JP4193028B2 - Optical pickup and optical disk drive - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical pickup and an optical disc driving apparatus provided in an optical disc drive or the like for recording and reproducing signals on an optical recording medium.
[0002]
[Prior art]
In recent years, optical disk drives (optical disk drive devices) have been demanded to be miniaturized on the premise that they are mounted on small information terminals together with a demand for higher density. Development in pursuit of computerization is actively conducted.
FIG. 7 is a cross-sectional view illustrating a configuration example of an optical integrated device on which a laser light source and a light detection device mounted on an optical pickup are mounted.
As shown in the figure, this optical integrated device includes an element substrate 10, a laser diode (hereinafter referred to as LD) 11, a FAPC photodetector (hereinafter referred to as PD) 12, a reproduction signal detection PDIC 13, a rising mirror 14, a λ / A two-plate 15, a grating 16, a hologram 17, a lid 18, a laminated prism 19, a mold composite element 20 and the like are mounted.
Here, a part of the light emitted from the LD 11 and transmitted through the rising mirror 14 is reflected by the lid 18 and then enters the FAPC PD 12.
In this optical integrated device, by using an optical system that detects the amount of light without using a condensing lens, the optical path length can be shortened, and the optical pickup can be further miniaturized.
[0003]
[Problems to be solved by the invention]
However, in such an optical integrated device, as shown in FIG. 8, if the light emitted from the LD 11 is efficiently incident on the PD 12 without condensing, a large area PD is required. When the area of the PD 12 is increased, the capacitance between terminals is increased, and there is a problem that the frequency characteristics of the light detection output of the PD 12 are deteriorated.
In addition, when the optical pickup is miniaturized, the distance between the LD and the PD is shortened. Therefore, in general, a high-frequency driving current applied to the LD to reduce the LD noise is also propagated to the PD, so that accurate light quantity detection is performed. There was a problem of preventing.
[0004]
For the latter problem of being affected by noise from the LD, for example, as disclosed in Japanese Patent Laid-Open No. 6-37556, a PD output device devised to reduce the influence of amplifier noise is applied. Is possible. That is, since the output on the anode side and the output on the cathode side of the PD output device have opposite polarities, high-frequency noise from the LD leaking into the wiring is removed in phase by differential amplification at the subsequent stage. .
However, when such a noise removal method is used, the output on either the anode side or the cathode side has a large DC offset due to the influence of the reverse bias voltage applied by the PD. Since the optical signal reproduction PD uses only the output AC component, the influence of such DC offset can be avoided. For example, in the case of the FAPC PD shown in FIG. If there is a DC offset, it will be difficult to eliminate the influence of the high-band amplifier in the subsequent stage.
In other words, since the input / output voltage range is generally limited with respect to the power supply voltage in a high-band operational amplifier, the reverse bias voltage applied to the PD is limited when the DC offset is controlled within this range. Problems arise.
[0005]
SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an optical pickup and an optical disc driving apparatus that can improve the frequency characteristics of the light detection output and can reduce noise.
[0006]
[Means for Solving the Problems]
In order to achieve the above object, the present invention is an optical pickup for irradiating an optical recording medium with light emitted from a light source and detecting return light thereof, and a plurality of optical pickups arranged in an optical path after being emitted from the light source. The light detection element or a light detection element having a plurality of divided detection regions, and a light amount detection means for detecting a light amount of the light emitted from the light source using a detection output from the light detection element. A reverse bias voltage is applied to the element, and the reverse bias voltage is applied so that a terminal on the side where a signal output is obtained is close to a ground potential. Signal outputs having different polarities are obtained from the anode from the divided detection region and the other photodetecting element or the cathode from the other divided detection region .
Further, the present invention is an optical disc driving apparatus including an optical pickup that irradiates an optical recording medium with light emitted from a light source and detects return light thereof, and is disposed in an optical path after being emitted from the light source. A light detecting element having a plurality of light detecting elements or a plurality of divided detection regions, and a light amount detecting means for detecting a light amount of the light emitted from the light source using a detection output from the light detecting element, A reverse bias voltage is applied to the detection element, and the reverse bias voltage is applied so that a terminal on which a signal output is obtained is close to a ground potential, and the light amount detection means has a pair of signal outputs having different polarities. By means of differential amplification in the latter stage, the anode from one photodetecting element or one split detection area and the cap from the other photodetecting element or the other split detection area. Wherein the obtained polarity different signals output from each other and a over de.
