JP2006286140A - Optical pickup and optical information processor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a compact optical pickup and optical information processor by concentrating optical components and specifying movable parts. <P>SOLUTION: An expander optical system 104 is a two-group construction of two lenses. A lens 104a is a single lens of a positive refracting power, whereas a lens 104b is a single lens of a negative refracting power and they are placed on an optical axis of an emitted light from a semiconductor laser 101. A diffraction grating is formed on a face on the side of an optical recording medium 110 of the lens 104b, a light flux from a light source is divided into three beams of a zero order diffracted light and ± primary diffracted lights, and a main beam of zero diffracting light and sub-spot of the ± primary diffracted light form three spots linearly with equal intervals on a recording surface of the optical recording medium 110. By dynamic control of each lens of the expander optical system 104, the spots of the three beams are on-truck positions in accordance with the kind of the optical recording media. Also in accordance with the respective optical recording media, a spherical aberration deterioration equivalency quantity caused by a substrate thickness error and a coma aberrantion deterioration equivalency quantity due to tilt are corrected to obtain an optimum characteristic. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an optical pickup and an optical information processing apparatus that perform at least one of information recording, reproduction, and erasing on a plurality of types or multilayer optical recording media.

  As means for storing video information, audio information, or data on a computer, optical recording media such as a CD with a recording capacity of 0.65 GB and a DVD with a recording capacity of 4.7 GB are becoming widespread. In recent years, there has been an increasing demand for further improvement in recording density and increase in capacity.

  As means for increasing the recording density of such an optical recording medium, in an optical pickup for writing or reading information on the optical recording medium, the numerical aperture (hereinafter referred to as NA) of the objective lens is increased, or the light source It is effective to reduce the diameter of the beam spot that is collected by the objective lens and formed on the optical recording medium by shortening the wavelength.

  Therefore, for example, in the “CD optical recording medium”, the NA of the objective lens is 0.50 and the wavelength of the light source is 780 nm, whereas the recording density is higher than that of the “CD optical recording medium”. In the “DVD optical recording medium”, the NA of the objective lens is 0.65 and the wavelength of the light source is 660 nm. As described above, the optical recording medium is desired to further improve the recording density and increase the capacity. For this purpose, the NA of the objective lens is set to be larger than 0.65 or the wavelength of the light source is increased. It is desired to make it shorter than 660 nm.

  Two standards have been proposed for such a large-capacity optical recording medium and optical information processing apparatus. One is a standard of “Blu-ray Disc” that satisfies the capacity securing of 22 GB by using a light source in a blue wavelength region and an objective lens of NA 0.85 as described in Non-Patent Document 1. Hereinafter referred to as BD). The other is the “HD-DVD” standard which has the same blue wavelength as described in Non-Patent Document 2, but satisfies a capacity of 20 GB using an objective lens of NA 0.65. (Hereinafter referred to as HD).

The former increases the capacity by shortening the wavelength and increasing the NA, compared to the DVD system, and the latter allows the linear recording density to be improved by improving signal processing instead of increasing the NA. To increase the capacity by narrowing the track pitch.
JP 2001-312831 A JP 2001-357550 A Manju Oku, 8 other people, “What Blu-ray Disc aims”, Nikkei Electronics, No. 2003.03.31, p.135-150 Naoshi Yamada, 4 others, “Next generation specification born from DVD“ HD DVD ”, Nikkei Electronics, 2003.10.13, p.125-134

  Thus, the two standards using a light source in the blue wavelength band have been proposed. However, as a user, it is desirable that these two standards of optical recording media can be handled by the same optical information processing apparatus without distinction.

  As the simplest method, there is a method of mounting a plurality of optical pickups. However, with this method, it is difficult to achieve downsizing and cost reduction. Therefore, an optical pickup that can perform recording or reproduction with a common light source and a common objective lens for two blue standards having different substrate thicknesses and NAs is desired.

  There are various methods for detecting a track error (hereinafter referred to as TE) signal in an optical information processing system. As a typical method, a DPP (differential push-pull) method is known. In the DPP method, as shown in FIG. 24, the spots of the three beams are arranged on the recording surface of the optical recording medium linearly and at equal intervals by shifting the track pitch by 1/2 track pitch in the track lateral direction at the position in the track longitudinal direction. The reflected light of the main spot m1 located on the track (groove) is detected by the four-divided light receiving element, the sub spot s1 located on the inner peripheral land adjacent to the track where the main spot m1 is located, and the main spot The reflected light of the sub-spot s2 located on the outer peripheral land adjacent to the track on which m1 is located is detected by the two-divided light receiving element, and the detection signal is added and subtracted for each of the four-divided light receiving element and the two-divided light receiving element. To obtain three push-pull signals and calculate the TE signal with a predetermined arithmetic expression so as to cancel these offsets. It is.

  The three spots are obtained by irradiating an optical recording medium by dividing one light beam emitted from a light source into at least three light beams of 0th order diffracted light and ± 1st order diffracted light by a diffraction grating. . The three spots formed on the optical recording medium by the light beam emitted from the optical pickup are tracked by arranging the diffraction grating in the optical pickup with the grating direction inclined at a predetermined angle with respect to the disk radial direction. As a result, the three spots can be obtained in an arrangement shifted by ½ track pitch in the left-right direction of the track at the position in the front-rear direction of the track.

  The DPP method is also used for the two standards of the blue recording medium, but the track pitch is different between the two media. For example, the track pitch of the HD-DVD standard (HD) is 0.45 μm while the track pitch of the Blu-ray Disc standard (BD) is 0.3 μm. When two diffraction gratings corresponding to each are inserted, diffracted light on the unused side becomes flare light. Therefore, a method of rotating one diffraction grating about the optical axis can be considered (see Patent Documents 1 and 2).

  As a problem outside the optical pickup, the occurrence of aberration associated with the tilt (tilt) of the optical recording medium or the thickness error of the transparent substrate is known. This is because when the wavelength of the light source is shortened and the numerical aperture (NA) of the objective lens is increased, that is, as the spot focused on the optical recording medium is densified to increase the density, the margin decreases.

  Also, spherical aberration occurs due to the thickness error of the transparent substrate of the optical recording medium. When this spherical aberration occurs, the spot formed on the information recording surface of the optical recording medium deteriorates, so that normal recording / reproducing operation cannot be performed. The spherical aberration caused by the thickness error of the transparent substrate of the optical recording medium is generally expressed by the following (Equation 1).

与えられる。ここで、λは使用波長、ＮＡは対物レンズの開口数、ｎは光記録媒体の等価屈折率、Δｔは球面収差が最小となるスポット位置からの光軸方向へのずれを表す。

Given. Here, λ is the wavelength used, NA is the numerical aperture of the objective lens, n is the equivalent refractive index of the optical recording medium, and Δt is the deviation in the optical axis direction from the spot position where the spherical aberration is minimized.

  FIG. 25A shows the amount of each aberration associated with the substrate thickness error of the optical recording medium in an optical recording medium (BD) having NA of 0.85, a substrate thickness of 0.1 mm, and a working wavelength of 405 nm. In FIG. 25A, SA represents spherical aberration, COMA represents coma, AS represents astigmatism, TOTAL represents the total value of these third-order aberrations, and STREHL represents the peak intensity of the spot. FIG. 25B shows the amount of each aberration associated with the substrate thickness error of the optical recording medium in an optical recording medium (HD) having NA of 0.65, substrate thickness of 0.6 mm, and operating wavelength of 405 nm.

  In general, it is known from experience that a wavefront aberration value needs to be smaller than a Marechal criterion (0.07 λrms) in reading a signal from an optical recording medium. The wavefront aberration includes aberrations of an objective lens and an optical recording medium. Therefore, the allowable amount of W40 rms is required to be less than or equal to 1/2 of about 0.07 λrms. Further, the substrate thickness error of the optical recording medium needs to allow a forming tolerance of about ± 10 μm, and the optical recording medium (BD) needs to be corrected.

  Further, coma aberration occurs depending on the tilt (tilt) of the optical recording medium. When this coma aberration occurs, the spot formed on the information recording surface of the optical recording medium is deteriorated, so that normal recording / reproducing operation cannot be performed. The coma generated by the tilt of the optical recording medium is generally expressed by the following (Equation 2).

で与えられる。ここで、ｎは光記録媒体の透明基板の屈折率、ｄは透明基板の厚み、ＮＡは対物レンズの開口数、λは光源の波長、θは光記録媒体のチルト量を意味する。

Given in. Here, n is the refractive index of the transparent substrate of the optical recording medium, d is the thickness of the transparent substrate, NA is the numerical aperture of the objective lens, λ is the wavelength of the light source, and θ is the tilt amount of the optical recording medium.

  FIG. 26A shows the amount of each aberration associated with the tilt of the optical recording medium in an optical recording medium (BD) having an NA of 0.85, a substrate thickness of 0.1 mm, and a working wavelength of 405 nm. Similarly, FIG. 26B shows the amount of each aberration associated with the tilt of the optical recording medium in the optical recording medium (HD) having NA 0.65, substrate thickness 0.6 mm, and operating wavelength 405 nm.

  As described above, it is known from experience that when reading a signal from an optical recording medium, the wavefront aberration value needs to be smaller than the Marechal criterion (0.07λrms). Since it is necessary to consider the aberration caused by the thickness error of the optical recording medium, the allowable amount of W31 rms is required to be less than or equal to 1/2 of about 0.07 λrms. Further, it is necessary to expect a tilt of about ± 0.3 deg from the manufacturing tolerance of the optical recording medium and the mounting accuracy of the optical recording medium, and correction is required for the optical recording medium (HD).

  As described above, in the optical pickup that records and / or reproduces both the optical recording medium (BD) and the optical recording medium (HD), the correction of the sub-spot position of the three beams generated due to the difference in the track pitch of each medium is corrected. There is a need to do. Further, it is necessary to correct both the spherical aberration that occurs due to the substrate thickness error of the optical recording medium (BD) and the coma aberration that occurs due to the tilt of the optical recording medium (HD). In any case, a dynamic movable mechanism is required, and providing a movable mechanism for each of them has a problem of increasing the number of components and increasing the size of the optical pickup.

  The present invention is directed to solving the problems of the prior art, and aims to provide an optical pickup and an optical information processing apparatus that are miniaturized by consolidating optical components and specifying movable parts. To do.

  In order to achieve the above object, an optical pickup according to a first aspect of the present invention includes a first optical recording medium having a wavelength λ1, a substrate thickness t1, a used numerical aperture NA1, a wavelength λ1, a substrate thickness t2 ( > T1) In an optical pickup for recording and / or reproducing information with respect to a second optical recording medium having a numerical aperture NA2 (<NA1), a light source and a light beam from the light source are condensed on the optical recording medium And an expander optical system in which a diffraction grating that divides a light beam into three beams is formed on any one surface of the objective lens, and first and second lenses. Drive means for driving each lens of the expander optical system based on a discrimination signal for discriminating one of the optical recording media.

  Furthermore, the optical pickup according to claim 2 is the optical pickup according to claim 1, wherein when the expander optical system recognizes the second optical recording medium, the optical pickup is converged as compared with the first optical recording medium. An over-spherical aberration caused by light is generated.

  In the optical pickup according to claim 3, the information recording surface is formed with a p layer (p ≧ 2) in the thickness direction, and the (pq) layer on the near side near the objective lens is an information recording layer with a narrow track pitch. In an optical pickup for recording and / or reproducing information on an optical recording medium comprising an information recording layer having a wide track pitch, the q layer on the far side from the objective lens is a light source and a light flux from the light source is recorded on the optical recording medium. An expander optical system that includes an objective lens for condensing light and two lenses having different refractive powers, and a diffraction grating that divides a light beam into three beams is formed on one surface of the lens; drive means for driving each lens of the expander optical system based on a selection signal for selecting one of the p-q) to q layers.

  The optical pickup according to claim 4 is the optical pickup according to claim 3, wherein the expander optical system selects convergent light when selecting the near (pq) layer close to the objective lens of the optical recording medium. The under spherical aberration due to the above is generated, and when the q layer farther from the objective lens is selected, the over spherical aberration due to the convergent light is generated as compared with the (pq) layer.

The optical pickup according to any one of claims 5 to 8 is the optical pickup according to any one of claims 1 to 4, wherein the drive means of the expander optical system emits a lens formed with a diffraction grating that divides the light beam into three beams. First driving means for rotating about the axis, second driving means for moving at least one lens of the expander optical system in the optical axis direction, and at least one lens of the expander optical system for the optical axis orthogonal plane And a third drive unit that is movable in the radial direction of the optical recording medium, and further, the first drive unit of the expander optical system has three beams on the optical recording medium in the assembly process of the optical pickup. The first neutral point in the on-track state is stored, and the second and third driving means determine the second and third neutral points in the best state of aberration or the information signal in the optical pickup assembly process. Record The lens surface that initially moves the lens to the first to third neutral points stored at the time of setting the optical recording medium, and further forms a diffraction grating that divides the light beam of the expander optical system into three beams is provided by the expander. Of the four lens surfaces of the optical system, the lens surface has the largest radius of curvature, or the lens surface is a plane. The optical pickup according to claim 9 is characterized in that: 4 is characterized in that the optical recording medium has an information recording surface at a thickness position of at least two of 0.1 mm, 0.6 mm, and 1.2 mm from the objective lens side.

  An optical pickup according to any one of claims 10 to 12 is the optical pickup according to any one of claims 1 to 4, wherein the objective lens is a lens having the best aberration with respect to the first optical recording medium, and the objective lens A diffraction element or phase shifter element between the optical system and the expander optical system, and the diffraction element or phase shifter element selectively uses light beams of different diffraction orders depending on the optical recording medium, The element or the phase shifter element is formed integrally with the objective lens, and the element surface is formed on the light source side surface of the objective lens.

  An optical information processing apparatus according to claim 13 is an optical information processing apparatus for recording and / or reproducing information on an optical recording medium, and includes the optical pickup according to any one of claims 1 to 12. It is characterized by that.

  According to the above-described configuration, the first optical recording medium (BD) is formed by the expander optical system that includes two lenses having different refractive powers and has a diffraction grating that splits three beams on one surface. , Optimization of sub-spot position for track error detection with respect to second optical recording medium (HD), multilayer recording medium, spherical aberration caused by substrate thickness error of optical recording medium (BD), optical recording medium The coma generated by the tilt of (HD) can be corrected, and optical recording media having different information recording layers can be recorded and / or reproduced by one optical pickup.

  According to the present invention, optimization of a sub-spot position for track error detection by the DPP method associated with a difference in track pitch of an optical recording medium (BD), an optical recording medium (HD), or a multilayer recording medium, and an optical recording medium ( Each of the spherical aberration caused by the substrate thickness error of BD) and the coma caused by the tilt of the optical recording medium (HD) can be corrected by one expander optical system.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a diagram showing a schematic configuration of an optical pickup according to Embodiment 1 of the present invention. In the first embodiment, the first optical recording medium is an optical recording medium (BD) that is a “blue optical recording medium having a working wavelength of 405 nm, NA of 0.85, and a light irradiation side substrate thickness of 0.1 mm”. As an example, an optical pickup capable of recording and / or reproducing together with an optical recording medium (HD) of a “blue optical recording medium having a working wavelength of 405 nm, NA of 0.66, and a light irradiation side substrate thickness of 0.6 mm” is taken as an example. explain.

  1 includes a semiconductor laser 101 having a wavelength of 405 nm, a collimating lens 102, a polarizing beam splitter 103, an expander optical system 104, a deflecting prism 105, a liquid crystal aperture limiting element 106, an aberration correcting diffractive optical element 107, A quarter wavelength plate 108, an objective lens 109, a detection lens 111, and a light receiving element 112 are included. Here, the objective lens 109 has an infinite system and minimizes the wavefront aberration with respect to the optical recording medium (BD) of “blue optical recording medium having a working wavelength of 405 nm, NA of 0.85, and a light irradiation side substrate thickness of 0.1 mm”. Designed to be In general, the tolerance becomes more severe as the objective lens becomes higher NA. Compared with NA 0.85 and 0.65, it is more difficult to obtain desirable characteristics with NA 0.85, and in particular, aberration was corrected with NA 0.85. Use an aspheric lens.

  The optical recording media are optical recording media having different substrate thicknesses, the optical recording medium (BD) 110a is a blue optical recording medium having a substrate thickness of 0.1 mm, and the optical recording medium (HD) 110b is a substrate thickness. This is a blue optical recording medium having a thickness of 0.6 mm. At the time of recording or reproducing, only one of the optical recording media is set in a rotating mechanism (not shown) and rotated at a high speed.

  First, a description will be given of a case where an optical recording medium (BD) of “blue optical recording medium having a used wavelength of 405 nm, NA of 0.85, and a light irradiation side substrate thickness of 0.1 mm” is recorded or reproduced. The linearly polarized divergent light emitted from the semiconductor laser 101 having a wavelength of 405 nm is made substantially parallel light by the collimator lens 102, passes through the polarization beam splitter 103 and the expander optical system 104, and is deflected by 90 degrees by the deflecting prism 105. , Passes through the liquid crystal aperture limiting element 106 and the aberration-correcting diffractive optical element 107, passes through the quarter-wave plate 108, becomes circularly polarized light, enters the objective lens 109, and is a minute spot on the optical recording medium (BD) 110a. It is condensed as. Information is recorded, reproduced, or erased by this spot. The light beam reflected from the optical recording medium (BD) 110a becomes circularly polarized light in the opposite direction to the outward path, is converted into substantially parallel light again, passes through the quarter-wave plate 108, and becomes linearly polarized light orthogonal to the outward path. The light is reflected by the beam splitter 103, is converged by the detection lens 111, and reaches the light receiving element 112. An information signal and a servo signal are detected from the light receiving element 112.

  Next, a description will be given of a case where an optical recording medium (HD) of “a blue optical recording medium having a used wavelength of 405 nm, NA of 0.65, and a light irradiation side substrate thickness of 0.6 mm” is recorded or reproduced. The linearly polarized divergent light emitted from the semiconductor laser 101 having a wavelength of 405 nm is made substantially parallel light by the collimator lens 102, passes through the polarization beam splitter 103 and the expander optical system 104, and is deflected by 90 degrees by the deflecting prism 105. The aperture is limited to 0.66 by the liquid crystal aperture limiting element 106, a predetermined spherical aberration is added by the aberration correcting diffractive optical element 107, and the light enters the objective lens 109 and is condensed as a minute spot on the optical recording medium (HD) 110 b. Is done. Information is recorded, reproduced, or erased by this spot. The light beam reflected from the optical recording medium (HD) 110b becomes circularly polarized light in the opposite direction to the outward path, again becomes substantially parallel light, passes through the quarter wavelength plate 108, and becomes linearly polarized light orthogonal to the forward path, and is polarized. The light is reflected by the beam splitter 103, is converged by the detection lens 111, and reaches the light receiving element 112. An information signal and a servo signal are detected from the light receiving element 112.

  The configuration of the expander optical system 104 will be described. The expander optical system 104 has a two-group configuration of two lenses. When the semiconductor laser 101 side of the light source is the lens 104a and the optical recording medium 110 side is the lens 104b, the lens 104a is a lens having a positive refractive power, and the lens 104b. Are negative refractive power lenses, both of which are single lenses. Both lenses are arranged on the optical axis of outgoing light emitted from the semiconductor laser 101 toward the optical recording medium 110.

  A diffraction grating is formed on the side surface of the optical recording medium 110 of the lens 104b of the expander optical system 104. A light beam from the light source enters the diffraction grating, and at least three of 0th-order diffracted light and ± 1st-order diffracted light. Are divided into luminous fluxes. Among the light beams divided by the diffraction grating, the 0th order diffracted light is used as a main beam for recording and reproducing information, and the ± 1st order diffracted light is used as a sub-spot for tracking control. Three spots that converge on the recording surface of the optical recording medium 110 through the objective lens 109 and are linearly arranged at equal intervals by the zero-order diffracted light and the ± first-order diffracted light are formed on the recording surface.

  The expander optical system 104 is mounted on driving means such as an actuator as shown in FIG. 2, and in the case of the optical recording medium (BD) 110a, it detects a spherical aberration deterioration equivalent amount caused by the substrate thickness error. The lens of the expander optical system 104 can be dynamically controlled to obtain optimum characteristics. In the case of the optical recording medium (HD) 110b, it is possible to detect the coma aberration degradation equivalent amount caused by the tilt and dynamically control the lens of the expander optical system 104 to obtain optimum characteristics.

  Here, a method for dynamically controlling the expander optical system 104, that is, a method for correcting spherical aberration and coma aberration will be described below with reference to FIG. In FIG. 2, the optical components are the same as those in FIG. The lens 104a and the lens 104b constituting the expander optical system 104 are held on actuators 114a, 114b, 114 which are driving means. The actuator 114a is configured to drive the lens 104a uniaxially in the optical axis direction. Thereby, the space | interval of the lens 104a and the lens 104b can be made variable. The actuator 114b is configured to move the lens 104b in one axis perpendicular to the optical axis, specifically in the radial direction of the optical recording medium. The actuator 114 is configured to rotate the lens 104b about the optical axis.

  In addition, as a specific means of the actuator, a generally known voice coil type actuator, piezoelectric actuator, or the like may be used.

  FIG. 3 is a flowchart showing the adjustment process of the expander optical system. After the optical information processing apparatus is turned on, the lens state of the expander optical system is moved to a predetermined position stored in advance (step S1). The predetermined position is stored as an optimum value in the assembling process, and is, for example, a position where three beams are in an on-track and aberration best state with respect to the optical recording medium (BD).

When the medium is set (step S2), either the optical recording medium (BD) or the optical recording medium (HD) is detected (step S3). As a method of determining the medium,
1. At the stage of setting the optical recording medium, a thickness detecting optical system including an LED (light emitting diode) and a light receiving element is provided, and the determination is made based on the output.
2. A focus error signal is detected, and it is determined whether a TE (track error) signal is detected in the vicinity of the focus.
3. The cartridge shape of the optical recording medium is set to be different, and the determination is made based on the difference.
4). The medium type is printed with a barcode written on the label of the optical recording medium, and the information is determined by reading the information with a barcode reader.
5. The determination is made based on the movable amount of the objective lens actuator up to the in-focus position.
And the like.

  In the case of an optical recording medium (BD) (Yes in step S3), the SA correction driver 31 shown in FIG. 2 performs recording and reproduction processing while performing an aberration correction operation described later according to the control signal (step). S4).

  If it is not an optical recording medium (BD) (No in step S3), a control signal is sent to the three-beam correction driver 33, and the three beams are rotated so as to be on-track with respect to the optical recording medium (HD). (Step S5). Thereafter, the tilt correction driver 32 performs recording and reproduction processing according to the control signal while performing an aberration correction operation described later (step S6).

  Further, the lens 104b of the expander optical system 104 shown in FIG. 2 is rotatable about the optical axis of the objective lens 109, and is rotated by the actuator 114 between the optical recording medium (BD) 110a and the optical recording medium (HD) 110b. The moving angle can be switched. This rotation angle is stored in an internal memory (not shown) or the like, and is moved in advance to a neutral point (reference position) optimum for the optical recording medium (BD) 110a before the medium is set, so that the optical recording medium (HD) When it is recognized that 110b has been inserted, the CPU 34 obtains a predetermined rotation angle stored in the memory from the neutral point, and as shown in FIGS. 4 (a) and 4 (b), according to the angle. The three-beam correction driver 33 is adjusted to rotate the lens 104b.

  As shown in FIGS. 4A and 4B, since the NA is switched in the optical recording medium (BD) and the optical recording medium (HD) in the first embodiment, the spot size of the three beams. Will also change. Furthermore, since the NA between the optical recording medium (BD) and the optical recording medium (HD) is switched, the spot interval between the sub-spots s1, s2 and the main spot m1 slightly changes. Such a rotation process is performed.

  Further, as shown in FIG. 5, the rotating portion configuration for rotating the lens 104 b is a configuration in which a ball frame 26 to which the lens 104 b is fixed is held by a fixed frame 25. A combination of a piezo element 21a and a rod 22a, and a combination of the piezo element 21b and a rod 22b is arranged, and the arrangement is symmetrical about the optical axis. As a result, the ball frame 26 is rotated by an expansion and contraction operation equivalent to the piezo elements 21a and 21b. Further, an LED 24 is arranged on the ball frame 26, and a PSD (semiconductor light incident position detecting element) 23 on the fixed frame 25 is arranged at a position opposite to the LED 24 so that the rotation angle can be detected.

  Further, the actuators 114a and 114b of the expander optical system 104 shown in FIG. 2 are connected to the CPU 34 via the SA correction driver 31 and the tilt correction driver 32, respectively. The CPU 34 receives a signal from the TE signal generator 36 and a signal from the RF signal generator 35 via the peak hold circuit 37. Further, a correction profile memory (not shown) is provided in the CPU 34.

  The light receiving element 112 shown in FIG. 2 is divided into eight parts, and the detection signals Sa to Sh from the detection surfaces A to H are supplied to the TE signal generation unit 36 and the RF signal generation unit 35. The TE signal generation unit 36 uses the detection signals Sa to Sh (Equation 3)

に従ってＴＥ信号を生成してピークホールド回路３７へ供給する。ピークホールド回路３７は、ＴＥ信号のピークレベルをホールドし、ＣＰＵ３４に供給する。また、ＲＦ信号生成部３５は、検出信号Ｓａ〜Ｓｄを使用して（数４）

And a TE signal is generated and supplied to the peak hold circuit 37. The peak hold circuit 37 holds the peak level of the TE signal and supplies it to the CPU 34. Further, the RF signal generation unit 35 uses the detection signals Sa to Sd (Equation 4).

に従ってＲＦ信号を生成し、これをＣＰＵ３４へ供給する。

According to the above, an RF signal is generated and supplied to the CPU 34.

  The CPU 34 uses the TE signal received from the peak hold circuit 37 and the RF signal received from the RF signal generation unit 35 to determine the lens position with the maximum amplitude of the TE signal and the lens position with the maximum amplitude of the RF signal, which will be described later. Perform an offset measurement process to measure the difference. Using the offset amount obtained by this offset measurement process, for example, a correction profile creation process for creating a correction profile instructing spherical aberration correction or spherical aberration correction for each medium, and substrate thickness correction or spherical aberration correction according to the correction profile The correction process is performed. That is, the lenses 104a and 104b are moved according to the type of optical recording medium.

  In addition, the correction profile described above is divided into three positions of the optical recording medium in the radial direction, for example, an inner peripheral area, an intermediate peripheral area, and an outer peripheral area, and the optimum aberration correction amount in each area is defined. Can do.

  When the optical recording medium is an unrecorded medium, an RF signal cannot be obtained at each position on the medium, so that an aberration correction amount that maximizes the RF signal amplitude cannot be obtained. Therefore, an aberration correction amount that maximizes the TE signal amplitude is used as an alternative value. However, the aberration correction amount that maximizes the RF signal amplitude does not necessarily match the aberration correction amount that maximizes the TE signal amplitude, and has an offset amount. That is, for an unrecorded medium, an aberration correction amount that maximizes the TE signal amplitude is acquired, and the aberration amount that maximizes the RF signal amplitude is calculated based on the acquired aberration correction amount and set to the optimum aberration amount. By doing so, it is possible to determine the optimum aberration amount and create a correction profile for both the recorded medium and the unrecorded medium.

  Next, a process for correcting the spherical aberration that occurs due to the substrate thickness error of the optical recording medium (BD) will be described with reference to the flowchart of FIG. In the spherical aberration correction, the CPU 34 shown in FIG. 2 basically determines a spherical aberration correction amount that maximizes the RF signal amplitude, and controls the SA correction driver 31 based on this amount to move the lens 104a.

  Now, when the medium is set, the CPU 34 performs measurement processing of the offset amount ΔSA (steps S10 to S17).

  Specifically, the spherical aberration amount that maximizes the RF signal amplitude and the TE signal amplitude are maximized at the boundary position between the recorded area where the RF signal is obtained on the medium and the unrecorded area where the RF signal is not obtained. The spherical aberration amount is acquired, and the offset amount ΔSA is calculated as the difference. Further, in the case of an unrecorded medium, it may be detected at the boundary portion of the prewrite portion where recording is performed in advance in the lead-in area.

  Further, the offset amount measurement process will be described in detail. First, the CPU 34 determines whether or not the set medium is an unrecorded medium (step S10). In the case of an already recorded medium, management information or the like has already been recorded immediately before the prewrite part. On the contrary, if it has not been recorded, the fact that it has not been recorded may be used.

  If it is determined in step S10 that the recording medium is an unrecorded medium (Yes in step S10), the CPU 34 changes the spherical aberration correction amount in the pre-write unit, and the aberration correction amount SA (α ) Is detected (step S11).

  The aberration correction amount SA (β) that maximizes the TE signal amplitude is detected by changing the spherical aberration correction amount in the unrecorded portion near the pre-write portion (step S12).

  Then, the CPU 34 calculates an offset amount ΔSA from the aberration correction amounts SA (α) and SA (β) and stores it in an internal memory (step S13).

  On the other hand, if it is determined in the process of step S10 that the medium is not an unrecorded medium (No in step S10), the CPU 34 searches for the presence / absence of an RF signal boundary from the medium inner periphery to the outer periphery (step S14). This search is executed by moving the optical pickup from the inner circumference of the medium toward the outer circumference with the tracking servo open, and monitoring the change in the amplitude of the RF signal obtained in the process. In the presence or absence of the RF signal boundary, the RF signal amplitude obtained so far disappears, so the position may be set to the presence or absence of the RF signal boundary.

  Then, the presence / absence of the boundary of the RF signal is confirmed (step S15). When the presence / absence of the boundary is found (Yes in step S15), the spherical aberration correction amount is changed in the recorded portion in the vicinity to maximize the RF signal amplitude. An aberration correction amount SA (α) is detected (step S16).

  In addition, the aberration correction amount SA (β) that maximizes the TE signal amplitude is detected by changing the aberration correction amount SA (β) in a nearby unrecorded portion (step S17).

  Then, the CPU 34 calculates an offset amount ΔSA from the aberration correction amount SA (α) and the aberration correction amount SA (β) and stores it in an internal memory or the like (step S13).

  As described above, the offset amount ΔSA can be obtained by the offset amount measurement process regardless of whether it is a recorded medium or an unrecorded medium.

  Subsequently, the CPU 34 creates a correction profile (steps S18 to S22). First, the CPU 34 moves the optical pickup to a predetermined correction reference position on the medium (step S18). The correction reference position is a position at which spherical aberration correction is performed, and can be, for example, three regions of an inner circumference, a middle circumference, and an outer circumference. Therefore, initially, the correction reference position is set to the inner peripheral area.

  The CPU 34 reads the correction reference position and determines whether or not an RF signal can be obtained (step S19). If no RF signal is obtained in the process of step S19 (No in step S19), it can be seen that the correction reference position is an unrecorded area. Therefore, the CPU 34 determines the optimum SA correction amount using the TE signal amplitude. That is, the TE signal amplitude is detected while changing the spherical aberration amount at the correction reference position, and the spherical aberration correction amount that maximizes the TE signal amplitude is determined (step S20).

  Next, the CPU 34 adds the offset amount ΔSA obtained by the previous offset amount measurement process to the spherical aberration amount obtained by the process of step S20. The amount of spherical aberration obtained by the addition corresponds to the amount of spherical aberration that maximizes the RF signal amplitude, and is used as the optimum SA correction amount (step S21).

  On the other hand, when the RF signal is obtained in the process of step S19 (Yes in step S19), the spherical aberration correction amount is changed at the correction reference position to determine the spherical aberration correction amount that maximizes the RF signal amplitude. This is set as the optimum SA correction amount (step S23).

  Then, the CPU 34 stores the optimum SA correction amount obtained in the process of step S31 or step S23 in the correction profile memory (step S22).

  When a correction profile is created by the above processing, the CPU 34 performs a recording or reproducing operation while correcting spherical aberration.

  Next, the spherical aberration correction process (steps S24 to S28) performed with recording or reproduction will be described.

  First, the CPU 34 determines whether or not an instruction for recording information on the medium or reproducing information from the medium is given by the user (step S24). When an instruction for recording or reproduction is given (Yes in step S24), the CPU 34 obtains an address to be recorded or reproduced using a TE signal or the like (step S25), and an optimum SA corresponding to that address. The correction amount is acquired from a correction profile memory (not shown) in the CPU 34 (step S26).

  Then, the CPU 34 controls the SA correction driver 31 to perform spherical aberration correction according to the obtained optimum SA correction amount (step S27).

  Further, the CPU 34 determines whether or not an instruction to end recording or reproduction is input by the user (step S28), and repeats the processing of steps S25 to S27 until the end instruction is input (No in step S28). . Then, when an end instruction is input, the process ends (Yes in step S28).

  As described above, in the first embodiment, first, the spherical aberration correction amount and the TE signal amplitude that maximize the RF signal amplitude from the boundary between the recorded portion and the unrecorded portion on the recording or reproducing target medium. Is obtained from the spherical aberration correction amount, and the offset amount ΔSA is calculated therefrom. Next, with respect to the reference correction position on the medium, the optimum SA correction amount is determined based on the RF signal if already recorded, and based on the TE signal and the offset amount ΔSA if not recorded, and stored as a correction profile. To do. When recording or reproducing the medium, spherical aberration correction is performed with reference to the correction profile.

  Since spherical aberration correction is performed using a correction profile created for each medium, spherical aberration correction can be accurately executed regardless of the type of medium.

  In addition, since the optical information processing apparatus itself that performs recording or reproduction determines the optimum SA amount and creates a correction profile, even if the characteristics of the optical pickup, optical system, etc. of the optical information processing apparatus vary, the characteristics The optimum SA amount based on

  Furthermore, since a correction profile is created prior to actual recording and reproduction, there is little influence due to characteristic fluctuation due to aging of the optical system of the apparatus and characteristic fluctuation due to temperature change during recording or reproduction.

  Similarly, in the first embodiment, the coma aberration generated by the tilt of the optical recording medium can be corrected by moving the lens 104b of the expander optical system 104 in the direction orthogonal to the optical axis. First, the coma aberration correction amount that maximizes the RF signal amplitude and the coma aberration correction amount that maximizes the TE signal amplitude are obtained from the boundary between the recorded portion and the unrecorded portion on the recording or reproduction target medium. An offset amount ΔTilt is calculated. Next, with respect to the reference correction position on the medium, an optimum coma aberration correction amount is determined based on the RF signal if already recorded, and based on the TE signal and the offset amount ΔTilt if not recorded. Remember. When recording or reproducing the medium, tilt correction is performed with reference to the correction profile.

  Although the tilt direction can be divided into two directions, that is, the rotational direction and the radial direction, the main problem is the radial direction, and only the radial direction may be used as the correction direction. This is because the optical recording medium is not manufactured in a flat surface, has a certain degree of warping, and has a warp like a mikoshi in the radial direction.

  Here, the correction of the spherical aberration with respect to the substrate thickness of a specific optical recording medium will be described. First, spherical aberration caused by the thickness error of the optical recording medium (BD) can be corrected by changing the lens interval between the lens 104a and the lens 104b of the expander optical system 104. That is, the spherical aberration caused by the thickness error of the optical recording medium (BD) is corrected by moving any lens of the expander optical system 104 in the optical axis direction.

  When the thickness error of the optical recording medium becomes 0 μm to 20 μm with respect to the design value, the aberration value when there is no expander optical system 104 and the distance between the lens 104a and the lens 104b about the optical axis are changed. Aberration values when corrected are shown in FIGS. 7 (a) and 7 (b).

  From the graph shown in FIG. 7A, when the expander optical system 104 is not provided, the specified aberration value of 0.035 λrms is obtained when the substrate thickness error is about 4 μm. However, it is known that the thickness error of the optical recording medium is due to the injection molding accuracy at the time of manufacturing the medium, and generally a thickness error of about ± 10 μm occurs. Without the expander optical system 104, It turns out that it is unacceptable.

  On the other hand, as shown in FIG. 7B, when the lens 104a and the lens 104b are corrected by changing the distance around the center of the optical axis, the substrate thickness error can be allowed to be ± 20 μm or more, and compared with the manufacturing tolerance ± 10 μm. You can see that it is possible.

  Next, coma aberration generated from the tilt of the optical recording medium (HD) can be corrected by shifting the lens 104b of the expander optical system 104 in the radial direction of the optical recording medium.

  Here, when the tilt of the optical recording medium becomes 0 deg to 0.4 deg, the aberration value when there is no expander optical system 104 and the aberration value when the shift amount of the lens 104b is changed and corrected. It shows to Fig.8 (a), (b).

  From the graph shown in FIG. 8A, when the expander optical system 104 is not provided, the specified aberration value of 0.035λrms is obtained when the tilt amount of the optical recording medium is 0.15 deg. However, the tilt amount of the optical recording medium (HD) is ± 0. 0 in consideration of what the optical recording medium itself has and what occurs when the optical recording medium is chucked on a turntable (not shown). It is known that 3 deg equivalent occurs, and it can be seen that this cannot be allowed without tilt correction.

  On the other hand, as shown in FIG. 8B, when correction is performed by changing the shift amount of the lens 104b, the tilt amount of the optical recording medium can be allowed to be ± 0.4 deg, and can be manufactured. Recognize.

  Further, in the optical pickup of the first embodiment, in order to make the optical recording medium (HD) having different substrate thickness compatible with the objective lens optimized for the optical recording medium (BD) as shown in FIG. An aberration correcting diffractive optical element 107 and a liquid crystal aperture limiting element 106 are arranged.

  As shown in FIG. 9A, the aberration-correcting diffractive optical element 107 includes a plurality of annular zones around the optical axis. The aberration-correcting diffractive optical element 107 is formed so that its cross section has a sawtooth shape as shown in FIG. 9B or a step shape as shown in FIG. 9C. For example, a diffractive optical element (diffraction grating) having a sawtooth cross section is advantageous because it has a higher diffraction efficiency than others. As a method for creating the cross-sectional shape of the diffractive optical element, there are a method of applying a photolithography technique and a method of precision cutting with a diamond tool or the like. In addition, a so-called 2P (photo-polymer) method is used in which a mold having a desired shape is formed on a mold, a resin is applied to an injection molding or base member, and the mold is pressed by a mold and cured by irradiating ultraviolet rays. It is also possible to duplicate a plurality of diffractive optical elements from a transparent material.

  As shown in FIGS. 10A and 10B, the aberration correction diffractive optical element 107 transmits the zero-order diffracted light on the optical recording medium (BD) 110a via the objective lens 109 and the first-order diffracted light. It is formed so as to be condensed on the optical recording medium (HD) 110b through the objective lens 109. Note that the 0th-order diffracted light and the 1st-order diffracted light are not in focus on the optical recording media having different substrate thicknesses, so that these diffracted lights have little influence on recording or reproduction.

  Note that the reason why the 0th-order diffracted light is selected to be NA 0.85 as the diffraction order is that the objective lens 109 is light of “blue optical recording medium having a working wavelength of 405 nm, NA of 0.85, and a light irradiation side substrate thickness of 0.1 mm”. This is because the recording medium (BD) is designed to have a minimum wavefront aberration in an infinite system.

  In FIGS. 10A and 10B, for the sake of simplicity, the quarter-wave plate 108 between the aberration-correcting diffractive optical element 107 and the objective lens 109 shown in FIG. 1 is omitted.

  Next, as a specific example of calculating the diffraction efficiency shown in FIG. 11, the grating groove depth d of the blazed cross-sectional diffractive optical element shown in FIG. 9 is changed from 0 μm to 2 μm, and the base material is, for example, glass made by HOYA. This is a change in diffraction efficiency calculated when using MLaC110 (nd = 69.4, νd = 53.2). The diffraction efficiency ηm of the diffractive optical element is (Expression 5)

で表される。（数５）において、ｄは格子溝深さ、ｍは回折次数、ｎは材料屈折率を示している。

It is represented by In (Expression 5), d is the grating groove depth, m is the diffraction order, and n is the material refractive index.

  FIG. 11 shows the result of calculating the groove depth d of the diffractive optical element on the horizontal axis and the change in diffraction efficiency of the diffractive optical element on the vertical axis. “B0”, “B1”, “B2”, and “B3” in FIG. 11 indicate the diffraction efficiencies of the 0th-order diffracted light, 1st-order diffracted light, 2nd-order diffracted light, and 3rd-order diffracted light, respectively.

As shown in FIG. 11, the diffraction efficiency can be adjusted by adjusting the groove depth of the diffractive optical element, so that the diffraction efficiency can be selected according to the irradiation power characteristics of the optical recording medium (BD) and the optical recording medium (HD). What is necessary is just to select the groove depth. In general, the smaller the diameter spot, the more power is collected. The beam spot diameter on the optical recording medium is proportional to the wavelength λ and decreases in inverse proportion to NA, and the power increases in inverse proportion to the spot area. That is, when comparing NA 0.85 and NA 0.65, the power collected on the optical recording medium is larger at NA 0.85 at a ratio of (0.85 / 0.65) ² . Therefore, when the optical recording medium (BD) and the optical recording medium (HD) are used with the same material and the same linear velocity, the condensing power required for each medium is equivalent, and therefore the 0th-order diffracted light and The efficiency ratio of the first-order diffracted light may be set to 1: 1.7. That is, the lattice groove depth may be selected in the vicinity of 0.32 μm.

  Alternatively, if only one of the optical recording medium (BD) and the optical recording medium (HD) is a reproduction-only optical information processing apparatus, if the reproduction side efficiency is reduced, the other optical recording medium can be used. Makes it possible to irradiate with sufficient power and facilitates speeding up.

  The numerical aperture (NA) used for the optical recording medium (BD) and the optical recording medium (HD) is different from 0.85 and 0.65, respectively. As the aperture limiting element, a liquid crystal element that functions as a selective annular light shielding filter as shown in FIG. That is, the liquid crystal shutter 106a has an annular pattern, and transmits or blocks the outer periphery of the light beam incident on the objective lens. As shown in FIGS. 12B and 12C, when no voltage is applied, that is, when the liquid crystal is off, the entire surface is transmitted, and when a voltage is applied, that is, when the liquid crystal is on, it is partially. An element that transmits light may be used.

  Next, the shape of the objective lens 109, the aberration correction diffractive optical element 107, and the expander optical system 104 shown in FIGS. 13A and 13B will be described below with specific numerical examples.

  Here, the aspherical shape of the lens surface is: coordinate in the optical axis direction: X, coordinate in the optical axis orthogonal direction: Y, paraxial radius of curvature: R, conic constant: K, higher order coefficients: A, B, C , D, E, F,.

で表される。

It is represented by

  Further, the phase function φ (r) of the diffractive optical element is expressed as follows using the diffraction order m, the wavelength λ, the radius from the optical axis r, and coefficients C1 to C5:

で表される。

It is represented by

  The configuration of the optical system according to the first embodiment will be described with reference to FIGS. 13A, 13B, and 14. FIG. Here, the objective lens 109 has a working wavelength of 405 nm, NA of 0.85, f: 1.765 mm, nd: 1.694, and νd: 53.2. Symbols in FIG. 14 are as follows. “OBJ” means an object point (semiconductor laser as a light source), but the incident beam to the expander optical system 104 is “infinite system”, and “INFINITY (infinity) with radius of curvature: RDY and thickness: THI”. ) "Means that the light source is at infinity. Unless otherwise specified, the unit of the quantity having the dimension of length is “mm”. “S1” to “S4” represent lens surfaces of the expander optical system 104, “S1” represents the light source side surface of the lens 104a of the expander optical system 104, and “S2” represents the side surface of the objective lens 109.

  The thickness of “S1” of 2.00 mm means the thickness of the lens 104a. The thickness of “S2” represents the distance between the lenses of the expander optical system 104. When correcting spherical aberration, this interval is changed from the neutral position. “S5” means the side surface of the light source of the aberration correcting diffractive optical element 107, and “S6” means the side surface of the optical recording medium. “S7” means the side surface of the light source of the objective lens 109 for optical pickup, and “S8” means the side surface of the optical recording medium. Note that “S4” of the lens 140b is a lens surface or a plane having the largest curvature radius among the four lens surfaces of the expander optical system 104, and a diffraction grating for dividing the light beam into three beams is formed.

  The thickness of the objective lens 109 in this example is 2.38 mm, and the thickness of 0.43 mm described on the right side of the radius of curvature in the column “S8” indicates “working distance: WD”. “S9” is a light source side surface of the light irradiation side substrate of the optical recording medium 110, and “S10” is a surface that matches the recording surface. The space between these surfaces “S9” and “S10”, that is, the substrate thickness is light. The recording medium (BD) 110a is 0.1 mm, the optical recording medium (HD) 110b is 0.6 mm, nd: 1.551610, and νd: 64.1. “WL: Wavelength” represents a used wavelength (405 nm).

  The on-axis wavefront aberration of the optical system obtained by combining the objective lens 109, the aberration correction diffractive optical element 107, and the expander optical system 104 is 0 for the system (0th order diffracted light) recorded / reproduced on the optical recording medium (BD). The system (first-order diffracted light) for recording / reproducing on / from an optical recording medium (HD) is 0.0007λrms, which is suppressed to the Marshall limit of 0.07λrms or less.

  The aberration correction diffractive optical element 107 may be integrated with the objective lens 109. As shown in FIGS. 15A and 15B, a diffractive optical element is formed on the incident surface on the light source side of the aspherical objective lens 109, and both the diffractive optical element and the exit surface of the objective lens 109 are aspherical. It was. Therefore, the first surface (S2) and the second surface (S3) are a diffractive optical element surface and an output surface which are integrated condenser lenses. Data of each aspherical lens manufactured by automatic design is as shown in FIG.

  The on-axis wavefront aberration of the system obtained by combining the objective lens and the diffractive optical element thus obtained is 0.0011λrms for the optical recording medium (BD) and 0.0005λrms for the optical recording medium (HD), and the Marshall limit is 0.00. It is suppressed to 07λrms or less.

  The rotation of the lens 104b of the expander optical system 104 for correcting the position of the three beams may be finely adjusted from a value stored in advance. For example, coarse adjustment is performed as adjustment based on information from the memory, and then the amplitude of the TE signal is maximized, or the push-pull signals of the sub-spots s1 and s2 detected by the light receiving element 112 and the push-pull signal of the main spot m1 Alternatively, a rotation angle with a phase difference of 180 degrees may be obtained and finely adjusted and fixed at that position.

  Note that, as a method of moving the expander optical system 104, the case where the lens 104a is moved in the optical axis direction and the lens 104b is moved in the radial direction of the optical recording medium in the plane orthogonal to the optical axis has been described. You may make it move only. In that case, the movable lens may be mounted on an actuator that moves in two directions in the optical axis direction and the radial direction of the optical recording medium in the plane orthogonal to the optical axis.

  In the first embodiment, the expander optical system 104 performs aberration correction by using a lens having a positive refractive power on the light source side and a lens having a negative refractive power on the optical recording medium side. However, the reverse may be possible depending on the configuration of the optical system. Specifically, it is only necessary to select one that can be miniaturized as a whole optical pickup.

  Furthermore, the expander optical system 104 may have both a spherical aberration correction and a role as a collimating lens. In this case, the number of parts can be reduced, and the labor and cost of manufacturing the optical pickup can be reduced.

  In the first embodiment, a single lens is used as the objective lens 109, but a bonded lens or the like may be used. Or you may use what was comprised from the lens of 3 groups or more.

  In the first embodiment, an optical system having a light source wavelength of 405 nm has been exemplified. However, the wavelength used is not limited to this, and the effect does not change at other wavelengths.

  In the actual optical system, manufacturing errors other than the substrate thickness error of the optical recording medium are also included. Therefore, the aberration correction optical system is adjusted so as to satisfy the optimum conditions while monitoring the amplitude of the RF signal or the TE signal. May be stored in the optical pickup assembly stage.

  Next, a second embodiment of the present invention will be described. The difference from the first embodiment described above is that the expander optical system is configured to also correct spherical aberration that occurs when two recording media are compatible. That is, the aberration correction diffractive optical element 107 in FIG. 1 can be eliminated.

  FIG. 17 is a diagram showing a schematic configuration of the optical pickup according to the second embodiment of the present invention. As shown in FIG. 17, the main parts of the optical pickup are a semiconductor laser 101 having a wavelength of 405 nm, a collimating lens 102, a polarizing beam splitter 103, an expander optical system 104 ′, a deflecting prism 105, a liquid crystal aperture limiting element 106, and 1/4. It comprises a wave plate 108, an objective lens 109, a detection lens 111, and a light receiving element 112.

  First, description will be made regarding a case where an optical recording medium (BD) of “blue optical recording medium having a working wavelength of 405 nm, NA of 0.85, and a light irradiation side substrate thickness of 0.1 mm” is recorded or reproduced in the optical pickup shown in FIG. . The linearly polarized divergent light emitted from the semiconductor laser 101 having a wavelength of 405 nm is converted into substantially parallel light by the collimator lens 102 and converted into a predetermined convergent beam by the polarization beam splitter 103 and the expander optical system 104 ′. Is deflected through the liquid crystal aperture limiting element 106, passes through the quarter-wave plate 108, becomes circularly polarized light, enters the objective lens 109, and is a small spot on the optical recording medium (BD) 110a. It is condensed as. Information is recorded, reproduced, or erased by this spot. The light beam reflected from the optical recording medium (BD) 110a becomes circularly polarized light in the opposite direction to the outward path, is converted into substantially parallel light again, passes through the quarter-wave plate 108, and becomes linearly polarized light orthogonal to the outward path. The light is reflected by the beam splitter 103, is converged by the detection lens 111, and reaches the light receiving element 112. An information signal and a servo signal are detected from the light receiving element 112.

  Next, a description will be given of a case where an optical recording medium (HD) of “a blue optical recording medium having a used wavelength of 405 nm, NA of 0.65, and a light irradiation side substrate thickness of 0.6 mm” is recorded or reproduced. The linearly polarized divergent light emitted from the semiconductor laser 101 having a wavelength of 405 nm is converted into substantially parallel light by the collimator lens 102, passes through the polarization beam splitter 103 and the expander optical system 104 ′ infinitely, and the optical path is changed by 90 by the deflecting prism 105. Is deflected by the liquid crystal aperture limiting element 106 to be NA 0.65, enters the objective lens 109, and is condensed as a minute spot on the optical recording medium (HD) 110b. Information is recorded, reproduced, or erased by this spot. The light beam reflected from the optical recording medium (HD) 110b becomes circularly polarized light in the opposite direction to the outward path, again becomes substantially parallel light, passes through the quarter wavelength plate 108, and becomes linearly polarized light orthogonal to the forward path, and is polarized. The light is reflected by the beam splitter 103, is converged by the detection lens 111, and reaches the light receiving element 112. An information signal and a servo signal are detected from the light receiving element 112.

  FIG. 18 is a graph showing the relationship between the substrate thickness and the divergence of a general objective lens. The horizontal axis represents the thickness of the substrate, and the vertical axis represents the magnification of the objective lens in use as a function of the divergence of the light beam incident on the objective lens. Since the light beam emitted from the objective lens toward the substrate is always convergent light, the sign when the convergent light is incident on the objective lens is “+”, and the sign when the divergent light is incident is “−”. When this magnification is “0”, parallel light enters the objective lens. The curve in FIG. 18 is obtained by connecting the magnification for minimizing the wavefront aberration with respect to each substrate thickness. For example, when the parallel light incidence is the best at the substrate thickness X, “−”, that is, divergent light increases as the substrate thickness increases. It is generally known that as the thickness becomes thinner, “+”, that is, when the convergent light is incident, the aberration becomes smaller.

  In the second embodiment, as shown in FIGS. 19A and 19B, both the optical recording medium (BD) 110a and the optical recording medium (HD) 110b have the shape of the objective lens 109 that has the best aberration when incident with convergent light. Is obtained. In the case of the optical recording medium (BD) 110a, the over spherical aberration caused by the thinning of the substrate thickness is canceled out by the under aberration caused by the convergent light. In the case of the optical recording medium (HD) 110b, the optical recording is performed. A magnification with a small convergence is given compared to the medium (BD) 110a.

  Similarly to the first embodiment, the expander optical system 104 ′ is configured to adjust the rotation of the three beams, the spherical aberration accompanying the substrate thickness error of the optical recording medium (BD) 110a, and the tilt of the optical recording medium (HD) 110b. The correction operation is the same as that of the first embodiment.

  In Embodiment 1 described above, in both cases of the optical recording medium (BD) 110a and the optical recording medium (HD) 110b, parallel light is emitted from the expander optical system 104 at the neutral point. In the second embodiment, the light beam from the expander optical system 104 ′ is a convergent system for both the optical recording medium (BD) 110a and the optical recording medium (HD) 110b. In the case of the optical recording medium (HD) 110b, the optical recording medium is used. (BD) The degree of convergence is smaller than that of 110a.

  That is, the degree of convergence is controlled according to the discrimination of the optical recording medium. When the optical recording medium (BD) 110a is determined, the distance between the lens 104a 'and the lens 104b' is adjusted to the center of the optical axis so as to be a convergent system, and thereafter spherical aberration correction due to substrate thickness error is started. If the optical recording medium (HD) 110b is determined, the distance between the lens 104a ′ and the lens 104b ′ is adjusted so that the convergence degree is smaller than that of the optical recording medium (BD) 110a. Thereafter, coma aberration correction is started by tilting the optical recording medium.

  FIG. 20 shows numerical examples of the objective lens 109 and the expander optical system 104 ′ having the specific configurations shown in FIGS. 19 (a) and 19 (b).

  FIG. 21 is a schematic diagram illustrating an example of a multilayer optical recording medium according to Embodiment 3 of the present invention. As the information recording surface of the multilayer optical recording medium 110e, the information recording surface is a p layer (p ≧ 2) in the thickness direction. The (pq) layer on the near side close to the objective lens is the information recording layer 11 with a narrow track pitch and high recording density, and the q layer on the far side far from the objective lens is information with a wide track pitch and low recording density. An optical recording medium comprising the recording layer 14 may be used. In this case, as the optical pickup, the light flux of the first NA is condensed on the (pq) layer having a high information recording density, and the second q layer having a numerical aperture smaller than that of the first NA is condensed on the back q layer. The light flux of NA may be condensed.

  As in the first embodiment described above, it is necessary to correct spherical aberration for the front side (pq) layer having a high NA, and to correct coma aberration for the q layer on the back side having a low NA and a large substrate thickness. Yes, this can be corrected using the aberration correction optical system and its control means described in the first to third embodiments.

  Furthermore, as a multilayer optical recording medium, for example, as shown in FIG. 22, a multilayer optical recording medium 110f having two formats corresponding to the optical recording medium (BD) and the optical recording medium (HD) of the first embodiment. It may be. That is, in FIG. 22, the information recording layer 11a is a layer having “optimal NA 0.85, light irradiation side substrate thickness 0.1 mm”, and the information recording layer 14a is “NA 0.65, light irradiation side substrate thickness 0.6 mm”. Layer.

  In the case of such a multilayer optical recording medium 110f, the three beams are rotated and adjusted in accordance with the information recording layers 11a and 14a, and the coma aberration correcting mechanism is held at the neutral point for the information recording layer 11a. Is corrected to the best position, the spherical aberration correction mechanism is held at the neutral point for the information recording layer 14a, and the coma aberration correction mechanism is corrected to the best position.

  FIG. 23 is a block diagram showing a schematic configuration of the optical information processing apparatus according to Embodiment 4 of the present invention. This is an apparatus for recording and / or reproducing information signals with respect to the optical recording medium in each of the above-described embodiments, and includes an optical pickup 51 corresponding to the optical pickup described above. A spindle motor 58 that rotationally drives the optical recording medium 110, a feed motor 52 for moving the optical pickup 51 used for recording and reproducing information signals to the inner and outer circumferences of the optical recording medium 110, and a predetermined modulation And a modulation / demodulation circuit 54 that performs demodulation processing, a servo control circuit 53 that performs servo control of the optical pickup 51, and a system controller 56 that controls the entire optical information processing apparatus.

  The spindle motor 58 shown in FIG. 23 is driven and controlled by the servo control circuit 53 and is driven to rotate at a predetermined rotational speed. That is, the optical recording medium 110 to be recorded and reproduced is chucked on the drive shaft of the spindle motor 58 and driven and controlled by the servo control circuit 53. By this spindle motor 58, the optical recording medium 110 is rotationally driven at a predetermined rotational speed.

  When recording and reproducing information signals to and from the optical recording medium 110, the optical pickup 51 irradiates the optical recording medium 110 that is rotationally driven with laser light and detects the return light flux as described above. This optical pickup 51 is connected to a modem circuit 54. When recording the information signal, a signal input from the external circuit 55 and subjected to a predetermined modulation process by the modulation / demodulation circuit 54 is supplied to the optical pickup 51. Based on the signal supplied from the modulation / demodulation circuit 54, the optical pickup 51 irradiates the optical recording medium 110 with laser light that has undergone light intensity modulation. When reproducing the information signal, the optical pickup 51 irradiates the rotationally driven optical recording medium 110 with a laser beam having a constant output, and a reproduction signal is generated from the return light. The reproduction signal is supplied to the modem circuit 54.

  The optical pickup 51 is also connected to a servo control circuit 53. Then, as described above, the focus servo signal and the tracking servo signal are generated from the return light beam reflected and returned by the rotationally driven optical recording medium 110 at the time of recording and reproducing the information signal. It is supplied to the servo control circuit 53.

  The modem circuit 54 is connected to the system controller 56 and the external circuit 55. The modulation / demodulation circuit 54 receives a signal to be recorded on the optical recording medium 110 from the external circuit 55 under the control of the system controller 56 when the information signal is recorded on the optical recording medium 110, and performs a predetermined process on the signal. The modulation process is performed. The signal modulated by the modem circuit 54 is supplied to the optical pickup 51.

  Further, the modem circuit 54 receives a reproduction signal reproduced from the optical recording medium 110 from the optical pickup 51 under the control of the system controller 56 when reproducing the information signal from the optical recording medium 110, and performs this reproduction. A predetermined demodulation process is performed on the signal. Then, the signal demodulated by the modem circuit 54 is output from the modem circuit 54 to the external circuit 55.

  The feed motor 52 is for moving the optical pickup 51 to a predetermined position in the radial direction of the optical recording medium 110 when recording and reproducing the information signal, and based on a control signal from the servo control circuit 53. Driven. That is, the feed motor 52 is connected to the servo control circuit 53 and is controlled by the servo control circuit 53.

  The servo control circuit 53 controls the feed motor 52 so that the optical pickup 51 is moved to a predetermined position facing the optical recording medium 110 under the control of the system controller 56. The servo control circuit 53 is also connected to the spindle motor 58 and controls the operation of the spindle motor 58 under the control of the system controller 56. That is, the servo control circuit 53 controls the spindle motor 58 so that the optical recording medium 110 is rotationally driven at a predetermined rotational speed when information signals are recorded and reproduced on the optical recording medium 110.

  Further, the servo control circuit 53 is also connected to the optical pickup 51. When recording and reproducing information signals, the servo control circuit 53 receives a reproduction signal and a servo signal from the optical pickup 51, and is mounted on the optical pickup 51 based on the servo signal. The focus servo and tracking servo are controlled by the two-axis actuator (not shown), and each one-axis actuator of the expander optical system is controlled to adjust the distance between the lens groups of the expander optical system. Then, the aberration is corrected.

  Thereby, it is possible to obtain a miniaturized optical information processing capable of recording, reproducing, or erasing information with a single optical pickup for a plurality of types or multilayer optical recording media.

  An optical pickup and an optical information processing apparatus according to the present invention are designed to optimize a sub-spot position for detecting a track error associated with a difference in track pitch of an optical recording medium, a spherical aberration caused by a substrate thickness error of the optical recording medium, and a tilt. And an optical information which can correct each of coma generated by the optical recording medium by one expander optical system, and perform at least one of information recording, reproduction and erasing on a plurality of types or multilayer optical recording media Useful for processing equipment.

The figure which shows schematic structure of the optical pick-up in Embodiment 1 of this invention. The figure which shows the control part of the expander optical system of the optical pick-up in this Embodiment 1. The flowchart which shows the adjustment process of the expander optical system in this Embodiment 1. (A) of three beams in the first embodiment is an optical recording medium (BD), and (b) is a diagram showing an on-track spot position of the optical recording medium (HD). The perspective view which shows the rotation part which rotates the lens of the expander optical system in this Embodiment 1. FIG. The flowchart which shows the correction process of the spherical aberration which arises with the board | substrate thickness error in this Embodiment 1. (A) of the optical recording medium (BD) in Embodiment 1 has an expander optical system, and (b) is a diagram showing a substrate thickness error characteristic without an expander optical system. (A) of the optical recording medium (HD) according to the first embodiment has an expander optical system, and (b) shows a tilt characteristic without the expander optical system. In Embodiment 1, (a) is a front view of the aberration-correcting diffractive optical element, (b) is a sawtooth-shaped annular zone sectional view, and (c) is a step-like annular zone sectional view. (A) of the aberration correction diffractive optical element and the objective lens in the first embodiment is a 0th-order diffracted light, and (b) is a diagram showing a focused state of the 1st-order diffracted light The figure which shows the specific diffraction efficiency calculation example in this Embodiment 1. (A) in the first embodiment is a front view of the liquid crystal aperture limiting element, (b) is a sectional view in a liquid crystal off state, and (c) is a sectional view in a liquid crystal on state. (A) of the objective lens, the aberration correction diffractive optical element, and the expander optical system according to the first embodiment is a diagram showing a light condensing state of the optical recording medium (BD) and (b). The figure which shows the specific numerical example of the objective lens in this Embodiment 1, an aberration correction diffractive optical element, and an expander optical system FIG. 5A is a diagram illustrating a light condensing state of an optical recording medium (BD), and FIG. 5B is a diagram illustrating a condensing state of the optical recording medium (HD), in which a diffractive optical element is formed on a light source incident surface of an objective lens according to the first embodiment. The figure which shows the lens data of the objective lens in this Embodiment 1. The figure which shows schematic structure of the optical pick-up in Embodiment 2 of this invention. The figure which shows the relationship between the board | substrate thickness of the objective lens in this Embodiment 2, and a divergence degree (A) of the objective lens and the expander optical system according to the second embodiment is a diagram showing a condensing state of the optical recording medium (BD), and (b) is a condensing state of the optical recording medium (HD). The figure which shows the specific numerical example of the objective lens in this Embodiment 2, and an expander optical system. Schematic diagram showing an example of a multilayer optical recording medium in Embodiment 3 of the present invention Schematic diagram showing another example of the multilayer optical recording medium in the third embodiment The block diagram which shows schematic structure of the optical information processing apparatus in Embodiment 4 of this invention The figure explaining the conventional DPP method The conventional (a) is the optical recording medium (BD), (b) is a diagram showing the substrate thickness error characteristics of the optical recording medium (HD) without the expander optical system. The conventional (a) is the optical recording medium (BD), and (b) is the optical recording medium (HD) showing the tilt characteristics without the expander optical system.

Explanation of symbols

11, 11a, 12, 13, 14, 14a Information recording layers 21a, 21b Piezo elements 22a, 22b Rod 23 PSD
24 LED
25 Fixed frame 26 Ball frame 31 SA correction driver 32 Tilt correction driver 33 Three beam correction driver 34 CPU
35 RF signal generator 36 TE signal generator 37 Peak hold circuit 51 Optical pickup 52 Feed motor 53 Servo control circuit 54 Modulation / demodulation circuit 55 External circuit 56 System controller 58 Spindle motor 101 Semiconductor laser 102 Collimator lens 103 Polarizing beam splitter 104, 104 ' Expander optical system 104a, 104b, 104a ', 104b' Lens 105 Deflection prism 106 Liquid crystal aperture limiting element 106a Liquid crystal shutter 107 Aberration correction diffractive optical element 108 1/4 wavelength plate 109 Objective lens 110 Optical recording medium 110a Optical recording medium (BD )
110b Optical recording medium (HD)
110e, 110f Multi-layer optical recording medium 111 Detection lens 112 Light receiving element 114, 114a, 114b Actuator

Claims (13)

Information for a first optical recording medium having a wavelength λ1, a substrate thickness t1, a used numerical aperture NA1, and a second optical recording medium having a wavelength λ1, a substrate thickness t2 (> t1), and a used numerical aperture NA2 (<NA1) In an optical pickup for recording and / or reproducing
Consists of a light source, an objective lens for condensing the light beam from the light source on an optical recording medium, and two lenses having different positive and negative refractive powers, and the light beam is divided into three beams on one surface of the lens An expander optical system having a diffraction grating formed thereon, and drive means for driving each lens of the expander optical system based on a discrimination signal that discriminates one of the first and second optical recording media. An optical pickup characterized by that.   2. The optical pickup according to claim 1, wherein when the expander optical system recognizes the second optical recording medium, the expander optical system generates over-spherical aberration due to convergent light as compared with the first optical recording medium. . An information recording surface is formed in a p-layer (p ≧ 2) in the thickness direction, the (pq) layer on the near side near the objective lens is an information recording layer with a narrow track pitch, and the q layer on the far side far from the objective lens is In an optical pickup for recording and / or reproducing information on an optical recording medium comprising an information recording layer having a wide track pitch,
Consists of a light source, an objective lens for condensing the light beam from the light source on an optical recording medium, and two lenses having different positive and negative refractive powers, and the light beam is divided into three beams on one surface of the lens And an expander optical system in which a diffraction grating is formed, and a drive means for driving each lens of the expander optical system based on a selection signal for selecting any one of the (pq) to q layers And an optical pickup.   When the expander optical system selects the near (pq) layer close to the objective lens of the optical recording medium, it generates under spherical aberration due to convergent light, and selects the q layer farther from the objective lens. 4. The optical pickup according to claim 3, wherein over-spherical aberration due to convergent light is sometimes generated as compared with the (pq) layer.   The drive means for the expander optical system is a first drive means for rotating a lens formed with a diffraction grating that divides a light beam into three beams around the optical axis, and at least one lens of the expander optical system A second driving unit that moves in the axial direction; and a third driving unit that moves at least one lens of the expander optical system in the radial direction of the optical recording medium in the plane orthogonal to the optical axis. The optical pickup according to any one of claims 1 to 4.   The first drive means of the expander optical system stores a first neutral point in a state where the three beams are on-track in the optical recording medium in the assembly process of the optical pickup, and second and third drive means However, in the assembly process of the optical pickup, the second and third neutral points in the state where the aberration is best or the information signal is best are stored, and the lens is placed at the stored first to third neutral points when the optical recording medium is set. 6. The optical pickup according to claim 5, wherein the optical pickup is initially moved.   The lens surface forming a diffraction grating that divides the light beam of the expander optical system into three beams is a lens surface having the largest curvature radius among the four lens surfaces of the expander optical system. Item 5. The optical pickup according to Item 5.   6. The optical pickup according to claim 5, wherein a lens surface forming a diffraction grating for dividing the light beam of the expander optical system into three beams is a flat surface. 5. The optical pickup according to claim 3, wherein the optical recording medium has an information recording surface at a thickness position of at least two of 0.1 mm, 0.6 mm, and 1.2 mm from the objective lens side. . The objective lens is a lens that has the best aberration with respect to the first optical recording medium,
The optical pickup according to claim 1, further comprising a diffraction element or a phase shifter element between the objective lens and the expander optical system.   11. The optical pickup according to claim 10, wherein the diffraction element or the phase shifter element selectively uses light beams having different diffraction orders depending on the optical recording medium.   11. The optical pickup according to claim 10, wherein the diffractive element or phase shifter element is formed integrally with an objective lens, and an element surface is formed on a light source side surface of the objective lens.   13. An optical information processing apparatus for recording and / or reproducing information on an optical recording medium, comprising the optical pickup according to any one of claims 1 to 12.

Images