An optical disk and an optical disk recording method

Abstract: An optical disk comprises a stripe-like mark array of sub-information in a region where main information is not recorded. The sub-information is divided in a plurality of frames each having a predetermined number of information words. m pieces of information symbols comprising at least one word of each frame are added n pieces of dummy symbols to generate amplers n pieces of information symbols. i pieces of parity symbols are generated so as to generate a code for error correction, and said m pieces of information symbols and said parity symbols are recorded with using said mark array.

Description: TECHNICAL FIELD The present invention relates to an optical disk, and an disk reproduction apparatus. BACKGROUND ART In the manufacturing process of optical disks, it has been commonly practiced to record a serial number, lot number, etc. on each optical disk in the form of a barcode. Since such information cannot be written to a pit information area of the optical disk, it has been practiced to write the barcoded information to a non-information area, or unused space, on the optical disk. When reproducing (playing back) such an optical disk, the pit information is read by an optical pickup; to read the barcoded information such as a serial number, etc. recorded in the non-information area, however, a separate reading device has been used. In the above prior art optical disk, since information carrying a serial number and the like is not recorded in a pit area but recorded in a non-information area, as described above, a separate reading device has had to be provided in addition to the usual optical pickup, the resulting problem being increased complexity of the playback apparatus construction. EP 0 549 488 A1 discloses an optical disk as described by the preamble part of claim 1. In view of the above problem with the prior art, it is the object of the present invention to provide an optical disk which allows to read barcode like marks and main information recorded on the disk by a single optical pickup. It is another object of the invention to provide a corresponding optical disk reproduction apparatus for such an optical disk. These objects are achieved by the features of claim 1 and claim 5, respectively. Preferred embodiments thereof are subject matter of the dependent claims. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a diagram showing a disk manufacturing process and a secondary recording process; Figure 2(a) is a top plan view of a disk, (b) is a top plan view of the disk, (c) is a top plan view of the disk, (d) is a transverse sectional view of the disk, and (e) is a waveform diagram of a reproduced signal; Figure 3 is a flowchart illustrating a process of recording encrypted position information on a disk in the form of a barcode; Figure 4 is a diagram showing a disk fabrication process and a secondary recording process (part 1); Figure 5 is a diagram showing the disk fabrication process and the secondary recording process (part 2); Figure 6(a) is a diagram showing part (b) of Figure 12 in further detail, (b) is a diagram showing an equivalent data structure for ECC encoding/decoding, (c) is a diagram showing a mathematical equation for EDC computation, and (d) is a diagram showing a mathematical equation for ECC computation; Figure 7 is a block diagram of a low-reflectivity position detector; Figure 8 is a diagram illustrating the principle of detecting address/clock positions of a low-reflectivity portion; Figure 9A is a flowchart illustrating a procedure for encryption, etc. using an RSA function; Figure 9B is a flowchart illustrating a position information check process; Figure 10 is a diagram showing the arrangement of stripes on a disk and the contents of control dada according to the embodiment; Figure 11 is a flowchart illustrating how control mode is switched between CAV and CLV when playing back stripes according to the embodiment; Figure 12(a) is a diagram showing a data structure after ECC encoding, (b) is a diagram showing a data structure after ECC encoding when n = 1), and (c) is a diagram showing an ECC error-correction capability; BEST MODE OF EMBODIMENTS The preferred embodiments of the present invention will be described below with reference to the accompanying drawings. In the description hereinafter given, position information for piracy prevention, which is a form of ID, is taken as an example of information to be barcoded. We will first describe a general process flow from disk manufacturing to the completion of an optical disk by using the flowchart of Figure 1. In this patent specification, laser trimming is also referred to as laser marking, while a nonreflective optical marking portion is simply referred to as the barcode, stripe, marking, or optical marking or, sometimes, as the physical ID unique to a disk. First, the software company performs software authoring in software production process 820. The completed software is delivered from the software company to the disk manufacturing factory. In disk manufacturing process 816 at the disk manufacturing factory, the completed software is input in step 818a, a master disk is