JP2762708B2 - Optical head - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention has an information recording medium, and detects a focus error signal for recording, reproducing, and erasing information by irradiating a light beam such as a laser beam. And an optical head of an optical disk apparatus having a tracking error signal detecting means.

2. Description of the Related Art There have been many reports on techniques relating to focus error signal detection means and tracking error signal detection means in conventional optical heads.

Hereinafter, a conventional optical head will be described with reference to the drawings.

FIG. 4 shows an example of a schematic configuration of a conventional optical head.

In FIG. 4, 1 is a light source, 2 is a beam splitter A, 3 is an objective lens, 4 is an optical disk as an information recording medium, 5 is a beam splitter B, 6 is a lens A, 7 is a two-segment photodetector A, 8 Is a differential amplifier A, 9 is a light spot A,
7p is a dividing line of the two-part photodetector 7, 10 is a lens B,
11 is a knife edge, 12 is a two-segment photodetector B, 13 is a differential amplifier B, 14 is a light spot B, and 12p is a dividing line of the two-segment photodetector 12. Reference numeral 15 denotes a summing amplifier.

Hereinafter, the operation of the conventional optical head will be described with reference to the drawings.

The light emitted from the light source 1 passes through the beam splitter A2 and then forms an optical spot on the optical disk 4 via the objective lens 3. At this time, the direction of the recording track on the optical disc 4 is perpendicular to the paper surface. The reflected light from the optical disc 4 follows the reverse path, passes through the objective lens 3, is reflected by the beam splitter A2, enters the beam splitter B5, and is separated into transmitted light and reflected light. This transmitted light becomes converged light through the lens A6, and forms a light spot A9 on the two-divided photodetector A7. Here, the dividing line 7p of the two-segment photodetector A7 is changed to the light spot A9.
Is set at a position where the light amount of the light is approximately divided into two, and two
The tracking error signal can be detected by the so-called push-pull method by taking the difference between the electric signals generated in the two light receiving areas of the split photodetector A7.

On the other hand, the reflected light of the beam splitter B5 becomes converged light through the lens B10, and the light spot B14
To form Here, the knife edge 11 is arranged at a position where almost half of the light converged by the lens B10 is shielded, and the dividing line 12p of the two-divided photodetector B12 is connected to the knife edge 11 on the light beam cross section.
Approximately 2 parallel to the edge line of
Detecting a focus error signal by the so-called knife edge method by setting equal division and taking the difference between each electric signal generated in the two light receiving areas of the two-divided photodetector B12 by the differential amplifier B13 Can be.

Further, the information signal of the optical disk 4 can be detected by adding the sum of all the electric signals generated by the split photodetector A7 and the split photodetector B12 by the addition amplifier 15.

SUMMARY OF THE INVENTION In the conventional optical head described above, a beam splitter for separating reflected light from the optical disc 4 into transmitted light and reflected light in order to detect a focus error signal and a tracking error signal independently of each other. B5 is required, lens A6, lens B10 and split photodetector A7, split photodetector
As in B12, substantially the same components are required in duplicate. Therefore, since there are many components, there is a serious drawback that an increase in the size and cost of the optical head cannot be avoided.

In view of the above-described problems, the present invention realizes a configuration in which a focus error signal and a tracking error signal are also used for detection, thereby eliminating the need for a beam splitter for separating reflected light from an optical disc into transmitted light and reflected light. Also, duplicate components can be deleted. That is, the present invention provides a small and inexpensive optical head with a minimum number of components.

Means for Solving the Problems In order to achieve this object, an optical head according to the present invention comprises a light source, an objective lens for causing light emitted from the light source to converge on an information recording medium having a recording track, and an Detecting means for detecting an information signal, a focus error signal, and a tracking error signal by reflected light; a focus direction substantially parallel to an optical axis direction of the objective lens; and a tracking direction substantially perpendicular to the recording track and the focus direction. Means for applying focus servo and tracking servo by driving the optical disc, and means for detecting the focus error signal and the tracking error signal. The means for transmitting the reflected light from the information recording medium and having substantially the same light beam section as the recording track. With the vertical center line as the axis of symmetry, the luminous flux at the center including this axis of symmetry and the periphery not including the axis of symmetry Part 2
Into two light beams, spatially symmetrically separated from the plane of the multi-segmented photodetector, and each light beam to a spatially different focal position apart from the plane of the multi-segmented photodetector including the optical axis direction. When the split converging element to be converged and the transmitted light of the split converging element are incident and the objective lens is focused on the information recording medium, the two peripheral light fluxes on the cross section of the reflected light flux are converged and formed. A multi-segment photodetector located at an intermediate position between two focal points in the optical axis direction, wherein two peripheral light beams not including the axis of symmetry are incident, and each of two substantially congruent light spots formed by each light beam. On the other hand, the first and second two light receiving regions, which are arranged so as to receive the light amount almost uniformly by the dividing line substantially parallel to the symmetry axis, and the central light flux including the symmetry axis enter, For one light spot formed by the central beam, Multi-split light detection formed by a third light receiving area arranged so as to receive the light amount substantially uniformly with at least one split line substantially coincident with the center line substantially parallel to the recording track in the light beam cross section. In the first and second two-divided light receiving regions, the light receiving regions existing at different positions are electrically connected to each other to obtain the sum of the shapes of the substantially congruent light spots formed in each of the first and second divided light receiving regions. A first differential amplifier that takes the difference between the electric signals obtained by taking the sum thereof, and a second differential amplifier that takes the difference between the electric signals generated in each light receiving area divided by the dividing line in the third light receiving area. It is characterized by comprising a differential amplifier.

Operation With this configuration, it is possible to detect both the focus error signal and the tracking error signal, and there is no need for a means for separating reflected light from the information recording medium into transmitted light and reflected light. Can be deleted.
That is, a small and inexpensive optical head with a minimum number of components can be realized.

Embodiment Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a schematic configuration diagram of an optical head according to a first embodiment of the present invention.

In FIG. 1, 1 is a light source, 2 is a beam splitter A, 3 is an objective lens, and 4 is an optical disk as an information recording medium.

Reference numeral 16 denotes a divided converging element, which transmits reflected light from the optical disc 4 and, in a cross section of the light beam, receives a light beam at a central portion including a symmetric axis with a center line substantially perpendicular to the recording track as a symmetric axis. First lens 16a converged on 17a
Then, each of the two light beams in the peripheral portion not including the axis of symmetry is incident, and the second light beam converges at a focal position 17b, 17c spatially different from the focal point 17a of the first lens 16a including the optical axis direction. , And the third two lenses 16b and 16c. Reference numeral 18 denotes a multi-segment photodetector on which three light beams having passed through the split-convergence element 16 are incident. 19a, 19b, and 19c are three light spots formed on the multi-segment photodetector 18 by the split-convergence element 16, 18a and 18b. , 18
c is three light receiving areas in the multi-segment photodetector 18 that receives each of the three light spots 19a, 19b, and 19c, and 20b and 20c are light spots 19b and 19c formed in the light receiving areas 18b and 18c. In the cross section of the light beam reflected from the optical disc 4, the dividing line is a dividing line substantially parallel to the symmetry axis which is a center line substantially perpendicular to the recording track, and is arranged so as to receive the light amount almost uniformly.
Reference numeral 20a denotes a dividing line that substantially coincides with a center line substantially parallel to the recording track in a light beam cross section reflected from the optical disc 4 with respect to the light spot 19a formed in the light receiving area 18a.
It is arranged to receive the light amount almost uniformly.

21b is a dividing line that divides the light receiving regions 18a and 18b, 21c is a dividing line that divides the light receiving regions 18a and 18c, 22A and 22B are differential amplifiers,
23 is an addition amplifier. When the objective lens 3 has a focal point on the optical disc 4, the multi-split photodetector is located at an intermediate position between the two focal points 17b and 17c in the optical axis direction.

Hereinafter, the operation of the optical head according to the embodiment of the present invention will be described with reference to the drawings.

The light emitted from the light source 1 passes through the beam splitter A2 and then forms an optical spot on the optical disk 4 via the objective lens 3. At this time, the direction of the recording track on the optical disc 4 is perpendicular to the paper surface.

The reflected light from the optical disk 4 follows the reverse path, is reflected by the beam splitter A2 via the objective lens 3, and enters the divided converging element 16.

The transmitted light of the split converging element 16 is spatially split into three light beams, and three light spots 19a, 19b, 19c are formed on the multi-split photodetector.
Is formed.

At this time, in the light receiving region 18b and the light receiving region 18c, the light receiving regions divided by the dividing lines 20b and 20c and located at different positions are electrically connected to the shapes of the substantially congruent light spots 19b and 19c formed respectively. To obtain a sum, and the difference between the summed electric signals is taken by a differential amplifier 22A to detect a focus error signal. In this case, in order to obtain a focus error signal from the shape change of the two light spots 19b and 19c, the focus error signal is affected by the position change of the multi-segment photodetector 18 as compared with the knife edge method described in the conventional example of FIG. Never.

