JP2008112558A - Optical head device, optical information apparatus, computer, video recording/reproducing apparatus, video reproducing apparatus, server, and car navigation system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical head device having a light source with two or more light-emitting elements mounted together to achieve stable tracking control. <P>SOLUTION: The optical head device 100 performs at least either of recording and reproducing of information for a plurality of types of optical recording media 7. A light source 1 emits a plurality of kinds of light having mutually different wavelengths. The positions for emitting the plurality of kinds of light from the light source are mutually deviated. A center C 1 of first light 2a is matched with a pattern center C3 of a first diffracting plane 3a. A center C2 of second light 2b is matched with a pattern center C4 of a second diffracting plane 3b. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an optical head device, an optical information device including the optical head device, a computer, a video recording / reproducing device, a video reproducing device, a server, and a car navigation system.

  A DVD (Digital Versatile Disc) has been attracting attention as a large-capacity optical recording medium in recent years because it can record digital information at a recording density about 6 times that of a CD (Compact Disc). As the DVD, there are various standards such as a write-once type or a rewritable type, such as a DVD-RAM, a DVD-R, and a DVD-RW. There are two types of DVD-RAMs: a track pitch of 1.48 μm and a recording capacity of 2.6 GB, and a track pitch of 1.23 μm and a recording capacity of 4.7 GB. The track pitch of DVD-R and DVD-RW is 0.74 μm. Thus, the track pitch varies depending on the type of DVD.

  When recording and playback are performed with a single optical head device on a plurality of types of discs having different track pitches, the tracking error signal is good due to the different track pitches in the general three-beam tracking method. Can't get to. Therefore, Patent Document 1 proposes an optical head device that can satisfactorily obtain tracking error signals from all disks having different track pitches.

  Here, an optical head device that can satisfactorily obtain tracking error signals from all disks having different track pitches will be described with reference to the drawings.

  FIG. 14 is a diagram showing the optical head device 140. The optical head device 140 includes a light source 141, a diffraction grating 142, a half mirror 143, a collimator lens 144, an objective lens 145, a detection lens 147, and a photodetector 148.

  The light source 141 includes a semiconductor laser element, and emits coherent light that irradiates the recording layer of the optical recording medium 146 during recording and reproduction. The diffraction grating 142 is an optical element that diffracts and separates the light emitted from the light source 141 into at least three light beams, and a tracking error signal can be obtained using the diffracted light generated by the optical element. Details of the diffraction grating 142 will be described later.

  A multilayer film is formed on the half mirror 143, and 50% of incident light is reflected and 50% is transmitted. The collimator lens 144 converts divergent light emitted from the light source 141 into parallel light. The objective lens 145 focuses light on the recording layer of the optical recording medium 146. The exit surface of the detection lens 147 is a cylindrical surface, and astigmatism is given to incident light in order to detect a focus error signal by the astigmatism method. The photodetector 148 receives the light reflected by the recording layer of the optical recording medium 146 and converts the light into an electrical signal.

  Next, the operation of the optical head device 140 will be described in more detail. Light emitted from the light source 141 is diffracted into at least three lights by the diffraction grating 142. The diffracted light is reflected in the direction of the optical recording medium 146 by the half mirror 143 and converted into parallel light by the collimating lens 144. The parallel light is converged on the recording surface of the optical recording medium 146 by the objective lens 145. The three lights formed by the diffraction grating 142 are independently converged on the recording surface of the optical recording medium 146 to form three focused spots. FIG. 15 shows the three focused spots 149a, 149b, and 149c. The optical recording medium 146 is periodically provided with guide grooves 151, and the focused spots 149a, 149b, and 149c are arranged in a substantially straight line so that the same guide grooves 151 are simultaneously irradiated.

  The light reflected by the recording surface of the optical recording medium 146 passes through the objective lens 145, the collimating lens 144, and the half mirror 143. This transmitted light passes through the detection lens 147 and is given astigmatism, and enters the photodetector 148. The photodetector 148 performs photoelectric conversion according to incident light, and generates an electrical signal for obtaining an information signal and a servo signal (a focus error signal for focus control and a tracking error signal for tracking control).

  The electric signals generated by the light receiving surfaces 148a, 148b and 148c of the photodetector 148 shown in FIG. 15 are input to an arithmetic circuit (subtractors 152a, 152b and 152c, an adder 153, an amplifier 154, and a subtractor 155). A tracking error signal is detected.

  The photodetector 148 has a light receiving surface divided into two in a direction corresponding to a direction orthogonal to the radial direction of the disk (that is, a tangential direction of the disk). A push-pull signal corresponding to each condensing spot is detected from a difference between signals output from each of the divided light receiving surfaces. Generally, the push-pull signal is detected based on a difference between output signals from the light receiving surface divided into two in a direction corresponding to the radial direction of the disk. However, since the astigmatism method is adopted here as the focus error signal detection method, the intensity distribution of the light spot on the light receiving surface is rotated approximately 90 degrees around the optical axis. Therefore, the push-pull signal is detected based on the difference between the output signals from the light receiving surface divided in two in the direction corresponding to the tangential direction of the disk.

  Next, the diffraction grating 142 will be described in more detail. FIG. 16 is a perspective view showing a grating pattern of the diffraction grating 142. On the grating surface of the diffraction grating 142, grating grooves are formed at a constant period. The lattice plane is divided into at least three regions by a dividing line orthogonal to the groove direction. That is, the optical recording medium 146 is divided into at least three regions in a direction corresponding to the tracking direction. In the example shown in FIG. 16, the lattice plane is divided into three regions 161, 162, and 163 by dividing lines L1 and L2. The central region 162 has a predetermined width W.

  The phase of the grating grooves in the region 161 adjacent to the region 162 is shifted by +90 degrees with respect to the phase of the grating grooves in the central region 162. That is, the lattice grooves in the region 161 are displaced from the lattice grooves in the central region 162 by about ¼ of the lattice groove period. On the other hand, the phase of the lattice grooves in the region 163 adjacent to the opposite side is shifted by −90 degrees with respect to the phase of the lattice grooves in the central region 162. That is, the lattice grooves in the region 163 are displaced from the lattice grooves in the central region 162 by about ¼ of the lattice groove period on the side opposite to the lattice grooves in the region 161. Therefore, the lattice grooves in the region 161 and the lattice grooves in the region 163 are shifted from each other by 180 degrees (1/2 of the lattice groove period) in phase.

  The light transmitted through the diffraction grating 142 having the above-described grating pattern is converged by the objective lens 145 to form light spots 149a, 149b and 149c (FIG. 15) on the recording surface of the optical recording medium 146. Push-pull obtained from light spots 149b and 149c corresponding to ± 1st-order diffracted light formed by diffraction grating 142 with respect to push-pull signal obtained from light spot 149a corresponding to zero-order diffracted light formed by diffraction grating 142 The signal is out of phase. Since all the light spots are collected on one track, there is no problem even if the track pitch differs depending on the type of the optical recording medium. Note that the degree of deterioration of the tracking error signal with respect to lens shift depends on the width W of the central region, and the degree of deterioration decreases as the width W increases. However, the wider the width W, the smaller the tracking error signal when the lens shift is zero.

Since the optical head device 140 irradiates three light spots onto one track, the quality of the tracking error signal does not depend on the track pitch. Therefore, a stable tracking error signal can be obtained from each of the optical recording media having different track pitches, and stable reproduction and recording can be performed on each optical recording medium.
JP 2004-145915 A

  However, when a two-wavelength light source in which two light-emitting elements having different emission wavelengths are mounted in one module is used as the light source 141 (two light-emitting elements are arranged along the radial direction), two light-emitting elements Are mounted apart from each other, the centers of the light spots formed by the diffraction grating 142 by the light emitted from the two light emitting elements are shifted from each other. For this reason, when the center of the light spot corresponding to one light emitting element and the center of the central region 162 are combined, the center of the light spot corresponding to the other light emitting element is shifted from the center of the central region 162. It looks as if a lens shift has occurred from the beginning. Therefore, stable tracking control is possible when using the light with the center of the light spot and the center of the central region 162 matching, but stable tracking control is possible when using the light with the mismatched center. The recording / reproduction characteristics deteriorate.

  The present invention has been made in view of the above problems, and enables stable tracking control even when a plurality of types of light having different wavelengths are used, and performs stable recording and / or reproducing operations. Provided is an optical head device capable of The present invention also provides an optical information device, a computer, a video recording / playback device, a video playback device, a server, and a car navigation system equipped with the optical head device.

  The optical head device of the present invention is an optical head device that executes at least one of information recording and reproduction with respect to a plurality of types of optical recording media, a light source that emits light, and the light to the optical recording medium. An objective lens for condensing; a diffraction element having a plurality of diffractive surfaces, and disposed between the light source and the objective lens; and the light source emits a plurality of types of light having different wavelengths from each other, The positions of the plurality of types of light emitted from the light source are shifted from each other, the plurality of types of light include first and second light, and the plurality of diffraction surfaces include first and second diffractions. A distance between the center of the first light and the pattern center of the first diffraction surface is a distance between the center of the second light and the pattern center of the first diffraction surface. Shorter than the center of the second light and the pattern of the second diffraction surface The distance between the is characterized by shorter than a distance between the pattern center of the second diffraction plane of the first light.

  According to an embodiment, a ratio at which the first diffraction surface diffracts the first light is higher than a ratio at which the second diffraction surface diffracts the first light, and the second light. The ratio at which the second diffraction surface diffracts is higher than the ratio at which the first diffraction surface diffracts the second light.

  According to an embodiment, the pattern center of the first diffractive surface is shifted from the pattern center of the second diffractive surface.

  According to an embodiment, at least a part of the material of the diffractive element is glass, and the first diffractive surface has a first uneven portion formed on the first surface of the glass, and The second diffractive surface has a second concavo-convex portion formed on the second surface opposite to the first surface of the glass, and the depth of the concave portion with respect to the convex portion is the first concavo-convex portion. And the second uneven portion are different from each other.

  According to an embodiment, the diffraction element further includes a first resin layer that fills the first uneven portion and a second resin layer that fills the second uneven portion.

  According to an embodiment, glass is provided on the first and second resin layers.

  According to an embodiment, the number of types of light emitted by the light source and the number of the plurality of diffraction surfaces are the same.

  According to an embodiment, the center of the first light and the pattern center of the first diffractive surface coincide with each other, and the center of the second light and the pattern center of the second diffractive surface are Match.

  According to an embodiment, the light source includes a first light emitting element that emits the first light, and a second light emitting element that emits the second light, and the first and second light emitting elements. The light emitting element emits the first and second lights in the same direction.

  According to an embodiment, the diffraction element further includes a separation unit that is disposed between the light source and the objective lens and separates light emitted from the light source and reflected light from the optical recording medium. And between the light source and the separation part.

  According to an embodiment, each of the first and second lights is one of light having a wavelength of 390 nm to 420 nm, light having a wavelength of 640 nm to 680 nm, and light having a wavelength of 760 nm to 800 nm, The first light and the second light have different wavelengths.

  According to an embodiment, the plurality of types of light further include third light, and the plurality of diffraction surfaces further include a third diffraction surface, and the first light center and the first light The distance between the pattern center of the diffractive surface is shorter than the distance between the center of the second and third light and the pattern center of the first diffractive surface, and the center of the second light and the The distance between the pattern center of the second diffractive surface is shorter than the distance between the center of the first and third light and the pattern center of the second diffractive surface. The distance between the center and the pattern center of the third diffractive surface is shorter than the distance between the center of the first and second light and the pattern center of the third diffractive surface.

  The optical information device of the present invention includes the optical head device and a control unit that controls the operation of the optical head device.

  The computer of the present invention includes the optical information device.

  The video recording / reproducing apparatus of the present invention includes the optical information device, and performs recording and reproduction of video information on the optical recording medium.

  The video reproduction apparatus of the present invention includes the optical information device and reproduces video information from the optical recording medium.

  The server of the present invention includes the optical information device.

  The car navigation system of the present invention includes the optical information device.

  According to the present invention, in the optical head device including the light source that emits the first and second lights from positions shifted from each other, the distance between the center of the first light and the pattern center of the first diffraction surface. Is shorter than the distance between the center of the second light and the pattern center of the first diffractive surface, and the distance between the center of the second light and the pattern center of the second diffractive surface is: It is shorter than the distance between the center of the first light and the pattern center of the second diffractive surface. As described above, since the diffraction element has a plurality of diffraction surfaces corresponding to a plurality of types of light having different wavelengths, stable tracking control is possible even when a plurality of types of light is used, and stable recording and / or reproduction is possible. The action can be performed.

  According to an embodiment, the rate at which the first diffractive surface diffracts the first light is higher than the rate at which the second diffractive surface diffracts the first light, and the second light is reflected by the second light. The ratio at which the first diffraction surface diffracts is higher than the ratio at which the first diffraction surface diffracts the second light. Further, the pattern center of the first diffractive surface and the pattern center of the second diffractive surface are shifted from each other in correspondence with the first and second lights emitted from the positions shifted from each other. As described above, since the diffraction element has a plurality of diffraction surfaces corresponding to a plurality of types of light having different wavelengths, stable tracking control is possible even when a plurality of types of light is used, and stable recording and / or reproduction is possible. The action can be performed.

  According to an embodiment, at least a part of the material of the diffractive element is glass. The first diffractive surface has a first uneven portion formed on the first surface of the glass. The 2nd diffraction surface has the 2nd unevenness part formed in the 2nd surface on the opposite side to the 1st surface of glass. The depth of the concave portion relative to the convex portion is different between the first uneven portion and the second uneven portion. Accordingly, a diffraction element having wavelength selectivity with a simple configuration can be realized, and thus the diffraction element can be manufactured at low cost.

  According to an embodiment, the diffractive element further includes a first resin layer that fills the first uneven portion and a second resin layer that fills the second uneven portion. Thereby, since the depth of each uneven | corrugated | grooved part can be made shallow, a highly efficient diffraction element with few high order diffractions is realizable.

  According to an embodiment, glass is provided on the first and second resin layers. Thereby, since the resin layer does not touch the air, the reliability and durability of the diffraction element can be improved.

  According to an embodiment, the diffraction element is disposed between the light source and the separation unit. Thereby, since the diffraction element does not diffract the reflected light from the optical recording medium, the loss of light quantity and the generation of stray light can be suppressed.

  According to an embodiment, each of the light emitted from the light source is one of light having a wavelength of 390 nm to 420 nm, light having a wavelength of 640 nm to 680 nm, and light having a wavelength of 760 nm to 800 nm. Thereby, stable tracking error signals can be obtained from different types of optical recording media such as BD (Blu-ray Disc), DVD, and CD.

  In addition, since the optical information apparatus, computer, video recording / reproducing apparatus, video reproducing apparatus, server, and car navigation system of the present invention are equipped with the above-described optical head apparatus, stable recording and / or reproducing operations can be performed. Can do.

  Hereinafter, an optical head device according to an embodiment of the present invention and various devices including the same will be described with reference to the drawings.

(Embodiment 1)
FIG. 1 is a diagram showing an optical head device 100 according to Embodiment 1 of the present invention. The optical head device 100 records and / or reproduces information on the optical recording medium 7 by irradiating the optical recording medium 7 with laser light. The optical head device 100 includes a light source 1, a diffraction element 2, a polarization beam splitter 3, a collimator lens 4, a quarter wavelength plate 5, an objective lens 6, a detection lens 8, a photodetector 9, And a light source light quantity control photodetector 10.

  The light source 1 is a two-wavelength light source in which two light emitting elements 1a and 1b having different emission wavelengths are mounted on one module. For example, the light emitting element 1a emits one of coherent light having a wavelength of 640 nm to 680 nm and coherent light having a wavelength of 760 nm to 800 nm, and the light emitting element 1b emits the other light. The light emitting elements 1 a and 1 b are arranged along a direction corresponding to the radial direction of the optical recording medium 7.

  The diffraction element 2 is an optical element having wavelength selectivity. The diffractive element 2 includes a plurality of diffractive surfaces having the grating pattern shown in FIG. 16, and diffracts and separates each light emitted from the light source 1 into at least three light beams. A tracking error signal can be obtained using the diffracted light. The transmittance of the diffraction element 2 is about 80%, for example, and the ± first-order diffraction efficiency is about 8%, for example.

  The polarization beam splitter 3 is an optical element formed of a multilayer film, and is a separation unit that separates the light emitted from the light source 1 and the reflected light from the optical recording medium 7. The diffraction element 2 and the polarization beam splitter 3 are disposed between the light source 1 and the objective lens 6, and the diffraction element 2 is disposed between the light source 1 and the polarization beam splitter 3.

  The polarization beam splitter 3 transmits 90% of linearly polarized light and reflects 10% of light having a wavelength of 640 nm to 680 nm, and reflects 100% of linearly polarized light orthogonal to the polarization direction of the linearly polarized light. Have The polarizing beam splitter 3 has a characteristic of transmitting 90% and reflecting 10% of light with a wavelength of 760 nm to 800 nm regardless of the direction of linearly polarized light.

  The collimating lens 4 converts divergent light of all wavelengths emitted from the light source 1 into parallel light. The quarter-wave plate 5 is an optical element that converts linearly polarized light into circularly polarized light, and is formed of a birefringent material (for example, crystal or resin). The objective lens 6 is a lens that condenses light on the recording layer of the optical recording medium 7, and has a numerical aperture (NA) of 0.65 for light having a wavelength of 640 nm to 680 nm and a wavelength of 760 nm to 800 nm. The diffraction grating is formed on the lens surface so that the numerical aperture (NA) is 0.5.

  The entrance surface of the detection lens 8 is a cylindrical surface, and the exit surface is a rotationally symmetric surface with respect to the lens optical axis. In order to detect the focus error signal by the astigmatism method, Gives point aberration. The photodetector 9 receives the light reflected by the recording layer of the optical recording medium 7 and converts the light into an electric signal. The light source light quantity control photodetector 10 receives the light reflected by the polarization beam splitter 3 and converts it into an electrical signal, and the output power of the light source 1 is controlled based on the electrical signal.

  Next, the operation of the optical head device 100 will be described in more detail. Here, it is assumed that the optical recording medium 7 is a DVD (DVD-RAM, DVD-R, DVD-RW, etc.) having a high recording density.

  The light (wavelength 640 nm to 680 nm) emitted from the light emitting element 1 a of the light source 1 is diffracted by the diffraction element 2 into at least three lights (0th order diffracted light and ± 1st order diffracted light). The diffracted light is 90% transmitted through the polarization beam splitter 3 and reflected by 10%. The light transmitted through the polarization beam splitter 3 is converted into parallel light by the collimating lens 4. The parallel light is converted from linearly polarized light to circularly polarized light by the quarter wavelength plate 5 and converged on the recording surface of the optical recording medium 7 by the objective lens 6. The three lights formed by the diffractive element 2 are independently converged on the recording surface of the optical recording medium 7 to form three condensing spots. Referring to FIG. 15, the three focused spots 149 a to 149 c are substantially aligned so as to be simultaneously irradiated onto the same guide groove among the guide grooves 151 periodically provided on the optical recording medium 7. Are lined up.

  The circularly polarized light reflected by the recording surface of the optical recording medium 7 passes through the objective lens 6 and is converted from circularly polarized light to linearly polarized light by the quarter wavelength plate 5. This linearly polarized light is converted into linearly polarized light in a direction orthogonal to the linearly polarized light emitted from the light emitting element 1a. The linearly polarized light passes through the collimating lens 4 and is 100% reflected by the polarizing beam splitter 3, and this reflected light passes through the detection lens 8 to give astigmatism and enters the photodetector 9. The photodetector 9 performs photoelectric conversion according to incident light, and generates an electrical signal for obtaining an information signal and a servo signal (a focus error signal for focus control and a tracking error signal for tracking control).

  Further, 10% of the light emitted from the light emitting element 1 a and reflected by the polarization beam splitter 3 is received by the photodetector 10 and is emitted based on the electrical signal output from the photodetector 10. The output power of 1a is controlled.

  Next, the operation of the optical head device 100 when the optical recording medium 7 is a CD (recording-only CD, write-once CD-R, rewritable CD-RW, etc.) having a recording density lower than that of a DVD will be described.

  Light (wavelength 760 nm to 800 nm) emitted from the light emitting element 1b of the light source 1 is diffracted into at least three lights (0th order diffracted light and ± 1st order diffracted light) by the diffractive element 2. The diffracted light is 90% transmitted through the polarization beam splitter 3 and reflected by 10%. The light transmitted through the polarization beam splitter 3 is converted into parallel light by the collimating lens 4. The parallel light is converted from linearly polarized light to circularly polarized light by the quarter wavelength plate 5 and converged on the recording surface of the optical recording medium 7 by the objective lens 6. The three lights formed by the diffractive element 2 are independently converged on the recording surface of the optical recording medium 7 to form three condensing spots. Referring to FIG. 15, the three focused spots 149 a to 149 c are substantially aligned so as to be simultaneously irradiated onto the same guide groove among the guide grooves 151 periodically provided on the optical recording medium 7. Are lined up.

  Although the track pitches of the same type of optical recording medium 7 are all the same, the track pitch may vary due to manufacturing errors. In the present invention, since a tracking error signal detection system that condenses three lights on the same one track is employed, a stable tracking error signal can be obtained even with such variations.

  The circularly polarized light reflected by the recording surface of the optical recording medium 7 passes through the objective lens 6 and is converted from circularly polarized light to linearly polarized light by the quarter wavelength plate 5. This linearly polarized light is converted into linearly polarized light in a direction orthogonal to the linearly polarized light emitted from the light emitting element 1b. The linearly polarized light passes through the collimating lens 4 and is reflected by 10% by the polarizing beam splitter 3. The reflected light passes through the detection lens 8 and is given astigmatism, and enters the photodetector 9. The photodetector 9 performs photoelectric conversion according to incident light, and generates an electric signal for obtaining an information signal and a servo signal (a focus error signal for focus control and a tracking error signal for tracking control).

  Further, 10% of the light emitted from the light emitting element 1 b and reflected by the polarization beam splitter 3 is received by the photodetector 10, and the light emitting element is output based on the electrical signal output from the photodetector 10. The output power of 1b is controlled.

  Here, it will be described that the characteristics of the polarization beam splitter do not depend on the direction of linearly polarized light. When the optical recording medium 7 causes birefringence, the polarization characteristics of the light that is reflected by the optical recording medium 7 and enters the polarization beam splitter changes depending on the amount of birefringence. Therefore, in order to guide a constant amount of light to the photodetector 9 regardless of the amount of birefringence, the characteristic of the polarization beam splitter 3 is made independent of the polarization direction. Thus, the reason for taking measures against birefringence is that in the case of CD, there are a large number of those having large birefringence.

  Next, the diffraction element 2 will be described in more detail with reference to FIGS. 2, 3, 4A, and 4B. 2, 4A, and 4B are diagrams showing the diffraction element 2 when viewed along the optical axis direction of the light emitted from the light source 1, and FIG. 3 is a cross-sectional view of the diffraction element 2. FIG.

  Two light emitting elements 1a and 1b are mounted on the light source 1 apart from each other. Therefore, the light 2a emitted from the light emitting element 1a and the light 2b emitted from the light emitting element 1b travel in the same direction, but the center C1 of the light 2a (FIG. 2) and the center C2 of the light 2b are diffracted. They are displaced from each other on the element 2. In the case where the diffraction pattern 2 has only one grating pattern shown in FIG. 16, if the center of the central region 162 and the center C1 of the light 2a are matched, the center of the central region 162 and the center of the light 2b are deviated. Thus, the lens shift is equivalent to the occurrence of lens shift from the beginning, and stable tracking control cannot be performed.

  Referring to FIGS. 3, 4A and 4B, the diffraction element 2 of the present invention includes a diffraction surface 3a corresponding to the light 2a of the light emitting element 1a and a diffraction surface 3b corresponding to the light 2b of the light emitting element 1b. . FIG. 3 is a cross-sectional view illustrating one of the three regions 161 to 163. The diffractive surface 3a contributes only to the light 2a, and the diffractive surface 3b contributes only to the light 2b.

  Here, a configuration in which each of the diffraction surfaces 3a and 3b contributes to only one of the lights 2a and 2b will be described. The wavelength of the light 2a is λa, the wavelength of the light 2b is λb, the depth of the groove of the diffractive surface 3a (the depth of the concave portion relative to the convex portion of the concavo-convex portion of the diffractive surface 3a) is d1, and the depth of the groove of the diffractive surface 3b ( The depth of the concave portion of the concavo-convex portion of the diffractive surface 3b is d2, the refractive index of the diffractive element 2 with respect to light having the wavelength λa is na, and the refractive index of the diffractive element 2 with respect to light having the wavelength λb is nb.

In order for the diffractive surface 3a to diffract only the light 2a and not diffract the light 2b, the depth d1 diffracts 8% light by transmitting 80% light with respect to the light having the wavelength of the light 2a. The depth may correspond to the phase, and the depth may correspond to the phase that transmits 100% of the light having the wavelength of the light 2b (even multiple of the wavelength λb). The phase that transmits 80% light and diffracts 8% light is L, and the circumference is π, and the above condition can be expressed by the following equation.
(Na-1) · d1 · 2π / λa = L + 2π · ma (ma is an integer of 0 or more)
(Nb-1) · d1 · 2π / λb = 2π · ka (ka is an integer of 0 or more)

  Here, when λa is set to 660 nm, λb is set to 780 nm, na is set to 1.51, nb is set to 1.5 (refractive index of glass), and L is set to 0.927 rad (phase where the 0th-order diffraction efficiency is 80%), When d1 is 1560 nm, ma is 1 and ka is 1, which satisfies the above condition, and the diffraction surface 3a contributes only to the light 2a.

Similarly, the condition that the diffractive surface 3b contributes only to the light 2b can be expressed by the following mathematical formula.
(Nb-1) · d2 · 2π / λb = L + 2π · mb (mb is an integer of 0 or more)
(Na-1) · d2 · 2π / λa = 2π · kb (kb is an integer of 0 or more)

  Here, when d2 is 7920 nm, mb is 5 and kb is 6, which satisfies the above conditions, and the diffractive surface 3b contributes only to the light 2b.

  As shown in FIG. 4A, the grating patterns of the diffraction surfaces 3a and 3b are arranged so as to be shifted from each other so as to correspond to the shift between the center C1 of the light 2a and the center C2 of the light 2b. The center C3 of the central region 162 of the diffractive surface 3a is the center between the dividing lines L1 and L2, and is the center of the width W in the direction of the grating grooves. The center C4 of the central region 162 of the diffractive surface 3b is the center between the dividing lines L1 and L2, and is the center of the width W in the direction of the grating grooves. The center of the central region 162 is also referred to as the pattern center. As shown in FIG. 4B, the diffractive surface 3a is such that the pattern center C3 of the diffractive surface 3a coincides with the center C1 of the light 2a, and the pattern center C4 of the diffractive surface 3b coincides with the center C2 of the light 2b. By shifting the grid patterns of 3 and 3b so as to be shifted from each other, stable tracking control can be performed regardless of whether the light 2a or 2b is used.

  The width W of the central region 162 of the diffractive surface 3a and the width W of the central region 162 of the diffractive surface 3b may be the same or different.

  By using the diffraction element 2 as described above, the center of the light emitted from all the light emitting elements and the pattern center can be matched. Further, since each of the diffractive surfaces contributes only to one type of light corresponding thereto, stray light is not generated. For this reason, a highly accurate tracking error signal can be obtained for light of all wavelengths, and stable tracking control and recording / reproducing operations can be performed.

  Although it is desirable that the pattern center of each diffractive surface and the center of the light corresponding thereto are substantially completely coincident with each other, the present invention is not limited to this, and a highly accurate tracking error signal can be obtained. The distance between the center of the light 2a and the pattern center of the diffractive surface 3a is shorter than the distance between the center of the light 2b and the pattern center of the diffractive surface 3a, and the center of the light 2b and the diffractive surface It is sufficient that the distance between the pattern center of 3b is shorter than the distance between the center of the light 2a and the pattern center of the diffractive surface 3b. This also applies to the relationship between the diffractive surface and light in an optical head device including a light source on which three light emitting elements described later are mounted.

  Each of the diffractive surfaces desirably diffracts only one corresponding type of light. However, the present invention is not limited to this, and the ratio at which the diffractive surface 3a diffracts the light 2a within a range in which stray light can be kept within an allowable range. However, it is sufficient that the ratio of diffracting the light 2b by the diffractive surface 3b is higher than the ratio of diffracting the light 2b by the diffractive surface 3b. This also applies to the relationship between the diffractive surface and light in an optical head device including a light source on which three light emitting elements described later are mounted.

  In addition, although the optical element which etched glass only to desired depth is used as the diffraction element 2, you may use the optical element which filled the uneven | corrugated | grooved part formed in the glass by etching with resin. FIG. 5 is a cross-sectional view showing the diffraction element 2 in which such uneven portions are filled with resin. Referring to FIG. 5, one surface of glass 51 is a first diffractive surface 3a, and the other surface is a second diffractive surface 3b. The first diffractive surface 3 a is filled with a first resin layer 52, and the second diffractive surface 3 b is filled with a second resin layer 53.

The material of the 1st resin layer 52 and the 2nd resin layer 53 is UV resin, for example, and a refractive index changes according to the quantity of an additive. Here, the refractive index of the glass 51 with respect to the light with the wavelength λa is nga, the refractive index of the glass 51 with respect to the light with the wavelength λb is ngb, the refractive index of the first resin layer 52 with respect to the light with the wavelength λa is nja, and the light with the wavelength λb. The refractive index of the first resin layer 52 is njb, the refractive index of the second resin layer 53 is njja for light of wavelength λa, the refractive index of the second resin layer 53 is njjb for light of wavelength λb, and the first The etching depth of the diffractive surface 3a is d3, and the etching depth of the second diffractive surface 3b is d4. At this time, the phase Isa for the light of wavelength λa and the phase Isb for the light of wavelength λb on the first diffractive surface 3a, the phase Issa for the wavelength λa and the phase Issb for the wavelength λb of the second diffractive surface 3b are It is expressed as follows.
Isa = (nga−nja) · d3 · 2π / λa
Isb = (ngb−njb) · d3 · 2π / λb
Issa = (nga−njja) · d4 · 2π / λa
Issb = (ngb−njjb) · d4 · 2π / λb

  Here, if the refractive indexes of the first and second resin layers 52 and 53 are adjusted so that ngb = njb and nga = njja, Isb = 0 and Issa = 0. That is, the first diffractive surface 3a does not contribute to the light having the wavelength λb, but only contributes to the light having the wavelength λa. Similarly, the second diffractive surface 3b does not contribute to the light with the wavelength λa, but contributes only to the light with the wavelength λb.

  Further, the depths d3 and d4 are determined so that the phases Isa and Issb are in a phase where the 0th-order diffraction efficiency is 80%, and the grating patterns of the diffraction surfaces 3a and 3b are determined by the positions of the light emitting elements 1a and 1b. If the pattern corresponds to the deviation, the diffraction element 2 having the same characteristics as described above can be obtained. As described above, since it is not necessary for each diffractive surface to satisfy the conditions for light of two types of wavelengths, the phase can be reduced. Thereby, generation | occurrence | production of a high-order diffraction can be suppressed and a highly efficient diffraction efficiency can be obtained.

  Further, as shown in FIG. 6, the second and third glasses 61 and 62 are further provided above the first and second resin layers 52 and 53, so that the resin layer does not directly contact the air, so that the diffraction element. Reliability and durability can be improved.

  In the present embodiment, the characteristics of the polarization beam splitter 3 vary depending on the wavelength, but the same characteristics may be exhibited for different wavelengths.

  In the present embodiment, a quarter wavelength plate is used as the n / 4 wavelength plate 5, but it is sufficient if n is an odd number wavelength plate.

  In the present embodiment, a single lens is used as the objective lens 6, but a combination lens having a high NA may be used.

  The optical head device 100 according to the present embodiment is an infinite optical head device, but may be a finite optical head device that does not use a collimating lens.

  The optical head device 100 of the present embodiment is a polarizing optical system optical head device, but may be a non-polarizing optical system optical head device.

  In this embodiment, the light is directly directed to the objective lens. However, an optical system that reduces the thickness of the optical head device by bending the optical path using a mirror may be used.

  In the present embodiment, the diffraction element 2 is disposed between the light source 1 and the polarization beam splitter 3. In this arrangement, light passes through the diffractive element 2 in the forward path but does not pass in the return path. Therefore, the light in the return path is not affected by diffraction, and the reflected light from the optical recording medium 7 is lost or stray light is emitted. Therefore, a highly accurate tracking error signal can be obtained.

  If a polarization hologram having polarization characteristics is used as the diffraction element 2 and the polarization characteristics are switched between the forward path and the return path, the diffraction element 2 can be disposed between the polarization beam splitter 3 and the objective lens 6. In this case, since the light spot on the diffractive element 2 can be increased, the influence of the deviation between the light beam and the diffractive element 2 is reduced.

  Further, in the present embodiment, the pattern of the diffraction element 2 is divided into three, but it is sufficient that the pattern is at least two or more. The pattern center when dividing into two is located on the dividing line, and the pattern center when dividing into four is located on the middle dividing line of the three dividing lines.

  In this embodiment, a light source in which two light emitting elements having different emission wavelengths are mounted in one is used. However, a light source in which three light emitting elements having different emission wavelengths are mounted in one may be used. Good. The light emitted from the three light emitting elements is, for example, light having a wavelength of 390 nm to 420 nm, light having a wavelength of 640 nm to 680 nm, and light having a wavelength of 760 nm to 800 nm. In this case, a diffraction element 2 as shown in FIG. 7A is used. In addition to the first glass 51, the first resin layer 52, and the second resin layer 53, the diffraction element 2 includes a second glass 71 provided on the second resin layer 53, A third resin layer 72 filling the diffractive surface 3c of the glass 71. This diffractive element 2 has three diffractive surfaces corresponding to the three light emitting elements, and is arranged so that the pattern center of each diffractive surface coincides with the center of the corresponding light. A tracking error signal with high accuracy can be obtained even when using. Next, an optical head device 100 including such a diffraction element 2 will be described.

(Embodiment 2)
As shown in FIG. 7B, the light source 1 of the optical head device 100 of the present embodiment is a three-wavelength light source on which a light emitting element 1c is mounted in addition to the light emitting elements 1a and 1b. The light emitting element 1c emits coherent light with a wavelength of 390 nm to 430 nm, for example. The light emitting elements 1 a to 1 c are arranged along a direction corresponding to the radial direction of the optical recording medium 7.

  With respect to light having a wavelength of 390 nm to 430 nm, the polarization beam splitter 3 transmits 90% of linearly polarized light and reflects 10%, and reflects 100% of linearly polarized light orthogonal to the polarization direction of the linearly polarized light. A diffraction grating is formed on the surface of the objective lens 6 so that the numerical aperture (NA) is 0.85 for light having a wavelength of 390 nm to 430 nm.

  Next, the diffraction element 2 of this embodiment will be described. Three light emitting elements 1a to 1c are mounted on the light source 1 apart from each other. For this reason, the centers of the light emitted from the respective light emitting elements 1 a, 1 b, 1 c are shifted from each other on the diffraction element 2.

  As shown in FIG. 7A, the diffraction element 2 of the present embodiment corresponds to the diffraction surface 3a corresponding to the light of the light emitting element 1a, the diffraction surface 3b corresponding to the light of the light emitting element 1b, and the light of the light emitting element 1c. And a diffractive surface 3c. The diffraction surface 3a contributes only to the light of the light emitting element 1a, the diffraction surface 3b contributes only to the light of the light emitting element 1b, and the diffraction surface 3c contributes only to the light of the light emitting element 1c.

  Similarly to the grating patterns described with reference to FIGS. 4A and 4B, the grating patterns of the diffraction surfaces 3a to 3c are arranged so as to be shifted from each other so as to correspond to the shift of the centers of the lights. The pattern center of the diffractive surface 3c is coincident with the center of light of the light emitting element 1a, the pattern center of the diffractive surface 3b is coincident with the center of light of the light emitting element 1b, and the pattern center of the diffractive surface 3c is the light emitting element 1c. Stable tracking control can be performed even when using light emitted from any of the light emitting elements 1a to 1c by arranging the grating patterns of the diffractive surfaces 3a to 3c to be shifted from each other so as to coincide with the center of light. I can do it.

  By using the diffraction element 2 as described above, the center of the light emitted from all the light emitting elements and the pattern center can be matched. Further, since each of the diffractive surfaces contributes only to one type of light corresponding thereto, stray light is not generated. For this reason, a highly accurate tracking error signal can be obtained for light of all wavelengths, and stable tracking control and recording / reproducing operations can be performed.

  Next, the operation of the optical head device 100 of this embodiment will be described.

  Recording and / or reproducing operations for a DVD using light having a wavelength of 640 nm to 680 nm, and recording and / or reproducing operations for a CD using light having a wavelength of 760 nm to 800 nm are the same as those of the optical head device 100 of the first embodiment. Therefore, the description is omitted here.

  Here, recording and / or reproduction with respect to the optical recording medium 7 when the optical recording medium 7 is a BD (Blu-ray disc) or an HD-DVD (High Definition DVD) corresponding to light having a wavelength of 390 nm to 430 nm. The operation will be described.

  Light (wavelength 390 nm to 430 nm) emitted from the light emitting element 1 c of the light source 1 is diffracted into at least three lights (0th order diffracted light and ± 1st order diffracted light) by the diffraction element 2. The diffracted light is 90% transmitted through the polarization beam splitter 3 and reflected by 10%. The light transmitted through the polarization beam splitter 3 is converted into parallel light by the collimating lens 4. The parallel light is converted from linearly polarized light to circularly polarized light by the quarter wavelength plate 5 and converged on the recording surface of the optical recording medium 7 by the objective lens 6. The three lights formed by the diffractive element 2 are independently converged on the recording surface of the optical recording medium 7 to form three condensing spots. Referring to FIG. 15, the three focused spots 149 a to 149 c are substantially aligned so as to be simultaneously irradiated onto the same guide groove among the guide grooves 151 periodically provided on the optical recording medium 7. Are lined up.

  The circularly polarized light reflected by the recording surface of the optical recording medium 7 passes through the objective lens 6 and is converted from circularly polarized light to linearly polarized light by the quarter wavelength plate 5. This linearly polarized light is converted into linearly polarized light in a direction orthogonal to the linearly polarized light emitted from the light emitting element 1c. The linearly polarized light passes through the collimating lens 4 and is 100% reflected by the polarizing beam splitter 3, and this reflected light passes through the detection lens 8 to give astigmatism and enters the photodetector 9. The photodetector 9 performs photoelectric conversion according to incident light, and generates an electrical signal for obtaining an information signal and a servo signal (a focus error signal for focus control and a tracking error signal for tracking control).

  Of the light emitted from the light emitting element 1c, 10% of the light reflected by the polarization beam splitter 3 is received by the photodetector 10, and the light emitting element is output based on the electrical signal output from the photodetector 10. The output power of 1c is controlled.

  Note that the diffractive element 2 of the present embodiment has three diffractive surfaces and corresponds to each light emitting element, but has a characteristic of diffracting light having a wavelength that does not correspond to a certain diffractive surface due to a manufacturing error of the diffractive element. The more diffractive surfaces, the greater the effect. Therefore, in order to reduce the number of diffractive surfaces as much as possible, the diffractive element has only two diffractive surfaces, one diffractive surface corresponds to a certain light emitting element, and the other diffractive surface corresponds to the remaining two light emitting elements. Of these, the light emitting element having the shorter wavelength may be supported. In this case, the diffractive element is not completely compatible with a light emitting element having a longer wavelength, but since the margin for tracking of an optical recording medium using light having a longer wavelength is wide, the influence on tracking naturally occurs, but the diffractive surface is It is possible to do so in preference to less.

  In this embodiment, three light emitting elements are mounted on one light source. However, the optical head device has one light source having two light emitting elements (for example, light having a wavelength of 640 nm to 680 nm and a wavelength of 760 nm to 800 nm). And a single light source having one light emitting element (for example, emitting light having a wavelength of 390 nm to 430 nm), and the above-described diffraction in the optical path after the respective lights are combined Element 2 may be arranged. Furthermore, before the light from the light source having two light emitting elements and the light from the light source having one light emitting element are combined, the light from the light source having two light emitting elements corresponds to the two light emitting elements. The diffractive element 2 may be transmitted.

(Embodiment 3)
FIG. 8 is a diagram showing an optical information device 80 according to the third embodiment of the present invention. The optical information device 80 records and / or reproduces information with respect to the optical recording medium 7.

  The optical information device 80 includes an optical head device 100, a motor 82, an electric circuit 83, a turntable 84, a clamper 85, and a drive device 86 for the optical head device. The optical head device 100 is the same as the optical head device 100 of the first and second embodiments. The electric circuit 83 functions as a control unit that controls operations of the optical head device 100 and other components.

  The optical recording medium 7 is placed on a turntable 84 and rotated by a motor 82. The optical head device 100 is moved by the driving device 86 to a track position where desired information of the optical recording medium 7 is recorded.

  The optical head device 100 sends a focus error signal and a tracking error signal to the electric circuit 83 in accordance with the positional relationship with the optical recording medium 7. In response to these signals, the electric circuit 83 sends a signal for finely moving the objective lens to the optical head device 100. In response to this signal, the optical head device 100 performs focus control and tracking control on the optical recording medium 7, and reads, writes, or erases information.

  Since the optical information device 80 includes the optical head device 100 described above, a single optical head device can perform stable recording and reproduction operations on a plurality of types of optical recording media.

(Embodiment 4)
FIG. 9 is a diagram showing a computer 90 according to the fourth embodiment of the present invention. The computer 90 includes the optical information device (optical disk drive) 80 shown in FIG.

  The computer 90 includes an optical disk drive 80, a keyboard 92 that is an input device for inputting information, a monitor 93 that is an output device for displaying information, and an arithmetic device 94. The computing device 94 is a central processing unit (CPU) that performs computation based on information input from the keyboard 92 or information read from the optical disk drive 80. Here, the input device may be a mouse, a touch panel, or the like, and the output device may be a printer or the like.

  A computer 90 equipped with an optical disk drive 80 as a storage device can stably record or reproduce information on a plurality of types of optical disks such as BD, HD-DVD, DVD, CD, etc., and can be used for a wide range of applications. The optical disk 7 mounted on the optical disk drive 80 can take advantage of its large capacity to back up a hard disk in a computer. Taking advantage of the fact that optical disks are inexpensive and easy to carry, and that information can be read by other optical disk drives, programs and data can be exchanged with people or carried for personal use.

(Embodiment 5)
FIG. 10 is a diagram showing an optical disc recorder (video recording / reproducing apparatus) 101 according to the fifth embodiment of the present invention.

  The optical disc recorder 101 includes the optical information device (optical disc drive) 80 shown in FIG. The optical disc recorder 101 is used by being connected to a monitor 102 for displaying video information recorded on the optical disc.

  The optical disc recorder 101 provided with the optical disc drive 80 can stably record or reproduce video information on a plurality of types of optical discs such as BD, HD-DVD, DVD, and CD, and can be used for a wide range of applications. The optical disk recorder 101 records video information on a medium (optical disk), and the user can reproduce it at any time. In an optical disk, it is not necessary to perform rewinding after recording or reproduction, unlike a video tape. Further, it is possible to perform chasing playback in which a certain program is recorded and playback is started from the beginning of the program, or simultaneous recording and playback in which another program recorded before is recorded while recording a certain program. Taking advantage of the fact that optical discs are cheap and easy to carry, and that other optical disc recorders can read information, you can exchange recorded video information with others or carry it for yourself. .

  The optical disk recorder 101 may include a hard disk drive in addition to the optical disk drive 80 or may have a video tape recording / playback function. In that case, video information can be easily copied, moved, backed up, and the like.

(Embodiment 6)
FIG. 11 is a diagram showing an optical disc player (video playback device) 111 according to Embodiment 6 of the present invention. The optical disc player 111 includes the optical disc drive (optical information device) 80 and the liquid crystal monitor 112 shown in FIG.

  The optical disc player 111 displays the video information recorded on the optical disc on the liquid crystal monitor 112. An optical disc player 111 having an optical disc drive 80 can stably reproduce video information on a plurality of types of optical discs such as BD, HD-DVD, DVD, CD, and can be used for a wide range of applications.

  The user can play back video information recorded on the optical disc at any time using the optical disc player 111. An optical disc does not need to be rewound after reproduction like a video tape, and can access and reproduce a position on an arbitrary optical disc on which certain video information is recorded.

(Embodiment 7)
FIG. 12 is a diagram illustrating the server 121 according to the seventh embodiment of the present invention. The server 121 includes the optical information device (optical disk drive) 80 shown in FIG.

  The server 121 is connected to a monitor 124 for displaying information, a keyboard 123 for inputting information, and a network 125.

  The server 121 including the optical disk drive 80 can stably record or reproduce information on a plurality of types of optical disks such as BD, HD-DVD, DVD, and CD, and can be used for a wide range of applications. The optical disk drive 80 can record and reproduce a large amount of information by taking advantage of the large capacity of the mounted optical disk. In response to a request from the network 125, the optical disc drive 80 transmits information (image, audio, video, HTML document, text document, etc.) recorded on the optical disc. Further, the information sent from the network 125 is recorded at the requested location on the optical disc.

(Embodiment 8)
FIG. 13 is a diagram showing a car navigation system 130 according to the eighth embodiment of the present invention.

  The car navigation system 130 includes the optical information device (optical disk drive) 80 shown in FIG. The car navigation system 130 is connected to a liquid crystal monitor 131 for displaying a map and destination information.

  The car navigation system 130 provided with the optical disk drive 80 can stably record or reproduce information on a plurality of types of optical disks such as BD, HD-DVD, DVD, and CD, and can be used in a wide range of applications. The car navigation system 130 determines the current position using information obtained from a ground position determination system (GPS), a gyroscope, a speedometer, an odometer, and map information recorded on an optical disk, and the position is displayed on a liquid crystal display. Displayed on the monitor 131. When the destination is input, the optimum route to the destination is determined based on the map information and the road information and displayed on the liquid crystal monitor 131.

  By using a large-capacity optical disc for recording map information, it is possible to provide detailed road information while covering a wide area with a single disc. In addition, information about restaurants, convenience stores, gas stations, etc. associated with the vicinity of the road can be stored and provided on the optical disc at the same time. In addition, road information becomes old with time and does not match the actual road conditions, but since the optical disc is compatible and the media is inexpensive, the latest information can be obtained by replacing it with a disc containing new road information. Obtainable. In addition, since it also supports playback and / or recording of BD, HD-DVD, DVD, CD, etc., it is possible to watch movies and listen to music in a car.

  The embodiments of the present invention have been described above by way of examples. However, the present invention is not limited to the above-described embodiments, and can be applied to other embodiments based on the technical idea of the present invention.

  In the description of the above embodiment, an apparatus for recording information on an optical recording medium using light has been described. However, the present invention is applied to an apparatus for recording information on a magneto-optical recording medium using both light and magnetism. Alternatively, the same effect as described above can be obtained.

  In the description of the above embodiment, the case where the optical recording medium is an optical disk has been described. However, the optical recording medium may be a card-like optical recording medium, and the present invention is a type in which information is recorded and reproduced using light. It can be applied to other devices.

  The present invention is particularly useful in the technical field of recording and reproducing information using light.

It is a figure which shows the optical head apparatus by embodiment of this invention. It is a figure which shows the relationship between the pattern of a diffraction element, and the light spot on a diffraction element. It is sectional drawing which shows the diffraction element by embodiment of this invention. It is a figure which shows the pattern of the diffraction element by embodiment of this invention. It is a figure which shows the relationship between the pattern of the diffraction element by embodiment of this invention, and the light spot on a diffraction element. It is sectional drawing which shows the diffraction element by embodiment of this invention. It is sectional drawing which shows the diffraction element by embodiment of this invention. It is sectional drawing which shows the diffraction element by embodiment of this invention. It is a figure which shows the optical head apparatus by embodiment of this invention. It is a figure which shows the optical information apparatus by embodiment of this invention. It is a figure which shows the computer by embodiment of this invention. It is a figure which shows the video recording / reproducing apparatus by embodiment of this invention. 1 is a diagram illustrating a video reproduction apparatus according to an embodiment of the present invention. FIG. 3 illustrates a server according to an embodiment of the present invention. 1 is a diagram showing a car navigation system according to an embodiment of the present invention. It is a figure which shows an optical head apparatus. It is a figure which shows the light spot formed on an optical recording medium, and the electric circuit which detects the reflection from an optical recording medium, and produces | generates a tracking error signal. It is a figure which shows the pattern of a diffraction element.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Light source 1a 1st light emitting element 1b 2nd light emitting element 1c 3rd light emitting element 2 Diffraction element 3 Polarizing beam splitter 4 Collimating lens 5 1/4 wavelength plate 6 Objective lens 7 Optical recording medium 8 Detection lens 9 Photo detector DESCRIPTION OF SYMBOLS 10 Light source light quantity control photodetector 100 Optical head apparatus

Claims (18)

An optical head device that performs at least one of recording and reproduction of information on a plurality of types of optical recording media,
A light source that emits light;
An objective lens for condensing the light on the optical recording medium;
A diffractive element having a plurality of diffractive surfaces, and disposed between the light source and the objective lens,
The light source emits a plurality of types of light having different wavelengths from each other,
The positions of the plurality of types of light emitted from the light source are shifted from each other,
The plurality of types of light includes first and second lights,
The plurality of diffractive surfaces include first and second diffractive surfaces;
The distance between the center of the first light and the pattern center of the first diffractive surface is shorter than the distance between the center of the second light and the pattern center of the first diffractive surface,
The distance between the center of the second light and the pattern center of the second diffractive surface is shorter than the distance between the center of the first light and the pattern center of the second diffractive surface, Optical head device. The ratio at which the first diffraction surface diffracts the first light is higher than the ratio at which the second diffraction surface diffracts the first light.
2. The optical head device according to claim 1, wherein a rate at which the second diffraction surface diffracts the second light is higher than a rate at which the first diffraction surface diffracts the second light.   3. The optical head device according to claim 2, wherein a pattern center of the first diffractive surface and a pattern center of the second diffractive surface are shifted from each other. At least a part of the material of the diffraction element is glass,
The first diffractive surface has a first uneven portion formed on the first surface of the glass,
The second diffractive surface has a second uneven portion formed on a second surface opposite to the first surface of the glass,
2. The optical head device according to claim 1, wherein the depth of the concave portion with respect to the convex portion is different between the first uneven portion and the second uneven portion. The diffraction element is
A first resin layer filling the first uneven portion;
The optical head device according to claim 4, further comprising: a second resin layer that fills the second uneven portion.   The optical head device according to claim 5, wherein glass is provided on the first and second resin layers.   The optical head device according to claim 1, wherein the number of types of light emitted from the light source is the same as the number of the plurality of diffraction surfaces. The center of the first light coincides with the pattern center of the first diffraction surface,
2. The optical head device according to claim 1, wherein a center of the second light coincides with a pattern center of the second diffraction surface. The light source includes a first light emitting element that emits the first light, and a second light emitting element that emits the second light,
The optical head device according to claim 1, wherein the first and second light emitting elements emit the first and second lights in the same direction. A separation unit that is disposed between the light source and the objective lens and separates the light emitted from the light source and the reflected light from the optical recording medium;
The optical head device according to claim 1, wherein the diffraction element is disposed between the light source and the separation unit. Each of the first and second lights is any of light having a wavelength of 390 nm to 420 nm, light having a wavelength of 640 nm to 680 nm, and light having a wavelength of 760 nm to 800 nm,
The optical head device according to claim 1, wherein the first light and the second light have different wavelengths. The plurality of types of light further includes a third light,
The plurality of diffractive surfaces further include a third diffractive surface;
The distance between the center of the first light and the pattern center of the first diffractive surface is greater than the distance between the centers of the second and third light and the pattern center of the first diffractive surface. Short,
The distance between the center of the second light and the pattern center of the second diffractive surface is greater than the distance between the centers of the first and third light and the pattern center of the second diffractive surface. Short,
The distance between the center of the third light and the pattern center of the third diffractive surface is greater than the distance between the centers of the first and second light and the pattern center of the third diffractive surface. The optical head device according to claim 1, wherein the optical head device is short. An optical head device according to claim 1;
An optical information device comprising: a control unit that controls the operation of the optical head device.   A computer comprising the optical information device according to claim 13.   A video recording / reproducing apparatus comprising the optical information device according to claim 13, wherein video information is recorded on and reproduced from the optical recording medium.   A video reproduction apparatus comprising the optical information apparatus according to claim 13 and reproducing video information from the optical recording medium.   A server comprising the optical information device according to claim 13.   A car navigation system comprising the optical information device according to claim 13.