JP2886353B2 - Optical information recording / reproducing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical information recording / reproducing apparatus for recording, reproducing and erasing information using reflected light from an optical information recording medium.

[0002]

2. Description of the Related Art As a first conventional example of a conventional optical information recording / reproducing apparatus, Japanese Patent Laid-Open Publication No.
Is disclosed in Japanese Unexamined Patent Application Publication No. 2000-205,878. That is, as shown in FIG. 6, light emitted from the laser light source 1 is incident on the diffraction grating surface 3 formed on one surface of the diffraction element 2 and has three luminous fluxes of 0-order light and ± 1st-order light. 4a, 4b and 4c. After passing through the holographic grating surface 5 formed on the other surface of the diffraction element 2, these three light fluxes are condensed by an objective lens (not shown) and irradiated on the surface of an optical disk (not shown) as an optical information recording medium. .
At this time, the zero-order light 4a is used for reading information, and the ± first-order lights 4b and 4c detect the track state of the surface thereof, become reflected light, and enter the holographic grating surface 5 of the diffraction element 2 again. Then, the three light beams incident on the holographic grating surface 5 are diffracted, and two sets of three beams 6a, 6b, 6c and 7 are respectively provided.
a, 7b, and 7c (a total of six beams) and guided to the surface of the light receiving element 8. In this case, the light receiving element 8 has light receiving surfaces a, b, c, d, e, and f divided into six parts, and six beams are guided to each of the six light receiving surfaces in a state of a light spot. Thereby, the information reproduction signal Rf
And the focus error signal Fo and the track error signal T
r can be detected.

The value of each signal can be detected by using the wedge prism method as follows: Fo = (a + d) − (b + c) (1) Tr = ef (2) Rf = a + b + c + d (3) it can.

FIGS. 7A to 7C show a state of a light spot irradiated on the surface of the light receiving element 8 when the focus error signal Fo is detected. (B) is for focusing.
(A) is when the optical disk is closer to the optical disk than at the time of focusing.
(C) shows a state when the optical disk is further away from the optical disk than at the time of focusing. As described above, it is possible to detect a signal using the magnitude relation of the beam diameter of the light spot.

Next, as a second conventional example, Japanese Patent Application No. Hei.
No. 273754 has been filed by the present applicant. This is a configuration in which the read-only configuration as described in the first embodiment described above is advanced by one step so that a magneto-optical signal can be detected. That is, as shown in FIG.
The light emitted from the semiconductor laser 9 travels as zero-order light, passes through the light branching diffraction grating 10, becomes parallel light by the collimating lens 11, is condensed by the objective lens 12, and is converged on the surface of the magneto-optical disk 13. Irradiation is performed, thereby forming a light spot P. Then, the light reflected by the magneto-optical disk 13 enters the light splitting diffraction grating 10 again via the objective lens 12 and the collimating lens 11. At this time, the reflected light is + 1st-order light 14 and -1st-order light 15
The + 1st-order light 14 is guided to a polarization separation diffraction grating 16 having a minute pitch (less than the wavelength). Since the polarization separation diffraction grating 16 has polarization dependence on the diffraction efficiency, it is separated into transmitted light T and diffracted light K depending on the polarization direction, and is guided to the light receiving element 18 provided on the same substrate 17, respectively. The magneto-optical signal can be detected by calculating the difference between the output signals from the light receiving elements 18. By leading to the polarization separation diffraction grating 16 having a minute pitch in this manner,
Magneto-optical signals can be detected by polarization separation.

[0006]

In the case of the first conventional example,
Since the diffraction element 2 is provided, the laser light source 1 and the light receiving element 8 can be arranged on the same plane, so that a stable signal can be detected with a compact structure. By doing so, it is possible to correspond to a compact disc or a write-once disc. However, such a configuration cannot be adapted to a rewritable magneto-optical disk, and cannot detect a magneto-optical signal because the diffraction element 2 does not have a polarization separation function.

In the case of the second conventional example, such a magneto-optical signal can be detected. However, since the black angle of the fine pitch grating is large, the diffraction angle of the light splitting diffraction grating 10 must be increased. There is. However, with such a configuration, the fluctuation of the diffraction angle due to the fluctuation of the wavelength of the semiconductor laser 9 also increases, so that the position of the light spot on the light receiving element 18 also fluctuates, and the signal is likely to be offset. In particular, when a light spot needs to be accurately aligned on a four-divided light receiving element or a two-divided light receiving element, such as a focus error signal or a track error signal, this becomes a serious problem.

[0008]

According to the first aspect of the present invention, light emitted from a laser light source is condensed by an objective lens, and the surface of the optical information recording medium is irradiated with a light spot to record information. In an optical information recording / reproducing apparatus for reproducing and erasing, a first optical branch having a diffraction grating divided into a plurality of regions having different grating pitches or grating directions on an optical path between the laser light source and the optical information recording medium. A diffraction grating is provided, and a second light branching diffraction grating having a high-density diffraction grating whose diffraction efficiency changes depending on a polarization direction on an optical path of at least one light beam diffracted by the diffraction grating of the first light branching diffraction grating is provided. Provided.

According to a second aspect of the present invention, in the first aspect of the invention, the light is transmitted through the diffraction grating of the second light branching diffraction grating.
A non-divided light receiving element is provided on the optical path of the diffracted light spot. According to a third aspect of the present invention, in the first aspect, the diffraction grating of the first light branching diffraction grating and the diffraction grating of the second light branching diffraction grating are integrally formed on both front and back surfaces of the same substrate.

According to a third aspect of the present invention, in the first aspect of the present invention, the diffraction grating of the first light branching diffraction grating and the diffraction grating of the second light branching diffraction grating are integrally formed on both front and back surfaces of the same substrate. .

[0011]

According to the first aspect of the present invention, a magneto-optical signal is detected by light passing through the first light branching diffraction grating and the second light branching diffraction grating, and is detected by light passing through only the first light branching diffraction grating. By detecting the focus error signal and the track error signal, it is possible to always perform stable and low-noise signal detection, and the detected light spot for the focus and track error signal is a diffraction grating having a large pitch. Since the light is a diffracted light from the light source, the displacement of the spot position due to the wavelength fluctuation is small and the offset can be suppressed to a small value.

According to the second aspect of the present invention, since a light spot having a large spot position shift due to wavelength fluctuation is detected by a non-divided light receiving element, a high C / N is ensured in a state stable against offset. Can be.

According to the third aspect of the present invention, since two types of diffraction gratings are integrally formed on the front and back surfaces of one substrate, the diffraction gratings are always stable against aging and one such diffraction grating is provided. Since it can be formed by cutting out a large amount of a large-sized substrate and then cutting it out, the cost can be reduced.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described with reference to FIGS. First, as shown in FIG.
The light emitted from the optical information recording / reproducing apparatus for recording, reproducing and erasing information by condensing the light by an objective lens (not shown) and irradiating a light spot on the surface of an optical disk as an optical information recording medium (not shown). , On the optical path between the laser light source 19 and the optical information recording medium,
A light splitting diffraction grating 20 as a first light splitting diffraction grating is provided. As shown in FIG. 2, the light splitting diffraction grating 20 is formed with diffraction gratings 20a, 20b, and 20c divided into three regions having different grating pitches or grating directions. The pitch of the diffraction grating 20a is different from that of the other diffraction grating 2.
The pitch is smaller than the pitches 0b and 20c.
On the optical path of each light beam diffracted by the diffraction grating 20a of the light splitting diffraction grating 20, high-density deep groove diffraction gratings 21 and 22 as second light splitting diffraction gratings are provided. The high-density deep-groove diffraction gratings 21 and 22 are formed with high-density diffraction gratings 21a and 22a whose diffraction efficiency changes depending on the polarization direction, respectively. Further, as shown in FIG. 3, undivided light receiving elements 23a and 23b are provided at positions of light spots a and b formed through the high-density deep-groove diffraction grating 21. The light spot c formed after passing through the grating 22,
The non-divided light receiving elements 23c and 23d are provided at the position d. Light receiving elements 23e, 23f, 23g, and 23h are provided at positions of light spots e, f, g, and h formed by passing through the light branching diffraction grating 20, respectively.

In such a configuration, the semiconductor laser 1
The light emitted from 9 passes through the light splitting diffraction grating 20, is condensed by the objective lens, and is irradiated on the surface of the optical disk. The reflected light receives the rotation of the polarized light according to the signal of the optical disk, and again enters the light splitting diffraction grating 20. The light incident on the diffraction grating 20a of the light splitting diffraction grating 20 is guided to the high-density deep groove diffraction gratings 21 and 22, while the light incident on the diffraction gratings 20b and 20c is irradiated with light spots e, f, g, and
Proceed toward position h.

Therefore, first, the high-density deep groove diffraction grating 21,
The diffraction grating 20a that guides light to 22 will be described. Now, the diffraction grating 20a capable of detecting a magneto-optical signal needs to have a wavelength / pitch of about 1.6 to 2.0. Therefore, if the wavelength of the semiconductor laser 19 is 780 nm, the pitch is 0.39. About 0.49 μm. Since the black angle θ is θ = sin wavelength / (pitch × 2) ≒ 53 °, in order to make light incident on the high-density deep groove diffraction gratings 21 and 22 at such an angle, the pitch of the diffraction grating 20a must be:
Pitch = wavelength / sin θ = 0.78 to 0.98 μm, which is a considerably small value. Along with this, the fluctuation of the diffraction angle due to the wavelength fluctuation of the semiconductor laser 19 becomes considerably large, and the light spot moves at the positions of the light spots a and d of the diffracted light passing through the high-density deep groove diffraction gratings 21 and 22. It is very difficult to align the light receiving element with the divided (two-part or four-part) light-receiving elements (the light spots b and c are canceled out by the high-density deep-groove diffraction gratings 21 and 22 in which the diffraction angle fluctuation is canceled. The movement is slightly smaller). Therefore, the light spots a, b, c,
At the position of d, the large undivided light receiving elements 23a, 23b,
23c and 23d are arranged so that only the magneto-optical signal is detected.

On the other hand, the diffraction grating 20 of the light splitting diffraction grating 20
A diffraction grating such as b, 20c having a large grating pitch and having a grating direction different from that of the diffraction grating 20a is formed. In this case, the light spots e and h of the semicircular diffracted light are formed by the diffraction grating 20b, and the light spots f and g of the semicircular diffracted light are formed by the diffraction grating 20c.
By arranging the light receiving elements 23e, 23f, 23g and 23h as shown in FIG. 3 at the positions of the light spots e, f, g and h, it is possible to detect a focus error signal and a track error signal. In this case, the light spots e, by the diffraction gratings 20b, 20c having a large grating pitch.
Since f, g, and h have small diffraction angle fluctuations due to wavelength fluctuations, the offset can be kept small.

Next, a second embodiment of the present invention will be described with reference to FIGS. Here, the shape of the diffraction grating of the light splitting diffraction grating 24 (corresponding to the light splitting diffraction grating 20 of the first embodiment described above) as the first light splitting diffraction grating is changed. As shown in FIG.
4, light spots e and f diffracted by the diffraction grating 24c
Is used to detect a focus error signal by the knife edge method. In this case, if only one of the light spots e and f (for example, the light spot e) is divided into two, the other may be undivided. In this case, the side for detecting the light spot e is a two-divided light receiving element 25e. The side on which the light spot f is detected is defined as a non-divided light receiving element 25f.

The diffraction gratings 24a and 24b are used as second light branching diffraction gratings (not shown), such as polarization separation diffraction gratings (the high-density deep groove diffraction gratings 21 and 22 of the first embodiment described above).
(Equivalent to 2) will be described. Diffraction grating 2
By making the grating pitches of 4a and 24b slightly different with the X axis as a boundary, four light beams of light spots a, b, c and d are formed. Thereby, a track error signal can be detected from the intensity difference between the light spot a and the light spot b or the light spot c and the light spot d. Further, by considering these four light beams as transmitted light and diffracted light, the light receiving elements 25a, 25
b, 25c, and 25d, whereby a magneto-optical signal can be detected. In this case, all the light having a large displacement of the light spot due to the wavelength fluctuation is guided to the non-divided light receiving element, so that stable signal detection can always be performed.

Next, in the embodiments described above, the diffraction gratings (20a to 20c, 24) of the first light branching diffraction gratings (light branching diffraction grating 20, light branching diffraction grating 24) are used.
a to 24c) and diffraction gratings (21) of the second light branching diffraction gratings (high-density deep-groove diffraction gratings 21, 22 and polarization separation diffraction gratings).
a, 22a) may be integrally formed on the front and back surfaces of the same substrate. By integrating the front and back surfaces in this way, it is possible to maintain a stable state over time, and to cut out such a diffraction grating after making it in large quantities on one large substrate. Therefore, the cost can be further reduced.

[0021]

According to the first aspect of the present invention, recording, reproducing, and erasing of information can be performed by condensing light emitted from a laser light source with an objective lens and irradiating a light spot on the surface of the optical information recording medium. In the optical information recording / reproducing apparatus to be performed, a first optical branching diffraction grating having a diffraction grating divided into a plurality of regions having different grating pitches or grating directions is provided on an optical path between the laser light source and the optical information recording medium. Since the second light-branching diffraction grating having a high-density diffraction grating whose diffraction efficiency changes depending on the polarization direction is provided on the optical path of at least one light beam diffracted by the diffraction grating of the first light-branching diffraction grating, A magneto-optical signal is detected based on the light that has passed through the first light branching diffraction grating and the second light branching diffraction grating, and the focus error signal and the tracking error are detected based on the light that has passed only the first light branching diffraction grating. By detecting the error signal, it is possible to always perform stable and low-noise signal detection, and the detected light spots of the focus error signal and the track error signal are diffracted light from a diffraction grating having a large pitch. Therefore, the displacement of the spot due to the wavelength variation is small, and the offset can be suppressed to a small value.

According to the second aspect of the present invention, since the non-divided light receiving element is provided on the optical path of the light spot transmitted and diffracted by the diffraction grating of the second light splitting diffraction grating, light having a large spot position shift due to wavelength fluctuation. The spot is detected by the non-segmented light receiving element, so that a stable high C / N against offset is obtained.
Can be secured.

According to the third aspect of the present invention, the diffraction grating of the first light branching diffraction grating and the diffraction grating of the second light branching diffraction grating are formed integrally on the front and back surfaces of the same substrate. Since two types of diffraction gratings are integrally formed, they are always stable against changes over time, and such diffraction gratings can be formed by cutting a large number of pieces on a single large substrate and then cutting them out. Therefore, the cost can be further reduced.

[Brief description of the drawings]

FIG. 1 is a principle diagram showing a basic configuration of a first embodiment of the present invention.

FIG. 2 is a front view showing a surface shape of a light splitting diffraction grating.

FIG. 3 is an explanatory diagram showing an arrangement relationship of light receiving elements for receiving each light spot.

FIG. 4 is a front view showing a light splitting diffraction grating and a light spot obtained through the light splitting diffraction grating according to a second embodiment of the present invention.

FIG. 5 is an explanatory diagram showing an arrangement relationship of light receiving elements for receiving each light spot.

FIG. 6 is a perspective view showing a first conventional example.

FIG. 7 is a front view showing a beam state when a focus error signal is detected.

FIG. 8 is a front view showing a second conventional example.

[Explanation of symbols]

 Reference Signs List 19 laser light source 20 first light branching diffraction grating 20a to 20c diffraction grating 21 second light branching diffraction grating 21a diffraction grating 22 second light branching diffraction grating 22a diffraction grating 23a to 23d undivided light receiving element

Claims (3)

(57) [Claims] 1. An optical information recording / reproducing apparatus for recording, reproducing and erasing information by condensing light emitted from a laser light source by an objective lens and irradiating a light spot on a surface of an optical information recording medium, A first light branching diffraction grating having a diffraction grating divided into a plurality of regions having different grating pitches or grating directions on an optical path between the laser light source and the optical information recording medium; An optical information recording / reproducing apparatus comprising a high-density diffraction grating having a high-density diffraction grating whose diffraction efficiency changes depending on a polarization direction on an optical path of at least one light beam diffracted by the diffraction grating. . 2. The transmission and transmission through a diffraction grating of a second light splitting diffraction grating.
2. The optical information recording / reproducing apparatus according to claim 1, wherein a non-divided light receiving element is provided on the optical path of the diffracted light spot. 3. The optical information recording / reproducing apparatus according to claim 1, wherein the diffraction grating of the first light branching diffraction grating and the diffraction grating of the second light branching diffraction grating are integrally formed on both front and back surfaces of the same substrate. apparatus.