JP2007280524A - Objective lens unit, and optical disk device having the objective lens - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an objective lens unit enabling tracking control even in an optical disk having narrow track pitch, and an optical disk device using it. <P>SOLUTION: The unit is the objective lens unit for condensing light on an information recording plane, and is provided with an objective lens in which light condensed on the optical disk is transmitted and which has a lens function part in which signal light reflected by the optical disk is transmitted, and a light receiving element which is arranged at a position which is area being the outside more than the lens function part and on which the reflected light from the optical disk is made incident without through the objective lens. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

    The present invention relates to an objective lens unit and an optical disc apparatus having the objective lens unit. In particular, the present invention relates to an objective lens unit used for an optical disc recorded with high density, and an optical disc apparatus having the objective lens unit.

  In recent years, optical recording media (optical discs) such as DVDs, HD-DVDs (High definition DVDs), and BDs (Blu-ray Discs) have been commercialized or products in order to meet the need for large capacity optical recording media. It is becoming. DVD has a recording capacity of 4.7 GB per layer, 8.5 GB per layer, HD-DVD 15 GB per layer, 30 GB per layer, BD 25 GB per layer, and 50 GB per layer.

  In order to produce such a large-capacity optical disc product, it is necessary to increase the density of the recording medium. Therefore, an optical head device for recording / reproducing needs to reduce the spot diameter collected on the optical disk surface. For example, in the case of DVD, the wavelength of the laser light source is about 655 nm and the numerical aperture (NA) of the objective lens is 0.6. Further, in HD-DVD, the wavelength of the laser light source is about 405 nm and NA is 0.65, and in BD, the wavelength of the laser light source is about 405 nm and NA is 0.85.

  As the density of such optical disks increases, the track pitch is narrowed, and the length of pits or recording marks on which signals are recorded is shortened. For this reason, in an optical disc, the allowable range in focus control and tracking control is reduced, and more accurate control is required. This focus control is to control the light incident on the optical head to be condensed on the information recording surface of the optical disc by moving the optical head. The tracking control is to adjust the position of the optical head so that the optical head correctly traces the center of the track of the optical disk.

  In the tracking control described above, there is a DPD (Differential Phased Detection) method as an example of tracking control in a read-only disk (ROM) (for example, Patent Document 1). Tracking control in the DPD method is performed by a method of detecting a phase difference between light amounts at the time of rising and falling of a pit. At this time, the reflected light of the disk taken in by the objective lens is detected by a four-divided light receiving element, and the difference in the amount of light in the oblique direction corresponds to the radial deviation of the light spot focused on the disk with respect to the track of the optical disk. We are using.

FIG. 12 shows a configuration diagram of a signal conversion circuit 90 for converting a signal detected by a photodetector into a tracking signal in the conventional DPD method. The signal conversion circuit 90 includes a photodetector 91, addition operation circuits 92a and 92b, and a phase operation circuit 93. The photo detector 91 is divided into four photo detectors 91a to 91d. The sum of the light quantity I _2a detected by the photodetector 91a and the light quantity I _2c detected by the photodetector 91c, and the sum of the light quantity I _2b detected by the photodetector 91b and the light quantity I _2d detected by the photodetector 91d are added to an addition operation circuit 92a, The operation is performed at 92b. The phase calculation circuit 93 detects the phase difference between the I _2a + I _2c and I _2b + I _2d .

FIG. 13 is a plot of I _2a + I _2c and I _2b + I _2d after AC coupling plotted against the time axis when it is considered that the light spot is focused at the center of the track of the optical disk. . The horizontal axis is time, and the vertical axis is the change in light quantity. When the light spot is focused at the center of the track of the optical disc, there is no phase difference between I _2a + I _2c and I _2b + I _2d . Therefore, in FIG. 13, the change in the light amount between I _2a + I _2c and I _2b + I _2d is shown by one solid line. This is because the light reflected from the track is symmetric with respect to the optical axis, and there is no phase difference between I _2a + I _2c and I _2b + I _2d .

