JP2010267337A - Laminated phase plate and optical head device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laminated phase plate compatible with three wavelengths including only one wavelength allowing a polarization angle to rotate. <P>SOLUTION: First, second and third phase plates are disposed in optical paths of three mutually different wavelengths. Combinations of angles of a fast axis of the first phase plate, a fast axis of the second phase plate and a fast axis of the third phase plate to a linear polarization direction of a wavelength λ1, or the combinations of the angles of a slow axis of the first phase plate, a slow axis of the second phase plate and a slow axis of the third phase plate to the linear polarization direction of the wavelength λ1, are θ1, θ2 and θ3, respectively. Retardation values of the first, second and third phase plates at the wavelength λ1 are approximately (m1-1/2)λ1, (m2-1/2)λ1 and (m3-1/2)λ1 (m1, m2 and m3 are natural numbers), respectively. When three linearly polarized wavelengths in an identical direction are made incident, the rotation angle of output light having the wavelength λ1 in a polarization direction is 2×(θ3-θ2+θ1), and the long axes of polarization of the output light having the wavelength λ2 and the wavelength λ3 are -10° or greater and +10° or smaller. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a laminated phase plate and an optical head device.

  Optical discs such as DVDs and CDs and high-density information recording optical discs BD (Blu-ray Discs) exist as optical recording media, and optical recording is performed to record information on these optical discs and to reproduce recorded information. A head device is used.

  As such an optical head device, there is an optical head device corresponding to a plurality of light sources. For this reason, as a phase plate used in an optical path common to a plurality of lights having different wavelengths, for example, a 650 nm wavelength corresponding to a DVD A phase difference of 2π × (m1−1 / 2) (m1 is a natural number) occurs for the band, and a phase difference of 2π × m2 (m2 is a natural number) corresponds to the 790 nm wavelength band corresponding to the CD. A phase plate made of an organic thin film is disclosed (for example, Patent Document 1).

  Such a phase plate forms a phase difference by forming a birefringent film by stretching a polycarbonate film. The phase difference with respect to incident light having a wavelength of 650 nm is 5π and the wavelength is 790 nm. The phase difference with respect to the incident light is approximately 4π. In this phase plate, when linearly polarized 650 nm light and 790 nm light having an angle of 45 ° with respect to the optical axis (fast axis or slow axis) of the phase plate are incident, the wavelength is 650 nm. The light is linearly polarized light whose rotation direction is rotated by 90 ° with respect to the incident light, but the light having a wavelength of 790 nm is linearly polarized light having the same polarization direction as that of the incident light.

  Further, in Patent Document 2, the first intermediate phase difference half-wave plate and the second intermediate phase difference half-wave plate are made of a transparent adhesive so that the optical axis direction becomes a desired angle. A bonded broadband half-wave plate is described. This wideband half-wave plate is, for example, for the light of the 405 nm wavelength band corresponding to BD, the light of 660 nm wavelength band corresponding to DVD, and the light of 785 nm wavelength band corresponding to CD. The rotation angle can be made the same.

JP 2001-290017 A JP 2006-155743 A

  By the way, as an optical head device corresponding to light of a plurality of wavelengths, for example, in an optical head device corresponding to light of three wavelengths, the polarization direction of only one wavelength of the three wavelengths is rotated, and the remaining 2 If it is possible to obtain a phase plate that does not change the polarization direction for light of one wavelength, the number of optical components used in the optical head device corresponding to light of three wavelengths having various configurations can be reduced. Therefore, the optical head device can be reduced in size.

  The present invention has been made in view of the above, and a laminated phase in which only one wavelength of light of three wavelengths is rotated in the polarization direction, and the polarization direction of the remaining two wavelengths of light is hardly changed. An object of the present invention is to provide an optical head device that can be miniaturized using the laminated phase plate.

The laminated phase plate of the present invention is used in an optical path of light of wavelength λ ₁ , light of wavelength λ ₂ , and light of wavelength λ ₃ , and includes a first phase plate, a second phase plate, 3 phase plates are arranged, and the fast axis of the first phase plate, the fast axis of the second phase plate, the fast axis of the third phase plate with respect to the direction of linearly polarized light of the wavelength λ ₁ A combination of an angle with a fast axis, or a slow axis of the first phase plate, a slow axis of the second phase plate, a slow axis of the third phase plate with respect to the direction of linearly polarized light of the wavelength λ ₁ Combinations of angles with the slow axis are θ ₁ , θ ₂ , and θ ₃ , respectively, and the first phase plate, the second phase plate, and the third phase plate are light having the wavelength λ ₁ . Are substantially (m ₁ -1/2) λ ₁ , substantially (m ₂ -1/2) λ ₁ , and (m ₃ -1/2) λ ₁ (m ₁ , m ₂ , m ₃ Natural number), if made incident said for the wavelength lambda ₁ of light and the wavelength lambda ₂ of the light and the wavelength lambda ₃ of the light in the same direction of linearly polarized light, the polarization direction of the incident light in the wavelength lambda ₁ of the light The rotation angle α expressed by the polarization direction of the emitted light with respect to is α = 2 × (θ ₃ −θ ₂ + θ ₁ ), and the polarization of the emitted light with respect to the incident light in the light of the wavelength λ _{2 and} the light of the wavelength λ ₃ The major axis direction of is -10 ° or more and + 10 ° or less.

In the present invention, the wavelength λ ₁ is 395 nm ≦ λ ₁ ≦ 415 nm, the wavelength λ ₂ is 645 nm ≦ λ ₂ ≦ 675 nm, and the wavelength λ ₃ is 765 nm ≦ λ ₃ ≦ 805 nm. It is characterized by that.

In the present invention, the angle θ ₁ is (α / 5) −2 ° ≦ θ ₁ ≦ (α / 5) + 2 °, and the angle θ ₂ is − (α / 10) −2 ° ≦. θ ₂ ≦ − (α / 10) + 2 °, and the angle θ ₃ is (α / 5) −2 ° ≦ θ ₃ ≦ (α / 5) + 2 °.

Further, the present invention provides an optical head device for recording or reproducing information in an optical disk information recording layer is provided, the wavelength lambda ₁ of the light, the wavelength lambda ₂ light and the wavelength lambda ₃ of the light A laser light source that emits light, an objective lens that condenses the light emitted from the laser light source, a photodetector, and a polarization beam splitter that deflects and separates the light in the direction of the optical disc and the direction of the photodetector. The light of wavelength λ ₁ emitted from the laser light source is linearly polarized light, and the light of wavelength λ _{2 and} the light of wavelength λ ₃ emitted from the laser light source are straight lines of the wavelength λ ₁ . The laminated phase plate described above is provided in the optical path between the laser light source and the objective lens, which is linearly polarized light in a direction different from the polarization direction.

Further, the invention is characterized in that the light of wavelength λ _{2 and} the light of wavelength λ ₃ emitted from the laser light source are linearly polarized light in a direction orthogonal to the linear polarization direction of the wavelength λ _1. And

  According to the present invention, it is possible to provide a laminated phase plate that rotates the polarization direction of only one wavelength of light of three wavelengths and hardly changes the polarization direction of the remaining two wavelengths of light. An optical head device that can be miniaturized can be provided.

Configuration diagram of laminated phase plate according to the first embodiment Explanatory drawing of the laminated phase plate in 1st Embodiment Configuration of another laminated phase plate according to the first embodiment (1) Configuration of another laminated phase plate according to the first embodiment (2) Sectional drawing of the optical head apparatus in 2nd Embodiment

  The form for implementing this invention is demonstrated below.

[Embodiment related to laminated phase plate]
An embodiment relating to a laminated phase plate will be described. The laminated phase plate in the present embodiment is a phase plate used in an optical head device corresponding to three wavelengths.

The optical head device using the laminated phase plate in this embodiment includes a semiconductor laser that emits light of 395 to 415 nm having a wavelength λ ₁ corresponding to BD, and light of 645 to 675 nm that is wavelength λ ₂ corresponding to DVD. a semiconductor laser that emits, and a semiconductor laser that emits light of 765~805nm is the wavelength lambda ₃ corresponding to CD. Each semiconductor laser emits light corresponding to BD, DVD, and CD optical disks. In such an optical head device corresponding to three wavelengths, one or two semiconductor lasers including semiconductor lasers that emit light of a plurality of wavelengths are used (hybrid type, monolithic type two-wavelength light emitting semiconductor lasers or 3 (Wavelength-emitting semiconductor laser), light of different wavelengths follows substantially the same optical path. Therefore, in the optical head device corresponding to the three wavelengths, the number of components of the optical element can be reduced by using the optical element that can be shared in the optical path of the two-wavelength light or the three-wavelength light. Miniaturization and cost reduction can be realized.

  The laminated phase plate according to the present embodiment will be described with reference to FIGS. FIG. 1 is a cross-sectional view of a laminated phase plate, and FIG. 2 is a plan view showing the relationship between the incident polarization direction and the optical axis of each phase plate as seen from the planar direction of the laminated phase plate. The laminated phase plate 10 in the present embodiment is obtained by laminating a first phase plate 11, a second phase plate 12, and a third phase plate 13. The laminated phase plate 10 is not limited to the first phase plate 11 and the second phase plate 12, and the second phase plate 12 and the third phase plate are not adjacent to each other. It may have a structure in which an adhesive layer or a translucent substrate is sandwiched as a layer that does not emit refraction, or may be separated by an air layer (space). The first phase plate 11, the second phase plate 12, and the third phase plate 13 do not emit birefringence, such as an adhesive layer or a translucent substrate, respectively, and the refractive index is isotropic. It may be configured to include a layer of a material that becomes a property.

The optical axes of the first phase plate 11, the second phase plate 12, and the third phase plate 13 are aligned in a direction parallel to the plane of the phase plate. In addition, the optical axes are either a combination of fast axes or a combination of slow axes, but in the following description, unless there is a particular description, it is assumed that all are combinations of fast axes. In the XY plane of FIG. 2, the fast axis of the first phase plate 11 is θ ₁ and the fast axis of the second phase plate 12 is based on the X axis corresponding to the polarization direction of incident light described later. θ ₂ , the fast axis of the third phase plate 13 is θ ₃ . The first phase plate 11, the second phase plate 12, and the third phase plate 13 each have a retardation (birefringence phase difference) value (m ₁ −1/2) with respect to light having a wavelength λ _1. λ ₁ , (m ₂ −1/2) λ ₁ , and (m ₃ −1/2) λ ₁ . Note that m ₁ , m ₂ , and m ₃ are natural numbers. Regarding the sign of the angle, it is considered that the counterclockwise rotation is plus (+) and the clockwise rotation is minus (−) with reference to the X axis when viewed from the light emitting direction. The unit of angle is represented by [°] unless otherwise specified.

A case where linearly polarized light in the X direction having a wavelength λ ₁ is incident on the laminated phase plate 10 will be described. First, when linearly polarized light in the X direction having a wavelength λ ₁ is incident on the first phase plate 11, the first phase plate 11 functions as a ½ wavelength plate for the light having the wavelength λ ₁ . The light that has passed through one phase plate 11 becomes linearly polarized light having an angle of 2 × θ _{1 with} respect to the X axis. Next, when linearly polarized light having an angle of 2 × θ ₁ of wavelength λ ₁ is incident on the second phase plate 12, the second phase plate 12 becomes a half-wave plate with respect to the light of wavelength λ _1. In order to function, it becomes the light of the linearly polarized light which has the angle shown to (1) Formula with respect to an X-axis.

θ ₂ + (θ ₂ −2 × θ ₁ ) = 2 × (θ ₂ −θ ₁ ) (1)
Next, when linearly polarized light having a wavelength λ ₁ having an angle of the expression (1) with respect to the X axis is incident on the third phase plate 13, the third phase plate 13 is _{1 for} the light having the wavelength λ 1. Since it functions as a / 2 wavelength plate, it becomes linearly polarized light having an angle shown in equation (2) with respect to the X axis. Α ₁ is an angle formed by the direction of the linearly polarized light after passing through the laminated phase plate 10 with respect to the X axis, the linearly polarized light having the wavelength λ _{1 in} the X axis direction (for α ₁ , , And may be described as α).

α ₁ = θ ₃ + {θ ₃ −2 × (θ ₂ −θ ₁ )} = 2 × (θ ₃ −θ ₂ + θ ₁ ) (2)
Table 1 shows that the polarization states of the light of wavelength λ _{2 and} the light of wavelength λ ₃ after the linearly polarized light of wavelength λ ₂ and wavelength λ _{3 in} the X-axis direction pass through the laminated phase plate 10 hardly change. A combination of θ ₁ , θ _2, and θ ₃ is shown with respect to the angle α _{1 in} equation (2). Further, the major axis angle of the emitted light corresponds to an angle in a direction in which the amplitude of the electric field of the emitted light is the largest when the X-axis direction is taken as a reference. That is, if the outgoing light is linearly polarized light, this is the angle formed by the linearly polarized light direction with respect to the X-axis direction. If the outgoing light is elliptically polarized light, this corresponds to the angle formed by the major axis direction of the elliptically polarized light with respect to the X-axis direction. . Further, the major axis angle of the emitted light may be referred to as “azimuth angle”. Table 1 shows angles in the major axis direction (major axis angle of outgoing light) α ₂ and α ₃ , wavelength λ ₁ , wavelength λ _{2 with} respect to linearly polarized light in the X-axis direction at wavelengths λ ₂ and λ _3. The calculation results for the output light ellipticity and the output polarization intensity at the wavelength λ ₃ are shown.

