JP2005116004A - Optical pickup device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical device capable of reducing spherical aberrations and the size of the device. <P>SOLUTION: Incidence and emission side lenses 23, 24 in a condensing unit 16 are fixed by a thermal expansion member 25 so that they can be displaced in the optical axis direction with respect to each other. When heat is generated by an actuator coil 17 in the light pickup device 10, the thermal expansion member 25 is displaced in the optical axis direction by the temperature change, thus reducing the spherical aberrations in the incidence and emission side lenses 23, 24. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

The present invention irradiates an information recording medium such as an optical disc with light of a semiconductor laser, thereby recording information on the recording surface of the information recording medium, or information written on the recording surface of the information recording medium The present invention relates to an optical pickup device that reproduces sound.
In the present invention, “substantially parallel” includes “parallel”.

  In recent years, in the field of information recording, research on optical information recording methods has been promoted in various places. This optical information recording system has a number of advantages such as non-contact recording and reproduction, and compatibility with each of the read-only, write-once, and rewritable types of memory, and allows for inexpensive large-capacity media. A wide range of applications from industrial use to consumer use is considered as possible.

  The following two coordinate axes are mentioned as recent trends in the optical information recording type optical disc apparatus. In other words, the information recording capacity per unit area of a disc that has already become the de facto standard, such as a 120 mm diameter disc such as a compact disc (abbreviated CD: Compact Disc) and a digital versatile disc (abbreviated DVD: Digital Versatile Disc). Two coordinate axes that reduce the size of the disk and the disk reproducing device are mentioned in the direction of increasing and the direction of increasing rather than reducing the amount of information recording, and research has been actively conducted in recent years.

  The direction of increasing the information recording capacity per unit area includes shortening the wavelength of the light source or increasing the numerical aperture (NA) of the objective lens. Although there has been a great leap forward with the emergence of blue lasers for the shortening of the wavelength of the light source, a dramatic improvement cannot be expected due to the fact that the absorption of optical components becomes a problem when further shortening the wavelength. On the other hand, with respect to the increase in the lens NA, it is possible to design a lens having a high NA with a single lens or two lenses depending on the lens design, but it is known that each lens has the following characteristics.

(Single lens)
Since the distance between the objective lens and the disk, that is, the working distance becomes wide, the collision between the lens surface and the disk surface hardly occurs. In addition, compatibility with conventional DVDs is easy. On the other hand, since the off-axis aberration characteristic is generally deteriorated, it is necessary to increase the adjustment accuracy of the pickup as compared with the double lens.

(Two lenses)
Since the off-axis aberration characteristic is better than that of a single lens, there is no need to increase the adjustment accuracy of the pickup. On the other hand, the working distance is narrower than that of a single lens, and the collision between the lens surface and the disk surface is likely to occur. In addition, it is difficult to achieve compatibility with conventional DVDs.

  Although the single lens has the advantage of a wide working distance, it is considered that a wider off-axis aberration margin is more suitable for mass production, especially when compatibility with DVD is not required. Often used as a lens. Furthermore, when it is intended to expand the actuator band in response to recording and reproduction at double speed, it is necessary to reduce the weight of the entire actuator. Therefore, as an objective lens, a resin lens having a lighter specific gravity than a glass lens is used instead of a conventional glass lens.

  FIG. 11 is a diagram schematically showing a configuration of an optical pickup device including a conventional temperature detection element 1. In the optical pickup device, a technique for correcting the spherical aberration of the lens caused by a temperature rise in the device has been proposed (Patent Document 1). In this optical pickup device, the spherical aberration is corrected by changing the position in the optical axis direction of the coupling lens 2 for correcting spherical aberration in response to the temperature change in the pickup device monitored by the temperature detecting element 1. It is configured.

  FIG. 12 is a diagram schematically showing a configuration of an optical pickup device including a conventional thermal expansion member 3. In the optical pickup device, a configuration in which a coupling lens 4 and a holder 5 are attached via a thermal expansion member 3 for correcting spherical aberration has been proposed (Patent Document 1).

