JP2011238304A - Optical pickup lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical pickup lens that can be formed with a higher degree of accuracy when an orbicular zone structure is provided for preventing aberration deterioration due to wavelength variation or a temperature change.SOLUTION: A plastic optical pickup objective lens for focusing a light flux emitted from a laser light source onto an optical disc such as a Blu-ray disc comprises multiple orbicular zone regions on both surfaces of a lens surface (R1 surface) 101 on a side of the laser light source and a lens surface (R2 surface) 102 on a side of the optical disc. The optical pickup objective lens comprises an orbicular zone structure, in which the lens surfaces are divided into multiple concentric orbicular zone regions 103 by steps and connection regions 104 are provided between the respective orbicular zone regions. The multiple steps have step heights that cause an incident light flux to generate a phase difference for reducing aberration generated in the light pickup objective lens when the ambient temperature changes, and are configured so as to satisfy NA≥0.8 and 1.0≤f≤1.8, where NA is a numerical aperture of the optical pickup objective lens and f (mm) is a focal length.

Description

  The present invention relates to an optical pickup lens used in an optical system that performs recording or reproduction on an optical disc.

  In recent years, the recording capacity of optical discs continues to increase, and the recording density also continues to increase. Reading of information recorded on the optical disc is performed by the optical disc apparatus. Laser light emitted from the laser light source of the optical disk device passes through a transparent member such as a wave plate or a collimator disposed in the optical path, and finally enters the optical pickup lens. Then, the optical pickup lens condenses the incident laser light on the optical disc and forms a light spot on the optical disc.

  Thereby, the information recorded on the optical disc is read. Usually, laser light emitted from a laser light source is converted into substantially parallel light by a collimator lens or the like, and the substantially parallel light enters an optical pickup lens. The numerical aperture NA of an optical pickup lens used for such a large-capacity optical disk is often 0.8 or more or 0.84 or more. In many cases, the wavelength of the laser beam used for the large-capacity optical disk is 405 nm.

  As a glass material of an optical pickup lens for a blue-ray disc (BD) having a numerical aperture NA of 0.85 or more, glass is often used in order to cope with various problems. For example, glass is more excellent in light resistance than a resin material such as plastic.

  If the plastic continues to be exposed to light before it absorbs light and releases this absorbed energy, the plastic will decompose and lead to material degradation. Further, once the material deterioration occurs, the broken resin breaks the surrounding resin, so that the speed of the material deterioration is accelerated. In general, a short wavelength laser beam having high energy is incident on the optical pickup lens for BD. Therefore, as the glass material of the optical pickup lens for BD, glass that is more excellent in light resistance than plastic is often used.

  However, the power at the condensing position of the laser beam for BD is a little less than 0.40 mW. There are also resin materials having light resistance to this level of laser light. Even at the present stage, a resin having light resistance to a high-power laser beam such as a recording laser is being developed, and it is expected to be realized. In addition, resin materials such as plastics are more excellent in moldability and productivity than glass materials.

  Therefore, when trying to design an optical pickup lens for BD having a NA of 0.85 or more using a resin material such as plastic, the following problems were confirmed.

  First, since the amount of change in the refractive index of glass is small, when glass is used as a glass material, it is possible to manufacture a lens with little aberration deterioration based on wavelength variation or temperature change. For example, even if the lens is formed by using glass so that the laser light source side and the disk surface side have a single aspherical surface, it is assumed due to manufacturing variation of the BD laser light source and usage environment. Less aberration deterioration due to wavelength fluctuations and temperature changes assumed in the usage environment.

  On the other hand, since the amount of change in the refractive index of a resin material such as plastic is larger than that of glass, when a resin material is used as the glass material, aberration deterioration due to wavelength variation and temperature change becomes large. That is, it is difficult to say that a lens formed using a resin material as a glass material can sufficiently cope with manufacturing variations of laser light sources, wavelength fluctuations assumed in the use environment, and temperature changes assumed in the use environment. Therefore, it is necessary to design an optical pickup lens made of a resin material that can sufficiently cope with wavelength fluctuations and temperature changes.

  In order to solve the problem of aberration deterioration due to wavelength variation and temperature change, a blazed diffraction structure as shown in FIG. 2 of Patent Document 1 is designed on the lens surface (optical function surface) of the optical pickup lens. Sometimes. On the other hand, an annular structure different from the diffractive structure shown in FIG. 1 of Patent Document 1 may be designed on the lens surface of the optical pickup lens. FIG. 7 shows an optical pickup lens (hereinafter referred to as a non-diffractive annular lens) in which an annular structure different from the diffractive structure is formed on the lens surface.

  As shown in FIG. 7, also in the non-diffractive annular lens, a step amount between adjacent annular zones is large, and a protrusion is formed on the outer edge portion of the lens. Even in the non-diffractive annular zone lens, there may be a problem in molding due to a step amount between the annular zones or a projection.

Japanese Patent No. 4193914

  However, in the non-diffractive annular zone lens, it is very difficult to solve the molding problem due to the difference in level between the annular zones and the protrusion.

  Here, from the lens center of the non-diffractive annular lens toward the outer edge of the lens, each annular region is defined as the first annular zone, the second annular zone, ..., the Nth annular zone (N is a positive integer). And As shown in FIG. 7, in the non-diffractive annular zone lens, the aspheric surface of each annular zone has a shape such that the lens surface on which the annular zone structure is formed is convex.

  In the non-diffractive annular zone lens, in the range from the lens center to a predetermined position, a step is formed in the direction in which the lens center thickness decreases from the lens center to the lens outer edge portion, between adjacent zones. In the range from the predetermined position to the lens outer edge, a step is formed between adjacent annular zones in the direction in which the lens center thickness increases from the lens center toward the lens outer edge.

Here, when an aspherical surface of an n ring zone (n is an integer satisfying 1 ≦ n ≦ N) is virtually extended toward the lens center, the intersection of the aspherical surface and the optical axis passing through the lens center is represented by C. _n (n is an integer satisfying 1 ≦ n ≦ N). Assuming that the distance between the intersection C ₁ and the intersection C _n is the axial step amount D _n (n is an integer satisfying 1 ≦ n ≦ N), and the direction parallel to the optical axis toward the optical disk side is a positive direction. The non-diffractive annular lens shown in FIG. 7 includes an m-th annular zone that satisfies the following expressions (4) and (5). However, m is an integer satisfying 1 <m <N.
| D _m-1 | <| D _m | (4)
| D _m |> | D _{m + 1} | (5)

In other words, in the non-diffractive annular zone lens shown in FIG. 7, in the range from the first annular zone to the m-th annular zone, the axial step amount from the lens center to the lens outer edge portion between adjacent annular zones. A step is formed in the direction in which D _n increases, and in the range from the m-th zone to the N-th zone, the axial step amount D _n is between adjacent zones from the lens center to the lens outer edge. A step is formed in the decreasing direction.

  That is, in the range from the first annular zone to the m-th annular zone from the lens center toward the lens outer edge, a step is formed in the direction in which the lens center thickness becomes thinner between adjacent annular zones, In the range up to the Nth annular zone, a step is formed in the direction in which the lens center thickness increases between adjacent annular zones. That is, the ring zone structure is formed so that the lens middle thickness in the m-th zone is the thinnest. Therefore, hereinafter, the m-th ring zone is referred to as a valley ring zone.

  When the non-diffractive annular lens is formed from a resin material using a mold, a transfer failure of a step between the annular zones of the mold becomes a problem. When a transfer failure occurs between certain adjacent annular zones, the wavefront aberration is degraded based on the transfer failure. In addition, the resin material is likely to be insufficiently filled in the portion corresponding to the valley zone of the mold. Furthermore, the portion of the mold corresponding to the lens center side of the valley ring zone and the portion of the mold corresponding to the lens outer edge side of the valley ring zone, the degree of biting of the resin to the mold, and transfer defects. The direction is different. In particular, transfer failure becomes a problem in the valley zone that becomes a joint between the different transfer properties.

  If a transfer failure occurs in the entire annular zone of the valley ring zone, spherical aberration occurs based on the transfer failure. Further, the order of the spherical aberration varies depending on the position of the valley zone where the transfer defect occurs. Further, when a transfer failure occurs in a part of the annular zone of the valley ring zone, coma and astigmatism occur based on the transfer failure. Further, the order of the coma aberration and astigmatism varies depending on the position of the valley zone where the transfer failure occurs. Therefore, in forming a non-diffractive annular zone lens having a valley zone, it is important to improve the step between the zone zones and the transfer accuracy in the valley zone.

  When a lens is formed from a resin material using a mold, the molten resin is filled into the mold and hardened. Then, the resin contracts as the mold cools from the time when the resin is filled in the mold. The degree of shrinkage of this resin is greater than the degree of shrinkage of the mold. Therefore, when the resin shrinks, the resin in the stepped portion between adjacent ring zones in the lens center side portion from the valley ring zone shrinks in a direction that is easily detached from the mold, but the portion on the lens outer edge side from the valley ring zone The resin in the stepped portion between adjacent ring zones contracts in the direction to bite into the mold.

  Therefore, it becomes difficult for the resin after molding to come off the mold. And, the shape of the valley zone is distorted due to the difference in the difficulty of detachment from the resin mold between the lens center side of the valley zone and the portion on the outer edge side of the valley zone lens. It ’s broken. In other words, the aberration is deteriorated due to the difference in difficulty of the resin from coming off from the mold between the lens center side of the valley zone and the portion on the outer edge side of the valley zone lens.

  Also, the resin at the step between adjacent ring zones in the lens center side of the valley ring zone shrinks in a direction that is easy to come off from the mold, so it may come off the mold early in the molding process. In some cases, the transferability of the portion closer to the center of the lens than the trough is deteriorated.

  Therefore, a method of delaying the time for removing the resin from the mold or applying pressure to the resin is taken. However, on the other hand, the resin in the step portion between adjacent annular zones on the lens outer edge side from the valley annular zone shrinks in the direction to bite into the mold, so the time for removing the resin from the mold is delayed, or the resin If pressure is applied to the lens, the resin on the lens outer edge side of the trough will further bite into the mold. This also deteriorates the transferability in the valley ring zone.

  That is, in the non-diffractive annular zone lens shown in FIG. 7, the transferability at the lens center side portion from the valley zone, the valley zone, and the portion at the lens outer edge side from the valley zone is deteriorated.

  Furthermore, when the ring zone width of the valley zone is narrow, the transferability in the valley zone is further deteriorated and the aberration is deteriorated. When the laser light is transmitted through a lens with poor transfer, the laser light does not pass through the designed optical path and is scattered as unnecessary light or stray light.

  The present invention has been made to solve such problems, and provides an optical pickup lens that can be molded more accurately when an annular structure is provided in order to prevent aberration deterioration based on wavelength fluctuations and temperature changes. For the purpose.

  The optical pickup lens of the present invention is an optical pickup lens having a numerical aperture NA of 0.8 or more for condensing laser light on an optical disk. In addition, the optical pickup lens is divided into a plurality of concentric annular zones on a laser light source side lens surface (R1 surface) and an optical disk side lens surface (R2 surface) by steps. An annular zone structure is provided.

In addition, the annular structure on the surface having the larger number of annular zones has the respective annular zones as the first annular zone, the second annular zone,..., Nth, from the lens center toward the lens outer edge. When the aspheric surface of the n-th annular zone (n is an integer satisfying 1 ≦ n ≦ N) is virtually extended toward the lens center, The intersection with the optical axis passing through the center of the lens is C _n (n is an integer satisfying 1 ≦ n ≦ N), the distance between the intersection C ₁ and the intersection C _n is the axial step amount D _n , and the optical axis , And the direction toward the optical disk side as a positive direction is at least one m-th zone (m is an integer satisfying 1 <m <N) satisfying the following expressions (4) and (5): Prepare.
| D _m-1 | <| D _m | (4)
| D _m |> | D _{m + 1} | (5)

Further, the radius of the boundary on the lens center side of the m-th annular zone is Rb, the radius of the boundary on the lens outer edge side of the m-th annular zone is Re, and the annular zone width is Rw (= Re−Rs). When the effective radius of the optical pickup lens when the numerical aperture NA is 0.85 is Rs, the following expression (6) is preferably satisfied.
Rw / Rs × 100 ≧ 25 (%) (6)

  If the annular zone width of the m-th annular zone is too narrow, the mold portion corresponding to the m-th annular zone cannot be sufficiently filled with resin, and the aberration performance of the lens is deteriorated. On the other hand, when the zone width (Re-Rb) of the m-th zone is 25% or more of the effective radius Rs of the optical pickup lens, the mold portion corresponding to the m-th zone is sufficiently filled with resin. Not only can this be performed, but also the resin can be prevented from being disturbed when the mold is filled with the resin. This more reliably prevents the deterioration of the aberration performance of the lens.

More preferably, it is satisfy | filling (16) Formula.
25 ≦ Rw / Rs × 100 ≦ 35 (%) (16)
On the contrary, if the ring width of the m-th ring zone is too wide, it becomes easy to sufficiently fill the mold part corresponding to the m-th ring zone with the resin. When providing an annular structure for preventing aberration deterioration due to temperature change, it is necessary to take a large amount of adjacent steps, which makes it difficult to mold. Here, the adjacent step amount is a step amount of a step between each annular zone region.

More preferably, it is satisfy | filling (17) Formula.
27 ≦ Rw / Rs × 100 ≦ 33 (%) (17)
This further reliably prevents deterioration of the aberration performance of the lens.

In the optical pickup lens of the present invention, when D _n > 0, D _m−1 <D _m and D _m > D _{m + 1} is satisfied, or when D _n <0, D _m−1 > D _m and D _At least one m-th zone that satisfies _m <D _{m + 1} is provided. In other words, when D _n > 0, in the range closer to the lens center than the m-th annular zone, a step is formed in the direction in which the axial step amount D _n increases from the lens center to the lens outer edge, In the range on the lens outer edge side from the m ring zone, a step is formed in the direction in which the axial step amount D _n decreases from the lens center toward the lens outer edge. Further, when D _n <0, a step is formed in the direction in which the axial step amount D _n decreases from the lens center toward the lens outer edge in the range closer to the lens center than the m-th ring zone, and the m-th ring In the range on the lens outer edge side from the band, a step is formed in the direction in which the axial step amount D _n increases from the lens center toward the lens outer edge.

That is, in the case of D _n > 0, a step is formed in the direction in which the lens center thickness becomes thinner between adjacent annular zones in the range closer to the lens center than the m-th annular zone from the lens center toward the lens outer edge. In the range on the lens outer edge side from the m-th annular zone, a step is formed in the direction in which the lens center thickness increases between adjacent annular zones. In the case of D _n <0, a step is formed in the direction from the lens center toward the lens outer edge portion in the direction of increasing the lens center thickness between adjacent annular zones in the range closer to the lens center than the m-th annular zone, In the range on the lens outer edge side from the m-th annular zone, a step is formed between adjacent annular zones in a direction in which the lens center thickness becomes thinner.

That is, when D _n > 0, the lens zone structure is formed such that the lens center thickness in the m-th zone is the thinnest, and when D _n <0, the lens center thickness in the m-th zone is the thickest. An annular structure is formed so as to be.

  Furthermore, by providing an annular structure on the side of the disk opposite to the laser light source side, it is possible to obtain a desired phase difference with a light beam passing between the annular areas, particularly for wavelength fluctuations and temperature changes. In order to prevent the deterioration of aberration based on the annular zone structure, even if an annular zone structure that facilitates molding is taken into consideration, the adjacent step amount between the annular zones on the laser side must be about 3 to 11 μm. The necessity of reducing the amount of adjacent steps between the laser side annular zones, in other words, the amount of phase difference burden between the laser side annular zones is increased. Therefore, instead of obtaining the desired phase difference only from the ring of the laser side only, the desired phase difference is obtained from the ring of the laser side and the ring of the disk side. Since the burden of the phase difference between the bands can be reduced, the method of forming the ring on the side surface of the laser becomes easy.

  Specifically, it is possible to reduce the depth of the on-axis step and the adjacent step, or to reduce the bonding region range described later, and to make an optical pickup lens that is easier to mold. Can be provided. In addition, since the depth of the annular step on the laser side surface can be reduced, the amount of sag on the laser side surface can be reduced, leading to downsizing of the laser side surface. It is possible to reduce the possibility that the objective lens will collide with other parts such as the rising mirror of the optical pickup during operation.

In a first aspect of the present invention, ring-shaped structure of the surface with the larger the number of zones is, D _n-1> between at least one of the first n-1 annular and the n zones satisfying D _n A joining region provided on the surface.

  The surface shape of the joining region is such that the positions of substantially all points on the surface of the joining region in the optical axis direction are in the optical axis direction of the boundary on the lens outer edge side of the n-1 ring zone. The shape is closer to the optical disc than the position at.

Conventionally, a projection that protrudes toward the laser light source side is formed between the n-1 zone and the n-th zone that satisfies D _n-1 > D _n , and the moldability of the lens due to the projection. Becomes worse.

In the first aspect of the present invention, the ring zone structure includes a junction region between at least one n-1 zone and the nth zone that satisfy D _n-1 > D _n . The surface shape of the junction region is such that the positions in the optical axis direction of substantially all points on the surface of the junction region are more than the positions in the optical axis direction of the boundary on the lens outer edge side of the n-1th annular zone. The shape is also on the optical disc side. In other words, the surface shape of the joining region is a shape that does not protrude to the laser light source side from the boundary on the lens outer edge side of the (n-1) -th zone. Therefore, a problem in forming an optical pickup lens due to the formation of the protrusions between adjacent annular zones is less likely to occur. Therefore, it is possible to provide an optical pickup lens that is easier to mold.

In the second aspect of the present invention, the annular zone structure on the surface having the larger number of annular zones is between all the n-1 annular zones and the nth annular zone satisfying D _n-1 > D _n. It is provided with a joint region to be provided.

  The surface shape of the joining region is such that the positions of substantially all points on the surface of the joining region in the optical axis direction are in the optical axis direction of the boundary on the lens outer edge side of the n-1 ring zone. The shape is closer to the optical disc than the position at.

Further, conventionally, a projection that is convex toward the laser light source side is formed between the n-1 zone and the n-th zone that satisfies D _n-1 > D _n . The moldability becomes worse.

In the second aspect of the present invention, the annular structure includes a junction region between all the n−1 annular zones and the nth annular zone satisfying D _n−1 > D _n . The surface shape of the junction region is such that the positions in the optical axis direction of substantially all points on the surface of the junction region are more than the positions in the optical axis direction of the boundary on the lens outer edge side of the n-1th annular zone. The shape is also on the optical disc side.

