JPH1049884A - Optical pickup device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an optical pickup device in which the degradation of a focus error signal due to change in oscillation wavelength and in condensing means is suppressed, by detecting reflection luminous fluxes diffracted in two regions diagonal to each other among four regions in a transmission type hologram element (diffraction element). SOLUTION: A luminous flux from a light source 2 is divided, by a transmission-type trisecting diffraction grating 3, into three luminous fluxes composed of zero-order diffracted luminous flux M, first-order diffracted luminous flux S1 for a tracking servo, and minus-first-order diffracted luminous flux S2. Then, a transmission-type hologram element 4, on which the luminous fluxes are made incident, divides the luminous fluxes M, S1, S2 reflected from an optical disk 1 into four parts, and it gives a spatial change corresponding to the focus state. At this time, the hologram element 4 is provided with a dividing line 41 which is parallel to the track direction of the optical disk 1 and with four regions 4a, 4b, 4c, 4d by a dividing line 4m in the radial direction at right angles to the dividing line. The reflected luminous fluxes which are diffracted in the regions 4a, 4c and 4b, 4d are detected respectively by a light detection part 6, and the degradation of a focus error signal is suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pickup device.

[0002]

2. Description of the Related Art In recent years, an optical pickup device using a hologram element (diffraction element) as a separating means has been researched and developed.

FIG. 14 is a diagram of Japanese Patent Application Laid-Open No. 3-76035 (G1).
FIG. 1B is a schematic configuration diagram of an optical pickup device that performs a focus servo by an astigmatism method and a tracking servo by a three-beam method described in Japanese Patent Laid-Open No. 1B 7/135).

In FIG. 1, reference numeral 101 denotes an optical disk; 102, a semiconductor laser element for outputting a laser beam (light flux) upward;
Numeral 03 denotes a three-division grating for splitting the light beam into three light beams, and 104 a light beam which transmits the three light beams and diffracts a return light beam (reflected light beam) from the disk 101 and focuses on the light beam. A hologram element (diffraction element) 105 for giving astigmatism corresponding to the above, and the three luminous fluxes transmitted through the hologram element 104
A condensing lens (condensing means) for condensing as three spots of a main spot and sub spots located on both sides thereof;
Reference numeral 106 denotes a photodetector that detects a diffracted light beam of the return light beam from the optical disk 101 diffracted by the hologram element 104.

FIG. 15 is a schematic top view of a six-segment photodetector, which is an example of the photodetector 106.

The photodetector 106 comprises photodetectors 106a to 106d for detecting a reflected light beam relating to the main spot and outputting a focus error signal FES and a reproduction signal by a conventionally known astigmatism method. Photodetectors 106e and 106f located on both sides of the above-mentioned four-divided light detector for outputting a tracking error signal TES by a conventionally known three-beam tracking method using the divided light detector and the reflected light beam relating to the sub spot. Having.

[0007] The follower - Kasuera signal FES using the output signal S _a to S _d of each optical detector 106a~106d of the 4-division optical _{detector, FES = (S a + S} c) - (S b
+ S _d ).

In addition, the tracking error signal TES
Is the difference (S _e −S) between the output signals S _e and S _f of the light detection units 106 e and 106 _f that independently detect the reflected light fluxes related to the sub-spots that generate an output signal difference in accordance with the track shift of the main spot. _f ).

By the way, the semiconductor laser device 102
Is caused by the oscillation wavelength fluctuation depending on the element temperature, and the diffraction angle of the diffracted light beam generated by diffracting the feedback light beam by the hologram element 104 due to the fluctuation of the oscillation wavelength. Therefore, the FES = (S _a + S _c ) − (S
_b + _Sd ) may fluctuate.

For this reason, the FES caused by the oscillation wavelength fluctuation
Is divided by a dividing line 106g substantially along the direction in which the diffracted light beam of the hologram element 104 moves due to the oscillation wavelength fluctuation.

However, even when the photodetector 106 is arranged in consideration of the wavelength variation as described above, when the wavelength variation becomes large, the condensed spot of the diffracted light beam becomes an intersection of the division line 106g and the division line 106h. As a result, there arises a problem that an accurate FES cannot be obtained.

In order to solve this problem, the applicant of the present application has proposed, as a focus servo photodetector, a photodetector 4 which is divided by the above-mentioned mutually orthogonal dividing lines 106g and 106h.
Instead of the split light detecting section, a three-split light detecting section 206 for focus servo which is split by parallel split lines as shown in FIG. In this case, the light detection unit 20
From the output signal S _a to S _c of 6a~206c, FES = (S
focus error signal is obtained by calculating the _a + S _c) -S _b.

However, when the light detection unit 206 is used, the amount of movement of the condenser lens 105 in the optical axis direction and the FES
In order to improve the S-curve characteristic indicating the relationship between the intensities, it is necessary to set the condensed spot of the diffracted light beam so as to equally straddle the light detection units 206a and 206c, but this adjustment is difficult.

Then, the applicant further made a pickup device as shown in FIG. 17 and conducted an experiment.

