JP2006012202A - Optical path correcting apparatus and optical pickup using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical path correcting apparatus in which fixed transmission light can be obtained in a monitor light detector independently of the wavelength of a laser beam, and an optical pickup using the same. <P>SOLUTION: In an optical path compensating apparatus 14, respective function elements are integrally laminated, and the apparatus is constituted of a first double refraction plate 15, a first wavelength plate 5, a second double refraction plate 2, and a second wavelength plate 16. The optical path correcting apparatus 14 is arranged at the front of a compound optical element 17, linearly polarized light having two different wavelengths whose polarization directions are parallel to each other and whose optical paths are parallel to each other are made incident from the first double refraction plate 15, the optical path is corrected while the transmitted laser beam is converted to circular polarization to be emitted from the second wavelength plate 16, and on the other hand, the circular-polarized laser beam is made incident from the second wavelength plate 16, the optical path is changed to the prescribed position and the circular-polarized laser beam is emitted from the first double refraction plate 15. <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, after correcting optical paths of two different wavelengths of linearly polarized light whose polarization directions emitted from a two-wavelength laser unit are parallel to each other, propagates on the same optical path. The present invention relates to an optical path correction apparatus that emits light to a monitor light detection unit after making outgoing light circularly polarized light and correcting the optical path by entering laser light reflected from an optical disk, 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, 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 laser diode is incident on the dichroic prism and transmitted through the separation surface, and the laser light emitted from the other laser diode 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, monolithic 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. 7 is a diagram for explaining the principle of a conventional optical path correction device disclosed in Japanese Patent Laid-Open No. 2001-283457. In FIG. 7, the optical path correction device 1 includes a birefringent plate 2, and the birefringent plate 2 receives laser light L 1 having a wavelength of 650 nm and laser light L 2 having a wavelength of 780 nm that are emitted from a two-wavelength laser 3. The polarization plane of the laser beam L1 and the polarization direction of the laser beam L2 are orthogonal to each other. Birefringent plate 2 is a crystal having birefringence is obtained by cutting out the plate such that the optical axis A ₀ is an angle of the main surface and 45 °.
With this configuration, transmitted straight through birefringent plate 2 the laser beam L2 becomes an ordinary ray to the optical axis A _0. 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. 7 requires that the polarization directions of two laser beams are orthogonal to each other, but a monolithic integrated two-wavelength laser has two 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. 8 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. 7 and is made of a crystal or liquid crystal having birefringence, and its optical axis is coplanar with the polarization direction of one laser beam L2. 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. 9 shows an example of a schematic diagram when a conventional optical path correction device 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 beam reflected 90 ° at the pit 10 of the optical disc 9, and the laser beam reflected on the pit 10 formed on the optical disc 9 through the objective lens 11 and the half mirror 8. It comprises a photodetector 12 that detects via, and a monitor photodetector 13 that monitors the emission level of the two-wavelength laser 6 that passes through the separation surface of the half mirror 8.

  9 will be described. For example, the laser light L1 having a wavelength of 650 nm or the laser light L2 having a wavelength of 780 nm emitted from the two-wavelength laser 6 is linearly polarized light having polarization directions 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 and passes 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. The linearly polarized light of the laser light L1 is La and the linearly polarized light of the laser light L2 is Lb. Let 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 L <b> 14 is transmitted 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. 13 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 method as described above, the laser beam is composed of laser beams of linearly polarized light La and Lb as described above. Is transmitted through the separation surface and incident on the monitor light detector 13, since it has wavelength dependency with respect to laser beams of La and Lb having different polarization directions as shown in FIG. 10, the wavelengths λ1 and λ2 A difference in the transmittance at the time was caused, and the monitor accuracy required for controlling the laser light amount could not be satisfied.

FIG. 10 is a diagram showing a change in transmittance when the wavelength is varied in the linearly polarized laser beams La and Lb. As shown in the figure, in the optical thin film formed on the incident surface of the half mirror 8, the transmission characteristics are realized so that the transmittances at the wavelengths λ1 and λ2 are both 10% with respect to the laser beams of La and Lb. Is very difficult.
The present invention has been made to solve the above-described problems. An optical path correction device capable of obtaining a constant transmitted light in a monitor photodetector regardless of the wavelength of a laser beam and an optical pickup using the same. The purpose is to provide.

