JPH0440632A - Optical head - Google Patents

Abstract

PURPOSE:To minimize a constitutional element and to obtain a compact and inexpensive optical head by constituting the optical head so as to detect both of a focus error signal serving also as a tracking error signal. CONSTITUTION:The shapes of approximately congruent optical spots 19b, 19c formed in respective light receiving areas 18b, 18c are electrically formed on the light receiving ares existing in different positions dividied by dividing lines 20b, 20c are added to obtaine a sum and the difference of respective electric signals is found out by a differential amplifier 22A to detect a focus error signal. On the other hand, the difference between respective electric signals generated in respective light receiving areas divided by a division line 20a is found out by a differential amplifier 22B to detect a tracking error signal. Consequently, the compact and inexpensive optical head minimizing the number of constitutional elements can be obtained.

Description

[Detailed Description of the Invention] Industrial Field of Application The present invention has an information recording medium and a focus error signal detection method for recording, re-aiming, erasing information, etc. by irradiating a light beam such as a laser beam. 2. Related Art Regarding Optical Head of Optical Disk Device Having Tracking Error Signal Detecting Means Conventional Technology There have been many reports regarding the techniques relating to focus error signal detecting means and tracking error signal detecting means in conventional optical heads, but the following are as follows. A conventional optical head will be explained with reference to the drawings.

An example of a schematic configuration of a conventional optical head is shown in FIG.

In Figure 4, 1 is the leading edge 2 is the beam splitter A
, 3 is an objective lens, 4 is an optical disk which is an information recording medium, 5 is a beam splitter I3, 6 is a lens A, 7 is a two-split photodetector A, 8 is a differential amplifier A, 9 is an optical spot A, 7p is the dividing line of the two-split photodetector 7, and 10
is the lens B, 11 is the knife, 12 is the two-split photodetector B, 13 is the differential amplifier B, 14 is the optical spot B, 12p is the dividing line of the two-split photodetector 12, and 15 is the summing amplifier. Below, we will explain the operation of a conventional optical head with reference to the drawings. The light emitted from the light source 1 passes through the beam splitter A2, passes through the objective lens 3, and forms a light spot on the optical disk 4. The direction of the recording track on the optical disk 4 is perpendicular to the plane of the paper.The reflected light from the optical disk 4 follows the opposite path, passes through the objective lens 3, is reflected by the beam splitter A2, enters the beam splitter B5, and becomes transmitted light. Even though it is separated into reflected light, this transmitted light passes through lens A6 and becomes convergent light, resulting in a light spot A9 on two-split photodetector A7.
Here, the dividing line 7p of the two-split photodetector A7 is set at a position that roughly divides the light intensity of the light spot A9 into two, and the differential amplifier A8 generates light in the two light receiving areas of the two-split photodetector A7. By taking the difference between each electrical signal, the tracking error signal can be detected by the so-called push-pull method.
The light becomes convergent after passing through, and forms a light spot B14 on the two-split photodetector B12. Here, the knife 11 is placed at a position that blocks approximately half of the convergent light from the lens BIO, and the dividing line of the two-split photodetector B12 12p is set to be approximately parallel to the edge line of the knife edge 11 on the cross section of the light beam so as to divide the light amount of the light spot B14 into approximately two equal parts,
By taking the difference between the electric signals generated in the two light receiving areas of the two-split photodetector B12 using the differential amplifier B13, a focus error signal can be detected by the so-called Knifezi method. Split photodetector A7
．． By taking the sum of all the electrical signals generated by the two-split photodetector B12, the information signal on the optical disc 4 can be detected.

Problems to be Solved by the Invention In the above-mentioned conventional optical head, a focus error signal and a tracking error signal are each independently detected.A beam splitter separates reflected light from the optical disk 4 into transmitted light and reflected light. B5 is required, and lens A6. As with the lens B10 and the two-split photodetector A7 and the two-split photodetector B12, it is not necessary to duplicate the components between the two paths.Therefore, the number of components is large, thus avoiding an increase in the size and cost of the optical head. There is a serious drawback that it cannot be done.

In view of the above problems, the present invention realizes a configuration that detects both the focus error signal and the tracking error signal, thereby eliminating the need for a beam splitter that separates the reflected light from the optical disk into transmitted light and reflected light. In other words, a small and inexpensive optical head with a minimum number of components can be provided.

Means for Solving the Problem To achieve this object, the optical spatula of the present invention includes: a light source, an objective lens that converges the emitted light from the light source onto an information recording medium having a recording track, and a Information signal by reflected light.

A focus servo is provided by a detection means for detecting a focus error signal and a tracking error signal, and by driving an objective lens in a focus direction substantially parallel to the optical axis direction of the objective lens and in a tracking direction substantially perpendicular to the recording track and the focus direction. A means for applying a tracking servo is used to detect the focus error signal and the tracking error signal.The means for detecting the focus error signal and the tracking error signal transmits the reflected light from the information recording medium, and in the cross section of the light beam, the center line which is approximately perpendicular to the recording track is used as the axis of symmetry. The beam is divided spatially symmetrically away from the plane of the multi-split photodetector into two beams: a central beam that includes the symmetry axis and a peripheral beam that does not include the symmetry axis, and each beam includes the optical axis direction. When the transmitted light of the divided convergence element is incident on a divided convergence element that converges at spatially different focal positions away from the plane of the multi-divided photodetector, and the objective lens is focused on the information recording medium, the reflected light flux is A multi-segment photodetector exists at an intermediate position in the optical axis direction between two focal points formed by convergence of two peripheral light beams, and two peripheral light beams that do not include the axis of symmetry are incident on each beam cross section. For each of the two substantially congruent light spots forming the luminous flux, a first and a second two light spots are arranged so as to receive a substantially uniform amount of light at a dividing line substantially parallel to the axis of symmetry.
A central light beam including a divided light receiving area and a symmetry axis is incident, and for one light spot formed by the central light beam, at least one divided light beam substantially coincides with a center line substantially parallel to the recording track in a beam cross section of the central light beam. A multi-segment photodetector is formed by a third light-receiving area arranged so as to receive a substantially uniform amount of light in a line, and a substantially split light-receiving area formed in each of the first and second two-segment light-receiving areas. a first differential amplifier that calculates the sum by electrically connecting the light receiving areas located at different positions with respect to the shape of the congruent light spot; and a second differential amplifier that takes the difference between the electrical signals generated in each of the three light-receiving regions divided by the dividing line.With this configuration, the focus error signal and the tracking error can be detected. It is also possible to detect signals, and there is no need for means for separating the reflected light from the information recording medium into transmitted light and reflected light, and redundant components can also be eliminated. In other words, it is possible to realize a small and inexpensive optical head with a minimum number of components. In FIG. 1, which is a schematic configuration diagram of an optical head in an embodiment, 1 is a beam 1t2 is a beam splitter A
, 3 is an objective lens, and 4 is an optical disk which is an information recording medium.

Reference numeral 16 denotes a split convergence element, which transmits the reflected light from the optical disk 4, and in the cross section of the light beam, the central light beam including the axis of symmetry is incident with the center line substantially perpendicular to the recording track as the axis of symmetry, and is focused at a focal point 17a. a first lens 16a that converges the beam, and a focal point 17b that is spatially different from the focal point 17a of the first lens 16a, including the optical axis direction, on which each of the two peripheral light beams that do not include the axis of symmetry enters. , 17
2nd to converge to C. Third two lenses 16b, 1
From 6c, L 18 is 3 after passing through the split convergence element 16.
Multi-division light detection with two incident light beams it9 a, 19
b, 19 c are three light spots formed on the multi-split photodetector 18 by the split convergence element 16, 1
8 a, 18 b, 18 c + & 3 light receiving areas vj, 2 within the multi-division photodetector 18 that receive each of the three light spots 19a, 19b, 19c.
0b and 20c are dividing lines approximately parallel to the axis of symmetry, which is the center line approximately perpendicular to the recording track, in the cross section of the beam of reflected light from the optical disk 4 for the optical spots 19b and 19c formed in the light receiving areas 18b and 18c. and 20a is the light receiving area 1.
For the light spot 19a formed on the optical disc 8a, the dividing line is a dividing line that substantially coincides with a center line that is substantially parallel to the recording track in the cross section of the beam of reflected light from the optical disc 4, and is arranged so that the amount of light is received almost uniformly. The light receiving area 21b is the light receiving area 1.
The divided IL 21c that divides 8a and 18b is the light receiving area 18.
The dividing line 22 which divides a and 18c, 22B is a differential amplifier, and 23 is an addition amplifier. Note that the multi-segment photodetector exists at an intermediate position in the optical axis direction between the two focal points 17b and 17c when the focal point of the objective lens 3 is on the optical disk 4.Hereinafter, the present invention will be explained with reference to the drawings. To explain the operation of the optical head of the embodiment, the light emitted from the light source 1 passes through the beam splitter A2, passes through the objective lens 3, and forms a light spot on the optical disk 4. At this time, the recording track on the optical disk 4 is formed. The direction is perpendicular to the plane of the paper, and the reflected light from the optical disk 4 follows the opposite path, passes through the objective lens 3, and enters the beam splitter A.
The transmitted light of the split convergent element 16 is spatially split into three light fluxes, and three light beams are projected onto the multi-split photodetector (19a).
Even if the light spots 19b and 19c are formed, at this time, the shapes of the substantially congruent light spots 19b and 19c formed in the light receiving area 18b and the light receiving area 18c are divided by the dividing lines 20b and 20c at different positions. The focus error signal can be detected by electrically connecting the light-receiving areas existing in the two areas, calculating the sum, and using the differential amplifier 22A to calculate the difference between the summed electric signals. Compared to the Knifezi method described in the conventional example of FIG. 4, which obtains a focus error signal from changes in the shape of the light spots 19b and 19c, it is not affected by changes in the position of the multi-segment photodetector 18 (X).