produced (step 818b), disks are pressed (steps 818e, 818g), reflective films are formed on the respective disks (steps 818f, 818h), the two disks are laminated together (step 818i), and a ROM disk such as a DVD or CD is completed (step 818m, etc.). The thus completed disk 800 is delivered to the software maker or to a factory under control of the software maker, where, in secondary recording process 817, an anti-piracy marking 584, such the one shown in Figure 2, is formed (step 819a), and accurate position information of this mark is read by a measuring means (step 819b) to obtain the position information which serves as the physical feature information of the disk. This physical feature information of the disk is encrypted in step 819c. The encrypted information is converted to a PE-RZ-modulated signal which is then recorded in step 819d as a barcode signal on the disk by using a laser. The disk physical feature information may be combined together with software feature information for encryption in step 819c. The above processes will be described in further detail. That is, a disk fabrication process, a marking formation process, a marking position reading process, and an encrypted information writing process for an optical disk according to the present invention will be described in detail with reference to Figures 4 and 5. In the following description, the marking formation process and the marking position reading process are collectively called the secondary recording process. First, the disk fabrication process will be described. In the disk fabrication process 806 shown in Figure 4, first a transparent substrate 801 is pressed in step (1). In step (2), a metal such as aluminum or gold is sputtered to form a reflective layer 802. An adhesive layer 804 formed from an ultraviolet curing resin is applied by spin coating to a substrate 803 formed in a different processing step, and the substrate 803 is bonded to the transparent substrate 801 having the reflective layer 802, and they are rotated at high speed to make the bonding spacing uniform. By exposure to external ultraviolet radiation, the resin hardens, thus firmly bonding the two substrates together. In step (4), a printed layer 805 where a CD or DVD title is printed, is printed by screen printing or offset printing. Thus, in step (4), the ordinary laminated-type optical ROM disk is completed. Next, the marking formation process will be described with reference to Figures 4 and 5. In Figure 4, a laser beam from a pulsed laser 813 such as a YAG laser is focused through a converging lens 814 onto the reflective layer 802, to form a nonreflective portion 815 as shown in step (6) in Figure 5. That is, a distinct waveform, such as the waveform (A) shown in step (7), is reproduced from the nonreflective portion 815 formed in step (6) in Figure 5. By slicing this waveform, a marking detection signal such as shown by waveform (B) is obtained, from which hierarchial marking position information comprising an address, such as shown in signal (d), and an address, a frame synchronizing signal number, and a reproduced clock count, such as shown in signal (e), can be measured. At the rising edge of the thus obtained marking detection signal, a specific address (indicated by address n in Figure 5(d)) is read by the optical pickup from within the plurality of addresses shown in Figure 5(d). Figure 5(b) shows the physical location of the specific address in schematic form. On the other hand, Figure 5(e) shows the logical structure of the data. As shown in Figure 5(e), there are m frame synchronization signals under address n, and k reproduced clock pulses under each frame synchronization signal. Therefore, the position of the marking measured by the optical pickup can be represented by address, frame synchronization signal number, and reproduced clock count. Next, the process of reading the position of the thus formed marking will be described. Figure 7 is a block diagram showing a low reflectivity light amount detector 586 for detecting the nonreflective optical marking portion, along with its adjacent circuitry, in an optical disk manufacturing process. Figure 8 is a diagram illustrating the principle of detecting address/clock positions of the low reflectivity portion. For convenience of explanation, the following description deals with the operating principle when a read operation is performed on a nonreflective portion formed on an optical disk constructed from a single disk. It will be recognized that the same operating principle also applies to an optical disk constructed from two disks laminated together. As shown in Figure 7, the disk 800 is loaded into a marking reading apparatus equipped with a low reflectivity position detector 600 to read the marking, and in this case, since a signal waveform 823 due to the presence and absence of pits and a signal waveform 824 due to the presence of the nonreflective portion 584 are significantly different in signal level, they can be clearly distinguished using a simple circuit. By removing the reflective film by laser light, as described above, a waveform easily distinguishable from that of a pit signal is obtained. Rather than forming an