JP3378739B2 - Optical pickup 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 pickup device.

[0002]

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

FIG. 14 shows Japanese Patent Laid-Open No. 3-76035 (G1).
1B 7/135) 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 Publication No. 1B 7/135).

In the figure, 101 is an optical disk, 102 is a semiconductor laser element for outputting a laser beam (light flux) in an upward direction, 1
Reference numeral 03 designates a three-division diffraction grating for splitting the light flux into three light fluxes, and 104 transmits the three light fluxes and diffracts a return light flux (reflected light flux) from the disc 101, and the light flux is in a focused state. , A hologram element (diffraction element) for giving an astigmatism corresponding to, the three light beams 105 transmitted through the hologram element 104 on the disc 101,
A condensing lens (condensing means) for condensing the main spot and three sub-spots located on both sides of the main spot.
Reference numeral 106 denotes a photodetector that detects the diffracted light flux of the return light flux from the optical disc 101 diffracted by the hologram element 104.

FIG. 15 is a schematic top view of a 6-division photodetector which is an example of the photodetector 106.

The photodetector 106 is composed of photodetectors 106a to 106d for detecting the reflected light flux related to the main spot and outputting a focus error signal FES and a reproduction signal by a conventionally known astigmatism method. The split light detection units and the light detection units 106e and 106f positioned on both sides of the four split light detection unit for outputting the tracking error signal TES by the conventionally known three-beam tracking method using the reflected light flux related to the sub-spot. Have.

[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 ).

Further, the tracking error signal TES
Is a difference (S _e −S) between the output signals S _e and S _f of the photodetection units 106e and 106f, which independently detect the reflected light fluxes related to the sub-spots that produce an output signal difference according to the track shift of the main spot. _f ) required.

By the way, the above-mentioned semiconductor laser device 102 is used.
Causes the fluctuation of the oscillation wavelength depending on the element temperature, and the diffraction angle of the diffracted light flux generated when the feedback light flux is diffracted by the hologram element 104 is different due to the fluctuation of the oscillation wavelength. Therefore, FES = (S _a + S _c )-(S
_b + S _d ) may fluctuate.

Therefore, the FES caused by the oscillation wavelength fluctuation
In order to prevent the fluctuation of the above, the four-division photodetector section of the photodetector 106 is divided by a dividing line 106g that is substantially along the direction in which the diffracted light flux 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 converging spot of the diffracted light beam makes the intersection of the dividing line 106g and the dividing line 106h. Since it comes off, there arises a problem that an accurate FES cannot be obtained.

In order to solve this problem, the applicant of the present application divides the photodetection unit for focus servo by the division lines 106g and 106h which are orthogonal to each other.
Instead of the divided light detection unit, a three-divided light detection unit 206 for focus servo, which is divided by parallel division lines as shown in FIG. 16, is adopted. In this case, the light detection unit 20
From the output signals S _{a to} S _{c of} 6a to 206c, FES = (S
_The focus error signal is obtained by calculating _a + S _c ) −S _b .

However, when the photodetector 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 intensity relationship, it is necessary to set the focused spots of the diffracted light flux evenly over the photodetectors 206a and 206c, but this adjustment was difficult.

Therefore, the applicant of the present application further manufactured a pickup device as shown in FIG. 17 and conducted an experiment.

In the figure, 301 is an optical disk, 302 is a semiconductor laser element for outputting a laser beam (light flux) upward, and 3 is a semiconductor laser element.
Reference numeral 03 denotes a three-division diffraction grating for splitting the light flux into three light fluxes (main light flux and a pair of sub-light fluxes located on both sides thereof), and 304 transmits the three light fluxes and the disc 30
A hologram element (diffraction element) for dividing the three return light fluxes (reflected light fluxes) from 1 into two and diffracting them and giving astigmatism corresponding to the focus state to the two light fluxes, 305 is the above A condenser lens 306 for condensing the three light fluxes transmitted through the hologram element 304 onto the disk 301 as three spots of a main spot and sub-spots located on both sides of the main spot, and 306 is diffracted by the hologram element 304. This is a photodetector that detects the diffracted light flux of the return light flux from the disk 301.

