JP2003232997A - Joint objective lens, objective optical system for optical disc, and method of manufacturing joint objective lens - Google Patents

Abstract

(57) [Problem] To provide a cemented objective lens that can be easily manufactured regardless of the surface shape of the cemented surface and without requiring the edge surface to be secured. A cemented objective lens (20) has a mold on the side of a light source of a first lens (21) placed on a joint surface (22a) of a second lens (22), which is a resin lens formed in advance, and photocuring is performed in a space formed thereby. It is formed by injecting and hardening a conductive resin or a thermosetting resin.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cemented objective lens obtained by cementing a plurality of lenses made of different media, an optical system for an optical disc including the cemented objective lens mounted on an optical head of an optical disc drive apparatus, and The present invention relates to a method for manufacturing the above-mentioned cemented objective lens.

[0002]

2. Description of the Related Art For example, an optical head of an optical information recording / reproducing apparatus for reading information from or recording information on an optical disk such as a DVD (digital versatile disk), a CD (compact disk) and a CD-R. As an objective optical system for an optical disc used for, a cemented objective lens configured by bonding a plurality of lenses made of media having different wavelength dispersions to each other to correct chromatic aberration is generally adopted. . What has been conventionally known as such a cemented objective lens is one in which a glass lens and a glass lens are bonded together.

[0003]

However, when the numerical aperture of the cemented objective lens is increased to reduce the spot diameter, or when laser light in the short wavelength region from blue to ultraviolet is used, chromatic aberration is corrected. Therefore, even if the cemented lens is a spherical surface, the chromatic aberration of spherical aberration remains large if the cemented surface remains a spherical surface, so that the practically usable wavelength width becomes narrow. In order to deal with this, it is necessary to make the cemented surfaces aspherical, but it is a very difficult task to process the cemented surfaces of the lenses into the same shape on the front and back so that the surfaces contact each other without any gap. In particular, it is extremely difficult to grind a glass lens with a precise aspherical shape. Moreover, the accuracy required for the centering work becomes extremely high when the aspherical surfaces processed separately in this way are bonded together. Therefore, in reality, its implementation is difficult.

In the diffractive lens, a hybrid aspherical surface is formed by adding a photocurable resin having an aspherical base shape or a diffractive surface by a thermosetting resin on the lens surface of a glass lens processed into a spherical shape. Has been proposed. However, it is difficult to apply the configuration as it is to the cemented objective lens as described above. This is because, in a cemented objective lens having a large resin volume, distortion and peeling may occur due to the difference in shrinkage amount between the glass and the resin having different thermal shrinkages during cooling.

The present invention has been made in view of the above problems, and the problem is easily produced regardless of the surface shape of the joint surface and without the need to secure the edge surface. Is to provide a cemented objective lens that can

[0006]

The cemented objective lens according to the first aspect of the present invention devised to solve the above-mentioned problems is a cemented objective lens composed of a plurality of lenses that are in contact with each other via a cemented surface. The plurality of lenses are each made of a resin, and one of the lenses is made of a photocurable resin.
The cemented objective lens according to the second aspect of the present invention is a cemented objective lens composed of a plurality of lenses that are in contact with each other via a cemented surface, and the plurality of lenses are each made of resin, and The two lenses are formed of a thermosetting resin.

Among a plurality of lenses constituting the cemented objective lens according to the present invention, a lens formed of a thermosetting resin or a photo-curable resin is a "first lens", and a cemented surface for the first lens. The lenses that are in contact with each other via the above will be referred to as "second lenses", respectively. In the cemented objective lens according to the present invention, after the second lens is formed by injection molding or the like, the second lens is set in the mold. Along with
The thermosetting resin or the photocurable resin, which has fluidity at room temperature, may be put into the space left in the mold and the resin may be cured. That is, since the cemented surface of the first lens is molded on the cemented surface of the second lens,
It is formed without needing to be processed into the same shape as the cemented surface of the second lens in advance, nor to be centered with respect to the cemented surface of the second lens. Therefore, the shape of the joint surface is not limited, and any complicated shape can be adopted. For example, the shape of the cemented surface may be an aspherical shape for correcting the chromatic aberration of the cemented objective lens as a whole.

