JPH09185836A - Optical system for recording and reproducing optical information recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To shorten a wavelength of used light up to 450nm and to attain a higher NA(numerical aperture) of the order of up to 0.75 of a lens by obtaining an optical system restricting the variation of wavefront aberration due to temperature change to a degree allowing a tolerance of a lens, even when an objective lens of resin is used under a high-NA solution. SOLUTION: This optical system is comprised of a light source, a coupling means, an objective lens, and an optical information recording medium having a transparent substrate. In this case, the above coupling means transforms diverging rays emitted from the light source into converging rays, and the objective lens converges this converging rays further and forms and image on the optical information medium. This objective lens has a minimum wavefront aberration for the range of 0.05#M, where M is defined as the lateral magnification of the objective lens, an is compensated for aberration so that the wavefront aberration does not exceed Marechal's limit.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical system for condensing a light beam from a light source on an optical information recording medium to record / reproduce optical information, and more particularly to an optical system in which the influence of temperature change is suppressed.

[0002]

2. Description of the Related Art A recording / reproducing optical system for an optical information recording medium having a degree of accuracy required for conventional CDs (the recording / reproducing optical system in the present invention means a recording optical system, a reproducing optical system, Examples of the optical system for both recording and reproduction include the infinite conjugate type JP-A-57-76512 and the finite conjugate type JP-A-61-56314. Further, in order to prevent the occurrence of aberration due to temperature change when a resin lens is used, there is one that uses a coupling lens.
It is disclosed in Japanese Patent No. 258573. However, in recent years, the recording density on an information recording medium such as an optical disk has been further increased, and along with this, the high N of the optical system and the objective lens has been increased.
A conversion is in progress. In addition to this, requirements for performance such as wavefront aberration (spherical aberration) are becoming more severe.

An optical system using a finite conjugate type objective lens is known in which divergent light from a light source is imaged on a recording surface of an optical information medium with a double-sided aspherical objective lens whose spherical aberration and sine conditions are corrected. However, in this case, since the refracting power of each surface becomes large, there is a limit to increase the NA when the NA becomes large. The amount of spherical aberration generated is large when focusing is performed by moving the objective lens in the optical axis direction. A large amount of spherical aberration is generated due to a change in the refractive index of the objective lens. There is a problem. When attempting to meet such demands for higher NA and higher accuracy, the change in the distance between the object images due to the shake of the disc or the like, and when the objective lens is made of resin,
The change in the wavefront aberration due to the change in the refractive index due to the change in the environment such as the temperature change becomes large. In addition, performance requirements may become strict, and the allowable error for the objective lens becomes stricter than in the past, and in some cases the error may not be allowed. In particular, when the objective lens is made of resin or of the finite conjugate type, at the level of accuracy required for the conventional CD correspondence, it is disclosed in Japanese Patent Laid-Open No. 6-258573.
Although the method using the coupling lens disclosed in Japanese Patent No. 6-96952 has been able to cope with this, the performance required for coping with the recent increase in recording density can no longer be coped with.

Further, in the case of the infinite conjugate type, the change in the wavefront aberration due to the change in the distance between the object images disappears, but if the NA is increased to about 0.60, the change in the wavefront aberration due to the temperature change will increase the recording density. In the performance required for compliance, the tolerance becomes severe. As an example, the focal length F =
In the case of an infinite conjugate type lens (parallel light is incident from the light source side) with a resin lens of 3.36 mm and NA of 0.6, the wavefront aberration is about 0.043λ (λ = 635 nm) with respect to a temperature change of 30 degrees. Changes. In fact, the currently announced D
In the required accuracy such as VD correspondence, this change will be a considerable restriction.

[0005]

SUMMARY OF THE INVENTION The present invention, under these high NA, uses an objective lens made of resin,
It is intended to obtain an optical system in which a change in wavefront aberration due to a temperature change is suppressed to an extent that a lens tolerance can be secured. In addition, it is expected that standards for higher recording density will come out in the future, and it is expected that a shorter wavelength of light used up to a wavelength of 450 nm and a higher NA of a lens up to about NA 0.75 will be required. It If the objective lens has an NA of 0.65 or more, it will be difficult to maintain performance even with an infinite conjugate glass lens unless the axial thickness of the lens is increased. It is what

[0006]

The recording / reproducing optical system for an optical information recording medium of the present invention comprises at least a light source, a coupling means and an objective lens, and records and / or records information on the optical information recording medium. In the optical system for reproducing, the coupling means converts the divergent light emitted from the light source into convergent light, and further converges the converged light to form an image on the optical information medium. It is characterized in that the wavefront aberration is minimized and falls within the Marechal limit upon incidence of light, and the lateral magnification M at which the wavefront aberration is minimized and within the Marechal limit is in the following range. 0.05 ≤ M (1) where M: lateral magnification of the objective lens alone

The objective lens is movable at least in the optical axis direction, and when the distance between the image side surface of the coupling means and the light source side surface of the objective lens is Dco, F is the focal length of the objective lens. , Dco / F may be in the range of 0.1 ≤ Dco / F ≤ 5.0 (2), but is preferably 1.0 ≤ Dco / F ≤ 5.0 (2 '). More preferably, 1.0 ≦ Dco / F ≦ 3.0 (2 ″) is satisfied.

The above objective lens is characterized by satisfying the following conditions. 0.05 ≦ M ≦ 0.23 (1 ′) NA · (1-M) ≦ 0.65 (3) 0.48 ≦ NA (4) where NA: of optical system However, it is generally desirable that the numerical aperture on the image side be 0.05 ≤ M ≤ 0.125 (1 "), but 0.65 ≤ NA ≤ 0.8 (4 '). In this case, it is preferable that 0.125 ≦ M ≦ 0.23 (1 ′ ″) The objective lenses are preferably made of resin, but may be made of glass. Further, from the viewpoint of compactness, it is desirable that the objective lens satisfies (1-M) · F ≤ 6.0 (5).

The coupling means is preferably a coupling lens which is a refractive optical system. Specifically, it can be composed of one or a plurality of spherical lenses. In some cases, it is desirable that at least one surface be an aspherical surface. Further, when the objective lens is made of resin, it is desirable that at least one coupling lens is also a resin lens having a positive refractive power, and at least one surface thereof is an aspherical surface. Desirably, at least one surface of the coupling lens is a non-spherical resin lens. The coupling lens is characterized by satisfying the following conditions. −0.10 ≦ Mt · M · Fcp / F ≦ −0.04 (6) where Mt: Lateral magnification of the entire optical system Fcp: Focal length of resin lens in coupling lens Coupling lens under the above conditions In the case of a single lens made of resin, if the focal length of the coupling lens is Fc, then naturally Fc = Fcp.

The above optical system satisfies the condition of 0.06 ≦ | Mt | · NA ≦ 0.21 (7), but as an optical system for reproduction, 0.06 ≦ | Mt | · NA ≦ 0. .12 (7 ') It is desirable for the recording optical system to satisfy 0.12 ≦ | Mt | · NA ≦ 0.21 (7 ″).

The objective lens, when the convergent light flux enters,
The wavefront aberration is the minimum, and the lateral magnification M and the numerical aperture NA, which are within the Marechal's limit, are in the range of the objective lens 0.05 ≤ M ... (1) 0.3 ≤ NA ... (4 "). At least the surface on the light source side is an aspherical surface, preferably a double-sided aspherical surface, and the convergent light beam is converged to one point at a diffraction limited spot when the objective lens is not provided. , The above-mentioned objective lens is −0.25 ≦ F · (n−1) / r ₂ ≦ 0.7 (8) where n is the refractive index of the material forming the lens r ₂ : The image-side surface of the lens Radius of curvature of −0.045 ≦ x ₂ · (n−1) / {F · (NA) ² } ≦ 0.1 ··· (9) where NA is the numerical aperture on the image side of the objective lens x ₂ : Lens Of the effective diameter of the axial ray on the image-side surface of the The difference in the optical axis direction position of the top) and the said surface apex of, and a direction displaced toward the image side farther from the optical axis and the positive _{-0.005 ≦ △ 2 · (n-} 1) 3 / {F · (NA) ⁴ ≦≦ 0.018 (10) where Δ _{2 is the} outermost periphery of the effective diameter of the axial ray on the image side surface of the lens (the image side surface on which the peripheral ray of the above NA is incident) At the position above, the difference in the optical axis direction between the aspherical surface and the reference spherical surface having the vertex radius of curvature r ₂ of the surface is such that the direction that is displaced toward the image side as the distance from the optical axis becomes positive becomes It is desirable to satisfy all or some.

Furthermore, the recording / reproducing objective lens of the optical information recording medium of the present invention is (1-M) .multidot.F.ltoreq.6.0 (5) 0.05.ltoreq.M.ltoreq.0.23 ... (1 ′) NA · (1-M) ≦ 0.65 ・ ・ ・ (3) 0.48 ≦ NA ・ ・ ・ (4) is satisfied, but in the case of resin, 0.05 ≦ M ≦ 0.125 (1 ″) NA · (1−M) ≦ 0.65 (3) It is desirable to satisfy the following condition: 0.65 ≦ NA ≦ 0.8 (4 In the case of '), it is desirable that the condition of 0.125 ≤ M ≤ 0.23 (1''') is satisfied.It is desirable that these objective lenses are made of resin, but they are not made of glass. May be.

The coupling lens of the recording / reproducing optical system of the present invention has the smallest wavefront aberration when convergent light is incident, and is formed between the objective lens and the light source for forming an image on the optical information recording medium within the Marechal limit. A coupling lens arranged to convert a divergent light beam emitted from a light source into a convergent light beam and further satisfy the following conditions. -7.0 ≤ Mc ≤ -0.5 (11) 0.06 ≤ NAo ≤ 0.21 (12) where Mc: lateral magnification of the coupling lens with respect to the light source side NAo: Numerical aperture on the light source side, and the objective lens combined with this coupling lens satisfies the condition of 0.05 ≤ M ... (1) 0.3 ≤ NA ... (4 "). The ring lens may be a lens system including one or a plurality of spherical systems, or may be a lens system including at least one surface, preferably both surfaces, of which is an aspherical surface. The coupling lens may be made of glass,
It may be made of resin. When the coupling lens is a single lens, it may be a meniscus lens having both convex surfaces, a light source side surface having a convex surface, or a meniscus lens having a light source side surface having a concave surface.

[0014]

By providing a means for changing the divergence of divergent light from the light source as a coupling means between the light source and the objective lens, the refractive power shared by the objective lens can be reduced. In particular, by providing the coupling means with the function of converting the divergent light from the light source into the convergent light, it is possible to optimize the refractive power shared by the objective lens when the NA is large. The numerical aperture NA ∞ converted to infinite light incidence on a finite conjugate type objective lens with lateral magnification M and numerical aperture NA (hereinafter referred to as the converted NA) is NA ∞ = (1−M) · NA. Can be represented. When the conversion NA increases, the influence of environmental changes such as lens design, difficulty in maintaining performance, and temperature characteristics increases. At this time, the converted NA can be reduced by making M positive, that is, by making the convergent light incident. Further, the wavefront aberration is minimized when the lateral magnification M of the objective lens itself is within the range of the conditional expression (1) and the wavefront aberration is within the Marechal limit, so that the optical axis of the coupling means and the optical axis of the objective lens. When the optical axis is decentered, the aberration is less deteriorated, which is a desirable configuration for the optical information recording / reproducing optical system. As such a coupling means, a lens, a mirror, a transmission type diffraction element, a reflection type diffraction element or the like can be considered.

By moving the objective lens at least in the direction of the optical axis, the weight of the movable portion can be reduced, and the recording surface of the optical information medium can be focused with a small amount of movement. Further, when the NA is further increased, the change in the distance between the object images due to the shake of the disc or the like and the occurrence of the spherical aberration due to the change in the temperature are increased. To cope with this, not only the objective lens but also the light source and the coupling means Similarly to the objective lens, it is also possible to perform focusing by moving each independently or integrally with the objective lens.

In conditional expression (2) regarding the distance between the coupling means and the objective lens normalized by the focal length of the objective lens, if the upper limit is exceeded, the size of the coupling means in the direction perpendicular to the optical axis increases, and the lower limit. Above this, even in a movable mechanism in which the objective lens and the coupling element move integrally, there is a problem in realization due to mechanical interference. If the lower limit of conditional expression (2 ′) is exceeded, the mechanical coupling of the coupling element with the movable mechanism around the objective lens may occur when only the objective lens is attached to the movable mechanism. Furthermore, by setting the value within the upper limit of the conditional expression (2 ″), the distance from the light source to the optical information recording medium can be shortened within the specifications such as the determined magnification.

The optical system of the present invention can be advantageously used when a spot of diffraction-limited performance is imaged on the recording surface of an optical information recording medium when NA is large and the wavelength of the used light is short. It is an optimal optical system when it is 48 or more. At that time, it is desirable that the lateral magnification M of the objective lens itself satisfies the conditional expression (1 ′). If the lateral magnification M exceeds the upper limit, the size of the coupling means in the direction perpendicular to the optical axis increases, and if it exceeds the lower limit. The error when the NA is high, especially the spherical aberration due to the refractive index error of the objective lens becomes large. Conditional expression (3)
If the upper limit of the above is exceeded, the thickness of the objective lens becomes thicker, so that in order to secure a necessary working distance, it becomes necessary to enlarge the entire optical system.

When the upper limit of conditional expression (1 ") is exceeded, when a change in the distance between object images due to a shake of the optical information medium or the like occurs,
When the objective lens is moved in the optical axis direction to perform focusing, the amount of spherical aberration generated increases. If the lower limit is exceeded, an error in the case of a high NA, in particular, the amount of spherical aberration generated due to the refractive index error of the objective lens increases. In particular, the resin material has a large change in the refractive index due to temperature changes. In the case of resin, if temperature change is ΔT and refractive index change due to temperature change is Δn, and Δn / ΔT = α ... It is almost constant and negative. Also, the change in wavefront aberration (spherical aberration) ΔWT with respect to the change in refractive index Δn is 4 of the converted NA.
It is proportional to the power and is also proportional to the focal lengths F and Δn. That is, ΔWT = β · (NA∞) ⁴ · F · Δn. Where β is a proportional coefficient. By substituting the equation into the equation, ΔWT = β · {NA · (1-M)} ⁴ · F · α · ΔT From the equation, by making M positive, the effect of temperature change is It can be seen that the value becomes smaller according to the fourth power of M. Therefore, the conditional expression (1 ″) is satisfied and the conditional expression (3) is satisfied.
By satisfying the above condition, a compact recording / reproducing optical system for an optical information recording medium can be realized by a lightweight and low-cost resinous objective lens.

In order to realize a high NA which has not existed in the past as an objective lens for recording / reproducing of an optical information recording medium such as the conditional expression (4 ′), it is desirable to satisfy the conditional expression (1 ″ ′). . When the upper limit is exceeded, the size of the coupling means in the direction perpendicular to the optical axis becomes large, and when the lower limit is exceeded, the thickness of the objective lens becomes thicker. Therefore, in order to secure the necessary working distance, the optical system There is a need to make the whole bigger. Further, by using a resin lens under this condition, weight reduction and cost reduction can be realized. Conditional expression (5)
If the upper limit of is exceeded, the objective lens becomes large and the entire optical system becomes large.

Various means are conceivable as the coupling means, but the reflection system is vulnerable to manufacturing errors, and the diffraction means has a problem of diffraction efficiency, and it is necessary to increase the power of the light source. It is desirable to use a coupling lens which is a refracting optical system as a recording / reproducing optical system of an optical information recording medium. By using one or more spherical lens systems as the coupling lens, the coupling means can be manufactured by the same manufacturing method as the conventional collimator. But,
Since the coupling lens has the function of converting the divergent light emitted from the light source into convergent light, it has a larger refracting power than conventional collimators, and when trying to capture a large amount of light from the light source, the light source The NA of the side will be taken large. Therefore, the number of lenses to be used increases with only the spherical system. Therefore, it is desirable to introduce at least one aspheric surface to correct spherical aberration.

When the objective lens is made of resin, the change of the spherical aberration due to the change of the refractive index due to the temperature change of the refractive index can be reduced by the optical system of the present invention, but at least it has a positive refractive power which constitutes the coupling lens. By making one lens made of resin, it is possible to further correct the spherical aberration change of the entire optical system due to the change of the refractive index with respect to the temperature change. This is because when the temperature rises by ΔT (0 <ΔT), the refractive index change Δnc of the coupling lens becomes negative (Δn
c <0). For this reason, the refractive power of the coupling lens becomes small, and the luminous flux emitted from the coupling lens has a smaller convergence degree than before the temperature rise. Therefore, the lateral magnification M of the objective lens itself changes in a decreasing direction (ΔM <0).
ΔM for the magnification M that minimizes the wavefront aberration of the objective lens
If changes in the negative direction, the spherical aberration moves under. Further, the refractive index change Δn of the objective lens itself becomes Δn <0 because the refractive index decreases as the temperature rises, and the spherical aberration moves excessively at this time. Therefore, the influence on the spherical aberration due to the change in the lateral magnification of the objective lens due to the change in the refractive index of the coupling lens and the influence due to the change in the refractive index of the objective lens itself are canceled out, so that the coupling lens has a positive refractive power. By using the resin lens, the effect of temperature change can be further reduced. Further, the correction effect is larger than that in the case where at least one of the collimator lenses is made of resin having a positive refractive power in the configuration of the conventional collimator and the resin single-lens objective lens. This is because even if the NA on the light source side is the same as that of the collimator, the coupling lens has a negative magnification, so the converted NA of the coupling lens is large and the absolute value of the magnification change ΔM of the objective lens itself is large. This is because

Further, in this case, since the coupling lens has a large NA on the light source side and has a negative magnification, it is desirable to use an aspherical surface as described above. Further, by using a single-lens aspherical lens made of resin as the coupling lens, it is possible to obtain the required performance at low cost. It is desirable that at least the surface on the objective lens side is an aspherical surface in view of the imaging magnification of the coupling lens. Furthermore, if the lateral magnification Mc of the coupling lens becomes even larger, it becomes necessary to make both surfaces aspherical in order to correct spherical aberration satisfactorily. For this, a known finite conjugate type objective lens design / production technology can be applied.

When the upper limit of conditional expression (6) is exceeded, the change in magnification of the objective lens alone due to the change in temperature due to the resin coupling lens becomes small, and the effect of offsetting the change in the refractive index of the objective lens becomes small. Further, if the lower limit is exceeded, the change in magnification of the objective lens itself due to the temperature change due to the resin coupling lens becomes smaller, but the wavefront aberration change due to the change in the refractive index caused by the resin coupling lens cannot be ignored, and the canceling effect is In some cases, the change in wavefront aberration due to the temperature characteristics of the entire optical system becomes larger than that in the case where the coupling lens is made of glass.

| Mt | .NA in conditional expression (7) substantially corresponds to the numerical aperture NAo on the light source side of the optical system. If the lower limit of conditional expression (7) is exceeded, a sufficient amount of light cannot be obtained. On the other hand, when the value exceeds the upper limit, the effect of astigmatism of the laser becomes large, and the effect of uneven light amount becomes large. If the upper limit of conditional expression (7 ') is exceeded, a concave lens or the like is required in the detection system for the reproduction optical system, resulting in an increase in cost. Further, considering the recording optical system, if the lower limit of conditional expression (7 ″) is exceeded, a sufficient amount of light cannot be obtained.

Converging light is made incident on the objective single lens,
By satisfying the conditional expression (1), the NA can be increased without increasing the lens thickness, and the influence of a change in the refractive index is reduced. This is 0 as shown in the above equation.
This is because the converted NA becomes smaller by setting <M (convergent light incidence). When NA is 0.3 or more, by making the convergent light incident side aspherical, spherical aberration can be corrected while keeping the sine condition, and the wavefront aberration can be kept within the Marechal limit. In addition, since the objective lens itself can maintain its performance independently by keeping the wavefront aberration within the Marechal limit when the convergent light is incident within the range of the conditional expression (1) of the lateral magnification M, the objective lens can maintain its performance independently, and thus the divergent light from the light source is emitted. Can be easily combined with the means for making the convergent light, and the error sensitivity of the arrangement including the eccentricity can be reduced. The objective single lens is aberration-corrected with respect to the imaginary light source, and by making the wavefront aberration within the Marechal limit,
It becomes easy to combine with the means for converting the divergent light from the light source into the convergent light, and the lens has a wide range of applications. Although the imaginary light source is virtual, it is practically equivalent to converging the incident light beam at one point at the diffraction limited spot. By making both surfaces of the objective single lens aspherical, spherical aberration and sine conditions can be corrected. Therefore, even when the objective lens is moved in the direction perpendicular to the optical axis for tracking, such as the objective lens of the recording / reproducing optical system of the optical information recording medium, the occurrence of aberration can be reduced.

When the upper limit of conditional expression (8) is exceeded and the refractive power of the image-side surface of the objective single lens becomes negative and becomes strong, negative spherical aberration is largely generated on the surface on the convergent light incident side, and the convergent light incident The amount of aspherical surface on the side becomes large, resulting in a lens that is difficult to manufacture. If the lower limit is exceeded and the refractive power of the image-side surface of the objective single lens becomes positive and strong, negative spherical aberration on the image-side surface will be large, and the aspherical amount on the convergent light incident side will be large,
It becomes a lens that is difficult to manufacture. If the upper limit of conditional expression (9) is exceeded, in order to correct the spherical aberration and the sine condition, the image side surface is also made aspherical, and the aspherical amount becomes large on both surfaces, making it difficult to manufacture. It becomes a lens. Similarly, when the lower limit is exceeded, in order to correct the spherical aberration and the sine condition, the image side surface is made aspherical, and the aspherical amount becomes large on both surfaces.
It becomes a lens that is difficult to manufacture. When the upper limit of conditional expression (10) is exceeded, the sine condition is overcorrected, and when the lower limit is exceeded, the sine condition is undercorrected.

When an objective single lens whose aberration is corrected for such a convergent light flux is used as an objective lens of a recording / reproducing optical system of an optical information recording medium, a cup for converting a divergent light flux from a light source into a convergent light flux. Ring means are required.
In an optical system having a large NA of 0.48 or more and a short wavelength of used light, the lateral magnification M of the objective lens alone preferably satisfies the conditional expression (1 ′). If the upper limit is exceeded, the size of the coupling means in the direction perpendicular to the optical axis increases,
When the value goes below the lower limit, the error in the case of a high NA, especially the occurrence of spherical aberration due to the error in the refractive index of the objective lens increases.
Further, if the upper limit of conditional expression (3) is exceeded, the thickness of the objective lens becomes thicker, so that in order to secure the necessary working distance, it becomes necessary to enlarge the entire optical system. Further, if the upper limit of conditional expression (5) is exceeded, the objective lens becomes large and the entire optical system becomes large. When focusing by moving the objective lens in the optical axis direction,
It is desirable that the lateral magnification M of the objective lens alone satisfies the conditional expression (1 ″). Above the upper limit, the amount of spherical aberration generated is large when the objective lens is moved in the optical axis direction for focusing. In the case of a high NA, the spherical aberration is large due to the error, especially the error of the refractive power of the objective lens.

The resin material has a large change in refractive index with temperature. Therefore, by satisfying the conditional expression (1 ″) and the conditional expression (3), a lightweight and inexpensive objective lens required for a recording / reproducing optical system of a compact optical information recording medium can be obtained. If the upper limit of Expression (3) is exceeded, the thickness of the objective lens becomes thicker, so that it is necessary to enlarge the entire optical system in order to secure the necessary working distance.

When an objective lens for recording / reproducing of an optical information recording medium satisfying the conditional expression (4 ″) is realized with a high NA which has never been obtained, it is desirable to satisfy the conditional expression (1 ″ ′). When the upper limit is exceeded, the size of the coupling means in the direction perpendicular to the optical axis becomes large, and when the lower limit is exceeded, the thickness of the objective lens becomes large, and therefore, in order to secure the necessary working distance, It becomes necessary to make the entire system large, and by using a resin lens under these conditions, weight reduction and cost reduction can be realized.

It has been described above that the refractive power of the objective lens can be reduced by using an objective lens that minimizes the wavefront aberration when the convergent light is incident and forms an image on the optical information recording medium within the Marechal limit. In order to realize an optical system using such an objective lens, a coupling lens having a positive refracting power that makes divergent light emitted from a light source into a predetermined convergent light may be used. The magnification Mc of the coupling lens is determined by Mc = Mt / M from the magnification Mt of the optical system and the magnification M of the objective lens. At this time, the coupling lens alone minimizes the wavefront aberration and the Marechal limit. It is desirable to be within. This makes it possible to reduce the deterioration of the aberration when the objective lens is decentered with respect to the optical axis.

The magnification Mc of the coupling lens is preferably within the range of conditional expression (11). If the upper limit is exceeded, the burden of the refracting power of the coupling lens will increase, and the influence of error sensitivity will increase, and the requirements for mounting and manufacturing accuracy will become stricter than with conventional collimator lenses.
It is necessary to increase the size of the coupling lens in the direction perpendicular to the optical axis as compared with the objective lens. When the value goes below the lower limit, the burden of the refractive power of the objective lens becomes large, and there is no great difference in effect from the infinite conjugate type objective lens using the collimator. Also, regarding the numerical aperture NAo on the light source side,
It is desirable to satisfy the conditional expression (12). If the lower limit is exceeded, a sufficient amount of light cannot be obtained. On the other hand, if the value exceeds the upper limit, the effect of astigmatism of the laser becomes large, and the effect of uneven light amount becomes large. At this time, if the objective lens satisfies the conditional expression (1), the image-side numerical aperture NA can be increased without increasing the lens thickness. Also,
If NA exceeds the lower limit of the conditional expression (4 ″), a well-known method such as a collimator and an objective lens for parallel light incidence can sufficiently perform without using such a coupling lens and an objective lens for which convergent light is incident. Can be maintained, and even in the case of a resin lens, the performance change due to temperature change can be sufficiently reduced.

By using one or more spherical lens systems as the coupling lens, the coupling lens can be manufactured by the same manufacturing method as the conventional collimator.
However, since the coupling lens has a function of converting the divergent light emitted from the light source into the convergent light, the refracting power becomes larger than that of the conventional collimator, and if a large amount of light from the light source is to be captured. , A large NA on the light source side will be taken. Therefore, the number of lenses to be used increases with only the spherical system. Therefore, it is desirable to introduce at least one aspheric surface to correct spherical aberration. When the objective lens is made of glass, by making the coupling lens also of glass, the change in performance due to temperature change can be made small, and it is particularly useful for a high NA lens having an NA of 0.65 or more.

By forming both surfaces of the coupling lens to be convex, the moldability is improved and the shape becomes easy to manufacture. The shape also satisfies the sine condition. By making the coupling lens a meniscus lens having a convex surface on the light source side, especially when the coupling lens is made of resin, the distance Dco between the coupling lens and the objective lens, the magnification M of the objective lens, and the magnification of the entire optical system. When the specifications of Mt are the same, the effect of changing the magnification of the objective lens alone due to temperature changes can be made greater than that of other shapes, and the degree of cancellation with respect to performance changes due to changes in the refractive index of the objective lens itself becomes greater. Further, by using a meniscus lens having a concave surface on the light source side as the coupling lens, in the specification where the distance Dco between the coupling lens and the objective lens, the magnification M of the objective lens, and the magnification Mt of the entire optical system are the same, Due to the positional relationship, the length of the entire optical system can be shortened as compared with other shapes.

[0034]

Embodiments will be described below. In each of the examples, a recording / reproducing optical system of a high-density optical information recording medium having a transparent substrate is assumed, and the numerical aperture NA is 0.6 or more. In addition, the thickness of the transparent substrate is all set to 0.6 mm. Examples 1 to 5 and 8 show only the objective lens, and Examples 6 and 7 show examples of the optical system using the objective lens of Example 1. Further, Examples 9 to 18 show a single-lens coupling lens and an optical system in which the coupling lens and an objective lens are combined.
At this time, Examples 9 to 16 use the objective lens of Example 1, Example 17 uses the objective lens of Example 2, and Example 18 uses the objective lens of Example 3.

The symbols in the table are F, the focal length of the objective lens, ri the radius of curvature of the i-th surface in order from the light source side, and the thickness on the optical axis between the i-th surface and the (i + 1) -th surface. , The distance is di, the refractive index of the medium between the i-th surface and the (i + 1) -th surface at the light source wavelength is ni, the lateral magnification of the objective lens is M, the image-side numerical aperture is NA, and the working wavelength is λ. It is represented by. In Examples 6 and 7, Ft is the focal length of the entire optical system, Mt is the lateral magnification of the entire optical system, and T is the distance from the first surface to the light source, where the direction of light travel is positive. U represents the distance between the object images, and in Examples 1 to 5 and Example 8, since the incident light is a convergent light flux in Examples in which only the objective lens is used, it is a negative value. In Examples 6 and 7 and Examples 9 to 18, Ft is the focal length of the entire optical system, Mt is the lateral magnification of the entire optical system, U is the object-to-image distance of the optical system, and T is the first lens of the coupling lens. Shows the distance to the light source when viewed from one side.
Further, in the coupling lenses alone of Examples 9 to 18, Fc is the focal length of the single lens coupling lens, Mc is the lateral magnification of the coupling lens alone, and Uc is the coupling lens alone in the arrangement at that time. The object-to-image distance, NAo, represents the numerical aperture on the light source side.

Regarding the temperature characteristics, it is assumed that when the objective lens or the coupling lens is made of resin, it changes by -12 × 10 ^{-5 when the} temperature rises by 1 degree. Further, when the objective lens or the coupling lens is made of glass, it is assumed that the temperature changes by 39 × 10 ⁻⁷ when the temperature rises by 1 degree. The temperature characteristics are evaluated by the wavefront aberration rms value. The rms value of this wavefront aberration is calculated by ray tracing by a known method. The Marechal limit means that the wavefront aberration rms value is 0.07λ. Further, the wavefront aberration can be measured by using an interferometer or the like capable of numerical analysis. Since the influence of the linear expansion of the material on the wavefront aberration due to the temperature change is considerably smaller than the influence due to the change of the refractive index, it is not included in the calculation here.

As for the aspherical shape of the lens surface, κ is a conical coefficient, Ai is an aspherical surface coefficient, and Pi (4 ≦ Pi) is a non-spherical surface in an orthogonal coordinate system with the vertex of the surface as the origin and the optical axis direction as the X axis. When it is a power of the sphere,

[Equation 1] It is represented by

Example 1 F = 3.7685433 M = + 1/12 U = -37.068 NA: 0.60 λ = 635 nm i ri di ni 1 2.165 2.60 1.49810 2 -8.4801 0.57 3 ∞ 0.60 1.58000 4 ∞ Aspheric surface data First surface κ = −8.367770 × 10 ⁻¹ A ₁ = 5.07210 × 10 ^-3 P ₁ = 4.0000 A ₂ = 3.24900 × 10 ^-4 P ₂ = 6.0000 A ₃ = 2.13140 × 10 ^-5 P ₃ = 8.00000 A ₄ = −3.996600 × 10 ⁻⁶ P ₄ = 1.0000 2nd surface κ = −2.225490 × 10 A ₁ = 1.227980 × 10 ⁻² P ₁ = 4.0000 A ₂ = −5.04840 × 10 ⁻³ P ₂ = 6.00000 A ₃ = 1.03830 × 10 ⁻³ P ₃ = 8.00000 A ₄ = −9.09999 × 10 ⁻⁵ P ₄ = 1.0000

In this embodiment, the objective lens is made of resin. FIG. 1 shows an optical path diagram of this objective lens, FIG. 2 shows an aberration diagram of its spherical aberration and sine conditions, and FIG. 3 shows temperature characteristics. Temperature characteristic changes by 30 degrees and wavefront aberration is 0.02
Only the change of 8λ is generated, and the influence of the temperature change is considerably smaller than that of the infinite conjugate type objective lens. In this example, x ₂ = −0.08606 Δ ₂ = 0.04569 and x ₂ · (n−1) / {F · (NA) ² } = − 0.03160 Δ ₂ · (n−1) ³ / {F · (NA) ⁴ } = 0.01156

Example 2 F = 4.5893756 M = + 1/5 U = −13.610 NA: 0.60 λ = 635 nm i ri di ni 1 2.304 2.60 1.49810 2 -179.9922 1 .57 3 ∞ 0.60 1.58000 4 ∞ Aspheric surface data First surface κ = −8.28170 × 10 ⁻¹ A ₁ = 5.44430 × 10 ⁻³ P ₁ = 4.0000 A ₂ = 4.26990 × 10 ⁻⁴ P ₂ = 6.00000 A ₃ = 2.89730 × 10 ⁻⁵ P ₃ = 8.00000 A ₄ = 3.555070 × 10 ⁻⁶ P ₄ = 1.0000 2nd surface κ = −2.25490 × 10 A ₁ = 7.41970 × 10 ⁻³ P ₁ = 4.0000 A ₂ = −1.45950 × 10 ^-3 P ₂ = 6.0000 A ₃ = 1.25000 × 10 ^-5 P ₃ = 8.0000 A ₄ = 2.08630 × 10 ^-5 P ₄ = 1.0000

This embodiment is similar to the first embodiment in that the objective lens is made of resin. An optical path diagram of this objective lens is shown in FIG. 4, an aberration diagram of its spherical aberration and sine conditions is shown in FIG.
The temperature characteristics are shown in FIG. The second embodiment is M compared with the first embodiment.
Is even larger, so the effect is great. In this example, x ₂ = 0.01337 Δ ₂ = 0.01894 and x ₂ · (n−1) / {F · (NA) ² } = 0.00403 Δ ₂ · (n−1) ³ / {F · (NA) ⁴ } = 0.00394

Example 3 F = 3.6959252 M = + 1/15 U = −47.370 NA: 0.60 λ = 635 nm i ri di ni 1 2.130 2.60 1.49810 2 −8.053 1 0.57 3 ∞ 0.60 1.58000 4 ∞ Aspheric surface data First surface κ = −5.06170 × 10 ⁻¹ A ₁ = 8.72330 × 10 ⁻⁴ P ₁ = 4.0000 A ₂ = 8.86100 × 10 ⁻⁵ P ₂ = 6.00000 A ₃ = 7.50840 × 10 ⁻⁶ P ₃ = 8.00000 A _{4 ^{= -1.22820 × 10 -6 P 4 =}} 10.0000 second surface _{κ = -2.25510 × 10 A 1 =} 1.31840 × 10 -2 P 1 = 4.0000 A 2 = -3.62900 × 10 ⁻³ P ₂ = 6.00000 A ₃ = 6.28660 × 10 ⁻⁴ P ₃ = 8.00000 A ₄ = −4.999790 × 10 ⁻⁵ P ₄ = 1.0000

The objective lens of this embodiment is also made of resin,
FIG. 7 shows the optical path diagram, FIG. 8 shows the spherical aberration and the aberration diagram of the sine condition, and FIG. 9 shows the temperature characteristic. In this example, x ₂ = −0.08076 Δ ₂ = 0.05734 and x ₂ · (n−1) / {F · (NA) ² } = − 0.03023 Δ ₂ · (n−1 ) ³ / {F · (NA) ⁴ } = 0.01479

Example 4 F = 4.6109005 M = + 1/5 U = -13.641 NA: 0.7 λ = 450 nm i ri di ni 1 2.318 2.60 1.50870 2 123.320 1. 57 3 ∞ 0.60 1.60000 4 ∞ Aspheric surface data First surface κ = −8.09110 × 10 ⁻¹ A ₁ = 5.222310 × 10 ⁻³ P ₁ = 4.0000 A ₂ = 4.60510 × 10 ⁻⁴ P ₂ = 6.00000 A ₃ = 1.66010 × 10 ⁻⁵ P ₃ = 8.00000 A _{4 ^{= 7.33260 × 10 -6 P 4 =}} 10.0000 second surface _{κ = -2.25490 × 10 A 1 =} 6.72560 × 10 -3 P 1 = 4.0000 A 2 = -6.93750 × 10 _{^{-4 P 2 = 6.0000 A 3 =}} -1.29380 × 10 -4 P 3 = 8.0000 A 4 = 2.24440 × 10 -5 P 4 = 10.0000

The objective lens of this embodiment is also made of resin,
In this example, the NA is 0.7 and the wavelength of the used light is 450 nm. FIG. 10 shows the optical path diagram, FIG. 11 shows the aberration diagram of the spherical aberration and the sine condition, and FIG. 12 shows the temperature characteristic. If M is 0.2 times, even if the resin lens has NA 0.7, the temperature is 3
The change of the wavefront aberration is about 0.028λ with respect to the change of 0 degree, and the initial aberration is well corrected in the design. In this example, x ₂ = 0.05248 Δ ₂ = 0.03962 and x ₂ · (n−1) / {F · (NA) ² } = 0.01182 Δ ₂ · (n−1) ³ / {F · (NA) ⁴ } = 0.00471

Example 5 F = 4.6141726 M = + 1/5 U = −17.811 NA: 0.75 λ = 450 nm i ri di ni 1 2.524 2.30 1.71017 2 6.823 1. 57 3 ∞ 0.60 1.60000 4 ∞ Aspherical surface data 1st surface κ = −8.28404 × 10 ⁻¹ A ₁ = 5.01710 × 10 ⁻³ P ₁ = 4.0000 A ₂ = 3.07860 × 10 ⁻⁴ P ₂ = 6.0000 A ₃ = 6.37850 × 10 ⁻⁵ P ₃ = 8.0000 A ₄ = -7.41820 × 10 ⁻⁶ P ₄ = 1.0000 A ₅ = 1.38190 × 10 ⁻⁶ P ₄ = 1.20,000 Second surface κ = −2.225430 × 10 A ₁ = 1.04510 × 10 _{^{-2 P 1 = 4.0000 A 2 =}} -2.51340 × 10 -3 P 2 = 6.0000 A 3 = 7.11610 × 10 -4 P 3 = 8.0000 A 4 = -1.44630 × 10 ^-4 P ₄ = 1.0000 A ₅ = 1.38190 × 10 ^-5 P ₄ = 120,000

The objective lens of this embodiment is made of glass and has N
This is an example with A0.75 and a wavelength of 450 nm, and initial aberrations are well corrected even with NA0.75. The optical path diagram is shown in Figure 1.
3 shows an aberration diagram of the spherical aberration and the sine condition in FIG.
FIG. 15 shows the temperature characteristics. In this example, x ₂ = 0.25188 Δ ₂ = 0.00660 and x ₂ · (n−1) / {F · (NA) ² } = 0.06892 Δ ₂ · (n−1) ³ / {F · (NA) ⁴ } = 0.00162

Example 6 Ft = 6.4164274 Mt = -1 / 6 T = -25.149 F = 3.7685433 M = + 1 / 12.12 U = 42.822 NA: 0.6 λ = 635 nm i ri di ni 1 24.427 1.00 1.83925 2 7.230 2.00 1.72623 3 -18.300 9.90 4 2.165 2.60 1.49810 5 -8.480 1.573 6 ∞ 0.60 1.58000 7 ∞ Aspherical surface data 4th surface κ = −8.367770 × 10 ⁻¹ A ₁ = 5.07210 × 10 ^-3 P ₁ = 4.0000 A ₂ = 3.24900 × 10 ^-4 P ₂ = 6.0000 A ₃ = 2.13140 × 10 ^-5 P ₃ = 8.00000 A ₄ = -3.96600 × 10 ^-6 P ₄ = 1.0000 5th surface κ = -2.25490 × 10 A ₁ = 1.27980 × 10 ^-2 P ₁ = 4.0000 A ₂ = -5.04840 × 10 ⁻³ P ₂ = 6.00000 A ₃ = 1.03830 × 10 ⁻³ P ₃ = 8.00000 A ₄ = −9.09999 × 10 ⁻⁵ P ₄ = 1.0000

The optical system of this embodiment is an example in which the objective lens used in the first embodiment is used and the coupling lens is combined with a lens made of glass of 1 group. The optical path diagram is shown in Figure 1.
6 and the temperature characteristics are shown in FIG. The amount of change in wavefront aberration due to temperature change is almost the same as in Example 1, and is due to the objective lens. Further, since the aberration due to the coupling lens is corrected, the magnification of the wavefront aberration best of the objective lens is slightly different from that of the first embodiment. In this example
Dco = 9.90.

Example 7 Ft = 6.4537445 Mt = -1 / 6 T = −25.557 F = 3.768433 M = + 1/12 U = 42.327 NA: 0.6 λ = 635 nm ir i di ni 1 17.470 2.00 1.49810 2 -16.738 10.00 3 2.165 2.60 1.49810 4 -8.480 1.57 5 ∞ 0.60 1.58000 6 ∞ Aspheric data No. One surface κ = -6.444530 x 10 ^-1 Second surface κ = -3.72840 x 10 ^-1 A ₁ = 8.92470 × 10 ⁻⁵ P ₁ = 4.0000 Third surface κ = −8.367770 × 10 ⁻¹ A ₁ = 5.07210 × 10 ^-3 P ₁ = 4.0000 A ₂ = 3.24900 × 10 ^-4 P ₂ = 6.0000 A ₃ = 2.13140 × 10 ^-5 P ₃ = 8.00000 A _{4 ^{= -3.96600 × 10 -6 P 4 =}} 10.0000 fourth surface _{κ = -2.25490 × 10 A 1 =} 1.27980 × 10 -2 P 1 = 4.0000 A 2 = -5.04840 × 10 ⁻³ P ₂ = 6.00000 A ₃ = 1.03830 × 10 ⁻³ P ₃ = 8.00000 A ₄ = −9.09999 × 10 ⁻⁵ P ₄ = 1.0000

The optical system of this example is an example of an optical system in which the objective lens is made of resin, the one of the example 1 is used, and the coupling lens is made of a resin double-sided aspherical single lens. Its optical path diagram is shown in FIG. 18, and its temperature characteristic is shown in FIG. The change in the wavefront aberration due to the change in temperature is smaller than half of that in the first embodiment. This is because the temperature rises, the refractive index of each lens decreases, the angle of the convergent light by the coupling lens decreases, and the lateral magnification of the objective lens decreases (in this case only, the spherical surface of the objective lens decreases). This is because the aberration moves to the under side) and the influence of the decrease in the refractive index of the objective lens itself (in this case, the spherical aberration moves to the over side) cancel each other. In this example, Dco = 10.0
It is.

Example 8 F = 4.5192426 M = + 1/5 U = −13.441765 NA: 0.6 λ = 635 nm i ri di ni 1 2.345 2.60 1.49810 2 −35.299 1 0.57 3 ∞ 0.60 1.58000 4 ∞ Aspherical surface data First surface κ = −9.441850 × 10 ⁻¹ A ₁ = 5.48260 × 10 ⁻³ P ₁ = 4.0000 A ₂ = 2.30790 × 10 ⁻⁴ P ₂ = 6.0000 A ₃ = 2.16950 × 10 ⁻⁵ P ₃ = 8.0000 A ₄ = -2.43340 x 10 ^-6 P ₄ = 10.0000

This embodiment is an example in which only the objective lens is used. The objective lens is made of resin, the surface on the light source side is aspherical, and the surface on the image side is spherical. The optical path diagram is shown in FIG. 20, the aberration diagram of the spherical aberration and the sine condition is shown in FIG. 21, and the temperature characteristic is shown in FIG. In this example, x ₂ = −0.029622 Δ ₂ = 0.00 (because it is a spherical surface) x ₂ · (n−1) / {F · (NA) ² } = − 0.00907 Δ ₂ · (n−1) ³ / {F · (NA) ⁴ } = 0.00

Example 9 Coupling lens Fc = 15.117 Mc = −2.0 Uc = 68.664 T = −21.826 NAo: 0.1 λ = 635 nm i ri di ni 1 19.564 2.00 1.49810 2 -11.825 44.838 Aspherical surface data First surface κ = -4.50630 Second surface κ = -8.10280 × 10 ^-1 A ₁ = 3.82380 × 10 ⁻⁵ P ₁ = 4.0000 All optical systems Ft = 3.8011 Mt = -1 / 6 M = + 1/12 U = 31.596 T = -21.826 NA: 0. 6 λ = 635 nm i r i d i n i 1 19.564 2.00 1.49810 2 -11.825 3.00 3 2.165 2.60 1.49810 4 -8.480 1.57 5 ∞ 0.60 1 0.58000 6 ∞ aspherical surface data 1st surface κ = −4.550630 2nd surface κ = −8.10280 × 10 ⁻¹ A ₁ = 3.82380 × 10 ⁻⁵ P ₁ = 4.0000 Third surface κ = −8.367770 × 10 ⁻¹ A ₁ = 5.07210 × 10 ^-3 P ₁ = 4.0000 A ₂ = 3.24900 × 10 ^-4 P ₂ = 6.0000 A ₃ = 2.13140 × 10 ^-5 P ₃ = 8.00000 A _{4 ^{= -3.96600 × 10 -6 P 4 =}} 10.0000 fourth surface _{κ = -2.25490 × 10 A 1 =} 1.27980 × 10 -2 P 1 = 4.0000 A 2 = -5.04840 × 10 ⁻³ P ₂ = 6.00000 A ₃ = 1.03830 × 10 ⁻³ P ₃ = 8.00000 A ₄ = −9.09999 × 10 ⁻⁵ P ₄ = 1.0000

Example 9 is an example of a biconvex lens whose coupling lens is made of resin and whose both surfaces are aspherical, and its aberration diagram is shown in FIG.
It is shown in FIG. The spherical aberration and the sine condition are also sufficiently satisfied.
The objective lens combined with this is the resin objective lens of Example 1, and an optical path diagram of the entire optical system is shown in FIG. 23 and its temperature characteristic is shown in FIG. In this embodiment, Dco = 3 Mt.M.Fcp / F = -0.05569. Here, since the resin coupling lens is a single lens, Fc = Fcp. The change in wavefront aberration due to temperature change is 0.013 when the temperature rises 30 degrees from the reference design temperature.
λ is about half that of the objective lens of Example 1 alone. This is because the refractive index of each lens decreases as the temperature rises, the angle of the convergent light by the coupling lens decreases, and the lateral magnification of the objective lens decreases. (In this case only, the spherical aberration of the objective lens This is because the effect of decreasing the refractive index of the objective lens itself (in this case, the spherical aberration moves over) cancels each other out.

Example 10 Coupling lens Fc = 17.450 Mc = −2.0 Uc = 79.165 T = −25.327 NA: 0.1 λ = 635 nm i ri di ni 1 22.683 2.00 1.49810 2 -13.678 51.838 Aspherical data 1st surface κ = -4.34470 2nd surface κ = -7.48710 x 10 ^-1 A ₁ = 2.93000 × 10 ⁻⁵ P ₁ = 4.0000 All optical systems Ft = 6.3705 Mt = −1 / 6 M = + 1/12 U = 42.097 T = −25.327 NA: 0. 6 λ = 635 nm i ri di ni 1 22.683 2.00 1.49810 2 -13.678 10.00 3 2.165 2.60 1.49810 4 -8.480 1.57 5 ∞ 0.60 1 0.58000 6 ∞ Aspheric surface data First surface κ = -4.34470 Second surface κ = -7.48710 × 10 ^-1 A ₁ = 2.93000 × 10 ⁻⁵ P ₁ = 4.0000 Third surface κ = −8.367770 × 10 ⁻¹ A ₁ = 5.07210 × 10 ^-3 P ₁ = 4.0000 A ₂ = 3.24900 × 10 ^-4 P ₂ = 6.0000 A ₃ = 2.13140 × 10 ^-5 P ₃ = 8.00000 A _{4 ^{= -3.96600 × 10 -6 P 4 =}} 10.0000 fourth surface _{κ = -2.25490 × 10 A 1 =} 1.27980 × 10 -2 P 1 = 4.0000 A 2 = -5.04840 × 10 ⁻³ P ₂ = 6.00000 A ₃ = 1.03830 × 10 ⁻³ P ₃ = 8.00000 A ₄ = −9.09999 × 10 ⁻⁵ P ₄ = 1.0000

The tenth embodiment is an example of a biconvex lens in which the coupling lens is made of resin and has aspherical surfaces on both sides, and the magnification is Mc = −2.0 as in the ninth embodiment, but the focal length Fc is slightly longer. As an example, the aberration diagram is shown in FIG. Spherical aberration,
The sine condition is also satisfied. The all-optical system is a combination of this coupling lens and the resin objective lens of the first embodiment, and the magnifications M and Mt have the same specifications as those of the seventh and ninth embodiments. The lens spacing Dco is also the same as in the seventh embodiment. FIG. 26 shows the optical path diagram and FIG. 28 shows the temperature characteristic. In this embodiment, Dco = 10 Mt.M.Fcp / F = -0.06429. Here, since the resin coupling lens is a single lens, Fc = Fcp. The change in wavefront aberration due to temperature change is 0.011 when the temperature rises 30 degrees from the reference design temperature.
λ is almost equal to that of the seventh embodiment and slightly smaller than that of the ninth embodiment. This is because the focal length Fc of the coupling lens becomes longer than that in the ninth embodiment, and the degree of the angle of the converged light by the coupling lens becoming smaller due to the temperature rise becomes larger than that in the ninth embodiment.

Example 11 Coupling lens Fc = 14.864 Mc = −2.0 Uc = 67.577 T = −20.739 NAo: 0.1 λ = 635 nm i ri di ni 1 -40.000 2. 00 1.49810 2 −6.351 44.838 Aspherical surface data First surface κ = −4.475790 A ₁ = 2.74370 × 10 ⁻⁴ P ₁ = 4.00000 Second surface κ = −1.27670 A ₁ = -2.999160 x 10 ^-5 P ₁ = 4.0000 A ₂ = 2.54920 x 10 ^-6 P ₂ = 6.0000 A ₃ = 1.42550 x 10 ^-8 P ₃ = 8.0000 All optics System Ft = 3.6150 Mt = -1 / 6 M = + 1/12 U = 30.509 T = -20.739 NA: 0.6 λ = 635 nm i ri di ni 1 -40.000 2.00 1. 49810 2-6.351 3 .00 3 2.165 2.60 1.49810 4 −8.480 1.57 5 ∞ 0.60 1.58000 6 ∞ Aspheric surface data 1st surface κ = −4.475790 A ₁ = 2.74370 × 10 ^-4 P ₁ = 4.0000 second surface _{κ = -1.27670 A 1 = -2.99160 ×} 10 -5 P 1 = 4.0000 A 2 = 2.54920 × 10 -6 P 2 = 6.0000 A ₃ = 1.42550 × 10 ⁻⁸ P ₃ = 8.00000 3rd surface κ = −8.367770 × 10 ⁻¹ A ₁ = 5.07210 × 10 ^-3 P ₁ = 4.0000 A ₂ = 3.24900 × 10 ^-4 P ₂ = 6.0000 A ₃ = 2.13140 × 10 ^-5 P ₃ = 8.00000 A _{4 ^{= -3.96600 × 10 -6 P 4 =}} 10.0000 fourth surface _{κ = -2.25490 × 10 A 1 =} 1.27980 × 10 -2 P 1 = 4.0000 A 2 = -5.04840 × 10 ⁻³ P ₂ = 6.00000 A ₃ = 1.03830 × 10 ⁻³ P ₃ = 8.00000 A ₄ = −9.09999 × 10 ⁻⁵ P ₄ = 1.0000

The eleventh embodiment is an example in which the coupling lens is made of resin and has a double-sided aspherical surface and the light source side surface is a concave meniscus lens. The magnification is Mc = −2.0, which is the same as that of the ninth embodiment, and the aberration thereof. The figure is shown in FIG. The sine condition is overcorrected. The entire optical system is a combination of this coupling lens and the resin objective lens of the first embodiment, the magnifications M and Mt have the same specifications as those of the ninth embodiment, and the distance Dco between the objective lens and the coupling lens is Dco. The same as in Example 9. FIG. 29 shows the optical path diagram and FIG. 31 shows the temperature characteristic. In this embodiment, Dco = 3 Mt.M.Fcp / F = -0.05476. Here, since the resin coupling lens is a single lens, Fc = Fcp. The change in wavefront aberration due to temperature change is 0.016 when the temperature rises 30 degrees from the reference design temperature.
Although λ is slightly larger than that of the ninth embodiment having substantially the same specifications, the object-image distance is shorter. This is because the light source side surface of the coupling lens is a meniscus lens having a concave surface, so that the principal point position of the lens is closer to the objective lens than in the ninth embodiment, which is a biconvex coupling lens.

Example 12 Coupling lens Fc = 15.479 Mc = −2.0 Uc = 70.351 T = −23.513 NAo: 0.1 λ = 635 nm i ri di ni 1 6.438 2.00 1.49810 2 35.000 44.838 aspheric data first surface _{κ = -2.50830 A 1 = 1.45610 ×} 10 -3 P 1 = 4.0000 second surface κ = -8.15100 × 10 ^{- 1} A ₁ = 1.03270 × 10 ⁻³ P ₁ = 4.0000 A ₂ = 1.61260 × 10 ⁻⁵ P ₂ = 6.0000 A ₃ = −5.04670 × 10 ⁻⁷ P ₃ = 8.0000 All Optical system Ft = 4.0894 Mt = -1 / 6 M = + 1/12 U = 33.283 T = −23.513 NA: 0.6 λ = 635 nm i ri di ni 1 6.438 2.00 1. 49810 2 35.000 3.00 3 2.165 2.60 1.49810 4 -8.480 1.57 5 ∞ 0.60 1.58000 6 ∞ Aspheric surface data 1st surface κ = -2.550830 A ₁ = 1.45610 × 10 ⁻³ P ₁ = 4.0000 Second surface κ = −8.15100 × 10 ⁻¹ A ₁ = 1.03270 × 10 ⁻³ P ₁ = 4.0000 A ₂ = 1.61260 × 10 ⁻⁵ P ₂ = 6.0000 A ₃ = −5.04670 × 10 ⁻⁷ P ₃ = 8.00000th 3 planes κ = −8.36770 × 10 ⁻¹ A ₁ = 5.07210 × 10 ^-3 P ₁ = 4.0000 A ₂ = 3.24900 × 10 ^-4 P ₂ = 6.0000 A ₃ = 2.13140 × 10 ^-5 P ₃ = 8.00000 A _{4 ^{= -3.96600 × 10 -6 P 4 =}} 10.0000 fourth surface _{κ = -2.25490 × 10 A 1 =} 1.27980 × 10 -2 P 1 = 4.0000 A 2 = -5.04840 × 10 ⁻³ P ₂ = 6.00000 A ₃ = 1.03830 × 10 ⁻³ P ₃ = 8.00000 A ₄ = −9.09999 × 10 ⁻⁵ P ₄ = 1.0000

The twelfth embodiment is an example in which the coupling lens is made of resin and has a double-sided aspherical surface, and the light source side surface is a convex meniscus lens. The figure is shown in FIG. The sine condition is undercorrected. The entire optical system is a combination of this coupling lens and the resin objective lens of the first embodiment, the magnifications M and Mt have the same specifications as those of the ninth embodiment, and the distance Dco between the objective lens and the coupling lens is Dco. The same as in Example 9. FIG. 32 shows the optical path diagram and FIG. 34 shows the temperature characteristic. In this embodiment, Dco = 3 Mt.M.Fcp / F = -0.05703. Here, since the resin coupling lens is a single lens, Fc = Fcp. The change in wavefront aberration due to temperature change is 0.010 when the temperature rises 30 degrees from the reference design temperature.
It is smaller than that of Example 9 having almost the same specifications as λ. This is because the side surface of the light source of the coupling lens is a convex meniscus lens, so that the principal point position of the lens is located closer to the light source than that of the biconvex coupling lens of the ninth embodiment. This is because the focal length Fc becomes long.

Example 13 Coupling lens Fc = 14.963 Mc = −2.0 Uc = 67.994 T = −21.156 NAo: 0.1 λ = 635 nm ir di ni 1 196.414 2.00 1.49810 2 −7.721 44.838 Aspheric surface data Second surface κ = −8.157760 × 10 ⁻¹ A ₁ = 3.11570 × 10 ^-5 P ₁ = 4.0000 All optical systems Ft = 3.686 Mt = -1 / 6 M = + 1/12 U = 30.926 T = -21.156 NA: 0. 6 λ = 635 nm i ri di ni 1 196.414 2.00 1.49810 2 −7.721 3.00 3 2.165 2.60 1.49810 4 −8.480 1.57 5 ∞ 0.60 1 0.58000 6 ∞ Aspheric surface data 2nd surface κ = −8.157760 × 10 ⁻¹ A ₁ = 3.11570 × 10 ⁻⁵ P ₁ = 4.0000 Third surface κ = −8.367770 × 10 ⁻¹ A ₁ = 5.07210 × 10 ^-3 P ₁ = 4.0000 A ₂ = 3.24900 × 10 ^-4 P ₂ = 6.0000 A ₃ = 2.13140 × 10 ^-5 P ₃ = 8.00000 A _{4 ^{= -3.96600 × 10 -6 P 4 =}} 10.0000 fourth surface _{κ = -2.25490 × 10 A 1 =} 1.27980 × 10 -2 P 1 = 4.0000 A 2 = -5.04840 × 10 ⁻³ P ₂ = 6.00000 A ₃ = 1.03830 × 10 ⁻³ P ₃ = 8.00000 A ₄ = −9.09999 × 10 ⁻⁵ P ₄ = 1.0000

The thirteenth embodiment is an example of a biconvex lens in which the coupling lens is made of resin, the surface on the light source side is a spherical surface, and the surface on the image side is an aspherical surface. At the same magnification Mc = −2.0 as in the ninth embodiment. FIG. 36 shows the aberration diagram thereof. The sine condition is overcorrected. The entire optical system is a combination of this coupling lens and the resin objective lens of the first embodiment, the magnifications M and Mt have the same specifications as those of the ninth embodiment, and the distance Dco between the objective lens and the coupling lens is Dco. The same as in Example 9. FIG. 35 shows the optical path diagram and FIG. 37 shows the temperature characteristic. In this embodiment, Dco = 3 Mt.M.Fcp / F = -0.05512. Here, since the resin coupling lens is a single lens, Fc = Fcp. The change in wavefront aberration due to temperature change is 0.015 when the temperature rises 30 degrees from the reference design temperature.
becomes λ.

Example 14 Coupling lens Fc = 9.047 Mc = −4.0 Uc = 57.166 T = −10.328 NAo: 0.2 λ = 635 nm i ri di ni 1 15.135 2.00 1.49810 2 −6.135 44.838 Aspherical surface data First surface κ = −9.28300 Second surface κ = −9.65600 × 10 ⁻¹ A ₁ = −1.76460 × 10 ⁻⁵ P ₁ = 4.0000 A ₂ = 6.69660 × 10 ⁻⁷ P ₂ = 6.00000 All optical systems Ft = 3.774 Mt = −1 / 3 M = + 1 / 12 U = 20.098 T = -10.328 NA: 0.6 λ = 635 nm i ri di ni 1 15.135 2.00 1.49810 2 -6.135 3.00 3.2.165 2.60 1.49810 4 −8.480 1.57 5 ∞ 0.60 1.58000 6 ∞ Aspheric surface data 1st surface κ = −9.28300 2nd surface κ = −9.65600 × 10 ⁻¹ A ₁ = -1.76460 × 10 ^-5 P ₁ = 4.0000 A ₂ = 6.669660 × 10 ^-7 P ₂ = 6.00000 Third surface κ = -8.36770 × 10 ^-1 A ₁ = 5.07210 × 10 ^-3 P ₁ = 4.0000 A ₂ = 3.24900 × 10 ^-4 P ₂ = 6.0000 A ₃ = 2.13140 × 10 ^-5 P ₃ = 8.00000 A _{4 ^{= -3.96600 × 10 -6 P 4 =}} 10.0000 fourth surface _{κ = -2.25490 × 10 A 1 =} 1.27980 × 10 -2 P 1 = 4.0000 A 2 = -5.04840 × 10 ⁻³ P ₂ = 6.00000 A ₃ = 1.03830 × 10 ⁻³ P ₃ = 8.00000 A ₄ = −9.09999 × 10 ⁻⁵ P ₄ = 1.0000

The fourteenth embodiment is an example of a biconvex lens whose coupling lens is made of resin and whose both surfaces are aspherical surfaces, and its aberration diagram is shown in FIG. Further, the all-optical system is a combination of this coupling lens and the resin objective lens of Example 1, and its optical path diagram is shown in FIG. 38 and its temperature characteristic is shown in FIG. In this embodiment, Dco = 3 Mt.M.Fcp / F = -0.066666. Here, since the resin coupling lens is a single lens, Fc = Fcp. The change in wavefront aberration due to temperature change is 0.008 when the temperature rises 30 degrees from the reference design temperature.
λ, which is smaller than that in the ninth embodiment. In addition, the distance between the images is quite short.

Example 15 Coupling lens Fc = 10.447 Mc = −4.0 Uc = 65.913 T = −12.075 NAo: 0.2 λ = 635 nm i ri di ni 1 17.965 2.00 1.49810 2 −7.055 51.838 Aspherical surface data First surface κ = −5.16870 A ₁ = −1.16400 × 10 ⁻⁴ P ₁ = 4.0000 Second surface κ = −7.02230 × 10 ^-1 A ₁ = 6.393330 × 10 ⁻⁵ P ₁ = 4.0000 A ₂ = −8.95530 × 10 ⁻⁷ P ₂ = 6.00000 A ₃ = −1.37400 × 10 ⁻⁸ P ₃ = 8.00000 All optical system Ft = 11.429 Mt = -1 / 3 M = + 1/12 U = 28.845 T = -12.075 NA: 0.6 λ = 635 nm i ri di ni 1 17.965 2.00 1 .49810 2 -7.055 10.00 3 2.165 2.60 1.49810 4 -8.480 1.57 5 ∞ 0.60 1.58000 6 ∞ Aspheric surface data 1st surface κ = -5.168870 A ₁ = −1.16400 × 10 ⁻⁴ P ₁ = 4.0000 Second surface κ = −7.02230 × 10 ⁻¹ A ₁ = 6.393330 × 10 ⁻⁵ P ₁ = 4.0000 A ₂ = −8.95530 × 10 ⁻⁷ P ₂ = 6.00000 A ₃ = −1.37400 × 10 ⁻⁸ P ₃ = 8.00000 Third surface κ = −8.36770 × 10 ⁻¹ A ₁ = 5.07210 × 10 ^-3 P ₁ = 4.0000 A ₂ = 3.24900 × 10 ^-4 P ₂ = 6.0000 A ₃ = 2.13140 × 10 ^-5 P ₃ = 8.00000 A _{4 ^{= -3.96600 × 10 -6 P 4 =}} 10.0000 fourth surface _{κ = -2.25490 × 10 A 1 =} 1.27980 × 10 -2 P 1 = 4.0000 A 2 = -5.04840 × 10 ⁻³ P ₂ = 6.00000 A ₃ = 1.03830 × 10 ⁻³ P ₃ = 8.00000 A ₄ = −9.09999 × 10 ⁻⁵ P ₄ = 1.0000

The fifteenth embodiment is an example of a biconvex lens whose coupling lens is made of resin and whose both surfaces are aspherical. The focal length is long at the same magnification Mc as in the fourteenth embodiment. The aberration diagram is shown in FIG. The all optical system is a combination of this coupling lens and the resin objective lens of the first embodiment, and the magnifications M and Mt have the same specifications as the fourteenth embodiment. FIG. 41 shows the optical path diagram and FIG. 43 shows the temperature characteristic. In this embodiment, Dco = 10 Mt.M.Fcp / F = -0.07697. Here, since the resin coupling lens is a single lens, Fc = Fcp. The change in wavefront aberration due to temperature change is 0.006 when the temperature rises 30 degrees from the reference design temperature.
It is quite small, λ.

Example 16 Coupling lens Fc = 19.476 Mc = −1.33 Uc = 80.168 T = −33.33 NAo: 0.067 λ = 635 nm i ri di ni 1 21.378 2.00 1.49810 2 -17.208 44.838 Aspherical surface data First surface κ = -3.282840 Second surface κ = -5.250210 × 10 ^-1 A ₁ = 2.60800 × 10 ⁻⁵ P ₂ = 4.0000 All optical systems Ft = 3.812 Mt = −1 / 9 M = + 1/12 U = 43.100 T = −33.330 NA: 0. 6 λ = 635 nm i ri di ni 1 21.378 2.00 1.49810 2 -17.208 3.00 3 2.165 2.60 1.49810 4 -8.480 1.57 5 ∞ 0.60 1 0.58000 6 ∞ aspherical surface data 1st surface κ = −3.282840 2nd surface κ = −5.250210 × 10 ⁻¹ A ₁ = 2.60800 × 10 ^-5 P ₂ = 4.0000 Third surface κ = −8.367770 × 10 ⁻¹ A ₁ = 5.07210 × 10 ^-3 P ₁ = 4.0000 A ₂ = 3.24900 × 10 ^-4 P ₂ = 6.0000 A ₃ = 2.13140 × 10 ^-5 P ₃ = 8.00000 A _{4 ^{= -3.96600 × 10 -6 P 4 =}} 10.0000 fourth surface _{κ = -2.25490 × 10 A 1 =} 1.27980 × 10 -2 P 1 = 4.0000 A 2 = -5.04840 × 10 ⁻³ P ₂ = 6.00000 A ₃ = 1.03830 × 10 ⁻³ P ₃ = 8.00000 A ₄ = −9.09999 × 10 ⁻⁵ P ₄ = 1.0000

The sixteenth embodiment is an example of a biconvex lens whose coupling lens is made of resin and whose both surfaces are aspherical surfaces, and its aberration diagram is shown in FIG. Further, the all-optical system is a combination of this coupling lens and the resin objective lens of Example 1, and its optical path diagram is shown in FIG. 44 and its temperature characteristic is shown in FIG. In this embodiment, Dco = 3 Mt.M.Fcp / F = -0.04783. Here, since the resin coupling lens is a single lens, Fc = Fcp. The change in wavefront aberration due to temperature change is 0.016 when the temperature rises 30 degrees from the reference design temperature.
λ.

Example 17 Coupling lens Fc = 12.069 Mc = −0.83 Uc = 49.303 T = −25.923 NA: 0.1 λ = 635 nm i ri di ni 1 10.762 2.00 1.49810 2 −12.777 21.38 Aspheric surface data First surface κ = −4.446790 A ₁ = 3.01970 × 10 ⁻⁴ P ₁ = 4.0000 Second surface κ = −8.107730 × 10 ^-1 A ₁ = 1.59270 × 10 ⁻⁴ P ₁ = 4.0000 A ₂ = 4.39000 × 10 ⁻⁶ P ₂ = 6.00000 A ₃ = −8.09630 × 10 ⁻⁸ P ₃ = 8.00000 All Optical system Ft = 4.26969 Mt = -1 / 6 M = + 1/5 U = 35.693 T = −25.923 NA: 0.6 λ = 635 nm i ri di ni 1 10.762 2.00 1. 49810 2 -12.777 3.00 3 2.304 2.60 1.49810 4 179.922 1.57 5 ∞ 0.60 1.58000 6 ∞ Aspheric data 1st surface κ = -4.47690 A ₁ = 3.01970 × 10 ⁻⁴ P ₁ = 4.0000 Second surface κ = −8.10730 × 10 ⁻¹ A ₁ = 1.59270 × 10 ⁻⁴ P ₁ = 4.0000 A ₂ = 4.39000 × 10 ⁻⁶ P ₂ = 6.0000 A ₃ = −8.09630 × 10 ⁻⁸ P ₃ = 8.00000th 3 planes κ = −8.28170 × 10 ⁻¹ A ₁ = 5.44430 × 10 ⁻³ P ₁ = 4.0000 A ₂ = 4.26990 × 10 ⁻⁴ P ₂ = 6.00000 A ₃ = 2.89730 × 10 ⁻⁵ P ₃ = 8.00000 A ₄ = 3.555070 × 10 ⁻⁶ P ₄ = 1.0000 4th surface κ = −2.25490 × 10 A ₁ = 7.41970 × 10 ⁻³ P ₁ = 4.0000 A ₂ = −1.45950 × 10 ^-3 P ₂ = 6.0000 A ₃ = 1.25000 × 10 ^-5 P ₃ = 8.0000 A ₄ = 2.08630 × 10 ^-5 P ₄ = 1.0000

The seventeenth embodiment is an example of a biconvex lens in which the coupling lens is made of resin and whose both surfaces are aspherical, and its aberration diagram is shown in FIG. Further, the all-optical system is a combination of this coupling lens and the resin objective lens of Example 2, and its optical path diagram is shown in FIG. 47 and its temperature characteristic is shown in FIG. In this embodiment, Dco = 3 Mt.M.Fcp / F = -0.08767. Here, since the resin coupling lens is a single lens, Fc = Fcp. The change in wavefront aberration due to temperature change is 0.014 when the temperature rises 30 degrees from the reference design temperature.
λ, which is slightly larger than that of the objective lens alone. This is because the power of the coupling lens becomes large and the change in the wavefront aberration of the coupling lens itself due to the temperature change becomes so large that it cannot be ignored.

Example 18 Coupling lens Fc = 15.886 Mc = -2.50 Uc = 78.482 T = -21.342 NAo: 0.1 λ = 635 nm i ri di ni 1 22.844 2.00 1.49810 2 -11.754 55.140 Aspheric surface data First surface κ = -4.52490 A ₁ = -1.69110 × 10 ^-5 P ₁ = 4.0000 Second surface κ = -9.02040 × 10 ^-1 A ₁ = 1.60060 × 10 ⁻⁵ P ₁ = 4.0000 A ₂ = −8.69710 × 10 ⁻⁸ P ₂ = 6.00000 A ₃ = −1.73030 × 10 ⁻¹⁰ P ₃ = 8.00000 All optical systems Ft = 3.734 Mt = -1 / 6 M = + 1/15 U = 31.112 T = -21.342 NA: 0.6 λ = 635 nm i ri di ni 1 22.844 2.00 1 .49810 2 -11.754 3.00 3 2.130 2.60 1.49810 4 8.0053 1.57 5 ∞ 0.60 1.58000 6 ∞ Aspherical data 1st surface κ = −4.52490 A ₁ = −1.69110 × 10 ⁻⁵ P ₁ = 4.0000 Second surface κ = −9.02040 × 10 ⁻¹ A ₁ = 1.60060 × 10 ⁻⁵ P ₁ = 4.0000 A ₂ = −8.69710 × 10 ⁻⁸ P ₂ = 6.00000 A ₃ = −1.73030 × 10 ⁻¹⁰ P ₃ = 8.00000 Third surface κ = -5.06170 x 10 ^-1 A ₁ = 8.72330 × 10 ⁻⁴ P ₁ = 4.0000 A ₂ = 8.86100 × 10 ⁻⁵ P ₂ = 6.00000 A ₃ = 7.50840 × 10 ⁻⁶ P ₃ = 8.00000 A _{4 ^{= -1.22820 × 10 -6 P 4 =}} 10.0000 fourth surface _{κ = -2.25510 × 10 A 1 =} 1.31840 × 10 -2 P 1 = 4.0000 A 2 = -3.62900 × 10 ⁻³ P ₂ = 6.00000 A ₃ = 6.28660 × 10 ⁻⁴ P ₃ = 8.00000 A ₄ = −4.999790 × 10 ⁻⁵ P ₄ = 10.00000

The eighteenth embodiment is an example of a biconvex lens whose coupling lens is made of resin and whose both surfaces are aspherical, and its aberration diagram is shown in FIG. Further, the all-optical system is a combination of this coupling lens and the resin objective lens of Example 3, and its optical path diagram is shown in FIG. 50 and its temperature characteristic is shown in FIG. In this embodiment, Dco = 3 Mt.M.Fcp / F = -0.04776. Here, since the resin coupling lens is a single lens, Fc = Fcp. The change in wavefront aberration due to temperature change is 0.017 when the temperature rises 30 degrees from the reference design temperature.
λ. Although all of the coupling lens examples from Example 9 to Example 18 described above are made of resin, similar results can be obtained even in the case of glass, except for the temperature characteristics of the optical system.

[0074]

According to the present invention, as can be seen in each of the embodiments, even when a resin objective lens is used under a high NA, a change in wavefront aberration due to a temperature change can be ensured with a lens tolerance. An optical system that is suppressed to the extent possible is obtained. Moreover, even with the expectation that the recording density will be further increased in the future,
Shortening the wavelength of light used up to a wavelength of 450 nm, NA 0.75
It has become clear that it is possible to increase the NA of the lens to some extent.

[Brief description of the drawings]

FIG. 1 is an optical path diagram of Example 1 of an objective lens in a recording / reproducing optical system of an optical information recording medium of the present invention.

FIG. 2 is an aberration diagram of a spherical aberration and a sine condition of the objective lens in the first example.

FIG. 3 is a temperature characteristic diagram of the objective lens of the first embodiment.

FIG. 4 is an optical path diagram of Example 2 of the objective lens in the recording / reproducing optical system of the optical information recording medium of the present invention.

FIG. 5 is an aberration diagram of a spherical aberration and a sine condition of the objective lens in the second example.

FIG. 6 is a temperature characteristic diagram of the objective lens according to the second embodiment.

FIG. 7 is an optical path diagram of Example 3 of the objective lens in the recording / reproducing optical system of the optical information recording medium of the present invention.

FIG. 8 is an aberration diagram of a spherical aberration and a sine condition of the objective lens according to the third example.

FIG. 9 is a temperature characteristic diagram of the objective lens according to the third embodiment.

FIG. 10 is an optical path diagram of Example 4 of the objective lens in the recording / reproducing optical system of the optical information recording medium of the present invention.

FIG. 11 is an aberration diagram of a spherical aberration and a sine condition of the objective lens in the fourth example.

FIG. 12 is a temperature characteristic diagram of the objective lens according to the fourth embodiment.

FIG. 13 is an optical path diagram of Example 5 of the objective lens in the recording / reproducing optical system of the optical information recording medium of the present invention.

FIG. 14 is an aberration diagram of a spherical aberration and a sine condition of the objective lens in the fifth example.

FIG. 15 is a temperature characteristic diagram of the objective lens of the fifth embodiment.

FIG. 16 is an optical path diagram of Example 6 of the recording / reproducing optical system of the optical information recording medium of the present invention.

FIG. 17 is a temperature characteristic diagram of the optical system of Example 6 described above.

FIG. 18 is an optical path diagram of Example 7 of the recording / reproducing optical system of the optical information recording medium of the present invention.

FIG. 19 is a temperature characteristic diagram of the optical system of Example 7 described above.

FIG. 20 is an optical path diagram of Example 8 of the objective lens in the recording / reproducing optical system of the optical information recording medium of the present invention.

FIG. 21 is an aberration diagram of spherical aberration and sine conditions of the objective lens in Example 8 described above.

FIG. 22 is a temperature characteristic diagram of the objective lens according to the eighth embodiment.

FIG. 23 is an optical path diagram of Example 9 in the recording / reproducing optical system of the optical information recording medium of the present invention.

FIG. 24 is an aberration diagram of spherical aberration and sine conditions of the coupling lens of Example 9 described above.

FIG. 25 is a temperature characteristic diagram of the optical system of Example 9 above.

FIG. 26 is an optical path diagram of Example 10 in the recording / reproducing optical system of the optical information recording medium of the present invention.

FIG. 27 is an aberration diagram of a spherical aberration and a sine condition of the coupling lens of Example 10 described above.

28 is a temperature characteristic diagram of the optical system of Example 10 described above. FIG.

FIG. 29 is an optical path diagram of Example 11 in the recording / reproducing optical system of the optical information recording medium of the present invention.

FIG. 30 is an aberration diagram of spherical aberration and sine conditions of the coupling lens of Example 11 described above.

FIG. 31 is a temperature characteristic diagram of the optical system of Example 11 described above.

32 is an optical path diagram of Example 12 in the recording / reproducing optical system of the optical information recording medium of the present invention. FIG.

FIG. 33 is an aberration diagram of spherical aberration and sine conditions of the coupling lens of Example 12 described above.

FIG. 34 is a temperature characteristic diagram of the optical system of Example 12 described above.

FIG. 35 is an optical path diagram of Example 13 in the recording / reproducing optical system of the optical information recording medium of the present invention.

FIG. 36 is an aberration diagram of spherical aberration and sine conditions of the coupling lens of Example 13 described above.

FIG. 37 is a temperature characteristic diagram of the optical system of Example 13 described above.

FIG. 38 is an optical path diagram of Example 14 of the recording / reproducing optical system of the optical information recording medium of the present invention.

FIG. 39 is an aberration diagram of a spherical aberration and a sine condition of the coupling lens of Example 13 described above.

FIG. 40 is a temperature characteristic diagram of the optical system of Example 14 described above.

FIG. 41 is an optical path diagram of Example 15 of the recording / reproducing optical system of the optical information recording medium of the present invention.

42 is an aberration diagram of spherical aberration and sine conditions of the coupling lens of Example 15 described above.

FIG. 43 is a temperature characteristic diagram of the optical system of Example 15 described above.

FIG. 44 is an optical path diagram of Example 16 in the recording / reproducing optical system of the optical information recording medium of the present invention.

FIG. 45 is an aberration diagram of a spherical aberration and a sine condition of the coupling lens of Example 16 described above.

FIG. 46 is a temperature characteristic diagram of the optical system of Example 16 described above.

FIG. 47 is an optical path diagram of Example 17 of the recording / reproducing optical system of the optical information recording medium of the present invention.

FIG. 48 is an aberration diagram of a spherical aberration and a sine condition of the coupling lens of Example 17 described above.

FIG. 49 is a temperature characteristic diagram of the optical system of Example 17 described above.

FIG. 50 is an optical path diagram of Example 18 in the recording / reproducing optical system of the optical information recording medium of the present invention.

FIG. 51 is an aberration diagram of spherical aberrations and sine conditions of the coupling lens of Example 18 described above.

52 is a temperature characteristic diagram of the optical system of Example 18 described above. FIG.

Claims (43)

[Claims] 1. A recording / reproducing optical system, comprising at least a light source, a coupling means, and an objective lens, for recording and / or reproducing information on an optical information recording medium, wherein the coupling means is emitted from a light source. The objective lens that converts the divergent light into convergent light and further converges the convergent light to form an image on the optical information medium has a lateral magnification M within the Marechal limit within the following range in which the wavefront aberration is minimum. Recording / reproducing optical system for optical information recording medium characterized by: 0.05 ≤ M, where M: lateral magnification of objective lens alone 2. The recording / reproducing optical system for an optical information recording medium according to claim 1, wherein the objective lens is movable in at least an optical axis direction. 3. The recording / reproducing of the optical information recording medium according to claim 1, wherein the following condition is satisfied, where Dco is the distance between the image side surface of the coupling means and the light source side surface of the objective lens. Optical system for use 0.1 ≤ Dco / F ≤ 5.0 where F: focal length of objective lens 4. The recording / reproducing of the optical information recording medium according to claim 1, wherein the following condition is satisfied, where Dco is the distance between the image side surface of the coupling means and the light source side surface of the objective lens. Optical system 1.0 ≤ Dco / F ≤ 5.0 5. The recording / reproducing of the optical information recording medium according to claim 1, wherein the following condition is satisfied, where Dco is the distance between the image side surface of the coupling means and the light source side surface of the objective lens. Optical system 1.0 ≤ Dco / F ≤ 3.0 6. The recording / reproducing optical system for an optical information recording medium according to claim 1, wherein the following condition is satisfied: 0.05 ≦ M ≦ 0.23 NA · (1-M) ≦ 0.65 0.48 ≦ NA where NA is the numerical aperture of the optical system on the image side. 7. The recording / reproducing optical system for an optical information recording medium according to claim 1, wherein the following condition is satisfied: 0.05 ≦ M ≦ 0.125 8. The recording / reproducing optical system NA. (1−M) ≦ 0.65 of the optical information recording medium according to claim 7, wherein the objective lens is made of resin and satisfies the following conditions. 9. The recording / reproducing optical system for an optical information recording medium according to claim 1 or 6, characterized by satisfying the following conditions: 0.65 ≤ NA ≤ 0.8 0.125 ≤ M ≤ 0 .23 10. The optical system for recording / reproducing an optical information recording medium according to claim 9, wherein the objective lens is made of resin. 11. The recording / reproducing optical system (1-M) · F ≦ 6.0 of the optical information recording medium according to claim 1, wherein the following condition is satisfied. 12. The recording / reproducing optical system for an optical information recording medium according to claim 1, wherein the coupling means is a coupling lens which is a refractive optical system. 13. The coupling lens comprises one or a plurality of spherical lenses.
Optical system for recording / reproducing optical information recording medium 14. The recording / reproducing optical system for an optical information recording medium according to claim 12, wherein at least one surface of the coupling lens is an aspherical surface. 15. The recording / reproducing of the optical information recording medium according to claim 12, wherein the objective lens is made of resin, and at least one coupling lens is also made of resin having a positive refractive power. Optical system 16. The recording / reproducing optical system for an optical information recording medium according to claim 15, wherein at least one surface of the coupling lens is an aspherical surface. 17. The recording / reproducing optical system for an optical information recording medium according to claim 16, wherein the coupling lens is a resin single lens. 18. The coupling lens according to claim 15, wherein the coupling lens satisfies the following conditions.
7. Optical system for recording / reproducing optical information recording medium according to any one of 7-0.10≤Mt.M.Fcp / F≤-0.04 where Mt: lateral magnification of entire optical system Fcp: resin in coupling lens Lens focal length 19. The optical system for recording / reproducing an optical information recording medium according to claim 12, wherein the optical system satisfies the following condition: 0.06 ≦ | Mt | · NA ≦ 0.21 20. The optical system for recording / reproducing an optical information recording medium according to claim 12, wherein the optical system satisfies the following condition: 0.06 ≦ | Mt | · NA ≦ 0.12 21. The optical system for recording / reproducing an optical information recording medium according to claim 12, wherein the optical system satisfies the following condition: 0.12 ≦ | Mt | · NA ≦ 0.21 22. When a convergent light beam is incident, the wavefront aberration is minimized, the lateral magnification M and the numerical aperture NA which are within the Marechal's limit are in the following ranges, and at least the surface on the light source side is an aspherical surface. Objective lens characterized by being a lens 0.05 ≤ M 0.3 ≤ NA 23. The objective lens according to claim 22, wherein the convergent light beam is converged at one point at a diffraction limited spot when the objective lens is not provided. 24. The objective lens according to claim 22, wherein the objective lens is a double-sided aspherical single lens. 25. The objective lens according to claim 22, wherein the following condition is satisfied: −0.25 ≦ F · (n−1) / r ₂ ≦ 0.7, where n: of the material forming the lens. Refractive index r ₂ : radius of curvature of vertex of image-side surface of lens 26. The objective lens according to claim 22 or 25, characterized in that the following condition is satisfied: −0.045 ≦ x ₂ · (n−1) / {F · (N
A) ² } ≤ 0.1 where NA is the image-side numerical aperture of the objective lens x ₂ : The outermost periphery of the effective diameter of the axial ray on the image-side surface of the lens (the image-side surface on which the peripheral rays of the NA are incident) The difference in the optical axis direction between the (top position) and the apex of the surface is positive when the direction further away from the optical axis is displaced toward the image side. 27. Claim 22, characterized by satisfying the following condition, according to claim 25 or claim any of the objective lens of claim _{26 -0.005 ≦ △ 2 · (n} -1), 3 / { F ・ (NA)
⁴ } ≤ 0.018 where Δ ₂ : the aspherical surface and the apex of the surface at the outermost periphery of the effective diameter of the axial ray on the image side surface of the lens (the position on the image side surface where the peripheral ray of NA is incident) The difference in the direction of the optical axis from the reference spherical surface having the radius of curvature r ₂ is positive when the direction further away from the optical axis is displaced toward the image side. 28. The objective lens (1-M) · F ≦ 6.0 for recording / reproducing of the optical information recording medium according to claim 22, wherein the following condition is satisfied. 29. The objective lens for recording / reproducing of an optical information recording medium according to claim 22, wherein the following condition is satisfied: 0.05 ≦ M ≦ 0.23 NA · (1-M) ≦ 0.65 0.48 ≤ NA 30. The objective lens for recording / reproducing of an optical information recording medium according to claim 22, wherein the following condition is satisfied: 0.05 ≦ M ≦ 0.125 31. An objective lens for recording / reproducing of an optical information recording medium according to claim 30, which is made of resin and satisfies the following condition: NA · (1-M) ≦ 0.65 0.48 ≦ NA 32. The objective lens for recording / reproducing of an optical information recording medium according to claim 30, characterized by satisfying the following conditions: 0.65 ≤ NA ≤ 0.8 0.125 ≤ M ≤ 0.23 33. A recording / reproducing objective lens for an optical information recording medium according to claim 32, which is made of resin. 34. A coupling lens arranged between a light source and an objective lens which has a minimum wavefront aberration when convergent light is incident and which forms an image on an optical information recording medium within the Marechal limit, and which is emitted from the light source. A diverging light beam is converted into a convergent light beam, and the following conditions are satisfied, and a recording / reproducing coupling lens for an optical information recording medium -7.0 ≤ Mc ≤ -0.5 0.06 ≤ NAo ≤ 0 .21 where Mc: lateral magnification of image side of coupling lens with respect to light source side NAo: numerical aperture of light source side 35. The recording / reproducing coupling lens of the optical information recording medium according to claim 34, wherein the objective lens satisfies the following condition: 0.05 ≦ M 0.3 ≦ NA 36. A recording / reproducing coupling lens for an optical information recording medium according to claim 34, comprising one or a plurality of spherical systems. 37. A coupling lens for recording / reproducing an optical information recording medium according to claim 34, wherein at least one surface is composed of one lens having an aspherical surface. 38. A coupling lens for recording / reproducing an optical information recording medium according to claim 37, which is made of glass. 39. A recording / reproducing coupling lens for an optical information recording medium according to claim 37, which is made of resin. 40. A coupling lens for recording / reproducing of an optical information recording medium according to claim 37, characterized in that both surfaces are aspherical surfaces. 41. A recording / reproducing coupling lens for an optical information recording medium according to claim 37, characterized in that both surfaces are convex. 42. A recording / reproducing coupling lens for an optical information recording medium according to claim 37, wherein the surface on the light source side is a meniscus lens having a convex surface. 43. A recording / reproducing coupling lens for an optical information recording medium according to claim 37, wherein the surface on the light source side is a meniscus lens having a concave surface.