JP2007179741A - Optical device and optical disk device using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: In conventional focus servo control based on a focus error signal by an astigmatism method, there is a problem that an error is caused in a focus error signal due to an offset caused by an asymmetry of intensity distribution of return light, and a focus servo operation cannot be performed correctly. It was.
A signal derived from a relationship between a positional shift amount between a light receiving surface and a light receiving beam generated in a tangential direction on a photodetector and a lens shift amount of an objective lens is expressed as a flat plate type optical element or a hologram optical device. Corrected by the offset due to asymmetry of the intensity distribution of the return light generated by passing through the element, obtain the integrated value with a predetermined constant, and subtract this calculated value from the calculation formula of the conventional astigmatism method Focus servo control is performed based on the focus error signal.
[Selection] Figure 5

Description

  The present invention relates to an optical device that observes the surface shape and distance of an object using a light beam from a light source such as a laser, and a CD (Compact Disc), DVD (Digital Versatile Disc), The present invention relates to an optical disc apparatus that records and reproduces information on an MD (Mini Disc), an optical disc capable of high-density recording, and the like.

  Techniques for measuring the distance to an object using a laser beam and focusing the laser beam are widely used. Here, as an example, an optical disc apparatus that writes and reads digital data using an optical information recording medium (hereinafter referred to as an optical disc) will be described.

  In an optical disc apparatus that records information on an optical disc and reproduces the recorded information, a light beam emitted from a light source such as a laser is focused on the optical disc via an objective lens, and the focused state is maintained. In addition, a focus error signal corresponding to the positional deviation between the focal point of the light beam on the optical disc and the recording surface of the optical disc is generated based on the electrical signal obtained by detecting the reflected beam from the optical disc on a plurality of light receiving surfaces. As a control signal, focusing servo control is performed so that the objective lens is driven in the optical axis direction to be focused.

  On the other hand, optical disk devices are capable of large-capacity recording as semiconductor laser technology advances and microfabrication technology improves, and they are becoming widespread not only in computer data recording but also in audio, video, and other fields. Particularly in recent years, the amount of data handled, such as moving image information, has increased dramatically, and the pitch of a line (hereinafter referred to as a track) in which information signals and information signals on an optical disk are linearly connected in the rotation direction of the optical disk is reduced. Increasing the capacity of optical disk devices is further advancing due to the trend toward shorter wavelengths of semiconductor lasers.

  In such a background, in order to accurately record on an optical disc or to reproduce recorded information signals, an optical device having a light collecting function that is not affected by variations in manufacturing, position displacement of components due to aging, etc. Equipment is needed.

As a typical focus error detection method for generating a focus error signal, there is an astigmatism method.
The astigmatism method is not only an optical disk device, but also an optical device that performs focus error detection and correction, a measuring instrument that observes the surface shape of an object by detecting changes in the focus error signal as a minute distance change from the distance This is a focus error detection method widely used in optical devices such as instruments.

  In the astigmatism method, a light beam condensed by an objective lens or the like is irradiated onto an object (in the optical disk device, an optical disk), and astigmatism is given to the reflected light beam from the reflection surface of the object, for example, After being converted into a convergent beam by a lens or the like, the direction is set according to the direction of occurrence of astigmatism, and light is received by a light receiving surface divided into four by intersecting dividing lines, and a pair of output signals from each light receiving surface is paired. A focus error signal is generated by subtracting two sets of sum signals obtained by adding the corner components.

  The level of this focus error signal changes according to the distance between the focal point of the light beam and the reflecting surface of the object, and the focal point of the light beam and the reflecting surface of the object (in the optical disc apparatus, the recording surface of the optical disc) match. Sometimes, the light beam on the light receiving surface is almost the minimum circle of confusion, and the position of the light receiving surface and the light receiving beam is adjusted so that the output value of the focus error signal is a predetermined value close to zero. Shows the characteristic that the polarity is reversed depending on whether the focal point is forward or backward with respect to the recording surface of the optical disc.

That is, when the focal point of the objective lens scans from a point sufficiently far ahead of the recording surface of the optical disk to a point far enough backward, a focus error signal waveform that changes in an S shape is obtained. This is called “S-curve waveform”.
In particular, in an optical disc apparatus that performs a reproduction / recording operation on an optical disc, the objective lens is driven in the focal direction so that the focus error signal becomes a predetermined value (for example, zero), thereby condensing the recording surface of the optical disc and the objective lens. Focusing servo control is performed so that the focused light beam is in focus.

However, in this method, the positional deviation of the reflected light beam with respect to the four-divided light receiving surface is oblique with respect to the dividing line of the light receiving surface due to insufficient adjustment of the position of the light receiving surface and optical components during optical assembly of the optical disk device or due to change over time. When it occurs in the direction, the focus error signal does not coincide with the predetermined value when the recording surface of the optical disc and the focal position of the light beam become equal.
That is, an offset occurs in the focus error signal, and if focusing servo control is performed in the same manner as described above, there is a problem that the light beam causes a defocus on the recording surface of the optical disk.

  Therefore, a correction signal is generated by multiplying the sum difference signal of the left and right pairs of the photodetector and the sum difference signal of the upper and lower pairs, and the focus error signal by the conventional astigmatism method is corrected by this correction signal. However, even if this countermeasure is used, there is a positional shift of the received light beam in an oblique direction with respect to the dividing line of the four-divided light receiving surface. If an offset due to the asymmetry of the intensity distribution of the reflected light beam occurs, a focus error signal cannot be obtained correctly, and therefore focusing servo control cannot be performed.

Japanese Patent Laid-Open No. 10-64080 (FIG. 7, Formula 4)

  The present invention has been made in order to solve the above-described problems. The position shift of the light receiving beam with respect to the light receiving surface divided into four parts due to insufficient positioning adjustment or time-dependent adjustment of the light receiving surface and optical components during assembly of the apparatus, Or, the positional deviation of the light receiving beam with respect to the light receiving surface that occurs when the objective lens moves (hereinafter referred to as the lens shift) in the radial direction of the optical disk (hereinafter referred to as the radial direction), or the intensity distribution of the reflected light beam becomes asymmetric. It is an object of the present invention to provide an optical apparatus and an optical disk apparatus including a focus error signal generation circuit that generates a focus error signal that does not cause a defocus even when an offset due to the occurrence occurs.

