JP2008047255A - Optical disk drawing method and optical disk - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To perform drawing while performing tracking control. <P>SOLUTION: A pre-pit 24 is formed and arranged in a drawing layer 26 of an optical disk 10. The pre-pit 24 is irradiated with laser light 12 emitted from an optical pickup 42 while the optical disk 10 is rotated and controlled by CAV control to make the laser light 12 follow the arrangement of the pre-pit 24 by tracking control of a phase difference method. In this state, the laser light 12 is modulated by a drawing signal and visible light characteristics of a drawing region are changed at a part out of an edge of the pre-pit 24 to form a visible image according to the drawing signal. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for forming (drawing) a visible image on a disk surface of an optical disc so that drawing can be performed while tracking control is performed. The present invention also relates to an optical disc used in this method.

Patent Documents 1 and 2 below describe a method of drawing a visible image on the surface of an optical disk using laser light emitted from an optical pickup. In the method described in Patent Document 1, a drawing layer is separately formed on the label surface side of the data recording layer of the optical disc, the label surface side is faced to the optical pickup, the optical disc is rotated, and synchronized with the rotation. While sequentially moving the optical pickup toward the outer periphery of the disk, the laser light modulated by the drawing signal is emitted from the optical pickup and irradiated to the drawing layer, thereby changing the visible light characteristics of the drawing layer and An image corresponding to a drawing signal is drawn. The method described in Patent Document 2 is for drawing on a data recording layer, and tracking control of laser light emitted from an optical pickup to a groove (pre-groove) formed on the data recording layer of the optical disk while rotating the optical disk. Then, by modulating the laser light with a drawing signal, the visible light characteristics of the data recording layer are changed, and an image corresponding to the drawing signal is drawn on the data recording layer.
JP 2004-5848 A JP 2004-355664 A

  According to the method described in Patent Document 1, since there is no track in the drawing layer, it is impossible to draw at a precise pitch while performing tracking control. On the other hand, according to the method described in Patent Document 2, although drawing can be performed with a fine pitch while tracking control is performed, since data is drawn on the data recording layer, data cannot be recorded in the drawn area and the data recording area becomes narrow ( (Alternatively, drawing cannot be performed in the data recording area, and the drawing area becomes narrow).

  Further, the drawing method with tracking control in the groove of Patent Document 2 has the following problems. That is, a three-beam method and a phase difference method are known as optical disk tracking control methods. In the 3-beam method, the preceding side spot arranged on the outer peripheral side of the main spot in the disc is arranged in the unrecorded area, whereas the subsequent side spot arranged on the inner peripheral side of the main spot in the disc is arranged in the recorded area. Therefore, the amount of reflected light differs between the two side spots, and an offset occurs in the tracking error detected as the difference between both reflected light amounts. In this case, in the case of data recording, since the pits are uniformly formed in the recorded area, the offset is kept constant. However, in the case of drawing, there are a part where there is an image and a part where there is no image even in the drawn area, and there is an image when the trailing side spot enters a part where there is no image from a part where there is an image or from a part where there is no image When entering a part, the tracking error may fluctuate rapidly, and the tracking servo may become unstable. In particular, when the image is drawn with high contrast and the groove is drawn with a large width to improve visibility, or when the reflectance ratio before and after the drawing is increased, this tendency becomes stronger and the tracking servo becomes more unstable. become. The phase difference method does not cause the problem of the three-beam method, but detects a tracking error using the edge of the pit, so it cannot be used for tracking a groove having no edge.

  An object of the present invention is to solve the above-mentioned problems in the prior art and to provide an optical disc drawing method and an optical disc used in this method, which can be drawn while performing tracking control by a phase difference method.

  In the optical disk drawing method of the present invention, prepits are arranged in a spiral or concentric manner with respect to the center of the disk on a drawing layer formed separately from the data recording layer of the optical disk, and the optical pickup is rotated while driving the optical disk. The pre-pits are irradiated with emitted laser light, the laser light is controlled to follow the pre-pit arrangement by phase difference tracking control, and in this state, the laser light is modulated with a drawing signal to display visible light on the drawing layer. By changing the characteristics, a visible image corresponding to the drawing signal is formed on the drawing layer. According to the present invention, since the prepits are arranged in the drawing layer of the optical disc, drawing can be performed while tracking control is performed by the phase difference method using the edges of the prepits.

  In this method, the power of the laser light can be maintained at the bottom power that does not change the visible light characteristic of the drawing layer at the timing when the laser light is irradiated to each edge of the prepit. In this way, a tracking error due to the phase difference method can be detected stably.

