WO2007054908A2

WO2007054908A2 - Method and system for shifting at least one light spot with a phase-modulator

Info

Publication number: WO2007054908A2
Application number: PCT/IB2006/054185
Authority: WO
Inventors: Robert Frans Maria Hendriks; Gerardus Petrus Karman; Sjoerd Stallinga
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2005-11-14
Filing date: 2006-11-10
Publication date: 2007-05-18
Also published as: WO2007054908A3; TW200822099A

Abstract

A system for shifting at least one light spot (103) relative to an information carrier (101) during data read - out. The system comprises a phase-modulator (706) comprising a layer of liquid crystal sandwiched between upper and lower substrates. A first set of electrodes (903a) is provided on the upper substrate, arranged in a first lateral shifting direction (x) and a second set of electrodes (903b) is provided on the lower substrate, arranged in a second lateral shifting direction, orthogonal to the first. A first voltage gradient is applied across the first set of electrodes (903a) and a second voltage gradient is applied across a second set of electrodes (903b) so as to generate first and second respective phase profiles for shifting the at least one light spot (103) in the respective first direction (x) and second direction (y) .

Description

METHOD AND SYSTEM FOR SHIFTING AT LEAST ONE LIGHT SPOT WITH A

PHASE-MODULATOR

FIELD OF THE INVENTION

The invention relates to a system for shifting at least one light spot with a phase-modulator, for example over an information carrier in view of data recovering.

The invention may be used in the field of optical data storage and microscopy.

BACKGROUND OF THE INVENTION

The use of optical storage is nowadays widespread for content distribution, for example in storage systems based on the DVD (Digital Versatile Disc) standards. Optical storage has a big advantage over hard-disk and solid-state storage in that information carriers are easy and cheap to duplicate.

However, due to the large amount of moving parts in the drives, known applications using this type of storage are not robust to shocks when performing read operations, considering the required stability of said moving parts during such operations. As a consequence, optical storage cannot easily be used in applications which are subject to shocks, such as in portable devices.

New optical storage solutions have thus been developed. These solutions combine the advantages of optical storage in that a cheap and removable information carrier is used, and the advantages of solid-state storage in that the information carrier is still and that its reading requires a limited number of moving elements.

A known optical storage solution aims at reading data stored on an information carrier. The information carrier is intended to store binary data organized according to an array, as in a data matrix. If the information carrier is intended to be read in transmission, the states of binary data stored on the information carrier are represented by transparent areas and non- transparent areas (i.e. light-absorbing). Alternatively, if the information carrier is intended to be read in reflection, the states of binary data stored on the information carrier are represented by non-reflective areas (i.e. light absorbing) and reflective areas. The areas are marked in a material such as glass, plastic or a material having magnetic properties.

The described system comprises: an optical element for generating an array of light spots from an input light beam, said array of light spots being intended to scan said information carrier, a detector for detecting said data from an array of output light beams generated by said information carrier.

In a first embodiment depicted in Fig.l, the system for reading data stored on an information carrier 101 comprises an optical element 102 for generating an array of light spots 103 from an input light beam 104, said array of light spots 103 being intended to scan the information carrier 101.

The optical element 102 corresponds to a two-dimensional array of micro-lenses to the input of which the coherent input light beam 104 is applied. The array of micro-lenses 102 is placed parallel and distant from the information carrier 101 so that light spots are focused on the information carrier. The numerical aperture and quality of the micro-lenses determines the size of the light spots. For example, a two-dimensional array of micro- lenses 102 having a numerical aperture which equals 0.3 can be used. The input light beam 104 can be realized by a waveguide (not represented) for expanding an input laser beam, or by a two-dimensional array of coupled micro lasers.

The light spots are applied on transparent or non-transparent areas of the information carrier 101. If a light spot is applied on a non-transparent area, no output light beam is generated in response by the information carrier. If a light spot is applied on a transparent area, an output light beam is generated in response by the information carrier, said output light beam being detected by the detector 105. The detector 105 is thus used for detecting the binary value of the data of the area to which the optical spot is applied.

The detector 105 is advantageously made of an array of CMOS or CCD pixels. For example, one pixel of the detector is placed opposite an elementary data area containing one data (i.e. one bit) of the information carrier. In that case, one pixel of the detector is intended to detect one data of the information carrier.

Advantageously, an array of micro-lenses (not represented) is placed between the information carrier 101 and the detector 105 for focusing the output light beams generated by the information carrier on the detector, for improving the detection of the data.

In a second embodiment depicted in Fig.2, the system for reading data stored on an information carrier 201 comprises an optical element 202 for generating an array of light spots 203 from an input light beam 204, said array of light spots 203 being intended to scan the information carrier 201.

The optical element 202 corresponds to a two-dimensional array of apertures to the input of which the coherent input light beam 204 is applied. The apertures correspond for example to circular holes having a diameter of lμm or much smaller. The input light beam

204 can be realized by a waveguide (not represented) for expanding an input laser beam, or by a two-dimensional array of coupled micro lasers.

The light spots are applied to transparent or non-transparent areas of the information carrier 201. If a light spot is applied to a non-transparent area, no output light beam is generated in response by the information carrier. If a light spot is applied to a transparent area, an output light beam is generated in response by the information carrier, said output light beam being detected by the detector 205. Similarly as the first embodiment depicted in Fig. l, the detector 205 is thus used for detecting the binary value of the data of the area on which the optical spot is applied.

The detector 205 is advantageously made of an array of CMOS or CCD pixels. For example, one pixel of the detector is placed opposite an elementary data area containing a data of the information carrier. In that case, one pixel of the detector is intended to detect one data of the information carrier. Advantageously, an array of micro-lenses (not represented) is placed between the information carrier 201 and the detector 205 for focusing the output light beams generated by the information carrier on the detector, improving the detection of the data.

The array of light spots 203 is generated by the array of apertures 202 in exploiting the Talbot effect which is a diffraction phenomenon working as follows. When a coherent light beam, such as the input light beam 204, is applied to an object having a periodic diffractive structure (thus forming light emitters), such as the array of apertures 202, the diffracted lights recombine into identical images of the emitters at a plane located at a predictable distance zθ from the diffracting structure. This distance zθ is known as the Talbot distance. The Talbot distance zθ is given by the relation zθ = 2.n.d² / λ, where d is the periodic spacing of the light emitters, λ is the wavelength of the input light beam, and n is the refractive index of the propagation space. More generally, re-imaging takes place at other distances z(m) spaced further from the emitters and which are a multiple of the Talbot distance z such that z(m) = 2.n.m.d² /λ, where m is an integer. Such a re-imaging also takes place for m = V₂ + an integer, but here the image is shifted over half a period. The re- imaging also takes place for m = ¹A + an integer, and for m = ³A + an integer, but the image has a doubled frequency which means that the period of the light spots is halved with respect to that of the array of apertures.

Exploiting the Talbot effect allows to generate an array of light spots of high quality at a relatively large distance from the array of apertures 202 (a few hundreds of μm, expressed by z(m)), without the need for optical lenses. This allows to insert for example a cover layer between the array of aperture 202 and the information carrier 201 to prevent the latter from contamination (e.g. dust, finger prints ). Moreover, this facilitates the implementation and allows to increase in a cost-effective manner, compared to the use of an array of micro-lenses, the density of light spots which are applied to the information carrier.

Fig.3 depicts a detailed view of a known optical storage system described above. It depicts a detector 305 which is intended to detect data from output light beams generated by the information carrier 301. The detector comprises pixels referred to as 302-303-304, the number of pixels shown being limited to facilitate the understanding. In particular, pixel

302 is intended to detect data stored on the data area 306 of the information carrier, pixel

303 is intended to detect data stored on the data area 307, and pixel 304 is intended to detect data stored on the data area 308. Each data area (also called macro-cell) comprises a set of elementary data. For example, data area 306 comprises binary data referred to as 306a-306b-306c-306d.

In this embodiment, one pixel of the detector is intended to detect a set of data, each elementary data among this set of data being successively read by a single light spot generated either by the array of micro-lenses 102 depicted in Fig. l, or by the array of apertures depicted in Fig.2. This way of reading data on the information carrier is called macro-cell scanning in the following.

Fig.4 which is based on Fig.3, illustrates by a non-limitative example the macro-cell scanning of an information carrier 401.

Data stored on the information carrier 401 have two states indicated either by a black area (i.e. non-transparent) or white area (i.e. transparent). For example, a black area corresponds to a "0" binary state while a white area corresponds to a "1" binary state.

When a pixel of the detector 405 is illuminated by an output light beam generated by the information carrier 401, the pixel is represented by a white area. In that case, the pixel delivers an electric output signal (not represented) having a first state. On the contrary, when a pixel of the detector 405 does not receive any output light beam from the information carrier, the pixel is represented by a cross-hatched area. In that case, the pixel delivers an electric output signal (not represented) having a second state.

In this example, each set of data comprises four elementary data, and a single light spot is applied simultaneously to each set of data. The scanning of the information carrier 401 by the light spots 403 is performed for example from left to right, with an incremental lateral displacement which equals the distance between two elementary data. In position A, all the light spots are applied to non-transparent areas so that all pixels of the detector are in the second state.

In position B, after displacement of the light spots to the right, the light spot to the left is applied to a transparent area so that the corresponding pixel is in the first state, while the two other light spots are applied to non-transparent areas so that the two corresponding pixels of the detector are in the second state.

In position C, after displacement of the light spots to the right, the light spot to the left is applied to a non-transparent area so that the corresponding pixel is in the second state, while the two other light spots are applied to transparent areas so that the two corresponding pixels of the detector are in the first state.

In position D, after displacement of the light spots to the right, the central light spot is applied to a non-transparent area so that the corresponding pixel is in the second state, while the two other light spots are applied to transparent areas so that the two corresponding pixels of the detector are in the first state.

The scanning of the information carrier 401 is complete when the light spots have been applied to all data of a set of data facing a pixel of the detector. It implies a two- dimensional scanning of the information carrier. Elementary data which compose a set of data opposite a pixel of the detector are read successively by a single light spot.

Fig.5 depicts a three-dimensional view of the system as depicted in Fig.2. It comprises an array of apertures 502 for generating an array of light spots applied to the information carrier 501. Each light spot is applied and scanned over a two-dimensional set of data of the information carrier 501 (represented by bold squares). In response to this light spot, the information carrier generates (or not, if the light spot is applied to a non-transparent area) an output light beam in response, which is detected by the pixel of the detector 503 opposite the set of data which is scanned. The scanning of the information carrier 501 is performed in displacing the array of apertures 502 along the x and y axes. The array of apertures 502, the information carrier 501 and the detector 503 are stacked in parallel planes. The only moving part is the array of apertures 502.

It is noted that the three-dimensional view of the system as depicted in Fig.l would be the same as the one depicted in Fig.5 in replacing the array of apertures 502 by the array of micro-lenses 102.

The scanning of the information carrier by the array of light spots is done in a plane parallel to the information carrier. A scanning device provides translational movement of the light spots in the two directions x and y for scanning all the surface of the information carrier.

Fig.6 depicts a known system in which the scanning of the information carrier 601 is realized without moving components. Fig.6 is based on Fig.2 but additionally comprises a phase-modulator 606 placed in the path light of the input light beam 604.

The non-mechanical scanning is realized by applying a phase profile defined by the phase- modulator 606 to the input light beam 604, and in varying this phase profile. The phase- modulator 606 varies the phase of the input light beam 404 with respect to the lateral distance x (and/or y).

It is noted that the phase-modulator 606 can also be placed between the array of apertures 902 and the information carrier 601 (not represented).

When the phase-modulator 606 acts so as the phase φ(x) varies in a linear way with respect to the position x, this leads to a lateral shift Ax of the array of lights spots 603 along the lateral axis x. It can be defined that the phase φ(x) and the lateral position x are linked by the following relation: φ(x) = Eq.l a λ where x is the lateral position (taken for example from the extreme left side of the phase-modulator 606), λ is the wavelength of the input light beam 604, a is a variable parameter.

It can be shown that if a phase profile as defined in Eq.1 is performed by the phase- modulator 606, the lateral shift Ax of the array of light spots 603 is given by the following relation: Δx = αZ Eq.2

where Z is a fixed value corresponding advantageously to the Talbot distance zθ, or to an integer multiple or a sub-multiple of the Talbot distance zθ

The parameter a allows modifying the linearity factor of the phase profile in view of changing the lateral shift Ax. For each value of the parameter a, a different phase profile is defined. A variation of the parameter a results as a consequence in a shift spots in x.

For scanning all the surface of the information carrier 601, each macro-cell data of the information carrier must be scanned by a light spot of the array of light spots. The scanning of a macro-cell data thus corresponds to a two-dimensional scanning along the x and y axis.

This two-dimensional scanning is performed in defining simultaneously a linear phase modulation according to the x and y axis, the defined phase profile resulting from a linear combination of a linear phase profile according to the x (as defined by Eq.1) axis and a linear phase profile according to the y axis (similarly as defined by Eq.1 in substituting x by y).

In a known system, the phase-modulator 606, may comprise controllable liquid crystal (LC) cells. For example, pixelated linear nematic LC cells can be used such that each aperture of the array of apertures 602 has its own pixel, and can be given its own phase φ(x). Thus, the phase-modulator 606 corresponds to a two-dimensional array of pixels. Nematic substances can be aligned by electric and magnetic fields, resulting in a phase change. Nematic cells are optically equivalent to a linear wave plate having a fixed optical axis, but the birefringence of which is a function of the applied voltage. As the applied voltage varies, the birefringence changes, resulting in a change of the optical path length, thus in a phase change.

Since each of the apertures of the array of apertures 602 has its own pixel, the phase profile defines a ramp having incremental steps, the ramp globally fitting the linear Eq.1.

Fig.7 depicts a three-dimensional view of the system as depicted in Fig.6. It comprises an array of apertures 702 for generating an array of light spots applied to the information carrier 701. Each light spot is applied and scanned over a two-dimensional set of data of the information carrier 701 (represented by squares in bold). In response to this light spot, the information carrier generates (or not, if the light spot is applied to a non-transparent area) an output light beam detected by the pixel of the detector 703 opposite the set of data which is scanned. The scanning of the information carrier 701 along the x and y axis is performed by means of a phase-modulator 706 placed below the array of apertures 702, without moving any elements.

The phase-modulator 706, the array of apertures 702, the information carrier 701 and the detector 703 are stacked in parallel planes.

Fig.8 depicts an example of a LC cell. It comprises an LC layer 801, a glass substrate 802, transparent electrodes 803, alignment layers 804. In this Fig., the parameter d corresponds to the cell thickness, while θ corresponds to the angle of the LC molecules. As the liquid crystal molecules rotate, due to the applied electric field by the voltage generator 805, linearly polarised light propagating through the cell will experience a different effective refractive index, resulting in a phase change.

As an example, the resulting graph of a phase change Δφ versus voltage is also illustrated in Fig.8. The characteristics of the curve depend on the LC material which is used, the wavelength of the light and the cell thickness d. When the phase-modulator 606 acts so as the phase (juc of the input light beam 604 varies in a quadratic way with respect to the position x, this leads to an axial shift Δz of the array of light spots 603 along the axial axis z. It can be defined that the phase φ(x) and the lateral position x are linked by the following relation:

^(JC) = — •— Eq.3

where x is the lateral position, λ is the wavelength of the input light beam 604,

R is a variable parameter corresponding to the radius of curvature of the phase profile,

Δz is the axial shift with respect to the position for z=0.

It can be shown that if a phase profile as defined by Eq.3 is performed by a phase- modulator 606, the axial shift Δz of the array of light spots 603 can be accurately approximated by the following relation:

Z² Δz « — Eq.4

where Z is fixed value corresponding advantageously to the Talbot distance zθ, or to an integer multiple or a sub-multiple of the Talbot distance zθ.

The variable parameter R allows modifying the quadratic factor of the phase profile in view of changing the axial shift Δz. For each value of the parameter R, a different phase profile is defined. A variation of the parameter R results as a consequence in a shift Az. The light spots 603 will thus focus closer to or further away from the surface of the information carrier 601. The quadratic phase profile plays the same role as a focus actuator in more traditional recording, but without using any mechanical elements.

The phase profile defined by the phase-modulator 606 may result from a linear combination of a linear phase profile as defined by Eq.1 (according to the x and/or y axis) and a quadratic phase profile as defined by Eq.4. This allows performing at the same time a two-dimensional scanning of the light spots, while setting accurately the focus of the light spots on the surface of the information carrier 601.

Thus, in summary, for lateral scanning of the optical probe array, a linear phase profile is required. The surface normal of the plane of equal phase indicates the direction in which the phase profile is shifted. In the known reader system described above, scanning in both the horizontal (x) and vertical (y) direction is required. For displacement of the probe array along the optical axis (z), a parabolic-curved phase profile is required. The radius of curvature determines the shift in z. The required phase profiles are generated by an LC phase shifter in the system described above, where all the pixels are individually addressable (effectively an active matrix display). However, this is a relatively costly element because each pixel needs some electronics, as described above in relation to Fig.8 of the drawings.

OBJECT AND SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a system for shifting at least one light spot, for example, over an information carrier for data recovery, wherein the phase- modulator is of reduced complexity, and therefore less expensive, relative to the prior art.

In accordance with the present invention, there is provided a system for shifting at least one light spot generated from an input light beam, said system comprising: a phase-modulator for applying a phase profile to said input light beam, said phase-modulator comprising a layer of liquid crystal material between first substrate and a second substrate, said first substrate comprising a first set of electrodes and said second substrate comprising a second set of electrodes, said first and second sets of electrodes being oriented in respective first and second directions, means for applying a first voltage gradient across said first set of electrodes to generate a first phase profile for shifting said at least one light spot in said first direction, means for applying a second voltage gradient across said second set of electrodes to generate a second phase profile for shifting said at least one light spot in said second direction.

Thus, by applying the correct phase profiles one-dimensionally along each of the shifting axes, two-dimensionally linear and quadratic profiles can be produced in order to effect the desired shift of the at least one light spot in the x, y and/or z directions.

The present invention extends to an information carrier reading apparatus comprising a probe array generating means for generating from an input light beam an array of light spots, and a system as defined above for shifting the light spots relative to an information carrier.

The present invention also extends to a method of shifting at least one light spot in a system as defined above, the method comprising a method of shifting at least one light spot in a system, the method comprising applying a first voltage gradient across said first set of electrodes to generate a first phase profile for shifting said at least one light spot in said first direction, and applying a second voltage gradient across said second set of electrodes to generate a second phase profile for shifting said at least one light spot in said second direction.

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

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will now be described by way of examples only and with reference to the accompanying drawings, in which:

Fig.l depicts a first information carrier reading system,

Fig.2 depicts a second information carrier reading system, Fig.3 depicts a detailed view of components dedicated to macro-cell scanning used in information carrier reading systems,

Fig.4 illustrates the principle of macro-cell scanning,

Fig.5 depicts a three-dimensional view of the system of Fig.1,

Fig.6 depicts a third information carrier reading system,

Fig.7 depicts a three-dimensional view of the system of Fig.6,

Fig.8 depicts an electrically controllable liquid crystal cell and a voltage control curve of such a liquid crystal cell,

Fig.9 depicts, schematically the layout of electrodes on a phase-modulation for use in a system according to an exemplary embodiment of the invention,

Fig.10 illustrates graphically the phase response of an LC cell to the applied voltage,

Fig.11 illustrates various apparatus and devices comprising a system according to the invention.

DETAILED DESCRIPTION OF THE INVENTION A phase-modulator according to an exemplary embodiment of the present invention comprises a liquid crystal element consisting of a layer of liquid crystal material sandwiched between an upper and a lower substrate. It is proposed herein to simplify the layout of the electrodes of the LC element relative to the prior art, in order to achieve the above-mentioned object. Referring to Fig.9 of the drawings, a set of horizontal electrodes 903a are arranged on the upper substrate, which electrodes run parallel to the x axis, and a set of vertical electrodes 903b are arranged on the lower substrate, which electrodes are orthogonal to the horizontal electrodes 903a and run parallel to the y axis. It will be appreciated that, in practice, the number of electrodes will be much greater than that shown in Fig.9 (possibly of the order of 100-1000 on each substrate).

The horizontal and vertical electrodes 903 a, 903b provided on the upper and lower substrates respectively, can be individually addressed. Thus, whereas in the prior art arrangement described above with reference to Fig.7 and Fig.8 of the drawings, a plurality of LC cells is provided, one for each pixel, and each LC cell comprises a pair of electrodes, in the arrangement of the present invention, a single LC layer is provided between an upper and a lower substrate, with a set of horizontal electrodes being provided on the upper substrate and a set of vertical electrodes being provided on the lower substrate.

As explained above, scanning can be achieved by applying a phase profile to the input light beam and varying this phase profile. The phase profile can be varied as a function of the voltage profile along the x and y axes respectively.

Thus, it is required to generate a linear voltage profile V_x(x) in the x direction and a linear voltage profile V_y(y) in the y direction. Such a linear voltage profile is illustrated graphically in Fig.8. This is achieved by applying a voltage gradient over the electrodes on the substrates so as to define the following voltage profiles: V_x(x) = ax

V(x,y) = ax - by Eq.5

Wherein x and y are the distance along (x) and (y) directions, respectively, a and b are the voltage gradients (in V/m),

V(x,y) is the voltage between top and bottom substrate at the given position on the screen.

The values a and b determine the lateral shift of the probe array when this module is used in a system according to an exemplary embodiment of the present invention. When a quadratic phase profile is applied to both substrates the resulting wave front is spherical:

V_x (x) = ex

V (x,y) = ex² - cy² Eq.6

= cr

with r - yjx² - y² wherein the value c determines the shift of the probe array in the z direction.

The above shows that given the electrode design of Fig.9 it is possible to generate a linear and spherical two-dimensional voltage profile.

In Fig.10, this relation between the phase and the applied voltage can be seen. On the vertical axis is the phase shift in arbitrary units and on the horizontal axis is the applied voltage.

One embodiment is to wire each electrode line individually (passive addressing). This requires quite some wiring, and a control that can generate sufficient independent voltages.

A second option is to implement some logic on the substrates and address each of the lines actively (in the same way as an individual pixel would be addressed in an active matrix display). The latter solution has the advantage that less wiring is required. Compared to a full active matrix display, the advantage is that the transistor does not block the light (it can be placed outside the light transmitting area), and that of course less transistors are required (because less electrodes per pixel are employed).

Thus a simple layout for the LC scanning element is proposed herein, which layout allows the generation of the required phase profiles (for defocus and lateral scanning of the probe arrays), without addressing all pixels individually.

The exemplary design consists of horizontal and vertical electrodes that are placed on the top and bottom substrate respectively. Without such a design an active matrix LC element would be required to generate the necessary profiles. Implementation of this design will result in a major decrease in complexity of the scanning element. The concept is based on the observation that two-dimensional linear and quadratic profiles can be produced by applying the corresponding profiles one-dimensionally along both axes. Preferably, the applied voltage should be kept within the linear range (roughly 2 to 4 volts in the graph of Fig.10) to ensure optimum separation of the profile in the horizontal and vertical directions and therefore ensure optimum performance.

As illustrated in Figure 11 , the system according to the invention may advantageously be implemented in a reading apparatus RA (e.g. home player apparatus....), a portable device PD (e.g. portable digital assistant, portable computer, a game player unit....), or a mobile telephone MT. These apparatus and devices comprise an opening (OP) intended to receive an information carrier IC as previously described, and a system according to the invention for shifting light spots over said information carrier IC in view of data recovering.

The shifting system in accordance with the invention may be used in a microscope. Microscopes with reasonable resolution are expensive, since an aberration-free objective lens with a reasonably large field of view and high enough numerical aperture is costly. Scanning microscopes solve this cost issue partly by having an objective lens with a very small field of view, and scanning the objective lens with respect to the sample to be measured (or vice-versa). The disadvantage of this single-spot scanning microscope is the fact that the whole sample has to be scanned, resulting in cumbersome mechanics. Multi- spot scanning microscopes solve this mechanical problem, since the sample does not have to be scanned over its full dimensions, the scanning range is limited to the pitch between two spots.

In a microscope in accordance with the invention, a sample is illuminated with the spots that are created by the probe array generating means, and a camera takes a picture of the illuminated sample. By scanning the spots over the sample by means of the shifting system of the invention, and taking pictures at several positions, high-resolution data are gathered. A computer may combine all the measured data to a single high-resolution picture of the sample.

The focus distance can be controlled manually, by looking at a detail of the picture of the sample. It can also be performed automatically, as is done in a digital camera (finding the position in which the picture has the maximum contrast). Note that the focusing of the imaging system is not critical, only the position of the sample with respect to the probes is important and should be optimized.

A microscope in accordance with the invention consists of an illumination device, a probe array generator, a sample stage, optionally an imaging device (e.g. lens, fiber optic face plate, mirror), and a camera (e.g. CMOS, CCD). This system corresponds to the system of Fig. 6 and 7, wherein the information carrier (601, 701) is a microscope slide on which a sample to be imaged may be placed, the microscope slide being deposited on a sample stage.

Light is generated in the illumination device, is focused into an array of foci by means of the probe array generator, it is transmitted (partly) through the sample to be measured, and the transmitted light is imaged onto the camera by the imaging system. The sample is positioned in a sample stage, which can reproducibly move the sample in the focal plane of the foci and perpendicular to the sample. A position measurement system can be implemented into the stage, or it can be implemented in the system. In order to image the whole sample, the information carrier is scanned by means of the shifting system in accordance with the invention so that all areas of the sample are imaged by an individual probe.

Instead of a transmissive microscope as described above, a reflective microscope may be designed. In a reflective microscope in accordance with the invention, light that has passed through the sample is reflected by a reflecting surface of the microscope slide and then redirected to the camera by means of a beam splitter. It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be capable of designing many alternative embodiments without departing from the scope of the invention as defined by the appended claims. In the claims, any reference signs placed in parentheses shall not be construed as limiting the claims. The word "comprising" and "comprises", and the like, does not exclude the presence of elements or steps other than those listed in any claim or the specification as a whole. The singular reference of an element does not exclude the plural reference of such elements and vice-versa. The invention may be implemented by means of hardware comprising several distinct elements, and by means of a suitably programmed computer. In a device claim enumerating several means, several of these means may be embodied by one and the same item of hardware. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

Claims

CLAIMS:

1. A system for shifting at least one light spot generated from an input light beam (104), said system comprising: - a phase-modulator (706) for applying a phase profile to said input light beam

(104), said phase-modulator (706) comprising a layer of liquid crystal material between first substrate and a second substrate, said first substrate comprising a first set of electrodes (903a) and said second substrate comprising a second set of electrodes (903b), said first and second sets of electrodes (903a, 903b) being oriented in respective first direction (x) and second direction (y), means for applying a first voltage gradient (a) across said first set of electrodes to generate a first phase profile for shifting said at least one light spot (103) in said first direction (x), means for applying a second voltage gradient (b) across said second set of electrodes to generate a second phase profile for shifting said at least one light spot (103) in said second direction (y).

2. A system according to claim 1, wherein said first and second set of electrodes (903a, 903b) are oriented substantially orthogonally relative to each other.

3. A system according to claim 1, wherein said first and second voltage gradients are such that substantially uniform respective voltage profiles along said first direction (x) and second direction (y) are generated.

4. A system according to claim 3, wherein when a linear phase profile is applied to said input light beam (104): the voltage profile V_x(x) of said first set of electrodes in said first direction (x) is expressed as the product of said first voltage gradient (a) and the distance by which said at least one light spot is shifted in said first direction, - the voltage profile V_y(y) of said second set of electrodes in said second direction

(y) is expressed as the product of said second voltage gradient (b) and the distance by which said at least one light spot is shifted in said second direction.

5. A system according to claim 4, wherein the voltage profile V(x,y) between said first substrate and said second substrate is expressed as the difference between said voltage profile V_x(x) in said first direction (x) and said voltage profile V_y(y) in said second direction (y).

6. A system according to claim 5, wherein when a quadratic phase profile is applied to said input light beam (104), the resulting voltage profile V(x,y) between said first substrate and said second substrate is spherical for shifting said at least one light spot (103) in a third direction (z).

7. A method of shifting at least one light spot (103) in a system comprising a phase- modulator for applying a phase profile to said input light beam, said phase- modulator comprising a layer of liquid crystal material between first substrate and a second substrate, said first substrate comprising a first set of electrodes (903a) and said second substrate comprising a second set of electrodes (903b), said first and second sets of electrodes (903a, 903b) being oriented in respective first direction (x) and second direction (y), said method comprising the steps of: applying a first voltage gradient across said first set of electrodes (903a) to generate a first phase profile for shifting said at least one light spot (103) in said first direction, applying a second voltage gradient across said second set of electrodes (903b) to generate a second phase profile for shifting said at least one light spot (103) in said second direction.

8. An apparatus for scanning an information carrier, said apparatus comprising: a probe array generating means (102) for generating from an input beam (104) an array of light spots (103), a system according to claim 1 for shifting said light spots (103) relative to an information carrier (101).

9. A portable device comprising a system as claimed in anyone of claims 1 to 6.

10. A mobile telephone comprising a system as claimed in anyone of claims 1 to 6.

11. A game player unit comprising a system as claimed in anyone of claims 1 to 6.

12. A microscope comprising a system as claimed in anyone of claims 1 to 6.