However, as shown in FIG. 14, when the light spot 94 deviates from the center of the track 95, a phase difference Δt between I _2a + I _2c and I _2b + I _2d occurs. FIG. 14A shows a case where the light spot 94 is displaced radially inward from the center of the track 95, and FIG. 14B shows a case where the light spot 94 is displaced radially outward from the center of the track 95. Show. FIG. 15A shows the time dependence of the light amount change of I _2a + I _2c and I _2b + I _2d when the light spot 94 is positioned as shown in FIG. 14A, and the light as shown in FIG. 14B. FIG. 15B shows the time dependency of the light amount change of I _2a + I _2c and I _2b + I _2d when the spot 94 is located.

When the light spot is deviated from the track center of the optical disk, a phase difference Δt occurs at I _2a + I _2c and I _2b + I _2d . This phase difference Δt increases as the light spot deviates from the track center of the optical disk. Further, the phase difference Δt is reversed between positive and negative depending on which side of the pit the light spot shifts. From these facts, by measuring this phase difference, it is possible to detect how much and in which direction the light spot deviates from the track center.
JP 2005-182927 A

  However, the amount of DPD signals that can be detected for tracking control decreases as the track pitch is narrowed to further increase the density of the optical disk. This is because the light reflected from the optical disk causes a strong diffraction phenomenon as the track pitch becomes narrower. That is, as the track pitch becomes narrower, the light reflected from the optical disk is diverged, and the DPD signal contained in the light reflected from the optical disk is not detected by the photodetector. Therefore, when the track pitch is narrowed, a signal that can be reproduced if tracking control can be performed cannot be reproduced because tracking control is unstable or cannot be performed. For this reason, when the density of the optical disk is further increased, the tracking signal cannot be detected, so that the reproduction cannot be performed.

  The present invention has been made to solve such problems, and it is an object of the present invention to provide a detection method and apparatus capable of easily performing tracking control even when the track pitch of an optical disk is narrowed. And

  An objective lens unit according to a first aspect of the present invention is an objective lens unit for condensing light on an information recording surface of an optical disc, and the light to be condensed on the optical disc is transmitted from the optical disc. An objective lens having a lens function part through which reflected signal light passes, and an area outside the lens function part, where the reflected light from the optical disc is incident without passing through the objective lens The light receiving element is provided. By using such an objective lens unit, light reflected outside the lens function part of the objective lens can be detected by a light receiving element. By using the signal, an optical disc with a narrow track pitch can be used. Will also be able to control tracking.

  In the objective lens unit according to the second aspect of the present invention, in the objective lens of the objective lens unit described above, the optical disc side is closer to the optical disc side than the lens surface on the side on which the light focused on the optical disc is incident. The light receiving element is located in the position. This makes it possible to more detect light reflected from the optical disc outside the lens function unit. The objective lens unit according to a third aspect of the present invention is characterized in that the objective lens of the objective lens unit described above is located on the surface on the optical disc side. Accordingly, since the light receiving element is disposed on the optical disc side with respect to the objective lens, it is possible to detect the light reflected from the optical disc to the outside of the lens function unit.

  The objective lens unit according to a fourth aspect of the present invention further includes a lens barrel that is fixed by fitting the objective lens in the objective lens unit according to the first aspect or the second aspect, The light receiving element is provided on the surface of the objective lens and the lens barrel on the optical disc side. By doing in this way, the area which can arrange | position a light receiving element can be enlarged. The objective lens unit according to a fifth aspect of the present invention is characterized in that the light receiving element in the objective lens unit according to the third aspect or the fourth aspect is in contact with the surface. is there. By doing so, the light receiving element can be easily fixed.

  In the objective lens unit according to a sixth aspect of the present invention, the light receiving element in the objective lens unit described above passes through the intersection of the optical axis of the objective lens and the surface of the objective lens on the optical disc side, and the tanger of the optical disc. It has two sets of light receiving elements having the same shape at symmetrical positions with respect to a line parallel to the local direction. By doing so, tracking control in the DPD method can be performed. The objective lens unit according to a seventh aspect of the present invention is characterized in that the light receiving element in the objective lens unit includes a light receiving element that is equally divided into four or more parts. By doing so, it is possible to detect almost all of the light on the outer periphery from the lens function unit.

