JPH07130023A - Optical pickup - Google Patents

Abstract

PURPOSE:To disperse light to first, second photosensers in the proportion of about 50% respectively by diffracting return diffracted beams in the prescribed direction to a polarization direction of a light beam from a light emitting element. CONSTITUTION:A grating space of a hologram 8 is reduced, and the incident angle of the return diffracted beams 14 to a polarizing separation film 15 is enlarged. Further, when the diffractive efficiency of a P polarization is defined etaP, and the diffractive efficiency of an S polarization etaS, a semiconductor laser chip 2, a reflection prism 4 and the hologram 8 are constituted so that the return diffracted beams 14 from an optical disk 11 is diffracted in the direction of an angle (theta) given by theta=tan<-1>(etaP/etaS) to the polarization direction of the beam from the light emitting element, and the beams are dispersed to the first photosenser 22 and the second photosenser 29 in the proportion of 50% respectively by the polarizing separation film 15. By such a manner, an excellent RF signal in which the same phase noise component except a magneto-optical signal is eliminated by the differential width of the first, second photosensers 22, 29 is provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pickup which records or reproduces information on an optical disc by using a laser beam.

[0002]

2. Description of the Related Art In order to provide an optical disk device with a small size, a light weight and a low cost, studies and attempts have been made to reduce the size, weight and cost of an optical pickup by reducing the number of optical components. Reducing the size and weight of the optical pickup is advantageous not only for downsizing the entire optical disk device but also for shortening the access time.
In recent years, as one of the attempts, the size and weight of an optical pickup have been reduced by using a hologram optical element.

First, the structure of a conventional optical pickup using a hologram optical element will be described with reference to the drawings. FIG. 13 is a plan view of a conventional optical pickup, and FIG. 14 is a sectional view taken along line ZZ of FIG.

In FIGS. 13 and 14, the sensor substrate 30 is shown.
The semiconductor laser chip 302 and the reflecting surface of the triangular prism 304 are mounted on the sensor substrate 301 at predetermined positions so as to face each other.
The light receiving sensor 323 and the second light receiving sensor 329 are formed at predetermined positions.

The sensor substrate 301 is a lead frame 338.
And various signals are input to and output from the sensor substrate 301 via the lead frame 338. further,
The lead frame 338 is loaded into the package 317,
The space 318 is filled with an inert gas such as nitrogen gas and is sealed with a parallel-plate optical guide member 305.

The optical guide member 305 is an optical disc board 311.
The first surface 305a on the side facing the semiconductor laser chip 3
02 and the second surface 305b on the side facing each other are formed in parallel with each other. The hologram 308 and the return path 325 are provided on the first surface 305a, and the laser beam 30 is provided on the second surface 305b.
3, an entrance window 306 and a transmission window 327, and a polarization splitting section 315 coated with a polarization splitting film are formed.

Further, an objective lens 310 and an optical disc board 311 are arranged at a position separated from the optical pickup by a predetermined distance.

The operation of the conventional optical pickup configured as described above will be described according to the path of the laser beam 303.

In FIG. 14, the semiconductor laser chip 30 is shown.
The laser beam 303 emitted from the laser beam 2 is reflected by the reflection prism 30.
The light guide member 3 is reflected from the incident window 306 by being reflected by the reflecting surface 4
05 enters the inside and becomes diffused light 307. Diffused light 307
Passes through the hologram 308 and is emitted to the outside of the light guide member 305 to become diffused light 309. The diffused light 309 enters the objective lens 310 and is focused on the information recording layer 311a of the optical disc board 311 as a spot 312.
Converted to 3. The focused light 313 is reflected by the information recording layer 311a, and the return-path reflected light passes through the objective lens 310 and enters the hologram 308 to be converted into the return-path diffracted light 314.

At this time, the backward-path diffracted light 314 is diffracted in the direction of 45 ° with respect to the backward-path reflected light and is incident on the polarization splitting section 315. The polarization splitting film of the polarization splitting unit 315 is used for the return path diffracted light 314.
Has a property of transmitting the P-polarized component and reflecting the S-polarized component, and is separated into the first transmitted light 322 and the first reflected light 324. As shown in FIG. 13, the polarization direction of the backward diffracted light 314 is 45 ° with respect to the linearly polarized light 321, so that the P-polarized component and the S-polarized component are halved, respectively, and the first transmitted light 322 is transmitted.
And the amount of each of the first reflected light 324 is half that of the backward diffracted light 314.

