WO2011042048A1

WO2011042048A1 - Optical component for influencing a light beam

Info

Publication number: WO2011042048A1
Application number: PCT/EP2009/062951
Authority: WO
Inventors: Gerald FÜTTERER
Original assignee: Seereal Technologies Gmbh
Priority date: 2009-10-06
Filing date: 2009-10-06
Publication date: 2011-04-14
Also published as: DE112009005301A5

Abstract

The invention relates to an optical component (10) for influencing a light beam, comprising a cell (12) having an inlet window (14) and an outlet window (16) for the light beam; a plurality of layers arranged one behind the other in the cell (12) in the direction from the inlet window (14) to the outlet window (16), wherein a boundary is formed between every two layers adjacent to each other, wherein at least one of the layers (18) is birefringent, and wherein at least two layers adjacent to each other contain a first or a second fluid, respectively, which have different indices of refraction; and an electrowetting apparatus (22a, b, c, d) for controlling the orientation of the boundary between the two fluid layers adjacent to each other. The cell (12) has at least three layers, at least two birefringent boundaries between a birefringent (18) and a monorefringent (20, 20') layer, one following behind the other in the direction from the inlet window (14) to the outlet window (16), said layers being parallel to each other, and the electrowetting apparatus (22a, b, c, d) is designed to control the orientation of the two birefringent boundaries or of a monorefringent boundary that is arranged between the birefringent boundaries and the inlet window (14).

Description

Optical component for influencing a light beam

The present invention relates to an optical component for influencing a light beam, comprising a cell having an entrance window and an exit window for the light guide; a plurality of layers sequentially disposed in the cell in the direction from the entrance window to the exit window, wherein an interface is formed between each two adjoining layers, at least one of the layers being birefringent, and wherein at least two contiguous layers comprise a first and a second fluid, respectively containing different refractive indices; and an electrowetting device for controlling the orientation of the interface between the two adjacent fluid layers.

Such an optical component is known, for example, from WO 2005/093489 A2. In the optical component presented there, the line contains exactly one layer of a birefringent medium. As is known, the term "birefringence" refers to the fact that in certain liquid, solid or even gaseous media optical properties are not isotropic, ie the same in all spatial directions, but anisotropic, ie depend on the propagation direction of a light beam. Light which propagates through the medium along a preferred direction, the so-called optical axis or main axis, always has the same propagation velocity, regardless of its direction of polarization. On the other hand, if a light beam propagates orthogonally to the optical axis or main axis in the medium, the propagation speed depends on the polarization direction: wave trains that are polarized orthogonally to this axis propagate at the same speed. On the other hand, the propagation velocity of WelSenzügen with the other polarization direction, ie polarized parallel to the optical axis or main axis, deviating from this. For the former ordinary ray and the latter extraordinary ray, the birefringent medium thus has different refractive indices. This is used in the optical component disclosed in WO 2005/093489 A2 to split an initially unpolarized light beam into two orthogonally polarized light beams which propagate in birefringent medium in different directions and thus can be easily separated from one another. For example, this prior art document discloses optical components in which an unpolarized beam of light first enters through the entrance window into a refractive fluid. Adjacent to this is an immiscible birefringent fluid. The course of the interface between the single refractive and the birefringent fluid can be controlled via an electrowetting device. These are essentially two electrodes arranged on opposite sides of the cell, the voltages of which can be adjusted individually in order to vary the strength and course of the electric field built up between them. While the non-polarized light beam initially traversed by the single-refractive layer of a hydrophobic medium such as a silicone oil, the adjoining birefringent layer containing liquid crystal molecules, which are aligned by a provided in the region of the exit window transparent alignment layer linear. This direction defines the optical axis or main axis of the birefringent layer.

At the interface between the birefringent and birefringent layers, the initially unpolarized light beam is split into two beams, namely the ordinary and extraordinary beams, which propagate in different directions in the birefringent medium. By changing the voltages applied to the electrodes, the electrowetting device allows to change the orientation of this interface and thus in particular the angle at which the light beam strikes the interface. As a result, the propagation directions of the ordinary and extraordinary beams in the birefringent medium change, which they leave spatially separated by the exit window. WO 2005/093489 A2 proposes various applications of this basic principle, all of which are based on spatial separation of the ordinary and extraordinary beams, for example for a rapidly adjustable beam splitter or for an optical scanning device in which a data carrier with two data storage layers arranged at different depths should be read by the two spatially separated beams.

The present invention has a different purpose. Object of the present invention is to develop a generic optical component such that it can serve as a fast phase or amplitude modulator.

According to the invention, this object is achieved in a generic optical component in that the row has at least three layers that at least two in the direction of the entrance window to the exit window successively birefringence interfaces between a birefringent and a single-refractive layer to each other are substantially parallel, and that the Electro wetting device is designed to control the orientation of the two birefringence interfaces or a Einfachbrechungs-Grenzfiäche, which is arranged between the birefringence interfaces and the entrance window.