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 has a structure in which a first birefringent plate, a first waveplate, a second birefringent plate, and a second waveplate are arranged in order, When two differently-polarized linearly polarized laser beams whose directions are parallel to each other and whose optical paths are parallel to each other are incident from the first birefringent plate, two circularly polarized laser beams traveling on the same optical path are transmitted from the second wavelength plate. On the other hand, when two circularly polarized laser beams having different wavelengths traveling on the same optical path are incident from the second wavelength plate, the optical path exiting from the first birefringent plate as linearly modified laser beams traveling on the two different optical paths The correction device, wherein the first birefringent plate has an optical path changing distance due to refraction when an extraordinary ray is incident as d1, a refractive index of the birefringent plate with respect to an ordinary ray, and a refractive index of the birefringent plate with respect to the extraordinary ray. The ratio is ne, the principal surface normal of the birefringent plate and the optical axis When the degree theta, where the thickness of the birefringent plate was t1,
t1 = d1 · | (n0 ² · tan θ + ne ² ) / ((n0 ² −ne ² ) · tan θ) |
Satisfying
The first wave plate generates a phase difference of 2π · m for one of the linearly polarized laser beams and a phase difference of π · (2n-1) for the other linearly polarized laser beam. (M and n are integers), and the second birefringent plate is arranged so that one of the two linearly polarized laser beams incident on the optical axis is an ordinary ray and the other is an extraordinary ray. The optical path interval between the two linearly polarized laser beams is d2, 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 principal surface normal of the birefringent plate and the optical axis Is θ, and the thickness of the birefringent plate is t2.
t2 = d2 · | (n0 ² · tan θ + ne ² ) / ((n0 ² −ne ² ) · tan θ) |
Satisfying
The second wave plate generates a phase difference of π / 2 · (2p−1) for any incident linearly polarized laser beam or circularly polarized laser beam (p is an integer). Constitute.

The optical path correction device according to claim 2 has a structure in which a first birefringent plate, a first wave plate, a second birefringent plate, a second wave plate, and a grating are sequentially arranged. When two linearly polarized laser beams having different polarization directions and parallel optical paths are incident on the first birefringent plate, two circularly polarized laser beams traveling on the same optical path are obtained. On the other hand, when two circularly polarized laser beams having different wavelengths traveling on the same optical path are incident from the grating, an optical path exiting from the first birefringent plate as linearly polarized laser beams traveling on two different optical paths A correction device,
The first birefringent plate has an optical path changing distance due to refraction when an extraordinary ray is incident, d1, a refractive index of the birefringent plate with respect to an ordinary ray, n0, a refractive index of the birefringent plate with respect to an extraordinary ray, ne, and birefringence. When the angle between the principal surface normal of the plate and the optical axis is θ, and the thickness of the birefringent plate is t1,
t1 = d1 · | (n0 ² · tan θ + ne ² ) / ((n0 ² −ne ² ) · tan θ) |
Satisfying
The first wave plate generates a phase difference of 2π · m for one of the linearly polarized laser beams and a phase difference of π · (2n-1) for the other linearly polarized laser beam. (M and n are integers), and the second birefringent plate is arranged so that one of the two linearly polarized laser beams incident on the optical axis is an ordinary ray and the other is an extraordinary ray. In addition, the first birefringent plate and the first birefringent plate are arranged so that their main cross-sections are orthogonal to each other, the optical path interval between the two linearly polarized laser beams is d2, the refractive index of the birefringent plate with respect to ordinary rays is n0, When the refractive index for 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 t2.
t2 = d2 · | (n0 ² · tan θ + ne ² ) / ((n0 ² −ne ² ) · tan θ) |
Satisfying
The second wave plate generates a phase difference of π / 2 · (2p−1) with respect to any incident linearly polarized laser beam or circularly polarized laser beam (p is an integer), The grating is configured to diffract one or both of the incident circularly polarized laser beams having different wavelengths into three beams of zero-order light and ± first-order light.

  The optical path correction device according to claim 3 has a structure in which the first birefringent plate, the first wave plate, the second birefringent plate, and the second wave plate are bonded and integrated. Configure to have.

  5. The optical path correction device according to claim 4, wherein the first birefringent plate, the first wave plate, the second birefringent plate, the second wave plate, and the grating are bonded and integrated. It is configured to have the structure described above.

  The optical path correction apparatus according to claim 5 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 6 is configured such that the first birefringent plate and the second birefringent plate are lithium niobate or rutile.

  The optical pickup according to claim 7 includes a composite optical element including a two-wavelength laser unit that emits linearly polarized laser beams having two different wavelengths whose polarization directions are parallel to each other, and a pair of monitor light detection units, 7. The optical path correction device according to claim 1, wherein two linearly polarized laser beams are incident from the two-wavelength laser unit, and monitor light is emitted to the monitor light detection unit, and the optical path correction device is emitted. And an objective lens for condensing the light beam on the optical storage medium.

  The optical pickup according to claim 8 includes a composite optical element including a two-wavelength laser unit that emits linearly polarized laser beams having two different wavelengths whose polarization directions are parallel to each other, and a pair of monitor light detection units, 7. The optical path correction device according to claim 1, wherein two linearly polarized laser beams are incident from the two-wavelength laser unit, and monitor light is emitted to the monitor light detection unit, and the optical path correction device is emitted. An objective lens for condensing the light beam on the optical storage medium, and the composite optical element and the optical path correction device are integrated.

  According to the first, fifth, and sixth aspects of the invention, since the outgoing light of the optical path correction device is circularly polarized light, when the optical path correction device is used for an optical pickup, the optical thin film against the linearly polarized light on the mirror surface of the half mirror is used. Wavelength dependence can be avoided, the performance of the optical pickup can be improved, and a great effect can be exhibited in constructing the optical pickup.

