JPH01260654A - Information signal detector - Google Patents

Abstract

PURPOSE:To obtain a high quality information signal by detecting an information signal recorded on a magnetic medium and a control signal for positioning a light beam at the information track of a recording medium respectively from the terminal of one side and the terminal of other side of a photodiode. CONSTITUTION:The title device is provided with a bias voltage source 5, the photodiodes 1, 2, resistors 3, 4, 26, a differential amplifying means 10, adding means 20-23 and subtracting means 24, 25. Then, the information signal recorded on the magnetic medium and the control signal for positioning the light beams 6, 7 at the information track of the recording medium are made to be detected respectively from the terminals of one sides and the terminals of other sides of the photodiodes 1, 2 to convert the intensities of the light beams 6, 7 into electric signals. Namely, since the differential amplifying means 10 for high frequency signal detection and the adding means 20-23 for low frequency signal detection are separated, mutual interference between the differential amplifying means 10 and the adding means 20-23 is reduced. Thus, the high quantity information signal can be obtained.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an information signal detector, and in particular,
Relating to an information signal detector in a magneto-optical disk device, etc., which reproduces information recorded on a magnetic recording medium by rotating the plane of polarization of reflected light or transmitted light of a light beam irradiated onto the recording medium. It is something.

[Conventional technology]

In magneto-optical disk devices, information recorded on a magnetic recording medium is processed by the Kerr effect or Faraday effect, which occurs when the reflected or transmitted light of a linearly polarized light beam irradiated onto the recording medium is affected by the Kerr effect or Faraday light, depending on the magnetic polarity of the recording medium surface. Reading is performed by utilizing the rotation of the plane of polarization due to the effect.

For example, reflected light or transmitted light is optically separated into light beams with two polarization planes shifted by 90 degrees using a birefringent element such as calcite or a polarizing beam splitter, and each signal is sent to a photodiode. The information is detected by converting the signal into an electrical signal using a light-to-electrical signal conversion element such as the above, and taking the difference between the signals.

When reading such information, it is necessary to position the light beam on the information trunk of the recording medium. Therefore, in conventional optical heads for magneto-optical disk drives,
In order to focus the light beam on the information trunk on the recording medium, it was equipped with an optical system and an optical-to-electrical conversion element for detecting the focal position error of the light beam with respect to the recording medium and for detecting the tracking position error.

[Problem to be solved by the invention]

However, the conventional method requires an optical system and an optical-to-electrical signal conversion element to detect the emotional signal and control the focal position of the light beam, and is a component of the optical head for recording and reproducing the signal. As a result, there are problems in that it takes a long time to make adjustments because there are many adjustment points, and the cost is also high because there are many optical parts.

Therefore, the present applicant first attempted to detect information signals using a single optical system.
Patent application No. 61-263866 for the technology for optical nozzles that can obtain information signals and focal position control signals of light beams.
This was proposed in the issue of ``Magneto-Optical Recording/Reproducing Head''.

Although this proposal is superior to the conventional one because it can construct a simple optical system that serves both the detection of information signals and the detection of position control signals of the light beam, it still has the following points. There is room for improvement.

This will be explained with reference to FIG.

In FIG. 6, photodiodes 1 and 2 are optical heater 1,
It is an optical-to-electrical signal conversion element that converts the intensity of the signal into an electrical signal, and is connected to a bias voltage &,5. The photoquot 2 has four light receiving surfaces 2a to 2d.

The anode of the photodiode 1 is connected to one input terminal of the differential amplifying means 10 via a resistor 72, and the detection signal S14 is supplied as one input signal of the differential amplifying means 10 for high frequency signal detection. The other input terminal of the differential amplification means 10 is connected to the light receiving surfaces 2a to 2d of the photodiode 2.
Anode terminals corresponding to are connected via resistors 68 to 71, and detection signals S1.2a to 512d are supplied.

An information signal 11 is taken out from this differential amplification means 10.

The control signal for positioning the light beam on the information track of the recording medium is provided by adding means 20 to 23 for low frequency signal detection.
obtained using Input resistors 60 to 67 are inserted into the input side of each of the adding means 20 to 23, and are connected to the anode terminal of the photodiode 2 via these, respectively.
and 512c, detection signals 512a and 512b, detection signal 5
12c and 512d are added.

The output of the addition means 20.21 is inputted to the subtraction means 24 to obtain the focus position error signal 30, and the addition means 22.2
3 is input to the subtraction means 25 to obtain a tracking position error signal 31.

