JP2006073116A - Optical path correcting device and optical pickup using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To make a predetermined quantity of two wavelength laser beams stably incident to a monitoring photo-detector 13, and to make a monitoring light quantity easily changeable when the light quantity is desired to change. <P>SOLUTION: The light path correction device 18 is provided with a 1st wavelength plate 5, a birefringent plate 2, a 2nd wavelength plate 16, and a rotatory polarizer 19, and is arranged in front of the two wavelength laser beams 6. The 1st wavelength plate 5 rotates the direction of polarization of only one laser beam L2 emitted from the two wavelength laser 6 by 90 degrees, and forms the laser beams L1, L2 to have the directions of polarization perpendicular to each other. The birefringent plate 2 is arranged so that the optical axis thereof coincides with the direction of polarization of one laser beam L2, and operates so that the laser beam L1 and the laser beam L2 are propagated in the same optical path. The 2nd wavelength plate 16 rotates the direction of polarization of only the other laser beam L1 passing through the birefringent plate 2 by 90 degrees, and forms the laser beams L1 and L2 to have the same direction of polarization. The rotatory polarizer 19 rotates the direction of polarization of linearly polarized light passing through the 2nd wavelength plate by a predetermined value. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an optical path correction device and an optical pickup using the same, and in particular, corrects optical paths of two different wavelengths of linearly polarized light that are parallel to each other and then propagates on the same optical path. The present invention relates to an optical path correction device capable of arbitrarily setting the amount of monitor light emitted and an optical pickup using the same.

Optical pickups used in optical disk devices and magneto-optical disk devices have a structure that uses a plurality of laser beams having different wavelengths in order to support different types of optical disks such as CDs and DVDs.
Therefore, conventionally, for example, in order to propagate two laser beams in the same optical path, two laser diodes (hereinafter referred to as LDs) are arranged so that the optical paths are orthogonal to each other, and a dichroic prism is arranged at the intersection in a predetermined optical path direction. The laser light emitted from one LD is incident on the dichroic prism and transmitted through the separation surface, and the laser light emitted from the other LD arranged orthogonally is incident on the dichroic prism and is 90 ° on the separation surface. By reflecting the two laser beams, the two laser beams are propagated in the same optical path, and an optical pickup corresponding to the two laser beams is configured.
However, in such a conventional two-wavelength synthesizing method, it is difficult to reduce the size of the optical pickup because two LDs are used and their optical paths must be arranged orthogonal to each other.

  On the other hand, in recent years, monolithically integrated two-wavelength lasers have been proposed and put into practical use. This two-wavelength laser is obtained by forming laser light sources having two different wavelengths (for example, 650 nm and 780 nm) on one semiconductor substrate, and the two laser light sources have a predetermined distance (several tens to hundreds of tens μm). Are spaced apart and emit parallel light of two different wavelengths. Therefore, in order to use such a two-wavelength laser for an optical pickup, an optical path correction function is required in order to propagate two laser beams to the same optical path.

As means for such an optical path correction function, there is a method disclosed in Japanese Patent Laid-Open No. 2001-283457.
FIG. 4 is a diagram for explaining the principle of an optical path correction device disclosed in Japanese Unexamined Patent Publication No. 2001-283457. In FIG. 4, the optical path correction device 1 is constituted by a birefringent plate 2, which is cut out in a plate shape so that the optical axis A ₀ forms an angle of 45 ° with the main surface. . The plane including the optical axes of the two laser beams of the laser beam L1 having a wavelength of 650 nm and the laser beam L2 having a wavelength of 780 nm emitted from the two-wavelength laser 3 is parallel to the polarization direction of the laser beam L1, and the polarization of the laser beam L2 The directions are assumed to be orthogonal.
Further, since the plane including the optical axes of the two incident laser beams is configured to be parallel to the optical axis A ₀ , the laser beam L 2 becomes an ordinary ray with respect to the optical axis A ₀ . Go straight through and see through. In contrast, so that the transmitted and refracted by the birefringent plate 2 the laser beam L1 becomes extraordinary light to the optical axis A _0. At this time, by appropriately setting the thickness t of the birefringent plate 2, two laser beams can be emitted on the same optical path.

  On the other hand, the conventional optical path correction method shown in FIG. 4 requires that the polarization directions of the two laser beams are orthogonal to each other. However, a monolithic integrated two-wavelength laser has two components on one semiconductor substrate. Since laser light sources having different wavelengths are formed, the polarization directions of the linearly polarized light of the two emitted laser beams are generally the same. Since the two-wavelength lasers are not easy to make the polarization directions orthogonal to each other due to restrictions on the manufacturing process and are unsuitable for mass production and expensive, it is practical to apply a monolithic integrated two-wavelength laser to the above optical path correction method. It was not right.