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

Further, as shown in FIG. 19, a photodetector 30
Reference numeral 6 denotes photodetection units 316a to 316c that detect the diffracted light flux of the return flux related to the main light flux diffracted in the area 304a.
The photodetector 306a, which is composed of the photodetectors 316d to 316f, which detects the diffracted light flux of the return light flux related to the main light flux diffracted by the area 304b, and the light which is diffracted by the areas 304a and 304b. Photodetector 306 that detects the diffracted light flux of the return light flux relating to one sub-light flux
c, and a photodetector 306d for detecting the diffracted light flux of the return light flux related to the other sub-light flux diffracted by the regions 304a and 304b.

The output signals S _{a to} S _f obtained from the photodetectors 316a to 316f and the photodetectors 306c,
Based on the output signals 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 FES = (S _A −S _B ).

Since the focus error signal FES is thus obtained as described above, even if the focused spot deviates from the center of the photodetecting portions 306a and 306b, the focus error signal FES is calculated to correct it, and the focus error signal is correct. 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 focused spot to a desired track position, as shown in FIG. Although 305 is moved in a direction (disc radial direction) substantially perpendicular to the track direction, at this time, as shown in FIG. 21, the sizes of the passing regions of the reflected light flux in the regions 304a and 304b of the hologram element 304 are different. Becomes

Therefore, as the condenser lens 305 moves in the radial direction, the photodetector 306a and the photodetector 306b are moved.
Since the detected light quantity of the diffracted light flux of the return light flux relating to the main light flux received by and fluctuates, the S curve characteristic when the condenser lens 305 is moved in the radial direction by, for example, 0 μm or ± 400 μm is as shown in FIG. The focus error signal FES cannot be obtained.

The present invention has been made in view of the above problems, and an object of the present invention is to provide an optical pickup device capable of performing preferable focus servo regardless of track position movement and wavelength variation.

[0023]

An optical pickup device of the present invention irradiates a light beam emitted from a light source onto an optical disc through a condensing means, and reflects a light beam reflected from the optical disc to a light detecting means side by a transmission type diffraction. In an optical pickup device in which an element diffracts and the diffracted reflected light beam is detected by the light detecting means, the diffractive element is arranged so as to be orthogonal to a dividing line extending substantially along the track direction of the optical disc. It has four regions divided by a dividing line extending substantially along the radial direction of the optical disc, and two regions at one diagonal position and two regions at the other diagonal position of the four regions are Corresponding to the focus state so that the focus state can be detected by comparing the reflected light beam diffracted by one of the two regions and the reflected light beam diffracted by the other two regions Variation is applied to each of 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. Is provided with at least two light-receiving surfaces divided by a dividing line substantially along the moving direction of the condensed spot of the diffracted reflected light flux for detecting the far-cass state, each light-receiving surface being longer than the moving distance. There are two sets of light detection units for detecting a focus state having a length, the one light detection unit detects a reflected light beam diffracted in two regions at the one diagonal position, and the other light is detected. It is characterized in that the detection unit detects the reflected light beam diffracted in the two regions at the other diagonal position.

A semiconductor laser is preferable as the light source.

Further, one of the two areas at one diagonal position and the other two areas at the other diagonal position out of the four areas are a reflected light beam diffracted by the one two areas and the other two areas. It is preferable that the reflected light beams diffracted by are subjected to spatial fluctuations having a reciprocal relationship with each other in accordance with the focus state.