In this way, the optical system was simplified in patent application No. 6],
-, No. 263866 ``Magneto-optical recording/reproducing head'', as shown in Fig. 6, an information signal 11 having a high frequency component is transmitted from the same terminal of a photodiode used as an optical-electrical signal conversion means. Control signals having low frequency components, that is, a focus position error signal 30 and a tracking position error signal 31 are detected. In such a configuration, a high frequency amplifier having a band of several M'Hz or more, for example, the differential amplification means 10 described above, is connected to the same terminal of the photodiode.
and a low frequency amplifier for a servo band of about several tens of KHz, for example, the above-mentioned adding means 20 to 23, are both connected. Generally, it is difficult to manufacture a high frequency amplifier with good DC characteristics, and it is also difficult to obtain sufficient characteristics for high frequency signals in a low frequency amplifier for servo. For this reason, when adopting a configuration in which a high-frequency amplifier and a low-frequency amplifier are connected to the same terminal as shown in Figure 6, fluctuations in the input high-ass states of each amplifier, noise generated in the amplifiers, etc. Therefore, the above-mentioned earlier application enables the use of a simple optical system, which is different from the conventional one. However, there is still room for improvement when trying to obtain an information signal with even higher signal quality.

SUMMARY OF THE INVENTION An object of the present invention is to provide an information signal detector that solves the problems in the prior art and can obtain information signals with high signal quality using a simple optical system.

[Means to solve the problem]

The present invention provides an information signal detector that reads information recorded on a magnetic recording medium by detecting rotation of the polarization plane of reflected light or transmitted light of a light beam irradiated onto the recording medium. The recorded information signal and the control signal for positioning the optical beam on the information track of the recording medium are detected from one terminal and the other terminal of a photodiode that converts the intensity of the optical beam into an electrical signal, respectively. It is characterized by

[Effect]

In the present invention, it is possible to position an information signal with a high frequency component and a control signal with a low frequency component, that is, a light beam, on an information track even if a simple optical system is used to detect both an information signal and a light beam position control signal. An information signal detection system circuit for detecting high frequency signals and a control signal detection system circuit for detecting low frequency signals are separated. Separation of these detection system circuits prevents interference between information signals, optical beam focus position errors, and amplifiers that detect control signals such as I-racking position error signals, and reduces mutual interference between each detection system circuit. Therefore, it is possible to perform signal detection with little quality deterioration using a simple optical system.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a diagram showing an embodiment of an information signal detector according to the present invention.

The information signal detector shown in Fig. 1 detects the rotation of the polarization plane of reflected light or transmitted light of a light beam irradiated onto a magnetic recording medium when reading information recorded on a magnetic recording medium. The information signal detector shown in FIG. 1 is an information signal detector that reads information by , an optical system capable of simultaneously detecting information signals, detecting focal position errors of optical beams, and detecting racking position errors is used.

In such an information signal detector, as shown in FIG. 1, resistors 3 and 4 are inserted between the bias voltage r The photodiode 1'2 is also connected to a control signal detection system circuit, that is, addition means 20 to 23, and the like.

The information signal detection system circuit, that is, the differential amplification means 10 is connected to the connection point between the photodiode 1 and the resistor 3 and the connection point between the photodiode 2 and the resistor 4. 23 are not connected to the same terminal side of the photodiode as shown in FIG. 6, but are separated from each other.

In this way, the information signal detector of this embodiment detects the information recorded on the magnetic recording medium by detecting the rotation of the polarization plane of the reflected light or transmitted light of the light beam irradiated onto the recording medium. In a readout information signal detector, the anode of a photodiode converts the intensity of the light beam into an electrical signal, which converts the information signal recorded on the magnetic medium and the control signal for positioning the light beam onto the information track of the recording medium. Detect from terminal and cathode terminal respectively.

An outline of signal detection in the signal detector having the configuration shown in FIG. 1 will be explained below. In the embodiment shown in FIG. 1, photodiode 1 has a single light-receiving surface, and photodiode 2 has four light-receiving surfaces.

Focus position errors and tracking position errors can be detected by detecting focus position errors using the well-known astigmatism method and tracking position errors using the Bushpull method from the light beam 7 incident on one photodiode 2. Is going. Signals obtained from the anode terminals of the four divided light-receiving surfaces 2a, 2b, 2c, and 2d of the photodiode 2 are detected as detection signals 5L2a and 5L2a, respectively.
512b, 512c, and 512d. At this time, for the detection signals 512a-312d from the photodiode 2, ((S12a +512d) (S12b
The focus position error signal 3 is calculated by the calculation +512c)).
0 is obtained, ((S12a +512b) (S12
The tracking position error signal 31 is obtained by the calculation c +512d) ). In addition, the light beams 6 and 7 can be generated by adding a birefringent element such as calcite to the same optical system for detecting position error signals, so that the reflected light from the recording medium can be reduced by 90%.
The beam is divided into two light beams with different planes of polarization.

Therefore, if the signal detected from the cathode terminal of the photodiode 1 is the detection signal S14, and the signal detected from the cathode terminal of the photodiode 2 is the detection signal S15, then the detection signal 314. 315, (S14-3
By the calculation 151, the information signal 11 can be obtained from information optically detected as rotation of the plane of polarization. In information signal detection according to the present invention, the configuration of the optical head itself is not an essential problem and a known signal detection method is used. The details of the principle of detection and tracking position error detection will be omitted.

Next, prevention of quality deterioration of information signals and control signals obtained by the above-described calculations will be explained.

In FIG. 1, photodiodes 1 and 2 are connected to resistors 3,
A bias voltage is applied from a bias voltage source 5 via 4. When a light beam 6.7 containing an information signal is incident on the photodiodes 1 and 2, a current IL8.7 proportional to the light beam 6.7 flows through the photodiodes 1 and 2. IL 9 is playing. As described above, the light beams 6.7 are light beams whose polarization planes are shifted by 90 degrees. When the polarization plane of the light beam reflected or transmitted from the medium is rotated by an optical system not shown in the figure in accordance with the direction of magnetization on the recording medium due to the Kerr effect or the Faraday effect,
The light intensity of one of the light beams 6.7 increases, and the light intensity of the other light beam decreases. There is a current rL a across the resistor 3゜4.
, IL 9 generates a voltage proportional to the amount of light beam 6.7. When the voltage appearing at each cathode terminal of the photodiode 1.2 is supplied to the input of the differential amplification means 10, an information signal 1 corresponding to the direction of magnetization on the recording medium is generated.
1 can be obtained. When the bias voltage of the bias voltage source 5 fluctuates, the voltage at the anode terminal of the photodiode 1.2 is equally affected by the bias voltage fluctuation of the bias voltage source 5, so the output of the differential amplification means 10 is biased. There is almost no effect of voltage fluctuations.

The light beam 7 passes through the photodiode 2 as shown in FIG.
The light-receiving surface 2a, 'lb is divided into four parts.

2c and 2d. The above-mentioned patent application Sho 61-2638
Taking the optical system of No. 66 "Magneto-Optical Recording and Reproducing Head" as an example, the signals 512a and 512d obtained from the anode terminals corresponding to the light receiving surfaces 2a and 2d are added to the adding means 2 as described above.
0, the signals S 12 b and S 12 c obtained from the anode terminals corresponding to the light receiving surfaces 2 b and 2 c are input to the adding means 21, and the output of the adding means 20.21 is input to the subtracting means 24 to calculate the focal position. An error signal 30 is obtained.

At the same time, signals 512a and 512b obtained from the anode terminals corresponding to the light receiving surfaces 2a and 2b are input to the adding means 22, and signals 512c and 512d obtained from the anode terminals corresponding to the light receiving surfaces 2c and 2d are input to the adding means 23. ,
The outputs of the addition means 22 and 23 are input to the subtraction means 25 to obtain a tracking position error signal 31. The anode terminal of the photodiode 1 is grounded via a resistor 26 corresponding to the impedance obtained by connecting the input impedances of the adding means 20 to 23 in parallel. Due to the resistor 26, the current IL8. The difference in bias fluctuation of the photodiodes 1.2 caused by the flow of IL 9 can be suppressed to a small value.

In the configuration according to the method according to the earlier application shown in FIG. 6, the inputs of the differential amplifying means 10 and the adding means 20 to 23 are
Since the input resistors 60 to 72 are connected to each other, input bias fluctuations and noise generation of the differential amplifying means 10 and the adding means 20 to 23 influence each other, and the information signal 1
1, the focal position error signal 30, and the tracking position error signal 31. However, in the signal detection method with the configuration shown in FIG. Since the differential amplifying means 10 and the adding means 20 to 23 for low frequency signal detection are separated, mutual interference between the differential amplifying means 10 and the adding means 20 to 23 is reduced, and quality can be improved with a simple optical system. It becomes possible to perform signal detection with less deterioration.

