JP4941586B2 - Objective lens unit and optical pickup device - Google Patents

Description

The present invention relates to an objective lens unit suitable as an objective lens incorporated in an optical head for an optical pickup, and further relates to an optical pickup device including such an objective lens unit.

Up to now, various optical pickup devices for reproducing and recording information on optical information recording media such as CD (compact disc) and DVD (digital versatile disc) have been developed and manufactured, and are widely used. Yes. As an optical head device incorporated in such an optical pickup device, there is an optical head device in which an objective lens body is fixed to a holder together with a phase control element so as to stably record and reproduce both a CD and a DVD. At this time, a center axis alignment positioning mark is provided on the objective lens body and the phase control element, respectively, to prevent decentration and reduce wavefront aberration (see Patent Document 1).
JP 2001-6203 A

  However, in the optical head device as described above, the alignment between the objective lens body and the phase control element is based on the premise that they are arranged very close to each other, and the alignment accuracy decreases as the distance between them increases.

  Furthermore, recently, a higher-density BD (Blu-ray) or HD (HD DVD) type optical pickup device has been developed, and is compatible with DVD and BD, or compatible type objective lenses compatible with DVD and HD. There is a need. In general, this type of objective lens has a configuration in which the objective lens body, which has been aberration-corrected for BD or HD, is provided with compatibility with a DVD by the phase control element. Position and tilt, especially shift decentering of the phase structure objective lens body formed in the phase control element, has a significant effect on the imaging characteristics of the DVD system on the long wavelength side. Micron accuracy is required.

Therefore, an object of the present invention is to provide an objective lens unit that can easily improve the alignment accuracy between the objective lens body and the phase control element regardless of the distance between them.

It is another object of the present invention to provide an objective lens unit that can easily improve the imaging characteristics of a compatible objective lens compatible with BD or HD without complicating the assembly process.

Another object of the present invention is to provide a high-precision optical pickup device incorporating the above-described objective lens unit.

In order to solve the above problems, an objective lens unit according to the present invention has a BD light source that emits a BD light beam, a DVD light source that emits a DVD light beam, and a CD light source that emits a CD light beam. BD information is recorded and / or reproduced using a BD light beam, DVD information is recorded and / or reproduced using a DVD light beam, and CD information is recorded and reproduced using a CD light beam. And / or an objective lens unit used in an optical pickup device for performing reproduction, wherein (a) an objective lens body disposed on the optical information recording medium side and having a unique first optical axis; and (b) disposed on the light source side. A phase control element having a unique second optical axis; and (c) fixing the phase control element in a state where the second optical axis is inclined by a predetermined amount with respect to the first optical axis with respect to the objective lens body; The second optical axis passes At least one of the two center points on the opposing surfaces of the phase control element, e Bei and a support member for holding the state of being aligned to the central extension optical path extending through the first optical axis, the phase control element first phase The first phase structure has a diffractive property with respect to a DVD light beam, but does not have a diffractive property with respect to a BD light beam and a CD light beam. The second phase structure is diffractive with respect to the CD light beam, but is not diffractive with respect to the BD light beam and the DVD light beam . Here, the “phase control element” means an optical element having a phase structure, and the “phase structure” has a plurality of steps in the second optical axis direction and has an optical path difference (phase difference) with respect to the incident light flux. ) Is a general term for structures to which. The optical path difference added to the incident light flux by this step may be an integer multiple of the wavelength of the incident light flux or a non-integer multiple of the wavelength of the incident light flux. Specific examples of such a phase structure include a diffractive structure in which the above steps are arranged at periodic intervals in the direction perpendicular to the optical axis, and the above steps are arranged at non-periodic intervals in the direction perpendicular to the optical axis. This is an optical path difference providing structure (also referred to as a phase difference providing structure).

In the objective lens unit, since the support member holds at least one of the two center points on the opposing surface of the phase control element in a state aligned with the center extension optical path extending through the first optical axis, the phase control is performed. Regardless of the tilt amount of the element, coma aberration as the objective lens unit can be reduced. That is, in imaging using both the objective lens body and the phase control element, even if the phase control element is inclined with respect to the objective lens body, one of the central points of the phase control element is used as the first light of the objective lens body. The occurrence of coma aberration can be suppressed by arranging and aligning them on the central extension optical path extending through the axis. Therefore, the optical performance of the objective lens unit can be easily improved regardless of the distance between the objective lens body and the phase control element and the relative inclination between them.

According to a specific aspect or aspect of the present invention, in the objective lens unit, the phase control element has one surface on the opposing surface having the first phase structure and the other surface on the opposing surface has the second phase structure. Have.
Moreover, in another specific aspect of the present invention, the support member holds the center point of the surface having the first phase structure in an aligned state on the center extension optical path extending through the first optical axis.
In another specific aspect of the present invention, the phase control element provides the objective lens body with compatibility with the use light of at least two different wavelengths, and uses the longer one of the at least two use lights. In addition, the numerical aperture is in a state of 0.6 or more. In this case, high-density objective lens unit enables high-density recording, and phase control element alignment is required to have submicron accuracy, for example. However, as described above, the occurrence of coma aberration can be suppressed, The optical performance required for the objective lens unit can be easily achieved.

In another specific aspect of the present invention, when the phase control element uses the DVD light flux , the wavelength is changed when the second optical axis is shifted in parallel by 3 μm with respect to the first optical axis. A coma of 5 mλ RMS or more is generated as λ. However, RMS represents “Root Mean Square”. In this case, an accuracy of several microns or less is required for the alignment of the phase control element, but the occurrence of coma aberration can be suppressed as described above, and the optical performance required for the objective lens unit can be easily achieved. it can.

  Further, in another specific aspect of the present invention, the support member is on a central extension optical path extending through the first optical axis at a center point on the surface where the phase structure is formed on the opposing surface of the phase control element. To keep it aligned. In this case, the occurrence of coma aberration can be reliably suppressed according to the phase structure forming surface.

  In another specific aspect of the present invention, the phase control element is a flat member having an opposing surface, and has a phase structure in a central region around the second optical axis of at least one of the opposing surfaces. And a flat surface in the peripheral region around the second optical axis. In this case, it is possible to perform condensing using incident light on the central region of the phase control element and relatively high NA condensing using incident light on the entire surface of the phase control element.

  In another specific aspect of the present invention, when the longer one of the at least two used lights is used, the used light having the longer wavelength is incident on the central region of the phase control element. In this case, in general, light having a long wavelength with a low recording density is used to collect light using the phase structure in the central region of the phase control element, and generally the entire surface of the phase control element is used with a short wavelength having a higher recording density. Condensation with a higher NA is performed using. When condensing the light having a short wavelength, for example, the phase structure is prevented from acting on the condensing.

  In another specific aspect of the present invention, at least one of the two central points of the phase control element and at least one of the two central points on the opposing surface of the objective lens body through which the first optical axis passes, A positioning mark is formed. In this case, simple alignment using positioning marks provided on both the phase control element and the objective lens body is possible.

  In another specific aspect of the invention, the objective lens body has a positioning mark at the center point on the phase control element side. In this case, it becomes easier to observe the objective lens body from the phase control element side.

  Moreover, in another specific aspect of the present invention, the phase control element has a positioning mark at a center point on the surface where the phase structure is formed on the opposing surface of the phase control element. In this case, the phase control element can be aligned with reference to the phase structure of the phase control element.

  In another specific aspect of the invention, the phase control element has at least one of a diffraction structure and an optical path difference providing structure as the phase structure.

  In another specific aspect of the present invention, the phase structure does not add a phase difference to a shorter wavelength of at least two used lights, and adds a phase difference to a longer wavelength. . In this case, it is possible to condense using the objective lens body with the use light having a short wavelength, and it is possible to condense using the objective lens body and the phase control element with the use light having a long wavelength.

  In another specific aspect of the present invention, the lens unit is used for at least two different wavelengths of use light, and one of the opposing surfaces of the phase control element is at least two different wavelengths of use light. A second wavelength light having a first phase structure that acts on a first wavelength light that is one and the other of the opposing surfaces is the other one of at least two different wavelength use lights Having a second phase structure acting on. In this case, the lens unit can have a condensing characteristic corresponding to two wavelengths or three wavelengths, and the optical performance of the lens unit can be improved by reducing the occurrence of coma aberration as the lens unit.

  In another specific aspect of the present invention, the phase control element is aligned with the objective lens body on the basis of one of the first and second phase structures that is more affected by coma generated by decentration. It is held by the support member in a state where In this case, the optical performance of the lens unit can be improved as a whole by precisely aligning the phase structure side having a large influence on the coma aberration.

  Further, in another specific aspect of the present invention, the objective lens body has a positioning mark at the center point on the phase control element side, and the phase control element is a coma generated due to eccentricity of the first and second phase structures. A positioning mark is provided at the center point on the surface where the aberration is more affected.

  Moreover, in another specific aspect of the present invention, the lens unit is used for at least two different wavelengths of use light, and one of the opposing surfaces is one of at least two different wavelengths of use light. A first phase structure that acts on light of a first wavelength, and the other of the opposing surfaces acts on light of a second wavelength that is the other of the used light of at least two different wavelengths. The support member holds the two center points on the opposing surface of the phase control element in a state of being shifted from the center extension optical path in opposite directions perpendicular to the center extension optical path. In this case, the lens unit can have a condensing characteristic corresponding to two wavelengths or three wavelengths, and coma aberration of each wavelength generated by the first and second phase structures can be appropriately adjusted, and the coma aberration of the lens unit can be adjusted. Generation can be reduced.

  In another specific aspect of the present invention, the phase control element is aligned with the objective lens body so that the effects of coma generated by the decentering of the first and second phase structures are substantially balanced. It is held by the support member in a state where In this case, coma aberration of each wavelength generated by the first and second phase structures can be balanced.

  In another specific aspect of the present invention, the objective lens body has a positioning mark at the center point on the phase control element side, and the phase control element has a positioning mark at each center point on the opposing surface.

  In another specific aspect of the invention, at least one of the phase control element, the objective lens body, and the support member has an inclination mark that indicates an inclination direction of the second optical axis with respect to the first optical axis. In this case, the optical pickup device can be assembled in consideration of the inclination of the phase control element.

  A first optical pickup device according to the present invention includes the above-described lens unit for forming a spot on a recording surface of an optical information recording medium, reads information on the optical information recording medium, or an optical information recording medium You can write information to

  In the above optical pickup device, the optical performance of the lens unit can be easily improved without complicating the assembly process, so that it is possible to record and / or reproduce optical information with high accuracy.

  A second optical pickup device according to the present invention is capable of generating light having a first wavelength and the above-described lens unit for forming a spot on a recording surface of an optical information recording medium, and extending the center of the lens unit. A first light source arranged in alignment on the path and a second wavelength light can be generated and deviated from the central extension optical path of the lens unit so as to reduce the coma aberration of the lens unit generated with respect to the second wavelength. A second light source arranged, and can read information from or write information to the optical information recording medium.

  In the above optical pickup device, the optical performance of the lens unit can be easily improved without complicating the assembly process, so that it is possible to record and / or reproduce optical information with high accuracy. In this case, the coma aberration of each wavelength generated by the first and second phase structures can be achieved by the alignment of the first phase structure and the position shift of the second light source, and the occurrence of coma aberration as the lens unit is extremely high. Can be reduced.

  In a specific aspect of the optical pickup device, the first phase structure is more affected by coma aberration caused by decentration than the second phase structure. In this case, the cancellation of coma aberration can be reduced by shifting the position of the second light source, and the design and manufacturing burden can be reduced.

  In another specific aspect of the optical pickup device, the objective lens body has a positioning mark at the center point on the phase control element side, and the phase control element is generated due to eccentricity of the first and second phase structures. A positioning mark is provided at the center point on the surface on which the influence of coma aberration is greater.

[First Embodiment]
FIG. 1 is a side sectional view of an objective lens unit 50 for an optical pickup according to a first embodiment of the present invention. This objective lens unit 50 has two types of optical discs (for example, different recording densities) (for example, DVD and BD), and is configured to be able to record / reproduce information on these optical disks. Further, the objective lens unit 50 collects laser light (use light) from a light source (not shown) to form a focused spot on an optical disk (not shown), and forms diffracted light. A diffractive lens 2 as a phase control element, and a cylindrical lens frame 3 as a support member for integrally fixing the objective lens body 1 and the diffractive lens 2. Here, the objective lens body 1 is made of, for example, a material such as glass, and the diffraction lens 2 and the lens frame 3 are made of, for example, plastic or a material obtained by adding several tens of percent of glass particles to plastic.

  The objective lens body 1 is an aspherical biconvex lens in which the first surface 1a on the diffractive lens 2 side protrudes greatly and the second surface 1b on the optical disk side (right side in the drawing) is formed relatively flat. The diffracted light or non-diffracted light corresponding to a pair of different wavelengths is condensed at a predetermined location on each optical disk.

  The diffractive lens 2 can form diffracted light by having a phase structure on the first surface 2 a opposite to the objective lens body 1. Note that the second surface 2b on the objective lens body 1 side is a flat surface in this case, and does not affect the image formation.

  As shown in FIG. 2, the first surface 2a of the diffractive lens 2 is divided into a circular central area CA centered on the optical axis OA2 and a peripheral area PA around the central area CA. The central area CA has a phase structure, and the peripheral area PA is a flat surface. The central area CA has a diffractive property with respect to a laser beam with a wavelength of 655 nm for DVD, but does not have a diffractive property with respect to a laser beam with a wavelength of 405 nm for BD. That is, when a laser beam with a wavelength of 655 nm for DVD enters the central area CA, the laser light is diverged with a predetermined power due to a diffraction effect, and a laser beam with a wavelength of 405 nm for BD enters the central area CA and the peripheral area PA. In this case, the laser beam passes without any diffraction effect. In other words, in the case of this embodiment, the combination of the objective lens body 1 and the diffractive lens 2 makes it possible to form images compatible with both DVD and BD laser beams with a desired accuracy, and each laser beam is transmitted to each optical disc. It can be used as information reading light or information recording light.

  The objective lens body 1 and the diffractive lens 2 are formed with circular protruding markers M1 and M2 as positioning marks that serve as a reference for positioning the center positions through which the optical axes OA1 and OA2 pass. Has been.

  3A to 3F are cross-sectional views illustrating a specific example of a multilevel diffractive structure as a phase structure formed in the central area CA provided on the first surface 2a of the diffractive lens 2. FIG. In this multi-level diffractive structure, a pattern whose cross-sectional shape including the optical axis OA2 is stepped is arranged concentrically, and has a predetermined number of level planes (five level planes in FIGS. 3A to 3F). For each DVD, a laser beam having a wavelength of 655 nm is used for a DVD having a structure in which the height is shifted by the height corresponding to the number of level surfaces (four in FIGS. 3A to 3F). When incident, diffracted light is generated, and when a laser beam having a wavelength of 405 nm is incident, it has a characteristic of transmitting as it is without generating a diffraction effect. Such a multi-level diffractive structure is described in the technical digest pages 230 to 231 of ISOM'03 (INTERNATIONAL SYMPOSIUM ON OPTICAL MEMORY 2003), so detailed description thereof is omitted here. FIGS. 3A and 3B show examples of multilevel diffractive structures in which the inclination of each pattern is in the same direction with respect to the optical axis OA2, and FIGS. 3C and 3D show the outer periphery. 3 (e) and 3 (f) show examples of a multilevel diffractive structure in which the inclination of each pattern is reversed outside the phase inverting part. An example is shown.