Further, in the cemented objective lens according to the present invention, the cemented surfaces of the first and second lenses can be cemented together without using an adhesive, so that the thickness of the adhesive layer is not uneven. Problems can also be avoided.

Further, the cemented objective lens according to the present invention is
Since both the first and second lenses are made of resin, the expansion coefficients of both lenses are the same as each other or only slightly different. Therefore, regardless of the volume of the first lens, when the temperature changes, the cemented surface of the first lens contracts or expands at substantially the same rate as the cemented surface of the second lens. Therefore, defects such as distortion and peeling do not occur between both lenses.

Since the first lens is not formed by injection molding, even if the first lens has a positive refractive power, a gate is installed at the edge of the first lens. There is no need to secure a width for. Therefore, the edge of the first lens can be made as narrow as possible, so that the inter-plane distance of the first lens is minimal, and therefore the back focus can be made relatively long.

Chromatic aberration can be satisfactorily corrected by devising a cemented surface and forming a diffractive ring zone structure on a pair of external contact surfaces (surfaces in contact with air) of the cemented objective lens. By the way, if it is attempted to correct the chromatic aberration only with such a diffractive ring zone structure, the numerical aperture is high (for example, when NA exceeds 0.6) or the wavelength used is in the short wavelength region from blue to ultraviolet. If (for example, 45
(When it is 0 nm or less), the diffraction ring zone structure formed on the surface is inevitably narrow in zone width and has a large number of zones. Therefore, when attempting to form such a diffractive ring zone structure by injection molding of glass or resin, the transferability of the edge portion often becomes insufficient due to the low fluidity of these materials. In addition, the heat shrinkage of the lens that occurs during cooling from the molding temperature to room temperature may cause the edge to bite into the mold, resulting in sagging or cracking of the diffractive ring zone, which results in high diffraction efficiency. Will be difficult. On the other hand, the first aspect of the present invention
If such a diffractive ring structure is formed on the external contact surface of the lens, the thermosetting resin or the photocurable resin, which is the material of the first lens, has a relatively high fluidity at room temperature before curing. Therefore, it is possible to obtain a good diffractive ring zone structure by being well adapted to the type of the diffractive structure. In particular, if a photocurable resin that can be cured at room temperature is used, the problems associated with heat shrinkage will not occur.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of an optical system for an optical disk including a cemented objective lens according to the present invention will be described below.

FIG. 1 shows the structure of an optical pickup of an optical disk drive device equipped with an optical system for an optical disk according to this embodiment. This optical pickup has a function of converging laser light emitted from the semiconductor laser 12, which is a light emitting element, onto the signal recording surface of the optical disc D.

More specifically, the laser light emitted from the semiconductor laser 12 as divergent light is reflected by the prism 13
Of the cemented objective lens 2
It is converged on the signal recording surface of the optical disc D by 0. When the optical disc D is a magneto-optical disc and information is recorded on the optical disc D, the substance on the signal recording surface is heated by the converged laser beam and applied by a magnetic coil (not shown). The material is magnetized in the magnetization direction. When the optical disc D is a CD-R, the converged light forms dots on the signal recording surface. On the other hand, at the time of reading information from the optical disc D, the reflected light modulated according to the state of the signal recording surface re-enters the cemented objective lens 20 and returns to the collimator lens 14 as parallel light, which is converged by this collimator lens. , Passes through the separation surface of the prism 13 and enters the detector 11. The detector 11 photoelectrically converts the reflected light according to the modulation state of the reflected light and outputs a detection signal indicating the modulation state. After that, the original information recorded on the signal recording surface is reproduced by a detection circuit (not shown).

