JP4121895B2 - Optical pickup - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical pickup that performs tracking by displacing a lens that condenses laser light from a light source onto an optical disk.
[0002]
[Prior art]
Some optical pickups that irradiate and receive a laser beam with an optical disk are used in combination between optically different optical disks such as a CD (Compact Disc) and a DVD (Digital Versatile Disc). is there. However, in such an optical pickup used in combination between different optical discs such as CD and DVD, there is a problem that aberration occurs in the laser irradiated on the optical disc.
[0003]
This aberration is caused by the fact that the numerical aperture NA of the objective lens for condensing the laser from the light source onto the optical disk is large because DVD has a higher data recording density than CD. In addition, this aberration is such that the thickness of the cover layer, which is a protective layer covering the recording layer of the optical disc, is “1.2 mm” for CD, but “0.6 mm” for DVD. This also occurs because the DVD cover layer is thinner than the CD.
[0004]
In order to suppress such aberration, it is conceivable to use different objective lenses for CD and DVD. However, in this case, the structure of the optical pickup becomes complicated, and it becomes a factor that hinders downsizing of the optical pickup.
[0005]
Therefore, conventionally, for example, as seen in Patent Document 1, a liquid crystal panel is provided in the optical path between the light source and the optical disk, and it is also proposed to compensate for aberrations by controlling the alignment state of the liquid crystal in the liquid crystal panel. ing. FIG. 12 shows the configuration of such an optical pickup.
[0006]
In this optical pickup, the forward path of the laser beam is as follows. First, the laser light L 1 emitted from the laser light source 10 is converted into parallel light by the collimator lens 12 and enters a PBS (polarized beam splitter) 14. Then, the phase of the laser beam L2 reflected by the PBS 14 is adjusted when passing through the liquid crystal panel 20, and becomes the laser beam L3. The laser light L3 becomes circularly polarized laser light L4 in the quarter-wave plate 30. The laser beam L4 is collected by the objective lens 40, passes through the disc cover layer 1a of the optical disc 1, and forms an image on the disc recording layer 1b.
[0007]
In the optical pickup, the return path of the laser light is as follows. The laser beam having circularly polarized light reflected by the disc recording layer 1b of the optical disc 1 becomes a laser beam L4 that is parallel light in the objective lens 40. The laser light L4 becomes laser light L3 linearly polarized on the quarter-wave plate 30. Then, after passing through the liquid crystal panel 20, the light enters the PBS 14. Since the laser beam L2 incident on the PBS 14 is linearly polarized light opposite to the outward path, it passes through the PBS 14. Then, the laser light that has passed through the PBS 14 is condensed on the light receiver 52 by the objective lens 50.
[0008]
Here, since the thickness of the disc cover layer 1a of the optical disc 1 is different between the CD and the DVD, when an optical pickup is designed together with one of them, an aberration on a concentric circle mainly occurs on the other side. Therefore, in the optical pickup, the aberration is corrected by controlling the liquid crystal panel 20 by the control circuit 60.
[0009]
FIG. 13A shows the electrodes of the liquid crystal panel 20. As shown in FIG. 13A, the electrodes 21 of the liquid crystal panel 20 are configured by arranging electrodes in a fine grid pattern (10 × 10 electrodes are illustrated in the figure).
[0010]
FIG. 13B shows a refractive index distribution of the liquid crystal in the liquid crystal panel 20 generated when a voltage is applied to the electrodes in order to correct the concentric aberration. In FIG. 13B, the difference in hatching indicates the difference in refractive index. As shown in FIG. 13B, concentric aberrations can be corrected by forming a refractive index pattern symmetrical to the center of the laser beam L2.
[0011]
By the way, although the optical pickup irradiates the laser following the spiral track in the optical disc 1, it is easy to perform tracking control for irradiating the laser at an appropriate position on the optical disc 1 only by the operation of the optical pickup. is not. In particular, when the optical disc 1 is mounted on a recording device or a reproducing device, the eccentricity may slightly occur with respect to the rotation axis, and the disc itself may also be eccentric, so that the tracking control is difficult.
[0012]
Therefore, normally, in the optical pickup, the objective lens 40 can be displaced minutely (for example, “0.4 mm”) in the radial direction of the optical disc 1. Then, the tracking control is appropriately performed by displacing the objective lens 40 in the optical pickup in this way.
[0013]
However, when tracking control is performed by displacing the objective lens, a relative shift occurs between the objective lens 40 and the liquid crystal panel 20. Therefore, in the optical pickup, as shown in FIG. 13C, by controlling the pattern of the voltage applied to the electrode 21 of the liquid crystal panel 20, the refractive index distribution by the liquid crystal in the liquid crystal panel 20 is changed to the laser light L2. It corresponds to the irradiation position. Accordingly, even when the objective lens 40 is displaced, the aberration can be corrected appropriately using the liquid crystal panel 20.
