WO2006043187A1

WO2006043187A1 - Multiiple layer optical record carrier scanning

Info

Publication number: WO2006043187A1
Application number: PCT/IB2005/053303
Authority: WO
Inventors: Johannes Schleipen; Sjoerd Stallinga
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2004-10-18
Filing date: 2005-10-07
Publication date: 2006-04-27
Also published as: TW200627435A

Abstract

An optical scanning device for scanning a record carrier, the carrier having a first information layer and a second information layer. The device includes a radiation source for generating a radiation beam of a predetermined wavelength, and an objective lens. The objective lens has a first surface divided into at least a first set of zones and a second set of zones. The first set of zones is arranged to focus incident radiation of the predetermined wavelength to scan the first information layer. The second set of zones is arranged to focus incident radiation of the predetermined wavelength to scan the second information layer.

Description

MULTIPLE LAYER OPTICAL RECORD CARRIER SCANNING

FIELD OF THE INVENTION

The present invention relates to an optical scanning device for scanning an optical record carrier having two or more information layers, to an objective lens suitable for use in such a device, and to methods of manufacture and operation of the same.

BACKGROUND OF THE INVENTION

Optical record carriers exist in a variety of formats, with each format generally being designed to be scanned by a radiation beam of a particular wavelength. For example, CDs are available inter alia, as CD-A (CD-Audio), CD-ROM (CD-Read Only Memory) , CD-R (CD-Recordable) and CD-RW (CD-Re Writable), and are designed to be scanned by means of a radiation beam having a wavelength (1) of around 785nm. Red-DVDs (conventional Digital Versatile Disks), on the other hand, are designed to be scanned by means of a radiation beam having a wavelength of about 650nm, and Blu-ray Disks (BD) are designed to be scanned by means of a radiation beam having a wavelength of about 405nm. Generally, the shorter the wavelength, the greater the corresponding capacity of the optical disk e.g. a BD-format disk has a greater storage capacity than a DVD format disk.

It is desirable to increase storage capacity within optical record carriers. Consequently, for DVD-R, DVD-RW and BD systems, dual layer recording is becoming more and more important. Such dual layer optical record carriers comprise two information layers. Generally, the information layers are parallel, and at different depths in the optical record carrier. As each layer lies a different depth beneath the surface of the record carrier, then different amounts of spherical aberration compensation must be applied to the beams scanning different layers. For high-NA (high Numerical Aperture) systems, like BD, one has to actively control and correct for spherical aberration introduced when switching from scanning a first information layer to scanning a second information layer.

Many optical scanning devices are designed to scan optical record carriers of a variety of formats. Each format generally has a different cover layer thickness i.e. the information layer depth is different for each format. It is known to provide an objective system for compensating for the consequential different levels of spherical aberration. For instance, US 6,480,344 describes an objective lens including a diffractive lens structure suitable for minimising spherical aberration for different disk formats. However, such multi-format systems use a different wavelength for scanning each format, with the optical performance of the system being wavelength dependant, such that different wavelengths will provide the desired different levels of spherical aberration compensation.

Such multi-format solutions are not suitable for providing spherical aberration compensation in optical scanning devices for dual (or multiple i.e. three or more) layer optical record carriers, as generally each information layer in the optical record carrier is scanned using a common wavelength of electromagnetic radiation.

Several solutions have been described within the literature, for providing spherical aberration compensation in dual layer optical record carriers.

For instance, spherical aberration compensation in dual layer optical record carriers can be provided by control of the optical phase of the wavefront of the scanning radiation beam by means of a controllable (or switchable) liquid crystal (LC) cell. However, such an LC cell can introduce a considerable amount of coma when the objective system starts radial tracking, if the cell is located in the 'fixed world' optics domain (i.e. not on the 2D-tracking actuator). Alternatively, if the LC cell is mounted fixed with respect to the moving objective lens (i.e. inside the 2D-tracking actuator) the wiring of the LC cell and the mass of the LC cell both negatively influence the dynamic behaviour of the actuator. Furthermore, the necessary thickness of the LC cell can prohibit such an implementation in miniaturised optical scanning devices, in which building height is sparse.

