WO2006061757A1

WO2006061757A1 - Optical scanning device, optical player and method for adjusting an optical scanning device

Info

Publication number: WO2006061757A1
Application number: PCT/IB2005/054033
Authority: WO
Inventors: Coen A. Verschuren; Ferry Zijp
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2004-12-10
Filing date: 2005-12-02
Publication date: 2006-06-15
Also published as: TW200634759A

Abstract

An optical scanning device (12) for scanning an optical record carrier (14) comprises an optical system (20) having at least a focusing lens (32) and a solid immersion lens (34), an optical radiation source (16) for emitting a scanning optical beam 18 passing through the focusing lens (32) and the solid immersion lens (34), a detector (56) for detecting a reflected optical beam (44) reflective from an optical exit face (38) of the solid immersion lens (34) and for generating a control signal the magnitude of which is representative of the amount of reflective radiation reflected from the optical exit face (38) of the solid immersion lens (34), and an adjuster (60, 62) for adjusting the solid immersion lens (34). The adjuster (62) uses the said control signal to adjust the solid immersion lens (34) with respect to the scanning optical beam (18). Further, an optical recording apparatus comprising the optical scanning device (12) and a method for adjusting an optical scanning device are described.

Description

Optical scanning device, optical player and method for adjusting an optical scanning device

The invention relates to an optical scanning device for scanning an optical record carrier according to the preamble of claim 1.

The invention further relates to an optical player having such an optical scanning device. The invention still further relates to a method for adjusting an optical scanning device according to the preamble of claim 7.

An optical scanning device and a method for adjusting an optical scanning device of the kind mentioned at the outset are generally known.

An optical scanning device using an optical system having a focusing lens and a solid immersion lens (SIL) is generally referred to as near- field scanning device. An optical player having such a near- field scanning device is generally referred to as near-field player.

In the context of the present invention, scanning an optical record carrier means reading from and/or writing on an information layer in or on an optical record carrier.

A reason for the use of near- field scanning devices in the field of optical recording is the following.

The maximum data density that can be recorded on an optical record carrier in an optical scanning system inversely scales with the size of the radiation spot that is focused onto the record carrier. The smaller the spot focused onto the carrier the larger the data density that can be recorded on the record carrier. The afore-mentioned spot size in turn is determined by the ratio of the wavelength λ of the scanning optical beam generated by the optical radiation source, for example a laser, and the numerical aperture (NA) of the focusing lens, which, in the context of the present invention, can also be referred to as objective lens.

Referring to Fig. Ia) there is shown a focusing lens 100 and an optical scanning beam 102 passing through the lens 100. The NA of the lens 100 is defined as NA = n sin(θ), wherein n is the refractive index of the medium in which the optical beam is focused and θ the half angle of the focused cone of the optical beam in that medium. It is evident that the upper limit for the NA of lenses that focus in air (as it is the case for lens 100 in Fig. Ia) or through a plane parallel plate (like a flat disk) is unity. The NA of a lens can exceed unity if the light is focused in a high index medium without refraction at the air-medium interface, for example by focusing in the center of a hemispherical solid immersion lens 104 as shown in Fig. Ib). In this case, the effective NA is NA_eff = n NA₀, wherein n is the refractive index of the hemispherical solid immersion lens 104 and NA₀ is the NA in air of the focusing lens 100 according to Fig. Ia).

In order to further increase the NA, it is known in the art to use a super- hemispherical solid immersion lens as shown in Fig. Ic). A super-hemispherical lens refracts the optical beam towards the optical axis. Now, the effective NA is

NA₀. The optical thickness of the super-hemispherical solid immersion lens is R(l+l/n), where n is the refractive index of the lens material and R is the radius of the semi-spherical portion of the lens 106.