  The objective lens unit according to an eighth aspect of the present invention is characterized in that the light receiving element in the objective lens unit described above is in contact with the outer periphery of the objective lens and the first region. This makes it possible to make maximum use of the area of the light receiving element. The optical disk in the objective lens unit according to the ninth aspect of the present invention is a read-only optical disk having a pit in a track.

  An optical disc device according to a tenth aspect of the present invention includes a light source, an objective lens for condensing the light from the light source onto the optical disc, and the light from the light source of the objective lens is transmitted from the optical disc. An objective lens unit having a light receiving element disposed in a region outside the lens function part through which the reflected signal light is transmitted and where the reflected light from the optical disc is incident without passing through the objective lens Are provided. As a result, the light reflected from the lens function part of the objective lens can be detected by the light receiving element, and tracking control can be performed even on an optical disk having a narrow track pitch by using the signal. Become.

  The optical disc apparatus according to an eleventh aspect of the present invention is the objective lens of the above-described optical disc apparatus, wherein the light focused on the optical disc is closer to the optical disc side than the lens surface on the side where the light is incident on the objective lens. The light receiving element is located. This makes it possible to more detect light reflected from the optical disc outside the lens function unit. An optical disc apparatus according to a twelfth aspect of the present invention is characterized in that the objective lens of the optical disc apparatus described above is located on the surface on the optical disc side. Accordingly, since the light receiving element is disposed on the optical disc side with respect to the objective lens, it is possible to detect the light reflected from the optical disc to the outside of the lens function unit.

  An optical disc device according to a thirteenth aspect of the present invention further includes a lens barrel that is fixed by fitting the objective lens unit in the optical disc device according to the tenth aspect or the eleventh aspect, The light receiving element is provided on the surface of the objective lens and the lens barrel on the optical disc side. By doing in this way, the area which can arrange | position a light receiving element can be enlarged. An optical disk device according to a fourteenth aspect of the present invention is characterized in that the light receiving element in the optical disk device according to the twelfth aspect or the thirteenth aspect is in contact with the surface. By doing so, the light receiving element can be easily fixed.

  An optical disc apparatus according to a fifteenth aspect of the present invention is the optical disc apparatus according to the fifteenth aspect, wherein the light receiving element in the optical disc apparatus passes through an intersection between the optical axis of the objective lens and the surface of the objective lens on the optical disc side, and the tangential direction of the optical disc. It is characterized by having two sets of light-receiving elements having the same shape at symmetrical positions with respect to a line parallel to. By doing so, tracking control in the DPD method can be performed. An optical disc apparatus according to a sixteenth aspect of the present invention is characterized in that the light receiving element in the optical disc apparatus includes a light receiving element that is equally divided into four or more. By doing so, it is possible to detect almost all of the light on the outer periphery from the lens function unit.

  An optical disc apparatus according to a seventeenth aspect of the present invention is the above-described optical disc apparatus, wherein the optical disc apparatus further includes a low-pass filter for removing noise. Thereby, noise incident on the light receiving element from the outside can be canceled. An optical disc apparatus according to an eighteenth aspect of the present invention is characterized in that the light receiving element in the optical disc apparatus described above is in contact with the outer periphery of the objective lens and the first region. This makes it possible to make maximum use of the area of the light receiving element. An optical disc apparatus according to a nineteenth aspect of the present invention is characterized in that the optical disc in the above-described optical disc apparatus is a read-only optical disc having pits in a track.

  According to the objective lens unit and the optical disk apparatus having the objective lens unit according to the present invention, tracking control can be performed even when the track pitch is narrow. In addition, this makes it possible to perform disk reproduction due to the inability to perform tracking control, and thus the capacity of the disk can be increased.