  An optical apparatus and an optical disc apparatus according to the present invention include a light source that emits a light beam, a condensing unit that condenses the light beam on an object, and an astigmatism in the return light beam reflected from the object. The astigmatism adding means to be added, the light receiving area divided into four by the first dividing line and the second dividing line intersecting each other, and the astigmatism added by the astigmatism adding means An optical unit having a light detector that detects the light quantity of the return light beam in the light receiving area and converts it into an electric signal, and an electric signal corresponding to the light quantity detected from the four light receiving areas output from the optical unit Among them, the amount of focus error of the light beam collected by the light collecting means with respect to the object is detected using a diagonal sum difference signal obtained by subtracting the addition signals of the signals of the light receiving regions located diagonally to each other. Scorching In the optical apparatus including the error detecting unit, the astigmatism adding unit includes a return light condensing unit that condenses the return light beam, and light of the return light beam collected by the return light condensing unit. A planar optical element disposed at an angle with respect to the axis, wherein the return light beam is transmitted through the planar optical element, and among the four light receiving regions, the light receiving adjacent to the first dividing line. A first control signal generating means for detecting a first control signal by taking a difference between the added light amounts detected in the areas, adjacent to the second dividing line among the four light receiving areas; And a second control signal generating means for detecting a second control signal by taking a difference between the addition values obtained by adding the light amounts detected in the light receiving area. The first control signal and the second control signal Astigmatism is added to the control signal. The diagonal sum difference signal is corrected by an offset due to the asymmetry of the intensity distribution of the returned light beam, and an integrated signal obtained by multiplying the corrected first control signal, second control signal, and a predetermined constant. It is characterized by correcting.

  According to the optical apparatus and the optical disk apparatus of the present invention, it is possible to detect the focus error of the light beam on the optical disk and to cause an asymmetry of the intensity distribution of the returning light beam caused by passing through the flat plate type optical element or the hologram optical element. Even if an offset occurs, there is an effect that defocusing does not occur.

Embodiment 1 FIG.
FIG. 1 is a schematic diagram showing a configuration of an optical disk device according to Embodiment 1 of the present invention, and FIG. 2 is a schematic diagram showing a light receiving state on a four-divided light receiving surface of a photodetector 12.
The configuration will be described with reference to the drawings. A light beam 2 emitted from a semiconductor laser 1 as a light source is converted into parallel light by a collimator lens 3, deflected to a light beam 5 directed in the + z-axis direction by an internal reflection surface of a deflection prism 4, and then a condensing unit. Is focused on the optical disk 6 by the objective lens 7.

  The objective lens 7 is mounted on a two-dimensional actuator 8 which is a focused spot optical axis direction moving means and a focused spot optical axis vertical direction moving means. The z-axis direction) and the radial direction (same y-axis direction) of the optical disc 6 can be driven.

The light beam reflected by the optical disk 6 passes through the objective lens 7 and the deflecting prism 4 again and is converted into a convergent beam by the objective lens 9. This convergent beam is added with astigmatism by a cylindrical lens 11 which is astigmatism adding means, and a light beam 10 is generated. When astigmatism is given, when the optical disc 6 is in focus, the reflected light is irradiated on the light detector 12 in a substantially circular shape, and when the focus is shifted, an elliptical shape is used. An error is detected, but since this technique is well known, a detailed description thereof is omitted here.
The optical recording / reproducing unit including the above components is referred to as an “optical unit 13”.

  As shown in FIG. 2, the photodetector 12 receives the light beam 10 in a light receiving region divided into four by a dividing line Lx as a first dividing line and a dividing line Ly as a second dividing line, Electrical signals corresponding to the amounts of light received by these four light receiving surfaces are output to the focus error detection circuit 30 and the tracking error signal generation circuit 40.

The focus error detection circuit 30 includes a FESo generation circuit 31 that generates a FESo that is a diagonal sum difference signal of four light receiving surfaces, and a first control signal that is a difference between respective addition values of light receiving regions adjacent to the dividing line Lx. PX ₁ arithmetic circuit 32 is a first control signal generating means for detecting PX _1, a second control for detecting the second control signal PY is the difference between the respective sum values of the light-receiving region adjacent to the dividing line Ly A PY arithmetic circuit which is a signal generating means, DC offset correction circuits 34 and 35 for correcting offsets caused by asymmetry of the intensity distribution of the return light beams included in PX ₁ and PY, respectively, and a setting circuit 36 for a constant K _{1 to be} multiplied , PX ₁ offset is corrected respectively PY, and multiplication circuit 37 for generating an integrated signal of a constant K _1, the correction circuit 3 to correct the accumulated signal from the diagonal sum difference signal It is equipped with a.

  A control signal obtained by performing the above correction calculation is output to a focusing drive circuit 39 which is an optical axis direction drive circuit. The focusing drive circuit 39 drives the two-dimensional actuator 8 based on this control signal, moves the objective lens 7 in the optical axis direction (z-axis direction), and focuses the optical beam on the optical disc 6 so as to focus the optical beam. Outputs a drive signal.

  Although not shown, the focusing drive circuit 39 also has a function of switching between a focusing servo operation state and a focusing servo non-operation state as necessary for a recording / reproducing operation of the optical disc apparatus or an optical disc insertion / ejection operation.

  On the other hand, the tracking error signal generation circuit 40 is not described here, but is based on a tracking error detection method such as a push-pull method, a DPD method (phase difference method), or a differential push-pull method that has been often used conventionally. Then, a tracking error signal is generated and input to a tracking drive circuit 41 which is an optical axis vertical direction driving circuit. The tracking drive circuit 41 amplifies the tracking error signal, drives the two-dimensional actuator 8 to move the objective lens 7 in the radial direction of the optical disc 6, and sets the radial direction position of the light beam condensed on the optical disc. A tracking drive signal is output so as to follow the information track.

  Although not shown, the tracking drive circuit 41 moves the optical unit to the target recording area by dynamically moving the optical unit in the radial direction of the optical disk surface by an optical unit feeding means such as a recording / reproducing operation of the optical disk device or an external motor. A function of switching between a tracking servo operation state and a tracking servo non-operation state according to a so-called seek operation in which data access is performed.