[0007]
In the optical pickup and the optical disc driving device of the present invention, a plurality of light detection elements or light detection elements having a plurality of divided detection regions are arranged in the optical path of the divergent light after being emitted from the light source. The frequency characteristics of the light quantity detection output can be improved by lowering the inter-terminal capacitance and converting the current output from each photodetecting element or each divided detection area individually into a voltage.
Further, in the optical pickup and the optical disc driving apparatus of the present invention, the light output is obtained by taking out the signal output from one anode side of the plurality of light detecting elements or the plurality of divided detection regions and taking out the signal output from the other cathode side. Two signals having opposite polarities proportional to the amount of light incident on the element can be obtained.
For this reason, by differentially amplifying these two outputs by a subsequent circuit, it is possible to remove common-mode noise such as high-frequency jump noise into the wiring.
In this case, reverse bias is applied to the anode side terminal so as to keep the cathode side at a positive potential, and reverse bias is applied to the cathode side terminal so as to keep the anode side at a negative potential. As a result, both of the two outputs can obtain an output in the vicinity of the ground potential, so that the above-described problem of the DC offset of the output can also be solved.
Furthermore, by adjusting the gain of at least one of the two outputs having opposite polarities, it is possible to finely adjust so that the common-mode noise is minimized.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of an optical pickup and an optical disk drive according to the present invention will be described below.
The optical pickup according to the embodiment of the present invention reduces the inter-terminal capacitance of each PD element by arranging a plurality of small area PDs or multi-divided PDs in the optical path of the divergent light of the LD, The frequency characteristics of the light quantity detection output are improved by individually converting the current output of each element into a voltage.
Further, by taking out the signal output from the anode side of one element of a plurality of PDs or multi-division PDs and taking out the signal output from the cathode side of the other element, two signals having opposite polarities proportional to the amount of light incident on the PD are obtained. A signal can be obtained.
[0009]
Then, by differentially amplifying these two outputs with a subsequent circuit, common-mode noise such as high-frequency jump noise into the wiring can be removed. Further, in this case, a reverse bias is applied to the element that takes out the output from the anode so as to keep the cathode side at a positive potential, and the anode side is kept at a negative potential for the element that takes out the output from the cathode. Apply reverse bias. As a result, both of the two outputs can obtain an output in the vicinity of the ground potential, so that the above-described problem of the DC offset of the output can also be solved.
Further, if at least one of the two outputs having opposite polarities can be gain-adjusted, fine adjustment can be performed so that the common-mode noise is minimized.
[0010]
FIG. 1 is an explanatory diagram showing the configuration of an optical disk drive on which an optical pickup according to this embodiment is mounted with a main optical path as the center, and a configuration example including an optical integrated device similar to that shown in FIG. Show. However, in the present embodiment, the configuration of the PD portion of the optical integrated device and the configuration of the subsequent circuit are different.
First, the configuration of the optical integrated device 100 of this example is basically the same as that shown in FIG. 7, and the device substrate 110, the LD 111, the FAPC PD 112, the reproduction signal detection PDIC 113, the rising mirror 114, λ / 2 plate 115, grating 116, hologram 117, lid 118, laminated prism 119, mold composite element 120, and the like.
Further, a collimator lens 210, an anamorphic prism 220, an expander 230, a λ / 4 plate 240, and a two-group objective lens 250 are arranged in the optical path of the light emitted from the optical integrated device 100, and the optical disk supported by the spindle 300. The signal recording surface 310 is led.
[0011]
Hereinafter, the operation of the optical pickup having such a configuration will be described.
Most of the divergent light emitted from the LD is reflected by the rising mirror 114 90 degrees directly above, and then passes through the λ / 2 plate 115, the grating 116 on the mold composite element 120, and the PBS film 119A of the laminated prism 119. The light passes through to the collimator lens 210.
After collimated light is collimated by the collimator lens 210, the light is shaped by the anamorphic prism 220 and travels toward the expander lens 230.
The expander lens 230 is composed of a second group lens, and plays a role of correcting spherical aberration that appears prominently when a high NA objective lens is used by adjusting the distance between the two groups.
[0012]
The beam that has passed through the expander 230 is focused on the signal recording film on the optical disk 310 by passing through the λ / 4 plate 240 and the second group objective lens 250. Then, the beam whose light intensity is modulated by the change in reflectance of the phase change film on the optical disk 310 returns to the PBS film 119A of the laminated prism 119 through the same optical path, but is bent 90 degrees here and further totally reflected 90. Then, the light enters the PDIC 113 through the mirror 119B.
A hologram 117 is formed on the mold composite element 120 in front of the PDIC 113, and two side spots for focus servo are formed here.
[0013]
FIG. 2 is a front view showing a configuration example of the FAPC PD 112 which is a light detection element in this example.
The PD 112 is applicable to all the claims of the present invention. The PD 112 has a horizontally long light receiving portion 112A in order to efficiently detect the beam spot 400 having a horizontally long elliptical shape, and the light receiving portion 112A is divided into two in the longitudinal direction.
[0014]
In the claims of the present invention, the expressions “a plurality of light detection elements” and “a light detection element having a plurality of divided detection regions” are used. This is a difference between a unit and a photodetecting element having a plurality of light receiving units as a unit, and the two are not substantially different from each other.
Therefore, PD1 and PD2 of the light receiving section 112A shown in FIG. 2 may be regarded as independent photodetecting elements, and the light receiving section 112A of one photodetecting element is regarded as having two divided detection areas PD1 and PD2. May be.
Therefore, in the following description, each PD1 and PD2 is treated as an independent photodetecting element.
In addition, the PD substrate 112B on which the PD1 and PD2 are formed is provided with anode terminals 121A and 122A and cathode terminals 121B and 122B led from the PD1 and PD2.
[0015]
Next, the configuration and operation of the signal processing circuit for processing the detection signal by the FAPC PD 112 having such a structure will be described.
FIG. 3 is a block diagram showing a first example of the signal processing circuit in the present embodiment.
This signal processing circuit includes three operational amplifiers 510, 520, and 530.
The output of PD1 is taken out from the anode side and input to the inverting input terminal of the operational amplifier 510. The cathode side of PD1 is connected to Vcc (+ 5V) through a resistor (1k), and is connected to GND through a capacitor. It is connected to the.
On the other hand, the output of PD2 is taken out from the cathode side and inputted to the inverting input terminal of the operational amplifier 520. The anode side of PD2 is connected to VEE (−5V) via a resistor (1k), and the capacitor is connected to the PD2. Is connected to GND.
That is, the reverse bias voltage is applied to the two PD1 and PD2 so that the potential on the cathode side is high, but the output is not taken out so that the potential of the electrode from which the output is taken out is close to the ground. Positive and negative voltages are applied to the electrodes.
[0016]
The non-inverting input terminals of the operational amplifiers 510 and 520 are grounded, and negative feedback resistors R1 and R2 are provided, respectively. The output signals of the operational amplifiers 510 and 520 are output to the input terminal of the operational amplifier 530, and the operational amplifier 530 outputs a difference signal between them.
The output signals of the operational amplifiers 510 and 520 are connected to the input terminal of the operational amplifier 530 through resistors, respectively, but the resistance of the output terminal of one operational amplifier 510 is a variable resistor VR.
[0017]
In such a configuration, when light is incident on each PD1, PD2, currents IPD1, IPD2 flow in each PD1, PD2. The respective current outputs are converted into voltages Vpd1 and Vpd2 by current-voltage (IV) conversion resistors R1 and R2, respectively.
These voltages Vpd1 and Vpd2 are signals having opposite polarities, but leakage noise from the LD or the like leaks almost equally with respect to Vpd1 and Vpd2, so that the downstream of the optical pickup is disposed at a later stage. By differentially amplifying the voltages Vpd1 and Vpd2 with the amplifier, only the leakage component is canceled as the common mode noise (that is, the common mode noise leaking into the region indicated by A in the figure can be removed).
On the other hand, the gain of the voltage Vpd1 can be adjusted by the variable resistor VR. By this adjustment, high-frequency common-mode noise from the LD contained in Vpd1 and Vpd2 can be more strictly removed.
[0018]
FIG. 4 is a block diagram showing a second example of the signal processing circuit in the present embodiment. The configurations shown in FIGS. 1 and 2 other than the signal processing circuit are common in this example.
In this example, the outputs of PD1 and PD2 are directly coupled to the non-inverting input and the inverting input of the operational amplifier 540 at the subsequent stage. The output of PD1 is extracted from the anode side and input to the non-inverting input terminal of the operational amplifier 540, and the output of PD2 is extracted from the cathode side and input to the inverting input terminal of the operational amplifier 540. The non-inverting input terminal of the operational amplifier 540 is grounded via the IV conversion resistor R1, and the inverting input terminal of the operational amplifier 540 is connected to the output terminal via the IV conversion resistor R2.
