WO2010078662A1

WO2010078662A1 - Electroactive optical device

Info

Publication number: WO2010078662A1
Application number: PCT/CH2009/000009
Authority: WO
Inventors: Manuel Aschwanden
Original assignee: Optotune Ag
Priority date: 2009-01-09
Filing date: 2009-01-09
Publication date: 2010-07-15
Also published as: WO2010078666A1; US8902520B2; KR20110107812A; US20110267680A1; US8553341B2; JP5535240B2; US20140002877A1; CN102265202A; EP2386070A1; JP2012514764A

Abstract

An optical device includes a soft polymer film (101) having a first (103) and second (102) surface. A first compliant electrode (106) is connected to the first surface and a second compliant electrode (105) is connected to the second surface. A rigid optical element (104) is connected on the first and/or second surface or integrated into the polymer film.

Description

i Electroactive optical device

Field of the invention

The invention relates to adjustable optical devices, in particular to an electroactive light scrambler, as well as to methods for operating and manufacturing such a device, and to the use of such a device for light scrambling or lens positioning.

Background of the invention

An electroactive optical device is an optical device using the electroactive effect.

The term electroactive effect describes an electric-field induced de- formation of a solid or liquid. The deformation can be due to Coulomb forces between electrodes and/or due to the rearrangement of electrical ions and/or multipoles, in particular dipoles, in an electric field. Examples of electroactive materials are: dielectric elastomers, electrostrictive relaxor ferroelectric polymers, piezoelectric polymers (PVDF), liquid crystal elastomers (thermal), ionic polymer-metal composites, and mechano-chemical polymers/gels.

A variety of optical light scramblers have been known. So as to suppress the speckle noise, the exposure illumination apparatus of JP 07-2971 H-A that uses laser light includes a diffuser plate that can rotate in its optical system such that the diffuser plate may turn coherent light into incoher- ent light, for example.

Moreover, the projection display apparatus of JP 06-208089, which uses laser light, includes a movable diffuser plate (that can rotate and/or vibrate etc.) in its optical system such that the diffuser plate may turn coherent light into incoherent light. WO 2006/098281 (US 2008/198334), for example, describes a reflector element that reflects collimated coherent light and is capable of vibrating in parallel with a direction normal to a reflector surface of said reflector element; and a reflector element driver unit that drives the reflector element in vibrating motion. This device consists on a complicated and expensive to manufacture element driver unit and a reflector element that requires a more complex optical design than a transmis- sive optical light scrambler. Object and summary of the invention

It is an object of the invention to propose an improved optical device, in particular a light scrambler. This object is achieved by the optical device of claim 1.

To this end, the optical device according to the invention comprises: a, preferably prestretched, polymer film comprising a first surface and a second surface, a first electrode located on said first surface, a second electrode located on said second surface, and a rigid optical element connected to said- first and/or second surface. The device is configured such that, when a voltage difference is applied between the first and second electrodes, the axial distance between the electrodes changes, i.e. it increases or decreases due to Coulomb forces (Maxwell stress), causing the polymer film to change dimension in planar direction, i.e. in the direction parallel to the polymer film. This planar deformation is transmitted to the region with the rigid optical element causing a lateral displacement, i.e. a displacement in the direction parallel to the polymer film, of the rigid optical element resulting in a change of the optical characteristics of the device. Since the optical element is in direct contact with the electroactive polymer film, the device is of small size. Furthermore, since the Coulomb forces can cause a large lateral deformation of the polymer film, a displacement of the optical element, e.g. for light scrambling, can be achieved at low frequencies, thereby preventing actuation frequencies in the audible range and guaranteeing noise free opera- tion.

Since the planar elongation of the polymer film depends on the voltage difference applied between the electrodes, the displacement of the optical element can easily be controlled.

In particular, the optical element is an optical diffuser, a refractive, reflective or a diffractive structure.

The optical device can thus be used for light scrambling or for any other light manipulation by changing the lateral position of the rigid optical element.

In an advantageous embodiment, the optical element is made of a plastic, in particular a polymer (e.g. polymethylmethacrylat), or a glass. Such materi- als have characteristics that lead to a good compromise between optical quality and the ability to resist the deformation of the polymer. Depending on the intended appli- cation, the optical element can e.g. also be made of crystalline material, in particular a single crystal.

