WO2004059351A1

WO2004059351A1 - Optical component with polarization dependent properties

Info

Publication number: WO2004059351A1
Application number: PCT/IB2003/006211
Authority: WO
Inventors: Bianca M. I. Van Der Zande; Hendrik R. Stapert
Original assignee: Koninklijke Philips Electronics NV
Current assignee: Koninklijke Philips NV
Priority date: 2002-12-30
Filing date: 2003-12-22
Publication date: 2004-07-15
Anticipated expiration: 2005-06-30
Also published as: TW200502587A; AU2003285689A1

Abstract

A method of manufacturing an optical component is described. The component (200-203) includes a material having polarization dependent optical properties. The method includes applying a beam (104) of radiation to a layer (108) of material so as to induce an anisotropy in the layer of material. The same beam may also be used to shape the layer.

Description

Optical component with polarization dependent properties

Field of the Invention

The present invention relates to a method of manufacturing an optical component having polarization dependent properties, a component manufactured according to the method, and devices including such components. The method is particularly suitable for, but not limited to, manufacturing lenses and periodic and non-periodic phase structures for use in optical scanning devices, and also for manufacturing components having areas of differently orientated molecules and/or polarization dependent properties.

Background of the Invention Optical pickup units for use in optical scanning devices are known. The optical pickup units are mounted on a movable support for scanning across the tracks of the optical disk. The size and complexity of the optical pickup unit is preferably reduced as much as practicable, in order to reduce the manufacturing cost and to allow additional space for other components being mounted in the scanning device. Modern optical pickup units are generally compatible with at least two different formats of optical disk, such as the Compact Disc (CD) and the Digital Versatile Disc (DND) format. Recently proposed has been the Blue-ray Disk (BD) format, offering a data storage capacity of around 25GB (compared with a 650MB capacity of a CD, and a 4.7GB capacity of a DND). Larger capacity storage is enabled by using smaller scanning wavelengths and larger numerical apertures (ΝA), to provide small focal spots, (the size of the focal spot is approximately λ/ΝA), so as to allow the readout of smaller sized marks in the information layer of the disk. For instance, a typical CD format utilizes a wavelength of 785nm and an objective lens with numerical aperture of 0.45, a DND uses a wavelength of 655nm and a numerical aperture of 0.65, and a BD system uses a wavelength of 405nm and a numerical aperture of 0.85.

Typically, the refractive index of materials vary as a function of wavelength. Consequently, a lens will provide different focal points and different performance for different incident wavelengths. Further, the discs may have different thickness transparent layers, thus requiring a different focal point for different types of discs.

In some instances, storage capacity is further increased by increasing the number of information layers per disc. For example, a dual layer BD-disc has two information layers separated by a 25/-ιm thick spacer layer. Thus, the light from the optical pickup unit has to travel through the spacer layer when focusing on the second information layer. This introduces spherical aberration, the phenomenon that rays close to the axis of the converging cone of light have a different focal point compared to the rays on the outside of the cone. This results in a blurring of the focal spot, and a subsequent loss of fidelity in the read-out of the disc.

To enable dual layer readout and backward compatibility (i.e. the same optical system being used for different disc formats), polarization sensitive (PS) lenses , gratings and periodic and non-periodic phase structures have been proposed. Such PS components can be formed of a birefringent material, such as a liquid crystal. Birefringence denotes the presence of different refractive indexes for the two polarization components of a beam of light.

Birefringent materials have an extraordinary refractive index (ne) and an ordinary refractive index (no), with the difference between the refractive indices being Δn=n_e-n₀. PS components can be used to provide different focal points for different wavelengths by ensuring that different wavelengths are incident upon the lens with different polarization. In order to form the component with the desired optical properties, the liquid crystal molecules need to be directed in a specific orientation. Well known materials to induce this orientation are polyimides. These polyimides are usually applied in a solution via spincoating, and subsequently rubbed with a non-fluff cloth to induce a specific orientation of the polyimide alignment layer, which subsequently determines the orientation of the liquid crystal molecules placed upon the layer.

However, such a rubbing process, as it involves physical contact with the alignment layer, is relatively difficult to automate. Further, the rubbing process itself may lead to dust particles being rubbed into the alignment layer. An additional drawback of the rubbing process is that it can only be applied on flat or slightly curved surfaces, as it is extremely difficult to provide good alignment by rubbing on surfaces with a topography including grooves or if the surface is steeply curved. Further, using rubbing it is difficult to orient the alignment layer in corners and along edges satisfactorily. It is an aim of embodiments of the present invention to provide an improved manufacturing process which addresses one or more of the problems of the prior art, whether referred to herein or otherwise.