[0019]
With such a configuration, there is an advantage that a differential output can be obtained with one operational amplifier. However, in general, since the high-band current output cannot make the wiring length so long, an amplifier must be arranged in the vicinity of the PD. If noise leaks into the signal after passing through the amplifier, the common mode can be removed. This configuration also has the demerit that it cannot be performed (that is, the region where common-mode noise can be removed becomes small as shown in FIG. 3B).
Further, in the configuration of this example, the gain cannot be finely adjusted by the variable resistor, but it is possible to realize the same function by making R1 or R2 a variable resistor, for example (not so much). is there.
In the example shown in FIGS. 3 and 4 above, two PD1 and PD2 (same in the case of multi-division PD) are arranged in one optical path, but the optical path is divided into a plurality of optical paths. The light quantity may be detected by a plurality of PDs.
[0020]
FIG. 5 is a block diagram showing a third example of the signal processing circuit in the present embodiment.
This example also shows a PD signal processing circuit. In particular, only one PD is used, and the gain adjustment function by the variable resistor VR is added to the circuit configuration of the above-mentioned JP-A-6-37556. Yes. Therefore, the description of the configuration of the PD itself is omitted.
As shown in FIG. 5, this signal processing circuit includes three operational amplifiers 610, 620, and 630. An IV conversion resistor R1 is disposed on the cathode side of one PD, and an IV conversion resistor R2 is disposed on the anode side. Is arranged. However, in this configuration, since a large DC offset occurs in the cathode side output, a positive voltage Vcc (+5 V) is applied to the inverting input side of the operational amplifier 610 in the subsequent stage to cancel the generation of the offset.
[0021]
As can be seen from FIG. 5, in a high-band operational amplifier driven at ± 5 V, the input / output voltage range is usually about ± 2.5 to 3 V, so that it can be applied to the PD as in this example. Therefore, the reverse bias voltage Vc is limited to + 2.5V.
Also in this example, similar to the example shown in FIGS. 3 and 4, the common-mode noise can be more strictly removed by finely adjusting the variable resistor VR (that is, in the region indicated by C in the figure). Leaked common mode noise can be removed).
In addition, the configuration of the signal processing circuit according to this example can be applied to the optical integrated element of the optical pickup shown in FIG. 1 described above, but particularly applicable to a configuration using one PD as a photodetecting element. It is. However, the present invention can also be applied to a configuration in which one of a plurality of PDs or one detection area of a multi-division PD is used.
[0022]
FIG. 6 is a block diagram showing a fourth example of the signal processing circuit in the present embodiment.
The signal processing circuit of this example includes three operational amplifiers 640, 650, and 660, and uses only one PD as in the configuration shown in FIG.
The output from the anode side of the PD is coupled to the inverting input of one amplifier 640 and the non-inverting input of the other amplifier 650 of the two amplifiers 640 and 650 in the subsequent stage.
Therefore, since two amplifiers 640 and 650 can obtain two outputs V and −V having different polarities, if these are differentially amplified by the amplifier 660 disposed away from the optical pickup, the wiring between them can be obtained. The common-mode noise that leaks can be canceled in the same manner as the examples shown in FIGS. 3 to 5 described above (that is, the common-mode noise leaked into the region indicated by D in the figure can be removed).
Also in this example, the in-phase noise can be more strictly removed by finely adjusting the variable resistor VR.
The configuration of the signal processing circuit according to this example can be applied to the above-described optical integrated device of the optical pickup shown in FIG. 1, but can be applied particularly to a configuration using one PD as a photodetecting device. It is. However, the present invention can also be applied to a configuration in which one of a plurality of PDs or one detection area of a multi-division PD is used.
Further, in this example, the PD is arranged in the divergent light. However, even if the PD is arranged in the convergent light obtained after passing through the lens, the size of the pickup is increased, but the PD in FIGS. Similarly, the detection circuit has the effect of increasing the output bandwidth and removing common-mode noise. Therefore, such a configuration is also included in the present invention.
[0023]
【The invention's effect】
As described above, according to the optical pickup and the optical disk drive device of the present invention, a plurality of light detection elements or light detection elements having a plurality of divided detection regions are arranged in the optical path of the diverging light after being emitted from the light source. As a result, the inter-terminal capacitance of the light detection element is reduced, and the current output from each light detection element or each divided detection region is individually voltage-converted, thereby improving the frequency characteristics of the light amount detection output. is there.
