An optical disk and an optical disk reproduction apparatus

Abstract: An optical data disk on which data is recorded and which comprises an identifier for indicating whether a barcode-like mark is present or not on said disk is constructed from two disk substrates. The first substrate may have a semi-transparent reflection layer and the second substrate may have an almost non-transparent reflection layer, and data from both recording substrates are reproduced from one side of said disk. Further, a reproduction apparatus for such type of optical disk is provided.

Description: The present invention relates to an optical disk according to the preamble part of claim 1 and an optical disk reproduction apparatus for use with such disk. An optical disk and reproduction apparatus of this kind are known from EP-A-741382. 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. In view of the above problem with the prior art, it is an object of the present invention to provide an optical disk wherein data such as a disk ID number, etc. is converted into a barcode and recorded in a pit area, thereby permitting the use of a single pickup to read both the bit data and barcode data. The invention is an optical disk as set forth in claim 1, on which data is recorded wherein, in a prescribed region on said disk, all or part of a barcode is written and wherein an identifier for indicating the presence or absence of said barcode is recorded on said disk, said optical disk being constructed from two disk-substrates laminated together. The invention further provides an optical disk reproduction apparatus as set forth in claim 5, wherein recorded contents of a recording area of an optical disk of the aforementioned kind, are reproduced. 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 diagram illustrating a piracy prevention algorithm; 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 is a diagram showing a two-layer disk fabrication process (part 1); Figure 7 is a diagram showing the two-layer disk fabrication process (part 2); Figure 8(a) is an enlarged view of a nonreflective portion of a laminated type according to the present embodiment, and (b) is an enlarged view of a nonreflective portion of a single-plate type; Figure 9(a) is a reproduced-waveform diagram for a nonreflective portion, (b) is a reproduced-waveform diagram for a nonreflective portion, (c) is a reproduced-waveform diagram for a nonreflective portion, and (d) is a plan view of a master disk produced by a master disk method; Figure 10(a) is a cross-sectional view of a nonreflective portion of the laminated type, and (b) is a cross-sectional view of a nonreflective portion of the single-plate type; Figure 11 is a schematic diagram, based on an observation through a transmission electron microscope, illustrating a cross section of the nonreflective portion; Figure 12(a) is a cross-sectional view of a disk, and (b) is a cross-sectional view of the non-reflective portion of the disk. Figure 13 is a block diagram of a low-reflectivity position detector; Figure 14 is a diagram illustrating the principle of detecting address/clock positions of a low-reflectivity portion; Figure 15 is a diagram showing a detected waveform of a first-layer marking signal; Figure 16 is a diagram showing a detected waveform of a second-layer marking signal; Figure 17 is a diagram showing the arrangement of stripes on a disk and the contents of control dada; Figure 18 is a flowchart illustrating how control mode is switched between CAV and CLV when playing back stripes; Figure 19 is a diagram showing a stripe area and an address area on a disk; Figure 20 is a diagram showing a procedure for reading control data for playback, and Figure 21 is a perspective view showing a nonreflective portion formed in a two-layer disk. BEST MODE OF EMBODIMENT The preferred embodiment 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. 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. As previously stated, a supplementary explanation will be given below of an alternative type of disk (a two-layer laminated disk) with reference to Figures 6 and 7. Figures 4 and 5 showed a disk generally known as a single-layer laminated disk which has a reflective layer only on one substrate 801. On the other hand, Figures 6 and 7 show a disk generally known as a two-layer laminated disk which has reflective layers on both substrates 801 and 803. For laser trimming, the processing steps (5) and (6) are fundamentally the same for both types of disks, except with significant differences which are briefly described below. First, while the single-layer disk uses a reflective layer formed from an aluminum film having reflectivity as high as 70% or over, in the two-layer disk the reflective layer 825 formed on the reading-side substrate 801 is a semi-transparent gold (Au) film having a reflectivity of 30%, while the reflective layer 802 formed on the print-side substrate 803 is the same as that used in the single-layer disk. Second, as compared with the single-layer disk, the two-layer disk is required to have high optical accuracy; for example, the adhesive layer 804 must be optically transparent and be uniform in thickness, and the optical transparency must not be lost due to laser trimming. Parts (7), (8), and (9) of Figure 7 show the signal waveforms obtained from the first layer of the two-recording-layer disk. Likewise, parts (10), (11), and (12) of Figure 7 show the signal waveforms obtained from the second layer of the two-recording-layer disk. The contents of these signal