JPH0950646A - Optical information recording and reproducing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a multipurpose optical information recording and reproducing device capable of performing a more constant recording and reproducing by making intervals among projection spots of a 0-order diffracted luminous flux and ±1-st order diffracted luminous fluxes on an photodetector almost equal. SOLUTION: This reproducing device is made to transmit plural reflected luminous fluxes from an optical information recording medium through an anamorphic optical system consisting of a spherical lens and a cylindrical lens and guides them to a photodetector having plural light receiving parts. At this time, the axis (the direction in which a lens has not a lens action) of the cylindrical lens is arranged so as to almost coincide with respect to the straight line connecting either one pair of the ±1-th order diffracted luminous fluxes among plural diffracted luminous fluxes diffracted by a diffraction grating. Then, at least one light receiving part among plural light receiving parts is a quadripartite photodetector C1 consisting of four light receiving surfaces symmetrically arranged with respect to axes orthogonally crossed each other and the photodetector is arranged so that the angle θ formed by the one side axis of the axes orthogonally crossed each other and the straight line becomes 0 dgree<θ<45degrees or 45 degrees<θ<90 dgrees.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention irradiates an optical information recording medium having a plurality of tracking tracks and a plurality of information tracks with a plurality of light fluxes, receives reflected light from the light fluxes with a photodetector, and The present invention relates to an optical information recording / reproducing apparatus that records and / or reproduces information.

[0002]

2. Description of the Related Art Heretofore, various types of information recording media for recording and reproducing information using light have been known, such as a disc, a card and a tape. Some of these optical information recording media are recordable and reproducible, and only reproducible. Information is recorded on a recordable medium in the form of an information bit string that is optically detectable when an information track is scanned by a light beam that is modulated according to the record information and is focused into a minute spot.
Done.

Further, in reproducing information from a recording medium, an information bit string of an information track is scanned by a light beam spot having a constant power such that recording is not performed on the recording medium (no information bit string is generated). Then, the reflected light or transmitted light from the recording medium is detected.

The optical head used for recording / reproducing information on / from the recording medium is configured to be relatively movable with respect to the recording medium in the information track direction and in the direction traversing the direction. By this movement, the information track scanning of the light beam spot is performed. As the lens for narrowing the light beam spot in the optical head, for example, an objective lens is used. This objective lens can move independently in its optical axis direction (focusing direction) and in a direction (tracking direction) orthogonal to both the optical axis direction and the information track direction of the recording medium. In this state, it is held by the optical head body. The holding of such an objective lens is generally performed via an elastic member,
The movement of the objective lens in the above two directions is generally performed by driving an actuator utilizing magnetic interaction.

As an optical information recording / reproducing apparatus of this kind, an optical system as shown in FIG. 5 or 10 is known.
Here, a large number of information tracks 2 are arranged on the information recording surface of the optical card 1 in parallel with the LF direction. The information track 2 is provided on the information recording surface of the optical card 1.
There is provided a home position 3 serving as a reference position for access to. The information tracks 2 are, for example, reference numerals 2-1, 2-2, 2-in order from the side closer to the home position 3.
, Are arranged, and as shown in FIG. 11, adjacent to each of these information tracks, the tracking tracks 4 are sequentially labeled as 4-1, 4-2, 4-3 ,. Is provided. These tracking tracks 4
Is an auto-tracking (hereinafter referred to as AT) that controls the light beam spot scanning during information recording / reproduction so that the beam spot does not deviate from a predetermined information track.
Serves as a guide for.

The AT servo detects a deviation (AT error) of the light beam spot from the information track in the optical head, negatively feeds back the detection signal to the tracking actuator, and Move the objective lens in the tracking direction (D direction),
This is done by causing the light beam spot to follow the desired information track.

Further, at the time of recording / reproducing information, when scanning an information track with a light beam spot, the light beam
On the surface of the optical card, in order to form (focus) a spot with an appropriate size, auto focusing (hereinafter,
Servo is performed. This AF servo
In the optical head, a deviation (AF error) from the focused state of the light beam spot is detected, the detection signal is negatively fed back to the focusing actuator, and the objective lens is moved in the focusing direction with respect to the optical head body. Then, the light beam spot is focused on the surface of the optical card.

In FIG. 11, S1, S2, S
Reference numerals 3, S4, S5, S6, and S7 denote light spots on the optical card. The light spot S1 is used to create information bits during AF and recording, read information bits during reproduction, and to generate light spots S2. AT is performed by S3, information bits are verified by the light spots S4 and S5 almost at the same time as recording at the time of recording, and information bits at the time of reproduction are read by the light spots S6 and S7.

In the figure, reference numerals 5-1 and 5-2 are data portions (information bits). In addition, FIG.
21 is a semiconductor laser as a light source, and in this example, it is polarized in a direction perpendicular to the track.
It emits light with a wavelength of 30 nm. Reference numeral 22 is a collimator lens, 23 is a beam shaping prism, 24 is an aperture, 25 is a diffraction grating for splitting a light beam, 25 'is a diffraction grating portion, and 26 is a polarization beam splitter. Further, reference numeral 27 is a quarter wavelength plate, 28 is an objective lens, 29 is a spherical lens, 30 is a cylindrical lens, and 31 is a photodetector.

The light beam emitted from the semiconductor laser 21 becomes an elliptical divergent light beam and enters the collimator lens 22. Then, a parallel light beam is formed by the lens, and is further shaped into a circular beam by the beam shaping prism 23. The intensity of light emitted from the semiconductor laser 21 has a Gaussian distribution and propagates while maintaining the Gaussian distribution state.

Thereafter, in order to obtain a predetermined recording light spot, the light beam is restricted by the aperture 24 and the diffraction grating 25
Incident on. As shown in FIG. 12, the diffraction grating has three grating portions 25a, 25b,
The light beams are divided into 25c, and the light beams diffracted by the respective grating portions are different in the diffraction angle and the diffraction direction of the respective grating portions so as to satisfy the respective purposes. The diffraction grating 25b generates ± 1st-order diffracted light fluxes for performing AT, the diffraction grating 25a generates ± 1st-order diffracted light fluxes for performing verification, and the diffraction grating 25c ± 1st order for reproduction. Generates a second-order diffracted light beam.