In the optical pickup device of the present invention, the transmissive diffraction element includes a dividing line extending substantially along the track direction of the optical disc and a dividing line extending substantially along the radial direction of the optical disc so as to be orthogonal to the dividing line. The light-collecting means has four divided areas, and the light-collecting means is set so as to move substantially along the radial direction of the optical disk for tracking, and the one diagonal line detected by the one photodetecting section. 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 photodetection unit, Detect focus error signal. In this configuration, even if the position of the reflected light flux in the transmission diffraction element due to tracking by the light converging means changes, the incident areas of the reflected light flux in the two regions at the one diagonal position and the two diagonal position at the other diagonal position. Since the incident area of the reflected light flux of the area does not change substantially, deterioration of the focus error signal due to the movement of the focusing means due to tracking is suppressed.

In addition, in the optical pickup device of the present invention, the photodetector for detecting the focus state collects the reflected light beam for detecting the focus state diffracted by the transmissive diffraction element due to the wavelength fluctuation of the light source. The light-receiving surface is divided by a dividing line substantially along the moving direction of the spot, and 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 focused spot moves). Therefore, the deterioration of the focus error signal due to the wavelength fluctuation of the light source is suppressed.

As a result, the fluctuation of the wavelength of the light source, the movement of the focusing means, and the deterioration of the focus error signal due to 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 transmissive diffraction element is
It is characterized in that the transmissive diffraction element is substantially symmetrical with respect to a parting line extending substantially along the radial direction of the optical disc.

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

In particular, the radial direction of the optical disk and the moving direction of the focused spot due to the wavelength fluctuation 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 held, and The reflected light flux diffracted in the two areas at the diagonal position is detected by the one photodetection unit of the photodetection means, and the reflected light flux diffracted in the two areas at the other diagonal position is detected by the other light. Since it is detected by the department,
As a result, deterioration of the focus error signal is suppressed.

Further, the radial direction of the optical disk and the moving direction of the focused spot due to the wavelength fluctuation of the light source may be substantially orthogonal to each other.

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

In particular, the at least two light receiving surfaces are characterized in that they have a narrow light receiving surface and light receiving surfaces wider than the light receiving surface on both sides thereof.

In this case, the opposing points of the converging spots formed by the reflected light beams diffracted in the two diagonal positions may be located within the narrow light receiving surface, which is relatively easy. Can be set to, and by adding the detection signals from the wide light-receiving surfaces on both sides of each photodetection section and comparing the differences, the reception of the reflected light flux diffracted in the two regions at the one diagonal position can be received. It is possible to compare the difference between the area and the light receiving area of the reflected light beam diffracted in the two regions of the other diagonal position detected by the other photodetector.
In addition, the signal from this narrow light receiving surface is used when obtaining the reproduction signal, that is, the sum of the detection signals of the narrow light receiving surfaces of the two detectors and the light receiving surfaces on both sides thereof is used. As a result, the intensity of the reproduction signal is increased, so that a good reproduction signal can be obtained.

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

Further, a three-division diffraction grating for generating a main light beam and a sub-light beam for tracking servo located on both sides of the light beam emitted from the light source is provided in the optical path between the light source and the transmissive diffraction element. And, the light detection means,
The reflected light flux from the optical disc relating to the main light flux diffracted by the transmissive diffraction element is detected by the two photodetection sections, and the reflection from the optical disc relating to each sub-light flux diffracted by the transmissive diffraction element In order to detect each of the light fluxes, a pair of photodetector units for detecting a tracking state having light receiving surfaces having a length longer than the moving distance on both sides so as to sandwich the two photodetector units are provided. To do.

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

In particular, the spatial variation is characterized by astigmatism.

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

Further, the two regions of the one side of the diffractive element and the two regions of the other side of the diffractive element impart astigmatism in a mutually orthogonal relationship.
It should be noted that one of the orthogonal directions is preferably substantially parallel to the dividing line of the two sets of photodetection units of the photodetection means.

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

[0044]

[0045]

[0046]

[0047]

[0048]

BEST MODE FOR CARRYING OUT THE INVENTION An optical pickup device according to a first embodiment of the present invention for performing focus servo by an astigmatism method and tracking servo by a three-beam method will be described with reference to the schematic configuration diagram of FIG.

