JP2005222612A - Objective optical element and optical pickup device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an objective optical element capable of dealing with an optical media having different substrate thicknesses by using a plurality of wavelengths and also capable of dealing with optical media of not only a single layer but also of a multilayer. <P>SOLUTION: The optical element is divided into a plurality of areas. As for a DVD, the absolute value of a spherical aberration SA of the optical element is increased in proportion to separation from an optical axis, and different codes are assigned for every adjacent area. On the other hand, the absolute value of the aberration is made to be equal to or smaller than a specified value by providing an optical path difference imparting structure to an aperture area required for forming an conversion spot on a CD. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an optical pickup device and an optical element used for the optical pickup device, and more particularly to an optical pickup device suitable for writing information on an optical disc having a plurality of layers.

  From the past to the present, information is reproduced and recorded on optical information recording media (also called optical discs or media) such as CDs (compact discs) and DVDs (digital video discs or digital versatile discs). Optical pickup devices (also referred to as optical heads, optical head devices, etc.) for carrying out have been developed and manufactured, and are in widespread use.

  Recently, research and development have also been conducted on a standard of an optical information recording medium that can record information at a higher density using a light source having a wavelength of about 405 nm.

  In such an optical pickup device, a light beam emitted from a light source (mainly a laser diode is used) is converted into an optical disk via an optical system including optical elements such as a beam shaping prism, a collimator, a beam splitter, and an objective optical element. The light is condensed on the information recording surface to form a spot, and the reflected light from the information recording hole (also referred to as pit) on the recording surface is condensed again on the sensor through the optical system, and converted into an electric signal. Information is reproduced by converting. At this time, since the light flux of the reflected light also changes depending on the shape of the information recording hole, information of “0” and “1” is distinguished using this. A protective substrate (a protective layer made of plastic, also referred to as a cover glass) is provided on the information recording surface of the optical disc.

  When information is recorded on a recording medium such as a CD-R or CD-RW, a spot by a laser beam is formed on the recording surface to cause a thermochemical change in the recording material on the recording surface. Thus, for example, in the case of CD-R, the heat diffusible dye is irreversibly changed to form the same shape as the information recording hole. In the case of CD-RW, since a phase change material is used, information can be rewritten because it changes reversibly between a crystalline state and an amorphous state by a thermochemical change.

  In an optical pickup device for reproducing information from a CD standard optical disk, the NA of the objective lens is around 0.45, and the wavelength of the light source used is around 785 nm. For recording, a recording material of about 0.50 is often used. The protective substrate thickness of the CD standard optical disk is 1.2 mm.

  Now, CD is widely used as an optical information recording medium, but DVD has been popular for several years. This is an increase in the amount of information recorded by making the protective substrate thinner than the CD and further reducing the information recording hole. The CD is about 600 to 700 MB (megabytes), but about 4 .7 GB (gigabytes), which has a large recording capacity, and is often used as a distribution medium for recording moving images such as movies.

  An optical pickup device for reproducing information from a DVD standard optical disc is in principle the same as that for a CD, but the NA of the objective lens is reduced because the information recording hole is small as described above. Is around 0.60, and the wavelength of the light source used is around 655 nm. Also, for recording, those with a value of about 0.65 are often used. The protective substrate thickness of the DVD standard optical disk is 0.6 mm.

  Also, recordable optical discs of the DVD standard have already been put into practical use, and there are various standards such as DVD-RAM, DVD-RW / R, and DVD + RW / R. The technical principle regarding these is also the same as in the CD standard.

Various techniques have been proposed for recording DVDs in the same manner as DVD-ROMs.
For example, a thin silver alloy is used as the first (upper) reflective layer through the substrate, and the reflectance is set to 18% so that the single-sided dual-layer DVD-ROM standard is satisfied.
Further, the transmittance of the recording surface of the first layer is 50% or more, thereby enabling reading and recording of the recording layer of the second layer (lower layer). Since the first layer absorbs and reflects part of the transmitted light, the recording surface of the second layer has high power sensitivity. The upper layer absorbs and reflects part of the transmitted light. Also, the lower recording surface has a higher reflectance than the upper layer (> 50%). The two-layer disc has a reflectivity of 18% by transmitting through the lower and upper recording surfaces.

  In order to deal with such multilayers, it is possible to dynamically drive the optical system and move the focal position.

  Patent Document 1 discloses a technique for forming an optimum focused spot for each optical disk having a different protective substrate thickness by driving a collimator or the like in order to cope with optical disks having different protective substrate thicknesses. (See Patent Document 1).

JP-A-9-17023

  However, in this technology, there is no disclosure about a technology that uses a plurality of wavelengths and corresponds to an optical disc having different standards, and further uses the same optical system to support multiple layers at the same time while using the same disc standard. There is no description about combination with technology.

  As a result of investigations by the present inventors, it has been found that it is preferable to increase the depth of focus when writing information to a multilayer optical disk, but such knowledge is not disclosed.

  In view of the problems of the prior art, the present invention can record and reproduce information on optical disks having different substrate thicknesses using a plurality of wavelengths, and at the same time, not only a single layer but also multiple layers. It is an object of the present invention to provide an optical pickup device that can cope with an optical disc having a recording layer and an optical element used in such an optical pickup device.

  In order to solve the above-described problems, an optical element according to the present invention forms a focused spot using a first light source having a wavelength λ1 on a first optical information recording medium having a first recording surface with a protective substrate thickness t1. By using the second light source having the wavelength λ2 (λ1 <λ2) for the second optical information recording medium having the second recording surface with the protective substrate thickness t2 (t1 <t2) Information is reproduced and / or recorded by forming a focused spot, and has a third recording surface with a protective substrate thickness t3 (t3 <t2) and a fourth recording surface with a protective substrate thickness t4 (t4 <t2). An objective optical element of an optical pickup device that reproduces and / or records information by forming a focused spot on a three-optical information recording medium using a first light source having a wavelength λ1, the optical element comprising: Multiple around the optical axis When the condensed spot is formed on the first optical information recording medium using the first light source, the absolute value of the spherical aberration increases as the distance from the optical axis increases. And has a refractive power such that the sign of the maximum value of the spherical aberration is different for each of the plurality of adjacent regions, and is necessary for forming a focused spot on the second optical information recording medium. The aperture equivalent region is provided with an optical path difference providing structure so that the absolute value of the aberration is not more than a predetermined value.

In a specific aspect of the present invention, the sign of spherical aberration is different for each of the adjacent regions.
In another specific aspect of the present invention, the spherical aberration of the adjacent region continuously changes.
According to still another specific aspect of the present invention, the fifth or higher order aberration is large.

  In order to solve the above-mentioned problem, another optical pickup device according to the present invention uses a first light source having a wavelength λ1 for a first optical information recording medium having a first recording surface with a protective substrate thickness t1. The information is reproduced and / or recorded by forming the second optical information recording medium having the second recording surface with the protective substrate thickness t2 (t1 <t2) and the second wavelength λ2 (λ1 <λ2). Information is reproduced and / or recorded by forming a focused spot using a light source, and a third recording surface having a protective substrate thickness t3 (t3 <t2) and a fourth recording having a protective substrate thickness t4 (t4 <t2). An optical pickup device that reproduces and / or records information by forming a condensing spot on a third optical information recording medium having a surface by using a first light source having a wavelength λ1. Objective optical element And an optical functional surface of the objective optical element has at least two or more concentric optical regions around the optical axis, and the first region including the optical axis is: An annular path having an optical path difference providing structure on the refracting surface and configured to be able to form a focused spot on the first recording surface and the second recording surface, and located outside the first region. The second region of the optical system is configured to condense the first light source onto the first recording surface and to be an optical surface that does not collect the second light source onto the second recording surface. Optical that is closest to the optical information recording medium that forms the condensed spot, changes a divergence angle of a light beam incident on an optical element closest to the optical information recording medium, and / or forms the condensed spot Have the function to change the phase of the light beam incident on the element And it features.

In order to solve the above problem, another optical pickup device according to the present invention condenses light on a first optical information recording medium having a first recording surface with a protective substrate thickness t1 by using a first light source having a wavelength λ1. Information is reproduced and / or recorded by forming a spot, and a second optical information recording medium having a second recording surface with a protective substrate thickness t2 (t1 <t2) has a wavelength λ2 (λ1 <λ2). Information is reproduced and / or recorded by forming a condensing spot using two light sources, and a third recording surface with a protective substrate thickness t3 (t3 <t2) and a fourth with a protective substrate thickness t4 (t4 <t2). An optical pickup device for reproducing and / or recording information by forming a focused spot on a third optical information recording medium having a recording surface by using a first light source having a wavelength λ1. Said each light A first optical element that has a condensing optical system for forming a condensing spot on an information recording medium and that is at least one optical element included in the condensing optical system includes at least two optical axes centered on the optical axis. The first region including a concentric optical region, including the optical axis, and the second region outside the first region have an optical path difference providing structure for providing an optical path difference to a light beam transmitted through the first region. The light beam from the first light source that has passed through the first region is emitted as m-th order diffracted light, and the light beam from the first light source that has passed through the second region is emitted as n (| n |> | m |) -order diffracted light. A light beam from the second light source that has contributed to the formation of a condensing spot on the first recording surface, the third recording surface, and the fourth recording surface and transmitted through the first region is emitted as m-th order diffracted light, and 2 which contributed to the formation of a light-condensing spot on the recording surface and transmitted through the second region A light beam from the two light sources is formed so as not to contribute to the formation of a condensing spot, and among the optical elements included in the condensing optical system, a second optical element that is the optical element closest to each of the optical information recording media The optical pickup device is characterized in that the amount of light at the open end of the optical pickup is 0% to 70% of the amount of light on the optical axis. (Where n and m are integers)
In specific embodiments of these inventions, the light quantity at the opening end of the second optical element is 10% or more and 20% or less of the light quantity of the optical axis.

