JP3380225B2 - Writable optical disk reader - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a writable optical disk reader. 2. Description of the Related Art In a writable optical disk, a synchronization signal for searching for a position, address information, and the like (hereinafter, these information are referred to as "pre-information") are recorded on the disk in advance at a pre-formatting stage. You. As a method of preformatting the pre-information, a track (groove or land) for recording information is wobbled, or pre-pits are recorded on the track. [0003] However, in the case of pre-formatting by wobbling, the track itself is swung left and right by a wobbling signal.
There is a problem that the modulation degree of the wobbling signal is limited and C / N is poor. Also, considering the interference with adjacent tracks due to wobbling, the track pitch cannot be made too narrow, and the recording capacity is limited. [0004] On the other hand, in the case of the pre-format using pre-pits, information cannot be recorded as much as the pre-pits are recorded, and there is a problem in that the efficiency of using the disc recording surface is poor. SUMMARY OF THE INVENTION The present invention is directed to a reading apparatus for generating a tracking error signal from a writable optical disk which has been made to solve the above-mentioned problem, and to reduce a noise signal due to a pre-pit that has entered into the tracking error signal. It is an object of the present invention to provide a reading device which can perform the reading. In order to achieve the above object, according to the present invention, there is provided a writable optical disk reader according to the present invention, comprising: an information recording track; A writable optical disc reader having a guide track for guiding a light beam and pre-pit information including address information recorded on the guide track, wherein the information recording track of the optical disc is irradiated. A first light receiving unit that receives a reflected light of the first light beam from the disk by a light receiving unit divided at least by a first division line that is optically substantially parallel to a tangential direction of an information recording track of the optical disk; Means for recording information reflected from the optical disc by a second light beam applied to a guide track of the optical disc, Second light receiving means for receiving light by a light receiving unit divided by a second division line optically substantially parallel to the tangential direction of the recording track and a third division line optically substantially parallel to the radial direction of the optical disc; First difference signal generating means for generating a first difference signal by taking the difference between the outputs of the light receiving sections of the first light receiving means divided by the first dividing line; and the second dividing line A second differential signal generating means for generating a second differential signal by taking a difference between outputs of the light receiving unit of the second light receiving means divided by the second light receiving means; and a signal having a level adjusted for the second differential signal. A tracking error generating means for subtracting the signal from the first differential signal and outputting the subtracted signal as a tracking error signal; 3 difference signal generation Comprising a stage, and is characterized in that to obtain the pre-pit information based on the third differential signal. According to the writable optical disk reader of the first aspect of the present invention, the second difference signal is obtained by calculating the difference between the outputs of the light receiving sections of the second light receiving means. A tracking error signal is obtained by generating and subtracting the signal obtained by adjusting the level of the second difference signal from the first difference signal,
A third difference signal is generated by taking the difference between the outputs of the light receiving units of the second light receiving unit divided by a third dividing line optically substantially parallel to the radial direction of the optical disk, and generating the third difference signal To obtain pre-pit information. An embodiment of the present invention will be described below. FIG. 1 shows an optical disk according to the present invention (hereinafter abbreviated as a disk).
Schematic enlarged perspective view of the groove and land portion of one embodiment,
FIG. 2 is a diagram showing the arrangement of prepits recorded on a land. In FIG. 1, reference numeral 1 denotes a disk made of a transparent resin such as polycarbonate.
A groove 2 serving as an information recording track and a land 3 serving as a guide track are spirally formed from the center position of the disk toward the outer peripheral position of the disk. In the case of the present invention, of the groove 2 and the land 3, a prepit 4 for giving prepit information to a land 3 constituting the guide track is recorded in a preformat. FIG. 1 schematically shows the invention so that the invention can be easily understood. A metal reflection film 5 is formed on the lower surface side of the groove 2 and the land 3, and a protective film (shown in FIG. (Abbreviation) is applied to complete a single veneer disk. Therefore, in the case of FIG. 1, the recording / reproducing laser beam is applied to the groove 2 and the land 3 from the upper side of the drawing. Further, in the case of the present invention, the pre-pit 4
Are recorded every other land 3 as shown in FIG. Recording on every other land in this way is for the following reason. That is, when the optical pickup tracks the groove 2 during recording or reproduction, if pre-pits are formed on all the lands, two pieces of pre-pit information on the lands 3 located on the left and right with the groove 2 interposed at the same time. This is because they are read and interfere, and it becomes impossible to accurately reproduce the pre-information. As another method for eliminating interference between the left and right pre-pit information, a method as shown in FIG. 2B can be adopted. That is, as a recording pattern for recording pre-pit information on a land portion, an EVEN (even number) pattern and an ODD (odd number)
In this method, two patterns are prepared, and prepit information is recorded using the two patterns. The EVEN pattern and the ODD pattern have sync Sy and ID information necessary for servo.
