WO2013093740A1

WO2013093740A1 - Optical device with a polymer actuator

Info

Publication number: WO2013093740A1
Application number: PCT/IB2012/057318
Authority: WO
Inventors: Mark Thomas Johnson; Dirk Brokken; Giovanni Cennini; Floris Maria Hermansz Crompvoets
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2011-12-19
Filing date: 2012-12-14
Publication date: 2013-06-27

Abstract

An optical device comprises a stack comprising a first optical element (11) and a second optical element (15), wherein the first optical element comprises a first polymer actuator, and the second optical element is at least partially light transmitting or specularly reflecting, thereby at least partly transmitting or mirror reflecting light received from the first optical element.

Description

Optical device with a polymer actuator

FIELD OF THE INVENTION

The present invention relates to an optical device with a stack comprising a first optical element and a second optical element, wherein the first optical element comprises a first polymer actuator.

BACKGROUND OF THE INVENTION

WO-2011/018728-A1 discloses a hybrid display device comprising an image display unit and a superjacent topology display unit. The image display unit may be constituted by simply a printed image or by a display screen comprising a cathode array tube, a liquid crystal display, an organic light emitting diode display or a di-electrophoretic device. The topology display unit comprises a polymer actuator providing for switching the topology or the three dimensional shape of the topology display unit's surface distal to the image display unit. The topology display unit provides for a switchable tactile display surface. The topology display unit transfers light from the image display unit and preferably the topology display unit is constructed to minimize optical distortion of the transferred image.

In general a device, as the above topology display unit, comprises polymer actuators or electroactive polymers (EAP), which offer the unique possibility to generate simple and cheap thin- film actuating surfaces, which may be made optically active.

However, the optical activity (defined e.g. by the change in Ad x n, where Ad is the change in film thickness and n is the refractive index) of such a thin film polymer actuator device is limited by the relatively small changes in refraction of such a device - being limited as it is by the fact that the geometric changes Ad of such a thin film device are inherently limited.

SUMMARY OF THE INVENTION

It is an object of the present invention to overcome this problem, and to provide an optical device with a polymer actuator providing for effectively switching the optical characteristics of the device. According to a first aspect of the invention, this and other objects are achieved by an optical device comprising a stack comprising a first optical element and a second optical element, wherein the first optical element comprises a first polymer actuator, and the second optical element is at least partially light transmitting or specularly reflecting, thereby at least partly transmitting or mirror reflecting light received from the first optical element.

Hereby is obtained, that the optical activity can be greatly enhanced, as a small optical change in the first optical element provided by the first polymer actuator (such as a small beam steering) can be massively amplified as the steered beam is directed towards a different part of the second optical element, which may have a completely different basis structure, whereby the combined optical effect becomes huge.

By "optical element" should be understood an element capable of transferring and refracting, reflecting or diffracting electromagnetic radiation, e.g. visible light, herein generally denoted light for the sake of convenience.

By "stack" should be understood a number of superposed coherent layers in mutual close and coherent contact.

Polymer actuators and possible architectures for providing different variable topologies of surfaces of film devices incorporating them are known e.g. from US-7567681- B2; Prahlad, H., Pelrine, R., Kormbluh, R., von Guggenberg, P., Chhokar, S., Eckerle, J., Rosenthal, M., Bonwit, N., "Programmable Surface Deformation: Thickness-Mode

Electroactive Polymer Activators and Their Applications ' ^', Proc. SPIE 5759, 102 - 113 (2005); Crompvoets, F., Brokken, D., de Koning, H., Martam, W., "Accurate free-form surface actuation using a non-pre-stretched silicone dielectric polymer actuator", Proc. SPIE 7976, 79761F-1 - 79761F-8 (2011); and the above WO-2011/018728-A1, all the documents are incorporated herein by reference.

In an embodiment the optical device comprises a substrate supporting the first optical element. Generally polymer actuators are very soft and the substrate provides for strength and may provide for manufacture of the optical device using roll-to-roll processing, which provides for cost effective manufacture.

In an embodiment the first optical element comprises an adjustable or switching first optical structure actuated by said first polymer actuator. The optical structure provides for optical characteristics of the optical device.

In an embodiment the second optical element is a static optical element comprising a static second optical structure. Hereby a relative simple optical device is obtained in which the static second optical structure may greatly enhance the optical effect provided by the first optical element.

In a further embodiment the second optical element constitutes the above mentioned substrate. Thus the static second optical element may comprise a relatively rigid material compared to the polymer actuator of the first optical element.

In another embodiment the second optical element comprises a second polymer actuator and an adjustable or switching second optical structure actuated by said second polymer actuator. This provided for greater versatility since also the optical structure(s) of the second optical element can be switched or adjusted using the second polymer actuator.

In an embodiment at least one of the optical structures are selected from a group comprising a lens structure, a beam steering structure, a grating structure, a wavelength separating structure, a barrier structure, a light incoupling structure, and a light outcoupling structure. Thus a variety of embodiments are provided for.

In an embodiment wherein an optical structure of the first optical element extends in a first longitudinal direction and an optical structure of the second optical element extends in a second longitudinal direction, the first longitudinal direction and the second longitudinal direction are parallel. This provides e.g. for using the second optical element to enhance the effect of the first optical element.

In another embodiment wherein an optical structure of the first optical element extends in a first longitudinal direction and an optical structure of the second optical element extends in a second longitudinal direction, the second longitudinal direction extends crosswise to the first longitudinal direction. This provides e.g. for adjusting beams in one direction by means of the first optical element and for adjusting said beams in another direction by means of the second optical element.

In an embodiment the second optical structure comprises a specularly reflecting area. This provides for reflecting the light received from the first optical element back through the first optical element enhancing the optical effect to which the light is subjected.

In an embodiment the second optical structure comprises a non-transparent area, particularly a specularly reflecting area, and the second optical element comprises transparent areas intermediate second optical structures. This provides for obtaining a shutter effect when directing light optionally towards the transparent areas or the non-transparent areas by means of the first optical element. In an embodiment the first optical structure comprises an adjustable first prism device and the second optical element comprises a second prism device. This provides e.g. for light tuning by separating the wavelengths of incoming light by means of the first prism device and direct the beams of the refracted spectrum thus provided in parallel or non-parallel through the optical device to be gathered by the second prism device, whereby the width of the refracted spectrum and the direction of the beams may be adjusted by rotation of the first prism device thus providing for sending the spectrum through different parts of the optical device having different characteristics to influence the spectrum in different ways to provide different gathered beams coming out from the second prism device.

In an embodiment where the second optical element comprise an adjustable or switching second optical structure the first and the second optical element together provides a light guide guiding light in a direction parallel to a joint plane. Thus the adjustable or switchable optical structures may be used to out-couple light optionally to either side of the optical device by deforming a free surface of the first or the second optical element.

In an embodiment at least one of the polymer actuators comprises transparent electrodes. Hereby is obtained a freedom of design of the device in that the design may provide for light traveling through the electrodes.

In an embodiment at least one of the polymer actuators comprises electrodes at least some of which are non-transparent. This may provide for a shutter effect or allow use of a material offering better stretchability than most transparent electrodes offer.

Regarding the optical structures generally any type of optical structures may be considered, for example (arrays of) micro lenses, lenticular lenses, Fresnel lenses, gratings, (parallax) barriers, pyramidal (in/out coupling) structures etc.

It is noted that the invention relates to all possible combinations of features recited in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

This and other aspects of the present invention will now be described in more detail, with reference to the appended schematic drawings showing embodiments of the invention. In the drawings:

Fig. 1 shows a part of a section of an embodiment of an optical element comprising a polymer actuator,

Fig. 2 shows a part of a section of another embodiment of an optical element comprising a polymer actuator, Fig. 3 shows a part of a first embodiment of an optical device according to the invention in a plan view,

Fig. 4 shows a part of a section, as indicated by line IV-IV in Fig. 3, of the first embodiment of an optical device according to the invention,

Fig. 5 shows a part of a section corresponding to Fig. 4 of a second embodiment of an optical device according to the invention,

Fig. 6 shows a part of a section corresponding to Fig. 4 of a third embodiment of an optical device according to the invention,

Fig. 7 shows a part of a section corresponding to Fig. 4 of a forth embodiment of an optical device according to the invention,

Fig. 8 shows a part of a section corresponding to Fig. 4 of a fifth embodiment of an optical device according to the invention,

Fig. 9 shows a part of a section corresponding to Fig. 4 of a sixth embodiment of an optical device according to the invention,

Fig. 10 shows a part of a variant of the sixth embodiment of an optical device according to the invention in a plan view,

Fig. 11 shows a part of a section corresponding to Fig. 4 of a seventh embodiment of an optical device according to the invention,