  According to the second aspect of the invention, in addition to the effect of the optical path correcting device according to the first aspect, since the emitted light is diffracted light, the effect of improving the performance of the optical pickup is greatly exhibited.

  According to the third and fourth aspects 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. With a great effect.

  According to the seventh aspect of the present invention, since the light emitted from the optical path correction device is circularly polarized and further converted into three beams, wavelength dependency due to a half mirror can be avoided when the optical path correction device is used for an optical pickup. In addition to improving the performance of the optical pickup, the two-wavelength laser part and the pair of monitor light detection parts are integrated, so the number of parts is reduced and the structure of the optical pickup can be made smaller and the optical pickup is used. Great effect on the top.

  According to the eighth aspect of the invention, since the composite optical element 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 unit are propagated on the same optical path using a birefringent plate in the optical path correction apparatus according to the present invention, and a quarter-wave plate The two linearly polarized light is converted into circularly polarized light by using and is emitted. By making the two linearly polarized light emitted from the optical path correction device circularly polarized, when the optical path correction device is used for an optical pickup, the wavelength dependence of the linear polarization in the optical thin film formed on the half mirror can be avoided. Regardless of the wavelength of the laser light, a certain amount of transmitted light can be obtained at the monitor light detection unit. On the other hand, in the optical path correction apparatus according to the present invention, when the optical path correction apparatus is used for an optical pickup, the laser beam reflected by the pits of the optical disk is incident, and the optical path is changed by using a birefringent plate to change the two wavelengths. It has a function of being incident on a pair of monitor light detection units that are integrated with the laser unit.

  FIG. 1 is a block diagram showing a first embodiment of an optical path correction apparatus according to the present invention. FIG. 1 (a) corrects the optical paths of two laser beams incident from a two-wavelength laser section and is circularly polarized. FIG. 1 (b) shows a configuration for integrating the two-wavelength laser unit by changing the optical path and entering the laser beam reflected by the pits formed on the optical disk. The figure for demonstrating a mode that it injects into a pair of monitor light detection part made. The optical path correction apparatus shown in the present embodiment shows a structure in which each functional element is laminated and integrated, and the optical path correction apparatus 14 includes a first birefringent plate 15, a first wave plate 5, and a second birefringent plate. 2 and the second wave plate 16 are disposed in front of the composite optical element 17. The composite optical element 17 includes a two-wavelength laser unit 18 that emits laser beams having two different wavelengths and a pair of monitor light detection units 19 that detect the monitor light of the two-wavelength laser.

The operation of FIG. 1A will be described. If the laser light emitted from the two-wavelength laser unit 18 is, for example, a laser light L1 having a wavelength of 650 nm propagating in the optical path 1 and a laser light L2 having a wavelength of 780 nm propagating in the optical path 2, the two laser lights have the same polarization. Linearly polarized light P1 and P2 having a direction, propagate in parallel at an optical path interval d1, and enter the first birefringent plate.
The first birefringent plate 15 is made of birefringent crystal such as lithium niobate or rutile or liquid crystal, and its main cross section is orthogonal to the linearly polarized light P1 and P2 of the two laser beams L1 and L2. Configure as follows. Therefore, two laser beams L1, L2 of the two-wavelength laser unit 18 is emitted is transmitted through the first birefringence plate 15 and go straight becomes an ordinary ray to the optical axis A _0.

Next, the laser beam that has passed through the first birefringent plate 15 enters the first wave plate 5. The first wave plate 5 is a birefringent crystal or polymer film, and the polarization direction of one linearly polarized light P1 transmitted through the first birefringent plate 15 is rotated by 90 ° to be linearly polarized light S1, The other linearly polarized light P2 is transmitted without rotating in the polarization direction, so that the laser beams L1 and L2 have linearly polarized light orthogonal to each other.
Therefore, the first wave plate 5 is configured to function as a half-wave plate with respect to the laser beam L1, that is, the laser beam so as to generate a phase difference of 2π · n with respect to the laser beam L2. For L1, the plate thickness is set so as to generate a phase difference of π · (2m−1).

  The first wave plate 5 has a structure in which two quartz wave plates are bonded as shown in FIG. 2 (a), or one parallel flat plate as shown in FIG. 2 (b). The one composed only of the quartz plate is used. Further, although the structure is slightly complicated as shown in FIG. 2 (c), a part of one quartz plate may be cut to have a different thickness, or one of the structures as shown in FIG. 2 (d). A retardation plate exhibiting a phase difference of π with respect to linearly polarized light having a wavelength may be realized by being attached to a part of a glass substrate.

