JP2006126284A - Objective lens and optical pickup with same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress aberration caused by the tensile stress of adhesive agent on a first lens 11 and a second lens 12 toward a lens barrel, even when using the first glass lens 11 and the second resin lens 12 for an objective lens 5, and to avoid the performance deterioration of the objective lens 5. <P>SOLUTION: A communication part 21 is disposed in the lens barrel 13 which holds the first lens 11 and the second lens 12. The communication part 21 is prepared for making a gap part 14 formed between the first lens 11 and the second lens 12 communicate with the outside, and the communication part 21 is arranged in the lens barrel 13 so that the gap part 14 may communicate with the outside through a part of the outer peripheral surface of the first lens 11. Thus, even if the tensile stress on the first lens 11 toward the lens barrel 13 by the adhesive agent is unequally applied in the peripheral direction (direction around optical axis) of the first lens 11 when the first lens 11 is stuck and fixed to the lens barrel 13 with the adhesive agent, the first glass lens 11 is hard and hardly deforms, then, the occurrence of the aberration can be suppressed. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an objective lens having a plurality of lenses, and an optical pickup provided with the objective lens.

  Conventionally, various optical pickups corresponding to large-capacity next-generation optical discs (hereinafter referred to as BD) that record and reproduce information by irradiating blue laser light have been proposed (see, for example, Patent Document 1). In this type of optical pickup, it is necessary to increase the refractive power at the objective lens in order to reduce the spot diameter of the blue laser light applied to the BD. Therefore, in the optical pickup of Patent Document 1, an objective lens having a strong refractive power is obtained by configuring the objective lens with a plurality of lenses.

  Here, each lens constituting the objective lens is held by a lens barrel. When the gap formed between the lenses in the lens barrel is sealed, the lens in the gap due to a change in environmental temperature is sealed. Due to the expansion or compression of air, each lens receives stress in the direction of the optical axis, and its fixing position accuracy deteriorates. As a result, the performance of the objective lens deteriorates, such as the occurrence of aberrations.

  Therefore, in the optical pickup of Patent Document 1, the gaps between the lenses in the lens barrel are communicated with the outside through the air vents. In this configuration, even if the environmental temperature changes, the air in the gap moves to the outside via the air vent, so that no stress due to the air in the gap occurs on each lens in the barrel. As a result, the fixed position accuracy of each lens is kept good, and deterioration of lens performance is avoided.

In addition, when the gap is sealed, water vapor contained in the air in the gap is likely to condense when the use environment suddenly changes from high temperature and high humidity to low temperature. However, since the lens barrel is provided with an air vent, air (water vapor) in the gap can be released to the outside through the air vent, so even if there is a sudden change in the usage environment. It is thought that dew condensation in the void can be prevented.
JP 2003-21773 A

  By the way, in recent years, an optical pickup that performs recording and reproduction of information on the above-described BD and a conventional DVD by sharing a part of an optical system has been actively developed. As described above, in an optical pickup compatible with BD and DVD, in order to appropriately correct the aberration of the light beam for DVD, for example, a diffraction surface is provided on one of the two lenses constituting the objective lens. There is a need. A lens having such a diffractive surface is generally made of plastic because it is technically difficult to make it with glass.

  On the other hand, when recording / reproducing information on the BD, it is necessary to increase the power of the objective lens in order to narrow down the spot of the blue laser light irradiated on the BD as described above. It is difficult to make a lens other than glass.

  Therefore, from the above, the two lenses constituting the objective lens for BD / DVD compatibility are each composed of a plastic lens and a glass lens. The plastic lens and the glass lens are fixed to the lens barrel that holds them by, for example, bonding the outer peripheral surface thereof with an adhesive.

  However, when the configuration of Patent Document 1 is applied to a BD / DVD compatible objective lens (when an air bleeding portion is provided in the lens barrel of the objective lens), if an air bleeding portion is provided on the plastic lens side, the plastic The tensile stress on the lens barrel side due to the adhesive acts on the lens unevenly. In other words, the plastic lens is bonded to the lens barrel with an adhesive at a portion other than the air vent, so that in the circumferential direction of the plastic lens (the direction around the optical axis), there are a bonded portion and a non-bonded portion of the plastic lens. Exists. As a result, the tensile stress on the lens barrel side caused by the adhesive acts unevenly on the plastic lens in the circumferential direction of the plastic lens.