  In other words, the surface shape of the joining region is a shape that does not protrude to the laser light source side from the boundary on the lens outer edge side of the (n-1) -th zone. Therefore, there is no problem in forming the optical pickup lens due to the formation of the protrusions between the adjacent annular zones. Therefore, it is possible to provide an optical pickup lens that is easier to mold.

  The optical pickup lens according to the third aspect of the present invention is an optical pickup lens having a numerical aperture NA of 0.8 or more for condensing laser light on an optical disk.

Further, the annular structure of the surface having the larger number of annular zones is such that the position in the lens radial direction of the boundary on the lens center side of the n-th annular zone satisfying D _n−1 > D _n is the position of the optical pickup lens. When the tangent angle of the lens surface is within a range of 40 ° or more, a joining region is provided between the n-1 annular zone adjacent to the nth annular zone and the nth annular zone.

  The surface shape of the joining region is such that the positions of substantially all points on the surface of the joining region in the optical axis direction are in the optical axis direction of the boundary on the lens outer edge side of the n-1 ring zone. The shape is closer to the optical disc than the position at.

Further, conventionally, a projection that is convex toward the laser light source side is formed between the n-1 zone and the n-th zone that satisfies D _n-1 > D _n . The moldability becomes worse. However, the degree of deterioration of moldability due to the protrusions is greater in the outer edge portion than in the center portion of the lens. And it turned out that the deterioration of the moldability by the said protrusion part arises in the range in which the tangent angle of the lens surface of an optical pick-up lens becomes 40 degrees or more especially.

In the third aspect of the present invention, in the annular structure, the position in the lens radial direction of the lens center side boundary of the n-th annular zone that satisfies D _n−1 > D _n is a tangent to the lens surface of the optical pickup lens. When the angle is within a range of 40 ° or more, a junction region is provided between the n-1 annular zone adjacent to the nth annular zone and the nth annular zone. The surface shape of the junction region is such that the positions in the optical axis direction of substantially all points on the surface of the junction region are more than the positions in the optical axis direction of the boundary on the lens outer edge side of the n-1th annular zone. The shape is also on the optical disc side.

  In other words, the surface shape of the joining region is a shape that does not protrude to the laser light source side from the boundary on the lens outer edge side of the (n-1) -th zone. Therefore, there is no problem in forming the optical pickup lens due to the formation of the protrusions between the adjacent annular zones. Therefore, it is possible to provide an optical pickup lens that is easier to mold.

As described above, the on-axis step amount D _n has been described. However, in the lens having the same or almost the same shape as the present invention, the on-axis step amount D _n can be set to a completely different value in a lens having a zonal structure. The same effect as the present invention can be obtained. This is because different sag amounts on the axis can be obtained to obtain the same sag amount as the sag amount at the position of the radius away from the optical axis. This is also clear from the aspherical surface that defines the surface shape described later.

  The optical pickup lens of the present invention is an optical pickup lens having a numerical aperture NA of 0.8 or more for condensing laser light on an optical disk. In addition, the optical pickup lens is divided into a plurality of concentric annular zones on a laser light source side lens surface (R1 surface) and an optical disk side lens surface (R2 surface) by steps. An annular zone structure is provided.

Further, the ring structure of the surface with the larger number of ring zones is that the ring zones are divided into the first ring zone, the second ring zone,..., The N-th ring from the lens center toward the lens outer edge. When the band (N is a positive integer) and the optical path difference between the light beam passing through the nth annular zone (n is an integer satisfying 1 ≦ n ≦ N) and the light beam passing on the optical axis is E _n (λ), It includes at least one m-th annular zone (m is an integer satisfying 1 <m <N) that satisfies the following expressions (7) and (8).
| E _m-1 | <| E _m | (7)
| E _m | >> | E _{m + 1} | (8)

The surface shape of the bonding region is preferably a planar shape inclined at an angle θ (°) in a direction from the laser light source side to the optical disk side from a surface perpendicular to the optical axis.
Furthermore, it is preferable to satisfy the following expression (9).
0 ≦ θ ≦ 15 (9)

  Thereby, the inclination angle of the (n-1) -th zone can be made close to the inclination angle of the joining region. Then, the shrinkage direction in the (n-1) -th zone during molding and the shrinkage direction in the joining region can be matched as much as possible. Therefore, it becomes possible to more easily find molding conditions for accurately obtaining the dimensions of the optical pickup lens.

  Note that the inclination angles of the plurality of bonding regions provided in one optical pickup lens may be different depending on the positions in the lens radial direction where the bonding regions are provided.

Further, D _{n-1 <all} the (n-1) annular in satisfying D _n and the n-th annular zone, on-axis step difference D _n between the on-axis step difference of the n-1 wheel band of the n-th annular zone A value obtained by adding the absolute value | dn ₀ | of the difference from the quantity D _n−1 is α, and for all the n−1 zones and the nth zone that satisfy D _n−1 > D _n , When the value obtained by adding the absolute value | dn ₀ | of the difference between the on-axis step amount Dn of the n-th zone and the on-axis step amount D _n-1 of the ( _{n-1) -th} zone is β In addition, it is preferable that the following expression (14) is satisfied.
α−β ≧ 0 (14)

The bonding region is not an optical function surface. For this reason, when the above-described joining region is provided between adjacent annular zones, the light amount of the light spot is reduced accordingly. Here, it is assumed that the laser light incident on the lens is not absorbed by the lens and is not reflected on the lens surface, an annular structure is formed on the lens surface on the laser light source side of the optical pickup lens, and the lens surface on the optical disk side is continuous. When it has a typical shape, the light amount ratio (%) of the light spot can be expressed by the following equation (18).
Light intensity ratio (%) = (1 − ((area of lens surface within effective radius) − (area other than optical functional surface)) / (area of lens surface within effective deformation)) × 100 ( 18)

  Here, (area other than the optical functional surface) in the equation (18) is substantially equal to the sum of the areas of all the junction regions. Therefore, the light quantity of the light spot can be improved by reducing the number of joining regions provided in the optical pickup lens as much as possible.

A portion of the junction region is provided is between zones of the D _n-1> a n-1 annular satisfying D _n and the n zones. Therefore, it is possible to improve the light amount of the light spot by making the cumulative value of the step amount between the annular zones not provided with the joint region larger than the cumulative value of the step amount between the annular zones provided with the joint region. Conceivable. Therefore, in the present invention, by satisfying the expression (14), α, which is a cumulative value of the step amount between the annular zones where the joint region is not provided, is represented by β, which is a cumulative value of the step amount between the annular zones where the joint region is provided. Thus, the light quantity of the light spot can be improved.

  On the other hand, the refractive index of the optical pickup lens changes due to the wavelength change of the laser diode, and the position of the light spot converged by the optical pickup lens changes abruptly. This change is called axial chromatic aberration (hereinafter referred to as chromatic aberration). In order to improve the light quantity of the light spot, if the configuration satisfying the equation (14) is adopted, chromatic aberration is deteriorated, and when the optical pickup lens is used, recording / reproduction on the optical disc cannot be performed, or focus control is performed. It comes off.

In other words, in order to prevent deterioration of chromatic aberration, it is preferable to satisfy the following expression (19).
α−β ≦ 0 (19)

Therefore, in order to balance the light amount of the light spot and the chromatic aberration, it is preferable to satisfy the following expression (15).
0.8 ≦ α / β ≦ 1.2 (15)

The optical pickup lens preferably focuses laser light having a wavelength in the range of 395 nm to 415 nm on the optical disc.
Thereby, it is possible to provide an optical pickup lens that forms a light spot favorably with respect to the BD. The operating wavelength of the BD is 405 nm, but considering the manufacturing variation of the laser light source, the operating wavelength range of the optical pickup lens of the present invention is set to the wavelength of 395 nm or more and 415 nm or less.

  Further, the plurality of steps on the lens surface (R1 surface) on the laser light source side and the lens surface (R2 surface) on the optical disk side of the optical pickup lens are such that the phase of incident light at the design wavelength and design temperature is in the mutual zone region. It is preferable that the difference in level is approximately an integral multiple of the wavelength. As a result, it is possible to have a step amount that causes the light flux to generate a phase difference that reduces the aberration that occurs in the optical pickup objective lens when the ambient temperature changes.

In addition, the absolute value of the adjacent step amount between the n-th annular zone (2 ≦ n ≦ m) and the n−1-th annular zone is | dn | (mm), the wavelength is λ (mm), and the optical pickup objective lens is refracted. When the rate is N, it is preferable to satisfy the following expression (10).
3 ≦ (N−1) × | dn | / λ ≦ 15 (10)

  In other words, the adjacent step amount × (refractive index−1) is preferably 3 to 15 times the design wavelength. When the adjacent step amount × (refractive index−1) is less than three times the design wavelength, it is necessary to increase the number of annular regions formed in the optical pickup objective lens in order to sufficiently correct the aberration. For this reason, the light utilization efficiency is lowered. On the other hand, when the adjacent step amount × (refractive index-1) is larger than 15 times the design wavelength, the step amount becomes large, and it becomes difficult to manufacture the optical pickup objective lens. Therefore, by forming the step so as to satisfy the expression (10), it is possible to prevent the light use efficiency from being lowered and to easily manufacture the optical pickup objective lens.

Further, the absolute value of the difference between on-axis step difference _{D n-1} of the n-th annular zone on-axis step difference amount _{D n} and the (n-1) th wheel band (2 ≦ n ≦ N) | dn 0 | ( mm), the wavelength is λ (mm), and the refractive index of the optical pickup objective lens is N, it is preferable that the following expression (11) is satisfied.
3 ≦ (N−1) × | dn ₀ | / λ ≦ 12 (11)

In other words, the absolute value | dn ₀ | × (refractive index−1) of the difference between the _n- th annular zone axial step amount D _n and the n−1-th annular zone axial step amount D _n−1 is obtained. The wavelength is preferably 3 to 12 times the design wavelength. When | dn ₀ | × (refractive index−1) is less than three times the design wavelength, it is necessary to increase the number of annular zones formed in the optical pickup objective lens in order to sufficiently correct the aberration. For this reason, the light utilization efficiency is lowered. On the other hand, when | dn ₀ | × (refractive index-1) is larger than 12 times the design wavelength, the amount of the step becomes large, making it difficult to manufacture the optical pickup objective lens. Therefore, by forming the step so as to satisfy the expression (11), it is possible to prevent the light use efficiency from being lowered and to easily manufacture the optical pickup objective lens.

  Also, the maximum value of the cumulative value Σ | d | of the absolute value of the adjacent step amount in the n-th annular zone (2 ≦ n ≦ m) is Σ | d | max, and the minimum value of the cumulative value Σ | d | is Σ | When d | min, the difference between the maximum value Σ | d | max and the minimum value Σ | d | min of the cumulative value Σ | d | of the adjacent step amount is preferably 10λ or more and 40λ or less.

  When the difference between the maximum value Σ | d | max and the minimum value Σ | d | min of the cumulative value Σ | d | of the adjacent step amount is less than 10λ, the wavefront aberration caused by the change in the ambient temperature can be sufficiently reduced. It becomes difficult.

  On the other hand, if the difference between the maximum value Σ | d | max and the minimum value Σ | d | min of the cumulative value Σ | d | of the adjacent step amount is larger than 40λ, the wavefront aberration caused by the change in the ambient temperature is excessively corrected. On the contrary, the wavefront aberration is deteriorated. In addition, the amount of step becomes large, making it difficult to manufacture the optical pickup objective lens.

Further, when the axial step amount of the step on the surface with the larger number of ring zones is d ₀ (mm), the difference between the maximum value Dmax and the minimum value Dmin of the axial step amount D _n is 10λ or more, It is preferable that it is 40λ or less.

If the difference between the maximum value Dmax and minimum value Dmin of the axial step difference D _n of less than 10 [lambda], it is difficult to sufficiently reduce the wavefront aberration occurring due to a change in ambient temperature. On the other hand, if the difference between the maximum value Dmax and minimum value Dmin of the axial step difference D _n is larger than 40Ramuda, since from excessively corrected wavefront aberration caused by changes in ambient temperature, rather, the wavefront aberration is deteriorated End up. In addition, the amount of step becomes large, making it difficult to manufacture the optical pickup objective lens.

  Further, it is preferable that the effective radius Rs when the numerical aperture NA is 0.85 is substantially equal to the opening radius of the actuator on which the optical pickup lens is mounted.

  Actually, since the actuator to which the optical pickup lens is attached is made of plastic, the opening radius of the actuator varies from product to product. In the present invention, since the effective radius Rs when the numerical aperture NA of the optical pickup lens is 0.85 is substantially equal to the aperture radius of the actuator, the aperture radius of the actuator reflects the aperture radius of the actuator. The zone width can be defined.

Further, the optical pickup lens is preferably molded from a resin material or a material obtained by dispersing an inorganic material or a material mainly composed of an inorganic material in the resin material. The optical pickup lens is preferably molded from a glass material.
Thereby, an optical pickup lens having the same effects as any of the first to third aspects can be manufactured from a general lens material.

  The optical pickup lens is preferably mounted on a BD pickup.

  According to the present invention, it is possible to provide an optical pickup lens that can be molded with higher accuracy when an annular structure is provided in order to prevent aberration deterioration based on wavelength variation or temperature change.

FIG. 1 shows an example of an optical pickup optical system according to an embodiment of the present invention. FIG. 2 is a diagram (FIG. 2A) showing the wavefront (phase) of the laser light that passes through the pickup lens according to the present embodiment at the design wavelength and design temperature, and the ambient temperature becomes lower than the design temperature, and the laser FIG. 2B shows a wavefront (phase) of laser light that passes through the pickup lens according to the present embodiment when the wavelength of the light is shorter than the design wavelength (FIG. 2B), the ambient temperature becomes higher than the design temperature, and the laser It is a figure (Drawing 2 (c)) which shows the wavefront (phase) of the laser beam which permeate | transmits the pick-up lens concerning this embodiment when the wavelength of light becomes longer than a design wavelength. FIG. 3 is a side view (a) showing an example of an optical pickup lens according to an embodiment of the present invention, and a side view (b) showing an example of an optical pickup lens similar to the embodiment of the present invention. FIG. 4 is a side view (a) showing an example of the optical pickup lens according to the embodiment of the present invention, and an enlarged view (b) showing an enlarged part of the side view (a). FIG. 5 is a side view schematically showing the lens surface shape of the optical pickup lens. FIG. 6 is a side view schematically showing the lens surface shape of the optical pickup lens. FIG. 7 is a side view showing a conventional non-diffractive annular lens. FIG. 8 is a wavefront aberration diagram of Examples 1 to 4 of the present invention. FIG. 9 is a wavefront aberration diagram of Examples 5 to 8 of the present invention. FIG. 10 is a wavefront aberration diagram of Examples 9 to 12 of the present invention. FIG. 11 is a wavefront aberration diagram of Examples 13 to 16 of the present invention. FIG. 12 is a wavefront aberration diagram of Examples 17 to 20 of the present invention. FIG. 13 is a wavefront aberration diagram of Examples 21 to 24 of the present invention. FIG. 14 is a wavefront aberration diagram of Examples 25 to 28 of the present invention. FIG. 15 is a wavefront aberration diagram of Examples 29 to 30 of the present invention.

  Hereinafter, specific embodiments to which the present invention is applied will be described in detail with reference to the drawings. Note that the present invention is not limited to the following embodiments. FIG. 1 shows an example of an optical pickup optical system 1 according to an embodiment of the present invention. The optical pickup optical system 1 according to the present embodiment is used in an optical pickup device or an optical disc device according to the present invention.

  The optical pickup optical system 1 includes a light source 11 (laser light source), a beam splitter 12, a collimator lens 13, a pickup lens 14 (optical pickup objective lens), a detection system 16, and the like. In the present embodiment, a BD (Blu-ray disc) is used as the optical disc 15.

  The light source 11 includes a blue laser diode used for BD. A beam splitter 12 is provided on the optical path of the laser light (light beam) emitted from the light source 11.

  A collimator lens 13 is provided on the optical path of the laser light emitted from the beam splitter 12. The collimator lens 13 adjusts the degree of divergence of the laser light emitted from the beam splitter 12 and emits the laser light.

  A pickup lens 14 is provided on the optical path of the laser light that has passed through the collimator lens 13.

  The pickup lens 14 has a function of condensing incident light on the information recording surface of the optical disc (BD) 15. As the BD, a single layer BD having only one recording layer and a multilayer BD having a plurality of recording layers are known. The transparent substrate thickness of the single layer BD is 0.100 mm. The transparent substrate thickness of each recording layer of the two-layer BD having two recording layers is 0.075 mm and 0.100 mm.

  When the pickup lens 14 focuses the laser light on the recording layer of the two-layer BD, a large spherical aberration of about 0.25 λ rms occurs due to a substrate thickness difference of 0.025 mm between the recording layers. Therefore, normally, the spherical aberration is corrected by moving the collimator lens 13 along the optical axis and adjusting the degree of divergence of the light beam incident on the pickup lens 14.

  Here, the correction by moving the collimator lens 13 along the optical axis means adjusting the degree of divergence of the laser light incident on the pickup lens 14. This is equivalent to adjusting the virtual issue point position (object position) of the light incident on the pickup lens 14 and causing the pickup lens 14 to enter from the virtual issue point position without passing through the collimator lens 13. is there. In other words, the spherical aberration is corrected by adjusting the object distance of the pickup lens 14.

  Therefore, the pickup lens 14 according to the embodiment of the present invention is favorably gathered at 0.0875 mm, which is an intermediate transparent substrate thickness of the transparent substrate thickness (0.075 mm, 0.100 mm) of each recording layer in the two-layer BD. Designed to shine. Thereby, by using the above-described method, it is possible to reduce the spherical aberration caused by the substrate thickness difference even in the transparent substrate thickness (0.075 mm, 0.100 mm) between the recording layers.

Therefore, the thickness of the transparent substrate that can be used by the pickup lens 14 according to the embodiment of the invention is not limited to 0.0875 mm designed in this example.
In the present embodiment, the transparent substrate of the optical disk 15 is polycarbonate (PC).

  The pickup lens 14 further has a function of guiding the laser beam reflected by the information recording surface of the optical disc 15 to the detection system 16.

  In addition, a plurality of annular zones that are concentric with the optical axis of the pickup lens 14 are formed on both surfaces of the lens surface (R1 surface) on the laser light source side and the lens surface (R2 surface) on the optical disk side of the pickup lens 14. Yes. Further, a step is formed between adjacent annular zones.

