JPH0792929B2 - Optical pickup device - Google Patents

Description

The present invention relates to an optical pickup device, and more particularly to an optical pickup device used for reading information from an optical disc.

[Prior Art] FIG. 4 is a diagram of an optical system of a conventional general optical pickup device that does not use a holographic grating.

In FIG. 4, first, the laser light 16 emitted from the semiconductor laser light source 1 is read by the diffraction grating 12 to read the pit signal on the disk 7 and to shift the tracking from the 0th order light 17a for reading the shift of the focus. One to one for reading
It is divided into the next lights 17b and 17c. These three light beams 17a, 17b,
After 17c is reflected by the flat plate beam splitter 13,
It is made parallel by the collimator lens 5, and the objective lens 6
Incident on the information surface of the disc 7 and three light spots 18
Form a, 18b, 18c. At this time, light spots 18b, 18c
Is a light spot that goes ahead or behind in the tangential direction of the disk 7 across the light spot 18a of the 0th order light.

The reflected light reflected by the information surface of the disk 7 returns to the same optical path again and passes through the flat plate beam splitter 13. At this time, astigmatism is generated in the light flux that has passed through the flat plate beam splitter 13, and light spots 19a, 19b, 19c are formed on the 6-division light receiving element 15 via the plano-concave lens 14, and the pits of the disk 7 are formed. An RF signal, which is a signal, a tracking error signal by the three-beam method that represents the deviation of tracking, and a focus error signal by the astigmatism method that represents the deviation of the focus of the light spot 18a on the disk 7 are detected. The states of the light spots 19a, 19b, and 19c on the six-division light receiving element 15 at this time are shown in FIGS. 5A, 5B, and 5C.

FIG. 5A is a diagram when the disc is near, FIG. 5B is a diagram when the focus is just, and FIG. 5C is a diagram when the disc is far. In the figure, the focus error signal (FE
S), tracking error signal (RES) and RF signal (R
F) is expressed by the following equation.

FES = (A + D)-(B + C) RES = EF RF = A + B + C + D FIG. 6 is a diagram of an optical system of a conventional general optical pickup device using a holographic grating.

The laser light 22 emitted from the semiconductor laser light source 1 is incident on the holographic grating 20, and then the 0th-order diffracted light is collimated by the collimator lens 5 and a light spot 23 is formed on the information surface of the disk 7 by the objective lens 6. Form.

The reflected light reflected by the information surface of the disk 7 again enters the holographic grating 20 along the same optical path, and the first-order diffracted light enters the four-division light receiving element 21. The above holographic grating 20 is the above disk 7
Two parts with a dividing line parallel to the tangential direction of 20
Since the light is divided into a and 20b, and the focal position of the first-order diffracted light is different, the light incident on the holographic grating 20 is divided into two first-order diffracted lights 24a and 24b, and the four-division light receiving element 21. At the light spot 25
RF signals, a tracking error signal by the push-pull method and a focus error signal by the wedge prism method are detected by forming a and 25b. At this time, the state of the light spots 25a and 25b on the four-division light receiving element 21 is
7A, 7B and 7C are shown.

FIG. 7A is a diagram when the disc is close, FIG. 7B is a diagram when the focus is just, and FIG. 7C is a diagram when the disc is far.

FES, RES and RF are represented by the following equations.

FES = (A + D)-(B + C) RES = (A + B)-(C + D) RF = A + B + C + D [Problems to be solved by the invention] The conventional optical pickup device is configured as described above. However, the optical pickup device that does not use the holographic grating has a large number of parts and also has a large number of adjustment points, resulting in high cost.
On the other hand, in the case of the optical pickup device using the holographic grating, the number of parts is smaller than that of the optical pickup device not using the holographic grating, and the number of adjustment points is small, so that the cost is low. The push-pull method, which is a tracking error signal detection method in the case of an optical pickup device using a graphic grating, has a problem in its performance as compared with the three-beam method using a diffraction grating, and stable tracking error signal detection is possible. There was a drawback that it could not be obtained.

The present invention has been made to solve the above problems, and it is an object of the present invention to provide an optical pickup device which has a small number of parts, is low in cost, and enables tracking error signal detection by the 3-beam method. To aim.

[Means for Solving Problems] An optical pickup device according to the present invention includes a light source, an objective lens for converging a light beam from the light source onto a disc, and a light receiving element for detecting reflected light from the disc. Equipped with. The apparatus is also provided in the optical path of a light beam incident on the disk from the light source, and reads the light beam from the light source for tracking deviation between 0th order light for reading a pit signal on the disk and tracking. A diffraction grating for splitting the light into a pair of primary light. The apparatus is further provided in a holographic grating that guides the reflected light from the disk to the light receiving element, and an optical path of a light beam that enters the light receiving element from the holographic grating, and a signal is produced by the lens action thereof. And a lens unit for increasing the detection sensitivity of. The diffraction grating, the holographic grating, and the lens section are integrally formed in a diffractive element. The diffractive element has a holographic grating surface on which the holographic grating is formed, and a diffraction grating surface on which the diffraction grating and the lens portion are formed.

[Operation] Since the optical pickup device according to the present invention includes the diffraction grating and the holographic grating, stable tracking error signal detection similar to the performance of the three-beam method using the diffraction grating can be obtained. In addition, the diffraction grating, holographic grating and lens part,
Since it is integrally formed in the diffractive element, the number of parts is reduced. In addition, the focus error signal becomes clear and the sensitivity is improved because it is provided in the optical path of the light flux that enters the light receiving element from the holographic grating, and the lens function increases the signal detection sensitivity. To be

[Embodiment] An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a sectional view of a diffraction element of an optical pickup device according to the present invention.

The diffraction element 2 includes a holographic grating surface 3 on the disk side and a diffraction grating portion 4a on the semiconductor laser light source 1 side.
And a diffraction grating surface 4 having a lens portion 4b which is the second optical means.

In the diffraction grating portion 4a of the diffraction grating surface 4 of the diffraction element 2, the light beam 9 from the semiconductor laser light source 1 is read as a 0th order light 9a for reading the pit signal and the focus shift on the disk 7 and tracking light. A pair of primary lights to read the deviation
A diffraction grating divided into 10a and 11a is formed. The diffraction grating can be formed by a commonly used conventional technique.

The three luminous fluxes 9a, 10a, 11a formed here pass through the holographic grating surface 3, and the zero-order diffracted light of the three luminous fluxes 9a, 10a, 11a is converted into the disk 7 described above.
Head to.

On the holographic grating surface 3 of the diffractive element 2, the three-dimensional light beams 9a, 10a, 11a reflected by the disk 7 are directly returned to the semiconductor laser light source 1, and the 0th-order diffracted light and the lens portion 4b are provided. Light receiving element 8
The action of a cylindrical lens (not shown), which is the first optical means for splitting the first-order diffracted lights 9c, 10c, and 11c to be incident on, and generating the astigmatism of the first-order diffracted lights 9c, 10c, and 11c. A hologram having both is formed. The hologram can be formed by a commonly used conventional technique. In addition, the lens portion 4b of the diffraction grating surface 4 is provided with the light from the holographic grating 3
In order to prevent the generation of stray light due to the next-order diffracted lights 9c, 10c, and 11c again passing through the diffraction grating formed in the diffraction grating section 4a,
No diffraction grating is formed. A concave lens surface is formed on the lens portion 4b, and the light beams 9c, 10 incident on the light receiving element 8 are
The vertical magnification of c and 11c is extended to increase the sensitivity of the detected signal.

FIG. 2 is a perspective view showing an optical system of the optical pickup device according to the present invention.

The optical pickup device according to the embodiment includes a semiconductor laser light source 1, an objective lens 6 for focusing a light beam from the light source 1 on a disc 7, a light receiving element 8 for detecting reflected light from the disc 7, and the light source. The light flux from the light source 1 is provided in the optical path of the light flux incident on the disk 7 from the first light source, and a pair of the zero light for reading the pit signal on the disk 7 and the tracking deviation A diffraction grating for splitting into primary light, a holographic grating that guides the reflected light from the disk 7 to the light receiving element 8, and a holographic grating provided in the optical path of a light beam entering the light receiving element 8 from the holographic grating, Optical means that increases the detection sensitivity of the signal by the lens action, and collimates the light flux that has passed through the holographic grating. And a collimator lens 5 to be sent to the object lens 6. The diffraction grating, the holographic grating, and the optical means are integrally formed of plastic or glass to form the diffraction element 2.
The diffractive element 2 is a holographic grating surface 3 having the first optical means (not shown).
And the diffraction grating portion 4a and the lens portion 4b which is the second optical means.
And a diffraction grating surface 4 composed of

Next, the operation will be described.

The laser light 9 emitted from the semiconductor laser light source 1 is incident on the diffraction grating portion 4a of the diffraction grating surface 4 of the diffraction element 2 and the 0th-order light 9a for reading the pit signal on the disk 7 and the focus shift. , For reading tracking deviations 1
It is divided into a pair of primary lights 10a and 11a. These three luminous flux 9
a, 10a, 11a pass through the holographic grating, and the 0th-order diffracted lights of the three light beams 9a, 10a, 11a are collimated by the collimator lens 5 and are incident on the objective lens 6 to be incident on the disk 7 of the disc 7. Three light spots 9b, 10b, 11b are formed on the information signal surface. The three light beams 9a and 10 formed by the holographic grating surface
The first-order diffracted lights a and 11a do not form a spot on the disk 7 and do not affect the signal.
The light spots 10b and 11b are light spots that precede or follow the light spot 9b of the 0th order light 9a in the tangential direction of the disk 7.

The reflected light reflected by the information signal surface of the disk 7 again enters the holographic grating surface 3 of the diffractive element 2 via the objective lens 6 and the collimator lens 5. At this time, on the holographic grating surface 3, the 0th-order diffracted light and the 1st-order diffracted lights 9c, 10c, and 11c whose astigmatism is increased by the action of the cylindrical lens (not shown) of the hologram are formed. The folded light becomes the return light to the semiconductor laser light source, and the first-order diffracted lights 9c, 10c, and 11c pass through the lens portion 4b having the concave lens surface, and the longitudinal magnification is further extended to the 6-division light receiving element 8. It enters and forms light spots 9d, 10d, and 11d. Then, in the 6-division light receiving element 8, as shown in FIG.
A focus error signal by the astigmatism method, a tracking error signal by the three-beam method, and an RF signal which is a pit signal of the disk 7 are detected as shown in FIGS. 3B and 3C.

FIG. 3A is a diagram when the disc is close, FIG. 3B is a diagram when the focus is just right, and FIG. 3C is a diagram when the disc is far. FES, RES and RF are represented by the following equations.

FES = (A + D) − (B + C) RES = EF−RF = A + B + C + D [Advantages of the Invention] As described above, the optical pickup device according to the present invention has both the diffraction grating and the holographic grating. By using the stable tracking error detection method by the three-beam method, the semiconductor laser and the light receiving element can be placed in the same plane. Therefore, it can be easily applied to a light pen having a semiconductor laser and a light receiving element as one element. In addition, the focus error signal becomes clear and the sensitivity is enhanced because it is provided in the optical path of the light flux that enters the light receiving element from the holographic grating and has a lens portion that increases the signal detection sensitivity by its lens action. . Furthermore, since the diffraction grating, the holographic grating, and the lens portion are integrally formed in the diffraction element, the number of parts can be reduced. As a result, it is possible to make an optical pickup device that is much smaller than conventional ones, is cheaper, and has stable performance.

[Brief description of drawings]

FIG. 1 is a sectional view of a diffraction element of an optical pickup device according to the present invention, and FIG. 2 is a perspective view showing an optical system of the optical pickup device according to the present invention, FIGS. 3A, 3B and 3C.
FIG. 4 is a diagram showing the shapes and positions of spots on the 6-division light receiving element of the optical pickup device according to the present invention, and FIG. 4 is a cross section showing the optical system of the conventional optical pickup device without using a holographic grating. Figure, Figure 5A, Figure
5B and 5C are views showing the shape and position of the spot on the 6-division light receiving element, and FIG. 6 is a conventional holographic image.
A perspective view showing an optical system of an optical pickup device using a grating, FIGS. 7A, 7B, and 7C are diagrams showing the shape and position of a spot on a four-division light receiving element. In the figure, 1 is a light source, 2 is a diffraction element, 3 is a holographic grating surface, 4 is a diffraction grating surface, 4a is a diffraction grating portion, 4b is a lens portion, 6 is an objective lens, 7 is a disc, and 8 is a light receiving element. Is. In each drawing, the same reference numerals indicate the same or corresponding parts.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Mitsuharu Tomura 22-22 Nagaike-cho, Abeno-ku, Osaka-shi, Osaka Within Sharp Corporation (56) References JP-A-62-103857 (JP, A) JP-A-58 -102342 (JP, A)

Claims (1)

[Claims] 1. A light source, an objective lens for converging a light beam from the light source on a disc, a light receiving element for detecting reflected light from the disc, and an optical path of a light beam incident on the disc from the light source. And a diffraction grating for dividing the luminous flux from the light source into a 0th-order light for reading a pit signal on the disc and a pair of 1st-order light for reading the deviation of tracking, and a reflected light from the disc A holographic grating that guides the light to the light receiving element, and a lens portion that is provided in the optical path of the light beam that is incident on the light receiving element from the holographic grating, and that increases the detection sensitivity of the signal by the lens action, The diffraction grating, the holographic grating, and the lens portion are integrally formed in a diffractive element. The child is an optical pickup device having a holographic grating surface on which the holographic grating is formed, and a diffraction grating surface on which the diffraction grating and the lens portion are formed.