Fig. 12 shows a part of a section corresponding to Fig. 4 of an eighth embodiment of an optical device according to the invention,

Fig. 13 shows a part of a section corresponding to Fig. 4 of a ninth

embodiment of an optical device according to the invention, and

Fig. 14 shows a part of a section corresponding to Fig. 4 of a tenth embodiment of an optical device according to the invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Polymer actuators or electroactive polymers (EAP) are thin film actuators that consist of a sandwich with traditionally two stretchable electrodes (compliant enough not to restrict actuator movement and deformable enough not to break or fail during actuation) with in between a soft elastic polymer. The basic functionality of a polymer actuator is a controllable stretch motion under influence of a driving voltage applied to the electrodes, whereby they are attracted to each other compressing the sandwiched elastic polymer. The stretchable electrode surfaces of an EAP grow larger as the other dimension, i.e. the distance between the electrodes, shrinks due to incompressibility (Poisson ratio is close to 0.5) of the elastic polymer. The stretch motion can be used for instance to move other objects or to alter the appearance of the EAP's surface.

To provide an element with a deformable surface it is known, cf. the prior art mentioned above, to provide a thickness enhancement layers on one or both sides of the polymer actuator. The properties of the materials used for the thickness enhancement layers influences the deformation of the surfaces of the thickness enhancement layers and of the polymer actuator proper. Though the electrodes as mentioned above are traditionally both stretchable it is known from the above prior art that one of the electrodes may be more or less un-stretchable to provide for intended deformation.

According to the present invention a stack is provided comprising layers at least one of which is an active optical element comprising a polymer actuator. Since these active optical elements will have a surface deformed, i.e. have the surface contour switched or adjusted when the polymer actuator is activated or inactivated the active optical elements will in the following be denoted switching elements and likewise optical structures of the active elements that are adjusted or switched when the polymer actuators are activated will be denoted switching optical structures. In the embodiments disclosed herein the active optical elements comprise a free surface and an internal surface intimately connected to another layer in the stack.

Figs. 1 and 2 show parts of sections of two embodiments of sheet like active or switching optical elements la, lb each comprising a soft elastic polymer layer or EAP layer 2, a thickness enhancement layer or surface layer 4 and another thickness enhancement layer or base layer 6. Sandwiching the EAP layer 2 electrodes are provided, namely mostly transparent electrodes 8 (e.g. PEDOT:PSS, ion-implanted, single-walled carbon nanotube (SW-CNT) or PANI electrodes) (Figure 1) and non-transparent electrodes 10 (e.g. carbon- black, corrugated metallic, silver or carbon grease electrodes) (Figure 2).

When the optical elements la, lb are activated by applying voltage to the electrodes 8, 10 the free surfaces of the surface layers 4 are deformed or switches to present switching first optical structures provided as lens structures 3 in the present embodiments.

Figure 1 shows a first beam 5 passing through an inactivated part or the optical element la and another beam 7 passing through the lens structure 3 provided by an activated part of the optical element la. For the transparent electrodes 8, it is no problem to design the system in such a way that the light travels through the electrode material.

Figure 2 correspondingly shows a first beam 5 passing through an inactivated part of the optical element lb and another beam 7 passing through the lens structure 3 provided by an activated part of the optical element lb. For the non-transparent electrodes 10 (which generally offer superior stretchability at this point in time), an actuator design should be pursued where the light travels next to the electrodes as shown.

The materials of the EAP layer 2, the surface layer 4 and the base layer 6 are transparent and are generally soft having e.g. a Young's modulus smaller than 10 MPa or even smaller than 1 MPa (Young's modulus describes tensile elasticity, or the tendency of an object to deform along an axis when opposing forces are applied along that axis. It is defined as the ratio of tensile stress to tensile strain, and it is often referred to simply as the elastic modulus). Since the base layer 6 is attached to another layer of the stack and since general distortion of the stack is not intended when the polymer actuator is activated to deform the free surface of the surface layer 4, the base layer 6 should allow deformation of the electrodes without transferring the deformation to the adjacent layer of the stack. Thus a transparent, i.e. non-diffusing, foam material or a transparent gel such as styrene ethylene butylene styrene block copolymer (SEBS) may e.g. be used for the base layer 6.

In the embodiments shown in Figs. 3 to 7 a first active or switching optical element comprising a polymer actuator (not shown) is connected to a passive or static second optical element, comprising static optical structures i.e. areas with a pronounced optical character (e.g. micro lens array, lenticular lens, prismatic structures). The static optical structures can e.g. be realized by embossing methods.

