MXPA99011773A - Apparatus for reading from or writing to optical recording media having different information carrier layers - Google Patents

Abstract

The present invention relates to an apparatus for simultaneously reading from or writing to different information carrier layers (71, 72 ...) of an optical recording medium (7) having at least two different information carrier layers (71, 72, ...), the apparatus having partial beam generating means (5, 91, 92, ...) for generating different partial beams (31, 32, ...), focusing means (6, 61, 62) for focusing the partial beams (31, 32, ...) onto different information carrier layers (71, 72, ...) and detection means (81, 82, ...) for detecting the partial beams (31, 32, ...). The object of the invention is to propose an apparatus of this type which provides a largely common optical path for the individual partial beams (31, 32 ...) and is nevertheless tolerant with regard to deviations in the spacing of individual information carrier layers (71, 72 ...) from one another. This object is achieved by virtue of the fact that a partial beam generating means (5, 41, 42, ...) is provided for coupling out a partial beam (31, 32, ...) and a beam influencing means (61, 62, 22, 23, ...) is provided for independently influencing the coupled-out partial beam (32, 33, ...). The apparatus according to the invention is suitable both for recording media having read-only information carrier layers and for recording media having write-once or write-many information carrier layers.

Description

APPARATUS FOR READING AND WRITING IN AN OPTICAL RECORDING MEDIA THAT HAS DIFFERENT INFORMATION BEARING COVERS DESCRIPTION OF THE INVENTION The present invention relates to an apparatus for simultaneously reading or writing to different information carrying layers of an optical recording medium having at least two different information carrying layers. The recording medium of this type is used to increase the data capacity. In this case, the information-carrying layers are semi-transparent and each is placed parallel to the other. Their spatial separation is typically 30 to 50 μm with a tolerance of +, 5 μm. Interference between channels is suppressed during the reading of the data when considering spatial separation. For many applications, it may be appropriate to read the data simultaneously from two or more information carriers, or read the data and simultaneously write other data. The simultaneous reading or writing of two or more information-carrying layers requires that the light be correctly focused on data tracks placed generally spiral or circular of the various layers of information and that the corresponding focal points are tracked in the direction of tracking, is say, generally perpendicular to the direction of the track, in the plane of the tracks. Since, when considering manufacturing tolerances, the information-carrying layers are not placed exactly equidistant over the entire plane of the recording medium, and neither are the data tracks congruently on top of each other, it is necessary to follow the two focal points both axially, that is, in the focus direction, and laterally, that is, in the tracking direction, ie perpendicular to the track. Similarly, simultaneous reading or writing allows the data rate to increase. A possible way to read two or more layers in parallel is to use two or more browsers. However, this is complicated and expensive. EP-A-0 837 455 discloses an apparatus for simultaneously reading or writing two different information carriers of an optical recording medium having at least two different information carrying layers. This device works with a single scanner. It has a partial beam generating means for generating different partial beams, a focusing means for focusing the partial beams on different information carrying layers and a detection means with at least one detector element for each partial beam. The known apparatus can be considered to have the disadvantage that the partial beams traverse a mainly common optical path, as a result of which only slight tolerances are accepted with respect to the separation of the information carrying layers from each other and the relative deviation of the information tracks of the different information carrying layers laterally one with respect to the other. The object of the present invention is to propose an apparatus which provides a mainly common optical path for the individual partial beams and yet is more tolerant with respect to the deviations mentioned above. For this purpose, according to the invention, at least one partial beam generating means is provided for coupling a partial beam inside and outside a beam pencil and a means is also provided that affects the beam to independently affect the partial beam coupled. This has the advantage that a mainly common optical path can be used for the concentrated partial beams from their generation through detection, as a result of which it becomes possible to use a small number of components, a compact structure of the explorer and lower production costs. However, it is possible to correct tolerances with respect to the separation of the individual information carrying layers from one another and the individual information tracks of different information carrying layers with respect to each other, which increases the reliability of both reading and writing. This means that the tracking or focusing of the track, or both, according to the invention, are carried out individually for at least two different partial