Advantageously, the polymer film has a thickness larger than 100 nm and/or smaller than 1 mm. A thickness below 100 nm makes the device difficult to manufacture, while a thickness above 1 mm requires a large voltage to be applied to the electrodes for a given displacement.

In an advantageous embodiment, the polymer film is made of polymers (e.g. PDMS Sylgard 186 by Dow Corning or Optical Gel OG-1001 by Litway) or acrylic dielectric elastomers. Such materials allow a substantial deformation so that the optical element can be displaced by a large distance.

In a very compact embodiment, the first and second electrodes are laterally adjacent to said optical element and/or at a distance d > 0 from the surrounding holding frame.

In an alternative embodiment, the first and second electrodes have a lateral distance d > 0 to the optical element and the surrounding holding frame. This design has the advantage that it reduces mechanical stress in the polymer film.

The invention also relates to a polymer film sandwiched between two electrodes intended to receive a voltage difference, for the lateral displacement of a rigid optical element in contact with said polymer film. The electroactive property of such a film and the particular arrangement of the polymer film with respect to the electrodes are advantageously used for the displacement of the rigid optical element under an electrical control.

The invention also relates to a method for operating an optical device, which optical device comprises a polymer film having a first surface and a sec- ond surface, a first electrode located on said first surface, a second electrode located on said second surface, and a rigid, undeformable optical element connected to said first surface. The method comprises the step of applying a voltage difference between said first electrode and said second electrode, thereby displacing said rigid optical element substantially along a plane parallel to said polymer film. An embodiment of a an optical device according to the present invention may be obtained by a procedure comprising the following steps: stretching a polymer film by a certain amount, e.g. 200 % in x- direction and 300 % in y-direction attaching the polymer film to a holding means, e.g. an encompass- ing frame; applying a first electrode on a first surface of the polymer film applying a second electrode on a second surface of the polymer film applying a rigid optical element consisting of a mechanically harder material than the polymer film to at least one of the surfaces of the polymer film adjacent to at least one of said electrodes.

A second embodiment of a manufacturing process comprises the steps of: placing the rigid optical element onto a supporting surface; distributing a polymer over the rigid optical element and curing it at least partially to form a polymer film; removing the assembly obtained by said steps a) and b) from the supporting surface and prestretching the polymer film with the rigid optical element; attaching the polymer films to a holding means, e.g. an encompassing frame; applying a first electrode on a first surface of the polymer film; and applying a second electrode on a second surface of the polymer film.

Detailed explanations and other aspects of the invention will be given below.

Brief Description of the Drawings

The invention will be better understood and objects other than those set forth above will become apparent when consideration is given to the following detailed description thereof. Such description makes reference to the annexed drawings, wherein: Fig. IA depicts a first embodiment of an optical device according to the invention, in a first state,

Fig. IB depicts the first embodiment in a second state, Fig. 1 C depicts the first embodiment in a top view, Fig. ID depicts an alternative to the first embodiment, Fig. 2A depicts a second embodiment of an optical device according to the invention in a first state,

Fig. 2B depicts the second embodiment in a second state, Fig. 2C depicts the second embodiment in a third state, Fig. 2D depicts a third embodiment in top view, Fig. 2E depicts the third embodiment in a third state.

Detailed description of embodiments Definitions

The term "axial" is generally used to designate a direction perpendicular to the surface of the polymer film in its relaxed state. The term "lateral" is used to designate a direction perpendicular to the axial direction, i.e. a direction parallel to the polymer film.

The term "a rigid, undeformable optical element" designates an element that is substantially more rigid than the polymer film, i.e. by having a Young's modulus exceeding the one of the polymer film by a factor of at least 10, in particular at least 100.

Introduction

The invention utilizes displacements due to Maxwell stress induced deformation. This phenomenon relates to the deformation of a polymer material sandwiched between two compliant electrodes. When a voltage is applied between said electrodes, the electrostatic forces resulting from the free charges squeezes and stretches the polymer. The present invention can be implemented in a variety of forms, e.g. as electroactive light scrambler or as an electroactive optical element displacement device. In the following, we describe some of these applications.

Electroactive light scrambler

One possible embodiment of the present invention is an electroactive light scrambler as shown in Figs. IA — 1C. This embodiment comprises:

- A polymer film 101 comprising a first surface 102 and a second surface 103. The polymer film 101 is advantageously made of elastomers such as silicon rubber, acrylic dielectric elastomer, duroplastic elastomers, thermoplastic elastomers or polyurethane. The characteristics of dielectric polymers are such that they are soft (compliant), have a relatively high dielectric constant (approximately 2 or more), and have a high electric breakdown strength (a few tens up to a hundred kV/mm).

- A first electrode 105 located on the first surface 102,

- A second electrode 106 located on the second surface 103,

- A rigid optical element 104 connected to the first or second surface or integrated into the polymer film 101. The optical element corresponds to a diffusive (refractive, reflective, diffractive or absorptive) structure. The optical element may be fixed directly on the first or second surface or by means of an adhesive or a weld. The optical structure is rigid and does not deform during operation. The polymer film 101 is preferably prestretched and connected to a first and second holding frame 107 and 108, respectively, which form a holding means of the polymer film. In the present embodiment, an edge region of polymer film 101 is clamped between the first and the second holding frame 107, 108 and thus held in the holding means.

The polymer film is freely suspended in the holding means, i.e. it is only supported by the holding means with no further stationary, rigid elements being in contact with its surfaces.

The first electrode 105 is connected to a first conductor 109 and the second electrode 106 is connected to a second conductor 110. Conductors 109 and 110 are intended to be connected to a voltage difference V.

The electrodes should be compliant, i.e. they should be able to follow the deformations of the polymer film 101 without being damaged. Advantageously, the electrodes are therefore manufactured from one of the following materi- als:

- Carbon nanotubes (see "Self-clearable carbon nanotube electrodes for improved performance of dielectric elastomer actuators", Proc. SPIE, Vol. 6927, 69270P (2008);)

- Carbon black (see "Low voltage, highly tunable diffraction grating based on dielectric elastomer actuators", Proc. SPIE, Vol. 6524, 65241N (2007);)

- Carbon grease / conducting greases

- Metal ions (Au, Cu, Cr,....) (see "Mechanical properties of elec- troactive polymer microactuators with ion-implanted electrodes", Proc. SPIE, Vol. 6524, 652410 (2007);) - Liquid metals (e.g. Galinstan)

- Metallic powders, in particular metallic nanoparticles (Gold, silver, copper)

- Conducting polymers (intrinsically conducting or composites) The electrodes may be deposited by means of any of the following techniques:

- Spraying

- Ion-implantation (see "Mechanical properties of electroactive polymer microactuators with ion-implanted electrodes", Proc. SPIE, Vol. 6524, 652410 (2007);) - PVD, CVD

- Evaporation

- Sputtering - Photolithography

- Printing, in particular contact printing, inkjet printing, laser printing, and screen printing.

- Field-guided self-assembly (see e.g. "Local surface charges direct the deposition of carbon nanotubes and fullerenes into nanoscale patterns", L. See- mann, A. Stemmer, and N. Naujoks, Nano Letters 7, 10, 3007-3012, 2007)

- Brushing

- Electrode plating

Optionally, optical element 104 can be structured. Suitable shapes can e.g. be:

- Spherical lenses (convex and concave)

- Fresenel lenses

- Cylindrical lenses

- Aspherical lenses (convex and concave) - Flat

- Squares, triangles, lines or pyramids

- Any micro (e.g. micro lens array, diffraction grating, hologram) or nano (e.g. antireflection coating) structure 1 11, 211 can be integrated into the optical element 104 and the compliant electrode containing polymer layer. When an anti- reflective layer is to be applied to at least one surface of the optical element 104, it is advantageously formed by fine structures having a size smaller than the wavelength of the transmitted light. Typically, this size should be smaller than 5 μm for infrared applications, smaller than 1 μm for near-infrared applications, and smaller than 200 run for applications using visible light. Any of the following methods can e.g. be applied for forming and structuring the optical element 104:

- Casting, in particular injection molding / mold processing

- Nano-imprinting, e.g. by hot embossing nanometer-sized structures - Etching (e.g. chemical or plasma)

- Sputtering

- Hot embossing

- Soft lithography (i.e. casting a polymer onto a pre-shaped substrate) - Chemical self-assembly (see e.g. "Surface tension-powered self- assembly of microstructures - the state-of-the-art", R.R.A. Syms, E. M. Yeatman, V.M. Bright, G.M. Whitesides, Journal of Microelectromechanical Systems 12(4), 2003, pp. 387 - 417)

- Electro-magnetic field guided pattern forming (see e.g. "Electromagnetic field guided pattern forming", L. Seemann, A. Stemmer, and N. Naujoks, Nano Lett., 7 (10), 3007 - 3012, 2007. 10.1021M0713373.

