JP2008130156A - Optical element, objective optical element unit, and optical pickup device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical element, an objective optical element unit, and an optical pickup device capable of properly recording and/or reproducing information by suppressing erroneous detection in a photodetector. <P>SOLUTION: Because surfaces P11, P12 in a flange part FL1 of the optical element OE1 are inclined with respect to a direction perpendicular to an optical axis, and the surface roughness of a surface P13 is deteriorated, when a light beam parallel to the optical axis is incident on the optical element OE1, the light beam reflected by the flange part FL1 is prevented from being incident on a light receiving surface of the photodetector PD so that information can be properly recorded and/or reproduced. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an optical element, an objective optical element unit, and an optical pickup device, and more particularly to an optical element suitable for recording and / or reproducing information on a high-density optical disc, an objective optical element unit, and an optical device. The present invention relates to a pickup device.

  In recent years, research and development of high-density optical disc systems that can record and / or reproduce information (hereinafter, “recording and / or reproduction” is referred to as “recording / reproduction”) using a blue-violet semiconductor laser having a wavelength of about 405 nm. Development is progressing rapidly. As an example, in an optical disc for recording / reproducing information with specifications of NA 0.65 and light source wavelength of about 405 nm, so-called HD DVD (hereinafter referred to as HD), information of 15 to 20 GB per layer with respect to an optical disc having a diameter of 12 cm. Can be recorded. As another example, an optical disc that records and reproduces information with specifications of NA 0.85 and a light source wavelength of about 405 nm, that is, a so-called Blu-ray Disc (hereinafter referred to as BD) per layer for an optical disc having a diameter of 12 cm. Information of 15 to 25 GB can be recorded. Hereinafter, such an optical disc is referred to as a “high density optical disc” in the present specification.

In an optical pickup device using a blue-violet semiconductor laser, axial chromatic aberration of the objective optical element may become a problem due to minute fluctuations in the oscillation wavelength of the light source. In general lens materials, the change in refractive index due to minute wavelength fluctuations increases with shorter wavelength light, so defocusing caused by minute wavelength fluctuations in objective optical elements used to collect blue-violet laser light. The amount tends to be large. The depth of focus of the objective optical element is used as can be seen from k · λ / NA ² (k is a proportional constant, λ is the wavelength, and NA is the image-side numerical aperture of the objective optical element). The shorter the oscillation wavelength of the light source, the smaller the depth of focus, and a slight defocus amount is not allowed. Therefore, in an optical system using a short wavelength light source such as a blue-violet semiconductor laser and an objective optical element having a high image-side numerical aperture, wavelength variation due to output changes such as a mode-hop phenomenon of the blue-violet semiconductor laser, In order to prevent deterioration of wavefront aberration due to high frequency superposition, correction of axial chromatic aberration is important. Patent Document 1 discloses a configuration in which a parallel plate having a diffractive structure is disposed on the light source side of an objective lens in order to correct axial chromatic aberration.
JP 2002-082280 A

  However, since the flange portion of the parallel plate is orthogonal to the optical axis, when light outside the effective diameter is incident on the flange portion, the reflected light from the flange portion is incident on the photodetector. There is a risk of reading errors.

  The present invention has been made in view of the problems of the prior art, and an optical element, an objective optical element unit, and an optical pickup capable of appropriately recording / reproducing information while suppressing erroneous detection of a photodetector. An object is to provide an apparatus.

  The optical element according to claim 1 condenses a light beam having a wavelength λ1 emitted from a light source on an information recording surface of an optical information recording medium having a thickness t1 of a protective substrate to record / reproduce information. An optical element used in the apparatus, wherein the optical element has two optical functional surfaces each having power and a flange portion, and a light beam parallel to the optical axis is incident on the flange portion. Further, a reflection structure for reducing light reflected in a direction parallel to the optical axis is provided.