It is an aim of embodiments of the present invention to provide a manufacturing process that is easily automated.

It is an aim of embodiments of the present invention to provide a manufacturing process that can be used to manufacture components having a relatively complex topology.

Statements of the Invention

In a first aspect, the present invention provides a method of manufacturing an optical component comprising a material having polarization dependent optical properties, the method comprising: applying a first beam of radiation to a layer of material so as to induce an anisotropy in the layer of material. Such a manufacturing technique does not require contact to orientate the alignment layer. Consequently, the method can easily be dust-free. Further, as no physical contact is required with the alignment layer, the method can easily be automated. Also relatively complex shapes of alignment layer can be uniformly orientated. The method can be used to make patterns with individually controlled orientations. Furthermore, complex shapes can be entirely made from the alignment material, such as by using a combination of photo alignment and photo lithographic techniques.

In another aspect, the present invention provides an optical component (150, 203; 181) comprising a material having polarization dependent optical properties, at least a portion of the optical component being formed according to the method as described above. In a further aspect, the present invention provides an optical scanning device

(1) for scanning an information layer (4) of an optical record carrier (2), the device (1) comprising a radiation source (11) for generating a radiation beam (12, 15, 20) and an objective system (18) for converging the radiation beam on the information layer, wherein the device comprises an optical component formed according to the method as described above.

Brief Description of Drawings For a better understanding of the invention, and to show how embodiments of the same may be carried into effect, reference will now be made, by way of example, to the accompanying diagrammatic drawings in which:

Figure 1A and Figure IB illustrate method steps in the orientation of an alignment layer in accordance with an embodiment of the present invention;

Figures 2A-2F illustrate method steps in the formation of a liquid crystal lens in accordance with an embodiment of the present invention;

Figure 3 illustrates a device for scanning an optical record carrier including a liquid crystal lens in accordance with an embodiment of the present invention; and Figures 4A and 4B illustrate how the optical system of the scanning device shown in Figure 3 may be used with different polarization of light to scan different layers within a dual layer optical record carrier;

Figure 5 A illustrates a cross sectional view of photo alignment using a mask in accordance with a preferred embodiment of the present invention; Figure 5B illustrates a plan view of an alignment layer that has been photo- aligned in accordance with the method illustrated in Figure 5 A;

Figures 6A and 6B illustrate a more complex structure produced by successive (repeated) use of the photo alignment photo lithographic technique; and to Figure 7 illustrates an alternative photo-alignment technique using a mask to provide (non)-periodic structures in accordance with an embodiment of the present invention.

Detailed Description of Preferred Embodiments

The present invention uses a layer that induces alignment for polarization dependent materials (such as liquid crystals) by a non-contact method to replace the conventional rubbing process. Such a method is termed photo-alignment. Typically, the alignment occurs due to a photosensitive material (e.g. a polymer) layer being exposed to polarized UN (ultra-violet) light. The UN light induces a (photo chemical) reaction in which chemical bonds can be formed or destroyed, preferentially in the direction of the electric field of the polarized light. After the polarized UN exposure, the polymer layer exhibits a chemical anisotropy to which the director of polarization dependent materials (such as birefringent liquid crystals) is sensitive. As a result, polarization sensitive materials placed upon the polymer layer will align in a monodomain. Figures 1 A and IB illustrate a photo-alignment method in accordance with an embodiment of the present invention. A mould 100, with a curved surface 102 has an alignment layer 108 placed on the curved surface.

The alignment layer 108 could be placed on the curved surface by spincoating, blade coating or printing. However, in this particular embodiment, a photo-dimerised monolayer is used as an alternative to the other coating processes.

The photo-dimerised monolayer is formed by firstly adsorbing (from a solution or vapor) a self assembled monolayer of tri-ethoxy aminopropyl silane on to the mould. Subsequently, a chromofore, such as cinnamoyl chloride, is attached to the monolayer of ethoxy aminopropylsilane to form a photopolymerisable monolayer consisting of chromofores (in this example, cinnemate groups). This chemical modification is performed by bringing the mould into a solution containing the chromofores. The chromofores will react upon polarized UN exposure to induce liquid crystal alignment. Of course, it will be appreciated that other types of chromofores can also be used. This step can replace the step of coating the photosensitive alignment layer on to the mould.

