JPH06162531A - Optical head - Google Patents

Abstract

PURPOSE:To make the thickness of a polarizing beam splitter thin without reducing the detection range of focusing (an almost linear part near the origin of, what is called, sigmoid line). CONSTITUTION:From a voltage corresponding to the quantity of light received in the areas, Ai, Bi, Ci, Di, Ao, Bo, Co and Do of a photodetector 9, a focus error signal FES is determined in accordance with the following equation. FES= k{(Ao+Co)-(Bo+Do)}+{(Ai+Ci)-(Bi+Di)}, where k>1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical head suitable for use in an optical disc or a magneto-optical disc device for recording or reproducing information on an optical recording medium such as an optical disc or a magneto-optical disc.

[0002]

2. Description of the Related Art FIG. 9 is a block diagram showing a configuration of an example of a conventional magneto-optical disk device. The semiconductor laser 2 is
A laser beam of a predetermined wavelength is emitted and emitted to the collimator lens 3. The laser light from the semiconductor laser 2 is converted into parallel light by the collimator lens 3 and is incident on the beam splitter 4. The beam splitter 4 transmits the laser light incident from the semiconductor laser 2 through the collimator lens 3 and makes it enter the objective lens 5. The objective lens 5 receives the incident laser light from a magneto-optical disk (hereinafter, disk).
Focus on 1.

At the time of recording information on the disc 1,
In this way, the light beam is focused on the disc 1, and in accordance with the information (0 or 1 of the signal) to be recorded,
The magnetic pole of a magnet (not shown) arranged so as to face the disk 1 is changed, and the disk 1 is magnetized in the vertical direction by the so-called Curie point recording method.

During reproduction of information recorded on the disk 1, when the light beam focused on the disk 1 is reflected by the so-called magnetic Kerr effect, its polarization plane corresponds to the magnetization direction of the disk 1. To the right or left (θ
Or, the rotation angle of the polarization plane of the reflected light from the disc 1 is detected.

That is, the reflected light from the disk 1 passes through the objective lens 5 and is reflected by the beam splitter 4 to be 1 /
It is incident on the two-wave plate 6. The half-wave plate 6 is the disk 1
The polarization plane of the reflected light from is rotated to the right or left by 1/2 wavelength, that is, 45 degrees. Then, the light whose polarization plane is rotated is condensed by the condenser lens 7 and enters the polarization beam splitter 41.

The polarization beam splitter 41 is a flat plate-shaped transparent body having a polarizing film (not shown) formed on the surface facing the condenser lens 7, and the disc 1 condensed by the condenser lens 7 is used.
A predetermined angle (for example, 4
It is arranged at an angle of 5 degrees or the like), reflects the polarization component (for example, S polarization component) of the reflected light from the disk 1 which is perpendicular to the plane of incidence on the polarizing film, and outputs it to the two-division light receiving element 43. , And transmits the polarization component (for example, P polarization component) of the reflected light from the disc 1 parallel to the incident surface to the polarization film to the four-division light receiving element 42.

The two-division light receiving element 43 is divided into two by a division line 43a in the same direction as the track direction of the disk 1, and the center of the light spot of the S-polarized component reflected by the polarization beam splitter 41 on the division line 43a. Are arranged so that Then, the S-polarized component from the polarization beam splitter 41 is received on each split surface, and a voltage corresponding to the amount of received light is output. This voltage is output to a signal processing circuit (not shown), where the tracking error signal is detected by the so-called push-pull method.

On the other hand, the four-division light receiving element 42 is divided into four by two division lines 42a and 42b which are orthogonal to each other, and the P-polarized component transmitted through the polarization beam splitter 41 is located on the intersection of the division lines 42a and 42b. Is arranged so that the center of the light spot is located approximately in the middle of the astigmatism generated by the condensing lens 7 and the polarization beam splitter 41 by the meridional surface and the sagittal surface. Then, on each split surface, the polarization beam splitter 41
The P-polarized light component from is received, and a voltage corresponding to the amount of received light is output. This voltage is output to the signal processing circuit, and the focus error signal is detected by the so-called astigmatism method.

The tracking error signal or focus error signal detected as described above is supplied to a servo circuit (not shown), and the tracking error signal or focus error signal is set to 0 in the servo circuit. The tracking or focusing is controlled as described above.

Further, the voltages corresponding to the amount of received light output from the four-division light-receiving element 42 or the two-division light-receiving element 43 are respectively added in the signal processing circuit, and the difference or the sum thereof is taken to obtain the reproduction difference signal. Alternatively, a reproduction sum signal is generated.

Even at the time of recording, the tracking error signal and the focus error signal are generated as described above, and the tracking and focusing are controlled.

[0012]

By the way, when astigmatism is generated by the polarization beam splitter 41 in the form of a parallel plate as shown in FIG. In order to increase the thickness of the polarization beam splitter 41, it is necessary to increase the thickness d of the polarization beam splitter 41.

