting device comprising a. As the display device 401, An image forming member 402 having at least partially controllable transmittance; And Controllable lighting device 404 according to claim 11 Wherein the controllable lighting device is positioned behind the image forming member at the viewer's point of view and configured to illuminate the image forming member to act as a controllable backlight. As a display device, An image forming member having at least partially controllable reflectance; And Controllable lighting device according to claim 11 Wherein the controllable lighting device is positioned in front of the image forming member at the viewer's point of view and configured to illuminate the image forming member to act as a controllable frontlight.

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