Subsequently, the photosensitive layer is exposed to polarized light 104 that induces a photo chemical reaction preferentially in the direction of the electric field of the polarized light. In this particular example, the cinnamoyl chloride is photoreacted to cyclobutane rings, via a 2+2 cyclo-addition inducing photo-alignment. The result is an alignment layer 109 with a preferred direction of orientation, as indicated by the arrow 110. Such an alignment layer can subsequently be used to manufacture an optical component comprising a material having polarization dependent optical properties.

As alternatives to the photoalignment method of organic layers, non-contact alignment methods such as ion beam alignment and plasma on both inorganic (e.g. diamond like carbon) and organic layers may be applied. Νon contact alignment of liquid crystals can also be achieved by slantwise evaporation or sputtering of SiO_x or AlO_x.

Figures 2A-2F illustrate respective steps in forming an optical component in accordance with a preferred embodiment of the present invention. In this particular instance, the optical component is a liquid crystal birefringent lens. In the first step, shown in Figure 2A, mould 100 is provided, the mould having a shaped surface 102 which subsequently serves to define a portion of the shape of the resulting optical component, hi this particular instance, the liquid crystal is ultimately photopolymerised, and consequently the mould is formed of a material transparent to the radiation used to polymerize the liquid crystal e.g. glass, polymer. An alignment layer is arranged on the curved surface 102, so as to induce a predetermined orientation (indicated by the arrow direction 110) in the liquid crystal subsequently placed upon the alignment layer.

In this particular example, the alignment layer is a layer of polyimide (PI). The polyimide has been applied using spincoating from a solution. The polyimide may then be aligned so as to induce a specific orientation using photo alignment as described above (this orientation determining the resulting orientation of the liquid crystal molecules), or by using other techniques, such as ion beam alignment, or plasma.

A substrate 150, which in this particular embodiment will form part of the optical component, has a bonding layer 120 applied to a first surface 152. The bonding layer is arranged to form a bond with the liquid crystal. In this particular instance, the bonding layer is also an alignment (or orientation) layer comprising polyimide, and may be aligned using photo alignment, ion beam or plasma. The bonding layer contains reactive groups arranged to form a chemical bond with the liquid crystal molecules, and in this instance has a similar type of reactive group as the liquid crystal molecules, such that when photopolymerising the liquid crystal molecules, chemical bonds with the bonding layer on the substrate are also created. This results in very good adhesion between substrate and the liquid crystal layer. The bonding layer may be deposited on the substrate using the same type of process used to deposit and align the alignment layer on the mould 100. The bonding layer, which in this instance also functions as an alignment layer, is oriented in a predetermined orientation (arrow 120) depending upon the desired properties of the resulting liquid crystal components.

In this particular example, a PS lens is being formed, so the bonding layer is aligned so as to be parallel to the direction 110 of the alignment layer on the mould. Preferably, the rotation of the bonding layer is parallel but in the opposite direction to the orientation of the alignment layer.

As illustrated in Figure 2B, a compound 200 incorporating one or more liquid crystals is then placed between the first surface 152 of the substrate 150 and the shaped surface 102 of the mould 100. hi this particular example, as illustrated in Figure 2B, the compound 200 comprises a mixture of two different liquid crystals. These two different liquid crystals have been chosen so as to provide the desired refractive index properties once at least one of the liquid crystals has been polymerized. A droplet of the liquid crystals 200 is placed on the first surface 152 of the substrate. The compound 200 has been degassed, so as to avoid the inclusion of air bubbles within the resulting optical component. It also avoids the formation of air bubbles from dissolved gases coming out of the solidifying liquid during polymerization, as the driving force from polymerization shrinkage during isochorous polymerization leads to a large pressure drop inside the polymerizing liquid.

The glass mould is then heated so that the liquid crystal is in the isotropic phase (typically to about 80°C -120 °C), so as to facilitate the subsequent flow of the liquid crystal into the desired shape. The substrate and the mould are subsequently brought together, so as to define the shape of the liquid crystal portion 201 of the final resulting optical component (Figure 2C). In order to ensure that the liquid crystal forms a homogenous layer between the mould and the substrate, a pressure may be applied to push the substrate towards the mould (or vice versa). The substrate/mould/liquid crystal may then be cooled, for instance down to room temperature for 30 minutes, so as to ensure that the liquid crystal enters the nematic phase, coming from the isotropic phase.