The 0th-order diffracted light beam is emitted from the diffraction grating 25 with a light beam diameter limited by the aperture 24. Each of the other ± 1st-order diffracted light beams is emitted from the diffraction grating 25 in the area and shape in which the light beam limited by the aperture 24 is diffracted by each diffraction grating. The seven light beams divided by the diffraction grating 25 enter the polarization beam splitter 26 as P-polarized light beams and are transmitted therethrough.

Next, the seven light beams are converted into circularly polarized light when passing through the quarter-wave plate 27, and the objective lens 28
Is focused on the optical card 1. FIG. 13 (a)
2B and 2B show the shape and positional relationship of each light beam when it exits the objective lens. Although the number of light beams emitted from the objective lens is seven, in order to make it easier to understand the positional relationship with the 0th-order diffracted light beam and the respective shapes, in FIG. Two verifying luminous fluxes e
4 and e5 and two reproduction light beams e6 and e7 are shown, and in FIG. 13B, a 0th-order diffracted light beam el and two AT light beams e2 and e3 are shown.

Of the seven light spots focused on the optical card 1, S1 is used for recording, reproduction and AF control, and S2 is used.
And S3 are used for AT control, S4 and S5 are used for verification, and S6 and S7 are used for reproduction. As for each spot position on the optical card 1, as shown in FIG. 11, the optical spots S2 and S3 are located on the adjacent tracking tracks 4, and the optical spot S1 is on the information track 2 between the tracking tracks. Position to,
The light spots S4 and S5 are in the same information track as the light spot S1 and are located so as to sandwich the light spot S1 in the information track direction. Also, the light spots S6 and S
7 are separately located on the information tracks on both sides of the information track of the light spot S1, and are light spots S1, S6, S7,
Three information tracks can be played simultaneously.

Thus, the reflected light from each light spot formed on the optical card 1 again passes through the objective lens 28, becomes a parallel light flux, and passes through the quarter-wave plate 27, so that it becomes incident. Is converted into a light beam whose polarization direction is rotated by 90 °. Then, in the polarization beam splitter 26, S
It enters as a polarized light beam and is reflected to the spherical lens 29 side, and each reflected light beam is a spherical lens 2 which is a detection optical system.
After passing through the lens 9 and the cylindrical lens 30, the light enters the photodetector 31.

Incidentally, here, the cylindrical lens 3 is used.
0 is arranged so that its generatrix (direction not having a lens action) substantially coincides with the information track direction A (see FIG. 5).
(See FIG. 10), or it is arranged so as to be perpendicular to the information track direction (see FIG. 10), and is further arranged so as to be inclined by 45 degrees with respect to the information track direction.

FIG. 6 shows the incident state of each diffracted light beam at the position of the cylindrical lens 30, and as shown in FIG. 5, the generatrix direction of the cylindrical lens 30 substantially coincides with the track direction A. 10 shows a case where they are arranged, and a case where they are arranged so that the generatrix direction B of the cylindrical lens 30 is perpendicular to the track direction A as shown in FIG. Further, FIG. 14 shows a case in which the generatrix direction B of the cylindrical lens 30 is inclined by 45 degrees with respect to the track direction A.

In the figure, b1 is a 0th-order diffracted light beam for reproduction and AF control, b2 and b3 are AT light beams, b4 and b5 are verification light beams, and b6 and b7 are reproduction light beams.

FIGS. 7 and 15 show a four-division photodetector C having four light receiving surfaces for performing AF control and reproduction.
1 and a projected image of the 0th-order diffracted light beam incident thereon are shown. Dividing lines f orthogonal to each other of the four-division photodetector C1
Is arranged at a position of 45 degrees with respect to the generatrix direction A or B of the cylindrical lens 30 in order to perform AF by the astigmatism method. The dotted circle (minimum circle of confusion) in the figure is the projected image of the focused spot on the optical card, and the solid ellipse is the defocused state (one side of the optical card is more focused than the focused point of the objective lens). It is a projected image in the state of approaching and the other being far away).

FIG. 9 and FIG. 16 show a plurality of light receiving portions of the photodetector 31, the respective luminous fluxes incident thereon, and the signal processing system. In the figure, using the difference signal obtained by subtracting the sum of the respective outputs of the photodetectors C1a and C1c and C1b and C1d of the four-division photodetector C1 arranged in the direction of crossing each other, the above-mentioned AF Control is performed, and reproduction is performed using the sum signal of the outputs of the four photodetectors. Also, the photodetectors C2 and C
AT control (three-beam method) is performed by taking the difference between the outputs of 3 and the outputs of the photodetectors C4 and C5 are used to perform verification, and further, the outputs of the photodetectors C6 and C7 are used. Replay each. As described above, information is recorded / reproduced by moving a plurality of light spots emitted from the optical head relative to the recording medium.

[0021]

However, the conventional examples shown in FIGS. 5 to 13 have the following problems. That is, as shown in FIG. 5, the AF control is performed 4
Dividing lines f of the divided photodetector C1 which are orthogonal to each other are arranged at 45 degrees with respect to the information track direction and the generatrix direction of the cylindrical lens 30. As mentioned above, AT
When the control or movement to another information track is performed by moving the objective lens, the objective lens is aligned with the information track direction A or orthogonal to this direction, and the generatrix direction A (Fig. (See (a) of 6)
Alternatively, it moves to B (see (b) of FIG. 6), which causes the light beam to shift in the generatrix direction.

The behavior of the projected image of the 4-division photodetector C1 when the luminous flux is shifted will be described with reference to FIGS. 8 (a) and 8 (b). When the irradiation spot on the optical card is in focus, the projected image of the light flux on the four-division photodetector C1 is as shown in FIG.
(A) is a circle of least confusion (defocused state) indicated by a dotted circle. This projection image moves to the position of the solid circle in FIG. 8A due to the light beam shift accompanying the movement operation of the objective lens.

