JP2011065175A - Wavelength plate and optical pickup device using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a half-wavelength plate in which two sheets of wavelength plates are pasted and temperature dependence of the phase difference of a plate is reduced. <P>SOLUTION: The wavelength plate becomes by pasting together a first wavelength plate having a phase difference τ<SB>1</SB>(deg) and an azimuth of an optical axis θ<SB>1</SB>(deg) and a second wavelength plate having a phase difference τ<SB>2</SB>(deg) and an azimuth of an optical axis θ<SB>2</SB>(deg). The first wavelength plate and the second wavelength plate are pasted to satisfy θ<SB>1</SB>=(90+θ/2)/2, θ<SB>2</SB>=θ<SB>1</SB>+90+θ/2, when the phase difference τ<SB>1</SB>(deg) of the first wavelength plate and that τ<SB>2</SB>(deg) of the second wavelength plate are taken as τ<SB>1</SB>=τ<SB>2</SB>=360n+180 (n=0, 1, 2, ...), and an angle between polarization faces of incoming light and outgoing light is taken as θ(deg). <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a wave plate used in an optical pickup device, and more particularly to a wave plate that compensates for temperature dependence of a phase difference.

  In recent years, with the spread of multimedia, it has become necessary to process a large amount of various information from characters to images and at high speed, and the storage capacity is markedly greater than that of conventional porcelain recording media despite its compact shape. The demand for optical disks such as CDs and DVDs that are large and capable of reading and writing at high speed is rapidly increasing. An optical pickup device is used as a device for reading digital signals such as audio and video written on the optical disc. The apparatus is structured to read a recording medium formed as irregularities (bits) on the surface by applying a laser beam onto the surface of the optical disk and picking up the reflected light. A wave plate used as an optical component of this optical pickup device has a function of changing the polarization state of light, and shifts the phase difference by 90 (deg) to convert linearly polarized light into circularly polarized light or circularly polarized light into linearly polarized light. There is a quarter wave plate or a half wave plate that rotates the plane of polarization of linearly polarized light by shifting the phase difference by 180 (deg). FIG. 5 shows the structure of the half-wave plate. When linearly polarized light enters the half-wave plate 11 and the angle between the incident polarization plane and the optical axis of the substrate is θ, the output is shown. The incident light becomes linearly polarized light rotated by 2θ with respect to the incident polarization plane.

  In the half-wave plate made of a crystal material such as quartz, in addition to the above-described half-wave plate made of a single plate, two half-wave plates are laminated to form a half-wave plate. is there. This is a half-wave plate that has a phase difference of 180 (deg) by laminating two wave plates, and has high incident angle dependency, although the cost is higher than that of a single plate structure. Can be realized. FIG. 6 shows the structure of a half-wave plate in which two wave plates are bonded together. Wave plate A has phase difference 1080 (deg) and optical axis azimuth angle 15 (deg), wave plate B has phase difference 900 (deg) and optical axis azimuth angle 105 (deg). The outgoing light polarization plane is rotated 30 (deg) by bonding the axes so that the angle formed by the axes is a right angle.

  The temperature dependence of the wave plate was examined. FIG. 7 is a diagram showing the temperature dependence of the retardation of the wave plate. The figure shows that the phase difference of the wave plate is 180 (deg) under the condition of room temperature of 25 ° C., but the phase difference changes from 180 (deg) when the temperature changes from room temperature. Thus, when the temperature dependence of the retardation of the wave plate is high, the phase difference of the emitted light changes depending on the temperature, and this phenomenon is not preferable in the optical pickup device. The present invention solves the above problems, and provides a wave plate in which two wave plates are bonded to each other, and a wave plate having a small phase difference in temperature dependence and an optical pickup device using the wave plate. With the goal.

In order to achieve the above object, the wave plate according to claim 1 of the present invention includes a first wave plate having a phase difference τ ₁ (deg) and an optical axis azimuth angle θ ₁ (deg), and the phase difference τ. ₂ (deg), and a second wave plate having _two optical axis azimuth angles θ ₂ (deg), and a phase difference τ ₁ (deg) of the _first wave plate and the second wave plate The phase difference τ ₂ (deg) of the wave plate is τ ₁ = τ ₂ = 360 n + 180 (n = 0, 1, 2,...), And the angle between the polarization planes of the incident light and the emitted light is θ (deg). Then, the first wave plate and the second wave plate are bonded to satisfy θ ₁ = (90 + θ / 2) / 2, θ ₂ = θ ₁ + 90 + θ / 2. . The invention according to claim 2 is the wave plate according to claim 1, wherein the first wave plate and the second wave plate are made of a quartz substrate. A third aspect of the present invention is an optical pickup device having the wave plate according to any one of the first and second aspects.