  3 (g), (h), and FIGS. 4 (a) to 4 (d), the phase structure includes a sawtooth diffraction structure having a sawtooth cross section including the optical axis optical axis OA2. 4E and 4F, a step-like diffraction structure in which all steps are in the same direction with respect to the optical axis OA2, or as shown in FIGS. 4G and 4H. The optical path difference providing structure in which the direction of the step is changed from the middle may be formed in the central area CA provided on the first surface 2 a of the diffractive lens 2. 3 (g) and 3 (h) show examples of sawtooth diffractive structures in which the inclination of each sawtooth is in the same direction with respect to the optical axis OA2, and FIGS. 4 (a) and 4 (b) are shown on the outer periphery. FIGS. 4C and 4D show examples of a sawtooth diffractive structure in which the inclination of each sawtooth is reversed outward from the phase inverting part. .

  Returning to FIG. 1, the lens frame 3 is cylindrical and has stepped first and second fitting parts 4, 5 at both ends, annular first and second reference surfaces 6, 7, and an annular aperture 10. And an annular third reference surface 11 and a third fitting portion 12. The first and second fitting portions 4 and 5 are cylindrical inner surfaces having steps, respectively, and fix the flanges 1f and 2f of the objective lens body 1 and the diffractive lens 2 with respect to the direction perpendicular to the optical axis. The first and second reference surfaces 6 and 7 are formed so as to be connected to the first and second fitting portions 4 and 5, respectively. When the objective lens body 1 and the diffractive lens 2 are attached, the flanges 1f and 2f are provided. This is a reference for alignment in the optical axis OA1 and OA2 directions. A play 8 is provided in the second fitting portion 5. This play 8 enables fine adjustment to align the center position with respect to the objective lens body 1 during alignment of the diffraction lens 2. A chamfered adhesive reservoir 9 is formed at the ends of the first and second fitting portions 4 and 5. The adhesive reservoir 9 cooperates with the outer periphery of the flanges 1f and 2f of the objective lens body 1 and the diffractive lens 2 to form a V-groove. After the lenses 1 and 2 are bonded or during bonding. , Prevent the adhesive from protruding to the surroundings. A diaphragm 10 disposed between the first fitting portion 4 and the second fitting portion 5 and disposed on the inner wall of the lens frame 3 cuts unnecessary light and adjusts the amount of light when the objective lens unit 50 is used. The third reference surface 11 serves as a reference for attachment with respect to the optical axis OA1 direction and inclination when attached to a holder or the like that is a component of the optical pickup device, and the third fitting portion 12 serves as a reference with respect to the optical axis vertical direction.

  The first surface 2 a of the diffractive lens 2 is slightly inclined with respect to the objective lens body 1. That is, the optical axis OA2 of the diffractive lens 2 has a slight non-zero inclination with respect to the optical axis OA1 of the objective lens body 1. Such an inclination is caused by a shape error at the time of manufacturing the lens frame 3 or a residual burr, and is exaggerated in FIG. 1, but is usually smaller. As described above, when the first surface 2a of the diffractive lens 2 is tilted, the central area CA is tilted with respect to the optical axis OA1 and shifted in a direction perpendicular to the optical axis OA1. Such a tilt or shift does not particularly affect the condensing characteristics of the laser beam having a wavelength of 405 nm for BD that is not diffracted by the multilevel diffraction structure formed in the central area CA. This may affect the condensing characteristics of the laser beam having a wavelength of 655 nm for DVD that is diffracted by the structure, and may cause aberrations during condensing. Although details will be described later in the objective lens unit 50 of the present embodiment, the diffractive lens 2 is inclined with respect to the optical axis OA of the objective lens body 1 by devising the alignment between the objective lens body 1 and the diffractive lens 2. Even in this case, an imaging accuracy of a certain level or more is achieved.

  Note that the optical axis OA1 may be inclined due to a manufacturing error of the objective lens body 1 or the like. Also in this case, since the optical axis OA2 of the diffractive lens 2 is inclined relative to the optical axis OA1 of the objective lens body 1, as a result, the relative inclination of the first surface 2a of the diffractive lens 2 is increased. Can be handled as

  Hereinafter, the manufacturing process of the objective lens unit 50 in the present embodiment will be described. First, the objective lens body 1 is attached to the lens frame 3. The flange surface of the objective lens body 1 is brought into contact with the first reference surface 6, and the adhesive is injected into the adhesive reservoir 9. Thereby, the objective lens body 1 is fixed at a predetermined position. At this time, since excess adhesive remains in the adhesive reservoir 9, it is possible to prevent the adhesive from protruding to the periphery during or after bonding.

  Next, the diffraction lens 2 is attached to the side facing the objective lens body 1 attached to the lens frame 3. The flange surface of the diffractive lens 2 is brought into contact with the second reference surface 7 to perform positioning with the objective lens body 1. At this time, the second fitting portion 5 is designed such that the inner diameter is slightly larger than the outer shape of the diffractive lens 2, and the difference is the play 8. Thereby, the diffractive lens 2 is movable in a direction perpendicular to the optical axis direction, and can be relatively positioned in the direction perpendicular to the optical axis while observing the opposing objective lens body 1.

  After positioning the diffractive lens 2, an adhesive is injected into the adhesive reservoir 9. Thereby, the diffractive lens 2 is fixed in an aligned state. At this time, since excess adhesive remains in the adhesive reservoir 9, it is possible to prevent the adhesive from protruding to the periphery during or after bonding. The diaphragm 10 serves to prevent sagging when the adhesive enters the lens frame 3.

  Thus, the objective lens unit 50 is manufactured. As described above, the objective lens unit 50 has a three-part configuration that further uses the lens frame 3 in addition to the objective lens body 1 and the diffraction lens 2. Thereby, relative positioning of the objective lens body 1 and the diffractive lens 2 in the optical axis vertical direction can be performed with high accuracy in advance.

  In this description, with respect to the mounting order, the objective lens body 1 is first and the diffraction lens 2 is rear. This is for the convenience of design that it is easier to observe from the side of the diffractive lens 2 having a small refractive power during positioning. However, for example, when positioning is performed with the objective lens body 1 behind, the order of attachment may be changed. When changing the order of attachment, play is provided on the first fitting portion 4 side. Further, as another fixing means, both the lenses 1 and 2 can be fixed to the lens frame 3 by laser welding, for example. In addition to the diffractive lens 2 side, there may be play in both the diffractive lens 2 and the objective lens body 1.

