JP2005189677A - Beam alignment polarization beam splitter and optical pickup - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a beam alignment polarization beam splitter which has high transmission and can be easily assembled to an optical pickup device. <P>SOLUTION: The beam alignment polarization beam splitter comprises first and second prisms 31, 32 having refractive indexes different from each other and a polarizing film 33 interposed between the first and second prisms 31, 32. Therein, the incident direction of a laser beam to an incident surface 311 and the outgoing direction of the laser beam from a first outgoing surface 321 are made parallel. Further, the angle between the first outgoing surface 321 and the outgoing direction of the laser beam outgoing from the first outgoing surface 321 is made to be 90° and the angle between a second outgoing surface 322 and the outgoing direction of the laser beam outgoing from the second outgoing surface 322 is made to be 90°. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a beam shaping polarization beam splitter, and more particularly, to a beam shaping polarization beam splitter used for an optical pickup of an optical disc apparatus.

  In order to improve the recording density of the optical disc, it is necessary to reduce the spot size at the focal point of the laser beam used for recording / reproduction. In order to reduce the spot size of the laser beam, the wavelength of the laser beam (laser diode oscillation wavelength) may be shortened and the numerical aperture (NA) of the objective lens may be increased. However, there is a limit to reducing the spot size by shortening the wavelength of the laser beam and increasing the numerical aperture of the objective lens.

  For example, the track pitch of a Blu-ray Disc capable of high density recording is 0.32 μm, and in order to obtain good recording / reproduction characteristics, a spot size of about 0.40 to 0.41 μm is required. Needed. However, even if the wavelength of the laser beam is 405 nm and the numerical aperture NA of the objective lens is 0.85, such a spot size cannot be obtained. Further, it is extremely difficult to realize a shorter wavelength of the laser beam and a higher numerical aperture of the objective lens.

  Apart from the wavelength of the laser beam and the numerical aperture of the objective lens, as a method of reducing the spot size, it is conceivable to increase the rim intensity by reducing the rim expected angle of the laser beam incident on the objective lens. However, in this method, only the central part (high intensity part) of the laser beam emitted from the laser diode is incident on the objective lens and the remaining part is discarded, so that the utilization efficiency of the laser beam is poor. Moreover, since the light emitted from the laser diode is an elliptical beam, the length of the short axis (generally the horizontal axis) of the far field image (FFP) is set to maximize the utilization efficiency. Even with the reference, the loss of the laser beam in the major axis (generally the vertical axis) direction is large.

  Therefore, conventionally, a beam shaping prism using a wedge prism is arranged on the optical path to perform beam shaping, and the utilization efficiency is improved by bringing the shape of the laser beam close to a circle.

  A conventional beam shaping prism is configured as shown in FIG. 1 (see, for example, Patent Document 1, 2, or 3).

  More specifically, the beam shaping prism 10 in FIG. 1 includes two wedge prisms (glass materials) 11 and 12 having different refractive indexes, and a polarizing film 13 disposed therebetween. That is, the beam shaping prism of FIG. 1 is configured as a polarizing beam splitter.

  A laser beam incident on the beam shaping prism 10 of FIG. 1 from the upper left is incident in a uniaxial direction (vertical direction in the figure) at the mirror field of the two wedge prisms 11 and 12, and the shape is circular. It can be approached. The laser beam brought close to a circle is emitted with a refraction angle γ in the right direction in the figure. By setting the refraction angle γ to 0 ° when the laser beam has a predetermined frequency, the influence of chromatic aberration can be suppressed. That is, when the laser beam frequency fluctuates due to a temperature change or the like, it is possible to suppress a change in the refractive index and a change in the emission angle γ. Further, the laser beam incident from the right side of the figure is reflected by the polarizing film 13 disposed between the two prisms 11 and 12, and is emitted downward in the figure. The refraction angle is also set to 0 ° with respect to the laser beam having a predetermined frequency so as to suppress chromatic aberration.

  Further, there is a conventional beam shaping prism configured as shown in FIG. 2 (see, for example, Patent Document 4).

  The beam shaping prism 20 of FIG. 2 is also configured to combine two wedge prisms 21 and 22 having different refractive indexes to make the beam shape close to a circle and to suppress chromatic aberration, as in FIG. Has been. In this beam shaping prism, the apex angle of the prism 22 is set to 45 ° or less, and a laser beam incident on the prism 21 at an incident angle β is emitted from the prism 22 at a refraction angle of 0 ° in parallel with the incident direction. . However, this beam shaping prism does not include a polarizing film between the two prisms 21 and 22. That is, the beam shaping prism 20 is not considered at all for use as a polarization beam splitter.

Japanese Patent Laid-Open No. 10-62611 JP-A-11-126363 JP-A-11-154344 JP 2001-305319 A

  The conventional polarizing beam splitter as shown in FIG. 1 has a problem that since the incident angle α of the laser beam is relatively large, the ratio of reflection at the incident surface is large, and thus the transmittance of the laser beam is low. In addition, the beam shaping prism has a problem that a slight deviation in the incident angle α of the laser beam appears as a large deviation in the emission angle γ, and it is difficult to assemble the beam shaping prism into the optical pickup device.

  In addition, the beam shaping prism as shown in FIG. 2 has a relatively small incident angle α of the laser beam and can make the incident direction and the emitting direction parallel to each other. Although there are few, there exists a problem that it cannot be comprised as a polarizing beam splitter combining with a polarizing film.

  Therefore, an object of the present invention is to provide a beam-shaping polarization beam splitter that has a high transmittance and can be easily assembled to an optical pickup device.

According to the present invention, the first and second prisms (31, 32) having different refractive indexes and the polarizing film (33) sandwiched between the first and second prisms (31, 32). And the first laser beam incident on the first prism (31) is transmitted through the polarizing film (33) and from the first emission surface (321) of the second prism (32). The second laser beam that has exited and entered the first exit surface (321) is reflected by the polarizing film (33) and exits from the second exit surface (322) of the second prism (32). In a beam-shaping polarization beam splitter (30) configured to:
A beam-shaped polarized beam characterized in that a direction in which the first laser beam is incident on the first prism (31) and a direction in which the first laser beam is emitted from the first emission surface (311) are parallel to each other. A splitter (30) is obtained.

  The beam shaping polarization beam splitter (30) has an angle formed by the first emission surface (311) and the emission direction of the first laser beam of 90 °, and the second emission surface (322). ) And the emission direction of the second laser beam is configured to be 90 °.

  In addition, according to the present invention, an optical pickup including the beam-like background polarization beam splitter can be obtained.

  The numbers in parentheses are given for easy understanding of the present invention and do not limit the present invention.

  According to the present invention, in the beam shaping polarization beam splitter, by making the incident direction and the emitting direction parallel, the incident angle can be reduced, and thereby the transmittance can be increased. In addition, since the incident direction and the outgoing direction are parallel, it is easy to assemble the optical pickup.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  3A, 3B, and 3C are a front view, a right side view, and a bottom view, respectively, of a beam shaping polarization beam splitter 30 according to an embodiment of the present invention.

  As shown in FIG. 3A, the beam-shaping polarization beam splitter 30 according to the present embodiment includes first and second prisms 31 and 32 having different refractive indexes and polarized light sandwiched between them. And a film 33.

  The first prism 31 includes an incident surface 311 on which a laser beam directed toward the left side or the right side in the drawing is incident.

  The second prism 32 is incident on the incident surface 311 of the first prism 31 and emits a laser beam that has been transmitted through the polarizing film 33, and a first emission from the right side of the drawing. A second emission surface 322 that emits a laser beam incident on the surface 321 and reflected by the polarizing film 33.

  Antireflection coatings are applied to the surfaces of the incident surface 311, the first exit surface 321, and the second exit surface, respectively.

  The polarizing film 33 transmits P-polarized light that is linearly polarized light and reflects S-polarized light, or transmits S-polarized light and reflects P-polarized light. Hereinafter, a case where P-polarized light is transmitted and S-polarized light is reflected will be described.

  The shape and refractive index of each of the first and second prisms 31 and 32 are determined so as to satisfy the following conditions (1) to (4).

(1) The beam shape (ellipse) of the laser beam incident on the incident surface 311 is enlarged with respect to the uniaxial direction so that the beam shape (ellipse) becomes circular when emitted from the first emission surface 321 (the beam shape is shaped). .

(2) The incident direction of the laser beam on the incident surface 311 and the emitting direction of the laser beam from the first emitting surface 321 are parallel to each other.

(3) The direction of the laser beam emitted from the first emission surface 321 is substantially 90 ° (refraction angle = 0 °) with respect to the first emission surface 321.

(4) The laser beam incident on the first emission surface 321 at an incident angle of 0 ° is reflected by the polarizing film 33 and is substantially at an angle of 90 degrees with respect to the second emission surface 322 (refraction angle = 0 °). Exit with

  A beam shaping polarization beam splitter that satisfies the above conditions may be configured as follows, for example.

  That is, S-NSL36 (manufactured by OHARA) having a refractive index n = 1.533934 (wavelength = 405 nm) is used as a glass material constituting the first prism 31, and refraction is used as a glass material constituting the second prism 32. S-LAL18 (also made by OHARA) having a rate n = 1.751073 is used. The angle formed between the incident surface 311 and the polarizing film 33 is 105.35 °, and the angle formed between each of the first output surface 321 and the second output surface and the polarizing film 33 is 58.6 °. That's fine. In this case, the incident angle of the laser beam on the incident surface 311 is 46.75 °. Note that some errors are allowed in the angles formed by the surfaces.

  Next, the operation of the beam-shaping polarization beam splitter that satisfies the above conditions will be described with reference to FIG.

  Assume that a laser beam (P-polarized light) traveling in the right direction from the left side in FIG. 4 is incident on the incident surface 311 of the first prism 31. The laser beam (P-polarized light) incident on the incident surface 311 is refracted when entering the inside of the first prism 31, changes its traveling direction upward, and enters the polarizing film 33.

  The polarizing film 33 transmits the incident laser beam (P-polarized light) and makes it incident on the second prism 32.

  When entering the second prism 32, the laser beam (P-polarized light) is refracted again, and its traveling direction becomes parallel to the laser beam incident on the incident surface 311. Further, since the polarizing film 33 is provided so that the laser beam from the incident surface 311 is incident at a large incident angle, the laser beam that has entered the second prism from the first prism side is the vertical direction in the figure. Expanded on.

  The laser beam (P-polarized light) incident on the second prism 32 from the polarizing film 33 is emitted outside without being refracted from the first emission surface 321.

  Further, the laser beam (S-polarized light) traveling from the right side to the left side in FIG. 4 is incident on the first emission surface 321 at an incident angle = 0 °, and enters the polarizing film 33 without being refracted.

  The polarizing film 33 reflects the laser beam (S-polarized light) from the first emission surface 321 so as to enter the second emission surface at an incident angle of 0 °. The laser beam (S-polarized light) reflected by the resist film 33 is emitted from the second emission surface to the outside without being refracted.

  As described above, in the beam-shaping polarization beam splitter according to the present embodiment, the direction in which the laser beam is incident on the incident surface and the direction in which the laser beam is emitted from the first emission surface are parallel to each other. Easy assembly.

  In addition, since the incident angle of the laser beam on the incident surface is relatively small, there is little reflection and high transmittance can be realized.

  Next, an optical pickup using the beam shaping polarization beam splitter of FIG. 3 will be described with reference to FIG.

  The optical pickup shown in FIG. 5 includes the beam shaping beam splitter 30 shown in FIG. 3, the laser diode 51 and the collimator lens 52 arranged on the incident surface 311 side, and the quarter wavelength arranged on the first emission surface 321 side. A plate 53, a rising mirror 54, an objective lens 55, a collimator lens 56, a sensor lens 57, and a photodiode 58 disposed on the second emission surface side 322 are provided.

  The laser diode 51 generates a linearly polarized laser beam (here, P-polarized light). The laser beam emitted from the laser diode 51 enters the collimator lens 51.

  The collimator lens 52 converts the incident laser beam into parallel light and emits it. The laser beam emitted from the collimator lens 52 is incident on the incident surface 311 of the beam shaping beam splitter 30 and is emitted from the first emission surface 321. The laser beam emitted from the first emission surface 321 is incident on the quarter wavelength plate 53.

  The quarter-wave plate changes the polarization state of the incident laser beam to circularly polarized light and makes it incident on the rising mirror 54.

  The raising mirror 54 changes the traveling direction of the laser beam from the quarter wavelength plate and makes it incident on the objective lens 55.

  The objective lens 55 focuses the laser beam on the optical disk 59 from the rising mirror 54. Further, the objective lens converts the reflected laser beam from the optical disk 59 into parallel light and makes it incident on the rising mirror 54.

  The raising mirror 54 causes the reflected laser beam from the objective lens 55 to enter the quarter wavelength plate 53.

  The quarter wavelength plate 53 changes the polarization state of the reflected laser beam from circularly polarized light to S polarized light and makes it incident on the beam shaping beam splitter 30. The reflected laser beam incident on the beam shaping beam splitter 30 exits from the second exit surface 322 and enters the collimator lens 56.

  The collimator lens 56 converts the incident reflected laser beam into convergent light and makes it incident on the sensor lens 57.

  The sensor lens 57 gives (adjusts) astigmatism to the incident reflected laser beam and makes it incident on the photodiode 58.

  The photodiode 58 detects the incident reflected laser beam and converts it into an electrical signal.

  As described above, the beam shaping beam splitter 30 in FIG. 3 is used for the optical pickup of the optical disc apparatus.

It is a front view of the conventional beam shaping prism. It is a front view of the other conventional beam shaping prism. It is (a) front view, (b) right side view, and (c) bottom view of the beam shaping splitter 30 which concerns on one embodiment of this invention. It is a figure for demonstrating the effect | action of the beam shaping splitter 30 of FIG. It is the schematic which shows the structure of the optical pick-up containing the beam shaping splitter 30 of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10,20 Beam shaping prism 11, 12, 21, 22 Wedge prism 13 Polarizing film 30 Beam shaping polarization beam splitter 31, 32 Prism 33 Polarizing film 311 Entrance surface 321 First exit surface 322 Second exit surface 51 Laser diode 52 Collimator lens 53 1/4 wavelength plate 54 Rising mirror 55 Objective lens 56 Collimator lens 57 Sensor lens 58 Photo diode 59 Optical disk

Claims (5)

A first laser beam having first and second prisms having different refractive indexes and a polarizing film sandwiched between the first and second prisms is incident on the first prism. The second laser beam that passes through the polarizing film and exits from the first exit surface of the second prism, and is incident on the first exit surface, is reflected by the polarizing film, and is reflected by the second prism. In a beam shaping polarization beam splitter configured to exit from the second exit surface,
A beam-shaping polarization beam splitter, wherein a direction in which the first laser beam is incident on the first prism and a direction in which the first laser beam is emitted from the first emission surface are parallel to each other. The beam-shaping polarization beam splitter according to claim 1,
The angle formed by the first emission surface and the emission direction of the first laser beam is 90 °, and the angle formed by the second emission surface and the emission direction of the second laser beam is 90 °. A beam-shaping polarization beam splitter, characterized in that it is   An optical pickup comprising the beam-shaping polarization beam splitter according to claim 1. The optical pickup according to claim 3,
A laser diode that generates the first laser beam; a first collimator lens that converts the first laser beam from the laser diode into parallel light and enters the first prism; and the first collimator lens A quarter-wave plate for changing the polarization states of the first laser beam emitted from the emission surface and the second laser beam incident on the first emission surface, and the quarter-wave plate from the quarter-wave plate A rising mirror for directing the first laser beam toward the optical disc and the second laser beam from the optical disc toward the quarter-wave plate, and the first laser going from the rising mirror toward the optical disc An objective lens for condensing the beam and converting the second laser beam from the optical disk toward the rising mirror into parallel light; A collimator lens that converts the second laser beam emitted from the emission surface into a convergent light, a sensor lens that adjusts the second laser beam from the collimator lens, and the second lens from the sensor lens. An optical pickup comprising a photodiode for detecting a laser beam. The optical pickup according to claim 4,
The optical pickup characterized in that the first laser beam from the laser diode is P-polarized light or S-polarized light.

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