Therefore, as an optical path correction method for solving this point, the present inventors have proposed the following method in Japanese Patent Application No. 2003-155617.
FIG. 5 is a diagram for explaining the principle of the optical path correction device proposed by Japanese Patent Application No. 2003-155617. The optical path correction device 4 includes a wave plate 5 and a birefringent plate 2 and is disposed in front of the two-wavelength laser 6.
Laser light L1 having a wavelength of 650 nm and laser light L2 having a wavelength of 780 nm emitted from the two-wavelength laser 6 are linearly polarized light having polarization directions parallel to each other, and propagate in parallel at an optical path interval d.
The wave plate 5 is a crystal or polymer film having birefringence, and rotates the polarization direction of one laser beam L2 emitted from the two-wavelength laser 6 by 90 °, and rotates the polarization direction of the other laser beam L1. The laser beams L1 and L2 are configured to be linearly polarized light orthogonal to each other by being transmitted without being transmitted.

The birefringent plate 2 is the same as the birefringent plate shown in FIG. 4 and is made of a crystal or liquid crystal having birefringence, and its optical axis has the same plane as the polarization direction of one laser beam L1. Has been.
At this time, the laser beam L1 laser light L2 since the ordinary ray to the optical axis A ₀ which is transmitted through the birefringent plate 2 and goes straight, the laser beam L2 and the polarization directions are perpendicular to the incident wavelength plate 5 , will be transmitted is refracted because the extraordinary ray relative to the optical axis a ₀ of the birefringent plate 2. The thickness t of the birefringent plate 2 is set so that the refracted laser beam L1 propagates through the same optical path as the laser beam L2 when it exits the birefringent plate 2.
In this way, the wave plate 5 and the birefringent plate 2 cooperate to propagate in parallel at a predetermined optical path interval d and to propagate two laser beams having the same polarization direction on the same optical path. It becomes possible to do.
JP 2001-283457 A Japanese Patent Application No. 2003-155617

However, the conventional optical path correction device has the following problems when used for an optical pickup.
FIG. 6 is a schematic diagram when a conventional optical path correction apparatus using a two-wavelength laser is applied to an optical pickup. The optical pickup 7 includes a two-wavelength laser 6 that emits linearly polarized light having two different wavelengths whose polarization directions are parallel to each other, a wave plate 5 that rotates the polarization direction of one linearly polarized light by 90 °, and two linearly polarized lights. A birefringent plate 2 that corrects an optical path so as to propagate on the same optical path, a half mirror 8 that separates linearly polarized laser light transmitted through the birefringent plate 2 at a predetermined ratio, and the half mirror 8 is a separation surface An objective lens 11 for condensing the laser light reflected by 90 ° on the pit 10 formed on the optical disc 9, and the laser light reflected on the pit 10 via the objective lens 11 and the half mirror 8. It comprises a photodetector 12 for detection and a monitor photodetector 13 for monitoring the emission level of the two-wavelength laser 6 that passes through the separation surface of the half mirror 8.

  6 will be described. Laser light L1 having a wavelength of, for example, 650 nm or laser light L2 having a wavelength of 780 nm emitted from the two-wavelength laser 6 is linearly polarized light having a polarization direction parallel to each other. It propagates in parallel and enters the wave plate 5. The wave plate 5 rotates the linearly polarized light of one laser beam L2 emitted from the two-wavelength laser 6 by 90 ° and transmits the linearly polarized light of the other laser beam L1 without rotating, so that the laser beams L1 and L2 are transmitted. Are configured to have linearly polarized light orthogonal to each other. Next, laser light that passes through the wave plate 5 is incident on the birefringent plate 2. The birefringent plate 2 has birefringence, and its main cross section (a plane parallel to the plane including the optical axis and the incident optical axis) is orthogonal to the linearly polarized light of the laser beam L2 that has passed through the one wavelength plate 5. It is configured as follows. Therefore, since the laser beam L2 is orthogonal to the optical axis, it becomes an ordinary ray and travels straight through the birefringent plate 2, and the linearly polarized light of the laser beam L1 that has passed through the wavelength plate 5 is the linearly polarized light of the laser beam L2. Since they are orthogonal to each other, they are parallel to the main cross section of the birefringent plate 2 and thus become extraordinary rays that are refracted and transmitted. Therefore, the laser beam L1 and the laser beam L2 that have passed through the birefringent plate 2 propagate in the same optical path. At this time, the linearly polarized lights of the two laser beams transmitted through the birefringent plate 2 are orthogonal to each other, and they are collectively referred to as a laser beam L11.

  Next, the laser beam L11 that has passed through the birefringent plate 2 is incident on the half mirror 8, and about 90% of the laser beam L11 is reflected by 90 ° on the separation surface as the laser beam L12 that is about 10% of the laser beam L11. % Are separated as laser light L13 that passes through the separation surface. The laser beam L12 is collected by the objective lens 11 and applied to the pit 10 formed on the optical disk 9, and the laser beam L14 reflected on the pit 10 becomes reflected light and passes through the objective lens 11 to be a half mirror. 8, the laser beam L14 passes through as it is, enters the photodetector 12, and reads the information written on the optical disk.