The schematic diagram of the optical pick-up apparatus which concerns on this invention is shown. It is the figure which showed the structure of the waveplate which concerns on this invention, (a) is a top view, (b) shows a side view. It shows a S ₁ -S ₂ plan view of the Poincare sphere showing the function of the wavelength plate according to the present invention. The relationship of the phase difference temperature dependence of the wavelength plate which concerns on this invention is shown. It is the figure which showed the structure of the wavelength plate of the conventional single plate structure. It is the figure which showed the structure of the conventional bonding type | mold wavelength plate, (a) is a top view, (b) shows a side view. The relationship of the retardation temperature dependence of the conventional bonding type | mold wavelength plate is shown.

  Hereinafter, the present invention will be described in detail based on the embodiments shown in the drawings. FIG. 1 is a schematic view of an optical pickup device according to the present invention. The light emitted from the semiconductor laser 1 is converted into parallel light by the collimator lens 2 and the polarization plane is rotated by the half-wave plate 3. The light that has passed through the half-wave plate 3 is incident on a polarizing beam splitter 4 that reflects almost S-polarized light and transmits almost P-polarized light. 6 is irradiated. The P-polarized light transmitted through the polarization beam splitter 4 is received by the light amount monitor 7. Further, the collimating lens 2 may be disposed after the polarization beam splitter 4.

  In the optical pickup device, the half-wave plate has a function of rotating the incident linearly polarized light and emitting light with a phase difference of 180 (deg). In the conventional wave plate, since the temperature dependence of the phase difference is high, the phase difference is shifted due to a temperature change, which has an adverse effect on the optical pickup device. In order to solve this problem, the present invention proposes a wave plate in which the temperature dependence of the phase difference is reduced.

Here, the wavelength plate according to the present invention will be described in detail. FIG. 2 shows a plan view and a side view of the wave plate according to the present invention, and a half-wave plate is formed by bonding two wave plates. Here, the optical axis azimuth angle of the wave plate A (first wave plate) is θ ₁ , the optical axis azimuth angle of the wave plate B (second wave plate) is θ ₂ , and the planes of polarization of incident light and outgoing light , And the phase differences τ ₁ , τ ₂ (deg) between the wave plate A and the wave plate B with respect to the wavelength of light τ ₁ = τ ₂ = 360 × n + 180 (n = 0, 1, 2,... ).

FIG. 3 shows the function of the wave plate expressed by the S ₁ -S ₂ plan view of the Poincare sphere. The optical axis azimuth angle of the wave plate A is θ ₁ , the optical axis azimuth angle of the wave plate B is θ ₂ , and the angle formed by the polarization plane of the incident light and the outgoing light is θ, and the actual angle on the Poincare sphere is I think twice. Further, the rotation axes R ₁ and R ₂ are taken at the positions rotated by 2θ ₁ and 2θ ₂ from the S ₁ axis, respectively rotated by the angles of the phase differences τ ₁ and τ ₂ , and the stopped positions indicate the polarization state of the emitted light. Represents. When passing through the wave plate A from the polarization state P _{0 of the} incident light, the phase changes to the polarization state of P ₁ by the rotation axis R ₁ , and when passing through the wave plate B, the phase changes to P ₂ by the rotation axis R _2. It shows how to do.

If the change in phase difference of the wave plate due to temperature change is Δ _T τ ₁ and Δ _T τ ₂ , the phase difference between the wave plate A and the wave plate B is set equal, so Δ _T τ ₁ = Δ _T τ ₂ Become. Furthermore, cos _T tau ₁ in the Poincare sphere the rotation axis R _1, the rotational angles, respectively delta _T tau ₁ of R _2, Δ _T τ ₂ varies with temperature change, the cos _T tau _2. Wherein each .DELTA.k ₁ a value converted to the length of the phase difference changes due to temperature P ₀ P ₁ and P ₁ P _2, when the _{Δk 2, Δk 1 = P 0} P 1/2 × (1-cosΔ T tau _1), it is expressed as _{Δk 2 = P 1 P 2/} 2 × (1-cosΔ T τ 2).