In this manner, the optical activity can be greatly enhanced, as a small optical change in the first optical element (such as a small beam steering, (de)focusing etc.) can be massively amplified as the steered beam is directed towards a different part of the static optical element which may have a completely different basis structure (i.e. a different part of a lens), whereby the combined optical effect becomes huge.

The optical device of the invention may e.g. be manufactured by roll-to-roll manufacturing.

Roll-to-roll manufacturing is typically performed using a thin film carrier or supporting substrate. As the polymer actuator materials, as mentioned above, are generally very soft the use of a stiffer supporting substrate is beneficial. As the static optical element does not switch like the first optical element it can e.g. be made of a stiffer elastomeric material such as polyurethane or of a thermo-plastic polymer that can be embossed at elevated temperatures. Such materials may have Young's moduli larger than 100 MPa and even harder materials may be used. Thereby the static optical element can constitute a supporting substrate of the optical device carrying directly the first optical element. Generally the material of the static optical element should be harder or stiffer than the materials of the first optical elements if the static optical element should serve as a supporting substrate acting as a carrier in roll-to-roll manufacturing and during further handling of the optical device. Correct mutual alignment of the optical structures of the two optical elements is facilitated when they are present on opposite sides of a supporting substrate. For this reason one or more of the structures created on one side of the second optical element e.g. the side opposite the side attached to the first optical element may be used, in a phase of a manufacturing process, to define the alignment of the structures on the other side of the optical device. Such a self- alignment approach enhances the mutual alignment of the optical structures of the first and the second optical element.

In the case of a roll-to-roll processing method, it is most logical that the static, non-switching optical element is produced in the earlier stage of the manufacturing process, as the embossing process can cause unwanted deformation of the film structure, and operates under higher pressures (and also temperature) which could damage the EAP. Features in the (embossed) pattern on the non-switching side of the carrier can then be used to align the electrodes used to drive the EAP on the switching side of the device.

Providing the first and second optical structures of respectively the first and the second optical element on either side of a supporting substrate, which in case of the second optic element being a static optic element, may be provided by the second optical element proper, provides for maintaining the first and the second optical structures in correct alignment with each other, even over larger areas (such as square meter areas) and even if the optical device is mounted on a non-flat surface.

Referring now to Figure 3 and 4 a first embodiment of an optical device comprises a first optical element 11 with a switching first optical structure in the form of a switching lens structure 13 and a static second optical element 15 comprising second optical structures in the form of static lens structures 17. In the embodiment shown in Figs. 3 and 4 the first and the second optical structures are lenticular type lens structures which extend in parallel to each other. It should be noted that in Figure 3 the switching lens structure 13 and the static lens structure 17 are shown lightly shifted from perfect alignment for the sake of clarity. In this case a stronger (i.e. a shorter focal length) static or non-switching lens structure 17 is combined with switching lens structure 13, which is intrinsically weaker (defined by the practical geometries). Small changes in the focal length of the switching lens structure are amplified by the non-switching lens structure to realize a larger optical effect than would be possible with the switching lens structure itself. Several types of lens structures may be considered, for example (arrays of) micro lenses, lenticular lenses, Fresnel lenses etc. Like Figs. 1 and 2 Figure 4 shows a first beam 5 passing through an inactivated part or the optical element 11 and another beam 7 passing through the lens structure 13 provided by an activated part of the optical element 11.

Figure 5 shows a second embodiment of an optical device comprising a first optical element 21 with a switching first optical structure 23 in the form of a switching beam steering structure and a static second optical element 25 with a second optical structure 27 in the form of a static beam steering structure. Thus the switching beam steering structure is an asymmetrical optical switching structure, where the change in optical activity of one side of the first optical element is different to the other side. In the present simple example the switching beam steering structure switches in the form of a triangle. As the first optical element 21 is activated, the light passing through the optical device will be steered slightly in the in-plane direction, whereby the light intensity distribution across the surface will be redistributed. This light re-distribution is used to realize a larger optical effect than is possible with the first optical element itself. Also in this embodiment a stronger non-switching optical element is combined with a switching element which is intrinsically weaker (defined by the practical geometries). In this manner, the optical activity can be greatly enhanced, as a small beam steering in the first optical element 21 can be massively amplified as the steered beam is directed towards a different part of the static, non-switching optical element 25 which may have a completely different basis structure (i.e. a different part of a lens structure), whereby the combined optical effect becomes huge. Like Figure 4, Figure 5 shows a first beam 5 passing through an inactivated part or the optical element 21 and another beam 7 passing through the a first switching optical structure 23 provided by an activated part of the optical element 21.

