JP3361155B2 - 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 for reading information recorded on an optical disc and a beam splitter used in the optical pickup device.

[0002]

2. Description of the Related Art An optical disk apparatus irradiates a recording track of an optical disk with a laser beam by an optical pickup apparatus and detects reflected light to record / reproduce information.

During such a recording / reproducing operation, the optical pickup device detects a tracking error, which is a deviation of the irradiation position of the laser beam with respect to a recording track, and a focusing error, which is a deviation of the focal point of the irradiation light, and minimizes them. Servo control is performed so that

In this case, for example, a push-pull method is adopted as a tracking error detection method, and a knife edge method is adopted as a focusing error detection method.

At present, there are two types of optical discs for data, a write-once type of a perforation recording system (hereinafter referred to as W / O type) and a rewritable type of a magneto-optical recording system (hereinafter referred to as M / O type). Things have been put to practical use.

FIG. 7 shows a conventional example of a photodetection system of a W / O type optical pickup device. This optical pickup device employs the push-pull method and the knife edge method.

That is, this optical pickup device irradiates the optical disc with laser light at a portion (not shown), and guides the reflected light into parallel light to this photodetection system.
The incident laser light is condensed by the lens 1. Most of the condensed light flux is reflected by the mirror surface of the prism 2 and enters the two-division light receiving element 3, while the other part passes through the edge portion of the prism 2 and enters the two-division light receiving element 4.

When the detection signal levels of the two light receiving portions of the two-divided light receiving element 4 are A and B, and the detection signal levels of the two divided light receiving element 3 are C and D, the focusing error signal Fo and the tracking error signal Tr are shown. , And the information reproduction signal Rf are taken out by the following formula. Fo = AB ... (1) Tr = CD ... (2) Rf = C + D ... (3)

Therefore, as shown in FIG. 8, each of these signals is obtained by detecting and extracting a certain portion of the light beam incident on the photodetection system.

The light condensed by the lens 1 is such that the entire light flux has its intensity changed according to the recorded information on the optical disk. However, when extracting the information reproduction signal Rf, only a certain portion of the light flux is detected as described above.

Therefore, for example, if there is a non-uniform portion on the information recording surface of the optical disc or the optical component, the luminous flux of the incident light on the photodetection system is partially disturbed, and only the disturbed portion is detected to detect the information. The reproduction signal Rf may be taken out.
In this case, there is a problem that the S / N ratio of the information reproduction signal Rf and other characteristics are deteriorated.

Incidentally, as a method of extracting the information reproduction signal Rf from the entire light flux of the incident light to the photodetection system, there is a method of calculating the information reproduction signal Rf by the following equation. Rf = C + D + A + B (4)

However, in the case of this method, the number of wirings and signal circuits of the device increases and the device becomes complicated. Further, since the information reproduction signal Rf is a signal having a high frequency, it is better to avoid such a long wiring of the signal circuit or an increase in the number of circuits in the device.

FIG. 9 shows a conventional example of a photodetection system of an M / O type optical pickup device. This optical pickup device also employs the push-pull method and the knife-edge method.

That is, also in this case, similarly to the above, the magneto-optical disk is irradiated with laser light at a portion not shown, and the reflected light is guided to this photodetection system in the state of being parallel light.

The incident laser light passes through the half-wave plate 5 and has its polarization direction rotated by 45 degrees and is condensed by the lens 1.
Most of the condensed light flux is reflected by the prism 2 and enters the polarization beam splitter 6, while the other part passes through the edge portion of the prism 2 and enters the two-divided light receiving element 4.

Of the laser light incident on the polarization beam splitter 6, the P-polarized component passes as it is and enters the two-divided light receiving element 3, and the S-polarized component is reflected on the mirror surface in the polarization beam splitter 6 and received on the light receiving element 7. Incident on.

Here, the detection signal levels of the two light receiving portions of the two-divided light receiving element 4 are A and B, the detection signal levels of the two-divided light receiving element 3 are C and D, and the detection signal level of the light receiving element 7 is E. Then, the focusing error signal Fo, the tracking error signal Tr, and the preformat signal P
f and the magneto-optical signal MO are taken out by the following formula. Fo = AB ... (5) Tr = CD ... (6) Pf = (C + D) + E ... (7) MO = (C + D) -E ... (8)

The pre-format signal Pf is a read signal of address information or the like which is fixedly recorded in advance on the magneto-optical disk, and the magneto-optical signal MO is a read signal of information arbitrarily recorded by the user. .

Even in the case of this configuration, as shown in FIG. 10, the preformat signal Pf and the magneto-optical signal M are used.
When O is taken out, only a certain part of the light beam condensed by the lens 1 is detected.

Therefore, in the same manner as described above, when the information recording surface of the magneto-optical disk or the optical component has a non-uniform portion,
The S / N ratio and other characteristics of those signals may be deteriorated.

In this case, the entire luminous flux cannot be utilized by the method of adding the detection signals of the two-divided light receiving element 4 as described in (4) above.

[0023]

As described above, conventionally, in the case of an optical pickup device which detects a focusing error by the knife edge method, when reading recorded information on an optical disc, a light flux of reflected light condensed by a lens is used. There was a problem that the whole system was not used effectively.

The present invention solves the above problems and provides an optical pickup device and a beam splitter capable of reading recorded information on an optical disk by effectively utilizing the entire luminous flux of reflected light condensed by a lens. The purpose is to

[0025]

To this end, the present invention reflects one of the polarized light components of the laser light including the S-polarized light component and the P-polarized light component reflected from the optical disk and reflects the other polarized light component. Polarizing film that allows the laser light of
It has an incident surface on which the laser light that has passed through the polarizing film is incident, and at least the angles of the mutually formed surfaces are different.
And a second light receiving element for receiving the laser light reflected by the polarizing film, and a prism for separating the laser light by emitting the light in an optical path according to the angle of each of the output surfaces. A first light receiving element and a third light receiving element for respectively receiving the laser beams whose optical paths have been separated.
~ It is characterized in that the information recorded on the optical disk is reproduced by the third light receiving element. In addition, the laser light reflected from the optical disk is provided with an incident surface that reflects the laser light at a predetermined ratio and allows the rest to pass therethrough, and at least two emission surfaces having mutually different angles are provided, depending on the angle of each emission surface. A prism for separating the laser light passing therethrough by emitting in the optical path, a second light receiving element for receiving the laser light reflected by the prism, and a first light receiving element for receiving the laser light separated by the prism. The first and third light receiving elements are provided, and the information recorded on the optical disc is reproduced by the first to third light receiving elements.

[0026]

[0027]

With the above means, the recorded information on the optical disk can be read by effectively utilizing the entire light flux of the reflected light condensed by the lens.

[0028]

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

FIG. 1 is a block diagram of an optical pickup device according to the first embodiment of the present invention. This optical pickup device is provided in an M / O type optical disc device. In the figure, a semiconductor laser 101
Emits P-polarized laser light. The collimator lens 102, the beam splitter 103, the objective lens 104, and the magneto-optical disk 10 are arranged on the optical axis of the emitted light.
5 and the magnetic head 106 are arranged in order. The beam splitter 103 reflects a certain proportion of the reflected light from the magneto-optical disk 105. On the optical axis of the light reflected by this, the half-wave plate 107,
A condenser lens 108, a prism 109, and a two-divided light receiving element 110 are sequentially arranged.

The prism 109 is a combination of a prism 1091 having a triangular cross section and a prism 1092 having a trapezoidal cross section. A polarizing film is formed on one of the joint surfaces, and 100% of P-polarized incident light is transmitted,
The S-polarized light is reflected 100%. A two-divided light receiving element 111 is arranged on the optical axis of the light reflected thereby. Further, a light receiving element 112 whose light receiving portion is not divided is arranged on the side of the two-divided light receiving element 110. The condenser lens 108, the prism 109,
Two-divided light receiving elements 110, 111 and light receiving element 112
Constitute a light detection system.

FIG. 2 shows a signal circuit for extracting each signal. Here, the detection signal levels of the two light receiving portions of the two-divided light receiving element 110 are a and b, the detection signal levels of the light receiving element 112 are c, and the detection signal levels of the two light receiving portions of the two-divided light receiving element 111 are d and e. Then, in this signal circuit, the focusing error signal Fo, the tracking error signal Tr, the preformat signal Pf, and the magneto-optical signal MO.
Is extracted by an operation such as the following equation. Fo = a-b ... (8) Tr = d-e ... (9) Pf = (a + b + c) + (d + e) ... (10) MO = (a + b + c)-(d + e) ... ( 11)

When the optical pickup device of the present embodiment operates with the above configuration, the semiconductor laser 101 emits P-polarized laser light. The emitted light is collimated by the collimator lens 102 and enters the beam splitter 103. The beam splitter 103 uses, for example, 7
Transmit 0%. The transmitted laser light is the objective lens 10
The light is condensed at 4, and is irradiated as spot light on the recording track of the magneto-optical disk 105.

The reflected light from the magneto-optical disk 105 enters the beam splitter 103 via the objective lens 104. The beam splitter 103 reflects, for example, 30% of the incident light. The reflected laser light passes through the half-wave plate 107, so that the polarization direction is rotated by 45 degrees.
The laser light is condensed by the condenser lens 108 and enters the prism 109.

Now, assuming that the recording information of the magneto-optical disk 105 is being read, the magneto-optical disk 105 is read.
The light intensity of the reflected light is changed by the recording information pre-formatted on the disc, and the polarization direction of the reflected light is displaced by a slight angle by the recording information recorded by the user. The prism 109 transmits the P-polarized component of such incident light.

In this case, the light of the P-polarized component enters the prism 1092 and has two surfaces 1092a and 1092b.
Will come out from. In this case, each side 1 of the transmitted light
Since the incident angles with respect to 092a and 1092b are different, the light of the P-polarized component emitted from the prism 1092 is branched into two directions. Then, the light emitted through the surface 1092a enters the two-divided light receiving element 110, and the surface 1092a
The light emitted through b is incident on the light receiving element 112.

By the way, of the light flux entering the prism 1092, a certain area including the optical axis is shielded by the prism 1092, and a part of the light flux is incident on the two-divided light receiving element 110. In this case, the surface 1092b acts as a knife edge.

Therefore, in this embodiment, the focusing error is detected by the known knife edge method. That is, when the defocus of the laser beam with respect to the magneto-optical disk 105 occurs, a difference occurs in the detection signal levels of the two light receiving elements of the two-divided light receiving element 110. Therefore, this difference is calculated by the equation (8). , Focusing error signal Fo is taken out.

The tracking error is detected by the known push-pull method. That is, if the irradiation position of the laser beam with respect to the recording track of the magneto-optical disk 105 is deviated, a difference occurs in the detection signal levels of the two light receiving elements of the two-divided light receiving element 111. The tracking error signal Tr is obtained by calculation.

On the other hand, the recorded information pre-formatted on the magneto-optical disc 105 is detected as a pre-format signal Pf by detecting the change in the light intensity of the reflected light from the magneto-optical disc 105 by the calculation of the equation (10). Take it out.

On the other hand, the recorded information of the user recorded on the magneto-optical disk 105 is extracted by detecting the displacement of the reflected light in the polarization direction. That is, the two-divided light receiving element 111
Receives the S-polarized component of the incident light on the prism 109,
The two-divided light receiving element 110 and the light receiving element 112 receive the P-polarized component. Therefore, in the present embodiment, (11)
The difference between the detection signal levels of the P-polarized component and the S-polarized component is calculated by the calculation of the formula, and is extracted as the magneto-optical signal MO.

