JP2004192783A - Optical element, optical lens, optical head device, optical information device, computer, optical information medium player, car navigation system, optical information medium recorder, and optical information medium server - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical element, an optical lens, and a device and a system employing these in which variation of focal distance and occurrence of spherical aberration are suppressed and reproduction and recording of information are stable at the time of variation in the wavelength such as switching of light quantity. <P>SOLUTION: An optical lens is provided with a hologram 134, a refraction type lens 144, and phase level difference 1442. The hologram 134 comprises a sawtooth type lattice of a sawtooth cross section type. In the hologram 134, +2 order diffraction light is generated most strongly for blue light by setting of depth of the sawtooth type lattice, +1 order diffraction light is generated most strongly for red light. The +2 order diffraction light of blue light is converged through a base material 9 having thickness t1, the +1 order diffraction light of red light is converged through a base material 10 having thickness t2, t1<t2 is satisfied, and difference of optical path length caused when blue light is transmitted through the phase level difference 1442 is five times as much as wavelength of blue light. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

  The present invention relates to an optical head device and an optical information device for recording / reproducing or erasing information stored on an optical information medium such as an optical disk, a recording / reproducing method in the optical information device, and a system to which these are applied. Further, the present invention relates to an objective lens (optical lens), a diffractive element, and a phase difference used in the optical head device.

  Optical memory technology using an optical disk having a pit-shaped pattern as a high-density, large-capacity storage medium has been put to practical use while expanding its applications to digital audio disks, video disks, document file disks, and data files. . The function of successfully recording / reproducing information on / from an optical disk through a minutely focused light beam is performed with high reliability. The light condensing function to form a diffraction-limited minute spot and the focus control of an optical system (Focus servo), tracking control, and pit signal (information signal) detection.

  2. Description of the Related Art In recent years, with the progress of optical system design technology and the shortening of the wavelength of a semiconductor laser as a light source, the development of an optical disk having a higher-density storage capacity than before has been progressing. As an approach for increasing the density, it has been considered to increase the numerical aperture (NA) on the optical disc side of a condensing optical system that narrows a light beam onto an optical disc.

  At this time, a problem is an increase in the amount of aberration generated due to the tilt (so-called tilt) of the optical axis. When the NA is increased, the amount of aberration generated with respect to the tilt increases. To prevent this, the thickness (base material thickness) of the substrate of the optical disk may be reduced.

  A compact disk (CD), which can be said to be the first generation of optical disks, uses infrared light (wavelength λ3 of 780 nm to 820 nm) and an objective lens of NA 0.45, and the substrate thickness of the disk is 1.2 mm. The second generation DVD uses red light (wavelength λ2 is 630 nm to 680 nm, standard wavelength 650 nm) and an objective lens with NA of 0.6, and the base material thickness of the disc is 0.6 mm. The third-generation optical disk uses blue light (wavelength λ1 is 390 nm to 415 nm, standard wavelength 405 nm) and an objective lens of NA 0.85, and the base material thickness of the disk is 0.1 mm.

  In this specification, the substrate thickness refers to a thickness from a surface on which a light beam is incident on an optical disk (or information medium) to an information recording surface.

  Thus, the thickness of the substrate of the high-density optical disk is reduced. From the viewpoints of economy and space occupied by the device, an optical information device capable of recording and reproducing optical disks having different substrate thicknesses and different recording densities is desired. For that purpose, an optical head device having a condensing optical system capable of condensing a light beam to a diffraction limit on an optical disk having a different substrate thickness is required.

  Further, when recording and reproducing a disk with a thick base material, it is necessary to focus a light beam on a recording surface located deeper than the disk surface, so that the focal length must be made longer.

  For this reason, there is disclosed a configuration aiming at compatible reproduction of optical disks of different types using light beams of a plurality of wavelengths. This will be described with reference to FIG. In FIG. 20, reference numerals 10 and 11 denote optical disks having transparent substrate thicknesses of 0.1 mm (t1) and 0.6 mm (t2), respectively. In order to enhance the rigidity, a protective substrate is attached to the back surface of the transparent substrate (the side opposite to the objective lens 40), but is omitted in the figure.

  The objective lens 40 is formed by joining a refraction lens 402 and a different material layer 401 to one surface of the refraction lens 402. The difference between the refractive index and dispersion of the refractive lens and the dissimilar material layer is used. Lights of different wavelengths are respectively made incident on the objective lens. It has a spherical aberration characteristic such that when the wavelength of the light beam of the light source shifts to the longer wavelength side, the spherical aberration shifts to the under side. As a result, when the thickness of the transparent substrate increases from t1 to t2, the excess of the spherical aberration is canceled by the under light due to the longer wavelength light. Thus, compatible recording / reproducing of optical disks having different thicknesses is enabled (for example, see Patent Document 1).

  As a second conventional example, a configuration in which a wavelength selection phase plate is combined with an objective lens is disclosed. This will be described with reference to FIGS. 21 and 22. FIG. 21 shows a schematic configuration of the optical head device. The parallel light emitted from the blue light optical system 51 having the blue light source with the wavelength λ1 = 405 nm passes through the beam splitter 161 and the wavelength selection phase plate 205, and is passed by the objective lens 50 to the optical disk 9 (base material thickness 0.1 mm). The light is focused on the information recording surface of a 3rd generation optical disc.

  The light reflected by the optical disk 10 follows the reverse path and is detected by the detector of the blue light optical system 51. The divergent light emitted from the red light optical system 52 having a red light source with a wavelength λ2 = 650 nm is reflected by the beam splitter 161 and passes through the wavelength selection phase plate 205, and is passed by the objective lens 50 to the optical disc 10 having a base material thickness of 0.6 mm. (2nd generation optical disc: DVD). The light reflected by the optical disk 10 follows the reverse path and is detected by the detector of the red optical system 52.

  The objective lens 50 is designed to transmit and converge a base material having a thickness of 0.1 mm when parallel light enters, and spherical aberration occurs due to a difference in the base material thickness during DVD recording / reproduction. In order to correct this spherical aberration, the light beam emitted from the red light optical system 52 and made into the objective lens 50 is converted into divergent light, and the wavelength selection phase plate 205 is used. When divergent light is incident on the objective lens, a new spherical aberration occurs, so the spherical aberration caused by the difference in the base material thickness is eliminated by this new spherical aberration, and the wavefront is also corrected by the wavelength selection phase plate 205. ing.

  22A and 22B are a plan view and a side view of the wavelength phase plate 205, respectively. The phase plate 205 has a refractive index at the wavelength λ1 of n1 and h = λ1 / (n1-1), and is constituted by phase steps 205a of heights h and 3h. For light of wavelength λ1, the difference in optical path length caused by height h is wavelength λ1, which is equivalent to a phase difference of 2π radians, and is therefore the same as phase difference 0.

  Therefore, it does not affect the phase distribution and does not affect the recording / reproducing of the optical disk 9. On the other hand, for light of wavelength λ2, if the refractive index of the phase plate 205 at wavelength λ2 is n2, h / λ2 × (n2-1) is about 0.6λ, that is, an optical path length that is not an integral multiple of the wavelength. Causes a difference. The above-described aberration correction is performed using the phase difference due to the difference in the optical path length (for example, see Patent Document 2 and Non-Patent Document 1).

  Further, as a third conventional example, a configuration in which a plurality of objective lenses are used by mechanically switching is disclosed (for example, Patent Document 3).

  Further, as a fourth conventional example, Japanese Patent Application Laid-Open No. H11-339307 discloses a configuration in which a mirror provided with a reflecting surface having a different radius of curvature also serves as a rising mirror for bending an optical axis (for example, see Japanese Patent Application Laid-Open No. H11-339307). 4).

As a fifth conventional example, as in the first conventional example, a refraction type objective lens and a hologram are combined, and the chromatic aberration generated in diffracted light of the same order of light of different wavelengths is used to obtain a difference in the base material thickness. Is disclosed (for example, Patent Document 5).
JP-A-2002-237078 (page 6-7, FIG. 1) JP-A-10-334504 (pages 7-9, FIGS. 1-4) JP-A-11-296890 (page 4-6, FIG. 1) JP-A-11-339307 (page 4-5, FIG. 1) JP-A-2000-81566 (pages 4 to 6, FIGS. 1 and 2) ISOM2001 TECHNICAL DIGEST Session We-C-05 (Preliminary 30 pages)

  The first conventional example has a spherical aberration characteristic in which the spherical aberration shifts to the under side when the wavelength of the light beam of the light source shifts to the longer wavelength side. With this configuration, when the thickness of the transparent substrate is increased from t1 to t2, the excess of the spherical aberration is canceled by the under light due to the longer wavelength light.

  For example, when switching from information reproduction to information recording on an optical disk having a transparent substrate with a thickness of t1, the light amount needs to be increased by about 10 times, and the wavelength also changes and becomes longer accordingly. Since the wavelength becomes longer, the spherical aberration changes under, but since the thickness of the disk does not change, there is a problem that unintended spherical aberration occurs and the light-collecting performance deteriorates.