With a single optical element comprising a polymer actuator it is difficult to form an optical shutter (i.e. an element where the light is switchably absorbed or transmitted by the element).

Referring to Figure 6 in a third embodiment an optical shutter is realized by providing a first optical element 31 with a switching first optical structure 33 in the form of a switching beam steering structure with a static second optical element 35 comprising second optical structures 37 in the form of surface areas, which are more and less absorbing or reflective, whereby the device operates an a variable intensity element (a shutter). Like Figure 4, Figure 6 shows a first beam 5 passing through an inactivated part or the optical element 31, thereby passing also through the transparent second optical element 35, and another beam 7 passing through the first switching optical structure 33 provided by an activated part of the optical element 31 , thereby being redirected towards the reflective surface area of the second optical structure 37 to be reflected thereby.

In a variant of the third embodiment, not shown in particular, but similar in configuration to the third embodiment shown in Figure 6, the second optical structures 37 is constituted by areas having a diffraction grating structure. The areas intermediate the second optical structures 37 may have a different diffraction grating structure i.e. a structure with a different pitch of the grating. In this manner, as the polymer activator of the first optical element is activated the light intensity is directed towards gratings of different pitch, whereby different colored light effects can be realized from the same optical device.

Figure 7 shows a forth embodiment of an optical device comprising a first optical element 41 with a beam steering or focusing switching first optical structure 43 like in the first or second embodiment, here shown in the form of a switching lens structure, and a static second optical element 45 with a second optical structure 47 in the form of a mirror or a specularly reflecting area. In this way, the light is modulated by the active part of the stack, i.e. the first optical element, twice, enlarging the focusing / beam steering effect, as illustrated in Figure 7 by beams 5 and 7 incident respectively on an inactivated part of the first optical element 41 and an activated part of said element.

Figs. 8 to 14 show embodiments of an optical device comprising a stack of two switching optical elements both comprising a polymer actuator, and thus both

comprising switching optical structures.

Fig. 8 shows a fifth embodiment of an optical device comprises a first optical element 51 with a switching first optical structure 53 in the form of a first switching lens structure and an switching second optical element 55 comprising switching second optical structures 57 in the form of second switching lens structures. Small changes in the focal length of the switching first lens structure 53 are amplified by the switching second lens structures 57 to realize a larger optical effect than would be possible with the first switching lens structure itself. Apart from the second lens structure being switching this embodiment is similar to the first embodiment shown in Fig. 4. Also here several types of lens structures may be considered, for example (arrays of) micro lenses, lenticular lenses, Fresnel lenses etc. Corresponding to Fig. 4, Fig. 8 shows a first beam 5 passing through an inactivated part or the first optical element 51 and an inactivated part of the second optical element 55, and another beam 7 passing through the lens structure 53 provided by an activated part of the first optical element 51 and the lens structure 57 provided by an activated part or the second optical element 55. To provide for strength of the optical device and to allow manufacture by roll-to-roll manufacturing the first optical element 51 and the second optical element 55 are attached to either side of a supporting substrate 59. The material of the supporting substrate 59 may be similar to the material used for the second optical element 15 of the first embodiment, which in itself serves as a supporting substrate.

A particularly attractive feature of such a device is that it is possible to switch from a non-optically active mode (where both EAP's or polymer actuators are in a non- activated state) to a range of optically active lens structures. This feature is especially desired for a switchable 2D/3D display, where the device must switch from a non-optically active mode (2D) to the lenticular lens structure required for 3D viewing. Furthermore, this feature is especially attractive for a computational optics type of system, where it is useful to be able to switch from a high quality, undistorted image (for standard viewing conditions) to an adjustable degree of defocus, as is required for re-creating scenes using the computational optics approach.