Therefore, in this case, the weight of the optical head increases, making it difficult to shorten the access time.
There was a problem that the entire device became large.

The present invention has been made in view of the above circumstances, and it is possible to reduce the weight and size of the apparatus.

[0015]

An optical head according to a first aspect of the present invention comprises a semiconductor laser 2 as a light emitting means for emitting light for irradiating a recording medium such as a disk 1, and an optical means for producing astigmatism. Polarized beam splitter 8
A circular circular dividing line 9a for dividing the light-receiving surface into an inner region and an outer region for receiving reflected light or transmitted light from the disc 1 through the polarization beam splitter 8; And four areas A _i ,
B _i , C _i , and D _i , and A _o , B _o , C _o , and D
Eight areas A _i , B _i , C _i , D _i , A _o , B _o , which are divided into _o by two straight line dividing lines 9 b and 9 c which are substantially orthogonal to each other with the center point of the circular dividing line 9 a as an intersection point. _Light receiving element 9 as first light receiving means divided into C _o and D _o
And four inner regions A _i , B _i , C of the light receiving element 9 are provided.
_i the difference of the sum of the light receiving signal _{((A i + C i)} , (B i + D i)) in, and D 2 pairs of diagonally located areas A _i and C _i of the _i or B _i and D _i respectively, ((A _i + C _i )
- to calculate the _{(B i + D i))} , 4 two outer regions _{A o, B o, C o} , and the area located two sets of diagonal D _o A _o and C _o or B _o and, D _o the sum of the received light signal in each _{((a o + C o)} , (B o + D o)) difference - calculates _{((a o + C o)} (B o + D o)), is calculated from the outer regions The difference ((A _o + C _o ) − (B _o + D _o )) is 1
The focus error signal is generated by multiplying by a predetermined number of times larger than the difference and then calculating the sum of the difference ((A _i + C _i ) − (B _i + D _i )) calculated from the inner area. Characterize.

The optical head according to a second aspect of the invention is a light receiving element 9
Of the two linear dividing lines 9b and 9c dividing the light receiving element 9 along the track direction of the disk 1 (regions A _i , A _o , B).
The difference ((A _i + A _o + B _i +) between the received light signals in the region composed of _i and B _o and the region composed of the regions C _i , C _o , D _i and D _o
The tracking error signal is generated by calculating B _o ) − (C _i + C _o + D _i + D _o )).

An optical head according to a third aspect of the invention is a light receiving element 9
The received light signals A _i in the four inner regions of
It is characterized in that a reproduction signal is generated based on only B _i , C _i and D _i .

In the optical head according to the fourth aspect, the polarizing beam splitter 8 is arranged so as to be inclined with respect to the optical axis of the reflected light or the transmitted light from the disk 1, and is a flat plate-shaped transparent body that reflects and transmits the light. The light receiving element 9 receives the light transmitted through the transparent body.

An optical head according to a fifth aspect is characterized by further including a light receiving element 10 as a second light receiving means for receiving the light reflected by the transparent body as the polarization beam splitter 8.

In the optical head according to the sixth aspect, the transparent body as the polarization beam splitter 8 transmits and reflects the reflected light or the transmitted light from the disk 1 to separate the light into polarized light components orthogonal to each other. It is characterized by

In the optical head according to the seventh aspect, the transparent body as the polarization beam splitter 8 forms an angle of 90 between the optical axis of the light transmitted through the transparent body and the optical axis of the light reflected by the transparent body.
It is characterized in that it is arranged to be less than the degree.

[0022]

In the optical head according to the present invention, a circular circular dividing line 9a for dividing the light receiving surface into an inner region and an outer region and four regions each of the inner region and the outer region are provided. A _i , B _i , C _i , and D _i , and A _o , B _o , C
_o, and D _o is divided into approximately two orthogonal straight division lines 9b and 9c the center point of the circular dividing line 9a as the intersection
And eight regions A _i , B _i , C _i , D _i , A _o , B _o ,
The light receiving element 9 divided into C _o and D _o receives the reflected light or the transmitted light from the disc 1 through the polarization beam splitter 8 which produces astigmatism. And 4
One of the inner area A _i, B _i, C _i, and the area located two sets of diagonal D _i A _i and C _i or B _i and D _i the sum of light receiving signals in each ((A _i + C _i, ), (B _i +
D _i )) difference ((A _i + C _i ) − (B _i + D _i )) is calculated, and the two outer regions A _o , B _o , C _o , and D _o are diagonally divided. The sum of the received light signals in each of the areas A _o and C _o or B _o and D _o ((A _o +
Difference between (C _o ), (B _o + D _o )) ((A _o + C _o ) − (B _o + D
_o )), and the difference ((A _o +
The difference ((A _i + C _i ) − calculated from the inner region after multiplying C _o ) − (B _o + D _o )) by a predetermined number larger than 1
The focus error signal is generated by calculating the sum of (B _i + D _i )). Therefore, even if the thickness of the polarization beam splitter 8 is reduced, a sufficiently large focusing detection range can be obtained, and the weight and size of the device can be reduced.

