JP3261227B2 - Optical pickup 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 pickup device suitable for irradiating a laser beam to an optical disk.

[0002]

2. Description of the Related Art In various optical disk devices, an optical pickup device irradiates a laser beam onto an optical disk to record information, detects reflected light thereof, detects a focusing error or a tracking error, and reproduces recorded information. ing.

[0003] The focusing error is a deviation of the focus of the laser light irradiated on the optical disk, and the tracking error is a deviation of the irradiation position of the laser light with respect to the information track of the optical disk.

FIG. 7 shows an example of a light detection system of a conventional optical pickup device using a magneto-optical recording type optical disk. That is, in this light detection system, the reflected light of the light from the disk is split into two directions by the beam splitter 101, and one of the split lights is detected by the light detection unit 102. The other light is split by the polarization beam splitter 103 into light in two directions of a P-polarized component and an S-polarized component, and the split light is detected by the light detection units 104 and 105. In this case, a focusing error and a tracking error are detected by the detection signal of the light detection unit 102, and the light detection unit 10
The information recorded on the optical disk is reproduced by the two detection signals 4105.

[0005] The photodetectors 102, 104, and 105 are provided with a light receiving element fixed on a substrate. Therefore,
In the case of the photodetection system having the configuration shown in the figure, since the photodetection section is separated into three places, three substrates for fixing the light receiving elements are also required, so that the number of parts and the number of steps for assembling the apparatus are increased. There was an inconvenience.

FIG. 8 shows another example of the light detection system.
In this light detection system, the reflected light from the optical disk is directly incident on the polarization beam splitter 103, and the P-polarized light component and the S-polarized light component are detected by the light detection units 106 and 107. Then, based on the detection signals of the light detection units 106 and 107, the recording information is reproduced, and a focusing error and a tracking error are detected.

In the case of this configuration, the photodetectors 106 and 107
It is necessary to use a light receiving element in which the light receiving unit is divided into a plurality. Then, it is necessary to calculate the signal sum and the signal difference of the detection signals of the respective light receiving sections. Such a signal operation is performed using a plurality of differential amplifiers.

In this case, the light intensity changes of the P-polarized light component and the S-polarized light component correspond to the information recorded on the optical disk, and the detection signals of the light detection units 106 and 107 are high-frequency signals. Therefore, a high-performance differential amplifier capable of processing a high-frequency signal must be used for the signal operation, and there has been an inconvenience of increasing the cost of parts.

FIG. 9 shows still another example of the light detection system. In this light detection system, the reflected light from the optical disk is incident on the polarization beam splitter 108, and the P-polarized light component and
The two light components of the polarization component are emitted in the same direction, and the two light components are detected by the light detection unit 109. Then, the light detection unit 10
Based on the various detection signals of No. 9, the recording information is reproduced, and a focusing error and a tracking error are detected.

In this configuration, since the two light receiving elements for receiving the two lights can be fixed to one substrate, the number of parts and the number of assembling steps of the device can be reduced as compared with the configurations of FIGS. . However, as in the case of FIG. 8, a plurality of differential amplifiers for processing a high-frequency signal are required, so that there is an inconvenience that the component cost is increased.

FIG. 10 shows another example of the light detection system. This configuration is described in, for example, Japanese Patent Application Laid-Open No. 63-18744.
No. 0 discloses this. In this light detection system, reflected light from an optical disk is converted into a three-beam Wollaston prism 1
10, the light is branched into three lights, that is, a P-polarized light component, an S-polarized light component, and a mixed light thereof, and the three light beams are detected by the light detection unit 111. Then, based on the various detection signals from the light detection unit 111, information is reproduced and a focusing error and a tracking error are detected in the same manner as described above.

In the case of this configuration, a circuit for detecting two lights of the P-polarized light component and the S-polarized light component and reproducing the information, and a circuit for detecting a focusing error and a tracking error by detecting another light in which the two are mixed. And can be configured independently. Therefore, the differential amplifier does not need to process a high-frequency signal, so that it is not necessary to use a high-performance and expensive component for the component.

However, the three-beam Wollaston prism 110 used here is a combination of two uniaxial crystals processed into a predetermined shape. Such an optical component is expensive, and there has been a disadvantage that the device cost is high.

In addition to the examples shown in FIGS. 7 to 9, there is known an optical element formed of a birefringent crystal as an optical element for separating reflected light from an optical disk into a P-polarized component and an S-polarized component. However, even when such an optical element is used, there are various disadvantages similar to those described above.

[0015]

As described above, the conventional optical pickup apparatus of the magneto-optical recording type requires a large number of parts and assembling man-hours, or requires expensive parts. There was a problem of getting high.

An object of the present invention is to solve the above-mentioned problems and to provide an optical pickup device capable of reducing the manufacturing cost.