Further, in the light receiving area 18a, a tracking error signal can be detected by using a differential amplifier 22B to take the difference between the electrical signals generated in each light receiving area divided by the dividing line 20a. The optical spot 19a, which is arranged approximately parallel to the track, has as a light amount component the ±1st-order diffracted light of the recording track that is symmetrical about the dividing line 20a. The differential amplifier 22B calculates the difference in the amount of light received by each light receiving area divided by
This is the principle of detecting the tracking error signal using the so-called push-pull method.4 Furthermore, if the sum of all the electrical signals generated in each light receiving area of the multi-division photodetector 18 is calculated using the summing amplifier 23, then the optical disc 4 is Information signals can be detected.

FIG. 2 is an explanatory diagram of the focus error signal detection operation in FIG. 1. Here, only the multi-divided photodetector 18 and the light spot formed are illustrated, and other components are omitted.

FIG. 2(A) shows a case where the objective lens 3 is focused on the optical disc 4. At this time, parallel light is incident on the split converging element 16, so that a light spot 19b is formed in the light receiving areas 18b and 18c. .

19c are substantially congruent, and even if the four light receiving areas receive a substantially uniform amount of light due to the dividing lines 20b and 20c, 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 in a direction away from the objective lens 3, and at this time, the divided converging element 16 receives converged light compared to FIG. 2(A). Light spot 19 formed in region 18b
b becomes large, and the light spora h19c formed in the force light receiving area 18c becomes small (this may cause an imbalance in the amount of light in the four light receiving areas formed by the dividing lines 20b and 20c. Therefore, the focus, which is the output of the differential amplifier 22A The error signal becomes negative.

FIG. 2(C) shows a case where the optical disc 4 is displaced in a direction approaching the objective lens 3, and at this time, the split converging element 16
The light that is diverging as compared to that in FIG. 2(A) is incident. Therefore, the light spot 19b formed in the light receiving area 18b becomes smaller, and the light spot 19c formed in the light receiving area 18c becomes larger, and the light spot 19c formed in the light receiving area 18c becomes larger.
An imbalance occurs in the amount of light in the two light receiving areas. Therefore, the focus error signal output from the differential amplifier 22A is positive. However, although the differential amplifier 22B and the summing amplifier 23 are omitted in FIGS. 2(B) and 2(C), the present embodiment shown in FIGS.
i A means for detecting both a focus error signal and a tracking error signal can be achieved with one split converging element 16 and one multi-segment photodetector 18. That is, the fourth
In contrast to the configuration of the conventional optical head shown in the figure, the optical disk 4
There is no need for a beam splitter that separates the reflected light from the beam into transmitted light and reflected light, and redundant components can also be eliminated, making it possible to create a compact and inexpensive optical head with a minimum number of components. A4 Here, the relative positional relationship between each light receiving area and each light spot on the multi-segmented photodetector 18 is not limited to the embodiment shown in FIG.
6 may have a function of deflecting the light beam to be split, and the relative positional relationship between each light receiving area and each light spot on the multi-segment photodetector 18 can be set arbitrarily. Only the detector 18 and the light spot formed are shown in FIG. 3 as a second embodiment of the invention. The other components are the same as those shown in FIG.
A sumo wrestler with the ability to deflect the light beam that only splits is omitted here.

In FIG. 3, the light receiving areas 18b and 18c are separated by a dividing line 24.
Therefore, the dividing line 20b
, 20c and the dividing lines 21b, 21c each become one dividing line to form four divided light receiving areas L. The four light receiving areas receive a uniform amount of light for the two substantially congruent light spots 19b, 19C. Therefore, the focus error signal can be detected by calculating the sum of the diagonals of the four light-receiving areas and calculating the difference between the sum signals using the differential amplifier 22A.

On the other hand, the light receiving area 18a is located adjacent to the light receiving areas 18b and 18c with the dividing lines 21b and 21c in between. On the other hand, in the cross section of the reflected light beam from the optical disk 4, the dividing line is a dividing line that approximately coincides with the center line that is approximately parallel to the recording track, and even if it is arranged so that the amount of light is received almost uniformly, the dividing line 2
Even if 0a is arranged approximately parallel to the recording track (optical spora) 19a has the ±1st-order diffracted light of the recording track that is symmetrical about the dividing line 20a as a light amount component, the dividing lines 25b and 25c are There are two dividing lines symmetrical to the dividing line 20a, and both ends of the dividing line 20a are dividing lines 25b.

Even if the light receiving area 18a is divided into two by a rectangular, substantially S-shaped dividing line, the dividing line 25b, 20 may be connected to one end of the optical disc 25c.
The principle that a tracking error signal can be detected by calculating the difference in the amount of light received by each light receiving area divided into two by the rectangular substantially S-shaped dividing line of a and 25c by the differential amplifier 22B. In this case, the dividing line 25b,
If you set the position of 25c to the appropriate position, light spora) 19
Compared to the general push-pull method in which a is divided into two by a dividing line 20a, it is possible to significantly reduce the offset of the tracking error signal caused by the positional deviation of the objective lens 3 in the tracking direction. In a disk device, if the objective lens 3 moves from the neutral position in the tracking direction due to acceleration etc. when moving the optical head, the retraction ability of the tracking servo will be greatly improved.If the objective lens 3 is moved from the neutral position in the tracking direction due to acceleration etc. when moving the optical head, the retraction ability of the tracking servo will be greatly improved. In the case where there is In the case of the relative positional relationship with the spot ζ, compared to the positional relationship shown in FIG. 18b, 18
C1 light spot 19a, 19b, 19c
, dividing lines 20a, 20b, 20c, dividing lines 21b, 21c.

The differential amplifiers 22 and 22B and the summing amplifier 23 are the same components as in the embodiment of FIG.

It goes without saying that a split convergence element (tomo) may be an integral element manufactured by press molding, etc., but it is also effective from the point of view of transmittance of the element. Needless to say, it is also effective in terms of the manufacturing transmittance of the element.As described above, the first and second embodiments of the present invention have a focus error signal and a tracking error signal. It is also possible to achieve the means for detecting both of
In contrast to the configuration of the conventional optical head shown in the figure, the optical disk 4
There is no need for a beam splitter to separate the reflected light from the beam into transmitted light and reflected light, and redundant components can be eliminated.In other words, a compact and inexpensive optical head with a minimum number of components can be realized. Effects of the Invention The Invention ζ A light source, an objective lens that converges light emitted from the light source onto an information recording medium having a recording track,
A detection means for detecting an information signal, a focus error signal, and a tracking error signal by reflected light from an information recording medium; A means for detecting the focus error signal and the tracking error signal by driving in the perpendicular tracking direction and means for detecting the focus error signal and the tracking error signal. The beam is divided spatially symmetrically away from the plane of the multi-split photodetector into two beams: a central beam that includes this axis of symmetry and a peripheral beam that does not include the axis of symmetry. and a split convergence element that converges each light beam to spatially different focal positions apart from the plane of the multi-split photodetector including the optical axis direction, and the transmitted light of the split convergence element is incident on the information recording medium. When the objective lens is focused, α on the beam cross section of the reflected beam is a multi-segment photodetector that exists at an intermediate position in the optical axis direction of two focal points formed by convergence of two peripheral beams, and is symmetrical. Two peripheral light beams that do not include the axis are incident, and each light beam forms two approximately congruent light spots,
A central light beam including the symmetry axis enters the first and second two two-part light-receiving areas, which are arranged so as to receive a substantially uniform amount of light along a dividing line that is substantially parallel to the symmetry axis, and forms a central light beam. A third light-receiving area is arranged to receive a substantially uniform amount of light for one light spot with at least one dividing line that substantially coincides with a center line that is substantially parallel to the recording track in a cross-section of the central light beam. A multi-division photodetector formed by A first differential amplifier that calculates the sum by electrically connecting each electrical signal and then taking the difference between the summed electrical signals; It is characterized by comprising a second differential amplifier that takes the difference between electrical signals.

With this configuration, a means for detecting both a focus error signal and a tracking error signal can be achieved with an extremely simple configuration of one segmented converging element and one multi-segmented photodetector, which is different from the conventional optical head. For the configuration of
There is no need for a beam splitter that separates the reflected light from the optical disk 4 into transmitted light and reflected light, and redundant components can also be removed. 4 In other words, a small and inexpensive optical head with a minimum number of components can be realized. In addition, the split convergence element may have the function of deflecting the light beam to be split, and the relative positional relationship between each light receiving area and each light spot on the multi-segment photodetector can be set arbitrarily. In particular, a system developed from the push-pull method can be used for tracking error signal detection, and the adjustment of the multi-segment photodetector can be simplified.

Furthermore, the segmented convergence element may be an integral element manufactured by press molding or the like, or it may be a hologram element.
This is also effective from the viewpoint of characteristic stability.

Therefore, the optical head of the present invention has an extremely simple configuration, and can realize an excellent optical head with stable characteristics that is small, inexpensive, and easy to adjust.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of an optical helad according to a first embodiment of the present invention. FIGS. 2(A), (B), and (C) are partial operation explanations of the embodiment. FIG. 3 is a diagram of the present invention. A doctor explaining the main parts of the optical head in the second embodiment of the invention. Figure 4 is a schematic diagram of the conventional optical head. 2. 5. ・Beam Subbrikkyu 3...
・Objective lens, 4. ・Optical disc length 6°10, 1
6a, 16b, 16c... Len, ;(7゜1
2.18・・Light detection edge 8, 13, 22, 22B・・
・Differential amplifier, 9. 14. 19a, 19b,
19c... light spot, 11... naifetsuji,
15.23...Summing amplifier, 16...Division converging element, 17a, 17b, 17cm...Focus A
18a, 18b, 18c...light receiving area
20a, 20b, 2oc... Parting line 21b,
21 c, 24. 25 b, 25 c...
・Name of split agent: Patent attorney Shigetaka Awano and 1 other person
u, Ilk lAC'-lens/7L 17b, /7cm! ! -color m, ulb, 21t, 2ftt, 21b, 2
/c - Separation line 12 diagram [4 disputes (rack diagram diagram 1 prisoner

Claims (3)

[Claims] (1) A light source, an objective lens that converges the light emitted from the light source onto an information recording medium having a recording track, and detecting an information signal, a focus error signal, and a tracking error signal by the reflected light from the information recording medium. a detection means, and a means for applying focus servo and tracking servo by driving the objective lens in a focus direction substantially parallel to the optical axis direction of the objective lens and in a tracking direction substantially perpendicular to the recording track and the focus direction; The means for detecting the focus error signal and the tracking error signal transmits the reflected light from the information recording medium, and the means for detecting the focus error signal and the tracking error signal transmits the reflected light from the information recording medium, and sets the center line substantially perpendicular to the recording track as an axis of symmetry in the cross section of the light beam. The light beam is divided spatially symmetrically away from the plane of the multi-split photodetector into a central beam including the axis of symmetry and two beams at the periphery that do not include the axis of symmetry, and each beam is aligned in the direction of the optical axis. A divided converging element converges to spatially different focal positions apart from the plane of a multi-divided photodetector, and transmitted light of the divided converging element is incident, and the focal point of the objective lens is on the information recording medium. In the multi-segment photodetector, the multi-segment photodetector is located at an intermediate position in the optical axis direction of two focal points formed by convergence of two peripheral light beams not including the symmetry axis on a cross section of the reflected light beam. Then, two peripheral light beams that do not include the axis of symmetry are incident, and the amount of light is made almost uniform for each of the two substantially congruent light spots formed by each light beam by a dividing line that is substantially parallel to the axis of symmetry. A central light beam including the axis of symmetry enters the first and second two-split light-receiving areas arranged to receive light, and the central light beam forms one light spot. The multi-divided light is formed by at least one dividing line that substantially coincides with a center line that is substantially parallel to the recording track in a cross section of the light beam, and a third light-receiving area that is arranged so as to receive a substantially uniform amount of light. a detector;
In the first two-part light-receiving area and the second two-part light-receiving area, the light-receiving areas located at different positions are electrically connected to each other with respect to the shapes of substantially congruent light spots formed therein. A first differential amplifier that calculates the sum and takes the difference between the summed electric signals, and a difference between the electric signals generated in each of the light receiving areas divided by the dividing line in the third light receiving area. and a second differential amplifier that takes (2) Claim 1, characterized in that the split convergence element is an integral element manufactured by press molding or the like.
Optical head described in section. (3) The optical head according to claim 1, wherein the split convergence element is a hologram element.