[0014]
[Patent Document 1]
Japanese Patent Laid-Open No. 9-128785
[0015]
[Problems to be solved by the invention]
By the way, in the above optical pickup, even when the objective lens 40 is displaced along with tracking control, although the aberration can be appropriately corrected by the liquid crystal panel 20, there is a problem that the pattern of the electrode 21 becomes complicated. is there. In particular, the more the aberration is corrected, the more the electrode of the liquid crystal panel needs to be divided. Such division of the electrodes not only complicates the electrode pattern, but also increases the gap between the electrodes, and as a result, increases the area where the liquid crystal does not operate.
[0016]
The present invention has been made in view of such circumstances, and an object thereof is to provide an optical pickup capable of appropriately correcting aberrations by the liquid crystal panel during tracking control while making the liquid crystal panel a simpler configuration. There is to do.
[0017]
[Means for Solving the Problems]
  In the following, means for achieving the above object and its effects are described.
  According to the first aspect of the present invention, a lens for condensing the laser beam from the light source onto the optical disc and the optical disc are condensed.SaidAn optical pickup comprising a liquid crystal panel for correcting aberration of laser light, and tracking by displacing the lensSoThen, during the tracking, by further changing the arrangement of the optical system other than the lens provided between the optical disk and the light source, the transmission state of the laser light in each of the lens and the liquid crystal panel is substantially constant. With holding means to keepThe liquid crystal panel is provided between the lens and the light source, and the holding unit rotates the liquid crystal panel according to the displacement amount of the lens during the tracking.This is the gist.
[0018]
  In the above configuration, by further changing the arrangement of the optical system other than the lens provided between the optical disc and the light source, the transmission state of the laser light in each of the lens and the liquid crystal panel is kept substantially constant. For this reason, it is possible to avoid making the alignment state of the liquid crystal panel for correcting the aberration of the laser light variable due to the tracking control. Therefore, the aberration correction by the liquid crystal panel can be appropriately performed at the time of tracking control while the liquid crystal panel has a simpler configuration.
  Further, by rotating the liquid crystal panel, it is possible to separate the optical axes while making incident light and outgoing light to the liquid crystal panel parallel to each other. For this reason, by rotating the liquid crystal panel according to the amount of displacement of the lens, the transmission state of the laser light transmitted through the lens can be made substantially constant regardless of the displacement of the lens. Furthermore, it is possible to make a setting in which a change in the transmission state of the laser light in the liquid crystal panel caused by rotating the liquid crystal panel can be ignored. For this reason, it becomes possible to accurately correct the aberration without changing the alignment state inside the liquid crystal panel according to the tracking control.
  It is desirable that the rotation axis of the liquid crystal panel substantially coincides with a straight line that passes through the intersection of the liquid crystal panel and the optical axis and is orthogonal to a plane defined by the displacement direction of the lens and the optical axis.
  In this case, the liquid crystal panel is configured by filling the liquid crystal between a pair of transparent substrates, and the thickness of the transparent substrate on the light source side is set to be smaller than the thickness of the transparent substrate on the lens side. May be.
[0019]
  The invention according to claim 2An optical pickup that includes a lens that condenses laser light from a light source onto an optical disc, and a liquid crystal panel that corrects aberrations of the laser light that is condensed onto the optical disc, and performs tracking by displacing the lens. In the tracking, by further changing the arrangement of the optical system other than the lens provided between the optical disc and the light source, the transmission state of the laser light in each of the lens and the liquid crystal panel is substantially changed. With holding means to keep it constant,Other than the lensSaidThe means for changing the arrangement of the optical system is not a member different from the means for displacing the lens.The liquid crystal panel is provided between the lens and the light source, and the holding unit rotates the liquid crystal panel in accordance with a displacement amount of the lens during the tracking.This is the gist.
[0020]
  In the above configuration,By further changing the arrangement of the optical system other than the lens provided between the optical disk and the light source, the transmission state of the laser light in each of the lens and the liquid crystal panel is kept substantially constant. For this reason, it is possible to avoid making the alignment state of the liquid crystal panel for correcting the aberration of the laser light variable due to the tracking control. Therefore, the aberration correction by the liquid crystal panel can be appropriately performed at the time of tracking control while the liquid crystal panel has a simpler configuration.
  AlsoSince the means for changing the arrangement and the means for displacing the lens are made of different members, it is possible to avoid an increase in force required for the means for displacing the lens. It becomes possible to make the responsiveness good.
  Further, by rotating the liquid crystal panel, it is possible to separate the optical axes while making incident light and outgoing light to the liquid crystal panel parallel to each other. For this reason, by rotating the liquid crystal panel according to the amount of displacement of the lens, the transmission state of the laser light transmitted through the lens can be made substantially constant regardless of the displacement of the lens. Furthermore, it is possible to make a setting in which a change in the transmission state of the laser light in the liquid crystal panel caused by rotating the liquid crystal panel can be ignored. For this reason, it becomes possible to accurately correct the aberration without changing the alignment state inside the liquid crystal panel according to the tracking control.