  The optical disk of the present invention is formed by arranging prepits in a spiral or concentric manner with respect to the center of the disk on a drawing layer formed separately from the data recording layer of the optical disk. The drawing layer can be made of a non-rewritable material such as a dye material or a rewritable material such as a phase change material.

  Embodiments of the present invention will be described below. FIG. 1 shows an embodiment of the layer structure of an optical disk according to the present invention. This optical disk 10 is configured as a drawable single-sided single-layer DVD-R. The laser beam 12 indicates the arrangement at the time of drawing. The optical disk 10 is composed of 1.2 mm thick as a whole by bonding polycarbonate substrates 14 and 16 each having a thickness of 0.6 mm. On the surface of the substrate 14 (opposite surface to the substrate 16), a groove 18 constituting a data recording track is formed on the entire area of the data recording area (data recording area) in the manufacturing process of the substrate 14. It is formed at a predetermined pitch spirally with respect to the center. A data recording layer 20 and a reflective layer 22 are stacked on the surface of the substrate 14 on which the groove 18 is formed. Thus, the substrate 16 and the laminated films 20 and 22 constitute one side of a normal DVD-R.

  On the surface of the substrate 16 (the surface facing the substrate 14), prepits 24 (uneven pits) are provided on the entire area where drawing is performed in the manufacturing process of the substrate 16 (drawing area, for example, the same area as the data recording area). An array is formed at a predetermined pitch in a spiral with respect to the center of 10. The arrangement of the prepits 24 constitutes a drawing track. A drawing layer 26 and a reflective layer 28 are laminated on the surface of the substrate 16 on which the prepits 24 are formed. The drawing layer 26 is made of, for example, a heat-sensitive material, and its visible light characteristic is changed by irradiation with the laser beam 12 having a drawing power, and an image is drawn. The substrate 14 and the substrate 16 are integrated by being bonded to each other with an intermediate layer 30 (adhesive) with the surface on which the laminated films 20 and 22 are formed facing each other and the surface on which the laminated films 26 and 28 are formed. Thus, the optical disc 10 is configured.

  At the time of drawing on the optical disc 10, the surface (label surface) 10a on the substrate 16 side faces the objective lens 32 of the optical pickup as shown in FIG. The image is drawn on the drawing layer 26 by changing the visible light characteristic of the drawing layer 26 by modulating the intensity of the image with the drawing signal. During data recording, the optical disk 10 is turned upside down from the state shown in FIG. 1 so that the surface (data surface) 10b on the substrate 14 side faces the objective lens 32, and the focus of the laser beam 12 on the reflective layer 22 is controlled. Then, the intensity of the laser beam 12 is modulated with the recording data, and data recording is performed on the data recording layer 20.

  An example of the arrangement pattern of the prepits 24 is shown in FIG. The prepits 24 are repeatedly arranged in a predetermined arrangement pattern. In the example of FIG. 2, the arrangement of the prepits 24 is composed of a pit arrangement pattern of 3T to 11T in accordance with the CD format. This prepit arrangement pattern is repeated every EFM frame period (588T) of the prepit arrangement. This pit arrangement pattern includes an EFM synchronization signal pattern of 11T-11T for each EFM frame period of the pre-pit arrangement. Any pattern other than the EFM sync signal pattern may be used, but the average duty ratio between the pre-pit 24 and the land 34 is set to 50%: 50% as in the normal CD pit. In the example of FIG. 2, the land 34 having the same length is formed after each pre-pit 24, so that the average duty ratio between the pre-pit 24 and the land 34 is set to 50%: 50%. The pre-pit 24 is a CAV (constant rotational speed) pit (a pit with a constant rotational angle per 1T regardless of the disk radial position) or a CLV (constant linear speed) pit (a distance per 1T regardless of the disk radial position). However, when drawing is performed by rotating the optical disk 10 by CAV, drawing control is easier for the CAV pit.

  The average duty ratio between the prepit 24 and the land 34 is not limited to 50%: 50%, and may be a constant value. That is, in the PLL circuit 88 shown in FIG. 5 to be described later, the RF signal is binarized using the average value of the RF signal from the prepit 24 as a slice level (threshold), so the average duty ratio between the prepit 24 and the land 34 varies. Then, the slice level fluctuates, and the binarization is not successful. Therefore, the average duty ratio between the prepit 24 and the land 34 is set to a constant value. Therefore, if the average duty ratio between the prepit 24 and the land 34 is not an extreme value, it may not be 50%: 50%, and for example, 70%: 30% may be adopted.

  Further, the arrangement pattern of the prepits 24 is not limited to the arrangement of the prepits 24 and lands 34 having various lengths as shown in FIG. 2, and a fixed-length prepit and land can be simply repeated.

  FIG. 3 shows the system configuration of the optical disc recording apparatus with a drawing function for performing data recording, reproduction and drawing on the optical disc 10 described above. In FIG. 3, illustration of a portion that performs signal processing of recorded data and reproduced data during data recording and reproduction is omitted. The optical disk recording apparatus with a drawing function is configured by connecting a host device (host computer) 36 and an optical disk drive with a drawing function (DVD-R drive) 38 so that they can communicate with each other. The optical disk 10 is rotationally driven by a spindle motor 40, and data recording, reproduction, and drawing are performed by a DVD laser beam 12 emitted from an optical pickup. The spindle servo 44 performs CLV control at the time of data recording and reproduction, and CAV control at the time of drawing, according to a command from a system control unit (CPU) 46. The CAV control is performed by PLL control so that the FG pulse output from the spindle motor 40 at every predetermined rotation angle is synchronized with a predetermined reference clock.

  The focus servo 48 performs focus control by driving the objective lens 32 in the optical axis direction by a focus actuator based on the return light of the laser beam 12 reflected by the optical disc 10. That is, the focus servo 48 controls the focus of the laser beam 12 on the reflective layer 22 of the optical disc 10 during data recording and reproduction, and controls the focus on the reflective layer 28 of the optical disc 10 during drawing. The tracking servo 50 performs tracking control by driving the objective lens 32 in the radial direction of the optical disk 10 by a tracking actuator based on the return light of the laser beam 12 reflected by the optical disk 10. That is, the tracking servo 50 follows the groove 18 by push-pull tracking control or the like during data recording and reproduction, and controls the tracking of the prepit 24 by phase difference tracking control during drawing. The stepping motor 52 is driven by a motor driver 54 and rotationally drives the feed screw 56 to move the optical pickup 42 in the disk radial direction. This transfer control is performed by driving the motor driver 54 via the system control unit 46 so that the DC component of the tracking error becomes zero at the time of data recording, reproduction and drawing. Note that data recording on the optical disk 10 is performed from the inner circumference side to the outer circumference side of the disk. The drawing of the optical disk 10 is usually performed from the inner periphery side of the disk toward the outer periphery side. On the contrary, it can be performed from the outer periphery side of the disk toward the inner periphery side.

  The laser driver 58 drives a laser diode (not shown) in the optical pickup 42 to emit the laser light 12. That is, the laser driver 58 modulates the laser beam 12 with recording data at the time of data recording, has a predetermined reproduction power at the time of data reproduction, and modulates and emits with a drawing signal at the time of drawing. The ALPC circuit 60 sets the power of the laser beam 12 to the values commanded by the system control unit 46 (recording power for forming pits in the data recording layer 20 during data recording, bottom power not forming pits, and reproducing power for data reproduction). During drawing, the drawing power for changing the visible light characteristic of the drawing layer 26 and the bottom power for changing the visible light characteristic are controlled.

  Image data of an image to be drawn is transmitted from the host device 36 at the time of drawing. This image data is a set of data (pixel data) representing gradation for each pixel of an image to be drawn. The image data is received by the interface 62 of the optical disk drive 38, temporarily stored in the buffer memory 64, and then sequentially read from the buffer memory 64 in the order of pixels to be drawn at a speed corresponding to the drawing speed. The drawing signal generation unit 68 generates a drawing signal for drawing each pixel with a corresponding gradation in accordance with each pixel data of the read image data. This drawing signal is composed of a pulse signal (drawing signal EFM3 in FIG. 6 (i) described later) that rises a plurality of times within the time (fixed time) for drawing one pixel, and the gradation value of the pixel indicated by each pixel data Accordingly, the total value (duty ratio) of the pulse rising time within the fixed time varies. Since the time for drawing one pixel is extremely short and the drawn pixel is recognized as only one dot by human eyes, a difference in duty ratio is recognized as a difference in dot density. Thereby, each pixel is drawn with the gradation according to each pixel data, and the image by multi-gradation is drawn by this.

  A configuration example of the tracking servo 50 of FIG. 3 is shown in FIG. This detects a tracking error by the phase difference method, and is used at the time of drawing. Since the phase difference method cannot be used during data recording, a tracking error is detected by a push-pull method or the like. The return light 12 a of the laser light 12 from the optical disk 10 is received by the four-divided light receiving element 70 in the optical pickup 42. The output currents Ia and Id at one diagonal light receiving position of the four-divided light receiving element 70 are converted into voltage values corresponding to Ia + Id by the current-voltage conversion and addition circuit 72. Further, the output currents Ib and Ic at the other diagonal light receiving position of the four-divided light receiving element 70 are converted into voltage values corresponding to Ib + Ic by the current-voltage conversion and addition circuit 74. The output signal Ia + Id of the current-voltage conversion and addition circuit 72 is compared with a predetermined threshold value by the comparator 76 and shaped into a pulse signal S1. The output signal Ib + Ic of the current-voltage conversion and addition circuit 74 is compared with a predetermined threshold value by the comparator 78 and shaped into a pulse signal S2. The phase comparator 80 compares the phases of the pulse signals S1 and S2, and when the phase of the pulse signal S1 is advanced, outputs a pulse having a pulse width corresponding to the advance time to the signal PDO +, and the phase of the pulse signal S2 is If it is advanced, a pulse having a pulse width corresponding to the advance time is output to the signal PDO− (see FIGS. 8 and 9 (k) and (l)). Signals PDO + and PDO− are smoothed by low-pass filters 82 and 84, respectively, and input to subtractor 86. As a result, the subtracter 86 outputs a signal corresponding to the difference between both smooth values as the tracking error signal TE. When the light spot by the laser beam 12 is at the center position of the prepit 24, the pulse signals S1 and S2 have the same phase, so that the tracking error signal TE becomes 0, and if the light spot deviates from the center position of the prepit 24, a tracking error occurs. The signal TE is output with a polarity according to the direction of deviation and a level according to the amount of deviation.

  A configuration example of the drawing signal generation unit 68 of FIG. 3 is shown in FIG. The operation waveform is shown in FIG. An RF signal (full addition signal Ia + Ib + Ic + Id of the four-divided light receiving element 70 in FIG. 4) (FIG. 6A) detected by the return light receiving signal of the laser beam 12 at the time of drawing is input to the PLL circuit 88. The signal is binarized and a 1T period clock signal WCLK (FIG. 6B) is generated. The PLL circuit 88 detects the 11T-11T pre-pit array EFM synchronization signal pattern included in the RF signal, and outputs a synchronization pattern detection signal EFMSY (FIG. 6C) having a predetermined pulse width at the detected timing. The mask signal generator 90 generates a mask signal MASK (FIG. 6 (d)) for the drawing signal and a mask signal (servo sampling mask signal) SSPMASK (FIG. 6 (FIG. 6) for the focus error detection from the synchronization pattern detection signal EFMSY and the reproduction clock signal WCLK. e)) is output. The mask signal MASK is a signal obtained by narrowing the rising edge and falling edge of the RF signal (FIG. 6A) by a predetermined width (for example, one period (1T) of the clock signal WCLK).

  Each of the mask signal MASK and the servo sampling mask signal SSPMASK is a signal output in a pattern set in advance corresponding to the RF signal pattern (that is, the arrangement pattern of the prepits 24 repeated in the EFM frame period of the prepit arrangement). . That is, the mask signal MASK is a signal output in a preset pattern in which the rising and falling edges of the RF signal are narrowed by the predetermined width. The mask signal MASK starts at the timing of the synchronization pattern detection signal EFMSY and is synchronized with the clock signal WCLK. The data is output in this preset pattern. This mask signal MASK is detected at the front and rear edges of the prepit 24 because the tracking error cannot be detected by the phase difference method when the laser light 12 reaches the drawing level at the front and rear edges of the prepit 24 when the laser light 12 is modulated by the drawing signal. This is used to prevent the laser beam 12 from reaching the drawing level. On the other hand, the servo sampling mask signal SSPMASK is a signal output in a preset pattern obtained by inverting the RF signal. The servo sampling mask signal SSPMASK starts at the timing of the synchronization pattern detection signal EFMSY, and is synchronized with the clock signal WCLK. Is output. This servo sampling mask signal SSPMASK is used to detect a focus error at a timing outside the prepit 24 because the focus error is not correctly detected when the laser beam 12 is on the prepit 24.