Fig. 9 shows a sixth embodiment of an optical device comprising a first optical element 61 with a switching first optical structure 63 in the form of a switching beam steering structure and a switching second optical element 65 with a second optical structure 67 in the form of a switching beam steering structure 67a or a switching lens structure 67b. In fact any type of optical structures may be considered for optical structures of the second optical element, for example (arrays of) micro lenses, lenticular lenses, Fresnel lenses, gratings,

(parallax) barriers, pyramidal (in/out coupling) structures etc. In the first optical element 61 the switching beam steering structure is an asymmetrical optical switching structure, where the change in optical activity of one side of the first optical element is different to the other side. In the present simple example the switching beam steering structure switches in the form of a triangle. As the first optical element 61 is activated, the light passing through the optical device will be steered slightly in the in-plane direction, whereby the light intensity distribution across the surface will be re-distributed. This light re-distribution may, like with the second embodiment described above, be used to realize a larger optical effect than is possible with the first optical element itself. Thus in a first variant, shown in Fig. 9, the second optical structure 67, i.e. the beam steering structure 67a, also has a beam steering functionality. If the beam steering is in the same direction as the first beam steering structure 61 (i.e. two "identical" structures) the device simply increases the possible beam deflection in the same direction. In a second variant switching beam steering structures aligned in a mutually perpendicular manner are combined as indicated in Fig. 10, which shows in plan view a part of an optical device with a second optical element 65 having switching beam steering second optical structures 67 and a subjacent first optical element having switching beam steering first optical structures 63a. Hereby beam deflection in two directions becomes possible. This is particularly attractive for following a user as he or she moves relative to the optical device.

In a third variant, also indicated in Fig. 9, the switching second optical element 65 also has a lens type functionality, cf. switching lens structure 67b. In this manner, the optical activity can be greatly enhanced, as a small beam steering in the first optical element can be massively amplified as the steered beam is directed towards a different part of the second optical element which may have a completely different basis structure (i.e. a different part of a lens), whereby the combined optical effect becomes huge.

Like in the fifth embodiment a supporting substrate 69 is provided between the first and the second optical element 61, 65.

Again, a particularly attractive feature of such a device is that it is possible to switch from a non-optically active mode (where both EAP's or polymer activators are in a non-activated state) to a range of optically active lens structures. This feature is especially desired for a 3D display with a viewer tracking option, where the device may switch from a non-optically active mode (3D viewing with a multiplicity of viewers) to the beam steering structure required for 3D viewing with a single (or limited number) of viewers.

In a situation where a beam steering switching first optical element is combined with a lenticular lens-type switching second optical element, it is furthermore possible to design an optical device which changes from a switchable 2D/3D display, where the device must switch from a non-optically active mode (2D - neither EAP activated) to the lenticular lens structure required for 3D viewing (lenticular EAP activated), to a beam steering structure required for 3D viewing with a single (or limited number) of viewers (both EAP's activated). Another option is to realize a beam steered 2D image for only a single viewer. Several other combinations are also possible.

Fig. 11 shows a seventh embodiment where a stack comprising two switching optical elements is used as light guide providing for optional out-coupling light from a free surface of either optical element. Thus a strip or sheet 70 comprises an upper part 71 and a lower part 72 of a soft elastic polymer. The upper part 71 constitutes a first optical element and the lower part 72 constitutes a second optical element. The upper part 71 and the lower part 72 sandwiches a set of transparent electrodes 73, which per se, together with a set of upper electrodes 74 and a set of lower electrodes 75 sandwich the upper part 71 and the lower part 72, respectively. Voltage may be applied to the transparent electrodes 73 and the upper electrodes 74 by means of a switch 76, and voltage may be applied to the transparent electrodes 73 and the lower electrodes 75 by means of a switch 77. Light enters the light guide from a first 78a and/or a second 78b light source (either being optional). Each of the light sources 78a, 78b may be a natural or artificial light source. Light from the first source 78a is directed into the elastic polymer sheet 70 via a prism 79a. Light from the second source 78b either propagates directly into the sheet 70 or is reflected against a curved mirror 79b. In either case, a substantial part of the light enters the sheet 70 at an angle such that the light will stay in the sheet by virtue of a sequence of total internal reflections and travel along the layer. Such total internal reflection occurs when the angle of incidence of the incident beams is sufficiently low. By applying voltage to a pair of the sets of electrodes e.g. to the transparent electrodes 73 and the upper electrodes 74, the latter will deform the upper surface of the upper part 71. Due to the deformation surface parts 74a of the upper surface of the upper part 74 at the side of the upper electrodes 74 closest to the light source will be rotated to provide a larger angle of incidence for the incident beams and accordingly beams of light will be out-coupled or escape at these points as indicated by dashed beam lines in Fig. 11. These surface parts 74a thus constitute switching first optical structures. Correspondingly surface parts 75a of the lower surface of the lower part 72 at the side of the lower electrodes 75 closest to the light source constitutes switching second optical structures. It is thus seen that by means of the two switches 76, 77, light may be optionally out-coupled from either of the upper and lower part 71, 72 or both. This is a particularly attractive feature for e.g. a luminary above a table which may be alternatively used to create functional light (out- coupling downwards towards the table), atmospheric light (out-coupling upwards towards the ceiling) or a combination of the two, by actuating the relevant polymer actuator, i.e.