  It is desirable that the rotation axis of the liquid crystal panel substantially coincides with a straight line that passes through the intersection of the liquid crystal panel and the optical axis and is orthogonal to a plane defined by the displacement direction of the lens and the optical axis.
  In this case, the liquid crystal panel is configured by filling the liquid crystal between a pair of transparent substrates, and the thickness of the transparent substrate on the light source side is set to be smaller than the thickness of the transparent substrate on the lens side. May be.
[0021]
  The invention described in claim 3 includes a lens for condensing the laser light from the light source onto the optical disc, and a liquid crystal panel for correcting the aberration of the laser light condensed on the optical disc, and displacing the lens. In the tracking, the optical pickup other than the lens provided between the optical disk and the light source is further changed to change the arrangement of the lens and the liquid crystal panel. A holding means for maintaining the transmission state of the laser light substantially constant;As, The lens and the light sourceBetweenTransparent parallel plateTheThe holding means rotates the parallel plate according to the amount of displacement of the lens during the tracking.
[0022]
  In the above configuration,By further changing the arrangement of the optical system other than the lens provided between the optical disk and the light source, the transmission state of the laser light in each of the lens and the liquid crystal panel is kept substantially constant. For this reason, it is possible to avoid making the alignment state of the liquid crystal panel for correcting the aberration of the laser light variable due to the tracking control. Therefore, the aberration correction by the liquid crystal panel can be appropriately performed at the time of tracking control while the liquid crystal panel has a simpler configuration.
[0023]
  Further, by rotating the parallel plate, it is possible to separate the optical axes while making the incident light and the emitted light to the parallel plate parallel to each other. For this reason, by rotating the parallel plate according to the displacement amount of the lens, it is possible to make the transmission state of the laser light transmitted through the lens substantially constant regardless of the displacement of the lens.
  And at this time, for example
A. 5. The optical pickup according to claim 3, wherein the parallel plate is provided between the light source and the liquid crystal panel, and the holding means is the lens and the liquid crystal panel. The liquid crystal panel is further displaced so as to maintain a relative positional relationship.
B. A configuration in which a liquid crystal panel is disposed between a light source and a parallel plate.
By doing so, the transmission state of the laser light inside the liquid crystal panel can be kept substantially constant. For this reason, it becomes possible to accurately correct the aberration without changing the alignment state inside the liquid crystal panel according to the tracking control.
[0024]
  It is desirable that the rotation axis of the parallel plate is substantially coincident with a straight line that passes through the intersection of the parallel plate and the optical axis and is orthogonal to a plane defined by the displacement direction of the lens and the optical axis.
[0025]
  The invention described in claim 4 includes a lens for condensing the laser light from the light source onto the optical disc, and a liquid crystal panel for correcting the aberration of the laser light condensed on the optical disc, and displacing the lens. In the tracking, the optical pickup other than the lens provided between the optical disk and the light source is further changed to change the arrangement of the lens and the liquid crystal panel. A holding means for maintaining the transmission state of the laser light substantially constant, the means for changing the arrangement of the optical system other than the lens is a member different from the means for displacing the lens, and the optical systemAs, The lens and the light sourceBetweenTransparent parallel plateTheThe holding means rotates the parallel plate according to the amount of displacement of the lens during the tracking.
[0026]
  In the above configuration,By further changing the arrangement of the optical system other than the lens provided between the optical disk and the light source, the transmission state of the laser light in each of the lens and the liquid crystal panel is kept substantially constant. For this reason, it is possible to avoid making the alignment state of the liquid crystal panel for correcting the aberration of the laser light variable due to the tracking control. Therefore, the aberration correction by the liquid crystal panel can be appropriately performed at the time of tracking control while the liquid crystal panel has a simpler configuration.
  Further, since the means for changing the arrangement and the means for displacing the lens are made of different members, it is possible to avoid an increase in the force required for the means for displacing the lens. Can be made responsive.
  AlsoBy rotating the parallel plate, it is possible to separate the optical axes while making incident light and outgoing light to the parallel plate parallel to each other. For this reason, by rotating the parallel plate according to the amount of displacement of the lens, the transmission state of the laser light transmitted through the lens can be made substantially constant regardless of the displacement of the lens..
  And at this time, for example
A. Claim 5InClaims as described3 or4. The optical pickup according to claim 4, wherein the parallel plate is provided between the light source and the liquid crystal panel.AndThe holding means further displaces the liquid crystal panel so as to hold a relative positional relationship between the lens and the liquid crystal panel.
B. A configuration in which a liquid crystal panel is disposed between a light source and a parallel plate.
By doing so, the transmission state of the laser light inside the liquid crystal panel can be kept substantially constant. For this reason, it becomes possible to accurately correct the aberration without changing the alignment state inside the liquid crystal panel according to the tracking control.
[0027]
It is desirable that the rotation axis of the parallel plate is substantially coincident with a straight line that passes through the intersection of the parallel plate and the optical axis and is orthogonal to a plane defined by the displacement direction of the lens and the optical axis.
[0028]
  The invention according to claim 6 is any one of claims 1 to 5.1 itemThe gist of the invention described in the paragraph is that the liquid crystal panel includes an electrode having a shape that is substantially axisymmetric with respect to an optical axis of the laser beam.
[0029]
The aberration of the laser beam is likely to occur as the distance from the optical axis increases.
In this respect, according to the above configuration, it becomes easy to control the alignment state of the liquid crystal in the liquid crystal panel so as to be symmetric with respect to the optical axis of the laser beam. As a result, the refractive index distribution in the liquid crystal panel can be easily axisymmetric with respect to the optical axis. Therefore, by using the liquid crystal panel, it becomes possible to suitably correct the aberration of the laser beam.
[0030]
DETAILED DESCRIPTION OF THE INVENTION
(First embodiment)
A first embodiment in which an optical pickup according to the present invention is applied to an optical pickup used for both a CD and a DVD will be described below with reference to the drawings.
[0031]
FIG. 1 shows an arrangement mode of an optical pickup according to the present embodiment in an optical disk reproducing apparatus or recording apparatus.
As shown in FIG. 1, the optical pickup 100 is disposed below the optical disc 200. The optical pickup 100 can be displaced by the slider motor 300 in the radial direction of the optical disc, that is, in the outer circumferential direction O and the inner circumferential direction I of the optical disc 200.
[0032]
FIG. 2 shows the configuration of the optical pickup 100. In the optical pickup 100, the forward path of the laser light is as follows. First, the laser light L 1 emitted from the laser light source 110 is converted into a parallel light beam by the collimator lens 112 and enters a PBS (polarization beam splitter) 114. Then, the phase of the laser light L2 reflected by the PBS 114 is adjusted when passing through the liquid crystal panel 120 to become the laser light L3. The laser light L3 becomes circularly polarized laser light L4 in the quarter-wave plate 130. The laser beam L4 is condensed by the objective lens 140, passes through the disc cover layer 210 of the optical disc 200, and forms an image on the disc recording layer 220.
[0033]
In the optical pickup 100, the return path of the laser light is as follows. The laser light having circularly polarized light reflected by the disk recording layer 220 of the optical disk 200 becomes laser light L4 that is parallel light in the objective lens 140. The laser light L4 becomes laser light L3 linearly polarized on the quarter-wave plate 130. Then, after passing through the liquid crystal panel 120, the light enters the PBS 114. The laser beam L2 incident on the PBS 114 passes through the PBS 114 because it is linearly polarized light opposite to the forward path. Then, the laser light that has passed through the PBS 114 is condensed on the light receiver 152 by the objective lens 150.
[0034]
Here, the configuration of the liquid crystal panel 120 will be described.
As shown in FIG. 2, the liquid crystal panel 120 includes a pair of transparent substrates 121 and 122 made of parallel plates and a liquid crystal 123 (for example, twisted nematic (TN) liquid crystal) filled between the pair of transparent substrates 121 and 122. And. The liquid crystal panel control circuit 160 controls the voltage application state to the transparent electrodes formed on the transparent substrates 121 and 122 to control the alignment state of the liquid crystal 123.
[0035]
FIG. 3A shows the electrode patterns of the transparent substrates 121 and 122, and FIG. 3B shows the refractive index distribution of the liquid crystal panel 120, respectively.
As shown in FIG. 3A, the electrodes of the transparent substrates 121 and 122 include a circular transparent electrode 124 at the center of the liquid crystal panel 120 (the center of the laser beam L2) and a ring-shaped transparent electrode on the outside thereof. And an electrode 125. The outer diameter of the transparent electrode 124 is set to a size covered by the laser light L2, and the inner diameter of the transparent electrode 125 is set to a size covering the laser light L2.
[0036]
Then, by grounding one of the transparent substrates 121 and 122 and applying a voltage to the other electrode, the refractive index distribution of the liquid crystal 123 is as shown in FIG. As described above, the aberration can be appropriately corrected by increasing the refractive index of the liquid crystal 123 outside the laser light transmitted through the liquid crystal panel 120. This is because in the absence of the liquid crystal panel 120, the aberration is less likely to appear at the center of the laser beam and is likely to exit outward.
[0037]
Note that the magnitude of the voltage applied to the electrode is variably controlled, for example, by feedback control based on the laser beam received by the light receiver 152 shown in FIG.
[0038]
Next, tracking control of the optical pickup 100 will be described.
As shown in FIG. 1, the optical pickup 100 can be displaced in the radial direction of the optical disc 200 by the slider motor 300. Further, in the optical pickup 100, for the purpose of tracking control for appropriately irradiating the laser following the spiral track in the optical disc 200, the objective lens 140 is further moved as shown by the broken line in FIG. The optical pickup 100 is slightly displaced.
[0039]
Specifically, this tracking control is performed by a control circuit 400 externally attached to the optical pickup 100 based on the laser light received by the light receiver 152. Specifically, the control circuit 400 extracts a signal indicating a tracking error from the laser light received by the light receiver 152 by a three-beam method, a push-pull method, or the like, and performs feedback control so as to reduce the error. It is. For details on the 3-beam method and the push-pull method, see, for example, “Compact Disc Reader (Revised 3rd Edition), Hirataro Nakajima, Hiroshi Ogawa (Ohm)”, etc.