5 and 6 are enlarged views for conceptually explaining the states before and after the alignment of the diffraction lens 2 with respect to the objective lens body 1. As shown in FIG. 5, in the state before the alignment, the diffractive lens 2 is allowed to tilt, and the optical axis OA2 of the diffractive lens 2 has an inner center IC that is an intersection of the second surface 2b and the optical axis OA2 as a fulcrum. Assume that the objective lens body 1 is inclined by an angle θ with respect to the optical axis OA1. Thus, in order not to deteriorate the imaging characteristics of the objective lens unit 50 even when the diffractive lens 2 is inclined, as shown in FIG. 6, for example, parallel to the optical axis OA1 of the objective lens body 1 from the light source side. The alignment may be performed so that the incident laser beam LL passes through the marker M2 that is the center of the diffractive lens 2 and further passes through the marker M1 that is the center of the objective lens body 1 and travels along the optical axis OA1. desirable. In this way, by using the markers M1 and M2 to match the centers of the objective lens body 1 and the diffractive lens 2 in the optical axis OA1 direction, at least the objective lens unit regardless of the value of the inclination angle θ of the diffractive lens 2. The coma generated as 50 can be reduced. As shown in FIG. 5, in the state before alignment, the positions of both markers M1 and M2 are shifted by a distance X with respect to the optical axis vertical direction. This distance X is calculated from the following equation X = d · (sin θ−sin (θ / n)) from the thickness d of the diffractive lens 2, the inclination angle θ, and the refractive index of the diffractive lens 2.
Given in. Before alignment, coma aberration related to the DVD wavelength of 655 nm occurs due to the shift amount X. Therefore, the alignment causes the marker M1 of the objective lens body 1 to be a distance in the direction perpendicular to the optical axis with respect to the marker M2 of the diffractive lens 2. It is necessary to substantially suppress the occurrence of coma aberration by shifting by X. Such alignment can be achieved relatively easily. Specifically, while observing the objective lens body 1 attached to the lens frame 3 on the optical axis OA1 from the left side of the drawing, The diffractive lens 2 is arranged on the front side, and the diffractive lens 2 is moved within the second fitting portion 5 of the lens frame 3 so that both the markers M1 and M2 coincide. Thereby, the state as shown in FIG. 6 is achieved, and the imaging characteristics of the objective lens unit 50 can be ensured. Note that the direction of the optical axis OA1 of the objective lens body 1 can be determined relatively easily by various measuring devices, so that the objective lens body 1 and the diffractive lens 2 can be seen from the direction of the optical axis OA1 determined in this way. Observe by etc. For observation, alignment may be performed so that the markers M1 and M2 coincide on the screen.

  Hereinafter, specific aberration generation and correction will be described with reference to FIGS. 5 and 6. For convenience of explanation, it is assumed that the diffractive lens 2 is inclined by θ = 3 ° with respect to the objective lens body 1 with the inner center IC, which is the intersection of the second surface 2b and the optical axis OA2, as a fulcrum. There are three eccentric errors that occur in this state: the inclination of the first surface 2a, the shift of the first surface 2a, and the inclination of the second surface 2b. The tilt angle of the first surface 2a and the tilt angle of the second surface 2b are both 3 °, and the coma aberration with respect to the wavelength 655 nm for DVD generated thereby is +105 mλRMS and −105λmλRMS, which are canceled each other. However, since the coma aberration related to the wavelength 655 nm for DVD due to the shift of the first surface 2a is −71 mλRMS, the coma aberration of the entire objective lens unit 50 is −71 mλRMS. If the thickness d of the diffractive lens 2 is 0.92 mm and the refractive index n of the diffractive lens 2 with respect to the DVD wavelength of 655 nm is 1.505, the shift amount X of the first surface 2a is 16 μm.

  If this is the case, the aberration of the DVD objective lens unit 50 will exceed the marshal limit, and will exceed the practical tolerance. Below, the alignment which makes the coma aberration of the objective lens unit 50 substantially zero is demonstrated. As shown in FIG. 6, the center of the objective lens body 1 and the center of the diffractive lens 2 are made to coincide with each other with respect to the optical path extending in the direction of the optical axis OA1 of the objective lens body 1 using the markers M1 and M2. As a result, the coma aberration of the objective lens unit 50 as a whole is 0 mλ. Therefore, regardless of the inclination angle θ of the diffractive lens 2, the thickness d of the diffractive lens 2, and the refractive index n of the diffractive lens 2, the coma generated in the objective lens unit 50 can be made substantially zero.

[Second Embodiment]
Hereinafter, the objective lens unit of the second embodiment will be described. The objective lens unit of the second embodiment is a modification of the objective lens unit 50 of the first embodiment shown in FIG. 1, and parts not specifically described are the same as those of the first embodiment.

  FIG. 7 is an enlarged view for explaining the objective lens unit of the second embodiment. In the objective lens unit 150 of the present embodiment, the second surface 102b on the objective lens body 1 side of the diffractive lens 102 has a phase structure, and the first surface 102a on the opposite side is a flat surface.

  As in the case of the first embodiment, the optical axis OA2 of the diffractive lens 102 is inclined with respect to the optical axis OA1 of the objective lens body 1 by an angle θ. In order to prevent the imaging characteristics of the objective lens unit 150 from deteriorating even when the diffractive lens 102 is tilted in this way, for example, the laser light LL incident in parallel to the optical axis OA1 of the objective lens body 1 from the light source side is reflected by the diffractive lens. It is desirable to pass through the marker M2 that is the center of 102, further pass through the marker M1 that is the center of the objective lens body 1, and travel along the optical axis OA1. In this way, by using the markers M1 and M2 to match the centers of the objective lens body 1 and the diffractive lens 102 in the optical axis OA1 direction, at least the objective lens unit regardless of the value of the inclination angle θ of the diffractive lens 102. The coma aberration generated as 150 can be reduced.

  As a method of arranging the marker M2 of the diffractive lens 102 on the optical axis OA1 of the objective lens body 1, the objective lens body 1 attached to a lens frame (not shown) is observed on the optical axis OA1 from the left side of the drawing while the objective is viewed. The diffractive lens 102 is arranged on the front side of the lens body 1 and the diffractive lens 102 is moved within the lens frame so that both the markers M1 and M2 coincide. Thereby, the state shown in FIG. 7 is achieved, and the imaging characteristics of the objective lens unit 150 can be ensured.

  Hereinafter, a specific example of alignment that makes the coma aberration of the objective lens unit 150 substantially zero will be described. As shown in FIG. 7, the center of the diffraction lens 2 is made to coincide with the extension of the optical axis OA1 of the objective lens body 1 using the markers M1 and M2. Also in this case, the inclination angle of the first and second surfaces 102a and 102b is assumed to be 3 °. In this state, the coma aberration related to the wavelength 655 nm for DVD due to the shift of the first surface 102a is 0 mλ, the coma aberration due to the inclination of the first surface 102a is +105 mλ, and the coma due to the inclination of the second surface 2b. Since the aberration is −105 mλ, the coma aberration of the objective lens unit 150 as a whole is 0 mλ. Therefore, regardless of the value of the tilt angle θ of the diffractive lens 102, the coma generated in the objective lens unit 150 can be made substantially zero.

[Third Embodiment]
The objective lens unit according to the third embodiment will be described below. The objective lens unit according to the third embodiment is a modification of the objective lens unit 50 according to the first embodiment shown in FIG. 1, and parts not specifically described are common to the first embodiment and the second embodiment. It has become a thing.

  FIG. 8 is a side sectional view of the objective lens unit 250 according to the third embodiment. Also in the case of the objective lens unit 250, the optical axis OA2 of the diffraction lens 202 has a slight non-zero inclination with respect to the optical axis OA1 of the objective lens body 1. However, such an inclination is not caused by a manufacturing error or the like of the lens frame 203 but is caused by a manufacturing error or the like of the diffractive lens 202 itself. When the first surface 202a and the second surface 202b of the diffractive lens 202 are tilted in this way, there is no particular influence on the light condensing with respect to the laser light with a wavelength of 405 nm for BD, but the light with respect to the laser light with a wavelength of 655 nm for DVD is collected. It affects light and causes aberrations when focused. Similar to the second embodiment shown in FIG. 6 and the like, such aberration is canceled by the alignment using the markers M1 and M2, and the diffractive lens 202 is inclined with respect to the optical axis OA1 of the objective lens body 1. In this case, a certain level of imaging accuracy is achieved.

[Fourth Embodiment]
The objective lens unit according to the fourth embodiment will be described below. The objective lens unit of the fourth embodiment is a modification of the objective lens unit 50 of the first embodiment shown in FIG. 1, and parts not specifically described are the same as those in the first embodiment.

  FIG. 9 is a sectional side view of an objective lens unit 350 according to the fourth embodiment. In the case of the objective lens unit 350, a notch 303d, which is an inclination mark for indicating the direction in which the optical axis OA2 of the diffraction lens 2 is inclined, is formed in the lens frame 3. By using the notch 303d, the tilt direction of the diffractive lens 2 can be controlled, and the optical characteristics of the diffractive lens 2 and other influences of tilt on transmitted light and reflected light can be controlled. In addition, the shape asymmetry of the lens frame 3 is not limited to unintentional manufacturing errors and the like including the case of the first embodiment, but includes intentionally provided. When the asymmetry of the shape of the lens frame 3 is not intended, the notch 303d is formed by specifying the inclination direction of the optical axis OA2 by measurement after manufacturing or the like, while the asymmetry of the shape of the lens frame 3 is intended. In this case, the notch 303d is formed by specifying the inclination direction of the optical axis OA2 according to the design.

  In addition, what displays the inclination direction of optical axis OA2 can be not only the notch 303d but various marks including a three-dimensional shape, coloring, etc.

[Fifth Embodiment]
The objective lens unit according to the fifth embodiment will be described below. The objective lens unit of the fifth embodiment is a modification of the objective lens unit 250 of the third embodiment shown in FIG. 8, and parts not specifically described are the same as those of the third embodiment.

  FIG. 10 is a front view of a diffractive lens in the objective lens unit according to the fifth embodiment. In the case of this objective lens unit, the diffractive lens 2 itself is formed with a notch 402d that is an inclination mark for indicating the direction in which the optical axis OA2 is inclined. By utilizing this notch 402d, the tilt direction of the first surface 2a and the like of the diffractive lens 2 can be controlled, and the optical characteristics of the diffractive lens 2 and other influences of tilt on transmitted light and reflected light can be controlled. it can. Note that the shape asymmetry of the diffractive lens 2 is not limited to unintentional manufacturing errors, including the case of the third embodiment, but includes intentionally provided ones. When the asymmetry of the shape of the diffractive lens 2 is not intended, the notch 402d is formed by specifying the inclination direction of the optical axis OA2 by measurement after manufacturing or the like, while the asymmetry of the shape of the diffractive lens 2 is intended. In this case, the notch 402d is formed by specifying the inclination direction of the optical axis OA2 according to the design.

  In addition, what displays the inclination direction of optical axis OA2 can be not only the notch 402d but various marks including a three-dimensional shape and coloring.

[Sixth Embodiment]
FIG. 11 is a diagram schematically showing the configuration of an optical pickup device incorporating the objective lens units 50, 150, 250, and 350 according to the first to fifth embodiments.

  This optical pickup device includes a laser beam for reproducing information from the first optical disk D1 (for example, a wavelength of 655 nm for DVD and NA 0.60) and a laser beam for reproducing information from the second optical disk D2 (for example, a wavelength of 405 nm for BD). NA 0.85) and the generated two-wavelength semiconductor laser 61, that is, laser beams having different wavelengths can be emitted. Laser light from the semiconductor laser 61 is applied to the optical discs D1 and D2, which are optical information recording media, using the objective lens units 50, 150, 250, and 350, and reflected light from the optical discs D1 and D2 is applied to the objective lens unit. Light is collected using 50 to 350.

  First, when reproducing the first optical disk D1, laser light having a wavelength of 655 nm is emitted from the semiconductor laser 61, and the emitted light beam passes through the collimator 62, the polarization beam splitter 63, and the quarter wavelength plate 64 and is circularly polarized. It becomes parallel light flux. This light beam is focused on the information recording surface MS1 of the first optical disc D1 by the objective lens units 50 to 350.

  The light beam modulated and reflected by the information bit on the information recording surface MS1 is transmitted again through the objective lens units 50 to 350 and the ¼ wavelength plate 64, enters the polarization beam splitter 63, is reflected there, and is a cylindrical lens. Astigmatism is given by 65, is incident on the photodetector 67, and a read signal of information recorded on the first optical disc D1 is obtained using the output signal.

  Further, a change in the amount of light due to a change in the shape of the spot and a change in position on the photodetector 67 is detected, and focus detection and track detection are performed. Based on this detection, the two-dimensional actuator 72 incorporated in the holder 71 that holds the objective lens units 50 to 350 forms an object on the information recording surface MS1 of the first optical disc D1 so that the light beam from the semiconductor laser 61 is imaged. The lens units 50 to 350 are moved in the optical axis direction, and the objective lens units 50 to 350 are moved in a direction perpendicular to the optical axis so that the light flux from the semiconductor laser 61 is imaged on a predetermined track.

  On the other hand, when reproducing the second optical disk D2, a laser beam having a wavelength of 405 nm is emitted from the semiconductor laser 61, and the emitted beam is transmitted through the collimator 62, the polarization beam splitter 63, and the quarter wavelength plate 64 to be circular. It becomes a polarized parallel light beam. This light beam is condensed on the information recording surface MS2 of the second optical disk D2 by the objective lens units 50 to 350.

  The light beam modulated and reflected by the information bit on the information recording surface MS2 is transmitted again through the objective lens units 50 to 350 and the ¼ wavelength plate 64, is incident on the polarization beam splitter 63, is reflected there, and is a cylindrical lens. Astigmatism is given by 65, is incident on the photodetector 67, and a read signal of information recorded on the second optical disc D2 is obtained using the output signal.

  Further, as in the case of the first optical disc D1, a change in the amount of light due to a change in the shape and position of the spot on the photodetector 67 is detected, and focus detection and track detection are performed, and the objective lens units 50 to 350 are held. The objective lens units 50 to 350 are moved for focusing and tracking by the two-dimensional actuator 72 incorporated in the holder.

  In the sixth embodiment described above, an integrated element in which the semiconductor laser 61 and the photodetector 67 are integrated can be used. In this case, the polarization beam splitter 63 and the like are not necessary. Conversely, the semiconductor laser 61 can be divided into a laser light source having a wavelength of 655 nm and a laser light source having a wavelength of 405 nm, and laser beams from both laser light sources can be combined by an additional polarization beam splitter.

[Seventh Embodiment]
The objective lens unit according to the seventh embodiment will be described below. The objective lens unit of the seventh embodiment is a modification of the objective lens unit 50 of the first embodiment shown in FIG. 1, and parts not specifically described are the same as those of the first embodiment.

  FIG. 12 is a sectional side view of an objective lens unit 550 according to the seventh embodiment. In the case of the objective lens unit 550, the diffraction lens 502 not only has a phase structure on the first surface 502a on the back side with respect to the objective lens body 1, but also on the second surface 502b on the front side with respect to the objective lens body 1. Has a phase structure.

  The first surface 502a of the diffractive lens 502 is diffractive with respect to a laser beam having a wavelength of 655 nm for DVD, but is used for a laser beam having a wavelength of 405 nm for BD or a laser beam having a wavelength of 780 nm for CD. On the other hand, it has no diffractive properties. On the other hand, the second surface 502b is diffractive with respect to a laser beam with a wavelength of 780 nm for CD, but with respect to a laser beam with a wavelength of 405 nm for BD or a laser beam with a wavelength of 655 nm for DVD. Has no diffractive properties. The objective lens body 1 is designed for laser light having a wavelength of 405 nm for BD, and is an aspheric glass lens or plastic lens.

  When laser light having a wavelength of 655 nm for DVD is incident on the lens unit 550 from the light source side (left side in the drawing), the laser light is appropriately condensed with a predetermined power by the diffraction effect on the first surface 502a of the diffractive lens 502. The light is diverged and condensed through the objective lens body 1 on the DVD information recording surface (not shown) on the right side of the drawing. Further, when laser light having a wavelength of 780 nm for CD is incident on the lens unit 550 from the light source side, the laser light is appropriately condensed or diverged with a predetermined power by the diffraction effect on the second surface 502b of the diffractive lens 502. Then, the light passes through the objective lens body 1 and is condensed on a CD information recording surface (not shown) on the right side of the drawing. When laser light having a wavelength of 405 nm for BD is incident on the lens unit 550 from the light source side, the laser light passes through the diffractive lens 502 without being diffracted and passes through the objective lens body 1 and on the right side of the drawing. On the BD information recording surface (not shown). In other words, in the case of the present embodiment, the combination of the objective lens body 1 and the diffraction lens 502 enables image formation that can be interchanged with a desired accuracy for each laser beam for DVD, CD, and BD. The light can be used as information reading light or information recording light for each optical disc.