Embodiment 1 FIG.
Hereinafter, specific embodiments to which the present invention is applied will be described in detail with reference to the drawings. In this embodiment, the present invention is applied to an objective lens unit and an optical disk apparatus using the objective lens unit. In the objective lens unit according to the present embodiment, an objective lens having a lens function part through which light condensed on the optical disk is transmitted and signal light reflected from the optical disk is transmitted, and an area outside the lens function part The light receiving element is disposed at a position where the reflected light from the optical disc is incident without passing through the objective lens. As a result, it is possible to detect the light incident on the area outside the lens function unit, and it is possible to deal with an optical disc in which tracking control has been densified. As used herein, the lens function unit refers to a region that includes the effective diameter of the objective lens and includes a region through which light incident on the PD that detects light that has been reflected from the optical disk and passed through the objective lens has passed. .

  In the present embodiment, an objective lens pickup unit in which the light receiving element is in contact with the surface of the objective lens is used, and the light receiving element is divided into four by dividing lines parallel to the tangential direction and the radial direction of the optical disk. An example will be described. The present invention is not limited to the above.

  FIG. 1 shows a schematic configuration diagram of an optical pickup device 1 equipped with the objective lens unit according to the present embodiment. The optical pickup device 1 includes a laser light source 11 that emits laser light. The laser light source 11 is preferably a semiconductor laser. The wavelength of the laser light emitted from the laser light source 11 is approximately 405 nm, and generates a light beam that is substantially linearly polarized and diverged. The light from the laser light source 11 is converted into a parallel light beam by the collimator lens 12. The light converted into a parallel light beam by the collimator lens 12 passes through the beam splitter 13 and is converted from linearly polarized light to circularly polarized light by the λ / 4 plate 14. The light converted into the circularly polarized light by the λ / 4 plate 14 is reflected by the reflecting mirror 15 and is condensed on the optical disk 18 by the objective lens 16 attached to an actuator (not shown) to form a light spot.

  The light reflected from the optical disk 18 passes through the objective lens 16 and is reflected by the reflection mirror 15. Of the reflected light from the optical disc 18, what passes through the objective lens 16 is part of the 0th-order diffracted light and the 1st-order diffracted light. The light reflected by the reflection mirror 15 passes through the λ / 4 plate 14 and becomes linearly polarized light perpendicular to the polarization direction when the optical disk is incident. This light is reflected by the beam splitter 13 and enters the condenser lens 19. The light incident on the condenser lens 19 is condensed on a PD (photo detector) 20. The PD 20 is for detecting a signal from the optical disk 18.

  The objective lens unit 10 according to the present embodiment includes an objective lens 16 and a light receiving element 17 provided on the optical disc 18 side of the objective lens 16. The light receiving element 17 is divided into four parts to use the DPD method, and is arranged so as to surround the effective diameter of the objective lens 16. This is because most of the first-order diffracted light from the reflected light from the optical disk 18 is received. In the present embodiment, the DPD method is used for tracking control, but the present invention is not limited to this.

  FIG. 2 is a circuit configuration diagram of the signal conversion circuit 2 used when the DPD method is used. The signal conversion circuit 2 includes a light receiving element 17, addition operation circuits 21 a and 21 b, and a phase detection circuit 22. The light receiving element 17 is composed of four divided light receiving elements 17a to 17d.

Signal I _c which is photoelectrically converted by the photoelectric conversion signals I _a and the light receiving element 17c by the light receiving element 17a is input to the addition operation circuit 21a. The signal I _d photoelectrically converted by the photoelectric conversion signal I _b and the light receiving element 17d by the light receiving element 17b is input to the addition operation circuit 21b. In addition operation circuit 21a, it calculates the sum of _{I a} and _{I c.} Further, it calculates the sum of the addition operation circuit 21b in _{I b} and _{I d.} By inputting the _I b + _{I d} outputted from the adder output from the operational circuit 21a a and _I a + _{I c} add operation circuit 21b to the phase conversion circuit _22, position of the _I a + I _c and _I b + _{I d} Phase difference is calculated. This phase difference represents the amount of deviation of the light spot from the track center of the optical disk.

  Here, FIG. 3 shows an enlarged view of the objective lens unit 10 according to the present embodiment. FIG. 3A is a diagram of the objective lens unit 10 as viewed from the optical disk side. FIG. 3B is a cross-sectional view seen from a direction perpendicular to the optical axis of the objective lens 16.

  As shown in FIG. 3A, the light receiving element 17 is divided into four light receiving elements 17a to 17d. These light receiving elements 17 a to 17 d are provided so as to surround an effective diameter 161 in the objective lens 16. The effective diameter 161 here is a region in the objective lens 16 through which light condensed on the optical disk passes.

  The light receiving element 17 is provided with a dividing line (dark line, dead zone) parallel to the tangential direction of the optical disk. That is, the dividing line 171 that divides the light receiving element 17a and the light receiving element 17d and the dividing line 172 that divides the light receiving element 17b and the light receiving element 17c are parallel to the tangential direction of the optical disc. The light receiving element 17 is provided with a dividing line parallel to the radial direction of the optical disk. That is, the dividing line 173 that divides the light receiving element 17a and the light receiving element 17b and the dividing line 174 that divides the light receiving element 17c and the light receiving element 17d are set to be parallel to the radial direction of the optical disc. The light receiving element 17 is divided into four light receiving elements 17a to 17d by a dividing line parallel to the tangential direction of the optical disc and a dividing line parallel to the radial direction of the optical disc.

  As described above, by arranging the light receiving element 17 around the effective diameter 161 of the objective lens 16, among the light reflected from the optical disk 18, a part of the zero-order light and the primary light is effective diameter 161 of the objective lens 16. Most of the primary light is incident on the light receiving element 17. When the primary light is incident on the light receiving element 17, DPD tracking control is performed using this light information.

  In particular, in an optical disc with a narrow track pitch, the light reflected from the optical disc is diffracted and the light is diverged, so that the amount of light incident on the light receiving element 17 increases. Therefore, a signal necessary for tracking control can be obtained even on a high-density optical disc. Further, in order to reduce malfunction due to external stray light, it is desirable that the light receiving element 17 be provided with a thin film having a band-pass filter function that transmits only a necessary wavelength on the surface of the light receiving portion.

  In FIG. 3, the light receiving element 17 is in contact with the objective lens 16, but it is sufficient that the light receiving element 17 is fixed to the objective lens 16, and the distance between the objective lens 16 and the light receiving element 17. Even if a spacer or the like is provided in the interval, the effect of the present invention is not affected at all. In addition, the light receiving element 17 may be a light receiving element that is not only divided into four but also divided into four or more.

  Here, the light beam focused on the light receiving element 17 and the PD 20 will be described. FIG. 4A shows a beam profile on the entrance pupil of the objective lens 16. FIG. 4B shows a beam profile at the light spot converged by the objective lens 16. In FIG. 4, the vertical direction is the radial direction, and the horizontal direction is the tangential direction. The beam profile on the entrance pupil has such a shape that the center of the light spot is raised as shown in FIG. Further, the outer peripheral portion of the light spot has a steep slope. The rim intensity in the tangential direction is 0.60, and the rim intensity in the radial direction is 0.65.

Further, the light spot converged by the objective lens 16 shows a beam profile in which the center of the light spot rises sharply as shown in FIG. 4B. Laser wavelength is 405nm, 1 / ^{e 2} spot diameter in the tangential direction when the NA of the objective lens is 0.85 0.404μm, 1 / ^{e 2} spot diameter of the radial direction is 0.401Myuemu.

  The optical spot is irradiated with a light spot having a beam profile as shown in FIG. FIG. 5 shows the positional relationship between the light spot at this time and the track of the optical disk and the pit located in the track. The track 30 of the optical disk according to the present embodiment has a groove called a pit 32. That is, the track 30 is composed of pits 32 and a mirror surface region 33 located between the pits. When the center of the light spot 31 comes to the center of the track 30, it is the optimum position for focusing on the optical disk.