[0040]
Incidentally, the mechanism for displacing the objective lens 140 may be, for example, as shown in FIG. That is, the tracking magnets 142a and 142b are arranged at positions facing each other with the tracking coils 141a and 141b attached to the holder that houses the objective lens 140 therebetween. When the currents Ia and Ib are passed through the tracking coils 141a and 141b, the tracking propulsive force F perpendicular to the currents Ia and Ib is generated by the interaction between the magnetic field B generated between the tracking magnets 142a and 142b and the currents Ia and Ib. Arise. The direction and magnitude of this tracking driving force F are adjusted by the direction and magnitude of the currents Ia and Ib.
[0041]
Further, in the tracking control, the liquid crystal panel 120 is rotationally controlled in accordance with the amount of displacement of the objective lens 140 in the optical pickup 100 as shown in FIG. Here, a mechanism for rotating the liquid crystal panel 120 will be described first.
[0042]
In FIG. 5A, the liquid crystal panel 120 and the shaft 126 for rotating the liquid crystal panel 120 are overwritten for convenience as in FIG. As shown in FIG. 5A, the center of the axis 126 (the rotation axis of the liquid crystal panel 120) passes through the intersection between the optical axis BL of the laser beam and the bottom surface of the transparent substrate 121 of the liquid crystal panel 120, and the objective lens 140. Are on a straight line perpendicular to a plane defined by the displacement direction of the optical axis BL and the optical axis BL.
[0043]
FIG. 5B shows a state in which the liquid crystal panel 120 is stored in the holder 127. Incidentally, this FIG.5 (b) is the figure seen from the same side surface as Fig.5 (a).
[0044]
5C is a side view orthogonal to FIG. 5B, in other words, a cross-sectional view of a plane including the optical axis BL of the laser beam and the rotation axis of the liquid crystal panel 120. In FIG. As shown in FIG. 5C, the shaft 126 is integrated with the holder 127. The holder 127 is configured to cover the side surface of the liquid crystal panel 120 and support the edge of the liquid crystal panel 120. Therefore, the portion of the liquid crystal panel 120 that emits and emits laser light is exposed to the holder 127.
[0045]
FIG. 6 shows a mechanism for rotating the liquid crystal panel 120.
As shown in FIG. 6, the shaft 126 formed integrally with the holder 127 is formed integrally with the holder 126h for rotational movement. The rotational movement coils 126a to 128d are attached to the rotational movement holder 126h. Furthermore, the rotational movement magnets 129a and 129b are arranged so as to face each other across the rotational movement coils 128a to 128d. A magnetic field RB is generated between these rotational movement magnets 129a and 129b. Then, by supplying current to the rotational movement coils 128a to 128d and operating the current value, the rotation state of the shaft 126, in other words, the rotation state of the liquid crystal panel 120 can be controlled.
[0046]
With the configuration shown in FIGS. 5 and 6, the liquid crystal panel 120 can be rotationally controlled according to the displacement of the objective lens 140. As a result, even when the objective lens 140 is displaced in the optical pickup 100 by tracking control, it is possible to appropriately correct the aberration using the electrode pattern shown in FIG.
[0047]
That is, as shown by the broken line in FIG. 2, when the objective lens 140 is displaced in the optical pickup 100, the liquid crystal panel 120 is rotated by rotating the liquid crystal panel 120 according to the displacement amount of the objective lens 140. The laser beam L4 ′ emitted from the laser beam can be made substantially coincident with the center of the objective lens 140. In other words, regardless of the displacement of the objective lens 140, the transmission state of the laser transmitting through the objective lens 140 can be made substantially constant.
[0048]
In addition, regardless of the rotation of the liquid crystal panel 120, the transmission state of the laser light transmitted through the liquid crystal panel 120 is kept substantially constant. This will be described below.
FIG. 7 shows an enlarged view of the liquid crystal panel 120. In FIG. 7, the thickness t 3 of the liquid crystal 123 is sufficiently thinner than the thickness t 1 of the transparent substrate 121 and the thickness t 2 of the transparent substrate 122. Further, the transparent substrates 121 and 122 are formed of, for example, a glass substrate made of the same material, and have the same refractive index. For this reason, the liquid crystal panel 120 can be regarded as a parallel plate as a whole. For this reason, the laser beam L2 incident on the liquid crystal panel 120 and the laser beam L3 emitted from the liquid crystal panel 120 are substantially parallel to each other.