The first transmitted light 322 irradiates the first light receiving sensor 323 formed on the sensor substrate 301. On the other hand, the first
The reflected light 324 is reflected by the return reflection part 325 of the first surface 305a and is again reflected by the second reflected light 326 toward the second surface 305b.
Becomes The second reflected light 326 becomes the second transmitted light 328 after passing through the transmission window 327 of the second surface 305b.
The light receiving sensor 329 is irradiated.

As a result, the read magneto-optical signal is the first
The light receiving sensor 323 and the second light receiving sensor 329 are split into 50% each, and the first light receiving sensor 323 and the second light receiving sensor 323 are split.
By differentially amplifying each output of the light receiving sensor 329,
It is possible to obtain a high-quality RF signal from which in-phase noise components other than the magneto-optical signal have been removed.

[0013]

However, in the above-described conventional configuration, it is necessary to increase the incident angle of the backward diffracted light 314 to the polarization separation film, and in order to increase the incident angle, the lattice spacing of the hologram 308 is reduced. Must.

However, when the lattice spacing of the hologram 308 is reduced to be near the wavelength of the laser beam 303, the diffraction efficiency of the P polarized light and the diffraction efficiency of the S polarized light of the hologram 308 become different. Therefore, such a hologram 3
Even if it is converted to the backward diffracted light 314 by 08, the polarization splitting unit 3
The P-polarized component and the S-polarized component of the light incident on 15 are not equal to each other, and the read magneto-optical signal is the first light receiving sensor 323.
The second light receiving sensor 329 and the second light receiving sensor 329 are not split at a rate of 50% respectively.
Even if each output of 9 is differentially amplified, it is not possible to obtain a high-quality RF signal from which in-phase noise components other than the magneto-optical signal are removed.

The present invention has been made to solve the above-mentioned problems, and it is possible to set a large incident angle to the polarization separation film, and the first light receiving sensor and the second light receiving sensor each have a ratio of 50%. An object is to provide an optical pickup that is spectrally separated.

[0016]

In the first embodiment of the present invention, the grating spacing of the hologram is reduced to increase the angle of incidence of the backward diffracted light on the polarization separation film, and P
When the diffraction efficiency of polarized light is ηP and the diffraction efficiency of S polarized light is ηS, the backward reflected light from the optical disc is given by θ = tan ⁻¹ (ηP / ηS) with respect to the polarization direction of the light from the light emitting element. A semiconductor laser chip, a reflection prism, and a hologram are configured so as to diffract in the angle θ direction, and the first light receiving sensor and the second light receiving sensor are each split into 50% by the polarization separation film. .

In the second and third embodiments of the present invention, the hologram spacing is increased to reduce the diffraction angle of the backward diffracted light, and the backward diffracted light is incident on the slope of the second light guide member. By refracting, the incident angle of the backward-path diffracted light to the polarization separation film is increased, and the backward-path reflected light from the optical disk board is diffracted in the direction of 45 ° with respect to the polarization direction of the light from the light emitting element. A reflection prism and a hologram are configured so that the first light receiving sensor and the second light receiving sensor are split into 50% of each by the polarization separation film.

[0018]

According to the present invention, since the backward diffracted light is diffracted in the direction of 45 ° with respect to the polarization direction of the light from the light emitting element, the P-polarized light component and the S-polarized light component are incident on the polarization splitting portion. The state of being split into 50% is maintained.
Therefore, the read magneto-optical signal is split into 50% of each of the first light receiving sensor and the second light receiving sensor. Therefore, by differentially amplifying the outputs of the first light receiving sensor and the second light receiving sensor, it is possible to obtain a high-quality RF signal from which in-phase noise components other than the magneto-optical signal are removed. Further, since the focal point of the backward-path diffracted light exists between the backward-path polarization separation section and the transmission window, the focus error signal can be obtained by means of the spot size method or the like due to the difference between the first light-receiving sensor and the second light-receiving sensor.

[0019]

【Example】

(First Embodiment) The structure of an optical pickup according to the first embodiment of the present invention will be described below with reference to the drawings. 1 is a plan view of an optical pickup according to a first embodiment of the present invention, and FIG. 2 is a sectional view taken along line WW of FIG.

1 and 2, a semiconductor laser chip 2 and a reflecting surface of a triangular prism 4 are opposed to each other on a sensor substrate 1, and a linearly polarized light 21 and an optical axis of a laser beam 3 are described later. The first light receiving sensor 2 is mounted at a predetermined position on the sensor substrate 1 so as to form an angle θ.
3 and the second light receiving sensor 29 are formed at predetermined positions.