  The encoder 92 performs EFM modulation on each pixel data (image data) read out from the buffer memory 64 (FIG. 3) in the drawing order, and outputs gradation data for one pixel in one EFM frame (regardless of the EFM frame in the prepit arrangement described above). The generated EFM signal EFM1 (NRZI-converted EFM signal) (FIG. 6F) is generated and output. Using this EFM signal EFM1, a final drawing signal EFM3 (FIG. 6 (i)) for modulating the laser beam 12 is created. However, the EFM signal EFM1 is generated regardless of the arrangement of the prepits 24. When the laser beam 12 reaches the drawing level at the edge of the prepits 24, the tracking error cannot be detected by the phase difference method as described above. Therefore, the EFM signal EFM1 is ANDed with the mask signal MASK by the AND gate 94. As a result, the signal EFM2 (FIG. 6) obtained by removing a portion corresponding to the edge of the prepit 24 (same timing as the rising edge and the falling edge of the RF signal in FIG. 6A) from the EFM signal EFM1. (G)) is output.

  The DOTX signal generation unit 96 sequentially decodes the EFM signal EFM1 to decode the gradation data one pixel at a time in one EFM frame, and the cycle is 1 EFM frame length and the duty ratio changes according to the gradation data of the decoded pixel. The pulse signal DOTX (FIG. 6 (h)) is generated and output (the duty ratio increases in proportion to the gradation value). The signal EFM2 is ANDed with the pulse signal DOTX by an AND gate 98. Accordingly, the signal EFM2 is output from the AND gate 98 for a period corresponding to the period in which the pulse signal DOTX rises to the “H” level, that is, the time corresponding to the gradation of each pixel. The output signal of the AND gate 98 constitutes the final drawing signal EFM3 (FIG. 6 (i)).

  The drawing signal EFM3 is generated based on the EFM signal EFM1, but has no meaning as data anymore. Since the EFM signal EFM1 is an NRZI-converted EFM signal, the average duty ratio is 50%. Accordingly, the average duty ratio of the drawing signal EFM3 included in one pulse section ("H" level section) of the pulse signal DOTX is also approximately constant at about 50%. On the other hand, since the duty ratio of the pulse signal DOTX increases in proportion to the gradation of the pixel, the total time during which the drawing signal EFM3 rises to “H” level per 1 EFM frame length (drawing per 1 EFM frame length) The total pulse width of the signal EFM3) corresponds to the duty ratio of the pulse signal DOTX, that is, the gradation of the pixel. Accordingly, by modulating the laser beam 12 with the drawing signal EFM3, drawing is performed in multiple gradations for each pixel in one EFM frame. Note that the time length of one EFM frame by the EFM signal EFM1 is set to [time for one rotation of the disk / number of pixels to be drawn per one rotation of the disk]. Further, the EFM frame based on the EFM signal EFM1 and the EFM frame based on the arrangement of the prepits 24 do not need to be synchronized and do not need to have the same time length.

  The encoder 92 also generates and outputs a servo sampling pulse SSP (FIG. 6 (j)) based on the EFM signal EFM1. The servo sampling pulse SSP is a sampling pulse for performing focus error sampling at a timing when the return light of the laser beam 12 is stable when the drawing signal EFM3 is at the bottom level. The servo sampling pulse SSP is output with a predetermined pulse width after a predetermined time Δt (FIG. 6 (j)) has elapsed from each falling edge of the EFM signal EFM1. Further, since the focus error is not correctly detected when the laser beam 12 is on the pre-pit 24, the focus error is detected at the timing when the pre-pit 24 is removed using the servo sampling mask signal SSPMASK. In other words, the servo sampling pulse SSP is ANDed by the AND gate 100 with the servo sampling mask signal SSPMASK. As a result, the AND gate 100 selectively outputs a pulse SSP2 (FIG. 6 (k)) generated at a timing outside the prepit 24 in the servo sampling pulse SSP.

  FIG. 7 shows a control procedure when drawing on the optical disk 10 of FIG. 1 using the optical disk recording apparatus with a drawing function of FIG. The optical disk 10 is loaded into the optical disk drive 38 so that the label surface 10a faces the optical pickup 42 (arrangement in FIG. 1). The laser beam 12 is turned on at the bottom level (S1), and the spindle motor 40 is CAV-driven at the rotation speed during drawing (S2). Next, the focus servo 48 is turned on, and the laser beam 12 is controlled to be focused on the reflective layer 28 (S3). At this time, since the laser beam 12 is at the bottom level and there is almost no influence on the focus error by the pre-pit 24, the focus servo 48 performs focus control by detecting the focus error continuously instead of sampling. In this state, the stepping motor 52 is driven to move the optical pickup 42 to a predetermined drawing start radius position (S4). The drawing start radius position can be detected, for example, by returning the optical pickup 42 to the innermost circumferential origin position where the optical pickup 42 is mechanically locked, and the thread feed amount from that position (the number of drive pulses applied to the stepping motor 48). it can.

  When image data is transmitted from the host device 36 and stored in the buffer memory 64 in a predetermined amount or more, drawing can be started. In this state, the tracking servo 50 and the thread servo based on the tracking error DC component (control of the stepping motor 52) are turned on (S5), and drawing is started (S6). During drawing, the focus servo 48 samples a focus error at a timing when the prepit 24 is removed using the servo sampling pulse SSP2 (FIG. 6 (k)), and focuses the laser beam 12 on the reflection layer 28 based on the focus error. Keep it in a good condition. Further, the laser beam 12 is caused to follow the pre-pit 24 by phase difference tracking control by the tracking servo 50 (FIG. 4). During drawing, the encoder 92 (FIG. 5) generates an EFM signal EFM1 (FIG. 6 (f)) corresponding to the image data in synchronism with the disk rotation. Further, the drawing signal EFM3 (FIG. 6 (i)) is generated based on the EFM signal EFM1. ) Is created, and the laser light 12 is modulated to the drawing level and the bottom level by the drawing signal EFM3, and drawing on the drawing layer 26 is performed. As the drawing progresses, image data is supplied from the host device 36 to the buffer memory 64. When drawing of all the image data is completed, the image is completed. When the optical pickup 42 reaches the drawing end radius position (S7), all servos are turned off (S8), and a series of drawing control is finished.

  A tracking error detected by phase difference tracking control during drawing by the control of FIG. 7 will be described. According to the drawing signal EFM3 in FIG. 6 (i), at the time of drawing, the laser beam 12 deviates from the edge of the prepit 24 (the edge of the RF signal in FIG. 6A), that is, the midway position of the prepit 24 and the land 34 (see FIG. 6). The drawing level is reached in the middle of 2). FIG. 8 shows an operation waveform of the tracking servo 50 shown in FIG. 4 when the laser beam 12 reaches the drawing level in the middle of the pre-pit 24 at the time of drawing. The left figure [A] of FIG. 8 shows an off-track state in which the laser beam 12 is irradiated off the center of the prepit 24, and the right figure [B] shows the laser beam 12 irradiated on the center of the prepit 24. Indicates the on-track state. In the spot of the laser beam 12 in (a), Ia, Ib, Ic, and Id indicate portions received by the corresponding regions of the four-divided light receiving element 70 in FIG. The drawing signal EFM3 in (b) is at the “H” level in the middle of the prepit 24, and at the “L” level in the other sections. The laser beam 12 becomes the drawing power when the drawing signal EFM3 is at the “H” level, and becomes the bottom power when the “L” level. As shown in (c) to (f), the output currents Ia, Ib, Ic, and Id at the respective light receiving positions of the four-divided light receiving element 70 are intervals in which the laser beam 12 has the drawing power both in off-track and on-track. Each increases. Further, the output currents Ia, Ib, Ic, and Id increase in the section where the laser beam 12 is applied to the prepit 24 as compared with the section applied to the land 34 according to the degree of the application.

  The operation during off-track in FIG. 8A will be described. At this time, as shown in (e) and (f), the currents Ic and Id increase in the section where the laser beam 12 is applied to the prepit 24. The fluctuations in the currents Ic and Id caused by the pre-pit 24 appear earlier in the current Id than in the current Ic, so that a phase difference occurs between the currents Ic and Id. In addition, because of the off-track state, as shown in (c) and (d), the currents Ia and Ib do not fluctuate due to the prepit 24 (even if they occur, they are smaller than the fluctuations due to the currents Ic and Id). As a result, the output signals Ia + Id and Ib + Ic of the current-voltage conversion and addition circuits 72 and 74 shown in FIG. 4 are as shown in (g) and (h), respectively. These signals Ia + Id and Ib + Ic are compared at a common threshold value (intermediate level between the level at the land 34 and the level at the pre-pit 24 by the bottom power) in the comparators 76 and 78 in FIG. Is done. As a result, the comparators 76 and 78 output pulse signals S1 and S2 shown in (i) and (j). A phase difference corresponding to the phase difference between the currents Ic and Id appears between the pulse signals S1 and S2. As a result, the phase comparator 80 outputs a pulse corresponding to the phase difference to the signal PDO + as shown in (k) (no pulse is outputted to the signal PDO− as shown in (l)). The output signals PDO + and PDO− of the phase comparator 80 are smoothed by the low-pass filters 82 and 84 in FIG. 4 and drive the tracking actuator in the optical pickup 42 via the subtractor 86. Thereby, the tracking servo operates so as to correct the tracking error.

  The on-track operation in FIG. 8B will be described. At this time, as shown in (c) to (f), the currents Ia, Ib, Ic, Id increase evenly in the section where the laser beam 12 is applied to the prepit 24. At this time, fluctuations in the currents Ia, Ib, Ic, and Id appear earlier than the currents Ia and Ic in the currents Ib and Id, so that a phase difference occurs between the currents Ib and Id and the currents Ia and Ic. However, the phase difference is canceled by Ia + Id and Ib + Ic. As a result, the output signals Ia + Id and Ib + Ic of the current-voltage conversion and addition circuits 72 and 74 shown in FIG. 4 are as shown in (g) and (h), respectively, and there is no phase difference. These signals Ia + Id and Ib + Ic are compared with threshold values indicated by arrows in (g) and (h) in the comparators 76 and 78 in FIG. As a result, the comparators 76 and 78 output pulse signals S1 and S2 shown in (i) and (j). There is no phase difference between the pulse signals S1 and S2. As a result, no pulse is output from the phase comparator 80 to either of the signals PDO + and PDO− as shown in (k) and (l). As a result, the on-track state is maintained.

  Next, FIG. 9 shows an operation waveform of the tracking servo 50 in FIG. 4 when the laser beam 12 reaches the drawing level at the midway position of the land 34 at the time of drawing. The left diagram [A] of FIG. 9 shows an off-track state in which the laser beam 12 is irradiated off the center of the prepit 24, and the right diagram [B] shows the laser beam 12 irradiated on the center of the prepit 24. Indicates the on-track state. The drawing signal EFM3 in (b) becomes “H” level in the middle section of the land 34 as in FIG. 8, and becomes “L” level in the other sections. Similarly to FIG. 8, the laser beam 12 becomes the drawing power when the drawing signal EFM3 is at "H" level and becomes the bottom power when it is at "L" level. As shown in (c) to (f), the currents Ia, Ib, Ic, and Id at the respective light receiving positions of the four-divided light receiving element 70 are the sections in which the laser beam 12 has the drawing power both during off-track and on-track. Increase. Further, the currents Ia, Ib, Ic, and Id increase in the section where the laser beam 12 is applied to the prepit 24, as compared with the section applied to the land 34, depending on the degree of application.

  The operation during off-track in FIG. 9A will be described. At this time, as shown in (e) and (f), the currents Ic and Id increase in the section where the laser beam 12 is applied to the prepit 24. The fluctuations in the currents Ic and Id caused by the pre-pit 24 appear earlier in the current Id than in the current Ic, so that a phase difference occurs between the currents Ic and Id. In addition, because of the off-track state, as shown in (c) and (d), the currents Ia and Ib do not fluctuate due to the prepit 24 (even if they occur, they are smaller than the fluctuations due to the currents Ic and Id). As a result, the output signals Ia + Id and Ib + Ic of the current-voltage conversion and addition circuits 72 and 74 shown in FIG. 4 are as shown in (g) and (h), respectively. These signals Ia + Id and Ib + Ic are compared at a common threshold value (intermediate level between the level at the land 34 and the level at the pre-pit 24 by the bottom power) in the comparators 76 and 78 in FIG. Is done. As a result, the comparators 76 and 78 output pulse signals S1 and S2 shown in (i) and (j). A phase difference corresponding to the phase difference between the currents Ic and Id appears between the pulse signals S1 and S2. As a result, the phase comparator 80 outputs a pulse corresponding to the phase difference to the signal PDO + as shown in (k) (no pulse is outputted to the signal PDO− as shown in (l)). The output signals PDO + and PDO− of the phase comparator 80 are smoothed by the low-pass filters 82 and 84 in FIG. 4 and drive the tracking actuator in the optical pickup 42 via the subtractor 86. Thereby, the tracking servo operates so as to correct the tracking error.

  The operation during on-track in FIG. 9B will be described. At this time, as shown in (c) to (f), the currents Ia, Ib, Ic, Id increase evenly in the section where the laser beam 12 is applied to the prepit 24. At this time, fluctuations in the currents Ia, Ib, Ic, and Id appear earlier than the currents Ia and Ic in the currents Ib and Id, so that a phase difference occurs between the currents Ib and Id and the currents Ia and Ic. However, the phase difference is canceled by Ia + Id and Ib + Ic. As a result, the output signals Ia + Id and Ib + Ic of the current-voltage conversion and addition circuits 72 and 74 shown in FIG. 4 are as shown in (g) and (h), respectively, and there is no phase difference. These signals Ia + Id and Ib + Ic are compared with threshold values indicated by arrows in (g) and (h) in the comparators 76 and 78 in FIG. As a result, the comparators 76 and 78 output pulse signals S1 and S2 shown in (i) and (j). There is no phase difference between the pulse signals S1 and S2. As a result, no pulse is output from the phase comparator 80 to either of the signals PDO + and PDO− as shown in (k) and (l). As a result, the on-track state is maintained.

  As described above, according to FIGS. 8 and 9, even if the pre-pit 24 is irradiated with a laser beam at the drawing level during drawing, a tracking error signal waveform similar to the phase difference tracking control during normal reproduction can be obtained. The tracking servo operates so as to correct the tracking error, so that the laser beam 12 can follow the pre-pit 24 stably.

  Unlike FIGS. 8 and 9, when the laser beam 12 changes from the bottom power to the drawing power or from the drawing power to the bottom power at the position where the laser beam 12 is applied to the edge of the prepit 24, the comparators 76 and 78 detect the edge of the prepit 24. Since the level fluctuation due to the change of the laser power is detected instead of the level fluctuation due to, a phase difference corresponding to the tracking error does not occur in the output signals S1 and S2. Therefore, in this case, it becomes difficult or impossible to apply the tracking servo.

  In the above-described embodiment, the prepits are arranged spirally with respect to the center of the disk, but can also be arranged concentrically.

  According to the optical disk drawing method of the present invention, drawing can be performed along the prepit arrangement, so if the drawing layer is made of a rewritable material (for example, a phase change material), an image along the prepit arrangement can be obtained. After the image is drawn once, the image can be erased or rewritten by irradiating the laser beam of the erasing power or the overwrite drawing power again along the prepit arrangement. In this case, if the data recording layer is also made of a rewritable material (for example, a phase change material), it can be used for rewriting an image (for example, a title) in accordance with the rewriting of data.

  Further, according to the optical disk drawing method of the present invention, it is possible to draw with a fine pitch while performing tracking control, and therefore it is possible to draw an image having a hologram visual effect as described in JP-A-2004-171605. .

1 is a diagram showing an embodiment of a layer structure of an optical disc according to the present invention, and is a schematic cross-sectional view showing a part of the optical disc cut along a plane passing through its central axis. FIG. 2 is a plan view showing an example of an arrangement pattern of prepits 24 in the optical disc of FIG. 1. It is a block diagram which shows the system configuration | structure of the optical disk recording device with a drawing function by this invention. FIG. 4 is a circuit diagram illustrating a configuration example of a tracking servo 50 in FIG. 3. FIG. 4 is a circuit diagram illustrating a configuration example of a drawing signal generation unit 68 in FIG. 3. FIG. 6 is an operation waveform diagram of the drawing signal generation unit 68 of FIG. 5. It is a flowchart which shows the control procedure at the time of drawing on the optical disk 10 of FIG. 1 using the optical disk recording device of FIG. FIG. 5 is an operation waveform diagram of the tracking servo 50 of FIG. 4 when the laser beam 12 reaches a drawing level in the middle position of the prepit 24 during drawing. FIG. 5 is an operation waveform diagram of the tracking servo 50 of FIG. 4 when the laser beam 12 reaches a drawing level in the middle of the land 34 during drawing.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Optical disk, 12 ... Laser beam, 24 ... Prepit, 26 ... Drawing layer, 42 ... Optical pick-up

Claims (3)

  A prepit is formed in a drawing layer formed separately from the data recording layer of the optical disc in a spiral or concentric manner with respect to the center of the disc, and laser light emitted from an optical pickup while rotating the optical disc is applied to the prepit. The laser beam is controlled to follow the pre-pit arrangement by phase difference tracking control, and the laser beam is modulated by a drawing signal in this state to change the visible light characteristic of the drawing layer. An optical disk drawing method for forming a visible image corresponding to the drawing signal on a layer.   The optical disk drawing method according to claim 1, wherein the laser light power is maintained at a bottom power that does not change the visible light characteristics of the drawing layer at a timing when the laser light is applied to each edge of the prepit.   An optical disc in which prepits are arranged in a spiral or concentric manner with respect to the center of the disc on a drawing layer formed separately from the data recording layer of the optical disc.

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