Japanese Patent Laid-Open No. 10-106010 (page 1-2, FIGS. 5 and 13)

  When a two-sheet resin lens is used as the objective lens, spherical aberration occurs with respect to the outgoing light of the objective lens. That is, due to the heat generated by the driving actuator coil, spherical aberration occurs with respect to the light emitted from the objective lens, as shown in the wavefront aberration profile of FIG. This tendency is prominent when a glass material having a large temperature change in the refractive index, such as a resin lens, is used as the objective lens. As a main cause of this spherical aberration, it can be considered that the refractive index of the double lens changes due to the high temperature of the lens and the focal length changes.

  In the optical pickup device shown in FIG. 11, the temperature detection element 1 for temperature monitoring is indispensable in order to monitor the temperature change in the pickup device and correct the spherical aberration. Therefore, the number of parts of the optical pickup device increases. In addition, since the number of temperature detection elements 1 increases, the number of signal processing circuits also increases, so that the manufacturing cost of the entire optical pickup device also increases. Further, when the temperature detection element 1 cannot be disposed close to the object, and when another heat source such as a semiconductor laser or a driving IC is disposed near the temperature detection element, the temperature detection element 1 is accurate. The temperature may not be detected.

The optical pickup device shown in FIG. 12 has a configuration in which the position of the coupling lens 4 is automatically adjusted by the expansion and contraction of the thermal expansion member 3, but has the following problems. The thermal expansion member 3 needs an amount of expansion and contraction of about 0.1 mm or more and 0.5 mm or less for spherical aberration adjustment. On the other hand, even if the linear expansion coefficient is large, it is about 2 × 10 ⁻⁴ / ° C. Therefore, assuming that the temperature rise amount is 50 ° C., the total length of the thermal expansion member 3 is the linear expansion coefficient in the expansion / contraction amount And a value obtained by further multiplying the amount of temperature rise, specifically 10 mm or more and 50 mm or less is required. In such a case, the size of the coupling lens portion including the holder 5 increases. Therefore, the overall size of the optical pickup device increases.

  An object of the present invention is to provide an optical pickup device capable of reducing spherical aberration and miniaturizing the device.

In the present invention, divergent light from a semiconductor laser is substantially collimated by a collimating lens, and after passing through a polarization branching element and a spherical aberration compensation element, is condensed on a recording medium by a condensing means, and reflected light from the recording medium. Is an optical pickup device that reads a recorded signal by coupling to a light receiving element,
The light collecting means includes
First and second objective lenses;
An optical pickup having a thermal expansion member that is displaced in the optical axis direction due to a temperature change, and that fixes the first and second objective lenses to be displaceable in the optical axis direction. Device.

  According to the present invention, the diverging light from the semiconductor laser is substantially collimated by the collimating lens. The substantially collimated light passes through the polarization branching element and the spherical aberration compensating element, and then condensed on the recording medium by the condensing means. The recording signal is read by coupling the reflected light from the recording medium to the light receiving element. The condensing means has first and second objective lenses and a thermal expansion member. The first and second objective lenses are fixed to each other by a thermal expansion member so as to be displaceable in the optical axis direction. When the optical pickup device generates heat, the thermal expansion member is displaced in the optical axis direction due to a temperature change. Accordingly, the spherical aberration of the first and second objective lenses that can be caused by the heat generation can be reduced by the displacement of the thermal expansion member.

The present invention also includes a light source,
A light branching element disposed on an optical axis between a light source and a recording medium on which information is recorded;
Condensing means disposed on the optical axis between the light branching element and the recording medium and condensing the light emitted from the light source on the recording medium, the first objective lens, and the first objective lens Condensing means comprising a second objective lens fixed to the objective lens via a thermal expansion member that is displaced in the optical axis direction due to temperature change;
An optical pickup device having light receiving means for detecting reflected light from a recording medium.