  Further, a change in wavelength due to a change in light amount also causes a change in focal length. In FIG. 3 of the first conventional example (Patent Document 1), when the wavelength of blue light changes by 10 nm, the focal length changes by about 10 μm. In FIG. 4 of the first conventional example, when the wavelength of red light changes by 10 nm, the focal length changes by about 3 μm. In particular, there is a problem that the focal length of blue light changes greatly, and the light-collecting characteristics deteriorate immediately after the light amount is changed until the objective lens moves by focus control.

  In the second conventional example, a wavelength selection phase plate is used as a compatible element. When recording / reproducing a disk with a thick base material, the focal length needs to be extended since the recording surface is farther from the objective lens by the thickness of the base material. The focal length can be extended by the compatible element having the lens power, but the wavelength-selective phase plate has no lens power.

  Further, if it is attempted to realize all of this lens power by converting red light to divergent light as in the second conventional example, a large aberration occurs when the objective lens moves due to track following or the like, and the recording / reproducing characteristics deteriorate. The problem arises.

  Furthermore, since the parallelism of the light reflected from the optical disk and returned through the objective lens varies depending on the thickness of the optical disk substrate, the detection lens and the photodetector cannot be shared, and the parallelism of the light depends on the parallelism of the light. There is also a problem that it has to be prepared separately.

  In the third conventional example, since the objective lenses are switched, a plurality of objective lenses are required, so that the number of parts is increased, and it is difficult to reduce the size of the optical head device. In addition, there is a problem that it is difficult to reduce the size of the device even in the point that a switching mechanism is required.

  In the fourth conventional example, the objective lens is driven independently of the mirror (see FIGS. 4 to 6 of Patent Document 4).

  However, since the light beam is converted from the parallel light by the mirror having the radius of curvature as described above, when the objective lens moves by track control or the like, the relative position of the objective lens with respect to the incident light wavefront changes, and aberration occurs. There is a problem that the light-collecting characteristics deteriorate.

  Further, the reflecting surface of the mirror is constituted by a surface having a radius of curvature, that is, a spherical surface. However, a spherical surface is not enough to correct the difference between the thickness of the base material and the difference between the wavelengths. There is also a problem that the secondary aberration cannot be sufficiently reduced.

  The present invention is to solve the conventional problems as described above, to achieve compatible playback and compatible recording of different types of optical discs using a single objective lens, and when changing the wavelength at the time of light amount switching, It is an object of the present invention to provide an optical element and an optical lens that suppress changes in the focal length and the occurrence of spherical aberration, stably reproduce or record information, and an apparatus and a system using the same. Further, the present invention also provides an optical element for recording and reproducing a single optical disk, an optical lens, and an apparatus and a system using the same.

  In order to achieve the above object, the optical element of the present invention is an optical element corresponding to at least two wavelengths of red light and blue light, and has a phase step when the blue light is transmitted through the phase step. The difference in the generated optical path length is five times the wavelength of the blue light.

  The first optical lens of the present invention is an optical lens having a phase step, wherein blue light is condensed by the optical lens through a substrate having a substrate thickness of t1, and red light is reflected by a substrate having a substrate thickness of t2. The light is condensed through the base material, and t1 <t2, and the difference in the optical path length that occurs when the blue light transmits through the phase step is five times the wavelength of the blue light.

  A second optical lens according to the present invention is an optical lens having a hologram, a refraction type lens, and a phase step, wherein the hologram includes a saw-tooth grating having a saw-tooth cross-sectional shape. By setting the depth of the grating, the + 2nd-order diffracted light is generated most strongly for blue light, and the + 1st-order diffracted light is generated most strongly for red light. When the blue light transmits through the phase step, The difference in the generated optical path length is five times the wavelength of the blue light.

  A third optical lens according to the present invention is an optical lens having a hologram, a refraction type lens, and a phase step, wherein the hologram generates +2 order diffracted light with respect to blue light, For the light, the + 1st-order diffracted light is generated most strongly, and the hologram grating of the hologram is formed at least on the inner periphery including the intersection with the optical axis of the hologram. The + 1st-order diffracted light of the red light that is collected through the base material having the thickness t1 and passes through the inner peripheral portion is collected through the base material having the base material thickness t2, and satisfies t1 <t2. The difference in optical path length that occurs when blue light is transmitted is five times the wavelength of the blue light.

  A first optical head device according to the present invention includes the optical lenses, a first laser light source that emits blue light of wavelength λ1, a second laser light source that emits red light of wavelength λ2, and recording of an optical information medium. A light detection unit that receives the light beam reflected on the surface and outputs an electric signal in accordance with the amount of the light beam, wherein the optical lens converts the first light beam from the first laser light source into a base material having a thickness t1. The light is condensed on the recording surface of the first optical information medium through the base material, and the second light beam from the second laser light source is condensed on the recording surface of the second optical information medium through the base material having the substrate thickness t2. And t1 <t2.

  The optical information device of the present invention is an optical head device including any one of the optical lenses and a laser light source, a motor for rotating an optical information medium, and a signal obtained from the optical head device, based on the signal, An electric circuit for controlling and driving at least one of the motor, the optical lens, and the laser light source is provided.

  The computer of the present invention includes any one of the optical information devices, and performs an arithmetic operation based on at least one of the input information and the information reproduced from the optical information device; and An output device for outputting at least one of information, information reproduced from the optical information device, and a result calculated by the calculation device is provided.

  An optical information medium player according to the present invention includes: any one of the optical information devices; and a decoder that converts an information signal obtained from the optical information device into an image.

  A car navigation system according to the present invention includes: any one of the optical information devices; and a decoder that converts an information signal obtained from the optical information device into an image.

  The optical information medium recorder according to the present invention includes any one of the optical information devices and an encoder that converts image information into information to be recorded by the optical information device.

  An optical information medium server according to the present invention is characterized by comprising any one of the optical information devices and an input / output terminal for exchanging information with the outside.

  The fourth optical lens according to the present invention is an optical lens corresponding to light of one wavelength, and has a phase step, and a difference in an optical path length generated when the light passes through the phase step is equal to the light level. Is an integral multiple of the wavelength.

  According to a second optical head device of the present invention, the fourth optical lens, a laser light source for emitting a light beam, and a light beam reflected on a recording surface of an optical information medium receive an electric signal in accordance with the light amount. And a light detection unit that outputs a light beam from the laser light source, and the optical lens condenses the light beam from the laser light source through the base material onto the recording surface of the optical information medium.

  According to the present invention, spherical aberration due to chromatic aberration can be corrected by a phase difference that causes an optical path length difference of five times the wavelength with respect to blue light, so that information reproduction and recording can be performed stably even when the wavelength changes. And the compatibility of different types of discs can be realized.

  According to the optical element and the first optical lens of the present invention, spherical aberration due to chromatic aberration can be corrected by a phase difference that causes a difference in optical path length of five times the wavelength with respect to blue light. In addition, information can be reproduced and recorded stably. In the present invention, the phase step is a step in which a height difference is formed in an optical element, and a phase difference is generated in light passing through the step. This is the same for the following inventions.

  According to the second optical lens of the present invention, the + 2nd-order diffracted light is generated most strongly for blue light, and the + 1st-order diffracted light is generated most strongly for red light. And correction of spherical aberration due to the difference in substrate thickness. Further, spherical aberration due to chromatic aberration can be corrected by a phase difference that causes a difference in optical path length of five times the wavelength with respect to blue light, so that information can be reproduced and recorded stably even when the wavelength changes. .

  According to the third optical lens of the present invention, the inner peripheral portion of the hologram is formed so that + 2nd-order diffracted light is generated most strongly for blue light and + 1st-order diffracted light is generated most strongly for red light. By doing so, the intensity of the diffracted light of the red light beam can be maximized, and the light use efficiency of the blue light beam with respect to the focused spot can be prevented from being reduced. Further, spherical aberration due to chromatic aberration can be corrected by a phase difference that causes a difference in optical path length of five times the wavelength with respect to blue light, so that information can be reproduced and recorded stably even when the wavelength changes. .

  According to the fourth optical lens of the present invention, chromatic aberration can be corrected, the grating pitch of the diffractive lens can be made coarse, and the efficiency of using the amount of light can be increased.

  According to the first optical head device of the present invention, a single optical head device can support a plurality of optical disks having different recording densities.

  According to the second optical head device of the present invention, it can be used for a device for recording and reproducing a single optical disk.

  According to the computer, the optical disk player, the optical disk recorder, the optical disk server, and the car navigation system of the present invention, different types of optical disks can be stably recorded or reproduced, so that they can be used for a wide range of applications.

  The first optical lens further includes a liquid crystal phase modulation element. By electrically switching the liquid crystal phase modulation element, the blue light is converted by the optical lens into a substrate having a substrate thickness of t1. The red light is focused through a material, the red light is focused through a substrate having a substrate thickness of t2 greater than the t1, and the amount of phase modulation applied to a transmitted wavefront is switched to correct aberration due to a substrate thickness difference. preferable. According to this configuration, the aberration due to the difference in the thickness of the base material can be corrected by the liquid crystal phase modulation element without using a hologram.

  Further, it is preferable that the optical lens is a refraction lens formed of two different materials. According to this configuration, the refractive lens has a chromatic aberration correcting action, and this correcting action does not cause loss of light amount due to diffraction, and can achieve both high light use efficiency and chromatic aberration correction.

  In the second optical lens, it is preferable that the depth of the sawtooth grating is h1, and the h1 is a depth that gives a difference of an optical path length of about two wavelengths to the blue light. According to this configuration, the + 2nd-order diffracted light intensity becomes maximum for blue light, and the + 1st-order diffracted light intensity becomes maximum for red light.

  In the hologram, the depth of the saw-toothed grating formed on the inner peripheral portion including the intersection with the optical axis of the hologram is h2, and the depth of h2 is about one wavelength with respect to the red light. The depth is preferably a depth that gives a difference in optical path length. According to this configuration, the intensity of the diffracted light of the red light beam can be maximized, and the light use efficiency of the light condensing spot of the blue light beam can be prevented from decreasing.

  In the third optical lens, a hologram grating is further formed on an outer peripheral portion outside the inner peripheral portion, and the hologram grating on the outer peripheral portion is a sawtooth lattice having a sawtooth cross-sectional shape. The depth of the sawtooth grating of the portion is h3, and the h3 is a depth that gives a difference of an optical path length of about one wavelength to the blue light, and at the outer peripheral portion, the depth is h3 to the blue light. It is preferable that the + 1st-order diffracted light is generated most strongly and the + 1st-order diffracted light is also generated most strongly for red light. According to this configuration, the numerical aperture NAb when recording / reproducing a thin optical disk with a blue light beam is larger than the numerical aperture NAr when recording / reproducing a DVD or the like with a red light beam (NAb> NAr). be able to.

  In each of the optical lenses, the blue light is condensed through a base material having a base material thickness t1, and the hologram is formed into a convex lens so as to reduce a change in focal length when the wavelength λ1 of the blue light changes. It is preferable that the blue light is subjected to a convex lens action by the hologram.

  Further, the blue light is focused by the optical lens through a substrate having a substrate thickness of t1, the red light is focused through a substrate having a substrate thickness of t2, and t1 <t2. When condensing through the substrate having the substrate thickness t1, the convex lens action by the hologram is increased compared to when the red light is condensing through the substrate having the substrate thickness t2, and the red light is condensed. It is preferable that the focal position on the substrate side is farther from the optical lens than the focal position of the blue light on the substrate side.

  The blue light is focused by the optical lens through a substrate having a substrate thickness of t1, the red light is focused through a substrate having a substrate thickness of t2, and t1 <t2. When condensing through the base material having the base material thickness t2, the convex lens action by the hologram is reduced as compared with when the blue light is condensed through the base material having the base material thickness t1. It is preferable that the focal position on the substrate side is farther from the optical lens than the focal position of the blue light on the substrate side.

  Further, it is preferable that the lattice cross-sectional shape of the hologram is a sawtooth shape having a slope on the outer peripheral side of the base material forming the hologram.

  Further, it is preferable that the hologram, the refractive lens, and the phase step are integrally fixed. Further, it is preferable that the hologram is formed integrally with the surface of the refractive lens. Further, it is preferable that the phase step is formed integrally with the surface of the refractive lens. According to these configurations, during focus control and tracking control, driving is performed integrally by a common driving unit, so that an increase in aberration due to a shift in the relative position between the hologram and the objective lens can be prevented.

  In addition, it is preferable that aberrations generated in the refraction lens or the refraction lens and the hologram due to the change in the wavelength be reduced by the aberrations generated in the phase difference.

  Further, assuming that the numerical aperture at which the blue light is condensed through the substrate having the substrate thickness t1 is NAb, and the numerical aperture at which the red light is condensed through the substrate having the substrate thickness t2 is NAr, t1 <t2, Further, it is preferable that NAb> NAr.

  In the optical head device, when the second light beam is converged on a recording surface of the second optical information medium, a collimating lens that converts the second light beam into substantially parallel light is provided on the second laser side. It is preferable that the second light beam converted into the diffused light is made incident on the optical lens so that the focal position on the side of the second optical information medium is separated from the optical lens.

  Further, by arranging both the emission points of the first laser and the second laser so as to form an image with respect to the focal position of the optical lens on the optical information medium side, a common photodetector can be obtained. Preferably, a servo signal is detected.

  In the optical information device, the laser light sources are a first laser light source that emits blue light having a wavelength λ1 and a second laser light source that emits red light having a wavelength λ2, and determine the type of the optical information medium. For an optical information medium having a substrate thickness of about 0.6 mm, it is preferable to move the collimating lens toward the second laser light source.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

(Embodiment 1)
FIG. 1 is a configuration diagram showing an optical head device according to Embodiment 1 of the present invention. In FIG. 1, reference numeral 1 denotes a blue laser light source that emits blue laser light having a wavelength λ1 (390 nm to 415 nm; a wavelength of 390 nm to 415 nm is generally referred to as about 405 nm since it is typically about 405 nm).

  Reference numeral 20 denotes a red laser light source that emits a red laser beam having a wavelength λ2 (630 nm to 680 n: 660 nm is generally used, so the wavelength of 630 nm to 680 nm is generally referred to as about 660 nm). 8 is a collimating lens (first convex lens), 12 is a rising mirror that bends the optical axis, and 14 is an objective lens (optical lens).

  Reference numeral 9 denotes a base material thickness t1 of about 0.1 mm (hereinafter, a base material thickness of 0.06 mm to 0.11 mm is referred to as about 0.1 mm) or a thinner base material. It is a third generation optical disk corresponding to the optical information medium to be used. Reference numeral 10 denotes a base material thickness t2 of about 0.6 mm (a base material thickness of 0.54 mm to 0.65 mm is called about 0.6 mm), which corresponds to an optical information medium recorded / reproduced by a light beam of wavelength λ2. It is a second generation optical disk such as a DVD.

  The optical disks 9 and 10 show only the base material from the light incident surface to the recording surface. In actuality, in order to reinforce the mechanical strength and make the outer shape 1.2 mm which is the same as that of the CD, it is bonded to a protective plate. The optical disk 10 is bonded to a 0.6 mm thick protective material. The optical disk 9 is bonded to a protective material having a thickness of 1.1 mm. In the drawings of the present invention, the protective material is omitted for simplicity.

  The blue laser light source 1 and the red laser light source 20 are preferably semiconductor laser light sources, so that the optical head device and the optical information device using the same can be reduced in size, weight and power consumption.

  When recording / reproducing data on / from the optical disc 9 having the highest recording density, the blue light beam 61 having the wavelength λ1 emitted from the blue laser light source 1 is reflected by the beam splitter 4 and converted into circularly polarized light by the quarter-wave plate 5. The quarter-wave plate 5 is designed to act as a quarter-wave plate for both the wavelength λ1 and the wavelength λ2.

  The collimator lens 8 converts the light into substantially parallel light, the optical axis of which is bent by a rising mirror 12, and a hologram (diffraction type optical element) 13 and a refraction type objective lens 14. The light is focused on the information recording surface through the material.

  The blue light beam 61 reflected on the information recording surface of the optical disk 9 reverses the original optical path (return path) and becomes linearly polarized light in a direction perpendicular to the initial direction by the 波長 wavelength plate 5. The light is substantially totally transmitted, totally reflected by the beam splitter 16, diffracted by the detection hologram 31, further extended in focal length by the detection lens 32, and enters the photodetector 33.

  By calculating the output of the photodetector 33, a servo signal and an information signal used for focus control and tracking control are obtained. As described above, the beam splitter 4 is a polarization splitting film that totally reflects the linearly polarized light in one direction and completely transmits the linearly polarized light in the direction perpendicular to the light beam of the wavelength λ1. In addition, as described later, the red light beam 62 emitted from the red laser 20 is completely transmitted with respect to the light beam having the wavelength λ2. As described above, the beam splitter 4 is an optical path branching element having wavelength characteristics as well as polarization characteristics.

  Next, when recording or reproducing data on or from the optical disk 10, a light beam having a wavelength λ2 of substantially linearly polarized light emitted from the red laser light source 20 passes through the beam splitter 16 and the beam splitter 4, and is substantially collimated by the collimating lens 8. Further, the optical axis is bent by the rising mirror 12, and the light is condensed on the information recording surface by the hologram 13 and the objective lens 14 through the base material of the optical disc 10 having a thickness of about 0.6 mm.

  The light beam reflected on the information recording surface of the optical disk 10 reverses the original optical path (return path), passes through the beam splitter 4 almost completely, is totally reflected by the beam splitter 16, is diffracted by the detection hologram 31, and is further diffracted. The focal length is extended by the detection lens 32, and the light enters the photodetector 33.

  By calculating the output of the photodetector 33, a servo signal and an information signal used for focus control and tracking control are obtained. As described above, in order to obtain the servo signals of the optical disks 9 and 10 from the common photodetector 33, the light emitting points of the blue laser 1 and the red laser 20 are focused on the common position on the objective lens 14 side. Place as shown in By doing so, the number of detectors and the number of wires can be reduced.

  The beam splitter 16 is a polarization splitting film that totally transmits linearly polarized light in one direction and totally reflects linearly polarized light in a direction perpendicular to the wavelength λ2. Further, the light beam of wavelength λ1 totally reflects the blue light beam 61. As described above, the beam splitter 16 is also an optical path branching element having wavelength selectivity as well as polarization characteristics.

  Next, the functions and configurations of the hologram 134 and the objective lens 144 will be described with reference to FIGS. In FIG. 2, reference numeral 134 denotes a hologram. The hologram 134 diffracts the blue light beam 61 having the wavelength λ1 and exerts a convex lens effect, and diffracts the light having the wavelength λ2 as described later and exerts a convex lens effect weaker than the blue light beam.

  Here, the lowest order diffraction having a convex lens effect is defined as + 1st order diffraction. As the order increases from the + 1st diffraction, the diffraction angle also increases. In the present embodiment, a design is made so that +2 order diffraction occurs most strongly for a blue light beam. At this time, the + 1st-order diffraction of the red light beam occurs most strongly. In this case, although the red light beam has a longer wavelength than the blue light beam, the diffraction angle at each point on the hologram 134 is small.

  In other words, the convex lens function when the hologram 134 diffracts the blue light beam 61 having the wavelength λ1 is stronger than the convex lens function exerted on the light having the wavelength λ2. In other words, the red light beam is subjected to the convex lens action by the hologram 134, but is subjected to the concave lens action due to the relative diffraction based on the action received by the blue light beam.

  The objective lens 144 is designed so that the blue light beam having the wavelength λ1 is subjected to + 2nd-order diffraction by the hologram 134 and subjected to a convex lens function, and then further condensed and condensed on the recording surface through the substrate thickness t1 of the optical disk 9. Is done.

  Next, the operation of the hologram 134 when recording / reproducing the optical disk 10 using the red light beam will be described in detail. The hologram 134 diffracts light of the wavelength λ2 (dotted line: red light beam 62) by + 1st order to exert a convex lens function. Then, the red light beam 62 is focused on the information recording surface 101 by the objective lens 144 through the base material having a thickness t2 of the optical disk 10 of about 0.6 mm.

  Here, the disk 10 has a base material thickness from the light incident surface to the information recording surface 101 of 0.6 mm, which is thicker than the focal position when recording / reproducing the optical disk 9 having a base material thickness of 0.1 mm. The focus position needs to be separated from the objective lens 144. As shown in FIG. 2, the blue light beam 61 is converted into condensed light by wavefront conversion, and the red light beam 62 is made to have a light concentration lower than that of the blue light beam. Correction of spherical aberration is realized. Both the blue light beam 61 having the wavelength λ1 and the red light beam 62 having the wavelength λ2 have their wavefronts converted by the hologram 134.

  Therefore, if there is an error in the relative position between the hologram 134 and the objective lens 144, the wavefront as designed does not enter the objective lens 144, causing an aberration in the wavefront incident on the optical disc 9 or the optical disc 10, deteriorating the light-collecting characteristics. I do. Therefore, the hologram 134 and the objective lens 144 are desirably fixed integrally, and the drive is performed integrally by the common drive means 15 (FIG. 1) during focus control and tracking control.

  FIG. 3 shows the hologram 134. FIG. 3A is a plan view, and FIG. 3B is a cross-sectional view similar to FIG. 2, viewed from a direction perpendicular to the plan view. The hologram 134 is different from the inside (inner periphery 134C) of the inner / outer boundary 134A and the outside (the outer periphery 134B between the inner / outer boundary 134A and the effective range 134D).

  The inner peripheral portion 134C is a region including the intersection of the hologram 134 and the optical axis, that is, the center. This area is used both when recording / reproducing the optical disk 10 using the red light beam and when recording / reproducing the optical disk 9 using the blue light beam.

  Therefore, the diffraction grating of the inner peripheral portion 134C and the portion of the objective lens 144 through which the red light beam diffracted therethrough passes, the +2 order diffracted light of the blue light beam is applied to the optical disc 9, and the +1 order diffracted light of the red light beam is applied to the optical disc. 10 is designed to be focused. Regarding the outer peripheral portion 134B, the numerical aperture NAb when recording / reproducing the optical disk 9 with the blue light beam 61 is larger than the numerical aperture NAr when recording / reproducing the optical disk 10 with the red light beam 62 (NAb> NAr). There is.

  For this reason, only the + 2nd-order diffracted light of the blue light beam 61, for example, is collected on the optical disk 9 around the inner periphery where the red light beam 62 and the blue light beam 61 are focused on the corresponding optical disks 9 and 10, respectively. It is necessary to provide the outer peripheral portion 134B and the outer peripheral portion of the objective lens 144 corresponding thereto so that the + 1st-order diffracted light of the red light beam 62 that emits light has an aberration with respect to the optical disk 10.

  That is, although not shown, it is desirable that the objective lens 144 be designed differently depending on the inner and outer circumferences, similarly to the hologram 134. Thereby, the optimum NA, that is, NAb> NAr can be realized.

  FIG. 4 is a diagram illustrating a cross section of the hologram 132 during one period (p4) of the hologram grating. FIG. 4A shows a physical shape. Such a shape like a saw tooth is called a saw tooth shape. Further, in order to represent the direction of the slope, the shape in FIG. 4A is expressed as a shape in which the base material has a slope on the left side.

  According to this designation, the cross-sectional shape of the hologram 134 in FIG. 3 is expressed as a sawtooth shape in which the base material has a slope on the outer peripheral side. FIG. 4B shows the amount of phase modulation for blue light. FIG. 4C shows the amount of phase modulation for red light.

  In FIG. 4A, the vertical direction indicates the depth of the sawtooth lattice. Assuming that the hologram material is, for example, BK7, the refractive index nb of the hologram material with respect to the blue light beam is nb = 1.5302.

  The depth of the sawtooth grating is set such that the difference in optical path length with respect to the blue light beam 61 is about two wavelengths, that is, the phase difference is about 4π radians. Here, the difference in the optical path length means a difference in the optical path length (also referred to as an optical distance; a value obtained by multiplying the length of the medium and the refractive index) caused by the presence or absence of a step.

  Therefore, the difference L in the optical path length is represented by the product of the depth h1 of the step and the difference (nb-1) in the refractive index between the medium and the air, and is as follows.

L = h1 × (nb-1)
When the difference between the optical path lengths is two wavelengths, L = 2 × λ1, the depth h1 is expressed by the following equation, and the value of h1 is obtained by substituting λ1 = 405 nm and nb = 1.5302.

h1 = 2 × λ1 / (nb-1) = 1.53 μm
Since the phase modulation amount for blue light in this shape changes by 4π (= 2π × 2) radians in one period of the grating, the + 2nd-order diffracted light intensity becomes maximum, and the scalar calculation results in 100% diffraction efficiency.

  On the other hand, when the refractive index of the hologram material with respect to the red light beam 62 is nr, when the hologram material is BK7, nr = 1.5142. The optical path length difference generated in the red light beam due to the step h1 is represented by h1 × (nr−1). Therefore, the multiple of the optical path length difference with respect to the wavelength λ2 of the red light beam is as follows, substituting λ1 = 405 nm and nr = 1.5142.

h1 × (nr-1) /λ2=1.19
That is, the optical path length difference is about 1.2 times the wavelength λ2, and the phase modulation amount is about 2.4π radians (1.2 × 2π). Therefore, the + 1st-order diffracted light intensity is the strongest, and the calculated diffraction efficiency is about 80%.

  For this reason, as shown in FIG. 4A, when the shape of one period of the grating is formed in a saw-tooth cross-sectional shape with a depth h1, the +2 order diffraction of the blue light beam 61 is the strongest as described above. The grating period that determines the diffraction angle is substantially p4 / 2, and the phase change is equivalent to that shown in FIG. Since the + 1st-order diffraction is the strongest for the red light beam 62, the grating period that determines the diffraction angle is substantially p4.

  With the above-described configuration, different types of disks can be interchanged by correcting the difference in the base material thickness, and chromatic aberration, particularly focal length dependence on wavelength change in the vicinity of a reference wavelength such as 405 nm or 660 nm (within several nm) can be offset and reduced. The effect described above can be obtained. However, since the spherical aberration is changed by the wavelength difference, the spherical aberration change occurs in the chromatic aberration with respect to the wavelength change near the reference wavelength (within several nm). A configuration for correcting this change in spherical aberration will be described with reference to FIGS.

  In FIG. 5, reference numeral 144 denotes an objective lens. Reference numeral 1441 denotes a surface of the objective lens 144 not directly facing the optical disk (first surface), and 1442 denotes a phase step formed on the first surface 1441. The phase step 1442 can be formed on a surface (second surface) of the objective lens 144 opposite to the first surface 1441 or on any surface of the hologram 134.

  Also, as shown in FIG. 5, by integrating with the objective lens 144, even if the objective lens 144 moves due to track following or the like, the relative position between the phase step 1442 and the objective lens 144 does not change, and the optical performance is improved. The effect of not deteriorating can be obtained.

  When the characteristic deterioration due to the relative position change between the phase step 1442 and the objective lens 144 is sufficiently small, the objective lens 144 and the phase step 1442 are not integrated, but are formed on the surface of the collimator lens 8 in FIG. It is possible. Further, although not shown, both the hologram and the phase step can be integrally formed on the surface of the refraction type objective lens.