The sensor substrate 1 is mounted on the lead frame 38, and various signals are input to and output from the sensor substrate 1 via the lead frame 38. Further, the lead frame 38 is loaded in the package 17, the space 18 is filled with an inert gas such as nitrogen gas, and the space 18 is sealed by the parallel-plate optical guide member 5. Alternatively, the space 18 may be filled with a transparent resin or the like having a refractive index similar to that of the light guide member 5.

The light guide member 5 has a first surface 5a facing the optical disc board 11 and a second surface 5b facing the semiconductor laser chip 2 formed in parallel with each other. First
The hologram 8 and the return reflection portion 25 are provided on the surface 5a, and the second surface 5
An incident window 6 and a transmission window 27 for the laser beam 3 and a polarization splitting portion 15 coated with a polarization splitting film are formed in b.

Further, a collimator lens 16, an objective lens 10 and an optical disk board 11 are arranged at positions separated from an optical pickup by a predetermined distance.

The operation of the optical pickup of the first embodiment of the present invention constructed as above will be described according to the path of the laser beam 3.

In FIG. 2, the laser light 3 emitted from the semiconductor laser chip 2 is reflected by the reflection surface of the reflection prism 4 and enters the inside of the light guide member 5 through the entrance window 6 to become diffused light 7. The diffused light 7 passes through the hologram 8 and is emitted to the outside of the light guide member 5 to become diffused light 9. After the diffused light 9 enters the collimator lens 16 and is converted into parallel light,
The light is incident on the objective lens 10 and is converted into focused light 13 which is condensed as a spot 12 on the information recording layer 11 a of the optical disc board 11. The focused light 13 is reflected by the information recording layer 11a, and the returning reflected light is again reflected by the objective lens 10 and the collimator lens 16
After passing through and entering the hologram 8, it is converted into the backward diffracted light 14.

At this time, the backward-path diffracted light 14 is diffracted with respect to the backward-path reflected light in the direction of the angle θ represented by (Equation 1), and the polarization splitting unit 1
It is incident on 5. The polarization separation film of the polarization separation unit 15 has a property of transmitting the P-polarized component of the backward-path diffracted light 14 and reflecting the S-polarized component, and is separated into the first transmitted light 22 and the first reflected light 24. Further, as shown in FIG. 1, since the polarization state of the backward diffracted light 14 is an angle θ with respect to the linearly polarized light 21, the P-polarized component,
The S-polarized components are each halved, and the respective amounts of the first transmitted light 22 and the first reflected light 24 are half of the backward diffracted light 14.

The first transmitted light 22 illuminates the first light receiving sensor 23 formed on the sensor substrate 1. On the other hand, the first reflected light 2
No. 4 is reflected by the return reflection part 25 of the first surface 5a, and again the second part
The second reflected light 26 is directed to the surface 5b. The second reflected light 26, after passing through the transmission window 27 of the second surface 5b, becomes the second transmitted light 28 and irradiates the second light receiving sensor 29.

As a result, the read magneto-optical signal is the first
The light receiving sensor 23 and the second light receiving sensor 29 each have 50
%, The magneto-optical signal component is doubled by differentially amplifying the outputs of the first light receiving sensor 23 and the second light receiving sensor 29, and the in-phase noise component is removed, and the quality is good. RF signals can be obtained.

Further, the backward diffracted light 14 has the first focus so that the focal point 30 exists between the backward reflection portion 25 and the second light receiving sensor 29.
The optical path length of the reflected light 24 is designed. Therefore, the arrangement is suitable for the focus error detection method based on the spot size method.

FIG. 3 is a diagram showing an example of the pattern drawn on the hologram 8. 1 and 3, the semiconductor laser chip 2 and the reflecting prism 4 are arranged so that the polarized state of the diffused light 7 entering the hologram 8 becomes the linearly polarized light 21 indicated by the arrow, and the linearly polarized light 21 is It is set so as to form an angle θ with the optical axis, which is obtained by (Equation 1). When the backward diffracted light 14 passes through the hologram 8, it is diffracted by the angle θ obtained by (Equation 1) with respect to the polarization direction of the linearly polarized light 21. At this time, the diffraction efficiency for the P polarized light of the hologram 8 is ηP, and the diffraction efficiency for the S polarized light is ηS.
And Therefore, the backward diffracted light 14 that is incident on the polarization splitting unit 15 has a P-polarization component and an S-polarization component that are about half of the polarization splitting unit 15, respectively, and thus the amount of the first transmitted light 22 from the polarization splitting unit 15 is It becomes about half of the backward diffracted light 14.