The positions of the sync Sy and the ID to be recorded in the EN pattern and the ODD pattern are shifted by 180 degrees. And
Of these two patterns, the pre-pit information is usually recorded using the EVEN pattern, and the positions of the sync Sy and the ID of the recording pattern of adjacent lands are likely to overlap during the spiral land recording. Is changed to the ODD pattern and recording is continued.
When the position of the sync Sy of the D pattern and the position of the ID are likely to overlap, the recording is continued by returning to the EVEN pattern again. To manufacture a disk having the above structure,
What is necessary is just to employ the method as shown in FIG. In the case of a conventional disc in which prepits are recorded in a groove portion, the groove portion is cut when cutting the glass master. For this reason, when the conventional cutting method is adopted, after cutting the groove portion, the pre-pit has to be cut again on the land portion, which requires a lot of man-hours and makes it difficult to perform accurate cutting. Accordingly, in the present invention, a master stamper is manufactured by exposing and developing a resist surface on a glass substrate based on prepit information recorded on a land portion, contrary to the prior art, during laser cutting. The master stamper is subjected to a single electroforming process to obtain a submaster, or the submaster is further subjected to an even number of electroforming processes to perform replication using one of the stampers. It is. By adopting such a method, the cutting process of the master is required only once, and the pre-pits on the land are not shifted, so that a high-precision disc can be produced. FIG. 4 shows a cutting machine used for the laser cutting. In the figure, reference numeral 10 denotes a high-power laser generator, and a laser beam generated by the laser generator 10 is transmitted to an optical modulator 11 by an encoder 1.
After the light is modulated by the land cutting information sent from the light source 2, the light is condensed by the objective lens 13,
A spot is formed on the resist 15 of FIG. The glass substrate 14 is set on a spindle motor 16. The spindle motor 16 is driven by a rotation detector 17 and a rotation servo circuit 18 at a constant linear velocity (CL).
V). Further, the spindle motor 16
The glass substrate 14 can be fed in the radial (radial) direction of the glass substrate 14 by the feed unit 19, and the position detector 20 and the feed servo circuit 21 control the feed in the radial direction at a predetermined feed speed. The land is spirally cut from the center of the disk toward the outer periphery of the disk. FIG. 5 shows a first embodiment of a reading apparatus according to the present invention for reading information from a disk manufactured as described above. In the figure, reference numeral 31 denotes an objective lens, and a laser beam for reproduction is guided to the objective lens 31 by a prism 32, and the laser beam is applied to the recording surface of the disk 1 as a beam spot.
The reflected light of the laser beam reflected on the recording surface of the disk 1 reaches the prism 32 through the same path, passes through the prism 32, and irradiates the light receiver 33 as it is. In this embodiment, the light receiving device 33 is a four-division light receiving device. As will be described later, the light receiving output of each of the four divided light receiving elements A to D (for easy understanding). In the following description, the received light output of each element is also indicated by A to D) to read the RF signal, the tracking error signal, and the pre-pit signal of the land. 34 to 37 are amplifiers connected to the light receiving elements A to D, and 38 to 43 and 47 are adder / subtracters. The positional relationship between the photodetector 34 for receiving the reflected light of the laser beam from the disk 1 and the grooves 2 and lands 3 on the disk 1 is as shown in the enlarged view P in the figure. I have. Therefore, in order to read the recorded information on the groove 2, all the outputs A to D of the four light receiving elements need to be added and output. In the case of the example shown,
The output (A + D) of the adder 40 and the output (B +
By adding C) by the adder 43, the RF signal (A + B + C + D) is output from the terminal 46. The tracking error signal can be obtained from the difference (A + D)-(B + C) between the right and left light receiving elements along the groove 3 in the tracking direction. In this case, a difference of the primary light is obtained instead of the zero-order light.