When entering the nematic stage, multi domains may appear in the liquid crystal mixture. Consequently, the mixture can be heated to above the clearing point to destroy the multidomain orientation (e.g. the mixture may be heated for 3 minutes to 105°C). Subsequently, the mixture may be cooled to obtain a homogenous orientation 202 (Figure 2D).

The homogenous liquid crystal mixture may then be photopolymerised using light 302 from an ultra violet radiation source 300 (Figure 2E), for instance by applying a UN-light intensity of lOmW/cm for 60 seconds. At the same time, chemical bonds will be formed between the liquid crystal and the bonding layer.

Subsequently, the optical component (150, 203) can be released from the mould 100 (Figure 2F). This could, for instance, be achieved by slightly bending the mould 100 over a cornered object 400. Alternatively, it could be achieved by pressing a portion of the flat substrate in a flat support, so as to slightly bend the flat substrate. The liquid crystal/substrate component should separate easily from the mould, as a conventional polyimide (without reactive groups) was used on the mould. The mould can be reused to produce subsequent components, by repeating steps illustrated in Figures 2B-2F. Typically, the alignment layer will remain upon the mould 100, and hence does not need to be reapplied.

If desired, a further processing step can be performed to remove the liquid crystal 202 from the substrate 150. However, in most instances it is assumed that the substrate 150 will form part of the final optical component.

A suitable polyimide for use in the photo-aligned alignment layer is the polyimide RN 1349 purchased from Nissan Chemical , whilst Merck ZLI2650, spincoated from a solution in γ-butyrolactone can be used as an appropriate reactive polyimide with methacrylate groups as the bonding layer.

As mentioned above, in the preferred embodiment a mixture of two liquid crystals was utilized to obtain the desired n_e and n₀. The two liquid crystals utilized were 1,4- di(4-(3-acryloyloxypropyloxy)benzoyloxy)-2-methylbenzene (RM 257) and E7 (a cyanobiphenyl mixture with a small portion of cyanotriphenyl compound) both from Merck, Darmstadt, Germany. The photoinitiator used to ensure the photo polymerisation of the liquid crystals was Irgacure 651, obtainable from Ciba Geigy, Basel.

In some instances, a surfactant was mixed with the liquid crystal to promote the lens release from the mould. The surfactants utilized were FC171 a perfluorinated surfactant (3M) and 2-(N-ethylperfluorooctane sulfonamido-ethylacrylate (Acros). The use of the surfactant was seen to influence the orientation of the liquid crystal (a lower Δn was seen when a surfactant was utilized).

Figure 3 shows a device 1 for scanning an optical record carrier 2, including an objective lens 18 according to an embodiment of the present invention. The record carrier comprises a transparent layer 3, on one side of which an information layer 4 is arranged. The side of the information layer facing away from the transparent layer is protected from environmental influences by a protection layer 5. The side of the transparent layer facing the device is called the entrance face 6. The transparent layer 3 acts as a substrate for the record carrier by providing mechanical support for the information layer.

Alternatively, the transparent layer may have the sole function of protecting the information layer, while the mechanical support is provided by a layer on the other side of the information layer, for instance by the protection layer 5 or by a further information layer and a transparent layer connected to the information layer 4. Information may be stored in the information layer 4 of the record carrier in the form of optically detectable marks arranged in substantially parallel, concentric or spiral tracks, not indicated in the Figure. The marks may be in any optically readable form, e.g. in the form of pits, or areas with a reflection coefficient or a direction of magnetization different from their surroundings, or a combination of these forms.

The scanning device 1 comprises a radiation source 11 that can emit a radiation beam 12. The radiation source may be a semiconductor laser. A beam splitter 13 reflects the diverging radiation beam 12 towards a collimator lens 14, which converts the diverging beam 12 into a collimated beam 15. The collimated beam 15 is incident on an objective system 18.

The objective system may comprise one or more lenses and/or a grating. The objective system 18 has an optical axis 19. The objective system 18 changes the beam 17 to a converging beam 20, incident on the entrance face 6 of the record carrier 2. The objective system has a spherical aberration correction adapted for passage of the radiation beam through the thickness of the transparent layer 3. The converging beam 20 forms a spot 21 on the information layer 4. Radiation reflected by the information layer 4 forms a diverging beam 22, transformed into a substantially collimated beam 23 by the objective system 18 and subsequently into a converging beam 24 by the collimator lens 14. The beam splitter 13 separates the forward and reflected beams by transmitting at least part of the converging beam 24 towards a detection system 25. The detection system captures the radiation and converts it into electrical output signals 26. A signal processor 27 converts these output signals to various other signals.

One of the signals is an information signal 28, the value of which represents information read from the information layer 4. The information signal is processed by an information processing unit for error correction 29. Other signals from the signal processor 27 are the focus error signal and radial error signal 30. The focus error signal represents the axial difference in height between the spot 21 and the information layer 4. The radial error signal represents the distance in the plane of the information layer 4 between the spot 21 and the center of a track in the information layer to be followed by the spot.

The focus error signal and the radial error signal are fed into a servo circuit 31, which converts these signals to servo control signals 32 for controlling a focus actuator and a radial actuator respectively. The actuators are not shown in the Figure. The focus actuator controls the position of the objective system 18 in the focus direction 33, thereby controlling the actual position of the spot 21 such that it coincides substantially with the plane of the information layer 4. The radial actuator controls the position of the objective lens 18 in a radial direction 34, thereby controlling the radial position of the spot 21 such that it coincides substantially with the central line of track to be followed in the information layer 4. The tracks in the Figure run in a direction perpendicular to the plane of the Figure.

The device of Figure 3 in this particular embodiment is adapted to scan also a second type of record carrier having a thicker transparent layer than the record carrier 2. The device may use the radiation beam 12 or a radiation beam having a different wavelength for scanning the record carrier of the second type. The NA of this radiation beam may be adapted to the type of record carrier. The spherical aberration compensation of the objective system must be adapted accordingly.

Figures 4A and 4B illustrate how the polarization sensitive lens manufactured in accordance with the above embodiment can be utilized to provide two different focal points, suitable for reading a dual-layer optical recording medium 2'. The dual-layer medium 2' has two information layers (4, 4') a first information layer 4 at a depth d within the transparent layer 3, and a second information 4' a further distance Δd beneath the first information layer 4. In the embodiment shown in Figures 4A and 4B, the objective system comprises a polarization sensitive lens 181 (comprising liquid crystal 203, and manufactured as described above), and a second lens 182.

The focal point of the objective system can be altered by using the bifocal nature of the liquid crystal lens 181. In this particular instance, the substrate 150 used in the lens manufacture is glass. Further, the substrate is a planar sheet, and as such does not effect the focusing power of the lens. The focal length of the lens 181 is thus f_e=r/(ne-n_a) and fo=r/(no-n_a) for the extraordinary and ordinary modes respectively, where n_a is the refractive index of air, and r is the curvature radius of the lens.

Consequently, it will be seen that by providing an optical signal with polarization parallel to the liquid crystal orientation, such that the extraordinary mode of the lens 181 is utilized, the objective system 18 will focus the collimated beam 15 on the nearer information layer 4. However, when the collimated beam is incident on to the objective system 18 with polarization perpendicular to the liquid crystal orientation, in the resulting ordinary mode the focal point of the objective system 18 is further away i.e. on the second information layer 4' .

It will be appreciated that the above embodiments are described by way of example only, and that various alternatives will be apparent to the skilled person. For instance, whilst a method has been described suitable for producing polarization sensitive lenses, it will be appreciated that any optical component can be manufactured from liquid crystal as desired, particularly if the resulting optical component has a shaped surface such as that might be defined by a curved surface or a step surface on a mould.

For instance, the method could be used to form components having large surfaces, such as compensation foils that can be used in or on the surface of visual displays for viewing angle optimization. In such a compensation foil, the display screen itself could be used as the substrate in the manufacturing method.

The mould may be formed of any material, including rigid materials such as glass.

Further, the shaped surface of the mould may be dimensioned so as to allow for any change in shape or volume of the liquid crystal material during the method. For instance, typically liquid crystal monomers shrink slightly upon polymerisation, due to double bonds within the liquid crystal being reformed as single bonds. By appropriately making the optical component shaped defined by the substrate and the mould slightly oversize, an appropriately sized and shaped optical component can be produced. Whilst the substrate has been seen in this particular example as comprising a single sheet of glass, with two flat, substantially parallel sides, it will be appreciated that the substrate can in fact be any desired shape.

