JPH07105059B2 - 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 from the 0th-order light 17a for reading the pit signal on the disk 7 and the focus shift and the tracking shift. 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, the light spots 18b and 18c sandwich the light spot 18a of the 0th-order light,
The light spot is a leading or trailing light spot in the tangential direction of.

The reflected light reflected by the information signal 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 beam 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 4, 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 6-division light receiving element 15 at this time are shown in FIGS. 5A and 5B,
Shown in Figure 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, focus error signal (FES), tracking error signal (RES)
And the RF signal (RF) 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 is again in the same optical path as the holographic grating 20.
, And the first-order diffracted light is incident on the four-division light receiving element 21. The holographic grating 20 is divided into two parts 20a and 20b by a dividing line parallel to the tangential direction of the disk 7, and the focal positions of the first-order diffracted light are different from each other. The incident light is two first-order diffracted lights 24a and 24b.
In the four-division light receiving element 21, the light spots 25a and 25b are formed, and the RF signal, the tracking error signal by the push-pull method, and the focus error signal by the wedge prism method are detected.

At this time, the light spots 25a, 2 on the four-division light receiving element 21
The state of 5b is shown in FIGS. 7A, 7B and 7C.

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 a large number of adjustment points, so that the cost is high.
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 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 holographic 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 you could not get.

The present invention has been made to solve the above problems, has a small number of parts, is low in cost, and enables tracking error signal detection by the three-beam method, and can prevent stray light from occurring. It is an object of the present invention to provide an improved optical pickup device capable of further increasing the sensitivity.

[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 device for detecting reflected light from the disc. And an element. The apparatus is further located in an optical path incident on the disk from the light source, and outputs a light flux from the light source to a 0th-order light for reading a pit signal on the disk and a tracking deviation. A first surface on which a diffraction grating portion for splitting into a pair of first-order lights is formed; and a second surface on which a holographic grating is formed, which guides the reflected light from the disk to the light-receiving element through the first surface. And a diffractive element having. On the first surface of the diffractive element, at least a portion through which a light beam incident on the light receiving element from the holographic grating passes is defined as a non-diffraction grating portion. The non-diffraction grating portion is provided with optical means for expanding the light beam incident on the light receiving element by its lens action, thereby increasing the signal detection sensitivity. The holographic grating, the diffraction grating section, and the optical means are integrally formed of plastic, glass, or the like.

[Operation] In the present invention, the light beam from the light source, which is located in the optical path of the light beam incident on the disc, is used for reading the deviation between the 0th-order light for reading the pit signal on the disc and the tracking. It has a first surface on which a diffraction grating portion for splitting into a pair of first-order lights is formed, and a second surface on which a holographic grating is formed, which guides the reflected light from the disk to the light receiving element through the first surface. Since the diffractive element is provided, stable tracking error signal detection similar to the performance of the three-beam method using a diffraction grating can be obtained, and the semiconductor laser and the light receiving element can be placed in the same plane. Further, since the non-diffraction grating portion is at least the portion of the first surface of the diffractive element through which the light beam incident on the light receiving element from the holographic grating passes, the first time from the holographic grating Even if folding light passes through this part, stray light does not occur. Further, the non-diffraction grating portion is provided with an optical means for expanding the light beam incident on the light receiving element by its lens action, thereby increasing the signal detection sensitivity, so that the sensitivity is increased. Moreover, since the holographic grating, the diffraction grating portion, and the optical means are integrally formed of plastic or glass, the number of parts is reduced.

[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 has a holographic grating surface 3 on the disk 7 side and a diffraction grating portion on the semiconductor laser light source 1 side.
It has a diffraction grating surface 4 having 4a and a lens portion 4b. 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 tracked with the 0th order light 9a for reading the pit signal and the focus shift on the disk 7. A pair of primary lights for reading the deviation 10
A diffraction grating divided into a 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
Passes through the holographic grating surface 3 and the zero-order diffracted light of the three light beams 9a, 10a, 11a is directed to the disk 7.

On the holographic grating surface 3 of the diffractive element 2, the three light beams 9a, 10a, 11a reflected by the disk 7 are directly reflected by the semiconductor laser light source 1
A hologram for branching into the 0th-order diffracted light that is returned to and the 1st-order diffracted light 9c, 10c, 11c that passes through the lens portion 4b and is incident on the light receiving element 8 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 has the first-order diffracted light 9c from the holographic grating surface 3,
In order to prevent stray light from being generated when 10c and 11c pass through the diffraction grating again, the diffraction grating is not formed, and the lens portion 4b is formed with a cylindrical lens surface that generates astigmatism. ing. The formation of this cylindrical lens surface can be performed by a commonly used conventional technique.

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 disk 7, a light receiving element 8 for detecting reflected light from the disk 7, and the light source 1. Is provided in the optical path of the light flux incident on the disk 7 from the light source 1, and the light flux from the light source 1 is a 0-order light for reading the pit signal on the disk 7 and a pair of 1 for reading the tracking deviation. A diffraction grating for splitting into the next light, a holographic grating for guiding the reflected light from the disk 7 to the light receiving element 8, and a lens function provided in the optical path of a light beam entering the light receiving element from the holographic grating The light flux that has passed through the lens section 4b, which is an optical means for increasing the signal detection sensitivity, and the holographic grating. And a collimator lens 5 to be sent to the objective lens 6 in the parallel light. The diffraction grating, the holographic grating, and the lens portion 4b serving as an optical means are integrally formed of plastic or glass to form the diffraction element 2. And this diffractive element 2
Is composed of a holographic grating surface 3 and a diffraction grating surface 4 on which a diffraction grating portion 4a and a lens portion 4b are formed.

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 and the focus shift of the disk 7 and the tracking One to one to read the deviation
It is divided into the next lights 10a and 11a. These three luminous fluxes 9a, 10
a and 11a pass through the holographic grating surface 3 and the 0th-order diffracted light of the three light fluxes 9a, 10a and 11a are collimated by the collimator lens 5 and are incident on the objective lens 6, and the information signal of the disc 7 is transmitted. 3 light spots on the surface
9b, 10b, 11b are formed. The three luminous fluxes 9a, 10a, 1 formed by the holographic grating surface 3
The 1st-order diffracted light of 1a does not form a spot on the disk 7 and does not affect the signal. Further, 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 diffraction element 2 via the objective lens 6 and the collimator lens 5. At this time, the holographic
On the grating surface 3, the 0th order diffracted light and the 1st order diffracted light 9c,
10c and 11c are formed, and the 0th-order diffracted light becomes the return light to the semiconductor laser light source 1, and the 1st-order diffracted lights 9c, 10c, and 11c pass through the cylindrical lens surface 4b, and astigmatism occurs. The light is incident on the split light receiving element 8 and the light spot 9d,
Form 10d and 11d. Therefore, in the 6-divided light receiving element 8, the focus error signal by the astigmatism method, the tracking error signal by the 3-beam method, and the RF signal which is the pit signal of the disk 7 as shown in FIGS. 3A, 3B and 3C. The signal is detected.

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, in the optical pickup device according to the present invention, in the optical path of the light flux incident on the disc from the light source. A first surface formed with a diffraction grating portion which is positioned and divides a light beam from the light source into a 0th order light for reading a pit signal on the disk and a pair of 1st order light for reading a deviation of tracking; , A second surface formed with a holographic grating that guides the reflected light from the disk to the light receiving element through the first surface is used, and thus a stable tracking error by the three-beam method is used. The detection method can be used, and the semiconductor laser and the light receiving element can be placed in the same plane. Therefore, the semiconductor laser and the light receiving element can be integrated into one element and easily applied to a light pen.
As a result, it is possible to make a stable optical pickup device that is much smaller and less expensive than the conventional one.

In addition, since the non-diffraction grating portion is the first surface of the diffractive element and at least the portion through which the light beam incident on the light receiving element from the holographic grating passes, the first-order diffracted light from the holographic grating is The effect that stray light does not occur even when passing through is achieved.

Furthermore, since the non-diffraction grating portion is provided with an optical means for expanding the light beam incident on the light receiving element by its lens action and thereby increasing the signal detection sensitivity, the sensitivity is said to be high. Produce an effect. Further, since the holographic grating, the diffraction grating portion and the optical means are integrally formed of plastic, glass or the like, the number of parts can be reduced.

[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 62-103857 (JP, A) JP 62 -124636 (JP, A) JP-A-56-156937 (JP, A) JP-A-62-132247 (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. A first diffraction grating part is formed which divides a light beam from the light source located inside and into a pair of first-order light for reading a pit signal on the disk and a pair of first-order light for reading a tracking shift. A diffractive element having a surface and a second surface formed with a holographic grating that guides the reflected light from the disk to the light receiving element through the first surface,
In the optical pickup device including: a non-diffraction grating portion, which is at least a portion of the first surface of the diffraction element, through which a light beam incident on the light receiving element from the holographic grating passes. In the diffraction grating section, the luminous flux incident on the light receiving element is
Optical means is provided for expanding by the lens action and thereby increasing the signal detection sensitivity, and the holographic grating, the diffraction grating section and the optical means are integrally formed of plastic or glass. An optical pickup device characterized in that