  FIG. 6 shows the beam profile of the reflected light when the light spot is located as shown in FIG. 6A is a beam profile of the entire reflected light obtained by irradiating the optical disk, FIG. 6B is a beam profile in the PD 20, and FIG. 6C is a beam profile in the light receiving element 17. is there. As shown in FIG. 6, among the entire reflected light obtained by irradiating the optical disk, the light located within the effective diameter is incident on the PD 20 and the light positioned near the effective diameter is incident on the light receiving element 17. I can see that

  Here, in order to observe the light intensity characteristic when the DPD method is used in the light receiving element 17 according to the present embodiment, the light intensity characteristic in the light receiving element 17 according to the present embodiment and the light intensity characteristic in the PD 20 are A comparison was made. FIG. 7 shows a light spot with a laser wavelength λ = 405 nm and an objective lens NA = 0.85, a track pitch = 0.32 μm, a pit width = 0.16 μm, a pit depth = 0.047 μm, and a pit length = 0. It is the figure which showed the signal output when a 276-micrometer optical disk was traced by track offset = 0.05 micrometer.

  FIG. 7A shows the light intensity characteristic of the light receiving element 17 according to the present embodiment, and FIG. 7B shows the light intensity characteristic of the PD 20. When the light intensity characteristics of the light receiving element 17 and the PD 20 are compared, the amplitude of the light receiving element 17 is about 0.72 times the amplitude of the PD 20 and is small. The phase difference Δt in the light receiving element 17 is about 2.10 times the phase difference Δt in the PD 20. That is, a large phase difference appears in the DPD signal in the light receiving element 17 provided in the objective lens 16.

  FIG. 8 is a table in which the same comparison is performed using optical disks with different track pitches, and the data is tabulated. FIG. 8A shows a case where the laser wavelength is 405 nm, the numerical aperture NA of the objective lens is 0.85, the pit length is 0.276 μm, and the pit depth is 0.047 μm. FIG. 8B shows the case where the laser wavelength is 405 nm, the numerical aperture NA of the objective lens is 0.65, the pit length is 0.408 μm, and the pit depth is 0.047 μm. In FIG. 8, the amplitude output is normalized with the total amount of light reflected by the optical disk as 1. The track offset is 0.05 μm.

  FIG. 9 is a plot of the phase difference ratio Δt / T, which is a value obtained by dividing the addition amplifier amplitude and the phase difference Δt by the ½ period T based on the table of FIG. 8A. . FIG. 10 is a plot of the summing amplifier amplitude and the phase difference ratio Δt / T against the track pitch based on the table of FIG. 9A and 10A, the horizontal axis represents the track pitch, and the vertical axis represents the summing amplifier amplitude. In FIGS. 9B and 10B, the horizontal axis represents the track pitch and the vertical axis represents the phase difference ratio Δt / T. 9 and 10, the chain line is a plot relating to the PD 20, and the solid line is a plot relating to the light receiving element 17.

  When the laser wavelength is 405 nm, the numerical aperture NA of the objective lens is 0.65, the pit length is 0.408 μm, and the pit depth is 0.047 μm, as shown in FIG. 9A, in the light receiving element 17 and the PD 20 The amplitude becomes smaller as the track pitch becomes shorter. In any track pitch, the amplitude in the light receiving element 17 is smaller than the amplitude in the PD 20. The absolute value of the phase difference rate Δt / T increases as the track pitch decreases in the light receiving element 17 provided in the objective lens of the present embodiment. Further, in the PD 20, as the track pitch becomes shorter, the value changes from a positive value to a negative value, and the phase difference is not clearly understood.