Next, the laser light transmitted through the first wave plate 5 is incident on the second birefringent plate 2. Like the first birefringent plate 15, the second birefringent plate 2 is made of a crystal or liquid crystal such as lithium niobate or rutile having birefringence, and the main cross section thereof is linearly polarized light of one laser beam L2. It is configured to be parallel to P2 and orthogonal to the linearly polarized light S1 of the other laser beam L1.
The first laser beam L1 incident from the wavelength plate 5 of the optical path 1 and propagates through the second birefringent plate 2 to go straight becomes an ordinary ray to the optical axis A _0, the laser beam L1 and the polarization direction There linearly polarized light of the laser beam L2 is perpendicular will be transmitted refracted becomes extraordinary ray relative to the optical axis a _0. When the refracted laser beam L2 passes through the second birefringent plate 2, the thickness t2 of the second birefringent plate 2 so that the laser beam L2 propagates through the optical path 1 which is the propagation optical path of the laser beam L1. And the optical path correction is performed so that the laser light L1 and the laser light L2 propagate along the same optical path.
Therefore, the relationship of the following equation (1) is established between the plate thickness t2 and the optical path interval d2 of the two linearly polarized light.
t2 = d2 · | (n0 ² · tan θ + ne ² ) / ((n0 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 laser light transmitted through the second birefringent plate 2 enters the second wave plate 16. The second wave plate 16 is a birefringent crystal or polymer film. When the two linearly polarized light S1 and P2 transmitted through the second birefringent plate 2 are incident, the linearly polarized ordinary light component and extraordinary light are incident. Since the phase difference with respect to the component acts to be 90 °, the transmitted light of the second wave plate 16 is composed of the ordinary light component and the extraordinary light component that are 90 ° out of phase with each other, and the laser light L1, L2 Become circularly polarized light having different rotation directions, and are emitted from the optical path correction device 14.
Therefore, the second wave plate 16 is configured to function as a quarter wave plate, and the wave plate generates a phase difference of π / 2 · (2p−1) with respect to the laser light L1. The plate thickness is set so as to generate a phase difference of π / 2 · (2p−1) with respect to the laser beam L2. The quarter-wave plate necessary in the present embodiment is a broadband wave plate corresponding to two wavelengths of laser light. For example, a quarter-wave plate as proposed in JP-A-10-68816 And a half-wave plate are often used together, and desired performance can be obtained by attaching the two wave plates at a predetermined optical axis angle. On the other hand, a wave plate that functions as a quarter wave plate for a plurality of desired wavelengths as proposed in WO 03/091768 may be used.

As described above, the optical path correction apparatus according to the present embodiment propagates laser light of two wavelengths on the same optical path and makes the two laser lights to be circularly polarized, and this optical path correction is applied to the optical pickup. When the apparatus is used, the wavelength dependence of linearly polarized light in the optical thin film formed on the half mirror can be avoided.

  Next, the operation of FIG. 1B will be described. FIG. 1 (b) shows an operation when a laser beam for monitoring reflected by a pit formed on an optical disc is incident to correct an optical path and enter a pair of monitor light detectors. The circularly polarized laser beams L1 ′ and L2 ′ reflected by the pits formed on the optical path 1 and propagating along the optical path 1 have their rotational directions reversed with respect to the circularly polarized laser beams L1 and L2 emitted from the optical path correction device 14. The light is incident on the second wave plate 16 constituting the optical path correction device 14.

As described above, the second wave plate 16 is configured to function as a quarter wave plate. The circularly polarized laser beam L1 ′ is converted into linearly polarized light P1, and the circularly polarized laser beam L2 ′ is converted into linearly polarized light S2. Thus, the linearly polarized light is orthogonal to each other.
Next, the laser beams L 1 ′ and L 2 ′ transmitted through the second wave plate 16 and linearly polarized are incident on the second birefringent plate 2.
The main cross section of the second birefringent plate 2 is configured to be parallel to the linearly polarized light P1 of one laser beam L1 ′ and orthogonal to the linearly polarized light S2 of the other laser beam L2 ′. .
The second laser beam L2 'is the optical path 1 passes through the second birefringent plate 2 to go straight becomes an ordinary ray to the optical axis A ₀ which from wave plate 16 is incident on the second birefringence plate 2 propagates linearly polarized light of the laser beam L2 'laser beam L1 and the polarization direction perpendicular' is transmitted by refraction becomes extraordinary ray relative to the optical axis a _0, to propagate the optical path 2.

  Next, the laser beams L 1 ′ and L 2 ′ transmitted through the second birefringent plate 2 are incident on the first wave plate 5. The first wave plate 5 is configured to function as a half-wave plate as described above, and is polarized light of the linearly polarized light P1 that is one laser light L1 ′ that is refracted and transmitted through the second birefringent plate 2. The direction is rotated by 90 ° and transmitted as linearly polarized light S1, and the polarization direction of linearly polarized light S2 that is the other laser beam L2 ′ is transmitted without rotating, and the laser beams L1 ′ and L2 ′ have the same polarization direction. Let it be linearly polarized light.