An extra adhesion layer may be applied to the mould and/or substrate (prior to deposition of the bonding layer onto the substrate and the orientation layer to the mould), so as to make sure that the applied layers are well attached to the mould and the substrate. For instance, organosilanes may be used to provide this adhesion layer. For the substrate an organosilane comprising a methacrylate group may be used and for the mould an organosilane comprising an amine end group may be used.

Equally, the alignment layers used may have any desired orientation. For instance, by placing the orientation of the alignment layer on the substrate perpendicular to the orientation of the alignment layer on the mould, a twisted nematic device can be formed.

If desired, an optical component having polarization dependent optical properties could be formed of the photo-alignment material itself, using lithographic techniques. Such a technique is particularly suitable for manufacturing (non-) periodic phase structures, which typically require annular stepped zones within an aligned liquid crystal mixture. On top of these annular stepped zones liquid crystal material has to be aligned in a monodomain.

Typically, when used only for alignment, alignment layers are of the thickness of around 10 - 100 nm. However, for lithography it may be desirable to have thicker layers of material e.g. of the order of l-10μm. Preferably, in lithography, the photo chemical reaction that causes the chemical anisotropy on the surface, should additionally enable cross linking or depolymerisation (degradation) throughout the film depth of the exposed areas (so as to provide a structure in a similar manner to the technique used in normal lithography). The compound polyvinyl cinnemate is suitable for such a process, and it is known for its good liquid crystal alignment properties.

Figure 5 A illustrates a cross sectional view of such a photo-alignment lithographic process using a negative photo alignment material, i.e. the structures are made by photopolymerisation upon UN exposure. A layer of the photo-alignment material is placed (e.g. by spin coating) upon a mould 500. This layer is subsequently shaped by the application of a UN radiation beam.

The mould 500 may simply be flat, acting as a base on which the resulting component is formed. Alternatively, the mould 500 may itself be shaped to help define a lower surface of the liquid crystal. It may sometimes be necessary to apply the alignment layer (e.g. the photo-alignment layer) on mould 500 before the photo-alignment lithographic process.

A mask 510 is placed so as to over lie the layer of photo-alignment material. The mask has apertures (in the example shown, two apertures) that serve to define the shape (or at least a portion of the shape) of the resulting component. For instance, in Figure 5 A, the mask 510 has two apertures, corresponding to the desired shapes of two portions of the desired liquid crystal component.

By applying the appropriate polarized radiation (e.g. UN radiation 505) through the mask 510, the layer will be polymerized and aligned only in the areas 520, 522 defined by the mask apertures. Subsequently, if desired, the remainder of the layer that has not been polymerized can be removed.

Structures 520 and 522 could be any desired shape e.g. cross-sections of concentric (or exocentric) circles, or rectangular blocks.

Alternatively, if desired, further processing steps could be performed. For instance, the mask 510 might be rotated through 90°, such that a new area of the layer is exposed by the aperture. Such an area could then be irradiated, and in the example shown in the plan view illustrated in Figure 5B, the second irradiation has been performed using orthogonally polarized light. This results in two cross members 524, 526 that are orthogonal to the members 522, 520 previously polymerized by the light source, with orthogonal alignment of the liquid crystal material. The arrows in Figure 5B indicate the alignment of the liquid crystal material.

The photo alignment lithographic method may be repeated a number of time, for instance to build more complex structures. This is illustrated in an example schematically shown in figures 6A and 6B. On mould 500 a structure 528, with photo-aligned surface 529 is made according to the photo-alignment photo-lithographic method. On top of this a new photo-alignment material can be applied (e.g. by spincoating, blade coating or printing) and processed according to the method such that structure 530 is formed with surface 531. This process can be continued for at least 10 successive times. Figure 6B shows a top view of figure 6 A to illustrate a possible (non)-periodic structure made of concentric circles.

It will be appreciated that this embodiment is also provided by way of example only, and that the lithography of a photo-alignment layer may be used to produce any desired structure. The structure may consist of a number of layers.

Further, the lithography can be used to not only define the positive (i.e. prominent above the background layer) portions of the desired optical device, but also to shape the negative (i.e. recessed) portions, such as channels.

