The present invention relates to tracking technology for an optical pickup device mounted on an optical disk apparatus.
In recent years, optical disk apparatus have been widely used which are capable of recording and reproducing information on a recording medium, such as a CD-R/RW, or a DVD-R/RW. Particularly, there has been recently developed an optical disk apparatus that employs a high-density optical disk, such as a Blue-ray, or a HD-DVD, as compared to a DVD. Such an optical disk apparatus is designed to record information by irradiating the optical disk with a light beam by an optical pickup device incorporated therein, and to read information by detecting a reflected light beam from the disk.
To record and reproduce the information by the optical pickup device in a stable manner, it is necessary to cause the light beam to follow a guide groove formed on the optical disk. The technology for permitting the light beam to follow the groove is called tracking. In the optical pickup device, a control signal for high-accuracy tracking is generated from the reflected light beam from the optical disk. The control signal is hereinafter referred to as a tracking error signal.
Various methods for detecting the tracking error signal are known. For example, a differential push pull method (hereinafter referred to as DPP) is disclosed in a patent document 1 (JP-B No. 4-34212, at page 6 and in FIG. 7). In the DPP method, a light beam is split into three beams, namely, one main light beam and two sub-light beams by a grating. The three beams are focused on the optical disk by an objective lens to form three beam spots thereon such that two spots of the sub-light beams on the disk are respectively spaced apart from the spot of the main beam by ±½ track in a radial direction of the disk. Each of three light beams reflected off the optical disk enters a pair of receiving areas, which are separated into two parts, to produce a corresponding push-pull signal. A difference between the push-pull signal generated from the main beam (hereinafter referred to as MPP), and the sum of the push-pull signals generated from the two sub-light beams (hereinafter referred to as SPP) is calculated to obtain a tracking error signal (hereinafter referred to as TES).
Another patent document 2 (for example, JP-A No. 12700/1993, at page 4 and in FIG. 2) discloses that two spots of the sub-light beams are formed at each of forward and backward parts on the disk with respect to a spot of the main light beam such that the spots of sub-light beams lie on different edges of a track where the main beam spot is located, thereby producing the tracking error signal by the reflected light. With this arrangement, no offset occurs in the tracking error signal at the boundary between a recorded part and a non-recorded part of the optical disk, so that the light beam can follow the track in a stable manner.
A further patent document 3 (for example, JP-A No. 307351/2001, at page 6 and FIG. 1) discloses that two spots of the sub-light beams are formed at forward and backward parts on the disk with respect to a spot of the main light beam such that these sub-beam spots are respectively spaced apart by 1.5 track from a track where the main beam spot is located, thereby producing the tracking error signal by the reflected light. The patent document 3 has the same effect as that of the aforesaid document 2.
A non-patent document 1 (Sharp Technical Journal, No. 90 (at pages 38 and 43 and in FIG. 3) proposes an original phase-shift DPP servo method. In this method, a predetermined phase is added to a sub-light beam using a phase diffraction grating, thereby detecting SPP signal having no amplitude as the push-pull signals from the reflected light beams from the optical disk. This can provide an optical pickup device whose performance does not depend on a distance between guide grooves on the disk, and on an angle of the guide groove.
The optical disk apparatus employing the DVD or CD are widely used, whereas low-cost competition is now heating up. For this reason, simplifying assembly steps is a very important factor, in addition to cost reduction of components.
In order to read out data from the rotating optical disk, the optical disk apparatus has a mechanism adapted to read all data from the disk by moving the optical pickup device from the inner track to the outer track of the disk. Such movement of the pickup from the inner to the outer tracks is generally called “seek”. In the DPP as described in the document 1, which is the most common method for generating a tracking error signal, seeks should be done by aligning the objective lens of the optical pickup device in the predetermined radial direction of the disk. This is because when the optical pickup device)seeks the disk apart from the predetermined radial direction of the disk, the angles of appropriate three beams on the inner track of the disk may become different from those on the outer track, leading to variations in amplitude of the tracking error signal. It should be noted that when the optical pickup device seeks the disk, such a seek operation of the pickup apart from the predetermined disk radial direction is called “off center”.
Thus, the optical pickup device needs to be mounted on the optical disk apparatus with very high accuracy, which takes much time to assemble, resulting in low in productivity, which is a factor of increase in cost.
It is supposed that in a pickup device having compatibility between the Blu-ray and the DVD, the optical pickup device should mount thereon two objective lenses for a high-speed operation. However, when two objective lenses are arranged in the rotational direction of the optical disk, at least one lens cannot be aligned in the predetermined radial direction of the disk, thus failing to seek. Further, the angles of appropriate three beams on the inner track of the disk may become different from those on the outer track, leading to large variations in amplitude of the tracking error signal, whereby the light beam cannot disadvantageously follow the predetermined track.
The tracking error detection method as disclosed in the patent document 3, which employs appropriate five beams, has the same problem as that in the document 1.
The method disclosed in the patent document 2 utilizes a diffraction grating with grid grooves formed on an incident surface and an exiting surface of the light beam so as to form five beam spots on the disk. The beams diffracted on the incident surface are further diffracted on the exiting surface to produce a lot of light beams. These light beams become stray lights, which cannot be avoiding from entering the photodetector, resulting in significantly degraded capability of reproduction of data from the disk.
In the optical disk apparatus, in the seeking operation of the optical pickup device, the object lens for focusing light beams on the disk precedes the pickup. After the movement of the lens, the pickup is moved. This kind of movement of the objective lens is hereinafter referred to as an “objective lens shift”.
In the non-patent document 1, the diffraction grating for adding a phase to sub-light beams is required to be separated in the radial direction of the disk. Thus, the center of the light beam may deviate from the separating line of the diffraction grating in the shift of the objective lens. When an amount of shift of the objective lens is large, the amplitude of the SPP signal occurs, resulting in variations in the amplitude of the tracking error signal. Accordingly, the shift amount of the objective lens must be limited to a small value.
The present invention has been accomplished in view of the above-mentioned problems, and it is an object of the invention to provide an optical pickup device which reduces variations in amplitude of the tracking error signal in the seek and shift operation of the objective lens due to an installation error of the optical pickup device into the optical disk apparatus, thereby generating the tracking error signal with high accuracy without any influence from the stray light, and which is high in productivity and low cost.
To solve the foregoing problems, in one aspect, the invention is directed to an optical pickup device comprising a laser source, a splitting unit for splitting a light beam emitted from the laser source into one main light beam, and a plurality of sub-light beams, an objective lens for focusing the main light beam and the sub-light beams on an optical disk, and a photodetector for receiving reflected light beams of the main light beam and the sub-light beams from the optical disk. The two sub-light beams are focused on at least one of forward and backward sides in a rotational direction of the disk with respect to the mainlight beam focused on the disk. When n is an integer number, and t is a distance between guide grooves of the disk, the two sub-light-beams focused are spaced apart from each other by a distance of t×(n+0.5) in a radial direction of the optical disk. As splitting means for splitting the light beams into a plurality of beams, a diffraction grating is used which has grid grooves spaced apart at equal intervals, but having different angles at the upper and lower parts of an exiting surface of the light beam.
According to the invention, the tracking error signal can be detected with high accuracy, as compared to the prior art.
These and other features, objects and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings wherein:
Reference will now be made to exemplary embodiments of the invention which are illustrated in the accompanying drawings. These embodiments should not be considered to limit the invention.
Now, a first embodiment of the invention will be described in detail with reference to the accompanying drawings. Reference will now be made to an optical pickup device for recording or reproducing information on or from a DVD−R (generating a tracking error signal) with a distance between guide grooves set to 0.74 μm. The invention is not limited to the DVD−R, and can be applied to any other recording type optical disk with guide grooves.
First, referring to
In the embodiment, five light spots, namely, a main light spot a, and sub-light spots b, c, d, and e are formed on the optical disk as shown in the figure. The main light spot a is used not only for recording and reproduction of information, but also for generation of a tracking error signal and a focusing error signal. The sub-light spots b, c, d, and e are used for generation of the tracking error signal. The sub-light spots b and c are disposed on the forward side in the rotational direction of the disk with respect to the main light spot a. The sub-light spots b and c are spaced apart from each other by a distance of t×(n+0.5) in the radial direction of the optical disk, wherein n is an integer number, and t is a distance between the guide grooves of the optical disk 001. For n=1, it is supposed in the figure that the light spots b and c are spaced apart from each other by a distance of 1.11 μm (=0.74×(1+0.5)). For n=0, the sub-light spots b and c may be spaced apart from each other by a distance of 0.37 μm.
The sub-light spots d and e are disposed on the backward side in the rotational direction of the optical disk 001 with respect to the main light spot a so as to be spaced apart from each other by the distance of t×(n+0.5), for example, by 1.11 μm, in the radial direction of the optical disk 001, as is the case with the sub-light spots b and c. Although in the figure, the sub-light spots b and c, or the spots d and e are symmetric with respect to the guide groove for the main light spot, the spot c or d may be positioned in the guide groove where the main light spot is disposed, with the distance between the adjacent sub-light spots being spaced apart from each other by the distance t×(n+0.5) in the radial direction of the disk.
Focusing the light spots on the disk in this manner can reduce variations in amplitude of the tracking error signal in the seek operation of the objective lens due to an installation error of the optical pickup device into the optical disk apparatus. This advantage will be described below in detail.
A method for generating the tracking error signal will be described below referring to
The upper diagram of
In general, rotation of the optical disk causes the optical disk to swing in the radial direction of the disk due to eccentricity. Thus, an irradiated point of the light spot on the disk swings largely in the disk radial direction. In the optical disk apparatus, the light spot should follow accurately the predetermined guide groove.
The difference between outputs of the reflected light beams from the optical disk is detected by a photodetector, which includes two parts separated in a direction corresponding to the rotational direction of the optical disk. This provides push-pull signals by the diffracted lights generated in the guide grooves of the optical disk. These push-pull signals are in common use for the optical disk apparatus, and detailed explanation thereof will be omitted.
The arrangement of spots in the figure are obtained when the time T =0. Suppose that the optical spot is moved in the disk radial direction (rightward in the figure) as the time goes by.
When the main light spot a is moved from a position shown in the figure in the radial direction of the optical disk, a push-pull signal a can be detected along the guide groove of the disk as shown in the lower diagram of
When MPP is the push-pull signal a, and SPP is an addition value of all push-pull signals b, c, d, and e, the tracking error signal (TES) is obtained by the operation of the following equation 1.
TES=MPP−k×SPP (1)
Note that k is a coefficient for compensating for a difference in the amount of light between the main light spot and the sub-light spots. As shown in the figure, the tracking error signal is equal to the MPP. Since the present operation is the same as that of the DPP method, it has an advantage in that the offset in the shift of the objective lens can be cancelled. In the known DPP method, when the objective lens is off center, an amplitude of the tracking error signal varies between the inner and outer tracks of the disk. This is due to a variation in amplitude of the SPP signal. In the system of the embodiment, however, since the amplitude of the SPP signal is constant at zero, the amplitude variation of the tracking error signal can be reduced.
In the known system as disclosed in the patent documents 1 and 2, a phase is added to each sub-light beam to maintain the amplitude of the SPP signal at constant zero. For example, the amplitude of the push-pull signal b or c is zero. The present system of the embodiment differs from the known system in that the amplitude of the SPP signal is maintained at constant zero by spacing the sub-light spots b and c, and/or the sub-light spots d and e apart from each other by a distance of t×(n+0.5) in the disk radial direction. The present system of the embodiment is different from the known system in the principle of detecting the tracking error signal, and thus has advantages in the shift of the objective lens, as will be described in detail later.
Reference will now be made to the fact that the amplitude of the SPP signal does not vary between the inner and outer tracks of the disk when the objective lens is off center.
The right diagram illustrates the MPP, SPP, and TES signals obtained from the light spots on the inner, intermediate, and outer tracks of the disk. In the known DPP method, the sub-light spot is spaced apart from the main light spot by a distance of δ=0.5×t. In this arrangement, the SPP signal is in reverse phase to the MPP signal, and the TES signal in phase with the MPP signal is obtained by the operation of the equation 1. It is shown that since the angles of the tangential lines in the guide grooves do not vary among the inner, intermediate, and outer tracks of the disk as shown in the left diagram, the same types of MPP, SPP, and TES signals are generated at any positions of the optical disk.
The right diagram illustrates the MPP, SPP, and TES signals obtained from the light spots on the inner, intermediate, and outer tracks of the disk. Like the normal setting of the optical pickup device, in this case, the three DPP spots are appropriately positioned on the intermediate track. First, the three spots on the intermediate track are considered. Since the three spots are positioned appropriately on the intermediate track, the main light spot is spaced apart from the sub-light spots by a distance of δ=0.5×t, whereby the same MPP, SPP, and TES signals as those in
Since the distance between the main light spot and the sub-light spots becomes larger on the outer track, the amplification of the SPP signal is largely decreased as is the case with the inner track. When the distance between the main light spot and the sub-light spots is 0.75×t, the amplification of the SPP signal is eliminated, leading to reduction in amplification of the TES signal by half.
In the known DPP method described above, since the amplification of the TES signal is largely varied when the objective lens is off center, the optical pickup device is required to be mounted on the optical disk apparatus with high accuracy such that the center of the objective lens is not off center.
The right diagram illustrates the MPP, SPP, and TES signals obtained from the light spots on the inner, intermediate, and outer tracks of the disk. In the method for detection of the tracking error signal in the embodiment, two sub-light spots preceding or following the main-light spot are spaced from each other by a distance of δ=t×(n+0.5). With this arrangement, the amplitude of the SPP signal is eliminated, and the TES signal obtained by the operation of the equation 1 is in phase with the MPP signal. It is shown that as shown in the left diagram, since the tangential angle of the guide groove is not varied among the inner, intermediate, and outer tracks, the same MPP, SPP, and TES signals are generated at any points on the optical disk.
The right diagram illustrates the MPP, SPP, and TES signals obtained from the light spots on the inner, intermediate, and outer tracks of the disk. Like the normal setting of the optical pickup device, in this case, the five spots are appropriately positioned on the intermediate track. First, the spots on the intermediate track are considered. Since the five spots are positioned appropriately on the intermediate track, the same MPP, SPP, and TES signals as those shown in
On the inner track of the disk, the angle of the guide groove on the disk is varied. However, a distance between the two sub-light spots preceding or following is not varied so much, and maintained at about δ=t×(n+0.5). Thus, even if the lens seeks the inner track of the disk, the same MPP, SPP, and TES signals as those on the intermediate track can be detected.
Likewise, also on the outer track of the disk, the same MPP, SPP, and TES signals as those on the intermediate and inner tracks can be detected.
Accordingly, in the detection method of the tracking error signal of the embodiment, the constant TES signal can be obtained regardless whether the objective lens is off center or not.
This eliminates the necessity of mounting the optical pickup device on the optical disk apparatus with high accuracy so that the center of the objective lens is not off center, thereby simplifying the assembly steps.
In the known DPP, it is necessary to control the rotation of the diffraction grating with high accuracy so as to form three beams by the grating in the optical pickup device. However, in the method for generating the tracking error signal not depending on the rotational angle according to the invention, adjustment of the rotation of the diffraction grating is not required, and the simple assembly steps of the optical pickup device can be achieved.
In a second embodiment, an optical pickup device for generating the tracking error signal of the first embodiment will be described below. An optical pickup device applicable for recording and reproducing information on the DVD−R is taken as an example in the second embodiment below. Note that the invention is not limited to the optical pickup device for the DVD−R, and may be applied to any other recording type optical disk with guide grooves.
In recording or reproducing information on or from the optical disk, such as a DVD, a semiconductor laser 102 with a wavelength band of 660 nm is usually used. The light beam with a wavelength of about 660 nm is emitted as a divergent ray from the semiconductor laser 102. The light beam emitted from the semiconductor laser 102 enters a splitting element 200, which maybe a diffraction grating. The light beam is split into five beams by the splitting element 200. The details of the splitting element 200 will be described later. The light beams passing through the splitting element 200 are reflected from a beam splitter 103, and then is converted into substantially parallel light beams by a collimator lens 104. Parts of the light beams pass through the beam splitter 103 to enter a front monitor 109. In general, when information is recorded on the recording type optical disk, such as the DVD−R, in order to irradiate the recording surface of the optical disk with the light with a predetermined intensity, it is necessary to control the emission intensity of the semiconductor laser with high accuracy. For this reason, when signals are recorded on the recording type optical disk, the front monitor 109 detects variations in emission intensity of the semiconductor laser 102, which are fed back to a driving circuit (not shown) of the semiconductor laser 102.
The light beams exiting the collimator lens 104 are applied to and focused on the optical disk by the objective lens 101 mounted on an actuator 106 to form five light spots on the disk. The light beams are reflected from the optical disk, and pass through the object lens 101, the collimator lens 104, the beam splitter 103, and a detection lens 107 to reach a photodetector 108. The astigmatism is given to the light beams when passing through the beam splitter 103. The light beams are used for detection of the focus error signal (hereinafter referred to as FES signal). The detection lens 107 has functions of rotating the direction of astigmatism in an arbitrary direction, and of determining the size of focused light spots on the photodetector 108. The light beams introduced into the photodetector 108 are used for detection of information signals recorded on the optic disk, and for detection of a position control signal for controlling the position of the focused light spot on the disk, such as a TES signal or a FES signal.
Now, a method for splitting the light beam into five beams will be explained below with reference to
In the embodiment, among the five light beams, the 0-th light beam 213 forms a main light spot a, the upper +1-st order diffracted light beam 214 forms a sub-light spot b, the lower +1-st order diffracted light beam 215 forms a sub-light spot c, the upper −1-st order diffracted light beam 217 forms a sub-light spot e, and the lower −1-st order diffracted light beam 216 forms a sub-light spot d. This can reduce variations in amplitude of the tracking error signal even if the objective lens is off center. The use of this splitting element eliminates the necessity of adjustment of rotation of the element itself, thereby readily assembling the optical pickup device.
Further, since the distance between the grid grooves at the upper part 210 is the same as that at the lower part 211, a detection surface pattern on the photodetector can be advantageously used in the known opto-electronic integrated circuit (OEIC). It is understood that the distances between the grid grooves at the upper and lower parts 210 and 211 may be changed by increasing the detection surface pattern.
Although in the second embodiment, a light path from the beam splitter 103 to the objective lens 108 is straight, the invention is not limited thereto. An optical component, such as a mirror or a prism, may be disposed in the light path to bend the path.
Another splitting element according to a third embodiment that is different from the splitting element 200 of the second embodiment will be described below. The third embodiment differs from the second embodiment only in the use of a splitting element 201, and other components of the third embodiment are the same as those of the second embodiment. The explanation of the same or like components will be omitted below. Referring to
Among the five light beams generated, the 0-th light beam 223 forms a main light spot a, the +1-st order diffracted light beam 224 forms a sub-light spot b, the +1-st order diffracted light beam 225 forms a sub-light spot c, the −1-st order diffracted light beam 226 forms a sub-light spot e, and the −1-st order diffracted light beam 227 forms a sub-light spot d. This can reduce variations in amplitude of the tracking error signal even if the objective lens is off center.
The use of this splitting element eliminates the necessity of adjustment of rotation of the element itself, thereby readily assembling the optical pickup device.
Now, a configuration of a specific optical pickup device according to the fourth embodiment, which is capable of using a method for generation of a tracking error signal of the invention, will be described in detail. The pickup device explained herein is an optical pickup device having compatibility between the Blu-ray and the DVD.
First, the Blue-ray optical system will be described below. In recording or reproducing information on or from the Blur-ray disk, a semiconductor laser with a wavelength band of 405 nm is normally used. The light beam with a wavelength of about 405 nm is emitted as a divergent ray from a BD semiconductor laser 301. The light beam emitted from the BC semiconductor laser 301 enters a splitting element 200-a. The splitting element 200-a may be a diffraction grating with the same grid groove pattern as that of the splitting element 200 as explained in the second embodiment. The light beam is split into five beams by the splitting element 200-a. Unlike the splitting element 200, the diffraction grating of the splitting element 200-a are set such that a distance between the grid grooves is tb×(n+0.5) in the disk radial direction when tb is a distance between the guide grooves of the Blue-ray disk. The light beams passing through the splitting element 200-a pass through a beam splitter 302, are reflected from a beam splitter 303, and are converted into substantially parallel light beams by a collimator lens 304. It should be noted that parts of the light beams pass through the beam splitter 303 to enter a front monitor 311. When signals are recorded on the optical disk, the front monitor 311 detects variations in emission intensity of the BD semiconductor laser 301, which are fed back to a driving circuit (not shown) of the BD semiconductor laser 301.
The light beams exiting the collimator lens 304 pass through a standing mirror 305, and are reflected by a standing mirror 306 in the Z direction of the figure. Then, the light beams are focused on the disk by an objective lens 308 for BD mounted on an actuator 307 to form five spots formed on the disk.
The actuator 307 installs thereon two objective lenses, that is, the objective lens 308 for BD, and the objective lens 315 for DVD, and is capable of simultaneously driving the two objective lenses.
The light beams reflected from the optical disk pass through the objective lens 308 for BD, the standing mirror 306, the standing mirror 305, the collimator lens 304, the beam splitter 303, and a detection lens 309, to reach a photodetector 310. The astigmatism is given to the light beams when passing through the beam splitter 303. The light beams are used for detection of the focus error signal (hereinafter referred to as FES signal). The detection lens 309 has functions of rotating the direction of astigmatism in an arbitrary direction, and of determining the size of focused light spot on the photodetector 310. The light beams introduced into the photodetector 310 are used for detection of information signals recorded on the optical disk, and for detection of a position control signal for controlling the position of the focused light spot on the disk, such as a TES signal or a FES signal.
Any other detection surface pattern on the photodetector 310 may be employed which enable detection of information signals recorded on the optical disk, and detection of the TES and FES signals.
Reference will now be made to the DVD optical system. In recording or reproducing information on or from the DVD disk, a semiconductor laser with a wavelength band of 660 nm is normally used. The light beam with a wavelength of about 660 nm is emitted as a divergent ray from a DVD semiconductor laser 312. The light beam emitted from the DVD semiconductor laser 312 enters a splitting element 200-b, which may be a diffraction grating with the same grid groove pattern as that of the splitting element 200 as explained in the second embodiment. The light beam is split into five beams by the splitting element 200-b. Unlike the splitting element 200, the diffraction grating of the splitting element 200-b are set such that a distance between the grid grooves of the diffraction grating is td×(n+0.5) in the disk radial direction when td is a distance between the guide grooves of the DVD−R disk.
The light beams passing through the splitting element 200-b enters a correcting lens 314. The Blu-ray system is different from the DVD system in an optical magnification (the focal distance of the collimator lens÷the focal distance of the objective lens). Thus, in the DVD optical system, providing the correcting lens 314 can set a magnification of the lens different from that in the Blu-ray optical system.
The light beams passing through the correcting lens 314 are reflected from the beam splitter 302 and the beam splitter 303, and is converted into substantially parallel light beams by the collimator lens 304. Parts of the light beams pass through the beam splitter 303 to enter the front monitor 311. When signals are recorded on the optical disk, the front monitor 311 detects variations in emission intensity of the DVD semiconductor laser 312, which are fed back to a driving circuit (not shown) of the semiconductor laser 312.
The light beams exiting the collimator lens 304 are reflected by the standing mirror 305 in the Z direction of the figure, and then focused on the disk by the objective lens 315 mounted on the actuator 307 to form five spots formed on the disk. The light beams reflected from the optical disk pass through the objective lens 315, the collimator lens 304, the beam splitter 303, and the detection lens 309 to reach a photodetector 310. The light beams introduced into the photodetector 310 are used for detection of information signals recorded on the optic disk, and for detection of a position control signal, such as a TES signal or a FES signal, for controlling the position of the focused light spot on the disk.
As mentioned above, even in the optical system including two objective lens arranged in the direction orthogonal to the disk radial direction as shown in the figure, the detecting method of the tracking error signal as disclosed in the first embodiment may be applied to enable the accurate tracking.
Reference will now be made to an optical disk apparatus according to a fifth embodiment which is equipped with the optical pickup device as described above.
When recording information is input from the recording information input terminal 80, the recording information signal conversion circuit 76 converts the recording information into a predetermined recording signal for driving the laser. The recording signal for laser driving is fed to the control circuit 78, where the laser light source control circuit 73 is driven to control the amount of light from the laser source, thereby recording the recording signals on the optical disk 001. The control circuit 78 is connected to the access control circuit 74 and the spindle motor driving circuit 77, and which controls the position of the optical pickup device 1 in the access direction, and the rotation of the spindle motor 002 of the optical disk 001.
Although in the embodiment, the optical pickup device and optical disk apparatus correspond to the DVD−R, the invention is not limited thereto. For example, the optical pickup device and optical disk apparatus may be used for any other optical disks, including a compact disk, a DVD-RAM, a DVD+R, and an optical disk with higher density than the DVD using a blue semiconductor laser.
The superiority of generation of the tracking error when the objective lens is shifted in a sixth embodiment will be described hereinafter in detail.
The diffraction grating of the non-patent document 1 as shown in
Reference will now be made to an effect of combination of the known system for generating the focus error signal in the astigmatism system and a method for generating the tracking error signal in the present embodiment.
When the distribution of intensity of the light spots is not rotated as shown in
By rotating the intensity distribution of the light spots on the photodetector by 90 degrees by the astigmatism method, the known simplest eight-divided detection surfaces can be used as the detection surface pattern of the photodetector as shown in
Reference will now be made to an optical pickup device suitable for the DVD−R (0.74 μm) and the DVD-RAM (1.23 μm) which have different distances between guide grooves.
As shown in
For the DVD−R (0.74 μm), however, the sub-light spots b and c are spaced apart from each other in the disk radial direction so as to satisfy the relationship t×(n+0.5). Much the same is true on the sub-light spots d and e. For example, the distance between these sub-light spots needs to be 0.37 μm for n=0, or 1.11 μm for n=1. If the sub-light spots b and c, or the sub-light spots d and e are spaced apart from each other only by 0.615 μm in the disk radial direction, the stable TES signal cannot be detected from the DVD−R.
That is, if the light spots are focused on the disk as shown in
As shown in
It is shown that the TES signal can be detected constantly from two disks, for example, the DVD−R (0.74 μm) and the DVD−RAM (1.23 μm), with different guide groove distances, regardless whether the optical pickup device is off center or not. The arrangement of spots as shown in
As mentioned above, the distances between the sub-light spots b and c, and between the sub-light spots d and e are respectively set to about 1.85 μm in the disk radial direction, whereby the optical pickup device suitable for both the DVD−R and DVD-RAM with the different guide groove distances can be achieved.
In the same principle, the distances between the sub-light spots b and c, and between the sub-light spots d and e are respectively set to about 1.85 μm in the disk radial direction, whereby the optical disk apparatus suitable for the DVD−R and DVD-RAM with the different guide groove distances can be provided.
While we have shown and described several embodiments in accordance with our invention, it should be understood that disclosed embodiments are susceptible of changes and modifications without departing from the scope of the invention. Therefore, we do not intend to be bound by the details shown and described herein but intend to cover all such changes and modifications within the ambit of the appended claims.
Number | Date | Country | Kind |
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2005-052246 | Feb 2005 | JP | national |