JPH05120754A - Optical pickup - Google Patents

Abstract

PURPOSE:To reduce the number of parts and to miniaturize an entire by mounting a semiconductor laser and a photodetector on a same substrate, providing a hologram element and a deflector between the substrate and a converging optical system and making be incident reflected light on the photodetector. CONSTITUTION:A light beam outgoing from the semiconductor laser 12 is converged to a recording medium 17 by a converging optical system and the reflected light is received by the photodetectors 13, 14 through a hologram substrate 15. The substrate 15 is provided on a semiconductor substrate 11 through a spacer 18 and the hologram element 19 separating the reflected light to (+ or -) 1st order light beams having inverse power is provided on the surface of the medium 17 side. Further, polarization gratings 20a, 20b making the separated (+ or -) 1st order light beams receive to the photodetectors 13, 14 as zero-order light are formed on the opposite side surface. In such a manner, by reproducing the hologram element and the deflector between the converging optical system and the semiconductor substrate, the number of parts is reduced and the entire is miniaturized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pickup used in a recording / reproducing apparatus for recording / reproducing information on / from an optical information recording medium such as an optical disc.

[0002]

2. Description of the Related Art As a conventional optical pickup, for example, Japanese Patent Laid-Open No. 63-32743 proposes an optical pickup as shown in FIG. In this optical pickup, the divergent beam from the semiconductor laser 1 is once converged by the lens 2, then again diverged, guided through the hologram lens 3 to the collimator lens 4, and converted into a parallel beam by the collimator lens 4. The objective lens 5 irradiates the magneto-optical recording medium 6 as a spot.

The return light reflected by the magneto-optical recording medium 6 is guided to the hologram lens 3 via the objective lens 5 and the collimator lens 4, where ± 1 having astigmatism is obtained.
Next-order diffracted light is generated, and these ± first-order lights are incident on the photodetectors 9 and 10 formed on the substrate 8 and each having four-divided light receiving regions via the polarizing lens 7. In this way, based on the outputs of the photodetectors 9 and 10, the magneto-optical signal is detected from the difference between them, and the focus error signal is obtained by the astigmatism method.

[0004]

However, in the conventional optical pickup shown in FIG. 4, the photodetectors 9 and 1 are
A hole is made in the substrate 8 on which 0 is formed, and a divergent beam from the semiconductor laser 1 arranged outside the substrate 8 is condensed by the lens 2 in this hole, so that a light emitting point is provided between the photodetectors 9 and 10. To form. For this reason, the number of parts such as the lens 2 increases, and there is a problem that the assembly is troublesome and the cost increases, and the lens 2 is arranged between the semiconductor laser 1 and the substrate 8 of the photodetectors 9 and 10. There is a problem that a space for doing so is required, and the whole becomes large.

The present invention has been made by paying attention to the above-mentioned conventional problems, and provides an optical pickup which is configured appropriately so that the number of parts can be reduced, and therefore it can be easily and inexpensively made and the entire size can be made small. The purpose is to do.

[0006]

In order to achieve the above object, according to the present invention, a photodetector and a semiconductor laser mounted on the same substrate, and a light beam emitted from the semiconductor laser are converged on an optical information recording medium. An optical system, a hologram element arranged between the optical system and the substrate, for separating reflected light from the optical information recording medium into ± first-order lights having powers in opposite directions, and the semiconductor laser. A polarizer is provided which is composed of a diffraction grating having a pitch smaller than the wavelength of the emitted light and which causes the ± first-order lights separated by the hologram element to enter the photodetector as zero-order lights.

[0007]

In the above structure, the light from the semiconductor laser mounted on the substrate is converged on the optical information recording medium by the converging optical system, and the reflected light is converted into ± first-order lights having mutually opposite powers by the hologram element. To be separated. The ± first-order light is a photodetector in which a polarizer made of a diffraction grating having a pitch smaller than the wavelength of the light emitted from the semiconductor laser is transmitted as the zero-order light and mounted on the same substrate as the semiconductor laser. Is received by.

[0008]

1 shows an embodiment of the present invention. In this embodiment, the semiconductor laser 12 is mounted on the semiconductor substrate 11, and the photodetectors 1 are provided on both sides of the semiconductor laser 12.
Mount 3,14. As the semiconductor substrate 11, for example, a silicon substrate is used, and as shown in FIG.
By chemically etching with a as 100 planes, 111 inclined surfaces 11b are formed and at the same time the main surface 11a is formed.
To form a plane 11c parallel to the semiconductor laser 12 and mount the semiconductor laser 12 on the plane 11c so that the light emitted from the semiconductor laser 12 is reflected by the slope 11b and emitted in the direction normal to the main surface 11a. To do.

The light emitted from the semiconductor laser 12 is reflected by the slope 11b shown in FIG.
After passing through the objective lens 16 and the objective lens 16, it is condensed on the magneto-optical recording medium 17, and the reflected light is received by the photodetectors 13 and 14 via the objective lens 16 and the hologram substrate 15. The hologram substrate 15 is provided on the semiconductor substrate 11 via a spacer 18, and on the surface of the objective lens 16 side thereof, the reflected light from the magneto-optical recording medium 17 is converted into ± first-order lights having powers in opposite directions. The hologram element 19 to be separated is formed, and ± 1 separated by the hologram element 19 is formed on the other surface.
The polarization gratings 20a and 20b are formed to cause the next light beams to enter the photodetectors 13 and 14 as the 0th light beams, respectively.

As shown in FIG. 3, the polarization grating 2
Reference numerals 0a and 20b denote orthogonal patterns which are orthogonal to each other with respect to the linearly polarized light from the semiconductor laser 12 in a direction inclined by 45 °. The depths thereof are formed deeper than the period of the grating, and in order to increase the light efficiency, In the above, it is not provided in the region where the light from the semiconductor laser 12 is transmitted. Further, the photodetectors 13 and 14 are divided into three light-receiving regions 13a, 13b, 13c and 14a, 14 which are divided by dividing lines parallel to the diffraction direction of the hologram element 19.
b, 14c.

In the above structure, the reflected light from the magneto-optical recording medium 17 is separated by the hologram element 19 into ± first-order lights having mutually opposite powers, and the photodetectors 13 and 14 are separated as shown in FIG. It is illuminated as spots 21 and 22 which are defocused back and forth. Therefore, the light receiving regions 13a, 13a of the photodetectors 13, 14 respectively,
13b, 13c; the outputs of 14a, 14b, 14c are
_{Assuming 1} , A ₂ , A ₃ ; A ₄ , A ₅ , and A ₆ , the focus error signal FES can be obtained by the following formula by the so-called beam size method.

FES = (A ₁ + A ₃ + A ₅ ) − (A ₂ + A ₄ + A ₆ ).

Further, the polarization gratings 20a and 20b
As described above, the patterns are orthogonal to each other with respect to the linearly polarized light from the semiconductor laser 12 and are inclined at an angle of 45 °, and their depths are formed deeper than the period of the grating. The 0th-order diffraction efficiency of each of the polarization gratings 20a and 20b greatly depends on the polarization state of light, and when the polarization direction of incident light changes due to Kerr rotation, one increases and the other decreases (the direction of Kerr rotation is If it is reversed, the increase and decrease will also be reversed). Therefore, the magneto-optical signal MS can be obtained by the following equation.

## EQU2 ## MS = (A ₁ + A ₂ + A ₃ )-(A ₄ + A ₅ + A ₆ ).

Further, the tracking error signal TES
Can be obtained by the following formula by the push-pull method.

[Equation 3] TES = (A ₁ + A ₄ ) − (A ₃ + A ₆ ).

In the above embodiment, the hologram element 19 and the polarization gratings 20a and 20b are formed on the front and back sides of the hologram substrate 15, but they may be formed on different substrates.

[0015]

As described above, according to the present invention, the semiconductor laser and the photodetector are mounted on the same substrate, and the light emitted from this substrate and the semiconductor laser is converged on the optical information recording medium. Since the hologram element and the polarizer are provided between the optical system and the reflected light from the optical information recording medium to be incident on the photodetector, the number of parts can be reduced, and therefore, it is possible to easily and inexpensively, and Can be made smaller. In particular, when the hologram element and the polarizer are provided on the front and back sides of one hologram substrate as in the above-described embodiment, the effect becomes remarkable.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of the present invention.

FIG. 2 is a partial detailed view of FIG.

3 is a partial detailed view of FIG. 1.

FIG. 4 is a diagram for explaining a conventional technique.

[Explanation of symbols]

11 semiconductor substrate 11a main surface 11b slope 11c plane 12 semiconductor laser 13, 14 photodetector 13a, 13b, 13c, 14a, 14b, 14c light receiving area 15 hologram substrate 16 objective lens 17 magneto-optical recording medium 18 spacer 18 19 hologram element 20a , 20b Polarizing grating 21,22 Spot

Claims (1)

[Claims] 1. A photodetector and a semiconductor laser mounted on the same substrate, a converging optical system for converging light emitted from the semiconductor laser onto an optical information recording medium, and arranged between the optical system and the substrate. And a hologram element for separating the reflected light from the optical information recording medium into ± first-order lights having mutually opposite powers, and a diffraction grating having a pitch smaller than the wavelength of the light emitted from the semiconductor laser. , ± 1 separated by the hologram element
An optical pickup, comprising: a polarizer for making each of the following lights incident on the photodetector as a 0th order light.