In FIG. 1, reference numeral 301 denotes an optical disk; 302, a semiconductor laser element for outputting a laser beam (light flux) in an upward direction;
Numeral 03 denotes a three-division diffraction grating for splitting the light beam into three light beams (a main light beam and a pair of sub-light beams located on both sides of the main light beam).
A hologram element (diffraction element) 305 for splitting and diffracting the three return light beams (reflected light beams) from 1 and giving astigmatism corresponding to the focus state to the two split light beams, and 305 A condensing lens for condensing the three light beams transmitted through the hologram element 304 on the disk 301 as three spots, a main spot and sub-spots located on both sides of the light spot, and 306 is diffracted by the hologram element 304 This is a photodetector that detects a diffracted light beam of the return light beam from the disk 301.

As shown in FIG. 18, the hologram element 30
4 has regions 304a and 304b divided by a division line 304l extending substantially along the track direction. still,
In the drawing, light spots by the three light beams are schematically shown.

Further, as shown in FIG.
Reference numeral 6 denotes light detectors 316a to 316c that detect a diffracted light flux of a return light flux related to the main light flux diffracted in the area 304a.
The light detecting unit 306a includes a light detecting unit 306b, and the light detecting unit 306b includes light detecting units 316d to 316f that detect a diffracted light beam of the return light beam related to the main light beam diffracted in the region 304b. A light detection unit 306 that detects a diffracted light beam of a return light beam related to one sub light beam
c, and a light detection unit 306d that detects a diffracted light beam of a return light beam related to the other sub light beam diffracted in the regions 304a and 304b.

The output signals S _{a to} S _f obtained from the respective light detectors 316 a to 316 _f and the respective light detectors 306 _c ,
Based on each output signal S _A and S _B of 306d, the focus error signal FES is FES = (S _a + S _c + S _e ) − (S _b
+ S _d + S _f ), and the tracking error signal TES is obtained by the calculation of FES = (S _A −S _B ).

As described above, since the focus error signal FES is obtained as described above, even if the condensed spot deviates from the center of the photodetectors 306a and 306b, it is calculated so as to correct this, and the focus error signal is correctly calculated. F
ES is obtained.

[0020]

However, in the apparatus using the hologram element 304 divided into two as described above, for example, in order to move the condensed spot to a desired track position, a condensing lens as shown in FIG. 305 is moved in a direction substantially perpendicular to the track direction (disc radial direction). At this time, as shown in FIG. 21, the size of the passing area of the reflected light flux in the area 304a and the area 304b of the hologram element 304 is different. Becomes

Accordingly, as the condenser lens 305 moves in the radial direction, the light detecting unit 306a and the light detecting unit 306b
Since the detected light amount of the diffracted light beam of the return light beam related to the main light beam received at the time f changes, the S-curve characteristic when the condenser lens 305 is moved in the radial direction by, for example, 0 μm or ± 400 μm becomes as shown in FIG. The focus error signal FES cannot be obtained.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to provide an optical pickup device capable of performing a preferred focus servo regardless of track position movement or wavelength fluctuation.

[0023]

An optical pickup apparatus according to the present invention irradiates a light beam emitted from a light source onto an optical disk via a light condensing means, and transmits a reflected light beam from the optical disk to a light detecting means side. In an optical pickup device diffracted by an element and detecting the diffracted reflected light beam by the light detecting means, the diffractive element is arranged so as to be orthogonal to the dividing line extending substantially along the track direction of the optical disc and the dividing line. The optical disc has four areas divided by dividing lines extending substantially along the radial direction of the optical disc, and two areas at one diagonal position and two areas at the other diagonal position of the four areas are The focus state is supported so that the focus state can be detected by comparing the reflected light beam diffracted in one of the two regions and the reflected light beam diffracted in the other two regions. Between the reflected light fluxes, the condensing means is set so as to move substantially along the radial direction of the optical disc for tracking, and the light detecting means is configured to change the wavelength of the light source. And at least two light receiving surfaces divided by a dividing line substantially along the direction in which the condensed spot of the diffracted reflected light beam moves for detecting the state of the furcus, and each light receiving surface is longer than the moving distance. Two sets of photodetectors for detecting a focus state having a length are provided. The one photodetector detects reflected light beams diffracted in two areas at the one diagonal position, and the other light is detected. A detection unit detects reflected light beams diffracted in the two regions at the other diagonal position.

The light source is preferably a semiconductor laser.

The two regions at one diagonal position and the two regions at the other diagonal position of the four regions are a reflected light beam diffracted by the two regions and the other two regions. The reflected light beams diffracted by the above-mentioned method are preferably given reciprocal spatial variations corresponding to the focus state.

In the optical pickup device of the present invention, the transmission type diffraction element is formed by a dividing line extending substantially along the track direction of the optical disk and a dividing line extending substantially along the radial direction of the optical disk so as to be orthogonal to the dividing line. It has four divided areas, and the condensing means is set to move substantially along the radial direction of the optical disc for tracking, and the one diagonal line detected by the one light detection unit By comparing the difference between the light receiving area of the reflected light beam diffracted in the two regions of the position and the light receiving area of the reflected light beam diffracted in the two regions of the other diagonal position detected by the other light detection unit, Detect a focus error signal. In this configuration, even if the position of the reflected light flux in the transmission diffraction element due to the tracking of the condensing means changes, the incident area of the reflected light flux in the two areas at the one diagonal position and the two areas at the other diagonal position Since the incident area of the reflected light flux in the region does not substantially change, the deterioration of the focus error signal due to the movement of the light collecting means due to tracking is suppressed.

In addition, in the optical pickup device of the present invention, the light detecting section for detecting the focus state is configured to collect the reflected light beam for detecting the focus state diffracted by the transmission type diffraction element due to the wavelength fluctuation of the light source. A light receiving surface divided by a dividing line substantially along the moving direction of the spot, wherein each light receiving surface has a length longer than the moving distance (that is, a length such that the light receiving surface is located within the light receiving surface even if the converging spot moves); ), The deterioration of the focus error signal due to the wavelength fluctuation of the light source is suppressed.

As a result, the deterioration of the focus error signal caused by the wavelength fluctuation of the light source, the movement of the light condensing means, and both of them are suppressed.

In particular, the shape of the light spot of the reflected light beam for detecting the focus state in the transmission type diffraction element is as follows:
The transmission type diffraction element is substantially symmetrical with respect to a dividing line extending substantially along a radial direction of the optical disc.

In this case, even if the focusing means is moved by tracking, the incident areas of the reflected light beams in the two areas at the one diagonal position and the incident areas of the reflected light beams in the two areas at the other diagonal position. Since the areas are more equal, the deterioration of the focus error signal due to the movement of the light collecting means due to tracking is further suppressed.

In particular, a radial direction of the optical disk and a moving direction of the converging spot due to a wavelength change of the light source are substantially parallel to each other.

In this case as well, the ratio of the incident area of the reflected light beam in the two regions at the one diagonal position to the incident area of the reflected light beam in the two regions at the other diagonal position is substantially maintained, and the one of the two regions is maintained. The reflected light flux diffracted in the two areas at the diagonal positions is detected by the one light detection unit of the light detection means, and the reflected light flux diffracted in the two areas at the other diagonal position is detected by the other light detection means. Since it is detected by the part,
Deterioration of the focus error signal is further suppressed.

Further, the radial direction of the optical disk may be substantially orthogonal to the direction in which the converging spot moves due to a wavelength change of the light source.

In this case, the incident area of the reflected light beam in the two areas at the one diagonal position and the area at the other diagonal position are two.
While substantially maintaining the ratio of the incident area of the reflected light flux in the two areas, the reflected light flux diffracted in the two areas at the one diagonal position is detected by the one light detection section of the light detection means, and Since the reflected light flux diffracted by the two regions at the other diagonal position is detected by the other light detection unit, the deterioration of the focus error signal is further suppressed.

In particular, the at least two light receiving surfaces are characterized by having a narrow light receiving surface and wider light receiving surfaces on both sides thereof.

In this case, the opposite point of the condensed spot formed by the reflected light fluxes diffracted at the two diagonal positions may be located within a narrow light receiving surface, so that it is relatively easy. Then, by adding detection signals from the wide light receiving surfaces on both sides of each light detection unit and comparing the difference, the reception of the reflected light flux diffracted in the two regions at the one diagonal position is performed. The difference between the area and the light receiving area of the reflected light flux diffracted in the two regions at the other diagonal position detected by the other light detection unit can be compared.
In addition, the signal from the narrow light receiving surface is used to obtain a reproduced signal, that is, the sum of the detection signals of the narrow light receiving surface of the two detectors and the light receiving surfaces on both sides thereof is used. As a result, the intensity of the reproduced signal is increased, and a good reproduced signal is obtained.

It should be noted that the two sets of light detecting sections of the light detecting means are arranged in a direction perpendicular to the moving direction of the light source rather than being arranged in a straight line substantially along the moving direction of the condensed spot due to the wavelength variation of the light source. By arranging them substantially in a straight line, the optical axis can be easily adjusted by rotating the diffraction element. In this case, it is preferable that the longitudinal direction of the light receiving surfaces constituting the two sets of light detecting portions of the light detecting means is substantially along the track direction, from the viewpoint of the symmetry of the light spot.

Further, a three-divided diffraction grating for generating a main light beam and sub-beams for tracking servo located on both sides of the light beam emitted from the light source is provided in an optical path between the light source and the transmission type diffraction element. And the light detection means,
The two light detectors detect reflected light fluxes from the optical disc relating to the main light flux diffracted by the transmission type diffraction element, and reflect the respective light beams reflected from the optical disc diffracted by the transmission type diffraction element. In order to detect the light beams, a pair of light detection units for tracking state detection having a light receiving surface longer than the moving distance on both sides to sandwich the two light detection units is provided. I do.

In this case, the tracking servo by the three-beam method can be performed while preventing the deterioration of the tracking signal due to the fluctuation of the wavelength of the light source and the movement of the light collecting means due to the tracking.

In particular, the invention is characterized in that the spatial variation is astigmatism.

In this case, focus servo can be performed by the astigmatism method.

Further, the one two regions of the diffractive element and the other two regions of the diffractive element impart astigmatism which is orthogonal to each other.
It is preferable that one of the orthogonal directions is substantially parallel to the dividing line of the two sets of light detecting sections of the light detecting means.

In this case, since the difference in the light receiving area becomes large, a good focus error signal can be obtained.

The focal position of the reflected light beam diffracted by the two regions of the diffractive element and the focal position of the reflected light beam diffracted by the other two regions of the diffractive element are different from each other during focusing. It is characterized by being located at different heights.

In this case, depending on the focus state, the size of the condensed spot related to the reflected light beam at one and the other of the two sets of light detection sections for detecting the focus state of the light detection means changes so as to differ. Focus servo can be performed.

In particular, at the time of focusing, the focal position of the reflected light beam diffracted by the one of the two regions of the diffraction element is located closer to the light receiving surface of the light detecting means,
The focal position of the reflected light beam diffracted by the other two regions of the diffraction element is located on the back side of the light receiving surface of the light detecting means.

In this case, according to the focus state, the sizes of the condensed spots related to the reflected light beams at one and the other of the two sets of light detection sections for detecting the focus state of the light detection means are in an opposite relationship to each other. The focus state is set when the size of the condensed spots related to the reflected light beam at one and the other of the two sets of light detection units for detecting the focus state of the light detection means is substantially the same. The focus servo can be easily performed.

[0048]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An optical pickup device for performing focus servo by an astigmatism method and tracking servo by a three-beam method according to a first embodiment of the present invention will be described with reference to the schematic configuration diagram of FIG.

In the figure, reference numeral 1 denotes a reflective optical disk such as a CD (compact disk), and 2 denotes a laser beam (light flux).
Outputting a semiconductor laser (light source), 3 at least 0-order diffracted light each said laser beam (main luminous flux) M, 1-order diffraction light for tracking servo (sub beam) S ₁ and -1st-order diffracted light (sub beam) S ₂ Is a so-called transmission-type three-division grating made of optical glass or optical resin that divides the light into three light beams. In the drawing, the three light beams are represented by one light beam.

Reference numeral 4 denotes the above-mentioned 3 which is emitted from the three-division diffraction grating 3.
Light beams M, S ₁ , and S ₂ are incident thereon, and each reflected light beam (return light beam) M from the optical disc 1 related to the three light beams M,
S ₁ and S ₂ are divided into four parts, and each of the divided light beams is separated by a first order so as to give a spatial variation (astigmatism in the present embodiment) corresponding to the focus state on the optical disc 1. It is a transmission type hologram element (transmission type diffraction element).

As shown in the schematic top view of FIG.
The hologram element 4 is moved in the track direction (track direction) of the optical disc 1.
Virtual direction extending substantially parallel (Y direction)
Is orthogonal to the dividing line 41, that is, the optical
Virtual extending substantially along the radial direction (X direction) of the disc 1
Are divided into four regions 4a, 4b, 4
It has a hologram surface divided into c and 4d. The figure
Medium, three beams M, S ₁, S_TwoLight spot M by
S₁, S_TwoIs shown.

Then, the dividing line 4l and the dividing line 4m
4a located symmetrically (diagonal position) with respect to the intersection of
And a region 4c (mesh hatching in the figure), a region 4b and a region 4d (hatched hatching in the diagram) have the same hologram surface pattern (diffraction surface pattern), respectively.
The area a and the area 4c and the area 4b and the area 4d give the diffracted luminous flux a spatial variation in an inverse relationship to each other (in the present embodiment, astigmatism in an orthogonal relationship to each other).

Numeral 5 is supported along the radial direction (X direction) of the optical disk 1 for tracking servo, and can be driven up and down (Z direction) for focus servo. A condensing lens (condensing means) for condensing the three light beams M, S ₁ , and S ₂ diffracted and transmitted on the optical disc 1 as condensed spots M, S ₁ , and S ₂ .

Here, as shown in FIG. 3, the condensed spot (main spot) M related to the main light beam M scans the track TR on which information is recorded, and collects the condensed light beams related to both the sub light beams S ₁ and S _2. The spots (sub spots) S ₁ and S ₂ scan so as to slightly straddle both sides of the track TR. Since the reflectivity outside this track is set higher than that of the track,
When the main spot M is deviated from the track, a difference occurs between the reflected light intensities from the two sub spots S ₁ and S ₂ . The converging spots M, S ₁ , and S ₂ are arranged such that the major axis or the minor axis is substantially perpendicular to the track.

Reference numeral 6 denotes the three light beams M, which have passed through the condenser lens 5 and have been transmitted and diffracted in the first order by the transmission hologram element 4,
This is a photodetector (light detection means) for detecting each reflected light beam from the optical disc 1 corresponding to S ₁ and S _{2. As} shown in the schematic top view of FIG. A pair of focus servo photodetectors 6 arranged in a straight line substantially along the extension direction (radial direction)
a and the light detector 6b, and the light detector 6a and the light detector 6b
And a pair of tracking servo photodetectors 6c and 6d extending substantially parallel to the direction in which the dividing line 4m extends, which is disposed on both sides of the photodetectors 6c and 6d.

The light detectors 6a are rectangular light detectors 16a, 16a extending substantially parallel to the radial direction.
b, 16c, having the same width.
This is a configuration in which a narrow light detection section 16b is arranged between the light detection sections 16c. The light detector 6b has the same configuration as the light detector 6a, and includes rectangular light detectors 16d, 16e, and 16f extending substantially parallel to the radial direction, and has the same width. This is a configuration in which a narrow light detection unit 16e is arranged between 16d and 16f.

In this embodiment, the photodetectors 6a and 6b
Each of the hologram elements 4 depends on the wavelength fluctuation of the light source 1.
The light detection units 16a to 16c and the light detection unit 16 are divided by a division line (virtual division line) along the direction in which the converging spot of the reflected light flux diffracted by the light detection unit 6 moves in the light detection unit 6.
d to 16f, and the length of each of the rectangular light detecting portions (light receiving surfaces) 6c, 6d, 16a to 16f in the longitudinal direction is changed by the wavelength variation of the light source 1.
The length is set to be longer than the moving distance of each converging spot in each light detecting unit that receives the reflected light flux diffracted by the above.

In such an optical pickup device, the optical system is set such that the condenser lens 5 enters the transmission hologram element 4 with the center of the reflected light flux M substantially positioned on the dividing line 4m for tracking. And the areas 4a, 4c
Is transmitted and diffracted at the first order in the regions 4a and 4c so as to be received by the light detection unit 6a, and is reflected by the regions 4b and 4c.
The reflected light flux M incident on 4d is transmitted and diffracted in the first order in the regions 4b and 4d so as to be received by the light detection unit 6b.

FIG. 5 is a schematic top view showing a light condensing state on the photodetector 6 when the main light beam M is focused on the optical disk 1.

The reflected light beam M is divided and diffracted in the areas 4a to 4d of the hologram element 4. Then, the reflected light beam M diffracted first-order in the region 4a and the reflected light beam M diffracted first-order in the region 4c are respectively condensed spots P on the light detection unit 6a.
_a and a converging spot _Pc ,
b In order diffraction reflected light beam M and region 4d in the primary diffracted reflected light beam M is focused as a focused spot P _b and condensing spot P _d on each light detecting unit 6b.

The reflected light flux S ₁ and the reflected light flux S ₂ are also split and diffracted in the areas 4 a to 4 d of the hologram element 4. Then, the reflected light flux S ₁ diffracted first-order in the area 4a and the area 4
The reflected light flux S _{1 that} has been first-order diffracted by _c is condensed as _a converging spot Q _a and _a converging spot Q c on the light detecting section 6a side on the light detecting section 6c, respectively, and is also subjected to first-order diffraction in the region 4b. reflected light beams S ₁ and the reflected light beam S ₁ which is 1-order diffraction in the region 4d, the light detecting portion 6b on the respective optical detection unit 6c
It is condensed as the condensed spot Q _b and condensing spot Q _d in the side. Similarly reflected light beam S ₂ is condensed as a condensed light spot R _a to R _d corresponds to a region 4a~4d on the optical detection unit 6d.

FIG. 6 shows the optical detector 6 when the optical disk 1 approaches the condenser lens 5 and a focus error occurs.
The schematic top view showing the above-mentioned light-collecting state is shown.

[0063] In this case, the light detection unit 6a focused spots P _a and converged spot P _c has a shape extending in a direction perpendicular to the direction of diffraction, the light detecting unit 6b focused spots P _b and The focused spot _Pd has a shape extending in the diffraction direction.

FIG. 7 shows a light detector 6 when the optical disk 1 is separated from the condenser lens 5 and a focus error occurs.
FIG. 4 shows a schematic top view showing the condensed spot above.

[0065] In this case, the light detection unit 6a focused spots P _a and converged spot P _c has a shape extending in the direction of diffraction, the light detecting unit 6b focused spots P _b and the focusing spot P _d has a shape extending in a direction orthogonal to the diffraction direction.

Therefore, the focus error signal FES is
Region 4 located on one diagonal line of hologram element 4
a light detection unit 6a for detecting the reflected light flux M from
Region 4 located on one diagonal line of hologram element 4
b and 4d, and the light detecting unit 6b for detecting the reflected light flux M from the light detecting unit 6b.

That is, using the output signals S _{a to} S _f of the photodetectors 16a to 16f, the focus error signal FES =
(S _a + S _c + S _e )-(S _b + S _d + S _f ) is processed.

Here, in the case of the focus state (FIG. 5),
Converged spot P _a, relative to P _c, the focused spot P _b, P _d
Since the position away from the hologram element 4, becomes a shape extending in the direction of diffraction, the light amount is equal to the focused spot P _a to P _d, and the direction perpendicular to the direction of diffraction, condensing at the same scale Is done. Therefore, FES = 0.

When the optical disk 1 approaches the condenser lens 5 and a focus error occurs, as shown in FIG. 6, FES> 0, and conversely, the optical disk 1 separates from the condenser lens 5 and the focus error occurs. In the state, as can be seen from FIG. 7, FES <0.

On the other hand, the reproduction signal RF is RF = (S _a + S _b
+ _Sc + _Sd + _Se + _Sf ).

The tracking error signal TES is
Difference between output signals S _A and S _B of photodetectors 6c and 6d, TES =
It is obtained by the calculation of (S _A -S _B ).

In this optical pickup device, the hologram surface of the hologram element 4 is divided by a dividing line 4l substantially along the track direction of the optical disc 1 and a dividing line 4m along the radial direction of the optical disc 1 (perpendicular to the track direction). It is divided into four parts 4a to 4d. The tracking operation of the condenser lens 5 is performed substantially along a radial direction substantially included in a plane including the optical axis of the reflected light beam M diffracted by the hologram element 4 and the optical axis of the main light beam M.

The light detecting section 6a and the light detecting section 6b of the photodetector 6 are divided into areas 4a to 4d divided by the dividing line 4l and the dividing line 4m, which are in a diagonal positional relationship orthogonal to each other. 4a, 4c and regions 4b, 4d
Are detected respectively.

In addition, the light detectors 6a and 6b of the light detector 6
Is composed of three light detecting portions (light receiving surfaces) 16a to 16c and 16d to 16f substantially divided in the radial direction, and each of the light detecting portions (light receiving surfaces) 16a to 16f extends in a direction substantially parallel to the radial direction. The light detectors (light receiving surfaces) 6c and 6d are also upper surface rectangles whose longitudinal directions are substantially parallel to the radial direction.

Accordingly, when the focusing lens 5 performs a tracking operation (movement in the radial direction), the center of the reflected light flux M in the hologram element 4 moves along the dividing line 4m, but the hologram surface of the hologram element 4 Is a dividing line 4m substantially along the radial direction and a dividing line 4 orthogonal to the dividing line 4m.
Since the light beam M is orthogonally divided by 1, the total area of the reflected light flux M incident on the region 4a and the region 4c is substantially equal to the total area of the reflected light beam M incident on the region 4b and the region 4d.

As a result, it is possible to prevent the FES signal from being deteriorated by the tracking operation of the condenser lens 5. As a result, good S-curve characteristics can be obtained even if the condenser lens 5 moves ± 400 μm in the radial direction as shown in FIG.

In addition, the light detectors 6a and 6b of the light detector 6
Means that the hologram element 4
Since the reflected light flux (diffracted light) diffracted by the above is divided by a dividing line substantially along the direction in which the light moves, and the longitudinal direction is substantially parallel to the direction in which the light moves, the upper surface is rectangular. The deterioration of the FES signal can be prevented. In addition, since the light detectors 6c and 6d also have a rectangular top surface whose longitudinal direction is substantially parallel to the moving direction,
It is possible to prevent the TES signal from deteriorating due to the wavelength fluctuation.

In addition, the light flux M reflected by the transmissive diffraction element 4
Is substantially symmetrical with respect to the dividing line 4m of the transmission type diffraction element 4 extending substantially along the radial direction of the optical disk 1, so that even if the focusing lens is moved by tracking, Two areas 4 at diagonal positions of
Since the incident areas of the reflected light beams a and 4c and the incident areas of the reflected light beams of the two regions 4b and 4d at the other diagonal positions become more equal, the deterioration of the focus error signal is further suppressed.

In particular, since the radial direction of the optical disk 1 and the moving direction of the converging spot due to the wavelength fluctuation of the light source 2 are substantially parallel to each other, the reflected light fluxes of the two areas 4a and 4c at the one diagonal position are provided. The reflected light flux diffracted by the two areas 4a, 4c at the one diagonal position is kept in a state where the ratio of the incident area of the reflected light flux at the two areas 4b, 4d at the other diagonal position is substantially maintained. The light is detected by the light detecting unit 6a and the other diagonal position 2 is detected.
The reflected light flux diffracted by the two regions 4b and 4d is
b. Therefore, the deterioration of the focus error signal is further suppressed.

In the above description, the astigmatism is given to the reflected light beam diffracted by the hologram element 4 according to the focus state, but it can be changed to various methods as appropriate.

FIG. 9 is a schematic configuration diagram of an optical pickup device according to the second embodiment of the present invention. In this embodiment,
The configuration is the same as that of the first embodiment except that the reflected light flux diffracted by the hologram element (diffraction element) 14 does not impart astigmatism.

As shown in the schematic top view of FIG. 10, the transmission hologram element 14 is a virtual dividing line 1 extending substantially parallel to the track direction (track extending direction) of the optical disk 1.
4l and the division line 14l, that is, the optical disk 1
Are divided into four regions 14a, 14b, 14c, and 14 having the same area by virtual dividing lines 14m extending substantially in the radial direction.
d. In the figure, three luminous fluxes M,
Light spot M by S _1, S _2, showing the S _1, S _2.

Then, the dividing line 14l and the dividing line 1
Regions 14a and 14c and regions 14b and 14d symmetrically located with respect to the intersection of 4m have the same hologram surface pattern (diffraction surface pattern), respectively.
The areas 4a and 14c and the areas 14b and 14d give the diffracted light beams spatial fluctuations in an inverse relationship (reciprocal relationship) to each other when out of focus.

In the present embodiment, the focal position of the reflected light flux diffracted by one of the two regions 14a and 14c of the hologram element 14 and the other two regions 14 of the hologram element 14
The focal positions of the reflected light beams diffracted by b and 14d are located at different heights during focusing.

That is, in the focus state, as shown in FIG. 9, each of the reflected light beams diffracted in the area 14a and the area 14c has a focal position on the near side of each of the detecting sections 6a, 6c, 6d of the light detecting means 6, and , 14b and the respective reflected light fluxes diffracted by the area 14d are detected by the respective detecting portions 6b of the light detecting means 6,
The far side of 6c and 6d is the focal position, and a condensed spot on the photodetector 6 similar to that of FIG. 5 is obtained.

Here, the reflected light beam M diffracted first-order in the region 14a and the reflected light beam M diffracted first-order in the region 14c are:
The reflected light flux M which is focused on the light detection unit 6a as the focused spot P _a and the focused spot P _c , and which is first-order diffracted in the area 14b and the reflected light flux M which is first-order diffracted in the area 14d, It is condensed as the condensed spot P _b and condensing spot P _d each photodetecting section on 6a.

