JPH0810852Y2 - Optical head - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention relates to an optical head of an optical disk device, and more particularly to an optical head to which a super-resolution method is applied.

[Prior Art] In an optical head of an optical disk device, a method of reducing a convergent diameter of a light beam converged by an objective lens by providing a light-shielding band in a collimated light beam incident on the objective lens is a so-called super-resolution method. Known as. By applying this super-resolution method to the optical head, the diameter of the convergent beam converged by the objective lens can be reduced to about 80% compared to the diameter of the convergent beam in a general optical head that does not apply this method. It is possible. If the convergent beam diameter can be made small, it becomes possible to deal with a high linear density disc having a high linear density of signal tracks.

In the conventional optical head to which the super-resolution method is applied,
The light-shielding band is fixedly provided in the collimated light beam.

[Problems to be solved] By the way, for example, a disc corresponding to MUSE, which is a standard of a high-definition video disc system (this is referred to as a MUSE disc), is an ordinary optical video disc (hereinafter,
The recording time of the disc is shorter because the amount of information is larger than that of (LD). In order to increase the recording time of this MUSE disc, that is, in order to obtain a long-time recording MUSE disc, it is conceivable to increase the track linear density of the disc. Not only for MUSE discs, if the track linear density of the disc is increased, an optical head capable of handling the high track linear density is required. However, the above super-resolution method is applied to the optical head to increase the convergent beam diameter. By making it smaller, it becomes possible to support high linear density discs such as long-time recording MUSE discs (however, those of the CLV (constant linear velocity) type).

However, if an optical head using this super-resolution method is
When used in a V (constant angular velocity) type LD, the SN ratio without noise reduction at the innermost circumference of the disc is about 48 dB, compared to about 45 dB when not applied, which is an effect of improving about 3 dB. , The SN ratio at the outermost circumference of the disc
It becomes 5 dB or less and deteriorates significantly. This is because the focused beam obtained by applying the super-resolution method to the pits having a long signal track is not suitable at the outermost circumference of the CAV LD.

As described above, in the case of the CAV LD, the SN at the outermost circumference
Since the ratio deteriorates, the conventional optical head described above can be used for CLV high linear density discs and C
Sharing with AV type LD is difficult.

Also, for high linear density discs, the side lobes of the convergent beam when the super-resolution method is applied affect the tracks adjacent to the currently read track of the disc, and crosstalk easily occurs. There is.

The present invention has been made in order to solve the above-mentioned conventional drawbacks, and it is possible to use a CLV type high linear density disc such as a long-time recording MUSE disc and a CAV type LD in common. An object of the present invention is to provide an optical head that can effectively prevent crosstalk when applied to a disc.

[Means for Solving the Problems] The optical head according to claim 1 for solving the above-mentioned problems is an optical head in which a light-shielding band parallel to a disk radial direction is provided in a collimated light beam entering an objective lens. Is provided so as to be rotatable around the center line in the radial direction of the disk.

3. The optical head according to claim 2, wherein the collimated light beam incident on the objective lens is provided with a light shielding band parallel to the disk radial direction, and the light shield is a bell having a rotation center axis parallel to the collimated light optical axis. Fixed to one end of the crank,
A cam follower is attached to the other end of the bell crank, and a stationary slope cam in which two cam surfaces parallel to the optical head feeding direction are connected by an inclined cam surface is provided on the optical head base side.
An optical head is characterized in that a spring for urging the bell crank so as to bring the cam follower into contact with the stationary slope cam is provided so that the light-shielding band can be retracted from the collimated light beam.

According to a third aspect of the present invention, in the optical head according to the first aspect, a rotation drive shaft concentric with the center line of the light-shielding band is provided integrally with the light-shielding band, and a rotary drive mechanism for rotating the rotation drive shaft is provided. Is characterized by.

According to a fourth aspect of the present invention, in the optical head according to the second aspect, the valley between the primary side lobe and the secondary side lobe of the convergent beam converged by the objective lens is located on a track adjacent to the currently read track on the disc. In addition, the rotation angle of the light-shielding band can be adjusted.

[Operation] In the optical head according to claim 1, the super-resolution method can be applied or not applied by rotating the light-shielding band. Therefore, it is possible to share a CLV type high linear density disc and a CAV type LD. The L of the CLV method with the current linear density
Of course, it can be used for D, CD (compact disc), CD-V, etc.

Further, in the case of being applied to a CSV LD, for example, in claim 3, the light shielding band is rotated by the rotation driving mechanism on the outer circumference of the disk so as not to block the collimated light beam, or in claim 2, When the head moves to the outer peripheral side of the disc, the cam follower at the other end of the bell crank moves along the stationary slope cam to rotate the bell crank, and the light blocking zone blocks the center of the collimated light beam and does not block it at the disk outer periphery. It is possible to use a shading band such as. Therefore, in the CAV method LD, the super-resolution method is applied only to the inner circumference of the disc, and
It is possible to improve the image quality of at least the inner circumference of the disc while avoiding a decrease in the ratio.

Embodiments Embodiments of the present invention will be described below with reference to the drawings.

 FIG. 1 shows an embodiment of the optical head of claim 1.

In the figure, 1 is a laser diode that is a laser light source, 2 is a diffraction grating that divides the laser light emitted from the laser diode 1 into three light beams, and 3 is the return light that transmits the incident light and is reflected by the disk in a perpendicular direction. A polarizing beam splitter 4 for reflecting the laser beam on a collimator lens for collimating the diffused light emitted from the laser diode 1 (collimated light) into a collimated light beam; Reference numeral 6 denotes a light-shielding band placed in the center of the collimated light beam entering the next objective lens 7 in parallel with the disc radial direction (direction along the one-dot chain line (a)). In addition, the light-shielding band 6 of the embodiment has a configuration in which a strip-shaped light-shielding portion is formed on a circular transparent plate as illustrated. And the light-shielding band 6
The drive shaft 8 for rotation is integrally fixed on the center line thereof, and a motor (rotation drive mechanism) 9 for rotating the drive shaft 8 for rotation is provided. The symbol O in the figure indicates the center of the optical disc, and the alternate long and short dash line (b) indicates the signal track of the disc.

A concave lens 10 and a cylindrical lens 11 are arranged in the reflection direction of the polarization beam splitter 3, and a photodetector 12 is arranged in front of them.

In the optical head having the above structure, the laser light emitted from the laser diode 1 is divided into three light beams by the diffraction grating 2 (that is, the details are omitted, but this embodiment is a three-beam method). The light beam is transmitted through the polarization beam splitter 3, converted into collimated light by the collimator lens 4, transmitted through the 1/4 wavelength plate 5, the polarization plane is rotated by 45 °, and the central portion thereof is shielded by the light shielding band 6. The light enters the objective lens 7 and is converged by the objective lens 7 to form a light spot on the disc signal surface.

The reflected light (return light) reflected by the disk returns through the same path in the order of the objective lens 7, the light-shielding band 6, the 1/4 wavelength plate 5, and the collimator lens 4, is reflected by the polarization beam splitter 3 in the direction perpendicular to the concave lens 10 And is focused on the photodetector 12.

By the way, since the central portion of the collimator light incident on the objective lens 7 is shielded by the light shielding band 6, as a phenomenon of so-called super-resolution method, the light intensity distribution as shown by the solid line (c) in FIG. The convergent beam diameter (however, the diameter of the main lobe M, which is the main part of the convergent beam) d is smaller than the light intensity distribution of the convergent beam (broken line (d)) in the normal case where no light-shielding band is provided. The convergent beam diameter d shown in the figure is the beam diameter at 50% light intensity of the convergent beam.

As described above, the diameter of the convergent beam that is converged on the disc signal surface becomes smaller, so CL for long-term recording MUSE discs, etc.
It is possible to support V type high linear density discs. Also, it can be applied to LDs of the current linear density of CLV method without any particular problem.

However, when the super-resolution method is applied, the diameter of the main lobe M becomes small as shown in FIG. 2, but side lobes (S ₁ , S ₂ etc. in the figure) having weak light intensity generated at the periphery thereof are generated. To do. However, the valley between the primary side lobe S ₁ and the secondary side lobe S ₂ is now T ₂ adjacent to the currently read track T _1.
This prevents the occurrence of crosstalk in which the signal is read erroneously.

Also, in the case of the CAV type LD, at the inner circumference of the disc,
As shown in FIG. 3 (same as the state of FIG. 1), the super-resolution method is used in which the center of the collimated light is blocked by the light-shielding band 6,
On the outer circumference of the disk, the light shielding band 6 is rotated by the motor 9 so as to be parallel to the optical axis of the collimated light so that the collimated light is not blocked. That is, the super-resolution method is not applied. As a result, it is possible to avoid deterioration of the SN ratio on the outer circumference of the disc.

 FIG. 5 shows an embodiment of the optical head of claim 2.

In this optical head, the light shielding band 6 is a bell crank 20 having an axis parallel to the collimated optical axis as a central axis 20a.
Is fixed to one end of the bell crank, and a cam follower 21 is attached to the other end of the bell crank 20, and the optical head is fed to the optical head base side (not shown) (arrow (a) direction which is the disc radial direction)
A stationary slope cam 22 in which cam surfaces 22a and 22b parallel to the inclined slope cam surface 22c are continuous, and a spring 23 for urging the bell crank 20 so that the cam follower 21 contacts the stationary slope cam 22 is provided. It has a different structure.