In the AF control using the astigmatism method, the outputs from the four light-receiving surfaces of the four-division photodetector C1 are summed with the outputs of the detectors arranged in the direction of crossing each other. The position of the objective lens is controlled so that the difference signal of the two output sums becomes zero. Since the difference signal is not 0 at the solid line circle position in FIG. 8A, the objective lens is moved from the in-focus position so that the difference signal becomes 0. The projected image on the 4-division photodetector C1 at that time is shown in FIG.
As shown in (b) of FIG. The irradiation spot on the optical card in this case is in a defocused state. That is, an offset occurs in AF.

Further, even when a relative inclination between the optical card and the incident light flux occurs due to the warp of the optical card or the inclination of the holder for holding the optical card, the light flux shifts and the light is divided into four. The projected image on the photodetector C1 moves. As described above, the shape of the optical card is rectangular, and when mounting the optical card on the holder, it is preferable to feed the edge in the longitudinal direction of the card along the feed guide because of the good placement accuracy. At this time, the warp of the card in the longitudinal direction is corrected by the feed guide, but the warp in the lateral direction is not corrected.

The short side direction of this optical card is as shown in FIG.
8A, the projected image on the 4-division photodetector is shown in FIG. 8A due to the shift of the light flux due to the warp of the optical card.
In the same manner as when the objective lens is moved, the objective lens is moved in the AF direction, resulting in the AF offset.

The amount of inclination of the holder is a design tolerance, and it is more difficult to obtain minute accuracy in the lateral direction than in the longitudinal direction, so that the inclination tends to occur in the Q direction of FIG. 8A. In any case, the movement of the projected image on the four-division photodetector C1 is concentrated in the Q direction of FIG.

The AF offset amount is maximized by moving the projected image when the projected image is moved in the Q direction and the A direction, that is, in the direction of 45 degrees with respect to the dividing line f. . In short, it can be said that in the conventional example, the AF offset is most likely to occur due to the movement of the projected image in the Q direction.

This AF offset causes blurring of information pits during recording, which causes signal deterioration during reproduction. Further, even if the information pit is normally recorded, if the AF offset occurs during reproduction, the signal similarly deteriorates. Furthermore, when external vibration is added, depending on the magnitude of the external vibration, the worst situation in which recording and reproduction cannot be performed is caused.

As described above, this conventional example has a problem that an offset is generated in the AF due to the movement of the objective lens and the relative inclination between the optical card and the light flux, which causes deterioration of the information signal during recording and reproduction. is there.

Further, the conventional example (see FIGS. 14 to 18) in which the cylindrical lens 30 is inclined by 45 degrees has the following problems. That is, as shown in FIG. 15, the generatrix B of the cylindrical lens 30 is arranged at 45 degrees with respect to the information track direction A. In the figure, b1 to b7 are incident light beams, of which the verifying light beams b4 and b5 are incident at positions asymmetric with respect to the generatrix B. Similarly, the reproduction light beams b6 and b7 also enter asymmetrically with respect to the generatrix. Each light beam emitted from the cylindrical lens 30 is projected as a circle of least confusion on the photodetector 31 when the light spot is focused on the optical card.

Further, in FIG. 15, the cylindrical lens 3 at the position of the line M containing the two verify light fluxes.
0 cross section, verifying light beams b4 and b5, and reproducing light beam b
1 is shown in FIG. Similarly, the cylindrical lens 30 at the position of the line A indicating the information track direction
18B shows the AT luminous fluxes b2, b3 and the reproducing luminous flux b1 as seen in the section of FIG. 18, and the sectional view of the cylindrical lens 30 at the position of the line N and the reproducing luminous fluxes b6, b7, b.
1 is shown in (c) of FIG.

By the way, of the seven luminous fluxes incident on the cylindrical lens 30, the reproduction 0 shown by the dotted line in the figure is used.
Since the diffraction angle of the second-order diffracted light beam b1 is 0 degree, it enters the cylindrical lens 30 almost perpendicularly to the lens center and enters the center of the four-division photodetector C1 in FIG. Then, as shown in (b) of FIG. 18, the two AT light beams b2 and b3 enter the cylindrical lens 30 at different diffraction directions but with the same amount of diffraction angle θ1 with respect to the 0th-order diffracted light beam. Moreover, since the cylindrical lens 30 is point-symmetric with respect to the 0th-order diffracted light flux, that is, is equidistant from the generatrix of the cylindrical lens 30, the lens functions of the cylindrical lens 30 are equal, and the 0th-order diffracted light flux on the photodetector 31 is the same. Interval h1 between projection spots of + 1st-order diffracted light flux for AT
Is equal to the interval h2 between the projection spots of the 0th-order diffracted light beam and the AT-first-order diffracted light beam.

However, as shown in FIG. 18 (a), the two verifying light beams have the same angle of diffraction θ2 with respect to the 0th-order diffracted light beam, but have a point with respect to the 0th-order diffracted light beam. It is not symmetrical, and as shown in FIG. 15, it does not enter at positions equidistant from the generatrix of the cylindrical lens 30. These light fluxes have an image height with respect to the cylindrical lens 30, and the cylindrical lens 30
Due to the effect of the unidirectional lens action, the distance h3 between the projection spots of the 0th-order diffracted light beam and the + 1st-order diffracted light beam for verification on the photodetector 31, and the 0th-order diffracted light beam and the -1st-order diffracted light beam for verification , The distance h4 between the projected spots is not equal.

As shown in (c) of FIG. 18 and FIG. 15, even in the projection spot of the ± 1st-order diffracted light flux for reproduction,
Similar to the verify light flux, the projection spot intervals h5 and h6 in FIG. 18C are not equal. This will be described with reference to FIG. 17. In the projection spot shown by the dotted line on each photodetector, each diffracted light beam is point-symmetric with respect to the 0th-order diffracted light beam,
It is a spot position when it is assumed that light is incident at a position equidistant from the generatrix of the cylindrical lens 30, and the projection spot intervals of the ± 1st-order diffracted light flux and the 0th-order diffracted light flux are equal.

In short, in the conventional example, each spot is projected at the position indicated by the solid line by the lens action of the cylindrical lens 30 described above. This projection position changes depending on the size of the diffraction angle and the position of incidence on the cylindrical lens, and as shown in FIG. 17, since all of the projection spots cannot be received by the photodetector, signal deterioration will result. Further, the incidence of adjacent projection spots having different purposes / functions causes mixing of signals, which makes verification or reproduction impossible.

As described above, the conventional example has the above-mentioned problems,
Stable recording / playback cannot be achieved.

The object of the present invention is to solve the problems of the prior art by making the intervals of the projection spots of the 0th-order diffracted light beam and the ± 1st-order diffracted light beams on the photodetector substantially equal to each other. It is another object of the present invention to provide a multipurpose optical information recording / reproducing device capable of stable recording / reproducing.

[0038]

In order to achieve the above object, among a plurality of ± 1st-order diffracted light beams diffracted by a diffraction grating, a straight line direction connecting the centers of any one set of ± 1st-order diffracted light beams is used. Then, the axes of the cylindrical lenses (directions without lens action) are arranged to be substantially coincident with each other or substantially perpendicular thereto, and a plurality of light receiving portions of the photodetector are arranged in the linear direction. . Then, in this case, at least one of the plurality of light receiving portions is composed of four light receiving surfaces symmetrically arranged with respect to mutually orthogonal axes, and one of the mutually orthogonal axes and the linear direction. By arranging so that the angle θ formed by and is 0 ° <θ <45 ° or 45 ° <θ <90 °, a reproduction and verify signal and further an AT / AF control signal are obtained.

As a result, it is possible to reduce the AF offset that occurs due to the movement of the objective lens and the relative inclination between the optical card and the light flux, and more stable recording / reproducing and reproducing using the astigmatism AF method. It is possible to provide an optical information recording / reproducing apparatus capable of simultaneously reproducing a plurality of information tracks and further verifying immediately after recording.

In this case, among the plurality of light receiving parts,
At least one is composed of four light-receiving surfaces symmetrically arranged with respect to mutually orthogonal axes, and one of the mutually orthogonal axes is arranged at 45 degrees with respect to the linear direction. Is used to obtain a reproduction and verify signal, and further an AT / AF control signal.

As a result, the astigmatism AF method is used,
It is possible to provide an optical information recording / reproducing apparatus capable of more stable recording / reproduction, simultaneous reproduction of a plurality of information tracks, and further verification immediately after recording.

[0042]

BEST MODE FOR CARRYING OUT THE INVENTION

(Embodiment 1) The following is a description of Embodiment 1 of the present invention.
One will be specifically described with reference to (a) to (e) of FIG. Here, the angle θ formed by one of the division lines orthogonal to each other of the four-division photodetector C1 for performing AF control by the astigmatism method and the straight line connecting the two verification light beams is 0 degree <θ <45. One of the division lines of the four-division photodetector C1 orthogonal to each other is arranged so as to satisfy the degree or 45 degrees <θ <90 degrees.

Incidentally, the straight line and the cylindrical lens 3
The relationship with the bus line of 0 and the relationship between the straight line and the photodetector 31 having a plurality of light receiving portions are ± 1 for the verification.
This is at the point where the generatrix of the cylindrical lens 30 is arranged in a direction substantially coincident with the linear direction connecting the second-order diffracted light beams (see FIG. 5), and the plurality of light receiving portions of the photodetector 31 are arranged in the linear direction. .

In FIGS. 1A to 1E, C1 is A
A four-division photodetector having division lines R orthogonal to each other for performing F control, wherein an arrow A indicates an information track direction and a generatrix direction of the cylindrical lens 30, and θ
Is an angle formed by the dividing line R and the linear direction A. The linear direction A and the cylindrical lens 30
The angle between the dividing line and the direction of the generatrix of the cylindrical lens 30 is θ degrees (see (a) in FIG. 6).

FIG. 1 (c) shows an arrangement example for comparison with the present invention. As described above due to the problem of the conventional example, the objective lens is moved in the information track crossing direction (arrow Q direction). Of the optical card, or the warp of the optical card in the lateral direction or the inclination of the optical card holder causes the projected image to move in the Q direction, which easily causes an AF offset. In addition, the dividing line is 4 with respect to the linear direction.
Since it is placed at 5 degrees, AF for the amount of movement of the projected image
The offset amount is the largest.

Further, in the arrangements shown in FIGS. 1A and 1E, there is no AF offset due to the movement of the projected image, but the irradiation spot may be in focus on the optical card. Although it may be in the defocused state, the signal for controlling AF is always in the 0 state, and AF control by the astigmatism method is impossible.

Therefore, here, as shown in FIG. 1B or 1D, the angle θ formed by the dividing line and the linear direction is 0 degree <θ <45 degrees or 45 degrees <θ <90. Arranged so that it will be repeated. This angle range excludes the point where AF control by the astigmatism method is possible and the effect of AF offset due to the movement of the projection image is the largest. In this setting range, as the angle θ approaches 0 degrees or approaches 90 degrees, the AF offset amount due to the movement of the projected image becomes smaller. Specific examples thereof are shown in FIGS. 2A and 2B.

Here, the θ is set to 22.
The four-division photodetector C1 and the projected image when arranged at 5 degrees are shown. In FIG. 2A, a dotted circle is a projected image when there is no light flux shift, and the irradiation spot on the optical card is in focus. Then, this projection image moves to the solid line circle position in FIG. 2A when the light flux is shifted due to the movement of the objective lens or the warp of the optical card. Due to this movement of the projected image, the difference signal for astigmatism AF control is not 0, and the objective lens can be moved in the AF direction so that the difference signal becomes 0. The state of the projected image on the four-division photodetector C1 where the difference signal becomes 0 is shown in FIG.
(B) of FIG. The projected image is elliptical, but θ is 45
In contrast to the elliptical shape of the projected image as shown in FIG. 8B of the conventional example, which is a degree, the elliptic shape is considerably close to a circular shape. This is because the projection image moves to the vicinity of the other dividing line, which is orthogonal to the dividing line R in the figure, and accordingly,
The offset amount of AF, that is, the defocus amount becomes small. (Embodiment 1) Next, the relationship between the shift of the luminous flux and the defocus amount of the irradiation spot on the optical card will be described based on the actually measured data in FIG. The conditions of the actually measured optical system are
Objective lens focal length f1 = 4.8 mm, NA = 0.4
5, the spherical lens has a focal length f2 = 33 mm, the cylindrical lens has a focal length f3 = 50 mm, and the incident light beam diameter to the objective lens is φ3.5 mm.

The amount L of shift of the luminous flux is L = f1 · tan (2 × 3 °) = 0.5 mm due to the reflection action of the optical card when the possible amount of warp of the optical card = 3 degrees. The moving amount of the objective lens is 0.1 to 0.2 m.
Since it is about m, the light flux shift amount L is 0.6 to 0.7.
It is necessary to consider mm.

In FIG. 3, the curve with the angle θ = 45 degrees is a conventional example, and the shift amount of the light beam is 0.7 mm.
In this case, the defocus amount is 4 μm. In contrast,
The defocus amount in the case of the angle θ = 22.5 degrees, which is the embodiment of the present invention, is half that in the case of θ = 45 degrees, as shown in FIG.

By the way, the diameter of the light spot changes due to defocusing, but the size and shape of the information pit and the quality of the signal when reproduced are always maintained at a constant level during information recording. Therefore, it is necessary to suppress the change amount of the spot diameter to about 10%. This is because when the spot diameter changes by 10%, the energy density is inversely proportional to the square, so that the energy density decreases by 20%. When an information pit recorded at a spot whose energy density is reduced by 20% is reproduced at a spot with a defocus amount of 0, the reproduction signal has a contrast of 10 to 10.
20% lower. Furthermore, when an information pit recorded with a spot whose energy density is reduced by 20% is reproduced with a defocused spot by the same amount as when recording, the contrast of the reproduced signal is reduced by 20 to 30%, which is remarkable. However, the signal quality is impaired, and in addition, it also affects the jitter of the reproduced signal, resulting in erroneous recognition of data.

FIG. 4 shows data obtained by actually measuring the relationship between the defocus amount and the spot diameter. In FIG. 4, the defocus amount is 3.5 μ when the spot diameter changes by 10%.
m. That is, the defocus amount that can be allowed for stable recording and reproduction is 3.5 μm. The defocus amount of 3.5 μm is a total value of defocus factors considered as a device. Defocus factors include external vibration, adjustment accuracy of the optical head, and movement of the projected image on the four-division photodetector caused by movement of the objective lens of the present invention and warpage of the optical card. The defocus amount due to the vibration in the room is about 1 μm, and the adjustment accuracy of the optical head is 1 μ, although it depends on the usage environment of the device.
Since it is slightly less than m, the defocus allowable amount due to the movement of the projection image is about 2 μm. That is, as shown in FIG. 3, when the shift amount of the light flux: 0.7 mm is taken into consideration, the straight line connecting the two ± 1st-order diffracted light flux centers for verification and the four-division photodetector C1 are orthogonal to each other. The dividing line may be arranged such that the angle θ formed by one of the dividing lines with respect to the following is 0 degree <θ ≦ 22.5 degrees. Further, the angle θ may be 67.5 degrees ≦ θ <90 degrees. This is because the relationship between one axis of the dividing line and the moving direction of the projected image is equivalent to the case where the angle θ is 0 degree <θ ≦ 22.5 degrees.

As described above, when θ is 0 ° and 90 °, the difference signal for AF control is always 0 regardless of defocus, so that AF control by the astigmatism method can be performed. Can not. That is, as the angle θ approaches 0 degrees or 90 degrees, the magnitude of the difference signal with respect to the movement amount of the projection image decreases as the angle θ approaches. Therefore, the AF control gain becomes small, and the AF control performance deteriorates.

The AF control gain and the defocus amount of 2
Considering the points, it is most desirable to set the angle θ to 22.5 degrees between 0 degrees and 45 degrees or to 67.5 degrees between 45 degrees and 90 degrees.

As described above, according to the present invention, it is possible to reduce the AF offset caused by the movement of the objective lens and the relative inclination between the optical card and the light flux.

Further, here, with reference to the straight line connecting the verifying ± 1st-order diffracted light beams applied to the same information track, each of the generatrices of the cylindrical lens and the dividing lines of the plurality of light receiving portions and the four-division photodetector is used. Although the arrangement and direction are determined, a straight line connecting the reproducing ± 1st-order diffracted light fluxes arranged on two different information tracks, or connecting the ± 1st-order diffracted light flux for ATs arranged on two different tracking tracks For verification with either straight line as the reference ±
It goes without saying that the same effect as when the first-order diffracted light flux is used as a reference is obtained. (Embodiment 2) As another embodiment of the present invention, the following structural features can be mentioned. That is, in this embodiment, unlike the above-described embodiment,
For the direction of the straight line connecting the ± 1st-order diffracted light beams for verification,
The point is that the generatrix of the cylindrical lens 30 is arranged in a substantially vertical direction (see FIG. 10) and the plurality of light receiving portions of the photodetector 31 are arranged in the linear direction. Therefore, in FIGS. 1A to 1E, the cylindrical lens 3
Since the generatrix direction B of 0 is orthogonal to the linear direction A, the angle formed by the dividing line and the generatrix direction B of the cylindrical lens 30 is (90−θ) degrees.

In FIGS. 1A to 1E, C1 is A
A four-division photodetector having mutually orthogonal dividing lines R for performing F control, an arrow A is an information track direction, an arrow B is a generatrix direction of the cylindrical lens 30, and θ is the dividing line R. It is an angle formed by the straight line direction A. The linear direction A and the cylindrical lens 3
Since the generatrix direction B of 0 is orthogonal to each other, the angle formed by the dividing line and the generatrix direction B of the cylindrical lens 30 ′ is (90−θ) degrees (see FIG. 6B).

FIG. 1C shows an arrangement example for comparison with the present invention. As described in the problem of the conventional example, the movement of the objective lens in the information track crossing direction (arrow B direction). Alternatively, due to the warp of the optical card in the lateral direction and the inclination of the optical card holder, the projected image moves in the B direction, which is likely to cause AF offset. Further, since the dividing line is arranged at an angle of 45 degrees with respect to the linear direction, the AF offset amount with respect to the moving amount of the projected image becomes the largest.

Further, in the arrangements shown in FIGS. 1A and 1E, no AF offset occurs due to movement of the projected image, but the irradiation spot may be in focus on the optical card. Although it may be in the defocused state, the signal for controlling AF is always in the 0 state, and AF control by the astigmatism method is impossible.

In the embodiment of the present invention shown here, as shown in FIG. 1B or 1D, the angle θ formed by the dividing line and the linear direction is 0 degree <θ <45 degree or 45 degrees. It was arranged so that the angle <θ <90 °. This angle range excludes the point where AF control by the astigmatism method is possible and the effect of AF offset due to the movement of the projection image is the largest. In this setting range, as the angle θ approaches 0 degrees or approaches 90 degrees, the AF offset amount due to the movement of the projected image becomes smaller.

A specific example is shown in FIGS. 2A and 2B.
Is shown in Here, the θ is 2 which is half of 45 degrees.
It is a 4-division photodetector C1 and a projection image when arrange | positioning at 2.5 degrees. In FIG. 2A, the dotted circle is a projected image when there is no shift of the light beam, and the irradiation spot on the optical card is in focus. When the light flux shifts due to the movement of the objective lens or the warp of the optical card, the projected image moves to the solid line circle position of FIG. Due to this movement of the projected image, the difference signal for astigmatism AF control is not 0, and the objective lens is moved in the AF direction so that the difference signal becomes 0.

This 4-division detector C1 in which the difference signal becomes 0
The state of the projected image above is shown in FIG. The projected image has an elliptical shape, but the angle θ is 45 degrees as shown in FIG.
Unlike the elliptical shape of the projected image as shown in (b) of
It is an ellipse that is fairly circular. This is because the projection image moves to the vicinity of the other dividing line which is orthogonal to the dividing line R in the figure, and the offset amount of AF, that is, the defocus amount decreases accordingly.

Since the example of this embodiment is the same as the above-described (Example 1), the description thereof is omitted here. (Embodiment 3) Here, the arrangement of the optical system of the optical information recording / reproducing apparatus of the present invention is the same as that of FIG. 5 showing a conventional example, and the difference from that is the arrangement of the generatrix of the cylindrical lens 30, The angle between the direction and the information track direction, and the internal structure of the photodetector 31.

The arrangement of the cylindrical lens 30 here is, as shown in FIG. 6A, the information track direction A.
And, the bus lines are matched. As a result, the ± first-order diffracted light beams diffracted at the same angle with respect to the 0th-order light diffracted light beam are diffracted substantially in the generatrix direction of the cylindrical lens 30, so that the cylindrical lens 30 is used in the diffraction direction. Of the 0th-order diffracted light beam and the ± 1st-order diffracted light beams are equal to each other, and enter the photodetector 31 'while maintaining the relationship.

Next, the projection spot of each light flux emitted from the cylindrical lens 30 on the photodetector 31 will be described with reference to FIG. Among the photodetectors 31 composed of a plurality of photodetectors, the photodetectors C2 to C7 have the same configuration as the photodetector of the conventional example. The difference from the conventional example is that the plurality of light receiving portions of the photodetector 31 are arranged so as to be in the direction of the straight line A and substantially coincide with the generatrix direction of the cylindrical lens, and further, the AF in the astigmatism method is performed. 4 for controlling
The division lines orthogonal to each other of the divided photodetector C1 are arranged so that the angle is 45 degrees with respect to the direction of the straight line A and the generatrix of the cylindrical lens as shown in FIG. 7A. It is in.

Since the generatrix direction of the cylindrical lens 30 and the direction of the straight line A substantially coincide with each other, the dividing line is arranged at an angle of 45 degrees with respect to the generatrix of the cylindrical lens 30, and the information This means that they are also arranged at an angle of 45 degrees with respect to the track direction. In addition,
In FIG. 9, each signal processing system is the same as that of the conventional example, and therefore the description thereof is omitted here.

As shown in FIG. 9, the distance between the reproduction and AF control spot projected on the photodetector C1 and the spot projected on another photodetector is determined by the photodetector C2 for AT control. And the spots projected onto C3, the spots projected onto the photodetectors C4 and C5 for verification, and the spots projected onto the photodetectors C6 and C7 for reproduction are equal to each other. As a result, each light beam can be projected as a spot at a desired position on the photodetector.

The shape of the four-division photodetector is shown in FIG.
7 (a), the outer shape may be circular. The common point is that the dividing line is arranged at an angle of 45 degrees with respect to the generatrix direction A of the cylindrical lens 30.

In this embodiment, the linear direction connecting the verifying ± 1st-order diffracted light beams has been described as being coincident with the information track direction, but the information pits are scanned within the same information track. If possible, the straight line connecting the verifying light fluxes does not necessarily have to coincide with the information track. (Fourth Embodiment) Here, the arrangement of the optical system of the optical information recording / reproducing apparatus of the present invention is the same as in FIG. 10 showing a conventional example, and the difference is that the cylindrical lens 30 is used.
It is the arrangement and direction of the bus bar and the angle formed by the information track direction, and the internal structure of the photodetector 31.

The cylindrical lens 30 is arranged so that the generatrix B is substantially perpendicular to the information track direction A, as shown in FIG. 6B. As a result, the ± first-order diffracted light beams diffracted at the same angle with respect to the 0th-order light diffracted light beam are incident at the same distance from the generatrix of the cylindrical lens 30, so that the lens action in the cylindrical lens 30 is Will be equal.

Next, the projection spot of each light flux emitted from the cylindrical lens 30 on the photodetector 31 will be described with reference to FIG. Among the photodetectors 31 composed of a plurality of photodetectors, the photodetectors C2 to C7 have the same configuration as the photodetector of the conventional example. The difference from the conventional example is that the plurality of light receiving portions of the photodetector 31 are arranged in the above-described straight line A direction and substantially perpendicular to the generatrix B direction of the cylindrical lens, and the astigmatism method is used. As shown in (a) of FIG. 7, the dividing lines of the 4-division photodetector C1 for performing the AF control of 45 degrees with respect to the straight line A direction and the generatrix B of the cylindrical lens are 45 degrees. It is arranged so that it becomes the angle of.

Since the generatrix B direction and the straight line A direction of the cylindrical lens 30 are substantially perpendicular to each other, the dividing line is arranged at an angle of 45 degrees with respect to the generatrix of the cylindrical lens 30, and The information track direction A is also arranged at an angle of 45 degrees. Note that, in FIG. 9, each signal processing system is the same as that of the conventional example, and therefore the description thereof is omitted here.

As shown in FIG. 9, the distance between the reproduction and AF control spot projected on the photodetector C1 and the spot projected on the other photodetector is equal to that of the AT control photodetector C2. The spots projected onto C3, the spots projected onto the photodetectors C4 and C5 for verification, and the spots projected onto the photodetectors C6 and C7 for reproduction are equal to each other. As a result, each light beam can be projected as a spot at a desired position on the photodetector.

The shape of the four-division photodetector is shown in FIG.
7 (a), the outer shape may be circular. The common point is that the dividing line is arranged at an angle of 45 degrees with respect to the generatrix direction B of the cylindrical lens 30.

In this embodiment, the linear direction connecting the verifying ± 1st-order diffracted light beams is made to coincide with the information track direction, but the information pits are scanned within the same information track. If possible, the straight line connecting the verifying light fluxes does not necessarily have to coincide with the information track.

[0076]

As described above, according to the present invention,
In an optical information recording / reproducing apparatus for performing recording / reproduction by an astigmatism AF method, a generatrix of a cylindrical lens is arranged in a straight line direction connecting any one set of ± 1st-order diffracted light beams among a plurality of ± 1st-order diffracted light beams. To substantially match, or arranged substantially perpendicular thereto, in a photodetector having a plurality of light receiving portions for receiving the plurality of light beams, the plurality of light receiving portions are arranged in the linear direction, At least one of the plurality of light receiving portions is formed by four light receiving surfaces symmetrically arranged with respect to axes orthogonal to each other, and an angle formed by one of the orthogonal axes and the straight line. By arranging one of the axes orthogonal to each other so that θ is 0 degree <θ <45 degree or 45 degree <θ <90 degree, the optical card such as the movement of the objective lens or the warp of the optical card can be obtained. Relative to the luminous flux It is possible to reduce the AF offset generated by the slope.

Naturally, in each projected spot on the photodetector, the spot intervals of the 0th-order diffracted light beam and the respective ± 1st-order diffracted light beams can be made substantially equal, so that the light from the photodetector It is possible to prevent signal deterioration and signal mixing due to leakage and light mixing, and to perform stable AF control by the astigmatism method.

As a result, the astigmatism AF method is used.
It is possible to achieve an optical information recording / reproducing apparatus capable of more stable recording, simultaneous reproduction of a plurality of information tracks, and further verification immediately after recording.

Further, according to the present invention, in the optical information recording / reproducing apparatus for recording / reproducing by the astigmatism AF method, any one set of ± 1 of ± 1st-order diffracted light beams is used.
In a photodetector having a plurality of light receiving portions for receiving the plurality of light fluxes, the generatrix of the cylindrical lens is arranged to be substantially coincident with or substantially perpendicular to the linear direction connecting the second-order diffracted light fluxes. , The plurality of light receiving portions are arranged in the linear direction, and at least one of the plurality of light receiving portions is arranged.
One light receiving portion is composed of four light receiving surfaces symmetrically arranged with respect to mutually orthogonal axes, and one of the orthogonal axes is arranged so as to form an angle of 45 degrees with respect to the straight line. By doing so, the distance between the 0th-order diffracted light beam and the spots of the ± 1st-order diffracted light beams can be made substantially equal for each projected spot on the photodetector. It is possible to prevent signal deterioration and signal mixture due to light leakage and light mixture, and to perform stable AF control by the astigmatism method.

That is, it is possible to achieve an optical information recording / reproducing apparatus which uses the astigmatism AF method and is capable of more stable recording and simultaneous reproduction of a plurality of information tracks, and further verifying immediately after recording.

[Brief description of drawings]

1 (a), 1 (c) and 1 (e) are views showing the direction of a dividing line of a four-division photodetector in an embodiment of the present invention. [Fig. 6] is a view showing a direction of a dividing line of a 4-division photodetector, which is compared with the above embodiment.

FIG. 2A and FIG. 2B are diagrams showing a division line direction and a projected image of a four-division photodetector in an embodiment of the present invention.

FIG. 3 is a graph showing a relationship between a light flux shift amount and a defocus amount for comparing the embodiment of the present invention with a conventional example.

FIG. 4 is a graph showing the relationship between the defocus amount and the spot diameter.

FIG. 5 is a configuration diagram of an optical system common to the present invention and a conventional example.

6A and 6B are diagrams showing the relationship between a cylindrical lens, its generatrix direction, and an incident light beam.

FIG. 7A and FIG. 7B are views showing the direction of the dividing line of the 4-division photodetector.

8A and 8B are diagrams showing a dividing line direction and a projected image thereof in a conventional example.

FIG. 9 is a diagram showing a photodetector and a signal processing system.

FIG. 10 is a configuration diagram of another optical system common to the present invention and the conventional example.

FIG. 11 is a schematic view showing partial enlargement of an optical card and arrangement of light spots.

FIG. 12 is a schematic explanatory diagram of a diffraction grating.

FIG. 13A and FIG. 13B are diagrams showing the relationship between the objective lens and the luminous flux.

FIG. 14 is a configuration diagram of still another optical system common to the present invention and the conventional example.

FIG. 15 is a diagram showing a relationship between a cylindrical lens, a light flux, and an information track.

FIG. 16 is a diagram showing an arrangement of four-division photodetectors that perform astigmatism AF control.

FIG. 17 is a diagram showing another form of the photodetector and the signal processing system.

FIG. 18A to FIG. 18C are diagrams showing the optical axis of each light beam and the incident position on the photodetector in three cross sections of the cylindrical lens.