  According to the present invention, the optical element has two optical function surfaces each having power and a flange portion, and when a light beam parallel to the optical axis is incident on the flange portion, Since a reflection structure that reduces light reflected in a direction parallel to the axis is provided, the light beam reflected from the flange portion is prevented from entering the light receiving surface of the photodetector of the optical pickup device, This makes it possible to appropriately record / reproduce information. For example, when the optical element is tilted and the flange portion is angled with respect to the direction perpendicular to the optical axis, when a light beam parallel to the optical axis enters the angled flange portion, light is emitted from the flange portion. It can suppress that light reflects in the direction parallel to an axis. However, when power is given to two optical function surfaces as in the optical element of the present invention, the optical element cannot be tilted because aberration is generated by tilting the optical element with respect to the optical axis. Therefore, when the light beam parallel to the optical axis is incident, the reflection structure that reduces the light reflected in the direction parallel to the optical axis is effective. The “flange portion” refers to a surface other than the optical functional surface of the optical element that intersects the optical axis. Specifically, it refers to a region where a light beam having an outside diameter is incident. The information recording medium side may be sufficient, and both the light source side and the optical information recording medium side may be sufficient.

  According to a second aspect of the present invention, there is provided the optical element according to the first aspect of the present invention, wherein the optical element has a function of correcting axial chromatic aberration at least with respect to a light beam having a wavelength λ1 from the light source. However, it is optional to provide the optical element with a diffractive structure for realizing compatibility with, for example, a DVD or a CD.

  The optical element according to claim 3 is parallel to the optical axis when the light beam with wavelength λ1 from the light source is incident as a light beam parallel to the optical axis in the invention according to claim 1 or 2. In this case, it is easy to assemble the optical pickup device.

  The optical element according to claim 4 is the invention according to any one of claims 1 to 3, wherein the reflection structure has a function of scattering a light beam incident on the reflection structure. By scattering the light beam incident on the flange portion of the optical element, it is possible to suppress the light beam reflected from the flange portion from entering the light receiving surface of the photodetector of the optical pickup device.

  An optical element according to a fifth aspect is characterized in that, in the invention according to any one of the first to fourth aspects, the flange portion is inclined with respect to a direction orthogonal to the optical axis. Thereby, it can suppress that the light beam reflected by the said flange part injects into the light-receiving surface of the photodetector of an optical pick-up apparatus.

  The “reflection structure for reducing light reflected in a direction parallel to the optical axis when a light beam parallel to the optical axis is incident” is not limited to the above-described example. For example, an antireflection film may be formed on the flange portion of the optical element or covered with a black resin cover.

  An objective optical element unit according to claim 6 includes the optical element according to any one of claims 1 to 5, an objective optical element, and a support member that supports the optical element and the objective optical element, In the optical pickup device, the reflection structure provided on the flange portion of the optical element is disposed at least on the light source side.

  The objective optical element unit according to claim 7 is the objective optical element unit according to claim 6, wherein the objective optical element is assembled to the support member from a direction opposite to a direction in which the optical element is assembled. Therefore, the assembling property of the objective lens unit is improved.

  The objective optical element unit according to claim 8 is characterized in that, in the invention according to claim 6 or 7, the diaphragm has a diaphragm between the optical element and the objective optical element, so that the number of parts can be reduced. .

  The optical pickup device according to claim 9 is a light source that emits a light beam having a wavelength λ1, a collimator that converts the light beam having a wavelength λ1 emitted from the light source into a parallel light beam, and a parallel light beam having a wavelength λ1 that has passed through the collimator. It has an optical element in any one of Claims 1 thru | or 5 with which a light beam injects.

  The optical pickup device according to claim 10, a light source that emits a light beam having a wavelength λ1, a collimator that converts the light beam having a wavelength λ1 emitted from the light source into a parallel light beam, and a parallel light having a wavelength λ1 that has passed through the collimator. The objective optical element unit according to any one of claims 6 to 8, wherein a light beam is incident.

  A preferable range of the light source wavelength λ1 is 350 to 440 nm. A preferred example of the optical information recording medium is BD. Therefore, a preferred range of the thickness t1 on the protective substrate of the optical information recording medium is 0.070 ≦ t1 (mm) ≦ 0.105.

  The objective optical element is an optical element having a light condensing function that is disposed so as to face the optical information recording medium at a position closest to the optical information recording medium in a state where the optical information recording medium is loaded in the optical pickup device, and the optical element. An element composed of an optical element operable at least in the optical axis direction by an actuator is assumed.

  According to the present invention, it is possible to provide an optical element, an objective optical element unit, and an optical pickup device capable of appropriately recording / reproducing information while suppressing erroneous detection of a photodetector.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram schematically showing a configuration of an optical pickup device PU1 of the present embodiment that can appropriately record / reproduce information to / from an optical disc BD. The optical pickup device PU1 can be mounted on various optical information reproducing devices, optical information recording / reproducing devices, and the like.

