JP2714033B2 - Optical pickup - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pickup used in an optical disk device and the like, and more particularly, to an integrated optical pickup capable of high-speed acceleration.

[Conventional technology]

FIG. 4 is a schematic diagram showing a configuration of an optical pickup using a conventional optical member, wherein 1 shows a semiconductor laser as a light source. After the light 26 emitted from the semiconductor laser 1 is split into two by the diffraction grating 21, it is focused on the pits 20 recorded on the optical disc 19 by the objective lens 23. Of the three divided lights, the central main beam 27, which is the zero-order diffracted light, is used for reading the HF signal and the focus error signal as pit information, and the sub-beams 28, which are the ± first-order diffracted lights, are used for tracking error signal. Used for reading each. The reflected light of the three-divided light from the optical disk 19 is split by the beam splitter 22, passes through the cylindrical lens 24, and is received by the light receiving elements 25a and 25b. At this time, the reflected light corresponding to the main beam 227 is reflected by the cylindrical lens 24.
The focal length of the light 27a in the vertical direction is different from the focal length of the light 27b in the horizontal direction.

FIG. 5 is an enlarged plan view of the light receiving elements 25a and 25b. The reflected light corresponding to the main beam 27 is detected by the central four-division light receiving elements 13a, 13b, 13c and 13d, and corresponds to the sub beam 28. The reflected light is detected by the light receiving elements 13e and 13f on both sides, and a focus error signal, an HF signal, and a tracking error signal are output by the calculation shown in FIG. 5 based on the detection signals from the respective light receiving elements. . In other words, in such an optical system, the focus error signal is read using the astigmatism method, and the tracking error signal is read using the three-point astigmatism method.
The beam method is adopted.

The reading method of the error signal in the optical pickup having the above-described configuration is used in almost all currently available CD players, and is mainstream in optical disk devices. However, since such an optical pickup is configured by combining conventional optical members, it has a drawback that it is bulky, heavy, and has a long access time.

In order to solve such a drawback, an integrated optical pickup in which an optical member is integrated on one substrate has been devised. FIG. 6 is a perspective view showing a configuration of an integrated optical pickup disclosed in, for example, "Optical Integrated Circuit of Optical Disc Pickup" (IEICE Technical Report OQE85-72, 1985). The waveguide 2 is formed on the Si substrate 4 with the buffer layer 3 interposed therebetween.
A grating coupler 5, a beam splitter 31, and a two-divided light receiving element 33 are integrated therein. A semiconductor laser 1 as a light source is coupled to an end face of the waveguide 2 by an end face direct coupling method.

When light from the semiconductor laser 1 enters the waveguide 2, the light 15 propagates through the waveguide 2, is emitted outside by the grating coupler 5, and is condensed on the pit 20 recorded on the optical disk 19. Is done. Reflected light 16 from optical disk 19
Is incident on the waveguide 2, and the beam splitter 31
In such an optical pickup, the tracking error signal of the optical disc is based on the push-pull method, and the focus error signal is based on the Foucault method. The HF signal, which is the error signal and the pit information, is obtained by a calculation as shown in FIG.

[Problems to be solved by the invention]

By the way, a commercially available CD player or CD-ROM
When replacing the non-integrated optical pickup of the driver with the integrated optical pickup as described above, the signal calculation method is different between the two optical pickups (see FIGS. 5 and 6). It is necessary to change the circuit at the same time, and there is a problem that the configuration becomes complicated. As a result, it is not easy to change to an integrated optical pickup, and there is a problem that conversion to the integrated optical pickup is not promoted.

The present invention has been made in view of the above circumstances, and has a means for dividing light from a grading coupler into three parts and a means for condensing reflected light from an optical disk to a six-part light receiving element. The present invention provides an integrated optical pickup in which signals can be detected in the same manner as in a non-integrated optical pickup in the same manner as in a non-integrated optical pickup, and only the optical pickup needs to be replaced without changing peripheral electronic circuits. The purpose is to do.

[Means for solving the problem]

An optical pickup according to the present invention includes a light source, a waveguide that guides light from the light source, a grating coupler that emits light guided by the waveguide toward an optical disc, and receives reflected light from the optical disc. In an optical pickup in which a light receiving element is integrated, the light receiving element is a six-division type light receiving element, and a transparent plate is perpendicular to an optical axis of the light in a light emitting direction of the grating coupler. A first condensing means for dividing the light emitted from the grating coupler into three and condensing the light at three points on the optical disc, on a surface of the transparent plate opposite to the waveguide, A second light condensing means for diffracting the reflected light from the optical disc in a direction different from the optical axis of the light on the waveguide-side surface of the transparent plate and condensing the light toward the six-segment light receiving element. Means are provided And wherein the Rukoto.

[Action]

In the optical pickup according to the present invention, the light emitted from the grating coupler is divided into three parts and is incident on the optical disk from a direction perpendicular thereto, and the reflected light from the optical disk is focused on the six-part light receiving element. Therefore, in the present invention, the tracking error signal is detected by the three-beam method and the focus error signal is detected by the astigmatism method, similarly to the conventional non-integrated optical pickup.

〔Example〕

Hereinafter, the present invention will be described in detail with reference to the drawings showing the embodiments.

FIG. 1 is a diagram showing a configuration of a first embodiment of an optical pickup according to the present invention, and FIG. 1 (a) is a plan view thereof.
FIG. 1 (b) shows a cross-sectional view thereof. In FIG. 1A, members that are not integrated on the substrate 4 are not shown.

In the figure, reference numeral 4 denotes a substrate made of n-type Si.
A waveguide 2 made of Corning # 7059 is formed via a buffer layer 3 made of SiO ₂ for preventing loss of guided light, and a semiconductor laser 1 as a light source is formed on the end face of the waveguide 2. Are combined. The waveguide 2 is not formed in a part of the region on the side opposite to the side where the semiconductor laser 1 is disposed. On the upper surface of the waveguide 2 on the side opposite to the side where the semiconductor laser 1 is coupled, a Si for emitting the light 15 guided through the waveguide 2 to the outside is provided.
A grating coupler 5 made of N is provided.
The shape of the grating coupler 5 is designed so that the outgoing light 16 from the grating coupler 5 becomes parallel light.

The direction of light emission from the grating coupler 5 is BK
A transparent plate 8 made of 7 is provided so as to be perpendicular to the optical axis. On the surface on the front side of the transparent plate 8 (the surface opposite to the waveguide 2), the light incident on the transparent plate 8 is divided into three parts and focused on three points of an optical disk (not shown). A three-part Fresnel lens (first condensing means) 9a, 9b, 9c is provided, and the surface on the back side of the transparent plate 8 (the surface on the side of the waveguide 2) receives reflected light from the optical disk as described later. An off-axis Fresnel lens (second light condensing means) 11 for condensing light on the six-divided light receiving element 13 is provided. The three-part Fresnel lenses 9a, 9b, 9c are designed so that their focal points are slightly shifted in the direction perpendicular to the optical axis.
The material of these Fresnel lenses 9a, 9b, 9c, 11 is Corning # 7059.

FIG. 2 is a cross-sectional view showing the vicinity of the six-divided light receiving element 13. FIG. 2 (a) is a cross-sectional view as viewed from the same direction as FIG. 1 (b), and FIG. 3 shows a cross-sectional view as seen from a direction perpendicular to FIG. In a plan view, the light receiving element 13 has the same configuration as the conventional non-integrated optical pickup (see FIG. 5).
It is composed of a pn junction 43 formed by partially doping a p-type impurity into the Si substrate 4. A grating coupler 12 corresponding to a cylindrical lens is provided on the buffer layer 3 above the light receiving element 13. The grating coupler 12 has a chirp shape whose period becomes shorter as it goes away from the center, and is obtained by etching the waveguide 2. In the figure, reference numerals 14a and 14b denote an upper electrode and a lower electrode of the light receiving element 13, which are made of Al and Au, respectively.

 Next, the operation will be described.

After the light 15 emitted from the semiconductor laser 1 is guided through the waveguide 2, it is emitted outside as parallel light 16 by the grating coupler 5. The light 16 emitted to the outside passes through the transparent plate 8 and is divided into three by Fresnel lenses 9a, 9b, 9c. The three divided beams (the main beam 17a at the center, which is the 0th-order diffracted light, and the sub-beams 18a at both sides, which are the ± 1st-order diffracted lights) are respectively focused on pits recorded on the optical disk. The reflected light from the optical disk passes through the transparent plate 8 again, and is focused on the light receiving element 13 through the Fresnel lens 11 and the grating lens 12. As in the case of the conventional non-integrated optical pickup, the reflected light 17b corresponding to the main beam 17a is detected by the central four-divided light receiving element, and the reflected light 18b corresponding to the sub-beam 18a is received by the peripheral two-divided light receiving element. Detected by the element,
Then, the HF signal as the pit information and the focus error signal are calculated using the main beam, and the tracking error signal is calculated using the sub beam 18 (see FIG. 5).

As described above, the arithmetic processing in the optical pickup of the present invention is exactly the same as that of the conventional non-integrated optical pickup. In other words, it is sufficient to simply convert the optical pickup into an integrated type.

FIG. 3 is a sectional view showing a second embodiment of the optical pickup according to the present invention. In FIG. 3, the same members as those in FIGS. 1 and 2 denote the same members. In this embodiment, another grating 7 is provided in the optical path between the grating coupler 5 and the transparent plate 8 on the front surface thereof (the surface opposite to the waveguide 2) for dividing the parallel emission light 16 into three. It has a configuration in which the transparent plate 6 is arranged. Therefore, since the Fresnel lens for condensing the light on the optical disk does not need to have the function of dividing into three, unlike the first embodiment, a single Fresnel lens 10 is provided on the front surface of the transparent plate 8. Is provided. The materials of the grating 7 and the transparent plate 6 are Corning # 705, respectively.
9, BK7.

In the second embodiment, the parallel outgoing light 16 from the grating coupler 5 is diffracted by the grating 7 formed on the transparent plate 6, and the 0th-order and ± 1st-order diffracted lights are used as three beams. The light split into three beams passes through the Fresnel lens 10 and is focused on the pits of the optical disk. The optical path of the reflected light from the optical disk and the arithmetic processing for detecting each signal are the same as those in the first embodiment described above, and a description thereof will be omitted.

The second embodiment requires an extra grating 7 for diffracting the parallel outgoing light 16 from the grating coupler 5 as compared with the first embodiment. Since the aperture can be enlarged, there is an advantage that the light-collecting characteristics are excellent.

In both of the above-described embodiments, the light emitted from the grating coupler 5 is a parallel light. However, the present invention is not limited to this.

〔The invention's effect〕

As described in detail above, in the present invention, when high-speed access is desired in a commercially available CD player or the like, the optical pickup may be simply changed to an integrated type, and the conventional electronic circuit for signal operation can be used as it is. Need not be changed. Therefore, when developing an optical disk device or the like that requires high-speed access, the required high-speed access can be realized only by changing only the optical pickup in the conventional optical disk device. As a result, it is possible to promote the spread of an integrated optical pickup using a waveguide suitable for miniaturization, and to make the light emitted from the grating coupler incident on the optical disk in a direction perpendicular to the optical disk, thereby forming a light spot shape. Can be made close to a perfect circle, and the light use efficiency can be improved, and the present invention exhibits an excellent effect.

[Brief description of the drawings]

FIG. 1 is a plan view and a sectional view showing the structure of an optical pickup according to a first embodiment of the present invention, and FIG. 2 is a sectional view near a light receiving element of the optical pickup according to the first and second embodiments of the present invention. ,
FIG. 3 is a sectional view showing the configuration of a second embodiment of the optical pickup of the present invention, FIG. 4 is a perspective view showing the configuration of a non-integrated optical pickup used in a general optical disk device, and FIG. The figure is an enlarged plan view in the vicinity of a six-divided light receiving element, and FIG.
FIG. 1 is a perspective view showing a configuration of a conventional integrated optical pickup. 1 ... semiconductor laser, 2 ... waveguide, 4 ... substrate, 5 ...
… Grating coupler, 9a, 9b, 9c, 10, 11 …… Fresnel lens, 12… Grating lens, 13 …… Light receiving element

Claims (1)

(57) [Claims] A light source, a waveguide for guiding light from the light source,
In an optical pickup in which a grating coupler for emitting light guided to the waveguide toward an optical disk and a light receiving element for receiving reflected light from the optical disk are integrated, the light receiving element is a six-division type light receiving element. A transparent plate is provided so as to be perpendicular to an optical axis of the light in a light emission direction of the grating coupler, and the grating coupler is provided on a surface of the transparent plate opposite to the waveguide. First condensing means for dividing the light emitted from the optical disc into three and condensing the light at three points on the optical disc; and reflecting light reflected from the optical disc on the waveguide-side surface of the transparent plate. An optical pickup comprising a second light condensing means for diffracting light in a direction different from the optical axis and condensing the light toward the six-divided light receiving element.