The angles α ₂ and α ₃ are calculated by calculating the Stokes parameters of the emitted light using the Mueller matrix. Moreover, in this Embodiment, the material which comprises each phase plate is comprised with the material which has a polymer liquid crystal. Birefringent materials such as polymer liquid crystals have a wavelength dependency (wavelength dispersion) specific to the material in refractive index anisotropy Δn. Thus, in Table 1, with respect to the refractive index anisotropy [Delta] n at a wavelength _{λ 1 (λ 1), 0.85} × Δn (λ 1) the birefringence at wavelength lambda _2, the birefringence at the wavelength lambda ₃ 0. It is calculated as 82 × Δn (λ ₁ ). Further, the outgoing polarization intensity at the major axis angle α ₁ of the outgoing light of wavelength λ ₁ is calculated from the major axis angle of the outgoing light and the outgoing light ellipticity. Similarly, the outgoing polarization intensity in the X-axis direction of the outgoing light with the wavelengths λ ₂ and λ ₃ is calculated from the major axis angle of the outgoing light and the outgoing light ellipticity. Table 1 shows the calculation results of the output polarization intensity at the wavelengths λ ₁ , λ ₂ and λ ₃ . Since output polarization intensity of the wavelength lambda ₁ of the wavelength also the major axis angle alpha ₁ of any of the emitted light lambda ₂ and wavelength lambda ₃ is not less than 99%, emitted light having a wavelength of lambda ₂ and wavelength lambda ₃ is the same as the incident light The linearly polarized light in the X-axis direction is maintained.

表１に示されるように、波長λ_１が４０５ｎｍの光について、Ｘ軸方向の直線偏光の光を入射させた場合において、出射光のＸ軸に対する偏光角度を自由に変化させても、波長λ_２が６６０ｎｍ及び波長λ_３が７８５ｎｍの光については、出射光の楕円率が、０．１０以下で、出射光の長軸方向のＸ軸に対する角度は±６°以下となる積層位相板１０を得ることができる。

As shown in Table 1, when light having a wavelength λ ₁ of 405 nm is incident with linearly polarized light in the X-axis direction, the wavelength λ ₁ can be changed even if the polarization angle of the emitted light with respect to the X-axis is freely changed. For light having a wavelength ₂ of 660 nm and a wavelength λ ₃ of 785 nm, the laminated phase plate 10 has an ellipticity of the emitted light of 0.10 or less and the angle of the emitted light with respect to the X axis in the major axis direction is ± 6 ° or less. Obtainable.

From Table 1, the angle theta ₁ [°] is in the range of _{(α 1/5) -1 °} ≦ θ 1 ≦ (α 1/5) + 1 °, the angle theta ₂ [°] is - (alpha _{1/10) -1 ° ≦ θ} 2 ≦ - ( in the range of _{α 1/10) + 1 °} , the angle theta ₃ [°] _{is, (α 1/5) -1} ° ≦ θ 3 ≦ (α 1 / 5) It is within the range of + 1 °. Therefore, the angle theta _1, the angle theta ₂ and the angle theta _3, if in this range, for light having a wavelength lambda ₁ of the linearly polarized light, by changing the angle of the linearly polarized light, the wavelength lambda ₂ and wavelength lambda ₃ With respect to linearly polarized light, it is possible to obtain the laminated phase plate 10 that hardly changes the polarization state.

  Consider the case where the laminated phase plate 10 is used as an optical element in an optical head device for recording and reproducing optical disks. At this time, if the ellipticity of the light transmitted through the laminated phase plate 10 is 0.15 or less and the change of the polarization angle in the major axis direction is within ± 10 °, the state of the linearly polarized light as the incident light is maintained. The laminated phase plate 10 satisfies this condition.

Further, as shown in Table 1, since the absolute value of the angle in the major axis direction of the emitted light with respect to the X axis is 5.6 ° or less, if the change in angle is within an allowable range of ± 10 °, θ The range of ₁ , θ ₂ and θ ₃ is considered to be allowed to vary by about twice.

Therefore, theta ₁ [°] is located (α _1/5) to _{-2 ° ≦ θ 1 ≦ (α} 1/5) + 2 in the range of °, θ ₂ [°] is, - (α _1/10) -2 ° ≦ θ ₂ ≦ - in the range of _{(α 1/10) + 2} °, θ 3 [°] _{is, (α 1/5) -2} ° ≦ θ 3 ≦ (α 1/5) + 2 ° It is considered that the same effect can be obtained if the laminated phase plate is in the range of.

Note that the retardation values of the first phase plate 11, the second phase plate 12, and the third phase plate 13 are approximately (m ₁ −1/2) λ ₁ in the light of the wavelength λ _1. Any birefringent material can be used as long as it is (m ₂ -1/2) λ ₁ , which is approximately (m ₃ -1/2) λ ₁ (m ₁ , m ₂ , and m ₃ are natural numbers). There may be. For example, a birefringent crystal such as quartz or LiNbO _3, a birefringent film in which a film of polycarbonate or the like is stretched in one axial direction to develop birefringence, or a liquid crystal in which molecular orientation is aligned in one axial direction Alternatively, a polymer liquid crystal obtained by solidifying a liquid crystal monomer having uniform molecular orientation by polymerizing can be used. Further, a structural refractive index material that gives a fine structure shorter than the wavelength used for a homogeneous material having a different refractive index and expresses the polarization dependence of the optical path length may be used.