anti-piracy identification mark by removing the reflective film by laser light, as described above, the anti-piracy mark may be formed by changing the shape of pits on the master disk. This method will be described below. By removing the reflective film by laser light, as described above, a waveform easily distinguishable from that of a pit signal is obtained. Rather than forming the barcode of the invention by removing the reflective film by laser light, as described above, the barcode may be formed by changing the shape of pits on the master disk. As shown in Figure 8(1), the start and end positions of the nonreflective portion 564 having the above waveform can be easily detected by the low reflectivity light amount detector 586 shown in the block diagram of Figure 7. Using the reproduced clock signal as the reference signal, position information is obtained in a low reflectivity position information output section 596. Figure 8(1) shows a cross-sectional view of the optical disk. As shown in Figure 7, a comparator 587 in the low reflectivity light amount detector 586 detects the low reflectivity light portion by detecting an analog light reproduced signal having a lower signal level than a light amount reference value 588. During the detection period, a low reflectivity portion detection signal of the waveform shown in Figure 8(5) is output. The addresses and clock positions of the start position and end position of this signal are measured. The reproduced light signal is waveshaped by a waveform shaping circuit 590 having an AGC 590a, for conversion into a digital signal. A clock regenerator 38a regenerates a clock signal from the waveshaped signal. An EFM demodulator 592 in a demodulating section 591 demodulates the signal, and an ECC corrects errors and outputs a digital signal. The EFM-demodulated signal is also fed to a physical address output section 593 where an address of MSF, from Q bits of a subcode in the case of a CD, is output from an address output section 594 and a synchronizing signal, such as a frame synchronizing signal, is output from a synchronizing signal output section 595. From the clock regenerator 38a, a demodulated clock is output. In a low reflectivity portion address/clock signal position signal output section 596, a low reflectivity portion start/end position detector 599 accurately measures the start posistion and end position of the low reflectivity portion 584 by using an (n-1) address output section 597 and an address signal as well as a clock counter 598 and a synchronizing clock signal or the demodulated clock. This method will be described in detail by using the waveform diagrams shown in Figure 8. As shown in the cross-sectional view of the optical disk in Figure 8(1), the low reflectivity portion 584 of mark number 1 is formed partially. A reflection selope signal such as shown in Figure 8(3), is output, the signal level from the reflective portion being lower than the light amount reference value 588. This is detected by the light level comparator 587, and a low reflectivity light detection signal, such as shown in Figure 8(5), is output from the low reflectivity light amount detector 586. As shown by a reproduced digital signal in Figure 8(4), no digital signal is output from the mark region since it does not have a reflective layer. Next, to obtain the start and end positions of the low reflectivity light detection signal, the demodulated clock or synchronizing clock shown in Figure 8(6) is used along with address information. First, a reference clock 605 at address n in Figure 8(7) is measured. When the address immediately preceding the address n is detected by the (n-1) address output section 597, it is found that the next sync 604 is a sync at address n. The number of clocks from the synch 604 to the reference clock 605, which is the start position of the low reflectivity light detection signal, is counted by the clock counter 598. This clock count is defined as a reference delay time TD which is measured by a reference delay time TD measuring section 608 for storage therein. The circuit delay time varies with reproduction apparatus used for reading, which means that the reference delay time TD varies depending on the reproduction apparatus used. Therefore, using the TD, a time delay corrector 607 applies time correction, and the resulting effect is that the start clock count for the low reflectivity portion can be measured accurately if reproduction apparatus of different designs are used for reading. Next, by finding the clock count and the start and end addresses for the optical mark No. 1 in the next track, clock m+14 at address n+12 is obtained, as shown in Figure 8(8). Since TD = m + 2, the clock count is corrected to 12, but for convenience of explanation, n+14 is used. We will describe another method, which eliminates the effects of varying delay times without having to obtain the reference delay time TD in the reproduction apparatus used for reading. This method can check whether the disk is a legitimate disk or not by checking whether the positional relationship of mark 1 at address n in Figure 8(8) relative to another mark 2 matches or not. That is, TD is ignored as a