JP2006313609A - Light path correction unit, and optical pickup - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light path correction unit not producing astigmatism, and an optical pickup having a light path correction unit. <P>SOLUTION: This light path correction unit corrects the one light path of the two laser beams L1, L2 different in wavelength so as to be aligned. It has a birefringent plate 10 to correct the light path of the laser beam L2 to be aligned with that of the laser beam L1, a collimator lens 1 to make the laser beam L1 from the birefringent plate 10 parallel light and to pass the laser beam L2, and an astigmatism correction plate 2 arranged at the emission surface of the collimator lens 1 to correct the astigmatism of the laser beam L2 produced by the birefringent plate 10. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an optical path correction apparatus that corrects optical paths of two laser beams having different wavelengths, and an optical pickup including such an optical path correction apparatus, and is particularly suitable for an optical disc apparatus.

An optical pickup used in an optical disc apparatus has a structure in which a plurality of laser beams having different wavelengths can be used to cope with different types of optical discs.
FIG. 3 is a diagram showing a configuration example of an optical system that synthesizes light of two different wavelengths used in an optical pickup.
In FIG. 3, 11 is an LD (laser diode) having a wavelength of 650 nm, 12 is an LD having a wavelength of 780 nm, and 101 is a dichroic prism that combines two wavelengths. In the optical system configured to synthesize light of two wavelengths configured in this way, approximately 90% or more of the light from the LD 11 having a wavelength of 650 nm is transmitted through the dichroic prism 101. Further, almost 90% or more of the light of the LD 12 having a wavelength of 780 nm is reflected by 90 degrees by the dichroic prism 101 and enters the same optical path as the transmitted light from the LD 11. It was common to synthesize two wavelengths by reflecting and transmitting each light in the same direction. However, in such a conventional method, since the LD is arranged in two directions, it is difficult to make the optical pickup compact.
Therefore, Patent Document 1 discloses a technique for arranging a plurality of LDs in one direction.
FIG. 4 is a diagram showing the configuration of the optical system disclosed in Patent Document 1. In FIG.
In the optical system shown in FIG. 4, laser beams L1 and L2 respectively emitted from the LD 11 and the LD 12 are vertically incident on the multiple wavelength combining element (birefringent plate) 10. At this time, the laser beam L1 emitted from the LD 11 is set to have the same polarization plane as that of the ordinary beam L1o when entering the multi-wavelength combining element 10. The laser beam L2 emitted from the LD 12 has the same polarization plane as that of the extraordinary beam L2e when entering the birefringent plate 10. That is, the vibration direction of the magnetic vector of the laser beam L1 is perpendicular to the main cross section (XY plane) (indicated by a small circle having a point inside), and the vibration direction of the magnetic vector of the laser beam L2 is parallel to the main cross section (up and down As shown by arrows, the adjustment is performed while rotating the LD 11 and LD 12 about the outgoing optical path.

However, in the two-wavelength synthesis method as described above, it is necessary to provide two LDs individually and arrange these optical paths so as to be orthogonal to each other. For this reason, it has been difficult to make the optical pickup compact.
Therefore, for example, it is conceivable to form laser light sources having two different wavelengths on one semiconductor substrate. However, it is not easy to make the planes of polarization orthogonal to each other due to restrictions in the manufacturing process, and 2 emitted from the laser light source. Since the polarization planes of the two laser beams are the same, the optical path correction method disclosed in Patent Document 1 cannot be applied.
Therefore, the applicant of the present application rotates the polarization plane of one of the laser beams of two different wavelengths whose polarization planes emitted from the laser light source are parallel to each other by 90 degrees, and changes the other laser beam. There has also been proposed an optical path correction device in which a wave plate configured to transmit a polarization plane without being rotated is disposed in front of a birefringent plate as an optical path correction element (Patent Document 2).
JP 2001-283457 A JP 2005-18960 A

However, the optical path correction devices proposed in Patent Documents 1 and 2 have the following problems.
FIG. 5 is a diagram schematically showing an optical path when a laser beam (diverged light) emitted from a laser light source passes through a birefringent plate. In FIG. 5, it is assumed that a laser unit 20 in which laser light sources 21 and 22 that emit laser beams L1 and L2 having two different wavelengths are integrally formed is provided as a laser light source.
In this case, as shown in FIG. 5A, the passing distance d1 when the divergent light of the laser beam L1 emitted from the laser light source 21 of the laser unit 20 and transmitted through the birefringent plate 10 passes through the birefringent plate 10. , D1 ′ are equal.
On the other hand, as shown in FIG. 5B, the laser beam L2 emitted from the laser light source 22 of the laser unit 20 and whose optical path is corrected so as to coincide with the optical path of the laser beam L1 in the birefringent plate 10 is obtained. A difference occurs in the passing distances d2 and d2 ′ when the diverging light passes through the birefringent plate 10. That is, when divergent light of the laser beam L2 passes through the birefringent plate 10, there is a problem that an optical path difference occurs and astigmatism occurs in the laser beam L2. For this reason, it has been difficult to apply the optical path correction device as described above to the optical pickup device.
Accordingly, the present invention has been made in view of the above-described points, and an object thereof is to provide an optical path correction device that does not cause astigmatism and an optical pickup including the optical path correction device. .

In order to achieve the above object, an invention according to claim 1 is an optical path correction device for correcting an optical path of two laser beams having different wavelengths so as to match an optical path of the first laser beam. An optical path correction unit that corrects the optical path of the second laser beam, and the first and second laser beams that are disposed on the exit surface side of the optical path correction unit and are emitted from the optical path correction unit. A collimator lens that converts the divergent light of one laser beam into parallel light and transmits the second laser beam; and the second laser that is disposed on the exit surface side of the collimator lens and that is generated in the optical path correcting means And astigmatism correction means for correcting the astigmatism of the light beam.
According to a second aspect of the present invention, in the optical path correction device according to the first aspect, the optical path correction means includes a uniaxial crystal plate and has an optical axis of 45 degrees with respect to both principal surfaces of the uniaxial crystal plate. It is characterized by that.
According to a third aspect of the present invention, there is provided an optical pickup including the optical path correcting device according to the first or second aspect.

According to the present invention, when the optical path correction is performed by the optical path correction unit so that the optical path of the second laser beam coincides with the optical path of the first laser beam, the second laser beam passes through the optical path correction unit. Since the astigmatism generated due to the difference in optical path difference is corrected by the astigmatism correction means, an optical path correction apparatus free of astigmatism can be realized.
Therefore, if the optical pickup is configured using the optical path correction apparatus of the present invention, the optical pickup for two wavelengths can be made compact.

Hereinafter, embodiments of the optical path correction apparatus of the present invention will be described.
FIG. 1 is a diagram showing a configuration of an optical path correction apparatus as an embodiment of the present invention.
The optical path correction apparatus shown in FIG. 1 is disposed on a birefringent plate (optical path correcting means) 10, a collimator lens 1 disposed on the exit surface side of the birefringent plate 1, and an exit surface side of the collimator lens 1. And an astigmatism correction plate (astigmatism correcting means) 2. Laser beams L1 and L2 emitted from two laser light sources 11 and 12 having different emission wavelengths are vertically incident on the birefringent plate 10, respectively. The laser light source 11 is an LD (laser diode) that emits a laser beam (first laser beam) L1 having a wavelength of 650 nm, and the laser light source 12 is an LD that emits a laser beam (second laser beam) L2 having a wavelength of 780 nm.
The birefringent plate 10 is formed by slicing a uniaxial crystal material having birefringence so that the optical axis Ao forms an angle of 45 degrees with the surface as described above with reference to FIG. The arrangement of the two laser beams L1 and L2 to be combined with the optical axis Ao of the plate 10 is such that the plane including the laser beam L1 and the laser beam L2 is parallel to the optical axis Ao. Also in this case, the laser beam L1 emitted from the laser light source 11 has the same polarization plane as the ordinary beam L1o when entering the birefringent plate 10. Further, the laser beam L2 emitted from the laser light source 12 has the same polarization plane as the extraordinary beam L2e when entering the birefringent plate 10.
The collimator lens 1 is designed to act on the laser beam L1 having the wavelength λ1 from the laser light source 11. That is, the laser beam L1 having the wavelength λ1 incident from the laser light source 11 is emitted as parallel light, but the laser beam L2 having the wavelength λ2 incident from the laser light source 12 functions as it is.
The astigmatism correction plate 2 is made of optical glass on a flat plate, for example, and functions to correct astigmatism of the laser beam L2 generated in the birefringent plate 10.

In the optical path correction apparatus according to the present embodiment configured as described above, the laser beam L1 having the wavelength λ1 emitted from the laser light source 11 is incident on the collimator lens 1 through the birefringent plate 10, and is converted into parallel light by the collimator lens 1. It is converted and incident on the astigmatism correction plate 2. In this case, since the laser beam L1 does not cause astigmatism in the birefringent plate 10, it is necessary to prevent the astigmatism from being corrected in the astigmatism correction plate 2 for the laser beam L1.
For this reason, in the present embodiment, the collimator lens 1 is disposed between the birefringent plate 10 and the astigmatism correction plate 2, and the divergence of the laser beam L1 that does not cause astigmatism in the birefringent plate 10 occurs. The light is converted into parallel light. As a result, the astigmatism correction is not performed on the laser beam L1 in the subsequent astigmatism correction plate 2.
On the other hand, the laser beam L2 in which astigmatism occurs in the birefringent plate 10 passes through the collimator lens 1 as it is and is incident on the astigmatism correction plate 2 without being converted into parallel light in the collimator lens 1. Therefore, the astigmatism generated in the birefringence plate 10 is corrected in the astigmatism correction plate 2.
Therefore, according to the optical path correction apparatus of this embodiment, when the birefringent plate 10 performs correction so that the optical path of the second laser beam L2 coincides with the optical path of the first laser beam L1, Since the astigmatism generated due to the difference in optical path difference when the second laser beam L2 passes through the birefringent plate 10 is corrected by the astigmatism correction plate 2, an optical path correction device free of astigmatism. Can be realized. Therefore, if the optical pickup is configured using the optical path correction apparatus of this embodiment, the optical pickup for two wavelengths can be made compact.

In the optical path correction apparatus shown in FIG. 1, the laser light sources 11 and 12 are individually provided. For example, as shown in FIG. 2, two different wavelength lasers are emitted onto one semiconductor substrate. It is of course possible to use the laser unit 20 in which the laser light sources 21 and 22 that can be used are formed.
However, in this case, as described in Patent Document 2, it is not easy to make the planes of polarization orthogonal to each other due to restrictions in the manufacturing process, and the planes of polarization of the two laser beams emitted from the laser light source are the same. Therefore, the polarization plane of one of the two laser beams of different wavelengths whose polarization planes emitted from the laser light sources 21 and 22 of the laser unit 20 are parallel to each other is rotated by 90 degrees, and the other It is necessary to arrange the wave plate 23 configured to transmit the laser beam as it is without rotating the plane of polarization in front of the birefringent plate 10. And if comprised in this way, it will become possible to reduce in size an optical pick-up.

The figure which showed the structure of the optical path correction apparatus as embodiment of this invention. The figure which showed the other structure of the laser light source. The figure which showed the structure of the conventional optical system. The figure which showed the structure of the conventional optical path correction element. The figure which showed typically the optical path when the laser beam (divergent light) radiate | emitted from the conventional laser light source passes a birefringent plate.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Collimator lens, 2 ... Astigmatism correction plate, 10 ... Birefringence plate, 11, 12, 21, 22 ... Laser light source, 23 ... Wave plate

Claims (3)

An optical path correction device that corrects the optical paths of two laser beams having different wavelengths to coincide with each other,
Optical path correction means for correcting the optical path of the second laser beam so as to coincide with the optical path of the first laser beam;
Of the first and second laser beams emitted from the optical path correcting unit, disposed on the exit surface side of the optical path correcting unit, the divergent light of the first laser beam is converted into parallel light, and the first A collimator lens that transmits two laser beams;
Astigmatism correcting means disposed on the exit surface side of the collimator lens and correcting astigmatism of the second laser beam generated in the optical path correcting means;
An optical path correction device comprising:   2. The optical path correction apparatus according to claim 1, wherein the optical path correction means is formed of a uniaxial crystal plate and has an optical axis of 45 degrees with respect to both principal surfaces of the uniaxial crystal plate.   An optical pickup comprising the optical path correcting device according to claim 1.

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