The cemented objective lens 20 is arranged in order from the light source side.
A first lens 21, which is a biconvex lens having a positive refractive power,
The second lens 22 is a rotationally symmetric lens having a concave surface facing the light source side and is a negative meniscus lens. The disk side surface of the first lens 21 and the light source side surface of the second lens 22 are joined together. Portions of the first lens 21 on the disk side surface and the second lens 22 on the light source side surface that are in contact with each other (hereinafter, referred to as “bonding surfaces”) have the same shape on the front and back sides. Further, the edge surface of the first lens 21 does not exist at all because the first lens 21 is a positive lens, or is extremely narrow as compared with the second lens 22 which is a negative lens. Further, the chromatic dispersion of the medium of the first lens 21 and the chromatic dispersion of the medium of the second lens 22 are different from each other, and since the two lenses 21 and 22 are cemented to each other, the chromatic aberration of the entire cemented objective lens 20. Has been corrected.

A method of manufacturing the cemented objective lens 20 will be described with reference to FIG. FIG. 2 schematically shows a molding apparatus for forming the first lens 21 on the cemented surface of the second lens 22, which is previously formed by injection molding, grinding, or the like, with the photo-curable resin. In FIG. 2, the second lens 22 is coaxially housed in a cylindrical outer frame 31 having an inner diameter slightly larger than its own outer diameter (diameter of the edge surface).

In the outer frame 31, the second lens 22
The glass mold 32 having the same diameter as that of the second lens 22 is in contact with the disk side surface (lower surface in FIG. 2). Since the upper surface of the glass mold 32 is not used as a mold for forming a surface, it does not necessarily have to have the same shape as the disk side surface of the second lens 22, but for precise lens formation. It is desirable that the second lens 22 is in close contact with the side surface of the disk.

The above-mentioned joining surface 22a is coaxially and integrally formed in advance in the center or the entire area of the light source side surface of the second lens 22 by injection molding as described above. The outer edge of the bonding surface 22a is in contact with the outer edge of the mold 33, which is the mold on the light source side surface of the first lens 21, over the entire circumference thereof. The mold 33 has a cylindrical shape as a whole, and a mold having the same shape as the light source side surface of the first lens 21 is formed on the tip surface thereof. The light source side surface of the first lens 21 is, of course, coaxial with the second lens 22. Therefore, the mold 33 needs to be coaxially arranged in the outer frame 31. To position the mold 33,
The outer peripheral surface of the mold 33, the inner peripheral surface of the outer frame 31, and the second lens 22.
When there is a gap between the light source side surface of the second lens 22 (that is, when the joint surface 22a has a smaller diameter than the outer edge of the light source side surface of the second lens 22), the cylindrical spacer 34 for filling this gap is It is inserted between the outer frame 31 and the mold 33.

A joint surface 2 between the mold 33 and the second lens 22.
A photo-curable resin is filled in the space formed between 2a and 2a.

As described above, the photo-curable resin (UV-curable resin in this case) filled between the mold 33 and the joint surface 22a of the second lens 22 in a state where the parts of the molding apparatus are set. ) Is irradiated with ultraviolet light through the glass mold 32 and the second lens 22. Then, the photocurable resin reacts with this ultraviolet light and cures into a shape that is exactly the shape of the space filled with it.

When a thermosetting resin is used as the medium of the first lens 21, a mold made of a heat-resistant material such as metal or ceramic is used in place of the glass mold 32, and the mold of ultraviolet light is used. Instead, heat is applied to the thermosetting resin.

Next, three examples of the cemented objective lens 20 that can be used in the above-described embodiment will be presented.

[0023]

Example 1 FIG. 3 shows a cemented objective lens 20 and an optical disk D of Example 1. In the first embodiment, the medium of the first lens 21 is an ultraviolet curable resin (photocurable resin), and the medium of the second lens 22 is a thermoplastic resin. The specific numerical configuration of the cemented objective lens 20 of Example 1 is as follows.
It is shown in Table 1. In Table 1, the surface number 1 is the light source side surface (first surface: aspherical surface) of the first lens 21, and the surface number 2 is the joint surface 22a (second surface) of the first lens 21 and the second lens 22.
Surface: aspherical surface, surface number 3 is the disk side surface of the second lens 22 (third surface: aspherical surface), surface number 4 is the surface (flat surface) of the disk protective layer of the optical disk D, and surface number 5 is the information recording of the optical disk. The planes are shown respectively. In the table, λ is the design wavelength, and f is the focal length of the entire cemented objective lens 20 (unit: m
m), NA is the numerical aperture, r is the paraxial radius of curvature of each lens surface (unit: mm), and d is the lens thickness or lens spacing to the next surface.
(Unit: mm), n (405 nm) is the design wavelength 405 of the medium up to the next surface
The refractive index with respect to nm, n (406 nm), is the refractive index with respect to the wavelength (406 nm) deviated by 1 nm from the design wavelength of the medium up to the next surface.