  Since the plastic lens is soft, when the uneven tensile stress due to the adhesive acts on the plastic lens as described above, the plastic lens is easily deformed. As a result, aberration tends to occur, and the performance of the objective lens decreases.

  The present invention has been made to solve the above-described problems, and its purpose is to form an air bleeding portion at an appropriate position in a lens barrel even when a plastic lens and a glass lens are used as an objective lens. Accordingly, an object of the present invention is to provide an objective lens capable of suppressing the occurrence of aberrations and avoiding performance degradation, and an optical pickup including the objective lens.

  The objective lens of the present invention is an objective lens having a first lens made of glass, a second lens made of resin (for example, plastic), and a holding body for holding the first lens and the second lens, The holding body is provided with a communicating portion that communicates the gap between the first lens and the second lens with the outside. The communicating portion has an outer peripheral surface of the first lens. It is characterized by being provided so that it may communicate with the exterior through a part of.

  According to said structure, the glass-made 1st lens and resin-made 2nd lens are hold | maintained at a holding body (for example, lens barrel), and the objective lens is comprised. The holding body is provided with a communication portion, and a gap formed between the first lens and the second lens communicates with the outside through the communication portion. As a result, even if the usage environment changes (for example, even when the temperature changes from high temperature to low temperature), the air in the gap can move between the outside and the first lens and the second lens are stressed by the air. In addition to being able to maintain the accuracy of the fixed position of each lens, it is possible to prevent condensation in the gap.

  Further, the communication part is provided on the holding body so that the gap part communicates with the outside through a part of the outer peripheral surface of the first lens. That is, the communication portion is provided on the glass first lens side, not on the resin second lens side, in the holding body. Thereby, for example, when the outer peripheral surface of the first lens is bonded and fixed to the holding body with an adhesive, the tensile stress on the holding body side by the adhesive with respect to the first lens is caused by the circumferential direction (optical axis) of the first lens. Even if it works unevenly in the surrounding direction), the first lens made of glass is hard and is not easily deformed. As a result, even if it is the structure which provides a communication part in a holding body, generation | occurrence | production of the aberration in an objective lens can be suppressed and it can avoid that the performance of an objective lens falls.

  By the way, it is desirable that the above-described communication portion is provided on the optical disc side of the holding body. That is, it is desirable that the communicating portion is provided so that the gap portion communicates with the outside on the optical disc side where the light beam is collected by the objective lens.

  In the case where the communicating portion is provided on the opposite side of the holding body from the optical disc, when the objective lens is supported by the bobbin configured to receive the surface of the objective lens opposite to the optical disc, the communicating portion is blocked by the bobbin. May be. However, if the communication portion is provided on the optical disc side, the communication portion is not blocked by the bobbin even when the objective lens is supported by the bobbin having the above-described configuration. As a result, the gap can be reliably communicated with the outside through the communication portion.

  Further, the first lens may be configured to be held by the holding body so as to be positioned closer to the optical disc side where the light beam is condensed by the objective lens than the second lens. If the first lens is held by the holding body in this way, the communicating portion is provided on the holding body so that the gap portion communicates with the outside through a part of the outer peripheral surface of the first lens. Eventually, the communication portion is provided on the optical disc side. As a result, similarly to the above, the communicating portion is not blocked by the bobbin having the above-described configuration, and the gap portion can be reliably communicated with the outside through the communicating portion.

  Further, it is desirable that the above-described communication portion is provided at three locations around the optical axis of the first lens in the holding body. In the case of this configuration, for example, when the outer peripheral surface of the first lens is bonded to the holding body with an adhesive, the first lens is bonded in a form close to three-point bonding, so the first lens is stably attached to the holding body. Can be glued.

  At this time, if the three communicating portions are provided on the holding body at equal intervals around the optical axis of the first lens, the first lens can be bonded to the holding body in a balanced manner, so that the bonding state of the first lens is more stable. Can be made.

  In addition, the communication portion described above has a wall surface facing the surface of the first lens through a gap, and the distance between the wall surface and the surface of the first lens is set to 0.05 mm or more. Configuration is desirable.

  When the distance is less than 0.05 mm, when the adhesive for adhering the outer peripheral surface of the first lens to the holding body flows into the communication part, the communication part may be buried with the adhesive, and the communication part May not perform its function. However, if the distance is 0.05 mm or more, it is possible to reduce to some extent the risk that the communication portion is completely filled with the adhesive when the adhesive flows into the communication portion.

  An optical pickup according to the present invention includes the above-described objective lens according to the present invention, and a light source that emits a light beam condensed on an optical disk by the objective lens. At this time, a plurality of the light sources may be provided corresponding to light beams having different wavelengths, and further, a blue light source that emits blue laser light may be included.

  With such a configuration, an optical pickup with excellent objective lens performance can be easily realized even when a light source that emits blue laser light corresponding to a next-generation optical disk is used as the light source of the optical pickup. In addition, an optical pickup compatible with BD / DVD / CD (a part of the optical system is shared) can be easily realized by adding a light source corresponding to DVD or CD to the blue light source.

  According to the present invention, the communicating portion is provided on the holding body such that the gap portion communicates with the outside via a part of the outer peripheral surface of the first lens. Accordingly, for example, when the first lens is bonded and fixed to the holding body via an adhesive, the first lens is made of glass even if the tensile stress on the holding body side by the adhesive acts unevenly on the first lens. Since the first lens is hard, it is difficult to deform. As a result, even if it is the structure which provides a communication part in a holding body, generation | occurrence | production of the aberration in an objective lens can be suppressed and it can avoid that the performance of an objective lens falls.

An embodiment of the present invention will be described below with reference to the drawings.
FIG. 2 is an explanatory diagram showing a schematic configuration of the optical pickup according to the present embodiment. This optical pickup comprises a first light source 1, a second light source 2, a beam splitter 3, a collimator lens 4, and an objective lens 5, and is compatible with BD 6 and DVD 7 which are optical disks. In other words, it has a configuration in which a part of the optical system is shared. Note that BD refers to a large-capacity next-generation optical disc that supports blue laser light.

  The first light source 1 is a semiconductor laser module that emits a light beam (blue laser light) for BD6. In the first light source 1, a first semiconductor laser 1a is disposed at the center of the bottom of a bottomed box-shaped housing 1d. The first semiconductor laser 1a emits a light beam having a wavelength of 405 nm (shown by a solid line X). At the bottom of the housing 1d, first photodetectors 1b are disposed on both sides of the first semiconductor laser 1a. Further, the first hologram 1c is disposed on the surface of the module in a lid shape with respect to the housing 1d.

  The second light source 2 is a semiconductor laser module that emits a light beam for the DVD 7. In the second light source 2, a second semiconductor laser 2a is disposed in the center of the bottom of the bottomed box-shaped housing 2d. The second semiconductor laser 2a emits a light beam having a wavelength of 650 nm (shown by a broken line Y). At the bottom of the housing 2d, second photodetectors 2b are disposed on both sides of the second semiconductor laser 2a. A second hologram 2c is disposed on the surface of the module in a lid shape with respect to the housing 2d.

  In the present embodiment, the semiconductor laser, the photodetector, and the hologram constituting each light source are modularized, but these may be provided separately.

  The beam splitter 3 is an optical element that selectively transmits or reflects a light beam by a wavelength-selective interference film, and is at a position where the optical paths of the light beams emitted from the first light source 1 and the second light source 2 intersect. Is arranged. The collimator lens 4 converts the laser light incident through the beam splitter 3 into parallel light. The objective lens 5 focuses the light beams emitted from the first light source 1 and the second light source 2 on the BD 6 or the DVD 7. The detailed configuration of the objective lens 5 will be described later.

  In the above configuration, the light beam emitted from the first semiconductor laser 1 a of the first light source 1 passes through the beam splitter 3, is converted into parallel light by the collimator lens 4, and is collected on the BD 6 by the objective lens 5. To be lighted. Then, the return light (reflected light) from the BD 6 follows the optical path opposite to the above, that is, enters the first light source 1 via the objective lens 5, the collimator lens 4 and the beam splitter 3. In the first light source 1, the return light is bent in the optical path by the first hologram 1 c and enters the first photodetector 1 b, where an optical signal (for example, a servo signal (focus error signal, tracking error signal, etc.) is input. ), An information signal, an aberration signal) are detected.