The reflected light beam S ₁ diffracted first-order in the region 14a and the reflected light beam S diffracted first-order in the region 14c
_1, respectively while being focused on the light detecting portion 6a side of the photodetecting section 6c as focused spot Q _a and focused spot Q _c, in the region 14b in the first-order diffraction reflected light beam S ₁ and region 14d 1 order diffracted reflected light beam S ₁ is converged as a focused spot Q _b and condensing spot Q _d respectively to the light detecting unit 6b side on the optical detection unit 6c. Similarly, the reflected light flux S
₂ is condensed as a condensed light spot R _a to R _d corresponds to a region 14a~41d on the optical detection unit 6d.

[0088] The optical disk 1 is close to the condenser lens 5, may become the focus error state, as shown in FIG. 11, the light detecting unit 6a focused spots P _a and converged spot P _c is small, light detection unit 6b focused spots P _b and the condensing spot P _d increases. Conversely, optical disk 1
There away from the condenser lens 5, may become the focus error state, as shown in FIG. 12, the light detecting unit 6a focused spots P _a and converged spot P _c is large, the light detection unit 6b Ueno condensing spot P _b and the condensing spot P _d is reduced.

Also in this embodiment, as in the first embodiment, the focus error signal FES is FES = (S _a + S _c).
+ S _e )-(S _b + S _d + S _f )
Also, the reproduction signal RF and the tracking error signal TES
Are respectively determined by the _{RF = S a + S b +} S c + S d + S e + S arithmetic processing _f and TES = S _A -S _B.

This optical pickup device can provide the same effects as the first embodiment.

In each of the above embodiments, the light detecting means 6
Although the photodetectors 6a and 6b are arranged in series substantially along the radial direction of the optical disc 1, the photodetectors 6a and 6b are arranged substantially along the radial direction as shown in FIG. The detection units 6a and 6b may be arranged in parallel with each other. In this case, the light detection units 6a and 6b
The light receiving surfaces 16a to 16d are indicated by dividing lines substantially along the track direction.
16c, 16d to 16f.

In the case where such a light detecting means is used, as compared with the optical pickup device used in the first and second embodiments, the converging spot of the reflected light beam is located on the light detecting portions 6a and 6b. When adjusting the optical axis, the hologram element 4,
This is preferable because the rotation can be easily performed by rotation of 14.

In such a case, the regions 4a to 4a of the hologram element 4
4d, the hologram surface patterns of the regions 14a to 14d of the hologram element 14 are of course set differently from the above embodiment.

In this case, the radial direction of the optical disk 1 and the moving direction of the condensed spot due to the wavelength variation of the light source 2 are substantially orthogonal to each other. Regions 4a, 4c (14
a, 14c) and the ratio of the incident area of the reflected light beam of the two regions 4b, 4d (14b, 14d) at the other diagonal position is substantially maintained, while maintaining the ratio of the incident area of the reflected light beam at the other diagonal position to 2 in the one diagonal position. Area 4a, 4c (14a, 14c)
The reflected light flux diffracted by is detected by the light detection unit 6a, and the two areas 4b, 4d (1
Since the reflected light flux diffracted by 4b, 14d) is detected by the light detection unit 6b, deterioration of the focus error signal is further suppressed.

In each of the above embodiments, the hologram element 4,
Although the photodetecting means 6 is arranged along the fourteen dividing lines 4m, 14m, or 41, 141, an effect can be obtained even if these dividing lines are arranged at an angle. However, in this case, the focus error signal is deteriorated as compared with the above embodiment.

In the above description, the optical pickup device using the transmission type three-division grating is described. However, the present invention can be applied to the optical pickup device using the reflection type three-division grating. Of course, the optical path can be refracted by interposing a reflection means such as a mirror between the light source and the information recording medium.

Further, an optical element in which the transmission type three-division diffraction grating 3 and the transmission type hologram element 4 are integrated may be used.

As a tracking servo method, a method other than the three-beam method can be appropriately used.

The photodetectors 6a and 6b each have a 3
Although the light receiving surface is divided into two light receiving surfaces, a configuration in which each light receiving surface is divided into two light receiving surfaces is also possible, but three light receiving surfaces are more sensitive.

[0100]

According to the present invention, the fluctuation of the oscillation wavelength of the light source, the movement of the focusing means during tracking, and the deterioration of the focus error signal due to both of them can be suppressed.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an optical pickup device according to a first embodiment of the present invention.

FIG. 2 is a schematic top view of the hologram element used in the first embodiment.

FIG. 3 shows a track of an optical disc and a converging spot M,
Is a main part schematic diagram showing the relationship of S _1, S _2.

FIG. 4 is a schematic top view of a light detecting means used in the first embodiment.

FIG. 5 is a schematic top view showing a light condensing state on the light detecting means in a focus state in the first embodiment.

FIG. 6 is a schematic top view showing a light condensing state on the light detecting means in the non-focus state in the first embodiment.

FIG. 7 is a schematic top view showing a light condensing state on the light detecting means in the non-focus state in the first embodiment.

FIG. 8 is an S-curve characteristic diagram when the light converging means moves in the first embodiment.

FIG. 9 is a schematic configuration diagram of an optical pickup device according to a second embodiment of the present invention.

FIG. 10 is a schematic top view of a hologram element used in the second embodiment.

FIG. 11 is a schematic top view showing a light condensing state on a light detecting means in a non-focus state in the second embodiment.

FIG. 12 is a schematic top view showing a light condensing state on a light detecting means in a non-focus state in the second embodiment.

FIG. 13 is a schematic top view of another light detection unit.

FIG. 14 is a schematic configuration diagram of an optical pickup device according to a conventional example.

FIG. 15 is a schematic schematic top view of the conventional light detecting means.

FIG. 16 is a schematic schematic top view of a light detection section of another conventional light detection means.

FIG. 17 is a schematic configuration diagram of an optical pickup device according to another conventional example.

FIG. 18 is a schematic top view of a hologram element used in another conventional example.

FIG. 19 is a schematic top view of a light detecting section of another conventional light detecting means.

FIG. 20 is a schematic configuration diagram of an optical pickup device when a light-collecting unit moves in another conventional example.

FIG. 21 is a schematic top view showing the relationship among reflected light beams M, S ₁ , and S ₂ in a hologram element used in the above another conventional example.

FIG. 22 is an S-curve characteristic diagram when the light-collecting means moves in the another conventional example.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Optical disk (optical recording medium) 2 Light source 3 Diffraction grating for 3 divisions 4 and 14 Transmission hologram element (transmission type diffraction element) 4a, 14a area 4b, 14b area 4c, 14c area 4d, 14d area 41, 14l Division line 4m , 14m division line 5 condenser lens (condenser) 6 photodetector (photodetector) 6a photodetector 6b photodetector 6c photodetector (light-receiving surface) 6d photodetector (light-receiving surface) 16a photodetector (Light receiving surface) 16b Light detecting unit (light receiving surface) 16c Light detecting unit (light receiving surface) 16d Light detecting unit (light receiving surface) 16e Light detecting unit (light receiving surface) 16f Light detecting unit (light receiving surface)

 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Shoken Goto 2-5-5 Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd.

Claims (10)

[Claims] 1. A light beam emitted from a light source is irradiated to an optical disk via a light condensing means, a light beam reflected from the optical disk is diffracted by a transmission type diffraction element toward a light detecting means, and the diffracted light beam is reflected. In the optical pickup device which is detected by the light detecting means, the diffraction element includes a dividing line extending substantially along a track direction of the optical disc and a dividing line extending substantially along a radial direction of the optical disc so as to be orthogonal to the dividing line. The two regions at one diagonal position and the two regions at the other diagonal position of the four regions are reflected light beams diffracted by the two regions. Providing a spatial variation corresponding to the focus state to each of the reflected light beams so that the focus state can be detected by comparing the reflected light beams diffracted by the other two areas; The means is set so as to move substantially along the radial direction of the optical disc for tracking, and the light detection means is configured to detect the focus state of the diffracted reflected light beam due to a wavelength change of the light source. A light detecting unit for detecting a focus state having at least two light receiving surfaces divided by a dividing line substantially along a direction in which the converging spot moves, wherein each light receiving surface has a length longer than the moving distance; Two sets are provided, wherein the one light detection unit detects reflected light fluxes diffracted in two regions at the one diagonal position, and the other light detection unit diffracts light at two regions at the other diagonal position. An optical pickup device for detecting a reflected light beam. 2. A shape of a light spot of a reflected light beam for detecting a focus state in the transmission type diffraction element is substantially equal to a division line of the transmission type diffraction element extending substantially in a radial direction of the optical disc. The optical pickup device according to claim 1, wherein the optical pickup device is symmetric. 3. The optical pickup device according to claim 1, wherein a radial direction of the optical disk and a moving direction of the converging spot due to a wavelength change of the light source are substantially parallel to each other. 4. The optical disk according to claim 1, wherein a radial direction of the optical disk and a moving direction of the converging spot due to a wavelength change of the light source are substantially orthogonal to each other.
An optical pickup device as described in the above. 5. The light receiving surface according to claim 1, wherein the at least two light receiving surfaces have a narrow light receiving surface and wider light receiving surfaces on both sides thereof. Optical pickup device. 6. A three-divided diffraction grating for generating a main light beam and sub-beams for tracking servo located on both sides of the light beam emitted from the light source in an optical path between the light source and the transmission type diffraction element. And the light detection means detects, with the two light detection units, a reflected light beam from the optical disk related to the main light beam diffracted by the transmission type diffraction element, and diffracts each of the light beams diffracted by the transmission type diffraction element. A set of light for tracking state detection having a light receiving surface longer than the moving distance on both sides so as to sandwich the two light detecting portions, for detecting reflected light beams from the optical disk related to the sub light beam, respectively. A detection unit is provided.
The optical pickup device according to 4 or 5. 7. The optical pickup device according to claim 1, wherein the spatial variation is astigmatism. 8. The method according to claim 7, wherein the one two regions of the diffractive element and the other two regions of the diffractive element impart astigmatism in a mutually orthogonal relationship. Optical pickup device. 9. A focus position of a reflected light beam diffracted by said one of the two regions of the diffraction element and a focal position of a reflected light beam diffracted by the other two regions of the diffractive element are different from each other during focusing. The optical pickup device according to claim 1, 2, 3, 4, 5, or 6, wherein the optical pickup device is located at different heights. 10. A focus position of a reflected light beam diffracted by said one of said two regions of said diffraction element during focusing is located closer to a light-receiving surface of said light detection means, and said other of said diffraction elements. 10. The optical pickup device according to claim 9, wherein a focal position of the reflected light beam diffracted in the two regions is located on a deeper side than a light receiving surface of the light detecting means.