  According to the present invention, the light emitted from the light source is collected on the recording medium via the light branching element and the light collecting means. The reflected light from the recording medium is detected by the light receiving means. The condensing means condenses light emitted from the light source on the recording medium. The condensing means includes first and second objective lenses and a thermal expansion member. Among these, the thermal expansion member is displaced in the direction of the optical axis due to a temperature change, and also has a function of fixing the first and second objective lenses. When the optical pickup device generates heat, the thermal expansion member is displaced in the optical axis direction due to a temperature change. Accordingly, the spherical aberration of the first and second objective lenses that can be caused by the heat generation can be reduced by the displacement of the thermal expansion member.

  In the invention, it is preferable that the linear expansion coefficient of the thermal expansion member is set so as to correct the spherical aberration generation amount of the first and second objective lenses due to heat generation of the optical pickup device.

  According to the present invention, spherical aberration occurs in the first and second objective lenses due to heat generated by the optical pickup device. A linear expansion coefficient of the thermal expansion member is set to correct the spherical aberration generation amount. In other words, the spherical aberration generation amount of the first and second objective lenses can be corrected only by setting the linear expansion coefficient of the thermal expansion member.

  In the invention, it is preferable that the condensing unit further includes a lens holder that holds the first and second objective lenses.

  According to the invention, the light collecting means further comprises a lens holder. The lens holder holds the first and second objective lenses. Therefore, it is possible to prevent at least one of the first and second objective lenses from undesirably dropping from the lens holder.

  According to the present invention, the first and second objective lenses are fixed to each other by the thermal expansion member so as to be displaceable in the optical axis direction. When the optical pickup device generates heat, the thermal expansion member is displaced in the optical axis direction due to a temperature change. Accordingly, the spherical aberration of the first and second objective lenses that can be caused by the heat generation can be reduced by the displacement of the thermal expansion member.

  Since the spherical aberration can be reduced by such a condensing means, according to the optical pickup device of the present invention, the temperature detecting element for temperature monitoring which has been conventionally required can be dispensed with. Therefore, the structure of the optical pickup device can be simplified. Further, since the first and second objective lenses are fixed via the thermal expansion member, the size of the optical pickup device in the optical axis direction can be suppressed. As a result, the optical pickup device can be miniaturized.

  Further, according to the present invention, the thermal expansion member of the condensing means is displaced in the optical axis direction due to a temperature change, and has a function of fixing the first and second objective lenses. Play. When the optical pickup device generates heat, the thermal expansion member is displaced in the optical axis direction due to a temperature change. Accordingly, the spherical aberration of the first and second objective lenses that can be caused by the heat generation can be reduced by the displacement of the thermal expansion member.

  Since the spherical aberration can be reduced by such a condensing means, according to the optical pickup device of the present invention, the temperature detecting element for temperature monitoring which has been conventionally required can be dispensed with. Therefore, the structure of the optical pickup device can be simplified. Further, since the first and second objective lenses are fixed via the thermal expansion member, the size of the optical pickup device in the optical axis direction can be suppressed. As a result, the optical pickup device can be miniaturized.

  Further, according to the present invention, the linear expansion coefficient of the thermal expansion member is set so as to correct the spherical aberration generation amount. In other words, the spherical aberration generation amount of the first and second objective lenses can be corrected only by setting the linear expansion coefficient of the thermal expansion member. Therefore, the spherical aberration generation amount can be corrected without using a complicated mechanism as in the prior art. Therefore, the manufacturing cost of the optical pickup device can be reduced.

  According to the invention, the light collecting means further includes a lens holder. The lens holder holds the first and second objective lenses. Therefore, it is possible to prevent at least one of the first and second objective lenses from undesirably dropping from the lens holder.

  FIG. 1 is a diagram schematically showing the configuration of an optical pickup device 10 according to the first embodiment of the present invention. The optical pickup device of this embodiment records information on a recording surface by irradiating a recording medium such as a CD and a DVD with a semiconductor laser beam, or reproduces information written on the recording surface of the recording medium. Applies to equipment that does. An optical pickup device 10 includes a semiconductor laser 11 as a light source, a collimating lens 12, an optical branching element 13 as a polarization branching element, a beam expanding element 14, a rising mirror 15, and a condensing unit as a condensing unit. 16, an actuator coil 17, a spot lens 18, a cylindrical lens 19, and a light receiving element 20 as a light receiving means.

  The divergent light from the semiconductor laser 11 is converted into a parallel beam by the collimator lens 12. The diameter of the light beam that has been converted into the parallel light beam is expanded by the beam expanding element 14 via the light branching element 13. The optical path of the expanded light is bent by the rising mirror 15, and then the light is condensed on the recording medium 21 by the light collecting unit 16. An actuator coil 17 is disposed in the vicinity of the outer periphery of the light collecting unit 16 described later. The recording medium 21 is also called an optical recording medium 21. The reflected light from the optical recording medium 21 is reflected by the light branching element 13 after sequentially following the optical path opposite to the incident light, that is, the condensing unit 16, the raising mirror 15, and the beam expanding element 14.

  The reflected light is collected by the spot lens 18 and then irradiated to the light receiving element 20 through the cylindrical lens 19. The light receiving element 20 has a multi-part light receiving portion on the same plane. A recording signal and a servo signal are detected by the light receiving portion of the light receiving element 20. The beam expanding element 14 which is a spherical aberration compensating element is intended to correct spherical aberration caused by a cover glass thickness error. As means for achieving such an object, spherical aberration correction means using a liquid crystal driving element may be used. A beam shaping element (not shown) for beam shaping, a λ / 2 plate for adjusting the polarization direction, and the like may be arranged in the middle of the optical path between the collimating lens 12 and the light branching element 13. For example, a λ / 4 plate may be disposed in the middle of the optical path between the light branching element 13 and the light collecting unit 16. The λ / 4 plate is for converting linearly polarized light into circularly polarized light.

  FIG. 2 is a diagram illustrating a main part of the optical pickup device 10 cut along a virtual plane including the optical axis direction. FIG. 3 is a diagram showing step by step how to assemble the first and second objective lenses. The condensing unit 16 includes a lens holder 22, an incident side lens 23, an exit side lens 24, and a thermal expansion member 25. The incident side lens 23 corresponds to a first objective lens, and the emission side lens 24 corresponds to a second objective lens. The entrance side and exit side lenses 23 and 24 are two-piece objective lenses. An exit side lens 24 is fitted to the entrance side lens 23 via a thermal expansion member 25. The fitted entrance and exit lenses 23 and 24 are fitted and held in the lens holder 22.

  The incident side lens 23 includes a lens main body 26 and a lens holder 27 integrally formed with the lens main body 26. Specifically, the lens body 26 and the lens holder 27 are made of a synthetic resin material, and the lens holder 27 is formed in a substantially cylindrical shape. The “substantially cylindrical shape” includes “cylindrical shape”. Of the outer peripheral portion of the lens holder 27, a portion facing the recording medium 21 and a portion on the light emitting side is reduced inward in the radial direction toward one side in the optical path direction indicated by an arrow L1 (see FIG. 2). It is formed in a tapered shape. A part of the lens holder 27 is referred to as a tapered portion 27a. As will be described later, an adhesive 28 (see FIG. 10) is applied to the annular gap between the lens holder 22 and the tapered portion 27a of the lens holder 27, and the lens holder 22 and the lens holder 27 are fixed together. The

  The lens holder 27 is formed with an inner peripheral portion 29 that opens to one side in the optical path direction. A lens body 26 is disposed at an end of the lens holder 27 on the light incident side, and the lens body 27 forms a bottomed cylindrical body by the lens body 26. The convex part of the lens body 26 facing the rising mirror 15 is formed so as to protrude a predetermined small distance from the end part of the lens holding body 27. In the inner peripheral portion 29 of the lens holder 27, a large diameter portion 29a formed facing the recording medium 21, a small diameter portion 29b formed in the vicinity of the lens body 26, the large diameter portion 29a and the small diameter portion 29b And a step portion 29c for interior of the thermal expansion member 25. The large diameter portion 29a is formed to have a slightly larger diameter than the small diameter portion 29b. After the thermal expansion member 25 is inserted into the stepped portion 29 c, an output side lens 24 described later is fitted into the large diameter portion 29 a of the incident side lens 23.