Also, so far the wavelength lambda ₁ of light, light of the wavelength lambda ₂ of the light and the wavelength lambda ₃ are all the incident light in the X axis direction of the linearly polarized light, optionally in the direction of the emitted wavelength lambda ₁ of the linearly polarized light Although the effect | action to adjust was demonstrated, it is not restricted to this. For example, the direction of the linearly polarized light having the wavelengths λ ₂ and λ ₃ is the same (X-axis direction), and the direction of the linearly polarized light having the wavelength λ ₁ is different from the X-axis direction and is incident on the laminated phase plate 10. It can also be used when adjusting the polarization direction of these three lights emitted from the laminated phase plate 10 to be aligned with the X-axis direction. In this case, it is possible to cope with any light having a wavelength λ ₁ incident in an arbitrary linearly polarized direction.

Next, FIG. 3 shows a laminated phase plate having another configuration in the present embodiment. The laminated phase plate 20 includes a first phase plate 31 in which a first birefringent material layer 22 having birefringence is formed on a translucent substrate 21 such as a glass substrate, and a translucent substrate 24. A second phase plate 32 in which a second birefringent material layer 25 having birefringence is formed, and a third birefringent material layer 27 having birefringence in the translucent substrate 28 are formed. The third phase plate 33 is laminated. The first phase plate 31, the second phase plate 32 and the third phase plate 33, the retardation value, there is to be a half wavelength relative to the wavelength lambda _1, fast axis light transmission Parallel to the surface of the conductive substrate and aligned in one direction. The first birefringent material layer 22, the second birefringent material layer 25, and the third birefringent material layer 27 may be formed with alignment films (not shown).

Next, the surface of the first birefringent material layer 22 in the first phase plate 31 and the surface of the translucent substrate 24 in the second phase plate 32 are bonded using a transparent optical adhesive. Are bonded together by forming. Further, the surface of the second birefringent material layer 25 in the second phase plate 32 and the surface of the third birefringent material layer 27 in the third phase plate 33 are made using a transparent optical adhesive. Bonding is performed by forming the adhesive layer 26. When the first phase plate 31, the second phase plate 32, and the third phase plate 33 are bonded, the angles of the respective fast axes become predetermined angles θ ₁ , θ ₂ , θ _3. To join. As a result, it is possible to obtain a laminated phase plate in which the polarization direction of the light having the wavelength λ ₁ is rotated by 90 °, but the polarization directions of the light having the wavelength λ _{2 and} the light having the wavelength λ ₃ are hardly changed.

  FIG. 4 shows a laminated phase plate of still another configuration in the present embodiment. This laminated phase plate 40 is formed on a first phase plate 51 and a first birefringent material layer 42 in which a first birefringent material layer 42 having birefringence is formed on a translucent substrate 41. A second phase plate 43 made of a second birefringent material layer and a third birefringent material layer 44 formed on the second phase plate 43 with a translucent substrate 46 and an adhesive layer 45 interposed therebetween. The The third phase plate is formed from the third birefringent material layer 44, the adhesive layer 45, and the translucent substrate 46.

Next, a method for manufacturing the first birefringent material layer 42, the second birefringent material layer (second phase plate) 43, and the third birefringent material layer 44 will be described. First, a liquid crystal monomer to which a photosensitive material having a photo-alignment function in which molecular alignment is aligned with respect to the linear polarization direction of ultraviolet light is added, and the liquid crystal monomer is applied to the surface of the translucent substrate 41, and then the phase advancement is performed. The first birefringent material layer 42 is formed by polymerization and solidification using ultraviolet light having a predetermined linear polarization so that the angle of the axis becomes θ ₁ . Further, after applying the same liquid crystal monomer on the first birefringent material layer 42, the fast axis angle is polymerized and hardened by a second using ultraviolet light having a predetermined linear polarization to be a theta ₂ A birefringent material layer (second phase plate) 43 is formed. Further, after applying the same liquid crystal monomer on the second birefringent material layer 43, the fast axis angle theta ₃ and so as to polymerized and hardened with ultraviolet light of a predetermined linear polarization of the third A birefringent material layer 44 is formed.

Thereafter, the third birefringent material layer 44 and the translucent substrate 46 are bonded together by forming an adhesive layer 45 using a transparent optical adhesive. As a result, it is possible to obtain the laminated phase plate 40 in which the polarization direction of the light having the wavelength of λ ₁ is rotated by 90 °, but the polarization directions of the light having the wavelengths of λ ₂ and λ ₃ are hardly changed.

  The laminated phase plate 40 corresponding to the three wavelengths in the present embodiment rotates a predetermined angle in the direction of the linearly polarized light with respect to the light of one wavelength when the light having the three wavelengths of linearly polarized light is incident. A laminated phase plate that emits light with almost no change in polarization direction with respect to light of the other two wavelengths can be obtained by laminating three or more phase plates. Therefore, a laminated phase plate in which two phase plates are laminated cannot have such characteristics.

Table 2 considers the configuration of two phase plates for generating a function equivalent to that of the laminated phase plate of the present invention, in which the laminated phase plate is composed of two phase plates. At this time, similarly to the setting in Table 1 relating to the laminated phase plate according to the present invention, the three incident lights are considered as wavelength λ ₁ = 405 nm, wavelength λ ₂ = 660 nm, and wavelength λ ₃ = 785 nm. Table 2 shows a laminated phase plate in which a phase plate that rotates linearly polarized light in the X-axis direction by an angle θ ₁ and a phase plate that rotates an angle θ ₂ are stacked, and the wavelengths are λ ₁ = 405 nm, λ ₂ = The outgoing light ellipticity at 660 nm and λ ₃ = 785 nm and the major axis angle of the outgoing light are shown.

表２に示されるように、波長が４０５ｎｍの直線偏光の光に対して９０°回転させる場合には、波長が６６０ｎｍ及び７８５ｎｍの光においては、出射光の長軸角度（出射光のＸ軸に対する偏光状態の長軸方向の角度）は殆ど、１０°を超えて大きくなってしまう。また、出射光の長軸角度が比較的小さい場合であっても、出射光楕円率の値が高くなり、直線偏光の光又は直線偏光に近い光とはならない。従って、２枚の位相板を積層させた場合では、６６０ｎｍ及び７８５ｎｍの直線偏光の光は偏光状態を殆ど変化させることなく出射し、４０５ｎｍの直線偏光の光は９０°回転させることが可能な積層位相板を得ることはできない。

As shown in Table 2, when the light is rotated 90 ° with respect to linearly polarized light having a wavelength of 405 nm, the major axis angle of the emitted light (with respect to the X axis of the emitted light) with respect to the light having wavelengths of 660 nm and 785 nm. The angle in the major axis direction of the polarization state is almost larger than 10 °. Further, even when the major axis angle of the outgoing light is relatively small, the value of the outgoing light ellipticity is high and the light is not linearly polarized light or light that is close to linearly polarized light. Therefore, when two phase plates are laminated, 660 nm and 785 nm linearly polarized light is emitted with almost no change in polarization state, and 405 nm linearly polarized light can be rotated by 90 °. A phase plate cannot be obtained.

[Embodiment related to optical head device]
Next, this embodiment will be described. The optical head device in this embodiment uses the laminated phase plate in the embodiment relating to the laminated phase plate.

  The optical head device according to the present embodiment will be described with reference to FIG. The optical head device 100 according to the present embodiment includes a blue semiconductor laser light source 111, a diffraction grating 112, a two-wavelength semiconductor laser light source 113, a diffraction grating 114, a polarization beam splitter 115, a polarization beam splitter 116, a ¼ wavelength plate 117, and a collimator. The lens 118, the dichroic mirror 119, the mirror 120, the objective lens 121, the objective lens 122, the cylindrical lens 123, the optical receiver 124, and the laminated phase plate 10 according to the first embodiment are used. Recording and reproduction are performed. The blue semiconductor laser light source 111 and the two-wavelength semiconductor laser light source 113 are collectively referred to as a laser light source. The laser light source emits light of two wavelengths, light of three wavelengths from substantially the same light emitting point, or emits light of a single wavelength from three different light emitting points. May be.

Blue semiconductor laser light source 111 emits a blue laser light corresponding to the wavelength lambda ₁ of the BD. The emitted blue laser light generates 0th-order diffracted light (straight forward transmitted light) and ± 1st-order diffracted light for detection of the tracking servo signal by the diffraction grating 112. These lights are linearly polarized light in the Y-axis direction and are incident on the polarization beam splitter 115. In the polarization beam splitter 115, the linearly polarized light in the Y-axis direction is deflected by reflection and proceeds in the + Z-axis direction.

On the other hand, the two-wavelength semiconductor laser light source 113 emits laser light having a wavelength λ ₂ corresponding to DVD and laser light having a wavelength λ ₃ corresponding to CD. The light emitted from the two-wavelength semiconductor laser light source 113 generates 0th-order diffracted light (straight forward transmitted light) and ± 1st-order diffracted light for detection of the tracking servo signal by the diffraction grating 114. These lights are linearly polarized light in the X-axis direction and enter the polarization beam splitter 115, and the polarized beam splitter 115 transmits linearly polarized light in the X-axis direction and travels in the + Z-axis direction.

When the polarization state of the emitted light from the blue semiconductor laser light source 111 is linearly polarized light different from S-polarized light (for example, linearly polarized light in the Y-axis direction) with respect to the polarizing beam splitter 115, it is not shown in the diffraction grating 112. By combining the half-wave plates, the light with the wavelength λ ₁ can be adjusted to be S-polarized light, and the efficiency of the light reflected by the polarization beam splitter 115 can be increased. Similarly, when the polarization state of the light emitted from the two-wavelength semiconductor laser light source 113 is different from the P-polarized light (for example, linearly polarized light in the X-axis direction) with respect to the polarization beam splitter 115, the diffraction grating 114 does not show 1/2 By combining the wave plates, the light of wavelength λ _{2 and} the light of wavelength λ ₃ can both be adjusted to be P-polarized light, and the efficiency of the light transmitted through the polarization beam splitter 115 can be increased. . The polarizing beam splitter 115 is made of, for example, an optical glass processed into two right-angled isosceles triangular prisms, and is formed by laminating an optical multilayer film on the slope of one optical glass. Is available.

Each light emitted from the polarization beam splitter 115 enters the laminated phase plate 10. At this time, for example, the laminated phase plate 10 is configured under the conditions of the angles (θ ₁ , θ ₂ , θ ₃ ) shown in the last stage of Table 1 with reference to the X-axis direction, and further the light from the third phase plate 13 Is incident on the laminated phase plate 10, the light having the wavelength λ ₁ that is linearly polarized light in the Y-axis direction is emitted as light having a polarization state with the polarization axis rotated by 90 °, and the light having the wavelength λ ₂ and the wavelength λ The light ₃ is emitted as the light in the polarization state as it is. Thereby, the light of wavelength λ ₁ emitted from the polarization beam splitter 115 becomes linearly polarized light in the X axis direction, and the light of wavelength λ _{2 and} the light of wavelength λ ₃ become linearly polarized light in the X axis direction. As described above, the light having the wavelength λ ₁ , the light having the wavelength λ ₂ , and the light having the wavelength λ ₃ transmitted through the laminated phase plate 10 are all linearly polarized light in the X-axis direction. In the description of the present embodiment, the case where the laminated phase plate 10 described in the embodiment relating to the laminated phase plate is used has been described. However, the laminated phase plate 20 and the laminated phase plate 40 are also used in the same manner. Is possible.

The light having the wavelength λ ₁ , the light having the wavelength λ ₂ , and the light having the wavelength λ ₃ transmitted through the laminated phase plate 10 are linearly polarized light in the X-axis direction, and thus pass straight through the polarization beam splitter 116. Then, the light of wavelength λ _1, the light of wavelength λ ₂ , and the light of wavelength λ ₃ pass through a broadband quarter-wave plate 117 having a function as a quarter-wave plate in each wavelength light, After being converted into polarized light, it is converted into parallel light by the collimator lens 118 and is incident on the dichroic mirror 119 and the mirror 120. The dichroic mirror 119 has a characteristic of reflecting light of wavelength λ ₁ but transmitting light of wavelength λ ₂ and light of wavelength λ ₃ . Further, the mirror 120 has a characteristic of reflecting at least light having a wavelength λ ₂ and light having a wavelength λ ₃ .

Thereby, the light of wavelength λ ₁ reflected by the dichroic mirror 119 is condensed on the information recording surface of the optical disc 130 by the objective lens 121. The condensed light is reflected by the information recording surface, passes through the objective lens 121, is reflected by the dichroic mirror 119, passes through the collimator lens 118, and is further linearly polarized light in the Y-axis direction by the quarter wavelength plate 117. It becomes. Then, the light is deflected by reflection at the polarization beam splitter 116 and becomes light traveling in the + X-axis direction. After astigmatism is given by the cylindrical lens 123, the light is incident on the photodetector 124 and the optical disk 130 (in the case of BD). The signal recorded in is played back.

Further, the light of wavelength λ _{2 and} the light of wavelength λ ₃ reflected by the mirror 120 are collected on the information recording surface of the optical disc 130 by the objective lens 122. The condensed light is reflected by the information recording surface, passes through the objective lens 122, is reflected by the mirror 120, passes through the dichroic mirror 119 and the collimator lens 118, and is further straightened in the Y-axis direction by the quarter wavelength plate 117. It becomes polarized light. After being deflected by reflection in the polarizing beam spirit 116, astigmatism is given by the cylindrical lens 123, the signal incident on the optical detector 124 and recorded on the optical disk 130 (in the case of DVD or CD) is received. Played.

Incidentally, the polarization beam splitter 116, wavelength lambda ₁ of the light, to the wavelength lambda ₂ of the light and the wavelength lambda ₃ of the light transmits light in the X-axis direction of the linearly polarized light, the light of the Y-axis direction of the linearly polarized light It has the property of reflecting and deflecting. Further, when the optical disk 130 is a CD, the cover layer of the optical disk is thicker than the cover layer of the BD and DVD, so that the polarization state of the reflected light varies due to the birefringence of the cover layer. Cheap. Therefore, in order to obtain a stable signal intensity that does not depend on the birefringence of the cover layer, it is desirable that the beam splitter has little polarization dependency. For example, a beam splitter having a transmittance of 50% and a reflectance of 50% (no polarization dependence) is used for reproducing a CD, and a transmittance of 90% is used for recording a CD in order to suppress a reduction in the amount of light in the forward path. A beam splitter having a reflectance of 10% (no polarization dependence) may be used.

  The objective lenses 121 and 122 are mounted on an actuator (not shown), and the positions of the objective lenses 121 and 122 can be adjusted at high speed according to the focus servo signal and the tracking servo signal. Further, in order to correct the spherical aberration caused by the variation of the cover layer of each optical disc, the collimator lens 118 may be provided with a mechanism that moves in a direction parallel to the optical axis.

  As described above, in the present embodiment, an optical head device with a small number of parts can be obtained, so that the optical head device can be reduced in size.

  Moreover, although the form which concerns on implementation of this invention was demonstrated, the said content does not limit the content of invention.

DESCRIPTION OF SYMBOLS 10 Laminated phase plate 11 1st phase plate 12 2nd phase plate 13 3rd phase plate 100 Optical head apparatus 111 Blue semiconductor laser light source 112 Diffraction grating 113 Two wavelength semiconductor laser light source 114 Diffraction grating 115 Polarization beam splitter 116 Polarization beam Splitter 117 1/4 wavelength plate 118 Collimator lens 119 Dichroic mirror 120 Mirror 121 Objective lens 122 Objective lens 123 Cylindrical lens 124 Photo detector 130 Optical disc

Claims (5)

Used in the optical path of light of different wavelengths λ ₁ , light of wavelength λ ₂ and light of wavelength λ ₃ ,
A first phase plate, a second phase plate, and a third phase plate are disposed;
A combination of angles with the fast axis of the first phase plate, the fast axis of the second phase plate, the fast axis of the third phase plate with respect to the direction of linearly polarized light of the wavelength λ ₁ , or Combinations of angles with the slow axis of the first phase plate, the slow axis of the second phase plate, and the slow axis of the third phase plate with respect to the direction of linearly polarized light of the wavelength λ ₁ θ ₁ , θ ₂ , θ ₃ ,
In the first phase plate, the second phase plate, and the third phase plate, the retardation values in the light of the wavelength λ ₁ are approximately (m ₁ −1/2) λ ₁ , approximately (m ₂ − 1/2) λ ₁ , approximately (m ₃ -1/2) λ ₁ (m ₁ , m ₂ , m ₃ are natural numbers),
When linearly polarized light in the same direction is incident on the light of wavelength λ _1, the light of wavelength λ ₂ , and the light of wavelength λ ₃ , the outgoing light with respect to the polarization direction of incident light in the light of wavelength λ ₁ The rotation angle α expressed by the polarization direction of α is α = 2 × (θ ₃ −θ ₂ + θ ₁ ), and the major axis of the polarization of the outgoing light with respect to the incident light in the light of the wavelength λ _{2 and} the light of the wavelength λ ₃ A laminated phase plate having a direction of -10 ° or more and + 10 ° or less. The wavelength λ ₁ is 395 nm ≦ λ ₁ ≦ 415 nm,
The wavelength λ ₂ is 645 nm ≦ λ ₂ ≦ 675 nm,
The laminated phase plate according to claim 1, wherein the wavelength λ ₃ satisfies 765 nm ≦ λ ₃ ≦ 805 nm. The angle θ ₁ is (α / 5) −2 ° ≦ θ ₁ ≦ (α / 5) + 2 °,
The angle θ ₂ is − (α / 10) −2 ° ≦ θ ₂ ≦ − (α / 10) + 2 °,
The laminated phase plate according to claim 1, wherein the angle θ ₃ satisfies (α / 5) −2 ° ≦ θ ₃ ≦ (α / 5) + 2 °. An optical head device for recording or reproducing information on an optical disc provided with an information recording layer,
A laser light source that emits light of wavelength λ ₁ , light of wavelength λ ₂ , and light of wavelength λ ₃ ;
An objective lens for condensing the light emitted from the laser light source;
A photodetector;
A polarizing beam splitter that deflects and separates the light in the direction of the optical disc and the direction of the photodetector,
The light of wavelength λ ₁ emitted from the laser light source is linearly polarized light, and the light of wavelength λ _{2 and} the light of wavelength λ ₃ emitted from the laser light source have the linear polarization direction of the wavelength λ _1. Linearly polarized light in different directions,
An optical head device, wherein the laminated phase plate according to claim 1 is provided in an optical path between the laser light source and the objective lens. The light of wavelength λ _{2 and} the light of wavelength λ ₃ emitted from the laser light source are linearly polarized light in a direction orthogonal to the linear polarization direction of the wavelength λ _1. The optical head device described.

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