waveforms are essentially the same as those of the waveforms described with reference to parts (a) to (c) of Figure 5. The waveform from the second layer is similar to that from the first layer, though the signal level is lower than from the first layer. However, since the first and second layers are bonded together, relative positional accuracy between them is random and can be controlled only with an accuracy of a few hundred microns. As will be described later, since the laser beam passes through the two reflective films, to make an illegal disk the position informations on the first and second layers for the first mark, for example, have to be made to match the same value on the legitimate disk. But making them match would require a near-submicron accuracy in laminating, and consequently, making illegal disks of the two-layer type is practically impossible. The technique for forming the nonreflective optical marking portion will be described in further detail in sections (a) to (d) below with reference to Figures 8 to 12, etc., dealing with the laminated type in comparison with a single-plate type. Figures 8(a) and (b) are micrographs showing plan views of nonreflective optical marking portions, and Figure 10(a) is a simplified schematic cross-sectional view of a nonreflective portion of the two-layer laminated disk. Using a 5 µj/pulse YAG laser, a laser beam was applied to a 500angstrom aluminum layer lying 0.6 mm below the surface of a 1.2mm thick ROM disk consisting of two 0.6mm thick disks laminated together, and, as a result, a 12 µm wide slit-like nonreflective portion 815 was formed, as shown in the X 750 micrograph of Figure 8(a). In this X 750 micrograph, no aluminum residues were observed on the nonreflective portion 815. Thick swollen aluminum layers, 2000 angstroms thick and 2 µm wide, were observed along boundaries between the nonreflective portion 815 and reflective portions. As shown in Figure 10(a), it was confirmed that no significant damage had occurred inside. In this case, the application of the pulsed laser presumably melted the aluminum reflective layer, causing a phenomenon of molten aluminum buildup along the boundaries on both sides due to the surface tension. We call this a hot melt surface tension (HMST) recording method. This is a characteristic phenomenon observed only on a laminated disk 800. Figure 11 is a schematic diagram, based on an observation through a transmission electron microscope (TEM), illustrating a cross section of the nonreflective portion formed by the above laser trimming process. And Figure 11 shows that the adhesive layer of the disk has been removed by using solvent. In the figure, if the aluminum film swollen portion is 1.3 µm wide and 0.20 µm thick, the amount of increased aluminum in that portion is 1.3 x (0.20 - 0.05) = 0.195 µm 2 . The amount of aluminum originally deposited in a half portion (5 µm) of the laser exposed region (10 µm) was 5 x 0.05 = 0.250 µm 2 . The difference is calculated as 0.250 - 0.195 = 0.055 µm 2 . In terms of length, this is equivalent to 0.055/0.05 = 1.1 µm. This means that an aluminum layer of 0.05µm thickness and 1.1µm length remained, and therefore, it can be safely said that almost all aluminum was drawn to the film swollen portion. Thus, the result of the analysis of the figure also verifies the explanation about the above-described characteristic phenomenon. Using Figures 12(a), 12(b), etc., a further description will be given dealing with the single-layer laminated disk type. As shown in Figure 12(a), the reflective layer 802 has the transparent substrate 801 of polycarbonate on one side, and the hardened adhesive layer 804 and a substrate on the other side, the reflective layer 802 thus being hermetically sealed therebetween. In this condition, pulsed laser light is focused thereon for heating; in the case of our experiment, heat of 5 µJ/pulse is applied to a circular spot of 10 to 20 µm diameter on the reflective layer 802 for a short period of 70 ns. As a result, the temperature instantly rises to 600°C, the melting point, melting state is caused. By heat transfer, a small portion of the transparent substrate 801 near the spot is melted, and also a portion of the adhesive layer 804 is melted. The molted aluminum in this state is caused by surface tension to build up along boundaries 821a and 821b, with tension being applied to both sides, thus forming buildups 822a and 822b of hardened aluminum, as shown in Figure 12(b). The nonreflective portion 584 free from aluminum residues is thus formed. This shows that a clearly defined nonreflective portion 584 can be obtained by laser-trimming the laminated disk as shown in Figures 10(a) and 12(a). Exposure of the reflective layer to the outside environment due to a damaged protective layer, which was the case with a single-plate type, was not observed even when the laser power was increased more than 10 times the optimum value. After the laser trimming, the nonreflective layer 584 has the structure shown in Figure 12(b) where it is sandwiched between the two transparent substrates 801, 803 and sealed with the adhesive layer 804 against the outside environment, thus producing the effect of protecting the structure from environmental effects. Another benefit of laminating two disks together will be described next. When secondary recording is made in the form of a barcode, an illegal manufacturer can expose the aluminum layer by removing the protective layer in the case of a single-plate disk, as shown in Figure 10(b). This gives rise to a