Information recording medium

Abstract: An information recording medium has a spiral or concentric groove structure along tracks formed on a disk-like substrate wherein each of the tracks is divided into a plurality of recording units, each of the recording units includes a blank portion in a circumferential direction of the groove structure, the groove structure is formed with a wobble in a fixed cycle in a radial direction, and either each length of the recording units is an integer multiple of a cycle of the wobble or the blank portion is so formed that a phase of the wobble formed on the blank portion is continued with a phase of the wobble of the groove structure within another recording unit adjacent to the blank portion.

Description: BACKGROUND OF THE INVENTION The present invention relates to information recording media, and particularly to a high-density information recording medium and a high-density optical recording medium of which the track width is smaller than a beam spot or a detecting means such as a magnetic head. Japanese laid-open patent publication No. 6-176404, for example, describes an example of a high-density (narrow track) recording medium. This example uses as a recording medium an optical recording medium in which groove portions and land portions are formed on a substrate and information recording areas are formed on both of the groove portions and the land portions. Prepits are formed on a virtual prolonged line of a boundary portion between the groove portion and the land portion as identification information of a recording unit (sector), whereby recording information is recorded on both of the groove portions and the land portions and identification (address) information indicative of a recording area is handled by the prepits. Also, one prepit commonly uses address information for a pair of groove portion and land portion. According to this system, when the recording medium of this system is applied to a phase change type recording medium and a magneto-optical recording medium, information from the adjacent land portion or groove portion can be prevented from being mixed into the groove portion and the land portion owing to an interference effect caused within the beam spot (i.e. crosstalk can be cancelled out), and hence the tracks of the recording medium can be narrowed, thereby making a high-density recording become possible. However, in the example according to the related art, inasmuch as information indicative of the position on the information recording medium is concentrated in the prepit portions and the prepit portions located in a discrete fashion, position information cannot be obtained from portions other than the prepit portions. As a consequence, it is difficult to control a rotational speed of a disk precisely with a high reliability. There is then presented the problem from a reliability standpoint that the recording medium according to the relate art is not persistent to, in particular, defects or the like. Japanese laid-open patent publication No. 6-243468 describes a technology in which grooves are wobbled and a linear velocity of a disk is calculated by a wobble cycle detecting circuit, thereby rotating the disk at a constant linear velocity (CLV). GB2016744, against which claim 1 is delimited, discloses a method and apparatus for writing on a record carrier. The record carrier has a structure from which a clocking signal is derived for controlling the rotation speed of the carrier. This structure may be 1) a sequence of pits in the sector address, for which the corresponding track portions are not wobbled, or 2) a servo track comprising a sector address, having address and sync portions, and a track portion for writing in which both sector address and track portions have a wobbled groove structure, and in which the length of the recording unit (sector address and track portion) is an integral number of wobble periods or 3) contained in tracking areas along the length of nonwobbled track portions. SUMMARY OF THE INVENTION The present invention is set out in claim 1. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a plan view illustrating the manner in which the tracks are disposed in an information recording medium according to an embodiment of the present invention; FIG. 2 is a plan view illustrating the manner in which identification information is disposed in the information recording medium according to an embodiment of the present invention; FIG. 3 is a plan view illustrating the manner in which identification information is disposed at a track connected portion in the information recording medium according to an embodiment of the present invention; FIG. 4 is a fragmentary perspective view illustrating the information recording medium according to an embodiment of the present invention in an enlarged scale; FIG. 5 is a plan view illustrating the manner in which the divided groups are disposed in the information recording medium according to an embodiment of the present invention; FIG. 6 is a plan view illustrating the manner in which identification information is numbered in the information recording medium according to an embodiment of the present invention; FIG. 7 is a block diagram showing an example of a recording and/or reproducing apparatus using an information recording medium according to the present invention; FIG. 8 is a diagram of a waveform of a reproduced signal obtained from an information recording medium according to the present invention; FIG. 9 is a diagram of a waveform of a signal that is used to record and/or reproduce an information recording medium according to the present invention; and FIGS. 10A through 10D are respectively diagrams used to explain a recording and/or reproducing method using an information recording medium according to the present invention. DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will hereinafter be described with reference to the accompanying drawings. Reference numerals in the sheets of drawings should identify the following elements and parts. Reference numeral 1 denotes a recording unit, reference numeral 2 denotes identification information, reference numeral 3 denotes a groove portion, reference numeral 4 denotes a land portion, reference numeral 5 denotes a track switching portion, reference numeral 6 denotes a non-switching portion, reference numeral 7 denotes a beam spot, reference numeral 15 denotes a wobbling, reference numeral 16 denotes a one cycle of wobbling, reference numeral 21 denotes identification information disposed at a first position, reference numeral 22 denotes identification information disposed at a second position, reference numeral 23 denotes a prepit, reference numerals 11 and 12 denote recording units, reference numerals 91, 92, 93 denote grooves, and reference numerals 81, 82 denote information