In the light receiving area 18a, the difference between the electric signals generated in each light receiving area divided by the dividing line 20a is represented by a differential amplifier 22.
By using B, a tracking error signal can be detected.

That is, since the division line 20a is arranged substantially parallel to the recording track, the light spot 19a has ± 1st-order diffracted light of the recording track whose line division is axisymmetric as the light amount component. In other words, the division line 20
Since the amount of received light in each light receiving area divided by a changes, if the difference is obtained by the differential amplifier 22B, the principle is that a tracking error signal is detected by a so-called push-pull method.

Further, if the sum of all the electric signals generated in each light receiving area of the multi-segment photodetector 18 is calculated by the addition amplifier 23, the information signal of the optical disk 4 can be detected.

FIG. 2 is an explanatory diagram of an operation of detecting a focus error signal in FIG. Here, only the light spot formed with the multi-segment photodetector 18 is shown, and other components are omitted.

FIG. 2A shows a case where the objective lens 3 is focused on the optical disk 4, and at this time, parallel light enters the divided converging element 16. Therefore, the light spots 19b and 19c formed in the light receiving regions 18b and 18c are substantially congruent, and the light receiving amounts are almost uniformly received in the four light receiving regions by the dividing lines 20b and 20c. Therefore, the focus error signal output from the differential amplifier 22A is zero.

FIG. 2 (B) shows a case where the optical disk 4 is displaced away from the objective lens 3 and, at this time, converged light enters the divided converging element 16 as compared with FIG. 2 (A). Therefore, the light spot 19b formed in the light receiving area 18b becomes larger, while the light spot 19c formed in the light receiving area 18c becomes larger.
Becomes smaller, and the light amount becomes unbalanced in the four light receiving regions by the dividing lines 20b and 20c. Therefore the differential amplifier
The focus error signal, which is the output of 22A, is negative.

FIG. 2C shows a case where the optical disc 4 is displaced in a direction approaching the objective lens 3, and at this time, the divided converging element 16 is displaced.
2A, light diverged as compared with FIG. Therefore, the light spot 19b formed in the light receiving area 18b becomes smaller, while the light spot 19c formed in the light receiving area 18c becomes larger, and the light amount becomes unbalanced in the four light receiving areas formed by the dividing lines 20b and 20c. Therefore, the focus error signal output from the differential amplifier 22A is positive. However, the second
Figures (B) and (C) show the differential amplifiers 22A and 22B and the summing amplifier 2
3 is omitted.

As described above, according to the present embodiment shown in FIGS. 1 and 2, a means for detecting both a focus error signal and a tracking error signal is provided by one divided converging element 16 and one multi-divided element. This can be achieved with the photodetector 18. That is, as compared with the configuration of the conventional optical head shown in FIG. 4, a beam splitter for separating reflected light from the optical disk 4 into transmitted light and reflected light is not required, and redundant components can be eliminated. In other words, a small and inexpensive optical head with a minimum number of components can be realized.

Here, the relative positional relationship between each light receiving area on the multi-segment photodetector 18 and each light spot is not limited to the embodiment shown in FIG. 1 and FIG. That is, the split converging element 16 may have a function of deflecting the split light beam, and the relative positional relationship between each light receiving area on the multi-split photodetector 18 and each light spot can be set arbitrarily. Only the light spot formed with the multi-segment photodetector 18 in this example is shown in FIG. 3 as a second embodiment of the present invention. Other components are the same as those in FIG. 1, and only the split and converging element 16 has a function of deflecting the split light beam, but is omitted here.

In FIG. 3, the light receiving regions 18b and 18c are present at positions adjacent to each other with the dividing line 24 interposed therebetween. Therefore, each of the dividing lines 20b and 20c and the dividing lines 21b and 21c is a single dividing line to form a four-part light receiving area, and the four light receiving areas are uniform for two substantially congruent light spots 19b and 19c. Receiving a large amount of light. Therefore, if the sum of the diagonals of the four light receiving areas is obtained and the difference between the sum signals is obtained by the differential amplifier 22A, the focus error signal can be detected.

