JP2007328886A - Optical pickup device, and optical information recording medium recording and reproducing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical pickup device and an optical information recording medium recording and reproducing device which can perform appropriately recording and/or reproducing of information even when temperature variation and wavelength variation of a light source are caused. <P>SOLUTION: A controller CPU shifts (displacement) a collimation lens CL in an optical axis by an one shaft actuator AC2 for the reference position (position where spherical aberration is the minimum in the case of that temperature variation is not caused) by shift quantity prescribed in experiment and simulation based on signals from temperature sensors TS1, TS2, TS3, and spherical aberration caused by that wavelength variation is caused in a semiconductor laser LD1 by temperature variation, spherical variation caused by variation of refractive index of an objective optical element OBJ or collimation lens CL by temperature variation, or the like are corrected. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an optical pickup apparatus and an optical information recording medium recording / reproducing apparatus capable of recording and / or reproducing information interchangeably with different types of optical disks.

  In recent years, in an optical pickup device, a laser light source used as a light source for reproducing information recorded on an optical disc and recording information on the optical disc has been shortened. For example, a blue-violet semiconductor laser, Laser light sources with wavelengths of 400 to 420 nm, such as blue SHG lasers that perform wavelength conversion of infrared semiconductor lasers using harmonics, are being put into practical use. When these blue-violet laser light sources are used, when an objective lens having the same numerical aperture (NA) as that of a DVD (digital versatile disk) is used, it is possible to record information of 15 to 20 GB on an optical disk having a diameter of 12 cm. When the NA of the objective lens is increased to 0.85, 23 to 25 GB of information can be recorded on an optical disk having a diameter of 12 cm. Hereinafter, in this specification, an optical disk and a magneto-optical disk using a blue-violet laser light source are collectively referred to as a “high density optical disk”.

  In a high-density optical disk using an NA 0.85 objective lens, coma aberration generated due to the inclination (skew) of the optical disk increases, so the protective layer is designed thinner than in the case of DVD (0 of DVD). Some have reduced the amount of coma due to skew. As such an optical disc, there is a Blu-ray Disc (hereinafter referred to as BD).

  By the way, the value of an optical disc player / recorder (optical information recording medium recording / reproducing apparatus) as a product cannot be said to be sufficient simply by being able to appropriately record / reproduce information with respect to a high-density optical disc. In light of the reality that DVDs and CDs (compact discs) on which a wide variety of information is recorded are currently being sold, it is not possible to record / reproduce information on high-density optical discs. Similarly, making it possible to appropriately record / reproduce information on DVDs and CDs leads to an increase in commercial value as an optical disc player / recorder for high-density optical discs. From such a background, an optical pickup device mounted on an optical disc player / recorder for high density optical discs can appropriately receive information while maintaining compatibility with both high density optical discs, DVDs, and even CDs. It is desired to have a performance capable of recording / reproducing.

  As a method for recording / reproducing information appropriately while maintaining compatibility with both high-density optical discs and DVDs, and even CDs, optical systems for high-density optical discs and optical systems for DVDs and CDs are used. A method of selectively switching the system to and from the recording density of an optical disk for recording / reproducing information is conceivable, but a plurality of optical systems are required, which is disadvantageous for miniaturization and increases the cost.

  Therefore, in order to simplify the configuration of the optical pickup device and reduce the cost, the optical system for high-density optical discs and the optical system for DVDs and CDs must be shared in compatible optical pickup devices. Therefore, reducing the number of optical components constituting the optical pickup device as much as possible is advantageous in simplifying the configuration of the optical pickup device and reducing the cost. In order to obtain a common optical system for a plurality of types of optical disks having different recording / reproducing wavelengths, an optical path difference providing structure having a wavelength dependency of spherical aberration is provided in at least one optical element of the condensing optical system. Need to form.

Patent Document 1 discloses an objective optical system having a diffractive structure as an optical path difference providing structure, which can be used in common with a high-density optical disc and conventional DVDs and CDs, and an optical pickup device equipped with the objective optical system Is described.
European Patent No. 1304689

  More specifically, the effect of the diffractive structure will be described. BD, DVD, and CD are defined so that their protective substrate thicknesses differ according to their standards, so if the objective optical element is designed optimally for the protective substrate thickness of one of the optical discs, another optical disc is used. In this case, spherical aberration corresponding to the difference in the thickness of the protective substrate occurs. Therefore, an optical path difference providing structure such as a diffractive structure is provided on the optical surface of the commonly used objective optical element, and the light beam passing through the objective optical element is given a predetermined diffraction angle according to its wavelength, thereby protecting it. The spherical aberration is corrected according to the difference in substrate thickness.

  However, if the objective optical element is a single lens made of plastic in order to reduce the cost, it becomes sensitive to changes in the environment, and there is a possibility that an appropriate focused spot cannot be formed on the information recording surface of the optical disc. For example, when the temperature of the objective optical element changes greatly with respect to the reference temperature, a relatively large refractive index change occurs depending on the characteristics of the plastic, thereby deteriorating the spherical aberration. There is a possibility that recording and / or reproduction cannot be performed. In addition, since the diffractive structure gives a diffraction effect depending on the wavelength of the light beam passing therethrough, when the wavelength of the light source fluctuates, the diffraction angle imparted to the light beam changes, so that the spherical aberration deteriorates, and the optical disk However, there is a possibility that information cannot be properly recorded and / or reproduced.

  The present invention takes the above-described problems into consideration, and provides an optical pickup device and an optical information recording medium recording / reproducing device capable of appropriately recording and / or reproducing information even when a temperature change or a wavelength variation of a light source occurs. The purpose is to provide.

In order to solve the above problems, an optical pickup device according to claim 1 includes a first light source that emits a first light flux having a first wavelength λ1 (350 nm ≦ λ1 ≦ 440 nm), and a second wavelength λ2 (λ1 <λ2). ) And a second light source that emits a second light beam, and the first light beam is condensed on an information recording surface of a first optical disk having a protective substrate having a thickness t1 (0.065 mm ≦ t1 ≦ 0.125 mm). An objective optical element for condensing the second light beam on an information recording surface of a second optical disc having a protective substrate having a thickness t2 (t1 <t2), and the first light beam is the first light beam. In an optical pickup device for recording and / or reproducing information by condensing on an information recording surface of one optical disc and condensing the second light beam on an information recording surface of the second optical disc,
Having spherical aberration correction means for correcting spherical aberration,
The objective optical element is a single plastic lens having an optical path difference providing structure.

  According to the present invention, since the spherical aberration correcting means for correcting the spherical aberration is provided, even if the objective optical element is a single plastic lens, it changes due to temperature change or wavelength variation of the light source. Since the spherical aberration can be corrected, it is possible to appropriately record and / or reproduce information on different types of optical disks regardless of temperature changes and wavelength variations of the light source. As the “spherical aberration correction means”, a liquid crystal element or the like can be used in addition to an optical element that can be displaced in the optical axis direction described later. Examples of the optical element that can be displaced in the optical axis direction include a coupling lens, a collimating lens, and a beam expander that can be displaced in the optical axis direction. When these optical elements are displaced in the optical axis direction, spherical aberration is corrected by changing the amount of change in at least one of the emission angle and the diameter of the light beam.

  According to a second aspect of the present invention, in the optical pickup device according to the first aspect, the optical pickup device includes a third light source that emits a third light flux having a third wavelength λ3 (λ2 <λ3), and The objective optical element condenses the third light beam on an information recording surface of a third optical disk having a protective substrate having a thickness of t3 (t2 <t3), and the third light beam is recorded on the information recording surface of the third optical disk. Since the information is recorded and / or reproduced by condensing on the information, the information can be recorded and / or reproduced in a compatible manner with, for example, three types of optical disks of BD, DVD, and CD. Can do.

  According to a third aspect of the present invention, there is provided the optical pickup device according to the first or second aspect, wherein the spherical aberration correcting unit corrects a spherical aberration generated based on a temperature change of the optical pickup device. To do.

  According to a fourth aspect of the present invention, there is provided the optical pickup device according to the second or third aspect, wherein the spherical aberration correction means is the first light emitted from the first light source, the second light source, or the third light source. Since spherical aberration caused by the change of the first wavelength, the second wavelength, or the third wavelength of the light beam, the second light beam, or the third light beam is corrected, for example, due to a temperature change Even when the wavelength variation of the light source occurs, the spherical aberration can be appropriately corrected.

  According to a fifth aspect of the present invention, in the invention according to any one of the second to fourth aspects, the optical pickup device includes the first light beam, the second light beam, and the light beam separately from the objective optical element. An optical element that passes the third light beam in common, and the optical element changes at least one of an emission angle of the light beam and a diameter of the light beam according to an optical disk to be used, and the spherical aberration The correcting means corrects a spherical aberration caused by a difference between the temperature of the optical element and the temperature of the objective optical element.

  According to a sixth aspect of the present invention, in the invention according to any one of the second to fifth aspects, the spherical aberration correction unit is caused by a manufacturing error of the first light source, the second light source, or the third light source. Since the spherical aberration generated due to the difference between the generated first wavelength, the second wavelength, or the third wavelength and the reference wavelength is corrected, the wavelength variation is caused by, for example, manufacturing variation of the laser light source. Even if it occurs, the spherical aberration can be appropriately corrected.

  An optical pickup device according to a seventh aspect of the present invention is the optical pickup device according to any one of the first to sixth aspects, wherein the optical pickup device has a temperature detection unit, and based on a detection result of the temperature detection unit. Since the spherical aberration is corrected by the spherical aberration correcting means, the spherical aberration can be corrected with high accuracy. Here, as the “temperature detection means”, in addition to the thermistor, temperature detection IC, etc., when measuring the coil current of the actuator that drives the objective optical element to obtain the temperature, a known ammeter or the like is used. it can. The temperature detection means may be provided in the vicinity of the light source (particularly preferably, in the vicinity of the first light source) or may be provided in the vicinity of the objective optical element.

  An optical pickup device according to an eighth aspect of the present invention is the optical pickup device according to the seventh aspect, wherein when the temperature detecting unit detects that the temperature change is equal to or higher than a predetermined temperature, the spherical aberration correcting unit performs spherical aberration. Therefore, it is possible to simplify, for example, sequence control for spherical aberration correction.

  An optical pickup device according to a ninth aspect of the present invention is the optical pickup device according to any one of the first to eighth aspects, wherein the optical pickup device has a spherical aberration detector, and the detection result of the spherical aberration detector is included in the detection result. On the basis of this, the spherical aberration correction means corrects the spherical aberration, so that accurate spherical aberration correction can be performed. As the “spherical aberration detection means”, for example, those described in Japanese Patent Application No. 2002-304763 can be used.

  The optical pickup device according to claim 10 is the invention according to any one of claims 2 to 9, wherein the optical pickup device is a current supplied to the first light source, the second light source, or the third light source. Current value detecting means for detecting the value of the current value, and the spherical aberration is corrected by the spherical aberration correcting means based on the detection result of the current value detecting means. Correction is possible. In particular, it is preferable to detect the current value of the first light source.

  The optical pickup device according to claim 11 is the wavelength detection according to any one of claims 2 to 10, wherein the optical pickup device detects the first wavelength, the second wavelength, or the third wavelength. And the spherical aberration correction unit corrects the spherical aberration based on the detection result of the wavelength detection unit, so that the spherical aberration can be corrected with high accuracy. In particular, it is preferable to detect the first wavelength.

  An optical information recording medium recording / reproducing apparatus according to a twelfth aspect uses the optical pickup apparatus according to any one of the first to eleventh aspects.

  In the present specification, it is preferable that the first optical disk is a high-density optical disk, the second optical disk is a DVD, and the third optical disk is a CD, but the present invention is not limited to this. The first optical disc, the second optical disc, or the third optical disc may be a multi-layer optical disc having a plurality of information recording surfaces.

  In the present specification, as an example of a high-density optical disc, a standard optical disc (for example, a BD) in which information is recorded / reproduced by an objective optical element having a NA of 0.85 and a protective substrate has a thickness of about 0.1 mm. : Blu-ray Disc). The high-density optical disk includes a magneto-optical disk in which a blue-violet semiconductor laser or a blue-violet SHG laser is used as a light source for recording / reproducing information. Further, in this specification, a DVD refers to a DVD series optical disc in which information is recorded / reproduced by an objective optical element having an NA of about 0.60 to 0.67 and the protective substrate has a thickness of about 0.6 mm. It is a generic name and includes DVD-ROM, DVD-Video, DVD-Audio, DVD-RAM, DVD-R, DVD-RW, DVD + R, DVD + RW, and the like. Further, in this specification, a CD is a CD series optical disc in which information is recorded / reproduced by an objective optical element having an NA of about 0.45 to 0.51 and the protective substrate has a thickness of about 1.2 mm. It is a generic name and includes CD-ROM, CD-Audio, CD-Video, CD-R, CD-RW, and the like. As for the recording density, the recording density of the high-density optical disk is the highest, and then decreases in the order of DVD and CD.

In addition, regarding the thicknesses t1, t2, and t3 of the protective substrate, it is preferable to satisfy the following conditional expression, but the present invention is not limited to this.
0.065mm ≦ t1 ≦ 0.125mm or 0.5mm ≦ t1 ≦ 0.7mm
0.5mm ≦ t2 ≦ 0.7mm
1.0mm ≦ t3 ≦ 1.3mm

  In the present specification, the first light source, the second light source, and the third light source are preferably laser light sources. As the laser light source, a semiconductor laser, a silicon laser, or the like can be preferably used.

  When BD, DVD, and CD are used as the first optical disc, the second optical disc, and the third optical disc, respectively, the first wavelength λ1 of the first light source is preferably 350 nm or more and 440 nm or less, more preferably 380 nm. The second wavelength λ2 of the second light source is preferably 570 nm or more and 680 nm or less, more preferably 630 nm or more and 670 nm or less, and the third wavelength λ3 of the third light source is preferably 750 nm. As mentioned above, it is 880 nm or less, More preferably, it is 760 nm or more and 820 nm or less.

  Further, at least two of the first light source, the second light source, and the third light source may be unitized. The unitization means that the first light source and the second light source are fixedly housed in one package, for example. However, the unitization is not limited to this, and the two light sources are fixed so that the aberration cannot be corrected. Is widely included. In addition to the light source, a light receiving element to be described later may be packaged.

  As the light receiving element, a photodetector such as a photodiode is preferably used. Light reflected on the information recording surface of the optical disc enters the light receiving element, and a read signal of information recorded on each optical disc is obtained using the output signal. Furthermore, it detects the change in the amount of light due to the change in the shape and position of the spot on the light receiving element, performs focus detection and track detection, and moves the objective optical element for focusing and tracking based on this detection I can do it. The light receiving element may comprise a plurality of photodetectors. The light receiving element may have a main photodetector and a sub photodetector. For example, two sub photodetectors are provided on both sides of a photodetector that receives main light used for recording and reproducing information, and the sub light for tracking adjustment is received by the two sub photodetectors. It is good also as a simple light receiving element. The light receiving element may have a plurality of light receiving elements corresponding to the respective light sources.

  The condensing optical system has at least one optical element such as an objective optical element. The condensing optical system may have only the objective optical element. In addition to the objective optical element, other optical elements such as a coupling lens such as a collimator, a beam expander, and a flat plate optical element having an optical function may be used. You may have an element. The coupling lens refers to a single lens or a lens group that is disposed between the objective optical element and the light source and changes the divergence angle of the light beam. Further, the condensing optical system has an optical element such as a diffractive optical element that divides the light beam emitted from the light source into a main light beam used for recording and reproducing information and two sub light beams used for tracking and the like. May be. In this specification, the objective optical element refers to an optical system that is disposed at a position facing the optical disk in the optical pickup device and has a function of condensing a light beam emitted from a light source on an information recording surface of the optical disk. Preferably, the objective optical element is an optical system that is disposed at a position facing the optical disc in the optical pickup device and has a function of condensing a light beam emitted from the light source on the information recording surface of the optical disc, An optical system that can be integrally displaced at least in the optical axis direction by an actuator. The objective optical element of the present invention is a single plastic lens having an optical path difference providing structure.

The plastic forming the optical element such as the objective optical element is preferably a cyclic olefin-based resin material. Among the cyclic olefin-based plastics, the refractive index at a temperature of 25 ° C. for a wavelength of 405 nm is 1.54 to 1.60. The refractive index change rate dN / dT (° C. ⁻¹ ) with respect to the wavelength of 405 nm accompanying the temperature change within the temperature range of −5 ° C. to 70 ° C. is −20 × 10 ^{−5 to} −5 × 10 ^It is more preferable to use a resin material in the range of ⁻⁵ (more preferably −10 × 10 ^{−5 to} −8 × 10 ⁻⁵ ). When the objective optical element is a plastic lens, the coupling lens is preferably a plastic lens.

  Alternatively, as the resin material suitable for the objective optical element of the present invention, there is “athermal resin” in addition to the above cyclic olefin. An athermal resin is a resin material in which particles having a diameter of 30 nm or less and having a refractive index change rate with an opposite sign to the refractive index change rate associated with a temperature change of a resin as a base material are dispersed.

  A preferred example of the objective optical element will be specifically described. At least one optical surface of the objective optical element has a central region and a peripheral region around the central region. More preferably, at least one optical surface of the objective optical element has an outermost peripheral region around the peripheral region. By providing the outermost peripheral area, recording and / or reproduction with respect to an optical disk with a high NA can be performed more appropriately. The central region is preferably a region including the optical axis of the objective optical element, but may be a region not including the optical axis. It is preferable that the central region, the peripheral region, and the most peripheral region are provided on the same optical surface. As shown in FIG. 1, the central region CN, the peripheral region MD, and the most peripheral region OT are preferably provided concentrically around the optical axis on the same optical surface. In addition, a first optical path difference providing structure is provided in the central area of the objective optical element, and a second optical path difference providing structure is provided in the peripheral area. In the case of having the outermost peripheral region, the outermost peripheral region may be a refractive surface, or the third optical path difference providing structure may be provided in the outermost peripheral region. The central region, the peripheral region, and the outermost peripheral region are preferably adjacent to each other, but there may be a slight gap between them.

  The first optical path difference providing structure is preferably provided in a region of 70% or more of the area of the central region of the objective optical element, and more preferably 90% or more. More preferably, the first optical path difference providing structure is provided on the entire surface of the central region. The second optical path difference providing structure is preferably provided in a region of 70% or more of the area of the peripheral region of the objective optical element, and more preferably 90% or more. More preferably, the second optical path difference providing structure is provided on the entire surface of the peripheral region. The third optical path difference providing structure is preferably provided in a region of 70% or more of the area of the outermost peripheral region of the objective optical element, and more preferably 90% or more. More preferably, the third optical path difference providing structure is provided on the entire surface of the outermost peripheral region.

  In addition, the optical path difference providing structure in this specification is a general term for structures that add an optical path difference to an incident light beam. The optical path difference providing structure also includes a phase difference providing structure for providing a phase difference. The phase difference providing structure includes a diffractive structure. The optical path difference providing structure has a step, preferably a plurality of steps. This step adds an optical path difference and / or phase difference to the incident light flux. The optical path difference added by the optical path difference providing structure may be an integer multiple of the wavelength of the incident light beam or a non-integer multiple of the wavelength of the incident light beam. The steps may be arranged with a periodic interval in the direction perpendicular to the optical axis, or may be arranged with a non-periodic interval in the direction perpendicular to the optical axis.

  The optical path difference providing structure preferably has a plurality of concentric annular zones centered on the optical axis. In addition, the optical path difference providing structure can have various cross-sectional shapes (cross-sectional shapes in a plane including the optical axis). The most common cross-sectional shape of the optical path difference providing structure is a case where the cross-sectional shape including the optical axis of the optical path difference providing structure is serrated as shown in FIG. When a planar optical element is provided with an optical path difference providing structure, the cross section looks like a staircase, but when a similar optical path difference providing structure is provided on an aspheric lens surface or the like, a saw blade as shown in FIG. It can be considered as a cross-sectional shape. Therefore, the sawtooth cross-sectional shape referred to in this specification includes a step-like cross-sectional shape. Moreover, it is also possible to obtain an optical path difference providing structure having a binary structure as shown in FIG. 2B by superimposing sawtooth optical path difference providing structures having different step directions. The first optical path difference providing structure and the second optical path difference providing structure of the present specification may have a structure in which cross-sectional shapes are superimposed with different sawtooth optical path difference providing structures, or an optical path difference providing structure on the sawtooth is superimposed. Alternatively, a sawtooth optical path difference providing structure may be superimposed on a binary optical path difference providing structure. For example, FIG. 2C shows a structure in which a sawtooth shape and a binary structure are superimposed, and FIG. 2D shows a structure in which a fine sawtooth structure and a rough sawtooth structure are superimposed.

  The first optical path difference providing structure provided in the central area of the objective optical element and the second optical path difference providing structure provided in the peripheral area of the objective optical element may be provided on different optical surfaces of the objective optical element. Are preferably provided on the same optical surface. Providing them on the same optical surface is preferable because it makes it possible to reduce eccentricity errors during manufacturing. Moreover, it is preferable that the first optical path difference providing structure and the second optical path difference providing structure are provided on the light source side surface of the objective optical element rather than the optical disk side surface of the objective optical element.

  In a preferred example of the objective optical element, the first light flux, the second light flux, and the third light flux that pass through the central region where the first optical path difference providing structure of the objective optical element is provided are formed as a condensed spot. Condensate. Preferably, the objective optical element can record and / or reproduce information on the information recording surface of the first optical disc by using the first light beam passing through the central region provided with the first optical path difference providing structure of the objective optical element. Condensate like so. In a preferred example of the objective optical element, the second light flux passing through the central region provided with the first optical path difference providing structure of the objective optical element is recorded on the information recording surface of the second optical disc and / or Light is collected so that it can be regenerated. Furthermore, a suitable example of the objective optical element is a method of recording information on the information recording surface of the third optical disc and / or recording the third light beam passing through the central region where the first optical path difference providing structure of the objective optical element is provided. Light is collected so that it can be regenerated. Further, when the thickness t1 of the protective substrate of the first optical disc is different from the thickness t2 of the protective substrate of the second optical disc, the first optical path difference providing structure has the first light flux that has passed through the first optical path difference providing structure and the second optical flux. It occurs due to the spherical aberration generated by the difference between the thickness t1 of the protective substrate of the first optical disk and the thickness t2 of the protective substrate of the second optical disk and / or the difference in the wavelengths of the first and second light beams. It is preferable to correct spherical aberration. Further, the first optical path difference providing structure has a thickness t1 of the protective substrate of the first optical disc and a thickness of the protective substrate of the third optical disc with respect to the first light beam and the third light beam that have passed through the first optical path difference providing structure. It is preferable to correct spherical aberration generated due to a difference from t3 and / or spherical aberration generated due to a difference in wavelength between the first light flux and the third light flux.

  The first best focus at which the spot diameter of the spot formed by the third light flux is minimized by the third light flux that has passed through the first optical path difference providing structure of the objective optical element, and the spot diameter of the spot formed by the third light flux. Is formed next to the second best focus which becomes smaller than the first best focus. Here, the best focus refers to a point at which the beam waist is minimized within a certain defocus range. That is, the first best focus and the second best focus are formed by the third light beam, which means that there are at least two points in the third light beam at which the beam waist is minimized within a certain defocus range. That's what it means. In the third light flux that has passed through the first optical path difference providing structure, it is preferable that the diffracted light having the largest light amount forms the first best focus, and the diffracted light having the second largest light amount forms the second best focus. . Further, when the difference between the diffraction efficiency of the diffracted light forming the first best focus and the diffraction efficiency of the diffracted light forming the second best focus is 20% or less, the effect of the present invention becomes more remarkable.

  The spot formed by the third light beam at the first best focus is used for recording and / or reproduction of the third optical disk, and the spot formed by the third light beam at the second best focus is recorded and / or recorded on the third optical disk. Alternatively, it is preferable that the spot formed by the third light beam at the first best focus is not used for recording and / or reproduction of the third optical disc, and the third light beam is formed at the second best focus. This does not deny an aspect in which the spot is used for recording and / or reproduction of the third optical disc. When the first optical path difference providing structure is provided on the light source side surface of the objective optical element, the second best focus is preferably closer to the objective optical element than the first best focus.

Further, the first best focus and the second best focus satisfy the following formula (1).
0.05 ≦ L / f ≦ 0.35 (1)
However, f [mm] refers to the focal length of the third light flux that passes through the first optical path difference providing structure and forms the first best focus, and L [mm] is between the first best focus and the second best focus. Refers to distance.

It is more preferable to satisfy the following formula (1) ′.
0.10 ≦ L / f ≦ 0.25 (1 ′)

  L is preferably 0.18 mm or more and 0.63 mm or less. Furthermore, it is preferable that f is 1.8 mm or more and 3.0 mm or less.

  With the above configuration, it is possible to prevent unnecessary light, which is not used during recording and / or reproduction of the third optical disk, from adversely affecting the tracking light-receiving element during recording and / or reproduction of the third optical disk. This makes it possible to maintain good tracking performance during recording and / or reproduction of the third optical disc.

  In a preferred example of the objective optical element, the first light flux and the second light flux that pass through the peripheral region where the second optical path difference providing structure of the objective optical element is provided are condensed so as to form a condensed spot, respectively. To do. Preferably, the objective optical element is capable of recording and / or reproducing information on the information recording surface of the first optical disc by using the first light flux that passes through the peripheral region provided with the second optical path difference providing structure of the objective optical element. Condensate like so. A preferred example of the objective optical element is to record the information on the information recording surface of the second optical disc and / or record the second light flux that passes through the peripheral area where the second optical path difference providing structure of the objective optical element is provided. Light is collected so that it can be regenerated. Further, when the thickness t1 of the protective substrate of the first optical disc is different from the thickness t2 of the protective substrate of the second optical disc, the second optical path difference providing structure has the first light flux that has passed through the second optical path difference providing structure and the second optical path difference providing structure. It occurs due to the spherical aberration generated by the difference between the thickness t1 of the protective substrate of the first optical disk and the thickness t2 of the protective substrate of the second optical disk and / or the difference in the wavelengths of the first and second light beams. It is preferable to correct spherical aberration.

  In addition, as a preferable aspect, there is an aspect in which the third light flux that has passed through the peripheral region is not used for recording and / or reproduction of the third optical disk. It is preferable that the third light flux that has passed through the peripheral region does not contribute to the formation of a focused spot on the information recording surface of the third optical disc. That is, it is preferable that the third light flux that passes through the peripheral region provided with the second optical path difference providing structure of the objective optical element forms a flare on the information recording surface of the third optical disc. As shown in FIG. 3, in the spot formed on the information recording surface of the third optical disk by the third light flux that has passed through the objective optical element, the light amount density is increased in the order from the optical axis side (or the center of the spot) to the outside. It has a high spot center portion SCN, a spot intermediate portion SMD having a light amount density lower than that of the spot center portion, and a spot peripheral portion SOT having a light amount density higher than that of the spot intermediate portion and lower than that of the spot center portion. The center portion of the spot is used for recording and / or reproducing information on the optical disc, and the spot intermediate portion and the spot peripheral portion are not used for recording and / or reproducing information on the optical disc. In the above, this spot peripheral part is called flare. That is, the third light flux that has passed through the second optical path difference providing structure provided in the peripheral region of the objective optical element forms a spot peripheral portion on the information recording surface of the third optical disc. In addition, it is preferable that the condensing spot or spot of a 3rd light beam here is a spot in 1st best focus. In the second light flux that has passed through the objective optical element, it is preferable that the spot formed on the information recording surface of the second optical disc has a spot central portion, a spot intermediate portion, and a spot peripheral portion.

  Further, the second optical path difference providing structure is a spherochromatism generated by a slight fluctuation in the wavelength of the first light source or the second light source with respect to the first light flux and the second light flux that have passed through the second optical path difference providing structure. It is preferable to correct (chromatic spherical aberration). A slight change in wavelength refers to a change of ± 10 nm or less. For example, when the first light beam changes by ± 5 nm from the wavelength λ1, the second optical path difference providing structure compensates for the variation in spherical aberration of the first light beam that has passed through the peripheral region, and on the information recording surface of the first optical disk. It is preferable that the change amount of the wavefront aberration is 0.010λ1 rms or more and 0.095λ1 rms or less. Further, when the second light flux changes by ± 5 nm from the wavelength λ2, the second optical path difference providing structure compensates for the variation of the spherical aberration of the second light flux that has passed through the peripheral region, and on the information recording surface of the second optical disc. It is preferable that the change amount of the wavefront aberration is 0.002λ2 rms or more and 0.03λ2 rms or less. This makes it possible to correct aberrations caused by wavelength variations due to manufacturing errors and individual differences in the wavelength of the laser that is the light source.

  When the objective optical element has the outermost peripheral area, the objective optical element can record and / or reproduce information on the information recording surface of the first optical disc by using the first light flux passing through the outermost peripheral area of the objective optical element. It is good to concentrate on. Further, it is preferable that the spherical aberration of the first light flux that has passed through the most peripheral area is corrected during recording and / or reproduction of the first optical disk.

  In a preferred embodiment, the second light flux that has passed through the outermost peripheral area is not used for recording and / or reproduction of the second optical disk, and the third light flux that has passed through the outermost peripheral area is recorded and / or recorded on the third optical disk. An embodiment that is not used for reproduction is included. It is preferable that the second light flux and the third light flux that have passed through the outermost peripheral region do not contribute to the formation of a condensed spot on the information recording surfaces of the second optical disc and the third optical disc, respectively. That is, when the objective optical element has the outermost peripheral region, it is preferable that the third light flux passing through the outermost peripheral region of the objective optical element forms a flare on the information recording surface of the third optical disc. In other words, it is preferable that the third light flux that has passed through the outermost peripheral region of the objective optical element forms a spot peripheral portion on the information recording surface of the third optical disc. When the objective optical element has the most peripheral area, the second light flux that passes through the most peripheral area of the objective optical element preferably forms a flare on the information recording surface of the second optical disk. In other words, the second light flux that has passed through the most peripheral area of the objective optical element preferably forms a spot peripheral portion on the information recording surface of the second optical disc.

  When the outermost peripheral region has the third optical path difference providing structure, the third optical path difference providing structure is generated by a slight variation in the wavelength of the first light source with respect to the first light flux that has passed through the third optical path difference providing structure. Spherochromatism (chromatic spherical aberration) may be corrected. A slight change in wavelength refers to a change of ± 10 nm or less. For example, when the first light beam changes by ± 5 nm from the wavelength λ1, the third optical path difference providing structure compensates for the variation in spherical aberration of the first light beam that has passed through the most peripheral region, and on the information recording surface of the first optical disc. It is preferable that the amount of change in wavefront aberration at 0.010λ1 rms to 0.095λ1 rms.

  The first optical path difference providing structure may have a configuration in which a sawtooth diffraction structure and a binary structure are superimposed. Further, the second optical path difference providing structure may have a configuration in which a sawtooth diffractive structure and a rougher (large pitch) sawtooth diffractive structure are superimposed. When the first optical path difference providing structure or the second optical path difference providing structure is the superposed structure, the sawtooth diffractive structure (the diffractive structure that is not rough (small pitch) in the case of the second optical path difference providing structure) The optical path difference corresponding to an even multiple of the first wavelength λ1 of the first light flux may be provided so that the phase of the wavefront of the first light flux does not change. Further, when the third wavelength λ3 of the third light flux is a wavelength that is substantially an even multiple of the first wavelength of the first light flux, an optical path difference of an integral multiple is given, and similarly the phase of the wavefront changes. Will not occur. With such a configuration, there is an advantage that the first light flux and the third light flux are not affected by the diffraction structure. Note that even-numbered equivalent means a range of (2n−0.1) × λ1 or more and (2n + 0.1) × λ1 or less when n is a natural number.

  The first optical path difference providing structure may be a structure in which at least the first basic structure and the second basic structure are overlapped.

  The first basic structure makes the second-order diffracted light amount of the first light beam that has passed through the first basic structure larger than any other order of diffracted light amount, and the first-order diffracted light amount of the second light beam has any other order In this optical path difference providing structure, the first order diffracted light amount of the third light flux is made larger than the diffracted light amount and larger than any other order diffracted light amount. The first basic structure emits the first light flux and the third light flux that have passed through the first basic structure in a state where the wavefronts are substantially aligned, and the second light flux that has passed through the first basic structure in a state where the wavefronts are not aligned. It is preferable that the optical path difference providing structure be emitted. The first basic structure is preferably an optical path difference providing structure that makes the diffraction angle of the second light beam that has passed through the first basic structure different from the diffraction angles of the first light beam and the third light beam.

  In addition, the second basic structure makes the 0th-order (transmitted light) diffracted light quantity of the first light flux that has passed through the second basic structure larger than any other order diffracted light quantity, and the 0th-order (transmitted light) of the second light flux. ) Is made larger than any other order diffracted light quantity, and the ± 1st order diffracted light quantity of the third light flux is made larger than any other order diffracted light quantity. The second foundation structure emits the first light flux and the second light flux that have passed through the second foundation structure in a state where the wavefronts are substantially aligned, and the third light flux that has passed through the first foundation structure in a state where the wavefronts are not aligned. It is preferable that the optical path difference providing structure be emitted. The second basic structure is preferably an optical path difference providing structure that makes the diffraction angle of the third light beam that has passed through the second basic structure different from the diffraction angles of the first light beam and the second light beam.

  The second optical path difference providing structure is preferably a structure having at least one of the first basic structure, the fifth basic structure, and the sixth basic structure. In addition, it is preferable that 2nd optical path difference providing structure is not the structure which overlaps 2 or more among 1st foundation structure, 5th foundation structure, and 6th foundation structure. In the case where the second optical path difference providing structure has at least the first basic structure, it has the same basic structure as the first optical path difference providing structure, which is preferable because it facilitates design.

  In the fifth basic structure, the first-order diffracted light amount of the first light beam that has passed through the fifth basic structure is made larger than any other order diffracted light amount, and the first-order diffracted light amount of the second light beam is set to any other order. In this optical path difference providing structure, the first order diffracted light amount of the third light flux is made larger than the diffracted light amount and larger than any other order diffracted light amount.

  In the sixth basic structure, the third-order diffracted light quantity of the first light beam that has passed through the sixth basic structure is made larger than any other order diffracted light quantity, and the second-order diffracted light quantity of the second light beam is set to any other order. In this optical path difference providing structure, the second order diffracted light quantity of the third light flux is made larger than the diffracted light quantity and larger than any other order diffracted light quantity.

  Since the objective optical element is a plastic lens, the first optical path difference providing structure is preferably a triple overlapping structure in which three types of basic structures are overlapped. More specifically, in addition to the first basic structure and the second basic structure, a triple overlapping structure in which the third basic structure or the fourth basic structure is overlapped is preferable. More preferably, in addition to the first foundation structure and the second foundation structure, the third foundation structure is superposed.

  In the third basic structure, the 10th-order diffracted light quantity of the first light flux that has passed through the third basic structure is made larger than any other order diffracted light quantity, and the sixth-order diffracted light quantity of the second light flux is set to any other quantity. In this optical path difference providing structure, the fifth order diffracted light amount of the third light flux is made larger than the diffracted light amount of the third order and larger than any other order diffracted light amount. In addition, the fourth basic structure makes the fifth-order diffracted light quantity of the first light beam that has passed through the fourth basic structure larger than any other order of diffracted light quantity, and the third-order diffracted light quantity of the second light beam becomes any other diffracted light quantity. This is an optical path difference providing structure that is larger than the diffracted light quantity of the order and makes the third and second diffracted light quantities of the third light flux larger than any other order diffracted light quantity. In the third light flux, it is preferable that the third-order diffracted light amount is slightly larger than the second-order diffracted light amount. Further, the third basic structure and the fourth basic structure have a function of making the spherical aberration under when the temperature rises and the wavelengths of the first light source, the second light source, and the third light source extend. As a result, it is possible to compensate for the over-spherical aberration accompanying the decrease in the refractive index of the plastic when the temperature rises, and it becomes possible to obtain a good spherical aberration. Note that the depth of the step can be made shallower in the fourth foundation structure than in the third foundation structure.

  In addition, since the objective optical element is a plastic lens, the second optical path difference providing structure includes the third basic structure or the third basic structure in addition to any one of the first basic structure, the fifth basic structure, and the sixth basic structure. A structure in which any one of the four basic structures is overlapped is preferable. Preferably, the first basic structure and the fourth basic structure are overlapped.

  Furthermore, when the objective optical element is a plastic lens, it is preferable to have the most peripheral region having the third optical path difference providing structure. In this case, the third optical path difference providing structure is preferably a structure having at least one of the third basic structure and the fourth basic structure. A structure having a fourth basic structure is preferable.

  Next, when the objective optical element is a lens made of an athermal resin, the first optical path difference providing structure is preferably a structure in which only the first basic structure and the second basic structure are overlapped.

  When the objective optical element is a lens made of an athermal resin, the second optical path difference providing structure includes the third basic structure in addition to any one of the first basic structure, the fifth basic structure, and the sixth basic structure. A structure in which any one of the structure and the fourth basic structure is overlapped is preferable. Preferably, the first basic structure and the fourth basic structure are overlapped.

  Furthermore, when the objective optical element is a lens made of an athermal resin, it is preferable that the objective optical element has a most peripheral region that is a refractive surface.

  The objective optical element necessary for reproducing and / or recording information on the first optical disk is NA1, and the objective optical necessary for reproducing and / or recording information on the second optical disk is NA1. The image side numerical aperture of the element is NA2 (NA1 ≧ NA2), and the image side numerical aperture of the objective optical element necessary for reproducing and / or recording information on the third optical disk is NA3 (NA2> NA3). .

  The boundary between the central region and the peripheral region of the objective optical element corresponds to a range of 0.9 · NA 3 or more and 1.2 · NA 3 or less (more preferably 0.95 · NA 3 or more and 1.15 · NA 3 or less). It is preferable to be formed in the part. More preferably, the boundary between the central region and the peripheral region of the objective optical element is formed in a portion corresponding to NA3. The boundary between the peripheral region and the most peripheral region of the objective optical element is in a range of 0.9 · NA 2 or more and 1.2 · NA 2 or less (more preferably 0.95 · NA 2 or more and 1.15 · NA 2 or less). It is preferable to be formed in a portion corresponding to. More preferably, the boundary between the peripheral region and the most peripheral region of the objective optical element is formed in a portion corresponding to NA2. The outer boundary of the outermost periphery of the objective optical element is formed in a portion corresponding to a range of 0.9 · NA1 or more and 1.2NA1 or less (more preferably 0.95 · NA1 or more and 1.15 · NA1 or less). It is preferable that More preferably, the outer boundary of the outermost periphery of the objective optical element is formed in a portion corresponding to NA1.

  When the third light beam that has passed through the objective optical element is condensed on the information recording surface of the third optical disk, it is preferable that the spherical aberration has at least one discontinuous portion. In that case, it is preferable that the discontinuous portion exists in a range of 0.9 · NA 3 or more and 1.2 · NA 3 or less (more preferably 0.95 · NA 3 or more and 1.15 · NA 3 or less). Also, when the second light flux that has passed through the objective optical element is condensed on the information recording surface of the second optical disc, it is preferable that the spherical aberration has at least one discontinuous portion. In that case, it is preferable that the discontinuous portion exists in a range of 0.9 · NA 2 or more and 1.2 · NA 2 or less (more preferably 0.95 · NA 2 or more and 1.1 · NA 2 or less).

  Further, when spherical aberration is continuous and does not have a discontinuous portion, and the third light flux that has passed through the objective optical element is condensed on the information recording surface of the third optical disk, NA2 It is preferable that the absolute value of the longitudinal spherical aberration is 0.03 μm or more, and in NA3, the absolute value of the longitudinal spherical aberration is 0.02 μm or less. More preferably, in NA2, the absolute value of longitudinal spherical aberration is 0.08 μm or more, and in NA3, the absolute value of longitudinal spherical aberration is 0.01 μm or less. When the second light flux that has passed through the objective optical element is condensed on the information recording surface of the second optical disk, the absolute value of the longitudinal spherical aberration is 0.03 μm or more at NA1, and the longitudinal spherical aberration at NA2. Is preferably 0.005 μm or less.

  In addition, since the diffraction efficiency depends on the ring zone depth of the diffractive structure, the diffraction efficiency for each wavelength in the central region can be appropriately set according to the use of the optical pickup device. For example, in the case of an optical pickup device that performs recording and reproduction with respect to the first optical disk and only performs reproduction with respect to the second and third optical disks, the diffraction efficiency in the central region and / or the peripheral region is considered to be focused on the first light flux. It is preferable to do this. On the other hand, in the case of an optical pickup device that performs only reproduction with respect to the first optical disc and performs recording and reproduction with respect to the second and third optical discs, the diffraction efficiency in the central region is focused on the second and third light fluxes. In addition, it is preferable that the diffraction efficiency of the peripheral region is focused on the second light flux.

  In any case, by satisfying the following conditional expression (11), it is possible to ensure a high diffraction efficiency of the first light flux calculated by the area weighted average of each region.

η11 ≦ η21 (11)
However, η11 represents the diffraction efficiency of the first light flux in the central region, and η21 represents the diffraction efficiency of the first light flux in the peripheral region. When the diffraction efficiency of the central region is focused on the light fluxes of the second and third wavelengths, the diffraction efficiency of the first light flux of the central region is low, but the numerical aperture of the first optical disc is the numerical aperture of the third optical disc. If it is larger than, the lowering of the diffraction efficiency in the central region does not have a significant effect when considering the entire effective diameter of the first light flux.

In addition, the diffraction efficiency in this specification can be defined as follows.
(1) The transmittance of an objective optical element that has the same focal length, lens thickness, and numerical aperture, is formed of the same material, and does not have the first and second optical path difference providing structures, is represented by a central region and a peripheral region. Measure separately. At this time, the transmittance of the central region is measured by blocking the light beam incident on the peripheral region, and the transmittance of the peripheral region is measured by blocking the light beam incident on the central region.
(2) The transmittance of the objective optical element having the first and second optical path difference providing structures is measured separately for the central region and the peripheral region.
(3) The value obtained by dividing the result of (2) above by the result of (1) is defined as the diffraction efficiency of each region.

  The light utilization efficiency of any two of the first to third light fluxes is 80% or more, and the light utilization efficiency of the remaining one light flux is 30% or more and 80% or less. Good. The light utilization efficiency of the remaining one light beam may be 40% or more and 70% or less. In this case, it is preferable that the light flux having a light utilization efficiency of 30% or more and 80% or less (or 40% or more and 70% or less) is the third light flux.

  Here, the light utilization efficiency is the information on the optical disk by the objective optical element in which the first optical path difference providing structure and the second optical path difference providing structure are formed (the third optical path difference providing structure may be formed). The amount of light in the Airy disk of the focused spot formed on the recording surface is A, and is formed of the same material and has the same focal length, axial thickness, numerical aperture, and wavefront aberration. The objective optical element in which the optical path difference providing structure, the second optical path difference providing structure, and the third optical path difference providing structure are not formed is used to change the amount of light in the airy disc of the condensing spot formed on the information recording surface of the optical information recording medium. , It shall be calculated by A / B. Here, the Airy disk refers to a circle having a radius r ′ centered on the optical axis of the focused spot. r ′ = 0.61 · λ / NA.

  Further, in the third light flux that has passed through the first optical path difference providing structure, the difference between the light amount of the diffracted light having the maximum light amount and the light amount of the diffracted light having the next largest light amount, ie, the first light amount. When the difference between the light amount of the diffracted light forming the best focus and the light amount of the diffracted light forming the second best focus is not less than 0% and not more than 20%, particularly the tracking characteristics in the third optical disk can be kept good. Although difficult, the present invention makes it possible to improve the tracking characteristics even in such a situation.

The first light beam, the second light beam, and the third light beam may be incident on the objective optical element as parallel light, or may be incident on the objective optical element as divergent light or convergent light. Preferably, the magnifications m1 and m2 of the first light beam and the second light beam incident on the objective optical element satisfy the following expressions (2) and (3).
-0.02 <m1 <0.02 (2)
−0.02 <m2 <0.02 (3)

Further, when the third light beam is incident on the objective optical element as parallel light or substantially parallel light, it is preferable that the magnification m3 of the third light beam incident on the objective optical element satisfies the following formula (4). When the third light flux is parallel light, a problem easily occurs in tracking. However, even if the third light flux is parallel light, the present invention can obtain good tracking characteristics, and can be used for three different optical disks. On the other hand, recording and / or reproduction can be appropriately performed.
−0.02 <m3 <0.02 (4)

On the other hand, when the third light beam is incident on the objective optical element as divergent light, it is preferable that the magnification m3 of the third light beam incident on the objective optical element satisfies the following expression (5).
-0.10 <m3 <0.00 (5)

  When the wavelength of the light beam emitted from each light source (especially the wavelength of the first light beam emitted from the first light source) changes by ± 5 nm, the wavefront aberration on the information recording surface of each optical disk (particularly the first optical disk) is changed. The change amount is preferably 0.010λ1 rms or more and 0.095λ1 rms or less. Further, when the environmental temperature is changed by ± 30 ° C. from the design reference temperature, the spherical aberration of the first light flux is corrected, and the amount of change of the wavefront aberration on the information recording surface of the first optical disc is 0.010λ1 rms or more, 0 0.095λ1 rms or less is preferable.

  In addition, the working distance (WD) of the objective optical element when using the third optical disk is preferably 0.20 mm or more and 1.5 mm or less. Preferably, it is 0.3 mm or more and 1.00 mm or less. Next, the WD of the objective optical element when using the second optical disc is preferably 0.4 mm or more and 0.7 mm or less. Furthermore, the WD of the objective optical element when using the first optical disk is 0.4 mm or more and 0.9 mm or less (in the case of t1 <t2, 0.6 mm or more and 0.9 mm or less is preferable). preferable.

  When the first optical disk is used, the entrance pupil diameter of the objective optical element is preferably φ2.8 mm or more and φ4.5 mm or less.

  Good temperature characteristics (temperature dependence of the third-order spherical aberration of the objective optical element at the working wavelength of 405 nm), and very good wavelength characteristics (wavelength dependence of the third-order spherical aberration of the objective optical element at the working wavelength of 500 nm or less) A non-objective optical element may be used. For example, “the temperature characteristic is good” means that the temperature characteristic (| δSA3 / δT | (λrms / ° C.)) of the entire optical system including the objective optical element is 0 or more and 0.02 or less. The temperature characteristic (| δSA3 / δT | (λrms / ° C.)) of the objective optical element alone is 0.03 or more and 0.08 or less. “Wavelength characteristics are not so good” means that the wavelength characteristics (| δSA3 / δλ | (λrms / nm)) of the objective optical element is smaller than 0.1 and 0.01 or more (0.02 or more). Means good).

  According to the present invention, it is possible to provide an optical pickup apparatus and an optical information recording medium recording / reproducing apparatus capable of appropriately recording and / or reproducing information even when a temperature change or a wavelength variation of a light source occurs.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. First, the optical pickup device PU1 using the objective optical element according to the present invention will be described with reference to FIG. Such an optical pickup device PU1 can be mounted on an optical information recording medium recording / reproducing device. FIG. 5 shows an optical pickup apparatus PU that can appropriately record and reproduce information on any of a BD (first optical disk), DVD (second optical disk), and CD (third optical disk) that are high-density optical disks. It is a figure which shows a structure schematically. The specification of BD is the first wavelength λ1 = 405 nm, the thickness t1 of the protective substrate PL1 is 0.1 mm, and the numerical aperture NA1 = 0.85. The specification of the DVD is that the second wavelength λ2 = 655 nm, the protective substrate PL2 The thickness t2 = 0.6 mm, the numerical aperture NA2 = 0.65, and the specifications of the CD are the third wavelength λ3 = 785 nm, the protective substrate PL3 thickness t3 = 1.2 mm, and the numerical aperture NA3 = 0.45. is there. However, the combination of the wavelength, the thickness of the protective substrate, and the numerical aperture is not limited to this.

  The optical pickup device PU1 emits a laser beam (first beam) of 405 nm that is emitted when information is recorded / reproduced with respect to the objective optical element OBJ, aperture stop ST, collimator lens CL, polarization dichroic prism PPS, and BD. A first semiconductor laser LD1 (first light source), a first light receiving element PD1 that receives a reflected light beam from the information recording surface RL1 of the BD, a laser module LM, and the like. In the present embodiment, the collimating lens CL constitutes spherical aberration correction means.

  The laser module LM also emits a 658 nm laser beam (second beam) when recording / reproducing information on a DVD and emits a 658 nm laser beam (second beam), and a CD. A third semiconductor laser EP2 (third light source) that emits a 785 nm laser beam (third beam) when recording / reproducing information and a second beam that receives a reflected beam from the information recording surface RL2 of the DVD. Light receiving element DS1, a third light receiving element DS2 that receives a reflected light beam from the information recording surface RL3 of the CD, and a prism PS.

  As shown in FIGS. 1 and 4, in the objective optical element OBJ of the present embodiment, a central region CN including the optical axis on the aspherical optical surface on the light source side, a peripheral region MD arranged around the central region CN, Further, the outermost peripheral region OT disposed around the periphery is formed concentrically with the optical axis as the center. Note that the ratios of the areas of the central region, the peripheral region, and the outermost peripheral region in FIGS. 1 and 4 are not accurately represented. A first optical path difference providing structure is provided on the entire surface of the central region CN, and a second optical path difference providing structure is provided on the entire surface of the peripheral region MD. Further, a third optical path difference providing structure is provided in the outermost peripheral region OT.

  In the optical pickup device PU, when information is recorded / reproduced with respect to the BD, the uniaxial actuator AC2 causes the collimator lens CL to emit the blue-violet laser light beam in a parallel light beam state. After adjusting the position in the optical axis direction, the blue-violet semiconductor laser LD1 is caused to emit light.

  The divergent light beam of the first light beam (λ1 = 405 nm) emitted from the blue-violet semiconductor laser LD1 is transmitted through the polarization dichroic prism PPS, converted into a parallel light beam by the collimator lens CL, and then straightened by a quarter wavelength plate (not shown). Polarized light is converted into circularly polarized light, its diameter is regulated by the stop ST, and becomes a spot formed on the information recording surface RL1 of the BD via the protective substrate PL1 having a thickness of 0.1 mm by the objective optical element OBJ. .

  The light beam reflected on the information recording surface RL1 is transmitted again through the objective optical element OBJ and the aperture stop ST, converted from circularly polarized light to linearly polarized light by a quarter wave plate (not shown), and converted into a convergent light beam by the collimating lens CL. After passing through the polarization dichroic prism PPS, it converges on the light receiving surface of the first light receiving element PD1. Then, by using the output signal of the first light receiving element PD1 to focus and track the objective optical element OBJ by the biaxial actuator AC, it is possible to record on the BD or read the recorded information.

  In addition, when information is recorded / reproduced with respect to the DVD in the optical pickup device PU1, the collimating lens CL is driven by the uniaxial actuator AC2 so that the red laser beam is emitted from the collimating lens CL in a parallel beam state. Is adjusted in the optical axis direction, and then the red semiconductor laser EP1 is caused to emit light.

  The divergent light beam of the second light beam (λ2 = 658 nm) emitted from the red semiconductor laser EP1 is reflected by the prism PS, then reflected by the polarization dichroic prism PPS, converted into a parallel light beam by the collimator lens CL, and is not shown in the figure. The light is converted from linearly polarized light to circularly polarized light by the quarter wavelength plate and enters the objective optical element OBJ. Here, the light beam condensed by the central region and the peripheral region of the objective optical element OBJ (the light beam that has passed through the most peripheral region is flared and forms a spot peripheral part) is a protective substrate PL2 having a thickness of 0.6 mm. And the spot formed on the information recording surface RL2 of the DVD, forming the center of the spot.

  The light beam reflected on the information recording surface RL2 is again transmitted through the objective optical element OBJ and the aperture stop ST, converted from circularly polarized light to linearly polarized light by a quarter wave plate (not shown), and converted into a convergent light beam by the collimating lens CL. After being reflected by the polarization dichroic prism PPS, then after being reflected twice in the prism, it converges on the second light receiving element DS1. And it can record on DVD using the output signal of 2nd light receiving element DS1, and can read the recorded information.

  Further, when information is recorded / reproduced with respect to the CD in the optical pickup device PU1, the collimating lens is collimated by the uniaxial actuator AC2 so that the infrared laser beam is emitted from the collimating lens CL in the state of a parallel beam. After adjusting the position of CL in the optical axis direction, the infrared semiconductor laser EP2 is caused to emit light.

  The divergent light beam of the third light beam (λ3 = 785 nm) emitted from the infrared semiconductor laser EP2 is reflected by the prism PS, then reflected by the polarization dichroic prism PPS, converted into a parallel light beam by the collimator lens CL, and then shown in the figure. It is converted from linearly polarized light to circularly polarized light by the quarter wave plate that is not, and enters the objective optical element OBJ. Here, the light beam condensed by the central region of the objective optical element OBJ (the light beam that has passed through the peripheral region and the most peripheral region is flared and forms a spot peripheral part) is a protective substrate PL3 having a thickness of 1.2 mm. And the spot formed on the information recording surface RL3 of the CD.

  The light beam reflected on the information recording surface RL3 is again transmitted through the objective optical element OBJ and the aperture stop ST, converted from circularly polarized light to linearly polarized light by a quarter wavelength plate (not shown), and converted into a convergent light beam by the collimating lens CL. After being reflected by the polarization dichroic prism PPS, then after being reflected twice in the prism, it converges on the third light receiving element DS2. And it can record on CD using the output signal of 3rd light receiving element DS2, and can read the recorded information.

  When the first light beam emitted from the blue-violet semiconductor laser LD1 enters the objective optical element OBJ as a parallel light beam, the first optical path difference providing structure in the central region, the second optical path difference providing structure in the peripheral region, and the most peripheral region The third optical path difference providing structure can appropriately correct the spherical aberration of the first light flux and appropriately record and / or reproduce information with respect to the BD having the thickness t1 of the protective substrate. When the second light beam emitted from the red semiconductor laser EP1 enters the objective optical element OBJ as a parallel light beam, the first optical path difference providing structure in the central region and the second optical path difference providing structure in the peripheral region are BD and The third optical path difference providing structure in the most peripheral region is corrected by appropriately correcting the spherical aberration of the second light beam caused by the difference in thickness of the protective substrate of the DVD and the wavelength difference between the first light beam and the second light beam. Since the second light flux is flare on the information recording surface of the DVD, information can be appropriately recorded and / or reproduced on the DVD having the protective substrate thickness t2. In addition, when the third light beam emitted from the infrared semiconductor laser EP2 is incident on the objective optical element OBJ as a parallel light beam, the first optical path difference providing structure in the central region is different in the thickness of the protective substrate of BD and CD. In addition, the spherical aberration of the third light beam generated due to the difference in wavelength between the first light beam and the third light beam is appropriately corrected, and the second optical path difference providing structure in the peripheral region and the third optical path difference providing structure in the most peripheral region are corrected. Since the third light beam flares on the information recording surface of the CD, information can be appropriately recorded and / or reproduced on the CD having the thickness t3 of the protective substrate. Further, the first optical path difference providing structure in the central region separates the condensing spot of the necessary light of the third light beam used for recording and reproduction from the condensing spot of the unnecessary light of the third light beam by an appropriate distance, thereby The tracking characteristics when using a CD are also improved. In addition, the second optical path difference providing structure in the peripheral region has a spherochromatism (color spherical surface) when the wavelength of the first light flux and the second light flux deviates from the reference wavelength due to a laser manufacturing error or the like. Aberration) can be corrected.

  In the optical pickup device PU1, the spherical aberration when using the BD can be corrected by driving the collimating lens CL in the optical axis direction by the uniaxial actuator AC2. With this spherical aberration correction mechanism, wavelength variation due to manufacturing error of the blue-violet semiconductor laser LD1, refractive index change and refractive index distribution of the objective optical system with temperature change, focus jump between information recording layers of the multilayer disk, manufacturing of the protective substrate PL1 It is possible to correct spherical aberration due to thickness variation and thickness distribution due to error. The spherical aberration correction mechanism may correct spherical aberration when using a DVD or CD.

  Further, in the optical pickup device of the present embodiment, a first temperature sensor (also referred to as temperature detection means, hereinafter the same) TS1 is disposed in the vicinity of the blue-violet semiconductor laser LD1, and the second temperature sensor TS2 is disposed in the vicinity of the collimating lens CL. The third temperature sensor TS3 is arranged in the vicinity of the objective optical element OBJ. Since the temperature near the objective optical element OBJ can be easily obtained by measuring the coil current of the biaxial actuator AC1, an ammeter that measures the current value is used instead of the third temperature sensor TS3. be able to. Signals from the temperature sensors TS1, TS2, TS3 are transmitted to the controller CPU.

  Based on the signals from the temperature sensors TS1, TS2, TS3, the controller CPU moves the collimating lens CL with respect to the reference position (position where spherical aberration is minimized when no temperature change occurs) by the uniaxial actuator AC2. It is shifted (displaced) in the direction of the optical axis by a shift amount determined in advance by experiments and simulations, and spherical aberration caused by wavelength variation in the semiconductor laser LD1 due to temperature change, and objective optical element OBJ due to temperature change. Alternatively, spherical aberration or the like due to a change in the refractive index of the collimating lens CL is corrected. In particular, the positional relationship between the objective optical element OBJ and the collimating lens CL is designed so that the spherical aberration is minimized at the reference temperature. Further, even if the temperature changes, the collimating lens CL and the objective optical element OBJ are designed. If both are plastic lenses and the temperature is almost the same, the spherical aberrations due to temperature changes can be canceled out to some extent, so if there is a temperature difference between them, the spherical aberration may become larger There is. On the other hand, in the present embodiment, spherical aberration can be corrected with higher accuracy by measuring the temperatures of both the objective optical element OBJ and the collimating lens CL. In this embodiment, when the temperature of the objective optical element OBJ increases, the collimating lens CL is shifted to the light source side, and when the temperature of the objective optical element OBJ decreases, the collimating lens CL is shifted to the optical disk side. It has become so. A temperature sensor may be arranged in the vicinity of the laser module LM to measure the temperature of the light source.

  In particular, when the optical pickup device is activated (for example, within 5 minutes from activation), an optical element having a temperature equal to room temperature is heated by an actuator, a light source, etc., and the temperature rises significantly. When the temperature rises (which can take various values depending on the design of the objective optical element), the position of the collimator lens CL can be shifted, or the controller CPU can be controlled by checking every short time. On the other hand, when the temperature reaches a steady state (for example, after 10 minutes from the start), it may be checked whether or not the position of the collimating lens CL is shifted at a lower frequency. Alternatively, the check may be stopped when the temperature reaches a steady state. However, since the tolerance of spherical aberration differs between the recording mode and the reproduction mode of the optical pickup device, for example, the check frequency in the recording mode is preferably higher than the check frequency in the reproduction mode.

  FIG. 6 is a schematic configuration diagram of an optical pickup device PU2 according to the second embodiment. The present embodiment is different from the above-described embodiment in that wavelength detecting means is provided instead of providing a temperature sensor. FIG. 7 is a diagram showing the principle of the wavelength detecting means. Other configurations are the same as those in the above-described embodiment, and thus description thereof is omitted.

  In the present embodiment, spherical aberration based on fluctuations in the light source wavelength is corrected. A part of the divergent light beam emitted from the blue-violet semiconductor laser LD1 is reflected by the polarization dichroic prism PPS and becomes a convergent light beam by the condensing lens LS. The light is divided in two directions by the wavelength filter FLT and is substantially condensed on the light receiving element MPD. As shown in FIG. 7A, the light receiving element MPD has two detectors PDA and PDB, and can output signals independently according to the intensity of received light. In the wavelength filter FLT, a first film MA is formed on one surface, and a second film MB is formed on another surface. As shown in FIG. 7B, the first film MA has a first transmittance characteristic A in which the light transmittance increases as the wavelength of the light beam passing therethrough becomes longer. As shown in FIG. 7 (b), the light transmittance decreases as the wavelength of the light beam passing therethrough increases, but the light transmittance of both is equal at 405 nm. Half of the light beam incident on the wavelength filter FLT is refracted after passing through the first film MA and incident on the detection unit PDB, and the other half is refracted after passing through the second film MB and detected. Incident on the PDA.

  Here, when a light beam having a wavelength of 405 nm equal to the reference wavelength is incident on the wavelength filter FLT, the light beam that has passed through the first film MA and the light beam that has passed through the second film MB are shown in FIG. 7B. And have the same light intensity. Therefore, the controller CPU that has input the signals output from the two detection units PDA and PDB can determine that the light source wavelength is 405 nm from the characteristics shown in FIG. 7B, and therefore sets the collimating lens CL to the reference position. .

  Further, when a light beam having a wavelength different from the reference wavelength is incident on the wavelength filter FLT, the light quantity of the light beam that has passed through the first film MA and the light beam that has passed through the second film MB is shown in FIG. 7B. There will be a difference. Therefore, the output signals of the detection unit PDA and the detection unit PDB are input to the controller CPU, the difference between the two signals is taken, and the calculation result is converted using the characteristics of FIG. 7B to obtain the wavelength or wavelength of the light source. A value having a correlation can be obtained. By using this result to shift the collimator lens CL to a position suitable for the changed wavelength, it is possible to suppress the spherical aberration that increases due to the wavelength change. The collimating lens CL may be shifted by measuring the wavelength fluctuation of the semiconductor lasers EP1 and EP2 by the same wavelength detecting means.

  By dividing the difference between the output signals of the detectors PDA and PDB by the sum of the output signals, spherical aberration can be suppressed even when the required light quantity is different, such as during recording or reproduction. Further, the sum of the output signals can also be used for light quantity control of the light flux of each light source.

  As the wavelength detection means or temperature detection means, an ammeter (current value detection means) for measuring the value of the current input to the semiconductor laser LD1 (or EP1, EP2) is provided, and the controller is based on the value of the ammeter. The CPU may obtain the fluctuation of the light source wavelength or the temperature change and appropriately shift the collimating lens CL.

  Further, when the spherical aberration is directly obtained using the spherical aberration detecting means as described in Japanese Patent Application No. 2002-304763, the controller CPU may appropriately shift the collimating lens CL accordingly. It is preferable to always detect the spherical aberration by the spherical aberration detecting means. Further, when a seek operation or an interlayer jump is performed, it is preferable to correct the spherical aberration within one second in response to the detection result. On the other hand, during normal recording / reproduction, it may take 1 second or more to correct the spherical aberration.

  Further, it is desirable to correct the spherical aberration in advance by the spherical aberration correcting means when assembling the optical pickup device.

(Example)

  An embodiment that can be used in the optical pickup device of FIGS. 5 and 6 will be described. In this embodiment, the objective optical element is a single polyolefin plastic lens. A first optical path difference providing structure is formed on the entire surface of the central region CN of the optical surface of the objective optical element. A second optical path difference providing structure is formed on the entire surface of the peripheral area MD of the optical surface. A third optical path difference providing structure is provided on the entire surface of the outermost peripheral region OT of the optical surface.

  In the present embodiment, the first optical path difference providing structure is a structure in which the third basic structure is superimposed in addition to the first basic structure and the second basic structure, and two types of sawtooth diffraction structures are provided. And a binary structure are superimposed on each other. The cross-sectional shape is shown as a portion indicated as CN in FIG. The third basic structure, which is a sawtooth diffractive structure, makes the light amount of the 10th-order diffracted light of the first light beam larger than the light amount of diffracted light of any other order (including 0th order, that is, transmitted light), The light amount of the sixth-order diffracted light of the light beam is made larger than the light amount of diffracted light of any other order (including 0th order, ie, transmitted light), and the light amount of the fifth-order diffracted light of the third light beam is changed to any other order ( It is designed to be larger than the diffracted light amount of the 0th order (including transmitted light).

  In the present embodiment, the second optical path difference providing structure is a structure in which the first basic structure and the fourth basic structure are overlapped as shown by MD in FIG. The structure is superimposed.

  In the present embodiment, the third optical path difference providing structure has a structure having only the fourth basic structure as shown as OT in FIG. 8, and has a shape having only one kind of sawtooth diffraction structure. It has become.

Table 1 below shows lens data of this example. In the following, a power of 10 (for example, 2.5 × 10 ⁻³ ) is expressed using E (for example, 2.5E−3). FIG. 9 is a longitudinal spherical aberration diagram of this example. 1.0 on the vertical axis of the longitudinal spherical aberration diagram represents NA 0.85 or Φ2.7 mm in BD, and a value slightly larger than NA 0.6 or slightly larger than Φ 2.28 mm in DVD. In CD, a value slightly larger than NA 0.45 or a value slightly larger than Φ 2.37 mm is represented. In the embodiment, L = 0.60 mm. Therefore, L / f = 0.60 / 2.53 = 0.237.

  The optical surface of the objective optical element is formed as an aspherical surface that is symmetric about the optical axis and is defined by a mathematical formula in which the coefficients shown in Table 1 are substituted into Formula 1.

  Here, X (h) is an axis in the optical axis direction (the light traveling direction is positive), κ is a conical coefficient, A2i is an aspherical coefficient, and h is a height from the optical axis.

  Further, the optical path length given to the light flux of each wavelength by the diffractive structure is defined by a mathematical formula in which the coefficients shown in the table are substituted into the optical path difference function of Formula 2.

  Λ is the wavelength of the incident light beam, λB is the manufacturing wavelength (blazed wavelength), dor is the diffraction order, and B2i is the coefficient of the optical path difference function. When the BD recording / reproduction is performed with the optical pickup device of FIGS. 5 and 6 using the objective optical element of this embodiment, the wavelength of the first light source is shifted from the reference wavelength due to a manufacturing error, or in the optical pickup device. Even if the temperature changes, the spherical aberration is corrected by moving the coupling lens CL by an appropriate amount in the optical axis direction, and recording / reproduction with respect to the BD is performed satisfactorily.

It is the figure which looked at the objective optical element which concerns on this invention in the optical axis direction. It is an expansion schematic sectional drawing of the optical path difference providing structure formed in the objective optical element which concerns on this invention. It is a figure which shows the spot which the 3rd light beam which passed the objective optical element based on this invention forms on the information recording surface of a 3rd optical disk. It is sectional drawing which shows typically an example of the objective optical element OBJ which concerns on this invention. It is a schematic block diagram of optical pick-up apparatus PU1 concerning 1st Embodiment. It is a schematic block diagram of optical pick-up apparatus PU2 concerning 2nd Embodiment. It is a figure which shows the principle of photodetector PD1 used for 2nd Embodiment. It is a figure for demonstrating the optical path difference providing structure of the objective optical element which concerns on this invention. It is a longitudinal spherical aberration diagram concerning the objective optical element of the example.

Explanation of symbols

AC1 2-axis actuator AC2 1-axis actuator CL Collimating lens CN Central region CPU Controller DS1 First light receiving element DS2 Second light receiving element EP1 Red semiconductor laser EP2 Infrared semiconductor laser FLT Wavelength filter LD1 Blue-violet semiconductor laser LM Laser module MA First Film MB Second film MD Peripheral area OBJ Objective optical element OT Most peripheral area PD1 Photodetector PDA Detector PDB Detector PL1 Protective substrate PL2 Protective substrate PL3 Protective substrate PPS Polarization dichroic prism PS Prism PU1 Optical pickup device PU2 Optical pickup device RL1 Information recording surface RL2 Information recording surface RL3 Information recording surface SCN Spot central portion SMD Spot intermediate portion SOT Spot peripheral portion ST Aperture TS1, TS2, TS3 Temperature sensor

Claims (12)

A first light source that emits a first light beam with a first wavelength λ1 (350 nm ≦ λ1 ≦ 440 nm), a second light source that emits a second light beam with a second wavelength λ2 (λ1 <λ2), and the first light beam Is focused on the information recording surface of the first optical disk having a protective substrate with a length of t1 (0.065 mm ≦ t1 ≦ 0.125 mm), and the protective substrate with a thickness of t2 (t1 <t2) An objective optical element for condensing on the information recording surface of the second optical disc, and condensing the first light flux on the information recording surface of the first optical disc, 2 In an optical pickup device for recording and / or reproducing information by focusing on an information recording surface of an optical disc,
Having spherical aberration correction means for correcting spherical aberration,
The optical pickup device according to claim 1, wherein the objective optical element is a single plastic lens having an optical path difference providing structure.   The optical pickup device includes a third light source that emits a third light beam having a third wavelength λ3 (λ2 <λ3), and the objective optical element has a thickness of t3 (t2 <t3). Information is recorded and / or reproduced by condensing on an information recording surface of a third optical disk having a protective substrate and condensing the third light beam on an information recording surface of the third optical disk. The optical pickup device according to claim 1.   The optical pickup device according to claim 1, wherein the spherical aberration correcting unit corrects spherical aberration generated based on a temperature change of the optical pickup device.   The spherical aberration correction means includes the first light beam, the second light beam, or the third light beam emitted from the first light source, the second light source, or the third light source. 4. The optical pickup device according to claim 2, wherein spherical aberration generated due to the change in the third wavelength is corrected. 5. The optical pickup device includes an optical element that allows the first light beam, the second light beam, and the third light beam to pass in common, in addition to the objective optical element. At least one of the light beam diameters is changed according to the optical disk to be used,
5. The light according to claim 2, wherein the spherical aberration correction unit corrects a spherical aberration caused by a difference between a temperature of the optical element and a temperature of the objective optical element. Pickup device.   The spherical aberration correction means is caused by a difference from a reference wavelength of the first wavelength, the second wavelength, or the third wavelength caused by a manufacturing error of the first light source, the second light source, or the third light source. 6. The optical pickup device according to claim 2, wherein spherical aberration generated by the correction is corrected.   The optical pickup device includes a temperature detection unit, and the spherical aberration correction unit corrects the spherical aberration based on the detection result of the temperature detection unit. 2. An optical pickup device according to item 1.   The optical pickup device according to claim 7, wherein when the temperature detection unit detects that the temperature change is equal to or higher than a predetermined temperature, the spherical aberration correction is performed by the spherical aberration correction unit.   9. The optical pickup device according to claim 1, further comprising a spherical aberration detector, wherein the spherical aberration is corrected by the spherical aberration corrector based on a detection result of the spherical aberration detector. The optical pick-up apparatus of any one of Claims.   The optical pickup device has current value detection means for detecting a value of a current supplied to the first light source, the second light source, or the third light source, and is based on a detection result of the current value detection means. The optical pickup device according to claim 2, wherein spherical aberration is corrected by the spherical aberration correcting means.   The optical pickup device includes wavelength detection means for detecting the first wavelength, the second wavelength, or the third wavelength. Based on the detection result of the wavelength detection means, the spherical pickup is corrected by the spherical aberration correction means. The optical pickup apparatus according to claim 2, wherein aberration is corrected. An optical information recording medium recording / reproducing apparatus using the optical pickup device according to claim 1.

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