  A light beam emitted from a semiconductor laser LD as a light source passes through a polarization beam splitter PBS, is converted into a parallel light beam by a collimator CL, passes through a λ / 4 wavelength plate QWP, and is optical disc (light) by an objective optical element OL. The light is condensed on the information recording surface RL via the protective substrate PL (thickness t1) of the BD (also referred to as an information recording medium), and a condensed spot is formed here.

  The light beam modulated by the information pits on the information recording surface RL is transmitted again through the objective optical element OL, the λ / 4 wavelength plate QWP, and the collimator CL, reflected by the polarizing beam splitter PBS, and detected by the sensor lens SEN. Since the light is incident on the light receiving surface of the device PD, a read signal of information recorded on the optical disc BD is obtained using the output signal.

  In addition, focus detection and track detection are performed by detecting a change in the amount of light due to a change in the shape and position of the spot on the photodetector PD. Based on this detection, the actuator AC1 moves the objective optical element OL so that the light beam from the semiconductor laser LD is imaged on the information recording surface of the optical disc BD.

  FIG. 2 is a cross-sectional view of the objective optical element unit OL according to the present embodiment. In FIG. 2, the objective optical element unit OL has a configuration in which the optical element OE1 on the light source side, the objective optical element OE2 on the optical disk side, and a holder HL which is a support member for the optical element OE1 and the objective optical element OE2 are coaxially coupled. Have. More specifically, the holder HL has a first reference surface SP11 and a first reference diameter surface SP12 on the light source side (left side in FIG. 2), and a second reference surface SP21 on the optical disc side (right side in FIG. 2). And a second reference radial surface SP22. The reference surfaces SP11 and 21 are orthogonal to the optical axis, respectively, and the reference radial surfaces SP21 and 22 are coaxial with the optical axis, respectively.

  The optical disk side surface of the flange portion FL1 of the optical element OE1 that secures orthogonality and coaxiality with respect to the optical axis is brought into contact with the first reference surface SP11, and the outer peripheral surface of the flange portion FL1 is in contact with the first reference diameter surface SP12. Similarly, the light source side of the flange portion FL2 of the objective optical element OE2 that ensures orthogonality and coaxiality with respect to the optical axis is brought into contact with the second reference plane SP21, and the outer peripheral surface of the flange portion FL2 is 2 The optical element OE1 and the objective optical element OE2 are coupled so as to be coaxial and have no inclination with respect to the optical axis by being brought into contact with the reference surface SP22.

  In the optical element OE1, a ring-shaped diffractive structure DOE having a sawtooth cross section around the optical axis is formed on the optical function surface S1 on the light source side. On the other hand, the optical functional surface S2 on the optical disc side is a concave refracting surface. That is, both the optical function surfaces S1 and S2 have power, and the light beam parallel to the optical axis incident on the optical function surface S1 is a light beam parallel to the optical axis having a smaller diameter from the optical function surface S2. It is injected. The axial chromatic aberration can be corrected by the optical element OE1. In addition, a diaphragm AP protruding from the inner periphery of the holder HL is formed between the optical element OE1 and the objective optical element OE2.

  Further, light source side surfaces P11, P12, P13 of the flange portion FL1 are formed in this order outside the effective diameter direction of the optical function surface S1 on the light source side in the direction orthogonal to the optical axis. Outside the effective diameter in the direction perpendicular to the optical axis of S2, the optical disk side surfaces P21, P22, and P23 of the flange portion FL1 are formed in this order. The surface P23 is orthogonal to the optical axis and abuts on the first reference surface SP11 of the holder HL.

  On the other hand, since the surface P11 on the light source side is a surface inclined so as to face outward with respect to the optical axis, the light flux parallel to the optical axis is reflected in the outward direction. Since the surface P12 is a surface inclined so as to be directed inward (optical axis side) with respect to the optical axis, the light flux parallel to the optical axis is reflected in the inward direction. The inclination angles of the surface P11 and the surface P12 are preferably 4 degrees or more and 10 degrees or less with respect to the optical axis, but are not limited thereto.

  Since the surface P13 has a surface roughness worse than that of the surface P11 in at least a region where the light beam from the light source is incident, the incident light beam from the surface P13 is scattered. The surface roughness of the surface P13 is preferably 2 μm or more and 4 μm or less in terms of the center line average roughness Ra, but is not limited thereto. The surfaces P11, P12, P13 form the reflective structure of the present invention.

  FIG. 3 is a cross-sectional view of a mold for molding the optical element OE1. The optical element OE1 is transferred and formed by the molds M1 and M2. The flange transfer surface MF of the mold M2 corresponding to the surface P13 of the optical element OE1 has been sandblasted in advance, and the surface roughness is deteriorated. Therefore, when the optical element OE1 is molded using the mold M2, the flange transfer surface MF is transferred to the surface P13, thereby deteriorating the surface roughness of the surface P13. The surface roughness of the flange transfer surface MF of the mold M2 is preferably 2 μm or more and 4 μm or less in terms of the center line average roughness Ra.

  According to the present embodiment, the surfaces P11 and P12 in the flange portion FL1 of the optical element OE1 are tilted with respect to the direction perpendicular to the optical axis, and the surface roughness of the surface P13 is deteriorated, and therefore parallel to the optical axis. Since a light beam reflected by the flange portion FL1 is prevented from entering the light receiving surface of the photodetector PD when a simple light beam enters the optical element OE1, information can be recorded / reproduced appropriately.

  In the above embodiment, an optical pickup device dedicated to BD is taken as an example. However, for example, it can be compatible with any one of HD, DVD, and CD, or with two or more types of optical disks such as BD, HD, DVD, and CD. In addition, the present invention can also be applied to an optical pickup device that records and / or reproduces information.

It is a figure which shows schematically the structure of optical pick-up apparatus PU1. It is sectional drawing of the objective optical element OL concerning this Embodiment. It is sectional drawing of the metal mold | die which shape | molds 1st element OE1.

Explanation of symbols

AP Diaphragm CL Collimator DOE Ring-like diffraction structure FL1 Flange FL2 Flange HL Holder LD Semiconductor laser M1, M2 Mold MF Flange transfer surface OE1 Optical element OE2 Objective optical element OL Objective optical element unit P11, P12, P13 On the light source side Surfaces P21, P22, P23 Optical disk side surface PBS Polarizing beam splitter PD Photodetector PU1 Optical pickup device QWP λ / 4 wave plate S1 Optical function surface SP11 Reference surface SP12 Reference diameter surface S2 Optical function surface SP21 Reference surface SP22 Reference diameter surface SEN sensor lens

Claims (10)

An optical element for use in an optical pickup apparatus that records and / or reproduces information by focusing a light beam having a wavelength λ1 emitted from a light source on an information recording surface of an optical information recording medium having a protective substrate thickness t1. ,
The optical element has two optical functional surfaces each having power and a flange portion. When a light beam parallel to the optical axis is incident on the flange portion, the optical element is parallel to the optical axis. An optical element comprising a reflection structure that reduces light reflected in a direction.   The optical element according to claim 1, wherein the optical element has a function of correcting axial chromatic aberration with respect to at least a light beam having a wavelength λ1 from the light source.   The optical element emits a light beam parallel to the optical axis when a light beam of wavelength λ1 from the light source is incident as a light beam parallel to the optical axis. The optical element described.   The optical element according to claim 1, wherein the reflection structure has a function of scattering a light beam incident on the reflection structure.   The optical element according to claim 1, wherein the flange portion is inclined with respect to the direction perpendicular to the optical axis.   An optical element according to claim 1, an objective optical element, and a support member that supports the optical element and the objective optical element, wherein in the optical pickup device, a flange of the optical element is provided. An objective optical element unit, wherein the reflection structure provided in the section is disposed at least on the light source side.   The objective optical element unit according to claim 6, wherein the objective optical element is assembled from a direction opposite to a direction in which the optical element is assembled to the support member.   The objective optical element unit according to claim 6, wherein the support member has a stop between the optical element and the objective optical element.   6. A light source that emits a light beam having a wavelength λ1, a collimator for converting the light beam having a wavelength λ1 emitted from the light source into a parallel light beam, and a parallel light beam having a wavelength λ1 that has passed through the collimator are incident. An optical pickup device comprising any one of the optical elements described above.   9. A light source that emits a light beam having a wavelength λ1, a collimator for converting the light beam having a wavelength λ1 emitted from the light source into a parallel light beam, and a parallel light beam having a wavelength λ1 that has passed through the collimator are incident. An optical pickup device comprising the objective optical element unit according to any one of the above.

Images