JPH0675300B2 - Optical head device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an optical information processing apparatus for recording, reproducing and erasing information by using light, and more particularly to an optical head apparatus using a holographic element. is there.

[Prior Art] An optical head device equipped with a holographic beam splitter is known as disclosed, for example, in Japanese Patent Publication No. 56-57013. 11th conventional optical head device
This will be described with reference to FIGS. In the figure, 1 is a semiconductor laser which is a light source, 2 is a light flux emitted from the semiconductor laser 1, 8 is a diffraction grating which is a three-flux generating means for separating the emitted light flux 2 into three light fluxes having different focusing positions, and 3 Is a condensing lens which is a condensing means for condensing the emitted light beam 2 on an optical disc 4 which is an information storage medium, and the optical disc 4 has a track 9 concentrically storing information. 5
Is a holographic beam splitter which is a beam splitter means. This holographic beam splitter 5 has a fringe shape in which the grating period is gradually different in the aperture because it imparts astigmatism to the reflected light beam 6a which is the first-order diffracted light.
The reflected light beam 6 diffused and reflected from the optical disk 4 is separated from the outgoing light beam 2 to form an astigmatic reflected light beam 6a. 7
Is a photodetector that receives the reflected light beam 6a. As shown in FIG. 12 (b), this photodetector 7 has an internal optical element 7a.
Based on the output signals of the main detector 7t which is divided into 4 to 7d and detects the main reflected light beam 6t, the optical elements 7e and 7f which are grounded on both sides of the main detector 7t, and the optical elements 7a to 7f. It is composed of arithmetic elements 18 and 19 for performing each arithmetic operation.

In the above structure, the outgoing light flux 2 emitted from the semiconductor laser 1 is separated into three outgoing light fluxes 2 by the diffraction grating 8. Next, the emitted light beam 2 passes through the holographic beam splitter 5, but only the 0th-order diffracted light beam is collected by the condenser lens 3
As a result, the tracks 9 on the optical disc 4 are irradiated with three substantially aberration-free focused spots 10a, 10e, 10f. Then, the reflected light beam 6 diffused and reflected from the optical disk 4 again enters the holographic beam splitter 5 via the condenser lens 3, and its traveling direction can be changed. The first-order diffracted reflected light beam 6a from the optical disc 4, that is, the reflected light beam 6a whose traveling direction is refracted by an angle θ by the holographic beam splitter 5, is detected by a photodetector 7 placed at a distance δ from the semiconductor laser 1. Received light. At this time, the reflected luminous flux 6a is 3
The reflected light flux 6a is received by the main light detecting portion 7t, the reflected light flux 6e is received by the optical element 7e, and the reflected light flux 7f is received by the optical element 7f. Each optical element of the main light detection unit 7t
The reflected light flux 6t is detected by 7a to 7d and a signal is output, and the arithmetic elements 18a to 18c are based on the above output [7a + 7b + 7c + 7d].
Then, the reproduction signal 17 is obtained to read the information of the track 9.

However, in the optical disc 4, the center of rotation of the drive unit for the optical disc 4 and the center of the optical disc 4 do not normally coincide with each other due to a mounting error or the like. Therefore, the track shift occurs due to the rotation. There is a twin spot method as a method of detecting the track deviation, for example, Japanese Patent Publication No. 53-131.
It is known as described in No. 23. Hereinafter, a method for detecting a track shift by the twin spot method will be described.
FIG. 12A shows an ideal positional relationship between the track 9 and the focused spot 10 on the optical disc 4. Since the reading of information must be performed correctly on the track 9 in order to perform reading at the focused spot 10a, the focused spots 10a, 10e, 10
The line connecting f is arranged so as to be slightly inclined with respect to the track 9. The focused spots 10e and 10f are diffused and reflected to become reflected light beams 6e and 6f, respectively, which are received by the optical elements 7e and 7f via the focusing lens 3 and the holographic beam splitter 5. Output of these optical elements 7e, 7f (focus spots 10e, 10f
Difference of the reflection intensity of) is obtained by the arithmetic element 19a,
An output proportional to the track shift, that is, the tracking error signal 11 is obtained. This tracking error signal 11
Is applied to a tracking actuator (not shown) that moves the condensing lens 3 in a direction perpendicular to the track 9, so that the condensing spot 10a can be constantly focused on the center of the track 9.