  The exit side lens 24 is made of a synthetic resin material, and a flange portion 24b is integrally formed on the outer peripheral portion of the lens portion 24a. The flange portion 24b is formed to have a slightly smaller diameter than the large diameter portion 29a. That is, the flange portion 24 b of the exit side lens 24 is tightly fitted to the entrance side lens 23. In a state in which the exit side lens 24 is fitted to the entrance side lens 23 via the thermal expansion member 25, at least the lens portion 24a and the lens body 26 are disposed apart from each other so as not to interfere with each other.

The thermal expansion member 25 is made of high-density polyethylene, for example, and is formed in an annular shape. The linear expansion coefficient of the thermal expansion member 25 is set so as to correct the spherical aberration generation amount of the incident side and emission side lenses 23 and 24 due to heat generation of the optical pickup device 10. Specifically, the linear expansion coefficient of the thermal expansion member 25 is 1.8 × 10 ⁻⁴ / ° C. However, the thermal expansion member is not necessarily limited to high-density polyethylene, and can be formed using various synthetic resin materials. Further, the linear expansion coefficient of the thermal expansion member 25 is not necessarily limited to 1.8 × 10 ⁻⁴ / ° C. The thickness of the thermal expansion member 25 in the optical path direction is set to about 1 mm, for example. The outer peripheral portion 25 a of the thermal expansion member 25 is set to be approximately the same as the size of the large diameter portion 29 a of the incident side lens 23. The inner peripheral portion of the thermal expansion member 25 is set to be substantially the same as the size of the small diameter portion 29 b of the incident side lens 23. “Substantially the same” includes “same”.

  The lens holder 22 is made of, for example, a synthetic resin material and is formed in a cylindrical shape. In the inner peripheral portion of the lens holder 22, a large diameter portion 22a formed facing the recording medium 21, a small diameter portion 22b near the lens body 26, and a step portion between the large diameter portion 22a and the small diameter portion 22b. 22c, and a step portion 22c that holds the lens holder 27 of the incident side lens 23. The large diameter portion 22a is formed to have a slightly larger diameter than the small diameter portion 22b. In a state where the lens holder 27 is fitted to the large diameter portion 22a of the lens holder 22, the convex portion of the lens body 26 does not protrude from the one end portion 22d of the lens holder 22, and the convex portion and the small diameter portion 22b. The lens holder 22 is formed so as not to interfere with each other.

Specifically, when the entrance side lens 23 and the exit side lens 24 are fixed, as shown in FIG. 3, first, the step portion 29c of the entrance side lens 23 and the thermal expansion member 25 are attached to the UV resin 30 (UV: Ultra).
Violet). Thereafter, the emission side lens 24 is fixed to the thermal expansion member 25 with the UV resin 30. As the UV resin 30, it is desirable to use a resin having a linear expansion coefficient as small as possible. Thereby, the thermal expansion of the UV resin 30 itself can be prevented as much as possible. In other words, without considering the thermal expansion of the UV resin 30, it is possible to adjust the lens interval and compensate for the spherical aberration using only the thermal expansion of the thermal expansion member 25. Therefore, it is possible to accurately reduce the spherical aberration caused by the incident side and outgoing side lenses 23 and 24 being heated by the heat generated from the actuator coil 17. As such a UV resin having the smallest possible linear expansion coefficient, for example, “TB3055” manufactured by ThreeBond Co., Ltd. is adopted. The linear expansion coefficient of “TB3055” is specifically about 1 × 10 ⁻⁴ cm / ° C.

FIG. 4 is a graph showing a comparison of the amount of wavefront aberration generated in a two-piece objective lens using glass as the glass material of the lens and using various resin materials. In the glass material, the temperature dependence coefficient of the refractive index is about 2 × 10 ⁻⁶ / ° C., whereas in the resin material, the temperature dependence coefficient of the refractive index is about 1 × 10 ⁻⁴ / ° C., which is about two digits larger. Therefore, the tendency to generate spherical aberration is remarkable when a resin material is applied to the objective lens. On the other hand, when a glass material is applied to the objective lens, the influence of aberration is hardly seen. Therefore, when the resin material is applied to at least one objective lens as the glass material of the two-piece objective lens, the effect of the configuration of the present embodiment is great.

  FIG. 5 is a graph comparing aberrations in the case where an acrylic resin is used for the glass material of the lens and in the case where compensation is performed using the thermal expansion member 25 in the two-piece objective lens. That is, in the optical system of the first embodiment, the result of performing an optical simulation when the temperature of the objective lens rises is shown in FIG. Before correcting the spherical aberration, the spherical aberration occurs due to the temperature rise of the objective lens, so that the wavefront aberration increases monotonously, and when the temperature rises by 26 ° C., the aberration rms becomes 30 mλ. By the way, in order to sufficiently narrow the condensing spot of the optical pickup, the aberration rms needs to be 30 mλ or less at the simulation stage. For this reason, if the temperature rise exceeds about 26 ° C., the focused spot cannot be sufficiently narrowed.

Here, the aspherical coefficients of the two lenses constituting the objective lens used in the optical simulation (the aspherical coefficients of the 12th order or higher and the effective digits of the aspherical coefficients of 3 or more are not described), and the refractive index The temperature dependence is shown below. The lenses are OL1 and OL2 in this order from the incident side, Z in the aspherical polynomial represents the lens surface displacement, and R represents the distance from the lens center. X is the height in the direction horizontal to the optical axis, K is the conic coefficient, and A, B, C, and D are aspherical coefficients. Α in the temperature dependence formula of the refractive index is a temperature dependence coefficient of the refractive index, and 1.1 × ⁻⁴ / ° C. of acrylic resin (PMMA) which is a typical lens resin material was used. However, the refractive index is a value when a virtual resin material is assumed instead of an acrylic resin.
(Aspherical polynomial)
Z = (X ² / R) / (1 + sqrt (1- (1 + K) · X ² / R ² ))
+ AX ⁴ + BX ⁶ + CX ⁸ + DX ¹⁰ + EX ¹² + FX ¹⁴ + GX ¹⁶ + ..
(Temperature dependence of refractive index)
Temperature dependent refractive index = refractive index @ 20 ° C.−α × temperature rise (° C.)

  FIG. 6 is a diagram showing the measurement results of the wavefront aberration profile of the light emitted from the objective lens when the temperature of the lens holder 22 is (i) = 22 ° C., (ii) = 47.3 ° C., and (iii) = 72.5 ° C. is there. FIG. 7 is a graph showing the spherical aberration and the amount of aberration generated with respect to the temperature rise of the lens holder 22. FIG. 8 is a graph showing the relationship between the temperature and the lens interval increase amount. FIG. 6 shows a wavefront aberration profile when an acrylic resin lens of a set of two sheets is actually used as the objective lens, and the actuator coil 17 for driving is heated by applying a predetermined current value. The values of spherical aberration and aberration rms at that time are shown in FIG. The holder temperature shown in FIG. 7 is synonymous with the temperature of the lens holder 22.

  As shown in FIG. 7, the spherical aberration and the aberration rms actually increase as the temperature of the lens holder 22 increases. It should be noted that the actual measurement values appear larger from the simulation results in FIG. 5 because the roughness of the lens surface and the aberration rms due to a small amount of residual coma aberration exist from the initial state. Is also getting bigger.

  In the present embodiment, in particular, the condensing unit 16 is configured by interposing the thermal expansion member 25 between the incident side lens 23 and the emission side lens 24, in other words, sandwiching the thermal expansion member 25 between the lenses 23 and 24. As a result, the following effects are produced. As shown in FIG. 8, the thermal expansion member 25 expands as the incident side and emission side lenses 23 and 24 are heated, and the distance between the incidence side and emission side lenses 23 and 24 increases. Thereby, spherical aberration can be compensated. At this time, for example, even when the lens temperature rises from about 20 ° C. to 80 ° C., the aberration rms is about 20 mλ, and the occurrence of spherical aberration can be sufficiently suppressed.

  According to the optical pickup device 10 described above, the entrance side and exit side lenses 23 and 24 of the light collecting unit 16 are fixed to each other by the thermal expansion member 25 so as to be displaceable in the optical axis direction. When the optical pickup device 10 generates heat by the actuator coil 17, the thermal expansion member 25 is displaced in the optical axis direction due to a temperature change. Therefore, the spherical aberration of the entrance side and exit side lenses 23, 24 that can occur due to the heat generation can be reduced by the displacement of the thermal expansion member 25.

  Since the spherical aberration can be reduced by such a condensing unit 16, according to the optical pickup device 10 of this embodiment, the temperature detecting element for temperature monitoring which has been conventionally required can be dispensed with. Therefore, the structure of the optical pickup device 10 can be simplified. In addition, since the entrance side and exit side lenses 23 and 24 are fixed via the thermal expansion member 25, the size of the optical pickup device 10 in the optical axis direction can be suppressed. As a result, the optical pickup device 10 can be miniaturized.

  The linear expansion coefficient of the thermal expansion member 25 is set so as to correct the amount of spherical aberration generated by the incident-side and emission-side lenses 23 and 24 due to heat generated by the optical pickup device 10. In other words, only by setting the linear expansion coefficient of the thermal expansion member 25, it is possible to correct the spherical aberration generation amount of the entrance side and exit side lenses 23 and 24. According to such a configuration, it is possible to correct the spherical aberration generation amount without using a complicated mechanism as in the prior art. Therefore, the manufacturing cost of the optical pickup device 10 can be reduced. In addition, the lens holder 22 holds the entrance side and exit side lenses 23 and 24. Therefore, it is possible to prevent at least one of the entrance side and exit side lenses 23 and 24 from being undesirably dropped from the lens holder 22 in advance.

  FIG. 9 is a diagram schematically showing the configuration of an optical pickup device 10A according to the second embodiment of the present invention. However, the same members as those in the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted. The second optical pickup device 10A includes a semiconductor laser 11 as a light source, an optical branching element 13 as a polarization branching element, a collimating lens 12A, a rising mirror 15, and a second condensing unit as a condensing unit. It has a unit 16A, an actuator coil 17, a cylindrical lens 19, and a light receiving element 20 as a light receiving means.

  The divergent light from the semiconductor laser 11 is converted into a parallel beam by the collimating lens 12A via the optical branching element 13. This parallel light beam is bent in the optical path by the rising mirror 15 and then condensed on the recording medium 21 by the second condensing unit 16A. An actuator coil 17 is disposed in the vicinity of the outer periphery of the second light collecting unit 16A. The reflected light from the recording medium 21 is reflected by the light branching element 13 after sequentially following the optical path opposite to the incident light, that is, the second condensing unit 16A, the raising mirror 15, and the collimating lens 12A. The reflected light is irradiated to the light receiving element 20 through the cylindrical lens 19. Here, a recording signal and a servo signal are detected. In the second embodiment, the collimating lens 12A also serves as an element that corrects spherical aberration due to a cover lens thickness error.

  FIG. 10 shows the main parts of the optical pickup devices 10 and 10A cut along a virtual plane including the optical axis direction, and (i) is a diagram in the case where the first objective lens is bonded to the lens holder 22; ) Is a diagram when the second objective lens is bonded to the lens holder 22. The second light collecting unit 16 </ b> A includes a lens holder 22, an incident side lens 31 that is a first objective lens, an emission side lens 32 that is a second objective lens, and a thermal expansion member 25. The entrance side and exit side lenses 31 and 32 are two-piece objective lenses. The incident side lens 31 is fitted to the emission side lens 32 via the thermal expansion member 25. Out of these entrance side and exit side lenses 31, 32, the exit side lens 32 is fitted and bonded to the lens holder 22.

  The lens and the lens holder 22 are bonded in two ways: a method of bonding with the structure shown in FIG. 10 (i) according to the first embodiment, and a method of bonding with the structure shown in FIG. 10 (ii) according to the second embodiment. Can be considered. In particular, in the structure according to the first embodiment, the entrance side and exit side lenses 23 and 24 are securely held by the step 22 c of the lens holder 22. Therefore, there is no possibility that the adhesive member of the thermal expansion member 25 is peeled off due to factors such as vibration caused by driving of the actuator, and at least one of the lenses is undesirably dropped.

1 is a diagram schematically illustrating a configuration of an optical pickup device 10 according to a first embodiment of the present invention. It is a figure which cut | disconnects and shows the principal part of the optical pick-up apparatus 10 by the virtual plane containing the optical axis direction. It is a figure which shows the method of assembling the 1st and 2nd objective lens in steps. 5 is a graph showing a comparison of the amount of wavefront aberration generated between a lens using a glass and a resin using various resin materials in a double objective lens. 6 is a graph comparing aberrations in a case where an acrylic resin is used for a glass material of a lens and in a case where compensation is performed using a thermal expansion member in a double objective lens. It is a figure showing the measurement result of the wavefront aberration profile of the objective lens emitted light when the temperature of the lens holder 22 is (i) = 22 ° C., (ii) = 47.3 ° C., and (iii) = 72.5 ° C. It is a graph which shows the amount of spherical aberration and the amount of aberration generated with respect to the temperature rise of the lens holder. It is a graph which shows the relationship between temperature and a lens space | interval increase amount. It is a figure which shows schematically the structure of 10 A of optical pick-up apparatuses which concern on the 2nd Embodiment of this invention. The main parts of the optical pickup devices 10 and 10A are shown cut along a virtual plane including the optical axis direction, (i) is a view when the first objective lens is bonded to the lens holder 22, and (ii) is the lens holder. FIG. 22 is a diagram when the second objective lens is bonded to 22. It is a figure which shows schematically the structure of the optical pick-up apparatus containing the conventional temperature detection element. It is a figure which shows schematically the structure of the optical pick-up apparatus containing the conventional thermal expansion member 3. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Optical pick-up apparatus 11 Semiconductor laser 12 Collimating lens 13 Optical branching element 14 Beam expansion element 16 Condensing unit 20 Light receiving element 21 Recording medium 22 Lens holder 23 Incident side lens 24 Outgoing side lens 25 Thermal expansion member

Claims (4)

The divergent light from the semiconductor laser is substantially collimated by a collimator lens, passes through a polarization branching element and a spherical aberration compensation element, and then condensed on the recording medium by a condensing means, and the reflected light from the recording medium is applied to the light receiving element. An optical pickup device that reads a recorded signal by being coupled,
The light collecting means includes
First and second objective lenses;
An optical pickup having a thermal expansion member that is displaced in the optical axis direction due to a temperature change, and that fixes the first and second objective lenses to be displaceable in the optical axis direction. apparatus. A light source;
A light branching element disposed on an optical axis between a light source and a recording medium on which information is recorded;
Condensing means disposed on the optical axis between the light branching element and the recording medium and condensing light emitted from the light source on the recording medium, the first objective lens, and the first objective lens Condensing means comprising a second objective lens fixed to the objective lens via a thermal expansion member that is displaced in the optical axis direction due to temperature change;
An optical pickup device comprising: a light receiving unit that detects reflected light from the recording medium.   3. The light according to claim 1, wherein the linear expansion coefficient of the thermal expansion member is set so as to correct a spherical aberration generation amount of the first and second objective lenses due to heat generation of the optical pickup device. Pickup device.   3. The optical pickup device according to claim 1, wherein the condensing unit further includes a lens holder for holding the first and second objective lenses.