Further, the shapes of the first surface to the third surface are the distance from the tangent plane on the optical axis to the target surface of the coordinate point on the target surface whose height from the optical axis is h (sag amount). ) Is X, the paraxial curvature of the plane of symmetry is C (= 1 / r), the conic coefficient is κ, the fourth order, 6
The aspherical coefficients of the 8th, 8th, 10th, and 12th orders are A ₄ , A ₆ , and A
₈ , A ₁₀ and A ₁₂ are represented by the following formula (1).

X = Ch ² / (1 + √ (1- (1 + κ) C ² h ² )) + A ₄ h ⁴ + A ₆ h ⁶ + A ₈ h ⁸ + A ₁₀ h ¹⁰ + A ₁₂ h ¹² …… (1) The coefficients applied to the 1st to 3rd surfaces are listed in Table 2.

[0026]

[Table 1] λ = 405nm f = 2.50mm NA 0.80 Surface number r d n (405nm) n (406nm)   1 1.585 2.30 1.50962 1.50947   2-2.230 0.50 1.62231 1.62190   3 −2.500 0.99   4 ∞ 0.10 1.62231 1.62190   5 ∞ −

[0027]

TABLE 2 Surface number 1 2 3 κ -0.65 0.00 0.00 A 4 -2.2100 × 10 -3 4.4000 × 10 -2 1.1200 × 10 -1 A 6 -4.2700 × 10 -4 2.2500 × 10 -3 -2.8600 × 10 - ² A ₈ 2.8 500 x 10 ^-5 -2.7000 x 10 ^-4 5.2 ₈ 10 x 10 ^-3 A ₁₀ 8.1 300 x 10 ^-5 0.0000 x 10 ⁺⁰ -1.2770 x 10 ^-4 A ₁₂ -7.4 150 x 10 ^-6 0.0000 x 10 ⁺⁰ -1.5987 × 10 ^-4 FIG. 4 shows various aberrations of the cemented objective lens 20 of the first example. 4A shows spherical aberration, and FIG. 4B shows spherical aberration and chromatic aberration at wavelengths of 405 nm and 406 nm. Graph
The vertical axis of (A) is the image height Y, and the vertical axis of (B) is the numerical aperture NA.
The horizontal axis of each graph shows the amount of occurrence of each aberration, and the unit is mm. As is clear from FIG. 4, in the cemented objective lens 20 of Example 1, the amounts of change in the refractive index of the first lens 21 and the second lens 22 that are in contact with each other via the cemented surface 22a, so-called wavelength dispersion, are different from each other. As a result, the axial chromatic aberration is sufficiently reduced. Further, since the cemented surface 22a is an aspherical surface, the difference in spherical aberration depending on the wavelength is small.

[0028]

Second Embodiment A cemented objective lens 20 of a second embodiment is a diffractive ring zone in which the paraxial radius of curvature of the first surface (the light source side surface of the first lens 21) of the cemented objective lens 20 of the first embodiment described above is changed. It has a configuration equivalent to that of adding a shape. Example 1
Table 3 shows a specific numerical configuration of the cemented objective lens 20. The aspherical coefficients of the first to third surfaces are
It is shown in Table 4. The meanings of the symbols in Tables 3 and 4 are exactly the same as those in the above-described first embodiment. However, the shape specified for the first surface by the numerical values shown in these tables is the base curve shape.

[0029]

[Table 3] λ = 405nm f = 2.50mm NA 0.80 Surface number r d n (405nm) n (406nm)   1 1.728 2.30 1.50962 1.50947   2-2.230 0.50 1.62231 1.62190   3 −2.500 0.99   4 ∞ 0.10 1.62231 1.62190   5 ∞ −

[0030]

[Table 4] Surface number 1 2 3 κ -0.50 0.00 0.00 A ₄ -2.2525 × 10 ^-3 4.4000 × 10 ^-2 1.1200 × 10 ^-1 A ₆ 1.2060 × 10 ^-3 2.2500 × 10 ^-3 -2.8 600 × 10 ^-2 A ₈ -5.8420 x 10 ^-4 -2.7000 x 10 ^-4 5.2 810 x 10 ^-3 A ₁₀ 2.5956 x 10 ^-4 0.0000 x 10 ⁺⁰ -1.2770 x 10 ^-4 A ₁₂ -2.4 805 x 10 ^-5 0.0000 x 10 ⁺⁰ -1.5987 × 10 ^-4 The added amount of optical path length (added amount at the height h from the optical axis) due to the diffractive ring structure added to the first surface is the n-th order (even order)
Optical path difference function coefficient of P _n , design wavelength of λ, second order, fourth order,
The 6th, 8th and 10th order optical path difference function coefficients are P ₂ , P ₄ and
P ₆ , P ₈ and P ₁₀ are represented by the optical path difference function φ (h) shown in the following equation (2).

Φ (h) = (P ₂ h ² + P ₄ h ⁴ + P ₆ h ⁶ + P ₈ h ⁸ + P ₁₀ h ¹⁰ ) × λ (2) Diffractive ring structure on the first surface The respective optical path difference function coefficients of are listed in Table 5.

[0032]

[Table 5] Surface number 1 P ₂ -3.2800 x 10 ⁺¹ P ₄ -2.3500 x 10 ⁺⁰ P ₆ 1.7580 x 10 ⁺⁰ P ₈ -9.4500 x 10 ^-1 P ₁₀ -3.0600 x 10 ^-2 Figure 5 shows 9 shows various aberrations of the cemented objective lens 20 of Example 2. FIG. 5A shows spherical aberration, and FIG. 5B shows spherical aberration and chromatic aberration at wavelengths of 405 nm and 406 nm. The meaning of each axis of each grab is the same as that of the first embodiment. As is clear from FIG. 5, the cemented objective lens 20 of Example 2 is
Since the light source side surface of the first lens 21 is a diffractive surface, the chromatic aberration is further reduced as compared with the first embodiment.

[0033]

Example 3 FIG. 6 shows a cemented objective lens 20 and an optical disk D of Example 3. In the third embodiment, the medium of the first lens 21 is an ultraviolet curable resin (photocurable resin), and the medium of the second lens 22 is also an ultraviolet curable resin.
That is, in the case of the present embodiment, only the second lens 22 is previously formed alone by UV irradiation in the glass mold,
After that, the first lens 21 is formed on the cemented surface 22 a of the second lens 22 by the method described with reference to FIG. 2. A diffractive ring zone shape is also added to the first surface of the cemented objective lens 20 (the light source side surface of the first lens 21) in the third embodiment, as in the second embodiment. Table 6 shows a specific numerical configuration of the cemented objective lens 20 of the third example. Table 7 shows the aspherical surface coefficients of the first surface to the third surface. However, the shape specified for the first surface by the numerical values shown in Tables 6 and 7 is the base curve shape. The optical path difference function coefficients of the diffractive ring structure on the first surface are listed in Table 8.

[0034]

[Table 6] λ = 405nm f = 1.25mm NA 0.76 Surface number r d n (405nm) n (406nm)   1 0.752 1.23 1.50962 1.50947   2-0.756 0.25 1.62522 1.62486   3-1.270 0.35   4 ∞ 0.10 1.62231 1.62190   5 ∞ −

[0035]

[Table 7] Surface number 1 2 3 κ -0.50 -1.00 0.00 A ₄ 1.9900 × 10 ^-3 4.0200 × 10 ^-1 5.1630 × 10 ^-1 A ₆ -2.3370 × 10 ^-2 -2.9000 × 10 ^-1 -6.1600 × 10 ^-1 A ₈ -4.24 30 x 10 ^-2 7.6000 x 10 ^-2 5.8750 x 10 ^-1 A ₁₀ 9.7900 x 10 ^-4 0.0000 x 10 ⁺⁰ -2.8 320 x 10 ^-1 A ₁₂ -1.0800 x 10 ^-1 0.0000 x 10 ^{+ 0} 6.4867 × 10 ^-2

[0036]

[Table 8] Surface number 1 P ₂ -3.2000 × 10 ⁺¹ P ₄ 0.0000 × 10 ⁺⁰ P ₆ -1.0000 × 10 ⁺¹ P ₈ 0.0000 × 10 ⁺⁰ P ₁₀ 0.0000 × 10 ⁺⁰ These Tables 6 to 7 The meanings of the respective symbols in are the same as those in the above-described first and second embodiments.

FIG. 7 shows various aberrations of the cemented objective lens 20 of Example 3. FIG. 7A shows spherical aberration, and FIG. 7B shows 405n.
The spherical aberration and the chromatic aberration of each wavelength of m and 406 nm are shown. The meaning of each axis of each grab is the same as that of the first embodiment. As is clear from FIG. 7 and Table 6, Example 3
In the cemented objective lens 20 of No. 2, since the second lens 22 is formed of an ultraviolet curable resin, as compared with the cemented objective lens 30 of Example 2 in which the same degree of chromatic aberration correction is performed,
The second lens 22 could be made thin.

[0038]

Example 4 FIG. 8 shows a cemented objective lens 20 and an optical disk D of Example 4. In Example 4, the medium of the first lens 21 is an ultraviolet curable resin (photocurable resin), the medium of the second lens 22 is a thermoplastic resin, and the design wavelength is 660 nm (red). There is. Table 8 shows a specific numerical configuration of the cemented objective lens 20 of Example 4. Table 9 shows the aspherical coefficients of the first to third surfaces.
Is shown in. The meaning of each symbol in Tables 8 and 9 is exactly the same as that of the above-described first embodiment. However, n (660 nm) in Table 8 is the refractive index for the design wavelength 660 nm of the medium up to the next surface, and n (661 nm) is the refractive index for the wavelength 1 nm away from the design wavelength of the medium up to the next surface (661 nm). is there.

[0039]

[Table 8] λ = 660nm f = 2.33mm NA 0.64 Surface number r d n (660nm) n (661nm)   1 1.450 1.50 1.49856 1.49853   2 -1.800 0.50 1.57961 1.57955   3 -2.800 0.92   4 ∞ 0.60 1.57961 1.57955   5 ∞ −

[0040]

[Table 9] Surface number 1 2 3 κ -0.50 0.00 0.00 A ₄ -3.2 480 × 10 ^-3 8.2000 × 10 ^-2 7.3 220 × 10 ^-2 A ₆ 2.5 250 × 10 ^-4 0.0000 × 10 ⁺⁰ 2.0 150 × 10 ^-2 A ₈ 1.4 200 × 10 ^-3 0.0000 × 10 ⁺⁰ -1.3700 × 10 ^-2 A ₁₀ 2.3060 × 10 ^-4 0.0000 × 10 ⁺⁰ 0.0000 × 10 ⁺⁰ A ₁₂ 0.0000 × 10 ⁺⁰ 0.0000 × 10 ⁺⁰ 0.0000 × 10 ^{+ 0} Figure 9 illustrates various aberrations of the cemented objective lens 20 of example 4. 9A shows spherical aberration, and FIG. 9B shows spherical aberration and chromatic aberration at wavelengths of 660 nm and 661 nm. The meaning of each axis of each grab is the same as that of the first embodiment. As is apparent from FIG. 9, the cemented objective lens 20 of Example 4 is
Since the aperture is lower and the design wavelength is longer than in Example 1, as compared with Example 1 in which other configurations are the same,
Furthermore, the chromatic aberration is low.

[0041]

As described above, according to the present invention,
The cemented objective lens can be easily manufactured regardless of the surface shape of the cemented surface and without the need to secure the edge surface.

[Brief description of drawings]

FIG. 1 is an optical configuration diagram of an optical pickup according to an embodiment of the present invention.

FIG. 2 is an explanatory view of a method for manufacturing a cemented objective lens.

FIG. 3 is a lens configuration diagram of a cemented objective lens of Example 1.

FIG. 4 shows various aberration diagrams of the cemented objective lens of Example 1.

FIG. 5 is a diagram of various types of aberration of the cemented objective lens of Example 2;

FIG. 6 is a lens configuration diagram of a cemented objective lens of Example 3;

FIG. 7 is a diagram showing various aberrations of the cemented objective lens in Example 3;

FIG. 8 is a lens configuration diagram of a cemented objective lens of Example 4;

FIG. 9 is a diagram showing various types of aberration of the cemented objective lens in Example 4;

[Explanation of symbols]

12 Semiconductor laser 20 cemented objective lens 21 First lens 22 Second lens D optical disc

Claims (14)

[Claims] 1. A cemented objective lens comprising a plurality of lenses that are in contact with each other via a cemented surface, wherein each of the plurality of lenses is made of resin, and one of the lenses is made of a photocurable resin. A cemented objective lens characterized in that 2. A cemented objective lens composed of a plurality of lenses that are in contact with each other via a cemented surface, wherein each of the plurality of lenses is made of a resin, and one of the lenses is made of a thermosetting resin. A cemented objective lens characterized in that 3. The plurality of lenses are a lens having a positive refracting power and a lens having a negative refracting power, respectively, and the lenses having the positive refracting power are formed of a photocurable resin. The cemented objective lens according to claim 1, wherein 4. The plurality of lenses are a lens having a positive refracting power and a lens having a negative refracting power, respectively, and the lenses having the positive refracting power are formed of a thermosetting resin. The cemented objective lens according to claim 2, wherein 5. The cemented objective lens according to claim 1, wherein the cemented surface is an aspherical surface. 6. The cemented objective lens according to claim 1, wherein a diffractive ring zone structure is formed on at least one external contact surface. 7. The cemented objective lens according to claim 6, wherein the lens having a surface on which the diffractive ring zone structure is formed is formed of a photocurable resin. 8. The cemented objective lens according to claim 2, wherein a diffractive ring zone structure is formed on at least one external contact surface. 9. The cemented objective lens according to claim 8, wherein the lens having a surface on which the diffractive ring structure is formed is formed of a photocurable resin. 10. The cemented objective lens according to claim 1, wherein the numerical aperture exceeds 0.6. 11. An optical system for an optical disc having a light emitting element for emitting a laser beam and an objective optical system for condensing the laser beam on a recording surface of the optical disc, wherein the objective optical system includes a bonding surface. An objective optical system for an optical disc, comprising: a plurality of resin lenses that are in contact with each other, and one of the plurality of lenses is formed of a photocurable resin. 12. An optical system for an optical disc having a light emitting element for emitting a laser beam and an objective optical system for condensing the laser beam on a recording surface of the optical disc, wherein the objective optical system includes a bonding surface. An objective optical system for an optical disc, comprising a plurality of resin lenses in contact with each other, and one of the plurality of lenses is formed of a thermosetting resin. 13. A method of manufacturing a cemented objective lens comprising a plurality of lenses that are in contact with each other via a cemented surface, wherein one of the plurality of lenses is molded in advance from a resin, and the cemented surface of the molded lens. To form a space corresponding to the shape of the other lens by facing a mold corresponding to the surface of the other lens opposite to the cemented surface of the plurality of lenses. A method of manufacturing a cemented objective lens, comprising: setting a curable resin, and curing the photocurable resin by irradiating the photocurable resin with light. 14. A method of manufacturing a cemented objective lens comprising a plurality of lenses that are in contact with each other via a cemented surface, wherein one of the plurality of lenses is molded in advance from a resin, and the cemented surface of the molded lens is formed. By facing a mold corresponding to the surface of the other lens opposite to the cemented surface of the plurality of lenses, a space corresponding to the shape of the other lens is formed, and the heat is applied to the space. A method of manufacturing a cemented objective lens, which comprises setting a curable resin and curing the thermosetting resin by applying heat thereto.