FIG. 13 is an enlarged view for conceptually explaining the alignment of the diffraction lens 502 with respect to the objective lens body 1. As is apparent from the figure, the tilt of the diffractive lens 502 is allowed, and the optical axis OA2 of the diffractive lens 502 is tilted by an angle θ with respect to the optical axis OA1 of the objective lens body 1. Thus, when the diffraction lens 502 is inclined, at least one of the marker M2 that is the center of the first surface 502a and the inner center IC of the second surface 502b is relative to the optical axis OA1 of the objective lens body 1. Will always be displaced. That is, when the first surface 502a is aligned with the optical axis OA1, the center of the second surface 502b is the distance X described in FIG. 5 from the optical axis OA1.
X = d · (sin θ−sin (θ / n))
When the second surface 502b is aligned with respect to the optical axis OA1 (see the light beam LL ′ in FIG. 13), the center of the first surface 502a is described with reference to the optical axis OA1 in FIG. The position is shifted in the opposite direction by the distance X.

  In general, coma aberration caused by the deviation of the center of the first surface 502a and the second surface 502b from the light beam LL extending the optical axis OA1 is the third power of the NA value of the objective lens unit 550, the substrate thickness of the optical disk, It is proportional to the reciprocal of the wavelength of the laser beam. Here, the first surface 502a is for DVD, for example, NA 0.60, substrate thickness 0.6mm, wavelength 655nm, and the second surface 502b is for CD, for example, NA 0.45, substrate thickness. 1.2 mm, wavelength 780 nm. Therefore, when the coma generated by the positional deviation of the second surface 502b for CD is 1, the coma generated by the positional deviation of the first surface 502a for DVD is about 2 to 6 times. This is because, when the amount of eccentricity of the first surface 502a is equal to the amount of eccentricity of the second surface 502b, the contribution of the eccentricity of the first surface 502a to the coma aberration contributes to the coma aberration of the eccentricity of the second surface 502b. This means that the amount of eccentricity of the first surface 502a is more meaningful in improving the overall performance than reducing the amount of eccentricity of the second surface 502b. I understand.

  On the other hand, when the diffractive lens 502 is inclined, either the eccentricity of the first surface 502a or the eccentricity of the second surface 502b cannot be avoided. That is, when the center of the first surface 502a is disposed on the light beam LL (that is, the center extension optical path) traveling along the optical axis OA1, the center of the second surface 502b cannot be disposed on the light beam LL. Conversely, when the center of the second surface 502b is arranged on the light beam LL, the center of the first surface 502a cannot be arranged on the light beam LL. For this reason, in this embodiment, the marker M2 is formed at the center of the first surface 502a, and the marker M2 is disposed on the light beam LL, thereby minimizing the coma caused by the first surface 502a for DVD. The coma aberration caused by the second surface 502b for CD is allowed. That is, as shown in FIG. 13, by using the markers M1 and M2, the center of the objective lens body 1 and the center of the diffractive lens 502 are matched with respect to the optical path extending in the direction of the optical axis OA1 of the objective lens body 1. Aberrations are reduced as a whole.

  FIG. 14 is a diagram schematically showing a configuration of an optical pickup device incorporating the objective lens unit 550 shown in FIG.

  In this optical pickup device, laser light from each of the semiconductor lasers 61B, 61D, and 61C is applied to the optical discs DB, DD, and DC that are optical information recording media using the objective lens unit 550, and the optical discs DB, DD, and The reflected light from the DC is collected using a common objective lens unit 550 and finally guided to the photodetectors 67B, 67D, and 67C.

  Here, the first semiconductor laser 61B generates laser light for reproducing information from the first optical disc DB (for example, for BD, wavelength 405 nm, NA 0.85), and the second semiconductor laser 61D is information on the second optical disc DD. Laser light for reproduction (for example, DVD for wavelength 655 nm, NA 0.60) is generated, and the third semiconductor laser 61C is a laser beam for information reproduction of the third optical disk DC (for example, CD for wavelength 780 nm, NA 0.54). ). The first photodetector 67B detects information recorded on the first optical disc DB as an optical signal (for example, for BD, wavelength 405 nm), and the second photodetector 67D is recorded on the second optical disc DD. The information is detected as an optical signal (for example, for DVD, wavelength 655 nm), and the third photodetector 67C detects the information recorded on the third optical disc DC as an optical signal (for example, CD for wavelength 780 nm).

  First, when reproducing the first optical disc DB, laser light having a wavelength of, for example, 405 nm is emitted from the first semiconductor laser 61B, and the emitted light beam is transmitted through the collimator 62B and the polarization beam splitter 63B to become a parallel light beam. This light beam passes through the other polarizing beam splitters 64D and 64C, and is then focused on the information recording surface MB of the first optical disc DB by the objective lens unit 550.

  The light beam modulated and reflected by the information bit on the information recording surface MB is again transmitted through the objective lens unit 550 and the like, is incident on the polarization beam splitter 63B, is reflected there, and is given astigmatism by the cylindrical lens 65B. Then, the light is incident on the first photodetector 67B, and a read signal of information recorded on the first optical disc DB is obtained using the output signal.

  Further, a change in the amount of light due to a change in the shape of the spot and a change in position on the first photodetector 67B is detected to perform focus detection and track detection. Based on this detection, the two-dimensional actuator 72 incorporated in the holder 71 that holds the objective lens unit 550 forms an object on the information recording surface MB of the first optical disc DB so that the light beam from the first semiconductor laser 61B is imaged. The lens unit 550 is moved in the optical axis direction, and the objective lens unit 550 is moved in a direction perpendicular to the optical axis so that the light flux from the first semiconductor laser 61B is imaged on a predetermined track.

  Next, when reproducing the second optical disk DD, laser light having a wavelength of, for example, 655 nm is emitted from the second semiconductor laser 61D, and the emitted light beam passes through the collimator 62D and the polarization beam splitter 63D to become a parallel light beam. This light beam passes through the other polarizing beam splitters 64D and 64C, and is then focused on the information recording surface MD of the first optical disc DD by the objective lens unit 550.

  The light beam modulated and reflected by the information bit on the information recording surface MD is transmitted again through the objective lens unit 550 and the like, reflected by the polarization beam splitter 64D and incident on the polarization beam splitter 63D, and reflected and reflected here by the cylindrical lens 65D. Astigmatism is given by the laser beam, the light is incident on the second photodetector 67D, and a read signal of information recorded on the second optical disk DD is obtained using the output signal.

  In addition, as in the case of the first optical disc DB, a change in the amount of light due to a change in the shape and position of the spot on the second photodetector 67D is detected, and focus detection and track detection are performed, and the objective lens unit 550 is held. The objective lens unit 550 is moved for focusing and tracking by a two-dimensional actuator 72 incorporated in the holder.

  Next, when reproducing the third optical disc DC, laser light having a wavelength of, for example, 780 nm is emitted from the third semiconductor laser 61C, and the emitted light beam is transmitted through the collimator 62C and the polarization beam splitter 63C and reflected by the polarization beam splitter 64C. It becomes a parallel light flux. This light beam is condensed by the objective lens unit 550 on the information recording surface MC of the first optical disc DC.

  The light beam modulated and reflected by the information bit on the information recording surface MC is transmitted again through the objective lens unit 550 and the like, reflected by the polarization beam splitter 64C and incident on the polarization beam splitter 63C, and reflected and reflected here by the cylindrical lens. Astigmatism is given by 65C, is incident on the third photodetector 67C, and a read signal of information recorded on the third optical disc DC is obtained using the output signal.

  As in the case of the first and second optical discs DB and DD, the spot shape change on the third photodetector 67C and the light quantity change due to the position change are detected, and focus detection and track detection are performed, and the objective is detected. The objective lens unit 550 is moved for focusing and tracking by a two-dimensional actuator 72 incorporated in a holder that holds the lens unit 550.

  In the above embodiment, the first surface 502a of the diffractive lens 502 is for DVD and the second surface 502b is for CD. However, the first surface 502a may be for CD and the first surface 502a may be for DVD. it can. In this case, the center of the second surface 502b is arranged on the light beam LL traveling along the optical axis OA1.

[Eighth Embodiment]
The objective lens unit according to the eighth embodiment will be described below. The objective lens unit of the eighth embodiment is a modification of the objective lens unit 550 of the seventh embodiment shown in FIG. 12, and parts not specifically described are the same as those in the seventh embodiment.

  FIG. 15 is a side sectional view of the objective lens unit 650 according to the eighth embodiment. In the case of the objective lens unit 650, in the diffractive lens 602, not only the marker M2 ′ is formed at the center of the first surface 502a, but also the marker M2 ″ is formed at the center of the second surface 502b.

  FIG. 16 is an enlarged view for conceptually explaining the alignment of the diffraction lens 602 with respect to the objective lens body 1. As is apparent from the figure, the tilt of the diffractive lens 502 is allowed, and the optical axis OA2 of the diffractive lens 602 is tilted by an angle θ with respect to the optical axis OA1 of the objective lens body 1. Thus, when the diffractive lens 602 is inclined, at least one of the marker M2 ′ that is the center of the first surface 502a and the marker M2 ″ that is the center of the second surface 502b is light of the objective lens body 1. The position is always displaced with respect to the axis OA1.

  As described in the seventh embodiment, a coma generally generated when the marker M2 ′, which is the center of the first surface 502a, and the marker M2 ″, which is the center of the second surface 502b, deviate from the light beam LL extending the optical axis OA1. The aberration is proportional to the third power of the NA value of the objective lens unit 650, the substrate thickness of the optical disk, and the reciprocal of the wavelength of the laser light, which is the amount of eccentricity of the first surface 502a and the eccentricity of the second surface 502b. By appropriately adjusting the amount, the coma aberration caused by the eccentricity of the first surface 502a and the coma aberration caused by the eccentricity of the second surface 502b can be balanced almost uniformly, or the eccentricity of the first surface 502a. It is possible to set the coma due to the coma and the coma due to the eccentricity of the second surface 502b to a desired ratio.

  FIG. 17 shows a microscopic field MF in which the lens unit 650 shown in FIG. 15 is observed from the light source side. While observing the objective lens body 1 attached to the lens frame 3 of the lens unit 650 on the optical axis OA1 from the left side of the drawing, a diffractive lens 602 is arranged on the front side of the objective lens body 1 and both markers M2 'and M2 " The diffractive lens 602 is moved in the second fitting portion 5 of the lens frame 3 so that the marker M1 is positioned between the first and second surfaces 502a and 502. For example, the coma aberration caused by the eccentricity of the first surface 502a and the eccentricity of the second surface 502b are caused. When it is desired to balance the coma aberration to be almost evenly divided, the first surface 502a is internally divided by the reciprocal of the ratio of the contribution of the decentering of the first surface 502a to the coma aberration of the second surface 502b. The diffractive lens 602 may be aligned so that the marker M1 is positioned at a position where the first surface 502a is for DVD, for example, NA 0.60, substrate thickness 0.6 mm, wavelength 655 nm, First The surface 502b is, for example, for a CD and has an NA of 0.45, a substrate thickness of 1.2 mm, and a wavelength of 780 nm, so that the coma caused by the positional deviation of the second surface 502b for CD is 1. The coma caused by the positional deviation of the first surface 502a for DVD is about 2 to 6. Accordingly, coma caused by the decentering of the first surface 502a and coma caused by the decentering of the second surface 502b. For example, when the coma aberration due to the positional deviation of the first surface 502a for DVD is doubled, between the markers M2 ′ and M2 ″, the marker M2 ′ It is understood that the marker M1 only needs to exist at a position of 0.33D from the marker M2 ″ and 0.66D from the marker M2 ″. In this way, by adjusting the positions of both the markers M2 ′ and M2 ″ with reference to the marker M1 In addition, the occurrence balance of coma aberration due to the inclination of both surfaces 502a and 502b can be appropriately adjusted.

[Ninth Embodiment]
Hereinafter, it is a figure which shows schematically the structure of the optical pick-up apparatus which concerns on 9th Embodiment. This optical pickup device uses an objective lens unit 550 according to the seventh embodiment shown in FIG.

  FIG. 18 is an enlarged view for conceptually explaining a state after the alignment of the diffraction lens 502 with respect to the objective lens body 1. As is apparent from the figure, the tilt of the diffractive lens 502 is allowed, and the optical axis OA2 of the diffractive lens 502 is tilted by an angle θ with respect to the optical axis OA1 of the objective lens body 1. As described in the seventh embodiment, coma aberration, which is generally generated when the center of the first surface 502a or the center of the second surface 502b deviates from the light beam LL extending the optical axis OA1, is the NA value of the objective lens unit 550. Is the third power, the substrate thickness of the optical disk, and the inverse of the wavelength of the laser beam. Specifically, when the amount of eccentricity of the first surface 502a is equal to the amount of eccentricity of the second surface 502b, the contribution of the eccentricity of the first surface 502a to the coma aberration of the second surface 502b contributes to the coma aberration of the eccentricity of the second surface 502b. The amount of eccentricity of the first surface 502a is more meaningful in improving the overall performance than reducing the amount of eccentricity of the second surface 502b. I understand that. Therefore, by forming the marker M2 at the center of the first surface 502a and placing the marker M2 on the light beam LL, the coma caused by the first surface 502a for DVD is minimized and the second for CD is used. The coma caused by the surface 502b is allowed. On the other hand, if the coma caused by the eccentricity of the second surface 502b can be reduced by another method, the aberration of the objective lens unit 550 can be extremely reduced. For this purpose, the coma aberration caused by the eccentricity of the second surface 502b is reduced by disposing the light source position for the wavelength of 780 nm for CD at a position away from the light source position for BD or DVD.

  FIG. 19 is a diagram schematically showing the configuration of the optical pickup device of the present embodiment. This optical pickup device incorporates the objective lens unit 550 shown in FIGS. 12 and 18, and has the same structure as the optical pickup device according to the sixth embodiment shown in FIG. 11 except for the light source.

  FIG. 20 is a view for explaining the longitudinal sectional structure of a three-wavelength semiconductor laser 761 incorporated in the optical pickup device shown in FIG. As is apparent from the drawing, the first and second laser elements 761a and 761b having a two-layer structure are formed on the left portion of the semiconductor laser chip 761X, and a single third laser element 761a and 761b is formed on the right portion of the semiconductor laser 761. A laser element 761c is formed. The first laser element 761a generates laser light for reproducing information on the first optical disc DB (for example, for BD, wavelength 405 nm), and the second laser element 761b is laser light for reproducing information on the second optical disc DD (for example, The third laser element 761c generates a laser beam for reproducing information from the third optical disc DC (for example, a wavelength of 780 nm for CD). As illustrated, the first and second laser elements 761a and 761b are arranged in alignment along the optical axis OA, while the third laser element 761c is arranged at a distance ΔX from the optical axis OA. ing. As a result, coma aberration occurs when the third laser element 761c forms an image. Such coma aberration has a magnitude opposite to the coma aberration caused by the decentering of the second surface 502b described in FIG. Are the same. That is, the coma aberration of the condensing spot formed by the objective lens unit 550 is close to zero in all of 405 nm for BD, 655 nm for DVD, and 780 nm for CD, and good aberration correction is performed.

