JP2010003371A - Optical head device and hologram element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical head device capable of dealing with different types of optical disks different from one another in wavelength of used semiconductor laser lights, and obtaining more stable focus error and tracking error signals. <P>SOLUTION: The optical head device is provided with a first light source 31 for emitting a first beam L1, a second light source 32 for emitting a second beam L2, a hologram element 20 for diffracting the first beam L1 and the second beam L2 reflected on an information recording medium 11, and a plurality of light receiving elements 40 for receiving lights diffracted by the hologram element 20. The hologram element 20 has a recessed and projected structure formed on one surface of a substrate 72. The depth of the recessed part of the recessed and projected structure is represented by λ1/än(λ1)-n0(λ1)}, λ2/än(λ2)-n0(λ2)} or λ1/än(λ1)-n0(λ1)}+λ2/än(λ2)-n0(λ2)}. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an optical head device and a hologram element, and more particularly to an optical head device and a hologram element that record, reproduce, or erase information on a plurality of types of information recording media.

  Recently, optical discs that optically record and read information as information storage media have been used in many fields.

  Currently, the most popular optical disks are compact disks (CD) and digital versatile disks (DVD). A near-infrared semiconductor laser device having a wavelength band of 780 nm to 820 nm is used for a CD as a light source for recording and reproduction. On the other hand, in order to increase the recording density of DVD compared with CD, a red semiconductor laser of 635 nm to 680 nm band is used as a light source for recording and reproduction. It is preferable that the drive for recording and reproducing the optical disc can perform recording and reproduction for two types of discs, CD and DVD. For this reason, an optical head device corresponding to both standards has been developed (for example, see Patent Document 1).

  FIG. 8 shows a conventional optical head device corresponding to CD and DVD. As shown in FIG. 8, the optical head device includes a first semiconductor laser device 301 that emits light of a first wavelength for DVD, and a second semiconductor laser that emits light of a second wavelength for CD. A device 302 is provided.

  The beam L1 emitted from the first semiconductor laser device 301 and the beam L2 emitted from the second semiconductor laser device 302 are reflected by the mirror 190 so as to enter the optical disc 100. Condensing means (not shown) is disposed between the mirror 190 and the optical disc 100, and the beam L1 and the beam L2 are condensed on the information recording surface of the optical disc 100 by the condensing means. The beam L1 and the beam L2 reflected by the optical disc 100 are diffracted by the hologram element 200 disposed between the condensing means and the mirror 190 and detected by the photodetector 400.

  The hologram element 200 has a first diffraction region 261 and a second diffraction region 262. In the case of reproducing a DVD, the beam L1 incident on the hologram element 200 is divided into two at the boundary line between the first diffraction region 261 and the second diffraction region 262 to generate + 1st order light and −1st order light. The generated + 1st order light enters the light detector 401 and the light detector 402, and the −1st order light enters the light detector 403 and the light detector 404. Based on the signals detected by the photodetector 401, the photodetector 402, the photodetector 403, and the photodetector 404, a focus error signal (spot size detection (SSD) method), tracking error signal (position) during DVD playback Phase difference detection (DPD) method) and reproduction signal generation are performed.

On the other hand, in the case of CD reproduction, the incident beam L2 is divided into two at the boundary line between the first diffraction region 261 and the second diffraction region 262 and generates + 1st order light and −1st order light. The generated + 1st order light enters the photodetector 401 and the photodetector 402, and the −1st order light enters the photodetector 405 and the photodetector 406. Based on signals detected by the light detector 401, the light detector 402, the light detector 405, and the light detector 406, a focus error signal (SSD method) and a tracking error signal (three-beam method or push-pull during CD reproduction) are reproduced. (PP) method) and reproduction signal generation.
JP 2001-176119 A

  However, in the conventional optical head device, the light emitting point of the first semiconductor laser device 301 and the light emitting point of the second semiconductor laser device 302 are not the same position, and the light emitting point interval is d. For this reason, if the first semiconductor laser device 301 is arranged at the center of the hologram element 200, the second semiconductor laser device 302 is displaced from the center of the hologram element 200. Therefore, the tracking error signal by the push-pull method becomes unbalanced in the second semiconductor laser device 302, and a stable tracking error signal cannot be obtained. Further, if the second semiconductor laser device 302 is positioned at the center of the hologram element 200, the first semiconductor laser device 301 is displaced from the center of the hologram element 200. For this reason, the tracking error signal by the DPD method is unbalanced in the first semiconductor laser device 301, and a stable tracking error signal cannot be obtained. Further, it is impossible to generate a tracking error signal by a differential push-pull (DPP) method or the like necessary for recording on an optical disc.

  The present invention solves the above-mentioned conventional problems and realizes an optical head device which can be applied to various optical disks having different wavelengths of semiconductor laser light to be used and can obtain more stable focus error signal and tracking error signal. The purpose is to be able to.

  In order to achieve the above object, according to the present invention, an optical head device includes a hologram element having a concavo-convex structure composed of a concave portion having a predetermined depth.

Specifically, an optical head device according to the present invention emits a first light source that emits a first beam having a first wavelength and a second beam having a second wavelength that is longer than the first wavelength. A second light source, a condensing optical system that receives the first beam and the second beam as fine spots and converges them on the optical information recording medium, and the first beam and the second beam reflected by the optical information recording medium. A hologram element that diffracts each element and a plurality of light receiving elements that receive the diffracted light diffracted by the hologram element are formed on one surface of the substrate that is transparent to the first beam and the second beam. The depth of the concave portion in the concavo-convex structure is a value represented by any one of Formulas 1 to 3.
λ1 / {n (λ1) −n0 (λ1)} Equation 1
λ2 / {n (λ2) −n0 (λ2)} Equation 2
λ1 / {n (λ1) −n0 (λ1)} + λ2 / {n (λ2) −n0 (λ2)} Equation 3
However, in Formula 1-Formula 3, (lambda) 1 represents a 1st wavelength, (lambda) 2 represents a 2nd wavelength, n ((lambda) 1) represents the refractive index with respect to the light of the 1st wavelength of a board | substrate, n ((lambda) 2) Represents the refractive index for light of the second wavelength of the substrate, n0 (λ1) represents the refractive index for light of the first wavelength in the recess, and n0 (λ2) represents the refractive index of light of the second wavelength in the recess. Represents.

  The optical head device according to the present invention includes a hologram element having a concavo-convex structure, and the depths of the recesses of the hologram element are λ1 / {n (λ1) −n0 (λ1)} and λ2 / {n (λ2) −, respectively. n0 (λ2)} and λ1 / {n (λ1) −n0 (λ1)} + λ2 / {n (λ2) −n0 (λ2)}. For this reason, even when one of the first beam and the second beam does not pass through the center of the hologram element, a stable tracking error signal without imbalance can be obtained. Therefore, a more stable focus error signal and tracking error signal can be generated, and stable recording and reproduction can be realized.

  The optical head device of the present invention is provided between the first light source and the second light source and the hologram element, diffracts the first beam and the second beam, and diffracts the main beam, the first sub beam, and the second sub beam, respectively. A diffraction grating may be further provided.

  In the optical head device of the present invention, the diffraction grating may be formed on the surface of the substrate opposite to the hologram element.

  In the optical head device of the present invention, the hologram element has a first diffraction region, a second diffraction region, and a third diffraction region, and the first diffraction region and the second diffraction region are adjacent to each other, The second diffraction region and the third diffraction region are adjacent to each other, and the first diffraction region diffracts the first beam as the first diffracted light having the first wavefront, and the second diffraction region and the second diffraction region The third diffraction region diffracts the first beam as second diffracted light having a second wavefront different from the first wavefront, and the first diffraction region and the second diffraction region cause the second beam to Diffracted as third diffracted light having a wavefront of 3, and the third diffraction region diffracts the second beam as fourth diffracted light having a fourth wavefront different from that of the third wavefront. The tracking error signal of the first beam is generated based on the signal obtained from the light and the signal obtained from the second diffracted light. And it may be configured to generate a tracking error signal of the second beam based on the signal obtained from the third signals obtained from the diffracted light and the fourth diffracted light.

  In the optical head device of the present invention, the first diffracted light and the third diffracted light are detected by the first light receiving element of the plurality of light receiving elements, and the second light receiving element of the plurality of light receiving elements detects the first diffracted light. The second diffracted light and the fourth diffracted light may be detected.

  In the optical head device of the present invention, the hologram element has a first diffraction region, a second diffraction region, and a third diffraction region, and the first diffraction region and the second diffraction region are adjacent to each other. The second diffraction region and the third diffraction region are adjacent to each other, and the first diffraction region and the second diffraction region diffract the main beam of the first beam as first diffracted light having a first wavefront, The third diffraction region diffracts the main beam of the first beam as second diffracted light having a second wavefront different from the first wavefront, and the first diffraction region and the second diffraction region are The first sub-beam is diffracted as a third diffracted light having a third wavefront, and the third diffracted light is a fourth diffracted light having a fourth wavefront different from the third wavefront of the first sub-beam of the first beam. And the first diffraction region and the second diffraction region have the second sub-beam of the first beam as the fifth The third diffraction region diffracts the second sub-beam of the first beam as a sixth diffracted light having a sixth wavefront different from the fifth wavefront, The diffraction region diffracts the main beam of the second beam as seventh diffracted light having a seventh wavefront, and the second diffraction region and the third diffraction region cause the main beam of the second beam to be the seventh wavefront. Diffracted as eighth diffracted light having a different eighth wavefront, the first diffracted region diffracts the first sub-beam of the second beam as ninth diffracted light having the ninth wavefront, and the second diffracted region And the third diffraction region diffracts the first sub-beam of the second beam as tenth diffracted light having a tenth wavefront different from the ninth wavefront, and the first diffraction region diffracts the second sub-beam of the second beam. Diffracted as eleventh diffracted light having an eleventh wavefront, and second diffracted region and third The diffraction region diffracts the second sub-beam of the second beam as a twelfth diffracted light having a twelfth wavefront different from the eleventh wavefront, and the first diffracted region is based on the signal obtained from the first to sixth diffracted lights. A configuration may be adopted in which a tracking error signal for the beam is generated and a tracking error signal for the second beam is generated based on signals obtained from the seventh to twelfth diffracted lights.

  In the optical head device of the present invention, the first diffracted light and the seventh diffracted light are detected by the first light receiving element of the plurality of light receiving elements, and the second light receiving element of the plurality of light receiving elements detects the first diffracted light. The second diffracted light and the eighth diffracted light are detected, the third light receiving element of the plurality of light receiving elements detects the third diffracted light and the ninth diffracted light, and the third light receiving element of the plurality of light receiving elements is detected. The fourth diffracted light and the tenth diffracted light are detected by the four light receiving elements, the fifth diffracted light and the eleventh diffracted light are detected by the fifth light receiving element of the plurality of light receiving elements, The sixth diffracted light and the twelfth diffracted light may be detected by the sixth light receiving element among the light receiving elements.

  In the optical head device of the present invention, the optical axis of the first beam passes through the boundary between the first diffraction region and the second diffraction region, and the optical axis of the second beam is the second diffraction region and the third diffraction region. It is good also as a structure which passes the boundary with an area | region.

  In the optical head device of the present invention, the boundary line between the first diffraction region and the second diffraction region, and the boundary line between the second diffraction region and the third diffraction region are straight lines extending in the track direction of the optical information recording medium. It may be.

A hologram element according to the present invention includes a substrate transparent to a first beam having a first wavelength and a second beam having a second wavelength, and a concavo-convex structure formed on one surface of the substrate. The depth of the recess in is represented by any one of Formulas 1 to 3.
λ1 / {n (λ1) −n0 (λ1)} Equation 1
λ2 / {n (λ2) −n0 (λ2)} Equation 2
λ1 / {n (λ1) −n0 (λ1)} + λ2 / {n (λ2) −n0 (λ2)} Equation 3
However, in Formula 1-Formula 3, (lambda) 1 represents a 1st wavelength, (lambda) 2 represents a 2nd wavelength, n ((lambda) 1) represents the refractive index with respect to the light of the 1st wavelength of a board | substrate, n ((lambda) 2) Represents the refractive index for light of the second wavelength of the substrate, n0 (λ1) represents the refractive index for light of the first wavelength in the recess, and n0 (λ2) represents the refractive index of light of the second wavelength in the recess. Represents.

  The hologram element of the present invention may have a diffraction grating that transmits and diffracts the first beam and the second beam to generate a main beam and a sub beam on the surface of the substrate opposite to the surface on which the uneven structure is formed. Good.

  According to the optical head device and the hologram element according to the present invention, it is possible to cope with various optical disks having different wavelengths of semiconductor laser light to be used, and to obtain more stable focus error signal and tracking error signal. An apparatus and a hologram element can be realized.

(First embodiment)
FIG. 1 shows an optical head device according to a first embodiment of the present invention. The optical head device according to the first embodiment is an optical head device corresponding to two different types of optical information recording media such as a DVD and a CD. Therefore, as shown in FIG. 1, a first semiconductor laser device 31 that emits a first beam L1 having a first wavelength, and a second semiconductor laser device 32 that emits a second beam L2 having a second wavelength, It has. The first semiconductor laser device 31 and the second semiconductor laser device 32 are fixed to the substrate 75. Laser light emitted from each of the first semiconductor laser device 31 and the second semiconductor laser device 32 is above the substrate 75 (z direction in the drawing) via a reflection mirror (not shown) disposed on the substrate 75. Emitted.

  The first beam L1 and the second beam L2 are condensed on the optical information recording medium 11 by a condensing optical system having a collimator lens 21 and an objective lens 22.

  The first beam L1 and the second beam L2 reflected by the optical information recording medium 11 enter the hologram element 20. The hologram element 20 diffracts the first beam L1 and the second beam L2 to generate diffracted light. Each diffracted light is incident on the photodetector 40 formed on the substrate 75.

  FIG. 2 shows the hologram element 20. The hologram element 20 includes a first diffraction region 61, a second diffraction region 62, and a third diffraction region 63, and diffracts the first beam L1 and the second beam L2. The approximate center of the first beam L1 (the optical axis of the first beam L1) passes through the boundary between the first diffraction region 61 and the second diffraction region 62, and the optical axis of the second beam is the second diffraction region 62. The hologram element 20 is disposed so as to pass through the boundary with the third diffraction region 63. The direction in which the boundary line between the first diffraction region 61 and the second diffraction region 62 and the boundary line between the second diffraction region 62 and the third diffraction region 63 extend is the track direction of the optical information recording medium 11. It is arranged to become. In this case, the track direction means a direction in consideration of an optical system provided between the hologram element 20 and the optical information recording medium 11.

  The hologram element 20 functions as different diffraction patterns for the first beam L1 and the second beam L2. For the first beam L1 having the first wavelength, the light incident on the first diffraction region 61 is collected at the first point, and the light incident on the second diffraction region 62 is collected at the second point. It becomes a diffractive lens that is illuminated. On the other hand, for the second beam L2 having the second wavelength, the light incident on the first diffraction region 61 and the second diffraction region 62 is collected at the third point and incident on the third diffraction region 63. The analyzed light is condensed to the fourth point.

  Next, the operation of the optical head device according to the first embodiment will be described with reference to the drawings. First, the type of the optical information recording medium 11 to be used is determined by an optical information recording medium determining means (not shown). Based on the determination result, the first semiconductor laser device 31 or the second semiconductor laser device is driven. In the following description, it is assumed that the types of the optical information recording medium 11 are DVD and CD, the first semiconductor laser device 31 is driven in the case of DVD, and the second semiconductor laser device 32 is driven in the case of CD. To do.

  When the optical information recording medium 11 is determined to be a DVD, the first semiconductor laser device 31 having a wavelength of 0.65 μm is driven, and when it is determined to be a CD, the second semiconductor laser device 32 having a wavelength of 0.78 μm is driven. Is driven.

  The first beam L 1 emitted from the first semiconductor laser device 31 and the second beam L 2 emitted from the second semiconductor laser device 32 are collected on the optical information recording medium 11 via the collimator lens 21 and the objective lens 22. Lighted. The condensed first beam L1 and second beam L2 are reflected by the optical information recording medium 11 and again enter the hologram element 20 as a light beam branching unit through the objective lens 22 and the collimator lens 21.

  The first beam L1 reflected from the optical information recording medium 11 is diffracted in the X direction in the figure by the first diffraction region 61 of the hologram element 20, and the ± first-order diffracted lights are respectively transmitted to the first photodetector 41 and the first detector 41. 4 photodetectors 44. The first beam L1 is diffracted in the X direction in the figure by the second diffraction region 62 or the third diffraction region 63, and the ± first-order diffracted lights are the second photodetector 42 and the third photodetector 43, respectively. Led to.

  On the other hand, the second beam L2 reflected by the optical information recording medium 11 is diffracted in the X direction by the first diffraction region 61 or the second diffraction region 62 of the hologram element 20, and the ± first-order diffracted lights are respectively Guided to the first photodetector 41 and the sixth photodetector 46. Further, the second beam L2 is diffracted in the X direction in the figure by the third diffraction region 63, and the ± first-order diffracted light is guided to the second photodetector 42 and the fifth photodetector 45, respectively.

  A focus error signal and a tracking error signal are generated from the first beam L1 and the second beam L2 respectively guided to the first photodetector 41 to the sixth photodetector 46, and an optical information recording medium is used by using these signals. 11 recording and reproduction are performed.

  Next, a method for generating a focus error signal and a tracking error signal from the first beam L1 and the second beam L2 will be specifically described.

  FIG. 3 shows a planar configuration of the photodetector 40 formed on the substrate 75. In FIG. 3, L1 and L2 indicate apparent light emission points of the first semiconductor laser device 31 and the second semiconductor laser device 32, respectively.

  Each photodetector 40 is divided into four light receiving regions in the Y-axis direction. For example, the first photodetector 41 is sequentially divided into a light receiving area 41a, a light receiving area 41b, a light receiving area 41c, and a light receiving area 41d in the Y-axis direction. The same applies to the second photodetector 42 to the sixth photodetector 46.

  The diffracted light diffracted by the hologram element 20 is incident on one of the photodetectors 40 as a beam spot. The diffracted light obtained by diffracting the first beam L1 by the first diffraction region 61 is incident on the first photodetector 41 and the fourth photodetector 44 as a beam spot 10a and a beam spot 10d, respectively. The diffracted light obtained by diffracting the first beam L1 by the second diffraction region 62 or the third diffraction region 63 is transmitted to the second photodetector 42 and the third photodetector 43 as a beam spot 10b and a beam spot 10c, respectively. Incident. The diffracted light obtained by diffracting the second beam L2 by the first diffraction region 61 or the second diffraction region 62 is transmitted to the first photodetector 41 and the sixth photodetector 46 as a beam spot 13a and a beam spot 13d, respectively. Incident. The diffracted light obtained by diffracting the second beam L2 by the third diffraction region 63 enters the second photodetector 42 and the fifth photodetector 44 as a beam spot 13b and a beam spot 13c, respectively.

  First, generation of a focus error signal will be described. The focus error signal FE is generated by a known SSD (spot size detection) method. The focus error signal FE1 from the first beam L1 is obtained by the calculation of Equation 1.

  The focus error signal FE2 from the second beam L2 is obtained by the calculation of Expression 2.

  Further, the focus error signal FE3 obtained by calculation corresponding to both the first beam L1 and the second beam L2 can be obtained by the calculation of Expression 3.

  However, F1 is an output signal from the light receiving area 41a, the light receiving area 41d, the light receiving area 42a, and the light receiving area 42d, and F2 is an output signal from the light receiving area 41b, the light receiving area 41c, the light receiving area 42b, and the light receiving area 42c, F3 is an output signal from the light receiving region 43a, the light receiving region 43d, the light receiving region 44a, and the light receiving region 44d, F4 is an output signal from the light receiving region 43b, the light receiving region 43c, the light receiving region 44b, and the light receiving region 44c, and F5 The light receiving area 45a, the light receiving area 45d, the light receiving area 46a, and the light receiving area 46d are output signals, and F6 is an output signal from the light receiving area 45b, the light receiving area 45c, the light receiving area 46b, and the light receiving area 46c.

  Next, generation of the tracking error signal will be described. The tracking error signal TE is generated by a known DPD (phase difference detection) method and PP (push-pull) method.

  The tracking error signal TE (DPD) 1 by the DPD method using the first beam L1 is obtained by phase comparison of TEa (DPD) 1 and TEb (DPD) 1 obtained by the calculations of Expression 4a and Expression 4b, respectively.

  Further, the tracking error signal TE (PP) 1 by the PP method using the first beam L1 is obtained by the calculation of Expression 5.

  The tracking error signal TE (DPD) 2 by the DPD method using the second beam L2 is obtained by phase comparison of TEa (DPD) 2 and TEb (DPD) 2 obtained by the calculation of Expression 6a and Expression 6b.

  Further, the tracking error signal TE (PP) 2 by the PP method using the second beam L2 is obtained by the calculation of Expression 7.

  However, T1 is an output signal from the light receiving region 41a and the light receiving region 41b, T2 is an output signal from the light receiving region 41c and the light receiving region 41d, T3 is an output signal from the light receiving region 42a and the light receiving region 42b, T4 is an output signal from the light receiving region 42c and the light receiving region 42d, T5 is an output signal from the light receiving region 43a and the light receiving region 43b, T6 is an output signal from the light receiving region 43c and the light receiving region 43d, and T7 is Output signals from the light receiving areas 44a and 44b, T8 is an output signal from the light receiving areas 44c and 44d, T9 is an output signal from the light receiving areas 45a and 45b, and T10 is a light receiving area 45c and an output signal from the light receiving region 45d, and T11 is an output signal from the light receiving region 46a and the light receiving region 46b. , T12 is the output signal from the light receiving regions 46c and the light receiving region 46d.

  The tracking error signal TE (DPD) 3 by the DPD method corresponding to both the first beam L1 and the second beam L2 is obtained from the TEa (DPD) 3 and TEb (DPD) 3 obtained by the calculation of the equations 8a and 8b. Obtained by phase comparison.

  Further, by the calculation of Expression 9, a tracking error signal TE (PP) 3 by the PP method can be obtained by the calculation corresponding to both the first beam L1 and the second beam L2.

  In the optical head device of the first embodiment, the first beam L1 can be divided into two in the radial direction at the boundary between the first diffraction region 61 and the second diffraction region 62, and the second beam L2 is It can be divided into two in the radial direction at the boundary between the second diffraction region 62 and the third diffraction region 63. Therefore, in order to cope with various optical discs having different recording / reproducing wavelengths, even in an optical head device in which semiconductor lasers having different wavelengths are arranged close to each other, it is possible to equally divide the light of each wavelength into two. . As a result, stable recording and reproduction using the PP method or DPP method can be realized.

(Second Embodiment)
The second embodiment of the present invention will be described below with reference to the drawings. FIG. 4 shows a cross-sectional configuration of a hologram element used in the optical head device according to the second embodiment. As shown in FIG. 4, an uneven structure is formed on the surface of the substrate 72 made of a material transparent to the first beam and the second beam. In FIG. 4, the convex part of the concavo-convex structure is the reference plane of the substrate 72, and the depth of the concave part (the depth from the surface of the convex part to the bottom surface of the concave part) is any one of d1, d2, and d1 + d2. The depth d1 and the depth d2 are set so as to satisfy the following relationship.

  Where n (λ1) is the refractive index of the substrate 72 at the wavelength λ1, n (λ2) is the refractive index of the substrate 72 at the wavelength λ2, n0 (λ1) is the refractive index of the recess at the wavelength λ1, and n0 (λ2) is the wavelength λ2. Is the refractive index of the recess.

  Therefore, for example, the wavelength λ1 of the first beam is 0.65 μm, the wavelength λ2 of the second beam is 0.78 μm, n (λ1) and n (λ2) are 1.5, n0 (λ1) and n0 (λ2). If is 1, d1 may be 1.3 μm and d2 may be 1.56 μm.

  Hologram that gives a desired phase difference Φ1 (x, y) to light of wavelength λ1 and a desired phase difference Φ2 (x, y) to light of wavelength λ2 at the point of coordinates (x, y) When obtaining an element, the depth d (x, y) at the point of the coordinates (x, y) is expressed as in Expression 12.

  Here, D1 (x, y) and D2 (x, y) may be as follows.

  Next, the operation of the hologram element of the present embodiment will be described. Consider a case where light having a wavelength λ is incident on the hologram element determined as described above. The phase of the transmitted light is subjected to phase modulation as shown in Equation 15.

  Expression 15 becomes the following Expressions 16 to 18 from Expressions 10 to 14.

  Considering that phase 2π and phase 0 are equivalent when light of wavelength λ1 is incident. φ2 (x, y) = 0, and φ (x, y) is expressed by Equation 19.

  This indicates that it acts as a hologram element that performs phase modulation of phase Φ1 (x, y) with respect to light of wavelength λ1.

  Similarly, when light having a wavelength λ2 is incident, φ1 (x, y) = 0 and φ (x, y) is expressed by Equation 20.

  This indicates that it acts as a hologram element that performs phase modulation of phase Φ2 (x, y) with respect to light of wavelength λ1.

  As described above, the hologram element of the present embodiment can act independently on the light of the wavelengths λ1 and λ2, and is used as the hologram element 20 in the optical head device according to the first embodiment. be able to.

  FIG. 5 shows the depth of the concave portion of the hologram element and the phase difference of each wavelength. The phase difference is expressed between 0 and 2π with reference to the phase at the position of d (x, y) = 0. A hologram element that acts as a diffraction grating having a grating period Λ for light having a wavelength λ1 and a diffraction grating having a grating period 3Λ for light having a wavelength λ2 is shown as an example. As shown in FIG. 5, it is clear that the phase of each wavelength acts as an independent diffraction grating.

(Third embodiment)
The third embodiment of the present invention will be described below with reference to the drawings. FIG. 6 shows an optical head device according to the third embodiment. In FIG. 6, the same components as those in FIG.

  As shown in FIG. 6, the optical head device according to the present embodiment includes a diffraction grating 24. The diffraction grating 24 is formed on the surface opposite to the hologram element 20 of the substrate 72 on which the hologram element 20 is formed. Thereby, the first beam L1 and the second beam L2 are branched into a main beam and two sub beams (± first order diffracted light), respectively.

  Next, the optical path of the sub beam in the optical head device of this embodiment will be described. Since the main beam is the same as that of the first embodiment, the description thereof is omitted.

  FIG. 7 shows a planar configuration of the photodetector portion formed on the substrate 75. In FIG. 7, L1 and L2 indicate apparent light emission points of the first semiconductor laser device 31 and the second semiconductor laser device 32, respectively. As shown in FIG. 7, in the light detection unit of the present embodiment, a plus side sub-light detector and a minus side sub-light detector are respectively formed on both sides in the Y-axis direction of each light detector. Specifically, a first plus-side sub-light detector 41A and a first minus-side sub-light detector 41B are formed on both sides of the first light detector 41, respectively. The same applies to the second photodetector 42 to the sixth photodetector 46.

  First, the type of the optical information recording medium 11 to be used is determined by an optical information recording medium determining means (not shown). Based on the determination result, the first semiconductor laser device 31 or the second semiconductor laser device is driven. In the following description, it is assumed that the types of the optical information recording medium 11 are DVD and CD, the first semiconductor laser device 31 is driven in the case of DVD, and the second semiconductor laser device 32 is driven in the case of CD. To do.

  The first beam L1 emitted from the first semiconductor laser device 31 and the second beam L2 emitted from the second semiconductor laser device 32 are separated into one main beam and two sub beams by the diffraction grating 24, respectively. Thereafter, the first beam L1 and the second beam L2 are condensed on the optical information recording medium 11 via the collimating lens 21 and the objective lens 22. The condensed first beam L1 and second beam L2 are reflected by the optical information recording medium 11 and again enter the hologram element 20 as a light beam branching unit through the objective lens 22 and the collimator lens 21.

  The first beam L1 reflected by the optical information recording medium 11 is diffracted in the X direction in the drawing by the first diffraction region 61 of the hologram element 20. The ± first-order diffracted light of the sub-beams is obtained by using a first plus-side sub-light detector 41A, a first minus-side sub-light detector 41B, a fourth plus-side sub-light detector 44A, and a fourth minus-side sub-light detector. 44B. As a result, the first plus-side sub-light detector 41A, the first minus-side sub-light detector 41B, the fourth plus-side sub-light detector 44A, and the fourth minus-side sub-light detector 44B are each subjected to the beam. A spot 10m, a beam spot 10n, a beam spot 10s, and a beam spot 10t are incident.

  The first beam L1 is diffracted in the X direction in the figure by the second diffraction region 62 or the third diffraction region 63. The ± 1st-order diffracted light of the sub-beams is obtained by using a second plus-side sub-light detector 42A, a second minus-side sub-light detector 42B, a third plus-side sub-light detector 43A, and a third minus-side sub-light detector. 43B. As a result, the beam is supplied to the second plus-side sub-light detector 42A, the second minus-side sub-light detector 42B, the third plus-side sub-light detector 43A, and the third minus-side sub-light detector 43B, respectively. A spot 10o, a beam spot 10p, a beam spot 10q, and a beam spot 10r are incident.

  On the other hand, the second beam L <b> 2 is diffracted in the X direction in the drawing by the first diffraction region 61 or the second diffraction region 62 of the hologram element 20. The ± first-order diffracted light of the sub-beams is obtained by using the first plus-side sub-light detector 41A, the first minus-side sub-light detector 41B, the sixth plus-side sub-light detector 46A, and the sixth minus-side sub-light detector. 46B. As a result, the first plus-side sub-light detector 41A, the first minus-side sub-light detector 41B, the sixth plus-side sub-light detector 46A, and the sixth minus-side sub-light detector 46B each have a beam. A spot 13m, a beam spot 13n, a beam spot 13s, and a beam spot 13t are incident.

  The second beam L2 is diffracted in the X direction in the figure by the third diffraction region 63. The ± 1st-order diffracted light of the sub-beams is obtained by using a second plus-side sub-light detector 42A, a second minus-side sub-light detector 42B, a fifth plus-side sub-light detector 45A, and a fifth minus-side sub-light detector. 45B. As a result, the beam is supplied to the second plus-side sub-light detector 42A, the second minus-side sub-light detector 42B, the fifth plus-side sub-light detector 45A, and the fifth minus-side sub-light detector 45B, respectively. A spot 13o, a beam spot 13p, a beam spot 13q, and a beam spot 13r are incident.

  A tracking error signal is generated from the first beam L1 or the second beam L2 guided to the first plus-side sub-light detector 41A to the sixth minus-side sub-light detector 46B, and this signal is used to generate optical information. Recording and reproduction of the recording medium are performed.

  Next, a method for generating a tracking error signal using sub beams from the first beam L1 and the second beam L2 will be described.

  The tracking error signal can be obtained by a known three beam method. The tracking error signal TE (3B) 1 of the three beam method using the first beam L1 is obtained by the calculation of Expression 21.

  The tracking error signal TE (3B) 2 of the three beam method using the second beam L2 is obtained by the calculation of Expression 22.

  Further, the tracking error signal TE (3B) 3 obtained by calculation corresponding to both the first beam L1 and the second beam L2 can be obtained by the calculation of Expression 23.

  However, ST1 is an output signal from the first plus side sub photodetector 41A, ST2 is an output signal from the first minus side sub photodetector 41B, and ST3 is a second plus side sub photo detector. ST4 is an output signal from the second minus-side sub-light detector 42B, ST5 is an output signal from the third plus-side sub-light detector 43A, and ST6 is the first output signal from the detector 42A. 3 is an output signal from the minus side sub photodetector 43B, ST7 is an output signal from the fourth plus side sub photodetector 44A, and ST8 is an output from the fourth minus side sub photodetector 44B. ST9 is an output signal from the fifth plus-side sub-light detector 45A, ST10 is an output signal from the fifth minus-side sub-light detector 45B, and ST11 is a sixth plus-side sub-light detector. An output signal from the detector 46A, ST12 is the output signal from the minus side sub-photodetectors 46B of the sixth.

  Next, calculation using the tracking error signal TE (SPP) by the sub push-pull method will be described.

  The tracking error signal TE (SPP) 1 of the sub push-pull method using the first beam L1 is obtained by the calculation of Expression 24.

  The tracking error signal TE (SPP) 2 of the sub push-pull method using the second beam L2 is obtained by the calculation of Expression 25.

  Further, the tracking error signal TE (SPP) 3 obtained by the calculation corresponding to both the first beam L1 and the second beam L2 can be obtained by the calculation of Expression 26.

  By combining the sub push-pull method and the tracking error signal detection method based on the PP method described in the first embodiment, tracking error signal detection based on the 3-beam push-pull method can be performed more stably than the PP method.

  Next, calculation by the 3-beam push-pull method will be described. A tracking error signal TE (3BPP) 1 of the three-beam push-pull method using the first beam L1 is obtained by the calculation of Expression 27.

  The tracking error signal TE (3BPP) 2 of the three-beam push-pull method using the second beam L2 is obtained by the calculation of Expression 28.

  Further, the tracking error signal TE (3BPP) 3 obtained by calculation corresponding to both the first beam L1 and the second beam L2 can be obtained by the calculation of Expression 29.

  However, in Expressions 27 to 29, k is an arbitrary value.

  The optical head device of the third embodiment can also divide the first beam L1 and the second beam L2 into two in the radial direction for the sub beam. Therefore, tracking error signals can be generated by the three-beam method and the three-beam push-pull method even in an optical head device in which semiconductor lasers having different wavelengths are arranged close to each other to cope with various optical discs having different recording and reproducing wavelengths. It becomes possible. As a result, it is possible to increase the types of tracking error signal detection methods, and it is possible to deal with more optical information recording media.

  In the present embodiment, the first plus-side sub-light detector 41A to the sixth minus-side sub-light detector 46B are provided. However, even without these, tracking error detection is possible although the error detection accuracy is slightly reduced.

  In the optical head device of the present embodiment, the hologram element 20 is formed on one surface of the substrate 73 and the diffraction grating 24 is formed on the opposite surface. Such a hologram element is generally formed by using glass or the like for a substrate and processing the substrate by photolithography or the like. However, in this case, it is necessary to form concave and convex shapes having different depths on one surface of the substrate, and further to form a diffraction grating on the back surface, which requires a plurality of processing steps and increases the manufacturing cost. In addition, characteristics are deteriorated due to misalignment in each process. The hologram element shown in the second embodiment can be formed by a mold because it is only necessary to form irregularities on the surface of a single substrate without using different materials. If the hologram element 20 and the diffraction grating 24 are formed on the substrate 73 by a mold, not only the productivity is improved but also an element with high accuracy can be obtained. Therefore, it is suitable as the hologram element 20 of the optical head device according to the third embodiment.

  In each embodiment, the optical information recording medium 11 includes a DVD (including DVD, DVD-ROM, DVD-RAM, DVD-R, DVD-RW, etc.) and a CD (CD, CD-ROM, CD-R, CD-). If a semiconductor laser having a wavelength of about 0.65 μm is used for the first semiconductor laser device 31 and a semiconductor laser having a wavelength of about 0.78 μm is used for the second semiconductor laser device 32, Good. For example, the first semiconductor laser device 31 may have a wavelength of 200 nm to 450 nm, and the second semiconductor laser device 32 may have a wavelength of about 650 nm or about 780 nm. Further, although the case where the first semiconductor laser device 31 and the second semiconductor laser device 32 are two independent semiconductor laser devices has been described, the same applies to the case of a monolithic two-wavelength semiconductor laser formed on the same substrate. Applicable to.

  The optical head device and the hologram element according to the present invention can be applied to various optical discs having different wavelengths of semiconductor laser light to be used, and provide an optical head device that can obtain more stable focus error signal and tracking error signal. In particular, it is useful as an optical head device, a hologram element, and the like corresponding to a plurality of types of optical information recording media.

It is a figure which shows the optical head apparatus which concerns on the 1st Embodiment of this invention. It is a top view which shows the hologram element used for the optical head apparatus which concerns on the 1st Embodiment of this invention. It is a top view which shows the photodetector used for the optical head apparatus which concerns on the 1st Embodiment of this invention. It is sectional drawing which shows the hologram element used for the optical head apparatus which concerns on the 2nd Embodiment of this invention. It is a graph showing the relationship between the depth of the recessed part of a hologram element used for the optical head apparatus which concerns on the 2nd Embodiment of this invention, and a phase difference. It is a figure which shows the optical head apparatus which concerns on the 3rd Embodiment of this invention. It is a top view which shows the photodetector used for the optical head apparatus which concerns on the 3rd Embodiment of this invention. It is a figure which shows the conventional optical head apparatus.

Explanation of symbols

10a beam spot 10b beam spot 10d beam spot 10m beam spot 10n beam spot 10o beam spot 10p beam spot 10q beam spot 10r beam spot 10s beam spot 10t beam spot 11 optical information recording medium 13a beam spot 13b beam spot 13c beam spot 13d Beam spot 13m Beam spot 13n Beam spot 13o Beam spot 13p Beam spot 13q Beam spot 13r Beam spot 13s Beam spot 13t Beam spot 20 Hologram element 21 Collimator lens 22 Objective lens 24 Diffraction grating 31 First semiconductor laser device 32 Second semiconductor laser device 32 Semiconductor laser device 40 Photo detector 41 First photo detector 1A First plus side sub-light detector 41B First minus side sub-light detector 41a Light receiving area 41b Light receiving area 41c Light receiving area 41d Light receiving area 42 Second light detector 42A Second plus side sub light detector 42B Second minus side sub-light detector 42a Light receiving region 42b Light receiving region 42c Light receiving region 42d Light receiving region 43 Third light detector 43A Third plus side sub light detector 43B Third minus side sub light detector 43a Area 43b light-receiving area 43c light-receiving area 43d light-receiving area 44 fourth photodetector 44 fifth photodetector 44A fourth plus-side sub-light detector 44B fourth minus-side sub-light detector 44a light-receiving area 44b light-receiving area 44c Light-receiving area 44d Light-receiving area 45 Fifth photodetector 45A Fifth plus-side sub-light detector 45B Fifth minus-side sub-light detector 4 a light-receiving area 45b light-receiving area 45c light-receiving area 45d light-receiving area 46 sixth photodetector 46A sixth plus-side sub-light detector 46B sixth minus-side sub-light detector 46a light-receiving area 46b light-receiving area 46c light-receiving area 46d light-receiving Area 61 first diffraction area 62 second diffraction area 63 third diffraction area 72 substrate 73 substrate 75 substrate

Claims (11)

A first light source that emits a first beam of a first wavelength;
A second light source that emits a second beam having a second wavelength that is longer than the first wavelength;
A condensing optical system that receives the first beam and the second beam and converges them on the optical information recording medium as fine spots,
A hologram element that diffracts each of the first beam and the second beam reflected on the optical information recording medium;
A plurality of light receiving elements that receive the diffracted light diffracted by the hologram element;
The hologram element has a concavo-convex structure formed on one surface of a substrate transparent to the first beam and the second beam,
The depth of the concave portion in the concave-convex structure is a value represented by any one of Formulas 1 to 3, respectively.
λ1 / {n (λ1) −n0 (λ1)} Equation 1
λ2 / {n (λ2) −n0 (λ2)} Equation 2
λ1 / {n (λ1) −n0 (λ1)} + λ2 / {n (λ2) −n0 (λ2)} Equation 3
(Where, λ1 represents the first wavelength, λ2 represents the second wavelength, n (λ1) represents the refractive index of the substrate with respect to the light of the first wavelength, and n1 (Λ2) represents the refractive index of the substrate with respect to the light having the second wavelength, n0 (λ1) represents the refractive index with respect to the light of the first wavelength in the concave portion, and n0 (λ2) represents the refractive index in the concave portion. Represents the refractive index for light of the second wavelength.)   A diffraction grating provided between the first light source and the second light source and the hologram element, which diffracts the first beam and the second beam and separates them into a main beam, a first sub beam and a second sub beam. The optical head device according to claim 1, further comprising:   3. The optical head device according to claim 2, wherein the diffraction grating is formed on a surface of the substrate opposite to the hologram element. The hologram element has a first diffraction region, a second diffraction region, and a third diffraction region,
The first diffraction region and the second diffraction region are adjacent to each other;
The second diffraction region and the third diffraction region are adjacent to each other;
The first diffraction region diffracts the first beam as first diffracted light having a first wavefront;
The second diffraction region and the third diffraction region diffract the first beam as second diffracted light having a second wavefront different from the first wavefront,
The first diffraction region and the second diffraction region diffract the second beam as third diffracted light having a third wavefront,
The third diffraction region diffracts the second beam as fourth diffracted light having a fourth wavefront different from the third wavefront;
Generating a tracking error signal for the first beam based on a signal obtained from the first diffracted light and a signal obtained from the second diffracted light;
The tracking error signal of the second beam is generated based on a signal obtained from the third diffracted light and a signal obtained from the fourth diffracted light. Optical head device.   The first diffracted light and the third diffracted light are detected by a first light receiving element of the plurality of light receiving elements, and the second diffracted light is detected by a second light receiving element of the plurality of light receiving elements. 5. The optical head device according to claim 4, wherein the fourth diffracted light is detected. The hologram element has a first diffraction region, a second diffraction region, and a third diffraction region,
The first diffraction region and the second diffraction region are adjacent to each other;
The second diffraction region and the third diffraction region are adjacent to each other;
The first diffraction region and the second diffraction region diffract the main beam of the first beam as first diffracted light having a first wavefront,
The third diffraction region diffracts the main beam of the first beam as second diffracted light having a second wavefront different from the first wavefront,
The first diffraction region and the second diffraction region diffract the first sub-beam of the first beam as third diffracted light having a third wavefront,
The third diffraction region diffracts the first sub-beam of the first beam as fourth diffracted light having a fourth wavefront different from the third wavefront;
The first diffraction region and the second diffraction region diffract the second sub beam of the first beam as fifth diffracted light having a fifth wavefront,
The third diffraction region diffracts the second sub-beam of the first beam as sixth diffracted light having a sixth wavefront different from the fifth wavefront,
The first diffraction region diffracts the main beam of the second beam as seventh diffracted light having a seventh wavefront;
The second diffraction region and the third diffraction region diffract the main beam of the second beam as eighth diffracted light having an eighth wavefront different from the seventh wavefront,
The first diffraction region diffracts the first sub-beam of the second beam as ninth diffracted light having a ninth wavefront,
The second diffraction region and the third diffraction region diffract the first sub-beam of the second beam as tenth diffracted light having a tenth wavefront different from the ninth wavefront,
The first diffraction region diffracts the second sub-beam of the second beam as eleventh diffracted light having an eleventh wavefront;
The second diffraction region and the third diffraction region diffract the second sub-beam of the second beam as a twelfth diffracted light having a twelfth wavefront different from the eleventh wavefront,
Generating a tracking error signal of the first beam based on signals obtained from the first to sixth diffracted lights;
4. The optical head device according to claim 2, wherein a tracking error signal of the second beam is generated based on a signal obtained from the seventh to twelfth diffracted lights. Detecting the first diffracted light and the seventh diffracted light by a first light receiving element of the plurality of light receiving elements;
The second diffracted light and the eighth diffracted light are detected by a second light receiving element of the plurality of light receiving elements,
Detecting the third diffracted light and the ninth diffracted light by a third light receiving element of the plurality of light receiving elements;
Detecting the fourth diffracted light and the tenth diffracted light by a fourth light receiving element of the plurality of light receiving elements;
The fifth diffracted light and the eleventh diffracted light are detected by a fifth light receiving element of the plurality of light receiving elements,
7. The optical head device according to claim 6, wherein the sixth diffracted light and the twelfth diffracted light are detected by a sixth light receiving element of the plurality of light receiving elements. The optical axis of the first beam passes through the boundary between the first diffraction region and the second diffraction region,
8. The optical head device according to claim 4, wherein an optical axis of the second beam passes through a boundary between the second diffraction region and the third diffraction region. 9.   The boundary line between the first diffraction region and the second diffraction region, and the boundary line between the second diffraction region and the third diffraction region are straight lines extending in the track direction of the optical information recording medium. The optical head device according to claim 4, wherein: A substrate transparent to the first beam of the first wavelength and the second beam of the second wavelength;
An uneven structure formed on one surface of the substrate,
The depth of the concave portion in the concave-convex structure is represented by any one of Formulas 1 to 3, respectively.
λ1 / {n (λ1) −n0 (λ1)} Equation 1
λ2 / {n (λ2) −n0 (λ2)} Equation 2
λ1 / {n (λ1) −n0 (λ1)} + λ2 / {n (λ2) −n0 (λ2)} Equation 3
(Where, λ1 represents the first wavelength, λ2 represents the second wavelength, n (λ1) represents the refractive index of the substrate with respect to the light of the first wavelength, and n1 (Λ2) represents the refractive index of the substrate with respect to the light having the second wavelength, n0 (λ1) represents the refractive index with respect to the light of the first wavelength in the concave portion, and n0 (λ2) represents the refractive index in the concave portion. Represents the refractive index for light of the second wavelength.)   11. A diffraction grating for transmitting and diffracting the first beam and the second beam and generating a main beam and a sub beam on a surface of the substrate opposite to the surface on which the concavo-convex structure is formed. The hologram element described in 1.

Images