In order to solve the above-mentioned problem, another optical pickup device according to the present invention uses a first light source having a wavelength λ1 for a first optical information recording medium having a first recording surface with a protective substrate thickness t1. The information is reproduced and / or recorded by forming the second optical information recording medium having the second recording surface with the protective substrate thickness t2 (t1 <t2) and the second wavelength λ2 (λ1 <λ2). Information is reproduced and / or recorded by forming a focused spot using a light source, and a third recording surface having a protective substrate thickness t3 (t3 <t2) and a fourth recording having a protective substrate thickness t4 (t4 <t2). An optical pickup device that reproduces and / or records information by forming a condensing spot on a third optical information recording medium having a surface by using a first light source having a wavelength λ1. , Each light A first optical element that has a condensing optical system for forming a condensing spot on the information recording medium and that is at least one optical element included in the condensing optical system has at least two optical centers around the optical axis. The first region including a concentric optical region, including the optical axis, and the second region outside the first region have an optical path difference providing structure for providing an optical path difference to a light beam transmitted through the first region. The light beam from the first light source that has passed through the first region is emitted as m-th order diffracted light, and the light beam from the first light source that has passed through the second region is emitted as n (| n |> | m |) -order diffracted light. A light beam from the second light source that has contributed to the formation of a condensing spot on the first recording surface, the third recording surface, and the fourth recording surface and transmitted through the first region is emitted as m-th order diffracted light, and 2 which contributes to the formation of a condensing spot on the second recording surface and transmits through the second area. The light beam from the light source is formed so as not to contribute to the formation of a condensing spot, and among the optical elements included in the condensing optical system, the second optical element that is the optical element closest to each of the optical information recording media. The light beam diameter H of the incident light beam is in a range determined by the following equation, where f is the focal length of the second optical element. (Where n and m are integers)
1.25f <H <1.29f
A specific aspect of the present invention is characterized in that m = 1.

  In a more specific aspect of the present invention, n = 2 to 5.

  In still another specific aspect of the present invention, the first optical element is any one of a collimator, a coupling, and a beam expander.

  In still another specific aspect of the present invention, the second optical element is an objective optical element.

  In still another specific aspect of the present invention, the first optical element is the same element as the second optical element.

In order to solve the above-mentioned problem, another optical pickup device according to the present invention uses a first light source having a wavelength λ1 for a first optical information recording medium having a first recording surface with a protective substrate thickness t1. The information is reproduced and / or recorded by forming the second optical information recording medium having the second recording surface with the protective substrate thickness t2 (t1 <t2) and the second wavelength λ2 (λ1 <λ2). Information is reproduced and / or recorded by forming a focused spot using a light source, and a third recording surface having a protective substrate thickness t3 (t3 <t2) and a fourth recording having a protective substrate thickness t4 (t4 <t2). An optical pickup device that reproduces and / or records information by forming a condensing spot on a third optical information recording medium having a surface by using a first light source having a wavelength λ1. , Each light A first optical element that has a condensing optical system for forming a condensing spot on the information recording medium and that is at least one optical element included in the condensing optical system has at least two optical centers around the optical axis. The first region including a concentric optical region, including the optical axis, and the second region outside the first region have an optical path difference providing structure for providing an optical path difference to a light beam transmitted through the first region. The light beam from the first light source that has passed through the first region is emitted as m-th order diffracted light, and the light beam from the first light source that has passed through the second region is emitted as n (| n |> | m |) -order diffracted light. A light beam from the second light source that has contributed to the formation of a condensing spot on the first recording surface, the third recording surface, and the fourth recording surface and transmitted through the first region is emitted as m-th order diffracted light, and 2 which contributes to the formation of a condensing spot on the second recording surface and transmits through the second area. The light beam from the light source is formed so as not to contribute to the formation of the condensing spot, and the sine condition violation amount in the condensing spot formed by the light beam from the first light source on the first recording surface is from the optical axis. The sine condition violation amount at the focused spot formed by the light beam from the second light source on the second recording surface becomes lower as the distance from the optical axis becomes longer. It is comprised so that it may become. (Where n and m are integers)
A specific aspect of the present invention is characterized in that m = 1.

  In a more specific aspect of the present invention, n = 2 to 5.

Moreover, the optical path difference providing structure of all the inventions is a diffractive structure.
Furthermore, the optical path difference providing structure may be a phase shift structure.
Furthermore, the optical path difference providing structure may be a multi-level structure.

  According to the present invention, information can be recorded and / or reproduced with respect to optical disks having different substrate thicknesses using a plurality of wavelengths, and not only an optical disk having a single recording layer but also multiple layers. It is possible to provide an optical pickup device that can cope with an optical disc having a recording layer, and an optical element used in such an optical pickup device.

  Hereinafter, the content of the present invention will be described in detail with reference to the drawings. However, embodiments of the present invention are not limited thereto.

  First, an outline of an optical system commonly used in each embodiment will be described.

  FIG. 1 is a schematic diagram showing an optical pickup device according to the present invention.

  In this embodiment, the target is mainly an optical pickup device compatible with two formats of DVD and CD, a DVD having a protective substrate thickness t1 of 0.6 mm as a first optical information recording medium, and a protective substrate as a second optical information recording medium. A CD with a thickness t2 of 1.2 mm is assumed. In addition, a dual-layer DVD is assumed as the third optical information recording medium.

  These will be described with reference to FIG. 1. The thickness of the protective substrate p1 of the single-layer DVD as the first optical information recording medium is t1, and the first recording surface is r1. Similarly, the thickness of the protective substrate p2 of the CD that is the second optical information recording medium is t2, and the first recording surface is r2.

  The thickness of the protective substrate p3 of the double-layer DVD that is the third optical information recording medium is t3, and the third recording surface is r3. The sum of the thicknesses of the protective substrate p3 and the protective substrate p4 is t4. The fourth recording surface is r4. In addition, B shows a base material, Although not shown in figure, the 1st optical information recording medium and the 2nd optical information recording medium also have the same base material.

By the way, t3 which is the thickness of p3 is appropriately selected between 0.53 and 0.57 mm, and p4 is appropriately selected between 0.61 and 0.69 mm.
The laser diode LD is a light source and is a so-called two-laser one-package light source unit in which two light emitting points of a first light source (light source for DVD) and a second light source (light source for CD) are housed in the same package. It is.

  In this package, the first light source is adjusted so as to be positioned on the optical axis. Therefore, the second light source is positioned slightly away from the optical axis, so that an image height is generated. Techniques for improvement are already known and can be applied as needed. Here, the correction is performed by using a correction plate (not shown). A grating is formed on the correction plate, thereby correcting the deviation from the optical axis.

A red laser having a wavelength λ2 of 655 nm is used as the first light source (wavelength λ1), but a laser having a wavelength in the range of 630 nm to 680 nm can be appropriately employed. As the second light source (wavelength λ2), an infrared laser having a wavelength of 780 nm is used, but a laser having a wavelength in the range of 750 nm to 800 nm can be appropriately employed.
The light beam projected from the LD 1 is incident on the collimator COL and collimated into infinite parallel light. After that, the light beam reaches the objective optical element Obj via the polarization beam splitter prism PS, and is recorded on the optical information recording medium. A focused spot is formed on the surface.

  Although not particularly shown here, the light beam projected from the LD may be transmitted through the beam shaper BSL (beam shaping element) and then incident on the collimator COL in order to improve the beam quality. Further, before the light beam is incident on the objective optical element, it may be passed through a beam expander BE composed of a concave lens and a convex lens.

  After a condensing spot is formed and reflected on the information recording surface, it follows the same path, and is converged on the sensor PD by the polarizing beam splitter prism PS via the sensor lens SL. This sensor PD photoelectrically converts it into an electrical signal.

  Note that a λ / 4 (quarter wavelength) plate (not shown) is disposed between the beam splitter BS and the objective optical element Obj, and the phase is shifted by exactly half a wavelength between the forward path and the return path, and the polarization direction changes. . For this reason, the traveling direction of the light flux in the return path changes depending on PS.

  The beam shaper BSL (not shown) has different curvatures in two directions, a certain direction perpendicular to the optical axis and a direction perpendicular to this direction (the rotation non-rotation about the optical axis). Have the target curvature).

  Due to the structure of the semiconductor light source, the luminous flux emitted from the light source has different divergence angles in two directions: a direction perpendicular to the optical axis and a direction perpendicular to this direction. Although it is an elliptical beam when viewed from the axial direction, it is not preferable as a light source light beam for an optical disk as it is, so that the output light beam has a substantially circular cross section by giving different refraction actions in each direction by the beam shaper BSL. It is trying to become a beam.

  Note that the objective optical element Obj is a single lens in this figure, but may be constituted by a plurality of optical elements as necessary. The material may be plastic resin or glass.

  FIG. 2 shows a state in which the light beam projected from each LD is condensed on the information recording surface via the protective substrate of the optical disc. The light source and the protective substrate for each standard of the recording medium to be reproduced / recorded. Although the distance from the surface does not change, the basic position (reference position) of the objective optical element is switched by the actuator, and focusing is performed from the reference position.

  The numerical aperture required for the objective optical element Obj varies depending on the thickness of the protective substrate of each optical information recording medium and the size of the pits. Here, the numerical aperture for CD is 0.45 and the basic numerical aperture for DVD is 0.65, but it is 0.43 to 0.50 for CD and 0.58 to 0.68 for DVD. The range is appropriately selected.

  A diaphragm for cutting unnecessary light may be provided on the incident side of the objective optical element.

  Further, although parallel light is incident on the objective lens OBL, a configuration in which finite divergent light is incident without collimating or a configuration in which finite convergent light is incident may be employed.

  Furthermore, a light intensity distribution conversion element that changes the intensity distribution of the incident light beam can be employed in the above-described example.