  Although the present invention has been described based on the above embodiments, the present invention is not limited to the above embodiments, and various modifications are possible. For example, the shape of the alignment markers M1 and M2 including the irregularities and contours is not limited to those exemplified in the embodiment, and is easy to use as long as it can be visually observed through a measuring device or the like. Various shapes can be used in consideration.

  In the above-described embodiment, the objective lens units 50 to 350, 550, 650, and 750 including two optical elements have been described. However, in the case of an objective lens unit including three or more optical elements, for example, any one of the adjacent ones is adjacent. The two optical elements can be aligned with the same positioning marker as in the above embodiment. Also in this case, the assembly of the objective lens unit is simplified and the optical performance is improved.

  In the above embodiment, the objective lens body 1, the diffractive lenses 2, 102, 502, 602, and the lens frame 3 are separated. However, the objective lens body 1 and the lens frame 3 are integrated to form a cylindrical flange. The diffractive lens 2, 102, 502, 602 and the lens frame 3 can be integrated to form the diffractive lens 2, 102, 502, 602 having a cylindrical flange. In any case, coma aberration can be eliminated by the alignment described with reference to FIGS.

  Further, in the seventh and eighth embodiments, an inclination mark can be provided on the lens frame 3 or the like in order to specify the inclination direction of the diffraction lenses 502 and 602 of the objective lens units 550 and 650 (notch 303d in FIG. 9). reference).

  In the above embodiment, the compatible objective lens units 50, 150, 250, 350, 550, and 650 including the BD are described. For example, the compatible objective lens unit including the HD instead of the BD is used. Of course, the present invention can be applied to the above. More specifically, the objective lens units 50, 150, 250, and 350 of the first to fifth embodiments can be made compatible with, for example, DVD and HD. The objective lens units 550 and 650 of the ninth embodiment can be made compatible with CDs, DVDs, and HDs, for example.

It is side sectional drawing of the lens unit of 1st Embodiment. It is a front view of the diffraction lens which comprises a lens unit. (A)-(h) is sectional drawing explaining the specific example of the phase structure formed in the center area | region of a diffractive lens. (A)-(h) is sectional drawing explaining the specific example of the phase structure formed in the center area | region of a diffractive lens. It is an enlarged view explaining alignment of the objective lens unit of FIG. It is an enlarged view explaining alignment of the objective lens unit of FIG. It is an enlarged view explaining alignment of the objective lens unit of 2nd Embodiment. It is a sectional side view of the lens unit of a 3rd embodiment. It is side sectional drawing of the lens unit of 4th Embodiment. It is a front view of the diffraction lens which comprises the lens unit of 5th Embodiment. It is a block diagram explaining the structure of the optical pick-up apparatus of 6th Embodiment. It is a sectional side view of the lens unit of 7th Embodiment. It is an enlarged view explaining alignment of the objective lens unit of 7th Embodiment. It is a figure which shows the optical pick-up apparatus incorporating the lens unit shown in FIG. It is a sectional side view of the lens unit of 8th Embodiment. It is an enlarged view explaining alignment of the objective lens unit of 8th Embodiment. The state which observed the lens unit from the light source side is shown. It is an enlarged view explaining alignment of the objective lens unit in 9th Embodiment. It is a figure which shows the optical pick-up apparatus of subject 9 embodiment. It is a figure explaining the longitudinal cross-section of a 3 wavelength semiconductor laser integrated in the optical pick-up apparatus shown in FIG.

  DESCRIPTION OF SYMBOLS 1 ... Objective lens main body, 2 ... Diffraction lens, 3 ... Mirror frame, 50 ... Objective lens unit, 61 ... Two wavelength semiconductor laser, 63 ... Polarizing beam splitter, 65 ... Cylindrical lens, 67 ... Photo detector, 72 ... Two-dimensional Actuator, CA ... central area, D1 ... first optical disc, D2 ... second optical disc, M1, M2 ... marker, S1 ... information recording surface, MS2 ... information recording surface, OA1, OA2 ... optical axis

Claims (13)

A BD light source that emits a BD light beam, a DVD light source that emits a DVD light beam, and a CD light source that emits a CD light beam, and recording and / or recording BD information using the BD light beam Alternatively, an objective lens used in an optical pickup device that performs reproduction, records and / or reproduces DVD information using the DVD light flux, and records and / or reproduces CD information using the CD light flux. A unit,
An objective lens body disposed on the optical information recording medium side and having a unique first optical axis;
A phase control element disposed on the light source side and having a unique second optical axis;
The phase control element is fixed to the objective lens body in a state where the second optical axis is inclined by a predetermined amount with respect to the first optical axis, and the second optical axis passes through the phase control element. at least one of the two center points on the opposing surface, e Bei and a support member for holding the state of being aligned to the central extension optical path extending through the first optical axis,
The phase control element has a first phase structure and a second phase structure;
The first phase structure has a diffractive property with respect to the DVD light beam, but does not have a diffractive property with respect to the BD light beam and the CD light beam,
The second phase structure, has the diffractive against the CD light beam, an objective lens, wherein for BD light beam and the DVD light beam, characterized in that has no diffractive unit. 2. The objective lens according to claim 1, wherein one surface of the facing surface has the first phase structure and the other surface of the facing surface has the second phase structure. unit. The support member holds a center point on a surface where a phase structure is formed on an opposing surface of the phase control element in an aligned state on a central extension optical path extending through the first optical axis. 3. The objective lens unit according to claim 1, wherein the objective lens unit is characterized in that: The said support member hold | maintains the center point of the surface which has the said 1st phase structure in the state aligned on the center extension optical path extended through the said 1st optical axis. The objective lens unit according to claim 1. The phase control element is held by the support member in a state of being aligned with the objective lens body so that the effects of coma generated by the decentering of the first and second phase structures are substantially balanced. The objective lens unit according to any one of claims 1 to 4, wherein the objective lens unit is provided. When the second optical axis is shifted by 3 μm parallel to the first optical axis when using the DVD light flux , the phase control element has a coma aberration of 5 mλ RMS or more with a wavelength λ. 6. The objective lens unit according to claim 1, wherein the objective lens unit is generated. The phase control element is a flat plate-like member having the opposing surface, and has a phase structure in a central region around the second optical axis in at least one of the opposing surfaces, and around the second optical axis. The objective lens unit according to claim 1, wherein the objective lens unit has a flat surface in a peripheral region. Positioning marks are formed on at least one of the two center points of the phase control element and at least one of the two center points on the opposing surface of the objective lens body through which the first optical axis passes. The objective lens unit according to any one of claims 1 to 7, wherein 9. The objective lens unit according to claim 8 , wherein the objective lens body has the positioning mark at the center point on the phase control element side. The phase control element, any one of claims 8 and claim 9 characterized by having the positioning mark to the center point on the surface where the phase structure is formed out on said opposite surface of said phase control element The objective lens unit described in the item . The objective lens unit according to any one of claims 1 to 10, wherein the phase control element has at least one of a diffraction structure and an optical path difference providing structure as a phase structure. The phase control element, the objective lens main body, and the at least one support member, wherein the preceding claims, characterized in that it has a tilt mark indicating the inclination direction with respect to the first optical axis of the second optical axis Item 12. The objective lens unit according to any one of Items 11 . The objective lens unit according to any one of claims 1 to 12 , comprising:
An optical pickup device capable of reading information on an optical information recording medium or writing information on the optical information recording medium.

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