In addition, the surface of the optical disk 4 is not usually flat, and surface wobbling occurs due to rotation, and defocusing occurs. As this defocus detection method, there is a method (astigmatism method) in which astigmatism is given to the reflected light beam 6 from the optical disk 4 and the defocus is detected from the change in the shape of the light beam, for example, Japanese Patent Publication No. 53-39123. It is known as described. Hereinafter, a method of detecting a focus shift will be described. The holographic beam splitter 5 gives astigmatism to the reflected light beam 6. At this time, in the detection area of the main photodetector 7t of the photodetector 7, the reflected light beam 6t changes such that the elliptical direction differs by 90 ° from the circle to the perspective due to the shift of the focal position of the condenser lens 3 on the optical disc 4. That is, from the reference state shown in FIG. 13 (b), when the optical disk 4 approaches from the focus position, it changes as shown in FIG. 13 (a), and when it moves away from it, it changes as shown in FIG. 13 (c). The change of the reflected light beam 6t is detected by the optical elements 7a to 7d. The optical elements 7a to 7d output an output according to the amount of received light, and the operation elements 18a, 18b, and 19b output [(7a + 7c)
-(7b + 7d)] is performed to obtain this comparison output, that is, the focusing error signal 12. If this focusing error signal 12 is applied to a focusing actuator (not shown) that moves the condenser lens 3 in the optical axis direction to operate it, it is possible to correct the defocus of the focused spot 10 on the optical disc 4.

As described above, the conventional optical head device has the holographic beam splitter 5, and the beam splitter function and the astigmatism generating function for detecting the focus shift can be realized by one component, so that the configuration is simple. Further, since the diffraction grating 8 is provided and the twin spot method is used, stable tracking deviation can be corrected.

[Problems to be Solved by the Invention] Since the conventional optical head device is configured as described above, in order to use the twin spot method, the diffraction grating 8 is provided with the semiconductor laser 1 and the holographic beam splitter 5.
It is necessary to dispose the light beam 6a and the reflection light beam 6a so that the traveling direction of the reflected light beam 6a is largely changed so that the reflected light beam 6a is not blocked by the diffraction grating 8. In order to have each diffraction of the angle θ, where P is the grating period of the holographic beam splitter 5 and λ is the wavelength of the semiconductor laser 1, a grating period given by P≈λ / θ is required. For example, θ = 0.7rad
(About 40 °) and λ = 0.78 μm, the grating period becomes P = 1.1 μm, which is very small, and it is difficult to fabricate the holographic beam splitter 5, and the semiconductor laser 1 and the photodetector 7 have a small gap. There has been a problem that the distance δ also becomes large and the optical head device becomes large.

The above problem occurs because the reflected light beam 6a reaches the photodetector 7 while avoiding the diffraction grating 8. Therefore, as shown in FIG. 14, an optical head device in which the reflected light beam 6a reaches the photodetector 7 after passing through the diffraction grating 8 again can be considered. This optical head device can be easily manufactured because the diffraction angle θ of the holographic beam splitter 5 can be made small, and the distance δ can be made small, so that the device can be made compact. However, since the reflected light beam 6a is transmitted through the diffraction grating 8, there are the following problems.

The diffraction grating 8 separates the luminous flux 2 emitted from the semiconductor laser into three luminous fluxes. These three light beams are diffusely reflected from the optical disk 4, and the reflected light beams 6a (6t, 6e, 6f) diffracted by the holographic beam splitter 5 are again reflected by the diffraction grating 8
Through. At this time, the reflected light beams 6t, 6e, 6f are each divided into three light beams, and a total of nine light beams are detected by the photodetector 7. This luminous flux is represented by 6tα, 6eα, 6fα (α: diffraction order-1,0 _{, + 1} ), and the state of the reflected luminous flux 6a with which the photodetector 7 is irradiated is shown in FIG. First, the main photodetector 7t includes two reflected light beams 6e ₊ 1,6 in addition to the original reflected light beam 6t.
Receives f _-1 . Since the unnecessary reflected light beams 6e ₊₁ and 6f _-1 read the information of the track 9 on the optical disc 4 different from the focused spot 10a, they become noise for the original signal, and as a result, the performance of the reproduction signal 17 deteriorates. . Next, the tracking error signal 11 is obtained by the differential output between the optical element 7e and the optical element 7f, but if the optical disk 4 tilts due to surface wobbling or the like, 2
There is a problem that the two optical elements 7e and 7f are out of balance and the tracking error signal 11 is offset. That is, in the optical element 7e, the two reflected light beams 6e ₀ and 6t _-1 are overlapped. Since the respective light fluxes from the semiconductor laser are reflected by the optical disk 4 and reach the optical element 7e, the optical path lengths are substantially equal to each other, which causes interference on the optical element 7e, and the output is two reflected light fluxes.
The sum of the intensities of 6e ₀ and 6t _-1 cannot be obtained. Further, when the optical disc 4 is tilted, the difference in the optical path length is slightly changed and the interference state is changed, so that the detection output is also changed, and as a result, the tracking error signal 11 is unstablely changed.

The present invention has been made to solve the above-mentioned problems, and the diffraction angle θ of the beam splitter means can be small, and the deterioration and instability of the signal due to the transmission through the diffraction grating twice can be prevented, Moreover, it is an object of the present invention to obtain an optical head device that can be simplified in size and compact in structure.

[Means for Solving the Problem] An optical head device according to the present invention includes three light generating means for separating a luminous flux emitted from a light source into at least three luminous fluxes having different converging positions, and a reflected luminous flux from a storage information medium. Is formed from one holographic element, and the holographic element is composed of a grating area which is the three light generating means and a grating area which is the beam splitter means on the same plane. A plurality of grating regions are formed, and each grating region has at least a different diffraction direction or angle.

[Operation] The optical head device according to the present invention has a plurality of grating regions, each of which is composed of a grating region serving as three light generating means and a grating region serving as beam splitter means, on the same plane. The holographic element having different diffraction angles separates the outgoing light beam, and diffracts only the reflected light beam that irradiates the grating area, which is the beam splitter means, and causes the photodetector to receive it, and separates it from other reflected light beams. .

[Embodiment] An optical head device according to an embodiment of the present invention will be described below with reference to FIGS. 1 to 4. Note that FIG. 11 to FIG.
The same parts as those in FIG. 13 are designated by the same reference numerals and the description thereof is omitted.
In the figure, 13 is a holographic element, and on the same plane, a grating region 13a having a function of a diffraction grating which is a three-beam generation means and a grating region 13b having a function of a holographic beam splitter which is a beam splitter means are provided. The grating regions 13a and 13b have different diffraction directions, that is, the grating region 13a has the Y-axis direction and the grating region 13b has the X direction.
It is provided so as to have an axial diffraction direction. The holographic element 13 has a substantially aberration-free condensing spot 10a through which the light beam 2 emitted from the semiconductor laser 1 is transmitted and only the 0th-order diffracted light is condensed on the track 9 on the optical disc 4 by the condensing lens 3. Become. At this time, if the holographic element 13 is prepared so that the 0th-order diffraction efficiencies in the grating regions 13a and 13b are equal, the 0th-order diffracted light is collected by the condenser lens 3 while maintaining the intensity distribution of the outgoing light beam 2. It can be illuminated and does not have a discontinuous intensity distribution. That is, as shown in FIG. 3, the holographic element 13 is a phase type diffraction grating, and SiO ₂ and TiO ₂ are formed on the glass substrate.
₂ or the like is vapor-deposited, or a relief is integrally molded on a plastic substrate.
It is manufactured so that the grating thickness d at b and the refractive index η are equal. When the wavelength in vacuum is λ, the light α and β have a phase difference amount (η-1) d · 2π / λ. When the phase difference amounts are equal in the grating regions 13a and 13b, the 0th-order diffracted light intensities are equal. In the grating region 13b, two light beams from the point light source arranged at the position of the semiconductor laser 1 and the astigmatism light source having the circle of least confusion at the center of the main detector 7t of the photodetector 7 are holographic element 13b. It has a corresponding fringe pattern when interfering above.

In the above configuration, the outgoing light flux 2 that has passed through the holographic element 13 is separated into only three light fluxes that are incident on the grating region 13a, and the three light fluxes 10a, 10e, 10f on the optical disk 4 are condensed by the condenser lens 3. become. The focused spots 10a, 10e, 10f are diffused and reflected by the optical disc 4 to form a reflected light beam 6a, which is incident on the holographic element 13 again via the condenser lens 3. Of the reflected light beam 6, only the light beam incident on the grating region 13b is transmitted and diffracted toward the photodetector 7 to be reflected light beams 6t, 6e, 6f as shown in FIG. Astigmatism is generated in the reflected light beam 6t by the grating region 13b of the holographic element 13, and the reflected light beam 6t is received by the main detector 7t and reproduced by the optical elements 7a to 7d and the arithmetic elements 18 and 19. Signal 1
7, a focusing error signal 12 is obtained. The reflected light beams 6e and 6f are received by the optical elements 7e and 7f, and the tracking error signal 1 is output by the outputs of the optical elements 7e and 7f and the arithmetic element 19b.
Get one. In the reflected light beam 6, the grating region 13a is again formed.
The light beams incident on are separated into three light beams, and nine light beams in total are generated, and they partially overlap and are diffracted light beams 14a to 14a.
4e. However, the diffracted light fluxes 14a to 14e are generated in the grating region 13
Since the diffraction directions of a and the grating region 13b are different, the light is not received by the photodetector 7. Therefore, the photodetector 7 can detect only the necessary reflected light beam 6a, and the unnecessary diffracted light beams 14a to 1a.
4e is never mixed.

As described above, the diffraction angle θ of the holographic element 13
Since it can be made small, the semiconductor laser 1 and the photodetector 7 can be arranged without providing a large distance δ.
It can be configured by a hybrid device 16 in which the semiconductor laser 1 and the photodetector 7 are enclosed in the same package as shown in the fourth example, which is known in -255169.

In this embodiment, the diffraction directions of the grating regions 13a and 13b of the holographic element 13 are different, but the diffraction angles of the grating regions 13a and 13b may be different. Another embodiment is shown in FIG. In the figure, the diffraction angles of the respective grating regions 13a, 13b of the holographic element 13 are different, that is, the diffraction angle of the grating region 13a is φ,
Let the diffraction angle of the grating region 13b be the angle θ, and the angle θ is the angle φ.
It is provided to have a larger angle. It goes without saying that the holographic element 13 has a fringe shape that gives astigmatism to the reflected light beam 6a. Using this holographic element 13, the photodetector 7 is moved in the direction of the diffraction angle,
That is, if provided on the Y-axis, the reflected light beams 6t, 6e, 6f are received by the photodetector 7 and unnecessary diffracted light beams 14a to 14e are not mixed, so that the same effect as this embodiment can be obtained. Also, each of the lattice regions 13a, 13b of the holographic element 13
The boundary line 13c of is a straight line in the X-axis or Y-axis direction,
The boundary line 13c may have any direction and curve, and the grid area 1
3a, 13b may be divided into any number. The holographic element 13 does not have to be arranged in the diffused and emitted light beam 2 of the semiconductor laser 1, but may be arranged in the parallel light beam 2a via the collimator lens 15 as shown in FIG.

Further, in the present embodiment, the astigmatism method is used as the defocus detection method, but other methods may be used. Another embodiment using the Foucault method known from JP-A-54-140533 is shown in FIGS. 7 to 8. In the figure, 20 is a holographic element, which is composed of a grating region 20a having a function of the diffraction grating 5 which is a three-beam generator, and grating regions 20b and 20d having a beam splitter function and a function for detecting defocus, The reflected light beams 6a ₁ and 6a ₂ diffracted by the grating region 20b and the grating region 20d are focused and irradiated in different positions on the photodetector 7 in a substantially aberration-free state. Since the reflected light beam 6a is composed of the three reflected light beams 6t, 6e, 6f from the focused spots 10a, 10e, 10f, it becomes six reflected light beams as shown in FIG. 8 (a). That is, reflected light beam 6e of row B
₁ , 6t ₁ and 6f ₁ are first-order diffracted light from the grating region 20b, and reflected light beams 6e ₂ , 6t ₂ and 6f _{2 in} the C row are first-order diffracted light from the grating region 20d. The grating areas 20b and 20d are stripe patterns when the light flux from the light source placed at the position of the respective reflected light flux spots 6t ₁ and 6t ₂ and the light flux from the semiconductor laser 1 interfere on the surface of the holographic element 20. Has a lattice pattern corresponding to. Alternatively, a lattice pattern of approximately linear approximation may be used. When the optical disk 4 moves back and forth in the optical axis direction due to surface wobbling or the like, the positions of the reflected light beams 6e, 6t, 6f on the photodetector 7 change. That is, when the optical disk 4 approaches the condenser lens 3, it changes as shown in FIG. 7 (b), and when it moves away from it, it changes as shown in FIG. 7 (c). Focusing error signal 12 is an optical element
The outputs of 7a to 7d are obtained by the calculation of [(7a + 7c)-(7b + 7d)]. The tracking error signal 11 is obtained as in the other embodiments. At this time, since the reflected light beam 6a ₁ and the reflected light beam 6a ₂ are separated, they do not interfere with each other, and since they are signals in phase with each other, there is no problem. Further, unnecessary diffracted light beams 14a to 14e are not mixed in the photodetector 7, and good reproduction characteristics can be maintained, and the same effect can be obtained.

Further, as shown in FIGS. 9 to 10, the holographic element 20 is arranged so that the diffracted light in the grating region 20b, that is, the reflected light beam 6a ₁ is condensed in front of the photodetector 7.
In order that the reflected light beam 6a ₂ in the grating region 20d may be received after being collected at the rear of the photodetector 7,
d has been made. That is, as shown in FIG. 10, the reflected light beam 6a ₁ forms an image on the condensing point 21 and the reflected light beam 6a ₂ forms an image on the condensing point 22. In order to generate such reflected light beams 6a ₁ and 6a ₂ ,
In FIGS. 9 and 10, the holographic element 20 is shown.
The grating regions 20b and 20d are designed in a grating shape corresponding to an interference pattern when the light beam having the light source placed at the positions of the condensing points 21 and 22 and the light beam of the semiconductor laser 1 interfere with each other.
Further, this may be a lattice of approximately linear approximation. When the luminous flux is correctly focused on the optical disc 4, the holographic element 20 causes the reflected luminous fluxes 6e ₁ , 6t ₁ , 6f ₁ from the grating region 20b to be in the B row as shown in FIG. 9 (a). , Grid area 20
The reflected light beams 6e ₂ , 6t ₂ and 6f ₂ from d are radiated to the column C and have the same size. In the detection area of the main detector 7t, the reflected light beams 6t ₁ and 6t ₂ are divided into _two by the dividing line in the X-axis direction. It is irradiated as described. In such a configuration of the reflected light flux 6a, when the optical disk 4 approaches the condenser lens 3, the reflected light flux 6a on the photodetector 7 is the reflected light flux 6e of the B row as shown in FIG. 9 (b).
₁ , 6t ₁ , 6f ₁ becomes smaller, the amount of light received at 7a is larger than that at 7b,
The reflected light beams 6e ₂ , 6t ₂ , 6f ₂ of the C row change so that the amount of light received by 7c becomes larger than that of 7d, and when the optical disk 4 moves away, as shown in FIG. 6e ₁ ,
6t ₁ and 6f ₁ become larger, the amount of light received at 7b becomes larger than that at 7a, and C
The reflected light beams 6e ₂ , 6t ₂ , 6f ₂ of the row become smaller and change so that the amount of light received by 7d is larger than that by 7c. Therefore, the focusing error signal 12 is obtained by the operation output of [(7a + 7c)-(7b + 7d)]. Further, since unnecessary diffracted light beams 14a to 14e are not mixed, the same effect as that of the other embodiments can be obtained.

As described above, according to the present invention, the optical head device is
A single holographic element having a plurality of grating regions, each of which is composed of a grating region serving as a three-beam generation unit and a grating region serving as a beam splitter unit, is formed on the same plane, and each grating region has at least different diffraction directions or diffraction angles. By doing so, a stable signal can be obtained, and the size is reduced by the simple configuration.

[Brief description of drawings]

1 is a block diagram of an optical head device according to an embodiment of the present invention, FIG. 2 is a block diagram of a photodetector, FIG. 3 is a partial sectional view of a holographic element, and FIG. 4 is a hybrid element. FIG. 5 to FIG. 7 are external perspective views, FIG. 5 to FIG. 7 are configuration diagrams of an optical head device of another embodiment, and FIG. 8 (a), (b), (c),
9 (a), (b), (c) and FIG. 10 are state diagrams of reflected light beams of other embodiments, FIGS. 11 and 14 are configuration diagrams of a conventional optical head device, and FIG. Figure (a) is a state diagram of the focused spot, Figure 12 (b) is a configuration diagram of the photodetector, Figures 13 (a), (b), (c) and Figure 15 are state diagrams of the reflected light flux. Is. 1 ... Semiconductor laser, 2 ... Emitting light flux, 3 ... Condensing lens, 4 ... Optical disk, 6,6a ... Reflected light flux, 7 ... Photodetector, 9 ... Track, 10 ... Focus spot , 11 ...... Tracking error signal, 12 ...... Focusing error signal, 13 ...... Holographic element, 13a, 13b ...... Grating area, 13c ...... Boundary line, 14 ...... Diffraction beam, 17 ...... Reproduction signal, 18, 19 ... Computing element.

Claims (1)

[Claims] 1. A light source, three light flux generating means for splitting a light flux emitted from the light source into at least three light fluxes having different light focusing positions, and light focusing means for focusing and irradiating the information storage medium with the light flux. In an optical head device having a beam splitter means for separating a reflected light beam from a storage information medium and the emitted light beam, and a photodetector for receiving the reflected light beam,
The three-beam generation means and the beam-splitter means are composed of a single holographic element, and the holographic element is composed of a plurality of grating areas which are the three-beam generation means and the grating area which is the beam-splitter means on the same plane. An optical head device, characterized in that each of the grating regions has at least a different diffraction direction or a different diffraction angle.