[0049]
Here, the parallel movement distance between the laser beam L2 and the laser beam L3 is a distance D. The laser beam L3 is applied to the center of the objective lens 140. Further, an intersection point between the normal line N of the substrate surface of the transparent substrate 121 of the liquid crystal panel 120 and the surface of the transparent substrate 121 on the liquid crystal 123 side is defined as a point nl. Further, the intersection of the laser beam L2 ′ in the liquid crystal panel 120 and the surface of the transparent substrate 121 on the liquid crystal 123 side is set as a point rl. At this time, the distance d between the point nl and the point rl, the angle formed between the normal line N and the laser beam L2 ′ is the angle θ2, the angle formed between the laser beam L2 and the normal line N is the angle θ1, the transparent substrate 121, Assuming that the refractive index n is 122, the following equation is established geometrically with respect to the distances D and d. However, in the expression of distance D, t3 is assumed to be negligible compared to t1 and t2.
[0050]
D = {(t1 + t2) × sin (θ1−θ2)} / cos θ2.
d = t1 × tan θ2
sin θ1 = n × sin θ2
Here, when the refractive index n is “1.51”, the thickness t1 is “0.5 mm”, the thickness t2 is “2 mm”, and the angle θ1 is “25 °”, the distances D and d are approximately “0. 4 mm "and" 0.15 mm ". That is, even if the objective lens 140 is displaced by “0.4 mm”, the deviation of the irradiation of the laser beam L4 ′ in the liquid crystal 123 is about “0.15 mm”.
[0051]
It should be noted that the thickness (t1 + t2 + t3) of the liquid crystal panel 120 can cope with a case where the displacement amount of the objective lens 140 is increased as the thickness increases. For this reason, it is desirable to set the thickness of the liquid crystal panel 120 as appropriate within a range in which both correction of aberration by the liquid crystal panel 120 and tracking of the displacement of the objective lens can be appropriately performed.
[0052]
As described above, when the objective lens 140 is displaced in the optical pickup 100, the liquid crystal panel 120 is rotated in accordance with the amount of displacement, thereby changing the transmission state of the laser light transmitted through the liquid crystal panel 120 and the objective lens 140. Regardless of these displacements, it can be kept substantially constant. Therefore, it is possible to correct aberrations without changing the electrode pattern of the liquid crystal panel 120 shown in FIG. 3, and thus the electrode pattern can be simplified.
[0053]
According to the embodiment described above, the following effects can be obtained.
(1) When the objective lens 140 is displaced in the optical pickup 100, the liquid crystal panel 120 is rotated according to the displacement amount. Thereby, tracking control can be appropriately performed while simplifying the electrode pattern.
[0054]
(2) By disposing the means for displacing the objective lens 140 in the optical pickup 100 and the means for rotating the liquid crystal panel 120 as separate members, the displacement of the objective lens by the means is responsive. Will be able to.
[0055]
(Second Embodiment)
Hereinafter, a second embodiment in which the optical pickup according to the present invention is applied to an optical pickup used for both a CD and a DVD will be described with reference to the drawings mainly focusing on differences from the first embodiment.
[0056]
FIG. 8 shows the configuration of the optical pickup according to the present embodiment. In FIG. 8, the same members as those shown in FIG.
In the present embodiment, the liquid crystal panel 120 is configured to be displaceable so as to maintain a relative positional relationship with the objective lens 140. Note that the mechanism for displacing the liquid crystal panel 120 may be, for example, as illustrated in FIG.
[0057]
Furthermore, in this embodiment, as shown in FIG. 8, a transparent parallel plate 170 is provided between the liquid crystal panel 120 and the PBS 114. The parallel plate 170 is configured to be rotatable about a shaft 172 as a rotation center. Here, a mechanism for rotating the parallel plate 170 will be described.
[0058]
In FIG. 9A, as in the case of FIG. 8, the parallel plate 170 and the shaft 172 for rotating the parallel plate 170 are overwritten for convenience. As shown in FIG. 9A, the center of the axis 172 passes through the intersection of the optical axis BL of the laser beam and the bottom surface of the parallel plate 170, and is formed by the displacement direction of the liquid crystal panel 120 and the optical axis BL. It is on a straight line perpendicular to the plane.
[0059]
FIG. 9B shows a state in which the parallel plate 170 is stored in the holder 174. Incidentally, FIG. 9 (b) is a view seen from the same side as FIG. 9 (a).
[0060]
9C is a side view orthogonal to FIG. 9B, in other words, a cross-sectional view of a plane including the optical axis BL of the laser beam and the rotation axis of the parallel plate 170. As shown in FIG. 9C, the shaft 172 is integrated with the holder 174. The holder 174 is configured to cover the side surface of the parallel plate 170 and support the edge of the parallel plate 170. Therefore, portions of the parallel plate 170 that emit and emit laser light are exposed to the holder 174.
[0061]
Such a mechanism for rotating the parallel plate 170 may be, for example, as illustrated in FIG.
During tracking control, the control circuit 410 follows the displacement of the objective lens 140 to cause the liquid crystal panel 120 to follow. In other words, the liquid crystal panel 120 is displaced so as to maintain the relative positional relationship between the objective lens 140 and the liquid crystal panel 120. Further, the parallel plate 170 is displaced according to the displacement of the objective lens 140. Here, the rotation amount of the parallel plate 170 depends on the displacement of the liquid crystal panel 120 based on the incident state of the laser beam L2b emitted from the parallel plate 170, in other words, the laser beam L2b incident on the liquid crystal panel 120 on the liquid crystal panel 120. The rotation amount is constant.
[0062]
Thereby, the transmission state of the laser light transmitted through the liquid crystal panel 120 and the objective lens 140 can be kept substantially constant regardless of these displacements. In particular, since the parallel plate 170 does not include liquid crystal or the like like the liquid crystal panel 120, the laser beam L2a incident on the parallel plate 170 and the laser beam L2b emitted from the parallel plate 170 are more appropriately parallel light. It can be. Therefore, the aberration can be corrected more appropriately without changing the electrode pattern of the liquid crystal panel 120, and the electrode pattern can be simplified.
[0063]
According to the present embodiment described above, the following effects can be obtained in addition to the effects according to the above (1) and (2) of the first embodiment.
(3) By constructing the parallel plate 170 as means for translating the path of the laser beam in accordance with the displacement of the objective lens 140, the laser beam can be translated more appropriately.
[0064]
(Third embodiment)
Hereinafter, a third embodiment in which the optical pickup according to the present invention is applied to an optical pickup used for both a CD and a DVD will be described with reference to the drawings mainly focusing on differences from the second embodiment.
[0065]
FIG. 10 shows the configuration of the optical pickup according to the present embodiment. In FIG. 10, the same members as those in FIG. 8 are given the same reference numerals for the sake of convenience.
As shown in FIG. 10, in this embodiment, a parallel plate 170 is disposed between the liquid crystal panel 120 and the objective lens 140 (a quarter wavelength plate 130).
[0066]
In tracking control, the control circuit 420 rotates the parallel plate 170 in accordance with the displacement of the objective lens 140. Here, the rotation amount of the parallel plate 170 depends on the displacement of the objective lens 140 based on the incident state of the laser beam L3b emitted from the parallel plate 170, in other words, the laser beam L3b incident on the objective lens 140 on the objective lens 140. The rotation amount is constant.
[0067]
As described above, in this embodiment, the laser light L3a emitted from the liquid crystal panel 120 is converted into the laser light L3b parallel to the laser light L3b by the parallel plate 170, so that the liquid crystal panel 120 can be fixed also in tracking control. it can.
[0068]
According to this embodiment described above, in addition to the effects (1) and (2) of the previous first embodiment and the effect (3) of the previous second embodiment, The effect will be obtained.
[0069]
(4) By arranging the parallel plate 170 between the liquid crystal panel 120 and the objective lens 140 (¼ wavelength plate 130), the liquid crystal panel 120 can be fixed even in tracking control. .
[0070]
Each of the above embodiments may be modified as follows.
The configuration of the liquid crystal panel 120 is not limited to that illustrated in the above embodiments. In particular, the electrodes are not limited to those illustrated in FIG. In short, in view of the fact that the aberration of laser light is more likely to occur in the radial direction from the optical axis, the refractive index distribution generated by the alignment state of the liquid crystal in the liquid crystal panel is more separated from the optical axis of the laser light. Any material can be used as long as it can have a substantially point-symmetrical refractive index distribution that increases the refractive index. This can be realized, for example, by providing at least one electrode pattern that is point-symmetric with respect to the optical axis.
[0071]
The configuration of the optical pickup is not limited to that illustrated in the above embodiments. For example, in the first embodiment, the PBS 114 may be provided between the liquid crystal panel 120 and the quarter wavelength plate 130 as shown in FIG. In this case, since the laser light passes through the liquid crystal panel 120 only in the forward path, it is effective to make the thickness of the transparent substrate 121 thinner than the thickness of the transparent substrate 122. That is, as a result, the transmission state of the laser light transmitted through the liquid crystal 123 of the liquid crystal panel 120 in the forward path is likely to be substantially constant regardless of the tracking control.
[0072]
The use of the optical pickup is not limited to being used in combination with a CD and a DVD, and any optical pickup may be used as long as it is used in combination between any plural types of optical disks. Furthermore, the optical disk is not limited to those used in combination with a plurality of types of optical disks. In short, any liquid crystal panel may be provided for aberration correction and the lens may be displaced in the optical pickup for tracking control.
[0073]
-When tracking the lens for condensing the laser beam on the optical disc, the arrangement of the optical system other than the lens provided between the optical disc and the light source is changed to change the laser beam in each of the lens and the liquid crystal panel. The holding means that keeps the transmission state substantially constant is not limited to those exemplified in the above embodiments.
[0074]
【The invention's effect】
Although the liquid crystal panel has a simpler configuration, aberration correction by the liquid crystal panel can be appropriately performed during tracking control.
[Brief description of the drawings]
FIG. 1 is a perspective view showing the configuration of a first embodiment of an optical pickup according to the present invention.Is.
FIG. 2 is a block diagram showing the configuration of the optical pickup according to the embodiment.Is.
