Method and apparatus for optically recording and/or reproducing information

Abstract: Disclosed is an optical information recording and/or reproducing system for recording or reproducing information in parallel from a first point towards a second point in which at least (N + 1) numbers of track turns are herein provided between the first and second points on a helical track by converging, when N is an integer being two or larger than two, N numbers of light beams respectively at N numbers of track turns adjacent to each other in the radial direction of the helical track on an optical information recording medium and positioning the light beams to form N numbers of beam spots through an optical system. Any portion of the information by N numbers of beam spots is recorded or reproduced from a third point between the first and second points towards the second point. The beam spots are moved from the second point in the radial direction of the helical track so that at least one or more beam spots of N numbers of beam spots come in front of the first point in a scanning direction of the beam spots. Other segments of the information are recorded or reproduced from the first point towards the third point by using at least one or more beam spots.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to an optical information recording and/or reproducing system and, especially, to an optical information recording and/or reproducing system for recording or reproducing information in parallel on or from a recording medium such as an optical disk by a plurality of laser light sources. Related Background Art In recent years, researches and developments for improving a transfer rate have been energetically conducted with respect to an optical information recording/reproducing apparatus such as a magneto-optic disk apparatus. In the magneto-optic disk apparatus offered as a product at the present, the disk has to make three revolutions for erasing/recording/reproducing (verifying) processes when writing data. The conventional apparatus presents such a defect that especially a data transfer rate during the record is comparatively remarkably inferior to that of a hard disk. Under such circumstances, there were proposed an overwritable information recording medium and an optical information recording/reproducing apparatus capable of overwriting, wherein recording and erasing processes are performed for a duration of one revolution of the disk. Proposed also were an optical information recording/reproducing apparatus for verifying the information immediately after recording by use of a plurality of beam spots and an optical information recording/reproducing apparatus for recording and/or reproducing the information in parallel by employing the plurality of beam spots. For instance, a system for modulating a magnetic field applied to a magneto-optic recording medium in accordance with the information recorded on the recording medium was proposed in the form of a magneto-optic disk apparatus capable of overwriting. Proposed in addition to the above system was a magneto-optic disk apparatus capable of all the erasing/recording/reproducing processes for a duration of one revolution of the disk, thereby enhancing a data processing speed of the magneto-optic disk. This is attained by irradiating the track with a plurality of light beams for use of recording and verifying as well to form beam spots, respectively. Those are all based on a magnetic field modulation overwrite system for recording the information by modulating the magnetic field applied to the magneto-optic recording medium. On the other hand, there was proposed a magneto-optic recording medium which is overwritable by modulating the light beams for writing the information. This recording medium has a structure in which multi-layered magnetic films exhibiting such a characteristic as to have different Curie temperatures and coercive forces are exchange-coupled. The recording medium is employed in the magneto-optic recording/reproducing apparatus of the optical modulation overwrite system. JP-A-4014623 describes a parallel recording and reproduction arrangement wherein two light beams are controlled so that areas of a data track which are not scanned by a first beam during track jumping are scanned subsequently by the second beam. JP-A-6284441 describes an arrangement wherein two optical heads are positioned at diametrically opposed locations in relation to an optical disk, and a helical data track is parallel scanned with alternate track turns scanned by respective heads by performing track jumps at each half revolution of the disc with alternate heads. Further, there was proposed an apparatus for recording and reproducing the information in parallel by forming the plurality of beam spots on track turns adjacent to each other on the magneto-optic recording medium. This apparatus aims at the parallel record and reproduction by use of substantially the same magneto-optic disk apparatus as the conventional one employing the single light source, applying a semiconductor laser array to a light source. In this manner, the magneto-optic disk apparatus is capable of enhancing the data transfer rate up to a hard disk level or higher by exploiting such a characteristic that the optical system is capable of multiplexing the plurality of light beams. There is known, e.g., a technique of recording and reproducing the information by forming beam spots in parallel respectively on a plurality of track turns adjacent to each other in the radial direction of the recording medium when irradiating a magneto-optic recording medium with beams emitted from a semiconductor laser array. In this case, the record and reproduction of the information at a high transfer rate can be easily attained by using the magneto-optic recording medium having a helical track. The following problems, however, arise when the magneto-optic disk apparatus capable of recording and reproducing the information in parallel by use of the plurality of beam spots records and reproduces the information in parallel on and from the magneto-optic recording medium, available as a product of nowadays, having the single helical track. This will be explained with reference to Figs. 1 and 2. Fig. 1 schematically illustrates the magneto-optic recording medium having the helical track. In Fig. 1, the numeral 1 represents a center of revolution; 2 designates a single helical track; and an arrowhead indicates a direction of revolution of the recording medium. Beam spots 3-1, 4-1 of the magneto-optic disk apparatus for recording and reproducing the information in parallel as described above are positioned on track turns adjacent to each other. For instance, it is assumed that the beam spot 3-1 starts recording the information from an arbitrary point A on the magneto-optic recording medium. It is similarly assumed that the beam spot 4-1 starts recording the information from a point B. The points A, B are, as obvious from the Figure, located in close proximity on the track turns adjacent to each other. In this state, when the magneto-optic recording medium makes one revolution, that is, explaining the revolution of this magneto-optic recording medium with the aid of movements of the beam spots, the two beam spots come on the downstream side for one track upon recording the information for one track. More specifically, the beam spot 3-1 reaches the point B, while the beam spot 4-1 comes to the point C. The beams spots moved are expressed by numerals 3-2, 4-2, respectively. If the recording information exists over totally two or more tracks, however, as illustrated in Fig. 2, for example, the beam spot 3-2 is required to effect no overwriting on the information already recorded by the beam spot 4-1 from the point B. For this purpose, the two beam spots have to jump the tracks to adjacent track turns. It is, however, impossible to instantaneously move to the adjacent tracks. Hence, a recordable state is not present till a track jumping time or a tracking servo settling time after jumping has elapsed. This will be explained referring to Fig. 2. The beam spot 3-2 is incapable of recording till the beam spot 3-2 jumps the track from the point B and reaches a point c. The beam spot 4-2 is similarly incapable of recording till the beam spot 4-2 jumps the track from the point C and reaches a point d. Namely, at least a portion (C-c) corresponding to a section L is not effectively used. When the information is continuously recorded on the magneto-optic recording medium, and if continuously recorded on, e.g., an A-E section, the C-c section is blank, or an absolutely different item of preceding information may be left in a case that the magneto-optic recording medium is overwritable. Then, when making an attempt to reproduce the above recording information by the magneto-optic disk apparatus serving as a recording/reproducing means using the single beam spot which is now being manufactured into a product, it can be easily imagined that some drawbacks appear therein. That is, it is difficult to keep a compatibility between the magneto-optic disk apparatus capable of recording and reproducing the information in parallel and the magneto-optic disk apparatus based on the single beam spot. This is quite inconvenient. Further, a wait for revolution without jumping the track may be possible for avoiding the above-stated situation till the beam spot 3-2 reaches the point C, and the beam spot 4-2 comes to the point D. If done so, however, there will be lost a significance that the transfer rate is enhanced by simultaneously recording and/or reproducing the information by the plurality of beam spots. SUMMARY OF THE INVENTION It is a primary object of the present invention, which has been devised in the light of the above problems, to provide an optical information recording and/or reproducing system (apparatus) for efficiently recording and reproducing information in parallel, in which no invalid recording area is produced even when jumping tracks. Further, according to the present invention, the compatibility with an apparatus for recording or reproducing the information by a single light beam can be maintained. According to a first aspect of the present invention there is provided a method for performing at least one of the functions of recording and reproducing information in parallel from a first point to a second point on a helical track of an optical information recording medium, at least N + 1 track turns being provided between the first and second points, by converging N radially aligned light beams respectively on N track turns adjacent to each other in the radial direction of the helical track to form N first beam spots by an optical system, where N is an integer equal to or greater than two, the method characterised by comprising the steps of: a) recording or reproducing a first portion of the information by scanning one or more of the N first beam spots along respective track turns of the helical track to scan the track from a third point situated between the first and second points to the second point, b) moving the N first beam spots in the radial direction of the helical track so that at least one of the N first beam spots is situated in front of the first point in the scanning direction of the beam spots along the helical track, and c) recording or reproducing the remainder of the information by scanning the helical track from the first point to the third point with a respective first beam spot scanning each track turn. According to a second aspect of the invention, there is provided an apparatus for performing at least one of the functions of recording and reproducing information in parallel from a first point to a second point on a helical track of an optical information recording medium ( ), wherein N + 1 track turns are provided between the first and second points and N is an integer equal to or greater than two, the apparatus comprising means for forming N light beams and an optical system to form N first beam spots to respectively irradiate N track turns which are adjacent to each other in the radial direction of the track, the apparatus further comprising: first controlling means for controlling the apparatus to record or reproduce a first part of the information by scanning one or more of the first beam spots along respective track turns of the helical track to scan the track from a third point situated between the first and second points to the second point; moving means for moving the N first beam spots in the radial direction of the helical track so that at least one of the first beam spots is situated in front of the first point in the scanning direction of the beam spots along the helical track; and second controlling means for controlling the apparatus to record or reproduce the remainder of the information by scanning the helical path from the first point to the third point with a respective first beam spot scanning each track turn. Other systems and constructions of the present invention will become apparent during the following discussion. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is an explanatory view showing a conventional problem in the prior art; Fig. 2 is an explanatory view showing a conventional problem in the prior art; Fig. 3 is an explanatory view illustrating an information recording/reproducing system of this invention; Fig. 4 is an explanatory view illustrating the information recording/reproducing system of this invention; Fig. 5 is an explanatory view illustrating the information recording/reproducing system of this invention; Fig. 6 is an explanatory view illustrating the information recording/reproducing system of this invention; Fig. 7 is an explanatory view illustrating the information recording/reproducing system of this invention; Fig. 8 is an explanatory view showing a compatibility between a recording medium according to the present invention and a conventional apparatus; Fig. 9 is a view showing a construction of an information recording and/or reproducing apparatus of this invention; Fig. 10 is an explanatory view showing optimization of the information recording/reproducing system of this invention; Fig. 11 is an explanatory view showing the optimization of the information recording/reproducing system of this invention; Fig. 12 is an explanatory view showing the optimization of the information recording/reproducing system of this invention; Fig. 13 is an explanatory view showing the optimization of the information recording/reproducing system of this invention; Fig. 14 is an explanatory view showing the optimization of the information recording/reproducing system of an embodiment; Fig. 15 is an explanatory view showing the optimization of the information recording/reproducing system of an embodiment; Fig. 16 is a view illustrating a light source in an embodiment of this invention; Fig. 17 is a view illustrating an optical system of the embodiment of this invention; Fig. 18 is an explanatory view showing a placement of beam spots on a recording medium in the embodiment of this invention; Fig. 19 is an explanatory view showing an RF/servo signal detecting method in the embodiment of this invention; and Fig. 20 is an explanatory view showing how the information recording/reproducing system of this invention is applied. DESCRIPTION OF THE PREFERRED EMBODIMENT A first embodiment of the present invention will hereinafter be described in detail with reference to Figs. 3 through 9. To start with, a recording system according to this invention will be discussed in terms of principle with reference to Figs. 3 to 6. For instance, Fig. 6 schematically illustrates a magneto-optic recording medium defined as an optical information recording medium having a single helical track 2 identical with the one shown in Figs. 1 and 2. Herein, points A to E irradiated with beam spots are located astride four track turns adjacent to each other. Now, it is considered that continuous bits of information on one or more track turns are to be recorded. The information, it is assumed, starts at A and ends at E via B, C, D in sequence. The point B is located at more downstream of the track than the point A as well as on the track turn substantially adjacent to the point A. The point C lies in still more downstream of the track and on the track turn adjacent to the point B. The point C lies in such a position that a more downstream side than B is reachable by jumping the track to the adjacent track turn positioned at more upstream of the track than C. Similarly, the point D is located on the downstream track turn adjacent to C. The point E is also located on the downstream track turn adjacent to D. According to the recording system of this invention on the magneto-optic recording medium, at the first onset, as depicted in Fig. 3, two beam spots 3-1, 4-1 are disposed adjacent to each other and astride the two track turns. The beam spots 3-1, 4-1 simultaneously start recording in parallel from the above-mentioned points C, D. That is, the record is started from a mid-part of continuous bits of information A to E. As in the same way with Figs. 1 and 2, revolutions of an optical disk will be explained with the aid of movements of the beam spots. When finishing the record for one-track, the beam spot 3-1 comes to the point D, while the beam spot 4-1 reaches the point E. The beam spots at that moment are expressed by numerals 3-2, 4-2, respectively. Next, the beam spot 3-2 jumps the track so as not to be overwritten with the information already recorded by the beam spot 4-1. This situation is illustrated in Fig. 4. Herein, the beam spots 3-2, 4-2 located at D, E jump the tracks over to respective points a, b located at upstream by 3 track turns. The points a, b are located at more upstream by L than A, B. Herein, L is identical with the quantity L explained in Figs. 1 and 2. L corresponds to a track jumping time or a settling time of a tracking servo after jumping and is just a distance at which the beam spot moves for that time. A, B are points at which the beam spots 3-3, 4-3 moving to the points a, b become capable of recording and resume the record. From these points, there is recorded the information (from the beginning to the mid-part) preceding to the recorded information (from the mid-part to the end). In consequence, as illustrated in Fig. 5, the beam spots 3-4, 4-4 resuming the record from the points A, B record the information of approximately one track, The former beam spot finishes recording all at the point B (a beam spot 3-5), while the latter beam spot finishes recording all at the point C (a beam spot 4-5). The record of the information existing astride about 4 track turns across points A to E shown in Fig. 6 can be thereby completed. Next, a process of recording the information will be explained in a time sequence by referring Fig. 7. The beam spots 3-1 through 3-5 in Figs. 3 to 6 are all the same and are therefore, in Fig. 7, shown as a beam spot 3. Similarly, the beam spots 4-1 through 4-5 are expressed as a beam spot 4. Then, the information recorded on the recording medium is expressed in the form of data sequences BLK1 to BLK4. A to E represents individual points on the track of the recording medium and relate Figs. 3 to 6 to Fig. 7. The axis of abscissa in Fig. 7 indicates a time T. When T = t 1 , the beam spot 3 records the data sequence BLK3 from the point C, while the beam spot 4 records the data sequence BLK4 from the point D. When T = t 2 , the recording medium makes one revolution. The beam spot 3 reaches D, and the beam spot 4 comes to E. Then, the track jumping action continues till T = t 3 , but no recording is performed during a time given by Δt = t 3 - t 2 . When T = t 3 , the beam spot 3 reaches the point A, while the beam spot 4 reaches the point B. Accordingly, the data sequences BLK 1, BLK 2 are recorded therefrom. When T = t 4 , the beam spot 4 reaches C and completes recording. When T = t 5 immediately thereafter, the beam spot 3 comes to B and similarly finishes recording. It therefore follows that the information existing astride approximately four track turns is recorded in about one-half of the time when using the normal single beam spot. The thus recorded bits of information are physically arranged in sequence such as BLK1 to BLK4 up to the points A to E. Therefore, for instance, when reproducing the data by means of a magneto-optic disk apparatus for recording/reproducing the data with the single beam spot, the data sequences BLK1 to BLK 4 continuous to the points A to E on the recording medium can be, as illustrated in Fig. 8, recorded in this order. The magneto-optic disk apparatus adopting the system according to this invention will be explained with reference to Fig. 9. Paying attention to Fig. 9, the numeral 5 designates a host device, e.g., a host computer for imparting the information to be recorded and reproduced by the magneto-optic apparatus of this invention. A buffer memory 6 temporarily stores the information given from the host device 5. A control means 7 properly determines a recording or reproducing permutation of the information from an information quantity thereof for parallel record and reproduction. A magneto-optic head driving means 8 positions a plurality of beam spots on a plurality of track turns adjacent to each other with the intention of recording and reproducing the information in parallel. When the information to be recorded is prepared for, e.g., four tracks, the control means 7 divides the information into the data sequences BLK1 to BLK4 as explained so far in Figs. 3 to 8. The magneto-optic head driving means 8 is operated to effect the parallel record on the recording medium. Further, in the case of reproducing the recorded information, the magneto-optic head driving means 8 is operated to reproduce the data sequences in the same order as recording . The bits of information are rearranged correctly in BLK1 to BLK4 and stored on the buffer 6. As described above, absolutely in the same way as that explained in Figs. 3 to 8, the control means 7 works for reading and reproducing the information in parallel by use of the plurality of beam spots. Now, there has been explained the example where the information can be recorded and reproduced at the highest efficiency with reference to Figs. 3 to 8. As a matter of fact, however, the information quantity is not restricted to the quantity for the four tracks, but various information quantities may be given. Then, some consideration will be given to an efficient magneto-optic recording/reproducing system using the plurality (two) of beam spots. To begin with, when the information has its quantity smaller than one track, there is no merit of performing the parallel record and reproduction with the two beam spots. It is therefore better to execute the parallel record and reproduction with only one beam spot. Further, if the information quantity is larger than one track but equal to or smaller than or equal to two tracks, as explained in the conventional example, the information is partitioned into the data sequences BLK1, BLK2. The respective data sequences are recorded and reproduced in parallel by employing the beam spots, 3, 4 (see Fig. 1). Then, if the information quantity is larger than two tracks but less than three tracks, the system of this invention becomes effective. Namely, for simplicity, it is considered that the information existing astride the three track turns is recorded and reproduced in parallel, a system shown in Figs. 10, 11 will be exemplified. Turning to Fig. 10, the information continues astride the three track turns across the points A to D. It is assumed that the information starts at A and ends at D via B, C in sequence. A positional relationship between the points A to D on the track is the same as that explained in Figs. 3 to 6. This information is, as depicted in Fig. 11, partitioned into the data sequences BLK1 to BLK3. When T = t 1 , the record (reproduction) is started from BLK3 by using only the beam spot 3 (3-1 in Fig. 10). At this point of time, a beam spot 4 may not be lit up or may be lit up at a reproducing power level. After finishing the record (reproduction) for one track, and when T = t 2 , the beam spot 3 reaches the point D. Then, the beam spots jump three track turns (not illustrated in Fig. 10). The beam spot 3 thus moves upstream of the point A. The beam spot 4 moves upstream of the point B. When T = t 3 , the beam spots 3, 4 come to A, B. Hereat, the record (reproduction) is started (shown by the beam spots 3-2, 4-2 in Fig. 10). Thereafter, the beam spots 3, 4 record (reproduce) the data sequences BLK1, BLK2. When T =t 4 , the beam spot 4 reaches C, thereby finishing the record (reproduction). When T = t 5 , the beam spot 3 reaches B, similarly the record (reproduction) is ended. Further, when T =t 1 , the record (reproduction) may be started from BLK3 by using only the beam spot 4 instead of the beam spot 3. In this case, when T =t 2 , the beam spot 4 comes to D. Hereat, the beam spot may jump two track turns towards in the upstream direction (the action is hereafter the same as the above-mentioned). Figs. 12 and 13 illustrate a second system when the information quantity is less than three tracks. Paying attention to Fig. 12, the information is continuous astride the three track turns across the points A to D. It is presumed that the information starts at A and ends at D via B, C in sequence. A difference from Figs. 3 to 6 is herein that the point B is located at more upstream than C and in close proximity to the point C on the adjacent track turn. The information is as illustrated in Fig. 13, partitioned into data sequences BLK1 - BLK3. When T = t 1 , Recording (reproducing) is initiated respectively from BLK2, BLK3 by using the beam spots 3, 4 (3-1, 4-1 in Fig. 12). When T = t 2 , the record (reproduction) for one track is ended. The spots 3, 4, when reaching C, D respectively, jump by three tracks (not shown in Fig. 12). The beam spot 4 moves upstream of the point A. At this time, a light source corresponding to the beam spot 3 may not be lit up or may be lit up at the reproducing power level. When T = t 3 , the beam spot 4, when coming to A, starts recording (reproducing) (the beam spot 4-2 in Fig. 12). Thereafter, the beam spot records (reproduces) the data sequence BLK1. When T = t 4 , the beam spot 4 finishes recording (reproducing) upon reaching the point B. In this case, substantially when T = t 3 - t 4 , the parallel recording/reproducing process is not conducted. Further, when T = t 3 , the data sequence BLK1 may be recorded (reproduced) by using only the beam spot 3 in place of the beam spot 4. In this instance, when T = t 2 , the beam spot 3 may jump two tracks in the upstream direction upon reaching C. At this moment, a light source corresponding to the beam spot 4 may not be lit up or may be lit up at the reproducing power level. Additionally, in the meantime, the verification may be performed by employing the beam spot 4. The present invention has been explained so far. However, The first and second systems are, it can not be said, expedient measures in terms of being applied to recording and reproducing a slightly larger amount of information than two tracks. The reason for this will be elucidated by considering that the data sequence is shortened in Figs. 11 and 13. It is because there increases a revolution wait time till the beam spots 3, 4 jump the tracks and then reach the points A, B respectively after finishing the record and reproduction of the data sequence BLK3 according to the first system. Further, according to the second system, there decreases a time for effecting the parallel record and reproduction when T = t 1 - t 2 . Under such circumstances, a third system adoptable would be adoptable which does not however fall within the scope of the invention. Figs. 14 and 15 show this system. Referring to Fig. 14, the information is continuous astride three track turns across the points A to D. It is assumed that the information starts at A and ends at D via B, C in sequence. The points A to D have such a relationship that the respective points are located in close proximity to the track turns adjacent to each other. The recording information is herein, as illustrated in Fig. 15, partitioned into data sequences BLK1, BLK2. When T = t 1 , the beam spots 3, 4 (the beam spots 3-1, 4-1 in Fig. 14) start recording (reproducing) the data sequences BLK1, BLK2 from the points A, B, respectively. When T = t 2 , the record (reproduction) for one track is ended. When the beam spots 3, 4 (beam spots 3-2, 4-2 in Fig. 14) reach the points B, C, the light source for the beam spot 3 is extinguished or set the reproducing power level so that the information already recorded by the beam spot 4 is not overwritten by the beam spot 3. When T = t 3 , the beam spot 4 continues the record (reproduction) as it is till reaching point D. With this operation, no parallel record and reproduction is not executed during T = t 2 - t 3 . Unlike the first and second systems, there is no necessity for jumping the tracks, and, even if the data sequence BLK2 is shortened, the efficiency does not drop down. However, if the information quantity is equal to or larger than three track but less than four tracks, there may be employed the system in the first embodiment of this invention, which has already been explained in Figs. 3 to 6. Besides, if the information quantity is equal to or larger than four tracks, the system of this invention, which has already been stated in Figs. 3 to 6, may be used. For remaining tracks, the systems (first through third systems) in the above cases may be applied. As discussed above, the control means 7 judges the optimum recording/reproducing system corresponding to the information quantity. The magneto-optic disk apparatus using the plurality of beam spots are capable of performing the parallel record and reproduction by operating the magneto-optic head driving means 8. Besides, the information recorded by this magneto-optic disk apparatus does not exhibit drawbacks at all even if reproduced by the conventional magneto-optic disk apparatus having the single beam spot. Further, the embodiments explained above have dealt with the case where the information is recorded and reproduced by use of the two beam spots according to the present invention. However, this invention is, as a matter of course, applicable to a case where the parallel record and reproduction are performed by employing N numbers of (three or more) beam spots. For example, when using the N numbers of beam spots for recording and reproducing the information extending over 2N sets of track turns, the information is partitioned into 2N sets of data sequences. The second half of the data sequences is recorded and reproduced in advance. Next, track-jumping (N + 1) numbers of tracks on the upstream side is carried out. The first half of the data sequences may be recorded and reproduced. If done so, it is possible to efficiently record and reproduce the information extending over approximately 2N numbers of tracks. Simultaneously, this is done keeping the compatibility with the magneto-optic disk apparatus having the single beam spot. Further, similarly, the recording/reproducing systems optimal to a variety of information quantities can be applied to the arrangement of using the N numbers of beam spots. The information extending over the N numbers of tracks may be at first recorded and reproduced by the second system stated above by partitioning the information into N numbers of data sequences. If the information quantity is less than the N numbers of tracks, there may be applied a parallel recording/reproducing system sequentially employing beam spots N-1, N-2,... The information quantity is more than the N numbers of tracks but less than the 2N numbers of tracks, the above recording/reproducing system is readily generalized and thus applicable. In the case of the (N + 1) numbers of tracks, the third system stated above can be applied. More specifically, when partitioning the information into the N-sets of data sequences, the record and reproduction of the data sequences longer than or equal to one track may be assigned to the beam spot located downstream most. In the case of (N + 2) numbers of tracks, the information is partitioned into (N + 2) sets of data sequences. The N numbers of data sequences in the second half thereof are previously recorded and reproduced. Next, the track-jumping is employed at effected upstream. Substantially two beam spots are capable of recording and reproducing the information for two tracks in parallel. Similarly considering, in the case of the (N + 3) numbers through (2N) numbers of tracks, after jumping the tracks, the number of beam spots for effecting the parallel record and reproduction may be incremented by ones till it numbers N. Further, the recording/reproducing system of this invention exhibits much more effects in combination with an overwrite technique and a direct verify technique. Another embodiment of the present invention will next be discussed with reference to Figs. 16 to 20. To begin with, Fig. 16 illustrates a configuration of a semiconductor laser array serving as a light source unit of the magneto-optic disk apparatus