activating the relevant switch 76, 77. It is seen that the upper electrodes 71 the transparent electrodes 73 and the lower electrodes 72 provide two (sets of) separately activated polymer actuators sharing a common electrode, namely the transparent electrode 73. The transparent electrodes 73 may be embedded in, or even constitute, a supporting substrate (not shown).

Fig. 12 shows an eighth embodiment in which color tuning of a light source with a wide spectral content, such as a white light source, is realized by incorporating two rotating prism devices in the first and the second optical element both of which are active elements comprising polymer actuators. By rotating the prisms, the geometrical wavelength distribution at the point in between the two active elements changes. The wavelength distribution (e.g. out-coupled color distribution) can be changed by absorbing or reflecting with a stationary part between or adjacent to the elements. This absorbing /reflecting part is not shown in Fig. 12. Thus Fig. 12 shows a part of an optical device having a switching first optical element 81 comprising a first polymer actuator (not shown) and a switching first optical structure in the form of a first adjustable or rotating prism device 83a, 83b, the optical device further having a switching second optical element 85 comprising a second polymer actuator (not shown) and a switching second optical structure in the form of a second adjustable or rotating prism device 87a, 87b. A beam 5a indicates the optical path through the optical device in an inactivated state of the first and the second polymer actuator and a beam 7a indicates the optical path through the optical device in an activated state of the first and the second polymer actuator. Thus, when the polymer actuators are in an inactivated state the prisms device 83a of the first optical element 81 will refract or out-couple the incoming beam 5a into a spectrum of colors 89a which are transferred through the optical device in a first direction to be received by the prisms device 87a of the second optical element 85, which will gather the spectrum again, and when the polymer actuators are activated the prisms device 83b of the first optical element 81 will rotate to out-couple the incoming beam 7a into a spectrum of colors 89b, which are transferred through the optical device in a second different direction to be received by the likewise rotated prism device 87b of the second optical element 85 which will gather the spectrum again. However due to rotation of the prism devices when the polymer actuators are brought from the inactive state into an activated state the character and the direction of the out-coupled spectrum will be different and the spectrum will pass through different areas of the optical device. These different areas may have different optical characteristics and the spectrum may accordingly be affected in different ways by the optical device depending on whether the polymer actuators are in the inactive state or the active state. Accordingly the out-coming beam 7a will be different from the out-coming beam 5a e.g. by having a different color due to part of the spectrum 89b having been absorbed in the optical device.

Fig. 13 shows a ninth embodiment combining switching optical elements one of which comprises a switchable diffraction grating. Thus Fig. 13 shows an optical device having a switching first optical element 91 with switching first optical structures 93 constituted by switching beam steering structures and a switching second optical element 95. The latter comprises alternating first areas 97 and second areas 98 having respective diffraction gratings with respective grating pitch, thus providing respective diffraction patterns. In an inactivated state of the polymer actuator(s) of the second optical element 95 the first area(s) 97a has a first basic width and the second area(s) 98a has a second basic width. When activating the polymer actuator(s) of the second optical element the width of the first area 97b is extended to a first activated width and correspondingly the width of the second area 98b is compressed to a second activated width. Due to the respective extension and compression of the widths the pitches of the diffraction gratings of the first area 97 and the second area 98 are altered correspondingly, and the diffraction patterns provided by the respective areas 97, 98 are likewise altered. Thus the second optical element 95 provides switchable diffraction gratings and the first and second areas provide switching second optical structures. By means of the switching beam steering structure 93 beams 5, 7 are directed to either the first or the second area 97, 98. Thus a great variety of diffraction patterns is achievable.

Other embodiments comprising switchable diffraction gratings are envisaged. Thus devices which may be considered are two switchable diffraction gratings after each other (for example with different pitches to create different diffraction patterns depending if the polymer activators of one, or the other, or both optical elements are activated) or alternatively single switchable diffraction gratings with an polymer actuator based lens/beam steering to focus or re-direct the diffracted light.