FIG. 3 is a diagram showing a configuration of a liquid crystal panel of the same embodimentIs.
FIG. 4 is a perspective view showing a configuration of a mechanism for displacing the objective lens according to the embodiment.Is.
FIG. 5 is a diagram showing a configuration of a mechanism around a liquid crystal panel according to the embodiment;Is.
FIG. 6 is a perspective view showing a configuration of a mechanism for rotating the liquid crystal panel according to the embodiment.Is.
FIG. 7 is a cross-sectional view showing a state of laser light irradiation on a liquid crystal panelIs.
FIG. 8 is a block diagram showing a configuration of a second embodiment of an optical pickup according to the present invention.Is.
FIG. 9 is a view showing a configuration of a mechanism around a parallel plate according to the embodiment;Is.
FIG. 10 is a block diagram showing a configuration of a third embodiment of an optical pickup according to the present invention.Is.
FIG. 11 is a block diagram showing a modification of the first embodiment.Is.
FIG. 12 is a block diagram showing the configuration of a conventional optical pickupIs.
FIG. 13 shows a conventional liquid crystal panelInPreparationIsDiagram showing the electrode patternIs.
[Explanation of symbols]
  DESCRIPTION OF SYMBOLS 100 ... Optical pick-up, 110 ... Laser light source, 112 ... Collimator lens, 114 ... Polarizing beam splitter (PBS), 120 ... Liquid crystal panel, 121, 122 ... Transparent substrate, 123 ... Liquid crystal, 124, 125 ... Transparent electrode, 126 ... Axis 126h: holder for rotational movement, 128a to 128d: coil for rotational movement, 127: holder, 129a, 129b ... magnet for rotational movement, 130: quarter wave plate, 140: objective lens, 141a, 141b ... tracking coil, 142a, 142b ... tracking magnet, 150 ... objective lens, 152 ... light receiver, 160 ... liquid crystal panel control circuit, 170 ... parallel plate, 172 ... axis, 174 ... holder, 200 ... optical disc, 210 ... disc cover layer, 220 ... Disc recording layer, 300... Slider motor, 400, 410 420 ... control circuit, BL: optical axis, L1, L2, L2 ', L2a, L2b, L3, L3a, L3b, L4, L4' ... laser light.

Claims (6)

A lens for condensing the laser light from the light source onto the optical disc;
A liquid crystal panel for correcting the aberration of the laser beam condensed on the optical disc,
An optical pickup that performs tracking by displacing the lens,
During the tracking, by further changing the arrangement of the optical system other than the lens provided between the optical disk and the light source, the transmission state of the laser light in each of the lens and the liquid crystal panel is kept substantially constant. Holding means,
The liquid crystal panel is provided between the lens and the light source, and the holding unit rotates the liquid crystal panel according to a displacement amount of the lens during the tracking. A lens for condensing the laser light from the light source onto the optical disc;
A liquid crystal panel for correcting the aberration of the laser beam condensed on the optical disc,
An optical pickup that performs tracking by displacing the lens,
During the tracking, by further changing the arrangement of the optical system other than the lens provided between the optical disk and the light source, the transmission state of the laser light in each of the lens and the liquid crystal panel is kept substantially constant. Holding means,
The means for changing the arrangement of the optical system other than the lens is a member different from the means for displacing the lens,
The liquid crystal panel is provided between the lens and the light source, and the holding unit rotates the liquid crystal panel according to a displacement amount of the lens during the tracking. A lens for condensing the laser light from the light source onto the optical disc;
A liquid crystal panel for correcting the aberration of the laser beam condensed on the optical disc,
An optical pickup that performs tracking by displacing the lens,
During the tracking, by further changing the arrangement of the optical system other than the lens provided between the optical disk and the light source, the transmission state of the laser light in each of the lens and the liquid crystal panel is kept substantially constant. Holding means,
As the optical system , a transparent parallel plate is provided between the lens and the light source, and the holding means rotates the parallel plate according to the amount of displacement of the lens during the tracking. . A lens for condensing the laser light from the light source onto the optical disc;
A liquid crystal panel for correcting the aberration of the laser beam condensed on the optical disc,
An optical pickup that performs tracking by displacing the lens,
During the tracking, by further changing the arrangement of the optical system other than the lens provided between the optical disk and the light source, the transmission state of the laser light in each of the lens and the liquid crystal panel is kept substantially constant. Holding means,
The means for changing the arrangement of the optical system other than the lens is a member different from the means for displacing the lens,
As the optical system , a transparent parallel plate is provided between the lens and the light source, and the holding means rotates the parallel plate according to the amount of displacement of the lens during the tracking. . The parallel plate is provided between the light source and the liquid crystal panel,
The optical pickup according to claim 3, wherein the holding unit further displaces the liquid crystal panel so as to hold a relative positional relationship between the lens and the liquid crystal panel. The optical pickup according to claim 1, wherein the liquid crystal panel includes an electrode having a shape that is substantially axisymmetric with respect to an optical axis of the laser beam.

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