[Explanation of symbols]

 1 Optical card 2 Information track 21 Semiconductor laser 25 Diffraction grating 28 Objective lens 29 Spherical lens 30 and 31 Cylindrical lens A Information track direction B Cylindrical lens generatrix direction 31 Photodetector C1 4-division photodetector b1 0th-order diffracted light beam b2 and b3 AT ± 1st order diffracted light beam b4 and b5 Verify ± 1st order diffracted light beam b6 and b7 Reproduction ± 1st order diffracted light beam Q Moving direction of projected image R Dividing line

Claims (9)

[Claims] 1. An optical information having a light source, a diffraction grating composed of at least two gratings having different characteristics for dividing a light beam emitted from the light source into a plurality of light beams, and a plurality of tracking tracks and a plurality of information tracks. A first optical system for irradiating the plurality of light fluxes on a recording medium, and a plurality of reflected light fluxes from the optical information recording medium are transmitted through an anamorphic optical system including a spherical lens and a cylindrical lens, An optical head configured with a second optical system for guiding to a photodetector having a plurality of light receiving parts,
In an optical information recording / reproducing apparatus for recording and / or reproducing information by the optical head, any one set of ± 1st-order diffracted light beams among a plurality of ± 1st-order diffracted light beams diffracted by the diffraction grating is connected. The axes of the cylindrical lenses (directions not having a lens action) are arranged so as to be substantially aligned with the linear direction, and at least one of the plurality of light receiving portions is symmetrical with respect to axes orthogonal to each other. Formed by the four light-receiving surfaces, and the angle θ formed by one of the axes orthogonal to each other and the linear direction.
Is 0 degrees <θ <45 degrees or 45 degrees <θ
An optical information recording / reproducing apparatus characterized by being arranged so as to be <90 degrees. 2. The angle θ is 22.5 degrees or 67.
The optical information recording / reproducing apparatus according to claim 1, wherein the optical information recording / reproducing apparatus is 5 degrees. 3. An optical information having a light source, a diffraction grating composed of at least two gratings having different characteristics for dividing a light beam emitted from the light source into a plurality of light beams, and a plurality of tracking tracks and a plurality of information tracks. A first optical system for irradiating the plurality of light beams on a recording medium, and a plurality of reflected light beams from the optical information recording medium are transmitted through an anamorphic optical system including a spherical lens and a cylindrical lens, An optical information recording / reproducing apparatus having an optical head composed of a second optical system for guiding to a photodetector having a plurality of light receiving parts, and recording and / or reproducing information by the optical head. Of the plurality of ± first-order diffracted light beams diffracted by the diffraction grating with respect to the linear direction connecting any one set of the ± first-order diffracted light beams. Are arranged so that their axes (directions that do not have a lens action) substantially coincide with each other, and at least one of the plurality of light receiving portions is formed from four light receiving surfaces symmetrically arranged with respect to axes orthogonal to each other. The optical information recording / reproducing apparatus is characterized in that one of the mutually orthogonal axes is arranged at 45 degrees with respect to the linear direction. 4. A light source, a diffraction grating composed of at least two gratings having different characteristics for dividing a light beam emitted from the light source into a plurality of light beams, and optical information having a plurality of tracking tracks and a plurality of information tracks. A first optical system for irradiating the plurality of light beams on a recording medium, and a plurality of reflected light beams from the optical information recording medium are transmitted through an anamorphic optical system including a spherical lens and a cylindrical lens, An optical information recording / reproducing apparatus having an optical head composed of a second optical system for guiding to a photodetector having a plurality of light receiving parts, and recording and / or reproducing information by the optical head, Among the plurality of ± 1st-order diffracted light beams diffracted by the diffraction grating, the cylindrical lens is arranged with respect to a linear direction connecting any one set of ± 1st-order diffracted light beams. An axis (direction not having a lens action) is arranged substantially vertically, a plurality of light receiving portions of the photodetector are arranged in the linear direction, and at least one of the plurality of light receiving portions is an axis orthogonal to each other. On the other hand, an angle θ formed by four light-receiving surfaces symmetrically arranged and one of the axes orthogonal to each other and the linear direction is 0 degree <θ <45 degree or 45 degree <θ.
An optical information recording / reproducing apparatus, which is arranged so as to be <90 degrees. 5. The angle θ is 22.5 degrees or 67.
The optical information recording / reproducing apparatus according to claim 4, wherein the optical information recording / reproducing apparatus is set at 5 degrees. 6. An optical information having a light source, a diffraction grating composed of at least two gratings having different characteristics for dividing a light beam emitted from the light source into a plurality of light beams, and a plurality of tracking tracks and a plurality of information tracks. A first optical system for irradiating the plurality of light beams on a recording medium, and a plurality of reflected light beams from the optical information recording medium are transmitted through an anamorphic optical system including a spherical lens and a cylindrical lens, An optical information recording / reproducing apparatus having an optical head composed of a second optical system for guiding to a photodetector having a plurality of light receiving parts, and recording and / or reproducing information by the optical head, Among the plurality of ± 1st-order diffracted light beams diffracted by the diffraction grating, the cylindrical lens is arranged with respect to a linear direction connecting any one set of ± 1st-order diffracted light beams. An axis (direction not having a lens action) is arranged substantially vertically, a plurality of light receiving portions of the photodetector are arranged in the linear direction, and at least one of the plurality of light receiving portions is an axis orthogonal to each other. On the other hand, the optical information recording is characterized in that it is composed of four symmetrically arranged light receiving surfaces, and one of the axes orthogonal to each other is arranged at 45 degrees with respect to the linear direction. Playback device. 7. The one of the ± 1st-order diffracted light fluxes of any one of the sets is a light flux applied to the same information track, according to any one of claims 1, 3, 4, and 6. Optical information recording and reproducing device. 8. Any one of the above-mentioned ± 1st-order diffracted light fluxes is a light flux projected onto two different information tracks, and any one of the above-mentioned 1st, 3rd, 4th, and 6th features. The optical information recording / reproducing apparatus described in 1. 9. The set of ± 1st-order diffracted light beams of any one of the above-mentioned sets is a light beam applied to two different tracking tracks. The optical information recording / reproducing apparatus described in 1.