Fig. 14 shows a tenth embodiment of an optical device comprising a first optical element 101 with a beam steering or focusing switching first optical structure 103 like in the first or second embodiment, here shown in the form of a switching lens structure, and a second optical element 105 with a mirror 106 or a specularly reflecting area like in the forth embodiment shown in Fig. 7. In the present embodiment, however, a second optical structure of the switching second optical element 105 comprises a switching surface structure 107 to provide for the specularly reflecting area, or parts thereof, to be e.g. planar or convex as shown in Fig. 14. In this way, the light is modulated by the active part of the stack, i.e. the first optical element, twice, enlarging the focusing / beam steering effect, and further enlarged by the effect of the switching surface structure 107 as illustrated in Fig. 17 by beams 5 and 7 incident respectively on an inactivated part of both optical elements 101, 105 and activated parts of said elements. It is noted that also in this embodiment, according to the invention just one of the optical elements 101, 105 may be activated at a time. The mirror 106 may be deposited in a suitable way (e.g. vacuum deposition or sputtering) on the surface of the second optical element, or be attached to the surface thereof as a separate foil.

The person skilled in the art realizes that the present invention by no means is limited to the preferred embodiments described above. On the contrary, many modifications and variations are possible within the scope of the appended claims. For example all the shown embodiments may comprise a separate supporting substrate between the first and the second optical element.

Claims

CLAIMS:

1. An optical device comprising a stack comprising a first optical element (11; 21; 31; 41; 51; 61; 71; 81; 91; 101) and a second optical element (15; 25; 35; 45; 55; 65; 75; 85; 95; 105), wherein the first optical element comprises a first polymer actuator (2, 8; 2, 10), and wherein the second optical element is at least partially light transmissive or specularly reflective, and arranged to at least partly transmit or reflect light received from the first optical element.

2. An optical device according to claim 1, wherein the stack comprises a substrate (15; 25; 35; 45; 59; 69) supporting the first optical element (11; 21; 31; 41; 51; 61).

3. An optical device according to any of the preceding claims, wherein the first optical element comprises an adjustable or switching first optical structure (13; 23; 33; 43; 53; 63; 75a; 83; 93; 103) actuated by said first polymer actuator.

4. An optical device according to any of the preceding claims, wherein the second optical element is a static optical element comprising a static second optical structure (17; 27; 37; 47).

5. An optical device according to claim 2 and claim 4, wherein the second optical element (15; 25; 35; 45) constitutes said substrate.

6. An optical device according to any of the claims 1 to 3, wherein the second optical element comprises a second polymer actuator and an adjustable or switching second optical structure (57; 67; 74a; 87; 97, 98; 107) actuated by the second polymer actuator.

7. An optical device according to any of claim 3 to 6, wherein at least one of the optical structures are selected from a group comprising a lens structure (13, 17; 43; 53; 67b; 103), a beam steering structure (23, 27; 33; 63, 67a; 93), a grating structure (97, 98), a wavelength separating structure, a barrier structure, a light incoupling structure, and a light outcoupling structure.

8. An optical device according to any of the preceding claims, wherein an optical structure (13) of the first optical element extends in a first longitudinal direction and an optical structure (17) of the second optical element extends in a second longitudinal direction and wherein the first longitudinal direction and the second longitudinal direction are parallel.

9. An optical device according to any of claims 1 to 8, wherein an optical structure (63 a) of the first optical element extends in a first longitudinal direction and an optical structure (67) of the second optical element extends in a second longitudinal direction, and wherein the second longitudinal direction extends crosswise to the first longitudinal direction.

10. An optical device according to any of claims 4 to 9, wherein the first or second optical structure comprises a specularly reflecting area (47; 106).

11. An optical device according to any of claims 4 to 89, wherein the second optical structure (37) comprises a non-transparent area, particularly a specularly reflecting area, and the second optical element (35) comprises transparent areas intermediate second optical structures (37).

12. An optical device according to any of claims 3 to 9, wherein the first optical structure comprises an adjustable first prism device (83) and the second optical element comprises a second prism device (87).

13. An optical device according to any of claims 4 to 9, wherein the first and the second optical element (71, 72) together provides a light guide for guiding light in a direction parallel to a joint plane.

14. An optical device according to any of the preceding claims, wherein at least one of the polymer actuators comprise transparent electrodes (8).

15. An optical device according to any of claims 1 to 14, wherein at least one of the polymer actuators comprise electrodes (10) at least some of which are non-transparent.