An alternative solution is to provide finite conjugate illumination of the objective lens, by actively adjusting the position of the collimator lens. In a typical dual layer BD system, the difference in cover layer thickness between the different information layers is around 25mm. This would result in the collimator lens having to be moved over a distance of several millimetres, when the device switches between the layers. Again, due to the limited space available in the miniaturised optical pickup this method is not preferable. Another solution is to provide an objective system comprising two separate objective lenses, with one lens being designed and used to scan one layer, and the other lens being designed and used to scan the other layer. Switching between the lenses can be performed by polarisation switching (using a polarisation beam splitter to split the laser beam into two paths), or by mechanically switching the positions of the two lenses using an appropriate actuator. Such a solution is undesirable, as it increases the complexity and mass of the 2D- tracking actuator, and is both relatively expensive and bulky.

SUMMARY OF THE INVENTION It is an aim of the embodiments of the present invention to address one or more of the problems of the prior art, whether referred to herein or otherwise. It is an aim of particular embodiments of the present invention to provide an optical scanning device suitable for scanning two layers in a single optical record carrier, incorporating an objective lens system that is relatively small.

According to a first aspect of the present invention there is provided an optical scanning device for scanning a record carrier comprising a first information layer and a second information layer, that device comprising a radiation source for generating a radiation beam of a predetermined wavelength, and wherein the device further comprises an objective lens comprising a first surface divided into at least a first set of zones and a second set of zones, the first set of zones being arranged to focus incident radiation of said predetermined wavelength to scan the first information layer, and the second set of zones being arranged to focus incident radiation of said predetermined wavelength to scan the second information layer. By using such a single objective lens, the scanning device can be used to appropriately focus a radiation beam on each information layer, as desired. Using a single lens in such an innovative way to effectively provide the functions of two different lenses provides a compact solution. Preferably, the first set of zones is arranged to apply a first predetermined spherical aberration to incident radiation for minimising spherical aberration of the radiation scanning the first information layer, and the second set of zones is arranged to apply a second predetermined spherical aberration to incident radiation for minimising spherical aberration of the radiation scanning the second information layer.

Preferably, each of the zones of the first set is shaped as a portion of a first aspherical surface, and each of the zones of the second set is shaped as a portion of a second, different aspherical surface.

Preferably, the device further comprises a directional optical element located between the radiation source and the objective lens, the element being arranged in a first mode to provide radiation from the radiation beam to the first set of zones, but not said second set of zones, and in a second mode to provide radiation from the radiation beam to the second set of zones, but not the first set of zones.

The directional optical element may be a transmission mask moveable between a first position and a second position, the first position corresponding to the first mode and the second position corresponding to the second mode. Preferably, the transmission mask is arranged as a grating structure to diffract the radiation beam into at least three spots.

The directional optical element may be a diffractive optical element.

The directional optical element may be a polarisation mask. Preferably, the record carrier further comprises a third information layer, and the first surface of the objective lens is divided into the first set of zones, the second set of zones and a third set of zones, the third set of zones being arranged to focus incident radiation to scan the third information layer.

Preferably, each of said zones extends across the surface of the lens in a direction substantially parallel to the radial tracking direction of the radiation on the information layers when the device is in use.

Preferably, each zone is annular and concentric.

Preferably, each set comprises at least five zones.

According to a second aspect of the present invention there is provided a lens for use in an optical scanning device for scanning a record carrier comprising a first information layer and a second information layer, the device comprising a radiation source for generating a radiation beam of a predetermined wavelength, wherein the lens comprises a first surface divided into at least a first set of zones and a second set of zones, the first set of zones being arranged to focus incident radiation of said predetermined wavelength to scan the first information layer, and the second set of zones being arranged to focus incident radiation of said predetermined wavelength to scan the second information layer.

According to a third aspect of the present invention there is provided a method of manufacturing an optical scanning device for scanning a record carrier comprising a first information layer and a second information layer, the method comprising: providing a radiation source for generating a radiation beam of a predetermined wavelength; and providing an objective lens comprising a first surface divided into at least a first set of zones and a second set of zones, the first set of zones being arranged to focus incident radiation of said predetermined wavelength to scan the first information layer, and the second set of zones being arranged to focus incident radiation of said predetermined wavelength to scan the second information layer.

According to a fourth aspect of the present invention there is provided a method of manufacturing a lens for use in an optical scanning device for scanning a record carrier comprising a first information layer and a second information layer, using radiation of a predetermined wavelength; wherein the method comprises: forming a lens comprising a first surface divided into at least a first set of zones and a second set of zones, the first set of zones being arranged to focus incident radiation of said predetermined wavelength for scanning the first information layer, and the second set of zones being arranged to focus incident radiation of said predetermined wavelength for scanning the second information layer.

These and other aspects of the invention will be apparent from and will be elucidated with reference to the embodiments described hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described in more detail, by way of example, with reference to the accompanying drawings, wherein: - Figures IA, IB and 1C show respectively front, side and plan views of an objective lens comprising first and second sets of zones, in accordance with an embodiment of the present invention;

Figures 2A and 2B illustrate pupil intensity distributions for scanning a first information layer on an optical record carrier and a second information layer on an optical record carrier, respectively;

Figure 3 illustrates an embodiment of a transmission mask;

- Figures 4A and 4B are simplified perspective diagrams of an optical scanning device scanning respectively a first information layer and a second information layer of an optical record carrier, in accordance with an embodiment to the present invention; - Figures 5A and 5B are simplified perspective diagrams of an optical scanning device scanning respectively a first information layer and a second information layer of an optical record carrier, in accordance with an embodiment to the present invention; Figure 6 illustrates an embodiment of a polarisation mask;

- Figures 7A and 7B are simplified perspective diagrams of an optical scanning device scanning respectively a first information layer and a second information layer of an optical record carrier, in accordance with an embodiment to the present invention; and - Figures 8A and 8B are simplified perspective diagrams of an optical scanning device scanning respectively a first information layer and a second information layer of an optical record carrier, in accordance with an embodiment to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Figures IA- 1C illustrate different views of an objective lens 1. One surface of the lens 1 (e.g. either the entrance surface or the exit surface of the lens) is divided up into a first set of zones 10, and a second set of zones 11. In this embodiment, the zones extend across the whole of the entrance face of the lens 1. Zones from the first set alternate with zones from the second set. Each zone is essentially rectangular in shape, mapped onto the curved entrance surface of the lens 1. The zones are aligned in a direction parallel to the radial tracking direction of the tracking actuator. As a result the intensity distribution is not changed as radial tracking occurs, and consequently no aberrations (e.g. coma) are introduced.

The first set of zones is optimised for scanning of a first layer of an optical record carrier, and the second set of zones is optimised for scanning of a second layer of an optical carrier. Switching between the information layers is accomplished by changing the intensity distribution of the radiation beam incident upon the lens (e.g. changing the intensity distribution of the pupil), such that either only the first set of zones or the second set of zones is illuminated. The zones of the first set each correspond to portions of a first aspherical surface, and the second set of zones correspond to portions of a second, different aspherical surface. It will be appreciated that, by using three (or four, or more) sets of zones, the lens can be arranged to scan three (or four, or more) information layers on an optical record carrier.

The intensity distribution of the radiation beam incident on the lens is altered by a directional optical element located between the radiation source and the objective lens. This optical element can be implemented in a number of forms.

For instance, the element can be formed as a transmission mask 3 (as shown in figure 3). The transmission mask also comprises two sets of zones (30, 31). The first set of zones 30 is opaque and the second set of zones 31 is transparent. The opaque (i.e. obstructing) zones or elements 30 are arranged to correspond to the dimensions of the individual zones 10, 11 on the objective lens 1. Preferably, each of the zones 10, 11 is of uniform width. Switching between scanning the two layers can be accomplished by shifting the position of the transmission mask 3 in a direction perpendicular to the optical axis of the scanning device, by an amount equal to the height of a single zone, thereby changing the pupil intensity distribution (2,2').

Figure 2 A shows the pupil intensity distribution 2 (with the rim of the objective lens indicated by circular line 1) suitable for scanning a first information layer, with Figure 2B showing the alternative intensity distribution 2' suitable for scanning the second information layer. White areas are regions with high intensity, black areas are dark (no intensity), or vice versa.

Figures 4A and 4B correspond respectively to Figures 2A, 2B, and indicate how the radiation would be focused by the relevant zones of the lens 1 to scan respectively a first information layer (Layer 0) and a second information layer (Layer 1). Arrows A indicate the radial tracking direction on the optical record carrier. Arrows B indicate the track direction on the optical record carrier.

A disadvantage of using a transmission mask as the directional optical element is that part of the radiation beam is being obstructed, and typically only 50% of the beam output from the radiation source will be utilised to scan an information layer. An alternative is to use a DOE (Diffractive Optical Element, e.g. a hologram) so as to redistribute the light output from the radiation source (e.g. a uniform plane wave) to the desired illumination pattern (patterns 2, 2', as shown in Figures 2A and 2B), without loss of beam intensity. Switching between scanning of the different layers (i.e. switching of the intensity between zones 10 and 11 of the lens) can be accomplished by shifting of or tilting the DOE, or by appropriate control of the polarisation of the radiation beam.

An alternative directional optical element can be provided by using a polarisation mask 4, as indicated in Figure 6. The polarisation mask 4 is again divided up into two sets of zones (40, 41). The first set of zones 40 is arranged to transmit incident radiation of a first polarisation (e.g. X-polarisation), and block other polarisations. The second set of zones 41 is arranged to transmit incident radiation of a second polarisation (e.g. Y-polarisation), and to block radiation of other polarisations. Figure 5 A and 5B illustrate the two modes of operation of a device including a zoned objective lens 1, and such a polarisation mask 4. In order to distinguish between the individual aspherical zones at the objective lens 1, a polarisation mask 4 is positioned in front of the lens 1. Preferably, the polarisation mask 4 is attached to, or integrated with, the objective lens 1. This way, the appropriate intensity distribution is imaged in the respective aspherical zones of the lens 1 by control of the polarisation of the incident radiation. Figure 5A indicates the radiation beam 5 having a first polarisation, such that the radiation transmitted through the polarisation mask 4 is incident only upon the first set of zones of the lens 1. Thus, the first information layer LO is scanned on the optical record carrier. In Figure 5B, the polarisation of the radiation beam 5' is incident upon the polarisation mask, such that the transmitted radiation beam is incident only upon the second set of zones of the lens 1, thus resulting of the second information layer Ll of the optical record carrier being scanned.

Control of the polarisation of the radiation beam (e.g. from a first linear polarisation, to a second, different linear polarisation) can be performed using a simple controllable liquid crystal cell. Preferably, the liquid crystal cell is located in the fixed world, changing the polarisation of the uniform intensity distribution from the radiation source. An advantage of this polarisation approach is that since the polarisation mask may be attached physically to the (movable) objective lens, other mask geometries than the rectangular one depicted in the figures can be utilised, since moving the actuator does not introduce any aberrations in this way. For instance, both the mask zones and the lens zones may comprise concentric circular zones.

When part of the light is cut out of the objective pupil, the intensity distribution in the imaged spot on the disc will also change. If part of the outer rim intensity is blocked, plane waves having a high spatial frequency will be suppressed, resulting in an undesirable broadening of the spot. Similarly, if part of the centre of the pupil is obscured, super- resolution effects may occur. By using a light distribution as depicted in Fig.2 (or using concentric circular zones as described above) the outer rim of the objective is illuminated and the high spatial frequencies are equally populated. Diffraction calculations showed that using only a fairly small number of zones (e.g. 5) produces a diffraction-limited spot, comparable in size as the one obtained without these zones. The number of zones is preferably chosen such that the lens structure can be made using standard mass fabrication techniques (e.g. glass-photo-polymerisation replication, plastic injection moulding or glass moulding), and diffraction effects are minimized.

In a preferred embodiment, the equally spaced rectangular stripes of the mask act as a grating structure, e.g. to produce 3 spots from the single incident radiation beam. Apart from the Oth order, producing the main spot with the correct spherical aberration, there will also be +lst and -1st order satellite spots on the disc. As the stripes extend in the radial tracking direction these satellite spots will be displaced with respect to the main spot in the forward (+lst order) and backward (-1st order) tangential direction. If the mask is slightly rotated around the optical axis of the system (this will not harm the basic functionality proposed in this disclosure) the satellite spots will fall on the disc halfway between the central track and the neighbouring tracks. If the rotation angle is doubled the satellite spots will fall exactly on the neighbouring tracks. These two cases correspond to the three-spots push-pull radial tracking method, in which the signal of the two satellite spots is measured at the photo- detector and used to improve robustness of radial tracking to alignment errors, and to cross¬ talk cancellation, in which the satellite signals are used to suppress the disturbance of the main data signal by the fraction of the light of the main spot that falls on the neighbouring tracks. Figures 7 A and 7B show a device for scanning a first information layer LO and a second information layer Ll of a first optical record carrier 57 by means of a first radiation beam 52, the device including a lens 56 in accordance with an embodiment of the present invention.

The optical record carrier 57 comprises a base transparent layer, on one side of which information layer Ll is arranged. An additional (semi-transparent) information layer LO and additional transparent layer is connected to the base transparent layer. The side of the outermost information layer Ll facing away from the transparent layer is protected, from environmental influences by a protective layer. The side of the transparent layer facing the device is called the entrance face. The transparent layer acts as a substrate for the optical record carrier 57 by providing mechanical support for the information layer. Alternatively, the transparent layer may have the sole function of protecting the information layers, while the mechanical support is provided by a layer on the other side of the information layers, for instance by the protective layer. It is noted that the first information layer is at a first information layer depth, and the second information layer is at a second information layer depth. The information layers are surfaces of the carrier.

Information may be stored in the information layers LO and Ll of the record carrier in the form of optically detectable marks arranged in substantially parallel, concentric or spiral tracks, not indicated in the figure. A track is a path that may be followed by the spot of a focused radiation beam. 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 magnetisation different from the surroundings, or a combination of these forms. In the case where the optical record carrier 57 has the shape of a disc, the following is defined with respect to a given track: the "radial direction" is the direction of a reference axis, the X-axis, between the track and the centre of the disc, and the "tangential direction" or the "track direction" is the direction of the Y-axis, that is tangential to the track and perpendicular to the X-axis.

As shown in Figure 7, the optical scanning device includes a radiation source 51, a collimator lens 54, a beam splitter 53, an objective lens system 56 having an optical axis, and a detection system 59. Furthermore, the optical scanning device includes a servo circuit, a focus actuator, a radial actuator, and an information processing unit for error correction.

In the following "Z-axis" corresponds to the optical axis of the objective lens system 56. It is noted that (X, Y, Z) is an orthogonal base.

The radiation source 51 is arranged to supply a first radiation beam 52. The radiation beam 52 has a predetermined wavelength 11 and may have a predetermined polarisation pi.

A directional optical element 510 in the form of either a transmission mask or a DOE is located on the optical axis. The element 510 is illustrated in a first mode of operation in

Figure 7 A, and in a second mode of operation in Figure 7B. In the first mode of operation, the element 510 is positioned so as to ensure that the radiation beam is incident only upon the first set of zones of the objective lens 56 (such that the lens focuses the incident beam on the first information layer LO). In the second mode of operation shown in Figure 7B, the element is conversely positioned so as to direct incident radiation only upon the second set of zones of the lens 56, such that the radiation beam scans the second information layer Ll.

The collimator lens 54 is arranged on the optical axis for transforming the radiation beam 52 into a substantially collimated beam. The beam splitter 53 is arranged for transmitting the radiation beam towards the objective lens system 56.The beam splitter 53 may be formed with a plane parallel plate that is tilted at an angle a with respect to the Z-axis, for example a=45°.

The objective lens system 56 is arranged for transforming the collimated radiation beam to a focused radiation beam 521 or 522, as described above, so as to form a scanning spot in the position of the desired information layer.

During scanning, the record carrier 57 rotates on a spindle (not shown in Figure), and the information layers LO and Ll can then be scanned through the transparent layers. The focused radiation beam 521, 522 reflects on the information layers, thereby forming a reflected beam which returns on the optical path of the forward converging beam. The objective lens system 56 transforms the reflected radiation beam to a reflected collimated radiation beam. The beam splitter 53 separates the forward radiation beam from the reflected radiation beam by transmitting at least part of the reflected radiation towards to detection system 59. In the particular embodiment shown, the beam splitter 53 is a polarising beam splitter. A quarter waveplate 55 is positioned along the optical axis between the beam splitter 53 and the objective lens system 56. The combination of the quarter waveplate 55 and the polarising beam splitter 53 ensures that the largest fraction of the reflected radiation beam is transmitted towards the detection system 59. The detection system 59 includes a lens 58 and a quadrant detector which are arranged for capturing said part of the reflected radiation beam and converting it to one or more electrical signals.

One of the signals is an information signal, the value of which represents the information scanned on the information layers. The information signal is processed by the information processing unit for error correction.

Other signals from the detection system are a focus error signal and a radial tracking error signal. The focus error signal represents the axial difference in height along the Z-axis between the scanning spot and the position of the relevant information layer. Preferably, this signal is formed by the "astigmatic method" which is known from, inter alia, the book by G. • Bouwhuis, J. Braat, A. Huijiser et al, "Principles of Optical Disc Systems", pp. 75-80 (Adam Hilger 1985, ISBN 0-85274-785-3). The radial tracking error signal represents the distance in the XY-plane of the information layer between the scanning spot and the centre of track in the information layer to be followed by the scanning spot. This signal can be formed from the . "radial push-pull method" which is also known from the aforesaid book by G. Bouwhuis, pp. 70-73.

The servocircuit is arranged for, in response to the focus and radial tracking error signals, providing servo control signals for controlling the focus actuator and the radial actuator respectively. The focus actuator controls the position of the objective lens 56 along the Z-axis, thereby controlling the position of the scanning spot such that it coincides substantially with the plane of the desired information layer. The radial actuator controls the position of the objective lens 56 along the X-axis, thereby controlling the radial position of the scanning spot such that it coincides substantially with the centre line of the track to be followed in the information layer.

The objective lens 56 is arranged for transforming the collimated radiation beam to the focus radiation beam, having a first numerical aperture NAl, so as to form the scanning spot, and the two associated tracking spots.

Figures 8 A and 8B correspond generally to figures 7 A and 7B. In Figures 8 A and 8B, the optical device comprises a zoned polarisation mask 511 as the directional optical element. The polarisation mask 511 is located directly in front of the objective lens 56 (and may be coupled to, or form a part of such a lens). In this particular embodiment, the polarisation of the radiation beam 52 is controlled via a polarisation rotating cell 512. The cell 512 is switchable between a first mode (shown in Figure 8A), in which it rotates the polarisation of the linearly polarised beam 52 through 90 degrees, and a second mode of operation (shown in figure 8B) in which no polarisation rotation occurs. The cell 512 may, for example, be constructed of liquid crystal. The cell 512 is located between the polarising beam splitter 53 and the polarisation mask 511.

It will be appreciated from the above description, that by providing a lens having a surface divided into at least two different sets of zones, with each zone having different optical properties, a compact device may be readily formed for dual information layer scanning of an optical record carrier.

Any reference -sign in the following claims should not be construed as limiting the claim. It will be obvious that the use of the verb "to comprise" and its conjugations does not exclude the presence of any other elements besides those defined in any claim. The word "a" or "an" preceding an element does not exclude the presence of a plurality of such elements.

Claims

1 An optical scanning device for scanning a record carrier (57) comprising a first information layer (LO) and a second information layer (Ll), that device comprising a radiation source (51) for generating a radiation beam (52) of a predetermined wavelength, and wherein the device further comprises an objective lens (1; 56) comprising a first surface divided into at least a first set of zones (10) and a second set of zones (11), the first set of zones (10) being arranged to focus incident radiation of said predetermined wavelength to scan the first information layer (LO), and the second set of zones (11) being arranged to focus incident radiation of said predetermined wavelength to scan the second information layer (Ll).

2 A device as claimed in claim 1, wherein the first set of zones (10) is arranged to apply a first predetermined spherical aberration to incident radiation for minimising spherical aberration of the radiation (521) scanning the first information layer (LO), and the second set of zones (11) is arranged to apply a second predetermined spherical aberration to incident radiation for minimising spherical aberration of the radiation (522) scanning the second information layer (Ll).

3 A device as claimed in claim 1 or claim 2, wherein each of the zones of the first set (10) is shaped as a portion of a first aspherical surface, and each of the zones of the second set (11) is shaped as a portion of a second, different aspherical surface.

4 A device as claimed in any one of the above claims, wherein the device further comprises a directional optical element (2, 2'; 4; 510; 511) located between the radiation source and the objective lens, the element being arranged in a first mode to provide radiation from the radiation beam to the first set of zones (10), but not said second set of zones (11), and in a second mode to provide radiation from the radiation beam to the second set of zones (11), but not the first set of zones (10).

5 A device as claimed in claim 4, wherein the directional optical element is a transmission mask (2; 510) moveable between a first position and a second position, the first position corresponding to the first mode and the second position corresponding to the second mode.

6 A device as claimed in claim 5, wherein the transmission mask is arranged as a grating structure (510) to diffract the radiation beam into at least three spots. 7 A device as claimed in claim 4, wherein the directional optical element is a diffractive optical element (510).

8 A device as claimed in claim 4, wherein the directional optical element is a polarisation mask (4; 511). 9 A device as claimed in any one of the above claims, wherein the record carrier (57) further comprises at least a third information layer, and the first surface of the objective lens is divided into the first set of zones, the second set of zones and at least a third set of zones, said third set of zones being arranged to focus incident radiation to scan said third information layer. 10 A device as claimed in any one of the above claims, wherein each of said zones (10, 11) extends across the surface of the lens in a direction substantially parallel to the radial tracking direction of the radiation on the information layers (LO, Ll) when the device is in use.

11 A device as claimed in any one of claims 1 to 9, wherein each zone (10, 11) is annular and concentric.

12 A device as claimed in any one of the above claims, wherein each set comprises at least five zones (10, 11).

13 A lens (1; 56) for use in an optical scanning device for scanning a record carrier (57) comprising a first information layer (LO) and a second information layer (Ll), the device comprising a radiation source (51) for generating a radiation beam (52) of a predetermined wavelength, wherein the lens (1; 56) comprises a first surface divided into at least a first set of zones (10) and a second set of zones (11), the first set of zones (10) being arranged to focus incident radiation of said predetermined wavelength to scan the first information layer (LO), and the second set of zones (11) being arranged to focus incident radiation of said predetermined wavelength to scan the second information layer (Ll).

14 A method of manufacturing an optical scanning device for scanning a record carrier (57) comprising a first information layer (LO) and a second information layer (Ll), the method comprising: providing a radiation source (51) for generating a radiation beam (52) of a predetermined wavelength; and providing an objective lens (1; 56) comprising a first surface divided into at least a first set of zones (10) and a second set of zones (11), the first set of zones (10) being arranged to focus incident radiation of said predetermined wavelength to scan the first information layer (LO), and the second set of zones (11) being arranged to focus incident radiation of said predetermined wavelength to scan the second information layer (Ll).

15 A method of manufacturing a lens (1; 56) for use in an optical scanning device for scanning a record carrier (57) comprising a first information layer (LO) and a second information layer (Ll), using radiation of a predetermined wavelength; wherein the method comprises: forming a lens (1; 56) comprising a first surface divided into at least a first set of zones (10) and a second set of zones (11), the first set of zones (10) being arranged to focus incident radiation of said predetermined wavelength for scanning the first information layer (10), and the second set of zones (11) being arranged to focus incident radiation of said predetermined wavelength for scanning the second information layer (Ll).