In the optical head according to the second aspect, of the two straight line dividing lines 9b and 9c for dividing the light receiving element 9, the straight line dividing line 9 along the track direction of the disk 1 is used.
Two regions of the light receiving element 9 divided by c (region consisting of regions A _i , A _o , B _i , B _o and regions C _i , C _o , D
_i, the difference between the light receiving signals in the area) consisting of D _o ((A _i +
A tracking error signal is generated by calculating A _o + B _i + B _o ) − (D _i + D _o + C _i + C _o )).
Therefore, since the focus error signal and the tracking error signal can be obtained from the same light receiving element 9, the weight and size of the device can be further reduced.

In the optical head according to the third aspect, the reproduction signal is generated only on the basis of the received light signals A _i , B _i , C _i and D _{i in} each of the four inner regions of the light receiving element 9. Therefore, since the focus error signal and the reproduction signal can be obtained from the same light receiving element 9, the weight and size of the device can be reduced.

In the optical head according to the fourth aspect, the polarization beam splitter 8 is arranged so as to be inclined with respect to the optical axis of the reflected light or the transmitted light from the disk 1, and is transparent in the form of a flat plate for reflecting and transmitting the light. The light receiving element 9 is a body and receives the light transmitted through the transparent body. Therefore, the weight and size of the device can be reduced.

In the optical head according to the fifth aspect, the light receiving element 10 receives the light reflected by the transparent body as the polarization beam splitter 8. Therefore, in addition to the tracking error signal, the S /
It is possible to easily obtain a reproduced signal having a high N.

In the optical head according to the sixth aspect, the transparent body as the polarization beam splitter 8 transmits and reflects the reflected light or the transmitted light from the disk 1 to separate the light into polarized light components orthogonal to each other. To do. Therefore, a reproduction signal of information based on the magnetic Kerr effect can be easily obtained.

In the optical head according to the seventh aspect, the transparent body as the polarization beam splitter 8 forms an angle of 90 between the optical axis of the light transmitted through the transparent body and the optical axis of the light reflected by the transparent body. It is arranged to be less than the degree. Therefore,
Since the elements that receive the light transmitted through the transparent body or the light reflected by the transparent body can be arranged in the same plane, the device can be downsized.

[0029]

1 is a block diagram showing the configuration of an embodiment of a magneto-optical disk device to which the optical head of the present invention is applied. In the figure, parts corresponding to those in FIG. 9 are designated by the same reference numerals. Polarizing beam splitter 8
Is a parallel plate-shaped thin transparent body and a condenser lens 7
A polarizing film (not shown) is formed on the surface facing
It is arranged at a predetermined angle (for example, 45 degrees) with respect to the optical axis of the reflected light from the disc 1 condensed by the condenser lens 7 and is perpendicular to the plane of incidence on the polarizing film. Polarization component of reflected light from the disc 1 (for example, S polarization component)
While being emitted to the light receiving element 10 by changing the direction by 90 degrees in the clockwise direction and transmitting the polarization component (for example, P polarization component) of the reflected light from the disk 1 parallel to the incident surface to the polarization film. And is emitted to the light receiving element 9.

The light receiving element 9 has a circular circular dividing line 9a for dividing the light receiving surface into an inner region and an outer region, and four regions A _i and B _{i for} the inner region and the outer region, respectively. C
_i and D _i and eight regions by two straight line dividing lines 9b and 9c which are substantially orthogonal to each other and which are divided by A _o , B _o , C _o and D _o with the center point of the circular dividing line 9a as an intersection. It is divided into A _i , B _i , C _i , D _i , A _o , B _o , C _o , and D _o . Then, the light receiving element 9 has a straight dividing line 9a.
And 9b so that the center of the light spot of the P-polarized component transmitted through the polarization beam splitter 8 is located, and the non-generated light generated by the meridional surface and the sagittal surface by the condenser lens 7 and the polarization beam splitter 8. It is located near the middle of the point aberration. Then, each area (division plane) A _i , B _i , C _i , D _i , A _o , B _o , C _o , or D
_{At o} , the P-polarized component from the polarization beam splitter 8 is received and a voltage corresponding to the amount of received light is output.

The circular dividing line 9a of the light receiving element 9 is made to be substantially the same as the substantially circular light spot of the P-polarized light component when it is in focus (exactly the same or more than the light spot of the P-polarized light component). It is formed to be slightly larger or slightly smaller).

The light receiving element 10 is divided into two regions E and F by a linear dividing line 10a in the same direction as the track direction of the disc 1, and the S-polarized light reflected by the polarization beam splitter 8 is on the linear dividing line 10a. It is arranged such that the center of the light spot of the component is located and before or after the focal position of the condenser lens 7. Then, the S-polarized component from the polarization beam splitter 8 is received in each region (division plane) E or F, and a voltage corresponding to the amount of received light is output.