possibility that nonecrypted data may be tampered with by redepositing an aluminum layer over the barcode portion on a legitimate disk and then laser-trimming a different barcode. For example, if the ID number is recorded in plaintext or separately from main ciphertext, in the case of a single-plate disk it is possible to alter the ID number, enabling illegal use of the software by using a different password. However, if the secondary recording is made on the laminated disk as shown in Figure 10(a), it is difficult to separate the laminated disk into two sides. In addition, when removing one side from the other, the aluminum reflective film is partially destroyed. When the anti-piracy marking is destroyed, the disk will be judged as being a pirated disk and will not run. Accordingly, when making illegal alterations to the laminated disk, the yield is low and thus illegal alterations are suppressed for economic reasons. Particularly, in the case of the two-layer laminated disk, since the polycarbonate material has temperature/humidity expansion coefficients, it is nearly impossible to laminate the two disks, once separated, by aligning the anti-piracy markings on the first and second layers with an accuracy of a few microns, and to mass produce disks. Thus, the two-layer type provides a greater effectiveness in piracy prevention. It was thus found that a clearly defined slit of a nonreflective portion 584 can be obtained by laser-trimming the laminated disk 800. The technique for forming the nonreflective optical marking portion has been described above. Next, the process of reading the position of the thus formed marking will be described. Figure 13 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 14 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 13, 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, as shown in the waveform diagram of Figure 9(a), they can be clearly distinguished using a simple circuit. Figure 9(a) is a diagram showing the waveform of a playback signal from a PCA area, described later, containing the nonreflective portion 584 formed by laser light. Figure 9(b) is a diagram showing the waveform of Figure 9(a) but with a different time axis. 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. Figure 9(c) shows the waveform of a playback signal when the anti-piracy identification mark was formed by making pits longer than other data pits on the master disk. It can be seen from the diagram that the waveform 824p of the anti-piracy identification mark is distinguishable from the waveform of other pit data. In this way, a waveform similar to that obtained from the PCA area described later can be obtained by forming longer pits on the master disk; in this case, however, the waveform is a little difficult to distinguish as compared to the waveforms shown in parts (a) and (b) of Figure 9. 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. This master disk method will be described below. Figure 9(d) is a plan view showing a portion of a master disk wherein pits 824q in a few hundred tracks on the master disk are made longer than other data pits and made equal to the barcode bar width t (= 10 µm). Since reflectivity drops in this longer-bit area, a waveform 824 p as shown in Figure 9(c) is obtained. It can be seen from the diagram that the waveform 824p by the master disk method is distinguishable from the waveform of other pit data. In this way, a waveform similar to that obtained from the PCA area described later can be obtained by the master disk method; in this case, however, the waveform is a little difficult to distinguish as compared to the waveforms shown in parts (a) and (b) of Figure 9. As shown in Figure 14(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 13. Using the reproduced clock signal as the reference signal, position information is obtained in a low reflectivity position information output section 596. Figure 14(1) shows a cross-sectional view of the optical disk. As shown in Figure 13, 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 14(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 position 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 14. As shown in the cross-sectional view of the optical disk in Figure 14(1), the low reflectivity portion 584 of mark number 1 is formed partially. A reflection slope signal such as shown in Figure 16(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 14(5), is output from the low reflectivity light amount detector 586. As shown by a reproduced digital signal in Figure 14(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 14(6) is used along with address information. First, a reference clock 605 at address n in Figure 14(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 14(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 14(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. The processing steps in the optical disk manufacturing process have been described above. Next, the constitution and operation of a reproduction apparatus (player) for reproducing the thus completed optical disk on a player will be described with reference to Figure 3. In the figure, the construction of an optical disk 9102 will be described first. A marking 9103 is formed on a reflective layer (not shown) deposited on the optical disk 9102. In the manufacturing process of the optical disk, the position of the marking 9103 was detected by position detecting means, and the detected position was encrypted as marking position information and written on the optical disk in the form of a