JPH03278330A - Optical pickup device - Google Patents

Abstract

PURPOSE:To easily perform the accurate positioning of a photodetector for error signal detection by reflecting light separated by a hologram element, and making it incident on a first photodetector. CONSTITUTION:A reflecting means 6 is provided which reflects the light separated by the hologram element 7 and makes it incident on the first photodetectors 4a-4h. Also, a fixing plane 3a fixing a semiconductor laser 1 is set in parallel with a fixing plane 3b fixing a semiconductor substrate 4, and also, the semiconductor substrate 4 is fixed by abutting with a fixing plane 3c. Thereby, position adjustment between the semiconductor laser 1 and the photodetectors 4a-4h for error signal detection on the semiconductor substrate 4 can be easily performed, which realizes the accurate positioning.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an optical pickup device that can be used in an optical disc device or the like.

2. Description of the Related Art Conventionally, optical pickup devices for reading signals written on recording media have used a combination of lenses, mirrors, prisms, etc. to detect focus and tracking error signals. Recently, a method of detecting focus and tracking error signals using a hologram element instead of conventional optical components has been devised.

FIG. 9 is a side sectional view of an example of an optical pickup device using a conventional hologram element, and FIG. 10 is a side sectional view of an example of an optical pickup device using the hologram element. Detect
ion (abbreviated as 5SD) method.

FIG. 3 is a diagram showing the relationship between a hologram area in which tracking error is detected by a push-pull method and an error signal detection photodetector, and an image when correctly focused on a recording medium.

In FIG. 9, 1 is a semiconductor laser as a light source, 2 is a heat sink for fixing and cooling the semiconductor laser 1,
Reference numeral 4 denotes a semiconductor substrate, on which a focus and tracking error signal detection photodetector for detecting the light separated by the hologram element 7 is constructed. Further, the semiconductor substrate 4 is fixed to a surface perpendicular to the semiconductor laser l fixed to the heat sink 2. 5 is a photodetector for controlling the optical output of the semiconductor laser, and 7 is a hologram element for separating the modulated reflected light from the recording medium 9 from the optical axis to generate a focus error signal and a tracking error signal. . 8 is a finite focus system focus lens for focusing on the recording medium, 9 is the recording medium, and 9a is a signal pit. 15 is a semiconductor laser 1. Heat sink 2. Semiconductor substrate 4, photodetector for controlling optical output 5. This is a package in which a hologram element 7 is integrated.

Note that in FIG. 9, the actuator for driving the focus lens 8 is omitted.

In FIG. 10, 7a+7b is a hologram area formed on the surface of the hologram element 7 that generates a tracking error signal, 7c and 7d are hologram areas that generate a focus error signal, and 7e and 7f are hologram areas that generate a tracking error signal on the hologram element 7. Far field pattern of reflected light, 4a
l4b is a photodetector for tracking error signal detection;
4c+ 4d, 4el 4L 4g+ 4
h is a photodetector for detecting a focus error signal. Hologram area 7 a.

7b, a spherical wave diverging from the position of the semiconductor laser 1;
Photodetector 4 a for tracking error signal detection.

A hologram corresponding to interference fringes with the spherical wave diverging from the detection point 4b is formed. In addition, the hologram area 7c
, 7d shows a spherical wave that diverges from the position of the semiconductor laser 1, a spherical wave that diverges from before the detection point of the photodetector 4d for detecting a focus error signal, and a spherical wave that diverges from the position of the semiconductor laser 1 and the photodetector. Two types of holograms are formed corresponding to interference fringes with the spherical waves that diverge from the detection point 4g.

The operation of the conventional optical pickup device configured as described above will be described below.

The light emitted from the semiconductor laser 1 is divided by a hologram area formed on the hologram element 7 into 0th-order light and diffracted light of ±1st-order or higher orders. Among them, the zero-order light travels straight, enters a focus lens 8 and focuses on a recording medium 9. The beam spot connected on the recording medium s is pit 9
It is modulated and reflected by a. Thereafter, the light follows the opposite path to the hologram element 7.

Next, a process of generating an error signal using the hologram element 7 from the light reflected by the recording medium 9 and returned will be described.

When the beam spot is focused on the recording medium 9, the reflected light from the recording medium 9 is diffracted by the hologram areas 7c and 7d and focused on two points above and below the photodetectors 4d and 4g, Beam spots with the same diameter are obtained on ~4e and 4f~4h.

On the other hand, when the beam is defocused, the focal point moves, so a difference occurs in the size of the beam spot diameter on the photodetectors 40 to 4e and 4f to 4h.

The focus error signal is obtained by adding the outputs of 4f and 4h to the output of 4d, and the output of 4c+4e to the output of 4g, and taking the difference between them.

In addition, the push-pull method, which is a tracking error signal detection method, diffracts the part where the intensity changes greatly due to tracking error in the far field image of the reflected light from the recording medium at the hologram area 7 at 7 b and detects the error signal. It is detected by photodetector 4 at 4 b. At this time 4
A tracking error signal is obtained by taking the difference between the outputs of a and 4b.

On the other hand, the light emitted from the rear end facet of the semiconductor laser 1 is detected by the light output control photodetector 5 and
The light output is controlled to be constant.

Problems to be Solved by the Invention In the optical pickup device configured as described above, it is difficult to ensure that the light reflected from the recording medium is diffracted by the hologram element and accurately forms a beam spot on the photodetector for error signal detection. , the position of the semiconductor laser and the photodetector for error signal detection must be precisely adjusted. However, in the above configuration, since the mounting surfaces of the semiconductor laser and the photodetector for detecting an error signal are perpendicular to each other, a problem arises in that accurate positioning is difficult.

The present invention solves the above-mentioned conventional problems, and aims to provide a compact optical pickup device that facilitates positioning of a semiconductor laser and a photodetector for detecting an error signal.

Means for Solving the Problems In order to achieve the above objects, the optical pickup device of the present invention includes a light source that emits light to a recording medium, and a condenser that focuses the light emitted from the light source onto the recording medium. a hologram element disposed between the light source and the condensing means to separate light reflected from the recording medium from the optical axis; a first photodetector for detecting the light separated by the hologram element; and a light source. and a second photodetector for detecting light emitted from the rear end surface, the optical pickup device comprising a reflecting means for reflecting the light separated by the hologram element and making it incident on the first photodetector. ing.

Further, there is provided an optical pickup device in which the reflecting means is composed of a prism, in which the photodetectors on the first photodetector surface side are formed on the same surface of the same semiconductor substrate, and the semiconductor substrate and the prism are connected to each other by the refractive index of the prism. The light source is fixed to a semiconductor substrate having a refractive index n2 smaller than the refractive index n1, which is smaller than the refractive index n1.

Operation With the optical pickup device of the present invention having the above-described configuration, the light emitted from the semiconductor laser serving as the light source is transmitted through the hologram element, and a beam spot is focused on the recording medium by the focusing means. Then, the reflected light from the recording medium travels backward, and the light diffracted by the hologram element is separated from the optical axis. The separated light is reflected by a reflection means fixed to the heat sink and enters the first photodetector to obtain a detection output. On the other hand, the light emitted from the rear end facet of the semiconductor laser is detected by a second photodetector on the heat sink, and the light output of the light source is controlled.

Further, according to the present invention, with the above-described configuration, light emitted from the semiconductor laser bonded to the semiconductor substrate constituting the photodetector is transmitted through the hologram element, and a spot is focused on the recording medium by the condensing means.

Then, the reflected light from the recording medium travels backward, and the light diffracted by the hologram element is separated along the optical axis. The separated light is reflected by a prism bonded to the semiconductor substrate and enters the first photodetector to obtain a detection output. On the other hand, the light emitted from the rear end facet of the semiconductor laser enters the prism, is reflected by the reflective surface of the prism, and is detected by the second photodetector to control the light output of the light source.

By using an adhesive having a refractive index n2 smaller than the refractive index n+ of the prism, the light from the rear end face of the semiconductor laser is totally reflected and is prevented from entering the first photodetector.

EXAMPLE Hereinafter, a first example of the present invention will be described with reference to the drawings.

FIG. 1 is a perspective view of an optical pickup device according to a first embodiment of the present invention, and FIG. 2 is a side sectional view of the optical pickup device according to this embodiment.

In FIGS. 1 and 2, 1. 2. 4. 7. 5
゜7a-7d, 8+ 9. 9a is the same as the component name of the conventional example.

3 is a semiconductor laser 1. a sub-heat sink for fixing the semiconductor substrate 4; 3a is a surface for fixing the semiconductor laser 1;
3b is a surface for fixing the semiconductor substrate 4, and 3c is a surface for fixing the semiconductor substrate 4.
The positioning surface 6 is a mirror for guiding the light diffracted by the hologram element 7 to the error signal detection photodetectors 4a to 4g.

Note that the actuator for driving the focus lens 8 is omitted in this figure.

The optical pickup af of this embodiment configured as described above
The operation of lt will be explained below.

The zero-order light emitted from the semiconductor laser 1 as a light source passes through the hologram element 7 and enters the focus lens 8, where it is focused on the recording medium 9.

The beam spot focused on recording medium 9 is bit 9
a, and the reflected light follows the original path. The reflected light returns to the hologram area 7 on the hologram element 7.
a+ 7b+ 7c+ When passing through 76, it is diffracted. The light diffracted by the hologram area 7C97d is reflected by the mirror 6, and then focused on the focus error signal detection photodetector 4c+4cL 4e and a beam spot 4f.

A beam spot is formed that focuses below 4g and 4h. After the light diffracted by the hologram area 7a+7b is reflected by the mirror 6, a beam spot is focused on two points of the tracking error signal detection photodetectors 4a and 4b. Then, an error signal is obtained as a result of calculation of the output of each photodetector.

On the other hand, the light emitted from the rear end facet of the semiconductor laser 1 enters the light output control photodetector 5 to obtain a signal, which is used to control the light output of the semiconductor laser 1.

As described above, according to this embodiment, the fixing surface 3a that fixes the semiconductor laser 1 and the fixing surface 3b that fixes the semiconductor substrate 4 are parallel, and the semiconductor substrate 4 is placed on the fixing surface 3C. Fix it. Therefore, the semiconductor laser 1 and the semiconductor substrate 4
Since the positional relationship of the above error signal detection photodetectors is not orthogonal as in the conventional example, adjustment becomes easy and accurate positioning becomes possible.

A second embodiment of the present invention will be described below with reference to the drawings.

FIG. 3 is a perspective view of an optical pickup device according to a second embodiment of the present invention, and FIG. 4 is a side sectional view of the optical pickup device according to this embodiment.

In FIGS. 3 and 4, L 7, 7a to 7d.

8+9,9a is the same as the component name of the first embodiment.

10 is a semiconductor substrate, on which are photodetectors 10a and 10b for detecting tracking error signals, and photodetectors 10c+10d for detecting focus error signals.

10 e, 10 f, 10 g, 10 h
, A photodetector 10i for controlling light output is formed.

11 is a prism with a refractive index n1, 11a is a reflective surface of the prism 11, 11b is an adhesive surface with the semiconductor substrate 10, and 12 is an adhesive (n + > np) with a refractive index n2.

The semiconductor laser 1 is fixed to the surface of the semiconductor substrate 10 on which the photodetector for error signal detection is formed.

Note that in this figure, the actuator for driving the focus lens 8 is omitted as in the first embodiment.

The operation of the optical pickup device of this embodiment configured as described above will be explained below.

The path through which the light emitted from the semiconductor laser 1 is reflected by the recording medium 9 and returns to the hologram element 7 is the same as in the first embodiment, and will therefore be omitted.

The light reflected by the recording medium 9 and diffracted by the hologram area 7C17d is incident on the prism 11 and then reflected by the reflector 11a, and is then reflected by the focus error signal detection photodetector 10C11.
A beam spot that focuses above 0d+10e and a beam spot that focuses below 1Of, Log, and 10h are formed. Further, the light diffracted by the hologram areas 7a and 7b is reflected by the incident double reflection surface 11a of the prism 11, and a beam spot is focused on two points of the tracking error signal detection photodetectors 10a and 10b.

An error signal is then obtained as a result of the calculation.

On the other hand, the light emitted from the rear end surface of the semiconductor laser 1 enters the prism 11 and reaches the adhesive surface 11b of the prism, where it is totally reflected because the refractive index n1 of the prism is larger than the refractive index n2 of the adhesive. The light is reflected by the light beam and enters the light output control photodetector 10j to obtain a signal, which is used to control the light output of the semiconductor laser 1.

It goes without saying that if there is no need to control the optical output of the semiconductor laser 1, the optical detector 10i for controlling the optical output does not need to be formed on the semiconductor substrate 10.

As described above, according to this embodiment, the photodetectors foa to 10i for error signal detection are formed on the semiconductor substrate 10, the semiconductor laser 1 and the prism 11 are bonded to the semiconductor substrate 10,
Since it is fixed, the factors that cause assembly errors are further reduced than in the first embodiment, making assembly easier.

Furthermore, since an adhesive having a refractive index smaller than the refractive index n of the prism is used to bond the prism 11 and the semiconductor substrate 10, the light emitted from the rear end surface of the semiconductor laser 1 once reaches the adhesive surface 11b. Total reflection. Therefore, the light emitted from the rear end facet of the semiconductor laser 1 does not enter the error signal detection photodetector, so that offset can be suppressed.

A third embodiment of the present invention will be described below with reference to the drawings.

FIG. 5 is a perspective view of an optical pickup device according to a third embodiment of the present invention, and FIG. 6 is a side sectional view of the optical pickup device according to this embodiment.

In FIGS. 5 and 6, 1. 7. 7a-7d.

8+9+9a is the same as the component name of the first embodiment.

Reference numeral 13 denotes a semiconductor substrate, and in this table, photodetectors for tracking error signal detection 13 a + 13 bl Photodetectors for focus error signal detection 13 c, 13 d, 1
3 e.

13f, 13g, and 13h, and a photodetector 13i for controlling light output is formed on the back side. 14 is a prism,
14a is a reflective surface of the prism, and 14b is a bonding surface to the semiconductor substrate 13. Further, the semiconductor laser 1 is connected to a semiconductor substrate 1.
It is fixed on the same surface as the light output control photodetector No. 3.

Note that the error signal detection photodetectors 13a to 13i may be composed of one semiconductor substrate, or the semiconductor substrate on which the error signal detection photodetectors 13a to 13h are formed and the light output control photodetector 13i The structure may also be constructed by bonding the back surfaces of the semiconductor substrate and the semiconductor substrate formed with the .

Note that in this figure, the actuator for driving the focus lens 8 is omitted as in the first embodiment.

The operation of the optical pickup device of this embodiment configured as described above will be explained below.

The light emitted from the semiconductor laser 1 is reflected by the recording medium 9 and the path from which the light returns to the hologram element 7 is the first path.
Since this is the same as the embodiment, the explanation will be omitted.

The light reflected by the recording medium 9 and diffracted by the hologram area 7 C17d enters the prism 14 and is reflected by the incident double-reflection surface 14a, and then passes through the focus error signal detection photodetector 13c+.
A beam spot focused above 13d and 13e and a beam spot focused below 13f, 13g and 13h are formed. Further, the light diffracted by the hologram areas 7a and 7b is reflected by the incident double reflection surface 14a of the prism 14, and beam spots are focused on two points of the tracking error signal detection photodetectors 13a and 13b. An error signal is then obtained as a result of the calculation.

On the other hand, the light emitted from the rear end facet of the semiconductor laser enters the light output control photodetector 13i to obtain a signal, which is used to control the light output of the semiconductor laser 1.

It goes without saying that if there is no need to control the optical output of the semiconductor laser 1, the optical detector f3i for controlling the optical output does not need to be formed on the semiconductor substrate 13.

As described above, according to this embodiment, since the error signal detection photodetectors 13a to 13h and the optical output control photodetector 13i are formed on the front and back sides, the light emitted from the rear end surface of the semiconductor laser 1 is This eliminates the problem of offset generation in the photodetector for error signal detection due to the error signal detection. Furthermore, since the semiconductor substrate 13, semiconductor laser 1, and prism 14 are integrated, the light emission and detection system becomes smaller.

A fourth embodiment of the present invention will be described below with reference to the drawings.

FIG. 7 is a perspective view of an optical pickup device according to a fourth embodiment of the present invention, and FIG. 8 is a side sectional view of the optical pickup device according to this embodiment.

In FIGS. 7 and 8, 1. 7. 7a-7d.

8, EL 9a+ 13+ 13a~131
．． 14. 14a and 14b are the same as the component names of the third embodiment.

The prism 14 is provided with a corner portion 14c for positioning the semiconductor substrate 13. The semiconductor substrate 13 and the prism 14 are bonded together at the prism surface 14b. Furthermore, the semiconductor laser 1 is fixed to the prism surface 14d.

Note that the error signal detection photodetectors 13a to 13i may be composed of one semiconductor substrate, or the semiconductor substrate on which the error signal detection photodetectors 13a to 13h are formed and the light output control photodetector 13i The structure may also be constructed by bonding the back surfaces of the semiconductor substrate and the semiconductor substrate formed with the .

Note that, in FIG. 8, the actuator for driving the focus lens 8 is omitted as in the first embodiment.

The operation of this embodiment is the same as that of the third embodiment, so a description thereof will be omitted.

It goes without saying that if there is no need to control the optical output of the semiconductor laser 1, the optical detector f3i for controlling the optical output does not need to be formed on the semiconductor substrate 13.

As described above, according to this embodiment, the semiconductor substrate 13 is positioned along the corner 14c by the error signal detection photodetector 1.
This can be easily realized by sliding while monitoring the signals 3a to 13h.

Although the first to fourth embodiments used the SSD method for focus error detection and the push-pull method for tracking detection, another detection method, for example, the double knife method was used for focus error detection.

It goes without saying that a hologram element using a single knife edge method, an astigmatism method, or a three-beam method for tracking error detection may be used.

Effects of the Invention As described above, according to the present invention, by configuring the light source and the photodetector for error signal detection on the same plane or parallel planes, it is possible to easily position them and reduce costs. In addition, since the light source, the photodetector for error signal detection, and the photodetector for controlling the optical output can be integrated, a small optical pickup can be installed in the 41-1
The practical effects are great.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of the optical pink-up device according to the first embodiment of the present invention, FIG. 2 is a side sectional view of the optical pink-up device according to the first embodiment of the present invention, and FIG. Second
FIG. 4 is a side sectional view of an optical pickup device in a second embodiment of the present invention, and FIG. 5 is a perspective view of an optical pink-up device in a third embodiment of the present invention. 6 is a side sectional view of an optical pickup device according to a third embodiment of the present invention, FIG. 7 is a perspective view of an optical pickup device according to a fourth embodiment of the present invention, and FIG. 8 is a side sectional view of an optical pickup device according to a fourth embodiment of the present invention. 9 is a side sectional view of an optical pickup device according to a fourth embodiment of the invention, FIG. 9 is a side sectional view of a conventional optical pickup device, and FIG. , 2... heat sink, 3... sub heat sink, 4. 10
．． 13... Semiconductor substrate, 4a to 4hy 1
0a to 10h, 13a to 13h...photodetector,
4L 5t 10it 131... Photodetector for controlling light output, 6... Mirror 7... Hologram element, 8... Focus lens, 9... Recording medium, 9a... Pit, 11.14 ···prism.

Claims (6)

[Claims] (1) a light source that emits light to a recording medium; a condenser that focuses the light emitted from the light source onto the recording medium; and a condenser disposed between the light source and the condenser; An optical pickup device comprising: a hologram element that separates light reflected from a recording medium from an optical axis; and a first photodetector that detects the light separated by the hologram element; An optical pickup device comprising a reflecting means for reflecting the light and making it incident on the first photodetector. (2) The optical pickup device according to claim 1, further comprising a second photodetector that detects the light emitted from the rear end surface of the light source. (3) The optical pickup device according to claim 1 or 2, wherein the light source and the first photodetector are fixed to the heat sink via a sub-heat sink. (4) In the optical pickup device according to claim 1 or 2, in which the reflecting means is constituted by a prism, the first photodetector and the second photodetector are formed on the same surface of the same semiconductor substrate, and the The substrate and the prism are bonded with an adhesive having a refractive index n_2 smaller than the refractive index n_1 of the prism,
An optical pickup device characterized in that a light source is fixed to a semiconductor substrate on the side of a photodetector. (5) In the optical pickup device according to claim 1 or 2, in which the reflecting means is constituted by a prism, the first photodetector and the second photodetector are formed on the front and back sides of the same semiconductor substrate, and the first photodetector and the second photodetector are formed on the front and back sides of the same semiconductor substrate. An optical pickup device characterized in that a photodetector surface and a prism are bonded together, and a light source is fixed to a semiconductor substrate on the second photodetector surface side. (6) In the optical pickup device according to claim 1 or 2, in which the reflecting means is composed of a prism, the first photodetector and the second photodetector are formed on the front and back sides of the same semiconductor substrate, and the first photodetector and the second photodetector are formed on the front and back sides of the same semiconductor substrate. An optical pickup device characterized in that a photodetector surface and a prism are bonded together, and a light source is fixed to the first photodetection surface and the parallel prism surface.