variable, and the difference between the position, A1 = a1 + TD, of mark 1 measured and the position, A2 = a2 + TD, of mark 2 measured is obtained, which is given as A1 - A2 = a1 - a2. At the same time, it is checked whether this difference matches the difference, a1 - a2, between the position a1 of the decrypted mark 1 and the position information a2 of the mark 2, thereby judging whether the disk is a legitimate disk or not. The effect of this method is that the positions can be checked after compensating for variations of the reference delay time TD by using a simpler constitution. Next, the encrypted information writing process will be described. The position information read is first converted into ciphertext or "signed" with a digital signature. Then, the marking position information thus encrypted or signed is converted into a barcode as an ID unique to the optical disk, and the barcode is recorded in overwriting fashion in a prescribed region of a pre-pit area on the optical disk. Barcode patterns 584c - 584e in Figure 2(a) indicate the barcode written to the prescribed region of the pre-pit area, that is, in the innermost portion of the pre-pit area. Parts (1) to (5) of Figure 3 show the process from the recording of the barcode to the demodulation of the barcode detection signal by a PE-RZ modulated signal demodulator. In part (1) of Figure 3, the reflective layer is trimmed by a pulsed laser, and a barcode-like trimming pattern, such as shown in part (2) of the figure, is formed. At the playback apparatus (player), an envelope waveform some portions of which are missing, as shown in part (3) of the figure, is obtained. The missing portions result in the generation of a low level signal that cannot occur with a signal generated from an ordinary pit. Therefore, this signal is sliced by a second slice level comparator to obtain a low-reflectivity portion detection signal as shown in part (4) of the figure. In part (5) of the figure, the playback signal of the barcode is demodulated from this low-reflectivity portion detection signal by the PE-RZ modulated signal demodulator 621 which will be described in detail in the second-half part (II). It will be appreciated that, instead of the PE-RZ modulated signal demodulator 621, a pulse-width modulated signal demodulator (PWM demodulator) may be used, in which case also, a similar effect can be obtained. When applying the above encryption or digital signature, a secret key of a public key encryption function is used. As an example of the encryption, Figures 9A and 9B show an encryption process using an RSA function. As shown in Figure 9A, the process consists of the following major routines: step 735a where marking position information is measured at the optical disk maker, step 695 where the position information is encrypted (or a digital signature is appended), step 698 where the position information is decrypted (or the signature is verified or authenticated) in the reproduction apparatus, and step 735w where a check is made to determine whether the disk is a legitimate optical disk or not. First, in step 735a, the marking position information on the optical disk is measured in step 735b. The position information is then compressed in step 735d, and the compressed position information H is obtained in step 735e. In step 695, the ciphertext of the compressed position information H is constructed. First, in step 695, a secret key, d, of 512 or 1024 bits, and secret keys, p and q, of 256 or 512 bits, are set, and in step 695b, encryption is performed using an RSA function. When the position information H is denoted by M, M is raised to d-th power and mod n is calculated to yield ciphertext C. In step 695d, the ciphertext C is recorded on the optical disk. The optical disk is thus completed and is shipped (step 735k). In the reproduction apparatus, the optical disk is loaded in step 735m, and the ciphertext C is decrypted in step 698. More specifically, the ciphertext C is recovered in step 698e, and public keys, e and n, are set in step 698f; then in step b, to decrypt the ciphertext C, the ciphertext C is raised to e-th power and the mod n of the result is calculated to obtain plaintext M. The plaintext M is the compressed position information H. An error check may be performed in step 698g. If no errors, it is decided that no alterations have been made to the position information, and the process proceeds to the disk check routine 735w shown in Figure 9B. If an error is detected, it is decided that the data is not legitimate one, and the operation is stopped. In the next step 736a, the compressed position information H is expanded to recover the original position information. In step 736c, measurements are made to check whether the marking is actually located in the position on the optical disk indicated by the position information. In step 736d, it is checked whether the difference between the decrypted position information and the actually measured position information falls within a tolerance. If the check is OK in step 736e, the process proceeds to step 736h to output software or data or execute programs stored on the optical disk. If the check result is outside the