In the figure, 1 is a reflection type optical disc such as a CD (compact disc), and 2 is 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 transmissive three-division diffraction grating made of optical glass, optical resin, or the like that divides the light beam into three light beams. In addition, in the figure, the above three light beams are represented by one light beam.

Reference numeral 4 denotes the above-mentioned 3 which is emitted from the diffraction grating 3 for three divisions.
Light fluxes M, S ₁ , S ₂ of the book are incident, and the respective reflected light fluxes (returned light fluxes) M from the optical disc 1 relating to the three light fluxes,
S ₁ and S ₂ are divided into four, and the divided light beams are separated as first-order diffracting means so as to give a spatial variation (in this embodiment, astigmatism) corresponding to the focus state on the optical disc 1. It is a transmission hologram element (transmission diffraction element).

As shown in the schematic top view of FIG.
The hologram element 4 moves in the track direction (trajectory) of the optical disc 1.
Phantom extending substantially parallel to the vertical direction (Y direction)
Of the dividing line 4l of the optical disc
Virtual that extends substantially along the radial direction (X direction) of the disk 1.
By the dividing line 4m of the four areas 4a, 4b, 4
It has a hologram surface divided into c and 4d. Note that the figure
Medium three luminous flux M, S ₁, S₂Light spot M by
S₁, S₂Indicates.

The dividing line 4l and the dividing line 4m
4a located symmetrically (diagonal position) with respect to the intersection of
And area 4c (mesh hatching in the figure), area 4b and area 4d (hatched area in the figure) have the same hologram surface pattern (diffraction surface pattern).
The areas a and 4c, and the areas 4b and 4d give spatial diffractive inverse relations (in this embodiment, astigmatisms orthogonal to each other) to the diffracted light flux.

Numeral 5 is supported substantially along the radial direction (X direction) of the optical disk 1 for tracking servo, and is vertically drivable (Z direction) for focus servo. It is a condensing lens (condensing means) for condensing the above-mentioned three light beams M, S ₁ , and S ₂ diffracted and transmitted by the optical disc 1 into respective condensing spots M, S ₁ , and S ₂ .

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

Reference numeral 6 denotes the above three light fluxes M which are transmitted and diffracted by the transmission hologram element 4 in the first order through the condenser lens 5.
It is a photodetector (photodetection means) for detecting each reflected light flux from the optical disc 1 corresponding to S ₁ and S ₂ , and as shown in the schematic top view of FIG. A pair of photodetection units 6 for focus servo, which are arranged side by side on a straight line substantially along the extending direction (radial direction).
a and the photodetector 6b, and the photodetector 6a and the photodetector 6b
And a pair of photodetection sections 6c and 6d for tracking servo that extend substantially parallel to the direction in which the dividing line 4m extends so as to face each other.

The photodetecting portions 6a are rectangular photodetecting portions 16a, 16 extending substantially parallel to the radial direction.
b and 16c, which have the same width,
This is a configuration in which the narrow photodetection section 16b is arranged between 16c. The photodetector 6b has the same configuration as the photodetector 6a, and is composed of rectangular photodetectors 16d, 16e, and 16f extending substantially parallel to the radial direction, and having the same width. In this configuration, the narrow photodetector 16e is arranged between 16d and 16f.

In the present embodiment, the photodetectors 6a and 6b are used.
Each of the hologram elements 4 depends on the wavelength variation of the light source 1.
The photodetection units 16a to 16c and the photodetection unit 16 which are divided by dividing lines (virtual dividing lines) along the moving direction of the focused spot in the light detecting unit 6 of the reflected light beam diffracted by
The lengths of the rectangular photodetectors (light receiving surfaces) 6c, 6d, 16a to 16f in the longitudinal direction are configured by the hologram element 4 depending on the wavelength variation of the light source 1.
It is set to be longer than the moving length of each converging spot in each photodetector that receives the reflected light beam diffracted by.