On the other hand, the light receiving area 18a is separated from the light receiving area 18 by the dividing lines 21b and 21c.
It exists at a position adjacent to b and 18c. A light spot 19a is formed on the light receiving area 18a, and the dividing line 20a is substantially the same as the light spot 19a in the cross section of the light beam reflected from the optical disc 4 and substantially coincides with the center line substantially parallel to the recording track. It is a line and is arranged so as to receive the light amount almost uniformly. That is, since the division line 20a is arranged substantially parallel to the recording track, the light spot 19a has ± 1st-order diffracted light of the recording track whose line division is axisymmetric as the light amount component. Here, the dividing lines 25b and 25c are two dividing lines symmetrical to the dividing line 20a, and both ends of the dividing line 20a are connected to one ends of the dividing lines 25b and 25c, respectively.
8a is divided into two by a rectangular substantially S-shaped dividing line.

Therefore, due to the eccentricity of the optical disc 4, the dividing line
Since the amount of received light in each light receiving area divided into two by a rectangular substantially S-shaped dividing line of 25b, 20a, and 25c changes, a tracking error signal is detected if the difference is obtained by the differential amplifier 22B. It is a principle. In this case, if the positions of the dividing lines 25b and 25c are set to appropriate positions, the light spot 19a is generated due to a displacement in the tracking direction of the objective lens 3 as compared with a general push-pull method in which the light spot 19a is divided into two by the dividing line 20a. The offset of the tracking error signal can be greatly reduced.

Thus, in the optical disk device, even when the objective lens 3 moves from the neutral position in the tracking direction due to acceleration or the like at the time of moving the optical head, the pull-in capability of the tracking servo is greatly improved. Moreover, even when the target track has a large eccentricity (about 100 μm or more), the followability to the target track is greatly improved, and a stable tracking servo can be realized.

In the case of the relative positional relationship between each light receiving area on the multi-segment photodetector 18 and each light spot shown in FIG. 3, the adjustment of the multi-segment photodetector 18 is significantly larger than the positional relationship in FIG. It also has the unique effect of being easier.

However, here, the light receiving areas 18a, 18b, 18c, the light spot 19
The components a, 19b, 19c, the dividing lines 20a, 20b, 20c, the dividing lines 21b, 21c, the differential amplifiers 22A, 22B, and the addition amplifier 23 are the same components as those in the embodiment of FIG.

It is needless to say that the split converging element may be an integrated element manufactured by press molding or the like, and is also effective in terms of the transmittance of the element.

Further, it goes without saying that the divided and converged element may be a hologram element, and it is also effective in terms of the element manufacturing surface, transmittance, and the like.

As described above, according to the first and second embodiments of the present invention, the means for detecting both the focus error signal and the tracking error signal is used as one split converging element 16 and one multi-element. This can be achieved by the split photodetector 18. That is, as compared with the configuration of the conventional optical head shown in FIG. 4, a beam splitter for separating reflected light from the optical disk 4 into transmitted light and reflected light is not required, and redundant components can be eliminated. That is, a small and inexpensive optical head with a minimum number of components can be realized.

Advantageous Effects of the Invention The present invention provides a light source, and an objective lens for causing light emitted from the light source to converge on an information recording medium having a recording track,
Detecting means for detecting an information signal, a focus error signal, and a tracking error signal based on reflected light from the information recording medium; and moving the objective lens in a focus direction substantially parallel to an optical axis direction of the objective lens, and in a recording track and a focus direction. Means for applying focus servo and tracking servo by driving in a vertical tracking direction, and means for detecting the focus error signal and the tracking error signal. , A center line substantially perpendicular to the recording track is set as a symmetry axis, and a light beam in a central portion including the symmetry axis and two light beams in a peripheral portion not including the symmetry axis are spatially separated from the plane of the multi-split photodetector. Split symmetrically and focus each light beam at a spatially different focal position away from the plane of the multi-segmented photodetector, including the optical axis direction. In the case where the split converging element and the transmitted light of the split converging element are incident and the objective lens is focused on the information recording medium, the two peripheral light fluxes on the cross section of the reflected light flux are formed by converging. A multi-segment photodetector located at an intermediate position between two focal points in the optical axis direction, wherein two peripheral light beams not including the axis of symmetry are incident, and each of two substantially congruent light spots formed by each light beam. For
First and second two divided light receiving regions arranged so as to receive the light amount substantially uniformly by a dividing line substantially parallel to the symmetry axis, and a central light beam including the symmetry axis are incident, and a central light beam is formed. A third light receiving portion arranged so as to receive the light amount substantially uniformly with at least one division line substantially coincident with the center line substantially parallel to the recording track in the light beam cross section of the central light beam with respect to one light spot to be formed. A multi-segment photodetector formed of the first and second regions,
For the shape of the substantially congruent light spot formed on each,
The light receiving areas existing at different positions are electrically connected to obtain a sum, and the sum is divided by a dividing line in the third light receiving area with a first differential amplifier for obtaining a difference between the respective electric signals. The difference between the electric signals generated in the respective light receiving areas
And a differential amplifier.

With this configuration, the means for detecting both the focus error signal and the tracking error signal can be achieved with a very simple configuration of one split convergence element and one multi-split photodetector. That is, as compared with the configuration of the conventional optical head, a beam splitter for separating reflected light from the optical disk 4 into transmitted light and reflected light is not required, and redundant components can be eliminated. That is, a small and inexpensive optical head with a minimum number of components can be realized.

Further, the split converging element may have a function of deflecting the split light beam, and the relative positional relationship between each light receiving area on the multi-split photodetector and each light spot can be set arbitrarily. This makes it possible to use a method developed from the push-pull method especially for tracking error signal detection, and to simplify the adjustment of the multi-segment photodetector.

Further, the divided converging element may be an integrated element manufactured by press molding or the like, or may be a hologram element. This is also effective in terms of the manufacturing surface of the element, transmittance, and characteristic stability.

Therefore, the optical head of the present invention can realize an excellent optical head having a very simple configuration, a small size, an inexpensive, easily adjustable characteristic, and a stable characteristic.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an optical head according to a first embodiment of the present invention, FIGS. 2A, 2B, and 2C are partial operation explanatory diagrams of the embodiment, and FIG. FIG. 4 is an explanatory view of a main part of an optical head according to a second embodiment of the present invention, and FIG. 4 is a schematic diagram of a conventional optical head. 1 ... light source, 2,5 ... beam splitter, 3 ... objective lens, 4 ... optical disc, 6,10,16a, 16b, 16c ... lens, 7,12,18 ... photodetector, 8, 13,22A, 22B …… Differential amplifier, 9,14,19a, 19b, 19c …… Light spot, 11 …… Knife edge, 15,23 …… Additional amplifier, 16 …… Divided converging element, 1
7a, 17b, 17c: Focus, 18a, 18b, 18c: Light receiving area, 20a, 2
0b, 20c ... dividing line, 21b, 21c, 24, 25b, 25c ... dividing line.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-1-182293 (JP, A) JP-A-63-228423 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G11B 7/09

Claims (3)

(57) [Claims] A light source; an objective lens for converging light emitted from the light source on an information recording medium having a recording track; and an information signal, a focus error signal, and a tracking error signal by reflected light from the information recording medium. Detecting means for detecting; applying a focus servo and a tracking servo by driving the objective lens in a focus direction substantially parallel to an optical axis direction of the objective lens and a tracking direction substantially perpendicular to the recording track and the focus direction; Means for detecting the focus error signal and the tracking error signal, wherein reflected light from the information recording medium is transmitted, and a center line substantially perpendicular to the recording track in a light beam cross section is set as a symmetry axis. A central light beam including the axis of symmetry and two light beams in the peripheral portion not including the axis of symmetry. Spatially symmetrically separates from the plane of the divided multi-segmented photodetector, and causes each light beam to converge at a spatially different focal position apart from the plane of the multisegmented photodetector, including the optical axis direction. A split convergence element, and when the transmitted light of the split convergence element is incident and the objective lens is focused on the information recording medium, does not include the symmetry axis on the cross section of the light flux of the reflected light flux. The multi-segment photodetector located at an intermediate position in the optical axis direction between two focal points formed by converging two peripheral light beams, wherein two peripheral light beams not including the axis of symmetry enter and form each light beam. A first and a second two-divided light receiving region arranged so as to receive the light amount substantially uniformly with a dividing line substantially parallel to the axis of symmetry for each of the two substantially congruent light spots; A central beam including the axis of symmetry enters, With respect to one light spot formed by the center light beam, the light amount is received substantially uniformly by at least one division line substantially coincident with the center line substantially parallel to the recording track in the light beam cross section of the center light beam. The multi-divided photodetector formed by a third light-receiving area disposed in the first light-receiving area; and a substantially congruent light spot formed in each of the first two-divided light-receiving area and the second two-divided area. A first differential amplifier that electrically connects light receiving regions existing at different positions to each other to obtain a sum, and obtains a difference between the summed electric signals; An optical head, comprising: a second differential amplifier that takes a difference between electric signals generated in each light receiving region divided by the division line in the region. 2. The optical head according to claim 1, wherein the divided converging element is an integral element manufactured by press molding or the like. 3. The optical head according to claim 1, wherein the divided converging element is a hologram element.