tolerance, that is, if the two pieces of position information do not agree, a display is produced to the effect that the optical disk is an illegally duplicated one, and the operation is stopped in step 736g. RSA has the effect of reducing required capacity since only the ciphertext need be recorded. In the case of a DVD disk in the present embodiment, all data are recorded in pits with CLV, as shown in Figure 10. Stripes 923 (forming a barcode) are recorded with CAV. CLV recording means recording with constant linear velocity, while CAV recording means recording with constant angular velocity. In the present invention, the stripes 923 are recorded with CAV, superimposed on a pre-pit signal in a lead-in data area holding an address which is recorded with CLV. That is, the data is overwritten with the stripes. In the present invention, the pre-pit signal area maps into all the data areas where pits are formed. The prescribed region of the pre-pit signal area, as mentioned in the present invention, corresponds to an inner portion of the optical disk; this region is also called a post-cutting area (PCA). In this PCA area, the barcode is recorded with CAV, superimposed on pre-bit signals. In this way, the CLV data is recorded with a pit pattern from the master disk, while the CAV data is recorded with laser-removed portions of the reflective film. Since the barcode data is written in overwriting fashion, pits are recorded between the barcode stripes 1T, 2T, and 3T. Using this pit information, optical head tracking is accomplished, and Tmax or Tmin of the pit information can be detected; therefore, motor rotational speed is controlled by detecting this signal. To detect Tmin, the relation between the trimming width t of stripe 923a and the pit clock T (pit) should be t > 14T (pit), as shown in Figure 10, to achieve the above effect. If t is shorter than 14T, the pulse width of the signal from the stripe 923a becomes equal to the pulse width of the pit signal, and discrimination between them is not possible, so that the signal from the stripe 923a cannot be demodulated. To enable pit address information to be read at the same radius position as the stripes, an address area 944 is provided longer than a unit of one address of pit information, address information can thus be obtained, making it possible to jump to the desired track. Furthermore, the ratio of the stripe area to the non-stripe area, that is, the duty ratio, is made less than 50%, i.e., T(S) < T(NS); since the effective reflectivity decreases only by 6 dB, this has the effect of ensuring stable focusing of the optical head. Next, we will describe an example of a condition in which tracking control cannot be applied during playback (this condition is also referred to as the tracking OFF condition). Since the stripes 923 are written over pits, interrupting pit signals and preventing correct playback of the pit data, tracking control may not be possible on some players. In such players, the strips 923, which are CAV data, can be read by the optical pickup by applying rotational control using a rotational pulse from a Hall element, etc. in the motor 17. Figure 11 shows a flowchart illustrating a procedure for operations in a playback apparatus when pit data in the optical tracks in the stripe area cannot be correctly played back. In Figure 11, when a disk is inserted in step 930a, the optical head is moved by a prescribed distance to the inner portion in step 930b. The optical head is thus positioned on the area where the stripes 923 of Figure 10 are recorded. Here, it is not possible to correctly playback data from all the pits recorded in the stripe area 923. In this case, therefore, usual rotation phase control cannot be applied for the playback of the pit data recorded with CLV. In step 930c, rotational speed control is applied by using a rotational sensor of a Hall element in the motor or by measuring the T(max) or T(min) or frequency of a pit signal. If it is determined in step 930i that there are no stripes, the process jumps to step 930f. If there are stripes, the barcode is played back in step 930d, and when playback of the barcode is completed in step 930e, the optical head is moved in step 930f to an outer area where no stripes are recorded. In this area, since no stripes are recorded, the pits are played back correctly and accurate focus and tracking servo are achieved. Since the pit signal can be played back, usual rotation phase control can be performed to rotate the disk with CLV. As a result, in step 930h, the pit signal is played back correctly. By switching between the two rotation control modes, i.e., the rotational speed control and the rotation phase control by pit signals, the effect is obtained that two different kinds of data, barcode stripe data and pit-recorded data, can be played back. Since the stripes are recorded in the innermost area, switching means measures the radius position of the optical head from the optical head stopper or from the address of a pit signal, and based on the result of the measurement, correctly performs switching between the two rotation control modes. In the present invention, as shown in Figure 10, the control data recorded in