Hereinafter, further explanation will be given with reference to FIGS. 2 to 4. In the information signal detector having the above configuration, the PIN/photodiode 1 used as the photo-electric conversion element shown in FIG. The human output characteristics (light-current conversion characteristics) are the second [
As shown in F(bl), the characteristic that the bias voltage of the appropriate bias voltage source 5 hardly changes with respect to fluctuations in the vicinity of the value 5 of the bias voltage source 5 is utilized.

When a load resistor 3.26 is connected to both the cathode and anode terminals of the PIN/photodiode 1 and the bias voltage of the bias voltage source 5 is applied, P
A signal output 32.33 proportional to the amount of light incident on the PIN photodiode 1 can be obtained from both ends of the resistor 3.26 connected to each terminal of the IN photodiode 1. In addition, as shown in FIG. 3(b), PI
When the amplifying means 34 is connected to the anode side of the N photodiode 2, a signal output of 35° 36 proportional to the amount of incident light can be obtained from the resistor 4 on the cathode side and the output of the amplifying means 34, respectively.

When an amplifier using an electronic circuit is connected to a PIN/photodiode used as an optical-to-electrical conversion element as an electric signal amplification means, the input high-ass of the amplifier and the noise inside the amplifier are It acts as a noise 40 to the source.

As shown in Figure 4(a), the PIN/photodiode 1
Considering the case where noise 40 is added to one side of the poor load resistor 26 on the anode terminal side of , the change in the amount of incident light shown in (a) of Figure 4 (bl) is due to the influence of noise 40 shown in (b) , the signal output 33 on the anode terminal side becomes a signal containing noise as shown in (c).

However, the photo-current conversion characteristics of the PIN photodiode 1 are hardly affected by fluctuations in the bias voltage of the bias voltage source 5, so as shown in (d), the PIN photodiode 1
The signal output 32 obtained from the cathode terminal side of the photodiode 1 is hardly affected by noise, and a signal proportional to the amount of light incident on the PIN/photodiode 1 can be obtained.

Similarly, in the configuration shown in FIG. 3, even if noise is added to the cathode terminal of the PIN/photodiode, the signal detected from the anode terminal will hardly be affected by the noise.

FIG. 5 shows another embodiment of the information signal detector of the present invention. FIG. 5 shows an example in which both photodiodes 1.2 have four-divided light-receiving surfaces, and the divided light-receiving surfaces 1a, lb, lc, ld
are connected in parallel. With this configuration, the same type of photodiodes 1 and 2 can be used, reducing variations in optical-to-electrical signal conversion characteristics between photodiodes 1 and 2, and at the same time reducing the variation necessary for manufacturing the optical head. The number of types of components can be reduced, and costs can also be reduced.

〔Effect of the invention〕

As explained above, by using the information signal detector of the present invention, even if a simple optical system that serves both the information signal detection and the light beam position control signal detection is used, the focal position error between the information signal and the light beam can be reduced. , it is possible to detect information signals that prevent interference with amplifiers and the like that detect tracking position error signals and obtain high-quality information signals.

[Brief explanation of the drawing]

Fig. 1 is a configuration diagram showing an embodiment of the information signal detector of the present invention; Fig. 2 is a diagram showing input/output characteristics of a photodiode to explain the operation of the detector according to the invention; Fig. 3; 4 is a diagram showing the main part when obtaining a signal output proportional to the amount of incident light, FIG. 4 is a diagram also showing the case where there is noise, and FIG. 5 is a configuration showing another embodiment of the present invention. 6 are diagrams showing the configuration of an information signal detector used in a magneto-optical recording/reproducing head according to a previous application filed by the present applicant. 1.2...Photodiode 3.4.26...Resistor 5...Bias voltage source 6.7...Light beam 10...Differential amplification means 11...Information signals 20-23. ... Addition means 24, 25 ... Subtraction means 30 ... Focus position error signal 31 ... Tracking position error signal

Claims (1)

[Claims] (1) An information signal detector that reads information recorded on a magnetic recording medium by detecting the rotation of the polarization plane of reflected light or transmitted light of a light beam irradiated on the recording medium. The information signal and the control signal for positioning the light beam on the information track of the recording medium are detected from one terminal and the other terminal of a photodiode that converts the intensity of the light beam into an electrical signal, respectively. An information signal detector characterized by: