JP2725549B2 - Optical head device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical head device ,
In particular, the present invention relates to an optical head device used for an information input / output device for recording and reproducing information using light or an optical disk device used for an image recording and reproducing device for recording and reproducing image signals.

[0002]

2. Description of the Related Art A conventional optical head device will be described with reference to the drawings. First, the principle of super-resolution will be described.

FIG. 6 is a plan view for explaining the principle of generation of a super-resolution beam in the optical head device shown in FIG. 1 and FIG.

The collimated light emitted from the light source is partially shielded by the variable width light-shielding band 3b, then passes through the beam splitter 5, is focused on the optical disk 7 by the objective lens 6, and is condensed beam. To form spots. The variable width shading band 3b is A in the figure.
The light-shielding width of the collimated light changes between when the light-shielding beam is in the position B and when the light-shielding width of the variable width light-shielding band 3b is large. When it is at a small B, a beam 31 is usually formed on the optical disk 7. The focused beam diameter of the super-resolution beam 32 is smaller than that of a normal beam focused to the diffraction limit.

In this example, the width-variable light-shielding band 3b is a rotary light-shielding band . Next, focus error detection using the conventional knife edge method in the super-resolution optical head device will be described in detail. FIG. 7 is a plan view for explaining a configuration of a super-resolution optical system using a knife edge focus error detection method in a conventional optical head device.

FIG. 7 shows an example in which a conventional focus error detection system using a knife edge is applied to a super-resolution optical head device. This optical head device includes a semiconductor laser 1 as a light emitting device, a collimating lens 2 for converting the emitted light into parallel light, and a variable width light shielding band capable of shielding a part of the parallel light beam or passing it as it is. 3b, a polarization beam splitter 4 for extracting signal light, and a beam splitter for extracting servo error light
5 and 13, an objective lens 6 for converging a parallel light beam,
An optical disk 7 for irradiating and reflecting light to store information, a track error detection system 8 for detecting a track error, a signal detection system 9 for detecting a signal, and a condensing lens 12 for collecting reflected return light from the optical disk 7 , A knife edge 10 that bisects the convergent light condensed by the condenser lens 12, and a focus detector 11 that receives the convergent light.

The semiconductor laser 1 emits light of a single wavelength radially. This light is once converted into parallel light by the collimating lens 2, and a part of the parallel light is blocked by the variable width light-shielding band 3 b, and the other light is stopped down by the objective lens 6 to form a condensed spot on the optical disk 7. The return light reflected on the optical disk 7 is divided into a beam splitter 5 and a polarizing beam splitter 4.
At the error detection system and the signal detection system.
The return light reflected by the beam splitter 5 is branched by the beam splitter 13 and a part is received by the track error detection system 8, and the other part is condensed by the condensing lens 12 and then split by the knife edge 10. Only one of the two is condensed on the focus detector 11. The focus detector 11 is divided into two parts. When the optical disk 7 is in the focal plane of the objective lens 6, the reflected return light from the optical disk 7 forms a condensing spot on a dividing line for dividing the focus detector 11 by the condensing lens 12. Image. The knife edge is inserted as shown in FIG. 7 so as to split the reflected return light in half when there is no light shielding by the variable width light shielding band. On the other hand, the reflected return light reflected by the polarization beam splitter 4 is received by the signal detection system 9. The width-variable light-shielding band 3b can rotate between A ← → B in FIG. 7 to change the light-shielding width. At this time, the condensed spot on the surface of the optical disk 7 becomes the super-resolution beam 72 when the light-shielding band is in the state A and the normal beam 71 when the light-shielding band is in the state B. When a super-resolution beam is generated, the efficiency of the optical head device is reduced, but the beam spot diameter is reduced, which is suitable for a reproducing operation. On the other hand, since the efficiency of the optical head device does not decrease when a normal beam occurs, it is suitable for a recording operation that requires a margin of allowable power rather than the size of the spot diameter. FIG. 7 shows a state A suitable for reproduction. Although the method of realizing the variable width light-shielding band and the light shielding band of the rotary in the present conventional example, other than the rotary long as it is a method capable of changing the light-shielding width super
A resolution beam can be generated.

Next, the principle of focus detection by the conventional knife edge method will be described with reference to the drawings.

FIG. 8 is a plan view showing the principle of focus detection by the conventional knife edge method in the super-resolution optical head, and FIG. 8A shows the principle of focus detection when the disk approaches a focal length shorter than the focal length of the objective lens. FIG. 8B is a plan view showing the principle of focus detection when the disc is separated farther than the focal length of the objective lens.
(C) is a plan view showing the principle of focus detection when the disc is located on the focal plane of the objective lens.

