JPH01146143A - Optical pickup device - Google Patents

Abstract

PURPOSE:To reduce the number of parts and to detect tracking error with the stable three-beam method by modulating integrally a holographic grating, a diffraction grating, a lens, etc., with plastics, a glass, or the like. CONSTITUTION:A diffraction grating 2 is provided with a holographic grating face 3 on the side of a disk 7 and is provided with a diffraction grating face 4 having a diffraction grating part 4a and a lens part 4b on the side of a semi conductor laser light source 1. A diffraction grating which divides a luminous flux 9 from the semiconductor laser light source 1 to 0th-order light 9a for read of a pit signal on a disk 7 and defocusing and a pair of 1st-order light 10a and 11a for read of deviation of tracking is formed in the diffraction grating part 4a. The diffraction grating 4, the holographic grating 3, and optical means are molded integrally with glass or plastics. Thus, the number of parts is re duced and the tracking error signal is stably detected by the three-beam method.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] 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, a laser beam 16 emitted from a semiconductor laser light source 1 is transmitted to a disk 7 by a diffraction grating 12.
0-order light 17a for reading the upper pit signal and reading the focus shift, and 1 for reading the tracking shift.
It is divided into a pair of primary lights 17b and 117c. These three light beams 17a.

17b and 17c are reflected by the flat beam splitter 13 and then made parallel by the collimating lens 5.
Three light spots 18a, 18b are incident on the objective lens 6 and on the information surface of the disk 7.

Form 18c. At this time, the light spot 18b118c
are leading or trailing light spots in the tangential direction of the disk 7, sandwiching the zero-order light spot 18a.

The reflected light reflected from the information signal surface of the disk 7 returns again along the same optical path and passes through the flat beam splitter 13. At this time, astigmatism occurs in the light beam that has passed through the planar beam splitter 13, and a light spot 19a s 19b is formed on the 6-divided light receiving cable 15 via the plano-concave lens 4.
s 19 c, a tracking error signal by the three-beam method representing the deviation of the RF multiplied signal tracking which is the pit signal of the disk 7, and an astigmatism method representing the deviation of the focus of the optical spot 18a on the disk 7. A focus error signal is detected.

At this time, the light spot 19 on the 6-divided light receiving element 15
The states of a, 19b, and 19c are shown in Figures 5A, 5B, and 5.
Shown in Figure C. FIG. 5A is a diagram when the disc is close, FIG. 5B is a diagram when the disc is in just focus, and FIG. 5C is a diagram when the disc is far away. In the figure, focus error signal (FES), tracking error signal (
RES) and RF multiplied signal RF) are expressed by the following equations.

FES■(A+D)-(B1C) RES■E-F RF control A+B+C+D FIG. 6 is a diagram of the optical system of a conventional general optical pickup device using a holographic grating.

After the laser light 22 emitted from the semiconductor laser light source 1 enters the holographic grating 20, the 0th order diffracted light is made into parallel light by the collimating lens 5, and the optical 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 enters the holographic grating 20 again along the same optical path, and the first-order diffracted light enters the four-split light receiving element 21. Above holographic grating 2
0 is divided into two parts 20a and 20b by a dividing line parallel to the tangential direction of the disk 7, and since the focal position of the first-order diffracted light is different in each part, the light incident on the holographic grating 20 is divided into two parts. The first-order diffracted light beams 24a and 24b are divided into two, which form light spots 25a and 25b in the four-split light receiving element 21, and a tracking error signal by the RF multiplied signal push-pull method and a focus error by a type of wedge prism method. A signal is detected.

At this time, the light spot 25 on the four-division light receiving element 21
The states of a and 25b are shown in FIGS. 7A, 7B, and 7C.

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

FESSRES and RF are expressed 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 many adjustment points, so the cost is high.

On the other hand, in the case of an optical pickup device that uses a holographic grating, the cost is lower because it has fewer parts and fewer adjustment points than the optical pickup device that does not use a holographic grating. The push-pull method, which is a method for detecting tracking error signals in optical pickup devices using holographic gratings, has problems in its performance compared to the three-beam method using diffraction gratings, and stable tracking error signal detection is difficult. The disadvantage was that it was not possible to obtain

The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide an optical pickup device that has a small number of parts, is low in cost, and is capable of detecting a tracking error signal using a three-beam method. purpose.