In addition, according to the optical pickup and the optical disc driving device of the present invention, by taking out the signal output from one anode side of the plurality of light detection elements or the plurality of divided detection regions, and taking out the signal output from the other cathode side, Two signals with opposite polarities proportional to the amount of light incident on the photodetecting element can be obtained. For example, by differentially amplifying these two outputs with a subsequent circuit, noise such as high-frequency jump noise into the wiring can be obtained. There is an effect that common-mode noise can be removed.
Furthermore, according to the optical pickup and the optical disk drive device of the present invention, the gain can be adjusted for at least one of the two outputs having opposite polarities so that the common mode noise can be finely adjusted. There is an effect that can.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram showing a configuration of an optical disk drive equipped with an optical pickup according to an embodiment, with a main optical path as a center.
FIG. 2 is a front view showing a configuration example of a FAPC PD of the optical pickup shown in FIG.
FIG. 3 is a block diagram showing a first example of a signal processing circuit in the optical pickup shown in FIG. 1;
4 is a block diagram showing a second example of a signal processing circuit in the optical pickup shown in FIG. 1. FIG.
FIG. 5 is a block diagram showing a third example of a signal processing circuit in the optical pickup shown in FIG. 1;
6 is a block diagram showing a fourth example of a signal processing circuit in the optical pickup shown in FIG. 1. FIG.
FIG. 7 is a cross-sectional view showing a configuration example of an optical integrated device on which a laser light source and a light detection device mounted on an optical pickup are mounted.
8 is an enlarged cross-sectional view showing a light detection portion of the optical integrated device shown in FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 100 ... Optical integrated device, 110 ... Element substrate, 111 ... LD, 112 ... FAPC PD, 113 ... Reproduction signal detection PDIC, 114 ... Rising mirror, 115 ... λ / 2 plate, 116 ...... grating 117 ...... hologram, 118 ...... lid 119 ...... laminated prism, 120 ...... mold composite elements, 210 ...... collimator lens, 220 ...... anamorphic prism, 230 ...... expander, 240 ...... lambda / 4 plates, 250... 2 group objective lens, 300... Spindle, 310... Optical disk, 400 .. beam spot, 510, 520, 530, 540, 610, 620, 630, 640, 650, 660.

Claims (6)

An optical pickup that irradiates an optical recording medium with light emitted from a light source and detects its return light,
A plurality of photodetectors arranged in the optical path after being emitted from the light source or a photodetector having a plurality of divided detection regions;
A light amount detecting means for detecting a light amount of light emitted from the light source using a detection output from the light detection element;
A reverse bias voltage is applied to the photodetecting element, and the reverse bias voltage is applied so that a terminal on the signal output side is near the ground potential,
The light amount detecting means includes means for differentially amplifying a pair of signal outputs having different polarities from each other in the subsequent stage, so that one of the light detection elements or the anode from one of the divided detection regions and the other light detection element or Obtain signal outputs with different polarities from the cathode from the other split detection region,
An optical pickup characterized by that. 2. The optical pickup according to claim 1, wherein the light quantity detecting means includes means for adjusting a gain of at least one of the signal outputs having different polarities. 2. The optical pickup according to claim 1, wherein the light source is a semiconductor laser. An optical disc driving apparatus including an optical pickup that irradiates an optical recording medium with light emitted from a light source and detects return light thereof
  A plurality of photodetectors arranged in the optical path after being emitted from the light source or a photodetector having a plurality of divided detection regions;
A light amount detecting means for detecting a light amount of light emitted from the light source using a detection output from the light detection element;
A reverse bias voltage is applied to the photodetecting element, and the reverse bias voltage is applied so that the terminal on the signal output side is near the ground potential,
The light amount detecting means includes means for differentially amplifying a pair of signal outputs having different polarities from each other in the subsequent stage, so that one of the light detection elements or the anode from one of the divided detection regions and the other light detection element or Obtain signal outputs with different polarities from the cathode from the other split detection region,
An optical disk drive characterized by the above. 5. The optical pickup according to claim 4, wherein the light quantity detection means includes means for adjusting a gain of at least one of the signal outputs having different polarities. The optical pickup according to claim 4, wherein the light source is a semiconductor laser.

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