JPH11312334A - Optical unit and optical pickup device using same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the optical unit which can detect a focusing state by using a small number of photodetection areas and make the optical pickup device small-sized and easy to assemble, and the optical pickup device using it. SOLUTION: The optical unit has a semiconductor laser 2 arranged on a semiconductor substrate 1, a tripartite optical detector 3 which is formed on the semiconductor substrate 1 and has three photodetection areas divided with two division lines, a going and return optical path separating means 4d which projecting the laser beam from the semiconductor laser 2 on the side of a recording medium 6 through an objective 5 and guides the return light from the recording medium 6 to the side of the tripartite optical detector 3, and luminous flux splitting means 4c and 9 which obtain pieces of luminous flux by dividing the section of the return light made incident on the tripartite optical detector 3; and the pieces of luminous flux split by the luminous flux splitting means are made incident on the photodetection areas on both the sides including one division line of the tripartite optical detector 3 and both the photodetection areas including the other division line to detect a focus state.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical unit and, more particularly, to a method using the optical unit. The present invention relates to an optical pickup device that performs recording and reproduction of information by being guided to a detector.

[0002]

2. Description of the Related Art As an example of an optical pickup device for causing a laser beam from a semiconductor laser to enter a recording medium and guiding a reflected beam from the recording medium to a photodetector to read information recorded on the recording medium, JP-A-64-4624
There is one described in Japanese Patent Publication No. In this optical pickup device, a semiconductor laser is disposed on a semiconductor substrate, and first and second light detecting portions are formed on the semiconductor substrate, and a total reflection grating is formed on the first and second light detecting portions. The laser beam from the semiconductor laser is reflected by the total reflection grating to obtain three light beams. These three light beams are made incident on a beam splitter composed of a hologram of a curved interference fringe pattern formed on the inner surface of the cover member of the package, and the three light beams transmitted through the beam splitter are transmitted through a collimator lens and an objective lens to an optical disk. To be irradiated.

[0003] The three return lights reflected by the optical disk are:
A first light detection unit is caused to enter a beam splitter via an objective lens and a collimator lens, to deflect and emit the beam from the beam splitter, and to enter the three deflected return lights from the upper surface of the prism. And the three return lights respectively reflected on the light receiving surface of the first light detection unit are reflected on the upper surface of the prism and received by the second light detection unit. Here, the first and second light detectors are located before and after the focal position of the return light, and each receive a central return light of the three return lights. It comprises two photodetectors for receiving the return light.

Thus, the outputs of the three light receiving areas of the central three-segment photodetector of the first photodetector and the three light receiving areas of the central three-segment photodetector of the second photodetector are obtained. Based on the output, an information signal is detected, and a focus error signal is detected by a beam size method. The outputs of the two photodetectors on both sides of the first photodetector and both sides of the second photodetector are detected. The tracking error signal is detected by the three-beam method based on the outputs of the two photodetectors.

As another conventional optical pickup device, there is one described in Japanese Patent Application Laid-Open No. 2-173937. In this optical pickup device, a light beam emitted from a light source and converted into parallel light is reflected by a half mirror, and is irradiated on a recording medium through an objective lens. The return light from the recording medium is made incident on the half mirror via the objective lens, the return light transmitted through the half mirror is converged by the convex lens and made incident on the polarization beam splitter, and the return light transmitted through the polarization beam splitter is reflected by two beams. Return light received by the split photodetector and reflected by the polarization beam splitter is split into two light beams in cross section by a reflecting optical element having a step and reflected, whereby these two light beams are split into four before and after the focal position of the convex lens. The light is received by the photodetector.

In this manner, the tracking error signal is detected by the push-pull method based on the outputs of the two light receiving areas of the two-segment photodetector, and the tracking error signal is detected based on the outputs of the four light receiving areas of the four-segment photodetector. A focus error signal is obtained by a point aberration method.

[0007]

However, in the optical pickup device described in JP-A-64-46243, a focus error signal is obtained by using two three-divided photodetectors. Therefore, the number of photodetectors is large, and thus the number of light receiving areas is also large. There is a problem in that the number of connection steps between the light receiving area and the corresponding arithmetic circuit increases, and assembly is troublesome.