As shown in FIG. 8C, when the optical disk 7 is in the focal plane of the objective lens 6, the reflected return light from the optical disk 7 forms a condensed spot on the dividing line of the focus detector 11 divided into two. , Focus error output α
-Β = 0. Next, as shown in FIG. 8A, when the optical disk 7 enters the focal length of the objective lens 6, the reflected return light from the optical disk 7 becomes defocused on the focus detector 11, and the focus error output α−β ( ≠
0) is detected. As shown in FIG. 8B, when the optical disk 7 is out of the focal length of the objective lens 6, the reflected return light from the optical disk 7 on the focus detector 11 is also defocused, and the focus error output α-β
(≠ 0) is detected.

[0011]

In adjusting the focus detection system using the conventional knife edge in the conventional super-resolution optical system having the variable width light-shielding band in the above-described conventional optical head device, the light passes through the objective lens 6. When the light beam is focused on the optical disk 7, it is necessary to adjust the position of the detector in the optical axis direction so that the focused spot focused by the focusing lens 12 is focused on the focus detector 11. Variable width shading band 3b
The change in the amount of reflected return light due to the change in the light-shielding width causes an imbalance in the amount of light on the divided focus detectors, resulting in a focus offset on the optical disk 7 surface.

An object of the present invention is to detect a servo error only with a light beam which is not affected by the modulation by the variable width light shielding band in the reflected return light, so that the servo offset is changed even when the light shielding width of the variable width light shielding band changes. An object is to realize a stable servo error detection system that does not occur.

[0013]

[Means for Solving the Problems] Optical head device of the present invention
Is a semiconductor laser that emits light as a light emitting device
And a collimating lens that converts the emitted light into parallel light,
By changing the light width, the vicinity of the optical axis of the parallel light
Attenuate some amplitudes or pass the parallel light
Variable-width light-shielding band that can pass as it is, and an optical disk
Information recorded on a disc by light irradiation and reflection
The optical disk that has passed through the variable-width light-shielding band
An objective lens for condensing the row light and a reflection return of the optical disk
Riri to Sir Take out the error light, and read the servo error
Track error detection system that detects track errors from light
And extracting signal light from the reflected return light of the optical disk
A polarizing beam splitter and an optical disc by the signal light.
A signal detection system for detecting a signal read from the
A condenser lens for collecting reflected return light from the optical disc;
Of the convergent light condensed by the condenser lens, the variable width shielding
Cuts convergent light affected by amplitude attenuation due to light band
Knife edge to be inserted
Focus to receive convergent light that is not cut by
It has a detector.

Further, the optical head device of the present invention has a light emitting device.
Semiconductor laser that emits light as device and its emission
A collimating lens that converts light into parallel light and a variable light blocking width
The amplitude of a part of the parallel light near the optical axis.
Attenuate or pass the parallel light as it is
Variable width light-shielding band that can be
In order to reproduce information by irradiating and reflecting light, the optical data
Focus parallel light passing through the variable width light-shielding band on the disk
The objective lens and the optical disk
Take out the error beam and track from the servo error light.
A track error detection system for detecting a
Polarized beams that extract signal light from the disk's reflected return light
Read from the optical disk by the splitter and the signal light
A signal detection system for detecting the detected signal;
A hologram lens for condensing the reflected return light,
Focuser that receives the convergent light collected by the program lens
An optical head device having a detector,
Programmable lens is light-shielding area and first hologram lens
And a second hologram lens.
Of these, the portion of the light beam that is modulated by the
All light is cut off by shading in the shading area.
Transmitting through the first and second hologram lenses,
And the second hologram lens has its transmitted light
Hologram to focus on the focus detector
Is formed as a double hologram.

[0015]

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a plan view showing an embodiment of the optical head device according to the first invention.

FIG. 1 shows an example in which the optical head device according to the first invention is applied to a super-resolution optical head optical system using a variable width light-shielding band.

In this optical head device, a semiconductor laser 1 for emitting light as a light emitting device, a collimating lens 2 for converting the emitted light into parallel light, and a part of the parallel light flux are shielded or passed as it is. A variable-width light-shielding band 3a capable of performing the following operations; a polarization beam splitter 4 for extracting signal light;
Beam splitters 5 and 13 for extracting a servo error light from a signal light, an objective lens 6 for converging a parallel light beam on an optical disk 7 for reproducing recorded information by irradiating and reflecting light, and an optical disk 7 From the reflected return light
A track error detection system 8 for extracting a servo error light and detecting a tracking error from the servo error light, a signal detection system 9 for detecting a signal read from the signal light from the optical disk 7, A condenser lens 12 for condensing the reflected return light, a knife edge 10 for blocking a part of the convergent light condensed by the condenser lens 12, and a focus detector 11 for receiving the convergent light. .