  The light intensity distribution conversion element is an optical element that mainly emits an incident light beam having a Gaussian distribution as a light beam having a different light intensity distribution.

  Depending on the purpose, the light intensity distribution of the emitted light beam may be made substantially uniform, or the light intensity at the outermost edge of the emitted light beam may be 45 to 90% of the light intensity near the optical axis. It is possible to squeeze.

  In the present invention, any one of the optical elements existing in the optical path is provided with an optical path difference providing structure to perform spherical aberration correction based on the substrate thickness difference of the optical information recording medium.

  A typical optical path difference providing structure is a sawtooth diffractive structure.

  This is a concentric fine step with the optical axis as the center, and the light flux that has passed through the adjacent annular zones is given a predetermined optical path difference.

  Then, by setting the pitch (diffraction power) and depth (blazed wavelength) of this saw blade, the light beam from the first light source in a specific NA is formed as a condensed spot by the first-order diffracted light for the DVD. For the CD, the light beam from the second light source in the same NA is formed as a condensed spot by the first-order diffracted light. However, the luminous flux from the outer area (area above a specific NA) contributes to the formation of a condensed spot as higher-order, for example, second-order diffracted light in the case of DVD, and flare light in the case of CD. Therefore, it does not contribute to the formation of the condensed spot.

  Thus, by using light having the same diffraction order or different light, the diffraction efficiency in each case can be increased, and the amount of light can be secured.

  Such a diffractive structure is an example of an optical path difference providing structure, but other known “phase difference providing structure” and “multilevel structure” can also be employed.

  Examples of the phase difference providing structure include an annular phase correction objective lens system, for example, Japanese Patent Application Laid-Open No. 11-2759 and Japanese Patent Application Laid-Open No. 11-16190.

  Japanese Patent Laid-Open No. 11-2759 describes that the surface shape of the basic objective lens is set to be optimum for DVD recording / reproduction as described above, and is based on a phase correction method for CD recording / reproduction. This is a case where correction is performed. In other words, an annular step is formed on the surface of the objective lens designed to minimize the wavefront aberration in the DVD system, and the wavefront aberration in the CD system is reduced while suppressing an increase in wavefront aberration in the DVD system. is there.

  In this technique, since the phase control element hardly changes the phase distribution with respect to the DVD wavelength, the RMS wavefront aberration maintains the value of the objective lens optimally designed for the DVD system, and the RMS wavefront aberration of the CD system is reduced. Therefore, the recording / reproducing performance is effective for a DVD system sensitive to wavefront aberration.

  On the other hand, the optical performance of the basic objective lens is set so as to be optimal in CD recording / reproduction, and correction by the phase correction method is performed for DVD recording / reproduction. In the issue.

  Both of these have improved RMS (Root Mean Square) wavefront aberrations for both DVD recording and playback and CD recording and playback.

  In the case of an annular phase correction objective lens, for example, in Japanese Patent Laid-Open No. 11-16190, an optical disk having a substrate thickness intermediate between CD and DVD is assumed, so that it is optimal for recording and reproduction of such an optical disk. In this case, the surface shape of a simple objective lens is set, and RMS (Root Mean Square) wavefront aberration correction for both DVD and CD is performed by a phase correction method.

  Japanese Patent Laid-Open No. 2001-51192 discloses a technique for reducing the RMS (Root Mean Square) wavefront aberration and changing the focal position of the light beam to one point by changing the step amount and surface shape of each annular zone. Yes.

  The multi-level structure is a shape in which a stepped shape having a predetermined number of steps is periodically repeated. The number of steps, the height and width (pitch) of the steps can be set as appropriate, and are described, for example, in JP-A-9-54973. With such a staircase structure, it is possible to selectively produce a diffractive action for a plurality of wavelengths.

  Here, the optical path difference providing structure is adopted for the purpose of correcting the spherical aberration based on the difference in the substrate thickness of the optical disc format. However, not only that, but also the wavelength difference of the used wavelength and the fluctuation (mode hop) of the used wavelength. Of course, it can also be used to correct aberrations that occur based on it. The former case is correction of spherical chromatic aberration that occurs based on a wavelength difference of 50 nanometers or more, and the latter case corrects minute wavelength fluctuations within 5 nm.

  In this example, the example in which the diffractive structure is provided in the objective optical element has been described, but it is of course possible to provide it in other elements such as a collimator and a coupling lens.

It is most preferable to use such a material for an optical element having a refractive surface and an aspherical surface.
[First Embodiment]
The inventions of claims 1 to 4 will be described.

  In the present invention, the objective optical element is divided into a plurality of regions so that the spherical aberration with respect to the DVD increases as the distance from the optical axis increases. Specifically, this is possible by making the aspherical shape different for each of a plurality of regions.

  Then, the spherical aberration with respect to the CD is set within an allowable range (preferably 0) by the optical path difference providing structure, and the spherical aberration (SA) is as shown in the spherical aberration diagram shown in FIG. 3 or FIG.

In the case of the invention of claim 2, the spherical aberration diagram is as shown in FIG. 3, and in the case of the invention of claim 3, the spherical aberration diagram is as shown in FIG.
With such a structure, as a result, the depth of focus with respect to the wavelength of λ1 becomes deep and the aberration increases, but it is possible to cope with various substrate thicknesses.
The aberration may be further deteriorated, but it is possible to prevent the formation of the condensed spot by causing the higher-order aberration, particularly the fifth-order aberration or more, to deteriorate. ).
[Second Embodiment]
The invention of claim 5 will be described.

  In the present invention, the spherical surface due to the substrate thickness difference is corrected using the optical path difference providing structure provided in the objective optical element, but other optical elements are used in order to cope with the multilayer DVD.

  Here, a collimator is used as the substrate thickness adjusting means, and the divergence degree (divergence angle) of the light beam incident on the objective optical element is changed by moving in the optical axis direction. As a result, as shown in FIG. 5, light can be condensed in a suitable aberration state for both single-layer DVD and multilayer DVD, which is very preferable.

  The substrate thickness adjusting means is not limited to a collimator, and may be a beam expander or the like.

Further, as a means for giving a phase difference, a liquid crystal element can be used, or it can be combined with a means for changing the divergence angle.
[Third Embodiment]
The inventions of claims 6 to 7 will be described.

  Also in this invention, the spherical surface due to the substrate thickness difference is corrected by using the optical path difference providing structure, but in particular, the rim intensity is intentionally reduced to substantially increase the condensing spot diameter, and with this, λ1 Increase the depth of focus for the wavelength. As a result, although the aberration increases, it is possible to cope with various substrate thicknesses.

  In particular, it is effective for increasing the depth of focus that the light quantity at the end portion of the aperture diameter is reduced to about 10 to 20% of the light quantity near the optical axis.

Here, the rim strength may be reduced by any optical element in the optical path. For example, such an optical surface may be formed on the collimator, or a similar effect may be obtained by coating or the like. Further, such an action may be imparted to the objective optical element itself.
[Fourth Embodiment]
The invention of claim 8 will be described.

  This is a concept similar to that of the third embodiment, but is a method of determining the shape of the focused spot by restricting the diameter of the incident light beam with a stop in order to increase the depth of focus more reliably.

  As a result of investigations, the present inventors have found an optimum condition for forming a good light-condensing spot on both a single layer DVD and a multilayer DVD.

  That is, the aperture diameter is obtained from the incident light beam diameter and the focal length of the objective optical element, and the focused spot diameter is proportional to the value obtained from the wavelength used and the aperture diameter.

  Based on the preferable aperture diameter range obtained as a result of the examination, if the relationship between the focal length of the objective optical element and the incident light beam diameter satisfies the following conditions, either a single-layer DVD or a multi-layer DVD can be used. In addition, a good condensing spot can be formed.

1.25f <H <1.29f
Here, the preferable narrowing conditions for the invention of claim 6 and the invention of claim 8 will be described.

  In order to form a condensing spot of DVD, it is preferable that m = 1 because the diffraction efficiency is high (claim 9).

  Further, since the peripheral portion is exclusively for DVD and does not require a CD, it is preferable that n = 2 to 5 (claim 10). As a result, the diffraction pitch of the peripheral portion does not become fine, and the optical element can be manufactured easily.

  Further, when the first optical element is a collimator other than the objective optical element, a coupling lens, or a beam expander, there is an advantage that an optical path difference providing structure can be easily formed because the surface shape is loose.

  If the second optical element is an objective optical element, there is an advantage that the relationship between the incident light and the condensing spot can be made so as not to greatly deviate from the Celsius value (claim 12).

Further, when the first optical element and the second optical element are dual-purpose elements (for example, objective optical elements), there is an advantage that the number of optical elements can be reduced and the apparatus can be made compact.
[Fifth Embodiment]
The invention of claim 14 will be described.

  This is to manipulate the sine condition violation amount (OSC) of the focused spot of DVD and CD, resulting in a deep depth of field.

  As shown in FIG. 6, the sine condition violation amount of DVD is formed to be over as it is away from the optical axis, and conversely, the sine condition violation amount of CD is formed to be under as it is away from the optical axis. . As a result, the depth of field with respect to the DVD is deepened, and as a result, a good condensing spot can be formed on both the single layer DVD and the multilayer DVD.

  The effects of the inventions of claims 15 to 16 are the same as those of the inventions of claims 9 and 10.

It is a schematic diagram of the optical pick-up concerning embodiment. It is a schematic diagram of the state in which a condensing spot is formed on each optical information recording medium. It is a schematic diagram which shows the state of the spherical aberration in connection with 1st Embodiment. It is a schematic diagram which shows the state of the spherical aberration in connection with 1st Embodiment. It is a schematic diagram which shows the state of the spherical aberration in connection with 2nd Embodiment. It is a schematic diagram which shows the state of the sine condition violation amount concerning 5th Embodiment.

Explanation of symbols

LD ... light source, PD ... sensor, SL ... sensor lens, PS ... prism (beam splitter), COL ... collimator, Obj ... objective optical element, r1 ... first recording surface, r2 ... second recording surface, r3 ... third recording Surface, r4 ... fourth recording surface, p1 ... first protective layer, p2 ... second protective layer, p3 ... third protective layer, p4 ... fourth protective layer, B ... substrate

Claims (22)

Information is reproduced and / or recorded by forming a focused spot on the first optical information recording medium having the first recording surface of the protective substrate thickness t1 using the first light source having the wavelength λ1.
Information reproduction by forming a focused spot using a second light source having a wavelength λ2 (λ1 <λ2) on a second optical information recording medium having a second recording surface with a protective substrate thickness t2 (t1 <t2). And / or record,
A third optical information recording medium having a third recording surface having a protective substrate thickness t3 (t3 <t2) and a fourth recording surface having a protective substrate thickness t4 (t4 <t2) is collected using a first light source having a wavelength λ1. An objective optical element of an optical pickup device that reproduces and / or records information by forming a light spot,
The optical element is divided into a plurality of regions around the optical axis,
When a focused spot is formed on the first optical information recording medium using the first light source, the absolute value of the spherical aberration is increased as the distance from the optical axis increases, and Each of the plurality of adjacent regions has a refractive power such that the sign of the maximum value of spherical aberration is different,
An optical path difference providing structure is provided in a region corresponding to the aperture necessary for forming a focused spot on the second optical information recording medium so that the absolute value of the aberration is equal to or less than a predetermined value. An objective optical element. The objective optical element according to claim 1, wherein the sign of the spherical aberration is different for each of the adjacent regions. The objective optical element according to claim 1, wherein the spherical aberration of the adjacent region continuously changes. The objective optical element according to any one of claims 1 to 3, wherein the fifth-order or higher aberration is large. Information is reproduced and / or recorded by forming a focused spot on the first optical information recording medium having the first recording surface of the protective substrate thickness t1 using the first light source having the wavelength λ1.
Information reproduction by forming a focused spot using a second light source having a wavelength λ2 (λ1 <λ2) on a second optical information recording medium having a second recording surface with a protective substrate thickness t2 (t1 <t2). And / or record,
A third optical information recording medium having a third recording surface having a protective substrate thickness t3 (t3 <t2) and a fourth recording surface having a protective substrate thickness t4 (t4 <t2) is collected using a first light source having a wavelength λ1. An optical pickup device that reproduces and / or records information by forming a light spot,
The optical pickup device has an objective optical element and a substrate thickness adjusting means,
The optical functional surface of the objective optical element has at least two or more optical regions that are concentric around the optical axis,
The first region including the optical axis has an optical path difference providing structure on the refracting surface, and is configured such that a condensed spot can be formed on the first recording surface and the second recording surface,
An annular second region located outside the first region condenses the first light source on the first recording surface, and an optical surface that does not collect the second light source on the second recording surface. Has been
The substrate thickness adjusting means forms the condensed spot, changes a divergence angle of a light beam incident on an optical element closest to the optical information recording medium, and / or forms the condensed spot, An optical pickup device having a function of changing a phase of a light beam incident on an optical element close to an optical information recording medium. Information is reproduced and / or recorded by forming a focused spot on the first optical information recording medium having the first recording surface of the protective substrate thickness t1 using the first light source having the wavelength λ1.
Information reproduction by forming a focused spot using a second light source having a wavelength λ2 (λ1 <λ2) on a second optical information recording medium having a second recording surface with a protective substrate thickness t2 (t1 <t2). And / or record,
A third optical information recording medium having a third recording surface having a protective substrate thickness t3 (t3 <t2) and a fourth recording surface having a protective substrate thickness t4 (t4 <t2) is collected using a first light source having a wavelength λ1. An optical pickup device that reproduces and / or records information by forming a light spot,
The optical pickup device has a condensing optical system for forming a condensing spot on each optical information recording medium,
The first optical element, which is at least one optical element included in the condensing optical system, has at least two concentric optical regions centered on the optical axis, the first region including the optical axis, and the first optical element The second region outside the one region has an optical path difference providing structure that provides an optical path difference to the light flux that passes through both regions,
The light beam from the first light source that has passed through the first region is emitted as the m-th order diffracted light, and the light beam from the first light source that has passed through the second region is emitted as the n (| n |> | m |) -order diffracted light. , Contributing to the formation of condensing spots on the first recording surface, the third recording surface and the fourth recording surface,
The light beam from the second light source that has passed through the first region is emitted as m-th order diffracted light, contributes to the formation of a condensing spot on the second recording surface, and from the second light source that has passed through the second region. The luminous flux is formed so as not to contribute to the formation of the focused spot,
Of the optical elements included in the condensing optical system, the light amount at the open end of the second optical element, which is the optical element closest to each optical information recording medium, is 0% to 70% of the light amount of the optical axis. An optical pickup device characterized by that. (Where n and m are integers) The optical pickup device according to claim 6, wherein the light amount at the opening end of the second optical element is 10% or more and 20% or less of the light amount of the optical axis. Information is reproduced and / or recorded by forming a focused spot on the first optical information recording medium having the first recording surface of the protective substrate thickness t1 using the first light source having the wavelength λ1.
Information reproduction by forming a focused spot using a second light source having a wavelength λ2 (λ1 <λ2) on a second optical information recording medium having a second recording surface with a protective substrate thickness t2 (t1 <t2). And / or record,
A third optical information recording medium having a third recording surface having a protective substrate thickness t3 (t3 <t2) and a fourth recording surface having a protective substrate thickness t4 (t4 <t2) is collected using a first light source having a wavelength λ1. An optical pickup device that reproduces and / or records information by forming a light spot,
The optical pickup device has a condensing optical system for forming a condensing spot on each optical information recording medium,
The first optical element, which is at least one optical element included in the condensing optical system, has at least two concentric optical regions centered on the optical axis, the first region including the optical axis, and the first optical element The second region outside the one region has an optical path difference providing structure that provides an optical path difference to the light flux that passes through both regions,
The light beam from the first light source that has passed through the first region is emitted as the m-th order diffracted light, and the light beam from the first light source that has passed through the second region is emitted as the n (| n |> | m |) -order diffracted light. , Contributing to the formation of condensing spots on the first recording surface, the third recording surface and the fourth recording surface,
The light beam from the second light source that has passed through the first region is emitted as m-th order diffracted light, contributes to the formation of a condensing spot on the second recording surface, and from the second light source that has passed through the second region. The luminous flux is formed so as not to contribute to the formation of the focused spot,
Of the optical elements included in the condensing optical system, the light beam diameter H of the light beam incident on the second optical element which is the optical element closest to each optical information recording medium represents the focal length of the second optical element as f. An optical pickup device having a range determined by the following formula: (Where n and m are integers)
1.25f <H <1.29f   The optical pickup device according to claim 6, wherein m = 1.   10. The optical pickup device according to claim 6, wherein n = 2 to 5.   11. The optical pickup device according to claim 6, wherein the first optical element is any one of a collimator, a coupling, and a beam expander. The optical pickup device according to claim 6, wherein the second optical element is an objective optical element. The optical pickup device according to claim 6, wherein the first optical element is the same element as the second optical element. Information is reproduced and / or recorded by forming a focused spot on the first optical information recording medium having the first recording surface of the protective substrate thickness t1 using the first light source having the wavelength λ1.
Information reproduction by forming a focused spot using a second light source having a wavelength λ2 (λ1 <λ2) on a second optical information recording medium having a second recording surface with a protective substrate thickness t2 (t1 <t2). And / or record,
A third optical information recording medium having a third recording surface having a protective substrate thickness t3 (t3 <t2) and a fourth recording surface having a protective substrate thickness t4 (t4 <t2) is collected using a first light source having a wavelength λ1. An optical pickup device that reproduces and / or records information by forming a light spot,
The optical pickup device has a condensing optical system for forming a condensing spot on each optical information recording medium,
The first optical element, which is at least one optical element included in the condensing optical system, has at least two concentric optical regions centered on the optical axis, the first region including the optical axis, and the first optical element The second region outside the one region has an optical path difference providing structure that provides an optical path difference to the light flux that passes through both regions,
The light beam from the first light source that has passed through the first region is emitted as the m-th order diffracted light, and the light beam from the first light source that has passed through the second region is emitted as the n (| n |> | m |) -order diffracted light. , Contributing to the formation of condensing spots on the first recording surface, the third recording surface and the fourth recording surface,
The light beam from the second light source that has passed through the first region is emitted as m-th order diffracted light, contributes to the formation of a condensing spot on the second recording surface, and from the second light source that has passed through the second region. The luminous flux is formed so as not to contribute to the formation of the focused spot,
The amount of violation of the sine condition in the condensing spot formed by the light beam from the first light source on the first recording surface becomes over as the distance from the optical axis becomes longer, and the amount on the second recording surface An optical pickup device, wherein a sine condition violation amount in a converging spot formed by a light beam from a second light source is configured to become under as the distance from the optical axis increases. (Where n and m are integers)   15. The optical pickup device according to claim 14, wherein m = 1.   16. The optical pickup device according to claim 14, wherein n = 2 to 5. The optical pickup device according to claim 5, wherein the optical path difference providing structure is a diffractive structure. The optical pickup device according to claim 5, wherein the optical path difference providing structure is a phase shift structure. The optical pickup device according to claim 5, wherein the optical path difference providing structure is a multi-level structure. The objective optical element according to claim 1, wherein the optical path difference providing structure is a diffractive structure. The optical pickup device according to claim 1, wherein the optical path difference providing structure is a phase shift structure. The optical pickup device according to claim 1, wherein the optical path difference providing structure is a multi-level structure.

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