In the case of the illustrated example, the output (A + D) of the adder 40 and the adder 4
1 is subtracted by the subtracter 42 from the output (B + C) of the terminal 1 so that the tracking error signal (A + D) −
It is output as (B + C). The pre-pit information recorded on the land 3 can be read out by the difference (A + B)-(C + D) between the front and rear light receiving elements along the radial direction of the disk. In this case, too, the primary light is different from the zero-order light. In the illustrated example, the output of the adder 38 (A
+ B) and the output (C + D) of the adder 39 are subtracted by the subtractor 47, so that the pre-pit signal (A +
B)-(C + D). As can be seen from the positional relationship in the enlarged view P,
Since the prepits 4 recorded on the lands 3 are recorded every other land 3, the information of the prepits 4 can be read. If the pre-pits 4 are recorded on all the lands, different pre-pit information on the left and right lands of the groove 3 may be read at the same time, and may not be used. In the present invention, in order to avoid such a situation, the pre-pits 4 are recorded every other land 3 as described above. As a result of recording the pre-pits 4 on every other land 3, as is clear from the layout diagram of FIG. Changes from the left side (right side) of the groove 2 to the right side (left side). This change in position is caused by the pre-pit signal (A +
B) It can be easily detected by reversing the polarity of-(C + D). FIG. 6 shows an example of actual reading of each signal by the reading device. As is clear from the actual measurement example, R
It can be seen that all of the F signal, the tracking error signal, and the pre-pit signal are sufficiently and reliably read. The effect of the RF signal on the pre-pit signal is hardly observed, but this is because the depth of the track groove is set as shown in FIG. FIG. 8 shows a second embodiment of the reading apparatus according to the present invention. The second embodiment is a three-beam type reading apparatus in which dedicated light receivers 54, 55 and 56 are prepared for each of the beam spots 50, 51 and 52, respectively. 57 to 72 are adder / subtracters, and 78 is a coefficient multiplier. In this embodiment, the RF signal is added to the adder 6
8 (F + H) and the output (E + G) of the adder 69 are added by the adder 71, so that (E + F)
+ G + H). The focus error signal is detected by an astigmatism method using a cylindrical lens (not shown), and the output (F + H) of the adder 68 and the output (E + G) of the adder 69 are subtracted. By subtracting at 72, the signal is output from the terminal 76 as (F + H)-(E + G). The pre-pit signal is obtained by subtracting the output (A + B) of the adder 57 and the output (C + D) of the adder 58 from the subtractor 6.
4 to obtain (A + B) − from the terminal 73.
It is output as (C + D). The tracking error signal is obtained as follows. First, the output of the adder 61 (F + G)
And the output (F + G) − (E + H) obtained by subtracting the output (E + H) of the adder 62 with the subtractor 66 is input to the + terminal of the subtractor 70. On the other hand, the output (B + C) of the adder 59 and the adder 6
0 (A + D) and the output (B +
C)-(A + D) is input to one terminal of the adder 67, the output (I + J) of the adder 63 is input to the other terminal of the adder 67, and the output ｛(B +
C)-(A + D) {+ {(I + J)} = constant K for correction
K [｛(B + C) − (A +
D) {+ {(I + J)}] is input to the − terminal of the subtractor 70. As a result, 減 算 (F +
G)-(E + H)｝-(A + D)｝-K [｛(B + C)
− (A + D) {+ {(I + J)}] is output as the tracking error signal. Therefore, the correction constant K
By properly adjusting, the noise signal due to the pre-pits 4 of the lands 3 sunk into the original tracking error signal (F + G)-(E + H) can be reduced. FIG. 9 shows a third embodiment of the reading apparatus according to the present invention. In this embodiment, the recording operation on the disk 1 is performed, and even on a disk on which information is written on the groove 2, the influence of the recorded information is reduced as much as possible to achieve a C / N ratio.
This makes it possible to obtain a good pre-pit signal. In the case of this embodiment, a four-divided light receiver is used as the light receiver 80. In this embodiment, a four-segment type photodetector is used to obtain an RF signal and a tracking signal in addition to the pre-pit signal. In the case of this embodiment, the pre-pit signal is obtained as follows. First, the original pre-pit signal (A + B) −
(C + D) is obtained. This pre-pit signal (A + B)-
(C + D) includes a noise component due to pit information recorded on the groove 2. Therefore, a groove pit cancel signal for canceling this noise component is output from the outputs A to
D is used in the waveform shaping circuit 82, and the subtractor 83 subtracts the groove pit cancel signal from the pre-pit signal (A + B)-(C + D) to cancel noise components. A method of generating a groove pit cancel signal in the waveform shaping circuit 82 will be described with reference to FIG. Now, when no pre-pits are recorded on the land, and the beam spot tracks on the groove of the disk on which pit information is recorded only on the groove, the added waveforms (A + B) and (C + D) become FIG.
Waveforms like 0 (A) and (B) are obtained. On the other hand, the push-pull signal (A + B)-(C + D), which is a pre-pit signal, has a waveform as shown in FIG. 10 (F), and an output is generated despite the premise that no pre-pit is recorded on the land. I will. This is a noise component due to pit information recorded on the groove. Therefore, if this noise component is canceled, the effect of the pit information recorded on the groove on the pre-pit signal can be canceled. Therefore, in the illustrated embodiment, first, FIG.
An output signal (A + B + C + D) as shown in FIG. 10 (C) is created from the signals of (A) and (B), and this waveform is differentiated to obtain the output signal of FIG.
The differential signal of (D) is obtained. Then, a groove pit cancel signal as shown in FIG. 10E is created based on the differentiated signal. The groove pit cancel signal shown in FIG. 10E and the push-pull signal (A + B) -FIG.
It can be seen that (C + D) has the same waveform. Therefore, in the subtracter 83 in FIG. 9, the push-pull signal (A + B)-(C + D), which is a pre-pit signal, is used as shown in FIG.
Fig. 1
The effect of pit information recorded on the groove, such as 0 (G), can be removed, and a pre-pit signal with a good C / N can be obtained. FIG. 11 shows a fourth embodiment of the reading apparatus according to the present invention. This embodiment shows an example of a reader capable of reading out pre-pit information of a land portion while recording information on a disk 1. In this example,
Although a four-divided photodetector is used as the photodetector 90, a two-divided photodetector is sufficient for reading out only the pre-pit signal as in the third embodiment. In the figure, 90 is a light receiver, 91 is a subtractor, 92 is a laser beam modulator, 93 is a laser beam generator, 94 is a prism, 95 is an objective lens, and 96 is a waveform shaping circuit. The disk 1 is irradiated with the laser beam output from the laser beam generator 93 via the prism 94 and the objective lens 94. Generally, turning on and off a laser beam when recording information on a disc is performed by a power control method as shown in FIG. That is, the laser power is controlled not to be 0 at the non-recording position, but to be reduced to the reading power. Therefore, it is possible to read the pre-pit information of the land even during the non-recording period in which no information is written in the groove. In this embodiment, the pre-pit signal is obtained as follows. First, an original pre-pit signal (A + B)-(C + D) is obtained from the outputs A to D of the light receiver 90. This pre-pit signal (A + B)-(C + D) contains a noise component due to pit information recorded on the groove 2. Therefore, a groove pit cancel signal for canceling the noise component is generated from a driving modulation signal waveform supplied from the modulator 92 to the laser beam generator 93 in the waveform generation circuit 96, and the groove pit cancellation signal is generated in the subtractor 91. The noise component is canceled by subtracting the pit cancellation signal from the pre-pit signal (A + B)-(C + D). A method of generating a groove pit cancel signal in the waveform shaping circuit 96 will be described with reference to FIG. When pit information is recorded on a groove by a recording light as shown in FIG. 13A in a state where no pre-pit is recorded on the land, the light receiver 90
The waveforms (A + B) and (C + D) of FIG.
The waveforms are as shown in (B) and (C). In FIG. 13 (B),
The waveform (C) indicates that a pit is recorded on the groove at a position where the added output decreases stepwise, and the amount of reflected light has decreased from the position due to the recorded pit. On the other hand, the push-pull signal (A + B)-(C + D) as a pre-pit signal has a waveform as shown in FIG. 13 (F), and an output is generated regardless of the premise that no pre-pit is recorded on the land. I will. This is a noise component due to pit information recorded on the groove. Therefore, if this noise component is canceled, the influence of the pit information recorded on the groove on the pre-pit signal can be canceled. Therefore, in the embodiment shown in FIG.
The delay waveform shown in FIG. 13D in which the recording light shown in FIG. 13A is delayed by the time t is created, and the groove pit cancel signal shown in FIG. The groove pit cancel signal shown in FIG. 13E and the push-pull signal (A + B)-
It can be seen that (C + D) has the same waveform. Therefore, in the subtractor 91 of FIG. 11, the push-pull signal (A + B)-(C + D), which is a pre-pit signal, is
By pulling the groove pit cancel signal of 3 (E), the influence of the pit information recorded on the groove can be removed, and a pre-pit signal having a good C / N can be obtained. In each of the above-described embodiments, the pre-pit information is obtained by the push-pull signals of the light receiving portions located before and after in the tracking direction. However, the light receiving portions located on the left and right sides in the tracking direction are obtained. Pre-pit information can also be obtained by a push-pull signal. In this case, the push-pull signal located on the left and right sides is obtained by superimposing a signal due to a tracking error and a pre-pit signal, but since the tracking error signal and the pre-pit signal have significantly different frequency bands, by using a filter, It can be easily discriminated. In the pre-pit information, it is possible to determine whether the pre-pit is a left pre-pit or a right pre-pit with respect to the groove according to the polarity of the obtained signal. Although the embodiments of the present invention have been described above, the present invention is not limited to these embodiments, and various modifications in accordance with the gist of the present invention are possible. According to the writable optical disk reader of the first aspect of the present invention, the noise due to the pre-pit information included in the tracking error signal can be reduced, and the configuration can be simplified. Pre-pit information can be read efficiently. [0055]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an enlarged perspective view schematically showing grooves and lands in an embodiment of an optical disk according to the present invention. FIG. 2 is a diagram showing an arrangement of pre-pits recorded on a land. FIG. 3 is an explanatory diagram of the optical disk manufacturing method of the present invention. FIG. 4 is a diagram showing an example of the structure of a cutting machine for a laser beam. FIG. 5 is a block diagram of a first embodiment of the reading apparatus according to the present invention. FIG. 6 is a diagram showing an actual measurement example of reading each signal by the reading device. FIG. 7 is a diagram showing the depth of a track groove and the output characteristics of a push-pull signal and an RF signal. FIG. 8 is a block diagram showing a second embodiment of the reading apparatus according to the present invention. FIG. 9 is a block diagram of a third embodiment of the reading device according to the present invention. FIG. 10 is an explanatory diagram of a method of generating a groove pit cancel signal in a third embodiment. FIG. 11 is a block diagram of a reading device according to a fourth embodiment of the present invention. FIG. 12 is an explanatory diagram of a control state of laser beam power during information recording. FIG. 13 is an explanatory diagram of a method of generating a groove pit cancel signal in the fourth embodiment. [Description of Signs] 1 Disk 2 Groove (Track for Information Recording) 3 Land (Track for Guide) 4 Prepit 54 Light Receiver (Second Light Receiver) 55 Light Receiver (First Light Receiver) 64 Subtractor (Third Light) 65 subtracter (second difference signal generating means) 66 subtractor (first difference signal generating means) 70 subtractor (tracking error generating means)

Continuation of the front page (56) References JP-A-6-333240 (JP, A) JP-A-3-86935 (JP, A) JP-A-6-251403 (JP, A) JP-A-63-269356 (JP) JP-A-61-42738 (JP, A) JP-A-61-94246 (JP, A) JP-A-6-139582 (JP, A) JP-A-3-1811023 (JP, A) 6-309672 (JP, A) JP-A-1-256026 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G11B 7/00-7/013 G11B 7/09-7 / Ten

Claims (1)

(57) Claims 1. An information recording track, a guide track for guiding a light beam to the information recording track, and a prepit recorded on the guide track and containing address information. A read device for a writable optical disk having information, said first optical disk being irradiated on an information recording track of said optical disk.
A first light receiving means for receiving reflected light of the light beam from the disk by a light receiving unit divided at least by a first division line optically substantially parallel to a tangential direction of an information recording track of the optical disk; The reflected light of the second light beam applied to the guide track of the optical disc from the optical disc is converted into a second division line optically substantially parallel to a tangential direction of the information recording track and a radius of the optical disc. A second light receiving unit that receives light by a light receiving unit divided by a third dividing line that is optically substantially parallel to the direction; and an output of the light receiving unit of the first light receiving unit that is divided by the first dividing line. A first difference signal generating means for generating a first difference signal by taking a difference between the first and second light receiving sections of the second light receiving means divided by the second dividing line. A second difference signal generating means for generating a difference signal, said second signal to adjust the level of the differential signal the first
A tracking error generating means for subtracting the differential signal from the differential signal and outputting as a tracking error signal; and a third differential for generating a third differential signal by calculating a difference between outputs of the light receiving sections divided by the third dividing line. An apparatus for reading a writable optical disk, comprising: signal generating means for obtaining the pre-pit information based on the third difference signal.