  When the laser wavelength is 405 nm, the numerical aperture NA of the objective lens is 0.65, the pit length is 0.408 μm, and the pit depth is 0.047 μm, as shown in FIG. The amplitude in the PD 20 becomes smaller as the track pitch becomes shorter. In any track pitch, the amplitude in the light receiving element 17 is smaller than the amplitude in the PD 20. The phase difference ratio Δt / T increases as the track pitch decreases in the light receiving element 17 provided in the objective lens of the present embodiment. Further, in the PD 20, as the track pitch becomes shorter, the value changes from a positive value to a negative value, and the phase difference is not clearly understood.

  From the above, even when the numerical aperture and pit length of the objective lens are changed, the phase difference rate Δt / T is higher in the light receiving element 17 provided in the objective lens according to the present embodiment than in the PD 20. Also found a clear value. Further, regarding the amplitude, the light receiving element 17 provided in the objective lens according to the present embodiment has a smaller value than the PD 20, but it is a sufficient value for detection. Conceivable. From these, it is considered that tracking control can be stably performed by using the light receiving element 17 provided in the objective lens according to the present embodiment.

Embodiment 2. FIG.
In the second embodiment, the light receiving element is not provided in the objective lens, but is provided in the lens barrel for fixing the objective lens. Components and operating principles similar to those of the first embodiment are omitted.

  FIG. 11 is a structural diagram of the objective lens barrel according to the present embodiment. FIG. 11A is a cross-sectional view seen from the optical disc side, and FIG. 11B is a cross-sectional view seen from a direction perpendicular to the optical axis of the objective lens. The objective lens 42 is fixed so as to be fitted to the lens barrel 43. In addition, the light receiving element 41 according to the present embodiment is disposed so as to surround the effective diameter 411 of the objective lens 42. The light receiving element 41 is provided not only on the optical disc side surface of the objective lens 42 but also on the optical disc side surface of the lens barrel 43. As a result, the surface area of the light receiving element 41 can be increased.

  The light receiving element 41 is a donut-shaped light receiving element having a hole in the center for transmitting a light beam incident on the optical disk 18. Further, the light receiving element 41 is divided into four light receiving elements 41a to 41d by a dividing line parallel to the tangential direction and a dividing line parallel to the radial direction. As described above, by arranging the light receiving element 41 on the optical disc side surface of the lens barrel 43 and the objective lens 42, the light receiving area is increased and the amplitude output is increased.

  It should be noted that the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the scope of the present invention. In the embodiment, light having a wavelength of about 405 nm is used, but the present invention is not limited to this.

1 is a schematic configuration diagram of an optical pickup device equipped with an objective lens according to Embodiment 1. FIG. It is a circuit block diagram of the signal conversion circuit used when using a DPD system. 2 is an enlarged view of an objective lens 16 according to Embodiment 1. FIG. (A) is a beam profile on the entrance pupil of the objective lens. (B) is a beam profile in the light spot converged by the objective lens. It is the figure which showed the positional relationship of a spot, the track | truck of an optical disk, and the pit located in a track | truck. It is a beam profile of reflected light. This is a light intensity characteristic in a light receiving element and a PD when a light spot is irradiated onto an optical disc having a track pitch of 0.32 μm. It is a table | surface which shows the track pitch dependence of an addition amplifier amplitude and a phase difference rate. It is a graph which shows the track pitch dependence of an addition amplifier amplitude and phase difference rate in case the numerical aperture NA of an objective lens is 0.85, a pit length is 0.276 μm, and a pit depth is 0.047 μm. It is a graph which shows the track pitch dependence of an addition amplifier amplitude and a phase difference rate in case the numerical aperture NA of an objective lens is 0.65, the pit length is 0.408 μm, and the pit depth is 0.047 μm. 6 is a structural diagram of an objective lens barrel according to Embodiment 2. FIG. It is a block diagram of the signal conversion circuit 90 in the conventional DPD system. It is the figure which plotted the light quantity change which added the intensity | strength in four PD to the diagonal direction with respect to the time-axis. It is a figure which shows the positional relationship of a track | truck and a light spot when a light spot has shifted | deviated from the track center. It is a figure which shows the time dependence of the light quantity change when a light spot has shifted | deviated from the track center.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Optical pick-up apparatus 2 Signal conversion circuit 10 Objective lens unit 11 Laser light source 12 Collimate lens 13 Beam splitter 14 (lambda) / 4 board 15 Reflection mirror 16 Objective lens 17 Light receiving element 18 Optical disk 19 Condensing lens 20 PD
DESCRIPTION OF SYMBOLS 21 Addition calculation circuit 22 Phase detection circuit 30 Track 31 Light spot 32 Pit 33 Mirror surface area 41 Light receiving element 42 Objective lens 43 Lens barrel 161, 411 Effective diameter 171, 172, 173, 174 Dividing line 90 Signal conversion circuit 91 Photo detector 92 Addition calculation Circuit 93 Phase arithmetic circuit