It is important to note that an effective NA_eff larger than unity is only present within an extremely short distance from the optical exit face (108) of the solid immersion lens were an evanescent wave exists. The distance is typically smaller than one tenth of the wavelength of the radiation. The afore-mentioned distance is also called the near- field. This short near- field means that during writing or reading an optical record carrier the distance between the solid immersion lens and the record carrier must at all times be smaller than a few tens of nanometers. This is because at least a part of the scanning optical beam incident on the optical exit lace 108 of the SIL is totally reflected at the lens-air- interlace wherein the totally reflected part of the optical beam evanesces just a very small distance into the optically thinner medium.

When an entrance face of an optical record carrier is arranged within this short distance, radiation is transmitted from the SIL to the record carrier by evanescent coupling. It goes without saying that the distance or so-called gap width between the exit face of the SIL and the entrance face of the record carrier has to be kept smaller than a few tens of nanometers when reading or writing the optical carrier. For example, the distance should be about 25 nm for a system using a blue laser as radiation source and an NA of the optical system of 1.9. It is evident, that controlling the gap width when reading or writing an optical record carrier is crucial for the correct function of the scanning device. To allow control of the gap width of the air gap using a mechanical actuator at such small distances, a suitable control signal is required as input for the gap servo system. It is known that a suitable gap signal can be obtained from a reflected optical beam with a polarization state which is, for example, perpendicular to that of the scanning optical beam that is focused on the record carrier. A significant fraction of the optical beam becomes elliptically polarized after reflection at the SIL-air-record carrier interfaces. This effect can create the well-known "Maltese cross" when the reflected beam is observed through a polarizer. The gap signal is generated by integrating all the light of this "Maltese cross" using polarizing optics and a radiation detector, for example a single photo detector. The value of the photo detector is close to zero for zero gap width and increases with increasing gap width and levels off at a maximum value when the gap width is approximately a tenth of the wavelength of the optical beam.

The desired gap width corresponds to a certain value of the gap signal, the so- called set-point. The gap signal and a fixed voltage equal to the set-point are input in a subtracter, which forms a gap error signal at its output. This gap error signal is used to adjust the gap width between the solid immersion lens and the optical record carrier.

However, this known technique only provides for adjusting the gap width and is based on the assumption that the gap signal only depends on the distance between the exit face of the SIL and the entrance face of the record carrier.

Further, document US 2001/0021145 Al discloses a position control apparatus of an optical system capable of positioning a lens at a high accuracy in a near- field optical system using a solid immersion lens in a optical recording system. In this known device and method, the gap width is controlled on the basis of the electrostatic capacitance occurring between an electrode positioned on the solid immersion lens and the optical record carrier and on the basis of light reflected from the optical record carrier.

The techniques known heretofore only deal with the control of the gap width on the basis of a gap width control signal, but they do not deal with the problem of malfunctions of the optical scanning device which can be caused by misalignments of the SIL in the optical system which, furthermore, could negatively affect the precision of the gap signal.

It is, therefore, an object of the present invention, to improve an optical scanning device, an optical player and a method for adjusting an optical scanning device of the kind mentioned at the outset so that the performance of the optical scanning device is improved. Further, the gap signal which is derived from the optical beam reflected from the optical exit face of the solid immersion lens should be as large as possible for a reliable gap control.

According to the invention, the object is achieved with respect to the optical scanning device as mentioned at the outset in that the adjuster for adjusting the solid immersion lens is arranged to adjust the solid immersion lens with respect to the scanning optical beam using the control signal the magnitude of which is representative of the amount of reflected radiation reflected from the optical exit face of the solid immersion lens.

With respect to the method mentioned at the outset, the object is achieved according to the invention, in that the solid immersion lens is adjusted with respect to the scanning optical beam in dependence on the control signal the magnitude of which is representative of the amount of reflected radiation reflected from the optical exit face of the solid immersion lens.

It was surprisingly found that the gap signal which is derived from the optical beam which is reflected from the optical exit face of the solid immersion lens exhibits a strong dependence on the correct position of the solid immersion lens with respect to the scanning, i.e. the forward optical beam. In particular, it has been found that a tilt angle as small as ±0.01° with respect to the scanning optical beam leads to a decrease of the reflection of the optical beam at the optical exit face of the solid immersion lens and, hence, of the gap signal by a factor of about 1.5 to about 2. A mispositioning of the solid immersion lens transverse to the scanning optical beam has been found to be much more critical than the maximum allowed tilt (field) of the solid immersion lens that follows from a tolerance analysis based on wavefront aberrations, and even more critical than the mechanical tilt tolerance between the exit face of the solid immersion lens and the record carrier's entrance face. A particular advantage of the method according to the invention is that the adjustment of the solid immersion lens can be carried out without an optical record carrier being inserted in the optical storage apparatus, because the adjustment of the solid immersion lens according to the invention uses a control signal which is derived from the reflected optical beam solely reflected at the exit face of the solid immersion lens. Thus, the method according to the invention can be particularly advantageously used for adjusting the solid immersion lens when assembling the optical scanning device.

In the context of the present invention, "adjusting the solid immersion lens" includes adjusting the solid immersion lens only or adjusting the assembly consisting of the solid immersion lens and the focusing lens. A further advantage of the scanning device and the method for adjusting the scanning device is that the preciseness of adjustment of the solid immersion lens is superior over the known conventional technique which uses light reflected from the entrance face of the record carrier or the capacitance between electrodes arranged on the solid immersion lens and the record carrier. The known technique would not align the exit face of the solid immersion lens but rather a reference like the front surface of the lens holder. Due to the manufacturing process of the solid immersion lens, however, the exit face of the solid immersion lens may be slightly tilted with respect to its holder or the focusing lens leading to an incorrect adjustment of the solid immersion lens in case of such a conventional technique. In the method according to the invention, always the exit face of the solid immersion lens is adjusted with respect to the scanning optical beam because it uses the light reflected from that exit face resulting in much better performance and increased reliability of the scanning device.

In a preferred refinement of the optical scanning device, the adjuster is arranged to adjust the solid immersion lens with respect to the scanning optical beam until the control signal the magnitude of which is representative of the amount of reflected radiation reflected from the optical exit face of the solid immersion lens reaches a maximum. In the method according to the invention, the solid immersion lens is adjusted with respect to the scanning optical beam until the said control signal reaches a maximum. The advantage here is that the optimum position of the solid immersion lens can be easily found by adjusting the solid immersion lens with respect to the scanning optical beam until the gap signal derived from the radiation reflected from the exit face of the solid immersion lens reaches a maximum value thus ensuring the optimum performance of the optical scanning device. Further, with respect to the method according to the invention, a very easy tool to find the correct position of the solid immersion lens is provided without a need for auxiliary equipment.

In a further preferred refinement of the optical scanning device, the adjuster comprises at least one actuator capable of tilting the solid immersion lens with respect to the scanning optical beam. In the method according to the invention, adjusting the solid immersion lens includes tilting the solid immersion lens with respect to the scanning optical beam.

As already mentioned, the correct alignment of the solid immersion lens is in particular crucial for the optimum performance of the optical scanning device. The optical scanning device according to this refinement is now advantageously capable of avoiding misalignments of the solid immersion lens with respect to the scanning optical beam.

While correct alignment of the solid immersion lens with respect to the scanning optical beam is important, the adjuster for adjusting the solid immersion lens can also preferably and additionally comprise at least one actuator capable of shifting the solid immersion lens parallel and/or transverse to the scanning optical beam.

Accordingly, in the method according to the invention, the adjusting of the solid immersion lens can also include shifting the solid immersion lens parallel and/or transverse to the scanning optical beam. By providing the possibility of a 3 -dimensional adjustment of the solid immersion lens, which includes tilting the solid immersion lens as well as shifting the solid immersion lens, a proper and precise adjustment of the solid immersion lens in all degrees of freedom of movement is achieved thus further improving the performance of the optical scanning device. In case that the optical (data) storage apparatus further comprises a gap with controller for controlling a gap width between the optical exit face of the solid immersion lens and the plane in which an optical entrance face of an optical record carrier is situated in use of the scanning device, it is further preferred, if the gap width controller uses the control signal representative of the correct adjustment of the solid immersion lens as an optimum gap width control signal.

The method according to the invention preferably further comprises controlling a gap width between the optical exit face of the solid immersion lens and the plane in which an optical entrance face of an optical record carrier is situated in use of the scanning device, and the method then further comprises controlling the gap width in dependence on the control signal representative of the correct adjustment of the solid immersion lens.

The advantage here is that gap width control and adjustment control are synergistically combined without increasing the structural and cost expenditure of the device.

As already mentioned, it is further preferred in the method according to the invention, if the adjustment of the solid immersion lens is carried out without an optical record carrier inserted in the optical (data) storage apparatus.

It is a particular advantage of the present invention that the adjustment procedure is simplified because it does not require an optical record carrier as it is the case with the known techniques for adjusting the solid immersion lens. In particular, it is preferred if the adjustment method is carried out when the optical scanning device is being assembled, wherein the step of adjusting the solid immersion lens includes adjusting the solid immersion lens prior to fixing the solid immersion lens in a lens holder. The advantage of this measure is that optical scanning devices can be manufactured which a priori exhibit an improved performance, and the need for an additional control of the position of the solid immersion lens is advantageously reduced in the actual scanning operation of the optical scanning device.

A further advantage of this measure is that the optical scanning device can be operated with an optimal gap width control signal that is not strongly affected by a mispositioning of the solid immersion lens.

In a further preferred refinement, the adjustment method can be carried out when a record carrier is being inserted in the scanning device prior to scanning the record carrier. In this refinement, the method according to the invention may be used

(quasi-)dynamically in an optical scanning device, for example when temperature or ageing effects cause a deterioration of the lens alignment, resulting in performance loss. An advantage is again, that no record carrier is required to the adjustment of the solid immersion lens, so that re-adjustment can be done easily and quickly for example every time a record carrier is inserted in the optical scanning device. Since alignment can be finished before the record carrier is inside the drive of the scanning device, the start-up time of the drive is not affected. Re-adjustment of the solid immersion lens may also be done before starting the reading and/or writing operation.

Further advantages will become apparent from the following description and the accompanying drawings.

It is to be understood, that the afore-mentioned features and those still to be explained below are not only applicable in the combinations given, but also in other combinations or in isolation without departing from the scope of the invention.

Preferred embodiments of the invention will be described below with reference to the accompanying drawings. In the drawings: Fig. Ia) through c) show a focusing lens focusing in air (Fig. Ia), a focusing lens focusing in an hemispherical solid immersion lens (Fig. Ib)), and a focusing lens focusing in an aplanatic super-hemispherical solid immersion lens (Fig. Ic));

Fig. 2 a schematic block scheme diagram of a near-field optical player; Fig. 3 a schematic illustration of a focusing lens focusing in a solid immersion lens adjacent to a record carrier for explaining the gap width;

Fig. 4 a schematic diagram of the functional relationship between the gap signal and the gap width;

Fig. 5 a solid immersion lens misaligned with respect to the scanning optical beam;

Fig. 6 a diagram showing the dependence of the gap signal on the tilt of the solid immersion lens in Fig. 5;

Fig. 7 a particular lens design including a focusing lens and a solid immersion lens; Fig. 8 a focusing lens and a solid immersion lens fixed in one lens holder; and

Fig. 9 a focusing lens and a solid immersion lens in separated lens holders.

Fig. 2 schematically shows a set-up of an optical player 10, for example a CD- player, a DVD-player and/or a BD-player.

The optical player comprises an optical scanning device 12 for optically scanning a record carrier 14, which is, for example, a CD, DVD or BD. "Scanning" means reading and/or writing information on the record carrier 14.

The optical scanning device 12 comprises a radiation source 16, which is, for example, a laser emitting a scanning optical beam 18. The scanning optical beam 18 has a wavelength λ which is 405 nm, for example.

The scanning optical beam 18 emitted by the radiation source 16 passes through an optical system 20, which, for example, includes a collimator lens 22, a beam shaper 24, a non-polarizing beam splitter 26, a polarizing beam splitter 28, and a movable lens assembly 30 for focus adjustment.

The optical system 20 further comprises a focusing lens 32 and a solid immersion lens 34. The optical player or (data) storage apparatus 10 further comprises a drive unit for driving the record carrier 14 which is known as such and not shown in the drawings. As shown in Fig. 3 the solid immersion lens 34 is of the type shown in Fig. Ic) already described in the introductory portion of the present description, i.e. the solid immersion lens 34 preferably is an aplanatic super-hemispherical solid immersion lens.

The solid immersion lens 34 provides an effective numerical aperture which is NA₀, wherein n is the refractive index of the lens material of the solid immersion lens 34 and NA₀ is the numerical aperture of the focusing lens 32 when focusing in air.

The scanning optical beam 18 passes through the focusing lens 42 and is focused into the solid immersion lens 34. When entering the solid immersion lens 34, the scanning optical beam 18 is refracted towards the optical axis 36 and is obliquely incident on an optical exit face 38 of the solid immersion lens 34. A part of the scanning optical beam 18 is totally reflected at the optical exit face 38, which forms an interface between an optical thicker medium (lens 34) and air 40.

An effective NA_eff larger than unity is only present within an extremely short distance, the so-called near- field, from the exit face 38 of the solid immersion lens. The near- field is only present in a distance which is typically smaller that 1/10^th of the wavelength λ of the optical radiation.

When the record carrier 14 is brought with its entrance face 42 in this aforementioned short distance to the optical exit face 38 of the solid immersion lens 34, the high NA optical scanning beam 18 is transmitted from the solid immersion lens 34 to the record carrier 14 by evanescent coupling. If the distance between the light entrance face 42 of the optical record carrier 14 from the optical exit face 38 of the solid immersion lens 34 is larger than the extension of the near- field, there is no transmission of the near- field to the optical record carrier.

Thus, the distance between the entrance face 42 and the exit face 38, which is referred to as the gap width GW, has to be maintained at a few tenths of the wavelength λ, i.e. at a few tens of nanometers, and should be controlled in a range of a few nanometers. For example, the gap width should be about 25 nm for a system using a blue laser as radiation source and an NA_eff of the objective system of 1.9.

As already mentioned, at least part of the scanning optical beam 18 entering the solid immersion lens 34 is totally reflected at the optical exit face 38 of the solid immersion lens 34, as indicated by arrows 44 in Fig. 3.

The amount of the reflected radiation depends on how much radiation of the scanning optical beam 18 is coupled out of the solid immersion lens 34 or, in other words, transmitted to the optical record carrier 14. However, the amount of reflected optical radiation also depends on a correct position of the solid immersion lens 34 with respect to the scanning optical beam 18, as will be described later in more detail.

As mentioned before, the gap width between the solid immersion lens 34 and the record carrier 14 is to be controlled for a proper performance of the scanning device 12. The reflected optical beam 44 is used to produce a suitable control signal for controlling the gap width GW, as described with reference to Fig. 2.

A significant fraction of the reflected optical beam 44 is elliptically polarized after reflection at the exit face 38 of the solid immersion lens and the entrance face 42 of the record carrier 14. The reflected optical beam 44 is coupled out by the polarizing beam splitter 28, and focused by a lens 54 onto a detector 56, which detects optical radiation that is polarized perpendicular to the direction of polarization of the forward scanning optical beam 18 that is focused on the record carrier 14.

The optical scanning device 12 comprises another detector 58, which is used for detection of optical radiation, that is polarized parallel to the forward optical beam 18 that is focused on the record carrier 14 and contains the information read from or written on the record carrier 14.