the control data area 936 of the optical disk contains a PCA stripe presence/absence identifier 937 recorded as a pit signal. Therefore, the optical head is first moved, in step 940n, to an outer area where the control data is recorded. And then the optical head moves inwardly jumping across a plurality of tracks until reaching the control data area 936. And then in step 940a, the control data is played back. It can thus be checked whether the stripes are recorded or not. If, in step 940b, the stripe presence/absence identifier is 0, the process proceeds to step 940f to initiate rotation phase control for normal playback with CLV. On the other hand, if, in step 940b, the presence/absence identifier 937 is 1, then the process proceeds to step 940h to check the presence or absence of a reverse-side record identifier 948 which indicates that the stripes are recorded on the side opposite from the side being played back, that is, on the reverse side. If the stripes are recorded on the reverse side, the process proceeds to step 940i to play back the recording surface on the reverse side of the optical disk. If the reverse side cannot be automatically played back, an indication is output for display, to urge the user to turn over the disk. If it is determined in step 940h that the stripes are recorded on the side being played back, the process proceeds to step 940c, where the head is moved to the stripe area 923 in the inner portion of the disk, and in step 940d, the control mode is switched to rotational speed control to play back the stripes 923 with CAV rotation. If the playback is completed in step 940e, then in step 940f the control mode is switched back to rotation phase control for CLV playback and the optical head is moved to the outer portion of the disk to play back pit signal data. Since the stripe presence/absence identifier 937 is recorded in the pit area holding the control data, etc., as described above, the second method has the effect of being able to play back the stripes more reliably and more quickly compared to the first playback method described with reference to Figure 11. When the PCA area is with tracking OFF, level of the noise signal which is generated by the pits drops. PCA signal level remains unchanged if tracking is set OFF. Therefore, in the filtered waveform, the pit signal drops, making it easier to distinguish between the PCA signal and the pit signal. This has the effect of simplifying the circuitry and reducing the error rate. Furthermore, the provision of the stripe reverse-side record identifier 948 makes it possible to identify that the stripes are recorded on the reverse side of the disk; the effect is that the barcode stripes can be played back reliably in the case of a double-sided DVD optical disk. According to the present invention, since the stripes are recorded penetrating through the reflective films on both sides of a disk, the stripe pattern can also be read from the reverse side of the disk. The stripes can be played back from the reverse side of the disk by checking the stripe reverse-side identifier 948 and by playing back the code in the reverse direction when reading the stripes. The present invention uses a bit string "01000110" as the synchronization code. When played back from the reverse side, the synchronization code is played back as "01100010", from which it can be detected that the barcode is being played back from the reverse side. In this case, by demodulating the code in reverse direction in the demodulator 942 in the playback apparatus of Figure 15, the barcode recorded in penetrating fashion can be correctly played back even if played back from the reverse side of a double-sided disk. The playback apparatus of Figure 7 will be described in more detail later. Further, if, as shown in Figure 10, a 300-µm wide guard-band area 999, where only address information is recorded but no other data is recorded, is provided between the PCA area 998 and the control data area 936, access to the control data can be made more stable. The guard-band area 999 will be described in more detail below. When the optical head accesses the control data from the outer portion of the disk, the optical head moves inwardly jumping across a plurality of tracks until reaching the control data area 936. In some cases, the optical head may be moved past the destination control data area 936, landing at a portion further inward of the control data area. At this time, if the PCA area 998 exists directly adjacent to the inner circumference of the control data area, the optical head will lose its own position since an address cannot be played back in the PCA area 998. It, then, becomes impossible to control the optical head. Accordingly, when the guard-band area with a width, for example, 300 µm, greater than one jump width of the optical head, is provided in the above-noted portion, if the optical head is moved past the control data area 936 the optical head will always land within the guard-band area. Then, by reading an address in the guard-band area, the optical head knows its own position and can thus be repositioned on the destination control data area. In this way, the optical head can be controlled more reliably and more quickly. Further, as shown in Figure 10, the control data also contains an additional stripe data presence/absence identifier and a stripe recording capacity. That is, after recording first stripes on an optical disk, additional stripes can be recorded in an empty, unrecorded portion of the area. The first recorded stripes will be referred to as the first set of stripes, and the additionally recorded stripes as the second set of stripes. With this configuration, when the first set of stripes 923 is already recorded by trimming, as shown in Figure 10, the capacity of the available space for trimming the second set of stripes 938 can be calculated. Accordingly, when the recording apparatus performs trimming to record the second set of stripes, the control data provides an indication of how much space is available for additional recording; this prevents the possibility of destroying the first set of stripes by recording more than 360° over the area. Furthermore, as shown in Figure 10, a gap 949 longer than one pit-signal frame length is provided between the first set of stripes 923 and the second set of stripes 938; this serves to prevent the previously recorded trimming data from being destroyed. Next, referring to Figure 7, a brief description will be given of a playback apparatus for playing back the barcode recorded on an optical disk by the above method. The description will also touch on productivity increases. Figure 7 is a block diagram of the playback apparatus already described above. Hereinafter, the apparatus of Figure 7 will be described as a barcode reading apparatus, that is, a playback apparatus. An explanation will be given again referring to Figure 7, this time focusing on the demodulation operation. First, high-frequency components generated by pits are removed by a low-pass filter (LPF filter) 94 from a stripe signal output. In the case of a DVD, there is a possibility that a maximum 14T signal may be played back, where T = 0.13 µm. In this case, it has been confirmed by experiment, a stripe signal and a high-frequency component generated by a pit can be separated by using the second-order or third-order Chevihov low-pass filter. That is, the use of a second- or higher-order LPF has the effect of being able to separate a pit signal and a barcode signal, thus ensuring stable playback of a barcode. Referring to Figure 7, a further description will be given. Digital data is demodulated by the PE-RZ demodulator 942 in the above manner. The data is then fed to an ECC decoder 928 for error correction. That is, deinterleaving is performed in a deinterleaver 928a, and Reed-Solomon code computation is performed in an RS decoder 928b for error correction. A brief description will now be given in relation to productive tact. Figure 12(a) shows the data structure after the barcode is ECC encoded according to the present embodiment. Figure 12(b) shows the data structure after ECC encoding when n = 1 according to the present embodiment. Figure 12(c) shows an ECC error-correction capability according to the present embodiment. In the present invention, the interleaving and Reed-Solomon error-correction coding shown in the data structure of Figure 12(a) are performed using the ECC encoder 927 shown in Figure 1 when recording stripes on an optical disk. With this error-correction method, a read error occurs in only one disk out of 10 7 = 10 million optical disks under the condition of that Byte error rate of 10 -4 occurs, as shown in Figure 12(c). In this data structure, to reduce the code data length the same sync code is assigned to four rows, reducing the number of sync codes by a factor of 4 and thus increasing efficiency. With further reference to Figure 12, the scalability of the data structure will be described. In the present invention, the recording capacity can be varied freely, for example, within a range of 12B (12 Byte) to 188B in increments of 16B. That is, n can be changed within a range of n=1 to n=12, as shown in Figure 12(c). As shown in Figure 12(b) and Figure 6(a), for example, in the data structure when n=1, there are only four data rows 951a, 951b, 951c, and 951d, followed by ECC rows 952a, 952b, 952c, and 952d. Figure 6(a) is a diagram showing Figure 12(b) in further detail. The data row 951 constitutes EDC of 4B. Figure 6(b) shows this in an equivalent form. Error-correction encoding computation is performed, assuming that data rows from 951e to 951z all contain 0s. Mathematical equations for EDC and ECC computations are shown in Figures 6(c) and 6(d), respectively. In this way, the data is ECC-encoded by the ECC encoder 927 in the recording apparatus of Figure 1 and recorded as a barcode on the disk. When n=1, data of 12B is recorded over an angle of 51 degrees on the disk. Likewise, when n=2, data of 18B can be recorded; when n=12, data of 271B can be recorded over an angle of 336 degrees on the disk. In the present invention, by encoding and decoding the data using the EDC and ECC computation equations shown in Figures 6(c) and 6(d), when the data amount is smaller than 188B, the computation is performed assuming all remaining bits are 0s, so that the data is stored with a small