JPH09127310A - Refractive index distribution type optical element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a refractive index distribution type lens showing excellent correcting property for color aberration and a curvature of field. SOLUTION: This optical element consists of a synthetic resin which is a copolymer of at least two monomers (A) and (B). When each monomer (A) and (B) is polymerized separately, the refractive index n and the Abbe number νof each polymer are in the relation of n(A)>n(B) and ν(A)>ν(B), respectively. With the higher ratio of the monomer (A) compounded in the resin, the resin has the higher refractive index, higher refractive index and larger Abbe number. Thus, the obtd. element shows excellent correcting property for color aberration and the curvature of field.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gradient index optical element for use in an optical instrument whose medium is made of synthetic resin and which is used especially under a white light source.

[0002]

2. Description of the Related Art A gradient index optical element (hereinafter referred to as GRIN
Described as a lens) is a new optical element having a refractive index distribution in a medium forming the lens. In the conventional lens in which the medium is homogeneous, the light ray incident inside travels straight, whereas in the GRIN lens, the incident light ray bends and advances due to the influence of the refractive index distribution in the medium. Specifically, the light bends toward the direction in which the refractive index of the medium is high. This property can exhibit various optical effects not found in conventional lenses. To briefly explain the effect, it is possible to correct the field curvature and the chromatic aberration, which is an advantage different from other homogeneous optical elements. Among them, the great advantage is that the chromatic aberration can be corrected. The "aspherical lens" that is now being used in various fields has a large optical effect and has the ability to control and remove many aberrations, but it has been found that field curvature and chromatic aberration cannot be theoretically controlled. There is. For this reason, the GRIN lens has an optical effect that is difficult to replace with other optical elements.

A lens for an optical instrument used under a white light source represented by a camera or a microscope is required to have chromatic aberration sufficiently removed. However, chromatic aberration is one of the most troublesome aberrations in optical design. For this reason, conventionally,
Aberrations are corrected by using cemented lenses, but on the contrary, it is a major factor that the number of lenses cannot be reduced to a certain extent. It has become one.

The GRIN lens can control this troublesome chromatic aberration in optical design, but its effect is not due to the shape of the refractive index distribution of a certain wavelength of the GRIN lens, but due to the relationship of the refractive index distribution between different wavelengths. It is decided.

The characteristics of this GRIN lens are the same whether the medium is glass or synthetic resin. GRIN lenses made of glass are thermally and chemically stable,
Difficult to manufacture and tends to be very expensive. On the other hand, although the GRIN lens made of synthetic resin is somewhat thermally and chemically unstable, it is relatively easy to synthesize, inexpensive to manufacture, and has a low specific gravity. Therefore, which GRIN lens is used for the glass or the synthetic resin is determined by various required specifications at appropriate places, and the optically required characteristics are basically the same.

[0006] Regarding the GRIN lens made of glass, various efforts have already been made to control chromatic aberration. The chromatic aberration is controlled so that the generated chromatic aberration is very small, and the direction opposite to that of ordinary homogeneous glass is used. Specific glass compositions for realizing a GRIN lens that causes chromatic aberration have already been disclosed in JP-A-3-141302 and JP-A-5-88003.

The fact that chromatic aberration can occur in the direction opposite to that of conventional homogeneous glass means that the GRIN lens is subjected to spherical surface processing with a certain radius of curvature to form a lens shape, which appears at the lens surface when light passes through. Chromatic aberration Since the direction of chromatic aberration generated in the medium of the GRIN lens is opposite, the chromatic aberration generated in the lens surface is canceled by the chromatic aberration generated in the medium of the GRIN lens by selecting the characteristic, and the chromatic aberration is not generated in the GRIN lens as a whole. This means that a single lens that does not exist can be manufactured.

The optical characteristics of the material required for the GRIN lens capable of generating chromatic aberration in the direction opposite to that of the conventional homogeneous glass and the GRIN lens capable of correcting the field curvature among the GRIN lenses having very small chromatic aberration generated are refraction. The higher the rate, the higher the Abbe number. As described above, the GRIN lens having the characteristic that both the removal of chromatic aberration and the removal of field curvature can be achieved at the same time is a very effective characteristic in optical design. Generally, it is also necessary to correct other aberrations, so it is not possible to use a single lens for all optical devices,
The GRIN lens brings an innovative progress to the optical design, and there is a strong demand from the optical designer to realize a GRIN lens having a larger Abbe number at a higher refractive index. A contact lens is a typical example of the single lens.

Conventionally, as disclosed in Japanese Unexamined Patent Publication No. 7-40455, by using a negative refractive index type GRIN lens having a concave refractive power distribution, Δn
It is also used by combining a GRIN lens having a large chromatic aberration and a large chromatic aberration generated in a medium so as to cancel the chromatic aberration generated in another convex lens.

[0010]

GR made of synthetic resin
IN lenses are not very active in addressing chromatic aberration. The method of producing a GRIN lens with a synthetic resin is basically a method of copolymerizing two kinds of monomers which are polymers having different optical characteristics (especially refractive index). Therefore, the optical characteristics of the GRIN lens can be roughly estimated from the optical characteristics when the monomer to be copolymerized becomes a polymer by itself.

Looking at the optical properties of polymers which are considered to be practically usable for optics, there is a remarkable tendency that the higher the refractive index, the smaller the Abbe number. Tends to be a characteristic that occurs largely. Therefore, select a monomer whose polymer Abbe number is as close as possible, and use GRIN with small chromatic aberration.
There have been attempts to make lenses, but no consideration has been given to the correction of field curvature.

Further, as described above, "looking at the optical properties of polymers considered to be practically usable for optics,
Since the higher the refractive index is, the smaller the Abbe number tends to be remarkable. ”Therefore, a polymer having a close Abbe number necessarily has a similar refractive index, and thus the manufactured GRIN lens has a drawback that Δn is small. In particular, when it is attempted to manufacture a GRIN lens which has a characteristic that the higher the refractive index is, the larger the Abbe number is, and the chromatic aberration occurs in the direction opposite to the conventional homogeneous glass,
There are not many monomer combinations that can realize such properties, and in most cases, Δn is limited to those having a very small value.

Here, Δn is a large parameter that determines the power (refractive power) of the GRIN lens, and in general, the larger the Δn, the higher the optical effect. The reason is complicated, but in simple terms, the larger Δn is, it is possible to bend the light beam so as not to cause much aberration in the GRIN lens medium, but when Δn is small, the light bending force is large. Is weak, the spherical surface is attached to the surface of the GRIN lens with a strong curvature to supplement the power, and as a result, a large aberration occurs when the light is bent on the spherical surface. For this reason, aberrations remain in the entire lens system, and various measures are required to correct aberrations generated on the spherical surface.Even if the aberrations can be removed, the lens system will become large and the number of lenses will be reduced. There is a strong tendency to create limits. Also,
There is also a method of obtaining a sufficient power from a GRIN lens having a small Δn such as a relay lens by increasing the lens length, but in this case, the entire lens becomes very large. Therefore, it is desirable that the GRIN lens material generally have a large Δn, except for a special optical system such as a relay lens that transmits an image at a long distance.

On the other hand, as disclosed in Japanese Unexamined Patent Publication No. 7-40455, it is a correction lens that cancels the chromatic aberration generated in another convex lens by making the refractive index distribution concave power. However, a great effect cannot be expected for the miniaturization of the light, thin, short, and miniaturized lenses.

The present invention has been made in consideration of such problems, and has a characteristic that a synthetic resin is used as a medium, Δn is practically large, and the higher the refractive index, the larger the Abbe number. It is an object of the present invention to provide a GRIN lens having the above copolymer composition.

[0016]

The GRIN lens of the invention according to claim 1 which achieves the above object is a copolymer of at least two monomers A and B, wherein the monomers A and B are independent. Refractive index n of the polymer polymerized by
(A)> n (B), and the Abbe number ν of the polymer obtained by polymerizing the monomers A and B alone is ν (A)> ν (B)
It is characterized by being.

The GRIN lens according to the invention of claim 2 is a copolymer of at least three monomers A, B and C, which is made of a synthetic resin, wherein the monomers A, B and C are polymerized alone to obtain an Abbe number. ν is ν (C)> ν (A)> ν
(B) and the concentration distribution of each monomer is A convex, B
It is characterized in that it is concave, C concave, A concave, B convex, or C convex.

The operation of the present invention will be described. In order to simplify the notation of the monomer, the monomer A will be referred to as MA,
The monomer B is described as MB and the monomer C is described as MC.

The invention of claim 1 shows the selection conditions of two monomers (MA, MB) in the case of forming a GRIN lens lens which gives a refractive index distribution by copolymerization of two monomers. When the refractive index of the polymer polymerized by MA and MB alone is n (A)> n (B), the Abbe number of the polymer polymerized by MA and MB alone is ν (A)> ν (B). If so, the higher the MA content ratio, the higher the refractive index and the larger the Abbe number. This makes the GRIN lens extremely excellent in correction of chromatic aberration and curvature of field. Even if a combination of monomers with similar Abbeth numbers is used, n (A)> n (B)
In addition, when ν (A)> ν (B), the optical effect is quite different especially in the imaging lens. However, the monomer composition of the present invention can be used for applications such as POF (plastic optical fiber) as in the conventional ones.

The invention of claim 2 is a GR which imparts a refractive index distribution by copolymerization of two ordinary monomers MA and MB.
It shows the composition condition in which the third monomer MC is further added to the IN lens and the Abbe number characteristic of the GRIN lens is controlled by the interaction thereof. In the case of claim 1,
Although the desired refractive index distribution and dispersion distribution were obtained by copolymerization of two monomers, claim 2 has a constitution in which one of the monomers to be copolymerized is replaced by a copolymer of two monomers, It is effective when there is no such monomer pair.

In claim 2, since one of the monomers is replaced, the monomer having the lower refractive index of claim 1 is replaced by 2
The case where it is replaced with a copolymer of one monomer, and
It can be classified into two cases, that is, a case in which the monomer having a higher refractive index is replaced with a copolymer of two monomers. When this is expressed by a refractive index, the former has a relationship between a refractive index of a polymer obtained by polymerizing MA alone and a refractive index curve obtained by copolymerization of MB and MC as shown in FIG. n (A)> n (B to C), and the latter is a case of n (A) <n (B to C) as shown in FIG. If n (A) ≈n (B to C), Δn of the gradient index optical element becomes extremely small, which is not suitable.

Each of these replacements will be described below. FIG. 1 (a) shows a case where the low refractive index monomer of claim 1 is replaced with a copolymer of two monomers,
The optical properties obtained by the copolymerization of MB and MC are located in the middle of the respective monomer properties, and the position is determined by the ratio of the monomers to be copolymerized. However, generally, on the nd-νd characteristic diagram showing the characteristics of the optical glass, the composition and the optical characteristics are not in a linear relationship and have a hyperbolic function. A characteristic curve having a bow shape is drawn like the F-LS-LLF system, and the characteristic shown by the broken line in FIG. 1A is shown. Therefore, by selecting an appropriate copolymerization ratio of MB and MC, it is possible to obtain a copolymer having properties equivalent to those of the hypothetical monomer MB ′ exhibiting properties of lower refractive index and smaller Abbe number than MA. You can

By performing copolymerization with MA while maintaining the MB / MC copolymerization ratio, a refractive index distribution type optical element having an excellent dispersion distribution characteristic that the Abbe number becomes larger as the refractive index becomes higher. Obtainable. In the case of this composition, when the concentration distribution of each monomer is A-convex, B-concave, and C-concave, the refractive index distribution is a convex distribution, and a positive refractive power type GRIN lens exhibiting a convex lens action is obtained. On the other hand, when the concentration distribution of each monomer is A concave, B convex, and C convex, the refractive index distribution is concave.
It becomes a negative index power type GRIN lens which exhibits a concave lens action.

FIG. 1 (b) shows the case where the monomer having a higher refractive index in claim 1 is replaced with a copolymer of two monomers. In this case, the optical characteristics obtained by the copolymerization of MB and MC are located in the middle of the respective monomer characteristics, as in the above case, and the position is shown in FIG. 1 (b).
The characteristic shown by the broken line is shown. Therefore, by selecting an appropriate copolymerization ratio of MB and MC, it is possible to obtain a copolymer having properties equivalent to the hypothetical monomer MB ′ which exhibits desired properties upon copolymerization with MA.

While maintaining the MB and MC copolymerization ratio, M
By carrying out the copolymerization with A, even in this case, it is possible to obtain a refractive index distribution type optical element having a desired dispersion distribution characteristic, that is, an excellent dispersion distribution characteristic that the higher the refractive index, the larger the Abbe number. . In the case of this composition, when the concentration distribution of each monomer is A-convex, B-concave, and C-concave, the refractive index distribution is a concave distribution, which is a negative refractive power GRIN lens exhibiting a concave lens action, and the concentration distribution of each monomer is A In the case of concave, B-convex, and C-convex, the refractive index distribution is a convex distribution, and the lens has a positive refractive power type GRIN lens exhibiting a convex lens action.

The Abbe number of the virtual copolymer MB 'is MB,
It can be freely controlled by the composition ratio of MC. In other words, the distribution characteristics of the GRIN lens produced (in FIG. 1, MA-
Corresponding to the gradient of MB ') can be controlled arbitrarily,
A GRIN lens having any characteristics (dispersion distribution characteristics) required by optical characteristics can be realized by selecting a limited number of monomers and setting the mixing ratio thereof. Therefore, the obtained characteristics are not limited to the dispersion distribution characteristics that the higher the refractive index, the larger the Abbe number.

The dispersion distribution characteristic of the GRIN lens shown in FIG. 1 is shown by a model in which the monomers to be copolymerized are completely exchanged to 0 to 100% of each other. That is, in FIG. 1 (a), all are MA in the central portion and MA in the outer peripheral portion.
It means that the GRIN lens does not contain at all. However, in reality, due to various restrictions, the monomers are not completely exchanged, and in the above example, the GRIN lens may include MB and MC at the center, and GRIN
MA may be included in the peripheral portion of the lens. In reality, it is almost always both. In that case, Δn is smaller than Δn estimated from the monomer combination, but the dispersion distribution (corresponding to the slope of the characteristic curve in the figure) does not change.

Thus, although claim 2 replaces one of the monomers of claim 1 with a copolymer of two monomers, by further expanding this method, both monomers of claim 1 can be obtained. A configuration in which a copolymer of two monomers is replaced together is also conceivable. FIG. 2 shows the composition of this expanded case, a copolymer M of monomers MA1 and MA2.
The curve connecting A'and the copolymer MB 'of the monomers MB and MC is the dispersion distribution characteristic of the GRIN lens.

In the present invention, it is possible to further expand this and replace the monomer with a copolymer of two or more monomers, whereby optical characteristics having an arbitrary refractive index distribution and dispersion distribution can be obtained. Obtainable.

The monomers used in the present invention include, as MA, diethylene glycol bisallyl carbonate (CR-39), methyl polyacrylate, polymethyl methacrylate (PMMA), isobutyl polymethacrylate, polycyclohexyl methacrylate, polytricyclo. Examples include decyl methacrylate, polybromomethyl acrylate, poly (methacrylic acid) 2,3-dibromopropyl, diallyl phthalate polymer, and polystyrene. MB
Examples include poly (pentachlorophenyl methacrylate), poly (phenyl methacrylate), diallyl phthalate, poly (vinyl benzoate) and diallyl isophthalate.
Examples thereof include fluorine-containing polymers such as polymethyl acrylate, polymethyl methacrylate (PMMA), polycyclohexyl methacrylate, polytricyclodecyl methacrylate and polyfluorotrimethacrylate.

The monomer is not limited to the above-mentioned monomer as long as it satisfies the above-mentioned conditions, and M
Any monomer may be used for A, MB and MC. However, it goes without saying that it is necessary to satisfy the basic monomer selection conditions for synthesizing the synthetic resin GRIN lens. That is, the basic conditions are, for example, that copolymerization is performed, that turbidity does not occur due to copolymerization, that a sufficient equivalent ratio can be secured in the visible region from the near-ultraviolet region to the near-infrared region, and the birefringence is There are small things.

The conditions of the refractive index and Abbe's number shown so far may be the conditions at the reference wavelength that meets the specifications of the optical equipment to be applied, but normally, the refractive index at the d-line or the e-line is used. (Nd, ne) and the Abbe number (νd, νe) may be considered.

[0033]

BEST MODE FOR CARRYING OUT THE INVENTION

(Embodiment 1) Diethylene glycol bisallyl carbonate (CR-39) is selected as MA, and a silicone polymer is selected as MB. Δn is a relatively large value of 0.03 and the refractive index is higher, the larger the Abbe number is G.
The RIN lens could be molded.

(Embodiment 2) MA is polybromomethyl acrylate, MB is polyphenyl methacrylate, MC is polyfluorotrimethacrylate, and GRIN
The composition distribution in the radial direction of the lens is such that MA is the largest at the center and decreases toward the periphery, and MB and MC are the smallest at the center and increases toward the periphery. As a result, the center has a refractive index of 1.54, the Abbe number is 44, and the periphery has a refractive index of 1.4.
9. A GRIN lens having a larger Abbe number could be manufactured at a place where the refractive index was 9 and Δn was 41, where Δn was 0.05.

(Embodiment 3) MA, MB, and MC are the same monomers as in Embodiment 2, but the ratio of MB to MC in Embodiment 2 is 3: 2, whereas in Embodiment 3 The form was 2: 1. As a result, Δn is 0.03
Although it is smaller than the fifth embodiment and the second embodiment, a GRIN lens having a slightly large Abbe number change of about 6 can be obtained. This GRIN lens had a characteristic that chromatic aberration could occur in the direction opposite to that of conventional homogeneous glass.

[0036]

According to the present invention, it is possible to obtain a GRIN lens made of synthetic resin having a characteristic that the Abbe number is larger as the refractive index is higher, and it is possible to manufacture a single lens without chromatic aberration. It is possible to make the lens system used under a white light source lighter, thinner, shorter, and smaller than before. In particular, since it is a synthetic resin, the lens system can be made much lighter in weight than glass. Further, due to the water content which the synthetic resin originally has, it can be suitably applied to a lens such as a contact lens having a good wearability.

[Brief description of the drawings]

1A and 1B are characteristic diagrams of refractive index and Abbe number obtained by copolymerization of monomers.

FIG. 2 is a characteristic diagram of a refractive index and an Abbe number when the number of copolymerizations of monomers is further increased.

Claims (2)

[Claims] 1. A copolymer of at least two monomers A and B, which is made of a synthetic resin, wherein the monomers A and B are independently polymerized to have a refractive index n of n (A)> n (B).
And the Abbe number ν of the polymer obtained by polymerizing the monomers A and B alone is ν (A)> ν (B). 2. A copolymer of at least three monomers A, B and C, which is made of a synthetic resin and comprises a monomer A,
Abbe number ν of polymer obtained by polymerizing B and C independently is ν
(C)> ν (A)> ν (B) and the concentration distribution of each monomer is A-convex, B-concave, C-concave or A-concave, B-convex, C-convex. Distributed optical element.