Explaining the operation of the optical head having the above structure, when the optical head moves from the inside of the disc to the outer periphery of the disc, the cam follower 21 at the other end of the bell crank 20 moves along the stationary slope cam 22 on the optical head base side along the disc radius. Move in the direction orthogonal to the direction. In this case, the cam follower 21 is in contact with the cam surface 22a on the inner peripheral side of the stationary slope cam 22 on the inner circumference of the disc as shown in FIG. 5, and the light-shielding band 6 is within the collimated light flux and the collimated light flux is present. The central part of is blocked, and the super-resolution method is applied. However, when the optical head moves to the outer circumference of the disk, the cam follower 21 contacts the cam surface 22b on the outer circumference side of the disk through the inclined cam surface 22c, as shown in FIG.
The light-shielding band 6 retreats from the inside of the collimated light beam as shown in the drawing by rotating around the center as shown by the arrow. That is,
The super resolution method is not applied to the outer circumference of the disc. Therefore, when applied to a CAV-type LD, the super-resolution method is applied to the inner circumference of the disc to improve the image quality, and the super-resolution method is not applied to the outer circumference of the disc to avoid a decrease in the SN ratio. It

Although the bell crank 20 is used as the mechanism for retracting the light-shielding band 6 in the embodiment, the invention is not limited to this. In short, a mechanism for allowing the light-shielding band to exist in the collimated light beam inside the disc and retracting it on the outer periphery of the disc is used. Good.

[Effects of the Invention] Since the present invention is configured as described above, it has the following effects.

In the optical head according to claim 1, since the light-shielding band is rotatably provided, it is possible to apply or not apply the super-resolution method, and a CLV system high linear density disc such as a long-time recording MUSE disc and a CAV. It is now possible to share the system with LD. Also,
It can also be used with the current linear density CLV LDs, CDs, CD-Vs, etc.

Further, for example, in the case of being applied to a CAV type LD, by adopting the configuration of claim 2 or claim 3, the light shielding band shields the collimated light on the inner circumference of the disc and does not shield the outer periphery of the disc. Can be used,
By applying the super-resolution method only to the inner circumference of the disc in the CAV LD, it is possible to improve the image quality at least on the inner circumference of the disc while avoiding a decrease in the SN ratio at the outer circumference of the disc.

In the fourth aspect, since the valleys of the primary side lobes and the secondary side lobes come to the adjacent tracks, there is no risk of crosstalk in which the signals of the adjacent tracks are erroneously read.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view showing an optical system configuration of an optical head according to an embodiment of the invention of claim 1, and FIG. 2 is a view for explaining a convergent beam shape. Figure, Figure 3, Figure 4
The figure is an illustration showing how the light-shielding band is used when it is applied to an LD (optical video disc) of the CLV system. Fig. 3 is a diagram showing the state of the light-shielding band on the inner circumference of the disc, and Fig. 4 is the same disc. FIG. 5, FIG. 6 and FIG. 6 on the outer circumference are perspective views showing an optical system configuration of an optical head according to an embodiment of the present invention.
FIG. 5 is a view of the inner circumference of the disc, and FIG. 6 is a view of the outer circumference of the disc. 1 ... Laser diode, 3 ... Beam splitter, 4
...... Collimator lens, 6 ...... Light shielding band, 7 ...... Objective lens, 8 rotation drive shaft, 9 ...... Motor (rotation drive mechanism),
20 …… Bell crank, 20a …… Center axis, 21 …… Cam follower, 22 …… Standing slope cam, 22a, 22b …… Cam surface parallel to optical head feed direction, 22c …… Inclined cam surface, 23 ……
Spring.

Claims (4)

[Scope of utility model registration request] 1. An optical head having a light-shielding band parallel to a disc radial direction in a collimated light beam incident on an objective lens, wherein the light-shielding band is rotatably provided around a center line of the disc radial direction. An optical head characterized by. 2. An optical head having a light-shielding band parallel to a disc radial direction in a collimated light beam incident on an objective lens, wherein the light-shielding member has one end of a bell crank having a rotation center axis parallel to the collimated light optical axis. Fixed to the bell crank, a cam follower is attached to the other end of the bell crank, and a stationary slope cam in which two cam surfaces parallel to the optical head feeding direction are connected by an inclined cam surface is provided on the optical head base side. An optical head, characterized in that a spring for urging the bell crank so as to contact the cam follower is provided on the light-shielding band so as to be retractable from the collimated light beam. 3. The rotating drive shaft concentric with the center line of the light-shielding band is provided integrally with the light-shielding band, and a rotary drive mechanism for rotating the rotating drive shaft is provided. Optical head. 4. The rotation angle of the light-shielding band is adjusted so that the valley between the primary side lobe and the secondary side lobe of the convergent beam converged by the objective lens is located on the track adjacent to the currently read track on the disk. The optical head according to claim 1, wherein the optical head is adjustable.