recording capacity. This serves to shorten the productive tact. When performing laser trimming, as in the present invention, the above-described scalability has a significant meaning. More specifically, when performing laser trimming at a factory, it is important to shorten the productive tact. With a slow-speed apparatus which trims one stripe at a time, it will take more than 10 seconds to record a few thousand stripes to the full capacity. The time required for disk production is 4 seconds per disk; if full-capacity recording has to be done, the productive tact increases. On the other hand, for the moment, disk ID number will be a main application area of the present invention; in this application, the PCA area capacity can be as low as 10B. If 271B are recorded when only 10B need to be written, the laser processing time will increase by a factor of 6, leading to a production cost increase. The scalability method of the present invention achieves reductions in production cost and time. In the playback apparatus shown in Figure 7, when n=1 as in Figure 12(b), for example, the ECC decoder 928 performs the EDC and ECC error-correction computations shown in Figures 6(c) and 6(d), assuming that the data rows 951e to 951z all contain 0s as shown in Figure 6(b); the effect of this is that data of 12 to 271B can be corrected for errors by using the same program. In this case, the number of program steps decreases, permitting the use of a small-capacity ROM in the microcomputer. Furthermore, the pulse width reproduced from each stripe width is made less than 1/2 of one pulse period. Since there are three difference pulse spacings, 1T, 2T, and 3T, the ratio of the sum of all the stripe areas in one track to the total area of the track is less than 1/3. With this arrangement, in the case of a disk of standard reflectivity of 70% the reflectivity of the stripe area is 2/3 of that, i.e., about 50%. Since this value is enough for focus control, the PCA area can be played back on a conventional ROM disk player.

Claims: An optical disk comprising: a first recording area where a main information is recorded, a second recording area where barcode-like marks (923) each of which has a strip-like configuration in a radial direction and which are disposed in a circumferential direction, are recorded as a sub information, said second recording area being formed in a circumferential direction and wherein there is a certain area (949) in a circumferential direction where barcode-like marks are not recorded within said second recording area, characterised in that said first recording area contains at least a lead-in area from which data recording starts, and a control data area (936) which represents physical property of the optical disk, said second recording area is disposed at a radial position which lies closer to the disk centre than said control data area (936) of said first recording area, and said second recording area is overlapped with said lead-in area, and said sub information is a PE-RZ modulated signal recorded on said second recording area as a barcode signal so that a width of said barcode-like marks (923a, 923b) is half or less than a period of said barcode-like marks (923). The optical disk according to claim 1, characterised in that a time period (t) of the width of the barcode-like mark in a circumferential direction has the following relation t > 14T, provided that (T) indicates a period of channel clock of the main information. The optical disk according to claim 1 or 2, characterised in that an identifier (937) which indicates whether the barcode-like marks (923) are present or not within said second recording area, is provided in the control data area (936). The optical disk according to claim 1,2, or 3, characterised in that address information are recorded in said certain area (949), where no barcode-like marks are recorded. An optical reproducing apparatus comprising a reproducing means arranged for reproducing the optical disk according to one of claims 1 to 4, PE-RZ demodulation means (942) for demodulating said sub information recorded on said second recording area, another demodulation means (591) for demodulating said main information by using other demodulating method than said PE-demodulation method the optical reproduction apparatus being arranged to read said sub information and said main information with the same optical head. The optical reproducing apparatus according to claim 5, characterised in that EFM-demodulating means (592) is used as the demodulation means for the main information. The optical reproducing apparatus according to claim 5 or 6, characterised in that when said certain area (949) where said barcode-like marks (923) are not recorded is reproduced, address information is read out.

Inventors: GOTOH YOSHIHO, KOISHI KENJI, MORIYA MITSURO, OSHIMA MITSUAKI, TANAKA SHINICHI, GOTOH, YOSHIHO, KOISHI, KENJI, MORIYA, MITSURO, OSHIMA, MITSUAKI, TANAKA, SHINICHI, Tanaka, Shinichi, C-403 Rose mansion
Applicants: MATSUSHITA ELECTRIC IND CO LTD, MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 1996
Main classification: G11B7
IPC codes: G11B27, G11B20, G11B19, G11B7, G06K19, G11B5, G11B23, G06K1, G11B13