  FIG. 6 is a schematic diagram in which the phase step 1442 is enlarged. One or more steps having a height of ha are formed per step. The step ha satisfies the following expression (1) when the refractive index nb of the base material forming the phase step 1442 is the refractive index for the wavelength λ1 (for example, 405 nm).

Equation (1) ha = 5 × λ1 / (nb−1)
Equation (1) can be transformed into the following equation (2).

Equation (2) 5 × λ1 = ha × (nb-1)
The right side of the equation (2) is a difference in the optical path length due to the step of the height ha. That is, one step of the phase step 1442 is set so as to generate a difference in optical path length five times the wavelength λ1, that is, a phase difference of 10π radian (5 × 2π) with respect to the light of the wavelength λ1. ing.

For example, if the base material forming the phase step 1442 is glass of a type called BK7,
When λ1 = 405 nm, nb = 1.5302, and from (Equation 1),
ha = 3819 nm
It becomes. When red light having a wavelength of λ2 = 655 nm is incident on this step, for example, the refractive index nr of BK7 for λ2 = 655 nm is 1.5144, and the resulting optical path length difference L is as follows.

L = ha × (nr−1) = 1964.5
This calculated value is approximately equal to 3 × λ2. That is, a step that causes a difference in optical path length of five times the wavelength with respect to blue light results in a difference in optical path length that is three times the wavelength with respect to red light. Since the phase change amount at which the difference in the optical path lengths is an integral multiple of the wavelength is an integral multiple of 2π radians (10π radians for λ1 = 405 nm, 6π radians for λ2 = 655 nm), it is practically significant. No phase difference occurs.

Therefore, the wavefront does not change for the reference wavelengths λ1 and λ2. Then, when a wavelength change of, for example, several nm from the reference wavelength occurs, a difference in optical path length deviates from an integral multiple of the wavelength, and thus a phase change occurs. The step can be dug into the base material side as shown in FIG. 6 or, conversely, can be raised, so that the direction of the phase change with respect to the wavelength shift can be freely set. For example, in the case of blue light, the phase change amount ΔφB with respect to a change of the wavelength of 1 nm is ΔφB = 10π / 405 = 0.024π (radian)
It is. The aberration can be corrected by stacking and forming a step having a height of ha at each position where the chromatic aberration per wavelength change of 1 nm caused by the lens or the hologram becomes 0.024π radian. For red light, the phase change amount ΔφR with respect to a change in wavelength of 1 nm is:
ΔφB = 6π / 655 = 0.09π (radian)
It is. Although the amount of phase change is smaller in red light than in blue light, there is no problem because chromatic aberration per 1 nm wavelength change caused by a lens or hologram is small.

  In the above description, 405 nm for blue and 655 nm for red are selected as the reference wavelengths. However, other wavelengths such as 408 nm and 410 nm can be selected for the blue reference wavelength, and accordingly, the unit step ha and the red reference wavelength can be selected. Can also be changed. The relationship is represented by the following equation (3).

Equation (3) ha = 3 × λ2 / (n2-1) = 5 × λ1 / (n1-1)
Although the phase step has ha as one unit, even if the integral multiple (two times, three times,...) Is one unit, no wavefront change is given to both the red and blue reference wavelengths, and the wavelength change from each. The wavefront can be changed only for.

  Further, a configuration in which chromatic aberration due to a change in wavelength is corrected by applying a step having a difference in optical path length of five times the wavelength with respect to blue light to the first conventional example. In this configuration, the phase step is formed on the objective lens formed of two different materials. According to this configuration, the chromatic aberration correcting action of the refraction lens does not cause loss of light amount due to diffraction, and can achieve both high light use efficiency and chromatic aberration correction.

  Further, it is possible in principle to correct the focal position change due to the wavelength change, but the number of steps increases, and the length of the flat portion per step (the portion having the same height in the direction along the light beam) 6 (for example, the length of c in FIG. 6) is narrowed, and it is difficult to manufacture as designed. Therefore, as shown in FIG. 5, the hologram described with reference to FIGS. 2 to 4 corrects the change in the focal length due to the thickness of the base material and the chromatic aberration, and reduces the difference in the optical path length five times the wavelength with respect to the blue light. A configuration in which spherical aberration due to chromatic aberration is corrected by the generated step allows easy production and an effect that expected performance as designed can be obtained, which is more preferable.

  The hologram having a sawtooth cross-sectional shape having a depth that causes a difference in optical path length twice the wavelength with respect to the blue light beam and causes + 2nd-order diffraction shown in the present embodiment is used to generate the red light beam. The concept of realizing interchangeability between different types of discs by + 1st-order diffracted light and correcting spherical aberration due to chromatic aberration by a step that causes a difference in optical path length of five times the wavelength with respect to blue light is any of the above-mentioned concepts. It is not disclosed in the conventional example.

  In the present embodiment, compatibility of different kinds of disks can be realized by the above-described novel configuration. Further, the hologram 134 has a convex lens action for both the blue light beam and the red light beam, and the diffraction action is such that the chromatic dispersion is in the opposite direction to the refraction action. When combined, there is an effect that the chromatic aberration with respect to a wavelength change within several nm, particularly the wavelength dependency of the focal length, can be offset and reduced. Furthermore, spherical aberration due to chromatic aberration can be corrected, and information can be reproduced and recorded stably even when the wavelength changes.

  Therefore, the hologram 134 and the phase difference alone have a remarkable effect that the problems of compatibility between different kinds of discs and chromatic aberration correction can be solved at once. That is, it is possible to instantaneously respond to a wavelength change due to an instantaneous change from reproduction to recording, for example, without performing focus control of an objective lens that is not suitable for an instantaneous response.

5 and 6 illustrate the case where the phase step 1442 is formed on the surface of the objective lens (refractive lens) 144, but the phase step 1462 is formed on the substrate surface of the hologram 136 as shown in FIG. Is also possible. FIG. 8 shows an enlarged view of the phase step portion in this case. FIG. 6 is the same as FIG. 6 in that the step of the phase step is set to be an integral multiple of the step ha that gives a difference in optical path length of five times the wavelength of blue light. The phase step according to the present embodiment may be formed in addition to an optical element such as an objective lens or a hologram or an optical lens as described above, or the phase step itself may be formed as an independent optical element. This is the same in the following embodiments.
Further, as the overall configuration of the optical head device, an additional effective configuration example will be described below. The following is valid in all the embodiments of the present application. However, the important points of the present application are a step that causes a difference in optical path length of five times the wavelength with respect to blue light, and an objective lens and a hologram used in combination therewith. For this reason, the beam splitter, the detection lens, and the detection hologram, which have already been described, are not indispensable components including the following, and the configurations described below are not essential. Can be used.

  In FIG. 1, a tracking error signal of the optical disk 9 is detected by a well-known differential push-pull (DPP) method by further arranging a three-beam grating (diffraction element) 3 between the blue laser 1 and the beam splitter 4. It is also possible.

  When two directions perpendicular to the optical axis are defined as an x direction and a y direction, for example, a beam shaping element 2 for enlarging only the x direction is further disposed between the blue laser 1 and the beam splitter 4. By doing so, the far-field pattern of the blue light beam 61 can be made closer to a point-symmetrical intensity distribution about the optical axis, and the light use efficiency can be improved. The beam shaping element 2 can be configured by using a double-sided cylindrical lens or the like.

  By further arranging the three-beam grating (diffraction element) 22 between the red laser 20 and the beam splitter 16, the tracking error signal of the optical disk 10 can be detected by a well-known differential push-pull (DPP) method. is there.

It is also effective to change the parallelism of the light beam by moving the collimating lens 8 in the direction of the optical axis (the left-right direction in FIG. 1). If the thickness error of the base material or the thickness of the base material caused by the interlayer thickness when the optical disc 9 is a two-layer disc causes spherical aberration, the collimating lens 8 is moved in the optical axis direction. Can correct the spherical aberration. As described above, the spherical aberration can be corrected by moving the collimating lens 8 when the NA of the condensed light on the optical disk is 0.85, which can be about several 100 mλ, and the base material thickness of ± 30 μm can be corrected. it can. However, when recording / reproducing a DVD using the objective lens 14 corresponding to the base material thickness of 0.1 mm, it is necessary to compensate for the base material thickness difference of 0.5 mm or more. The ability to correct spherical aberration is insufficient, and wavefront conversion by the hologram 13 (134 as an example) is required. However, when recording / reproducing the optical disk 10 using the red light beam, moving the collimator lens 8 to the left side in FIG. The beam is made divergent light, the focused spot on the optical disc 10 is further separated from the objective lens 14, and a part of the aberration due to the thickness of the base material is corrected, the amount of aberration correction required for the hologram 13 is reduced, and the hologram pitch is widened. In addition, creation of the hologram 13 can be facilitated.

  Further, the beam splitter 4 transmits a part (for example, about 10%) of linearly polarized light emitted from the blue laser 1, and the transmitted light beam is further guided to the photodetector 7 by the condenser lens 6. It is also possible to monitor the change in the amount of light emitted from the blue laser 1 using a signal obtained from the photodetector 7 and to control the amount of light emitted from the blue laser 1 to be constant by feeding back the change in the amount of light. .

  Further, the beam splitter 4 reflects part of the linearly polarized light emitted from the red laser 1 (for example, about 10%), and the reflected light beam is further guided to the photodetector 7 by the condenser lens 6. It is also possible to monitor the change in the amount of light emitted from the red laser 20 using the signal obtained from the photodetector 7 and to control the amount of light emitted from the red laser 20 to be constant by feeding back the change in the amount of light. .

(Embodiment 2)
Next, a second embodiment of the present invention will be described. This embodiment is different from the first embodiment only in that only the lattice cross-sectional shape of the inner peripheral portion 134C of the hologram 134 is changed. FIG. 9 illustrates a one-period lattice cross-sectional shape in the inner peripheral portion 134C of the hologram 134 described in the first embodiment. FIG. 9A shows a physical shape. FIG. 9B shows the amount of phase modulation for blue light. FIG. 9C shows the amount of phase modulation for red light.

  In FIG. 9A, the vertical direction indicates the depth of the sawtooth lattice. Unlike FIG. 4, the depth is determined based on the red light beam. nr is the refractive index of the hologram material for the red light beam. Assuming that the hologram material is, for example, BK7, nr = 1.5142 for λ2 = 660 nm.

The depth of the sawtooth grating is such that the difference in optical path length for the red light beam is about one wavelength, ie, the phase difference is about 2π radians. In this case, the depth h2 is
h2 = λ2 / (nr−1) = 1.28 μm.

  On the other hand, assuming that the refractive index of the hologram material with respect to the blue light beam is nb, when the hologram material is BK7, nb = 1.5302. The optical path length difference generated in the red light beam due to the depth h2 of the sawtooth grating is represented by h1 × (nr−1). Therefore, the multiple of the optical path length difference with respect to the wavelength λ1 of the blue light beam is as follows by substituting λ1 = 405 nm and nb = 1.5302.

h2 × (nb-1) /λ1=1.68
That is, the optical path length difference is about 1.7 times the wavelength λ1, and the amount of phase modulation is about 3.35π radians. For this reason, the + 2nd-order diffracted light intensity becomes maximum, and the scalar calculation results in a diffraction efficiency of about 80%.

  As shown in FIG. 9A, when the shape of one period of the grating is a saw-tooth cross-sectional shape having a depth h2, the +2 order diffraction of the blue light beam is the strongest as described above. The determined grating period is substantially p4 / 2, and the phase change is equivalent to FIG. 9B. For the red light beam, the + 1st-order diffraction is the strongest, and the diffraction efficiency is calculated to be 100%, and the light use efficiency can be increased.

  Further, the diffraction efficiency of the blue diffracted light is reduced to about 80%, but when the light amount in the central portion is reduced, the light amount in the outer peripheral portion is relatively increased. The far-field image of a semiconductor laser light source has a lower intensity at the outer periphery, and only a part of the far-field image can be used. However, if the light amount at the inner periphery decreases, a wider range of the far-field image can be used. Efficiency can be improved.

  This can be realized by shortening the focal length of the collimator lens 8, but this can compensate for the decrease in the amount of light in the inner peripheral portion. Accordingly, the effect of maximizing the diffracted light intensity of the red light beam by setting the inner peripheral portion to the height h2 as described with reference to FIG. 9 can be obtained. It is possible to obtain an effect that the light use efficiency of the condensing spot of the blue light beam does not decrease.

  Then, similarly to the first embodiment, the spherical aberration due to chromatic aberration can be corrected by combining with a step that produces a difference in optical path length of five times the wavelength of blue light.

  Also in the hologram of this embodiment, the hologram 134 has a convex lens function for both the blue light beam and the red light beam. Since the chromatic dispersion is in the opposite direction to the refraction effect, the diffraction effect cancels out the chromatic aberration with respect to a wavelength change within several nm, particularly the wavelength dependence of the focal length, when combined with the objective lens 144 which is a refraction type convex lens. There is an effect that it can be reduced.

  In combination with a step that produces a difference in optical path length of five times the wavelength of blue light, there is a remarkable effect that the problems of compatibility between different types of disks and chromatic aberration correction can be solved at once.

  A lens with a high NA has a high degree of difficulty in manufacturing, but the hologram has a convex lens function, which also has the effect of reducing the degree of difficulty in manufacturing the refraction type objective lens 144 to be combined.

  Further, as the overall configuration of the optical head device, it is possible to combine the configurations additionally described in the first embodiment.

(Embodiment 3)
Next, a third embodiment of the present invention will be described. In the third embodiment, as in the first and second embodiments, FIG. 1 can be cited as an example of the entire configuration of the optical head device, which is common. In FIG. 1, since the configuration of the hologram 13 is different, the function and configuration of the hologram 135 which is a characteristic element of the third embodiment will be described with reference to FIGS.

  10 and 11, reference numeral 135 denotes a hologram. The inner peripheral portion 135C is, for example, the same as the inner peripheral portion 134C of the hologram 134 shown in the first embodiment. FIG. 12 is a diagram illustrating a cross section of the outer peripheral portion 135B of the hologram 135 during one period (p7) of the hologram grating. FIG. 12A shows a physical shape. FIG. 12B shows the amount of phase modulation for blue light. FIG. 12C shows the amount of phase modulation for red light.

In FIG. 12A, the vertical direction indicates the depth of the sawtooth shape. The depth h3 of the sawtooth shape is such that the difference in optical path length with respect to the blue light beam is about one wavelength, that is, the phase difference is about 2π radians. Assuming that nb is the refractive index of the hologram material with respect to the blue light beam, when the hologram material is, for example, BK7, nb is 1.5302, and the sawtooth-shaped depth h3 is
h3 = λ1 / (nb−1) = 0.664 μm.

  On the other hand, when the refractive index of the hologram material with respect to the red light beam is nr, when the hologram material is BK7, nr = 1.5142. The optical path length difference generated in the red light beam due to the depth h3 is represented by h3 × (nr-1). Therefore, the multiple of the optical path length difference with respect to the wavelength λ2 of the red light beam is as follows by substituting λ2 = 660 nm and nr = 1.5142.

h3 × (nr-1) /λ2=0.595
That is, the optical path length difference is about 0.6 times the wavelength λ2, and the phase modulation amount is about 1.2π radians. Therefore, the intensity of the + 1st-order diffracted light is the strongest and is about 60%.

  In this manner, as shown in FIG. 12A, when the shape of one period of the grating is a saw-tooth cross-sectional shape with a depth h3, the + 1st-order diffraction of the blue light beam is the strongest (the first and second embodiments). In this case, the + 2nd-order diffracted light is the strongest also in the outer peripheral portion, but this embodiment is different in this respect.) Therefore, the grating period that determines the diffraction angle is substantially p7, and the phase change is equivalent to that in FIG. . The + 1st-order diffraction is also the strongest for the red light beam, and the grating period that determines the diffraction angle is also substantially p7.

  The outer periphery 135B of the hologram 135 is designed so that the blue light beam is focused through a substrate thickness of about 0.1 mm. At this time, the red light beam also receives + 1st-order diffraction of the same diffraction order as the blue light beam, and the diffraction angle increases because the red wavelength λ2 is longer than the blue wavelength λ1.

  The blaze direction of the hologram is designed so as to have a convex lens effect similarly to the inner peripheral portion. At this time, since the red light beam has a larger diffraction angle, it receives a strong convex lens effect. This is completely different from the case where the red light beam is subjected to a weak convex lens action or a concave lens action (such as 131C) at the inner peripheral portion (for example, 134C) than the blue light beam.

  Therefore, the red light beam diffracted by the outer peripheral portion 135B is not focused on the same place as the red light beam passing through the inner peripheral portion. In this way, the numerical aperture NAb for recording / reproducing the optical disk 9 with the blue light beam can be made larger than the numerical aperture NAr for recording / reproducing the optical disk 10 with the red light beam (NAb> NAr). it can.

  Then, similarly to the first embodiment, the spherical aberration due to chromatic aberration can be corrected by combining with a step that produces a difference in optical path length of five times the wavelength of blue light.

  Further, as the overall configuration of the optical head device, it is possible to combine the configurations additionally described in the first embodiment.

(Embodiment 4)
FIG. 13 is a schematic sectional view of a main part of an optical head device according to Embodiment 3 of the present invention. The optical head device shown in the figure uses a liquid crystal type phase modulation element instead of the hologram 134 in the configuration of FIG.

  The liquid crystal phase modulation element 137 can apply and cut off a voltage. That is, by electrically switching the liquid crystal phase modulation element 137, the amount of phase modulation applied to the transmitted wavefront can be switched to correct the aberration due to the difference in substrate thickness.

  In this case, the liquid crystal phase modulation element 137 cannot correct aberrations (both axial chromatic aberration and spherical aberration) caused by the wavelength change. Therefore, a configuration is provided in which all the chromatic aberrations including the axial chromatic aberration and the spherical aberration are corrected by combining the phase steps 1442.

  The phase step 1442 has the same configuration as that of the phase step 1442 shown in FIG. 5 described above. The phase step 1442 has a step that causes an optical path length difference of 5λ1 for blue light of wavelength λ1 and 3λ2 for red light of wavelength λ2. This is a phase step as a unit step.

  For example, if one phase step is formed every time the objective lens 144 generates an aberration of 5 nm, which is five times the blue wavelength fluctuation of 1 nm, the chromatic aberration for blue can be corrected. For red light, chromatic aberration occurs in the same direction, so that it can be similarly corrected.

(Embodiment 5)
FIG. 14 is a schematic cross-sectional view of a main part of an optical head device according to Embodiment 5 of the present invention. In the above-described Embodiment 1-4, an embodiment will be described in which a phase difference having a phase difference of 5 times the wavelength λ1 of blue as a unit step is combined with a diffraction type hologram or a liquid crystal phase modulation element. did. This embodiment is based on the premise that recording and reproduction are performed on a single optical disk. For this reason, one step of the phase step is not limited to a step that produces a phase difference of five times the wavelength, but is a step that produces a phase difference of an integral multiple of the wavelength.

  The optical head device shown in FIG. 14 is a combination of an objective lens 147 having a phase difference 1472 and a hologram 134, and the same components as those of the optical head device of FIG. . The optical head device shown in the figure is a device for recording and reproducing the optical disk 9 at the blue wavelength λ1. One of the phase steps 1472 formed on the surface 1471 of the objective lens 147 is an integral multiple of the wavelength λ1. Is a step that produces a phase difference of

  Also in this configuration, chromatic aberration can be corrected. Further, since the hologram 134 can share the phase difference 1472 and the chromatic aberration correction, the grating pitch of the hologram 134 can be made coarse, and the effect of increasing the light amount utilization efficiency can be obtained.

(Embodiment 6)
FIG. 15 shows an embodiment of an optical information device using the optical head device of the present invention. In FIG. 15, the optical disk 9 is placed on a turntable 82 and rotated by a motor 64. The optical head device 55 shown in the embodiment 1-4 is roughly moved by the drive device 51 of the optical head device up to the track on the optical disc 9 where desired information exists.

  The optical head device 55 sends a focus error (focus error) signal and a tracking error signal to the electric circuit 53 according to the positional relationship with the optical disc 9. The electric circuit 53 sends a signal for finely moving the objective lens to the optical head device 55 in response to this signal. With this signal, the optical head device 55 performs focus control and tracking control on the optical disk 9, and the optical head device 55 reads, writes (records), or erases information.

  The above description is the same even when the mounted optical disk is replaced with the optical disk 10 having a base material thicker than the optical disk 9. Since the optical information device of the present embodiment uses the optical head device of the present invention as the optical head device, a single optical head device can handle a plurality of optical disks having different recording densities.

  The optical head device 55 may be dedicated to a single optical disk as in the fifth embodiment. This is the same in the following embodiments 7-10.

(Embodiment 7)
The present embodiment is an embodiment of a computer including the optical information device 67 according to the sixth embodiment. FIG. 16 is a perspective view of the computer according to the present embodiment.

  The computer 100 shown in the figure includes an optical information device 67 according to Embodiment 6, an input device 65 such as a keyboard and a mouse or a touch panel for inputting information, information input from the input device 65, A computing device 64 such as a central processing unit (CPU) that performs computations based on information read from the information device 67, and a CRT, a liquid crystal display device, a printer, or the like that displays information such as results computed by the computing device 64. An output device 81 is provided.

  The computer according to the present embodiment includes the optical information device 67 according to the sixth embodiment and can stably record or reproduce different types of optical discs, so that it can be used for a wide variety of applications.

(Embodiment 8)
This embodiment is an embodiment of an optical information medium (optical disk) player including the optical information device 67 according to the sixth embodiment. FIG. 17 is a perspective view of the optical information medium player according to the present embodiment.

  The optical disc player 121 shown in the figure includes the optical information device 67 of the sixth embodiment, and an information-to-image conversion device 66 (for example, a decoder) for converting an information signal obtained from the optical information device 67 into an image. I have. This configuration can also be used as a car navigation system. Further, a mode in which a display device 120 such as a liquid crystal monitor is added is also possible.

  The optical information medium (optical disk) player according to the present embodiment includes the optical information device 67 according to the sixth embodiment, and can stably record or reproduce different types of optical disks, so that it can be used for a wide range of applications. .

(Embodiment 9)
The present embodiment is an embodiment of an optical information medium (optical disk) recorder including the optical information device 67 according to the sixth embodiment. FIG. 18 is a perspective view of the optical disc recorder according to the present embodiment.

  The optical disk recorder 110 shown in the figure includes an optical information device 67 according to Embodiment 6, and an image-to-information conversion device 68 (for example, an encoder) that converts image information into information to be recorded on an optical disk by the optical information device 67. It has.

  It is preferable to also have a device 66 (decoder) for converting an information signal obtained from the optical information device 67 into an image. According to this configuration, it is also possible to reproduce an already recorded portion. Further, an output device 61 such as a cathode ray tube, a liquid crystal display device, or a printer for displaying information may be provided.

  The optical disk recorder according to the present embodiment includes the optical information device 67 according to the sixth embodiment, and can stably record or reproduce different types of optical disks, so that it can be used for a wide range of applications.

(Embodiment 10)
This embodiment is an embodiment of an optical information device including the optical information device 67 according to the sixth embodiment. FIG. 19 is a perspective view of the optical information device according to the present embodiment.

  The optical information device shown in the figure includes the optical information device 67 according to the sixth embodiment. The input / output terminal 69 is a wired or wireless input / output terminal that takes in information to be recorded on the optical information device 67 and outputs information read by the optical information device 67 to the outside. This makes it possible to exchange information with a network, that is, a plurality of devices, for example, a computer, a telephone, a television tuner, and the like, and to use the information as a shared information server (optical information medium (optical disk) server) from the plurality of devices. Become. An output device 81 such as a cathode ray tube, a liquid crystal display device, or a printer for displaying information may be provided.

  The optical information device according to the present embodiment includes the optical information device 67 according to the sixth embodiment, and can stably record or reproduce different types of optical disks, so that it can be used for a wide variety of applications.

Further, by providing the changer 131 for taking a plurality of optical disks into and out of the optical information device 67, a large amount of information can be recorded and accumulated.
You.

  Although the output device 81 and the liquid crystal monitor 120 are shown in FIGS. 16 to 19 in the embodiment 7-10, the output device 81 and the liquid crystal monitor 120 are provided without the output device, and are sold separately. It goes without saying that there is a possibility.

  Although the input device is not shown in FIGS. 17 and 18, a product form including an input device such as a keyboard, a touch panel, a mouse, and a remote control device is also possible. Conversely, in the above-described Embodiments 7-10, the input device may be separately sold and may have only the input terminal.

  As described above, according to the present invention, compatible playback and compatible recording of different types of optical discs are realized using a single objective lens, and when the wavelength changes at the time of switching the light amount, the focal length changes and the spherical aberration change. Since it is possible to suppress occurrence of information and to stably reproduce or record information, it is useful for an optical head device, an optical information device, a computer, an optical information medium player, a car navigation system, an optical information medium recorder, and an optical information medium server.

FIG. 1 is a schematic sectional view of an optical head device according to an embodiment of the present invention. FIG. 1 is a schematic cross-sectional view of a main part of an optical head device according to an embodiment of the present invention. 1A is a plan view of a hologram according to an embodiment of the present invention, and FIG. 1B is a cross-sectional view of FIG. 2A is a schematic cross-sectional view of a principal part of a diffraction grating according to an embodiment of the present invention, and FIGS. FIG. 1 is a schematic cross-sectional view of a main part of an optical head device according to an embodiment of the present invention. FIG. 6 is an enlarged schematic cross-sectional view of a main part of the phase step shown in FIG. 5. FIG. 1 is a schematic cross-sectional view of a main part of an optical head device according to an embodiment of the present invention. FIG. 2 is an enlarged schematic cross-sectional view of a main part of a phase step according to the embodiment of the present invention. 2A is a schematic cross-sectional view of a principal part of a diffraction grating according to an embodiment of the present invention, and FIGS. FIG. 1 is a schematic cross-sectional view of a main part of an optical head device according to an embodiment of the present invention. 1A is a plan view of a hologram according to an embodiment of the present invention, and FIG. 1B is a cross-sectional view of FIG. 2A is a schematic cross-sectional view of a principal part of a diffraction grating according to an embodiment of the present invention, and FIGS. FIG. 1 is a schematic cross-sectional view of a main part of an optical head device according to an embodiment of the present invention. FIG. 1 is a schematic cross-sectional view of a main part of an optical head device according to an embodiment of the present invention. FIG. 1 is a schematic sectional view of an optical information device according to one embodiment of the present invention. FIG. 1 is a schematic perspective view of a computer according to an embodiment of the present invention. FIG. 1 is a schematic perspective view of an optical disc player according to one embodiment of the present invention. 1 is a schematic perspective view of an optical disk recorder (or a car navigation system) according to an embodiment of the present invention. FIG. 1 is a schematic perspective view of an optical disk server according to an embodiment of the present invention. FIG. 7 is a schematic cross-sectional view of a main part of an example of a conventional optical head device. FIG. 9 is a schematic cross-sectional view of an example of a conventional optical head device. (A) is a plan view of an example of a conventional hologram, and (b) is a cross-sectional view of (a).

Explanation of reference numerals

Reference Signs List 1,20 Laser light source 2 Beam shaping element 3,22 3 Beam grating 4,16 Beam splitter 5 1/4 wavelength plate 6 Condensing lens 7 Photodetector 8 Collimating lens 9,10 Optical disk 13 Hologram 14,144,145,146 , 147 Objective lens 15 Driving means 32 Detection lens 33 Photodetector 51 Driving device of optical head device 53 Electric circuit 55 Optical head device 64 Computing device 65 Input device 66 Decoder 67 Optical information device 68 Encoder 69 Input / output terminal 77 Optical disk player ( Or car navigation system)
81 Output device 100 Computer 110 Optical disk recorder 130 Optical disk server 1442, 1462, 1472 Phase difference

Claims (31)

An optical element corresponding to at least two wavelengths of red light and blue light, wherein the optical element has a phase step, and a difference in an optical path length generated when the blue light passes through the phase step is five times the wavelength of the blue light. An optical element characterized by the following. An optical lens having a phase difference, wherein blue light is focused by the optical lens through a substrate having a substrate thickness of t1, red light is focused through a substrate having a substrate thickness of t2, and t1 <t2. And an optical path length difference generated when the blue light passes through the phase step is five times the wavelength of the blue light. The optical lens according to claim 2, wherein the optical lens is a refraction lens formed of two different materials. The liquid crystal phase modulation device is further provided, and by electrically switching the liquid crystal phase modulation device, the blue light is condensed through the substrate having the substrate thickness of t1, and the red light is reflected by the substrate. 3. The optical lens according to claim 2, wherein the optical lens is focused through a substrate having a material thickness of t2, and switches the amount of phase modulation applied to a transmitted wavefront to correct aberration due to a difference in substrate thickness. A hologram is further provided, and by setting the depth of the diffraction grating of the hologram, the +2 order diffracted light is generated most strongly for blue light and the +1 order diffracted light is generated most strongly for red light. The optical lens according to claim 2, wherein an aberration due to a difference in substrate thickness is corrected. A hologram, a refractive lens, and an optical lens having a phase difference,
The hologram includes a sawtooth grating having a sawtooth cross-sectional shape. By setting the depth of the sawtooth grating, + 2nd-order diffracted light is generated most strongly for blue light and +1 for red light. The next-order diffracted light is generated most strongly,
An optical lens, wherein a difference in optical path length generated when the blue light passes through the phase step is five times the wavelength of the blue light. The optical lens according to claim 6, wherein the depth of the sawtooth grating is h1, and the h1 is a depth that gives a difference in optical path length of about two wavelengths to the blue light. In the hologram, the depth of the sawtooth grating formed on the inner periphery including the intersection with the optical axis of the hologram is h2, and the h2 is an optical path length of about one wavelength with respect to the red light. The optical lens according to claim 6, wherein the depth is a depth giving a difference of A hologram, a refractive lens, and an optical lens having a phase difference,
In the hologram, +2 order diffracted light is generated most strongly for blue light, +1 order diffracted light is generated most strongly for red light,
The hologram grating of the hologram is formed on an inner peripheral portion including at least an intersection with the optical axis of the hologram,
The + 2nd-order diffracted light of the blue light is collected through a substrate having a substrate thickness of t1, and the + 1st-order diffracted light of the red light passing through the inner peripheral portion is collected through a substrate having a substrate thickness of t2. t1 <t2,
An optical lens, wherein a difference in optical path length generated when the blue light passes through the phase step is five times the wavelength of the blue light. A hologram grating is further formed on an outer peripheral portion outside the inner peripheral portion,
The hologram grating in the outer peripheral portion is a sawtooth grating having a sawtooth cross-sectional shape, and the depth of the sawtooth lattice in the outer peripheral portion is h3, and the h3 is an optical path length of about one wavelength with respect to the blue light. Is the depth that gives the difference
The optical lens according to claim 9, wherein, at the outer peripheral portion, + 1st-order diffracted light is generated most strongly for the blue light, and + 1st-order diffracted light is also generated most strongly for the red light. The blue light is condensed through a base material having a base material thickness t1, and the hologram is formed into a convex lens shape so as to reduce a change in focal length when the wavelength λ1 of the blue light is changed. The optical lens according to any one of claims 6 to 10, wherein the hologram receives a convex lens effect. The blue light is focused by the optical lens through a substrate having a substrate thickness of t1, the red light is focused through a substrate having a substrate thickness of t2, and t1 <t2;
When the blue light is condensed through the substrate having the substrate thickness t1, the convex lens action by the hologram is increased as compared with when the red light is condensed through the substrate having the substrate thickness t2, The optical lens according to any one of claims 6 to 10, wherein a focal position of the red light on the substrate side is further away from the optical lens than a focal position of the blue light on the substrate side. The blue light is focused by the optical lens through a substrate having a substrate thickness of t1, the red light is focused through a substrate having a substrate thickness of t2, and t1 <t2;
When the red light is condensed through the substrate having the substrate thickness t2, the convex lens action by the hologram is reduced as compared with when the blue light is condensed through the substrate having the substrate thickness t1, The optical lens according to any one of claims 6 to 10, wherein a focal position of the red light on the substrate side is further away from the optical lens than a focal position of the blue light on the substrate side. 14. The optical lens according to claim 6, wherein the hologram has a lattice cross-section having a sawtooth shape having a slope on an outer peripheral side of a base material forming the hologram. 15. The optical lens according to claim 6, wherein the hologram, the refraction lens, and the phase step are integrally fixed. 15. The optical lens according to claim 6, wherein the hologram is formed integrally with the surface of the refraction lens. 15. The optical lens according to claim 6, wherein the phase step is formed integrally with a surface of the refractive lens. The optical lens according to any one of claims 6 to 17, wherein an aberration generated in the refraction lens or the refraction lens and the hologram due to a change in the wavelength is reduced by an aberration generated in the phase difference. Assuming that the numerical aperture at which the blue light is condensed through the substrate having the substrate thickness t1 is NAb, and the numerical aperture at which the red light is condensed through the substrate having the substrate thickness t2 is NAr, t1 <t2, and 19. The optical lens according to claim 2, wherein NAb> NAr. An optical lens according to any one of claims 2 to 18,
A first laser light source that emits blue light of wavelength λ1,
A second laser light source that emits red light of wavelength λ2,
A light detection unit that receives the light beam reflected on the recording surface of the optical information medium and outputs an electric signal according to the amount of light,
The optical lens focuses a first light beam from the first laser light source on a recording surface of a first optical information medium through a base material having a base material thickness of t1 and a second light beam from the second laser light source. An optical head device wherein a light beam is focused on a recording surface of a second optical information medium through a base material having a base material thickness of t2, and t1 <t2. When converging the second light beam on the recording surface of the second optical information medium, a collimating lens that converts the second light beam into substantially parallel light was brought closer to the second laser side to generate diffused light. 21. The optical head device according to claim 20, wherein the second light beam is made incident on the optical lens to move a focal position on the second optical information medium side away from the optical lens. By arranging both the emission points of the first laser and the second laser so as to form an image with respect to the focal position of the optical lens on the optical information medium side, a servo signal is output from a common photodetector. 21. The optical head device according to claim 20, wherein the optical head device detects an error. An optical head device including the optical lens according to any one of claims 2 to 18 and a laser light source,
A motor for rotating an optical information medium,
An optical information device comprising: an electric circuit that receives a signal obtained from the optical head device and controls and drives at least one of the motor, the optical lens, and the laser light source based on the signal. . The laser light source is a first laser light source that emits blue light of wavelength λ1, and a second laser light source that emits red light of wavelength λ2,
24. The optical information device according to claim 23, wherein the type of the optical information medium is determined, and the collimating lens is moved to the second laser light source side for the optical information medium having a base material thickness of about 0.6 mm. An optical information device according to claim 23 or 24,
A computing device that performs a computation based on at least one of the input information and the information reproduced from the optical information device,
A computer comprising: an output device that outputs at least one of the input information, information reproduced from the optical information device, and a result calculated by the calculation device. An optical information medium player comprising: the optical information device according to claim 23; and a decoder for converting an information signal obtained from the optical information device into an image. A car navigation system comprising: the optical information device according to claim 23 or 24; and a decoder that converts an information signal obtained from the optical information device into an image. An optical information medium recorder comprising: the optical information device according to claim 23 or 24; and an encoder that converts image information into information to be recorded by the optical information device. An optical information medium server comprising the optical information device according to claim 23 or 24, and an input / output terminal for exchanging information with the outside. An optical lens corresponding to light of one wavelength, comprising a phase step, wherein a difference in an optical path length generated when the light passes through the phase step is an integral multiple of the wavelength of the light. Optical lens. An optical lens according to claim 30,
A laser light source for emitting a light beam,
A light detection unit that receives the light beam reflected on the recording surface of the optical information medium and outputs an electric signal according to the amount of light,
The optical head device, wherein the optical lens focuses a light beam from the laser light source through a base material onto a recording surface of an optical information medium.

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