Further, FIG. 2 shows the focus error signal F from the voltage output from the light receiving elements 9 and 10 of FIG.
FIG. 3 is a circuit diagram showing a configuration of an embodiment of a signal processing circuit that calculates an ES, a tracking error signal TES, and a reproduction signal (RF sum signal and RF difference signal).

The computing unit 21a has two input terminals,
Two sets of diagonally located areas A outside the light receiving element 9
_{Of o} and C _o and B _o and D _o , the voltages (light reception signals) output from the regions A _o and C _o are supplied, and the voltages are added to add the voltage of the differential amplifier 22a. Supply to the non-inverting input terminal. The calculator 21b has, at its two input terminals, regions B _o and D _o out of regions A _o and C _o and B _o and D _o , which are diagonally located in two sets of regions outside the light receiving element 9. The output voltage (light reception signal) is supplied, and the voltages are added and supplied to the inverting input terminal of the differential amplifier 22a.

The computing unit 21c has two input terminals,
Two sets of diagonally located areas A inside the light receiving element 9
_{Of i} and C _i , and B _i and D _i , the voltages (light reception signals) output from the regions A _i and C _i are supplied, and the voltages are added to add the voltages to the differential amplifier 22b. Supply to the non-inverting input terminal. The arithmetic unit 21d has, at its two input terminals, regions B _i and D _i among regions A _i and C _i and B _i and D _i which are diagonally located in two pairs of regions inside the light receiving element 9. The output voltage (light reception signal) is supplied, and the voltages are added and supplied to the inverting input terminal of the differential amplifier 22b.

The differential amplifier 22a or 22b takes the difference between the voltage supplied to its non-inverting input terminal and the voltage supplied to its inverting input terminal, and outputs it to its output terminal. The output terminal of the differential amplifier 22a is connected to the input terminal of the multiplier 23, and the output voltage of the differential amplifier 22a is then multiplied by k (> 1) and supplied to one input terminal of the calculator 25. It is designed to be. The calculator 25 is
The other input terminal is connected to the output terminal of the differential amplifier 22b, and the voltages supplied to the two input terminals are added and output.

Further, the output terminals of the arithmetic units 21a to 21d are also connected to the four input terminals of the arithmetic unit 24, respectively. The calculator 24 adds the voltages supplied to the four input terminals and outputs the result to the output terminal. Calculator 24
The output terminal of is connected to the non-inverting input terminal of the differential amplifier 28 and one input terminal of the arithmetic unit 29.

The differential amplifier 26 is configured such that the voltage output from the region F or E of the light receiving element 10 is supplied to the inverting input terminal or the non-inverting input terminal thereof, respectively. Take the voltage difference and output to the output terminal. Further, the voltage output from the region F or E of the light receiving element 10 is also supplied to the two input terminals of the arithmetic unit 27, and the arithmetic unit 27 adds the voltages to the differential amplifier. 28 and the other input terminal of the arithmetic unit 29.

The differential amplifier 28 takes the difference between the voltage supplied from the calculator 24 and the voltage supplied from the calculator 27, and outputs the difference. The arithmetic unit 29 adds the voltage supplied from the arithmetic unit 24 and the voltage supplied from the arithmetic unit 27, and outputs it.

Next, the operation will be described. The linearly polarized light beam from the semiconductor laser 2 in FIG. 1 is converted into parallel light by the collimator lens 3 and focused on the disk 1 via the beam splitter 4 and the objective lens 5. This light beam is reflected on the disk 1 and again enters the beam splitter 4 via the objective lens 5.
The reflected light from the disk 1 is reflected by the beam splitter 4, changes its direction by 90 degrees, and enters the ½ wavelength plate 6, where the plane of polarization thereof is rotated by ½ wavelength. Then, the reflected light from the disc 1 enters the polarization beam splitter 8 via the condenser lens 7.

The polarization beam splitter 8 reflects the S-polarized light component as the polarization component of the reflected light from the disk 1 which is perpendicular to the plane of incidence on the polarization film, changes the direction by 90 degrees in the clockwise direction, and receives the light-receiving element 10. And the P-polarized light component as the polarized light component of the reflected light from the disc 1 parallel to the incident surface on the polarizing film is transmitted and emitted to the light receiving element 9.

The reflected light of the S-polarized component incident on the light receiving element 10 forms a light spot whose center is located on the straight dividing line 10a. Here, if the light beam applied to the disk 1 is displaced from the track of the disk 1, the light intensity distribution in the direction orthogonal to the linear dividing line 10a of the light spot on the light receiving element 10 is biased. The deviation of the light intensity due to the track deviation appears as a difference between the voltages output from the regions E or F of the light receiving element 10.

Therefore, in the differential amplifier 26 shown in FIG.
The difference between the voltages output from the regions E or F of the light receiving element 10 is taken, and this is the tracking error signal TE.
It is output as S.

That is, the tracking error signal TES
Will be calculated according to the equation TES = EF.

On the other hand, the reflected light of the P-polarized component incident on the light receiving element 9 forms a light spot whose center is located at the intersection of the straight dividing lines 9a and 9b. The light intensity distribution of this light spot corresponds to the distance between the focus position of the light beam irradiated on the disc 1 and the disc 1.

That is, as described above, since the light receiving element 9 is arranged near the middle of the astigmatism generated by the meridional surface and the sagittal surface by the condenser lens 7 and the polarization beam splitter 8, the disk 1 is arranged. If is at the in-focus position, a uniform light spot with a substantially circular light intensity is formed. Further, when the disc 1 is closer to the in-focus position, a light spot having an elliptical uniform light intensity is formed. Further, when the disc 1 becomes farther from the in-focus position, a uniform light spot is formed in which the light intensity is an elliptical shape obtained by rotating the elliptical shape by 90 degrees.

[0047] Thus, the deviation from the in-focus position of the disk 1, in the inner area A _i to D _i of the circular dividing line 9a of the light receiving element 9, is output from the area A _i and C _i diagonally positioned Between the sum of the voltages (light receiving signals) and the sum of the voltages (light receiving signals) output from the regions B _i and D _i ((A _i
+ C _i ) − (B _i + D _i )), and in the outer regions A _{o to} D _o , the sum of the voltages (light reception signals) output from diagonally located regions A _o and C _o , Area B _o
And the sum of the voltages (light reception signals) output from D _o ((A _o + C _o ) − (B _o + D _o )), which is the focus error signal.

However, as described above, when the thickness of the polarization beam splitter 8 is thin, any difference ((A _i +
C _i )-(B _i + D _i ), or (A _o + C _o )-(B _o + D
_{Even if (o} )) is used, the detection range of focusing (so-called S-shaped curve, almost linear portion near the origin) becomes small.

Therefore, in the present invention, the focus error signal is calculated by the signal processing circuit shown in FIG.

That is, the four inner regions A _{i of the} light receiving element 9
To D _i of two sets of diagonally located regions A _i and C _i , or the sum of received light signals in B _i and D _i ((A _i +
C _i ), (B _i + D _i )) is the arithmetic unit 21c or 21d
Is calculated by each of the above, and is output to the differential amplifier 22b, and the four outer regions A _{o to} D _{o of the} light receiving element 9 are calculated.
Two diagonally located regions A _o and C _o , or B _o
And the sum of the received light signals at D _o ((A _o + C _o ), (B _o +
D _o )) is calculated by the arithmetic unit 21a or 21b and output to the differential amplifier 22a.

In the differential amplifier 22a, the sum (A _o +) of the light receiving signals output from the arithmetic unit 21a or 21b, respectively.
The difference of ( _Co ) or ( _Bo + _Do ) (( _Ao + _Co )-( _Bo +
D _o )) is calculated and output to the multiplier 23. In the multiplier 23, the output of the differential amplifier 22a ((A _o + C _o ))
− (B _o + D _o )) is multiplied by k (> 1) and output to the calculator 25. At the same time, in the differential amplifier 22b, the difference ((A _i + C _i )) of the sum (A _i + C _i ) or (B _i + D _i ) of the received light signals output from the computing unit 21c or 21d, respectively.
− (B _i + D _i )) is calculated and output to the calculator 25.

In the calculator 25, the output of the multiplier 23 (k ((A _o + C _o ) − (B _o + D _o ))) and the differential amplifier 2
The output of 2b ((A _i + C _i ) − (B _i + D _i )) is added, and this is output as the focus error signal FES.

That is, the focus error signal FES is
It is calculated according to the formula FES = k ((A _o + C _o ) − (B _o + D _o )) + ((A _i + C _i ) − (B _i + D _i )).

In the above equation, when k = 1, FIG.
The result is similar to the case where the focus error signal is calculated by the astigmatism method using the four-division light receiving element 42 as in the case of 1. However, in the present invention, since k> 1, focusing is detected. It is possible to reduce the thickness of the polarization beam splitter 8 by enlarging the range (so-called S-shaped curve near the origin) without decreasing the range.

FIG. 4 shows the S-shaped curves of the focus error signal FES when k = 1 and when k = 5.
Shown in. It can be seen that when k = 5, the focusing detection range is about twice as large as when k = 1.

Therefore, when a focus error signal is detected by the so-called astigmatism method, if an attempt is made to obtain a sufficiently large focusing detection range, a polarizing beam splitter having a thickness as shown by a dotted line in FIG. Although the light receiving element had to be arranged at the position shown by the dotted line, according to the present invention, the detection range of focusing is increased and the thickness of the polarization beam splitter 8 is reduced.
Further, the light receiving element 9 can be arranged at a position closer to the polarization beam splitter 8.

As a result, the size and weight of the device can be reduced, and the access time can be shortened.

By the way, in the signal processing circuit of FIG. 2, the outputs of the arithmetic units 21a to 21d are also supplied to the arithmetic unit 24, where they are added and added to the non-inverting input terminal of the differential amplifier 28 and one of the arithmetic units 29. It is supplied to the input terminal.

Thus, the voltage (A _i + B _i + C _i + D _i + A _o + B _o + C _o + D _o ) corresponding to the light intensity of the P-polarized component of all the reflected light of the disk 1 received by the light receiving element 9 is obtained.
Are supplied to the differential amplifier 28 and the calculator 29.

Further, the voltages respectively output from the regions E or F of the light receiving element 10 are supplied to the arithmetic unit 27 where they are added and added to the inverting input terminal of the differential amplifier 28 and the other input terminal of the arithmetic unit 29. Supplied.

As a result, the light received by the light receiving element 10 is
The voltage (E + F) corresponding to the light intensity of the S-polarized light component of all the reflected light from the disk 1 becomes
9 will be supplied.

In the differential amplifier 28, the difference between the voltage supplied from the arithmetic unit 24 and the voltage supplied from the arithmetic unit 27 is calculated, and the RF difference signal RF _diff is output.

That is, the RF difference signal RF _diff is calculated according to the following formula: RF _diff = (A _i + B _i + C _i + D _i + A _o + B _o + C _o + D _o ) − (E + F).

In the arithmetic unit 29, the arithmetic unit 24
The supplied voltage and the voltage supplied from the calculator 27 are added, and the RF sum signal RF _sum is output.

That is, the RF sum signal RF _sum is calculated according to the formula RF _sum = (A _i + B _i + C _i + D _i + A _o + B _o + C _o + D _o ) + (E + F).

The RF difference signal RF _diff is used as a reproduction signal when the disc 1 is a magneto-optical disc, and
The sum signal RF _sum is used as a reproduction signal when the disc 1 is an optical disc or a signal for controlling the power of the laser light of the semiconductor laser 2, for example.

The circular dividing line 9a of the light receiving element 9 can be formed to be slightly larger than the substantially circular light spot of the P-polarized component when the light is in focus. In this case, if there is focus, the light receiving element 9
Since the P-polarized components of all the reflected light of the disk 1 are received in the areas A _{i to} D _i within the circular dividing line 9a of the above, the RF sum signal and the RF difference signal are processed by the signal processing shown in FIG. It becomes possible to calculate by the circuit.

That is, in FIG. 5, the 4-input arithmetic unit 2 of FIG.
The configuration is the same as that in FIG. 2 except that a 2-input arithmetic unit 30 is used instead of 4. The computing unit 30 has computing terminals 21c and 21d at its input terminals.
The output of is supplied, and it is added.

Therefore, the RF difference signal RF _diff is calculated according to the formula RF _diff = (A _i + B _i + C _i + D _i )-(E + F), and the RF sum signal RF _sum is calculated by the formula RF _sum = (A _i + B It is calculated according to _i + C _i + D _i ) + (E + F).

Therefore, in this case, as compared with the case in FIG. 2, the voltages A _{i to} D _i are added without adding the voltages A _{o to} D _o.
RF sum signal and RF difference signal can be obtained from
As a result, it is not necessary to add noise included in the signals A _{o to} D _o , so that the S / N of the signal can be improved.

Further, in the polarization beam splitter 8, one of the linear dividing lines 9b and 9c, for example, the linear dividing line 9c is aligned with the track direction of the disc 1, and the astigmatism on the light receiving element 9 is aligned with the track direction. Can be arranged so as to be generated in a direction inclined by 45 degrees.

In this case, if the disc 1 is at the in-focus position, a uniform light spot is formed in a substantially circular light intensity as shown in FIG. 3 (c). Further, when the disc 1 becomes closer to the in-focus position, for example, as shown in FIG.
An elliptical light spot of is formed. When the disc 1 comes closer to the in-focus position, a large elliptical light spot is formed, which rises to the right by 45 degrees with respect to the track direction, as shown in FIG. 3A, for example.

When the disc 1 becomes farther from the in-focus position, an elliptical light spot that rises 45 degrees to the left (downward 45 degrees to the right) with respect to the track direction is formed, for example, as shown in FIG. 3D. . When the disc 1 is farther from the in-focus position, a large elliptical light spot is formed, which rises to the left by 45 degrees with respect to the track direction, as shown in FIG.

Further, in this case, when the light beam irradiated on the disc 1 is displaced from the track of the disc 1, the light spot on the light receiving element 9 is in the same direction as the straight dividing line 9b orthogonal to the track direction. The light intensity distribution is biased. That is, the deviation of the light intensity due to this track shift is
As a difference between the sum of the voltages output from the regions A _i , A _o , B _i , and B _{o of the} light receiving element 9 and the sum of the voltages output from the regions C _i , C _o , D _i , and D _o appear.

Therefore, in this case, the signal processing circuit shown in FIG. 5 can be constructed as shown in FIG. In addition,
In the figure, parts corresponding to those in FIG. 5 are designated by the same reference numerals. In the signal processing circuit of FIG. 6, the voltages output from the areas A _i , A _o , B _i , and B _o are supplied to the 4-input arithmetic unit 31 a, and the voltages are added there and the difference is obtained. It is output to the non-inverting input terminal of the dynamic amplifier 32.

Further, the four-input arithmetic unit 31b is adapted to be supplied with the voltages output from the regions C _i , D _o , D _i , and D _o , where they are added and the differential amplifier 32 is added. It is output to the inverting input terminal of.

In the differential amplifier 32, the arithmetic unit 31a
(A _i + A _o + B _i + B _o ) and the output (C _i + C _o + C _i + C _o ) of the calculator 31b are calculated and output as a tracking error signal TES.

That is, the tracking error signal TES
Will be calculated according to the equation TES = (A _i + A _o + B _i + B _o ) − (C _i + C _o + C _i + C _o ).

Therefore, together with the focus error signal,
Since the tracking error signal is calculated by the voltage output from the light receiving element 9, the light receiving element 10 that receives the S-polarized component from the polarization beam splitter 8 does not need to be divided, as shown in the figure.

Therefore, as compared with the case where the light receiving element 10 is divided, the loss of the amount of received light due to the division gap is eliminated, and the RF sum signal and the RF sum signal with improved S / N can be obtained. .

Next, FIG. 7 is a block diagram showing the structure of a second embodiment of a magneto-optical disk device to which the optical head of the present invention is applied. In the figure, parts corresponding to those in FIG. 1 are designated by the same reference numerals.

In this optical disk device, the polarization beam splitter 8 is arranged so as to be inclined by less than 45 degrees with respect to the optical axis of the reflected light from the disk 1 which is condensed by the condenser lens 7, that is, polarized light. The beam splitter 8 is arranged so that the angle formed by the optical axis of the P-polarized component light passing therethrough and the optical axis of the S-polarized component light reflected there is less than 90 degrees.

Further, since the thickness of the polarization beam splitter 8 is thin, the distance (interval) between the P-polarized component passing therethrough and the S-polarized component reflected there is small. Therefore, as shown in FIG. The elements 9 and 10 can be formed on the substantially same plane in the light receiving element package 11.

Therefore, the light receiving elements 9 and 10 (light receiving element package 11) can be easily manufactured, assembled and adjusted. Further, the device can be made compact, and the cost can be reduced.

The case where the optical head of the present invention is applied to a magneto-optical disk device has been described above, but the present invention can be applied not only to the magneto-optical disk device but also to, for example, an optical disk device or an optical card reading device. You can

The collimator lens 3 is not arranged between the semiconductor laser 2 and the beam splitter 4, but rather is arranged between the semiconductor laser 2 and the beam splitter 4.
As shown in FIG. 8, the beam splitter 4 and the objective lens 5
It may be arranged between them.

Further, for example, in the signal processing circuit of FIG. 2, the output of the differential amplifier 22a is multiplied by k, but the output of the differential amplifier 22a is not multiplied by k, but the output of the differential amplifier 22b. May be multiplied by 1 / k.

The half-wave plate 6 is not always necessary.

[0089]

According to the optical head of the present invention, a circular circular dividing line that divides the light-receiving surface into an inner region and an outer region, and an inner region and an outer region each have four portions. The first light receiving means, which is divided into eight areas by two straight line dividing lines that are substantially orthogonal to each other with the center point of the circular dividing line as an intersection, is interposed by an optical means that generates astigmatism. The reflected light or transmitted light from the recording medium is received. Then, the difference in the sum of the received light signals in each of the two sets of diagonally located regions of the four inner regions is calculated, and the received light signal of each of the two sets of diagonally located regions in the four outer regions is calculated. A focus error signal is generated by calculating the difference between the sums, multiplying the difference calculated from the outer region by a predetermined number larger than 1, and then calculating the sum with the difference calculated from the inner region. . Therefore, even if the thickness of the optical means is reduced, a sufficiently large focusing detection range can be obtained, and the weight and size of the device can be reduced.

According to the optical head of the second aspect, the first
By calculating the difference between the light reception signals in the two regions of the first light receiving means divided by the straight line dividing line along the track direction of the recording medium among the two line dividing lines dividing the light receiving means Generate an error signal. Therefore, since the focus error signal and the tracking error signal can be obtained from the same first light receiving unit, the weight and size of the device can be further reduced.

According to the optical head of the third aspect, the first
The reproduction signal is generated only on the basis of the received light signals in each of the four inner regions of the light receiving means. Therefore, since the focus error signal and the reproduction signal can be obtained from the same first light receiving means, the weight and size of the device can be reduced.