Next, the laser beams L 1 ′ and L 2 ′ transmitted through the first wavelength plate 5 are incident on the first birefringent plate 15. In the first birefringent plate 15, the main cross section is configured to be parallel to the linearly polarized light S1 of the laser light L1 ′ and the linearly polarized light S2 of the laser light L2 ′. The main cross section of the first birefringent plate 15 is arranged so as to be orthogonal to the main cross section of the second birefringent plate 2.
Therefore, linearly polarized light of the first laser beam L1 is incident than the wavelength plate 5 'and L2' will be transmitted refracted becomes extraordinary ray relative to the optical axis A _0. When the refracted laser beams L1 ′ and L2 ′ are transmitted through the first birefringent plate 15, the first laser beam L2 ′ is propagated along the optical path 3 so that the laser beam L1 ′ propagates along the optical path 4. The thickness t1 of the birefringent plate 15 is set so that the laser light L1 ′ and the laser light L2 ′, which are the monitor lights of the two-wavelength laser unit 18, are incident on the predetermined positions of the pair of monitor light detectors 19, respectively. Perform optical path correction.
The relationship of the following formula (2) is established between the plate thickness t1 and the optical path correction distance d1 of the two linearly polarized light.
t1 = d1 · | (n0 ² · tan θ + ne ² ) / ((n0 ² −ne ² ) · tan θ) | (2)
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.

  As described above, the optical path correction device 14 according to the present invention propagates laser light of two wavelengths on the same optical path and makes the two emitted laser lights circularly polarized light. When the optical path correction device is used, the wavelength dependence of linearly polarized light in the optical thin film formed on the half mirror can be avoided. Further, the optical paths of the laser beams L1 ′ and L2 ′ reflected on the optical disk are corrected, and the laser beams L1 ′ and L2 ′ are added to a pair of monitor light detectors 19 integrated with the two-wavelength laser unit 18. Was made incident. Therefore, the composite optical element 17 in which the front monitor function and the laser light emission function are integrated can be used, and the structure can be reduced in size when the optical pickup is configured. Further, it is possible to fix the optical path correction device 14 to the entire entrance / exit surface of the composite optical element 17 to form a module, which is very 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 is a schematic diagram when the optical path correction device 14 according to the present invention is applied to an optical pickup. The optical pickup 20 includes a pair of monitors that detect a laser beam for monitoring reflected from a pit 10 formed on the optical disk 9 and a two-wavelength laser unit 18 that emits linearly polarized light having two different wavelengths whose polarization directions are parallel to each other. The composite optical element 17 provided with the light detection unit 19 and the two laser beams emitted from the two-wavelength laser unit 18 are propagated on the same optical path and the two laser beams emitted are circularly polarized, An optical path correction device 14 that corrects the optical path of the laser beam reflected by the pit 10 formed on the optical disc 9 and makes it incident on a pair of monitor light detectors 19, and the laser beam emitted by the optical path correction device 14 is all 90 °. A half mirror 21 that reflects the laser light reflected by the pits 10 formed on the optical disk 9 at a predetermined ratio; An objective lens 11 that condenses the laser light that is totally reflected by 90 ° on the separation surface onto the pit 10 of the optical disk 9, and the laser light reflected on the pit 10 formed on the optical disk 9 is the objective lens 11 and the half mirror 21. And a photodetector 12 that detects the light via the.

3 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 unit 18 are linearly polarized light having the same polarization direction, and the optical path interval d1 The light propagates in parallel and enters the optical path correction device 14. As described above, the optical path correction device 14 propagates the laser beams L1 and L2 having the two wavelengths on the same optical path, and converts the two laser beams to be emitted into circularly polarized light. Therefore, these laser beams are collectively referred to as a laser beam L15.

Next, the laser beam L15 that has passed through the optical path correction device 14 is incident on the half mirror 21, and the laser beam L16 that has been totally reflected by 90 ° on the separation surface is condensed by the objective lens 11 and formed on the optical disk 9. Is irradiated. Therefore, the laser light L17 reflected on the pit 10 becomes reflected light and enters the half mirror 21 through the objective lens 11, and about 90% of the laser light L17 passes through the separation surface. As a result, about 10% of the laser beam L17 is separated as a laser beam L19 that reflects 90 ° on the separation surface. At this time, the laser light incident on the half mirror 21 is circularly polarized for both wavelengths, and the separation surface made of an optical thin film formed on the half mirror 21 has no wavelength dependency on the circularly polarized light. The transmittance and reflectance do not change with respect to the laser beam having the wavelength.
The laser beam L18 that has passed through the half mirror 21 enters the photodetector 12 and reads information written on the optical disk.

  On the other hand, since the laser beam L19 reflected by 90 ° by the half mirror 21 is used as the monitor beam of the laser beams L1 and L2 emitted from the two-wavelength laser unit 18, the optical path correction device 14 emits a circularly polarized laser beam. Incident on the surface. The optical path correction device 14 corrects the optical paths of the laser beams L1 ′ and L2 ′ constituting the laser beam L19 reflected by the pits 10 formed on the optical disc 9 as described above, and is integrated with the two-wavelength laser unit 18. The laser beams L1 ′ and L2 ′ are incident on the configured pair of monitor light detectors 19 to detect the monitor light.