  On the other hand, the laser light L13 transmitted through the half mirror 8 enters the monitor light detector 13 and monitors the emission level of the laser light emitted from the two-wavelength laser 6. In the optical pickup, it is necessary to keep the emission level of the laser beam emitted from the laser element constant. Therefore, a part of the laser beam is received by a monitor photodetector and an APC (Auto Power Control) circuit is received. By controlling the laser element drive circuit, the laser beam emission level is kept constant. The optical pickup shown in FIG. 6 employs a highly accurate front monitor system as means for monitoring the emission level of laser light.

  By the way, when the laser beam is received by the front monitor system as described above, the laser beam is composed of the laser beams of linearly polarized light L1 and L2 orthogonal to each other as described above, and therefore the half mirror 8 is, for example, 10%. When the laser beam is transmitted through the separation surface and is incident on the monitor light detector 13, the half mirror 8 has a wavelength dependence, and it is possible to set only one wavelength of laser light to a transmittance of 10%. Although relatively easy, it is quite difficult to set the two-wavelength laser light, which is linearly polarized light orthogonal to each other, to a transmittance of 10%. When an optical film is formed on the half mirror 8, a time-consuming process is required while adjusting the film thickness using a sputter deposition method or the like.

On the other hand, when it is desired to change the amount of light incident on the monitor light detector 13, it is necessary to take measures by changing the transmittance of the half mirror 8, but in order to change the characteristics of the optical film formed on the half mirror 8. Considerable time is required for redesign and condition setting, and depending on the characteristics of the optical film, it is difficult to obtain stable film characteristics.

  Therefore, in order to solve these problems, the applicant of the present application has conceived of using a polarization beam splitter with less wavelength dependency in place of the half mirror. The polarization beam splitter transmits or reflects incident light according to the polarization direction of the incident linearly polarized light, transmits the linearly polarized light in the horizontal direction, and reflects the linearly polarized light in the vertical direction. Therefore, the polarization beam splitter transmits the component of the incident light in the x-axis direction and reflects the component of the y-axis direction. Therefore, when a polarizing beam splitter is used in the optical pickup, if the polarizing beam splitter is tilted by θ with respect to the polarization direction, the x-axis component and y-axis component of the linearly polarized light that is incident can be varied depending on the θ amount. I can do it. That is, the ratio of the transmission amount and the reflection amount of the polarization beam splitter can be varied by the tilt angle θ of the polarization beam splitter.

  FIG. 7 is a diagram for explaining the function of the polarization beam splitter. In FIG. 7, a polarization beam splitter 14 shows an incident surface. By tilting the polarization beam splitter by θ with respect to the polarization direction, the component in the x-axis direction and the component in the y-axis direction of the incident light are varied. The polarizing beam splitter transmits the component of the incident light in the x-axis direction and reflects the component in the y-axis direction. For example, by setting a predetermined angle θ, the ratio of the transmission amount and the reflection amount of the polarizing beam splitter Can be 1: 9.

  FIG. 8 is a configuration example of an optical pickup using a polarizing beam splitter. The optical pickup 15 shows only the part necessary for explaining the operation of the polarization beam splitter. The two-wavelength laser 6 that emits two different wavelengths of linearly polarized light whose polarization directions are parallel to each other, and the two-wavelength laser 6 The first wave plate 5 that rotates the polarization direction of one of the linearly polarized light beams emitted from the first wave plate 90 and two linearly polarized light beams that are incident from the first wave plate 5 are propagated on the same optical path. An optical path correction device 17 comprising a refracting plate 2 and a second wavelength plate 16 that rotates the polarization direction of one linearly polarized light transmitted through the birefringent plate 2, and a laser beam emitted from the optical path correction device 17. It comprises a polarization beam splitter 14 that separates at a predetermined ratio. Here, the polarization beam splitter 14 is disposed to be inclined by a predetermined angle θ with respect to the polarization direction.

  8 will be described. For example, the laser light L1 having a wavelength of 650 nm and the laser light L2 having a wavelength of 780 nm emitted from the two-wavelength laser 6 are linearly polarized light having the same polarization direction, and are parallel with an optical path interval d. And enters the optical path correction device 17. The first wave plate 5 provided in the optical path correction device 17 rotates the polarization direction of one laser beam L2 emitted from the two-wavelength laser 6 by 90 °, while keeping the polarization direction of the other laser beam L1 unrotated. By transmitting, the laser beams L1 and L2 are configured to have linearly polarized light orthogonal to each other.

Next, laser light that passes through the first wave plate 5 is incident on the birefringent plate 2. The birefringent plate 2 has birefringence and its main cross section is configured to be orthogonal to the polarization direction of one laser beam L2. Therefore, the laser beam L2 is transmitted through the birefringent plate 2 to go straight becomes an ordinary ray to the optical axis A _0, the laser beam L1 laser beam L2 and the polarization directions are perpendicular to the extraordinary ray relative to the optical axis A ₀ Refracted and transmitted. Therefore, the laser beam L1 and the laser beam L2 that pass through the birefringent plate 2 propagate in the same optical path.

Next, the two linearly polarized lights transmitted through the birefringent plate 2 enter the second wave plate 16, rotate the polarization direction of one laser light L2 by 90 °, and keep the polarization direction of the other laser light L1 unrotated. The laser beams L1 and L2 are converted into linearly polarized light having the same polarization direction.
Next, the linearly polarized light that has passed through the second wave plate 16 is incident on the polarization beam splitter 14, transmits the component in the x-axis direction of the incident light, and reflects the component in the y-axis direction. The polarization beam splitter 14 is arranged to be inclined with respect to the polarization direction by a predetermined amount, and the ratio of the transmission amount and the reflection amount of the polarization beam splitter 14 is determined by the inclination angle. At this time, since the polarization beam splitter 14 does not have wavelength dependency, the transmittance of the laser light of two wavelengths does not change. Further, the amount of light transmitted through the polarizing beam splitter 14 can be arbitrarily varied by setting the arrangement angle of the polarizing beam splitter 14 to a desired value.

However, since the conventional optical pickup as described above is arranged with the polarizing beam splitter tilted, the cost for designing and manufacturing the die is greatly increased in the processing of the aluminum die-cast housing for fixing the polarizing beam splitter. There are problems such as this, the necessity of high housing accuracy, and the difficulty in mechanically mounting the housing.
The present invention has been made to solve the above-described problems, and enables two-wavelength laser light to be accurately and stably incident on the monitor light detector 13 and change the monitor light amount. An object of the present invention is to provide an optical path correction device that can be easily changed when desired and an optical pickup using the same.

In order to achieve the above object, an optical path correction apparatus according to the present invention and an optical pickup using the same have the following configurations.
The optical path correction device according to claim 1 transmits a first wave plate that receives linearly polarized light having two different wavelengths whose polarization directions are parallel to each other and whose optical paths are parallel to each other, and transmitted through the first wave plate. A birefringent plate for incident two linearly polarized light, a second wave plate for incident two linearly polarized light transmitted through the birefringent plate, and an optical rotator for incident linearly polarized light transmitted through the second wave plate. The first wave plate has a phase difference of 2π · m for one of the linearly polarized light and a phase of π · (2n-1) for the other linearly polarized light. A phase difference is generated (m and n are integers), and the birefringent plate has one of two linearly polarized light transmitted through the first wave plate with respect to its optical axis, and the other is an ordinary ray. It is arranged so that it becomes an extraordinary ray, the optical path interval between the two linearly polarized light is d, and the birefringent plate is bent with respect to the ordinary ray. When the refractive index is n0, the refractive index of the birefringent plate with respect to extraordinary rays is ne, the angle between the principal surface normal of the birefringent plate and the optical axis is θ, and the thickness of the birefringent plate is t,
t = d · | (n 0 ² · tan θ + ne ² ) / ((n 0 ² −ne ² ) · tan θ) |
Is satisfied,
The second wave plate generates a phase difference of 2π · p for one of the linearly polarized light and a phase difference of π · (2q-1) for the other linearly polarized light (p and q are The optical rotator is configured to rotate the polarization angle of incident linearly polarized light to a desired angle.

  The optical path correction apparatus according to claim 2 is configured such that an angle θ formed by the principal surface normal of the birefringent plate and the optical axis is 45 °.

  The optical path correction apparatus according to claim 3 is configured to have a structure in which the first wave plate, the birefringent plate, the second wave plate, and the optical rotator are bonded and integrated.

  The optical path correction apparatus according to claim 4 is configured such that the first wave plate and the second wave plate are crystals having birefringence.

  The optical path correction apparatus according to claim 5 is configured such that the birefringent plate is lithium niobate or rutile.

  6. The optical pickup according to claim 6, wherein a light source that emits linearly polarized light having two different wavelengths whose polarization directions are parallel to each other, and two linearly polarized light are incident from the light source. And a third wavelength plate that transmits the light beam emitted from the optical path correction device, and an objective lens that condenses the light beam transmitted through the third wavelength plate on an optical storage medium. .

  The optical pickup according to claim 7 is a light source that emits linearly polarized light having two different wavelengths whose polarization directions are parallel to each other, and two linearly polarized light incident from the light source. The optical path correction device, a third wavelength plate that transmits the light beam emitted from the optical path correction device, and an objective lens that condenses the light beam transmitted through the third wavelength plate on an optical storage medium, the light source And the optical path correcting device are integrated.

  According to the inventions of claims 1, 2, 4, and 5, after propagating laser beams of two wavelengths on the same optical path and aligning the linearly polarized light of the two laser beams to be aligned with the linearly polarized light of the same polarization direction The linearly polarized light is rotated by a predetermined amount, and when the optical path correction device is used for an optical pickup, the wavelength dependence of the optical thin film formed on the polarizing beam splitter is avoided, and the transmittance of the two laser beams Can be easily set to a predetermined value by changing the rotation angle of the optical rotator, which is very effective in using the optical path correction device.

  According to the third aspect of the present invention, the elements constituting the optical path correction device are laminated and integrated so that the optical path correction device can be miniaturized and the cost can be reduced. Demonstrate the effect.

  According to the sixth aspect of the present invention, the two-wavelength light emitted from the optical path correction device is converted into linearly polarized light having the same polarization direction, and the linearly polarized light is further rotated by a predetermined value. When used, it is possible to set the transmittance to a desired value while avoiding the wavelength dependence due to the polarization beam splitter, which is very effective in improving the performance of the optical pickup.

  According to the seventh aspect of the present invention, since the two-wavelength laser and the optical path correction device are integrated, the optical pickup can be reduced in size, and a great effect can be achieved when the optical pickup is used.

Hereinafter, the present invention will be described in detail based on illustrated embodiments.
In the present invention, two linearly polarized laser beams having different wavelengths emitted from a two-wavelength laser are propagated on the same optical path in the optical path correcting apparatus according to the present invention, and two linearly polarized laser beams emitted from the optical path correcting apparatus are emitted. After aligning the polarization direction to a predetermined direction, the linearly polarized light is rotated by a predetermined amount using an optical rotator, and the transmitted light amount transmitted through the polarizing beam splitter is set by the rotation amount of the linearly polarized light. Therefore, in order to obtain a desired transmission characteristic of the polarization beam splitter, the degree of rotation (rotation angle) of the optical rotator may be determined according to the transmission characteristic of the mirror film of the polarization beam splitter.

FIG. 1 is a block diagram showing an embodiment of an optical path correction apparatus according to the present invention, FIG. 1 (a) shows a diagram for explaining the operation, and FIG. 1 (b) shows an integrated optical path correction apparatus. The figure is shown. The optical path correction device 18 includes a first wave plate 5, a birefringent plate 2, a second wave plate 16, and an optical rotator 19, and is disposed in front of the two-wavelength laser 6.
The laser beam L1 having a wavelength of 650 nm and the laser beam L2 having a wavelength of 780 nm emitted from the two-wavelength laser 6 are linearly polarized light having the same polarization direction, and propagate in parallel at an optical path interval d.

The first wave plate 5 is a birefringent crystal or polymer film, rotates the polarization direction of one laser beam L2 emitted from the two-wavelength laser 6 by 90 °, and polarizes the other laser beam L1. The laser beams L1 and L2 are configured to have linearly polarized light orthogonal to each other by transmitting the light without rotating.
Therefore, the first wave plate 5 is configured to function as a half-wave plate with respect to the laser beam L2 having the wavelength λ2, that is, the laser beam L1 emitted from the two-wavelength laser 6 through the first wave plate 5. Is set to a plate thickness that generates a phase difference of π · (2n−1) with respect to the laser light L2 (m and n are integers). .

Next, the birefringent plate 2 is made of a crystal or liquid crystal such as lithium niobate or rutile having birefringence, and its main cross section is parallel to the linearly polarized light of one laser beam L1, and the other laser beam. It is configured to be orthogonal to the linearly polarized light of L2.
The first laser beam L2 incident from the wavelength plate 5 is transmitted through the birefringent plate 2 and goes straight becomes an ordinary ray to the optical axis A _0, the linear laser beam L1 laser beam L2 and the polarization directions are orthogonal The polarized light becomes an extraordinary ray with respect to the optical axis A ₀ and is refracted and transmitted. The thickness t of the birefringent plate 2 is set so that the refracted laser light L1 propagates through the same optical path as the laser light L2 when passing through the birefringent plate 2.
Therefore, the relationship of the following equation (1) is established between the plate thickness t and the optical path interval d of the two linearly polarized light.
t = d · | (n 0 ² · tan θ + ne ² ) / ((n 0 ² −ne ² ) · tan θ) | (1)
Note that n0 is the refractive index for ordinary light, ne is the refractive index for extraordinary light, θ is the angle between the principal surface normal of the birefringent plate and the optical axis, and is usually set to 45 °. Is desirable.

Next, the second wave plate 16 is a birefringent crystal or polymer film, and is one of the laser beams L1 and L2 that are linearly polarized light beams that are transmitted through the birefringent plate 2 and whose polarization directions are orthogonal to each other. By rotating the polarization direction of the laser beam L2 by 90 ° and transmitting the other laser beam L1 without rotating, the laser beams L1 and L2 are configured to be linearly polarized light having the same polarization direction. .
Therefore, the second wave plate 16 is configured to function as a half-wave plate with respect to the laser beam L2 having the wavelength λ2, that is, the laser beam L2 that transmits the second wave plate 16 through the birefringent plate 2. Is set to a thickness that generates a phase difference of 2π · p for the laser light L1 (p and q are integers). .

Next, the optical rotator 19 rotates the linearly polarized light incident from the second wave plate 16, and determines the amount of light transmitted through the polarizing beam splitter when the optical path correction device 18 is used in an optical pickup. It is.
A method for determining the transmitted light amount of the polarizing beam splitter using the optical rotator 19 will be described with reference to FIG.

  FIG. 2 is a diagram for explaining the reason why the amount of transmitted light can be arbitrarily set in the polarization beam splitter when the optical path correction apparatus according to the present invention is used for an optical pickup. FIG. 2 shows a configuration relating to a monitor system of an optical pickup, in which a two-wavelength laser 6 that emits linearly polarized light having two different wavelengths whose polarization directions are parallel to each other, and one of the linearly polarized light emitted from the two-wavelength laser 6. A first wave plate 5 that rotates the polarization direction by 90 °, a birefringent plate 2 that corrects an optical path so that two linearly polarized lights incident from the first wave plate 5 propagate on the same optical path, and the birefringent plate An optical path correction device 18 including a second wave plate 16 that rotates the polarization direction of one linearly polarized light that transmits 2 by 90 ° and an optical rotator 19 that rotates the incident linearly polarized light by a predetermined amount, and the optical path correction device 18 includes: A polarization beam splitter 14 that separates the emitted laser light at a predetermined ratio, and a monitor photodetector 13 that monitors the emission level of the two-wavelength laser 6 that passes through the separation surface of the polarization beam splitter 14. Configure.

As described above, the laser beams L1 and L2 emitted from the two-wavelength laser 6 pass through the first wave plate 5, the birefringent plate 2, and the second wave plate 16, and are polarized on the optical rotator 19 with the same polarization. Directional linearly polarized light L1b and L2b enter. In the optical rotator 19, when the incident linearly polarized light is emitted as laser beams L1c and L2c rotated by α, components in the x-axis direction of the laser beams L1c and L2c change depending on the angle at which the linearly polarized light is rotated. Therefore, the polarizing beam splitter 14 functions to transmit only the components in the x-axis direction of the linearly polarized laser beams L1c and L2c incident from the optical rotator 19 and reflect the components in the y-axis direction. The transmittance of the polarization beam splitter 14 can be set by setting the rotation angle of the optical rotator 19 to a desired angle. The laser beams L1d and L2d that are components in the x-axis direction of the laser beams L1c and L2c that have passed through the polarizing beam splitter 14 are input to the monitor photodetector 13 to detect the monitor beam.
Here, the optical rotator 19 rotates the linearly polarized light incident from the second wave plate 16 by a predetermined value, and emits the laser beams L 1 d and L 2 d from the output surface of the optical path correction device 18.

As described above, the optical path correction apparatus in the present embodiment propagates laser light of two wavelengths on the same optical path, and after aligning the linearly polarized light of the two laser lights to be linearly polarized in the same polarization direction, When the optical path correction device is used for an optical pickup, the wavelength dependence of the optical thin film formed on the polarizing beam splitter is avoided and the transmittance of the two laser beams can be easily set to a predetermined value. It became possible to set to.

In the diagram for explaining the operation of the optical path correction apparatus shown in FIG. 1A, a first wave plate, a birefringent plate, a second wave plate, and an optical rotator are arranged at predetermined intervals. However, as shown in FIG. 1B, the optical path correction device 20 laminates the first wave plate 5, the second wave plate 16, and the optical rotator 19 on the birefringent plate 2 and stacks and integrates them. And can be downsized. Furthermore, an optical path correction device can be fixed and modularized over the entire emission surface of the two-wavelength laser, which is highly effective in improving handling and downsizing when assembling an optical pickup described later.

Next, an embodiment in which the optical path correcting apparatus according to the present invention is used for an optical pickup will be described.
FIG. 3 shows a schematic diagram when the optical path correction device 20 according to the present invention is applied to an optical pickup. The optical pickup 21 includes a two-wavelength laser 6 that emits two different wavelengths of linearly polarized light whose polarization directions are parallel to each other, and a first direction that rotates the polarization direction of one of the linearly polarized lights emitted from the two-wavelength laser 6 by 90 °. The birefringent plate 2 for correcting the optical path so that the two linearly polarized light incident from the first waveplate 5 and the first waveplate 5 propagate on the same optical path, and one of the linearly polarized light transmitted through the birefringent plate 2. An optical path correction device 20 including a second wave plate 16 that rotates the polarization direction by 90 ° and an optical rotator 19 that rotates incident linearly polarized light by a predetermined amount, and a laser beam emitted by the optical path correction device 20 at a predetermined ratio. The polarized beam splitter 14 to be separated, and the laser beam reflected by 90 ° on the separation surface of the polarized beam splitter 14 are incident and converted into circularly polarized light, and the reflected light from the optical disk 9 emitted from an objective lens 11 described later A third wave plate 22 that converts a certain circularly polarized laser beam into linearly polarized light, and a circularly polarized laser beam that passes through the third wave plate 22 is focused on the pit 10 formed on the optical disk 9. In addition, the objective lens 11 that receives the laser beam reflected on the pit 10 and the light detection that detects the linearly polarized laser beam that passes through the third wave plate 22 via the polarizing beam splitter 14. And a monitor light detector 13 for monitoring the emission level of the two-wavelength laser 6 that passes through the separation surface of the polarizing beam splitter 14.

  3 will be described. Laser light L1 (for DVD) having a wavelength of 650 nm, for example, or laser light L2 (for CD) having a wavelength of 780 nm emitted from the two-wavelength laser 6 is linearly polarized light having the same polarization direction. Yes, it propagates in parallel at the optical path interval d and enters the optical path correction device 20. The first wave plate 5 provided in the optical path correction device 20 rotates the polarization direction of one laser beam L2 emitted from the two-wavelength laser 6 by 90 °, while keeping the polarization direction of the other laser beam L1 unrotated. By transmitting, the laser beams L1 and L2 are configured to have linearly polarized light orthogonal to each other.

Next, laser light that passes through the first wave plate 5 is incident on the birefringent plate 2. The birefringent plate 2 has birefringence and its main cross section is configured to be orthogonal to the polarization direction of one laser beam L2. Therefore, the laser beam L2 is transmitted through the birefringent plate 2 to go straight becomes an ordinary ray to the optical axis A _0, the laser beam L1 laser beam L2 and the polarization directions are perpendicular to the extraordinary ray relative to the optical axis A ₀ Refracted and transmitted. Therefore, the laser beam L1 and the laser beam L2 that pass through the birefringent plate 2 propagate in the same optical path.

Next, the two linearly polarized lights transmitted through the birefringent plate 2 enter the second wave plate 16, rotate the polarization direction of one laser light L2 by 90 °, and keep the polarization direction of the other laser light L1 unrotated. The laser beams L1 and L2 are converted into linearly polarized light having the same polarization direction. Next, the linearly polarized light transmitted through the second wave plate 16 enters the optical rotator 19, and the two laser beams L1 and L2 are both rotated by a predetermined amount and emitted as laser beam L15.

  Next, the laser beam L15 that has passed through the optical path correction device 20 is incident on the polarization beam splitter 14, and, for example, about 90% of the laser beam L15 is reflected as 90 ° on the separation surface as the laser beam L16. About 10% of the light L15 is separated as laser light L17 that passes through the separation surface. At this time, the laser light incident on the polarization beam splitter 14 is linearly polarized light having the same polarization direction of two wavelengths, and the separation surface formed of the optical thin film formed on the polarization beam splitter 14 is linearly polarized light having the same polarization direction. On the other hand, since there is no wavelength dependency, the transmittance of laser light of two wavelengths does not change. Further, the laser beam L15 is rotated by a predetermined amount of linearly polarized light in the optical rotator 19, and the amount of light transmitted through the polarizing beam splitter 14 is arbitrarily set by setting the rotation angle of the linearly polarized light in the optical rotator 19 to a desired value. It can be changed from 10% to other transmittance.

Next, the laser beam L16 reflected by the polarization beam splitter 14 enters the third wave plate 22. The third wave plate 22 functions as a quarter wave plate, and causes the phase difference between the ordinary light component and the extraordinary light component of linearly polarized light to be 90 °, and the transmitted light of the third wave plate 22 is The ordinary light component and the extraordinary light component, whose phases are shifted by 90 ° from each other, are combined into a circularly polarized laser beam L18 with two wavelengths.

Next, the laser light L18 converted into circularly polarized light that has passed through the third wave plate 22 is condensed by the lens 11 and applied to the pit 10 formed on the optical disk 9, and is reflected on the pit 10. L19 becomes reflected light and is incident on the third wave plate 22 through the objective lens 11, and becomes linearly reflected reflected light L20 whose polarization direction is orthogonal to L16 which is the linearly polarized incident light. Through. Next, the laser beam L20 enters the polarization beam splitter 14, passes through the polarization beam splitter 14 as it is, enters the photodetector 12, and reads out information written on the optical disk.

  On the other hand, a predetermined amount of the laser beam L17 transmitted through the polarizing beam splitter 14 enters the monitor photodetector 13 and monitors the emission level of the laser beam emitted from the two-wavelength laser 6. In an optical pickup, it is necessary to keep the emission level of the laser beam emitted from the laser element constant. Therefore, a part of the laser beam is received by a photodetector for monitoring and the laser element is driven by an APC circuit. The circuit is controlled to keep the laser beam emission level constant. The optical pickup shown in FIG. 3 employs a highly accurate front monitor system as means for monitoring the emission level of laser light.

  As described above, the optical pickup according to the present embodiment can avoid the wavelength dependency that occurs in the optical thin film formed on the polarizing beam splitter. Therefore, when monitoring the emission level of each of the two-wavelength lasers, highly accurate monitor light detection is possible. It is possible to easily set the monitor light quantity to an arbitrary value.

It is a block diagram which shows the Example of the optical path correction apparatus concerning this invention. It is a figure for demonstrating the reason which can set arbitrarily the transmitted light quantity in a polarizing beam splitter, when using the optical path correction device concerning this invention for an optical pick-up. The schematic diagram when the optical path correction device 20 according to the present invention is applied to an optical pickup is shown. It is a figure for demonstrating the principle of the optical path correction apparatus disclosed by Unexamined-Japanese-Patent No. 2001-283457. It is a figure for demonstrating the principle of the optical path correction apparatus proposed by the conventional Japanese Patent Application No. 2003-155617. It is a schematic diagram at the time of applying the conventional optical path correction apparatus using a two-wavelength laser to an optical pickup. It is a figure explaining the function of a polarization beam splitter. It is a structural example of the optical pick-up using a polarization beam splitter.

Explanation of symbols

1 .... Optical path correction device, 2 .... Birefringence plate,
3 ・ ・ 2 wavelength laser, 4 ・ ・ Optical path corrector,
5 .... Wave plate (first wave plate), 6 .... Double wavelength laser,
7 ・ ・ Optical pickup, 8 ・ ・ Polarizing beam splitter,
9. ・ Optical disc, 10. ・ Pit,
11 .... objective lens, 12 .... photo detector,
13. ・ Monitor light detector, 14. ・ Polarizing beam splitter,
15 .... optical pickup, 16 .... second wave plate,
17. Optical path correction device, 18. Optical path correction device,
19 .... Optical rotator, 20 .... Optical path correction device,
21..Optical pickup, 22..Third wave plate

Claims (7)

A first wave plate for incident linearly polarized light of two different wavelengths whose polarization directions are parallel to each other and whose optical paths are parallel to each other; and a birefringent plate for incident of two linearly polarized light transmitted through the first wave plate; An optical path correction device comprising: a second wave plate that enters two linearly polarized light that has passed through the birefringent plate; and an optical rotator that enters linearly polarized light that has passed through the second wave plate,
The first wave plate generates a phase difference of 2π · m for one of the linearly polarized light and a phase difference of π · (2n-1) for the other linearly polarized light (m , N is an integer),
The birefringent plate is arranged such that one of two linearly polarized light transmitted through the first wave plate with respect to its optical axis is an ordinary ray, and the other is an extraordinary ray, and the optical path of the two linearly polarized light The interval is d, the refractive index of the birefringent plate with respect to the ordinary ray is n0, the refractive index of the birefringent plate with respect to the extraordinary ray is ne, the angle between the principal surface normal of the birefringent plate and the optical axis is θ, and the birefringent plate When the plate thickness is t,
t = d · | (n 0 ² · tan θ + ne ² ) / ((n 0 ² −ne ² ) · tan θ) |
Is satisfied,
The second wave plate generates a phase difference of 2π · p for one of the linearly polarized light and a phase difference of π · (2q-1) for the other linearly polarized light (p and q are Integer),
The optical path corrector according to claim 1, wherein the optical rotator rotates a polarization angle of incident linearly polarized light to a desired angle.   2. The optical path correction device according to claim 1, wherein an angle θ formed by a principal surface normal of the birefringent plate and an optical axis is 45 °.   3. The optical path correction device according to claim 1, wherein the first wave plate, the birefringent plate, the second wave plate, and the optical rotator are bonded and integrated.   4. The optical path correction device according to claim 1, wherein the first wave plate and the second wave plate are crystals having birefringence.   5. The optical path correction device according to claim 1, wherein the birefringent plate is lithium niobate or rutile. A light source that emits two different wavelengths of linearly polarized light whose polarization directions are parallel to each other;
The optical path correction device according to any one of claims 1 to 5, wherein two linearly polarized lights are incident from the light source;
A third wave plate that transmits the light emitted from the optical path correction device;
An optical pickup comprising: an objective lens that condenses the light beam transmitted through the third wave plate on an optical storage medium. A light source that emits two different wavelengths of linearly polarized light whose polarization directions are parallel to each other;
The optical path correction device according to any one of claims 1 to 5, wherein two linearly polarized lights are incident from the light source;
A third wave plate that transmits the light emitted from the optical path correction device;
An objective lens for condensing the light beam transmitted through the third wave plate on an optical storage medium,
An optical pickup having a structure in which the light source and the optical path correction device are integrated.

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