The temperature dependence which is the subject of the present invention occurs because the refractive index of the birefringent material changes with temperature. If Δk ₁ = Δk ₂ , the temperature dependence is canceled by the wave plates A and B. Therefore, in order to set Δk ₁ = Δk ₂ , the rotation axes R ₁ and R ₂ are positioned so that P ₀ P ₁ = P ₁ P ₂ , that is, the optical axis azimuth θ ₁ between the wave plate A and the wave plate B. , Θ ₂ must be set. Therefore, the inventors of the present invention set the optical axis azimuth θ ₁ (deg) of the wave plate A to θ ₁ = (90 + θ / 2) / 2, and the optical axis azimuth θ ₂ (deg) of the wave plate B to θ ₂ = θ. By setting ₁ + 90 + θ / 2, it was found that P ₀ P ₁ = P ₁ P ₂ , that is, Δk ₁ = Δk ₂ , and thought that the temperature dependence of the phase difference could be offset.

FIG. 4 is a diagram showing the temperature dependence of the phase difference in a half-wave plate in which two wave plates according to the present invention are bonded together. Design conditions waveplate, a phase difference tau ₂ retardation tau ₁ and the wavelength plate B wave plate A was equal to 900 (deg), the angle theta = 30 of the plane of polarization of the incident light and the outgoing light (deg ) So that the optical axis azimuth angle θ ₁ of the wave plate A is θ ₁ = (90 + θ / 2) / 2 to 52.5 (deg), and the optical axis azimuth angle θ ₂ of the wave plate B is θ ₂ = θ ₁ + 90 + θ / 2 to 157.5 (deg). FIG. 4 shows that the phase difference of the wave plate hardly changes even when the temperature changes from room temperature 25 ° C., and it is possible to realize a wave plate having a small temperature dependency of the phase difference.

As described above, the present invention is in the half-wave plate by bonding two wave plate, a phase difference tau ₁ wavelength plate A (deg) and the phase difference tau ₂ wavelength plate B (deg) τ ₁ = τ ₂ = 360 × n + 180 (n = 0, 1, 2,...), the optical axis azimuth θ ₁ (deg) of the wave plate A is θ ₁ = (90 + θ / 2) / 2, and the optical of the wave plate B If the axial azimuth angle θ ₂ (deg) is θ ₂ = θ ₁ + 90 + θ / 2, the temperature dependence of the phase difference can be reduced, and a stable phase difference independent of temperature can be obtained.

(The invention's effect)
As described above, according to the present invention, since the temperature dependence of the phase difference is reduced in the wave plate in which two wave plates are bonded, the phase difference of the emitted light is stabilized regardless of the temperature, and the optical pickup device And excellent effects in optical communication equipment.

  DESCRIPTION OF SYMBOLS 1 ... Semiconductor laser 2 ... Collimating lens 3 ... 1/2 wavelength plate 4 ... Polarizing beam splitter 5 ... Objective lens 6 ... Optical disk 7 ... Light quantity monitor.

Claims (3)

A first wave plate having a phase difference τ ₁ (deg) and an optical axis azimuth angle θ ₁ (deg), and a second wave plate having a phase difference τ ₂ (deg) and an optical axis azimuth angle θ ₂ (deg) In a wave plate formed by bonding two sheets of
The phase difference τ ₁ (deg) of the first wave plate and the phase difference τ ₂ (deg) of the second wave plate are τ ₁ = τ ₂ = 360 n + 180 (n = 0, 1, 2,...) And incident. Assuming that the angle between the polarization planes of the light and the outgoing light is θ (deg), the first wave plate and the first wave plate satisfy the following condition: θ ₁ = (90 + θ / 2) / 2, θ ₂ = θ ₁ + 90 + θ / 2 2. A wave plate obtained by bonding two wave plates.   2. The wave plate according to claim 1, wherein the first wave plate and the second wave plate are made of a quartz substrate.   The optical pick-up apparatus which has a wave plate as described in any one of Claim 1 and 2.

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