[0031]

[Equation 1]

FIG. 4 is a sectional view of FIG. 3 and shows details of the hologram grating. FIG. 5 is a graph showing the diffraction efficiency. Hereinafter, the angle θ is obtained according to (Equation 1) based on FIGS. 4 and 5. It is assumed that hologram hologram 8 has a sinusoidal cross section as shown in FIG. 4 and a refractive index n of 1.66. Where λ is the wavelength and d is the hologram 8
, H is the grating depth of the hologram 8. When the grating interval d is 0.7 × λ and the grating depth h is 2.0 × d, the diffraction efficiency of P-polarized light is about 0.95 and the diffraction efficiency of S-polarized light is about 0.45 from FIG. Therefore, from (Equation 1), θ
Is set to about 64.7 °.

FIG. 6 is a diagram showing the principle of magneto-optical signal detection. In the figure, the linearly polarized light 21 is the polarization direction of the backward diffracted light 14 incident on the hologram 8, and the angle θ is the angle given by the above-mentioned (Equation 1).

If no information is recorded on the information recording layer 11a of the optical disc board 11 (that is, if the information recording layer 11a is not magnetized), the backward reflected light of the spot 12 also has the same polarization direction as the linearly polarized light 21. When the light in such a state is incident on the hologram 8 having the diffraction efficiency ηP for P-polarized light and the diffraction efficiency ηS for S-polarized light, the backward diffracted light 14 passing through the hologram 8 is 45 with respect to the incident surface.
It becomes the return linearly polarized light 31 having a polarization direction of deg. The backward-path diffracted light 14 is incident on the polarization splitting unit 15 which transmits almost 100% of the P-polarized component and reflects almost 100% of the S-polarized component in the polarization direction of the linearly polarized light 31 on the backward path.

On the other hand, the information recording layer 11 of the optical disc board 11
If the information is recorded in a (that is, if the information recording layer 11a is magnetized), the linearly polarized light 21 is reflected by the magnetized information pit, and the rotation direction is ± θk depending on the magnetization polarity and the magnetization strength. Changes in the range of (Kerr effect). The state rotated by θk from the state of linearly polarized light 21 is now + k linearly polarized light 3
2. If the state rotated by −θk is −k linearly polarized light 33,
Similarly to the linearly polarized light 21, the magneto-optical signal modulated from the + k linearly polarized light 32 to the −k linearly polarized light 33 is the polarization separating unit 15 as the magneto-optical signal modulated from the backward + k linearly polarized light 34 to the backwardly −k linearly polarized light 35. Incident on the polarized light separating film. In this case, the P-polarized component detected by the first light receiving sensor 23 becomes like the signal 36, and S detected by the second light receiving sensor 29.
The polarization component looks like the signal 37. Signal 36 and signal 37
Since the phases are shifted by 180 °, the signal component is doubled by differentially amplifying both signals, and noise of the same phase component is canceled, resulting in a good S / N ratio.

FIG. 7 is a circuit block diagram for explaining the principle of signal detection. The shapes of the first light receiving sensor 23 and the second light receiving sensor 29 and the principle of signal detection will be described based on FIG. 7. First light receiving sensor 23 and second light receiving sensor 29
Are four parts 23a, 23b, 23c and 23, respectively.
d, and 29a, 29b, 29c, 29d. Here, the respective portions 23a, 23b, 23c, 23d and 2 of the first light receiving sensor 23 and the second light receiving sensor 29.
The currents from 9a, 29b, 29c, and 29d are respectively I (23a), I (23b), I (23c), and I (23
d), and I (29a), I (29b), I (29
c) and I (29d). As can be seen from the circuit block diagram of FIG. 7, the focus error signal (FE), the tracking error signal (TE), the RF signal (R.E.).
F. Each signal of () has a circuit configuration that can be obtained by the following mathematical formulas (2), (3), and (4).

[0037]

[Equation 2]

[0038]

[Equation 3]

[0039]

[Equation 4]

Of these signals, the focus error signal will be further described. Now, the spot 12 is accurately focused on the information recording layer 11a of the optical disc board 11, and in this focused state, the first light receiving sensor 23 is focused on the focused irradiation shape 38a and the second light receiving sensor 29 is focused on. Irradiation shapes 39a are formed respectively. At this time, the irradiation intensity distribution of the laser light and the positional relationship between the first light receiving sensor 23 and the second light receiving sensor 29 are adjusted so as to satisfy the following (Equation 5).

[0041]

[Equation 5]

Next, the optical disk board 11 and the objective lens 10
When the distance is close to the in-focus state, the first light receiving sensor 2
The irradiation shapes of the laser light on the third and second light receiving sensors 29 are a near irradiation shape 38c and a near irradiation shape 39c, respectively.
And F. E. Changes like (Equation 6).

[0043]

[Equation 6]

On the contrary, the optical disk 11 and the objective lens 10
When the distance between the two is out of focus, the first light receiving sensor 23
The irradiation shapes of the laser light on the second light receiving sensor 29 and the second light receiving sensor 29 are the separation irradiation shape 38b and the separation irradiation shape 39b, respectively. E. Changes like (Equation 7).

[0045]

[Equation 7]

The above focus error detection method is known as a spot size method, and the tracking error detection method is known as a push-pull method.

When the focus 30 of the backward diffracted light 14 is designed to be present between the backward reflection portion 25 and the transmission window 27 in this way, when a focus error is detected by the astigmatism method which has been often used conventionally. In comparison with the above, since a complicated hologram pattern for generating astigmatism is unnecessary, the hologram 8
Is a very simple pattern with only diffraction.

(Second Embodiment) Next, the structure of an optical pickup according to a second embodiment of the present invention will be described with reference to the drawings. 8 is a plan view of an optical pickup according to the second embodiment of the present invention, and FIG. 9 is a sectional view taken along line XX of FIG.

In FIG. 8 and FIG. 9, the sensor substrate 101 has a semiconductor laser chip 102 and a reflecting surface of a triangular prism reflecting prism 104 facing each other, and a laser beam 103.
Is mounted at a predetermined position on the sensor substrate 101 so that the linearly polarized light 121 and the optical axis form an angle of 45 °, and the first light receiving sensor 123 and the second light receiving sensor 129 are formed at the predetermined positions. There is.

The sensor substrate 101 is a lead frame 138.
The various types of signals are input to and output from the sensor substrate 101 via the lead frame 138. further,
The lead frame 138 is loaded into the package 117,
The space 118 is filled with an inert gas such as nitrogen gas and is sealed by the first light guide member 105 which is a parallel plate. Alternatively, the space 118 may be filled with a transparent resin or the like having a refractive index similar to that of the first light guide member 105.

The first optical guide member 105 is the optical disc board 1
The first surface 105a facing the semiconductor laser chip 102 and the second surface 105b facing the semiconductor laser chip 102 are formed in parallel with each other. The hologram 10 is formed on the first surface 105a.
8 is formed, an entrance window 106 for the laser light 103 is formed on the second surface 105b, and the second light guide member 14 is formed.
The first surface 140a of No. 0 is adhered.

The second light guide member 140 has the first surface 140 a bonded to the first light guide member 105 and the sensor substrate 10.
1 and the second surface 140b on the side facing each other are formed in parallel with each other, and further, the backward diffracted light 114 transmitted through the first light guide member 105 is incident on the second light guide member 140 again. An inclined surface 140c forming an obtuse angle is formed. The return path reflection portion 125 is provided on the first surface 140a.
The second surface 140b is provided with a polarization separation portion 115 coated with a polarization separation film that transmits the P polarization component of the backward diffracted light 114 and reflects the S polarization component, and a transmission window 127, respectively.

Further, the collimator lens 116 and the objective lens 11 are placed at a position separated from the optical pickup by a predetermined distance.
0 and the optical disc board 111 are arranged.

The operation of the optical pickup of the second embodiment of the present invention constructed as above will be described according to the path of the laser beam 103.

In FIG. 9, the semiconductor laser chip 102 is shown.
The laser light 103 emitted from the
Of the light guide member 10 through the entrance window 106.
5 enters the inside and becomes diffused light 107. The diffused light 107 passes through the hologram 108 and is emitted to the outside of the light guide member 105 to become diffused light 109. The diffused light 109 is incident on the collimator lens 116 and converted into parallel light, and then is incident on the objective lens 110 and focused as a spot 112 on the information recording layer 111 a of the optical disc board 111.
Converted to 3. The focused light 113 is reflected by the information recording layer 111a, and the return-path reflected light passes through the objective lens 110 and the collimator lens 116 again and is re-incident on the hologram 108 to be converted into the return-path diffracted light 114.

At this time, the backward-path diffracted light 114 is diffracted in the direction of 45 ° with respect to the backward-path reflected light, is refracted when it exits the second surface 105b, is converted into the convergent light 141, and is further inclined.
When incident on 0c, the light is further refracted and converted into the converged light 142, and then is incident on the polarization separation unit 115. Polarization splitter 1
The polarization splitting film 15 has a property of transmitting the P-polarized component of the backward-path diffracted light 114 and reflecting the S-polarized component thereof.
22 and the first reflected light 124 are separated. Further, as shown in FIG. 8, the polarization state of the backward diffracted light 114 is linearly polarized light 12
Since it is 45 ° with respect to 1, the P-polarized component and the S-polarized component are each halved, and the first transmitted light 122 and the first reflected light 124
The amount of each light is half of the backward diffracted light 314.

The first transmitted light 122 illuminates the first light receiving sensor 123 formed on the sensor substrate 101.

On the other hand, the first reflected light 124 is reflected by the return reflection portion 12
The second reflected light 126 is reflected at 5 and travels toward the second surface 140b again. The second reflected light 126 passes through the transmission window 127 and then becomes the second transmitted light 128.
Irradiate.

As a result, the read magneto-optical signal is the first
The light receiving sensor 23 and the second light receiving sensor 29 each have 50
%, The magneto-optical signal component is doubled by differentially amplifying the outputs of the first light receiving sensor 23 and the second light receiving sensor 29, and the in-phase noise component is removed, and the quality is good. RF signals can be obtained.

The return-path diffracted light 114 is reflected by the return-path reflecting portion 12.
The optical path length of the first reflected light 124 is designed so that the focal point 130 exists between the fifth light receiving sensor 129 and the second light receiving sensor 129. Therefore, the arrangement is suitable for the focus error detection method based on the spot size method.

FIG. 10 is an explanatory diagram of a hologram pattern in the second embodiment of the present invention. For example, the first light guide member 105 and the second light guide member 140 have a refractive index of 1.
In the case of 511 glass (BK-7), when the inclination angle θ of the inclined surface 140c is 60 ° and the diffraction angle of the backward diffracted light 114 is 12 °, the incident angle of the converged light 142 with respect to the polarization separation unit 115 is 33.8 °. Become. Also in this case, the hologram 108
Has a lattice spacing of 3.18λ (λ: wavelength). Therefore,
As shown in FIG. 5, the diffraction efficiency of the P polarized light and the diffraction efficiency of the S polarized light of the hologram 108 can be made substantially equal.

As described above, even if the diffraction angle of the backward diffracted light 114 is small, the incident angle to the polarization splitting portion 115 is large, so that the lattice spacing of the hologram 108 can be increased and the diffraction efficiency of the P-polarized light of the hologram 108 can be increased. The diffraction efficiency of S-polarized light can be made substantially equal, and the hologram 108 can be manufactured at low cost.

In this embodiment, the diffraction direction of the backward diffracted light 114 is set to 45 ° with respect to the polarization direction of the linearly polarized light 121, but this angle may be 45 °, 225 ° or 315 °.

The focus error signal (FE) and the tracking error signal (TE) are detected by the spot size method and the push-pull method, respectively, as in the first embodiment.

(Third Embodiment) Next, the structure of an optical pickup according to a third embodiment of the present invention will be described with reference to the drawings. 11 is a plan view of an optical pickup according to the third embodiment of the present invention, and FIG. 12 is a sectional view taken along line YY of FIG.

11 and 12, the difference from the third embodiment is that the second light guide member 240 is attached to the sensor substrate 201.
To couple the backward diffracted light 214 to the second light guide member 240.
The incident light is incident on the inclined surface 240c, and the polarization splitting portion 215 is configured to be in contact with the first light receiving sensor 223.

In FIG. 12, a semiconductor laser chip 202 and a triangular prism reflecting prism 20 are provided on a sensor substrate 201.
4 is mounted on a predetermined position of the sensor substrate 201 such that the reflecting surfaces of the laser beams 203 face each other and the linearly polarized light 221 of the laser beam 203 and the optical axis form an angle of 45 °.
The first light receiving sensor 223 and the second light receiving sensor 229 are formed at predetermined positions.

The sensor substrate 201 is a lead frame 238.
And various signals are input to and output from the sensor substrate 201 via the lead frame 238. further,
The lead frame 238 is loaded into the package 217,
The space 218 is filled with an inert gas such as nitrogen gas and is sealed by the first light guide member 205 of a parallel plate. Alternatively, the space 218 may be filled with a transparent resin or the like having a refractive index similar to that of the first light guide member 205.

The first optical guide member 205 is the optical disc board 2
A first surface 205a facing the semiconductor laser chip 202 and a second surface 205b facing the semiconductor laser chip 202 are formed in parallel with each other. The hologram 20 is on the first surface 205a.
8 is formed, and an incident window 206 for the laser beam 203 is formed on the second surface 205b.

The second light guide member 240 includes the first surface 240a facing the first light guide member 205 and the sensor substrate 2.
The second surface 240b bonded to 01 is formed parallel to each other, and the second surface 240b is bonded to the sensor substrate 201. Further, a sloped surface 240c forming an obtuse angle with the first surface 240a for allowing the backward diffracted light 214 transmitted through the first light guide member 205 to enter the second light guide member 240 again is formed. The return path reflection portion 225 is provided on the first surface 240a.
The second surface 240b is provided with a polarization separation section 215 coated with a polarization separation film that transmits the P polarization component of the backward diffracted light 214 and reflects the S polarization component, and a transmission window 227.

Further, the collimator lens 216 and the objective lens 21 are placed at a position separated from the optical pickup by a predetermined distance.
0 and the optical disc board 211 are arranged.

The optical pickup according to the third embodiment of the present invention configured as described above has the same path as the laser beam 203 according to the second embodiment, and therefore the duplicated description of the operation is omitted. However, P of the backward diffracted light 214 transmitted through the polarization splitting unit 215
The polarized component directly enters the first light receiving sensor 223, and the S-polarized component of the backward diffracted light 214 reflected by the polarized light separating unit 215 is reflected by the backward reflecting unit 225 and transmitted through the transmission window 227 and directly to the second light receiving sensor 229. The point of incidence is different.

In this case, the second light guide member 240
Since it suffices that the polarization splitting portion 215 formed on the surface 240b is in contact with the first light receiving sensor 223, the second light guide member 240 can be easily arranged and processed with high precision.

[0074]

According to the present invention, when the light reflected from the optical disk by the hologram is a linearly polarized light, the diffraction efficiency of the P polarized light of the hologram is ηP and the diffraction efficiency of the S polarized light is ηS. The reflected light is diffracted in the direction of the angle θ given by θ = tan ⁻¹ (ηP / ηS) with respect to the polarization direction of the light from the light emitting element, or the diffraction grating of the backward diffracted light has a large diffraction grating pitch. By making the return path diffracted light incident on the inclined surface of the second light guide member to be smaller, the return path diffracted light incident on the polarization separation section has a P polarization component and S The polarized light components are incident on the polarized light separating portion in a state of about 50% each. Therefore, the read magneto-optical signal is split into about 50% in the first light receiving sensor and the second light receiving sensor, respectively. Further, by differential amplification of the first light receiving sensor and the second light receiving sensor, it is possible to obtain a high-quality RF signal from which in-phase noise components other than the magneto-optical signal are removed. Further, since the focal point of the backward-path light exists between the backward-polarization splitting section and the transmission window, the focus error signal can be obtained by means of the spot size method or the like due to the difference between the first light-receiving sensor and the second light-receiving sensor.

[Brief description of drawings]

FIG. 1 is a plan view of an optical pickup according to a first embodiment of the present invention.

FIG. 2 is a sectional view taken along line WW of FIG.

FIG. 3 is a diagram showing an example of a pattern drawn on a hologram.

FIG. 4 is a sectional view of FIG.

FIG. 5 is a graph showing diffraction efficiency

FIG. 6 is a diagram showing the principle of magneto-optical signal detection.

FIG. 7 is a circuit block diagram illustrating the principle of signal detection.

FIG. 8 is a plan view of an optical pickup according to a second embodiment of the present invention.

9 is a sectional view taken along line XX of FIG.

FIG. 10 is an explanatory diagram of a hologram pattern according to the second embodiment of the present invention.

FIG. 11 is a plan view of an optical pickup according to a third embodiment of the invention.

12 is a sectional view taken along line YY of FIG.

FIG. 13 is a plan view of a conventional optical pickup.

14 is a sectional view taken along line ZZ of FIG.

[Explanation of symbols]

 1, 101, 201, 301 Sensor substrate 2, 102, 202, 302 Semiconductor laser chip 3, 103, 203, 303 Laser light 4, 104, 204, 304 Reflecting prism 5,305 Light guide member 6, 106, 206, 306 Entrance window 8, 108, 208, 308 Hologram 10, 110, 210, 310 Objective lens 11, 111, 211, 311 Optical disc board 12, 112, 212, 312 Spot 14, 114, 214, 314 Return path diffracted light 15, 115, 215, 315 Polarization separating unit 16, 116, 216 Collimator lens 17, 117, 217, 317 Package 21, 121, 221, 321 Linearly polarized light 23, 123, 223, 323 First light receiving sensor 25, 125, 225, 325 Return reflection Parts 27, 127, 227, 327 Transmission window 29,129,229,329 Second light receiving sensor 105,205 First light guide member 140,240 Second light guide member

Claims (5)

[Claims] 1. A light emitting element for irradiating an optical disk with linearly polarized light, an objective lens for condensing the light emitted from the light emitting element onto the optical disk, and a first light receiving device for receiving reflected light from the optical disk. The light from the light emitting element is arranged between the sensor and the second light receiving sensor, the first light receiving sensor and the second light receiving sensor, and the objective lens, and guides the light from the light emitting element to the objective lens and passes through the objective lens. An optical pickup having a transparent parallel plate optical guide member for guiding the reflected light from the optical disc board to the first light receiving sensor and the second light receiving sensor, the side of the light guiding member facing the objective lens. On the surface of the optical disc, the reflected light from the optical disc is diffracted to any one of the angles of 45 °, 225 ° and 315 ° with respect to the polarization direction of the light of the light emitting element. A transmissive hologram having a pattern having a function of converting to S is formed, and a polarization separation section is formed on a surface of the light guide member facing the light emitting element, and the polarization separation section forms an S of the reflected light. An optical pickup characterized in that the reflected light is incident on the polarization splitting portion at an incident angle larger than an angle at which polarized light is totally reflected. 2. A light emitting element for irradiating an optical disk with linearly polarized light, an objective lens for condensing the light emitted from the light emitting element onto the optical disk, and a first light receiving device for receiving reflected light from the optical disk. The light from the light emitting element is arranged between the sensor and the second light receiving sensor, the first light receiving sensor and the second light receiving sensor, and the objective lens, and guides the light from the light emitting element to the objective lens and passes through the objective lens. An optical pickup having a transparent parallel plate optical guide member for guiding the reflected light from the optical disc board to the first light receiving sensor and the second light receiving sensor, the side of the light guiding member facing the objective lens. , The reflection light from the optical disk disc is θ = ta with respect to the polarization direction of the light of the light emitting element, where ηP is the diffraction efficiency of P-polarized light and ηS is the diffraction efficiency of S-polarized light. ^-1 to form a hologram of the transmission type having a pattern having a function of converting into light diffracted to the angle θ direction given by (ηP / ηS), and the surface on the side facing said light-emitting element of the light guide member A polarized light splitting portion is formed on the polarized light splitting portion, and the reflected light is incident on the polarized light splitting portion at an incident angle larger than an angle at which the S-polarized light of the reflected light is totally reflected by the polarized light splitting portion. Optical pickup to do. 3. A light emitting element for radiating linearly polarized light to the optical disc, an objective lens for condensing the light emitted from the light emitting element on the optical disc, and a first light receiving device for receiving reflected light from the optical disc. The light from the light emitting element is arranged between the sensor and the second light receiving sensor, the first light receiving sensor and the second light receiving sensor, and the objective lens, and guides the light from the light emitting element to the objective lens and passes through the objective lens. The first light guide member is a transparent parallel plate that guides the reflected light from the optical disk board to the first light receiving sensor and the second light receiving sensor, and the second light guide member having an inclined surface on which the reflected light enters. 1. An optical pickup having a first light guide member and the first light receiving sensor and the second light receiving sensor, wherein a surface of the first light guiding member facing the objective lens is provided with a light beam. Angle 45 ° the reflected light from the disc plate to the polarization direction of light of the light emitting element, 225 °,
A transmissive hologram having a pattern having a function of converting into light diffracted in any one of the 315 ° directions is formed, and polarization separation is performed on the surface of the second light guide member facing the light emitting element. Part is formed, the reflected light is once refracted when entering the inclined surface, and then the reflected light is polarized and separated at an incident angle larger than the angle at which the S-polarized light of the reflected light is totally reflected by the polarized light separating portion. An optical pickup characterized in that it is configured to be incident on a portion. 4. The surface of the first light guide member facing the light emitting element and the surface of the second light guide member facing the objective lens are joined together. The optical pickup according to item 3. 5. The optical pickup according to claim 3, wherein a surface of the second light guide member facing the light emitting element is in contact with the first light receiving sensor and the second light receiving sensor. .