In the optical pickup device described in JP-A-2-173937, a focus error signal is obtained using a four-divided photodetector, so that the number of light receiving areas is large. As in the above case, there is a problem that the device becomes large and the assembly is troublesome.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and an optical unit which can detect a focus state with a small number of light receiving areas, and thus can reduce the size of an optical pickup device and facilitate assembly. And an optical pickup device using the same.

[0010]

According to an aspect of the present invention, there is provided an optical unit comprising: a semiconductor laser disposed on a semiconductor substrate; and an optical unit formed on the semiconductor substrate. A three-segment photodetector having three light-receiving regions divided by dividing lines, and a laser beam from the semiconductor laser is emitted toward a recording medium, and return light from the recording medium is sent to the three-segment photodetector. A reciprocating optical path separating means for guiding;
Beam splitting means for splitting a cross section of the return light incident on the three-segment light detector to obtain a plurality of light beams, wherein the plurality of light beams split by the light beam splitting means are divided by the three-segment light detector The light receiving regions on both sides including one of the dividing lines, and the light receiving regions on both sides including the other dividing line.

According to a second aspect of the present invention, in the optical unit according to the first aspect, the light beam splitting means is disposed on the three-division photodetector, and the light-flux splitting means is disposed on a light receiving surface of the three-division photodetector. A prism having an inclined surface, and a flat plate joined to the inclined surface of the prism, and allowing the return light separated by the reciprocating optical path separating means to enter the prism, While partially reflecting on the surface,
At least a part of the light beam transmitted through the inclined surface is incident on the flat plate, and the light is reflected by a surface of the flat plate opposed to the joint surface with the inclined surface to obtain a plurality of light beams. It is a feature.

According to a third aspect of the present invention, in the optical unit according to the first aspect, the light beam splitting means has a hologram, and the hologram divides a cross section of the return light from the recording medium to form a plurality of light beams. Is obtained.

According to a fourth aspect of the present invention, in the optical unit according to the first, second or third aspect, the reciprocating optical path separating means is disposed on the semiconductor laser and transmits or transmits laser light from the semiconductor laser. It is characterized by comprising a beam splitter that reflects light and reflects or transmits return light from the recording medium to separate a reciprocating optical path.

According to a fifth aspect of the present invention, in the optical unit according to the second aspect, further comprising a two-segment photodetector formed on the semiconductor substrate; It has a beam splitter that reflects and transmits the return light separated by the reciprocating light path separating means, and guides one of the return light to the two-divided photodetector and the other to the light beam splitting means. .

According to a sixth aspect of the present invention, there is provided an optical pickup device using the optical unit according to any one of the first to fifth aspects, wherein laser light emitted from the semiconductor laser is emitted from the optical unit. An objective lens is arranged between the optical unit and the recording medium so that the light beam incident on the light receiving regions on both sides including one of the dividing lines of the three-divided photodetector, and the other dividing line With the light flux incident on the light receiving areas on both sides including, in a focused state in which the recording medium is at the focal position of the objective lens, so as to be focused back and forth on the light receiving surface of the three-divided photodetector, The focus state of the objective lens with respect to the recording medium is detected based on the output of the three-divided photodetector.

[0016]

FIG. 1 is a diagram showing a configuration of an optical pickup device according to a first embodiment of the present invention. A semiconductor laser (here, a vertical cavity surface emitting laser) 2 is disposed on the semiconductor substrate 1 such that a laser beam emission surface of the semiconductor laser 2 coincides with the surface of the semiconductor substrate 1. The semiconductor substrate 1 is provided with a three-divided photodetector 3 having three light receiving surfaces (light receiving regions) e, d, and f divided by two parallel dividing lines on the surface thereof as shown in FIG. At the same time, the microprism 4 is placed on each light receiving surface of the three-divided photodetector 3 and on the laser beam emission surface of the surface emitting laser 2.

The microprism 4 has a parallelogram first shape.
, And a triangular second optical member 4b. The first optical member 4a is positioned above the three-segment photodetector 3, and the second optical member 4a is positioned above the surface emitting laser 2. The member 4b is located. Inclined surface 4 of first optical member 4a
In c, the upper half is a reflection surface and the lower half is a transmission surface, and the parallel plane plate 9 is joined to this transmission surface to constitute a light beam splitting means. Further, the first optical member 4a and the second optical member 4b
A beam splitter 4d composed of a beam splitter as a reciprocating optical path separating means is formed on the joining surface with the beam splitter 4d. Further, a hologram lens 8 for diffracting a light beam (return light from a recording medium 6 described later) incident on the microprism 4 from the upper surface is provided on the upper surface of the microprism 4 facing the surface emitting laser 2.

In this manner, an optical unit is constituted by including the semiconductor substrate 1, the surface emitting laser 2, the three-divided photodetector 3, the microprism 4, the hologram lens 8, and the plane-parallel plate 9.

In this embodiment, an objective lens 5 is arranged between the optical unit and the recording medium 6 so that the laser light from the surface emitting laser 2 emitted from the optical unit is incident. Construct a pickup device.

In the optical pickup device shown in FIG. 1, a laser beam emitted from a surface emitting laser 2 passes through a beam splitter 4d, further passes through a hologram lens 8, and is recorded on a recording medium 6 via an objective lens 5. Focus on. The return light reflected by the recording medium 6 is diffracted by the hologram lens 8 via the objective lens 5 and enters the microprism 4.

The return light incident on the microprism 4 is
The reflected light is reflected by the beam splitter 4d in the direction of the first optical member 4a, the upper half of the returned light is reflected by the reflecting surface of the inclined surface 4c, and the lower half is transmitted through the inclined surface 4c and the air of the parallel plane plate 9 is transmitted. The light is reflected by the reflection surface 9a which is in contact with the light-receiving portion 9a, and is divided into two sections. Of the return light divided into two sections, the return light reflected by the reflecting surface of the inclined surface 4c is, as shown in FIG. e, the light passes through the inclined surface 4c, is reflected by the reflecting surface 9a of the parallel plane plate 9, and is again
The return light incident on a enters the light receiving surfaces d and f on both sides including the other division line of the three-division photodetector 3. Here, the return light incident on the light receiving surfaces d and e and the return light incident on the light receiving surfaces d and f are focused at the respective focusing points when the recording medium 6 is located at the focal position of the objective lens 5. So that it is located before and after the surface. By providing the hologram lens 8 with a diffraction grating having a blaze characteristic, the ± first-order light diffracted by the hologram lens 8 on the outward path can be taken out of the pupil of the objective lens 5, whereby the recording medium 6 Stray light from the camera can be removed.

FIG. 2 shows a light receiving surface d,
FIG. 2 (a) shows the beam spot shape of the split return light formed on e and f. FIG. 2 (a) shows the beam in the focused state where the recording medium 6 is located at the focal position of the objective lens 5. The spot shape is shown. In this focused state,
The focus error signal SF becomes SF = d− (e + f) = 0.

FIG. 2B shows that the recording medium 6 is the objective lens 5.
3 shows a beam spot shape in a state of approaching the objective lens side from the focal position of FIG. In this state, since the return light is focused at a position farther than the focused state shown in FIG. 2A, the magnitude relationship between the beam spots is opposite to that at the time of focusing. Therefore, the focus error signal SF becomes SF = d− (e + f)> 0.

FIG. 2C shows that the recording medium 6 is the objective lens 5.
3 shows a beam spot shape in a state away from the focal position of the laser beam. In this state, since the return light is focused at a position closer to the focus than that shown in FIG. 2A, the spot formed on the light receiving elements d and e is inverted in shape from the spot at the time of focus, and The spots formed on the elements d and f have the same shape and are larger. Therefore, the focus error signal SF becomes SF = d− (e + f) <0.

According to the present embodiment, even when the optical axis of the return light is shifted due to a temperature change or the like, the two spots formed on the three-segment photodetector 3 move in the same direction. The offset occurring in each spot can be canceled, and the focus state can always be detected accurately and in a stable state.

FIG. 3 is a diagram showing the configuration of an optical pickup device according to a second embodiment of the present invention. In this embodiment, in the optical pickup device of the first embodiment shown in FIG. 1, the parallel plane plate 9 is removed while all the inclined surfaces 4c of the first optical member 4a constituting the microprism 4 are used as reflection surfaces. Instead of the hologram lens 8 on the upper surface of the microprism 4, a hologram lens 10 in which a diffraction grating is formed so that a Foucault prism effect acts on the return light is joined, and other configurations are the same as those of the first embodiment. is there.

Therefore, in this embodiment, the return light is divided into two light beams in cross section by the hologram lens 10, and these two light beams are divided into the dielectric multilayer surface 4d and the reflecting prism surface 4c.
The two beams are reflected by and become displaced from each other, and one of the beams includes one division line of the three-division photodetector 3 as shown in FIG. 4 as in the case of the first embodiment. The other beam is incident on the light receiving surfaces d and e on both sides so that the respective focal points are located before and after the light receiving surface in the focused state on the light receiving surfaces d and f on both sides including the other dividing line. Become.

FIG. 4 shows a beam spot shape of return light formed on the light receiving surfaces d, e, f of the three-segment photodetector 3 of the optical pickup device shown in FIG. Are the same as those shown in FIG. FIG.
(A) shows a beam spot shape in a focused state where the recording medium 6 is located at the focal position of the objective lens 5,
In this in-focus state, the focus error signal SF becomes SF = d− (e + f) = 0.

FIG. 4B shows that the recording medium 6 is the objective lens 5.
Shows the beam spot shape in a state close to the objective lens side from the focal position. In this state, the focus error signal SF is SF = d− (e + f)> 0.

FIG. 4C shows that the recording medium 6 is the objective lens 5.
Shows the beam spot shape in a state away from the focal position of the focus error signal SF in this state.
Is SF = d− (e + f) <0.

FIG. 5 is a diagram showing the configuration of an optical pickup device according to a third embodiment of the present invention. This embodiment is different from the first embodiment in that a two-part photodetector 13 for tracking error detection is further provided on the surface of the semiconductor substrate 1.
And a beam splitter 4e is further formed on the first optical member 4a of the microprism 4. The beam splitter 4e is a beam splitter 4d
The return light reflected by the beam splitter 4e is incident on the two-segment photodetector 13, and the return light transmitted therethrough passes through the inclined surface 4c. In the same manner as described above. Other configurations are the same as in the first embodiment.

In this embodiment, the laser beam emitted from the surface emitting laser 2 passes through the beam splitter 4 d and the hologram lens 8, and is focused on the recording medium 6 via the objective lens 5. The return light from the recording medium 6 is diffracted by the hologram lens 8 via the objective lens 5, is reflected by the beam splitter 4d, and is further incident on the beam splitter 4e to generate two lights of reflected light and transmitted light. Separated into beams. The light beam reflected by the beam splitter 4e is incident on a two-part photodetector 13 for tracking error detection, and the light beam transmitted through the beam splitter 4e is parallelized on the inclined surface 4c in the same manner as in the first embodiment. By the action of the plane plate 9, the light is further divided into two and enters the three-divided photodetector 3.

FIG. 6 shows the two-divided photodetectors 13 and 3
FIG. 3 is a plan view of a light receiving surface of a split photodetector 3. In the present embodiment, a tracking error signal can be detected by the push-pull method from the difference between the outputs of the two light receiving regions g and h of the two-segment photodetector 13. Also, the three-segment photodetector
By calculating d− (e + f) from the three light receiving areas d, e, and f, a focus error signal can be detected by the double knife edge method in the same manner as in the first embodiment. An information signal can be obtained from the sum of the outputs of the light receiving areas d to h of the divided photodetector 13 and the three-divided photodetector 3.

In each of the above embodiments, the surface emitting laser 2 was manufactured by Optronics (OPTRON) in 1990.
ICS), No. It is preferable to use the vertical cavity surface emitting laser described in No. 6, but it is also possible to use a horizontal cavity surface emitting laser or a bent cavity surface emitting laser described in the document. . For example, when the above-described vertical cavity surface emitting laser is used, since the + electrode is formed as a ring electrode, the surface emitting laser embedded portion of the semiconductor substrate is etched slightly thicker than the surface emitting laser. A ring-shaped tin solder region is provided in the buried portion, and the surface emitting laser is positioned against the edge of the buried portion to perform positioning, so that a gap is formed between the minus electrode and the end surface of the microprism. I do.

Further, the semiconductor laser is not limited to the surface emitting laser, but a stripe type laser can also be used. In this case, since the + electrode is formed on the entire lower surface of the laser structure, a tin solder region is provided on the semiconductor substrate, and a semiconductor laser is provided in this region, as described in JP-A-63-306548. What is necessary is just to solder and fix to a board | substrate.

[0036]

According to the optical unit of the present invention, the cross section of the return light is divided by the light beam dividing means to obtain a plurality of light beams, and these light beams are divided on the semiconductor substrate by two dividing lines. The three-divided photodetector having three light-receiving regions can be made to enter the light-receiving regions on both sides including one dividing line and the light-receiving regions on both sides including the other dividing line. In this case, the focus state of the objective lens with respect to the recording medium can be detected based on the output of one three-divided photodetector. Therefore, the number of light receiving areas can be reduced, and the size can be reduced.

According to the optical pickup device of the present invention, the recording medium is irradiated with the laser beam from the semiconductor laser through the objective lens by using the optical unit.
The cross section of the returned light is divided by the light beam dividing means in the optical unit to obtain a plurality of light beams, and these light beams include the light receiving regions on both sides including one of the divided lines of the three-divided photodetector and the other divided line. When the objective lens is in focus on the recording medium, it is made to enter the light receiving area on both sides so that the light is focused back and forth on the light receiving surface. Since the focus state of the lens with respect to the recording medium is detected, the number of arithmetic circuits for processing the output of the three-segment photodetector can be reduced. Easy.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a first embodiment of an optical pickup device according to the present invention.

FIG. 2 is a diagram showing a spot shape of return light in each focus state formed on a three-segment photodetector shown in FIG.

FIG. 3 is a diagram illustrating a configuration of an optical pickup device according to a second embodiment of the present invention.

FIG. 4 is a diagram showing a spot shape of return light in each focus state formed on the three-segment photodetector shown in FIG. 3;

FIG. 5 is a diagram illustrating a configuration of an optical pickup device according to a third embodiment of the present invention.

FIG. 6 is a diagram showing a spot shape of return light formed on the two-segment photodetector and the three-segment photodetector shown in FIG.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 semiconductor substrate 2 surface emitting laser 3 three-segment photodetector 4 microprism 5 objective lens 6 recording medium 8,10 hologram lens 9 parallel plane plate 13 two-segment photodetector

Claims (6)

[Claims] A semiconductor laser disposed on a semiconductor substrate; a three-division photodetector formed on the semiconductor substrate and having three light receiving regions divided by two division lines; Reciprocating optical path separating means for emitting the laser light to the recording medium side and guiding the return light from the recording medium to the three-divided photodetector; and dividing the cross section of the return light incident on the three-divided photodetector Beam splitting means for obtaining a plurality of light fluxes, the plurality of light fluxes split by the light flux splitting means are light receiving regions on both sides including one splitting line of the three-divided photodetector, and the other splitting An optical unit, wherein the optical unit is configured to be able to enter light receiving regions on both sides including a line. 2. A prism disposed on the three-divided photodetector, the prism having an inclined surface inclined with respect to a light receiving surface of the three-divided photodetector, and a prism provided on the inclined surface of the prism. A flat plate provided by bonding, the return light separated by the reciprocating optical path separating means is made incident on the prism, partially reflected on the inclined surface, and a light beam transmitted through the inclined surface. 2. The device according to claim 1, wherein a plurality of light fluxes are obtained by causing at least a part of the light to be incident on the flat plate and reflecting the light on a surface of the flat plate that is opposite to a joint surface with the inclined surface. 3. Optical unit. 3. The light beam splitting means has a hologram,
2. The optical unit according to claim 1, wherein a cross section of the return light from the recording medium is divided by the hologram to obtain a plurality of light beams. 4. The reciprocating optical path separating means is disposed on the semiconductor laser, transmits or reflects laser light from the semiconductor laser, and reflects or transmits return light from the recording medium to separate the reciprocating optical path. 4. The optical unit according to claim 1, wherein the optical unit comprises a beam splitter. 5. A two-divided photodetector formed on the semiconductor substrate, and reflecting and transmitting the return light disposed on the two-divided photodetector and separated by the reciprocating optical path separating means. 3. The optical unit according to claim 2, further comprising a beam splitter for guiding one of the light beams to the two-divided photodetector and the other light beam to the light beam splitting means. 6. An optical pickup device using the optical unit according to claim 1, wherein the laser unit emits laser light from the semiconductor laser emitted from the optical unit. An objective lens is arranged between the optical unit and the recording medium, and a light beam incident on both light receiving regions including one division line of the three-divided photodetector and a light beam incident on both light receiving regions including the other division line In a focused state in which the recording medium is at the focal position of the objective lens, and converges back and forth on the light receiving surface of the three-segment photodetector. An optical pickup device configured to detect a focus state of the objective lens with respect to the recording medium based on an output.