Figure 7 illustrates such a processing step. In the example shown, the component already comprises a layer of material 550, which has been shaped and/or aligned as desired. On top of this layer, a second layer of material 560 is provided. Recesses are provided in the second layer of material 560 corresponding to the apertures in the mask 510. These recesses are provided through photodegradation (e.g. depolymerisation) upon UN exposure of the material. The same beam, if polarized could also be used to also induce alignment in the areas of the layer 550 exposed by the photodegradtion.

It can be seen that non-contact alignment of an alignment layer for an optical component has a number of advantages. Such a manufacturing technique does not require contact to orientate the alignment layer. Consequently, the method can easily be dust-free. Further, as no physical contact is required with the alignment layer, the method can easily be automated and parallelised, and also relatively complex shapes of alignment layer can be uniformly orientated. Further, the method can be used to shape the layers i.e. to make patterns with individually controlled orientations. Furthermore, complex shapes can be entirely made from the alignment material using a combination of photo alignment and photo lithographic techniques.

The polarization sensitive component can be made from structures as shown in Figures 5,6 and 7 by applying a LC material (preferably a reactive LC material) on the obtained phase structures. A second, preferably flat substrate (on which an alignment layers may have been applied) can be put on top and the LC mixture can be polymerized (e.g. photopolymerised) to fix theorientation of the LC mixture.

Alternatively, the phase structures can be used as the mould itself (such as mould 100 in Figure 1), from which multiple negative replica's can be obtained according to the method illustrated in Figure 2.

Claims

CLAIMS:

1. A method of manufacturing an optical component comprising a material having polarization dependent optical properties, the method comprising: applying a first beam of radiation to a layer of material so as to induce an anisotropy in the layer of material.

2. A method as claimed in claim 1, wherein the first beam comprises polarized electromagnetic radiation and the layer of material is photosensitive.

3. A method as claimed in claim 1 or claim 2, wherein the first beam comprises corpuscular radiation.

4. A method as claimed in any one of the above claims, wherein the first beam also acts to shape the layer.

5. A method as claimed in any one of the above claims, wherein the method further comprises applying a second beam of radiation to a layer of material so as to shape the layer.

6. A method as claimed in claim 5, wherein the second beam is applied to the layer of material that has had anisotropy induced by the first beam.

7. A method as claimed inany one of the above claims, wherein said layer of material has polarization dependent optical properties.

8. A method as claimed in any one of the above claims, wherein said layer of material is a photo-alignment material.

9. A method as claimed in any one of the above claims, further comprising the step of utilizing said layer of material as an alignment layer to align the material having polarization dependent properties.

10. A method as claimed in any one of the above claims, wherein said layer of material is applied to a surface in a monolayer, and subsequently photoreacted so as to induce the anisotropy.

11. A method as claimed in claim 9, wherein said monolayer is tri-ethoxy aminopropyl silane, with cinnamoyl chloride being photoreacted so as to produce cyclobutane rings.

12. A method as claimed in any one of the above claims, wherein said layer of material is deposited upon a mould as an alignment layer, the method further comprising the steps of: placing a liquid crystal between a substrate and the mould, the mould having a shaped surface, at least a portion of the shaped surface having the alignment layer formed thereon, and the substrate having a first surface on which is formed a bonding layer; bringing the mould and the substrate together so as to sandwich the liquid crystal between the first surface of the substrate and the shaped surface of the mould; polymerizing the liquid crystal; adhering the liquid crystal to the bonding layer; and removing the substrate with the adhered polymerized liquid crystal from the mould.

13. A method as claimed in any one of the above claims, wherein the layer of material is irradiated through a mask, the mask serving to define a structure within the resulting component.

14. A method as claimed in claim 13, wherein the said mask comprises at least one aperture, the aperture allowing the transmission of radiation.

15. A method as claimed in claim 13 or claim 14, wherein the radiation incident on the layer of material acts to polymerize and align the material.

16. An optical component comprising a material having polarization dependent optical properties, at least a portion of the optical component being formed according to the method as described in any one of claims 1 to 14.

17. An optical component as claimed in claim 15, wherein said optical component comprises a lens.

18. An optical scanning device for scanning an information layer of an optical record carrier, the device comprising a radiation source for generating a radiation beam and an objective system for converging the radiation beam on the information layer, wherein the device comprises an optical component formed according to the method as claimed in any one of claims 1 to 14.

19. A device as claimed in claim 13, wherein the objective system comprises a lens formed according to the method as claimed in any one of claims 1 to 14.