As described above, in this embodiment, the reflected light from the optical disk is condensed by the condenser lens 108, and the entire light flux in the middle of condensing is separated into the P-polarized component and the S-polarized component by the prism 109. , The respective light intensities are detected by the two-divided light receiving element 110, the light receiving element 112, and the two-divided light receiving element 111, and the preformat signal Pf and the magneto-optical signal MO are extracted. Further, a part of the light beam separated into the S-polarized component is detected by the two-division light receiving element 110, and the focusing error signal Fo is extracted by the known knife edge method.

Conventionally, when the knife edge method is adopted,
Although a part of the luminous flux is used only to extract the focusing error signal Fo, in the present embodiment, the preformatted signal Pf and the magneto-optical signal MO can be extracted by effectively utilizing the entire luminous flux. become. As a result, the signal levels of the pre-formatted signal Pf and the magneto-optical signal MO are increased, and the S / N ratio and other characteristics are also improved.

Further, in this embodiment, the prism 109, which is an optical element, has two surfaces 1092a, 1 discontinuous with the polarizing film.
092b is formed, and the light components of P-polarized light and S-polarized light are separated by a polarizing film, while two surfaces 1092a and 1092b are formed.
The light flux passing therethrough is branched into two. In this case, the branched light flux is similar to the light flux that has passed through the edge portion of the knife edge, and therefore the focusing error signal Fo is obtained by detecting the light flux.

This eliminates the need for a knife edge member as in the prior art, so that the number of parts can be reduced and the space for arranging parts can be reduced.

When the focusing error signal Fo is obtained, the light passing through the surface 1092b side is detected, but this light flux does not include the optical axis of the light flux condensed by the lens 108.

It is known that when a focusing error is detected by the knife edge method, the detection sensitivity is maximized when detecting a light flux within a certain range not including the optical axis. Therefore, the focusing error can be detected with high sensitivity by setting the ratio of the light passing through the surface 1092b within the fixed range not including the optical axis.

Although the prism 109 of the above embodiment is designed to split the P-polarized light component transmitted through the polarizing film into two, the S-polarized light component reflected by the polarizing film is split into two. You may do it. In addition, the polarizing film is replaced with S
It may be formed so as to transmit the polarization component and reflect the P polarization component. In either case, as in the above-described embodiment, one of the two branched lights detects a focusing error,
It is possible to detect a tracking error with the other light that is not branched and read the recorded information with both lights.

FIG. 3 shows another embodiment of the photodetection system in the above optical pickup device. The difference from FIG. 1 is that instead of the prism 109, a prism 113
Is the point that is provided. The prism 113 has a trapezoidal cross section, and a polarizing film that separates P-polarized light and S-polarized light is formed on one surface of the condenser lens 108 side, as in the above embodiment.

With this configuration, the P-polarized component of the light incident on the prism 113 from the condenser lens 108 side is the prism 113.
S-polarized light component is reflected by the polarizing film and enters the two-divided light receiving element 111.

When the P-polarized light passes through the prism 113, it passes through the two surfaces 113a and 113b. As a result, the P-polarized light beam is split into two directions, as in the above-described embodiment. The light that has passed through the surface 113a of the prism 113 is
The light that has entered the two-divided light receiving element 110 and has passed through the surface 113 b enters the light receiving element 112.

Then, similarly to the above embodiment, the focusing error signal Fo, the tracking error signal Tr, the preformat signal Pf and the magneto-optical signal MO are taken out by the signal circuit of FIG.

As described above, even if the light beam is split by the single prism 113 having a trapezoidal cross section, it is possible to obtain the same effect as that of the above embodiment.

FIG. 4 shows another embodiment of the photodetection system. 3 is different from FIG. 3 in that a prism 114 is provided instead of the prism 113, and a light receiving element 112 is provided below the two-divided light receiving element 110. The prism 114 is a prism 1 whose cross section is a parallelogram.
Two of 141 and a triangular prism 1142 are joined together. A polarizing film is formed on the surface of the prism 1141 on the side of the condenser lens 108 as in the above.

With this structure, the P-polarized component of the light incident on the prism 1141 from the condenser lens 108 side is the prism 11
After passing through 41, the S-polarized component is reflected by the polarizing film and enters the two-divided light receiving element 111.

A part of the light flux transmitted through the prism 1141 enters the two-division light receiving element 110, and the other light flux further passes through the prism 1142 and enters the light receiving element 112. In this case, the upper edge of the prism 1142 acts as a knife edge.

Then, similarly to the above-mentioned embodiment, the focusing error signal Fo, the tracking error signal Tr, the preformat signal Pf and the magneto-optical signal MO are taken out by the signal circuit of FIG.

Even with such a structure of the prism 114, the light beam can be separated in three directions and one of the light beams can be subjected to knife edge processing, and the same effect as that of the above embodiment can be obtained.

FIG. 5 shows a second embodiment of the optical pickup device of the present invention. This optical pickup device is installed in a W / O type optical disc device. In the figure, the same reference numerals as in FIG. 1 indicate the same parts, and the following points are different.

That is, instead of the beam splitter 103, the magneto-optical disk 105 and the prism 109, a polarization beam splitter 115, an optical disk 116 and a prism 117 are provided. Further, the magnetic head 106 and the ½ wavelength plate 107 are removed, and a ¼ wavelength plate 118 is newly arranged below the objective lens 104. The polarization beam splitter 115 transmits 100% of P-polarized light and reflects 100% of S-polarized light. The prism 117 is composed of two prisms 1171 and 1172 having the same shape as the prism 109 of FIG. 1, and the joint surface thereof transmits or reflects incident light by 50%. .

With this configuration, the semiconductor laser 101 emits P-polarized laser light. The emitted light enters the quarter-wave plate 118 via the collimator lens 102 and the polarization beam splitter 115. 1 P-polarized laser beam
When it passes through the quarter wave plate 118, it becomes circularly polarized light. The laser light is condensed by the objective lens 104 and applied to the optical disc 116.

The reflected light from the optical disk 116 enters the polarization beam splitter 115 via the objective lens 104 and the quarter-wave plate 118. At this time, 1/4 wave plate 1
After passing through 18, the light changes to S-polarized light. As a result, the laser light is reflected in the polarization beam splitter 115 and enters the condenser lens 108. Then, the condenser lens 10
50% of the light condensed at 8 is reflected by the above-mentioned joint surface of the prism 117 and enters the two-divided light receiving element 111. on the other hand,
50% of the light that has passed through the cemented surface is 2 of the prism 1172.
It passes through the two surfaces 1172a and 1172b and is split into light beams in two directions. The luminous flux passing through the surface 1172a is 2
The light flux that has entered the split light-receiving element 110 and has passed through the surface 1172b enters the light-receiving element 112.

FIG. 6 shows the signal circuit in this embodiment. In this embodiment, the information reproduction signal Rf indicating the recorded information on the optical disk 116 is extracted by the calculation of Rf = a + b + c + d + e (12). .

With this configuration, the focusing error signal F
The o and the tracking error signal Tr are extracted as in the case of FIG. On the other hand, in this case, the optical disc 116
Since the light intensity of the reflected light changes according to the recorded information, the information reproduction signal Rf is extracted by the above equation (12).

As described above, in this embodiment, the lens 10
The entire light flux being condensed by 8 is branched by a prism 117 into two directions of reflected light and transmitted light, a part of one light flux is detected by a two-division light receiving element 110, and a focusing error signal Fo is extracted, and the other light flux is extracted. The light flux is detected by the two-division light receiving element 111, and the tracking error signal Tr is extracted. Further, the detection signals of the two-divided light receiving elements 110 and 112 and the light receiving element 112 are added and taken out as an information reproduction signal Rf.

As a result, in the W / O type optical pickup device, the information reproduction signal Rf can be extracted by effectively utilizing all the luminous fluxes incident on the photodetection system, as in the above-described embodiments.

The prisms 113 and 11 shown in FIGS.
If, instead of the polarizing film, a semi-transparent mirror that transmits / reflects the incident light at a constant rate is formed in 4, it can be used in a W / O type optical disk device as in the above embodiment.

[0067]

As described above, according to the present invention, it is possible to effectively use the entire luminous flux of the reflected light to reproduce the recorded information on the optical disc, and it is possible to improve the reproduction accuracy of the recorded information.

[0068]

[Brief description of drawings]

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

FIG. 2 is a circuit configuration diagram of a signal circuit of the optical pickup device.

FIG. 3 is a device configuration diagram showing another embodiment of a photodetection system in the optical pickup device.

FIG. 4 is a device configuration diagram showing still another embodiment of the photodetection system.

FIG. 5 is a device configuration diagram showing a second embodiment of the optical pickup device of the present invention.

FIG. 6 is a circuit configuration diagram of a signal circuit of the optical pickup device.

FIG. 7 is a device configuration diagram of a photodetection system of a conventional W / O type optical pickup device.

FIG. 8 is an explanatory diagram showing a relationship between an incident light flux of the photodetection system and each signal to be extracted.

FIG. 9 is a device configuration diagram of a photodetection system of a conventional M / O type optical pickup device.

FIG. 10 is an explanatory diagram showing a relationship between an incident light flux of the photodetection system and each signal to be extracted.

[Explanation of symbols]

Reference numeral 101 semiconductor laser 102 collimator lens 103 beam splitter 104 objective lens 105 magneto-optical disk 106 magnetic head 107 half-wave plate 108 condenser lenses 109, 113, 114, 117 prisms 110, 111 two-divided light receiving element 112 light receiving element 115 polarized beam Splitter 116 Optical disc 118 Quarter wave plate 1092a, 1092b, 113a, 113b, 117
2a, 1172b surface

Claims (5)

(57) [Claims] 1. A polarizing film which reflects a laser beam of one polarization component of a laser beam including an S-polarized component and a P-polarized component reflected from an optical disk and transmits a laser beam of the other polarized component, It has an incident surface on which the laser light that has passed through the polarizing film is incident, and at least the angles of the mutually formed surfaces are different.
A prism for separating the laser light by emitting in an optical path according to the angle of each emission surface, and a second light receiving element for receiving the laser light reflected by the polarizing film, A first light receiving element and a third light receiving element for respectively receiving the laser beams whose optical paths have been separated by the prism, and reproducing the information recorded on the optical disc by the first to third light receiving elements. Characteristic optical pickup device. 2. An incident surface for reflecting the laser light reflected from the optical disc at a predetermined ratio and passing the rest is provided, and at least two emitting surfaces having mutually different angles are provided. A prism for separating the laser light passing therethrough by emitting in an optical path according to the angle, a second light receiving element for receiving the laser light reflected by the prism, and a laser light whose optical path is separated by the prism. An optical pickup device comprising: first and third light receiving elements for respectively receiving light, and reproducing information recorded on the optical disk by the first to third light receiving elements. 3. The first and second light receiving elements are divided into two to detect a focusing error and a tracking error, respectively, while the third light receiving element is not divided. Or the optical pickup device according to item 2. 4. A focusing error is detected by a difference (ab) between two light reception signals a and b from the first light receiving element which is divided into two, and the second light receiving element which is divided into two is detected. Tracking error is detected by the difference (d−e) between the two received light signals d and e, and the sum (a + b + c) of the signals obtained from the first and third light receiving elements and the second light receiving element are obtained. The sum of the respective signals (d + e), and the difference ((a + b +
The optical pickup device according to claim 1, wherein the recorded information is reproduced by (c)-(d + e)). 5. A focusing error is detected by a difference (ab) between two light reception signals a and b from the first light receiving element which is divided into two, and the second light receiving element which is divided into two is detected. Tracking error is detected by the difference (d−e) between the two light receiving signals d and e, and the recorded information is reproduced by the sum (a + b + c + d + e) of the signals obtained from the first, second, and third light receiving elements. The optical pickup device according to claim 2 or 3, characterized in that: