JPH05159404A - Optical pickup device - Google Patents

Abstract

PURPOSE:To stabilize focusing servo control by operating the difference of the addition value of respective outputs of a bi-sected photodetector and forming a focus error signal. CONSTITUTION:The S polarized component of a reflected beam from a magneto- optical disk is reflected through a 1/2 wavelength plate and a polarizing beam splitter and the P polarized component is transmitted. The beam of the S polarized component is made incident on a track error detecting photodetector 9, and a part beam of the P polarized component is reflected by a dividing mirror constituting an knife edge and made incident on the photodetector 11 and a remaining part of the beam of the P polarized component is made incident on a focus error detecting photodetector 12 whose light receiving surface is bisected by a dividing line parallel with the ridgeline of the dividing mirror. The outputs of the elements 11, 12 are inputted to a subtractor 40 through a current-voltage converters 23, 24 and 25 and a light receiving signal from the element 11 is added to respective light receiving signals of the element 12 in a prescribed ratio and the difference of the addition value is operated and the focus error signal EF' is formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention comprises a split mirror having a knife edge for splitting reflected light reflected from a recording medium,
The present invention relates to an optical pickup device that detects a focus error signal using a knife edge method.

[0002]

2. Description of the Related Art In an optical pickup device that records / reproduces (/ erases) data on a recording medium such as a write-once optical disc or a magneto-optical disc (hereinafter referred to as an optical disc), the focus of the laser beam is on the recording surface of the optical disc. So-called focusing servo control is performed so as to follow.

Various methods have been put into practical use in order to obtain a focus error signal necessary for this focusing servo control, and one of them is the knife edge method.

3A and 3B show a conventional example of an optical system of an optical pickup device for detecting a focus error signal by using the knife edge method. In this optical pickup device, a magneto-optical disk in which a guide groove for a recording track is formed is used as a recording medium, and an error (track error) between a laser beam imaging position and the recording track is used.
Is detected by the push-pull method.

In the figure, the laser light output from the semiconductor laser device 1 is converted into parallel light by the coupling lens 2, passes through the beam splitter 3, enters the objective lens 4, and is focused by the objective lens 4. Then, an image is formed on the recording surface of the magneto-optical disk 5.

The reflected light from the magneto-optical disk 5 is converted into substantially parallel light by the objective lens 4, reflected by the beam splitter 3 and guided to the objective lens 6, and the reflected light focused by the objective lens 6 is reflected. Passes through the half-wave plate 7 and its plane of polarization is rotated by 45 degrees.

The S-polarized component of the reflected light that has passed through the half-wave plate 7 is reflected by the polarization beam splitter 8 and the P-polarized component thereof is transmitted. The light of the S-polarized component reflected by the polarization beam splitter 8 is incident on a light receiving element 9 (see FIG. 4B) for detecting a track error whose light receiving surface is divided into two in the tracking direction.

Further, 60 to 90% of the light flux of the P-polarized component transmitted through the polarization beam splitter 8 is reflected by the split mirror 10 constituting the knife edge and is incident on the light receiving element 11, and The remaining part of the P-polarized component light is incident on the light receiving element 12 for focus error detection, whose light receiving surface is divided into two by a dividing line parallel to the ridgeline 10a of the dividing mirror 10.

FIG. 5 shows an example of a processing circuit for forming a tracking error signal, a focus error signal and a reproduction signal in the optical pickup device shown in FIGS. 4 (a) and 4 (b).

In the figure, a current-voltage converter 21 composed of an operational amplifier OP1, a feedback resistor R1, and a grounding resistor R2 converts a light receiving signal Pa output from the light receiving surface 9a of the light receiving element 9 into a voltage signal. The current-voltage converter 22 including the operational amplifier OP2, the feedback resistor R3, and the grounding resistor R4 is the light receiving surface 9b of the light receiving element 9.
The light receiving signal Pb output from the device is converted into a voltage signal.

The current-voltage converter 23 composed of the operational amplifier OP3, the feedback resistor R5, and the grounding resistor R6 converts the light receiving signal Pc output from the light receiving surface of the light receiving element 11 into a voltage signal.

The current-voltage converter 24 including the operational amplifier OP4, the feedback resistor R7, and the grounding resistor R8 has a light receiving signal Pd output from the light receiving surface 12a of the light receiving element 12.
Of the operational amplifier OP5,
The current-voltage converter 25 including the feedback resistor R9 and the ground resistor R10 converts the light receiving signal Pe output from the light receiving surface 12b of the light receiving element 12 into a voltage signal.

The adder 26 including the operational amplifier OP6, the input resistors R11 and R12 connected to the inverting input terminal of the operational amplifier OP6, the feedback resistor R13, and the grounding resistor R14 is provided with a light receiving signal Pa and a light receiving signal Pb. The output signal of the current-voltage converter 21 is input via the input resistor R11, and the output signal of the current-voltage converter 22 is input via the input resistor R12. ing.

Operational amplifier OP7, input resistor R15 connected to the inverting input terminal of operational amplifier OP7, operational amplifier O
A subtractor 27 including an input resistor R16, a feedback resistor R17, and a ground resistor R18 connected to the non-inverting input terminal of P7 calculates a difference between the light receiving signal Pa and the light receiving signal Pb, and The output signal of the voltage converter 21 is input through the input resistor R15, and the current-voltage converter 2
The output signal of 2 is input via the input resistor R16. The output signal of the subtractor 27 is output to the tracking servo control unit (not shown) as the tracking error signal ET.

Operational amplifier OP8, and input resistors R19, R20, R2 connected to the inverting input terminal of operational amplifier OP8.
1, the adder 28 including the feedback resistor R22 and the ground resistor R23 is for calculating the total sum of the light receiving signal Pc, the light receiving signal Pd, and the light receiving signal Pe,
The output signal of the current-voltage converter 23 is input via the input resistor R21, the output signal of the current-voltage converter 24 is input via the input resistor R19, and the output signal of the current-voltage converter 25 is the input resistor. It is input via 20.

Operational amplifier OP9, input resistor R24 connected to the inverting input terminal of operational amplifier OP9, operational amplifier O
A subtractor 29 including an input resistor R25, a feedback resistor R26, and a ground resistor R27 connected to the non-inverting input terminal of P9 calculates the difference between the light receiving signal Pc and the light receiving signal Pd, and The output signal of the voltage converter 24 is input via the input resistor R24, and the current-voltage converter 2
The output signal of No. 5 is input via the input resistor R25. The output signal of the subtractor 29 is output to the focusing servo control unit (not shown) as the focusing error signal EF.

Operational amplifier OP10, operational amplifier OP10
Input resistors R28, R29 connected to the inverting input terminal of
The adder 30 including the feedback resistor R30 and the ground resistor R31 is for calculating the total sum of the received light signal Pa, the received light signal Pb, the received light signal Pc, the received light signal Pd, and the received light signal Pe, and is an adder. The output signal of 26 is input via the input resistor R29, and the output signal of adder 28 is input via the input resistor R28. Also,
The output signal of the adder 30 is output to the next-stage device (not shown) as the prepit signal RF.

Operational amplifier OP11, operational amplifier OP11
Input resistor R32 connected to the inverting input end of the operational amplifier OP11, and input resistor R3 connected to the non-inverting input end of the operational amplifier OP11.
The subtractor 31 including the feedback resistor R34, the feedback resistor R34, and the ground resistor R35 determines the difference between the intensity of the light component transmitted through the polarization beam splitter 8 and the intensity of the light component reflected by the polarization beam splitter. The output signal of the adder 28 is input via the input resistor R28, and the output signal of the current-voltage converter 26 is input via the input resistor R33. Also, this subtractor 27
The output signal of is output to the signal reproducing unit (not shown) at the next stage as the magneto-optical signal MO.

Here, the feedback resistors R1, R3, R5, R
7, R9 and ground resistors R2, R4, R6, R
The resistance values of 8 and R10 are all set to the same value, for example, Ra. Also, the input resistors R11, R12, R1
5, R16, R19, R20, R21, R24, R2
5, R28, R29, R32, R33, feedback resistor R1
The resistance values of 3, R17, R22, R26, R30, R34 and the ground resistors R18, R27, R35 are all set to the same value, for example, Rb. The resistance values of the ground resistors R14 and R31 are set to (Rb / 3). The resistance value of the ground resistor R23 is (Rb
/ 4) is set.

Therefore, in this apparatus, the values of the tracking error signal ET, the focusing error signal FT, the pre-pit signal RF and the magneto-optical signal MO are respectively expressed by the following equations (I), (II), (III) and (IV). It is expressed like.

ET = Ra (Pa-Pb) (volt) (I)

FT = Ra (Pd−Pe) (volt) (II)

RF = −Ra (Pa + Pb + Pc + Pd + Pe) (Volts) (III)

MO = Ra (Pa + Pb-Pc-Pd-Pe) (volt) (IV)

[0025]

However, such a conventional device has the following disadvantages.

That is, the focus error signal obtained by the knife edge method draws a known S-shaped curve according to the defocus amount (focus error amount), as shown in FIG.

Observing this S-curve, focusing servo control is performed because the effective detection range of focus error detection is not symmetric (point symmetry) around the point where defocus amount is 0 at the time of focusing. There was a problem that it became unstable.

The present invention has been made in view of the above circumstances, and an object thereof is to provide an optical pickup device capable of stably performing focusing servo control.

[0029]

SUMMARY OF THE INVENTION The present invention is an optical pickup device that includes a splitting mirror that forms a knife edge that splits reflected light reflected from a recording medium, and that detects a focus error signal using the knife edge method. A light receiving element that receives the split light reflected by the split mirror, and a light receiving element that receives the split light that is not reflected by the split mirror, and its light receiving surface is split into two by a split line parallel to the ridgeline of the split mirror. The divided light-receiving element and the light-receiving signals output from the light-receiving surfaces of the two-divided light-receiving element are added with the light-receiving signal output from the light-receiving element at a predetermined ratio to calculate an addition value, and the addition value is calculated. It is provided with a focus error signal calculating means for calculating a difference to form a focus error signal. Further, the focus error signal calculation means is
A value obtained by multiplying the difference between the light receiving signals output from the respective light receiving surfaces of the divided light receiving elements by a value obtained by subtracting 1 from the predetermined coefficient of the light receiving signal of the light receiving element is added, and the value is added to the above 2
The focus error signal is calculated by multiplying the feedback resistance value of the first stage amplifier that amplifies the light receiving signals of the divided light receiving element and the light receiving element.

Further, among the reflected light reflected from the magneto-optical recording medium, there is provided a split mirror having a knife edge for splitting the component light which is transmitted through the half-wave plate and transmitted through the polarization beam splitter. In an optical pickup device that detects a focus error signal using the knife edge method, a light receiving element that receives the split light reflected by the split mirror, and a split light that is not reflected by the split mirror and receives the split light The surface is divided into two by a dividing line parallel to the ridgeline of the dividing mirror.
The divided light-receiving element and the light-receiving signals output from the light-receiving surfaces of the two-divided light-receiving element are added with the light-receiving signal output from the light-receiving element at a predetermined ratio to calculate an addition value, and the addition value is calculated. It is provided with a focus error signal calculating means for calculating a difference to form a focus error signal.

[0031]

Therefore, the S-shaped curve drawn by the focus error signal is substantially point-symmetrical to the plus side and the minus side in the effective range centered on the position of the defocus amount 0, and the focusing servo control can be stably performed. become able to.

[0032]

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

First, the principle of the present invention will be described. In the following description, the case where the same optical system as that of the conventional device shown in FIGS. 3A and 3B is used will be described. Also, the same signal names and resistance values as those of the conventional device are used.

In order to improve the stability of the focusing servo control, for example, as shown in FIG. 1, the shape of the S-shaped curve drawn by the focus error signal EF is the defocus amount 0.
The focusing error signal EF may be determined so as to be point-symmetrical on the plus side and the minus side in the effective range of control centered on the position.

Therefore, in the present invention, the value of the focusing error signal FT 'is determined by the light receiving element 1 as shown in the following equation (V).
It is corrected by the light reception signal Pc of 1.

EF ′ = Ra (Pd + x · Pc−Pe− (1-x) · Pe) (volt) (V)

Here, x is the light receiving element 12 and the light receiving element 1.
It is a constant of 1 or less determined by the ratio of the amount of received light of 1, and for example, an appropriate value can be selected as necessary within the range of 0.5 ≦ x ≦ 0.7.

By transforming this equation (V), the following equation (VI)
Is obtained.

EF ′ = Ra (Pd + 2x · Pc−Pd−Pc) (volt) (VI)

FIG. 2 shows an example of a processing circuit for forming such a focusing error signal EF according to an embodiment of the present invention. In the figure, the same parts as those in FIG. 4 and corresponding parts are designated by the same reference numerals.

In the figure, an operational amplifier OP20 and an input resistor R connected to the inverting input terminal of the operational amplifier OP20.
40 and R41, input resistors R42 and R43 connected to the non-inverting input terminal of the operational amplifier OP20, and a feedback resistor R4.
4, a subtractor 40 including a ground resistor R45 connected to the inverting input terminal of the operational amplifier OP20 and a ground resistor R46 connected to the non-inverting input terminal of the operational amplifier OP20.
Is for calculating the focusing error signal EF ′, and the output signal of the current-voltage converter 24 is the input resistor R40.
, The output signal of the current-voltage converter 25 is input via the input resistor R42, and the output signal of the current-voltage converter 23 is input via the input resistors R43 and R44.

Here, the input resistors R40, R41, R4
The resistance values of 2 and the feedback resistor R44 are all set to the same value, for example, Rb, and the resistance values of the input resistor R43 and the ground resistor R45 are each set to Rc. The resistance value of the ground resistor R46 is (R
b / 2) is set.

In the subtractor 40, its output signal, that is, the focusing error signal EF ', is expressed by the following equation (VI
It is represented by I).

EF ′ = Ra (Pd + (Rc / Rb) · Pc−Pe−Pc) (volt) (VII)

Comparing equation (VII) with equation (VI), (Rc / Rb) corresponds to 2x. Here, for example, according to the ratio of the amount of light received by the light receiving element 12 and the light receiving element 11,
If the optimum value of x is 0.55, then (Rc / R
The value of b) is 1.1. Thus, for example, Rb
When the value of is set to 10 (kiloohm), the value of Rc is 11 (kiloohm).

As described above, when the resistance value Rc is set, the S-shaped curve drawn by the focusing error signal EF 'is, as shown in FIG. 1, within the effective range of control centered on the position where the defocus amount is 0. The positive side and the negative side are point-symmetrical, which enables stable focusing servo control.

The value of (Rc / Rb) can be set to an appropriate value according to the desired shape of the S-curve. Also, thereby, the focusing error signal E
The symmetry of the S-shaped curve drawn by F ′ around the position where the defocus amount is 0 can be set arbitrarily.

Although the present invention is applied to the magneto-optical disk device in the above-described embodiments, the present invention can be similarly applied to devices using other optical disks as recording media.

In the above-mentioned embodiment, the focus error signal is formed by using the light transmitted through the polarization beam splitter 8. However, the focusing error signal is formed by using the light reflected by the polarization beam splitter 8. The present invention can be similarly applied to the case of forming.

[0050]

As described above, according to the present invention,
The S-shaped curve drawn by the focus error signal becomes substantially point-symmetrical to the plus side and the minus side within the effective range centered on the position of the defocus amount 0, and stable focusing servo control can be performed. Get the effect.

[Brief description of drawings]

FIG. 1 is a graph for explaining the principle of the present invention.

FIG. 2 is a circuit diagram showing a signal processing device according to an embodiment of the present invention.

FIG. 3 is a schematic configuration diagram illustrating an optical system of an optical pickup device.

FIG. 4 is a circuit diagram showing a conventional example of a signal processing device.

FIG. 5 is a graph for explaining a conventional inconvenience.

[Explanation of symbols]

 40 Subtractor OP20 Operational amplifier R40, R41, R42, R43 Input resistor R44 Feedback resistor R45, R46 Ground resistor

Claims (3)

[Claims] 1. An optical pickup device comprising a splitting mirror having a knife edge for splitting a reflected light reflected from a recording medium, wherein the splitting mirror is used to detect a focus error signal by using a knife edge method. A light-receiving element that receives the split light, a split light-receiving element that receives the split light that is not reflected by the split mirror, and the light-receiving surface is split into two by a split line parallel to the ridgeline of the split mirror; While calculating the added value obtained by adding the light receiving signal output from the light receiving element to the light receiving signal output from each light receiving surface of the light receiving element at a predetermined ratio,
An optical pickup device comprising a focus error signal calculation means for calculating a difference between the added values to form a focus error signal. 2. The focus error signal calculating means multiplies the difference between the light receiving signals output from the respective light receiving surfaces of the two-divided light receiving element by a value obtained by subtracting 1 from a predetermined coefficient of the light receiving signal of the light receiving element. 2. The focus error signal is calculated by adding a value obtained by adding a value to the divided resistance, and further multiplying that value by the feedback resistance value of the first-stage amplifier that amplifies the received light signals of the two-divided light receiving element and the light receiving element. The optical pickup device described. 3. A split mirror that forms a knife edge for splitting a component of the reflected light reflected from the magneto-optical recording medium that is transmitted through the half-wave plate and transmitted through the polarization beam splitter, In an optical pickup device that detects a focus error signal using the knife edge method, a light receiving element that receives the split light reflected by the split mirror and a split light that is not reflected by the split mirror A two-divided light receiving element whose surface is divided into two by a dividing line parallel to the ridgeline of the split mirror, and a light receiving signal output from each light receiving surface of each of the two light receiving surfaces of the two-divided light receiving element. While calculating the added value added at a predetermined ratio,
An optical pickup device comprising a focus error signal calculation means for calculating a difference between the added values to form a focus error signal.