recording portions, respectively. EMBODIMENT 1: INFORMATION RECORDING MEDIUM FIG. 5 shows the manner in which tracks and sectors of the information recording medium according to an embodiment of the present invention are disposed. As shown in FIG. 5, a plurality of groups 91, 92 and 93 are disposed in the radius direction of a disk-like recording medium 8. The track 3 is wobbled by a very small amount in the radius direction of the disk-like recording medium 8. Each track 3 is divided into a plurality of circular arc-like sectors (recording units) 1 arrayed in the radius direction of the disk-like recording medium 8. The length of the circular arc-like sector 1 is selected in such a manner that the number of the divided sectors per circumference of the disk-like recording medium 8 increases in the groups located at the position of the larger radius so as to make the length of the circular arc-like sector 1 become almost constant independently of the groups. FIG. 1 shows an example of the manner in which tracks are disposed within one group of the information recording medium according to an embodiment of the present invention. As shown in FIG. 1, within one group, there are alternately located groove portion information tracks 3 having a width of 0.7 µm and a depth of 60 nm and a land portion information track 4 having a width of 0.7 µm. The groove portion information track 3 and the land portion information track 4 are connected to each other by a switching portion 5. Specifically, the groove portion information track 3 is arranged such that it is connected to the adjacent land portion information track 4 after one circumference of the track, and the land portion information track 4 is arranged such that it is connected to the adjacent groove portion information track 3 after one circumference of the track. Each track is divided into a plurality of circular arc-like recording units such as sectors, and identification information 2 is disposed at the head of each of the information recording units 1. In this example, the length of the sector is about 8 mm, which corresponds to a user capacity of 2048 bytes. The groove portion information track 3 and the land portion information track 4 are wobbled with an amplitude of about 20 nm in the radius direction of the disk-like recording medium 8. A wobble cycle during which the groove portion information 3 and the land portion information track 4 are wobbled in the radius direction was set to 1/145 of the sector length, i.e. about 55 µm. The ratio of 1 : 145 was selected in such a manner that the wobbling cycle becomes an integral multiple of the length (channel bit length) of recorded data. According to this arrangement, it becomes easy to generate a recording clock from the wobbling. FIGS. 2 and 3 are respectively fragmentary plan views illustrating information identification information portions in an enlarged scale. FIG. 2 schematically shows a portion 6 in which preceding and succeeding tracks of identification information are connected by the groove portion information tracks 3 and the land portion information tracks 4. Also, FIG. 3 schematically shows a portion in which preceding and succeeding tracks are connected at the groove portion information tracks 3 and the land portion information tracks 4, i.e. a portion in which identification information is disposed such that the positions of the directions extended along the information tracks are different in the adjacent tracks but agree with the track advanced or delayed by two tracks. As shown in FIG. 2, identification information is disposed to be radial in the radius direction at the two places of the first position 21 and the second position 22. The preceding and succeeding tracks are connected by the groove portion information tracks 3 and the land portion information tracks 4. In this illustrated example of FIG. 2, each identification information corresponds to the recording area of the right-hand side information track. Further, identification information corresponding to the right-hand side groove portion information track 3 is disposed at the first position 21, and identification information corresponding to the land portion information track 4 is disposed at the second position 22. Specifically, the positions of the identification information along the information tracks are different from each other in the adjacent tracks but agree with each other in the tracks advanced or delayed by the two tracks. In the switching portion 5 of FIG. 3, the preceding and succeeding tracks of identification information are connected to each other in the groove portion information track 3 and the land portion information track 4. Also in this case, each identification information corresponds to the recording area of the right-hand side information track. As shown in FIG. 3, Identification information corresponding to the right-hand side groove portion information track 3 is disposed at the first position 21, and identification information corresponding to the land portion information track 4 is disposed at the second position 22. As a consequence, when the beam spot 7 scans the land portion information track 4, only pits of the one side are constantly reproduced. There is then no risk that a crosstalk occurs from the adjacent track. Therefore, it becomes possible to satisfactorily reproduce address information from the prepits without crosstalk. The address information at the prepit is recorded by an 8/16 (eight-to-sixteen) modulation code (channel bit length is 0.2 µm). FIG. 4 is a perspective view illustrating the manner in which tracks and identification information are configured according to an embodiment of the present invention, highlighting the manner in which identification information is formed by small concave portions (pits) 23. According to this embodiment, since the pits 23 are equally disposed on both sides of the track (land portion or the groove portion), a bad influence exerted by the pits 23 upon a tracking servo signal can be cancelled out. Accordingly, it is possible to suppress a track offset to be sufficiently small. Further, when the land portion information track 4, for example, is reproduced, address information of the first prepit portion 21 and address information of the second prepit portion 22 are reproduced continuously. Therefore, if information is disposed in such a fashion that both of the address information of the first prepit portion 21 and the address information of the second prepit portion 22 may be integrated as one address information, then address (track No.), i.e. identification information can be set independently of the land portion information track 4 and the groove portion information track 3. Specifically, it becomes possible to discriminate the land portion information track 4 and the groove portion information track 3 from each other by continuously reproducing the address information of the first prepit portion 21 and the address information of the second prepit portion 22. FIG. 6 shows concretely an example of the manner in which identification information is numbered. In FIG. 6, there are illustrated the identification information of the recording area 11 and the identification information of the recording area 12. In this example, identification information is recorded on and/or reproduced from the recording medium by relatively scanning detection spots from left to right of FIG. 6. A groove portion information track K of the left-hand side, for example, is connected to a land portion information track K+1 of the right-hand side of the switching portion 5. A land portion information track K+1 of the left-hand side is connected to the land portion information track K+1 after one circumference. In this example, identification information of an information recording area 81 of the groove portion information track K, for example, is N-1+S where S denotes a sum of optical recording information units per circumference of the track. When the identification information portion 6 of this track is reproduced by the beam spot or the like, N-1+2S is reproduced as identification information located at the first position 21, and N-1+S is reproduced as identification information located as the second position 22. In this case, if a smaller number is constantly used as a recording area No. in advance, then N-1+S is used as identification information of the information recording area 81 of this groove portion information track K. When the land portion information track K-1 is scanned by the beam spot or the like, N-1 is similarly used as identification information located at the first position 21. At the same time, it is possible to discriminate the groove portion information track and the land portion information track from each other by detecting whether the identification information located at the first position 21 or the identification information located at the second position 22 is used. When the information track located at the track switching portion 5 is reproduced, a correspondence of identification information and recorded information can be judged in exactly the same manner, and also the groove portion information track and the land portion information track can be discriminated from each other in exactly the same way. Accordingly, it is possible to switch the track polarity between the groove portion information track and the land portion information track by making effective use of the above-mentioned relationship. While there are two sets of the first and second identification information portions as described above, the present invention is not limited thereto, and there may be provided a plurality of sets of identification information portions. If there are provided four sets of identification information portions, for example, then first and third prepit portions are located under the groove portions and second and fourth prepit portions are located above the groove portions. If the number of the prepit portions increases, then the information recording medium according to the present invention becomes resistant to defects or the like, and therefore becomes highly-reliable. Here, a phase change type recording film (GeSbTe) was used as a recording film of this information recording medium. Accordingly, a recording mark is produced in the form of amorphous area. INFORMATION RECORDING AND/OR REPRODUCING METHOD An example of an information recording and/or reproducing method using the recording medium according to the embodiment 1 will be described with reference to FIG. 7. As shown in FIG. 7, the information recording medium 8 according to the embodiment 1 is rotated by a motor 162. A light intensity control circuit 171 controls a light generating circuit 131 so that the light generating circuit 131 generates light 122 having a light intensity instructed by a central control circuit 151. A converging circuit 132 converges the light 122 generated from the light generating circuit 131 to form a beam spot 7 on the information recording medium 8. Reflected light 123 of the light 122 is detected by a photo detecting circuit 133. The photo detecting circuit 133 comprises a plurality of split photo detectors. A wobble detecting circuit 191 reproduces information from the information recording medium 8 by using a reproduced signal 130 from the split photo detectors of the photo detecting circuit 133. When a wobbling of the track on the information recording medium 8 is detected, there is used a differential output among the outputs from the split photo detectors of the photo detecting circuit 133. The reason that the differential output is utilized is based on such a fact that an intensity distribution of diffracted light from the beam spot is changed depending on a positional relationship between the beam spot and the track. On the basis of the wobble signal detected by the wobble detecting circuit 191, information indicative of the positional relationship between the beam spot and the track and further prepit identification information, a position control circuit 161 controls the position of the converging circuit 132 and a rotation frequency of the motor 162. When the position control circuit 161 controls the rotation frequency of the motor 162, the rotation frequency is controlled in such a manner that a reproduced wobble signal may have a previously-determined constant value. If the rotational frequency of the motor 162 is controlled by the position control circuit 161 as described above, then the rotational speed of the motor 162 can be automatically and properly controlled independently of the groups on the information recording medium 8. Also, since this rotation information of the motor 162 has one cycle of about 55 µm, the rotation information is very high in density, and it becomes possible to control the rotation of the motor 162 with a high accuracy. Furthermore, since this rotation information is disposed all over one revolution of the disk, even when a part of the rotation information is dropped out by some causes such as smudges or defects, the rotation information can be reproduced from the information recording medium 8 with a high accuracy satisfactorily. INFORMATION RECORDING AND/OR REPRODUCING METHOD A description will now be given of a method of recording and/or reproducing information on and/or from an information recording medium by generating a clock synchronized with a phase of a wobble signal when information is recorded and/or reproduced. In order to generate the above-mentioned clock synchronized with the phase of the wobble signal, there is used a PLL (Phase-Locked Loop) circuit. Since this clock is accurately synchronized with the wobble information of the information recording medium, if information is recorded on and/or reproduced from the information recording medium by using this clock, then information can be recorded on and/or reproduced from the information recording medium at a timing perfectly synchronized with the position on the information recording medium. Therefore, information can be recorded on and/or reproduced from the information recording medium without providing unnecessary buffer areas on the information recording medium, and it is possible to obtain an information recording medium which is high in format efficiency. As a consequence, there can be raised a recording capacity of the information recording medium. Furthermore, since the wobble information (rotation information) is disposed all over one revolution of the disk, even when a part of the wobble information is dropped out, information can be reproduced from the information recording medium with a high reliability satisfactorily. EMBODIMENTS 2: INFORMATION RECORDING MEDIUM FIG. 5 shows the manner in which the tracks and the sectors of the recording medium according to an embodiment of the present invention are disposed. As shown in FIG. 5, there are disposed a plurality of zones (groups) 91, 92, and 93 in the radius direction of the disk-like recording medium 8 having a diameter of 120 mm. In this example of FIG. 5, there are divided 24 zones of which the radiuses are ranging from about 24 mm to 58 mm. Accordingly, one zone has a band width of about 1.4 mm. The groove portion information track 3 is wobbled by a very small amount in the radius direction of the disk-like recording medium 8. Each of the groove portion information track 3 is divided into a plurality of circular arc-like sectors (recording units) 1 arrayed in the radius direction of the disk-like recording medium 8. The length of the circular arc-like sector 1 is made almost constant independently of the zones (groups) so that the number of the divided sectors per circumference increases in the zone located at the position of the larger radius. In this embodiment, each track 3 is divided in such a manner that there are provided 17 recording units 1 per circumference in the zone (innermost peripheral zone) of the radius of about 25 mm. The number of the divided zones increases one by one in the outer peripheral zone. By using the information recording medium having the groups divided in such a manner that the number of the divided groups increases in the outer peripheral zone as described above, the lengths of the recording units 1 in the inner and outer peripheries of the information recording medium 8 can be made almost constant. In other words, the density of the rotation information can be made substantially constant, and the surface area (i.e. whole surface) of the information recording medium 8 can be used effectively. Moreover, since information can be recorded on and/or reproduced from the information recording medium at the same rotational speed and with the same recording frequency within each group, an information recording and/or reproducing apparatus using the information recording medium can be simplified in configuration. It is needless to say that the lengths of the recording units are slightly different in the inside and the outside of each zone. FIG. 1 shows an example of the manner in which tracks within one group are disposed in an information recording medium according to the present invention. As shown in FIG. 1, there are alternately disposed the groove portion information tracks 3 having a width of 0.74 µm and a depth of 60 nm and the land portion information tracks 4 having a width of 0.74 µm. In each zone, there are disposed about 950 groove portion information tracks 3 and the land portion information tracks 4 of the same number as that of the groove portion information track 3. The groove portion information track 3 and the land portion information track 4 are connected to each other by the track switching portion 5 which is located at one place on one circumference of the disk. Specifically, the groove portion information track 3 is connected to the adjacent land portion information track 4 after one circumference of the track, and the land portion information track 4 is connected to the adjacent groove portion information track 3 after one circumference of the track. Each track is divided into a plurality of circular arc-like information recording units 1, and the identification information 2 is disposed at the starting portion of each information recording unit 1. In this example, the length of the information recording unit 1 is about 8.5 mm, which corresponds to a user capacity of 2048 bytes. The groove portion and the land portion are wobbled in the radius direction of the information recording medium by a half width amplitude of about 20 nm. The wobble cycle was set to 1/232 of the sector length or about 37 µm. The ratio of 1 : 232 is set not only within one group (zone) but also in all the recording units 1 on the disk. The ratio of 1 : : 232 was selected in such a fashion that the wobble cycle becomes an integral multiple (in this example, 186 times) of the unit length (channel bit length) of the recorded data. Accordingly, the length of the recording unit is equivalent to 232 x 186 = 43152 channel bits when it is expressed by the channel bit number. Since the wobble cycle is equal to the integral multiples of the recording channel bit as described above, it is possible to easily generate a recording clock by multiplying the wobble frequency with an integral number. Moreover, since the relationship between the information recording unit 1 and the duration of the wobbling cycle becomes equal over the whole surface of the disk, it becomes possible to generate the recording clock by using the signal obtained from the wobbling without switching the signal at the zone. Thus, a density within the disk can be made almost uniform by the apparatus of the simple configuration, and the whole surface of the disk can be used efficiently. Furthermore, if the rotational speed of the disk is controlled in such a manner that the wobbling frequency becomes constant, then it becomes possible to make a relative linear velocity between the beam spot and the information recording medium almost constant independently of the position of the information recording medium. If the linear velocity is made substantially constant as described above, then information can be recorded on and/or reproduced from the recording medium under the same recording conditions independently of the position of the information recording medium. Thus, the recording and reproducing characteristics of the information recording medium can be controlled with ease, and hence the recording apparatus and the information recording medium can be configured with ease. Here, since the lengths of the recording areas 1 are slightly different in the inside and the outside of the zone, the duration of the wobble cycle of a reciprocal of an integral number of the recording unit also is different in the inner and outer peripheries of the zone. Thus, it is needless to say that a linear velocity also is different slightly. However, because central angles formed by the recording units are constant within the zone, the revolution rate (angular velocity) within the zone become constants so that it becomes possible to access the information recording medium within the zone at a high speed. Moreover, since the integral multiple (232 times) of the wobbling cycle agrees with the length of the recording unit 1, the phases of the wobbling signals can be perfectly connected to each other without fractions between the adjacent recording units 1. Thus, it is easy to generate a timing signal such as a clock over the consecutive recording units 1 by using the wobbling signal. The fact that the phases of the wobbling signals are perfectly connected to each other without fractions means that the phases of the wobbling signals are made continuous between the adjacent recording units 1 but the wobbling signals need not always be continuous from a physical standpoint. Specifically, there might be used such an information recording medium in which a wobbling signal is dropped out at the boundary portion of the recording units 1 over several cycles. In that case, if such dropped-out portions are interpolated, then the phases of the wobbling signals may be connected between the adjacent recording units 1. In actual practice, according to this embodiment, the identification information composed of prepits is provided at the starting portion of the recording unit and neither the groove portion information track 3 nor the land portion information track 4 exists with the result that the wobble signal is not formed at all. That is, the wobble signal is dropped out during about 11.2 cycles due to this identification information 2. Accordingly, while there exist about 220.8 wobble signals in actual practice, the length of the recording information unit becomes exactly 232 times the cycle of the wobble signal. Here, the recording unit in this embodiment need not always agree with the length of the sector. For example, more than two sectors may be integrated as one recording unit, and identification information may be disposed within such integrated recording unit. Moreover, a plurality of recording units may be integrated as a logical sector or a logical block necessary for correcting errors. At any rate, the recording unit in this embodiment is referred to as an area of substantially a constant length in which identification information is disposed at the starting portion thereof. FIGS. 2 and 3 are respectively plan views illustrating identification information portions of the information recording medium in an enlarged scale. FIG. 2 shows a portion 6 in which preceding and succeeding tracks of identification information are connected at the groove portions and the land portions. FIG. 3 shows a portion 5 in which preceding and succeeding tracks are connected at the groove portions and the land portions, i.e. a portion in which the positions at which identification information is arrayed along the information tracks are different between the adjacent tracks but agree with the track advanced or delayed by two tracks. As shown in FIG. 2, identification information is disposed to be radial at a first position 21 and a second position 22 in the radius direction of the information recording medium. The preceding and succeeding tracks are connected to each other by the groove portion information tracks 3 and the land portion information tracks 4. In this illustrated example, each identification information corresponds to the recording area of the groove portion information track 3 on the right-hand side of FIG. 2. Further, identification information corresponding to the groove portion information track 3 on the right-hand side of FIG. 2 is placed at the first position 21, and identification information corresponding to the land portion information track 4 is placed at the second position 22. Specifically, the positions at which identification information is arrayed along the information tracks are different between the adjacent tracks but agree with the track which is advanced or delayed by two tracks. The wobble signal is of a sine wave shape which begins with the same phase relative to all information tracks. The wobble signal starts immediately after the identification information portion or starts via a few buffer areas. With this arrangement, if points at which phases of the sine-wave wobble signal become zero degree are connected to each other by the adjacent tracks, then these points are arrayed to be radial so that the track width is never changed by the wobble signal. There is then presented no risk that the wobble signal will exert a bad influence upon the recording and reproducing characteristics. If the phases of the wobble signals are not made uniform in each track, then there is produced a portion in which the track width is modulated by the wobble signal, thereby resulting in the recording and reproducing characteristics being affected considerably. Therefore, as is evident from the above description of the present invention, in order to realize an embodiment of the present invention, it is very important to make the phases (including polarities) of the wobble signals uniform between the adjacent tracks. In the track switching portion 5 shown in FIG. 3, the preceding and succeeding tracks of the identification information are connected to each other at the groove portion and the land portion. Also in this case, each identification information corresponds to the recording area of the information track on the right-hand side of FIG. 3. Identification information corresponding to the groove portion information track 3 on the right-hand side of FIG. 3 is placed at the first position 21, and identification information corresponding to the land portion information track 4 on the right-hand side of FIG. 3 is placed at the second position 22. Therefore, when the beam spot 21 scans the land portion information track 4, for example, only one pit is constantly reproduced. There is then no risk that a crosstalk from the adjacent track will occur. Accordingly, it becomes possible to satisfactorily reproduce address information provided at the prepits without crosstalk. In this example, the address information provided at the prepits is recorded on the information recording medium by an 8/16 (eight-to-sixteen) modulation code (channel bit length is 0.2 µm). Accordingly, a shortest pit length is about 0.6 µm. From a standpoint of simplifying the configuration of the information recording and/or reproducing apparatus, the modulation code of the prepit portion and the modulation code of the user information recording portion should preferably be made the same. In this embodiment, the modulation code and the recording linear density are both made the same with the result that most of the circuit portions of the information recording and/or reproducing apparatus can be made common. FIG. 4 is a perspective view illustrating the manner in which tracks and identification information according to this embodiment are configured, highlighting the manner in which identification information is formed by small concave portions (pits) 23. In this embodiment, since the pits 23 are equally disposed on both sides of the track (the land portion or the groove portion), an influence exerted upon a tracking servo signal by the pits 23 is cancelled out so that a track offset can be suppressed to be sufficiently small. Further, when the land portion information track 4 is reproduced, the address information of the first prepit portion 21 and that of the second prepit portion 22 are reproduced continuously. Therefore, if information is disposed in such a fashion that both of address information are integrated as one address information, then it is possible to separately set address (track No.), i.e. identification information independently of the land portion information track 4 and the groove portion information track 3. Specifically, if the address information of the first prepit portion 21 and the address information of the second prepit portion 22 are reproduced continuously, then it becomes possible to discriminate the land portion information track 3 and the groove portion information track 4 from each other. FIG. 6 concretely illustrates the example of the manner in which identification information is numbered, showing identification information of the recording area 11 and identification information of the recording area 12. In this example, information is recorded and/or reproduced while detection spots are relatively scanned from left to right of the information recording medium. As shown in FIG. 6, a groove portion information track k on the left-hand side is connected to a right-hand side land portion information track K+1. The left-hand side land portion information track K+1 is connected to this track after one circumference of the information recording medium. In this example, identification information of an information recording area 81 of the groove portion information track K is N-1+S where reference letter S denotes a sum of optical recording information units per circumference of the track. If the identification information portion 6 of this track is reproduced by the beam spot or the like, then N-1+2S is reproduced as identification information existing at the first position 21, and N-1+S is reproduced as identification information existing at the second position 22. In this case, if a smaller number is constantly used as a recording area No. in advance, then N-1+S is adopted as identification information of the information recording area 81 of this groove portion information track K. When the land portion information track K-1 is scanned, N-1 is adopted as the identification information existing at the first position 21 similarly. At the same time, by the identification information existing at the first position 21 or the identification information existing at the second position 22, it is possible to discriminate the groove portion information track 3 and the land portion information track 4 from each other. When the information track placed at the track switching portion 5 is reproduced, the correspondence between the identification information and the recording area can be detected, and the groove portion information track 3 and the land portion information track 4 can be discriminated from each other in exactly the same manner as that described above. Therefore, by using this relationship, it is possible to switch the track polarities of the groove portion information track and the land portion information track. While there are provided two sets of the first and second identification information portions as described above in this example, there may be provided a plurality of sets of identification information portions. If there are provided four sets of identification information portions, then the first and second prepit portions may be located on the lower side of the groove portion (inside of the radius direction), and the third and fourth prepit portions may be located on the upper side of the groove portion (outside of the radius direction). Alternatively, the first and third prepit portions may be located on the lower side of the groove portion, and the second and fourth prepit portions may be located on the upper side of the groove portion. The information recording medium can be made more resistant to the defects or the like and become highly-reliable by increasing the number of the prepit portions. Here, a phase change type recording film (GeSbTe) was used as a recording film. Accordingly, a recording mark is produced in the form of an amorphous area. INFORMATION RECORDING AND/OR REPRODUCING METHOD The manner in which information is recorded on and/or reproduced from the information recording medium of the previous embodiment by the information recording and/or reproducing apparatus shown in FIG. 7 will be described below. As shown in FIG. 7, the information recording medium 8 according to the previous embodiment is rotated by the motor 162. The light intensity control means 171 controls the light generating circuit 131 to generate the light 122 in such a way as to obtain a light intensity instructed by the central control circuit 151. The converging circuit 132 converges the light 122 to form the beam spot 7 on the information recording medium 8. The light 12 is detected by using the reflected light 123 from the beam spot 7 with the photo detecting circuit 133. The photo detecting circuit 133 comprises a plurality of split photo detectors. The wobble detecting circuit 191 reproduces information from the information recording medium 8 by using the reproduced signal 130 from the split photo detectors of the photo detecting circuit 133. When the wobble signal of the track on the information recording medium 8 is detected, there is used a differential output between the outputs from the split photo detectors of the photo detecting circuit 133. This utilizes the fact that an intensity distribution of diffracted light from the beam spot is changed depending upon a positional relationship between the beam spot and the track. On the basis of the wobble signal detected by the reproducing means 191, information indicative of the positional relationship between the beam spot and the track and prepit identification information, the position control circuit 161 controls the position of the converging circuit 132, and also controls the rotation frequency of the motor 162. In this case, the position control circuit 161 controls the rotation frequency of the motor 162 in such a manner that the frequency of the reproduced wobble signal becomes a previously-determined constant value. If the rotation frequency of the motor 162 is controlled by the position control circuit 161 as described above, then it is possible to automatically control the motor 162 independently of the zones on the information recording medium 8 so that the motor 162 can be rotated at a proper rotational speed. Also, since this rotation information has one cycle of about 37 µm, the rotation information is considerably high in density, and it becomes possible to control the rotation of the motor 162 with a high accuracy. Furthermore, since this rotation information is disposed all over one revolution of the disk, even when one portion of the rotation information is dropped out due to some causes such as smudges or defects, information can be satisfactorily reproduced from the information recording medium 8 highly reliably. FIG. 8 shows examples of a reproduced signal 41 of wobble information and a reproduced signal 42 of identification information portion. In this example, photo detectors which are split at least by a half in the radius direction are used as a detector, and there is obtained a differential signal between the outputs from the two split photo detectors. Specifically, there was used a detection system that is similar to a detection system of a push-pull signal used in an ordinary tracking control or the like. However, since the frequency of the wobble signal and the frequency of the identification information signal are higher than the band necessary for the tracking servo, there were prepared an amplifying apparatus and a differential circuit, both of which should be in accordance with the high frequency specification. There were obtained reproduced signals 421, 422, 423 and 424 in correspondence with the first, second, third and fourth identification information signals 21, 22, 23 and 24. When the beam spot 7 is not overlapping the prepit 23 of the identification information portion 2, reflected light is equally introduced into the above-mentioned split photo detectors so that a reproduced signal (differential signal) output is almost zero. Whereas, under the condition that the beam spot 7 partly overlaps the prepit 23 (see FIG. 2), a distribution of reflected light from the beam spot 7 is largely deviated due to a diffraction effect, and the outputs from the split photo detectors are unbalanced. As a consequence, there is obtained a large differential signal output. Inasmuch as the direction in which the distribution of reflected light is deviated at that time is different depending on the positional relationship between the beam spot and the pit, the differential output corresponding to the identification information portions 21, 22 and the differential output corresponding to the identification information portions 23, 24 are inverted in polarity. Accordingly, if this polarity of the differential outputs is used, then it is possible to determine any one of the groove portion information track and the land portion information track in which the beam spot is positioned. Identification information can be obtained when the resulting signal is converted into a binary signal and then decoded by a follow-up slice circuit (not shown). At that time, since error detection information is added to the identification information, it is possible to judge whether or not identification information is detected correctly. Hence, there can be used only correct identification information in a plurality of identification information. The wobble signal is detected in a similar manner. Specifically, since the positional relationship between the beam spot and the groove is modulated by the wobbling signal, there is obtained a signal output 41 shown in FIG. 8. However, since an amplitude (track displacement amount: 20 nm) of a wobble signal is small relative to the displacement amount (about 0.3 µm) of identification information, the amplitude of the wobble signal becomes smaller in proportion thereto. An example of the manner in which a timing signal (clock signal) is obtained from the wobble signal thus detected will be described with reference to FIGS. 10A through 10D. Initially, the reproduced signal 41 shown in FIG. 8 is supplied to a limiter circuit shown in FIG. 10A, in which an identification information is limited in amplitude. Then, by using the bandpass filter shown in FIG. 10B, only a signal having a component synchronized with the wobble signal is extracted from the reproduced signal. Then, the resulting signal is converted into a binary signal by a comparator shown in FIG. 10C, and eventually, there is obtained the clock signal by using a phase-locked loop (PLL) comprising a phase comparator, a filter circuit, a VCO (voltage-controlled oscillator) and a divide-by-186 circuit as shown in Fig. 10D. At that time, a filter characteristic used in the PLL is set to be sufficiently lower than the frequency corresponding to 11.2 wobble cycles in this example in such a manner that the clock signal may be prevented from being affected by a dropped-out portion (identification information portion) of the wobble signal. Since the frequency of the wobble signal becomes 160 kHz, the frequency band of the PLL is set to about 2kHz. This frequency should preferably be set to be larger than a frequency (about 700 Hz) corresponding to the length of the recording unit from a standpoint of a high-speed accessing. In this way, there was obtained the clock signal that was synchronized with the wobble signal. A method of recording and/or reproducing information on and/or from the information recording medium by using this clock signal and identification information will be described below. FIG. 9 is a timing chart used to explain the manner in which information is recorded on and/or reproduced from the information recording medium. In FIG. 9, reference letters (a), (b), (c), and (d) denote an identification information detecting signal, a wobble signal, a clock signal, and a recording and reproducing timing signal, respectively. The identification information detecting signal is a signal indicating that identification information is detected normally. It is customary that the recording unit areas that should be recorded and/or reproduced are discriminated from each other based on this identification information detecting signal and that the recording and/or reproducing timing can be controlled. According to this method, when the identification information could not be normally detected as shown in FIG. 9 (crosses on (a) in FIG. 9 show that identification information could not be detected normally), it is possible to obtain the recording and reproducing timing signal instead of the identification information detecting signal by counting the clock signal obtained from the wobble signal based on the final identification information that was detected normally. According to this arrangement, even when identification information cannot be detected normally, there can be obtained the recording and reproducing timing signal. Also, since this recording and reproducing timing signal is generated from the wobble signal synchronized with the information recording medium, even if there is an error such as a rotational speed of the information recording medium, the recording and reproducing timing signal can be obtained accurately. Furthermore, even when a plurality of identification information cannot be detected continuously, there is no risk that errors will be accumulated. Therefore, it becomes possible to configure an information recording and/or reproducing apparatus which can greatly allow errors of identification information itself. If the signal detected from the above-mentioned wobble signal and the identification information are combined as described above, then it becomes possible to identify the position of the beam spot at all positions on the disk. Thus, information can be recorded on and/or reproduced from the information recording medium highly reliably. With the above-mentioned advantage, even if the information recording medium is not inspected at al when the information recording medium is shipped, it becomes possible to maintain the recording and/or reproduction highly reliable, thereby making it possible to reduce the cost of the information recording medium considerably. Furthermore, since the information recording medium becomes very resistant to smudges, the information recording medium need not be protected from the smudges by some suitable means such as a case. Therefore, it becomes possible to provide an inexpensive information recording medium. According to the embodiments of the present invention, since information can be recorded on and/or reproduced from the information recording medium highly reliably, even if the information recording medium is not inspected at all when the information recording media are shipped, a high reliability with which information is recorded on and/or reproduced from the information recording medium can be maintained, thereby making it possible to reduce the cost of the information recording medium considerably. Moreover, since the information recording medium according to embodiments of the present invention becomes very resistant to smudges, the information recording medium need not be protected from the smudges by some suitable means such as a case. Therefore, it becomes possible to provide an inexpensive information recording medium. Further, since the recording units are arrayed to be radial in the radius direction of the information recording medium, the tracks can be accessed with ease, and a crosstalk between position information of respective recording units can be suppressed to the minimum. Moreover, since the recording units are disposed in such a manner that the lengths of the circular arc-shaped portions which are the recording units are made almost the same, a recording density becomes substantially uniform within the disk, and hence it becomes possible to use the whole surface of the disk efficiently. Moreover, the starting point and the ending point of the recording unit can be reliably detected by using the wobble cycle, and it becomes possible to detect the accurate position in the recording unit. Also, since the length of the recording unit and the wobble cycle are perfectly synchronized with each other, by making the wobble frequency become constant, it is possible to automatically control the rotational speed of the information recording medium in such a fashion that the relative velocity of the information recording medium becomes almost constant. Further, since it becomes easy to make the length of each recording unit on the information recording medium become constant, the length of the extra gaps on the information recording medium can be minimized. Furthermore, since it is possible to record and/or reproduce information on and/or from the information recording medium while monitoring the displacement amount of the track, a reliability with which the positioning servo is effected can be improved greatly. Since the identification information is provided at every recording unit and the position information can be reliably obtained from the recording portion owing to the wobbles of the groove portion and the land portion, the recorded information can be accessed reliably and the recording information can be positioned on the information recording medium with a high accuracy. Having described preferred embodiments of the invention with reference to the accompanying drawings, it is to be understood that the invention is not limited to those precise embodiments and that various changes and modifications can be effected therein by one skilled in the art within the scope of the invention as defined in the appended claims.

Claims: An information recording medium (8) having a spiral or concentric groove structure along tracks (3, 4) formed on a disk-like substrate, wherein each track (3, 4) is divided into a plurality of recording units (1) and the groove structure is formed with a radial wobble (15) having a fixed wobbling cycle (16), characterised in that each recording unit (1) includes, in the circumferential direction, a non-grooved and non-wobbling identification information portion (2), the phase of the wobble is continuous in the circumferential direction along the track (3, 4) without being shifted by the non-wobbling identification information portions (2), and the length of each recording unit is an integer multiple of the wobbling cycle (16). The recording medium of claim 1 which is divided, in the radial direction, into a plurality of groups having equivalent arc lengths. The recording medium of claim 1, wherein the recording unit (1) is divided, in the radial direction, in arc-like portions delimited by the same central angle. The recording medium of claim 1, wherein the identification information portion (2) includes information indicative of the recording unit (1).

Inventors: FUSHIMI TETSUYA, MINEMURA HIROYUKI, MIYAMOTO HARUKAZU, SUGIYAMA HISATAKA, SUZUKI MOTOYUKI, SUZUKI YOSHIO, TOKUSHUKU NOBUHIRO, FUSHIMI, TETSUYA, MINEMURA, HIROYUKI, MIYAMOTO, HARUKAZU, SUGIYAMA, HISATAKA, SUZUKI, MOTOYUKI, SUZUKI, YOSHIO, TOKUSHUKU, NOBUHIRO
Applicants: HITACHI LTD, HITACHI, LTD.
Application year: 1997
Main classification: G11B7
IPC codes: G11B7, G11B27, G11B19