As described above, in the present optical pickup 20, the two linearly polarized lights emitted from the optical path correction device 14 are circularly polarized, so that when the optical path correction device 14 is used for the optical pickup, the half mirror 21 Since the wavelength dependence of the linearly polarized light in the formed optical thin film can be avoided, a constant transmitted light can be obtained in the monitor light detection unit 19 regardless of the wavelength of the laser beam, and a pair of monitor light detections with the two-wavelength laser unit 18 Since the unit 19 is integrated with the composite optical element 17, the number of parts is reduced, and the structure of the optical pickup can be reduced.

Next, a second embodiment of the optical path correction apparatus according to the present invention will be described.
In general, when irradiating an optical disk with a laser beam for reproducing an optical disk, data reading / writing light irradiated on a pit formed on the optical disk and tracking light irradiated on grooves on both sides of the pit are required. In this case, the laser beam is required to be converted into three beams, and in the second embodiment, the emitted light of the optical path correction device is converted into three beams. Therefore, a grating that diffracts the laser beam is added to the exit side of the circularly polarized laser beam of the optical path correction apparatus described in the first embodiment, and the circularly polarized laser beam is emitted as three beams.

FIG. 4 is a block diagram showing a second embodiment of the optical path correction apparatus according to the present invention, and FIG. 4 (a) corrects the optical paths of the two laser beams incident from the two-wavelength laser section and circularly polarizes them. FIG. 4 (b) is a diagram for explaining a state in which the laser beam having three beams is emitted, and FIG. 4 (b) is a diagram showing a case where the laser beam reflected by the pit formed on the optical disk is incident and the optical path is changed to change the two-wavelength laser unit. The figure for demonstrating a mode that it injects into the monitor light detection part comprised integrally is shown. The optical path correction apparatus shown in the present embodiment shows a structure in which functional elements are laminated and integrated, and the optical path correction apparatus 22 includes a first birefringent plate 15, a first wave plate 5, and a second birefringent plate. 2, a second wave plate 16, and a grating 23, which are disposed in front of the composite optical element 17. The composite optical element 17 is the same as that described in the first embodiment, and includes a two-wavelength laser unit 18 and a pair of light detection units 19. In the second embodiment, it is also possible to fix the optical path correction device 22 to the entire entrance / exit surface of the composite optical element 17 to form a module, and to improve handling and downsizing when assembling an optical pickup described later. It has a great effect.
The second embodiment is different from the optical path correction device in the first embodiment shown in FIG. 1 only in that a grating 23 is added on the emission side of the second wave plate 16 that emits circularly polarized light. The operation of the grating 23 will be described, and the operation of the other elements is the same as that of the first embodiment, and the description thereof will be omitted.

FIG. 5 shows an example in which a grating is added to form a laser beam into three beams, and FIG. 5A shows an example in which laser beams of two different wavelengths λ1 and λ2 are made into three beams, respectively. ) Shows an example in which the laser beam λ1 of one wavelength is transmitted as it is, and only the laser beam λ2 of the other wavelength is converted into three beams. In FIG. 5, the optical paths of the laser beams having the wavelengths λ1 and λ2 are shown separately. However, this is for ease of explanation, and the laser beams of the respective wavelengths actually propagate through the same optical path. . Therefore, the grating 23 is formed by forming a grating having a predetermined refractive index on one side of a substrate with a predetermined depth and pitch. By appropriately setting the depth and pitch, the grating 23 can convert laser light having a desired wavelength. On the other hand, the incident laser light is diffracted into zero-order light as a main beam and two ± first-order lights as side beams.
Therefore, the optical path correction device 22 in this embodiment shown in FIG. 4 receives the circularly polarized laser beam emitted from the second wave plate 16 and diffracts it into three beams of laser beam.

  FIG. 6 is a schematic diagram when the optical path correction device 22 according to the present invention is applied to an optical pickup. The optical pickup 24 includes a two-wavelength laser unit 18 that emits linearly polarized light having two different wavelengths whose polarization directions are parallel to each other, and a pair of monitor light detection units that detect laser light reflected from the pits 10 formed on the optical disk 9. The two-wavelength laser light emitted from the two-wavelength laser unit 18 is propagated on the same optical path, and the two laser lights emitted are circularly polarized and converted into three beams, On the other hand, the optical path correction device 22 that corrects the optical path of the laser light reflected by the pits 10 formed on the optical disk 9 and enters the pair of monitor light detectors 19, and the laser light emitted from the optical path correction device 14 is 90. A half mirror 21 that totally reflects the laser light reflected by the pits 10 formed on the optical disk 9 at a predetermined ratio, and the half mirror 2 An objective lens 11 for condensing a laser beam totally reflected by 90 ° on the separation surface of the optical disc 9 on the pit 10 of the optical disc 9, and a laser beam reflected on the pit 10 formed on the optical disc 9 for the objective lens 11 and the half mirror. And a photodetector 12 for detecting via 21.

The second embodiment is different from the optical pickup 20 of the first embodiment shown in FIG. 3 only in that a grating 23 is added on the emission side of the optical path correction device 14, and thus related to this. Only the portion will be described, and the operation of the other portions is the same as that of the first embodiment, and the description thereof will be omitted.
The laser beam L20 transmitted through the optical path correcting device 22 and converted into three beams by the diffraction action is incident on the half mirror 21, and the laser beam L21 totally reflected by 90 ° on the separation surface is condensed by the objective lens 11 and is collected by the optical disk 9. Irradiated to the pits 10 formed in Therefore, the laser light L22 reflected on the pit 10 becomes reflected light and enters the half mirror 21 through the objective lens 11, and about 90% of the laser light L22 passes through the separation surface. As a result, about 10% of the laser beam L22 is separated as a laser beam L24 that reflects the separation surface by 90 °. At this time, both of the laser beams incident on the half mirror 21 are circularly polarized, and one or both are made into three beams, and the two optical thin films formed on the half mirror 21 are Since there is no wavelength dependence, the transmittance does not change for laser light of two wavelengths.
The laser beam L23 transmitted through the half mirror 21 enters the photodetector 12, and reads information written on the optical disk.

  On the other hand, the laser light 24 reflected by 90 ° by the half mirror 21 is incident on the surface of the grating 23 of the optical path correction device 22 in order to be used as monitor light for the laser light L1 and L2 emitted from the two-wavelength laser unit 18. The optical path correction device 22 corrects the optical paths of the laser beams L1 ′ and L2 ′ that constitute the laser beam L24 reflected by the optical disc 9, and detects a pair of monitor beams that are integrated with the two-wavelength laser unit 18. The laser beams L1 ′ and L2 ′ are incident on the unit 19, and monitor light is detected.

  The optical pickup 24 in this embodiment can avoid wavelength dependency in the optical thin film formed on the mirror surface because the laser light incident on the half mirror 21 is circularly polarized light. When the emission level of the two-wavelength laser unit 18 is monitored, it is possible to detect the monitor light with high accuracy and to make the laser beam irradiated to the pits 10 formed on the optical disc 9 into three beams. Further, since the two-wavelength laser unit 18 and the pair of monitor light detection units 19 are integrated into the composite optical element 17, the number of components is reduced, and the structure of the optical pickup can be reduced.

  As described above, the present invention has been described based on the embodiments. Examples of the material of the wave plate and the birefringent plate used in the present invention include quartz, lithium niobate (lithium niobate), sapphire, calcite, mica, Crystals having birefringence such as rutile, or polymer films or polymers having birefringence can be used.

It is a block diagram which shows the 1st Example of the optical path correction apparatus which concerns on this invention. It is an external view which shows the modification of a 1st wavelength plate. FIG. 2 is a schematic diagram when the optical path correction device 14 according to the present invention is applied to an optical pickup. It is a block diagram which shows the 2nd Example of the optical path correction apparatus which concerns on this invention. An example in which a grating is added to form a laser beam into three beams will be described. FIG. 2 is a schematic diagram when the optical path correction device 22 according to the present invention is applied to an optical pickup. It is a figure for demonstrating the principle of the conventional 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 Japanese Patent Application No. 2003-155617. The example of the schematic diagram at the time of applying the conventional optical path correction apparatus using 2 wavelength laser to an optical pick-up is shown. It is a figure which shows the change of the transmittance | permeability at the time of changing a wavelength in the laser beams of linearly polarized light La and Lb.

Explanation of symbols

1 .... optical path correction device, 2 .... birefringence plate (second birefringence plate),
3 ・ ・ 2 wavelength laser, 4 ・ ・ Optical path corrector,
5 .... Wave plate (first wave plate), 6 .... Double wavelength laser,
7. Optical pickup, 8. Half mirror,
9. ・ Optical disc, 10. ・ Pit,
11 .... objective lens, 12 .... photo detector,
13. ・ Monitor light detector, 14. ・ Optical path correction device,
15. First birefringent plate, 16. Second wave plate,
17. ・ Composite optical element, 18. ・ Double wavelength laser part,
19 .... a pair of monitor light detectors, 20 .... optical pickups,
21. ・ Half mirror, 22. ・ Optical path corrector,
23 ... Grating, 24 ... Optical pickup

Claims (8)

It has a structure in which a first birefringent plate, a first waveplate, a second birefringent plate, and a second waveplate are arranged in order, the polarization directions are parallel to each other, and the optical paths are parallel to each other. When two linearly polarized laser beams having different wavelengths are incident from the first birefringent plate, they are emitted from the second wavelength plate as two circularly polarized laser beams traveling on the same optical path, while two traveling on the same optical path. When a circularly polarized laser beam having two different wavelengths is incident from a second wavelength plate, an optical path correction device that emits from the first birefringent plate as a linearly modified laser beam traveling through two different optical paths,
The first birefringent plate has an optical path changing distance due to refraction when an extraordinary ray is incident, d1, a refractive index of the birefringent plate with respect to an ordinary ray, n0, a refractive index of the birefringent plate with respect to an extraordinary ray, ne, and birefringence. When the angle between the principal surface normal of the plate and the optical axis is θ, and the thickness of the birefringent plate is t1,
t1 = d1 · | (n0 ² · tan θ + ne ² ) / ((n0 ² −ne ² ) · tan θ) |
Satisfying
The first wave plate generates a phase difference of 2π · m for one of the linearly polarized laser beams and a phase difference of π · (2n-1) for the other linearly polarized laser beam. (M and n are integers)
The second birefringent plate is arranged such that one of the two linearly polarized laser beams incident on the optical axis is an ordinary ray and the other is an extraordinary ray, and the optical path of the two linearly polarized laser beams The interval is d2, 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 t2,
t2 = d2 · | (n0 ² · tan θ + ne ² ) / ((n0 ² −ne ² ) · tan θ) |
Satisfying
The second wave plate generates a phase difference of π / 2 · (2p−1) with respect to any incident linearly polarized laser beam or circularly polarized laser beam (p is an integer). An optical path correction device characterized by the above. It has a structure in which a first birefringent plate, a first waveplate, a second birefringent plate, a second waveplate, and a grating are arranged in order, the polarization directions are parallel to each other, and the optical path is When two linearly polarized laser beams having different wavelengths that are parallel to each other are incident from the first birefringent plate, two circularly polarized laser beams traveling on the same optical path are formed, and three beams are emitted from the grating, while the same An optical path correction device that emits from a first birefringent plate as a linearly polarized laser beam traveling through two different optical paths when two circularly polarized laser beams traveling through the optical path are incident from the grating,
The first birefringent plate has an optical path changing distance due to refraction when an extraordinary ray is incident, d1, a refractive index of the birefringent plate with respect to an ordinary ray, n0, a refractive index of the birefringent plate with respect to an extraordinary ray, ne, and birefringence. When the angle between the principal surface normal of the plate and the optical axis is θ, and the thickness of the birefringent plate is t1,
t1 = d1 · | (n0 ² · tan θ + ne ² ) / ((n0 ² −ne ² ) · tan θ) |
Satisfying
The first wave plate generates a phase difference of 2π · m for one of the linearly polarized laser beams and a phase difference of π · (2n-1) for the other linearly polarized laser beam. (M and n are integers)
The second birefringent plate is arranged such that one of two linearly polarized laser beams incident on the optical axis is an ordinary ray and the other is an extraordinary ray, and the first birefringent plate and Arranged so that their main cross-sections are orthogonal to each other, the optical path interval of the two linearly polarized laser beams is d2, 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, birefringence When the angle between the principal surface normal of the plate and the optical axis is θ, and the thickness of the birefringent plate is t2,
t2 = d2 · | (n0 ² · tan θ + ne ² ) / ((n0 ² −ne ² ) · tan θ) |
Satisfying
The second wave plate generates a phase difference of π / 2 · (2p−1) with respect to any incident linearly polarized laser beam or circularly polarized laser beam (p is an integer),
1. The optical path correction apparatus according to claim 1, wherein the grating diffracts one or both of the incident circularly polarized laser beams having different wavelengths into three beams of 0th order light and ± 1st order light.   2. The structure according to claim 1, wherein the first birefringent plate, the first wave plate, the second birefringent plate, and the second wave plate are bonded and integrated. Optical path correction device.   The first birefringent plate, the first wave plate, the second birefringent plate, the second wave plate, and the grating are bonded and integrated. 2. The optical path correction device according to 2.   5. The optical path correction apparatus according to claim 1, wherein the first wave plate and the second wave plate are crystals having birefringence.   7. The optical path correction device according to claim 1, wherein the first birefringent plate and the second birefringent plate are lithium niobate or rutile. A composite optical element comprising a two-wavelength laser unit that emits linearly polarized laser beams having two different wavelengths whose polarization directions are parallel to each other, and a pair of monitor light detection units;
The optical path correction device according to any one of claims 1 to 6, wherein two linearly polarized laser beams are incident from the two-wavelength laser unit, and monitor light is emitted to the monitor light detection unit;
An optical pickup comprising: an objective lens that condenses the light beam emitted from the optical path correction device on an optical storage medium. A composite optical element comprising a two-wavelength laser unit that emits linearly polarized laser beams having two different wavelengths whose polarization directions are parallel to each other, and a pair of monitor light detection units;
The optical path correction device according to any one of claims 1 to 6, wherein two linearly polarized laser beams are incident from the two-wavelength laser unit, and monitor light is emitted to the monitor light detection unit;
An optical pickup comprising an objective lens for condensing a light beam emitted from the optical path correction device onto an optical storage medium, and having a structure in which the composite optical element and the optical path correction device are integrated.

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