  In other words, at least one surface of the pickup lens 14 is divided into a plurality of annular regions that are concentric with the optical axis of the pickup lens 14 by a plurality of steps. The pickup lens 14 is formed from a plastic material.

  The steps of the plurality of steps formed on both the laser light source side lens surface (R1 surface) and the optical disk side lens surface (R2 surface) of the pickup lens 14 are at the design wavelength and design temperature (the wavelength of the laser light is designed). The wavelength of the laser light incident when the ambient temperature is the design temperature) is set so that the adjacent annular zones differ from each other by an approximately integer multiple of the wavelength.

Further, the plurality of steps formed on the pickup lens 14 have a step amount that causes a phase difference in the laser light so as to reduce aberrations that occur due to changes in the ambient temperature.
Here, the substantially integer multiple of the wavelength is preferably (integer) × 0.999 times the wavelength to (integer) × 1.001 times the wavelength.

  For example, in this embodiment, approximately 10 times the wavelength means 9.99 times to 10.01 times the wavelength from 10 × 0.999 = 9.99, 10 × 1.001 = 10.01. To do. The substantially integer multiple of the wavelength may be (integer) × 0.995 times the wavelength to (integer) × 1.005 times the wavelength. Even in this case, the wavefront aberration generated when the ambient temperature changes can be sufficiently reduced by the step formed on the pickup lens 14.

  At the time of focus servo and tracking servo, the pickup lens 14 is operated by an actuator (not shown).

  Next, the behavior until the laser beam emitted from the light source 11 is reflected by the information recording surface of the optical disc 15 and detected by the detection system 16 will be described. The laser light emitted from the light source 11 passes through the beam splitter 12 and enters the collimator lens 13.

  The collimator lens 13 adjusts the degree of divergence of the laser light emitted from the beam splitter 12 and emits the laser light.

  The laser light that has passed through the collimator lens 13 enters the pickup lens 14. Here, in the present embodiment, when the ambient temperature changes, the plurality of steps provided in the pickup lens 14 correct the phase of the laser beam so as to reduce the aberration caused by the change in the ambient temperature. .

  Then, the pickup lens 14 focuses the corrected laser beam on the information recording surface of the optical disc 15. The laser beam reflected by the information recording surface of the optical disc 15 enters the detection system 16 via the pickup lens 14 and is detected. The detection system 16 detects the laser beam and performs photoelectric conversion to generate a focus servo signal, a track servo signal, a reproduction signal, and the like.

  The optical pickup lens according to the present embodiment condenses laser light having a wavelength in the range of 395 nm to 415 nm on an information recording surface of a BD (Blu-ray disc). The numerical aperture NA of the optical pickup lens according to the present embodiment is 0.8 or more.

  Further, the optical pickup lens according to the present invention is divided into a plurality of concentric annular zones on the lens surface (R1 surface) on the laser light source side and the lens surface (R2 surface) on the optical disk side by steps. An annular zone structure is provided. In other words, both the laser light source side lens surface (R1 surface) and the optical disk side lens surface (R2 surface) of the optical pickup lens according to the present invention are concentrically divided into a plurality of annular zones, A step is formed between adjacent annular zones.

  Next, the optical pickup lens 14 used in the optical pickup optical system 1 according to the embodiment of the present invention will be described in detail.

  FIG. 2 is a diagram showing the optical pickup lens 14 in the optical pickup optical system 1 according to the present embodiment. 2A shows the wavefront (phase) of the laser beam at the design wavelength and the design temperature, and FIG. 2B shows the laser beam wavelength shorter than the design wavelength because the ambient temperature is lower than the design temperature. FIG. 2 (c) shows the wavefront (phase) of the laser light when the ambient temperature is higher than the design temperature and the wavelength of the laser light is longer than the design wavelength. Is shown. In the present embodiment, the plurality of steps described above are provided on the surface of the optical pickup lens 14 on the light source 11 side.

  The step amounts of the plurality of steps are set so that the phases of the transmitted laser light are different from each other between the adjacent annular zones by approximately an integral multiple of the wavelength. Further, the step of the optical pickup lens 14 has a step amount that causes a phase difference in the laser beam so as to reduce aberration caused by the change of the ambient temperature when the ambient temperature changes.

  That is, when the laser light is incident on the optical pickup lens 14 at the design wavelength and design temperature, the phases of the laser light transmitted through each annular zone differ from each other by an integral multiple of the wavelength. Therefore, as shown in FIG. 2A, at the design wavelength and design temperature, there is no phase difference in the laser light transmitted through different annular zones. Therefore, the laser light incident on the optical pickup lens 14 is emitted with the same phase. Accordingly, at the design wavelength and design temperature, the aberration of the laser beam condensed by the optical pickup lens 14 is the same as when no step is formed.

  On the other hand, as shown in FIGS. 2B and 2C, when the ambient temperature changes and the laser light whose wavelength has changed is incident on the optical pickup lens 14, the laser light transmitted through each annular region is transmitted. The difference in phase is not an integral multiple of the wavelength. Therefore, as shown in FIGS. 2B and 2C, when the wavelength changes, a phase difference occurs in the laser light transmitted through different annular regions.

  In the present invention, the phase difference is sized so as to reduce aberrations caused by changes in ambient temperature. For this reason, when the ambient temperature changes, conventionally, aberrations collected by the optical pickup lens increase. However, in the present invention, due to the phase difference of the laser light transmitted through each annular zone of the optical pickup lens 14. In addition, an increase in aberration associated with a change in ambient temperature is suppressed. Then, the laser beam emitted from the optical pickup lens 14 is favorably condensed on the information recording surface of the optical disc 15.

In the annular structure, each annular region is defined as a first annular zone, a second annular zone, ..., an Nth annular zone (N is a positive integer) from the lens center toward the lens outer edge. When the aspherical surface of the n-th annular zone (n is an integer satisfying 1 ≦ n ≦ N) is virtually extended toward the lens center, the intersection of the aspherical surface and the optical axis passing through the lens center is defined as C _n (N is an integer satisfying 1 ≦ n ≦ N), and the distance between the intersection C ₁ and the intersection C _n is the axial step amount D _n, and is parallel to the optical axis toward the optical disc (from the laser light source to the optical disc). When the positive direction is a positive direction, at least one m-th zone (m is an integer satisfying 1 <m <N) satisfying the following expressions (4) and (5) is provided.
| D _m-1 | <| D _m | (4)
| D _m |> | D _{m + 1} | (5)

That is, the ring zone structure satisfies D _m−1 <D _m and D _m > D _{m + 1} when D _n > 0, or D _m−1 > D _m and D _m <when D _n <0. At least one m-th zone that satisfies D _{m + 1} is provided. In other words, when D _n > 0, in the range closer to the lens center than the m-th zone, a step is formed in the direction in which the axial step amount Dn increases from the lens center toward the lens outer edge, and the m th In the range on the lens outer edge side from the annular zone, a step is formed in the direction in which the axial step amount D _n decreases from the lens center toward the lens outer edge.

Further, when D _n <0, a step is formed in the direction in which the axial step amount D _n decreases from the lens center toward the lens outer edge in the range closer to the lens center than the m-th ring zone, and the m-th ring In the range on the lens outer edge side from the band, a step is formed in the direction in which the axial step amount D _n increases from the lens center toward the lens outer edge.

That is, in the case of D _n > 0, a step is formed in the direction in which the lens center thickness becomes thinner between adjacent annular zones in the range closer to the lens center than the m-th annular zone from the lens center toward the lens outer edge. In the range on the lens outer edge side from the m-th annular zone, a step is formed in the direction in which the lens center thickness increases between adjacent annular zones.

In the case of D _n <0, a step is formed in the direction from the lens center toward the lens outer edge portion in the direction of increasing the lens center thickness between adjacent annular zones in the range closer to the lens center than the m-th annular zone, In the range on the lens outer edge side from the m-th annular zone, a step is formed between adjacent annular zones in a direction in which the lens center thickness becomes thinner. That is, when D _n > 0, the lens zone structure is formed such that the lens center thickness in the m-th zone is the thinnest, and when D _n <0, the lens center thickness in the m-th zone is the thickest. An annular structure is formed so as to be.

The annular structure includes a junction region provided between at least one n-1 annular zone and the nth annular zone that satisfies D _n-1 > D _n .

  And the surface shape of the said joining area | region is that the position in the optical axis direction of the substantially all points on the surface of a joining area | region is rather than the position in the optical axis direction of the boundary of the lens outer edge side of the said n-1 ring zone. The shape is on the optical disc side.

Conventionally, a projection that protrudes toward the laser light source side is formed between the n-1 zone and the n-th zone that satisfies D _n-1 > D _n , and the moldability of the lens due to the projection. Becomes worse. In the optical pickup lens according to the present embodiment, in the annular structure, a junction region is provided between at least one n-1 annular zone and the nth annular zone satisfying D _n-1 > D _n. Yes. The surface shape of the junction region is such that the positions in the optical axis direction of substantially all points on the surface of the junction region are more than the positions in the optical axis direction of the boundary on the lens outer edge side of the n-1th annular zone. The shape is also on the optical disc side.

  In other words, the surface shape of the joining region is a shape that does not protrude to the laser light source side from the boundary on the lens outer edge side of the (n-1) -th zone. Therefore, a problem in forming an optical pickup lens due to the formation of the protrusions between adjacent annular zones is less likely to occur. Therefore, it is possible to provide an optical pickup lens that is easier to mold.

  An example of the optical pickup lens according to the embodiment of the present invention is shown in FIG. In the optical pickup lens 14-1 shown in FIG. 3A, an annular structure is formed on the lens surface 101 on the laser light source side. An annular structure is also formed on the lens surface 102 of the optical pickup lens 14 on the optical disk side.

In the optical pickup lens 14-1, D _n > 0. The ring zone structure includes _{one m-} th zone 103 that satisfies D _m−1 <D _m and D _m > D _{m + 1} . In other words, in the range closer to the lens center than the m-th zone 103, a step is formed in the direction in which the axial step amount Dn increases from the lens center toward the lens outer edge, and the lens outside the lens from the m-th zone 103. In the range on the edge side, a step is formed in the direction in which the axial step amount Dn decreases from the lens center toward the lens outer edge.

  That is, in the range closer to the lens center than the m-th ring zone 103 from the lens center toward the lens outer edge, a step is formed in the direction in which the lens center thickness becomes thinner between adjacent ring zones. In the range on the lens outer edge side, a step is formed in the direction in which the lens center thickness increases between adjacent annular zones. That is, the annular structure is formed so that the lens center thickness in the m-th annular zone 103 is the thinnest.

  Also, the optical pickup lens 14-1 shown in FIG. 3A is provided with an annular structure on the side of the disk opposite to the laser light source side, so that a desired phase difference can be obtained with light passing between the annular areas. When trying to obtain, instead of obtaining the desired phase difference only with the annular zone of the laser side surface, by obtaining the desired phase difference from the annular zone of the laser side surface and the annular zone of the disk side surface, Since the burden of the phase difference between the laser side ring zones can be reduced, the method of forming the laser side ring zones becomes easy.

  For comparison, FIG. 3B shows an optical pickup lens 14-1 having an annular structure only on the laser light source side. In the optical pickup lens 14-1 shown in FIG. 3B, an annular structure is formed on the lens surface 101 on the laser light source side. Further, the lens surface 102 on the optical disc side of the optical pickup lens 14 is not formed with an annular structure, and the surface shape of the lens surface 102 on the optical disc side is a single aspherical shape.

  3 (a) and FIG. 3 (b) are different in the shape of the disk side surface opposite to the laser light source side, but have the same optical characteristics. Comparing FIG. 3 (a) and FIG. 3 (b), it can be seen that the depth of the annular zone step in the first annular zone and the second annular zone formed on the laser light source side is shallow.

As described above, the on-axis step amount D _n has been described. However, in the lens having the same or almost the same shape as the present invention, the on-axis step amount D _n can be set to a completely different value in a lens having a zonal structure. The same effect as the present invention can be obtained. This is because different sag amounts on the axis can be obtained to obtain the same sag amount as the sag amount at the position of the radius away from the optical axis. This is also clear from the aspherical surface that defines the surface shape described later.

Further, in the optical pickup lens 14-1, the annular structure includes a junction region 104 provided between the n-1 annular zone and the nth annular zone that satisfies D _n-1 > D _n . The bonding region 104 _may be provided between the _{D n-1> D n} at least one of the first n-1 annular meet and the n zones.
The surface shape of the bonding region 104 is such that the positions of substantially all points on the surface of the bonding region 104 in the optical axis direction are the positions in the optical axis direction of the boundary on the lens outer edge side of the n-1 ring zone. The shape is closer to the optical disc side. That is, the surface shape of the joining region 104 is a shape that does not protrude toward the laser light source side from the boundary on the lens outer edge side of the (n−1) -th zone. More specifically, in the optical pickup lens 14-1, the surface shape of the bonding region 104 is a planar shape perpendicular to the optical axis.

  Another example of the optical pickup lens according to the embodiment of the present invention is shown in FIG. An optical pickup lens 14-2 shown in (a) of FIG. 4 has substantially the same structure as the optical pickup lens 1 of (a) of FIG. Specifically, an annular structure is formed on the lens surface 201 on the laser light source side, and an annular structure is also formed on the surface shape of the lens surface 202 on the optical disk side.

In the optical pickup lens 14-2, D _n > 0. The ring zone structure includes _{one m-} th ring zone 203 that satisfies D _m−1 <D _m and D _m > D _{m + 1} . That is, the annular structure is formed so that the lens center thickness in the m-th annular zone 203 is the thinnest.

Further, in the optical pickup lens 14-2, the ring zone structure includes a junction region 204 provided between the n-1 zone and the n-th zone that satisfy D _n-1 > D _n . The bonding region 204 _may be provided between the _{D n-1> D n} at least one of the first n-1 annular meet and the n zones.

  And the surface shape of the said joining area | region 204 is a shape which does not protrude to the laser light source side rather than the boundary by the side of the lens outer edge of a n-1 zone.

Here, FIG. 4B shows an enlarged view of a portion satisfying D _n−1 > D _n (a portion surrounded by a one-dot chain line in FIG. 4A) in the optical pickup lens 14-2.

  As shown in FIG. 4A, in the optical pickup lens 2, the surface shape of the bonding region 204 is an angle θ (°) in a direction from the surface perpendicular to the optical axis toward the optical disc side from the laser light source side. It has an inclined planar shape.

Further, the surface shape of the bonding region 204 satisfies the following expression (9).
0 ≦ θ ≦ 15 (9)

  Thereby, the inclination angle of the (n-1) -th zone and the inclination angle of the bonding region 204 can be made close to each other. In addition, the shrinkage direction in the (n−1) -th zone during molding and the shrinkage direction in the joining region 204 can be matched as much as possible. Therefore, it becomes possible to easily find molding conditions for accurately obtaining the dimensions of the optical pickup lens 2.

  As shown in FIG. 4B, the inclination angles of the plurality of joining regions 204 provided in one optical pickup lens 2 are different depending on the positions in the lens radial direction where the joining regions 204 are provided. (For example, θ1, θ2, and θ3 shown in FIG. 4B).

  As a glass material of the optical pickup lens 14, a transparent resin material represented by polyolefin resin, polycarbonate resin, acrylic resin, epoxy resin, ABS resin, glass or the like can be used. However, since a laser beam having a wavelength of 405 nm is usually used for recording / reproducing BD, it is preferable to use a transparent resin material having a high transmittance of a laser beam having a wavelength in the range of 395 nm to 415 nm. Examples of such transparent resin materials include cycloolefin polymers and cyclic olefin polymers.

  Moreover, you may add the additive which improves light resistance to these transparent resin materials. The optical pickup lens 14 can be manufactured by injection molding these transparent resin materials. The optical pickup lens 14 may be molded by a 2P (Photo-Polymer) method. The optical pickup lens 14 may be cured by irradiating with ultraviolet rays after pouring a resin that cures at a specific wavelength, for example, an ultraviolet curable resin into a mold. Alternatively, the optical pickup lens 14 may be molded by pouring a resin material such as epoxy into a mold, mixing and curing. Alternatively, the optical pickup lens 14 may be molded by pouring and mixing a resin that cures at a specific temperature into a mold. As a material of the optical pickup lens 14, optical glass may be used, or polishing or molding may be used.

  Next, the lens surface shape of the optical pickup lens 14 will be described with reference to FIG. FIG. 5 is a side view showing an objective lens which is an example of a pickup lens. The definition of the surface shapes of the lens surface (R1 surface) on the laser light source side and the lens surface (R2 surface) on the optical disk side of the optical pickup lens 14 will be described. In the present embodiment, when the optical pickup lens 14 is defined, the direction is parallel to the optical axis and is directed from the laser light source side lens surface (R1 surface) to the optical disk side lens surface (R2 surface). The direction is the positive direction.

で表されるように、ディスク側面（Ｒ２面）の面形状が形成される。 Next, the surface shape of the disk side surface (R2 surface) of the optical pickup lens 14 in the present embodiment will be described. In FIG. 5, the vertex of the light incident surface R2 of the objective lens is e, the point of the light ray height h on the tangent surface in contact with the vertex e, and the light incident surface R1 in a direction parallel to the optical axis OA from this point c. Assuming that the upper point is d, the distance Z _B (mm) between the points c and d with respect to an arbitrary ray height h (mm) is

As shown, the surface shape of the disk side surface (R2 surface) is formed.

  When defining the surface shapes of the first and second annular zones on the disk side surface (R2 surface) of the pickup lens 14 according to the present embodiment, Then, the value of the annular zone position of the first annular zone shown in Table 5 is substituted. Further, the coefficient B in the equation (20) is substituted with the value of the axial step amount (mm) of the first annular zone region and the second annular zone region shown in Table 5, respectively. The surface shapes of the first and second annular zones on the disk side surface (R2 surface) of the pickup lens 14 are defined by the equation (20) and the coefficient values shown in Table 5.

It should be noted that the value of the coefficients C, K, A ₄ , A ₆ , A ₈ , A ₁₀ , A ₁₂ , A ₁₄ , A ₁₆ is substituted into the equation (20) to obtain an arbitrary light height h (mm) ( When the distance Z _B (mm) for ≠ 0) is obtained and the value becomes a negative value, the point d is closer to the laser side than the surface vertex e through which the optical axis OA of the optical disk side surface (R2 surface) passes (see FIG. 5 (left side in FIG. 5). When the distance Z _B (mm) is a positive value, it indicates that the point d is located on the disc side (right side in FIG. 5) from the vertex e.

で表されるように、レーザ側面（Ｒ１面）の面形状が形成される。 Next, the surface shape of the laser side surface (R1 surface) of the optical pickup lens 14 will be described. In FIG. 5, the vertex of the light incident surface R1 of the objective lens is f, the point of the ray height h on the tangent surface in contact with the vertex f is a, and the light incident surface R1 in a direction parallel to the optical axis OA from this point a. If the upper point is b, the distance Z _A (mm) between the points a and b with respect to an arbitrary ray height h (mm) is

As shown, the surface shape of the laser side surface (R1 surface) is formed.

  In the case where the surface shapes of the first annular region, the second annular region,..., The Nth annular region (N is a positive integer) of the pickup lens 14 according to the present embodiment are defined (21) The value of the annular zone position of the first annular zone region, the second annular zone region,..., The N-th annular zone shown in Table 5 is substituted for the ray height h in the equation. Further, when the surface shapes of the first annular region, the second annular region,..., The Nth annular region of the pickup lens 14 according to the first example are specified, the equation (21) and the coefficients shown in Table 5 are used. The surface shapes of the first to N-th zone regions of the pickup lens 14 according to the first example are defined by the above values.

Here, in the equation (21), regarding the value of the coefficient B corresponding to the axial step amount D _n , for example, even if the coefficient B of the n-th annular zone region (2 ≦ n ≦ N) is changed, the remaining coefficient C , K, A ₄ , A ₆ , A ₈ , A ₁₀ , A ₁₂ , A ₁₄ , A ₁₆ , it is understood that Z _A (mm) can be almost the same value.

  Also, the junction region formed after the m-th annular zone (m is an integer satisfying 1 <m <N) can be expressed by using the equation (21). According to the formula (21) and the coefficient values shown in Table 5 between the n- (n + 1) th annular zones (n is an integer satisfying m ≦ n ≦ N), which is the junction region in the present embodiment, The surface shape of the joining region of the pickup lens 14 is also defined.

  Next, the adjacent step amount of the pickup lens 14 will be defined. FIG. 6 is a side view schematically showing the pickup lens 14. As shown in FIG. 6, the adjacent step amount is a step amount between the annular zones. Note that the sign of the adjacent step amount d is the same as that of so-called geometric optics, and the innermost point of the next annular zone from the outermost point of the annular zone on the lens center side is the disc side (in FIG. 6). The sign of + (plus) is taken when it becomes the right side, and the sign of-(minus) is taken when it comes to the laser side (left side in FIG. 6).

  The lens surface (R1 surface) on the laser light source side or the lens surface (R2 surface) on the optical disk side of the optical pickup lens 14 is not limited to the above-described surface shape. For example, a structure may be formed on the laser light source side (R1 surface) or the optical disk side lens surface (R2 surface). Further, the surface shape of the lens surface (R1 surface) on the laser light source side of the optical pickup lens 14 is not limited to the above-described surface shape. For example, an annular zone having a certain width and depth may be formed concentrically or spirally on the laser light source side lens (R1 surface) or the optical disk side lens surface (R2 surface).

  Further, a film for controlling the transmittance of incident light, such as an antireflection film or a reflection film, is formed on the lens surface (R1 surface) on the laser light source side of the optical pickup lens 14 or the lens surface (R2 surface) on the optical disk side. May be. The film thickness and material of these films are selected so that the desired transmittance performance of the optical pickup lens 14 can be achieved. In addition, these films may have a single-layer structure including a single thin film, or may have a multiple-layer structure in which a plurality of thin films are stacked. When these films are composed of a plurality of thin films, thin films of different materials may be alternately stacked.

As the material of the thin film, AlF ₃ , AlN, Al ₂ O ₃ , BaF ₂ , BeO, Bi ₂ O ₃ , BiF ₃ , CaF ₂ , CdSe, CdS, CdTe, CeF ₃ , CeO ₂ , CsI, Cr ₂ O _{3 , DyF 2, Fe 2 O 3} , GaAs, GdF 3, Gd 2 O 3, Ge, HfO 2, HoF 3, In 2 O 3, ITO, LaF 3, La 2 O 3, LiF, MgF 2, MgO, NaF , Na ₃ AlF ₆ , Na ₅ Al ₃ F ₁₄ , Nb ₂ O ₅ , NdF ₃ , Nd ₂ O ₃ , PbCl ₂ , PbF ₂ , PbTe, PbO, PbS, Pr ₆ O ₁₁ , Sb ₂ S ₃ , Sb ₂ O ₃ , Sc ₂ O ₃ Si, Si ₃ N ₄ , SiO, Si ₂ O ₃ , SiO ₂ , SnO ₂ , SrO ₂ , SrF ₂ , Ta ₂ O ₅ , Te, Ti, _{TiN, TiN x W v, TiO} 2, TlCl, ThF 4, ThO 2, V 2 O 5, WO 3, YF 3, Y 2 O 3, YbF 3, Yb 2 O 3, ZnO, ZnS, ZnSe, ZrO 2 Etc.

  Examples 1 to 30 according to the present invention will be described below. The scope of the present invention is not limited by the examples.

  8 to 15 are wavefront aberration diagrams of Examples 1 to 30 of the invention. Here, each figure has two figures on the left and right, but shows two directions perpendicular to the optical axis, and the horizontal axis shows the relative pupil coordinates when the effective radius of each embodiment is 1, and the vertical axis. The axis is wavefront aberration (λ). The display range is ± 1 on the horizontal axis and ± 50λ on the vertical axis.

Tables 1 to 3 show a list of refractive indexes of the optical pickup lens 14 and the disk 15 used in Examples 1 to 30. The meaning of each symbol in the wavefront aberration characteristic is as follows.
TOTAL: TOTAL wavefront aberration SA3: third-order spherical aberration COMA3: third-order coma aberration AS3: third-order astigmatism

Table 4 shows configurations in Examples 1 to 30.

Table 5 shows lens data of the optical pickup lens 14 in Examples 1 to 30.

(Table 6) shows the amount of adjacent steps in Examples 1 to 30 (however, only between the annular zones inside the valley annular zone).

Table 7 shows a comparison table corresponding to each claim in Examples 1 to 30.

Table 8 shows a comparison table of optical characteristics in Examples 1 to 30.

Table 9 shows a comparison table of the sixth zone sag (Z _A ) of Example 2 and the sixth zone sag of Example 30.

Here, only Example 30 will be described in detail. In Example 30, only the on-axis step amount B (= D ₆ ) and the aspherical coefficient of the sixth annular zone on the R1 surface are changed from Example 2, and both examples have substantially the same shape.

Specifically, B (= D ₆ ) of Example 2 shown in (Table 5) was changed from 0.005410305 mm to 0.008 mm. _A comparison of the sixth annular zone sag (Z _A ) of Example 2 and the sixth annular zone sag of Example 30 is (Table 10).

As apparent from (Table 9), the on-axis step amount D ₆ differs by 2.6 μm, but the sag amount changes only 5 pm at the maximum at h = 1.169415 mm. In addition, as is clear from the comparison in Table 8 with respect to the optical characteristics, Examples 2 and 30 are equivalent. Therefore, in a lens having an annular zone, even if the on-axis step difference B (= D _n ) in a certain annular zone is set to a completely different value, the same effect as that of the present invention can be obtained.

11 Light source (laser light source)
12 Beam splitter 13 Collimator lens 14 Pickup lens (Optical pickup objective lens)
14-1 Pickup Lens 14-2 Pickup Lens 15 Optical Disk 16 Detection System 101 Lens Surface 102 Lens Surface 103 M-th Ring Zone 104 Joining Area 201 Lens Surface 202 Lens Surface 203 m-th Ring Zone 204 Joining Area

Claims (20)

A plastic optical pickup objective lens for condensing a light beam emitted from a laser light source onto an optical disk such as a BD (Blu-ray Disc), wherein the optical pickup objective lens includes a lens surface (R1 surface) on the laser light source side and an optical disk. A plurality of annular zones on both surfaces of the side lens surface (R2 surface), and the lens surface is divided into a plurality of concentric annular zones by a step, and a joining region is provided between the annular zones. The plurality of steps have a step amount that generates a phase difference in the incident light flux that reduces the aberration generated in the optical pickup objective lens when the ambient temperature changes, An optical pickup objective lens that satisfies the formulas (1) and (2) when the numerical aperture of the optical pickup objective lens is NA and the focal length is f (mm).
NA ≧ 0.8 (1)
1.0 ≦ f ≦ 1.8 (2) The optical pickup objective lens according to claim 1, wherein the numerical expression (1) ′ is satisfied, where NA is a numerical aperture of the optical pickup objective lens.
NA ≧ 0.84 ・ ・ ・ ・ ・ ・ (1) ′ The number of ring zones of the lens surface (R1 surface) on the laser light source side is RN (R1), the number of ring zones of the lens surface (R2 surface) on the optical disk side is RN (R2), and the absolute value of the step amount on the R1 surface axis is 2. The optical pickup objective lens according to claim 1, wherein the average value is d _0m (R1) (mm), and the average value of the absolute value of the step amount on the R2 plane axis is d _0m (R2). .
RN (R1) × d _0m (R1) ≧ RN (R2) × d _0m (R2) (3) The ring zone structure on the surface having the larger number of ring zones has the zone zones extending from the center of the lens toward the outer edge of the lens as the first zone, the second zone, ..., the Nth zone. (N is a positive integer), and when the aspheric surface of the n-th annular zone (n is an integer satisfying 1 ≦ n ≦ N) is virtually extended toward the lens center, the aspheric surface and the lens An intersection point with the optical axis passing through the center is C _n (n is an integer satisfying 1 ≦ n ≦ N), and a distance between the intersection point C ₁ and the intersection point C _n is an axial step amount D _n, which is parallel to the optical axis. When the direction toward the optical disk side is a positive direction, at least one m-th zone (m is an integer satisfying 1 <m <N) satisfying the following expressions (4) and (5) is provided:
| D _m-1 | <| D _m | (4)
| D _m |> | D _{m + 1} | (5)
In the lens of the m-th annular zone, when the radius of the boundary on the center side is Rb, the radius of the boundary on the outer edge side is Re, the zone width is Rw (= Re−Rs), and the numerical aperture NA is 0.85 The optical pickup lens according to claim 1, wherein when the effective radius of the optical pickup lens is Rs, the following expression (6) is satisfied.
Rw / Rs × 100 ≧ 25 (%) (6) The ring zone structure on the surface having the larger number of ring zones has the zone zones extending from the center of the lens toward the outer edge of the lens as the first zone, the second zone, ..., the Nth zone. (N is a positive integer), and when the optical path difference between a light beam passing through the n-th annular zone (n is an integer satisfying 1 ≦ n ≦ N) and a light beam passing on the optical axis is E _n (λ), Including at least one m-th zone (m is an integer satisfying 1 <m <N) satisfying the equations (7) and (8).
| E _m-1 | <| E _m | (7)
| E _m | >> | E _{m + 1} | (8)
In the lens of the m-th annular zone, when the radius of the boundary on the center side is Rb, the radius of the boundary on the outer edge side is Re, the zone width is Rw (= Re−Rs), and the numerical aperture NA is 0.85 The optical pickup lens according to claim 1, wherein when the effective radius of the optical pickup lens is Rs, the following expression (6) is satisfied.
Rw / Rs × 100 ≧ 25 (%) (6) The ring zone structure on the surface having the larger number of ring zones has the zone zones extending from the center of the lens toward the outer edge of the lens as the first zone, the second zone, ..., the Nth zone. (N is a positive integer), and when the aspheric surface of the n-th annular zone (n is an integer satisfying 1 ≦ n ≦ N) is virtually extended toward the lens center, the aspheric surface and the lens An intersection point with the optical axis passing through the center is C _n (n is an integer satisfying 1 ≦ n ≦ N), and a distance between the intersection point C ₁ and the intersection point C _n is an axial step amount D _n, which is parallel to the optical axis. When the direction toward the optical disk side is a positive direction, it includes a junction region provided between at least one n-1 annular zone and the nth annular zone satisfying D _n-1 > D _n
The surface shape of the bonding region is such that the positions of substantially all points on the surface of the bonding region in the optical axis direction are the positions in the optical axis direction of the boundary on the lens outer edge side of the n-1 zone. The optical pickup objective lens according to claim 1, wherein the objective lens has a shape that is closer to the optical disc side. The ring zone structure on the surface having the larger number of ring zones has the zone zones extending from the center of the lens toward the outer edge of the lens as the first zone, the second zone, ..., the Nth zone. (N is a positive integer), and when the aspheric surface of the n-th annular zone (n is an integer satisfying 1 ≦ n ≦ N) is virtually extended toward the lens center, the aspheric surface and the lens An intersection point with the optical axis passing through the center is C _n (n is an integer satisfying 1 ≦ n ≦ N), and a distance between the intersection point C ₁ and the intersection point C _n is an axial step amount D _n, which is parallel to the optical axis. When the direction toward the optical disk side is a positive direction, the apparatus includes a junction region provided between all the n-1 annular zones and the nth annular zone that satisfy D _n-1 > D _n .
The surface shape of the bonding region is such that the positions of substantially all points on the surface of the bonding region in the optical axis direction are the positions in the optical axis direction of the boundary on the lens outer edge side of the n-1 zone. The optical pickup objective lens according to claim 1, wherein the objective lens has a shape that is closer to the optical disc side. The ring zone structure on the surface having the larger number of ring zones has the zone zones extending from the center of the lens toward the outer edge of the lens as the first zone, the second zone, ..., the Nth zone. (N is a positive integer), and when the aspheric surface of the n-th annular zone (n is an integer satisfying 1 ≦ n ≦ N) is virtually extended toward the lens center, the aspheric surface and the lens An intersection point with the optical axis passing through the center is C _n (n is an integer satisfying 1 ≦ n ≦ N), and a distance between the intersection point C ₁ and the intersection point C _n is an axial step amount D _n, which is parallel to the optical axis. When the direction toward the optical disk side is a positive direction, the position in the lens radial direction of the boundary on the lens center side of the nth annular zone that satisfies D _n−1 > D _n is the lens surface of the optical pickup lens. When the tangent angle is within a range of 40 ° or more, a junction region provided between the n-1 ring zone and the nth ring zone is Prepared,
The surface shape of the bonding region is such that the positions of substantially all points on the surface of the bonding region in the optical axis direction are the positions in the optical axis direction of the boundary on the lens outer edge side of the n-1 zone. The optical pickup objective lens according to claim 1, wherein the objective lens has a shape that is closer to the optical disc side.   9. The surface shape of the bonding region is a planar shape inclined at an angle θ (°) in a direction from the surface perpendicular to the optical axis toward the optical disc side from the laser light source side. Optical pickup lens. The optical pickup lens according to claim 9, wherein the following expression (9) is satisfied.
0 ≦ θ ≦ 15 (9)   The optical pickup objective lens according to any one of claims 1 to 10, wherein the optical pickup objective lens focuses laser light having a wavelength in a range of 395 nm to 415 nm on the optical disc.   The plurality of steps on the lens surface (R1 surface) on the laser light source side and the lens surface (R2 surface) on the optical disk side are such that the phase of the incident light at the design wavelength and design temperature is approximately an integral multiple of the wavelength between the annular zones. 12. The step amount according to claim 1, wherein the step amount is a different step amount that causes the light flux to generate a phase difference that reduces an aberration that occurs in the optical pickup objective lens when the ambient temperature changes. The described optical pickup objective lens. The absolute value of the adjacent step amount between the n-th annular zone (2 ≦ n ≦ m) and the n−1-th annular zone is | dn | (mm), the design wavelength is λ (mm), the design wavelength and the design temperature. The optical pickup objective lens according to any one of claims 1 to 12, which satisfies Formula (10), where N is a refractive index of the optical pickup objective lens.
3 ≦ (N−1) × | dn | / λ ≦ 15 (10) Wherein the n zones (2 ≦ n ≦ N) of the on-axis step difference _{D n} of the absolute value of the difference between on-axis step difference _{D n-1} of the (n-1) th annular _| dn 0 _| (mm) The formula (11) is satisfied when the design wavelength is λ (mm) and the refractive index of the optical pickup objective lens at the design wavelength and the design temperature is N. Optical pickup objective lens.
3 ≦ (N−1) × | dn ₀ | / λ ≦ 12 (11) The maximum value of the cumulative value Σ | d | of the absolute value of the adjacent step amount of the n-th annular zone (2 ≦ n ≦ m) and the n−1-th annular zone is Σ | d | max, and the cumulative value Σ | d The optical pickup objective lens according to claim 1, wherein the minimum value of | is Σ | d | min, and the mathematical expression (12) is satisfied.
10 ≦ (N−1) × (Σ | d | max−Σ | d | min) / λ ≦ 40 (12) 15. The system according to claim 1, wherein the maximum value of the on-axis step amount D _n of the n-th annular zone (1 ≦ n ≦ N) is Dmax and the minimum value is Dmin, and satisfies Formula (13). The optical pickup objective lens described in 1.
18 ≦ (N−1) × (Dmax−Dmin) / λ ≦ 40 (13) For all n-1 zones and n-th zone that satisfy D _n-1 <D _n , an axial step amount D _n of the n- _th zone and an axial step amount D of the n-1 zone. _The value obtained by adding the absolute value | dn ₀ | of the difference from _n−1 is α, and for all the n−1 and nth annular zones that satisfy D _n−1 > D _n , In the case where β is a value obtained by adding the absolute value | dn ₀ | of the difference between the on-axis step amount D _n of the n-zone and the on-axis step amount D _n-1 of the ( _{n−1) -th} zone. The optical pickup lens according to claim 1, wherein the following expression (14) is satisfied.
α−β ≧ 0 (14) For all n-1 zones and n-th zone that satisfy D _n-1 <D _n , the on-axis step amount Dn of the n-th zone and the on-axis step amount D _{n of} the n-1 zone. _The value obtained by adding the absolute value | dn ₀ | of the difference from ₋₁ is α, and for all the n−1 and nth annular zones that satisfy D _n−1 > D _n , the n th When the value obtained by adding the absolute value | dn ₀ | of the difference between the on-axis step amount Dn of the annular zone and the on-axis step amount D _n-1 of the ( _{n−1) -th} zone is β, The optical pickup lens according to any one of claims 1 to 16, which satisfies the expression (15).
0.8 ≦ α / β ≦ 1.2 (15)   An optical pickup device using the objective lens according to any one of claims 1 to 18.   An optical disk apparatus using the objective lens according to any one of claims 1 to 18.

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