According to the optical head of the fourth aspect, the optical means is arranged in a tilted manner with respect to the optical axis of the reflected light or the transmitted light from the recording medium. The first light receiving means receives the light transmitted through the transparent body. Therefore, the weight and size of the device can be reduced.

According to the optical head of the fifth aspect, the second
The light receiving element receives the light reflected by the transparent body as the optical means. Therefore, in addition to the tracking error signal, the first
A reproduction signal having a high S / N ratio can be easily obtained in combination with the light received by the light receiving means.

According to the optical head of the sixth aspect, the transparent body as the optical means transmits and reflects the reflected light or the transmitted light from the recording medium, thereby separating the light into polarized light components orthogonal to each other. . Therefore, a reproduction signal of information based on the magnetic Kerr effect can be easily obtained.

According to the optical head of the seventh aspect, the transparent body as the optical means has the optical axis of the light transmitted through the transparent body,
It is arranged so that the angle formed with the optical axis of the light reflected by the transparent body is less than 90 degrees. Therefore, it is possible to arrange the elements that respectively receive the light transmitted through the transparent body and the light reflected by the transparent body in the same plane, so that the device can be made compact.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of a magneto-optical disk device to which an optical head of the present invention is applied.

FIG. 2 is a circuit diagram showing a configuration of an embodiment of a signal processing circuit that performs signal processing of a light reception signal (voltage) output from light receiving elements 9 and 10.

FIG. 3 is a diagram for explaining a change in a light intensity distribution of a light spot of a light beam corresponding to a focus shift.

FIG. 4 is a diagram showing an S-shaped curve of a focus error signal.

FIG. 5 is a circuit diagram showing a configuration of a second embodiment of a signal processing circuit that performs signal processing of light reception signals (voltages) output from light receiving elements 9 and 10.

FIG. 6 is a circuit diagram showing a configuration of a third embodiment of a signal processing circuit that performs signal processing of a light reception signal (voltage) output from light receiving elements 9 and 10.

FIG. 7 is a block diagram showing a configuration of a second embodiment of a magneto-optical disk device to which the optical head of the invention is applied.

FIG. 8 is a block diagram showing a configuration of a third embodiment of a magneto-optical disk device to which the optical head of the invention is applied.

FIG. 9 is a block diagram showing a configuration of an example of a conventional magneto-optical disk device.

[Explanation of symbols]

 1 disk 2 semiconductor laser 3 collimator lens 4 beam splitter 5 objective lens 6 1/2 wavelength plate 7 condensing lens 8 polarization beam splitter 9 light receiving element 9a circular dividing line 9b, 9c linear dividing line 10 light receiving element 10a linear dividing line 11 Light receiving element package 21a to 21d Operation unit 22a, 22b Differential amplifier 23 Multiplier 24,25 Operation unit 26 Differential amplifier 27 Operation unit 28 Differential amplifier 29, 30, 31a, 31b Operation unit 32 Differential amplifier 41 Polarization beam splitter 42 4-division light receiving element 42a, 42b division line 43 2-division light receiving element 43a division line

Claims (7)

[Claims] 1. A light emitting means for emitting light for irradiating a recording medium, an optical means for generating astigmatism, and a light receiving means for receiving reflected light or transmitted light from the recording medium via the optical means. A circular circular dividing line that divides the surface into an inner region and an outer region, and a center point of the circular dividing line that divides the inner region and the outer region into four regions, respectively A first light receiving unit divided into eight regions by two substantially orthogonal straight line dividing lines, each of two sets of diagonally positioned regions of the four inner regions of the first light receiving unit. And a difference in the sum of the received light signals in each of two diagonally located regions of the four outer regions, and the difference calculated from the outer region. Multiplied by a predetermined number greater than 1 Then, the focus error signal is generated by calculating the sum with the difference calculated from the inner area. 2. In the two areas of the first light receiving means divided by the straight line dividing lines along the track direction of the recording medium, of the two straight line dividing lines dividing the first light receiving means. The optical head according to claim 1, wherein the tracking error signal is generated by calculating the difference between the received light signals. 3. The optical head according to claim 1, wherein the reproduction signal is generated based only on the light receiving signals in each of the four inner regions of the first light receiving means. 4. The optical means is a flat plate-shaped transparent body that reflects and transmits light, and is arranged so as to be inclined with respect to an optical axis of reflected light or transmitted light from the recording medium. 4. The optical head according to claim 1, wherein the means receives light that has passed through the transparent body. 5. The optical head according to claim 4, further comprising a second light receiving unit that receives the light reflected by the transparent body as the optical unit. 6. A transparent body as the optical means separates into reflected light components having a polarization component orthogonal to each other by transmitting and reflecting the reflected light or the transmitted light from the recording medium. Or the optical head described in 5. 7. The transparent body as the optical means is arranged such that an angle formed by an optical axis of light transmitted through the transparent body and an optical axis of light reflected by the transparent body is less than 90 degrees. The optical head according to any one of claims 4 to 6, wherein: