JP4218393B2 - Optical head device - Google Patents

Optical head device Download PDF

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Publication number
JP4218393B2
JP4218393B2 JP2003090249A JP2003090249A JP4218393B2 JP 4218393 B2 JP4218393 B2 JP 4218393B2 JP 2003090249 A JP2003090249 A JP 2003090249A JP 2003090249 A JP2003090249 A JP 2003090249A JP 4218393 B2 JP4218393 B2 JP 4218393B2
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Prior art keywords
light
wavelength
optical
phase shifter
polarization
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JP2004296041A5 (en
JP2004296041A (en
Inventor
理恵 木全
浩一 村田
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旭硝子株式会社
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Description

[0001]
BACKGROUND OF THE INVENTION
  The present invention relates to an optical head device equipped with a phaser that controls the polarization state of light of different wavelengths emitted from a light source.
[0002]
[Prior art]
  Recording of information on optical recording media such as optical disks such as CDs and DVDs and magneto-optical disksAnd / orIn an optical head device that performs reproduction, light emitted from a semiconductor laser, which is a light source, is collected on an optical recording medium by an objective lens and reflected by the optical recording medium to become return light. This return light is guided to a light receiving element which is a photodetector using a beam splitter, and information on the optical recording medium is converted into an electric signal.
[0003]
  In order to record and / or reproduce information of CDs and DVDs, which are optical recording media of different standards, using the same optical head device, compatible optical head devices for CD and DVD have been commercialized. A semiconductor laser with a wavelength of 785 nm is used for CD, and a semiconductor laser with a wavelength of 660 nm is used for DVD.
[0004]
  In addition, a next-generation DVD optical head device has been proposed that uses a blue-violet semiconductor laser in the 410 nm wavelength band to improve the recording density by three times or more compared to a red semiconductor laser in the 660 nm wavelength band that has been conventionally used. Since the compatible optical head device for CD and DVD is widespread, a next-generation optical head device having compatibility with three wavelength bands, which can record and / or reproduce DVDs and CDs in particular, has been proposed. .
[0005]
  In the next-generation optical head device having compatibility with the three wavelength bands, 660 nm (λ1) Linearly polarized light in the wavelength band is transmitted without changing the polarization state, and 785 nm (λ2) For linearly polarized light in the wavelength band, a phase shifter that rotates the polarization plane by 90 ° and transmits it is desired.
[0006]
  In the conventional technique, for example, 660 nm (λ1) M for linearly polarized light in the wavelength band1λ1(M1Is a natural number), and at the same time, 785 nm (λ2) For linearly polarized light in the wavelength band (m2-1/2) λ2(M2A single birefringent plate whose retardation value is adjusted so as to generate a phase difference of (natural number) is conceivable. The phase shifter realized as described above has wavelength dispersion in the retardation value of the material. Therefore, when wavelength dispersion is not desired, it is difficult to obtain the expected effect for light in both wavelength bands. There was a problem.
[0007]
  For example, as a general organic birefringent material, the ratio R (785 nm) / R (660 nm) of the retardation value R (785 nm) in the 785 nm wavelength band to the retardation value R (660 nm) in the 660 nm wavelength band is about 0.95. Think about what is. 1980 nm (= 660 × 3, m for light in the 660 nm wavelength band1= 3) When the retardation value is 5/5 times the wavelength (m2Although the retardation value is close to 3), the light having a wavelength of 785 nm incident as linearly polarized light becomes elliptically polarized light having an ellipticity of about 0.34 after passing through the phase shifter, and linearly polarized light cannot be obtained.
[0008]
  In addition, there are cases where desired characteristics can be obtained by using higher order, that is, a phase shifter such as 7λ / 2, 9λ / 2, etc. instead of 5λ / 2. appear. That is, the wavelength dependency of the effect of the phase retarder, such as the phase difference on the polarization, increases, and it becomes difficult to maintain the accuracy of the retardation value of the phase retarder in the manufacturing process, resulting in a decrease in production yield and phase. The problem is that the cost of the child increases.
[0009]
[Patent Document 1]
  Japanese Patent Laid-Open No. 2002-14228
[0010]
[Problems to be solved by the invention]
  The object of the present invention is to eliminate the above-mentioned problems of the prior art.
[0011]
[Means for Solving the Problems]
  The present invention includes a plurality of light sources that respectively emit light of at least two different wavelengths,AboveAn objective lens for condensing the light emitted from the light source onto the optical disc,AboveA photodetector for detecting the light reflected by the optical disc;,In an optical head device comprising:AboveWith light sourceAboveAt least between optical discsAboveIn the optical path shared by the two lights, a phaser composed of two birefringent plates having different optical axis directions is installed,The wavelength of the two lights is the wavelength λ 1 , Wavelength λ 2 The phaser is the waveLongλ 1 Against the light ofOf the two birefringent platesPhase differenceButin frontWaveLongλ 1 Each of which is a natural number timesWaveLongλ 1 Against the light ofAboveThe phaser does not change the polarization state,The wavelength λ incident on the phaser as linearly polarized light 2 Is transmitted through the phaser as linearly polarized light, and the polarization direction of the transmitted light is at an angle of φ with respect to the polarization direction of incident light, and the two birefringent plates constituting the phaser The wavelength λ of 2 Phase difference R of each of the birefringent plates with respect to 1 And R 2 Are equal, and the optical axis directions of the two birefringent plates are equal to the wavelength λ. 2 Direction of incident light and θ 1 And θ 2 And the angle θ 1 And θ 2 Is the above φAn optical head device is provided.
[0012]
Also,A plurality of light sources that respectively emit light of at least two different wavelengths; an objective lens that condenses the light emitted from the light source onto an optical disc; and a light that is collected and reflected by the optical disc An optical head device comprising a photodetector, comprising two birefringent plates having different optical axis directions in an optical path shared by at least the two lights between the plurality of light sources and the optical disk. The phase shifter is installed, and the wavelength of the two lights is set to the wavelength λ 1 , Wavelength λ 2 The phase shifter is the wavelength λ 1 The phase difference of the two birefringent plates with respect to the light of 1 Each of which is a natural number multiple of the wavelength λ 1 The phase shifter does not change the polarization state with respect to the light of the wavelength λ incident on the phase shifter as linearly polarized light. 2 Is transmitted through the phase shifter as linearly polarized light, and the polarization direction of the transmitted light forms an angle of 90 ° with respect to the polarization direction of incident light, and the wavelength λ 1 The phase difference of each of the two birefringent plates for the light of λ is λ 1 And 2λ 1 And the phase difference is 2λ 1 The optical axis direction of the birefringent plate is the wavelength λ 2 An angle of 35 ° to 55 ° is formed with respect to the polarization direction of the incident light.An optical head device is provided.
[0013]
  Also,A plurality of light sources that respectively emit light of at least two different wavelengths; an objective lens that condenses the light emitted from the light source onto an optical disc; and a light that is collected and reflected by the optical disc An optical head device comprising a photodetector, comprising two birefringent plates having different optical axis directions in an optical path shared by at least the two lights between the plurality of light sources and the optical disk. The phase shifter is installed, and the wavelength of the two lights is set to the wavelength λ 1 , Wavelength λ 2 The phase shifter is the wavelength λ 1 The phase difference of the two birefringent plates with respect to the light of 1 Each of which is a natural number multiple of the wavelength λ 1 The phase shifter does not change the polarization state with respect to the light of the wavelength λ incident on the phase shifter as linearly polarized light. 2 Light emitted as circularly polarized light, the wavelength λ 1 The phase difference of each of the two birefringent plates is equal to λ 1 And the optical axis direction of the birefringent plate on the light exit side is the wavelength λ 2 An angle from 40 ° to 60 ° is formed with respect to the polarization direction of the incident light.An optical head device is provided.
[0014]
  Also,The wavelength λ incident on the phaser 1 And the wavelength λ 2 Are light of 660 nm wavelength band and 785 nm wavelength band, respectively.The above optical head device is provided.
[0015]
  In addition, the light enters the phaserSaidWavelength λ1andThe wavelengthλ2Are light of 660 nm wavelength band and 785 nm wavelength band, respectively.2HornAboveProvided is the above optical head device in which the ratio of the retardation value of the birefringent plate to light in the 660 nm wavelength band and 785 nm wavelength band is a value from 0.9 to 0.99.
[0016]
  further2HornAboveProvided is the above optical head device in which a birefringent plate is bonded and integrated.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
  An optical head device of the present invention includes a plurality of light sources that respectively emit at least two light beams having different wavelengths, an objective lens that condenses light emitted from the light sources onto an optical disc, and is collected and reflected by the optical disc. An optical head device comprising a photodetector for detecting light, wherein two optical axes having different optical axis directions are shared in an optical path shared by at least two lights between a plurality of light sources and an optical disk. This is an optical head device in which a phaser composed of a refracting plate is installed.
[0018]
  The phase difference with respect to the light of one wavelength of the two birefringent plates constituting the above phaser is a natural number multiple of the one wavelength, and the phaser has a polarization state with respect to the light of the one wavelength. Do not change. That is, the phase difference of the two birefringent plates with respect to the light of one wavelength is a natural number multiple of the one wavelength. The phase shifter is an optical head device that changes the polarization state with respect to light of another wavelength different from the one wavelength.
[0019]
  The optical head device of the present invention will be described below with reference to the drawings.
  FIG. 1 is a conceptual cross-sectional view showing an example of the basic configuration of the optical head device of the present invention, and a phase shifter 10 that controls the polarization state of transmitted light.3Are placed between the multi-wavelength light source unit 104 that emits light of at least two or more different wavelengths and the objective lens 105.
[0020]
  Lights of at least two or more different wavelengths emitted from the light source unit 104 are transmitted through the phase shifter 103, are condensed on the optical disk 106 through the objective lens 105, and then are reflected by the optical disk 106 to become return light. Then head to the photodetector system. Although the photodetector system is omitted in FIG. 1, the actual installation position may be on the multi-wavelength light source unit 104 side or the optical disk 106 side as viewed from the phase shifter 103. Good. In the former case, the light emitted from the light source unit 104 is transmitted through the phaser 103 in both the forward path toward the optical disk and the return path back from the optical disk. In the latter case, the phaser is transmitted only in the forward path from the light source unit to the optical disk 103 is transmitted. Further, the phase shifter 103 may be installed at a position where only return light reflected from the optical disk and returning to the photodetector system is transmitted.
[0021]
  The phase difference between the two birefringent plates 101 and 102 constituting the phase shifter 103 mounted on the optical head device of the present invention does not change the polarization state for light of one wavelength, but changes to light of other wavelengths. On the other hand, it is designed to change its polarization state. Therefore, the light of the one wavelength is transmitted through the phase shifter 103 without changing the polarization state thereof, and the light of another wavelength different from the one wavelength is changed in the polarization state of the phase shifter 10.3Transparent. Specifically, the phase difference between the two birefringent plates is the wavelength λ.1M for light1λ1, M2λ1(M1, M2Is a natural number) and the wavelength λ1For most light beams, the polarization state is hardly changed.1The polarization state can be changed only with respect to other light. M1, M2Takes values up to 1 or 2, up to 3.
[0022]
  Hereinafter, for the phaser mounted in the optical head device of the present invention, the light transmitted through the phaser has a wavelength λ1, Λ2However, a light source unit that emits light of three or more different wavelengths may be placed in the optical head device, and light of three or more different wavelengths is transmitted through the phase shifter. Of course, you can use it. When light of three different wavelengths is transmitted, it is possible to transmit one wavelength without changing the polarization state, and to transmit the phase shifter by changing the polarization state of the other two wavelengths of light. Since the optical head device of the present invention is compatible with CDs, DVDs, and next-generation optical discs, the wavelengths include a 785 nm wavelength band, a 660 nm wavelength band, a 410 nm wavelength band, and the like. Here, the wavelength band means a width of ± 10 nm. For example, the wavelength of the 660 nm wavelength band means a wavelength from 650 to 670 nm.
[0023]
  2A and 2B are cross-sectional views showing a configuration example of a phase shifter in the optical head device of the present invention. FIG. 2A is a view in which only two birefringent plates 201 and 202 are laminated, and FIG. Transparent substrate 2 on one side of two birefringent plates 201 and 2020(C) is a structure in which birefringent plates 201 and 202 are sandwiched between two transparent substrates 203 and 204. There may or may not be an adhesive layer or an adhesive layer between the birefringent plate and the birefringent plate, or between the birefringent plate and the transparent substrate. Moreover, the structure with which the birefringent plate of 2 sheets was integrated, or the structure which is not may be sufficient. However, it is preferable for handling that two birefringent plates are bonded and integrated.
[0024]
  As the birefringent plate constituting the retarder, a birefringent film having an optical axis aligned in the stretching direction by stretching an organic material such as polycarbonate, acrylic, or polyester can be used. In addition, a polymer liquid crystal subjected to a desired alignment treatment can be used, or a substrate such as a quartz substrate or lithium niobate having birefringence may be used.
[0025]
  As the transparent substrates 203 and 204 shown in FIG. 2, it is preferable to use an optically isotropic medium such as a glass substrate or a quartz glass substrate because the transmitted light is not affected by birefringence or the like.
  Wavelength λ of two birefringent plates1The phase difference for light is m1, M2M as a natural number in order from the incident side of light (laser light).1λ1, M2λ1And the wavelength λ2The phase difference for is n1, N2Each as a non-integer positive number1= N1λ2, R2= N2λ2It is. At this time, the birefringent plateRespectivelyFor wavelength λ1Wavelength for light2Ratio of light retardation value of(Or chromatic dispersion)K1, K2Is expressed as n for each birefringent plate.1= K1× m1λ1/ Λ2, N2= K2× m2λ1/ Λ2It becomes. In addition, the direction of the optical axis (fast axis) of the two birefringent plates intersecting each other has a wavelength λ2In the order in which the laser beams are incident on the basis of the polarization direction of the incident light1, Θ2(-90 ° ≦ θ1, Θ2≦ 90 °). In FIG. 3, the conceptual diagram which shows the optical axis direction of the two birefringent plates which comprise a phase element is shown.
[0026]
  The phase shifter thus configured has a wavelength λ1The retardation value of the two birefringent plates is λ1The polarization state is not changed because it is an integral multiple of2In general, for light of λ2≠ kiλ1Since (i = 1, 2), the polarization state is changed.
[0027]
  Further, as described above, the wavelength of the light emitted from the light source and transmitted through the phase shifter is λ1And λ2And the wavelength λ1The light transmitted through the phase shifter does not change its polarization state, whereas the wavelength λ incident on the phase shifter as linearly polarized light2The light passes through the phase shifter as linearly polarized light, and the polarization direction of the transmitted light forms an angle φ with respect to the polarization direction of the incident light. And the wavelength λ of the two birefringent plates constituting the phase shifter2Phase difference R of each birefringent plate for the light of1And R2Are equal. Also, the optical axis direction of each of the two birefringent plates has a wavelength λ2Direction of incident light and θ1And θ2The angle of θ1And θ2The sum of is φLightA head device is preferable.
[0028]
  That is, the wavelength λ of the two birefringent plates of the above phaser2Phase difference R with respect to1And R2Are adjusted to be approximately equal, θ1According to (Equation 1)2A value (θ determined from a phase difference R with respect to and an angle φ1c) And select θ2As θ2c= Φ-θ1cThe wavelength λ incident with linearly polarized light2It was found that the polarization direction at the time of emitting the light can be rotated by an angle φ with respect to the incident polarization direction.
[0029]
[Expression 1]
[0030]
  Therefore, wavelength λ1The wavelength λ of incident light is linearly polarized light without changing the polarization state of the light.2Of the two birefringent plates constituting the phase shifter, when the light is to be emitted as substantially linearly polarized light whose polarization direction is rotated by an angle φ,2Phase difference R with respect to1And R2Are approximately equal and the optical axis direction θ1, Θ2As the above θ1c, Θ2cIs preferable in order to obtain the best expected effect, but θ with respect to the retardation value R of the birefringent plate1= Θ1c± 10 °, θ2= Θ1+ (Φ-2θ1c)2The effect of rotating the polarization direction of the light by the angle φ can be obtained.
[0031]
  For example, wavelength λ1Is 660 nm and wavelength λ2Is 785 nm and m1= M2= 1, k1= K2When a birefringent plate with 0.95 is selected, (θ1, Θ2) = (23 °, 6 °) λ2The direction of polarization of the light rotates about 29 ° and the ellipticity is 0.004. k1= K2= 0.93 for a birefringent plate (θ1, Θ2) = (19 °, 10 °), it is possible to obtain outgoing light having an ellipticity of 0.002 rotated in a polarization direction of approximately 29 °. That is, in either case, θ1+ Θ2= 29 °, which coincides with the rotation angle of 29 °, and is almost a straight lineWhatYes.
    Since the above-described phase shifter can be prepared by adjusting the optical axis according to the retardation value of the birefringent plate to be used, a phase shifter having a desired effect can be easily realized using an existing birefringent plate.
[0032]
  Hereinafter, for the two wavelengths transmitted through the phase shifter, the wavelength λ1Is light in the 660 nm wavelength band, and the wavelength λ2Is assumed to be light in the 785 nm wavelength band. The wavelength λ incident on the phase shifter as linearly polarized light2The light exits the phase shifter as linearly polarized light, and the polarization direction of the emitted light forms an angle of 90 ° with respect to the polarization direction of the incident light. And wavelength λ1The phase difference of each of the two birefringent plates for the light of λ is λ1And 2λ1And the phase difference is 2λ1The optical axis direction of the birefringent plate is the wavelength λ 2 35 with respect to the polarization direction of the incident light°To an optical head device having an angle of from 55 ° to 55 °.
[0033]
  That is, the above phaser has an incident wavelength λ2Can be emitted as a substantially linearly polarized light whose polarization direction is rotated by 90 ° with respect to the incident polarization direction.2Against the light ofλ / 2Can function as a board. For the phase difference between the two birefringent plates, the wavelength λ1For light of λ in order from the light incident side11(M1= 1, m2= 2). Λ of birefringent plate1Λ for2K representing the chromatic dispersion of1, K2Are selected to be between 0.9 and 0.99. At this time, wavelength λ2The phase difference with respect to the light is R in order.1= K1× λ1, R2= 2 × k2× λ1(≒ 2R1).
[0034]
  Furthermore, the phase difference is 2λ1The optical axis (fast axis) θ of the second birefringent plate2For λ235 with respect to the incident polarization direction of light°Is designed to make an angle of up to 55 °, θ1Is the value θ determined from (Equation 2)1cBy selecting the range of ± 10 ° with respect to the wavelength λ2The polarization direction can be rotated by 90 ° while maintaining linearity. Furthermore, θ2Is a value determined from (Equation 3), and θ1For the above θ1cOn the other hand, increasing the accuracy to ± 5 ° and ± 3 ° is preferable because the linearity is better maintained and the rotation angle approaches 90 °.
[0035]
[Expression 2]
[0036]
[Equation 3]
[0037]
  The phase shifter thus configured has a wavelength λ1The polarization state of the light of the2With respect to the linearly polarized light, only the polarization direction is rotated by approximately 90 ° and transmitted while substantially maintaining the linearity.
[0038]
  For example, k as two birefringent plates1= K2= 0.95 when the same material is used (wavelength λ of the birefringent plate constituting the above phaser)2The phase difference with respect to light is 627 nm and 1257 nm in the order of light incidence, and the set in the optical axis direction is almost (θ1, Θ2) = (18 °, 50 °) or (72 °, 40 °), the above-mentioned effect is best exhibited, and the wavelength λ is incident as linearly polarized light.2Is emitted as substantially linearly polarized light having an ellipticity of about 0.002 and a polarization direction rotated by about 89.4 °.
[0039]
  When one birefringent plate having the same wavelength dispersion (k = 0.95) is used, for example, the wavelength λ13λ for light1For a birefringent plate having a phase difference of2The ellipticity of the light after passing through the phase shifter is about 0.33, and the linearity is not well maintained. In the phaser composed of the two birefringent plates, k1= 0.93, k2When two types of materials of 0.96 are used, the almost optimal set in the optical axis direction is (θ1, Θ2) = (20.5 °, 51.5 °) or (69.5 °, 38.5 °), the polarization direction is rotated by about 89.6 °, and the ellipticity is about 0.003. Is obtained as outgoing light.
[0040]
  In this way, by adjusting the optical axes of the two birefringent plates, the adjustment of the retardation value of the birefringent plate having wavelength dispersion alone is sufficient even when the performance is insufficient for the desired effect. It is possible to realize a phaser having excellent performance.
[0041]
  Further, in the above-described phase shifter according to the present invention, there is no distinction between the front and back as long as the polarization direction of the incident linearly polarized light is the same. For example, the phase shifter of FIG. The same effect can be obtained even if light is incident.
[0042]
  FIG. 5 is a conceptual cross-sectional view showing another example of the configuration of the optical head device of the present invention. That is, the above-mentioned light of 660 nm wavelength band does not change the polarization state, and light of 785 nm wavelength band that is incident as linearly polarized light is mounted with a two-wavelength phaser that emits by rotating the polarization direction by 90 °. It is an example of a structure of a compatible optical head apparatus. For example, the two-wavelength phase shifter is configured as shown in FIG. Here, FIG. 4 shows two different wavelengths λ in the phaser in the present invention.1, Λ2It is sectional drawing which shows the mode of a change of a polarization state when the linearly polarized light of this transmits.
[0043]
  As light sources of three different wavelengths, semiconductor lasers 411A, 411B, and 411C that emit light in the 785 nm wavelength band, 660 nm wavelength band, and 410 nm wavelength band, and the above-described two-wavelength phaser 410 in the 660 nm wavelength band and the 785 nm wavelength band are provided. I have.
[0044]
  The linearly polarized light of 785 nm wavelength band emitted from the semiconductor laser 411A (parallel to the paper surface in FIG. 4) isλ / 2After passing through the plate 412 and rotating the polarization direction by 90 °, the light is reflected by the polarization beam splitter 413, transmitted through the two-wavelength phase shifter 410, and further rotated by 90 ° in the polarization direction to become linearly polarized light parallel to the paper surface again. The light passes through the polarization beam splitter 414. Broadband for 660nm and 785nm wavelength bandsλ / 4The light passes through the plate 415 to become circularly polarized light, reflects light in the 410 nm wavelength band, passes through the wavelength selective beam splitter 418 that transmits light in the 785 nm wavelength band and 660 wavelength band, and then passes through the information on the optical disk 420 by the objective lens 419. Condensed on the recording surface.
[0045]
  The return light reflected from the optical disk 420 is a broadband for the objective lens 419, the wavelength selective beam splitter 418, 660 nm and 785 nm.λ / 4After passing through the plate 415 and becoming linearly polarized light whose polarization direction is orthogonal to the forward light, it is reflected by the polarization beam splitter 414 and condensed on the photodetector 421.
[0046]
  The linearly polarized light in the 660 nm wavelength band (parallel to the paper surface in FIG. 4) emitted from the semiconductor laser 411B passes through the polarizing beam splitter 413, the two-wavelength phaser 410, and the polarizing beam splitter 414 without changing the polarization state. Broadband for 660nm and 785nmλ / 4The light passes through the plate 415, the wavelength selective beam splitter 418, and the objective lens 419 and is condensed on the information recording surface of the optical disc 420.
[0047]
  The return light reflected from the optical disk 420 is a broadband for the objective lens 419, the wavelength selective beam splitter 418, 660 nm and 785 nm.λ / 4The light passes through the plate 415 and becomes linearly polarized light whose polarization direction is orthogonal to the forward light, and is reflected by the polarization beam splitter 414 and condensed on the photodetector 421.
[0048]
  On the other hand, the linearly polarized light in the 410 nm wavelength band emitted from the semiconductor laser 411C (parallel to the paper surface in FIG. 4) is used for the polarization beam splitter 416 and the 410 nm wavelength band.λ / 4After passing through the plate 417 to become circularly polarized light, the light is reflected by the wavelength selective beam splitter 418, travels by changing the traveling direction by 90 °, passes through the objective lens 419, and is condensed on the information recording surface of the optical disc 420.
[0049]
  The return light reflected from the optical disc 420 is used for the objective lens 419, the wavelength selective beam splitter 418, and the 410 nm wavelength band.λ / 4The light passes through the plate 417 and becomes linearly polarized light whose polarization direction is orthogonal to the outward light, and is reflected by the polarization beam splitter 416 and condensed on the photodetector 422.
[0050]
  In the optical head device of the present invention, by using the two-wavelength phase shifter 410, the polarization beam splitter is used with only one wavelength-selective beam splitter being used. Reflection can be used and light loss can be suppressed. Further, when recording and / or reproducing information on an optical recording medium (optical disc), the outgoing light from the semiconductor laser in each wavelength band and the polarization direction of the returning light from the optical recording medium are orthogonalized, so that the outgoing light and the backward light Unnecessary interference between the two can be prevented.
[0051]
  In particular, by using the two-wavelength phase shifter 410, the linearity of polarization and the angle of the polarization direction can be accurately controlled, so that the above advantages can be used more effectively. Therefore, more stable information recording and reproduction is possible. A three-wavelength compatible optical head device capable of performing In addition, polarization beam splitters are easier to design and manufacture and have more stable performance than wavelength selective ones, leading to cost reduction. In addition, since one photodetector can be used for light in the 660 nm wavelength band and light in the 785 nm wavelength band, the number of components of the optical head device can be reduced, which is advantageous for cost reduction and size reduction of the device. is there.
[0052]
  The wavelength λ incident on the phase shifter as linearly polarized light2Light exits as a circularly polarized wave with a wavelength λ1The phase difference of each of the two birefringent plates is equal to λ1It is. Also, the optical axis direction of the birefringent plate on the light exit side is the wavelength λ 2 40 with respect to the polarization direction of the incident light°It is preferable that the optical head device has an angle of from 60 ° to 60 °.
[0053]
  That is, the phaser in the present invention has an incident wavelength λ2Can be emitted as circularly polarized light, that is, λ2Against the light ofλ / 4 plateCan function as. For the phase difference between the two birefringent plates, the wavelength λ1For both light1(M1= 1, m2= 1). Λ of birefringent plate1Λ for2K representing the chromatic dispersion of1, K2Are selected to be between 0.9 and 0.99. At this time, wavelength λ2The phase difference with respect to the light is R in order.1= K1× λ1, R2= K2× λ1(≒ R1).
[0054]
  Further, the optical axis θ of the second birefringent plate on the light exit side2For λ240 with respect to the incident polarization direction of light°Is designed to make an angle of up to 60 °, θ1Is the value θ determined from (Equation 4)1The wavelength λ incident with linearly polarized light is selected by selecting a range of 10 ° around c.2Can be made almost circularly polarized light. Furthermore, θ2Is preferably selected to take the vicinity of the value determined from (Equation 5), since the effect of converting linearly polarized light into circularly polarized light can be maximized.
[0055]
[Expression 4]
[0056]
[Equation 5]
[0057]
  The phase shifter thus configured has a wavelength λ1The polarization state of the light of the2The linearly polarized light is changed into circularly polarized light and transmitted.
  For example, k birefringence plates1= K2= 0.95 when the same material is used, approximately (θ1, Θ2) = (9 °, 51 °) or (81 °, 39 °), the above-mentioned effect is best manifested, and the wavelength λ incident as linearly polarized light2After passing through the phase shifter, the light becomes an almost circle with an ellipticity of about 0.99. In the case of one birefringent plate having the same wavelength dispersion (0.95), an ellipticity of only about 0.7 can be obtained, which is not preferable. On the other hand, k1= 0.93, k2= 0.96, the optimal optical axis set is (θ1, Θ2) = (10.5 °, 53.5 °) or (79.5 °, 36.5 °). At this time, the ellipticity is approximately 0.99.
[0058]
  In this way, by adjusting the optical axes of the two birefringent plates, the adjustment of the retardation value of the birefringent plate having wavelength dispersion alone is sufficient even when the performance is insufficient for the desired effect. It is possible to realize a phaser having excellent performance.
[0059]
  FIG. 6 shows the structure of another example of the phase shifter according to the present invention and the wavelength λ of the phase shifter.1It is sectional drawing which shows a mode that a polarization state does not change, when linearly polarized light of this is reciprocated. FIG. 7 shows the wavelength λ incident as linearly polarized light on the same phaser as shown in FIG.2FIG. 5 is a cross-sectional view showing a state in which the light emitted as circularly polarized light is incident on the circularly polarized light and is diffracted and emitted as linearly polarized light by changing the polarization direction by 90 degrees. The two-wavelength phase shifter 511 composed of the above-described birefringent plates 501 and 502 laminated on the transparent substrate 504 is filled on the transparent substrate 503 to which the polarization selective diffraction function is added.5(Hereinafter collectively referred to as a phase shifter 512).
[0060]
  The polarization selective diffraction function can be realized, for example, by forming the diffraction element 506 on the transparent substrate 503 as follows. After a desired alignment treatment is performed on the transparent substrate 503, a liquid crystal monomer solution that is a birefringent material is applied, and the liquid crystal monomer is polymerized by irradiating light source light for photopolymerization to form a polymer liquid crystal. . The diffraction element 506 is formed on the polymer liquid crystal by processing a periodic grating having a cross-sectional shape of a rectangle, sawtooth, staircase, or the like by a technique such as photolithography or etching. By filling the space between the gratings with an optically isotropic adhesive 505, a polarization selective diffraction function can be realized.
[0061]
  The cross-sectional shape is determined from the difference between the wavelength of light to be diffracted and the target diffraction efficiency, the ordinary / abnormal light refractive index of the polymer liquid crystal, and the refractive index of the filling adhesive. As the filling adhesive 505, for example, when a diffraction function is required to linearly transmit linearly polarized light that is incident on ordinary light and diffracts linearly polarized light that is incident on extraordinary light, the refractive index of the cured adhesive has a high molecular weight. It is preferable to select a liquid crystal whose refractive index is approximately equal to the ordinary light refractive index because a desired diffraction function can be exhibited. On the other hand, if a filler having a refractive index after curing that is approximately equal to the extraordinary light refractive index of the polymer liquid crystal is selected, the linearly polarized light incident as extraordinary light is transmitted straight, and the linearly polarized light incident as ordinary light is diffracted. Can be equipped with functions.
[0062]
  The wavelength λ incident as ordinary light on the thus configured phase shifter 5121The linearly polarized light is transmitted through the polarization-selective diffraction element 506 without being diffracted in both the forward path and the backward path, and the wavelength λ is incident as ordinary light.2The linearly polarized light passes through the phase shifter 502 without being diffracted by the diffraction element 506 in the forward path and becomes circularly polarized light, and enters the diffraction element 506 as extraordinary light in the return path. Therefore, the phase shifter 512 has a function of a wavelength selective diffraction grating. Here, the same effects can be obtained even when the two-wavelength phase shifter 511 and the polarization selective diffraction grating 506 are not integrated but arranged in series.
[0063]
  In the phase shifter 512 having a wavelength-selective diffraction function, the polarization state can be accurately controlled with respect to light of two wavelengths by using the above-described two-wavelength phase shifter 511. Stable performance can be obtained.
[0064]
【Example】
"Example 1"
  This example is a specific example of the three-wavelength compatible optical head device equipped with the two-wavelength phase shifter 410 for wavelengths 660 nm and 785 nm shown in FIG.
[0065]
  First, the two-wavelength phase shifter 410 was produced as follows.
  An organic thin film, which is a birefringent plate 401 obtained by stretching polycarbonate to develop birefringence, is fixed to a transparent substrate 403 having a refractive index of about 1.5 with a polyester UV curable adhesive (see FIG. 4). ). The retardation value of the organic thin film is 660 nm for light in the 660 nm wavelength band for DVD optical disks, and 627 (= 660 × 0.95) nm for light in the 785 nm wavelength band for CD optical disks. there were.
[0066]
  Subsequently, a polyimide for alignment film is applied to a transparent substrate 404 made of the same material as that of the transparent substrate 403, and after a desired alignment treatment, a solution of a liquid crystal monomer that is a birefringent material is applied. The birefringent plate 402 was formed as a polymer liquid crystal film by polymerizing the liquid crystal monomer by irradiating UV light. The retardation value R of this polymer liquid crystal film is 1230 nm for light in the 660 nm wavelength band for DVD optical disks, and 1257 (= 660 × 2 × 0 for light in the 785 nm wavelength band for CD optical disks. .95).
[0067]
  Furthermore, the organic substance thin film and the polymer liquid crystal film were bonded using a polyester-based UV curable adhesive to produce a phaser 410 as shown in FIG. At this time, the angle of the optical axis of the birefringent plate 402 (polymer liquid crystal film) with respect to the optical axis of the birefringent plate 401 (organic thin film) was fixed to 32 °.
[0068]
  In the optical head device shown in FIG. 5 on which the phase shifter 410 manufactured as described above is mounted, the semiconductor lasers 411A, 411B, and 411C are 785 nm wavelength band for the CD system, 660 nm wavelength band for the DVD system, and the next generation. It is a laser that oscillates light in the 410 nm wavelength band for optical disks, and is installed so that the polarization directions of the respective linearly polarized light are parallel. In the phase shifter 410, light in both wavelength bands is vertically incident from the birefringent plate 401 side between the polarization beam splitters 413 and 414 in the optical path shared by the two linearly polarized lights in the 660 nm wavelength band and the 785 nm wavelength band. Arranged. At this time, by adjusting the optical axis of the birefringent plate 401 to form an angle of 18 ° with respect to the polarization direction of the linearly polarized light, the polarization direction of the linearly polarized light in the 785 nm wavelength band is maintained while maintaining the linearity substantially. It was possible to rotate about 90 °.
[0069]
  Alternatively, the phase shifter 410 may be arranged so that light enters from the birefringent plate 402 side, and adjusted so that the optical axis of the birefringent plate 402 forms an angle of −50 ° with respect to the polarization direction of linearly polarized light. The same effect could be obtained. Here, with respect to the angle, the left-handed rotation was positive and the right-handed rotation was negative, as viewed from the side of the semiconductor laser that oscillates incident light.
[0070]
  In the optical head device of this example, it was possible to record and reproduce information on the optical disc more stably by mounting the phaser 410 composed of two birefringent plates having different optical axes. Further, the use of a wavelength selective beam splitter can be reduced to one, and a polarizing beam splitter can be used. Furthermore, since one photodetector can be used for light of two wavelengths, the apparatus can be reduced in size and cost. We were able to reduce.
[0071]
【The invention's effect】
  The phaser mounted on the optical head device of the present invention transmits light of one wavelength with little change in the polarization state with respect to light of two or more incident wavelengths, and the light of other wavelengths. Can be transmitted with the polarization state changed. For example, when two linearly polarized lights having different wavelengths are incident on the phase shifter, only one light can be emitted with its polarization direction rotated. Alternatively, only one light can be changed to circularly polarized light and emitted. In particular, for the desired effect, even if the characteristics of the birefringent plate used in the phase shifter cannot be obtained by adjusting the retardation value of the birefringent plate by appropriately selecting the optical axes at which the two birefringent plates intersect, A phaser having sufficient characteristics can be realized.
[0072]
  Further, in the three-wavelength compatible optical head device of the present invention, by mounting a phaser that transmits light in the 660 nm wavelength band almost as it is and rotates by rotating the polarization direction of linearly polarized light in the 785 nm wavelength band by 90 °, The loss of light output can be suppressed, and stable information recording and reproduction can be performed.
[Brief description of the drawings]
FIG. 1 is a conceptual cross-sectional view showing an example of the configuration of an optical head device of the present invention.
2A and 2B are cross-sectional views showing a configuration example of a phase shifter in the optical head device of the present invention, in which FIG. 2A is a view in which only two birefringent plates 201 and 202 are laminated, and FIG. The transparent substrate 213 is bonded to one side of the two birefringent plates 201 and 202, and (c) shows the birefringent plates 201 and 202 sandwiched between the two transparent substrates 203 and 204.
FIG. 3 is a conceptual diagram showing an optical axis direction of two birefringent plates constituting a phase shifter in the optical head device of the present invention.
FIG. 4 shows two different wavelengths λ in the phaser of the present invention.1, Λ2Sectional drawing which shows the mode of a change of a polarization state when the linearly polarized light of this transmits.
FIG. 5 is a conceptual cross-sectional view showing another example of the configuration of the optical head device of the present invention.
FIG. 6 shows another example of the phase shifter according to the present invention.1Sectional drawing which shows a mode that a polarization state does not change, when linearly polarized light of this goes back and forth.
7 shows a wavelength λ in the phaser shown in FIG.2Sectional drawing which shows the mode of the change of a polarization state (linearly polarized light and circularly polarized light) which arises when this linearly polarized light reciprocates.
[Explanation of symbols]
101, 102, 201, 202, 401, 402, 501, 502: birefringent plate
103: Phaser
104: Light source unit, 105, 419: Objective lens
106, 420: Optical disc
203, 204, 403, 404, 503, 504: Transparent substrate
410, 511: Two-wavelength phase shifter
411A, 411B, 411C: Semiconductor laser
412:λ / 2Board
413, 414, 416: Polarizing beam splitter
415: Broadband λ / 4 plate
417: For 410nm wavelength bandλ / 4Board,
418: Wavelength selective beam splitter
421, 422: photodetectors,
505: Filling adhesive,
506: Diffraction element
512: Phaser

Claims (6)

  1. A plurality of light sources respectively emitting at least two different wavelengths of light;
    An objective lens for condensing light emitted from the light source to the optical disk,
    In the optical head device and an optical detector for detecting light reflected by the condenser has been said optical disk,
    At least the optical path of the two light share between a plurality of the light source and the optical disk, the phase shifter has been established composed of respective optical axis directions are different two birefringent plates,
    Wavelength lambda 1 and wavelength of the two lights, when the wavelength lambda 2, the phase shifter is a phase difference between two of said birefringent plate with respect to the wave length lambda 1 of the light each natural pre KIHA length lambda 1 a few times, before the phase shifter against KIHA length lambda 1 of the light without changing the polarization state, the light of the wavelength lambda 2 incident on the phase shifter as linearly polarized light, linearly the phase shifter Transmitted as polarized light, the polarization direction of the transmitted light is at an angle of φ with respect to the polarization direction of the incident light,
    The phase differences R 1 and R 2 of the birefringent plates are equal to the light of the wavelength λ 2 of the two birefringent plates constituting the phase shifter , and the optical axes of the two birefringent plates are the same. direction, the wavelength lambda 2 of an angle of polarization direction and theta 1 and theta 2 of the incident light, the theta 1 and the sum of the theta 2 is an optical head device that has become the phi.
  2. A plurality of light sources respectively emitting at least two different wavelengths of light;
    An objective lens for condensing the light emitted from the light source onto the optical disc;
    In an optical head device comprising a photodetector for detecting light that has been collected and reflected by the optical disc,
    In an optical path shared by at least the two lights between the plurality of light sources and the optical disc, a phaser composed of two birefringent plates having different optical axis directions is installed,
    Wherein the wavelength lambda 1 and wavelength of the two light, when the wavelength lambda 2, the phase shifter is a phase difference between two of said birefringent plate with respect to the wavelength lambda 1 of light in each natural number times the wavelength lambda 1 The phase shifter does not change the polarization state with respect to the light of the wavelength λ 1, and the light of the wavelength λ 2 incident on the phase shifter as linearly polarized light is transmitted through the phase shifter as linearly polarized light, The polarization direction of the transmitted light forms an angle of 90 ° with respect to the polarization direction of the incident light,
    Wherein each of the phase difference between two of the birefringent plate with respect to the wavelength lambda 1 of the light is the lambda 1 and 2 [lambda] 1, and enters the optical axis of the birefringent plate phase difference is 2 [lambda] 1 is the wavelength lambda 2 the optical head device from 35 ° to the polarization direction of the light that has an angle of up to 55 °.
  3. A plurality of light sources respectively emitting at least two different wavelengths of light;
    An objective lens for condensing the light emitted from the light source onto the optical disc;
    In an optical head device comprising a photodetector for detecting light that has been collected and reflected by the optical disc,
    In an optical path shared by at least the two lights between the plurality of light sources and the optical disc, a phaser composed of two birefringent plates having different optical axis directions is installed,
    Wherein the wavelength lambda 1 and wavelength of the two light, when the wavelength lambda 2, the phase shifter is a phase difference between two of said birefringent plate with respect to the wavelength lambda 1 of light in each natural number times the wavelength lambda 1 The phase shifter does not change the polarization state with respect to the light of the wavelength λ 1, and the light of the wavelength λ 2 incident on the phase shifter as linearly polarized light is emitted as circularly polarized light,
    The retardation is equal lambda 1, and the optical axis direction the polarization direction of the wavelength lambda 2 of the light incident on the birefringent plate on the exit side of light of the two said birefringent plate with respect to the wavelength lambda 1 of the light the optical head device that has an angle of up to 60 ° from 40 ° to.
  4. The wavelength λ incident on the phaser 1 And the wavelength λ 2 The optical head device according to claim 1, wherein the light beams are light beams in a 660 nm wavelength band and a 785 nm wavelength band, respectively.
  5. The light of wavelength lambda 1 and the wavelength lambda 2 you entering the retarder is light, respectively 660nm wavelength band and 785nm wavelength band, for two of the 660nm wavelength band and 785nm waveband light birefringent plate 4. The optical head device according to claim 2 , wherein the ratio of retardation values is a value from 0.9 to 0.99.
  6. Two said birefringent plate, the optical head device according to claim 1 which is stuck integrally to 5 any one.
JP2003090249A 2003-03-28 2003-03-28 Optical head device Expired - Fee Related JP4218393B2 (en)

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JP2008524773A (en) * 2004-12-16 2008-07-10 カラーリンク・インコーポレイテッドColorlink, Inc. Composite quarter wave plate for optical disk pickup head
KR100603770B1 (en) * 2005-02-03 2006-07-24 삼성전자주식회사 Compatible optical pickup
JP5056059B2 (en) * 2006-02-21 2012-10-24 旭硝子株式会社 Broadband wave plate
JP5083014B2 (en) * 2008-04-21 2012-11-28 旭硝子株式会社 Broadband wave plate and optical head device
JP5251671B2 (en) * 2009-03-30 2013-07-31 セイコーエプソン株式会社 Laminated half-wave plate, optical pickup device, polarization conversion element, and projection display device
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JP2001311821A (en) * 2000-04-27 2001-11-09 Asahi Glass Co Ltd Phase shifter and optical head device
JP4649748B2 (en) * 2001-02-22 2011-03-16 旭硝子株式会社 Two-wavelength phase plate and optical head device
JP2003037326A (en) * 2001-05-17 2003-02-07 Nippon Electric Glass Co Ltd Cap for semiconductor laser
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