The detector 56 generates the so-called gap signal GS which is representative of the gap width GW. The detector 56 can be a single photodetector.

In Fig. 4 the gap signal GS generated by the detector 56 is shown versus the gap width GW.

For zero gap width, i.e. when the entrance face 42 of the optical record carrier 14 is in contact with the exit face 38 of the solid immersion lens 34, the gap signal is close to zero. With increasing gap width, the gap signal increases, wherein the linear dependence of the gap signal on the gap width as shown in Fig. 4 is only arbitrary. At about 1/10 λ, the gap signal does not further increase with the gap width, because there is no longer an evanescent coupling of the scanning optical beam 18 into the record carrier 14 and reflection of the beams 18 from the exit face 38 is maximum.

There is a certain value of the gap signal GS, the set-point SP, which corresponds to the desired gap width between the record carrier 14 and the solid immersion lens 34. The gap signal GS and a fixed voltage equal to the set-point SP are input in a subtracter (not shown) which forms a gap error signal at its output. The gap error signal is used to control the adjuster 60 (gap servo system), which controls the gap width GW.

The description of the system up to here was made under the assumption that the solid immersion lens 34 is correctly adjusted in the optical scanning device 12. A misalignment of the SIL 34 has been considered up to the present invention only in terms of the maximum allowed tilt of the record carrier that follows from a tolerance analysis based on wavefront aberrations. For a typical design of a solid immersion lens (cf. Fig. 7) with NA=I.8 of the type of Fig. Ic), with λ = 405 nm, it is found that the maximum tilt of the record carrier which results in 15 milli- waves root-mean-square-optical path difference, is as large as 0.55°. This means that the optical quality of the spot is not significantly affected by quite a large tilt, which can even be much larger than the mechanical tilt margin between the exit face 38 of the solid immersion lens 34 and the entrance face 42 of the record carrier 14. For example, for a 20 μm radius of the exit face 38 of the solid immersion lens (34) at a distance of 25 nm from the record carrier 14, the maximum tilt angle is 0.072° which is much smaller than the afore-mentioned 0.55°.

However, there is another effect, that can crucially deteriorate the proper function of the optical scanning device 12, namely when the SIL 34 or the lens assembly (32+34) is not properly aligned with respect to the scanning optical beam 18 or the optical axis 36 of the scanning optical beam 18, which is even more critical than the mechanical tilt tolerance between the exit face 38 of the solid immersion lens 34 and the entrance face 42 of the record carrier 14.

Fig. 5 shows schematically such a misalignment of the lens assembly (solid immersion lens 34 and 32, wherein only the SIL 34 is shown for simplicity) with respect to the scanning optical beam 18, wherein the undesired tilt of the lens assembly with respect to the scanning optical beam 18 is indicated by an angle t. It is to be noted that the representation of the tilt in Fig. 5 is highly exaggerated.

Fig. 6 shows the dependence of the gap signal GS on the tilt angle t for the optical scanning device 12 in Fig. 2. The results shown in Fig. 6 are based on real experiments made with the optical scanning device 12 in Fig. 2.

Fig. 6 shows that a tilt angle t of about 0.05°, which is even smaller than the above-discussed allowed mechanical tilt tolerance of 0.072° and even much smaller than the maximum allowed tilt that follows from a tolerance analysis based on wavefront operations of 0.55°, leads to reduction of the gap signal of a factor of about 0.5. Thus, a proper adjustment of the lens assembly 32, 34, or in more detail, of the exit face 38 of the solid immersion lens 34 with respect to the scanning optical beam 18 is crucial for a proper performance of the scanning device 12, in particular for obtaining a gap signal as large as possible for a reliable gap width control. Therefore, the optical scanning device 12 according to Fig. 2 comprises an adjuster 62 which can also be combined with the gap width adjuster 60, for adjusting the solid immersion lens 34 with respect to the scanning optical beam 18, wherein the adjuster 62 uses the control signal (i.e. GS in the absence of an optical record carrier) of the detector 56, the magnitude of which is representative of the amount of reflected radiation reflected from the optical exit lace 38 of the solid immersion lens 34 to properly adjust the solid immersion lens 34 or the lens assembly with respect to the scanning optical beam 18.

The optimum tilt angle t of the solid immersion lens 34/ lens assembly corresponds to a maximization of the gap signal GS so that the adjuster 62 adjusts the solid immersion lens 34 with respect to the scanning optical beam 18 until the gap signal or control signal of the detector 56 reaches a maximum as shown in Fig. 6.

As shown in Fig. 8, the adjuster 62 comprises an actuator which is, for example, coupled to a lens holder 66, in which both, the focusing lens 32 and the solid immersion lens 34, are fixed. The actuator 34 is at least capable of tilting the solid immersion lens 34 by tilting the lens holder 66 with respect to the scanning optical beam 18 in directions according to a double arrow 68 in the plane of drawing in Fig. 8, and also preferably in corresponding tilting directions perpendicular to the plane of drawing in Fig. 8.

Fig. 9 shows an alternative embodiment, in which the focusing lens 32 is fixed in a first lens holder 70 and a solid immersion lens 34 is fixed in a second lens holder 72, which is separate from the first lens holder 70. In this case, it is preferred if the actuator 64 of the adjuster 62 only adjusts the solid immersion lens 34 via the lens holder 72 without simultaneously adjusting the focusing lens 32, thus enabling the solid immersion lens 34 to be adjusted independent from the focusing lens 32.

The actuator 64 can also be provided with the capability to adjust the solid immersion lens 34 by shifting same in longitudinal direction of the scanning optical beam 18 or in transverse direction thereto.

As already mentioned, the adjuster 62 and the gap width servo controller 60 can be combined such that the gap width controller 60 uses the control signal which is representative of the correct adjustment of the solid immersion lens 34 as an optimum gap width control signal.

With the adjuster 62, the optical scanning device 12 can provide for a (quasi-)dynamical adjustment of the solid immersion lens 34 by means of the actuator 64 in which case the actuator 64 is preferably a 3 -dimensional actuator which does not provide only focus and tracking but also alignment of the solid immersion lens 34. In this case, the gap signal GS is maximized by adjusting the control signal for the actuator 64 with respect to the tilting of the solid immersion lens 34 and then kept constant during the operation of the device.

The adjustment of the solid immersion lens 34/lens assembly according to the above technique does not require a record carrier inserted in the optical scanning device 12. Thus, re-alignment of the solid immersion lens 34/lens assembly can be done easily and quickly, for example every time a record carrier 14 is inserted in the device 12. Since the alignment of the solid immersion lens 34/lens assembly can be finished before the record carrier is inside the drive of the device, start-up time of the drive is not affected. Re- alignment may also be done before starting the reading and/or writing process.

In the method for adjusting the optical scanning device 12, the aforementioned adjustment technique using the signal derived from the reflected radiation 44, the magnitude of which is representative of the amount of detected reflected radiation reflected from the exit face 38 of the solid immersion lens 34 can be used to adjust the solid immersion lens 34/lens assembly when assembling the optical scanning device 12, because the technique does not require a record carrier 14 inserted in the scanning device 12, as already mentioned. In particular, the signal of the detector 56 derived from the detected reflected optical beam 44 can be used to properly adjust the solid immersion lens 34 when assembling the scanning device 12, in particular when positioning and fixing the solid immersion lens 34 in the holder 66 or 72 in Figs. 8 and 9. By means of the technique described before, the solid immersion lens 34 can be properly aligned with respect to the scanning optical beam 18 by monitoring the gap signal GS as in Fig. 6, and then fixing, for example gluing, the solid immersion lens 34 in the correct position in the lens holder 66 or 72.

Claims

CLAIMS:

1. An optical scanning device for scanning an optical record carrier (14), comprising: an optical system (20) having at least a focusing lens (32) and a solid immersion lens (34), an optical radiation source (16) for emitting a scanning optical beam (18) passing through the focusing lens (32) and the solid immersion lens (36), a detector (56) for detecting a reflected optical beam (44) reflected from an optical exit face (38) of the solid immersion lens (34) and for generating a control signal the magnitude of which is representative of the amount of reflected radiation reflected from the optical exit face (38) of the solid immersion lens (34), and an adjuster (60, 62) for adjusting the solid immersion lens (34), characterized in that the adjuster (62) is arranged to adjust the solid immersion lens (34) with respect to the scanning optical beam (18) using said control signal.

2. The optical scanning device of claim 1, characterized in that the adjuster (62) is arranged to adjust the solid immersion lens with respect to the scanning optical beam (18) until the said control signal reaches a maximum.

3. The optical scanning device of claim 1 or 2, characterized in that the adjuster (62) comprises at least one actuator (64) capable of tilting the solid immersion lens (34) with respect to the scanning optical beam (18).

4. The optical scanning device of anyone of claims 1 though 3, characterized in that the adjuster (62) comprises at least one actuator (64) capable of shifting the solid immersion lens (34) parallel and/or transverse to the optical scanning beam (18).

5. The optical scanning device of anyone of claims 1 through 4, further comprising a gap width controller (60) for controlling a gap width between the optical exit face (38) of the solid immersion lens (34) and a plane in which an optical entrance face (42) of an optical record carrier (14) is situated in use of the scanning device (12), characterized in that the gap width controller (60) arranged to use the control signal representative of the correct adjustment of the solid immersion lens (34) as an optimum gap width control signal.

6. An optical recording apparatus, characterized by/ comprising an optical scanning device (12) of anyone of claims 1 through 5.

7. A method for adjusting an optical scanning device, the scanning device comprising an optical system (20) having at least a focusing lens (32) and a solid immersion lens (34) and an optical radiation source (16), the method comprising the steps of: passing a scanning optical beam (18) from the radiation source through the focusing lens (32) and the solid immersion lens (34), detecting a reflected optical beam (44) reflected from an optical exit face (38) of the solid immersion lens (34), generating a control signal the magnitude of which is representative of the amount of detected reflected radiation, adjusting the solid immersion lens (34), characterized in that the solid immersion lens (34) is adjusted in dependence on the said control signal with respect to the scanning optical beam (18).

8. The method of claim 7, characterized in that the solid immersion lens (34) is adjusted with respect to the scanning optical beam (18) until the said control signal reaches a maximum.

9. The method of claim 7 or 8, characterized in that adjusting the solid immersion lens (34) includes tilting the solid immersion lens (34) with respect to the scanning optical beam.

10. The method of anyone of claims 7 to 9, characterized in that adjusting the solid immersion lens (34) includes shifting the solid immersion lens (34) parallel and/or transverse to the scanning optical beam (18).

11. The method of anyone of claims 7 through 10, further comprising controlling a gap width between the optical exit face (38) of the solid immersion lens (34) and a plane in which an optical entrance face (42) of an optical record carrier (14) is situated in use of the scanning device (12), characterized by controlling the gap width in dependence on the control signal representative of the correct adjustment of the solid immersion lens (34).

12. The method of anyone of claims 7 through 10, characterized in that it is carried out without a record carrier (14) cooperating with the optical scanning device (12).

13. The method of claim 12, characterized in that it is carried out when the optical scanning device (12) is being assembled, wherein the step of adjusting the solid immersion lens (34) includes adjusting the solid immersion lens (34) prior to fixing the solid immersion lens (34) in a lens holder (66, 72).

14. The method of anyone of claims 7 through 13, characterized in that it is carried out when a record carrier (14) is being inserted in the scanning device (12) prior to scanning the record carrier (14).