barcode 9104. Position information reading means 9101 reads the barcode 9104, and decrypting means 9105 contained therein decrypts the contents of the barcode for output. Marking reading means 9106 reads the actual position of the marking 9103 and outputs the result. Comparing/judging means 9107 compares the decrypted result from the decrypting means 9105 contained in the position information reading means 9101 with the result of reading by the marking reading means 9106, and judges whether the two agree within a predetermined allowable range. If they agree, a reproduction signal 9108 for reproducing the optical disk is output; if they do not agree, a reproduction stop signal 9109 is output. Control means (not shown) controls the reproduction operation of the optical disk in accordance with these signals; when the reproduction stop signal is output, an indication to the effect that the optical disk is an illegal duplicated disk is displayed on a display (not shown) and the reproduction operation is stopped. In the above operation, it will be recognized that it is also possible for the marking reading means 9106 to use the decrypted result from the decrypting means 9105 when reading the actual position of the marking 9103. Namely in this case, the marking reading means 9106 checks whether the marking is actually located in the position on the optical disk indicated by the position information which is decrypted by the decrypting means 9105. Thus the reproduction apparatus of the above construction can detect an illegally duplicated optical disk and stop the reproduction operation of the disk, and can prevent illegal duplicates practically . When a barcode is recorded by laser trimming on the above-described single-plate disk, the protective layer 862 is destroyed, as explained in connection with Figure 10(b). Therefore, after laser trimming at a press factory, the destroyed protective layer 862 has to be reformed at the press factory. This means that a barcode cannot be recorded on the optical disk at a software company or a dealer that does not have the necessary equipment. The problem expected here is that the application of barcode recording is greatly limited. On the other hand, when the marking position information was recorded as a barcode by laser trimming on the laminated-type disk of the invention formed from two transparent substrates laminated together, it was confirmed that the protective layer 804 remained almost unchanged, as already explained in connection with Figure 10(a). This was confirmed by experiment by observing the disk under an optical microscope of 800X magnification. It was also confirmed that no change had occurred to the reflective film in the trimmed portion after an environmental test of 96 hours at a temperature of 85°C and a humidity of 95%. In this way, when the laser trimming of the present invention is applied to a laminated disk such as a DVD, there is no need to reform the protective layer at the factory. This offers a great advantage in that a barcode can be recorded by trimming on the optical disk at a place other than the press factory, for example, at a software company or a dealer. The usefulness of barcode recording on the laminated-type optical disk was thus confirmed. In this case, since the secret key information for encryption that the software company keeps need not be delivered to a party outside the company, security increases greatly, particularly when security information such as a serial number for copy prevention is recorded as a barcode in addition to the above-described position information. Furthermore, in the case of a DVD, since the barcode signal can be separated from DVD pit signals by setting the trimming line width at a value greater than 14T or 1.82 microns, as will be described later, the barcode signal can be recorded in the pit recording area on the DVD in superimposing fashion. The barcode formed in this way offers the effect that the barcode can be read by the optical pickup used to read the pit signal. Thus, by applying the above barcode forming method and modulation recording method to a laminated-type disk such as a DVD, a laminated-type optical disk can be provided that permits secondary recording after shipment from the factory. The above description has dealt mainly with a case in which the barcode is formed by laser trimming on a laminated-type disk of a two-layer, single-sided structure (with two reflective layers formed on one side). This single-sided, two-layered optical disk is the type of disk that permits playback of both sides from one side of the disk without having to turn over the disk. On the other hand, when trimming is performed on a double-sided, laminated-type optical disk that needs turning over when playing back the reverse side, the laser light passes through the two reflective films each formed on one side of the disk. Therefore, the barcode can be formed simultaneously on both sides. This provides an advantage for media fabrication in that the barcode can be recorded simultaneously on both sides in a single step. In this case, when the optical disk is turned over to play back the reverse side on a playback apparatus, the barcode signal is played back in just the opposite direction to the direction that the barcode signal on the front side is played back. A method for identifying the reverse side is therefore needed. This will be described in detail later. In the case of a DVD disk in the present embodiment, all data are recorded in pits with CLV, as shown in Figure 17. 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 17, 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, as shown in Figure 19; 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. Figure 18 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 18, 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 17 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. The method for playing back the optical disk of the present embodiment will be described with reference to Figure 20 which shows a flowchart illustrating the operation. The second playback method is an improved version of a playback method for playing back an optical disk on which a stripe presence/absence identifier 937 is not defined. Since tracking is not applied in the stripe area on an optical disk of this type, it takes time to distinguish between a stripe pattern legally formed on the disk and an irregular pattern caused by scratches on the disk surface. Therefore, regardless of whether the stripes are recorded or not, the playback procedure has to perform a stripe reading operation first, to check the presence or absence of stripes or whether the stripes are recorded in the inner portion of the optical disk. This may cause a problem in that an extra time is required before the data can be actually played back. The improved playback method obviates this point. First, as shown in Figure 20, when an optical disk is inserted, control data is played back in step 940a. Usually, physical feature information and attribute information of the optical disk are recorded as control data in a control data area. The physical feature information includes, for example, information indicating that the optical disk is a laminated-type disk of a two-layer, single-sided structure. In the present invention, as shown in Figure 17, 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 18. 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. 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 13, 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 13 will be described in more detail later. Further, if, as shown in Figure 17, 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. Further, as shown in Figure 17, 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 17, 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 30, 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. (b) Next, referring to Figure 13, 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 13 is a block diagram of the playback apparatus. Hereinafter, the apparatus of Figure 15 will be described as a barcode reading apparatus, that is, a playback apparatus. An explanation will be given again referring to Figure 13, 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. Digital data is demodulated by the PE-RZ demodulator 942. The data is then fed to an ECC decoder 928 for error correction. Shown in Figure 15 is the signal from the first layer in a two-layer optical disk having two reflective layers. The signal (1) shows the condition when the start position of an optical mark on the first layer is detected. Figure 2 1 shows the condition of the signal from the second layer. To read the second layer, a first/second layer switching section 827 in Figure 13 sends a switching signal to a focus control section 828 which then controls a focus driving section 829 to switch the focus from the first layer to the second layer. Additional matters relating to the two-disk laminated optical disk will be further described below. Figure 16 shows address position information pertaining to the optical marking formed on the second layer. Since laser light penetrates the first and second layers through the same hole, as shown in the process step (6) in Figure 7, the nonreflective portion 815 formed on the first reflective layer 802 and the nonreflective portion 826 formed on the second reflective layer 825 are identical in shape. This is depicted in the perspective view of Figure 21. In the present invention, after the transparent substrate 801 and the second substrate 803 are laminated together, laser light is applied penetrating through to the second layer to form an identical mark thereon. In this case, since coordinate arrangements of pits are different between the first and second layers, and since the positional relationship between the first and second layers is random when laminating them together, the pit positions where the mark is formed are different between the first and second layers, and entirely different position information is obtained from each layer. These two kinds of position information are encrypted to produce an anti-piracy disk. If it is attempted to duplicate this disk illegally, the optical marks on the two layers would have to be aligned with a resolution of about 0.13 µm. At the present state of technology it is not possible to duplicate the disk by aligning the optical marks with the pits with an accuracy of 0.13 µm, that is, with an accuracy of the order of 0.1 µm, but there is a possibility that mass production technology may be commercially implemented in the future that enables large quantities of single-layer disks to be trimmed with a processing accuracy of 0.1 µm at low cost. Even in that case, since the top and bottom disks are trimmed simultaneously in the case of the two-layer laminated disk 800, the two disks must be laminated together with the pit locations and optical marks aligned with an accuracy of a few microns. However, it is next to impossible to laminate the disks with this accuracy because of the temperature coefficient, etc. of the polycarbonate substrate. When optical marks were formed by applying laser light penetrating through the two-layer disk 800, the resulting anti-piracy mark is extremely difficult to duplicate. This provides a greater anti-piracy effect. The optical disk with an anti-piracy mechanism is thus completed. For piracy prevention applications, in cases where the disk process and laser cut process are inseparable as in the case of the single-plate type, the encryption process, which is an integral part of the laser cut process, and processing involving a secret encryption key have to be performed at the disk manufacturing factory. This means that in the case of the single-plate type the secret encryption key maintained in the software company have to be delivered to the disk manufacturing factory. This greatly reduces the security of encryption. On the other hand, according to the method involving laser processing of laminated disks, the laser trimming process can be completely separated from the disk manufacturing process. Therefore, laser trimming and encryption operations can be performed at a factory of the software maker. Since the secret encryption key that the software maker keeps need not be delivered to the disk manufacturing factory, the secret key for encryption can be kept in the safe custody of the software maker. This greatly increases the security of encryption. The optical disk of the invention has a structure such that a reflective film is sandwiched directly or indirectly between two members resistant to laser light and a marking is formed by laser on the reflective film. The above mode of embodiment has dealt with examples in which this structure is used for secondary recording of a barcode, etc. and a piracy prevention technique, but it will be appreciated that such a structure may also be applied to other techniques. In the above mode of embodiment, the optical disk of the invention has been described as being fabricated by laminating two substrates with an adhesive layer interposed therebetween. However, the adhesive layer may be omitted, or instead, a member made of a different material, such as a protective layer, may be used; that is, any suitable structure may be used as long as the reflective film is sandwiched directly or indirectly between two members resistant to laser light. Furthermore, in the above mode of embodiment, the optical disk of the invention has been described as comprising substrates as the members that are laminated together, but other members such as protective layers may be used; that is, any member that has resistance to laser light may be used. As described, according to the present invention, since an ID unique to each individual disk, for example, is converted into a barcode and written in overwriting fashion to an ordinary pit area, both the pit data and barcode data can be read by using the same optical pickup. This has the effect of simplifying the construction of the playback apparatus, for example.

Claims: An optical disk on which data is recorded and comprising of a location (923) for receiving a barcode-like mark extending in a circumferential direction and having a plurality of bars (923a, 923b...) each extending in a radial direction, characterized in that said optical disk further comprises of an identifier (937) for indicating whether a barcode-like mark is present or not on said location (923) of the disk, said identifier (937) being provided in a pit area holding control data (936) and in that said optical disk is constructed from two disk substrates (801,803) The optical disk according to claim 1, wherein one of said bars (923a), when present, has a lower reflectivity than an average reflectivity of an area between said one of said bars (923a) and another of said bars (923b). The optical disk according to claim 1 or 2, wherein said optical disk comprises a first recording substrate (801) having a semi-transparent reflection layer (825) and a second recording substrate (803) having an almost non-transparent reflection layer (802), data from both said first and second recording substrates (801, 803) are reproduced from one side of said optical disk. The optical disk according to claim 3, wherein said first and second recording substrates (801, 803) have said barcode-like mark with approximately the same profile. An optical disk reproduction apparatus for use with a disk according to one of claims 1-4 characterized by comprising: reproduction means (9106) including an optical head for reproducing said barcode-like mark on said optical disk, identifier detection means (9106) for detecting said identifier (937) on said optical disk, control means for controlling a prescribed operation based on the contents of said identifier (937) detected by said identifier detection means (9106), wherein signals from said barcode-like mark in said location are obtained by switching the focus of said optical head. The optical disk reproduction apparatus according to claim 5, wherein in case said identifier (937) indicates absence of said barcode-like mark, said control means is signaled not to reproduce said barcode-like mark. The optical disk reproduction apparatus according to claim 5 or 6, wherein an indication of absence of said mark is output. The optical disk reproduction apparatus according to one of claims 5-7, wherein after said identifier (937) is detected, the focus on either said first and second recording layers (825, 802) is switched and said barcode-like mark (9104) is read.

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