[0017]

For this purpose, the first aspect of the present invention is described.
According to the invention, the light receiving elements for receiving the three lights of the P-polarized light component, the S-polarized light component, and the light obtained by mixing the two components are arranged and fixed on one substrate, while the optical element that splits the light into the three light beams The element is formed by forming a semi-transmissive reflective film on one surface of a flat plate of birefringent crystal and a reflective film on the other surface. And is incident on the corresponding one of the light receiving elements, and the light transmitted through the semi-transmissive reflective film is separated into a P-polarized component and an S-polarized component, and is reflected by the reflective film to form a P-polarized light. The component and the S-polarized component are configured to be incident on the corresponding two light receiving elements, respectively.

In the second invention, each light receiving element is fixed on one substrate in the same manner as described above, while the optical element that branches into three lights is formed by joining at least two light-transmitting flat plates,
A transflective film is formed on one of the two outer surfaces, a polarization separating film is formed on a joint surface between the two, and a reflective film is formed on the other outer surface. Is reflected by the semi-transmissive reflective film and is incident on the corresponding light-receiving element, and the P-polarized component or the S-polarized component of the light transmitted through the semi-transmissive reflective film is reflected by the polarization separation film. The light is reflected and made incident on another light receiving element, and the light of the other polarization component transmitted through the polarization separation film is reflected by the reflection film and made incident on another light receiving element. I have.

[0019]

According to the above inventions, the optical element can be manufactured by a relatively simple processing using inexpensive materials such as a birefringent crystal flat plate and a light transmitting flat plate. Also,
Since the three light receiving elements are fixed on one substrate, the number of parts and the number of assembling steps of the apparatus can be reduced. As a result, manufacturing costs are reduced.

[0020]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.

FIG. 1 shows a configuration diagram of a light detection system according to a first embodiment of the present invention. This light detection system is provided in an optical pickup device using a magneto-optical recording type optical disk. In the figure, a four-divided light receiving element 202 and two undivided light receiving elements 203 and 204 are fixed to a substrate 201. Above it, a flat optical element 205 is fixed at an angle of, for example, 45 degrees. The optical element 205 is formed of a crystalline material having birefringence with respect to incident light.
One surface has a semi-permeable film HM, and the other surface has a reflective film AM.
Are formed. The semi-transmissive film HM reflects a certain percentage of the incident light amount and transmits the others, and the reflective film AM
Is for totally reflecting incident light.

With this configuration, the optical disk is irradiated with laser light by a part (not shown) of the optical pickup device. Then, the reflected light from the optical disk is condensed by a lens, and the light in the middle of the condensing is incident on this light detection system. The incident light is partially reflected by the semi-transmissive film HM, and the reflected light enters the four-divided light receiving element 202.

Since the optical disk of this embodiment is of the magneto-optical recording type, the light incident on this photodetection system changes in the light intensity of the P-polarized component and the S-polarized component in accordance with the information recorded on the optical disk. I do. Light mixed with both components is incident on the four-divided light receiving element 202.

The four-divided light receiving element 202 is for detecting a focusing error and a tracking error. In the present embodiment, for example, the astigmatism method is used as the focusing error detection method, and the push-pull method is used as the tracking error detection method.

All of these detection methods are known, and if the detection signal levels of the four light receiving portions of the four-division light receiving element 202 are a to d, the focusing error F
E and the tracking error TE are detected by a signal calculation as in the following equation. FE = a + d- (b + c) TE = a + b- (c + d)

On the other hand, the light that has passed through the semi-transmissive film HM enters the medium of the optical element 205 and is refracted. At this time,
Since the medium has birefringence, the refracted light branches into ordinary light and extraordinary light. The branched ordinary light and extraordinary light are respectively reflected by the reflection film AM and radiated to the outside through the semi-permeable film HM. Then, the two lights are received by the light receiving element 2
03 and 204 respectively.

In this embodiment, one of the ordinary light and the extraordinary light is the P-polarized light component of the reflected light from the optical disk, and the other is the S-polarized light.
The polarization component is set. Further, the light amount ratio between the ordinary light and the extraordinary light incident on the light receiving elements 203 and 204 is as follows.
It is set to be approximately 1: 1. These settings can be made by selecting the direction of the incident light with respect to the optical axis of the crystal medium of the optical element 205.

The light receiving elements 203 and 204 are for reproducing recorded information on an optical disk. Now, assuming that the detection signal levels of the light receiving elements 203 and 204 are e and f, respectively, a magneto-optical signal MO representing recording information is extracted by a signal operation as in the following equation. MO = ef

As described above, in this embodiment, the four-divided light receiving element 202 and the light receiving elements 203 and 204 are mounted on one substrate 20.
Since it is fixed on the upper side, the number of substrates can be reduced as compared with the conventional configuration shown in FIGS. 7 and 8, and the number of assembling steps of the apparatus can be reduced. The optical element 205 that splits incident light into three lights is formed by forming a semi-transmissive film HM and a reflective film AM on a flat plate made of a crystalline material having birefringence. Such materials are inexpensive and relatively easy to process.

Thus, the manufacturing cost of the optical pickup device is reduced.

FIG. 2 shows a second embodiment of the light detection system.

In the figure, the same reference numerals as those in FIG. 1 indicate the same parts, and the optical element 206 is formed of a birefringent crystal material in the same manner as described above, and has a different shape from the optical element 205 in FIG.

Thus, in this embodiment, the ordinary light and the extraordinary light reflected by the reflection film AM are radiated from the bottom surface of the optical element 206 and are incident on the light receiving elements 203 and 204.

In the embodiment shown in FIG. 1, the light reflected by the reflection film AM is radiated to the outside through the semi-transmissive film HM. Therefore, when passing through the semi-transmissive film HM, a part of the light quantity is reflected. As a result, the amount of light radiated to the outside is reduced, but in the present embodiment, such inconvenience is eliminated.

FIG. 3 shows a third embodiment of the light detection system.

The optical element 207 of this embodiment is formed of a birefringent crystal material in the same manner as described above, and is slightly different in shape from the optical element 206.

In this embodiment, the reflected light from the optical disk is made to enter from above the optical element 207 in the direction of the optical axis of the crystal medium. Light incident in the optical axis direction is
Does not branch in the medium. In this case, the incident light reaches the translucent film HM, and a part of the incident light passes through the translucent film HM and enters the four-divided light receiving element 202. The light reflected by the semi-transmissive film HM branches into ordinary light and extraordinary light. The two lights are reflected by the reflection film AM and enter the light receiving elements 203 and 204 via the bottom surface of the optical element 207.

In the case where the reflected light from the optical disk is incident on the substrate 201 in the vertical direction, this configuration prevents a decrease in the amount of light incident on the light receiving elements 203 and 204 in the same manner as described above. be able to.

FIG. 4 shows a fourth embodiment of the light detection system.

The optical element 208 of this embodiment is provided below a crystal member 208a having substantially the same shape as the optical element 207.
It is configured by joining crystal members 208b having a triangular cross section. Both crystal members 208a and 208b have birefringence. Further, a translucent film HM is formed on the lower surface of the crystal member 208a, and a reflective film AM is formed on the other surface.

In this embodiment, the reflected light from the optical disk is made incident from above the optical element 208 in the same manner as described above. However, the incident direction is not aligned with the optical axis of the crystal medium.
Therefore, in this case, when the reflected light enters the crystal member 208a, it branches into ordinary light and extraordinary light. A part of each of the branched lights passes through the semi-permeable film HM, further passes through the crystal member 208b, and exits the optical element 208.
In this embodiment, one of the two lights is divided into four light receiving elements 2
02.

On the other hand, each light reflected by the translucent film HM is
Further, the light is reflected by the reflection film AM and goes out of the optical element 208. Then, the two lights enter the light receiving elements 203 and 204, respectively.

Even with such a configuration, the same operation and effect as the embodiment of FIG. 3 can be obtained. In the above-described embodiment, only one of the P-polarized light and the S-polarized light is made to enter the four-divided light receiving element 202, but both are made to enter to detect the focusing error FE and the tracking error TE by another method. You may do so.

FIG. 5 shows a fifth embodiment of the light detection system.

The optical element 209 of this embodiment is formed by joining two flat plates 209a and 209b that transmit laser light, and the semi-transmissive film HM and the flat plate 209 are formed on the outer surface of the flat plate 209a.
b, the reflection film AM on the outer surface, and the polarization separation film PS on the joint surface between them.
Are formed respectively. The polarized light separating film PS transmits one of the P-polarized light and the S-polarized light and reflects the other.

With this configuration, in this embodiment, the reflected light from the optical disk is incident from the flat plate 209a side. A part of the incident light is reflected by the semi-transmissive film HM and
02.

On the other hand, the light transmitted through the semi-transmissive film HM reaches the polarization separation film PS, and one of the P-polarized component and the S-polarized component is reflected. The reflected light exits the optical element 209 through the translucent film HM. The light is received by the light receiving element 2
03. On the other hand, the light of the other component passes through the polarization separation film PS and is reflected by the reflection film AM. The reflected light is
The light passes through the polarization separation film PS and the semi-transmissive film HM and exits the optical element 209. The light enters the light receiving element 204.

As described above, in this embodiment, the optical element 2
No. 09 is constituted by joining two flat plates having light transmissivity and forming a semi-transmissive film HM, a polarization separation film PS and a reflection film AM on their respective surfaces. Such a material is inexpensive and relatively easy to process, so that the manufacturing cost of the device can be reduced.

FIG. 6 shows a sixth embodiment of the light detection system.

The optical element 210 of this embodiment is configured by joining two flat plates 210a and 210b. The flat plates 210a and 210b are made of the same material as the flat plates 209a and 209b, and are formed in slightly different shapes.

Thus, the light reflected by the polarization separation film PS and the reflection film AM passes through the bottom surface of the planographic plate 210a and enters the light receiving elements 203 and 204.

In the embodiment shown in FIG. 5, the light reflected by the polarization separation film PS and the reflection film AM passes through the semi-transmissive film HM and goes out to the outside. Although the amount of light is reflected and the amount of light emitted to the outside is reduced, such a disadvantage is eliminated in the present embodiment.

[0053]

As described above, according to the present invention, an optical element that splits reflected light from an optical disk into three lights of P-polarized light, S-polarized light, and light in which both components are mixed can be compared with inexpensive materials. Since the light-receiving elements for detecting three lights are fixed on a single substrate to reduce the number of parts and the number of assembling steps of the device, the manufacturing cost of the optical pickup device is reduced. Become like

[Brief description of the drawings]

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

FIG. 2 is a configuration diagram showing a second embodiment of the light detection system.

FIG. 3 is a configuration diagram showing a third embodiment of the photodetection system.

FIG. 4 is a configuration diagram showing a fourth embodiment of the photodetection system.

FIG. 5 is a configuration diagram illustrating a fifth embodiment of the photodetection system.

FIG. 6 is a configuration diagram showing a sixth embodiment of the photodetection system.

FIG. 7 is a configuration diagram showing an example of a conventional photodetection system.

FIG. 8 is a configuration diagram showing another example of a conventional photodetection system.

FIG. 9 is a configuration diagram showing still another example of the conventional photodetection system.

FIG. 10 is a configuration diagram showing another example of a conventional photodetection system.

[Explanation of symbols]

Reference Signs List 201 substrate 202 quadrant light receiving element 203, 204 light receiving element 205, 206, 207, 208, 209, 210 optical element 208a, 208b crystal member 209a, 209b, 210a, 210b flat plate HM semi-permeable film AM reflection film PS polarization separation film

Claims (4)

(57) [Claims] 1. A means for irradiating a laser beam onto a magneto-optical recording medium, and a light beam comprising a mixture of a P-polarized component beam, an S-polarized component beam, and a reflected beam from the magneto-optical recording medium. An optical element that splits the light into three types of light, a first light receiving element that receives the light of the P-polarized component, a second light receiving element that receives the light of the S-polarized component, and a mixture of the two components An optical pickup device having a third light receiving element for receiving light, wherein the first to third light receiving elements are arranged and fixed on one substrate, while the optical element is a birefringent crystal. A semi-transmissive reflective film is formed on one surface of the flat plate, and a reflective film is formed on the other surface. While being incident on the third light receiving element, the light transmitted through the semi-transmissive reflective film is A structure in which a polarized light component and an S-polarized light component are separated and reflected by the reflective film, and two lights of the P-polarized light component and the S-polarized light component are respectively incident on the first and second light receiving elements. An optical pickup device characterized by the above-mentioned. 2. The device according to claim 1, wherein the two light components of the P-polarized light component and the S-polarized light component reflected by the reflection film do not pass through the semi-transmissive reflection film when exiting the optical element. Item 2. The optical pickup device according to item 1. 3. A means for irradiating a laser beam to a magneto-optical recording medium, and a device for irradiating a reflected light from the magneto-optical recording medium with a P-polarized component light, an S-polarized component light and a mixed light of both components. 3
An optical element for splitting the light into a seed light, a first light receiving element for receiving one of the P-polarized light component and the S-polarized light component, a second light receiving element for receiving the other light, And a third light receiving element for receiving the mixed light, wherein the first to third light receiving elements are arranged and fixed on one substrate, while the optical element is at least Two light-transmitting flat plates are joined, a semi-transmissive film is formed on one of the two outer surfaces, a polarization separating film is formed on the joint surface of the two, and a reflective film is formed on the other outer surface. A part of the reflected light formed and reflected by the semi-transmissive reflective film is reflected by the semi-transmissive reflective film, and the mixed light of both components is incident on the third light receiving element and transmitted through the semi-transmissive reflective film. The P-polarized light component or the S-polarized light component of the reflected light is reflected by the polarization separation film, and An optical pickup device, wherein the light is incident on the first light receiving element, and the other polarized light component transmitted through the polarization separation film is reflected by the reflection film and is incident on the second light receiving element. . 4. The light reflecting device according to claim 1, wherein the light reflected by the polarization separation film and the light reflected by the reflection film do not pass through the semi-transmissive reflection film when exiting the optical element. 4. The optical pickup device according to 3.