JP2693569B2 - Optical information recording / reproducing device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical information recording / reproducing apparatus that detects a focus error signal and a track error signal using reflected light from an optical information recording medium.

2. Description of the Related Art A first conventional example of a conventional optical information recording / reproducing apparatus is disclosed in Japanese Patent Application Laid-Open No. Sho 61-230634. This will now be described with reference to FIG. The light emitted from the semiconductor laser 1 is collimated by the collimator lens 2, and the collimated light is collimated.
, And the polarization direction of the incident beam 4 becomes the diffracted light 5 because the electric vector thereof is parallel to the groove of the polarization beam splitter grating 3 and enters the quarter-wave plate grating 6. The light beam becomes a circularly polarized light beam, is condensed by a lens 7, and is irradiated on the surface of an optical disk 8 as an optical information recording medium. Also, the reflected light from the optical disk 8 is 1 /
The light is converted into a linearly polarized wave by the four-wavelength plate grating 6, passes through the polarization beam splitter grating 3, becomes zero-order diffracted light 9, and enters the critical angle diffraction grating 10. The incident light undergoes two critical angle diffractions and total reflection, and becomes a diffracted light 11 which is detected by the four-split photodetector 12. As a result, the focus error signal is detected by the difference signal on the left and right light receiving surfaces, and the track error signal is detected by the difference signal on the light receiving surface in a direction perpendicular to the paper surface.

As a second conventional example, there is one filed by the present applicant in Japanese Patent Application No. 63-1518. This is because the light emitted from the semiconductor laser 13 is collimated by the collimator lens 14 as shown in FIG.
The beam is reflected by the beam splitter 16 via 15, is condensed by the objective lens 17 and is irradiated onto the surface of the magneto-optical disk 18, whereby information is recorded. The reflected light from the magneto-optical disk 18 passes through the beam splitter 16, is collected by the detection lens 19, and is guided to the dual grating 20. This dual grating 20
Is a grating 20 whose diffraction efficiency varies depending on the polarization direction.
a and 20b are formed on both front and back surfaces, and light passes through these two gratings 20a and 20b to form a zero-order light T.
And the first-order light K, and the zero-order light T is divided into four light receiving elements 21.
In addition, the primary light K is guided to the two-divided light receiving element 22.
When a magneto-optical signal is detected, it is detected based on the difference in light amount between the 0th-order light T and the 1st-order light K, the focus error signal is detected by the 0th-order light T using the astigmatism method, and the track error signal is 1 It can be detected by the next light K.

Problems to be Solved by the Invention First, the first conventional example can be applied to a case where a CD or a write-once optical disc 8 is used as an optical information recording medium, but it can be applied to a magneto-optical disc. There is no function to detect the signal. Further, in the case of the present apparatus, the problem that the diffraction angle fluctuates according to the wavelength fluctuation, which is a fundamental defect of the grating itself such as the polarizing beam splitter grating 3 and the quarter-wave plate grating 6, is not solved. .

Therefore, as in the second conventional example, not only the optical disk 8 but also the magneto-optical disk 18 can be used, and further, the dual grating 20 having the gratings 20a and 20b formed on the front and back surfaces of the substrate is used. In the case of the configured device, it is possible to greatly suppress the displacement of the spot with respect to the wavelength variation.

However, in the case of this device, the optical components arranged in the illumination optical system 23 until the light emitted from the semiconductor laser 13 is guided to the magneto-optical disk 18 are the same as those in the conventional optical pickup device as described above. Since there are many points, there is a problem in that the size and weight of the entire apparatus cannot be reduced.

Therefore, in order to solve such a problem, the present invention contemplates that light emitted from a laser light source is condensed by an objective lens to form a light spot, and the light information recording medium is irradiated with the light spot. While recording information, guide the reflected light from the optical information recording medium to the signal detection optical system, track error signal and focus error signal, further, in the optical information recording and reproducing apparatus for detecting the reproduction signal, On the optical path while the light emitted from the laser light source is guided to the optical information recording medium,
An optical path separating means having a semi-transmissive diffraction grating with a modulation pitch formed on one surface and a transmissive diffraction grating with an equal pitch formed on the other surface of the substrate located on the laser light source side is provided, and the optical path separation means and the optical information A collimator lens is arranged on the optical path between the recording medium and the reflected light from the optical information recording medium passes through the optical path that has passed through the optical path separating means. A photodetector for detecting the next light was provided.

As a result, the light emitted from the laser light source is reflected by the semi-transmissive diffraction grating having the modulation pitch of the optical path separation means, collimated by the collimator lens, and radiated to the optical information recording medium through the condenser lens. After that, the reflected light is again guided to the optical path separating means and transmitted through the semi-transmissive diffraction grating of the modulation pitch to be separated into the 0th-order light and the 1st-order light. By passing through and being emitted to the outside, these two lights are detected by the photodetector, whereby the focus error signal, the reproduction signal, etc. can be detected.

Embodiment An embodiment of the present invention will be described with reference to FIGS. On the optical path of the light emitted from the semiconductor laser 24 as a laser light source, a dual type grating 25 as an optical path separating means is provided. This dual type grating 25 has a semi-transmissive diffraction grating 26a with a modulation pitch formed on one surface located on the side of the laser light source 24 of a parallel plate type substrate 26, and the opposite surface facing this. A transmission type diffraction grating 26b having an equal pitch is formed on the.

Further, a collimator lens 27 is disposed on the optical path located on the side of the semi-transmissive diffraction grating 26a of the dual type grating 25, and an objective lens 28 is provided on the optical path of the light passing through the collimator lens 27. A magneto-optical disk 29 as an optical information recording medium is arranged via the optical disk.

Further, a 0th-order photodetector 30 and a 1st-order photodetector 31 as photodetectors are arranged in the same plane on the optical path located on the transmission type diffraction grating 26b side of the dual type grating 25. It is set up.

In such a structure, elliptical diffused light is emitted from the semiconductor laser 24, and this diffused light is emitted with the emission angle different depending on the direction, as shown in FIG. Semi-transmissive diffraction grating 26
incident on a. As shown in FIG. 2, the semi-transmissive diffraction grating 26a has a modulation pitch, and the diffused light incident on the diffraction grating 26a is corrected so that the outgoing angles thereof are all equal. The corrected diffused light passes through the collimator lens 27 to obtain a waveform A which is subjected to beam shaping (in this case, the beam shaping magnification can be freely changed depending on the degree of the modulation pitch). The light beam thus beam-shaped is condensed by the objective lens 28 and irradiated onto the surface of the magneto-optical disk 29, whereby information recording or the like is performed.

Further, the reflected light from the magneto-optical disk 29 returns to the dual type grating 25 again via the objective lens 28 and the collimator lens 27, and enters from the semi-transmissive diffraction grating 26a side. In this case, since the semi-transmissive diffraction grating 26a is in a semi-transmissive state, a part of the reflected light incident on the semi-transmissive diffraction grating 26a is transmitted, and at that time, the 0th-order light T (transmitted light) and the 1st-order light K (reflected light) are transmitted. ) And separated. Then, the light separated into these two rays travels through the substrate 26 and is emitted from the opposite side of the transmission type diffraction grating 26b having the equal pitch. The transmission type diffraction grating 2
6b is a high-density grating whose diffraction efficiency changes depending on the polarization direction of light, as shown in FIG.
A difference in light intensity occurs between the 0th-order light T and the 1st-order light K that have passed through this. The two lights having the intensity differences are respectively the 0th-order photodetector 30 and the 1st-order photodetector 31.
Is detected.

As a result, the magneto-optical signal can be detected by the light intensity difference between the 0th order light T and the 1st order light K. Further, as a method of detecting the focus error signal, there are shown in FIGS.
Various methods as shown in (c) can be considered. FIG. 5A shows the astigmatism generated on the side of the 0th order light T due to the action of the parallel plate, which is detected by using the astigmatism method. FIG. 5 (b) shows that the astigmatism generated on the side of the primary light K due to the action of the modulation pitch of the diffraction grating is detected by using the astigmatism method. FIG. 5 (c) shows the detection by the beam size method using a photodetector having a light receiving surface divided into three parts by utilizing the optical path difference existing between the 0th order light T and the 1st order light K. Is to do. In addition, the track error signal is
It can be detected using the well-known push-pull method.

As mentioned above, a semi-transmissive diffraction grating that is semi-transmissive on one side
By arranging the dual type grating 25 in which 26a is formed on the optical path of the light emitted from the semiconductor laser 24, a beam splitter, a beam shaping prism, etc. provided on the optical path of the conventional illumination optical system can be substituted. As a result, it is possible to significantly reduce the number of parts, and also to reduce the position variation of the light spot on the photodetector 31 with respect to the wavelength variation like the conventional dual type grating. You can

EFFECTS OF THE INVENTION The present invention provides an optical path separating means having a semi-transmissive diffraction grating with a modulation pitch formed on one surface on the optical path of light emitted from a laser light source and a transmissive diffraction grating formed on the other surface. Therefore, the optical components such as the beam splitter and the beam shaping prism used in the conventional illumination optical system are not required, and the illumination optical system and the signal detection optical system can be shared by using the optical components. The number of points can be drastically reduced to reduce the size and weight of the entire apparatus, and the cost can be further reduced.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing an embodiment of the present invention, FIG. 2 is a front view showing a state in which a beam is incident on the surface of a semi-transmissive diffraction grating, and FIG. 3 is an emission from a semiconductor laser. FIG. 4 is a perspective view showing the beam state, FIG. 4 is a waveform diagram showing the relationship of the light intensity with respect to the polarization direction of the high-density grating, and FIGS. 5 (a), (b) and (c) are explanatory diagrams showing the detection principle of the focus error signal. FIG. 6 is a block diagram showing a first conventional example, FIG. 7 (a) is a block diagram showing a second conventional example, and FIG. 7 (b).
FIG. 3 is a circuit diagram showing the principle of detecting various signals. 24 …… laser light source, 25 …… optical path separation means, 26 …… substrate,
26a ... Semi-transmissive diffraction grating, 26b ... Transmissive diffraction grating, 27
...... Collimating lens, 28 …… Objective lens, 29 …… Optical information recording medium, 30, 31 …… Photo detector

Claims (1)

(57) [Claims] 1. A light spot emitted from a laser light source is condensed by an objective lens to form a light spot, which is irradiated onto an optical information recording medium to record information, and reflected light from the optical information recording medium is recorded. In an optical information recording / reproducing apparatus that guides a signal detection optical system to detect a track error signal, a focus error signal, and further a reproduction signal, while the light emitted from the laser light source is guided to the optical information recording medium. Provided on the optical path is an optical path separating means in which a semi-transmissive diffraction grating with a modulation pitch is formed on one surface of the substrate located on the side of the laser light source and a transmissive diffraction grating with an equal pitch is formed on the other surface. A collimator lens is disposed on the optical path between the optical information recording medium and the optical information recording medium, and reflected light from the optical information recording medium passes through the optical path that has passed through the optical path separating means. The optical information recording and reproducing apparatus characterized in that a light detector for detecting the zero-order light and first order light.