Here, the term "birefringence interface" refers to an interface between a birefringent and a single-refractive layer, regardless of which of these two layers is a beam of light! into which other one enters. On the other hand, an interface between two single-refractive layers, that is to say layers, each of which has the same refractive index, regardless of the direction of polarization of the incident light, is referred to as the single-refraction boundary surface. The at least two inventively provided, mutually parallel birefringence interfaces thus lead to a splitting of an incident light beam into a regular and an extraordinary beam and, similar to the passage of a light beam through a plane-parallel plate, to a parallel offset of both the ordinary and extraordinary beams, which, unlike the prior art, do not diverge spatially after passing through both double-interference interfaces, but continue to be parallel to run. More specifically, the ordinary and extraordinary beams, after passing through the second birefringence interface, interfere with each other in a generally elliptically polarized beam, which in special cases may be circular or linear polarization in this elliptical polarization. By means of the design of the electrowetting device likewise provided according to the invention such that it can control the orientation of the two birefringence interfaces or an interface with single refraction, the relative phase of the ordinary and extraordinary beams in this interference and hence the polarization of the resulting overall beam after passage can be determined through both birefringence interfaces. The term "light beam" is also synonymous as a bundle of essentially parallel light beams, the light beam or the bundle of light beams forming a wavefront, thus forming the optical component according to the invention

Phase modulator that allows to vary the phase difference between the ordinary and the extraordinary light beam after exiting the cell through the exit window. For example, with the aid of the electrowetting device, the orientation of the two birefringence interfaces or an upstream single-refractive interface can be controlled such that the beam emerging through the exit window varies between linear polarization, circular polarization or any other more general case of elliptical polarization, depending on the phase difference between its sub-beams can be switched.

In a preferred embodiment of the invention, the optical component can be further developed into an amplitude modulator by further a arranged behind the exit window optical analyzer for Analysereren the polarization of the light beam comprises. Such an optical analyzer transmits only the projection of the electric field vector of the light beam emerging through the exit window in a preferred direction defined by the optical analyzer. Consider, for example, an initial situation in which the successive birefringence boundary surfaces are oriented such that the ordinary and extraordinary beams have a phase difference of π when leaving the cell (corresponding to an offset of the respective seesets relative to each other by λ / 2, where λ is the wavelength of the light beam), the resulting light beam exiting the optical component is linearly polarized and can be canceled by properly selecting the position of the analyzer, orthogonal to that direction of polarization. If the orientation of the two birefringence boundary surfaces or an upstream single-refractive interface and thus the angle of incidence at which the light beam strikes the birefringent layer are changed by means of the electrowetting device, the polarization of the light beam emerging from the component also changes. For example, the linear polarization of the initial situation can be lost and, for example, in the case of a phase difference between ordinary and extraordinary light beam of π / 2, a resulting light beam results behind the component, which is circularly polarized and thus can not be completely extinguished by the analyzer. This embodiment of the invention thus represents a rapidly switchable amplitude modulator. In principle, the optical component according to the invention can be used in the manner described above for phase or amplitude modulation of an unpolarized light beam, as long as it is ensured that the light source generating it actually emits perfectly unpolarized light. In this case, the birefringent layer, which contains, for example, linearly oriented liquid crystals, takes over the splitting of the initially unpolarized beam into a normal and an extraordinary one Light beam depending on the orientation of the liquid crystals relative to the propagation direction of the light beam as it were the role of a polarizer.

However, the light of many sources is not perfect unpolarisieri but has preferential directions. In order to avoid resulting inaccuracies, it is provided in a preferred embodiment of the optical component according to the invention that it further comprises an optical polarizer arranged in front of the entrance window for polarizing the light beam. Similar to the analyzer discussed above, the optical polarizer also transmits only half-waves of a particular linear polarization direction defined by its preferred direction. In this way, it is ensured that defined polarization conditions prevail when the light beam strikes the birefringent layer in the cell. In a particularly preferred embodiment with an optical

Polarizer and an optical analyzer, these can be adjusted relative to each other so that no light is transmitted through the optical analyzer in the de-energized state of the electrical wetting device. By varying the individual voltages at the electrodes of the electrowetting device, it is then possible to tilt interfaces in the interior of the line in such a way that the resulting change in the phase difference between the ordinary and extraordinary beams causes a change in the polarization of the light beam leaving the cell through the exit window, corresponding to FIG Formation of a passing through the optical analyzer light component.

Suitable fluids which can be used in the cell are gaseous and liquid substances as well as mixtures of liquids or gases with solids. Decisive for the functioning of electrowetting here is always that adjacent fluid layers do not mix or only slightly, that they have different electrical conductivities, and that they have a have sufficient flowability to adapt their contact surfaces on the opposite walls of the cell as the voltages on the electrodes of the electrowetting device change. Preferably, it is provided in the case of the optical component according to the invention that the first and the second fluid each contain liquids, for example a polar oil or water with salt dissolved therein for adjusting the conductivity.

In a specific embodiment, an optical component according to the invention is designed in such a way that a plane-parallel and liquid birefringent layer is provided in the cell, that the layers adjoining the plane-parallel layer are liquid and simply refractive, and that the electrowetting device is designed for orientation to control the interfaces between the plane-parallel layer and the two adjacent layers. In this design, the desired phase shift between ordinary and extraordinary beam is changed by tilting the plane-parallel birefringent layer in the cell as it were. The light beam entering the cell through the entrance window strikes the plane-parallel birefringent layer at an angle dependent on the tilt, and is split into the ordinary and extraordinary beams at this first birefringence interface. These are offset in parallel as they pass through the cell and, after passing through the second birefringence interface defining the plane-parallel layer, interfere with the already discussed elliptically polarized light beam exiting the cell through the exit window. The parallel offset of the two sub-beams when passing through the plane-parallel birefringent plate causes the light beam, which leaves the cell through the exit window, is laterally offset from the light beam incident through the entrance window. This offset can be avoided in a more complex embodiment of the optical component according to the invention by providing a further plane-parallel and liquid birefringent layer in the cell is, wherein the two plane-parallel layers are arranged mirror-symmetrically one behind the other, and that the electrowetting device is adapted to control the orientation of the interfaces between the two plane-parallel layers and the respective adjacent layers such that the mirror symmetry is substantially maintained. In this embodiment, the parallel offset of the light at the first plane-parallel birefringent layer is compensated for by an opposite parallel offset at the further, namely second plane-parallel birefringent layer, which is mirror-symmetrical to the first plane-parallel birefringent layer.

In these last-mentioned embodiments, the birefringence interfaces provided according to the invention are provided by the interfaces of a plane-parallel and liquid birefringent layer. The light beam thus first enters the cell in a simple refractive layer and then traverses the plane-parallel birefringent layer, at the back of which it again passes through an easily refractive layer, finally leaving the cell through the exit window.

In an alternative embodiment of the invention, however, it may be provided that a plane-parallel and liquid single-refractive layer is provided in the cell, that the layers adjacent to the plane-parallel layer are liquid and birefringent, and that the electrowetting device is designed to determine the orientation of the interfaces between to control the plane-parallel layer and the two adjacent layers. In this case, the splitting of the light beam into the ordinary and the extraordinary beam takes place at a birefringence interface at which the light beam leaves the birefringent medium and enters the single-refractive plane-parallel layer. Even with such an alternative embodiment with a simple-refractive plane-parallel layer, the parallel offset of the beam leaving the cell through the exit window can be compared with that passing through the exit window Incoming window into the cell occurred beam again be avoided by the fact that in the cell another planparalleie and liquid single-refractive layer is provided, the two pianparaiielen layers are mirror symmetrically arranged one behind the other, and that the electrowetting device is adapted to the orientation of the interfaces between the two To control pianparaiielen layers and the respective adjacent layers such that the mirror symmetry is substantially maintained. In a further alternative embodiment, the birefringent

Layer not formed from a liquid, but rather from a solid medium. Since the interfaces of a solid medium can not be influenced by electrowetting, the angle of incidence, at which the light beam strikes the birefringent medium, must be varied by means of a previously to be passed interface. Therefore, in this alternative embodiment of the optical component according to the invention, it is provided that a plane-parallel and solid birefringent layer is provided in the cell, that two liquid single-refractive layers are provided between the entrance window and the plane-parallel layer, and that the electrowetting device is designed for orientation to control an interface between the two simple refractive layers. By varying the orientation of the interface between the two single-refractive layers, the angle of incidence of the beam on the solid birefringent plane-parallel layer can thus be controlled, which in turn causes a parallel offset of the light beam and a change in its polarization.

Conveniently, it is provided in this embodiment that in the cell between the plane-parallel and solid birefringent layer and the exit window at least two further liquid refractive layers are provided, and that the electrowetting device is adapted to the orientation of the interfaces between the at least two further refractive layers Taxes. These more liquid single-refractive layers allow the beam leaving the line through the exit window to be either parallel to the incident beam or oblique, depending on the desired application, for example in the direction of an eye of a user.

In all embodiments of the optical component according to the invention is expediently provided that it comprises at least one aperture for trimming the light beam at the entrance window and / or at the exit window. In this way, the light beam can be cut both on the input side and on the output side to avoid edge effects. In particular, a smaller section can be coupled out of a broad beam of light, which remains unimpaired by the parallel offset of the ordinary and the extraordinary beam discussed above when passing through a plane-parallel layer. Thus, a defined sirahilage of the output-side beam and its uniform composition of ordinary and extraordinary light is ensured for all optical applications of the component according to the invention.

It is expediently provided in all those embodiments which comprise an optical polarizer that the optical polarizer is arranged on a main axis of the component defined by the center of the entry window and the center of the exit window.

On the other hand, due to the mentioned parallelism of the beam passing through a plane-parallel plate, it may be appropriate in all those embodiments incorporating an optical analyzer that the optical analyzer is displaced from a major axis of the component defined by the center of the entrance window and the center of the exit window is arranged.

According to a preferred embodiment, a major axis of the birefringent layer is orientable in a predeterminable direction. this could for example, by a suitable control of at least one electrode of the electrical wetting device. Preferably, the major axis of the birefringent layer is oriented parallel to a birefringence interface.

The invention further comprises an optical device comprising a plurality of such optical components, and a display device comprising such an optical device, wherein the optical components are arranged substantially side by side on a screen.

Preferred embodiments of the invention will be explained below with reference to the non-limiting figures. Show it:

Figure 1a is a schematic upper sectional view of a first

Embodiment of an optical device according to the invention with a plane-parallel birefringent liquid layer, which is enclosed between two simple-refractive liquid layers;

Figure 1b is a schematic perspective view of

Polarization conditions in a light beam passing through the optical component of Figure 1a;

Figure 2a is a schematic top sectional view of a second

Embodiment of the optical component according to the invention with a plane-parallel simple-refractive liquid layer, which is enclosed between two birefringent liquid layers;

Figure 2b is a schematic representation similar to Figure 2a, but in which the ratio of refractive indices between the plane-parallel layer and the adjacent layers is changed;

Figure 3 is a schematic upper sectional view of another

Embodiment of the optical component according to the invention with two mirror-symmetrical arranged plane-parallel layers;

Figure 4 is a schematic representation of another embodiment of the optical component according to the invention with a solid, relatively thin plane-parallel layer;

Figure 5a is a schematic representation of another embodiment of the optical component according to the invention with a solid, relatively thick plane-parallel layer;

FIG. 5b shows a schematic representation of the refractive index ellipsoid of a birefringent medium which can be used in all embodiments of the optical component according to the invention; and

Figure 6 is a schematic top sectional view of an optical

Component without parallel layer. FIG. 1a shows a schematic plan view of a first one

Embodiment of an optical component 10 according to the invention for influencing a light beam. The optical component 10 comprises a cell 12 with an entrance window 14 and an exit window 16 for the light beam, which is shown in the region of the entrance window 14 as a dash-dotted arrow, but should illuminate substantially the entire entrance window 14. In this embodiment, the cell 12 contains three layers of liquid, namely a plane-parallel middle layer 18 of birefringent liquid enclosed by two single-refractive liquids 20. The liquids are not miscible with each other, so that in the cell 12 clearly defined interfaces between the in the direction of the entrance window 14 to the exit window 18 successively arranged layers 20, 18, 20 form. The birefringent layer 18 can be formed, for example, of electrolyte (for example water and a dissolved salt) in which LC is dissolved, the thickness of the layer being, for example, 100 μm. The single-refractive layers 20, for example of the same thickness, may contain non-polar oil, such as, for example, chloro-naphthalene. The birefringent properties of the layer 18 are thus achieved by embedding liquid crystals in this layer 18, which can be aligned, for example, by structuring regions of the lateral surfaces of the cell 12 or by means of an electric field.

The orientation of the two birefringence interfaces between the entrance-window-side single-refractive layer 20 and the birefringent plane-parallel layer 18 or between the birefringent plane-parallel layer 18 and the exit-window-side refractive layer 20 takes place in a manner known per se with the aid of an electrowetting device. In the embodiment shown in FIG. 1a, this comprises four electrodes 22a, b, c, d arranged on the sides of the cell 12, to which respective voltages Ua, Ub, Uc, Ud can be applied by means of a control unit, not shown in the figures. Mutually diametrically opposite electrodes, that is, the electrodes 22a and 22c and the electrodes 22b and 22d are substantially at the same voltage level, ie üa = Uc = U1 and Ub = Ud = U2. In case U1 = U2, the birefringent layer 18 is oriented substantially "straight" in the cell 12, ie the birefringence interfaces delimiting it are oriented substantially orthogonal to the light beam incident through the entrance window 14. Depending on your choice For example, in the case of U1> U2, the materials of the layers 18, 20 can achieve the tilting of the birefringent layer 18 shown in FIG. 1a.

The aligned in the birefringent layer 18 aligned liquid crystals are indicated in the figures by corresponding lines in the layer 18.

In front of the entrance window 14 of the cell 12, an optical polarizer 24 is installed, behind the Ausffittsfenster 16 an optical analyzer 26. The terms ^! In this application, "front" and "rear" always refer to the direction of propagation of the light wavy line, from bottom to top in FIG. 1a, as indicated by the light beam arrows.

The optical phenomena occurring in the cell 12 at the mutually parallel birefringence interfaces depend significantly on the polarization of the light beam passing through the entrance window 14, caused by the polarizer 24, relative to the optical axis of the birefringent layer 18. Assuming, for example, that the optical axis of the birefringent layer 18 is substantially parallel to the birefringence interfaces defining it in the plane of the drawing of FIG. 1a, as indicated by the bars in the layer 18, a beam of light would is polarized by the polarizer 24 orthogonal to the plane, in the layer 18 undergo no birefringence. Rather, he would experience as normal beam when passing through the layer 18 only a parallel offset.

For this reason, the optical polarizer 24 is expediently adjusted in such a way that the linearly polarized light beam transmitted through it has a polarization direction which encloses an angle of approximately 45 ° with the drawing plane of FIG. 1a and which, of course, is necessarily oriented orthogonally to the propagation direction. Upon entry into the cell 12 in the region of the entrance window 14, this light beam initially strikes substantially orthogonal to the front outer interface of the front single refractive layer 20, with no refraction phenomena occurring. On the other hand, at the interface following in the direction of propagation from the entrance window 14 to the exit window 18, namely the first tilted birefringence interface 28 between the front refractive layer 20 and the central birefringent layer 18, the light beam is split into a normal and an extraordinary light beam. Defining in the usual way the plane defined by the incident light beam and the optical axis of the layer 18 as the main section of the system, the polarization direction of the ordinary light beam is orthogonal to the main section, the polarization direction of the extraordinary ray is parallel thereto. The ordinary ray is shown dotted in FIG. 1a, the extraordinary ray is dashed, and the light beam which has not yet been split before reaching the first birefringence interface 28 is correspondingly dot-dashed. In the example shown in FIG. 1a, therefore, the extraordinary ray is more strongly refracted than the ordinary one. Depending on the choice of materials for the layers 18, 20, a reverse behavior can be achieved, ie a stronger refraction of the ordinary than the extraordinary beam. After passing through the p-parallel birefringent layer 18, the ordinary and extraordinary beams strike another birefringence interface 30, namely the interface between the birefringent layer 18 and the rear single-refractive layer 20 in the cell 12. As shown in FIG As shown, when the medium contained in the back refractive layer 20 is advantageously identical to that of the front refractive layer 20, both beams are refracted at this second birefringence interface 30 so that their directions of propagation are again parallel to the direction of propagation of the light beam transmitted through the polarizer 24 , However, due to the different for them optical path length in the birefringent Schtcht 18 now occurs on the phase difference, which depends on Kippwinkei the birefringent layer 18 and thus a function of the Electrodes 22a, b, c, d applied voltages. After the exit window, this leads to a phase shift Δφ between the two light beams. In the most general case, this phase offset between the ordinary and the extraordinary beam causes the light beam leaving the cell 12 through the exit window 16 substantially orthogonal to the rear outer interface of the rear single-refractive layer 20 to be elliptically polarized, using circular polarization as a special case The elliptically polarized light beam strikes behind the exit window 16 on the optical analyzer 26, which allows only pass that polarization component, which is parallel to its preferred direction. The amplitude or intensity of the light beam which can be measured behind the analyzer 26 can therefore be cut by means of the voltages at the electrodes 22a, b, c, d and the thereby adjustable orientation of the two birefringence interfaces 28, 30! vary.

The polarization ratios present in the course of the light propagation through the optical component 10 according to the invention are also shown schematically in FIG. 1 b. First, a coordinate system is shown in perspective in FIG. 1b below. In this case, the z-axis corresponds to the optical main axis of the optical component 10 according to the invention defined by the center of the entry window 14 and the center of the exit window 16, along which the light beam to be influenced is to be irradiated. The x-axis is orthogonal to this in the drawing plane, the y-axis corresponding orthogonal to the x-axis and to the z-axis perpendicular to the plane.

After passing through the optical polarizer 24, the preferred direction of which is schematically represented in FIG. 1b by the lower hatched area, the light beam is initially linear and polarized parallel to this preferred direction. Behind the rear birefringence interface 30, ie after the ordinary and the extraordinary ray are superimposed again (spatial and / or temporal coherence of the ordinary and the temporal coherence) provided with an extraordinary light beam), the light beam is elliptically polarized, and the optical analyzer 28 fades out of this light beam that polarization component which oscillates parallel to its preferred direction. The mutually orthogonal hatches of polarizer 24 and

Analyzer 26 should represent the corresponding orthogonal orientation of the respective preferred directions to each other. Preferably, the analyzer 28 should be set in its preferred direction to pass only that polarization component which is not present in the case U1 = U2 = 0, and only in the case of a voltage difference j UU | 1-U2 | > 0 and a resulting tilting of the birefringent layer 18 occurs.

As can be seen in FIG. 1 a, the light beam has been displaced parallel in the x-direction after passing through the cell 12, the amount of the offset Δχ being from the tilt of the birefringent layer 18, ie from the angle of the front and rear birefringence interfaces 28 , 30 depends relative to the z axis. To avoid edge effects, the optical component according to the invention is therefore equipped with diaphragms 32 for trimming the light beam at the entrance window 14 and at the exit window 16. They make it possible to decouple an inner region from the cross section of the light beam, a plurality of light beams or the wavefront, so that the inevitably occurring parallel offset during passage through the cell 12 does not lead to fluctuations in intensity in the region of the analyzer 26. For example, assuming that the ordinary ray is dotted in FIG. 1a and the extraordinary ray is shown in phantom, due to the different propagation directions of both rays in the birefringent layer 18, the entire wavefront of the extraordinary ray in FIG. 1a is opposite that of the ordinary ray moved to the right. These two wavefronts are shown dotted or dashed in the exit window side single-refractive layer 20 schematically. With the help of the aperture 32 can be left in Figure 1a area of the light beam, which only the ordinary beam In the same way as the right-hand area in FIG. 1a, which contains only the extraordinary ray, respectively cut away, in other words the apertures 32 in the area of the exit window only pass that part of the light ray which contains the ordinary and the extraordinary ray.

An alternative embodiment of the optical component 10 according to the invention is shown in FIG. 2a. The same components as in FIG. 1a are provided with the same reference numbers. In the embodiment shown in FIG. 2 a, the cell 12 contains a central, single-refractive-index layer 20 adjoining two birefringent layers 18. In this case as well, the voltages applied to the electrodes 22a, b, c, d are adjusted in such a way that two birefringence interfaces 28, 30 parallel to one another are formed. Again, the splitting of the coming of the polarizer 24 and entering through the entrance window 14 in the cell 12 light beam at the front birefringence interface 28, from the rear birefringence interface 30, the ordinary and the extraordinary beam are superimposed due to their phase offset such that the resulting light beam is elliptically polarized.

In the embodiment according to FIG. 2a, both partial beams at the front birefringence interface 28 are broken away from the solder on the interface 28, corresponding to a refractive index of the central refractive layer 20 which is smaller than that of the front birefringent layer 18. This ratio of refractive indices between refractive indexes

Layer 20 and birefringent layers 18 is not mandatory. Alternatively, materials with a different refractive index ratio can also be selected for the layers 18, 20. This is shown schematically in the alternative embodiment of Figure 2b, in which the central single refractive layer 20 is optically more dense than the front birefringent layer 18 for both partial beams. Both the ordinary and extraordinary beams are therefore at the front birefringence interface 28 for Lot down Broken. It is thus understood that by appropriate dimensioning of the distance between the two inventively provided birefringence interfaces 28, 30 and by the choice of refractive indices of the provided in the line layers 18, 20, the degree of parallel displacement of the light beam when passing through the entire cell 12 is set can be.

In FIG. 2 b, the polarization states of the light beam at the respective location in the cell 12 are schematically indicated again below the cell 12.

FIG. 3 schematically shows a cell 12 of a further embodiment of the component 10 according to the invention. In this embodiment, the tent 12 contains two plane-parallel layers, which are arranged mirror-symmetrically with respect to an imaginary xy-plane in the center of the tents 12. In the embodiment shown in FIG. 3, there are two plane-parallel birefringent layers 18, which are separated from one another by a central, single-refractive layer 20 and from the entrance window 14 and the exit fender 16 by a front and a rear break-away layer 20. Of course, the role of single-refractive and birefringent layers can be reversed, so that alternatively two plane-parallel and mirror-symmetrically arranged single-refractive layers and a total of three birefringent layers can be provided in the cell.

As schematically indicated by the arrows in Figure 3, the Paraüelversatz on the rear plane-parallel birefringent layer 18 compensates for those on the front plane-parallel birefringent layer 18, so that the light beam leaving the cell 12 through the exit window 16 no offset from that through the Eintrittsfensfer 14th having incident light beam. In this embodiment, by means of the distribution of the electrodes

22 on the opposite sides of the cell 12 to ensure that the mirror symmetry between the two plane-parallel layers in the change its tilt in the cell 12 is maintained. For this purpose, under ideal conditions, for example, two voltages U1 and U2 can be used on a total of six electrodes 22a-f to rotate the plane-parallel surfaces by equal angles about mutually parallel axes and to set Δφ (U1, U2). This is shown in FIG.

In the embodiments described above, liquids were used in each case as a special case of fluid layers, in particular also for the at least one birefringent layer 18. However, the use of liquid layers can be associated with disadvantages. For example, filling the cell 12 with a sequence of liquids is expensive. Furthermore, in practice, liquids which are made birefringent by the addition of liquid crystals may occasionally segregate over time, so that the optical properties of the layer change, so that the long-term stability of the optical component 10 is no longer guaranteed.

For this reason, in a further embodiment of the optical component 10 according to the invention, which is shown schematically in FIG. 4, a solid birefringent layer 18 is provided.

As again indicated schematically by arrows, which are intended to represent the beam path through the optical component 10, also in this embodiment, the splitting of the light beam into a dotted ordinary and a dashed lines shown extraordinary beam when hitting the front in the propagation direction birefringence interface 28, which separates the solid birefringent layer 18 from a simple refractive layer 20 located immediately in front of it. of course, in contrast to the embodiments presented above with a liquid birefringent layer, in the case of a solid layer 18, this front birefringence interface 28 can no longer be changed in its orientation. The angle of incidence of the light beam on the Therefore, the front birefringence interface 28 must be altered in another way by means of the electrowetting device. For this purpose, in cell 12 immediately before the single-refractive-index layer 20 adjoining the birefringent layer 18 there is another single-refractive layer 20 'whose refractive index differs from that of the layer 20. Also on the exit window side, such a further, single-refractive layer 20 'is provided behind a simple refractive layer 20 immediately adjacent to the solid birefringent layer 28. With the aid of the electrowetting device, the single-junction interfaces between the adjoining single-refractive layers 20, 20 'are now tilted in the manner already described above, ie they are controlled in their orientation relative to the incident light beam. FIG. 4 shows that with the aid of four electrodes 22a, b. c, d, to which the voltage values Ua ~ Uc = U1 and ux = Ud = U2 are applied, both the front single-junction interface 34, which the light beam passes through before reaching the solid birefringent layer 18, and the rear single-junction interface 36, with which the resulting elliptically polarized light beam is adjusted in its propagation again parallel to the z-axis, can be controlled in their orientation. Otherwise, the structure and mode of operation of the embodiment of the optical component 10 shown in FIG. 4 with a solid double-barrier layer 18 correspond to the previously described embodiments with a corresponding liquid layer. FIG. 5a shows a further development of the embodiment from FIG. 4, in which the thickness of the solid birefringent layer 18, ie its length in the z direction, is increased. This embodiment makes it possible to use as the birefringent layer 18 a solid, sufficiently transparent substrate, for example made of glass, which acts as a carrier for the entire optical component 10. The increase in the thickness of the birefringent layer 18 also offers the advantage that due to the increased optical path length in the birefringent layer 18, even at small angles between the Spreading directions of the ordinary and the extraordinary Strahis can achieve a predetermined phase difference Δφ (U1, U2). Little hints! can be set faster than large angles, resulting in faster modulation. In addition, the lateral offset of the light beam, ie the parallel offset in the plane of the figure 5a, when passing through the optical component 10. Again, in this embodiment, aperture 32 expediently provided at the exit window 16 to hide those edge portions of the light beam, in whom he contains only the ordinary or the extraordinary ray. For example, assuming that the ordinary ray is dotted in Figure 5a and the extraordinary ray is shown in phantom, due to the different directions of propagation of both rays in the birefringent layer 18, the entire wavefront of the ordinary ray in Figure 5a is opposite that of the extraordinary ray moved up. These two wavefronts are shown schematically in dashed lines in the exit-window-side, simply refractive layer 20 '. With the help of the aperture 32, the upper portion of the light beam, which contains only the ordinary beam in FIG. 5a, can be cut away, as well as the lower portion, which contains only the extraordinary beam, in FIG. 5a. In other words, the apertures 32 in the area of the exit window allow only that part of the light beam which contains the ordinary and the extraordinary beam to pass through, as indicated by the dot-dash wavefront in the region of the apertures 32.

In all the previously presented embodiments of the optical component 10 according to the invention, it was assumed that the relevant boundary surfaces, ie the front birefringence interface 28 and the rear birefringence interface 30 in the embodiments with a liquid birefringent layer 18 as well as the front single-junction interface 34 and in the embodiments having a solid birefringent layer 18, the rear single-refractive interface 36 is tilted by the electrowetting device exclusively such that the respective interface normal remains in the plane of the drawing. It goes without saying for example, when viewing FIG. 1 a that the electrodes 22 a, b, c, d shown there and the effect of wetting the electrical wetting effect exclusively control an inclination or tilting of the birefringent layer 18 by an angle α with respect to the xy plane,

However, all of the discussed embodiments, particularly those of Figure 5a with a thick solid birefringent layer 18, may be further developed by adding additional electrodes to cell 12 in front of and behind the plane of the figures, respectively. The electrowetting effect triggered by these additional electrodes permits additional tilting of the respectively relevant boundary surfaces in such a way that the interface normal receives a component out of the plane of the drawing or into the plane of the drawing. In other words, not only a propagation component in the x-direction but also a further propagation component in the y-direction can be imparted to the ordinary and the extraordinary light beam with the aid of such additional electrodes. This leads to further interesting properties of the optical component 10, in particular because the refractive properties of uniaxial birefringent media in mutually orthogonal directions are usually very different. Figure 5b shows a plot of the refractive index of a birefringent medium for the ordinary and for the extraordinary ray. As already explained several times, the medium for the ordinary ray always has the same refractive index n, irrespective of its propagation direction in the xy plane. The calculation index curve in the n _x -n _y representation of FIG. 5 b for the ordinary ray is therefore a circle line. It is shown dotted in Figure 5b.

For the extraordinary ray, on the other hand, the refractive index n _{x is} greater when propagated in the x direction than for the ordinary ray. This is the basis for the birefringence phenomena detailed above. On the other hand, when propagated in the y-direction, ie in the drawing plane of the figures, the medium for the extraordinary ray has the same refractive index as for the ordinary ray. The refractive index curve for the extraordinary ray in the n _x -n _y plane according to FIG. 5 b is thus an ellipse which touches the refractive index circle for the ordinary ray at the n _y -axis,

If, for example, in the embodiment of FIG. 5 a, the front single-refraction interface 34 is set in such a way that the light beam incident on the front birefringence interface 28 is produced by means of an extended electrowetting device, which also has electrodes in front of and behind the plane of the drawing In addition to its z-particle component, not only has a propagation component in the x-direction, but also a further propagation component in the y-direction, this also leads to such y in the ordinary and extraordinary ray propagating in the birefringent layer 18 Thus, the optical path length that both partial beams cover in the birefringent layer 18 increases. However, due to the index of refraction of the medium, which is identical in the y-direction for both partial beams, the phase difference between them does not change as a result. Upon leaving the birefringent layer 18 at the rear birefringence interface 30, the absolute phase of both partial beams has thus changed, but their phase difference relative to one another has remained the same. In other words, the additional tilt of the front single-refraction interface 34 and the resulting y-component of the propagation direction of both partial beams causes a phase shift of the two beams without affecting their phase difference. This is of particular interest when a plurality of optical components 10 according to the invention are arranged side by side on a screen and combined to form an optical device which is used in a display device such as a holographic display. For the phase shift discussed above makes it possible to give the light beam of a screen pixel to which the optical component 10 according to the invention is assigned a different phase position than the neighboring pixel. A phase distribution inscribed in a field of phase shifting cells can be used, for example, as a diffractive lens (comparable to a binary lens) Fresnel zone phase plate) and in front of the display a real object point in the create the expected depth z, or, if a divergent white front is generated in the display plane, create an imaginary object point behind the display. The eye can focus on imaginary and real object points that are at different depths. The diffractive lens functions written into the display can be superimposed linearly to represent 3D scenes. The phase distribution of the individual lens functions defines the z distance of individual object points. The amplitude distribution of the individual lens functions defines the intensity of the individual object functions. Cells that can represent complex values, ie phase and amplitude, are advantageous for use with holographic display devices.

In the previously discussed embodiments of the optical component 10 according to the invention, it has always been assumed that the light beam is offset in parallel due to the passage through the plane-parallel layer. Strictly speaking, however, this requires that the two adjacent layers adjacent to the plane-parallel layer have the same refractive index. For example, in the embodiment illustrated in Figure 1a, the entrance window-side refractive layer 20 has a refractive index different from the exit window side refractive layer 20, the ordinary and extraordinary beams at the rear birefringence interface 30 are not exactly refracted in the z-direction, but also possess after passing through the rear birefringence interface 30 in its direction of propagation still an x-component. As a result, the elliptically polarized light beam after passing through the birefringent layer 18 has a fringe pattern in the far field, rendering it unsuitable for use in holographic displays, but not interfering with many other technical applications. It should therefore be made clear at this point that the two layers in the cell 12 adjacent to the birefringence interfaces 28, 30 provided according to the invention adjacent to a central plane-parallel layer do not necessarily have the same refractive index or even have to be formed from the same material , In contrast, according to the invention, essentially the parallel orientation of the two birefringence interfaces 28, 30 provided according to the invention is mandatory. FIG. 8 shows a noninventive example of an optical component which can be controlled with only two electrodes of an electrowetting device and which has a birefringent layer on the entrance window side and exit window side which adjoins a front or a rear refractive layer, between which in turn a central refractive layer is enclosed. As beam simulations show, the light beam can also be elliptically polarized with such a component with a small lateral offset Δχ, whereby a fringe pattern can be observed in the far field.

In addition, it should be pointed out that ensuring a parallel offset of the light beam in the optical component does not preclude the possibility of intentionally tilting the elliptically polarized light beam immediately before leaving the optical component 10 through the exit window 18 with respect to the z direction, for example when using it of the optical component 10 in a holographic display or other type of screen in the direction of the eye of a viewer to redirect. In this case, for example, in the embodiment of FIG. 5a, the rear single-junction interface 38 can be tilted differently than the front single-junction interface 34 by appropriate selection of the electrode voltages. Likewise, behind the rear single-refractive layer 20 'further single-plane refractive index layers could be formed. Boundaries are provided, with the aid of the emerging light beam is given a desired direction of propagation.

It should also be pointed out that the optical analyzer 28, with a suitable choice of its material, can take over the function of a simple refractive layer 20, 20 'behind the plane-parallel solid birefringent layer 18 according to FIG. 5a. Thus, in an embodiment not shown in the figures, the analyzer 26 can be located at the rear birefringence Boundary surface 30 adjacent to the birefringent solid layer 18, and behind the analyzer 26 may be provided further liquid single refractive layers 20 in the cell, which allow the adjustment of the propagation direction of the exiting light beam by means of the electrowetting device. Such films have, for example, a thickness of 50 μm to 250 μm. A structured layer of electrically conductive strips of a period smaller than 200 nm, ie wire grid polarizers, are less as a layer than 300 nm thick.

In the embodiments discussed with solid birefringent layer 18, known birefringent materials such as quartz as well as birefringent plastics can be used that are inexpensive to manufacture. The degree of birefringence, in particular the refractive index difference Δη between the ordinary and the extraordinary ray, and the position of the major axis of the refractive index ellipsoid can be adjusted in a targeted manner during production. Glasses with embedded metallic nano-ellipsoids are known as polarizer 24 and analyzer 26 with high transmission and are commercially available. If, in this case, the concentration of the metallic nano-ellipsoids is reduced by one order of magnitude, for example, a birefringent material is obtained in which the refractive-index difference Δη between ordinary and extraordinary ray and the position of the main axis of the refractive-index ellipsoid can be adjusted in a targeted manner during production. In this way it is possible to produce large flat birefringent glass paste which, unlike quartz, is non-crystalline, and which, unlike birefringent plastics, can also undergo manufacturing processes at very high temperatures, for example above 150 ° C. The present invention is not limited to the embodiments explained above purely by way of example. In particular, it is understood that It is also possible to provide other arrangements and sequences of single-refractive and birefringent layers in the cell 12 or, if appropriate, in a plurality of cells 12 arranged one behind the other. It is always important to be able to vary the angle of incidence of the light beam to at least two parallel double-interference interfaces 28, 30 with the aid of the electrowetting device.

The use of the terms "optical" and "light" is by no means to be understood as a restriction in that only electromagnetic radiation in the visible range can be influenced. Depending on the field of application, the present invention can also be applied to electromagnetic radiation outside the visible range, for example infrared radiation, THz radiation, X-ray radiation, or in principle also to particle radiation, such as, for example, radiation. Neutrons, apply.

Claims

claims

1. An optical component (10) for influencing a light beam, comprising:

a cell (12) having an entrance window (14) and a

Exit window (16) for the light beam;

a plurality of layers arranged in the cell (12) in the direction from the entrance window (14) to the exit window (18), wherein an interface is formed between each two adjoining layers, wherein at least one of the layers (18) is birefringent, and wherein at least two contiguous layers contain first and second fluids, respectively, having different refractive indices; and

an electrowetting device (22a, b, c, d) for controlling the orientation of the interface between the two adjacent fluid layers,

characterized, class

the cell (12) has at least three layers, that at least two birefringence interfaces following one another in the direction from the entrance window (14) to the exit window (18) substantially parallel to each other between a birefringent (18) and a single refractive (20, 20 ') layer and that the electrowetting device (22a, b, c, d) is adapted to control the orientation of the two birefringence interfaces or a single refractive interface disposed between the birefringence interfaces and the entrance window (14).

2. Optical component (10) according to claim 1,

characterized in that

it further comprises an optical analyzer (26) disposed behind the exit window (16) for analyzing the polarization of the light beam.

3. Optical component (10) according to one of the preceding claims, characterized in that it further comprises an optical polarizer (24) disposed in front of the entrance window (14) for polarizing the light beam.

4. Optical component (10) according to one of the preceding claims, characterized in that

the first and second fluids each contain liquids,

5. Optical component (10) according to one of the preceding claims, characterized in that

a plane-parallel and liquid birefringent layer (18) is provided in the cell (12) such that the layers adjacent to the plane-parallel layer are liquid and single-refractive, and in that the electro-leveling means (22a, b, c, d) are adapted to orient to control the interfaces between the plane-parallel layer and the two adjacent layers.

8. Optical component (10) according to claim 5,

characterized in that

a further plane-parallel and liquid birefringent layer (18) is provided in the cell (12), wherein the two plane-parallel layers are arranged mirror-symmetrically one behind the other, and that the electrowetting device (22a, b, c, d) is adapted to the orientation of the interfaces to control between the two plane-parallel layers and the respective adjacent layers such that the mirror symmetry is substantially maintained.

7. Optical component (10) according to one of claims 1 to 4, characterized in that

in the cell (12) there is provided a plane parallele and liquid refractive layer (20, 20 ') such that the layers adjacent to the planar parallels layer are liquid and birefringent, and in that the electrowetting device (22a, b, c, d) is adapted thereto , the orientation of the To control interfaces between the plane-parallel layer and the two adjacent layers.

8. An optical component (10) according to claim 7,

characterized in that

in the Zeiie (12) a further plane-parallel and liquid simple refractive layer (20) is provided, wherein the two plane-parallel layers are mirror-symmetrically arranged one behind the other, and that the E! ektrobenetzungseinrichtung (22a, b, c, d) is adapted to the orientation to control the interfaces between the two plane-parallel layers and the respective adjacent layers in such a way that the mirror symmetry is substantially preserved,

9. Optical component (10) according to one of claims 1 to 4, characterized in that

in the cell (12) a plane-parallel and solid birefringent layer (18) is provided, that between the entrance window (14) and the plane-parallel layer, two liquid single-refractive layers (20, 20 ') are provided, and that the Eiektrobenefzungseinrichtung (22a, b , c, d) is designed to control the orientation of an interface between the two single refractive layers (20, 20 '),

10. Optical component (10) according to claim 9,

characterized in that

in the cell (12) between the plane-parallel and solid birefringent layer (18) and the exit window (18) at least two further liquid refractive layers (20, 20 ') are provided, and in that the electrical bonding device (22a, b, c, d) is designed to control the orientation of the interfaces between the at least two further single refractive layers (20, 20 ').

11. Optical component (10) according to one of the preceding claims, characterized in that

it comprises at least one aperture (32) for trimming the light beam at the entrance window (14) and / or at the exit window (16).

12. An optical component (10) according to any one of the preceding claims in conjunction with claim 3,

characterized in that

the optical polarizer (24) is arranged on a main axis of the component (10) defined by the center of the entrance fender (14) and the center of the exit window (16).

13. Optical component (10) according to one of the preceding claims in conjunction with claim 2,

characterized in that

the optical analyzer (26) from one through the center of the

Entry window (14) and the center of the exit window (16) is arranged staggered main axis of the component (10),

14. Optical component (10) according to one of the preceding claims, characterized in that

a major axis of the birefringent layer (18) is orientable in a predeterminable direction, preferably parallel to a birefringence interface (28, 30).

15. An optical device comprising a plurality of optical

Components (10) according to one of the preceding claims.

16. A display device comprising an optical device according to claim 15, wherein the optical components (10) are arranged substantially side by side on a screen.