In such an optical pickup device, the optical system is set so that the condenser lens 5 enters the transmissive hologram element 4 so that the center of the reflected light beam M is substantially positioned on the dividing line 4m for tracking. And areas 4a, 4c
The reflected light beam M incident on the light is transmitted and diffracted by the first order in the regions 4a and 4c so as to be received by the photodetector 6a, and the region 4b,
The reflected light beam M that has entered the 4d is transmitted and diffracted in the first order in the regions 4b and 4d so that it is received by the photodetection section 6b.

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

The reflected light beam M is divided and diffracted by the areas 4a to 4d of the hologram element 4. Then, the reflected light beam M first-order diffracted by the area 4a and the reflected light beam M first-order diffracted by the area 4c are respectively focused spots P on the photodetector 6a.
_a and _a focused spot P _c , and the area 4
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 beam S ₁ and the reflected light beam S ₂ are also divided and diffracted by the areas 4a to 4d of the hologram element 4. Then, the reflected light beam S ₁ which is first-order diffracted in the region 4a and the region 4
reflected light beams S ₁ which is the first-order diffraction at c, 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, the primary diffracted by 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
The light is focused on the side as a focused spot Q _b and a focused spot Q _d . 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 photodetector 6 when the optical disk 1 approaches the condenser lens 5 and a focus error occurs.
The schematic top view showing the condensed state above is shown.

In this case, the condensing spot P _a and the condensing spot P _{c on the} photodetector 6a have a shape extending in the direction orthogonal to the diffraction direction, and the condensing spot P _b and the condensing spot P _b on the photodetector 6b are formed. The focused spot P _d has a shape extending in the diffraction direction.

FIG. 7 shows a photodetector 6 when the optical disk 1 is separated from the condenser lens 5 and a focus error occurs.
The schematic top view showing the condensing spot on the above is shown.

In this case, the condensing spot P _a and the condensing spot P _{c on the} photodetector 6a have a shape extending in the diffraction direction, and the condensing spot P _b and the condensing spot P on the photodetector 6b are formed. _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 of hologram element 4
a light detection unit 6a for detecting the reflected light flux M from a and 4c;
Region 4 located on one diagonal of hologram element 4
It is obtained by using the light detection unit 6b that detects the reflected light flux M from b and 4d.

That is, by 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 calculated.

Here, in the case of the focus state (FIG. 5),
Focusing spots P _b and P _{d are} compared with the focusing spots P _a and P _c .
Has a shape extending in the diffraction direction because it is located away from the hologram element 4, but the light amounts of the condensing spots P _{a to} P _d are equal and the directions orthogonal to the diffraction direction are condensed on the same scale. To be done. Therefore, FES = 0.

When the optical disc 1 approaches the condenser lens 5 and a focus error occurs, FES> 0, as shown in FIG. 6, and conversely, the optical disc 1 moves away from the condenser lens 5 and the focus error occurs. In the case of 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
+ S _c + S _d + S _e + S _f ).

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

In this optical pickup device, the hologram surface of the hologram element 4 is defined by the dividing line 4l substantially along the track direction of the optical disc 1 and the dividing line 4m along the radial direction of the optical disc 1 (direction orthogonal to the track direction). It is divided into four parts 4a to 4d. The tracking operation of the condenser lens 5 is carried out along a radial direction substantially included in a surface 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 photodetecting section 6a and the photodetecting section 6b of the photodetector 6 are in the mutually diagonally-divided positional relations among the regions 4a to 4d divided by the dividing line 4l and the dividing line 4m. 4a, 4c and regions 4b, 4d
The reflected light fluxes M from are respectively detected.

In addition, the photodetectors 6a and 6b of the photodetector 6
Is composed of photodetector sections (light-receiving surfaces) 16a to 16c and 16d to 16f which are divided into three substantially along the radial direction, and each photodetector section (light-receiving surface) 16a to 16f extends substantially parallel to the radial direction. Direction, and the light detection portions (light-receiving surfaces) 6c and 6d are also upper surface rectangles whose longitudinal direction is substantially parallel to the radial direction.

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

Moreover, the photodetectors 6a and 6b of the photodetector 6
Is the hologram element 4 due to the wavelength variation of the semiconductor laser 2.
The reflected light beam (diffracted light) diffracted by is divided by a dividing line substantially along the moving direction, and since the upper surface rectangle has a longitudinal direction substantially parallel to the moving direction, It is possible to prevent the FES signal from deteriorating. Further, since the photodetection portions 6c and 6d are also rectangular in the upper surface with the longitudinal direction being substantially parallel to the moving direction,
It is possible to prevent the TES signal from deteriorating due to the wavelength variation.

In addition, the reflected light beam M from the transmissive diffraction element 4
Since the shape of the light spot is substantially symmetrical with respect to the dividing line 4m of the transmissive diffraction element 4 extending substantially along the radial direction of the optical disc 1, even if the focusing lens is moved by tracking, Two areas 4 on the diagonal of
Since the incident areas of the reflected luminous fluxes of a and 4c and the incident areas of the reflected luminous fluxes of the other two diagonal positions 4b and 4d become more equal, deterioration of the focus error signal is further suppressed.

In particular, since the radial direction of the optical disc 1 and the moving direction of the focused spot due to the wavelength fluctuation of the light source 2 are substantially parallel to each other, the reflected light fluxes of the two regions 4a and 4c at the one diagonal position. Of the reflected light fluxes of the two diagonal regions 4b and 4d at the other diagonal position, the reflected light fluxes diffracted by the two regions 4a and 4c of the one diagonal position are maintained. The light is detected by the light detection unit 6a, and at the other diagonal position 2
The reflected light beams diffracted by the two regions 4b and 4d are detected by the light detection unit 6
It can be detected by b. Therefore, 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 in accordance with the focus state, but various methods can be appropriately changed.

FIG. 9 is a schematic configuration diagram of an optical pickup device according to a reference embodiment of the present invention. The present reference embodiment is the same as the first embodiment except that the reflected light beam diffracted by the hologram element (diffraction element) 14 is not provided with astigmatism, and therefore the same reference numerals are given and the description thereof is omitted. .

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 disc 1.
4l is orthogonal to the dividing line 14l, that is, the optical disc 1
The four regions 14a, 14b, 14c, 14 having the same area by the virtual dividing line 14m extending substantially along the radial direction of
It is divided into d. In the figure, three light fluxes M,
Light spot M by S _1, S _2, showing the S _1, S _2.

The dividing line 14l and the dividing line 1
The regions 14a and 14c, and the regions 14b and 14d, which are symmetrically located with respect to the intersection point of 4m, have the same hologram plane pattern (diffraction plane pattern).
4a and the area 14c, and the area 14b and the area 14d give the diffracted light beam a spatial variation having an inverse relationship (reciprocal relationship) with each other when not in focus.

[0084] The present in the reference form, the other of the two regions 14 of the focal position and the hologram element 14 of one of the two regions 14a, reflected light flux is diffracted by 14c 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 focused state, as shown in FIG. 9, the reflected light beams diffracted by the regions 14a and 14c are located on the front side of the detection portions 6a, 6c, 6d of the photodetection means 6 as the focal position. , 14b and the reflected light beams diffracted by the region 14d, the detection portions 6b of the light detection means 6,
The focal points are located on the inner sides of 6c and 6d, and a focused spot on the photodetector 6 similar to that in FIG. 5 is obtained.

Here, the reflected light beam M first-order diffracted by the area 14a and the reflected light beam M first-order diffracted by the area 14c are:
Each while being condensed as the condensed spot P _a and converged spot P _c on the optical detection unit 6a, the first-order diffraction reflected light beam M in the primary diffracted reflected light beam M and the region 14d in the region 14b, the It is condensed as the condensed spot P _b and condensing spot P _d each photodetecting section on 6a.

Then, the reflected light beam S ₁ which is first-order diffracted by the area 14a and the reflected light beam S which is first-order diffracted by the area 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 The first-order diffracted reflected light beam S ₁ is condensed as a condensed spot Q _b and a condensed spot Q _d on the photodetector 6 b side of the photodetector 6 c, respectively. 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.

Further, when the optical disc 1 approaches the condenser lens 5 and a focus error occurs, as shown in FIG. 11, the condensed spot P _a and the condensed spot P _{c on the} photodetector 6a are small, light detection unit 6b focused spots P _b and the condensing spot P _d increases. Conversely, optical disc 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 The spot P _b and the focused spot P _{d become} smaller.

Also in this reference 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 ),
In addition, 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.

With this optical pickup device, the same effect as that of the first embodiment can be obtained.

Further, in each of the above-mentioned embodiments , the photo-detecting sections 6a and 6b of the photo-detecting means 6 are arranged in series substantially in the radial direction of the optical disc 1, but as shown in FIG. 6b may be arranged substantially along the radial direction, and the photodetectors 6a and 6b may be arranged in parallel with each other. In this case, the light detectors 6a and 6b are divided into light receiving surfaces 16a to 16 by dividing lines substantially along the track direction.
c, 16d to 16f.

When such a light detecting means is used, each type
In comparison with the optical pickup device used in the state , the light detection unit 6
This is preferable because the hologram elements 4 and 14 can be easily rotated when the optical axis is adjusted so that the condensed spots of the reflected light flux are located on a and 6b.

In this case, the area 4a of the hologram element 4
4d, each hologram surface pattern of the regions 14a to 14d of the hologram element 14 is, 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 focused spot due to the wavelength fluctuation of the light source 2 are in a relationship of being substantially orthogonal to each other. Areas 4a, 4c (14
a, 14c) and an area of the incident area of the reflected light flux of the other diagonal positions of the two areas 4b, 4d (14b, 14d) of the other diagonal position, the ratio of the area of the two diagonal positions of the two areas 4b, 4d (14b, 14d) is substantially maintained. Areas 4a, 4c (14a, 14c)
The reflected light beam diffracted by is detected by the photodetector 6a, and at the same time, the two regions 4b, 4d (1
Since the reflected light beam diffracted by 4b and 14d) is detected by the photodetection section 6b, deterioration of the focus error signal is further suppressed.

In each of the above embodiments, the hologram element 4,
Although the photo-detecting means 6 is arranged along the 14 dividing lines 4m, 14m or 41, 141, the effect can be obtained by arranging the dividing lines at an angle. However, in this case, the focus error signal is deteriorated as compared with the above-described embodiment.

In the above description, the optical pickup device using the transmission type three-division diffraction grating has been described, but it is of course applicable to the optical pickup device using the reflection-type three-division diffraction grating. Of course, a reflecting means such as a mirror may be interposed between the light source and the information recording medium to refract the optical path.

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.

Further, as the tracking servo method, methods other than the above three-beam method can be appropriately used.

Further, the photodetectors 6a and 6b each have 3
Although the light-receiving surface is divided into two light-receiving surfaces, a structure in which the light-receiving surface is divided into two light-receiving surfaces is also possible.

[0100]

According to the present invention, it is possible to suppress 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.

[Brief description of 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] Track of optical disc and focused spots M, S
It is a principal part schematic diagram which shows the relationship of 1 and S2.

FIG. 4 is a schematic schematic top view of a light detection unit used in the first embodiment.

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

FIG. 6 is a schematic top view showing a 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 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 collecting means moves in the first embodiment.

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

FIG. 10 is a schematic top view of a hologram element used in the reference mode.