The optical system from which the laser beam is emitted from the semiconductor laser 1 to the optical disk 7 has the same configuration as the conventional optical system. The light reflected by the optical disk 7 travels backward through the optical system on the outward path, passes through the objective lens 6 and passes through the beam splitter 4.
The light is reflected at (5) and (5) to reach a signal detection system and a servo error detection system, respectively. The light reflected by the beam splitter 5 is branched by a beam splitter 13 and one of the two is separated by a track error detection system 8.
The other part is condensed by the condenser lens 12, then partially shielded by the knife edge 10, and the rest is received by the focus detector 11, which is divided into two parts, and a focus error is detected. The knife edge 10 is inserted so as to cut off all the portions affected by the modulation of the collimated light by the variable width light shielding band 3a.

On the other hand, the reflected return light reflected by the polarization beam splitter 4 is received by a signal detection system 9.

FIG. 2 is a plan view for explaining a focus detector adjustment method of the optical system in the optical head device of FIG . More specifically, FIG. 2A is a plan view showing a case where the focus detector is adjusted in the optical axis direction of the convergent light condensed by the condenser lens 12, and FIG. 2B is a plan view showing a case of focusing. FIG. 2C is a plan view showing a case where the focus detector is closer than the focal length of the condenser lens 12, and FIG.
FIG. 4 is a plan view showing a case where the distance is longer than a focal length of No. 2; FIG.
In (b), the focus error detection output α−β = 0
When the optical disk 7 is in the focal plane of the objective lens 6, the focus error output is zero. this
The position of the focus detector 11 at the time is shown in FIG.
(B). The focus detector 11 is closer than the focal plane of the condenser lens 12, ie,
Focus defocusing is performed on the portion indicated by (c) in FIG.
When there is the tractor 11, the state shown in FIG.
In this case, the error detection output = 0 by moving the focus detector 11 in parallel within the plane of the detector.
And can be adjusted. Similarly, the focus detector 11 is farther than the focal plane of the condenser lens 12, that is, FIG.
The focus detector 11 is located at a location indicated by (d) in FIG.
If there is, the state shown in FIG. in this case
Also, flat the focus detector 11 in the plane of the detector
The error output can be adjusted to 0 by moving the line .
Even when the width-variable light-shielding band 3a modulates collimated light, the modulated light beam is not received by the detector, so that the focused spot area on the focus detector does not change. Therefore, a stable servo system can be constructed before and after the change of the light shielding zone.

The principle of the generation of the super-resolution beam by the above-mentioned variable width light-shielding band is as described with reference to FIG. 6 in the section of the prior art, wherein the collimated light emitted from the light source is the variable width light-shielding band. After a part of the light is shielded by 3b, the light passes through the beam splitter 5 and is focused on the optical disk 7 to form a condensing beam spot. At one time, the super-resolution beam 32 is formed on the optical disk 7 when the super-resolution beam 32 is at B where the light shielding width is small.

In this example, the width-variable light-shielding band 3b is a rotary light-shielding band. In FIG. 1, a non-rotatable variable width light shielding band 3a is used.

FIG . 3 is a plan view when the optical system in the optical head device of FIG. 1 is used for detecting a track error.

[0025] For forward path optical system is the same as the optical system of a conventional example. The return light reflected from the optical disk 7 is condensed by the objective lens 6, reflected by the beam splitters 5 and 13, partially transmitted through the condensing lens 41, condensed, and irradiated on the track detector 42. A light-shielding plate 45 is provided between the beam splitter 13 and the condenser lens 41, and a region where the collimated light is modulated is cut by the light-shielding plate 45.
The track detector 42 split by the reflected light returning from the optical disk 7 receives the projected image 44 of the light-shielding plate, the first-order diffracted light 43 and other light amounts, but the track error is caused by the balance of the first-order diffracted light received by both split PDs. From the push-pull method. The error is detected only by the light beam which is not modulated by the width-variable light-shielding band 3a, so that a stable servo operation is possible before and after the width change .

Next, the embodiment using the optical head device of the present second invention will be now described in detail.

FIG . 4 is a plan view showing an embodiment of the optical system of the optical head device according to the second invention.

In this optical head device, a semiconductor laser 1 for emitting light as a light emitting device, a collimating lens 2 for converting the emitted light into parallel light, and a part of the parallel light flux are shielded or passed as it is. A variable-width light-shielding band 3a capable of performing the following operations; a polarization beam splitter 4 for extracting signal light;
Beam splitters 5 and 13 for extracting a servo error light from a signal light; an objective lens 6 for converging a parallel light beam onto an optical disk 7 for reproducing recorded information by irradiating and reflecting light; and an optical disk 7 From the reflected return light
Removed Boera light, a track error detection system 8 to detect the servo error light or al track error, a signal detection system 9 for detecting the signal read from the signal light from the optical disk 7, reflected from the optical disk 7 returns A double hologram lens 51 composed of hologram lenses A53 and B54 for condensing light;
Detector 5 that receives the convergent light collected by the
And 2.

The semiconductor laser - is a configuration of the same optical system as a conventional head for an optical system of going to the laser beam from The 1 reaches is emitted to the optical disk 7. The light reflected by the optical disk 7 travels backward through the going optical system, passes through the objective lens 6, is reflected by the beam splitters 4 and 5, and is respectively connected to the signal detection system and the server.
It leads to the error detection system. The light reflected by the beam splitter 5 is branched by the beam splitter 13, and one of the lights reaches the track error detection system 8 and the other reaches the double hologram lens 51.

Of the light beam that has entered the double hologram lens 51, the portion of the light beam that is modulated by the variable width light-shielding band 3a is shielded by the light-shielding region 55 and all is cut off, and the others pass through the hologram lens A53 and the hologram lens B54. . The hologram lenses A53 and B54 are formed with holograms centered on points F 'and E' so that the transmitted light converges on points E and F on the focus detector 52, respectively. In FIG. 4 , when the optical disk 7 is in the focal plane of the objective lens 6, the reflected return light from the optical disk 7 is collected by the hologram lenses A53 and B54 to form condensed spots at points F and E on the focus detector 52, respectively. I do.

Next, will be described with reference to FIG adjustment method of a focus detection system using a double-hologram 51.

FIG . 5 is a plan view for explaining a method of adjusting the focus detector of the optical system in the optical head device of FIG . More specifically, FIG. 5A is a plan view showing a case where a focus detector is adjusted in the optical axis direction of convergent light condensed by a double hologram lens, and FIG. 5B is a front view showing a case of focusing. FIG. 5C is a front view showing a case where the focus detector is closer than the focal length of the hologram lens, and FIG. 5D is a front view showing a case where the focus detector is farther than the focal length of the hologram lens.

In FIG . 5B, the focus error detection output (α + γ) − (β + δ) = 0, and the differential output is 0 when the optical disk 7 is in the focal plane of the objective lens 6. At this time, the focus detector 52
The position is at the position indicated by (b) in FIG.
Next, the focus detector 52 is moved to the hologram lens 5.
5C, which is closer than the focal plane of FIG. 1, that is, when the focus detector 52 is located at the position indicated by (c) in FIG. 5A, the state of FIG. Become. The focus detector 52 of the hologram lens 51
With the arrangement close to the focal plane , as shown in the left diagram of FIG.
The detection output becomes ≠ 0, but the right figure in FIG.
As shown, by rotating the focus detector 52, the detection output (α + γ) − (β + δ) = 0 can be adjusted. Similarly, if the focus detector 52 is focused farther FIG than the plane of the hologram lens 51 (d), Sunawa
5 (a) is a defocused area.
When there is the detector 52, the state shown in FIG.
You. If the focus detector 52 is arranged farther than the focal plane of the hologram lens 51, the detection output becomes ≠ 0 as shown in the left diagram of FIG.
By rotating the focus detector 52 as shown in the right diagram, the detection output (α + γ) − (β + δ) = 0 can be adjusted. Even when the width-variable light-shielding band 3a modulates collimated light, no change occurs in the focused spot area on the focus detector, so that a stable servo system can be constructed before and after the change of the light-shielding band.

[0034]

As described above, in the optical head device according to the present invention, of the reflected return light from the recording medium, only the light beam which is not affected by the attenuation of the amplitude by the modulation element is condensed and the servo error is generated. Is detected, there is an effect that a stable servo system free from servo offset can be configured before and after the modulation of the collimated light by the variable width light shielding band.

[Brief description of the drawings]

FIG. 1 is a plan view showing an embodiment of an optical head device according to the first invention.

FIG. 2 is a plan view for describing a focus detector adjustment method of an optical system in the optical head device of FIG. FIG. 2A is a plan view showing a case where the focus detector is adjusted in the optical axis direction of the convergent light condensed by the condenser lens 12. FIG. FIG. 2B is a plan view showing the case of focusing. FIG. 2C is a plan view showing a case where the focus detector is shorter than the focal length of the condenser lens 12. FIG. 2D is a plan view showing a case where the focus detector is farther than the focal length of the condenser lens 12.

FIG. 3 is a plan view when an optical system in the optical head device of FIG. 1 is used for detecting a track error.

FIG. 4 is a plan view showing an embodiment of the optical system of the optical head device according to the second invention.

FIG. 5 is a plan view for explaining a focus detector adjustment method of an optical system in the optical head device of FIG. 4;
FIG. 5A is a plan view showing a case where the focus detector is adjusted in the optical axis direction of the converged light collected by the double hologram lens. FIG. 5B is a front view showing the case of focusing. FIG. 5C is a front view showing a case where the focus detector is closer than the focal length of the hologram lens. FIG. 5D is a front view showing a case where the focus detector is farther than the focal length of the hologram lens.

FIG. 6 is a plan view for explaining the principle of generation of a super-resolution beam in the optical head device of FIGS. 1 and 7.

FIG. 7 is a plan view illustrating a configuration of a super-resolution optical system using a knife edge focus error detection method in a conventional optical head device.

FIG. 8 is a plan view showing a principle of focus detection by a conventional knife edge method in a super-resolution optical head. FIG.
FIG. 4A is a plan view illustrating a principle of focus detection when a disc approaches a focal length shorter than a focal length of an objective lens. FIG. 8B is a plan view showing the principle of focus detection when the disk is separated farther than the focal length of the objective lens. FIG. 8C is a plan view showing the principle of focus detection when the disc is located on the focal plane of the objective lens.

[Explanation of symbols]

1 Laser Diode 2 Collimating Lens 3a, 3b Variable Width Light Shielding Band 4 Polarization Beam Splitter 5 Beam Splitter 6 Objective Lens 7 Optical Disk 8 Track Error Detection System 9 Signal Detection System 10 Knife Edge 11 Focus Detector 12 Focusing Lens 13 Beam splitter 31 Normal beam 32 Super-resolution beam 41 Condensing lens 42 Track detector 43 First-order diffracted light 44 0th-order diffracted light 45 Shielding plate 51 Double hologram lens 52 Focus detector 53 Hologram lens A 54 Hologram lens B 55 Shielding area 71 Normal beam 72 Super-resolution beam

Claims (2)

(57) [Claims] 1. A semiconductor laser which emits light as a light emitting device, a collimating lens which converts the emitted light into parallel light, and an optical axis of the parallel light by changing a light shielding width.
A variable-width light-shielding band through which the amplitude of a part of the light can be attenuated or the parallel light can pass as it is, and the information recorded on the optical disc is reproduced on the optical disc by irradiation and reflection of light. An objective lens that collects parallel light that has passed through the variable width light shielding band, a track error detection system that extracts a servo error light from reflected return light of the optical disk, and detects a track error from the servo error light; a polarization beam splitter for taking out a signal light from the reflected return light, a signal detecting system for detecting a signal read from the optical disc by the signal light, and a focusing lens for focusing the light reflected back from the optical disc, wherein Of the convergent light condensed by the condenser lens,
Cuts convergent light affected by amplitude attenuation due to light band
A knife edge which is inserted so that, receiving the convergent light which is not cut by the knife edge
An optical head apparatus comprising: a focus detector that. 2. A semiconductor laser for emitting light as a light emitting device, a collimating lens for converting the emitted light into parallel light, and a part near the optical axis of the parallel light by varying a light shielding width. A variable-width light-shielding band capable of attenuating the amplitude or passing the parallel light as it is, and a variable-width light-shielding band on the optical disc for reproducing information recorded on the optical disc by irradiation and reflection of light. An objective lens for condensing parallel light passing through the light-shielding band, a track error detection system for extracting a servo error light from the reflected return light of the optical disk and detecting a track error from the servo error light, and a reflected return light for the optical disk A polarizing beam splitter for extracting signal light from the optical disk, a signal detection system for detecting a signal read from the optical disk by the signal light, and the optical disk A hologram lens for condensing light reflected back al, in an optical head device having a focus detector for receiving the convergent light condensed by the hologram lens, the hologram lens, the light shielding region and a first hologram lens Having a second hologram lens, of the incident light beam, a portion of the light beam that is modulated by the variable width light-shielding band is shielded by the light-shielding region and all cut off, and the others are the first and second holograms. An optical head device, wherein the first and second hologram lenses are double holograms each having a hologram formed so as to condense the transmitted light on the focus detector.