of this invention. A semiconductor laser array chip 17 includes, e.g., four light emitting points 11 to 14. The four light emitting points are constructed on the same n-type GaAs substrate 15. The substrate has two heights in arrowed directions. A typical internal stripe semiconductor laser structure is formed on this substrate. The chip construction of each semiconductor laser will be explained through the one including the light emitting point 11 as a representative thereof. For instance, the numeral 11-2 designates a positive electrode; 11-3 is a p-type GaAs cap layer; 11-4 is an upper clad layer of p-type GaAlAs; 11-5 is an active layer of n-type GaAlAs; 11-6 is a lower clad layer of n-type GaAlAs; and 11-7 is a current block layer of p-type GaAlAs. Further, the numeral 16 denotes a negative electrode. A construction of each laser chip including light emitting points 12 to 14 is also the same as the above-mentioned. Note that a V-shaped groove formed between the light emitting points is intended to shield a thermal electrical crosswalk between the adjacent light emitting points. For example, as illustrated in Fig. 16, the light emitting points 11, 13 among the four light emitting points 11 to 14 are formed on the substrates flush with each other. The light emitting points 12, 14 among them are also formed on the substrates flush with each other. Let d be the relative height difference therebetween, and let D be the interval between the light emitting points. Fig. 17 depicts a construction of the magneto-optic disk apparatus using the semiconductor laser array chip 17 of Fig. 16. Beams of light outgoing from the semiconductor laser array chip 17 are collimated by a collimator lens 18. The collimated beam penetrates a polarizing beam splitter 19, wherein an anisotropic beam configuration is shaped. The shaped beams are imaged through an objective lens 20 in the form of four microbeam spots on a magnetic film surface 22 of a magneto-optic disk 21 capable of, e.g., optical modulation overwriting. Herein, an arrowhead 23 indicates a track direction on the magneto-optic disk. Next, the beam spots on a magneto-optic disk 21 will be explained with reference to Fig. 18. The light emitting points 11 to 14 are imaged in the form of microbeam spots 32 to 35 on arbitrary adjacent track turns 36, 37 through the optical system of Fig. 17. The light emitting point 11 corresponds to beam spot 32 for overwriting on the track 36 in Fig. 18. The light emitting point 12 corresponds to the beam spot 33 for direct verifying. The light emitting point 13 corresponds to the over write beam spot on the track 37. Then, the light emitting point 14 corresponds to the direct verify beam spot 35. The numerals 38 to 40 designate guide grooves for tracking, and a track-to-track pitch is expressed by P. For instance, the light emitting points 11, 12 and the light emitting points 13, 14 are located on the track turns adjacent to each other. For this purpose, the semiconductor laser array chip 17 in Fig. 17 may be turned by a small angle  from a track direction 23. The beams emitted from the semiconductor laser 17 are, as illustrated in Fig. 17, polarized substantially in arrowed directions on the sheet of drawing. Selected is a beam splitter exhibiting such a characteristic as to reflect, e.g., S-polarized light at almost 100%. With this arrangement, the beams are substantially collimated in the track directions 23 on the magneto-optic disk 21. For positioning two couples of beam spots on the track turns adjacent to each other, the necessary physical quantity for the optical system may be set as follows. To be specific, let f 1 be the focal length of the collimator lens, and let f 2 be the focal length of the objective lens. A lateral magnification of the optical system is given by f 2 /f 1 in the radial direction. Hence, an interval between the beam spots in the radial direction is given substantially by the following formula: 2 d • f 2 f 1 = P Therefore, if the track P is predetermined, the equation is: d = f 1 2 f 2 • P For example, when P = 1.5 µm, f = 8 mm, and f 2 = 3 mm, the height difference is given such as d = 2 µm. The rotational angle is approximately 1.4°. Note that d' in Fig. 18 expresses that the height difference in Fig. 16 is imaged on the track of the magneto-optic disk 21 through the optical system shown in Fig. 17. A beam spot interval ℓ in the track direction is expressed by the following formula: ℓ = f 2 α f 1 • D where α is the beam shaping ratio. In this case, when D = 80 µm, f 1 = 8 mm, f 2 = 3 mm, and α = 2, the beam spot interval ℓ is given by ℓ = 15 µm. If it is presumed the magneto-optic recording medium 21 is capable of optical modulation overwriting, the beam spots 32, 34 are respectively formed on the tracks 36, 37 when overwritten in a state where a bias magnetic field is applied (not shown). On this occasion, however, the light source involves the use of comparatively high power level binary optical pulses P 1 , P 2 (P 1 > P 2 ) for writing the information. Then, magneto-optic pits having vertical magnetization directed opposite to each other are formed on the track, corresponding to high-and-low levels of the optical pulses. Further, the beam spots 33, 35 respectively correspond to the beam spots 32, 34 in order to read the information written by the beam spots 32, 34. The light source employed herein involves the use of a beam of a fixed value P 3 (P 2 > P 3 ) of a comparatively low power level. The information immediately after being recorded is thereby reproduced (directly verified). Note that P 1 to P 3 are light quantities on the magneto-optic recording medium 21. Given next is an explanation of a method for detecting an RF signal and a servo signal through the optical system of Fig. 17. The beams by which four beam spots 32 to 35 are formed on the magneto-optic disk 21 are reflected by a magnetic film 22. The reflected beams pass through the objective lens 20 and become collimated ones. Subsequently, the beams are further reflected by the polarizing beam splitter 19 and led to an RF signal/servo signal detection system. At this time, polarizing characteristics of the polarizing beam splitter 19 are set such that a P-polarized light reflectivity R P = 10 - 30%, and an S-polarized light reflectivity R S = 100%. Then, the Kerr rotational angle is increased, whereby the detection exhibiting a high S/N ratio can be attained. Turned by 45° is a polarizing direction of the beam passing through a halfwave plate 24 the optical axis of which is twisted through 22.5° with respect to the P-polarized light component. The beam passing through a condenser lens 25, a cylindrical lens 26 and a polarizing beam splitter 27 is split into two beams. The split beams are respectively led to photodetectors 28, 29. Note that the cylindrical lens 26 is interposed for taking an autofocus (AF) by an astigmatism method, and a bus is twisted by 45° in the track direction 23. Next, by referring Fig. 19 there will be explained photodetectors 28, 29 and a method for detecting the beam spots on the photodetectors and the RF/servo signals. The photodetector 28 consists of four light receiving areas 41 to 44. The light receiving area 41 is divided into subareas 41-1 through 41-4. Beam spots 45 to 48 corresponding to the beam spots 32 to 35 on the magneto-optic disk 21 are imaged in the respective light receiving areas. When the focal length f 3 of the condenser lens is set to 30 mm, each beam spot interval is approximately 150 µm. Similarly the photodetector 29 also consists of four light receiving areas 49 to 52. The light receiving area 49 is a quadrant sensor. Beam spots 53 to 56 corresponding to the beam spots 32 to 35 are imaged in the respective light receiving areas. The beam spot on the photodetector is shown as the one approximate to a minimum scatterd circle of confusion of the cylindrical lens 26. This is a state of being correctly AF-controlled (autofocus controlled). In accordance with an embodiment of Fig. 19, the beam spot 32 on the magneto-optic disk, i.e., the beam spots 45, 53 on the photodetectors are employed for detecting the servo signals. A focus error signal involves the use of a difference signal of a diagonal sum of the quadrant sensor. Further, an AF signal in the sensor 41 uses a suffix put on the sensor and is expressed by the following formula: AF 1 = (1 + 3) - (2 + 4) In addition, when taking the AF signal by use of an output of the sensor 49, the AF signal also employs the suffix put on the sensor and is expressed by the following formula (this is not shown, and the numerals are marked with (') in distinction from the formula (3)). AF 2 = (1' + 3') - (2' + 4') The AF signal may be generated by using the outputs of both of the formulae (3) and (4) AF = AF 1 + AF 2 When set as expressed by the formula (5), a focus offset caused due to a birefringence of the maneto-optic disk 21 can be effectively prevented. Further, an auto tracking (AT) signal involves the use of a difference signal of the sensor divided by dividing lines extending in the track direction (push-pull method). The AT signal in the sensor 41 is expressed by the following formula (6) using the suffix put on the sensor. AT 1 = (2 + 3) - (1 + 4) Herein, as in the case of the AF signal, the output of the sensor 49 may be employed, or the outputs of both of the sensors 41 and 49 may also be used. There has been already proposed a method of stably applying the tracking servo to the plurality of beam spots. Next, the system for detecting the RF signal will be explained. The beam spots 32, 34 are at first formed on the magneto-optic disk when overwritten. Then, the information immediately after being recorded is reproduced by using the beam spots 33, 35 (beam spots 46, 54 and 48, 56 on the photodetectors) while writing the information thereon. In this case, the information from the beam spot 33 serves to differentially amplify outputs of the photodetectors 42, 50 by using a differential amplifier 58. The information from the beam spot 35 serves to differentially amplify outputs of the photodetectors 44, 52 by using a differential amplifier 60. As a result, magneto-optic signals 62, 64 can be obtained. When normally reproduced, the information is reproduced by the beam spots 33, 35 while taking the servo with the beam spot 32 on the magneto-optic disk. On this occasion, the light source corresponding to the beam spot 34 may not be lit up. If done in this way, the beam spots 32, 34 can be dedicated to only OW (overwriting) (the beam spot 32 is also used for detecting the servo signal). It therefore follows that laser noise reducing means (high-frequency superposition, etc.) may be provided for only the beam spots 33, 35. Further, the servo and RF can be made independent, and, hence, there is no necessity for fetching the feeble magneto-optic signals out of the divided sensors like the sensors 41, 49. This is advantageous in terms of thermal noises of a pre-amplifier (the quadrant sensor is provided with the independent pre-amplifier, and, when detecting the magneto-optic signal therefrom, the thermal noises are doubled). In addition, preformatted address information on the magneto-optic disk 21 may be read by the beam spots 32, 34 apart from the magneto-optic signal. In this instance, the information from the beam spot 32 serves to amplify a sum signal of the photodetector 41 and a sum signal output of the photodetector 49 by using an adder 57. The information from the beam spot 34 serves to amplify outputs of the photodetectors 43, 51 through an adder 59. Preformat signals 61, 63 can be thereby obtained. As explained above, when the system according to the present invention is applied to the magneto-optic disk apparatus capable of overwriting and direct verifying, an information transfer rate can be further improved. Considered referring to Fig. 20 is a case where the continuous information existing astride four tracks across the points A to E is overwritten on and, immediately after this, verified from the medium having the single helical track identical with that in Figs. 3 to 6. Turning to Fig. 20, the four beam spots 32, 33, 34, 35 are expressed respectively by the symbols OW1, DV (direct verify)1, OW2, DV2. Herein, the information is divided into four sets of data sequences BLK1 to BLK4. Recording and reproducing are assigned to each beam spot. When T = t 1 , the beam spot OW1 starts overwriting the data sequence BLK3 from the point C. The beam spot DV1 reaches the point C after a time corresponding to a beam spot interval δt has elapsed and starts verifying the data immediately after recording. Besides, the beam spot OW2 starts overwriting the data sequence BLK4 after δt from D. The beam spot DV2 comes to D after δt and starts verifying the data immediately after recording. In accordance with this embodiment, the beam spot interval is substantially 15 µm, and, therefore, δ is well shorter than a time for which the beam spot passes through one sector. If the magneto-optic disk 21 makes one revolution, the beam OW1 reaches D and finishes overwriting BLK3. Hereafter, the beam spots finish overwriting and verifying the data at intervals of δt (T = t 2 ). Then, the four beam spots jump by three tracks in the upstream direction. The beam spots OW1, DV1 moves upstream of the point A, while OW2, DV2 move towards upstream of the point B. A moving time or a settling time of the beam spot is given by Δt = t 3 - t 2 . When T = t 3 , OW1 at first reaches A and starts overwriting the data sequence BLK1. Hereafter, DV1, OW2, DV2 starts overwriting and verifying the data at intervals of δt. When the magneto-optic disk 21 further makes one revolution, the beam spot OW2 at first reaches point C and finishes overwriting the data sequence BLK2. Hereafter, the beam spots DV2, OW1, OW2 sequentially finish overwriting and verifying the data (T = t 4 ). In this manner, the magneto-optic disk apparatus available as a current product, which has the single beam spot, makes three revolutions for deleting/recording/verifying per one track, thus recording and reproducing the information. As compared with this, the apparatus in accordance with the embodiment explained above is capable of recording and reproducing the information through one revolution per one track. Further, the conventional apparatus requires a time for 12 revolutions of the disk to record and reproduce the information by the 4 track turns. In comparison with this, according to the present invention, merely two revolutions of the disk may suffice by enhancing the recording/reproducing efficiency. Hence, a transfer rate can be improved six times at the maximum. As stated in detail, the use of the system according to this invention exhibits the following excellent effects. The optical information recording/reproducing apparatus such as the magneto-optic disk apparatus records and reproduces the information in parallel on and from the recording medium including the helical track by using the plurality of beam spots. The same apparatus is capable of recording and reproducing a comparatively large quantity of information extending over several tracks most efficiently. Besides, the information recorded can be reproduced by the optical disk apparatus having the single beam spot. It is apparent that, in this invention, a wide range of different working modes can be formed based on the invention without deviating from the scope of the invention, as defined by the appended claims.

Claims: A method for performing at least one of the functions of recording and reproducing information in parallel from a first point (A) to a second point (E) on a helical track (2) of an optical information recording medium, at least N + 1 track turns being provided between the first and second points, by converging N radially aligned light beams respectively on N track turns adjacent to each other in the radial direction of the helical track to form N first beam spots (3,4,32,34) by an optical system, where N is an integer equal to or greater than two, the method characterised by comprising the steps of: a) recording or reproducing a first portion of the information by scanning one or more of the N first beam spots (3,4,32,34) along respective track turns of the helical track to scan the track from a third point (C) situated between the first and second points to the second point (E), b) moving the N first beam spots in the radial direction of the helical track (2) so that at least one of the N first beam spots (3,4,32,34) is situated in front of the first point (A) in the scanning direction of the beam spots along the helical track, and c) recording or reproducing the remainder of the information by scanning the helical track (2) from the first point (A) to the third point (C) with a respective first beam spot (3,4,32,34) scanning each track turn. A method according to claim 1, wherein in step a) each of the first beam spots (3,4,32,34) scans a respective track turn. A method according to claim 1 or claim 2 wherein in step b) the first beam spots (3,4,32,34) are moved to positions wherein only one first beam spot is in front of the first point (A). A method according to any preceding claim further comprising the steps of: providing N second beam spots (33,35) to irradiate each of the N track turns respectively at a location immediately behind each of the N first beam spots (3,4,32,34) in the scanning direction of the beam spots along the track (2); detecting light reflected from the second beam spots (33,35) while the first beam spots (32,34) are recording information; and verifying the recorded information on the basis of the reflected light from the second beam spots (33,35). Apparatus for performing at least one of the functions of recording and reproducing information in parallel from a first point (A) to a second point (E) on a helical track (2) of an optical information recording medium, wherein N + 1 track turns are provided between the first and second points and N is an integer equal to or greater than two, the apparatus comprising means (17) for forming N light beams and an optical system (19,20) to form N first beam spots (3,4,32,34) to respectively irradiate N track turns which are adjacent to each other in the radial direction of the track (2), the apparatus characterised by comprising: first controlling means (7,8) for controlling the apparatus to record or reproduce a first part of the information (BLK3, BLK4) by scanning one or more of the first beam spots (3,4,32,34) along respective track turns of the helical track (2) to scan the track from a third point (C) situated between the first and second points to the second point (E); moving means (8) for moving the N first beam spots in the radial direction of the helical track (2) so that at least one of the first beam spots (3-1,4-1,32,34) is situated in front of the first point (A) in the scanning direction of the beam spots along the helical track (2); and second controlling means (7,8) for controlling the apparatus to record or reproduce the remainder of the information (BLK1, BLK2) by scanning the helical path (2) from the first point (A) to the third point (C) with a respective first beam spot (3-1,4-1,32,34) scanning each track turn. An apparatus according to claim 5 further comprising means for providing N second beam spots (33,35) to irradiate each of the N track turns respectively at a location immediately behind each of the first beam spots (3,4,32,34) in the scanning direction of the beam spots along the track (2); means for detecting light reflected from the second beam spots (33,35) while the first beam spots (32,34) are recording information (BLK1, BLK2, BLK3, BLK4); and means for verifying the recorded information on the basis of the reflected light from the second beam spots (33,35).

Inventors: KOYAMA OSAMU, KOYAMA, OSAMU, KOYAMA, OSAMU, C/O CANON KABUSHIKI KAISHA
Applicants: CANON KK, CANON KABUSHIKI KAISHA
Application year: 1993
Main classification: G11B7
IPC codes: G11B7, G11B11