  On the other hand, the light beam emitted from the second semiconductor laser 2 a of the second light source 2 is reflected by the beam splitter 3, converted into parallel light by the collimator lens 4, and condensed on the DVD 7 by the objective lens 5. The Then, the return light (reflected light) from the DVD 7 follows the optical path opposite to the above, that is, enters the second light source 2 via the objective lens 5, the collimator lens 4 and the beam splitter 3. In the second light source 2, the return light has its optical path bent by the second hologram 2c and is incident on the second photodetector 2b, where an optical signal similar to the above is detected.

Next, details of the objective lens 5 will be described.
FIG. 3 is a plan view of the objective lens 5 when viewed from the optical disc (BD6 or DVD7) side, and FIG. 1 shows a detailed configuration of the objective lens 5, and is shown by AA ′ in FIG. FIG. In addition, in FIG. 1, the bobbin 15 holding the objective lens 5 is shown incidentally. The objective lens 5 of the present embodiment includes a first lens 11, a second lens 12, and a lens barrel 13.

  The first lens 11 is made of glass and has a convex shape mainly on the side opposite to the optical disk. The second lens 12 is made of resin (for example, plastic), and a light incident surface facing the optical disc has a diffraction surface for diffracting a light beam emitted from the second light source 2 to correct aberrations. 12a. In the second lens 12, a diffractive surface may be provided on the surface opposite to the diffractive surface 12a (surface on the optical disc side).

  The lens barrel 13 is a holding body that holds the first lens 11 and the second lens 12 at predetermined intervals in the optical axis direction, and is formed in a substantially cylindrical shape. More specifically, the lens barrel 13 holds the first lens 11 and the second lens 12 so that the first lens 11 is positioned on the optical disc side (above) with respect to the second lens 12. An adhesive is applied between at least the outer peripheral surface of the first lens 11 and the second lens 12 and the inner wall surface of the lens barrel 13, and the first lens 11 and the second lens 12 are bonded to the lens barrel 13 by this adhesive. Fixed.

  In the present embodiment, since the communication portion 21 described later is provided on the first lens 11 side in the lens barrel 13, all of the outer peripheral surface of the first lens 11 is bonded and fixed to the lens barrel 13 with an adhesive. Instead, a portion of the outer peripheral surface of the first lens 11 that faces the inner wall surface of the lens barrel 13 other than the communication portion 21 is bonded and fixed to the lens barrel 13 with an adhesive.

  By holding the first lens 11 and the second lens 12 by the lens barrel 13, a gap portion 14 is formed between the first lens 11 and the second lens 12 in the lens barrel 13. The gap portion 14 communicates with the outside via a communication portion 21 described later.

  In addition, the lens barrel 13 is provided with a stop 13 a on the first lens 11 side with respect to the second lens 12 for restricting the beam diameter of the light beam traveling in the optical disc direction via the second lens 12. .

  The objective lens 5 configured as described above is held by a bobbin 15. A focus coil and a tracking coil (not shown) are wound around the bobbin 15, and the objective lens 5 moves in the focus direction (optical axis direction) and the tracking direction (on the optical axis) due to the interaction between the drive current flowing through them and the external magnetic field. It is moved in the vertical direction.

  Here, the bobbin 15 of the present embodiment holds the objective lens 5 so that the optical disk side of the objective lens 5, that is, the first lens 11 side is on the upper side. Therefore, the bobbin 15 holds the outer peripheral surface of the lens barrel 13 and supports the outer peripheral portion (the collar portion) of the second lens 12 and the lens barrel 13 from below (the side opposite to the optical disc).

Next, the communication unit 21 will be described.
The communication part 21 is for communicating the gap 14 between the first lens 11 and the second lens 12 with the outside, and includes a hole for communication and a wall surface of the lens barrel 13 forming the hole. is there. In this embodiment, the communication portion 21 is provided in the lens barrel 13 so that the gap portion 14 communicates with the outside via a part of the outer peripheral surface of the first lens 11. That is, the communication part 21 is provided not on the resin-made second lens 12 side but on the glass-made first lens 11 side in the lens barrel 13. Thus, the point which provided the communication part 21 has the biggest characteristic of this invention. The part of the outer peripheral surface of the first lens 11 described above refers to a portion to which no adhesive is applied when the outer peripheral surface of the first lens 11 is bonded and fixed to the lens barrel 13 with an adhesive.

  As shown in FIG. 3, the communication portions 21 are provided at equal intervals around the optical axis of the first lens 11 in the lens barrel 13. The wall surface of the lens barrel 13 constituting the communication portion 21 is a semi-cylindrical wall surface that is bent substantially along the surface of the first lens 11. At this time, the wall surface of the lens barrel 13 constituting the communication portion 21 is formed with a space of 0.05 mm or more from the surface of the first lens 11 in the optical axis direction and the direction perpendicular to the optical axis, for example.

  In addition, the shape of the said wall surface of the communication part 21 is not necessarily limited to this. In other words, the wall surface of the communication portion 21 may be in the shape of a groove, and may have a V-shaped cross section or other cross sectional shapes.

  As described above, since the communication portion 21 is provided in the lens barrel 13, when the use environment temperature of the objective lens 5 (or the optical pickup) changes, the air in the gap portion 14 is externally connected via the communication portion 21. Move between. That is, when the environmental temperature changes from a low temperature to a high temperature, the air in the gap portion 14 expands, but part of it escapes to the outside through the communication portion 21. On the other hand, when the environmental temperature changes from a high temperature to a low temperature, the air in the gap portion 14 is compressed, and accordingly, external air enters the gap portion 14 through the communication portion 21. For this reason, even if environmental temperature changes, the 1st lens 11 and the 2nd lens 12 do not receive a stress in an optical axis direction with the air in the space | gap part 14. FIG. As a result, it is possible to avoid a decrease in the positional accuracy of the first lens 11 and the second lens 12 due to environmental temperature changes. In particular, it is possible to prevent dew condensation from occurring in the gap portion 14 during a change from high temperature to low temperature.

  The communication portion 21 is provided in the lens barrel 13 so that the gap portion 14 communicates with the outside through a part of the outer peripheral surface of the first lens 11, and is not provided on the second lens 12 side. Therefore, uneven deformation of the first lens 11 and the second lens 12 due to the tensile stress of the adhesive does not occur.

  More specifically, since the second lens 12 is bonded to the lens barrel 13 by an adhesive over at least the entire outer peripheral surface thereof, the second lens 12 has an adhesive in the direction around the optical axis of the second lens 12. The tensile stress toward the lens barrel 13 due to the above works equally. For this reason, the resin-made second lens 12 does not deform unevenly.

  On the other hand, since the communication part 21 is provided on the first lens 11 side, the first lens 11 is bonded to the lens barrel 13 with an adhesive on the outer peripheral surface other than the part facing the communication part 21. For this reason, in the direction around the optical axis of the first lens 11, tensile stress to the lens barrel 13 side by the adhesive acts on the first lens 11 unevenly. However, since the first lens 11 is made of glass and is hard, even if the tensile stress of the adhesive acts on the first lens 11 unevenly, the first lens 11 does not deform.

  Therefore, according to the configuration of the present embodiment, it is possible to avoid the occurrence of aberration due to the deformation of the first lens 11 and the second lens 12 due to the tensile stress of the adhesive, and the performance of the objective lens 5. A decrease can be avoided.

  Further, since the first lens 11 is held by the lens barrel 13 so as to be positioned closer to the optical disc side than the second lens 12, the air in the gap portion 14 is part of the outer peripheral surface of the first lens 11. It proceeds to the optical disc side through the section. From this, it can be said that the communication portion 21 is provided in the lens barrel 13 so that the gap portion 14 communicates with the outside on the optical disc side.

  For example, in the case where the communicating portion 21 is provided on the side opposite to the optical disk in the lens barrel 13, the objective lens 5 is provided by the bobbin 15 configured to receive the surface of the objective lens 5 opposite to the optical disk as in the present embodiment. When supported, the communication part 21 may be blocked by the bobbin 15. In this case, the configuration in which the communication portion 21 is provided does not make sense, and the shape of the bobbin 15 needs to be changed so as not to block the communication portion 21.

  However, if the communication portion 21 is provided on the optical disk side of the lens barrel 13 as in the present embodiment, the communication portion 21 is blocked by the bobbin 15 even when the objective lens 5 is supported by the bobbin 15 having the above-described configuration. There is no peeling. As a result, the gap portion 14 can be reliably communicated with the outside via the communication portion 21. Further, since the communication portion 21 is not blocked by the bobbin 15, it is not necessary to change the design of the shape of the bobbin 15.

  Further, when the communication portion 21 is provided, for example, so as to penetrate the side wall of the lens barrel 13 between the first lens 11 and the second lens 12 in a direction perpendicular to the optical axis, the outer peripheral surface of the lens barrel 13 is a bobbin. Since the contact portion 21 is in close contact with the inner peripheral surface 15, the communication portion 21 is blocked by the bobbin 15, and the meaning of providing the communication portion 21 is lost. However, in the present embodiment, the communication portion 21 is provided so that the air in the gap portion 14 can escape to the optical disk side, so that the communication portion 21 is not blocked by the inner peripheral surface of the bobbin 15.

  Further, the communication portion 21 is provided at three positions around the optical axis of the first lens 11 in the lens barrel 13. As a result, when an adhesive is applied between the inner surface of the lens barrel 13 other than the communication portion 21 and the outer peripheral surface of the first lens 11 and these are bonded, a shape close to three-point bonding is obtained. As a result, the first lens 11 can be stably adhered and fixed to the lens barrel 13. In particular, as in the present embodiment, the three communication portions 21 are provided at equal intervals around the optical axis, so that the first lens 11 can be more stably adhered and fixed to the lens barrel 13.

  Note that three communication portions 21 are desirably provided as in the present embodiment, but if at least one communication portion 21 is provided, the first lens 11 and the second lens 12 are deformed by the tensile stress of the adhesive. It is possible to obtain the minimum effect of the present invention by avoiding the occurrence of aberration and avoiding the performance degradation of the objective lens 5.

  In addition, since the communication portion 21 has a wall surface that faces the surface of the first lens 11 via a gap, the gap portion 14 reliably communicates with the outside via a part of the outer peripheral surface of the first lens 11. To do. In addition, since the distance between the wall surface of the communication portion 21 and the surface of the first lens 11 is set to 0.05 mm or more, the adhesive used when the first lens 11 and the lens barrel 13 are bonded is not limited to the communication portion. Even if it flows into 21, it is possible to avoid as much as possible that the communication part 21 is blocked by the adhesive and cannot perform its function.

  By the way, although the case where the outer peripheral surface (side surface) of the lens barrel 13 is formed straight in the optical axis direction as shown in FIG. 1 has been described above, the shape of the lens barrel 13 is not limited to this. . For example, FIG. 4 is a cross-sectional view showing a schematic configuration of the objective lens 5 in which the outer peripheral surface of the lens barrel 13 is formed in a stepped shape. In this case, the bobbin 15 that holds the objective lens 5 can have a shape that supports the step portion 13 b of the lens barrel 13 from below along the shape of the outer peripheral surface of the lens barrel 13. Even if the lens barrel 13 has a stepped portion 13b on its outer peripheral surface, the communicating portion 21 is mirrored so that the gap portion 14 communicates with the outside through a part of the outer peripheral surface of the first lens 11. By providing the tube 13, it is still possible to obtain the effect of preventing the occurrence of aberration and avoiding the performance degradation of the objective lens 5.

  In the above description, the case where two light sources of the optical pickup are provided corresponding to light beams of different wavelengths has been described. However, the configuration of the present invention provides a single light source (for example, only a light source for BD is provided). The present invention can also be applied to a case where three or more light beams having different wavelengths are provided (for example, a light source for BD, DVD, or CD is provided). Hereinafter, an example in which an optical pickup is configured using three light sources will be described.

  FIG. 5 is an explanatory diagram showing a schematic configuration of an optical pickup provided with three light sources corresponding to light beams having different wavelengths. 2 is different from the optical pickup of FIG. 2 in that a third light source 31 for CD is provided in addition to the first light source 1 for BD and the second light source 2 for DVD, and a beam splitter 3 and a collimator lens 4. The beam splitter 32 is provided in the optical path between the two.

  The third light source 31 is a semiconductor laser module that emits a light beam for CD8. In the third light source 31, a third semiconductor laser 31a is disposed at the bottom center of the bottomed box-shaped housing 31d. The third semiconductor laser 31a emits a light beam having a wavelength of 780 nm (indicated by a one-dot chain line Z). At the bottom of the housing 31d, third photodetectors 31b are disposed on both sides of the third semiconductor laser 31a. A third hologram 31c is arranged on the surface of the module in a lid shape with respect to the housing 31d. The beam splitter 32 is an optical element that selectively transmits or reflects a light beam by a wavelength-selective interference film.

  The light beam emitted from the third semiconductor laser 31 a of the third light source 31 is reflected by the beam splitter 32, converted into parallel light by the collimator lens 4, and condensed on the CD 8 as an optical disk by the objective lens 5. Is done. Then, the return light (reflected light) from the CD 8 follows the optical path opposite to the above, that is, enters the third light source 31 via the objective lens 5, the collimator lens 4 and the beam splitter 32. In the third light source 31, the return light is bent in the optical path by the third hologram 31 c and enters the third photodetector 31 b, where an optical signal (for example, a servo signal (focus error signal, tracking error signal, etc.) is input. ), An information signal, an aberration signal) are detected.

  Here, as shown in FIG. 5, in the optical pickup corresponding to the light beams of three different wavelengths, for example, an objective lens 5 ′ shown in FIG. 6 is used for correcting the aberration of the light beams for DVD7 and CD8. Conceivable.

  FIG. 6 is a cross-sectional view showing a schematic configuration of an objective lens 5 ′ used in the optical pickup. The objective lens 5 'shown in FIG. 6 is provided with a second lens 12' instead of the second lens 12 of the objective lens 5 shown in FIG. The second lens 12 ′ has not only the diffractive surface 12 a on the light incident side surface but also the diffractive surface 12 b on the light exit side (optical disc side) surface. The diffractive surface 12b is for diffracting the light beam emitted from the third light source 31 to correct aberrations.

  Even in such a configuration, if the communicating portion 21 is provided in the lens barrel 13 so that the gap portion 14 communicates with the outside through a part of the outer peripheral surface of the first lens 11, the tensile stress of the adhesive Thus, the first lens 11 and the second lens 12 ′ can be prevented from being deformed unevenly. As a result, even in an optical pickup that uses light beams of three different wavelengths, it is possible to avoid the occurrence of aberration as much as possible and to prevent the performance of the objective lens 5 'from deteriorating.

  Note that the configuration of FIG. 4 in which the step 13b is provided in the lens barrel 13 can of course be applied to the objective lens 5 'of FIG.

It is sectional drawing which shows the detailed structure of the objective lens used for the optical pick-up concerning one Embodiment of this invention, Comprising: It is A-A 'arrow sectional drawing of FIG. It is explanatory drawing which shows the schematic structure of the said optical pick-up. It is a top view of the said objective lens when it sees from the optical disk side. It is sectional drawing which shows the other structural example of the said objective lens. It is explanatory drawing which shows the other structural example of the said optical pick-up. It is sectional drawing which shows the schematic structure of the objective lens used for the said optical pick-up.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 1st light source 2 2nd light source 5 Objective lens 5 'Objective lens 6 BD (optical disk)
7 DVD (optical disc)
8 CD (optical disc)
11 First lens 12 Second lens 13 Lens barrel (holding body)
14 Air gap part 21 Communication part 31 3rd light source

Claims (6)

An objective lens having a first lens made of glass, a second lens made of resin, and a holding body for holding the first lens and the second lens,
The holding body is provided with a communication portion that communicates the gap between the first lens and the second lens with the outside.
The objective lens according to claim 1, wherein the communicating portion is provided so that the gap portion communicates with the outside through a part of the outer peripheral surface of the first lens.   2. The objective lens according to claim 1, wherein the communicating portion is provided so that the gap portion communicates with the outside on the optical disc side where the light beam is collected by the objective lens.   The said 1st lens is hold | maintained at the said holding body so that it may be located in the optical disk side where a light beam is condensed with the said objective lens rather than the said 2nd lens. Objective lens.   The objective lens according to any one of claims 1 to 3, wherein the communication portion is provided at three positions around the optical axis of the first lens in the holding body. The communication part has a wall surface facing the surface of the first lens with a gap therebetween,
The objective lens according to any one of claims 1 to 4, wherein a distance between the wall surface and the surface of the first lens is set to 0.05 mm or more. The objective lens according to any one of claims 1 to 5,
An optical pickup comprising: a light source that emits a light beam condensed on an optical disk by the objective lens.

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