beams. Likewise, it is within the scope of the invention to use a partial beam generating means only for coupling in a partial beam or only for coupling a partial beam. Advantageously, a focusing means for focus and track regulation is provided as a beam alteration means, for each partial beam. This has the advantage of being cost effective since it is possible to use a conventional focusing means, the number of which only increases. A further advantage resides in the fact that it is possible to compensate large tolerances since the focusing means allows relatively large displacement amounts both in the axial direction and in the lateral direction. In this case, it is also possible to simultaneously explore on a single layer carrying information. In this context, the scanning medium not only reads, and writes, subsequently without reading or writing, but also reads and writes an information track of an information carrying layer. The partial beam generating means advantageously is a polarizing beam splitter. This means that only one component is needed for this. A further advantage resides in the fact that partial beams of different intensity can be placed by rotating the plane of polarization of the incident beam, for example, by means of the rotation of a laser that serves as a light source. This is particularly advantageous when the intention is to use a partial beam to carry out the reading while the other performs the writing, since the writing generally needs more power. However, the variability of the intensities is also advantageous for other applications, for example for reading from an information layer which is located at a deeper level with respect to the plane of light input within the recording medium, by means of of a greater intensity in the comparison with the reading of a layer that carries information, which is located at a higher level. As a result of this, a compensation of the corresponding attenuation of the corresponding partial beam is obtained due to the greater number of information carrying layers that are traversed. The invention provides a divider, in an input of which is present a detector output signal associated with one of the partial beams and the other input of which a signal corresponding to the control signal for the power of the source of the signal is present. light. This has the advantage that, by virtue of the division of the output signal of the detector by the power of the light source, even in the case of modulation of the power of the light source, a data signal is generated by the which is not affected by this modulation. Modulation of this type is used particularly in the case of writing to an information-carrying layer, as a result of which, however, inter-channel interference occurs with the other partial beam, ie, modulation of this partial beam, if the latter originates from the same source of light. According to the invention, this type of interference between channels is avoided. A further variant of the invention provides a single focusing means but also a means that affects a different beam which is provided for a plurality of partial beams. This has the advantage that only a single focusing means is necessary, which focuses all of the partial beams on the respective information carrier layer and uniformly follows the corresponding information tracks. A means is provided that affects the beam in each case for the second beam and each additional partial beam, and affects these independently of the first partial beam. A first partial beam is provided without a means that affects the separated beam, but in the same way has one, if so required. Variations in the separation of the information carrying layers from each other, and the information tracks in the lateral direction with respect to each other are carried out separately for each of the partial beams, while the approximate tracking is carried out to carried out by means of a common means of approach. The invention provides a partial beam generating means having a dedicated light source for each partial beam. This has the advantage that it is possible to simultaneously write different contents in a plurality of information-carrying layers without interfering between channels, since the power of the light sources can be regulated individually. In the same way, this measure has the advantage that the reading can be carried out with a different power. The medium that affects the beam advantageously is a collimator lens. The collimator lens, which is present in any case, is thus used as a means that affects the beam, with only a small additional expense. For this purpose, it is positioned so that it can be moved in the axial and / or lateral direction and is provided with corresponding actuators. The latter may be electromagnetically actuated actuators of the known kind for driving a focusing means, piezoelectric actuators, restrictive magnets or other suitable actuators. As an alternative to this, or additionally, a means is provided that affects the beam having an optically transparent element which is tunable in terms of the refractive index. In its simplest form, the element is a glass plate which is inserted into or removed from the beam path, or a plurality of such sheets having different thicknesses or a different refractive index, or other elements adequate. This has the advantage that it is possible to monitor the focus without a high expense, if appropriate in interaction with a medium that additionally affects the beam, for example a mobile collimator lens.

According to the invention, the light source and the associated detector are placed in an optically conjugated position with respect to each other. This has the advantage that the point of light incident on the respective detector does not move, or is only slightly displaced, by actuation of the medium affecting the beam. Additional advantages of the invention are specified in the following description of the advantageous configurations, with reference to the figures. It should be understood that the features that are specified may also be appropriately combined and / or modified without departing from the scope of the present invention. In the figures: Figure 1 shows an apparatus according to the invention with two focusing means and a light source, Figure 2 shows a schematic arrangement for data conditioning, Figure 3 shows an apparatus according to the invention. With a focusing means, a plurality of light sources and a plurality of means affecting the beam, FIG. 4 shows an apparatus according to the invention with a focusing means, two light sources and a medium affecting the beam. . Figure 1 shows the essential elements of a scanner of an apparatus according to the invention with two focusing means and a light source. The light source used is a laser diode 1, whose divergent output beam is converted into a parallel beam 3 by a collimator lens 2. After passing through a non-polarizing beam splitter 4, the beam 3 is decomposed into two partial beams 31, 32, which are polarized perpendicularly to each other, by a polarizing beam splitter 5. The partial beams 31, 32 are thus coupled outside the beam 3. The focusing means 6 has, as a means affecting the beam, a first objective lens 61 and a second objective lens 62, which can be moved in the direction of double arrows 63 and 64 by actuators that are not illustrated here. The first partial beam 31 is focused on a first information-carrying layer 71 of the optical recording medium 7 by the first objective lens 61. The second coupled beam 32 is reflected in a mirror 14 and then focused on a second information carrier layer 72 of the recording medium 7, by means of the second objective lens 62. The objective lenses 61, 62 are operated independently from each other, with the result that the focal points of the first partial beam 31 and the second partial beam 32 are followed independently of each other, on information tracks of the information layer 71, 72 respective. After reflection in the information carrier layer 71, 72, the partial beams 31, 32 pass through a beam splitter 5 in the opposite direction, in which case they are coupled inside a spoke pencil represented by the beam 3. This ray pencil is reflected by the non-polarizing beam splitter 4 in the direction of the detection means 8. In this case, the concentrated partial beams 31, 32 first pass through all the focusing lenses 13 and are then separated by an additional polarizing beam splitter 15 and fed to a first detector element 81 and a second element 82. detector, respectively. Instead of a polarizing beam splitter 15, it is also possible to provide a Wollaston prism or other optical element which divides the incident light beam according to its polarization. In the exemplary embodiment, a cylindrical lens 16 is provided between the focus lens 13 and the polarizing beam splitter 15, the cylindrical lens serves as an astigmatism producing element in the case where the astigmatism approach method is used. Instead of this focusing method, it is also possible to use any other suitable focusing method in an apparatus according to the invention. The elements 81, 82 detectors are designed as four quadrant detectors; here, too, any other suitable detection method known to a person skilled in the art can be used. The DI signals, Output D2 of the elements 81, 82 detectors and also a modulation signal as an input signal, determine the power of the laser diode 1 and are indicated schematically by means of an arrow, in each case. The writing of data modulated in pulse length to an information carrier layer, which is altered, for example, according to what is called the phase change method, takes place thermo-optically, that is, by modulation of the intensity of the diode 1 laser according to the data signal to be recorded and the corresponding heating of that position in layer 71, 72 information carrier, is going to be written. In order to optimize the geometric shape of the written information units, the so-called pitting, the power of the laser is further pressed in a manner dependent on the size of the pit to be written. In this way, asymmetries in stings of different lengths can be avoided. Accordingly, the modulation of the laser diode 1 corresponds to a superposition comprising the modulation according to the data information and the modulation for the write compensation. Let us assume that the first information-carrying layer 71 is a semitransparent layer that has been previously written, but which is not writable, a layer called ROM and the second information-bearing layer 72 is a layer that can be rewritten according to the Phase change method, which is called a RAM layer. If, with the scanner, the data is to be written to the information carrier layer 72 and the data is read simultaneously from the information carrier layer 71, the results in the first detector element 81 are a superposition of the data signal of the first information carrier layer 71, the ROM layer with the high frequency modulation of the laser diode 1 which is designed to write to the second information carrier layer 72. Therefore, the data signal detected by the first detector element 81 can not easily be subjected to further processing without errors by a decoder (not illustrated here). For this purpose, the invention provides for the output signal DI of the first detector element 81 and the modulation signal M of the laser diode 1 which is to be fed to a divider 17, the output signal D of which is proportional to the Dl / N ratio, that is, corresponds to the filtered signal of the first information carrier layer 71. Figure 2 shows this, in a schematic arrangement. In accordance with the exemplary embodiment described above, simultaneous reading of two data tracks is possible, as well as simultaneous writing and reading on two different information planes. Simple focus and tracking becomes possible even in the case of large tolerances between the information carrier layers 71, 72. In the case of a recording medium having more than two information carrying layers, two arbitrary information carrying layers can be accessed simultaneously by means of the exemplary embodiment described. There is also the possibility of data verification during a write operation. In this case, the two partial beams 31, 32 scan the same track, the data is written by means of a partial beam 31 while the written data is read by means of another partial beam 32. The read data is compared with the data entered by a control unit (not illustrated here), and appropriate countermeasures are initiated if errors are detected. Accordingly, the apparatus according to the invention is suitable both for a recording medium having one or a plurality of read-only information carrying layers, the so-called ROM layers, and for a recording medium having one or a plurality of single-write or multi-write information carrying layers, referred to as R, R or RAM layers. The laser diode 1 is positioned so that it can rotate about the optical axis according to arrow 18. In this way, it is possible to rotate the polarization direction of the parallel beam 3, as a result of which the intensity of the partial beams 31, 32 polarized one relative to the other can be varied. This allows the optical power to be distributed as desired between the partial beams 31, 32, which is advantageous in particular for the read-write mode. This embodiment of the invention is not limited to mechanically rotating the laser diode 1. Any other suitable measure for rotating the polarization direction of the beam 3 can advantageously be used here. The use of two partial beams 31, 32 which are polarized perpendicularly to each other and of the polarization sensitive detection means 8 allows it to be suppressed. effectively inter-channel interference between the two layers 71, 72 information carriers even in the case of very small separations.

The focal points of the partial beams 31 and 32 are advantageously placed one behind the other in the track direction, as a result of which a verification mode described above is possible without the objective lens 61 and / or 62 being deviated greatly. measured in the radial direction. Figure 3 shows, in a schematic illustration, an apparatus according to the invention with a focusing means 6, a plurality of light sources and a plurality of means 22, 23 affecting the beam. The generation and detection of the partial beam in this case is carried out in the optical units 91, 92 and 93 indicated schematically. The first partial beam 31 and the second partial beam 32 are combined in a first non-polarizing beam splitter 41, and the additional partial beams 33, 34 are coupled in the additional non-polarizing beam splitters 42, 43. The pencil of rays comprising the combined partial beams 31, 32 is deflected by a mirror 14 to the objective lens 6, which can be moved by means of actuators in the axial and lateral directions for the purpose of focusing and for the purpose of tracking . This is indicated by double arrow 63. When they pass through the beam splitters 41, 42, ..., the respective beams 31, 31, ..., are coupled again of the ray return pencil, which comprises the beams 31, 32,. .. reflected partial of the layers 71, 72, ... information carriers of the recording medium 7.

In the exemplary embodiment, the recording medium 7 has four layers 71-74 information carriers. In this case, the elements 81, 82, ... sensors of the optical units 91, 92, ... in each case are arranged in an optical conjugate manner with respect to the focal points on the layers 71, 72, .. Carriers of information. As a consequence, the information-bearing layers 72, 73, ... are reflected in a blurry manner on the first detector element 81 according to the geometric separation of the information carrier layers 71, 72 .... The same applies correspondingly to the elements 82, 83, ... detectors on which each layer 72, 73, ... carrying information, except for an associated one, is reflected in a blurred manner. Consequently, given a sufficient separation of the information carrying layers 71, 72, ..., the intensity of the light originating from the non-associated information carrier layers respectively is so low that virtually no interference occurs between channels. The focusing means 6 comprises an actuator lens and an objective that has a large control range and allows the simultaneous tracking of a plurality of focal points of a plurality of beams 31, 32, ... partial and therefore the correction of Approximate tolerances. This includes, for example, the vertical oscillation which typically constitutes up to + 0.5 mm in the case of an optical recording medium, and also the eccentricity of the recording medium, which may constitute up to + 280 μm. By way of example, a detector signal obtained from the first optical unit 91 is used as the regulating signal for the focusing means 6. As already described above, the information carrier layers 71, 72, ... generally do not have a constant separation from each other when considering, for example, manufacturing tolerances. In this case, the separation varies both from the recording medium and the recording medium and within a single recording medium. The information tracks on layers 71, 72, ... carriers of different information also generally do not correspond in terms of lateral assumption with respect to one another. The second beam 32 is therefore correspondingly readjusted by the second means 22 affecting the beam. The regulating signal for this is determined from the signal detected in the optical unit 92. Correspondingly, beams 33, 34 are readjusted, ... additional partial, by means 23, 24, ... of corresponding additional beam influence. However, only a small control interval is required for the medium 22, 23, ... which affects the beam, since only relative tolerances have to be corrected with respect to the first information carrier layer 71. Figure 4 shows an apparatus according to the invention corresponding to Figure 3 which has only two optical units 91, 92. The latter each comprises, in principle, a laser diode 11, 12, a semitransparent mirror 19, 29 and a detector element 81, 82. Instead of a non-polarizing beam splitter, a polarizing beam splitter 5 is provided with which, first of all, the first partial beam 31 after passing through the lens 2 collimator and the second partial beam 32 after passing through through the medium 22 affecting the beam are combined. The combined beam is directed to the objective lens 6 by the mirror 14 and is focused by the objective lens on the information carrier layers 71 and 72, respectively, of the recording medium 7. For the sake of simplicity, only two information carrier layers 71, 72 are illustrated here, but the recording medium 7 can perfectly well have additional information carrier layers. The focusing lens 6 can be moved by an actuator (not illustrated here) according to the double arrow 63. In this case, the laser diodes 11, 12 are oriented in such a way that the partial beams 31, 32 are biased perpendicularly to each other when they reach the polarizing beam splitter 15. This has the advantage that there is virtually no loss of optical power in the polarizing beam splitter 5, which increases the efficiency of the apparatus. A collimator lens 28 is provided as the second means 22 affecting the beam, collimator lens which belongs to the second laser diode 2 and corresponds to the lens 13 of figure 1. It can be moved by means of an actuator (not shown here) of according to the instructions indicated by arrow 65 double. It should be noted that, as a result of the influence by the collimator lens 28, the partial beam 32 does not additionally correspond exactly to the course of the beam illustrated between the collimator lens 28 and the recording medium 7. Partial beam 32 moves both laterally and becomes slightly convergent or divergent. This effect and also the corresponding effects in the exemplary embodiments are not taken into consideration in the schematic illustrations of the figures, for the sake of simplicity. As a supplement or as an alternative to the collimator lens 28, an optically transparent element 27 is shown in FIG. 4 which is tunable in terms of the refractive index. The focus regulation is possible with the help of the element 27 since the length of the optical path between the laser diode and / or the detector element 82 and the collimator lens 28 and therefore also between the objective lens 6 and the layer 72 information carrier can be readjusted within certain limits. The exemplary embodiments described in Figures 3 and 4 also allow simultaneous reading of two or more data tracks in layers 71, 72, ... carriers of different information, and also simultaneous writing and reading on two or more carrier layers. different information. When considering the use of a plurality of diodes 11, 12, ..., laser, simultaneous writing in a plurality of layers 71, 72, ... carriers of information, it is also possible. The apparatus is suitable both for a recording medium that presents information carrying layers with a predetermined and invariable data content, as well as for a recording medium having writable and / or rewritable information carrying layers, for example, which act as a recording medium. according to the phase change system. When considering the use of non-polarized light, in the exemplary mode according to figure 3, it is possible to generate more than two beams 31, 32, ... partial for the purpose of writing or reading.

Claims (9)

1. An apparatus for reading or writing, simultaneously, in different information carrying layers of an optical recording medium having at least two different information carrying layers, the apparatus has a partial beam generating means for generating different partial beams, a medium of focusing to focus the partial beams on different information carrier layers and a detection means for detecting the partial beams, the apparatus is characterized in that at least one partial beam generating means is provided for coupling a partial beam inside and outside a ray pen and a means is provided that affects the beam to independently affect the coupled partial beam.

2. The apparatus as described in claim 1, characterized in that a focusing means is provided as a means affecting the beam for each partial beam.

3. The apparatus as described in claim 2, characterized in that the partial beam generating means is a polarizing beam splitter.

4. The apparatus as described in any of claims 2 and 3, characterized in that a divider is present, at the inputs of which a detector output signal of one of the partial beams is present, on the one hand, and on the other hand , a control signal for the power of the light source is present.

5. The apparatus as described in claim 1, characterized in that a simple focusing means and a means affecting the different beam are provided for a plurality of partial beams.

6. The apparatus as described in claim 5, characterized in that the partial beam generating means has a dedicated light source for each partial beam.

7. The apparatus as described in claim 5 or 6, characterized in that the medium affecting the beam has a collimator lens.

8. The apparatus as described in one of claims 5 to 7, characterized in that the medium affecting the beam has an optical transparent element which is tunable in terms of the refractive index.

9. The apparatus as described in one of the preceding claims, characterized in that the light source and the associated detection means are placed in an optically conjugated position with respect to each other. SUMMARY OF THE INVENTION The present invention relates to an apparatus for reading or writing simultaneously in layers (71, 72 ...) different information carriers of an optical recording medium (7) having at least two layers (71, 72, .. .) carriers of different information, the device has a means (5, 91, 92, ...) partial beam generator to generate beams (31, 32, ...), different partial, a medium (6, 61, 62) to focus the beams ((31, 32, ...) partial on layers (71, 72, ...) different information carriers and a detection means (81, 82, ...) to detect The partial beams (31, 32, ...) The object of the invention is to propose an apparatus of this type which provides a common optical path largely for the individual partial beams (31, 32, ...) and that is nonetheless tolerant with respect to the deviations in the separation of the layers (71, 72, ...) that carry individual information among themselves. n by virtue of the fact that the medium (5, 41, 42, ...) partial beam generator is provided for coupling a partial beam (31, 32, ...) and a medium (61, 62, 22, 23, ...) that affects the beam is provided to independently affect the coupled beam (32, 33, ...) partial. The apparatus according to the invention is suitable for a recording medium having read-only information carrying layers as well as for a recording medium having layers of one-time write information or multiple writes.