FIG. 2 is a schematic diagram showing the four-divided light receiving surface of the photodetector 12 and the received light beam irradiated on the photodetector 12 as described above, and the four-divided light receiving surface is divided into a dividing line Lx intersecting with each other. The line Ly is divided into light receiving elements A, B, C, and D. In the configuration of the first embodiment, the dividing line Lx and the dividing line Ly are substantially parallel to the x axis and the y axis, respectively.
The areas of the light receiving beams irradiated to the light receiving elements A, B, C, and D are S _A , S _B , S _C , and S _D , respectively, and the light receiving beams detected by S _A , S _B , S _C , and _SD are used. the amount each _{P a, P B, P C} , is defined as _{P D.}
Note that the directions of the coordinate axes x, y, and z correspond to the directions of the coordinate axes x, y, and z shown in FIG. Further, the symbols x in FIG. 1 and z in FIG. 2 indicate the direction perpendicular to the paper surface (the front direction on the paper surface is +).

  As shown in FIG. 2A, the optical beam 6 is ideally positioned in the z-direction position so that the light beam 10 is almost in the minimum circle of confusion due to the effect of astigmatism while the optical beam 6 is in focus. It is adjusted and fixed on the xy plane so that the amount of light received by each of the light receiving elements A, B, C, D on the four-divided light receiving surface is substantially equal.

Next, the operation will be described. First, a conventional focusing servo operation based on focus error detection and its problems will be described.
As is well known, the focus error signal by the conventional astigmatism method is obtained by the diagonal sum difference signal FESo = (P _A + P _C ) − (P _B + P _D ) on the photodetector 12. As shown in FIG. 2 (a), if the state in which the focal point of the light beam 5 is coincident with the optical disk _6, because it is _{P A = P B = P C} = P D, the FESo is becomes zero, focusing There is no change in the operating point of the servo, and the light beam 5 continues to be focused on the optical disk 6.

Next, when the optical beam 6 is not focused on the optical disc 6 in this state, the shape of the light receiving beam irradiated on the photodetector is affected by astigmatism due to the cylindrical lens, and FIG. As shown in FIG. 3, the light receiving surface has an elliptical shape extending diagonally. In this case, since P _A = P _C , P _B = P _D , and P _A ≠ P _B , FESo is a value other than zero, and control is performed so that this FESo is zero (that is, FIG. 2A). Thus, the optical beam 6 can be correctly focused on the optical disc 6.

If the received light beam on the light receiving surface is adjusted to an ideal position with no positional deviation in the y direction, the received light beam on the light receiving surface on the dividing line Lx as shown in FIG. Therefore, P _A = P _D , P _B = P _C and no focus offset occurs in the focus error signal by the conventional astigmatism method, and based on this, the focusing servo is maintained so that FESo maintains zero. Even if it is operated, the operating point of the focusing servo does not change in principle, and the light beam 5 can continue to be focused on the optical disk 6.

  The reason why the received beam moves on the dividing line Lx is as follows. That is, in the astigmatism method, the z-direction position of the light detector 12 is arranged at a position where the light beam 10 is almost in the minimum circle of confusion, so that the y axis on the optical disk 6 is reversed 90 degrees on the light detector 12. This is because the received beam on the photodetector 12 moves in the x direction when it is projected on the x-axis and thus the objective lens 7 is lens-shifted in the y direction.

Here, in the state where the light receiving surface of the light detector 12 and the light receiving beam are displaced in the y-axis direction due to insufficient positioning adjustment of the light receiving surface and optical components during the assembly of the device or due to changes over time, the light receiving beam is split by lens shift. When the position shifted from the line Lx by a certain distance in the y-axis direction is moved substantially parallel to the dividing line Lx, the dividing line Lx and the dividing line Ly are detected from the intersection of the dividing line Lx and the dividing line Ly as shown in FIG. As a result, the received light beam is moved in an oblique direction. In this case, even in a focused state, that is, in a state where the light-receiving beam shape on the photodetector is a circle, as shown in FIG. 2D, FESo = (P _A + P _C ) − (P _B + P _D ) is not zero.

In the conventional method, since this FESo is controlled to be zero, as a result, as shown in FIG. 2 (e), as shown in FIG. In this state, FESo = 0, and the light receiving beam cannot maintain the state of the minimum circle of confusion that was initially adjusted. As a result, the light beam 5 is defocused on the optical disk surface.
The defocus causes various characteristics such as the amplitude of the tracking error signal, the quality of the reproduction signal, and the recording performance.

Further, FIGS. 2 (a) and 2 state that the focus as shown in (c) is correct, that is, in the state received light beam forms on the light detector has a circular, and a light-receiving area S _{A +} S _C even if the value of S B ₊ S _D are equal, when the intensity distribution of the return light beams by unbalance of the optical system are varied asymmetrical varies the amount of light detected by the light detector, and P a ₊ P _C The values of P _B + P _D are not equal, and as a result, FESo does not become zero and the focusing servo operation cannot be performed correctly.
The above is the conventional focusing servo operation by the focus error detection and its problems.

Next, the operation of the first embodiment of the present invention will be described.
The FESo generation circuit 31 in the focus error detection circuit 30 of FIG. 1 performs the same calculation as the focus error signal of the so-called conventional astigmatism method, and FESo = (P _A + P) which is a diagonal sum difference signal. _C )-(P _B + P _D ) is calculated and output. The PX ₁ calculation circuit 32 calculates and outputs PX ₁ = (P _A + P _D ) − (P _B + P _C ). The PY arithmetic circuit 33 calculates and outputs PY = (P _A + P _B ) − (P _C + P _D ). In the DC offset correction circuit 34 and 35, is corrected by the offset amount _{V DX} and _{V DY,} respectively due to the asymmetry in the intensity distribution of the returned light beam PX ₁ and PY. These outputs and the gain K ₁ multiplied by the multiplication circuit 37, focus error detection circuit 30 a calculation value FES obtained by correcting the output signal of FESo generating circuit 31 by the integrated value is output.

However, K ₁ can take a positive value or a negative value depending on the setting of the direction of astigmatism added by the cylindrical lens 11, and the multiplication circuit and the correction circuit are constituted by amplification circuits that are positive and negative, respectively. An operation can be performed on a signal having a value of.
The operation of the focus error detection circuit 30 described above is shown in Equation (1).

_{FES = FESo- K 1 × (PX} 1 + V DX1) × (PY + V DY) ··· (1)
here,
FESo = (P _A + P _C ) − (P _B + P _D )
PX ₁ = (P _A + P _D ) − (P _B + P _C )
PY = (P _A + P _B ) − (P _C + P _D )
V _DX1 : Offset amount relating to the dividing line Ly V _Dy : Offset amount relating to the dividing line Lx K ₁ : Constant

The constant K ₁ may be set so that the defocus due to the lens shift is almost zero (optimum value), but it is not always necessary to make the defocus zero in the entire range of the lens shift, that is, the lens shift. for the required range of small or optical disk device and an acceptable optical disk apparatus has tolerance to defocus amount, the gain value K ₁ is not necessarily the optimal value, the deviation from the optimum value in accordance with the system of the optical disk apparatus It was also set the gain value K _1, defocus incurred lenses shift in conventional astigmatism method can be obtained an effect of suppressing.

According to the inventor's consideration, if the optimum value of K ₁ is expressed by K _best , 0 <| K ₁ | ≦ 2 × | K _best | is effective as the setting range of the gain value for obtaining the defocus suppression effect. It is.
This setting range is the same also in the gain value in another embodiment described later.

The focus error signal FES obtained by Expression (1) is input to the focusing drive circuit 39, and the two-dimensional actuator 8 is driven in the optical axis direction (z-axis direction) of the objective lens 7 so that FES = 0.
Here, the meanings of PX ₁ and PY in Expression (1) will be described.
PY is a calculated value of (P _A + P _B ) − (P _C + P _D ), but (P _A + P _B ) is the sum of the amounts of light on the left side of the photodetector, as shown in FIG. _C + P _D ) is the sum of the right light quantity. Taking this difference can be considered as a value corresponding to a left-right shift of the light-receiving beam with respect to the light-receiving surface. Furthermore, PX ₁ is a calculated value of (P _A + P _D ) − (P _B + P _C ), and can be considered as a value corresponding to the vertical deviation of the received beam with respect to the light receiving surface. Therefore, a value obtained by multiplying the PY and PX ₁ can be said to be an amount corresponding to the moving amount with respect to the diagonal direction of the light receiving surface of the light receiving beam.

For example, even if the received beam moves on Lx, the left and right movement amounts are zero, so PY = (P _A + P _B ) − (P _C + P _D ) = 0, and there is no movement amount in the diagonal direction. On the other hand, even if it moves on Ly, since the vertical movement amount is zero, PX ₁ = (P _A + P _D ) − (P _B + P _C ) = 0, and it is determined that there is no movement amount in the diagonal direction. To do. In that case, as shown in FIG.2 (c), it can control by the same calculation as the conventional FESo.

The mathematical formula (1) is effective when the received light beam is shifted in the diagonal direction of the light receiving surface as shown in FIG. 2D. In this case, the constant K ₁ is appropriately set. As a result, correction can be performed with the value of the second item of the formula (1), and the FES can be made zero even in the state of FIG. 2D. As a result, the light beam 5 is correctly collected on the optical disc 6. Can continue to shine.

Further, since offsets V _DX and V _DY due to the asymmetry of the intensity distribution of the light beam returning to PX ₁ and PY are corrected, even if the intensity distribution of the return light beam varies, the light receiving surface of the light receiving beam It is possible to correctly detect the horizontal and vertical deviations relative to

  According to the first embodiment, it is possible to suppress defocus on the optical disk surface that has occurred during lens shift, enable focusing servo control in a wide lens shift range, Due to insufficient positioning adjustment of the optical components and changes over time, the received beam may be misaligned, or the received beam may be misaligned with the light receiving surface during the lens shift operation, or an offset may be caused by the asymmetry of the intensity distribution of the reflected light beam. However, defocus does not occur, and the reliability of the optical disc apparatus or optical apparatus can be improved, and the adjustment cost and manufacturing cost can be reduced.

Further, it is possible to remove the magnifying lens that has been used in the past in order to reduce the deviation of the light receiving beam on the light receiving surface, and to reduce the number of parts and the cost of the optical disk device or optical device.
Furthermore, even if the misalignment direction between the light receiving surface and the light receiving beam is an arbitrary direction including an oblique direction with respect to the dividing line of the light receiving surface, the defocus on the optical disk can be almost zero. The direction of the dividing line does not necessarily have to coincide with the lens shift direction of the objective lens 7, and design restrictions can be eliminated.

  Furthermore, when there is a positional deviation between the light receiving beam and the light receiving surface, when the light beam crosses a guide groove provided along the information track of the optical disc or a record mark row recorded in the information track. The crosstalk generated on the conventional astigmatism focus error signal due to the influence of the change in the diffracted light of the light beam can be suppressed at the same time. It is possible to stabilize the focusing servo control during the seek operation traversed by.

Furthermore, when the positional deviation between the light receiving beam and the light receiving surface in the conventional astigmatism method occurs, the peak value balance of the S-curve waveform generated in principle is improved, and focusing servo due to disturbances such as vibration and impact is improved. Detachment is less likely to occur and the focusing servo operation can be stabilized.
In addition to the astigmatism addition function, the cylindrical lens 11 may have a lens function for guiding the focal point of the light beam 10 to an optimal position. In this case, the objective lens 9 can be omitted, and the device can be omitted. It can be simplified.

Further, when formula (1) is expanded, formula (2) is obtained.
_{FES = FESo- K 1 × PX 1} × PY-K 1 × V DX1 × PY-K 1 × V DY × PX 1
―K ₁ × V _DY × V _DX1 (2)
Needless to say, the mathematical formula (2) may be used.

Embodiment 2. FIG.
FIG. 3 is a schematic diagram showing the configuration of an optical disc apparatus according to Embodiment 2 of the present invention.
The points different from the first embodiment will be mainly described. In the figure, an objective lens position sensor 100, which is a position sensor that detects a movement amount of the two-dimensional actuator 8 in the radial direction as a direction perpendicular to the direction along the optical axis of the light beam, is a voltage corresponding to the lens shift amount. Is output. Therefore, this voltage value can be said to be a value corresponding to the lens shift amount of the objective lens 7.

In the lens shift amount detection circuit 51, the output signal V _LS of the objective lens position sensor 100, calculates a value PX ₂ which corresponds to the vertical displacement with respect to the light receiving surface of the light receiving beam changes in accordance with the lens shift amount. This PX ₂ corresponds to PX ₁ in the formula (1). Using the data described above, the focus error detection circuit 50 performs the calculation of Expression (3).

_{FES = FESo- K 2 × (PX} 2 + V DX2) × (PY + V DY) ··· (3)

Equation (3) is, _{PX 2} instead of PX ₁ of Equation _{(1), V DX2} the offset _{V DX1,} which gain value _{K 1} was _{K 2,} that is, the position sensor a change in PX due to the lens shift 100 This information is used as a substitute to suppress defocusing at the time of lens shift, and V _{DX2 and} K ₂ are matched with the output of the position sensor 100. Since other configurations and operations are the same as those of the first embodiment, description thereof is omitted.

According to the second embodiment, the position sensor 100 is required, but in addition to the effect of the first embodiment, it is not necessary to perform the calculation of PX ₁ , so that the calculation can be simplified.
If the output signal V _LS of the objective lens position sensor 100 is matched with the subsequent circuit, the lens shift amount detection circuit 51 may be removed. In this case, the configuration can be further simplified. Of course, the output from the position sensor 100 may be a current.

Embodiment 3 FIG.
FIG. 4 is a schematic diagram showing the configuration of an optical disc apparatus according to Embodiment 3 of the present invention.
The points different from the first embodiment will be mainly described. In the figure, the tracking drive circuit 41 outputs a drive signal for moving the two-dimensional actuator 8 in the radial direction as a direction perpendicular to the direction along the optical axis of the light beam. Since the objective lens 7 is moved in the radial direction by this drive signal, this drive signal can be said to be a value corresponding to the lens shift amount of the objective lens 7.

In the lens shift amount detection circuit 61 calculates a value PX ₃ corresponding to the upper and lower deviation of the light receiving surface of the light receiving beam changes in accordance with the lens shift amount from the drive signal. This PX ₃ corresponds to PX ₁ in the formula (1). Using the data described above, the focus error detection circuit 60 performs the calculation of Expression (4).

_{FES = FESo- K 3 × (PX} 3 + V DX3) × (PY + V DY) ··· (4)

Equation (4) is, PX ₁ instead of the _{PX 3} in Equation _(1), which the offset _{V DX1} and _{V DX3,} the gain value _{K 1} and _{K 3,} i.e. tracking drive a change in the PX ₁ due to the lens shift The drive signal from the circuit 41 is used instead to suppress defocusing during lens shift, and V _{DX3 and} K ₃ are matched with the output of the tracking drive circuit 41. Since other configurations and operations are the same as those of the first embodiment, description thereof is omitted.

According to the third embodiment, in addition to the effects of the first embodiment, it is not necessary to perform the calculation of PX ₁ , so that the calculation can be simplified.

  If the drive signal from the tracking drive circuit 41 is matched with the subsequent circuit, the lens shift amount detection circuit 61 may be removed. In this case, the configuration can be further simplified.

  Further, instead of the drive signal from the tracking drive circuit 41, the offset value of the push-pull method or the DPD method tracking error signal generated by the tracking error signal generation circuit 40 in principle according to the lens shift amount, or A configuration using any of the offset values of the sub-beam push-pull signal required in the DPP tracking error detection method may be used. In this case, a signal output from the tracking error signal generation circuit 40 is input to the lens shift amount detection circuit 61 instead of the output of the tracking drive circuit 41 shown in FIG.

Embodiment 4 FIG.
In each of the above embodiments, the cylindrical lens 11 is used as means for adding astigmatism. However, astigmatism may be added by a flat plate half mirror in place of the cylindrical lens 11. An example of this is shown in FIG.
The points different from the first embodiment will be mainly described. In the figure, a light beam 2 emitted from a semiconductor laser 1 is deflected in a + z-axis direction by a flat plate half mirror 21 which is a flat plate optical element, and then converted into a parallel light beam 5 by a collimator lens 22. 7 is condensed on the optical disk 6.

The light beam reflected by the optical disk 6 is transmitted again through the objective lens 7, the collimator lens 22, and the flat plate half mirror 21, and the received light beam is condensed on the photodetector 12. The flat plate half mirror 21 is disposed so as to be inclined with respect to the optical axis of the return light beam.
The optical recording / reproducing unit including the above components is referred to as an “optical unit 23”.

  In this example, astigmatism is given by arranging the flat plate half mirror 21 so as to be inclined with respect to the optical axis. However, the shape of the light receiving beam on the light receiving surface of the light detector 12 is distorted or the light intensity is increased. Since the distribution is asymmetric, even if the light receiving surface and the light receiving beam of the light detector 12 are adjusted so that PY = 0 in a state where there is no lens shift, the offset amount due to the difference in the light amount of each light receiving element on the light receiving surface. As a result of the PY calculation, the value is as if the received light beam is shifted in the y-axis direction of the light receiving surface, and in the conventional astigmatism method, defocus on the optical disk occurs due to lens shift.

That is, the offset of the intensity distribution of the reflected light beam is largely offset, so that the effect of the present invention can be greatly obtained.
The other configuration is the same as that of the first embodiment, and is omitted.

  In the above example, the flat half mirror 21 is used as a means for adding astigmatism. However, a plurality of light sources are integrated to record and reproduce different types of optical disks using a plurality of light sources. Using a light emitting element, at least one light source is designed and arranged off the axis of the objective lens or collimator lens, or a light beam is wavelength-selectively bent by a diffraction element such as a hologram optical element to divide the optical path from a plurality of light sources. Even when the emitted light beam is received by a common light receiving surface and a focus error signal is generated, the shape of the light receiving beam on the light receiving surface is distorted or the light intensity distribution is asymmetrical. It goes without saying that the same effect can be obtained by performing servo control.

  In order to confirm the effect of the fourth embodiment, the inventor makes the light beam 5 on the optical disc 6 generated by the lens shift with respect to the initial positional deviation amount between the light receiving surface of the light detector 12 and the light receiving beam. The amount of defocus generated in the case of the conventional astigmatism method and the focusing servo operation of the fourth embodiment was calculated by simulation and compared.

Simulation conditions.
In the simulation, the numerical aperture NA of the objective lens was 0.6, the wavelength was 650 nm, the focal length of the objective lens was 3.36 mm, and the focal length of the collimator lens was 21.4 mm.
Here, as an indicator of the amount of positional deviation between the light receiving surface of the light detector 12 and the light receiving beam, the light quantity balance BX = ((A + D) − (B + C)) / (A + B + C + D) in the x direction, The light quantity balance BY = ((A + B)-(C + D)) / (A + B + C + D) is defined and expressed as a percentage value.

  The initial misalignment conditions of the light receiving surface and the light receiving beam with respect to the x-axis direction are as follows: (a) BX = −25%, (b) BX = 0%, (c) BX = + 25%, and (a) to (c ) Were simulated under the conditions of BY = ± 25%, 0%, and ± 15%.

simulation result.
The result of using the conventional astigmatism method is shown in FIG. Since the shape of the received light beam is distorted, the lens shift is asymmetrical with respect to 0 or BY = 0. Even if BY = 0, the influence of lens shift appears.
Also, a large defocus is likely to occur when BX is negative and the lens shift amount is in the negative direction (that is, lens shift toward the inner periphery), or BX is positive and the lens shift amount is in the positive direction (that is, the outer periphery side). Lens shift), and the amount of defocus generated under the above two conditions becomes the limit value of the lens shiftable range of the optical disc apparatus and the allowable range of misalignment between the photodetector 12 and the received light beam, As a result, the performance range of the optical disk device is narrowed.

Next, the result by Embodiment 4 is shown in FIG. In this case, it can be seen that even if either BX or BY is changed, the defocusing that has been a problem in the conventional astigmatism method hardly occurs.
The effect of Embodiment 4 was confirmed also from the result of the above simulation.

Embodiment 5 FIG.
In each of the above-described embodiments, the calculation formula of the focus error signal is specifically shown. Therefore, it is conceivable to realize it by, for example, software suitable for device development. Here, an example in which a hardware logic circuit is used as the implementation method will be described.
FIG. 8 is a schematic diagram showing the configuration of an optical disc apparatus according to Embodiment 5 of the present invention. In this example, since the first embodiment is realized by a hardware logic circuit, the same reference numerals are given to those having the same functions and operations as those in FIG. 1 showing the configuration of the first embodiment. The description of the operation is omitted. For the sake of simplicity, the calculation section of the focus error signal is mainly described.

PY = (P _A + P _B ) − (P _C + P _D ) output from the PY arithmetic circuit 33 is corrected for the offset, converted into a digital value by the A / D converter 130, and the switch setting value arithmetic unit 131. Is input. In the switch setting value calculation unit 131, the absolute value of Ke = K ₁ × (PY + V _DY ) corresponding to the coefficient of PX ₁ of Equation (1) described in the first embodiment, which is calculated based on the value of PY | Ke | And the polarity are calculated, and the set value RT1 and the set value RT2 corresponding to the absolute value | Ke | and the polarity are determined and sent to the gain value register 132 and the polarity value register 133, respectively.

The gain value register 132 and the polarity value register 133 hold the set value RT1 and the set value RT2, respectively, and send them to the input terminal CTL1 of the switch type variable resistor 134 and the input terminal CTL2 of the switch circuit 139.
The switch type variable resistor 134 is a variable resistor that can switch the resistance value between the input terminal IN and the output terminal OUT to N types of resistance values R _{1 to} R _N according to a value set in the control terminal CTL _1. The combination of the resistor 135 having the value Ro and the amplifier 136 constitutes an amplification stage having N types of gain values from R ₁ / R _{o to} R _N / R _o .

In the above configuration, since N types of gain values that can be switched are limited, the analog signal value output from the offset correction circuit 35 is actually R ₁ / R in the switch setting value calculation unit 131. _It is set to the set value RT1 and the set value RT2 that are associated with the gain values that are as close as possible among the N types of gain values of _{o to} R _N / R _o .

  The switch circuit 137 switches and outputs either the output signal from the amplification stage constituted by the switch type variable resistor 134, the resistor 135 having the resistance value Ro, and the amplifier 136 or the GND level. The switch circuit 139 Based on the value from the polarity value register 133, one of the two types of input is selectively output. In the configuration in which the inverting circuit 138 is arranged on one of the input terminals of the switch circuit 139, a signal obtained by inverting or non-inverting the output of the switch circuit 137 in the preceding stage is switched and output.

On the other hand, the output signal of the PX ₁ arithmetic circuit 32 is corrected for the offset, input to the amplifier 136 via the resistor 135, and amplified after being amplified at a magnification corresponding to the set value RT1 (ie, absolute value | Ke |). As described above, the output signal 140 having the polarity determined according to the set value RT2 (that is, the polarity of Ke) is output. The subtractor 141 generates a difference signal between the output signal FESo of the FESo generation circuit 31 and the output signal 140, and the difference signal is input to the focusing drive circuit 39.

  The focusing drive circuit 39 drives the two-dimensional actuator 8 provided in the optical unit 13 to move the objective lens 7 in the optical axis direction (z-axis direction) so that the differential signal maintains a predetermined value. A focusing drive signal is output so that the light beam is focused on the optical disk 6.

The amplifier 136, the inverting circuit 138, and the subtracter 141 have an input range and an output range that range from positive to negative, and can amplify or calculate a signal having a positive and negative value, respectively.
The operation of FIG. 8 described above will be described based on the flowchart shown in FIG.
The operation procedure of the flowchart shown in FIG. 9 is assumed to start immediately before entering the focusing servo operation, and will be described in order.

  When the optical disk 6 is inserted into the optical disk apparatus, the switch circuit 137 is connected to GND (step S1), and only the FESo output from the FESo generating circuit 31 is input to the subtractor 141.

  Next, the focusing drive circuit 39 is turned ON, and focusing servo control for the optical disk 6 is started by the optical unit 13 (step S2). At this time, the focusing drive circuit 39 amplifies the focus error signal FESo output from the subtractor 141 with an initially determined servo gain and outputs the amplified signal as a focusing drive signal. The dimension actuator 8 is driven. At this time, focusing servo control is performed so that the focus error signal FESo becomes zero, and electrical focus offset correction is not performed.

After the above operation, the PY value obtained by the offset correction circuit 35 is read (step S3), and the set value RT1 is set by the switch set value calculation unit 131 according to the PY value converted into a digital value by the A / D converter 130. And set value RT2 is determined (step S4).
The set value RT1 and the set value RT2 determined above are temporarily stored in the gain value register 132 and the polarity value register 133, respectively, and then sent to the switch-type variable resistor 134, and the switch type corresponding to the set value RT1. At the same time that the gain value of the variable resistor 134 is switched, the switch circuit 139 is switched in accordance with the set value RT2 (step S5).

Then, connect the switching circuit 137 to the amplifier 136 (step S6), PX ₁ value output from the offset correction circuit 34 to input the substantially Ke multiplied output signal 140 to the subtractor 141. In step 6, the signal calculated by FESo-Ke × PX ₁ is output from the subtracter 141 and input to the focusing drive circuit 39. At this time, the focus error signal FES = FESO-Ke × PX _{1 is used} for focusing. Servo operation will be started.

  After the above operation is completed, an offset is electrically applied to the focus error signal FES in the focusing drive circuit 39 so that the quality of the recording / reproducing signal (for example, recording / reproducing signal jitter value) is the best in the focusing drive circuit 39. Giving (step S7), the focus offset is adjusted. Further, a procedure may be inserted in which the step of optimally adjusting the focusing servo gain is inserted before or after step S7 so that the servo operation becomes more stable.

  According to the fifth embodiment, in addition to the effects of the first embodiment, it is not necessary to use a multiplication circuit, so that the effect of suppressing the defocus of the light beam on the optical disk 6 can be obtained with a simpler circuit configuration. it can.

  In the fifth embodiment, the example of the first embodiment has been described. However, the same effect can be obtained even when applied to the second to fourth embodiments. In that case, the coefficient Ke obtained by the switch set value calculation unit may be appropriately set so as to correspond to each embodiment.

  The optical unit 13 may be the optical unit 23 including the flat plate half mirror 21 described in the fourth embodiment.

In the above embodiments, PX ₁ = (P _A + P _D ) − (P _B + P _C ) and PY = (P _A + P _B ) − (P _C + P _D ) are received by the quadrant light receiving surface of the photodetector. _A value normalized by dividing by the total amount of light (P _A + P _B + P _C + P _D ) may be used. In this case, since it is possible to suppress the variation of the optimum gain value caused by the change in the total light amount, it is possible to obtain a defocus suppression effect with substantially the same gain value, for example, for optical disks having different reflectivities.

_{Further, (P A -P B),} (P D -P C), and were normalized them in light intensity sum _{(P A -P B) / (} P A + P B), and _(P D _-P C) Since / (P _C + P _D ) changes similarly to PX ₁ with a lens shift in a very small range, each of them can be used as a substitute for PX ₁ .
On the other _{hand, (P A -P D),} (P B -P C), and were normalized them in light intensity sum _{(P A -P D) / (} P A + P D), and _(P B _-P C) Since / (P _B + P _C ) changes in the same range as PY with lens shift in a minute range, each can be used as a substitute for PY.

Further, in the adjustment of the photodetector 12 in the xy plane, an optical unit having an initial position offset in the y-axis and x-axis directions so that PY = −V _{DY and} PX ₁ = −V _DX is used. For example, by simply applying a focus error detection circuit in which the DC offset correction circuit is omitted to the optical disc apparatus, it is possible to achieve a focus shift caused by distortion of the shape of the received beam and asymmetry of the light intensity distribution, and a conventional astigmatism method. It is possible to suppress defocusing that occurs in principle.

  Furthermore, there is no distinction between Lx, which is the first dividing line, and Ly, which is the second dividing line, in the first place. Therefore, no matter what direction the light-receiving beam moves on the photodetector 12, By performing this calculation, the influence of the offset can be reliably removed. That is, as shown in FIG. 2C, an example is shown in which the received light beam on the photodetector 12 moves in parallel to the dividing line Lx (or Ly) by lens shift, but is not parallel to the dividing line. Also good. In that case, since the restrictions on the arrangement of the optical system are relaxed, there is a further effect that the apparatus can be downsized.

  Furthermore, in each of the above embodiments, an example of application in the optical disk device has been described. However, any configuration in which reflected light from an object is received by a light detector and a defocus of the light beam with respect to the object is detected. For example, it is needless to say that the characteristics of defocus can be similarly improved even when applied to an optical device that measures the surface shape and distance of an object other than an optical disk.

1 is a configuration diagram of an optical disc device according to Embodiment 1 of the present invention. FIG. It is a top view which shows the light-receiving surface of the photodetector by Embodiment 1 of this invention. It is a block diagram of the optical disk apparatus by Embodiment 2 of this invention. It is a block diagram of the optical disk apparatus by Embodiment 3 of this invention. It is a block diagram of the optical disk apparatus by Embodiment 4 of this invention. 10 is a graph showing defocusing at the time of lens shift by conventional focus error detection in the configuration of Embodiment 4 of the present invention. It is a graph which shows the focus shift at the time of lens shift by Embodiment 4 of this invention. It is a block diagram of the optical disk apparatus by Embodiment 5 of this invention. It is a flowchart which shows the operation | movement step by Embodiment 5 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Semiconductor laser, 2 Light beam, 3 Collimator lens, 4 Deflection prism, 5 Light beam, 6 Optical disk, 7 Objective lens, 8 Two-dimensional actuator, 9 Objective lens, 10 Light beam, 11 Cylindrical lens, 12 Optical detector, 13 Optical unit, 21 Flat plate half mirror, 22 Collimator lens, 23 Optical unit, 30 Focus error detection circuit, 31 FESo generation circuit, 32 PX ₁ arithmetic circuit, 33 PY arithmetic circuit, 34 Offset correction circuit, 35 Offset correction circuit, 36 Gain setting circuit, 37 multiplication circuit, 38 correction circuit, 39 focusing drive circuit, 40 tracking error signal generation circuit, 41 tracking drive circuit, 50 focus error detection circuit, 51 lens shift amount detection circuit, 52 gain setting circuit, 60 focus error Detection circuit, 6 1 lens shift amount detection circuit, 62 gain setting circuit, 100 a position sensor, Lx dividing line, Ly dividing lines, A light-receiving element, B light-receiving element, C the light receiving element, D receiving element, _{P A} light amount, _{P B} quantity, _{P C} quantity, _{P D} quantity, _{S A} light receiving area, _{S B} light-receiving area, _{S C} light receiving area, _{S D} light receiving area.

Claims (11)

A light source that emits a light beam,
Condensing means for condensing the light beam on an object;
Astigmatism adding means for adding astigmatism to the return light beam reflected by the light beam from the object;
The light receiving region is divided into four by a first dividing line and a second dividing line that intersect each other, and the light quantity of the return light beam to which astigmatism is added by the astigmatism adding means A light detector that detects in the area and converts it into an electrical signal,
An optical unit with
Of the electrical signals corresponding to the light amounts detected in the four light receiving areas output from the optical unit, the diagonal sum difference signal obtained by subtracting the addition signals of the signals of the light receiving areas located diagonally to each other is used. A focus error detecting means for detecting a focus error amount of the light beam collected by the light collecting means for the object;
In an optical device comprising:
The astigmatism adding means includes a return light condensing means for condensing a return light beam, and a flat plate type arranged to be inclined with respect to the optical axis of the return light beam collected by the return light condensing means. An optical element, and the return light beam is transmitted through the flat plate optical element,
A first control signal generation for detecting a first control signal by taking the difference of the added values obtained by adding the light amounts detected in the light receiving areas adjacent to the first dividing line among the four light receiving areas. means,
Second control signal generation for detecting a second control signal by taking the difference of the added values obtained by adding the light amounts detected in the light receiving areas adjacent to the second dividing line among the four light receiving areas. means,
Further comprising
The first control signal and the second control signal are corrected by an offset due to an asymmetry of the intensity distribution of the return light beam to which the astigmatism is added, and the corrected first control signal and An optical apparatus, wherein the diagonal sum difference signal is corrected by an integrated signal obtained by multiplying a second control signal by a predetermined constant. A light source that emits a light beam,
Condensing means for condensing the light beam on an object;
Astigmatism adding means for adding astigmatism to the return light beam reflected by the light beam from the object;
The light receiving region is divided into four by a first dividing line and a second dividing line that intersect each other, and the light quantity of the return light beam to which astigmatism is added by the astigmatism adding means A light detector that detects in the area and converts it into an electrical signal,
An optical unit with
Of the electrical signals corresponding to the light amounts detected in the four light receiving areas output from the optical unit, the diagonal sum difference signal obtained by subtracting the addition signals of the signals of the light receiving areas located diagonally to each other is used. A focus error detecting means for detecting a focus error amount of the light beam collected by the light collecting means for the object;
In an optical device comprising:
The astigmatism adding means is a hologram optical element in which a diffractive surface is formed on at least one of an incident surface and an output surface, and
A first control signal generation for detecting a first control signal by taking the difference of the added values obtained by adding the light amounts detected in the light receiving areas adjacent to the first dividing line among the four light receiving areas. means,
Second control signal generation for detecting a second control signal by taking the difference of the added values obtained by adding the light amounts detected in the light receiving areas adjacent to the second dividing line among the four light receiving areas. means,
Further comprising
The first control signal and the second control signal are corrected by an offset due to an asymmetry of the intensity distribution of the return light beam to which the astigmatism is added, and the corrected first control signal and An optical apparatus, wherein the diagonal sum difference signal is corrected by an integrated signal obtained by multiplying a second control signal by a predetermined constant.   The optical apparatus according to claim 1, wherein the integrated signal is normalized by a total value of light amounts received by four light receiving regions of the photodetector. A converging spot optical axis direction moving means for moving a focal position of a condensing spot formed on the object by the light beam condensed by the condensing means in a direction along the optical axis of the light beam; focus error; An optical axis direction drive circuit that generates a drive signal used to drive the focused spot optical axis direction moving means based on a focus error amount detected by the detection means;
The optical apparatus according to claim 1, further comprising: A converging spot optical axis vertical direction for moving the focal position of the condensing spot formed on the object by the light beam condensed by the condensing means in a direction perpendicular to the direction along the optical axis of the light beam. transportation,
An optical axis vertical direction drive circuit for generating a drive signal used for moving the focal position of the focused spot in a direction perpendicular to the direction along the optical axis of the light beam;
The optical apparatus according to claim 1, further comprising:   It further has a position sensor for detecting the amount of movement of the condensing means in a direction perpendicular to the direction along the optical axis of the light beam, and the first control signal or the second control signal is an output of the position sensor. The optical apparatus according to claim 5, wherein the optical apparatus is a signal.   6. The first control signal or the second control signal is a drive signal that is output from an optical axis vertical direction drive circuit and drives a focused spot optical axis vertical direction moving means. Optical device.   The direction in which the return light beam moves on the photodetector corresponds to the direction in which the focused spot by the focused spot optical axis vertical direction moving means moves on the object. The optical apparatus according to claim 1, wherein the optical apparatus is not parallel to any of the lines.   9. The optical object recording medium according to claim 1, wherein the object is an optical information recording medium configured such that information data is recorded on or reproduced from a spiral or circular information track. An optical disk apparatus, wherein the information data is recorded or reproduced by the optical apparatus. Radial position control means for driving the light collecting means in the radial direction of the optical information recording medium;
A tracking error signal detecting means for generating a tracking error signal generated by combining the amounts of light received in the respective light receiving regions of the photodetector;
Further comprising
The first control signal or the second control signal is:
10. The optical disc apparatus according to claim 9, wherein the optical disc apparatus is an offset value of the tracking error signal generated by the tracking error signal detection means.   11. The optical disc apparatus according to claim 10, wherein the tracking error signal detecting means detects the tracking error signal by any one of a phase difference method, a push-pull method, and a differential push-pull method.

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