Claims (19)

An objective lens unit for condensing light on an information recording surface of an optical disc,
An objective lens having a lens function part through which light condensed on the optical disk is transmitted and signal light reflected from the optical disk is transmitted;
An objective lens unit comprising: a light receiving element disposed in a region outside the lens function unit and where reflected light from the optical disc is incident without passing through the objective lens.   2. The objective lens according to claim 1, wherein the light receiving element is positioned closer to the optical disc than a lens surface on the side on which light focused on the optical disc is incident on the objective lens. unit.   The objective lens unit according to claim 1, wherein the light receiving element is positioned on a surface of the objective lens on the optical disc side. The objective lens unit further includes a lens barrel that is fixed by fitting the objective lens;
3. The objective lens unit according to claim 1, wherein the light receiving element is provided on a surface of the objective lens and the lens barrel on the optical disc side.   The objective lens unit according to claim 3, wherein the light receiving element is in contact with the surface.   The light receiving element is a light receiving element having the same shape that is symmetric with respect to a line passing through the intersection of the optical axis of the objective lens and the surface of the objective lens on the optical disc side and parallel to the tangential direction of the optical disc. The objective lens unit according to claim 1, comprising two sets.   The objective lens unit according to any one of claims 1 to 7, wherein the light receiving element includes a light receiving element that is equally divided into four or more parts.   The objective lens unit according to claim 1, wherein the light receiving element is in contact with an outer periphery of the objective lens and the first region.   The objective lens unit according to any one of claims 1 to 8, wherein the optical disc is a read-only optical disc having pits in a track. A light source;
An objective lens for condensing the light from the light source onto the optical disk, and a region outside the lens function unit through which the light from the light source of the objective lens is transmitted and the signal light reflected from the optical disk is transmitted An optical disc apparatus comprising: an objective lens unit having a light receiving element disposed at a position where reflected light from the optical disc is incident without passing through the objective lens.   11. The optical disc apparatus according to claim 10, wherein the light receiving element is positioned closer to the optical disc than a lens surface on the side where light focused on the optical disc is incident on the objective lens. .   12. The optical disc apparatus according to claim 10, wherein the light receiving element is located on a surface of the objective lens on the optical disc side. The objective lens unit further includes a lens barrel that is fixed by fitting the objective lens;
12. The optical disc apparatus according to claim 10, wherein the light receiving element is provided on a surface of the objective lens and the lens barrel on the optical disc side.   The optical disc apparatus according to claim 12 or 13, wherein the light receiving element is in contact with the surface.   The light receiving element is a light receiving element having the same shape that is symmetric with respect to a line passing through the intersection of the optical axis of the objective lens and the surface of the objective lens on the optical disc side and parallel to the tangential direction of the optical disc. The optical disk apparatus according to claim 11, wherein two sets are provided.   16. The optical disc apparatus according to claim 11, wherein the light receiving element includes a light receiving element that is equally divided into four or more parts.   The optical disk apparatus according to claim 11, further comprising a low pass filter for removing noise.   18. The optical disc apparatus according to claim 11, wherein the light receiving element is in contact with an outer periphery of the objective lens and the first region.   The optical disc device according to any one of claims 11 to 18, wherein the optical disc is a read-only optical disc having a pit in a track.

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