The material for the optical element 104 can e.g. comprise or consist of:

- PMMA

- Glass - Plastic

- Polymer

- Crystalline paterial, in particular single crystal material

The material for the polymer film 101 can e.g. comprise or consist of:

- Gels (Optical Gel OG-1001 by Liteway),

- Elastomers (TPE, LCE, Silicones e.g. PDMS Sylgard 186, Acrylics, Urethanes)

- Thermoplast (ABS, PA, PC, PMMA, PET, PE, PP, PS, PVC,...) - Duroplast

The geometries of the electrodes can be round, square or any other appropriate form.

Fig. IA shows the device in a state without applied voltage. In a second state depicted in Fig. IB, a voltage difference V ≠ 0 is applied between the electrodes 105, 106 via the conductors 109, 110. The polymer film 101 in between the electrodes 105, 106 is compressed. Due to the volume-incompressibility of the polymer film, the region of the polymer film which is in between the compliant electrodes expands in lateral direction. As a consequence, the optical element is laterally displaced by the distance dl . Due to the prestreching of the polymer film, the region that is not in between the first and second electrodes 105,106 and not connected to the optical elements shrinks in lateral direction. This prevents the device from out of plane buckling.

The strain of the polymer film (generally of the order of several tens percents) has a quadratic relation to the voltage difference V. The voltage difference V can be of the order of a few kV, depending on the thickness of the polymer film. To reduce the voltage, a multi-layered structure may be advantageously made, which comprises a plurality of compliant electrodes stacked on top of each other and being alternatingly applied to two different potentials, i.e. with the first, third, fifth etc. electrodes connected to a first potential and the second, fourth, sixth electrodes connected to a second potential. Fig. 1C depicts the first embodiment of Fig. IA and Fig. IB in a top view. The polymer film is advantageously attached to a rectangular holding frame ^■ 107, 108.

Fig. ID depicts, in a top view, an alternative to the first embodiment according to the invention. It differs from Fig. IA, Fig. IB, and Fig. 1C in that sev- eral, in the present case two, pairs of first and second electrodes are located on the surfaces 102 and 103 on the polymer film 101. The voltage difference applied between the electrodes 105a and 106a control the lateral displacement of the rigid optical element 104 in x-direction. The voltage difference applied between the electrodes 105b and 106b control the lateral displacement of the rigid optical element 104 in y- direction.

Electroactive optical element displacement device

The technology described above can not only be applied to electro- active light scramblers, but to a variety of other electroactive optical devices, such as lens positioners. "Lens positioning" designates, in this context, the displacement of a lens in lateral direction, i.e. in a direction perpendicular to the optical axis of the lens.

An example of a lens positioner is shown in Fig. 2A — 2C. It differs from Fig. IA, Fig. IB, and Fig. 1C in that four pairs of first and second electrodes are located on the surfaces 202 and 203 on the polymer film 201 and that the diffusive optical element 104 is replaced by a refractive, diffractive, reflective or absorptive optical element 204, e.g. a lens or a mirror.

Fig. 2A depicts an embodiment of an optical device according to the invention in a first state. This embodiment comprises:

- A polymer film 201 having a first surface 202 and a second surface 203. The polymer film 201 is advantageously made of silicon rubber, acrylic dielectric elastomer, polyurethane or other deformable elastomers. The characteristics of dielectric polymers are such that they are soft (compliant), have a relatively high dielectric constant (approximately 2 or more), and have a high electric breakdown strength (a few tens up to a hundred kV/mm). - Two or more first electrodes 205a-b located on the first surface 202,

- Two or more second electrodes 206a-b located on the second surface 203, - A rigid optical element 204, e.g. lens, connected to the first or second surface or integrated into the polymer film 201. The optical element corresponds to a refractive or reflective structure. The optical element may be fixed directly to one of the surfaces of the polymer film 201 by means of an adhesive or welding. The rigid optical element 204 does not deform or at least not substantially deform during operation.

For the same reasons as in the first embodiment, the polymer film is advantageously prestretched and clamped at its edge region between a first and a second holding frame 207 and 208, respectively. The first electrodes 205a-b are connected to first conductors 209a-b and the second electrodes 206a-b are connected to second conductors 210a-b. Conductors 209 and 210 are intended to be connected to a voltage difference V.

The materials and production processes of the electroactive optical element displacement device are the same as the materials and production processes of the electroactive light scrambler. Fig. 3 A shows the device in a state without applied voltage difference. In a second state depicted in Fig. 2B, a voltage difference V is applied between the electrodes 205a and 206a via the conductors 209a and 210a, respectively. The polymer film 201 in between the electrodes 205a-206a is compressed. Due to the vol- ume-incompressibility of the polymer film, the region of the polymer film which is in between the compliant electrodes expands in lateral direction. As a consequence, the optical element 204 is laterally displaced by the distance d2. Due to the prestreching of the polymer film, the region that is not in between the actuated first and second electrode 205a-206a and/or connected to the optical elements shrinks in lateral direction. This prevents the device from out of plane buckling. In a third state depicted in Fig. 2C, a voltage difference V is applied between the electrodes 205b and 206b via the conductors 209b and 21 Ob, respectively. The polymer film 201 in between the electrodes 205b-206b is compressed. Due to the volume-incompressibility of the polymer film, the region of the polymer film which is in between the compliant electrodes 205b and 206b expands in lateral direction. As a consequence, the optical element 204 is laterally displaced by the distance d3. Due to the prestreching of the polymer film, the region that is not in between the actuated first and second electrode 205b-206b or connected to the optical elements shrinks in lateral direction. This prevents the device from out of plane buckling.

Fig. 2D depicts in a top view, an alternative of the third embodiment according to the invention in a state without applied voltage difference. It differs from Fig. 2A, Fig. 2B, and Fig. 2C in that four pairs of first and second electrodes are located on the surfaces 202 and 203 on the polymer film. The voltage differences applied between the electrodes 205a-b and 206a-b control the lateral displacement of the rigid optical element 204 in x-direction. The voltage differences applied between the electrodes 205c-d and 206c-d control the lateral displacement of the rigid optical ele- ment 204 in y direction.

Fig. 2E depicts a second state of the third embodiment. A voltage difference V is applied between the electrodes 205a and 206a via the conductors 209a and 210a, respectively. The polymer film 201 in between the electrodes 205a-206a is compressed. Due to the volume-incompressibility of the polymer film, the region of the polymer film between the compliant electrodes expands in lateral direction. As a consequence, the optical element is laterally displaced in x-direction. Due to the pre- streching of the polymer film, the region that is not in between the actuated first and second electrode 205a-206a and/or connected to the optical elements shrinks in lateral direction.

Notes:

The deformation of the film polymer depends on the elastic modulus and dielectric constant of the material used, the shape of the material, as well as the boundary conditions.

The shape of the optical element as well as of the polymer film and the electrodes can be adapted to these various applications. In particular, the electrodes, the film as well as the optical element can be of any suitable shape and e.g. by triangular, rectangular, circular or polygonial. The first and second electrodes can also have annulus shape.

The invention is not limited to the shapes of the polymer film as described above. Indeed, other shapes could be defined for displacing the optical element in a directions not parallel to the x- or y-direction.

As mentioned, the rigid optical element 104, 204 can also be inte- grated into the polymer film, i.e. it can be partially or fully embedded into the polymer film, as illustrated, by way of example, by the optical element 104' shown in dotted lines in Fig. IA. Some applications:

The optical device can be used in a large variety of applications, such as:

- Projection devices, e.g. for applications in the optical part of projectors for macro- and micro-projectors in beamers and hand-held devices

- Displays

- Image stabilization in cameras - Industrial applications including laser cutting or welding

- Microscopes

- Vision systems, having any kind of camera

- Light scrambling in research applications

- Telecommunication applications (amplitude modulation) - Illumination control, including color control by positioning absorbing elements over the illumination element, directional light control for illumination, intensity control of LED illuminations.

While there are shown and described presently preferred embodi- ments of the invention, it is to be distinctly understood that the invention is not limited thereto but may be otherwise variously embodied and practiced within the scope of the following claims.

Claims

1. An optical device, in particular a light scrambler, comprising: a polymer film (101 , 201) comprising a first surface (102, 202) and a second surface (103, 203), a first electrode located (105, 205) on said first surface, a second electrode (106, 206) located on said second surface, a rigid, undeformable optical element (104, 204) connected to said first surface, wherein said device is configured to displace said optical element (104, 204) substantially along a plane parallel to said polymer film upon application of a voltage difference between said first and said second electrodes (105, 205; 106, 206).

2. The optical device of claim 1, wherein the first (105, 205) and second (106, 206) electrodes are arranged such that when a voltage (V) is applied between the first and the second electrodes, the first and the second electrodes attract each other due to Coulomb forces (Fc) and compress the polymer film in-between.

3. The optical device of any of the preceding claims, wherein said optical element (104, 204) is a diffusive, diffractive, refractive, reflective and/or absorptive optical structure.

4. The optical device of of any of the preceding claims, wherein the rigid optical element (104, 204) is connected to a surface of the polymer film by means of an adhesive or a weld.

5. The optical device of any of the claims 1 to 3, wherein said rigid optical element (104') is partially or fully embedded into said polymer film (101, 201).

6. The optical device of any of the preceding claims, wherein said optical element (104, 204) is of polymer, glass or crystalline material.

7. The optical device of any of the preceding claims, wherein said polymer film (101 , 201) comprises or consists of a material selected from the group comprising gels, elastomers, thermoplasts, duroplasts, acrylic materials, and elastom- ers.

8. The optical device of any of the preceding claims, wherein the polymer film (101, 201) has a thickness larger than 100 run and/or smaller than 1 mm.

9. The optical device of any of the preceding claims, wherein the polymer film (101, 201) is freely suspended in a holding means (107, 207, 108, 208).

10. The optical device of claim 9, wherein the polymer film (101, 201) is attached to the holding means in a prestretched manner.

11. The optical device of any of the preceding claims, wherein said electrodes (105, 106; 205, 206) are made from at least one material selected from the group comprising carbon nanotubes, carbon black, conducting grease, metal ions, fluid metals, metallic powders, and conducting polymers.

12. The optical device of any of the preceding claims further comprising an antireflective layer (111, 211) on at least one surface of said optical element (104, 204), and in particular wherein said antireflective layer comprises structures having a size smaller than 5 μm, in particular smaller than 1 μm, and in particular smaller than 200 run.

13. The optical device of any of the preceding claims comprising several first electrodes (105a, 105b; 205a, 205b) and several second electrodes (106a, 106b; 206a, 206b) forming a plurality of electrode pairs.

14. A method for operating an optical device, wherein said optical device comprises a polymer film (101, 201) having a first surface (102, 202) and a second surface (103, 203), a first electrode located (105, 205) on said first surface, a second electrode (106, 206) located on said second surface, and a rigid, undeformable optical element (104, 204) connected to said first surface, wherein said method comprises the step of applying a voltage difference between said first electrode (105, 205) and said second electrode (106, 206), thereby displacing said rigid optical element (104, 204) substantially along a plane parallel to said polymer film.

15. A method for manufacturing the optical device of any of the claims 1 to 13 comprising the steps of a) stretching a polymer film (101 , 201); b) attaching the polymer film (101, 201) to a holding means (107, 207, 108, 208); c) applying a first electrode (105, 205) on a first surface (102, 202) of the polymer film (101, 201); d) applying a second electrode (106, 206) on a second surface (103, 203) of the polymer film (101, 201); and e) applying a rigid optical element (104, 204) consisting of a mechanically harder material than the polymer film to at least one of the surfaces of the polymer film adjacent to at least one of said electrodes.

16. A method for manufacturing the optical device of any of the claims 1 to 13 comprising the steps of a) placing a rigid optical element (104, 204) onto a supporting surface; b) distributing a polymer over the rigid optical element and curing it at least partially to form a polymer film (101, 201); c) removing an assembly obtained by said steps a) and b) from said supporting surface and prestretching the polymer film (101, 201) with the rigid opti- cal element (104, 204); d) attaching the polymer film (101, 201) to a holding means (107, 207, 108, 208); e) applying a first electrode (105, 205) on a first surface (102, 202) of the polymer film (101, 201); and f) applying a second electrode (106, 206) on a second surface (103,

203) of the polymer film (101, 201).

17. Use of the device of any of the claims 1 to 13 for light scrambling or lens positioning.