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

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

FIG. 13 is a schematic schematic top view of another light detecting means.

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

FIG. 15 is a schematic top view of the above-described conventional photodetector.

FIG. 16 is a schematic top view of a photodetector of another conventional photodetector.

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 the other conventional example.

FIG. 19 is a schematic top view of a photo-detecting portion of another conventional photo-detecting means.

FIG. 20 is a schematic configuration diagram of an optical pickup device in the case where the light converging means is moved in another conventional example.

FIG. 21 is a schematic top view showing the relationship between reflected light beams M, S1, and S2 in the hologram element used in the other conventional example.

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

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shoken Goto 2-5-5 Keihan Hondori, Moriguchi City, Osaka Sanyo Electric Co., Ltd. (56) Reference JP-A-3-86930 (JP, A) Kaihei 7-129980 (JP, A) JP 3-62327 (JP, A) JP 8-77578 (JP, A) JP 2-265038 (JP, A) JP 5-101417 ( JP, A) JP 4-238121 (JP, A) JP 8-22624 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) G11B ^7/ 09-7/22

Claims (7)

(57) [Claims] 1. A light beam emitted from a light source is irradiated onto an optical disc through a converging means, a reflected light beam from the optical disc is diffracted toward a light detecting means side by a transmissive diffraction element, and the diffracted reflected light beam is In the optical pickup device for detecting 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. Has four regions divided by, and two regions at one diagonal position and two regions at the other diagonal position of the four regions are the reflected light beam diffracted by the one two regions. respectively given astigmatism corresponding to the focus state as a focus state by comparing the reflected beam diffracted by the two areas can be detected in the other one of the respective reflected light beams, the current The means is set so as to move substantially along the radial direction of the optical disk for tracking, and the photodetector means detects the diffracted reflected light flux for focus state detection due to wavelength fluctuation of the light source. A light detection unit for detecting a focus state, comprising at least two light receiving surfaces divided by a dividing line substantially along the moving direction of the focused spot, each light receiving surface having a length longer than the moving distance. There are two sets, and the one photodetector detects the reflected light flux diffracted in the two regions at the one diagonal position, and the other photodetector diffracts in the two regions at the other diagonal position. An optical pickup device characterized by detecting the reflected light flux reflected. 2. The shape of the light spot of the reflected light flux for detecting the focus state in the transmissive diffraction element is substantially the same as a division line of the transmissive diffraction element extending substantially along the radial direction of the optical disc. The optical pickup device according to claim 1, wherein the optical pickup device is symmetrical. 3. The optical pickup device according to claim 1, wherein a radial direction of the optical disk and a moving direction of the focused spot due to a wavelength variation of the light source are substantially parallel to each other. 4. The radial direction of the optical disk and the moving direction of the focused spot due to the wavelength fluctuation of the light source are in a relationship substantially orthogonal to each other.
The optical pickup device described. 5. The light receiving surface having a narrow width and the light receiving surfaces wider than the light receiving surface on both sides of the at least two light receiving surfaces. Optical pickup device. 6. A three-division diffraction grating for generating a main light beam and sub-light beams for tracking servo positioned on both sides of the light beam emitted from the light source is provided in an optical path between the light source and the transmissive diffraction element. And the light detecting means detects the reflected light flux from the optical disc related to the main light flux diffracted by the transmissive diffraction element by the two photodetection sections, and the light diffracted by the transmissive diffraction element. A set of light for detecting a tracking state, which has light-receiving surfaces having a length longer than the moving distance on both sides so as to sandwich the two photodetector portions, in order to detect the reflected light fluxes from the optical disc related to the sub-light fluxes. A detection unit is provided, Claims 1, 2, 3,
4. The optical pickup device as described in 4 or 5. 7. The two regions of the one side of the diffractive element
And the other two regions of the diffractive element are directly
7. The optical pickup device according to claim 1 , wherein astigmatism in a cross relation is applied .