[Means for Solving the Problems] The optical pickup device according to the present invention includes: a light source, an objective lens for focusing a light beam from the light source onto a disk, a light receiving element for detecting reflected light from the disk, and the light source. is installed in the optical path of the light beam incident on the disk from the light source, and transforms the light beam from the light source into a pair of zero-order light for reading pit signals on the disk and a pair of first-order light for reading tracking deviations. a holographic grating that guides the reflected light from the disk to the light receiving element; and a holographic grating that is provided in the optical path of the light flux that enters the light receiving element from the holographic grating, and detects a signal by its lens action. The diffraction grating, the holographic grating, and the optical means are integrated into a diffraction element made of plastic, glass, etc., and the diffraction element is formed on the surface of the holographic grating. and,
It is composed of a diffraction grating surface on which a diffraction grating and a lens portion, which is the optical means, are formed.

[Operation] Since the optical pickup device according to the present invention includes a diffraction grating and a holographic grating, stable tracking error signal detection similar to the performance of the three-beam method using a diffraction grating can be obtained. Furthermore, since the diffraction grating, the holographic grating, and the optical means are integrated into a diffraction element made of glass or plastic, the number of parts is reduced. Further, since the optical device is provided with an optical means that is provided in the optical path of the light flux that enters the light receiving element from the holographic grating and increases the signal detection sensitivity through its lens action, the sensitivity is increased.

[Example] 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 surface 4 having a diffraction grating section 4a and a lens section 4b on the semiconductor laser light source 1 side. The diffraction grating portion 4a of the diffraction grating surface 4 of the diffraction element 2 receives the light beam 9 from the semiconductor laser light source 1, and the zero-order light 9a for reading the pit signal and focus shift on the disk 7, as well as the tracking beam. A diffraction grating is formed that divides the beam into a pair of primary beams 10a and lla for reading the deviation. This diffraction grating can be formed using commonly used techniques. The three light beams 9as, 10a and lla formed here are the holographic
The three light beams 9a pass through the grating surface 3,
The 0th order diffracted light of 10as lla heads toward the disk 7.

On the holographic fist grating surface 3 of the diffraction element 2, the 0th-order diffracted light that returns the three light beams 9as, 10a, and lla reflected by the disk 7 to the semiconductor laser light source 1 as is, and the lens portion 4b. First-order diffracted light 9cs 10 that passes through and enters the light receiving element 8
A hologram is formed to branch into c and llc. This hologram can be formed using commonly used techniques. Further, in the lens portion 4b of the diffraction grating surface 4, in order to prevent the first-order diffracted light 9 Cs 10 cs 11C from the holographic grating surface 3 from passing through the diffraction grating again, stray light is generated. No diffraction grating is formed, and the lens portion 4
A cylindrical lens surface that generates astigmatism is formed at b. This cylindrical lens surface can be formed using commonly used techniques.

FIG. 2 is a perspective view showing the 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 onto a disk 7, a light receiving element 8 for detecting reflected light from the disk 7, and the light source 1. The light beam from the light source 1 is provided in the optical path of the light beam incident on the disk 7 from the zero-order light for reading the pit signal on the disk 7, and a pair of light beams for reading the tracking deviation. A diffraction grating that separates the light into sub-order lights, a holographic grating that guides the reflected light from the disk 7 to the light receiving element 8, and a holographic grating that is provided in the optical path of the light flux that enters the light receiving element from the holographic grating, and has a lens effect. It is provided with a lens section 4b which is an optical means for increasing signal detection sensitivity, and a collimating lens 5 which converts the light beam passing through the holographic grating into parallel light and sends it to the objective lens 6. The diffraction grating, the holographic grating, and the lens portion 4b, which is an optical means, are integrally formed into a diffraction element 2 made of plastic, glass, or the like. The diffraction element 2 is composed of a holographic grating surface 3 and a diffraction grating surface 4 on which a diffraction grating section 4a and a lens section 4b are formed.

Next, the operation will be explained.

The laser beam 9 emitted from the semiconductor laser light source 1 enters the diffraction grating section 4a of the diffraction grating surface 4 of the diffraction probe 2, and is converted into zero-order beam 9a for reading pit signals and focus shifts on the disk 7. , 1 to read the tracking deviation
It is divided into a pair of primary lights 10a111a. These three light beams 9a110a111a pass through the holographic grating surface 3, and the three light beams 9a110a
The 0th-order diffracted light of 11a is made into parallel light by the collimating lens 5, and enters the objective lens 6 to form three light spots 9b110b, 1 on the information signal surface of the disk 7.
1b is formed. The three beams formed by the holographic grating surface 3 are 98% 10 as
The first-order diffracted light beam 11a does not form a spot on the disk 7 and does not affect the signal. The light spots 10b and llb are light spots that lead or follow in the tangential direction of the disk 7, sandwiching the light spot 9b of the zero-order light 9a.

The reflected light reflected by the information signal surface of the disk 7 enters the holographic grating surface 3 of the diffraction element 2 via the objective lens 6 and the collimating lens 5 again. At this time, the holographic
On the grating surface 3, the 0th-order diffracted light and the 1st-order diffracted light 9c
, 10C% 11c are formed, the 0th-order diffracted light becomes the return light to the semiconductor laser light source 1, and the 1st-order diffracted light 9c, 1
0C,llc passes through the cylindrical lens surface 4b,
With astigmatism occurring, the light enters the six-segment light receiving element 8, forming light spots 9d, 10d, and 11d. Therefore, in the six-divided light receiving element 8, FIG.
A focus error signal by the astigmatism method as shown in FIGS. 3B and 3C, a tracking error signal by the three-beam method, and an RF multiplied signal which is the pit signal of the disk 7 are detected.

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

FES-(A+D)-(B+C) RES-E-F RF A+B+C+D [Effects of the Invention] As explained above, the optical pickup device according to the present invention uses a holographic ψ grating, a diffraction grating, a lens, etc. made of plastic or glass. The number of parts can be reduced because it is integrally molded. In addition, since the semiconductor laser and the photodetector can be placed in the same plane using a stable three-beam tracking error detection method, it is easy to use a light pen that combines the semiconductor laser and photodetector into one element. It can be applied.

As a result, it is possible to create a much smaller, less expensive, and more stable optical pickup device than conventional ones.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of the diffraction element of the optical pickup device according to the present invention, FIG. 2 is a perspective view showing the optical system of the optical pickup device according to the present invention, and FIGS. 3A, 8, and 3C. 4 is a diagram showing the shape and position of a spot on the six-part light receiving element of the optical pickup device according to the present invention, and FIG. 4 is a cross-sectional view showing the optical system of the conventional optical pickup device that does not use a holographic grating. , 5th A
Figures 5B and 5C are diagrams showing the shape and position of a spot on a six-segment light receiving element, and Figure 6 is a perspective view showing the optical system of an optical pickup device using a conventional holographic grating. , FIG. 7A, FIG. 7B, and FIG. 7C are diagrams showing the shape and position of the spot on the 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 an aperture grating section, 4b is a lens section, 6 is an objective lens, 7 is a disk, and 8 is a light receiver It is element. In each figure, the same reference numerals indicate the same or corresponding parts. (2 others) Figure 1 4b2 Shi-nuo carp 12 Figure 3A Figure 3B Figure 3Cm Procedural amendment (Nagi January 17, 1999 2, Name of invention Optical pickup device 3, Amendment Relationship with the case of a person who does
504) Sharp Corporation Representative Haruo Tsuji 4, Agent address: 2-1-29 Minamimorimachi, Kita-ku, Osaka Sumitomo Bank Minamimorimachi Building Telephone: Osaka (06) 361-2021 Clause C 5, Date of amendment order 6 , "Fig. 8" in column 7 of the brief description of the drawings of the specification subject to amendment, page 15, line 7 of the specification of the contents of the amendment is corrected to "Fig. 3B."that's all

Claims (1)

[Scope of Claims] A light source, an objective lens for focusing a light beam from the light source onto the disk, a light receiving element for detecting reflected light from the disk, and a light receiving element provided in the optical path of the light beam incident on the disk from the light source. a diffraction grating that divides the light beam from the light source into a zero-order beam for reading a pit signal on the disk and a pair of first-order beams for reading a tracking deviation; A holographic grating that guides the light to the light receiving element, and an optical means that is provided in the optical path of the light flux that enters the light receiving element from the holographic grating and that increases signal detection sensitivity through its lens action. , the diffraction grating, the holographic grating, and the optical means are integrated into a diffraction element made of plastic, glass, etc., and the diffraction element includes a holographic grating surface, a diffraction grating portion, and a lens as the optical means An optical pickup device consisting of a diffraction grating surface formed with a portion.