JPH05306126A - Distributed index optical element and its production - Google Patents

Abstract

PURPOSE:To produce a distributed index optical element whose base has highly concave refractive index distribution without disturbing the desired concn. distribution of a metal. CONSTITUTION:When a distributed index optical element is produced by a sol-gel process, a silica sol is prepd., a salt of a metal other than silicon is added to the silica sol and wet gel is formed. This wet gel is immersed in a soln. contg. a salt of at least one kind of metal other than silicon for a short time and the salt is distributed in the gel so that the concn. is increased from the center of the gel toward the periphery. The gel is then dried and sintered to obtain the objective distributed index optical element.

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 used as an optical lens for cameras, microscopes and the like and a method for manufacturing the same, and relates to a gradient index optical element (hereinafter referred to as G
RIN), and particularly to a GRIN in which the content of metal oxide increases from the center toward the outer periphery, and a method for producing the GRIN.

[0002]

2. Description of the Related Art Generally, as a method for producing GRIN, an ion exchange method, a stuffing method and a sol-gel method are known.

The refractive index distribution of GRIN is due to the concentration gradient of the metal oxide concentration in the glass medium. When the concentration distribution of the metal oxide having a large contribution to the refractive index is distributed higher from the center toward the outer circumference, the refractive index also becomes a concave distribution GRIN in which the distribution becomes stronger from the center toward the outer circumference.

As a method for producing a concave distribution GRIN lens, an example in which Tl is distributed in a concave shape by an ion exchange method is described in JP-A-49-24447, and JP-A-5-24447.
In JP-A 6-24307, SiO ₂ porous glass is subjected to C control by temperature control and solvent exchange by the stuffing method.
An example is described in which sNO ₃ is introduced in a concave shape to fix the deposit. Japanese Patent Laid-Open No. 60-166240 discloses an example in which a dry gel or a sintered gel prepared by the sol-gel method is used as a matrix porous material, and the matrix porous material is dipped in a solution to distribute the phosphate in a concave shape. Have been described.

Further, although there is an example of producing a convex distribution GRIN, as a method for producing by processing a wet gel produced by the sol-gel method, a solution obtained by hydrolyzing a silicon alkoxide and a boron alkoxide is used. A method of exchanging lead acetate in the gel with potassium acetate in the solution by adding a mixed solution of an aqueous solution of lead acetate and acetic acid and impregnating a wet gel obtained by gelation with a solution containing potassium acetate (JP-A-3-2)
No. 95818) is known. GRIN obtained by this method contains convexly distributed lead acetate and concavely distributed potassium acetate.

[0006]

[Problems to be Solved by the Invention] However, the concave distribution GRI
The ion exchange method, which is known as a method for producing N, has a defect that the variation of the refractive index distribution is poor because the concavely distributed metal species are limited to monovalent metals such as Tl and Ag.

In addition, in the examples in which the concave distribution is provided by the stuffing method and the sol-gel method (Japanese Patent Laid-Open Nos. 56-24307 and 60-166240), it is possible to give the polyvalent metal a concentration gradient. Therefore, the variation of distribution characteristics is widened compared to the ion exchange method,
Conventionally, since a gel or glass having continuous pores is used as the SiO ₂ porous body which is the base material, when it is impregnated with a metal salt solution, when the solution penetrates into the pores, Capillary force acts on the resulting gas-liquid interface, and the base material porous body is easily broken.

On the other hand, when the wet gel obtained by the sol-gel method is immersed in the metal salt solution, a liquid-liquid interface exists in the pores, but the capillary force generated here varies depending on the solvent, but the drying occurs. Since it is much smaller than gel, cracks are less likely to occur when the gel is impregnated with a solution.

An example of producing a convex distribution GRIN by utilizing this is disclosed in Japanese Patent Laid-Open No. 3-295818. This is because a wet gel containing a metal salt is sequentially immersed in a solution having a low solubility in the metal salt, fine crystals of the metal salt are precipitated in the wet gel pores, and then a metal salt other than the metal salt contained in the gel is excluded. Dipping in a solution containing the metal salt of
After the metal salt in the gel is eluted and the metal salt in the solution is introduced into the gel, the microcrystals of the metal salt are wet gel pores by successively immersing the metal salt in a solution having a low solubility in the metal salt again. It is a method of precipitating it inside. However, there is no example in which the concave distribution GRIN is produced by using this method.

Therefore, the present inventor has conducted various studies on a method of producing a concave distribution GRIN by treating a wet gel. This is the metal salt which is eluted from the wet gel into the solution outside the gel in the above method (JP-A-3-295818) and distributed in a convex shape, and the metal salt dissolved in the solution to dope into the gel to form a concave shape. A method of using the metal salt to be distributed in reverse, that is, a metal salt that is a raw material of a metal oxide having a small contribution to the refractive index is previously introduced into the wet gel, and the contribution to the refractive index used for imparting the distribution is provided. Is a method of forming a concave concentration distribution of a metal salt that greatly contributes to the refractive index in the gel by dissolving a metal salt that is a raw material of a metal oxide having a large amount and immersing the gel therein.

Generally, in order to make the lens system more compact, it is necessary to increase the refractive power of each lens. This also applies to a lens system using GRIN, and it is necessary to increase the refractive power of GRIN, and for that purpose, it is desired to increase the base refractive index of GRIN.

Conventionally, in the examples in which the concave distribution is provided by the stuffing method and the sol-gel method (JP-A-56-24307 and JP-A-60-166240), a porous material as a base material is porous. Since SiO ₂ is used,
In all cases, the refractive index value of the base was small.

However, in the conventional example disclosing the method of manufacturing the above-mentioned concave distribution GRIN lens, SiO is used as the base glass.
Because of the use of ₂ porous body, the refractive index of the central portion is weak,
In JP-A-56-24307, n = 1.462 is described. JP-A-60-166240 discloses that
Although not described in the refractive index values of the central portion for the concave distribution manufacturing example, the refractive index the refractive index of the SiO ₂ glass of the center from the manufacturing process of immersing 5 minutes SiO ₂ sintered gel alkoxide solution of phosphorus It can be easily inferred that the value is small compared to.

In order to increase the refractive index of the base of the concave distribution GRIN, the metal salt distribution that makes a large contribution to the refractive index distribution increases the metal salt concentration in the central portion as shown in FIG. 1a. Is desired. In the figure, b indicates the conventional concave distribution. In order to impart a metal salt distribution such as a,
Increase the metal salt concentration in the metal salt solution used for distribution (hereinafter referred to as distribution application liquid) or increase the immersion time in the distribution application liquid (hereinafter referred to as distribution application time) to bring the metal salt to the gel center part. Methods such as permeation are possible.

However, there is a limit to the solubility in increasing the metal salt concentration in the distribution-imparting liquid, and there is also a limit to increasing the metal concentration in the center of the gel only by increasing the metal salt concentration. Further, when the distribution is imparted for a long time, the distribution-imparting liquid sufficiently penetrates into the gel central portion. In principle, the solvent of the distribution-imparting liquid must have a certain degree of solubility in the metal salt, so when this solution penetrates to the center of the gel, it precipitates once as fine crystals in the gel pores. The metal salts gradually dissolve. Furthermore, since many metal salts are in a state of being dissolved in the solution when the solvent is exchanged by immersing it in a solvent having a low solubility in the subsequent distribution fixing step, the metal salt remains in the pores together with the distribution-imparting liquid during the fixing operation. It is easy to work inside, and the distribution shape is likely to collapse.

As described above, when an attempt is made to fabricate a concave distribution GRIN in which the SiO ₂ porous body is doped with a metal salt from an external solution, the refractive index of the base is strengthened, it is necessary to give the distribution for a long time, and the distribution is fixed. There was a problem that was unstable.

Further, giving a distribution for a long time not only disturbs the distribution shape of the metal salt concentration that contributes to the refractive index distribution, but also changes the distribution of other metal salts present in the gel, that is, the glass transition point and the thermal expansion coefficient. There is a possibility that the distribution of the metal salt introduced beforehand during the preparation of the sol or in the subsequent steps for correction may be disrupted. If the concentration distribution of the metal salt having such an action collapses, it causes a problem that cracks occur in the step of baking the dry gel and vitrifying.

The present invention is manufactured by the sol-gel method in view of these conventional problems, that is, the variation in the optical characteristics of the concave distribution GRIN is poor, and the base material porous body is easily cracked when immersed in a solution. In order to solve the problem that the fixed distribution tends to become unstable when the concentration of the metal species in the concave distribution pattern is increased by applying a suitable treatment to the wet gel and selecting the method of giving the concave shape. The concave distribution GRIN having a high concentration at the central position of the concavely distributed metal species and thus a strong refractive index of the base GRIN.
It is an object of the present invention to provide a method for producing the same without disturbing the distribution shape of the desired metal salt concentration and its GRIN.

[0019]

In order to achieve the above object, in the present invention, when GRIN is produced by the sol-gel method, a salt of a metal species other than silicon is introduced into silica sol to prepare a wet gel. And a step of immersing the wet gel in a solution containing a salt of at least one metal species among the metal species, so that the concentration of the metal salt contained in the solution increases from the center of the wet gel toward the outer periphery. It was decided to provide a step of distributing so as to increase the height.

GRIN produced by the above manufacturing method is
In the glass medium, the refractive index increases from the center toward the outer periphery.

The metal salt used in the present invention is most preferably an organic acid salt such as acetate, formate or acetylacetone, or nitrate.

[0022]

The following is a description of each dipping operation for producing GRIN having a concavely distributed metal salt by the method of the present invention, and a behavior model of the metal salt in the gel at that time.

A salt of the metal M _{1 which} imparts a concave distribution is introduced in a later step from the time of preparing the sol, and thereafter, it is immersed in a solvent in which the solubility of the M ₁ salt is small. Fine crystals of the M ₁ salt are precipitated therein.

When the above-mentioned wet gel is immersed in the distribution-imparting liquid in which the M ₁ salt is dissolved, the distribution-imparting liquid permeates from the outer periphery of the gel in contact with the solution. When the immersion time becomes longer, the distribution-imparting liquid permeates to the central portion, and the liquid permeating into the gel pores gradually increases the solubility of the above-mentioned M ₁ salt microcrystals present in the gel pores within the range of solubility. It is thought that it will dissolve. Here, "gradually" means that between the metal salt concentration of the distribution-imparting liquid actually used and the solubility of the metal salt in the solvent,
This is because an extreme gap (≧ 1 order) is often not provided, and the solution in the gel pores cannot be forcibly stirred, so that the dissolution rate seems to be slow. Therefore, if the desired distribution shape can be achieved by applying the distribution for a short time, the distribution-imparting liquid does not penetrate to the extent that it dissolves the fine crystals of the gel center, and therefore the solubility of the M ₁ salt is low in the subsequent solvent exchange treatment. When immersed in the solution, it is considered that only the M ₁ salt introduced from the distribution-imparting liquid should be mainly deposited.

On the other hand, when the immersion is carried out for a long time, the distribution-imparting liquid penetrates to the center of the gel, so that the fine crystals precipitated in the gel pores gradually dissolve in the distribution-imparting liquid solvent. Thus, the M ₁ salt in a dissolved state, which is distributed with a concentration gradient by profile-imparting step, M ₁ in the pores dissolved again
Both the salt microcrystals must be deposited in the subsequent solvent exchange treatment, and these dissolved M ₁ salts tend to move in the pores of the gel, causing the distribution to collapse.

As described above, shortening the distribution application time has an effect of preventing the concentration distribution of the metal salt formed by the distribution application from being destroyed in the step following the distribution application.

According to the present invention, since the salt of the metal species M ₁ which imparts the concave distribution is introduced from the time of sol preparation, the metal can be used for a short time only in order to achieve the target metal salt concentration distribution. Immersion in a salt solution is sufficient.

Further, in consideration of the contribution to the distribution of the glass transition point and the coefficient of thermal expansion, the concentration distribution of the metal salt previously introduced into the gel pores is also disturbed, and the distribution application time is shortened. Can be kept to a minimum. Preventing these concentration distributions from collapsing in the subsequent steps following distribution application is an essential factor for obtaining a crack-free bulk body.

[0029] As described above, after were distributed a metal salt in a concave shape, immersed in low solubility of M ₁ salt solution to fix the distribution of the metal salt concentration to precipitate crystallites of M ₁ salt wetting GRIN in which the metal salt is distributed in a concave shape can be obtained by drying and then densifying the gel to densify it.

At this time, if a metal species having a large contribution to the refractive index is selected as the concavely distributed metal salt, GRIN having a concavely distributed refractive index, so-called concave distribution GRI.
You can get N.

[0031]

Example 1 To a solution prepared by mixing 50 ml of tetramethoxysilane and 12 ml of triethoxyboron, 0.01N H 2 was added.
To the solution obtained by adding 25 ml of Cl aqueous solution and hydrolyzing for 1 hour, 134.5 ml of 2N potassium acetate aqueous solution, 1.2
A solution prepared by mixing 22.42 ml of an aqueous lead acetate solution of N and 61.4 ml of acetic acid was added, and the mixture was vigorously stirred for about 3 minutes and then left standing for 3 minutes to prepare a sol. This sol was dispensed into a polypropylene test tube having a diameter of 18 mm and then gelled.
The gel was taken out of the test tube and immersed in a solution of isopropanol: acetone of 5: 5 and acetone in order to deposit fine crystals of potassium acetate and lead acetate in the gel pores.

Then, by immersing the lead acetate in the gel by immersing it in a 0.2M lead acetate methanol solution for 2 hours, Pb was introduced in a concave shape (giving distribution). The gel after the distribution was imparted again with isopropanol: acetone at 5: 5.
Was dissolved in the solution and the acetone, and fine crystals of lead acetate and potassium acetate were generated in the gel pores (fixed distribution). Remove the gel after fixing the distribution from acetone.
Drying was performed at 0 ° C. to obtain a dry gel. This dry gel
By sintering in a tubular furnace to 610 ° C., a colorless transparent glass rod without cracks was obtained.

The glass rod was cut in the radial direction, the cut surface was polished, and the refractive index distribution in the radial direction was measured. As shown in FIG. 2, the refractive index n _center = 1.538 in the central portion,
The refractive index distribution was n _edge = 1.610 at the outer peripheral portion.

[Comparative Example] Tetramethoxysilane 50 m
1 and 12 ml of triethoxyboron were mixed in a solution of 0.
To the hydrolyzed solution was added 25 ml of 01N HCl aqueous solution, and a solution of 13N ml of 2N potassium acetate aqueous solution and 61.4 ml of acetic acid was added.
I let it stand. The sol thus prepared has a diameter of 18 mm.
After dispensing into a polypropylene test tube of, gelled,
The same immersion treatment as in Example 1 was performed.

As a result of changing the distribution-applying time to 2, 4, 8, 12, and 16 hours, the Pb concentration at the base position that was almost the same as that of Example 1 was obtained by applying the distribution for 12 hours. Then, the dry gel obtained by applying the distribution for 12 hours was heated to 400 ° C. for firing, but it cracked to pop. This is because the gel was soaked in a solution with relatively high solubility of lead acetate for a long time, and the concentration gradient of potassium acetate in the gel collapsed during the subsequent fixing operation, resulting in a flat distribution. It is considered that the distribution of the transition point became convex, the holes were closed from the outer peripheral portion of the gel at the time of temperature rise, and the gas inside the gel could not escape and was broken.

Further, when the dry gel, which had a distribution providing time as short as 2 hours, was baked and vitrified, and the refractive index distribution was measured, the difference in refractive index was almost the same as in Example 1.
The refractive index difference Δn was 0.066, but the refractive index in the central portion was n _center = 1.500, which was weak.

[0037]

EXAMPLE 2 0.01N H was added to a solution prepared by mixing 50 ml of tetramethoxysilane and 12 ml of triethoxyboron.
To the solution obtained by adding 25 ml of Cl aqueous solution and hydrolyzing for 1 hour, 134.5 ml of 2 N potassium acetate aqueous solution, 33.63 ml of 1.2 N acetic acid aqueous solution, and 61.4 ml of acetic acid were added, and stirred vigorously for about 3 minutes. Then, the mixture was allowed to stand for 3 minutes to prepare a sol. This sol was dispensed into a polypropylene test tube having a diameter of 18 mm and then gelled to give Example 1.
The same immersion treatment as above was performed, and the resultant was dried at 30 ° C. to obtain a dry gel. The dry gel was sintered to 605 ° C. in a tubular furnace to obtain a colorless and transparent glass rod.

This glass rod was cut in the radial direction, the cut surface was polished, and the radial direction refractive index distribution was measured. As shown in FIG. 3, the refractive index n _center = 1.565 at the central portion,
The refractive index distribution was n _edge = 1.635 in the outer peripheral portion.

The refractive index of the central portion is higher than that of Example 1 by 0.027. By changing the amount of Pb introduced at the time of sol preparation, the refractive index of the base can be changed without changing the distribution application time. It turned out that the refractive index can be raised.

[0040]

Example 3 To a solution prepared by mixing 30 ml of tetramethoxysilane and 30 ml of tetraethoxysilane, 30 ml of 0.01N HCl aqueous solution was added and hydrolyzed to give a solution of 1N barium formate aqueous solution 84.4 ml and 2.5N sodium acetate aqueous solution. A liquid in which 112.5 ml and 78.0 ml of acetic acid were mixed was added and vigorously stirred, and then left standing for 3 minutes to prepare a sol. This sol was dispensed into a polypropylene test tube having a diameter of 18 mm and then gelled. The gel was dipped in ethanol to generate fine crystals of sodium acetate and barium formate in the pores of the gel.

Then, the barium salt was immersed in a 0.2N barium acetate methanol solution for 1.5 hours to give barium a concave concentration distribution, and then again immersed in an ethanol solution to determine the barium salt and sodium acetate concentration distributions. The gel was fixed, further immersed in ethanol, and dried at 30 ° C. to obtain a dry gel in which barium was concavely distributed and sodium was convexly distributed. By sintering this dry gel, a colorless and transparent glass rod without cracks was obtained.

As a result of measuring the refractive index distribution of this glass rod, the refractive index n _center = 1.
570, and the refractive index distribution was n _edge = 1.624 in the outer peripheral portion.

On the other hand, in the case where the barium salt was not used during the preparation of the sol, the barium salt was immersed in a methanol solution of 0.2N barium acetate for 30 hours instead, and the distribution was imparted, the refractive index of the central portion was almost the same as that of this example. However, it was found that the difference in barium concentration between the central portion and the outer peripheral portion was small and the difference in refractive index was about 1/2.

[0044]

Example 4 To a solution prepared by mixing 30 ml of tetramethoxysilane and 30 ml of tetraethoxysilane, 20 ml of 0.01N HCl aqueous solution and 3.2 g of boric acid were added to 5 ml of H ₂
A solution dissolved in O was added for hydrolysis, and a sol was prepared by adding a liquid in which 320 ml of a 0.5 N lanthanum acetate aqueous solution and 62.3 ml of a 2.5 N potassium aqueous solution were mixed. This sol was dispensed into a polypropylene test tube having a diameter of 18 mm and then gelled. The gel was dipped in a methanol / water mixed solution containing 0.6N lanthanum acetate and 0.6N potassium acetate for 24 hours and then dipped in acetone to give lanthanum acetate and potassium acetate microcrystals in the gel pores. Was generated.

Then, the solution was immersed in a 0.2N lanthanum acetate mixed solution of methanol / water for 2.0 hours to give a concave concentration distribution to the lanthanum, and then immersed in acetone to obtain a concentration of lanthanum acetate and potassium acetate. The distribution was fixed and dried at 30 ° C. to obtain a dry gel. By sintering this dry gel, a colorless and transparent glass rod without cracks was obtained.

As a result of measuring the refractive index distribution of this glass rod, the refractive index n _center = 1.
601 and a refractive index distribution of n _edge = 1.660 in the outer peripheral portion.

In the above examples, only the method of manufacturing GRIN having a concave refractive index is shown, but a concave distribution is used for a metal species having a small contribution to the refractive index and a metal having a large contribution to the refractive index. Even when a GRIN having a convex refractive index distribution is formed by providing a seed with a convex distribution, it is possible to increase the central portion concentration of the concavely distributed metal seed, so that it is possible to fire a glass body without cracking or Therefore, the dispersion distribution characteristic can be improved.

[0048]

As described above, according to the present invention, GRIN having a relatively high concentration at the central position of the concavely distributed metal species and, by extension, the concave portion having a relatively high refractive index of the base are obtained by the distribution giving step in a short time. The distribution GRIN can be manufactured stably without disturbing the distribution shape of the desired metal concentration.

[Brief description of drawings]

FIG. 1 is a graph showing a metal salt concentration distribution in a radial direction.

FIG. 2 is a graph showing a radial refractive index distribution of GRIN obtained in Example 1 of the present invention.

FIG. 3 is a graph showing a radial direction refractive index distribution of GRIN obtained in Example 2 of the present invention.

FIG. 4 is a graph showing a radial refractive index distribution of GRIN obtained in Example 3 of the present invention.

FIG. 5 is a graph showing a radial refractive index distribution of GRIN obtained in Example 4 of the present invention.

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[Procedure amendment]

[Submission date] December 7, 1992

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] Claim 2

[Correction method] Change

[Correction content]

[Procedure Amendment 2]

[Document name to be amended] Statement

[Name of item to be corrected] 0003

[Correction method] Change

[Correction content]

The refractive index distribution of GRIN is due to the concentration gradient of the metal oxide concentration in the glass medium. When the concentration distribution of the metal oxide having a large contribution to the refractive index is distributed higher from the center toward the outer circumference, the concave distribution GRIN is distributed such that the refractive index also increases from the center toward the outer circumference.

[Procedure 3]

[Document name to be amended] Statement

[Correction target item name] 0011

[Correction method] Change

[Correction content]

Generally, in order to make the lens system more compact, it is necessary to increase the refractive power of each lens. This also applies to a lens system using GRIN, and it is necessary to increase the refractive power of GRIN, and for that purpose, it is desired to increase the base refractive index of GRIN.

[Procedure amendment 4]

[Document name to be amended] Statement

[Correction target item name] 0013

[Correction method] Change

[Correction content]

However, in the conventional example disclosing the method of manufacturing the above-mentioned concave distribution GRIN lens, SiO is used as the base glass.
Because of the use of ₂ porous body, the refractive index of the central portion is low,
In JP-A-56-24307, n = 1.462 is described. JP-A-60-166240 discloses that
Although not described in the refractive index values of the central portion for the concave distribution manufacturing example, the refractive index the refractive index of the SiO ₂ glass of the center from the manufacturing process of immersing 5 minutes SiO ₂ sintered gel alkoxide solution of phosphorus It can be easily inferred that the value is small compared to.

[Procedure Amendment 5]

[Document name to be amended] Statement

[Correction target item name] 0014

[Correction method] Change

[Correction content]

To increase the refractive index of the base of the concave distribution GRIN
For that, the distribution of large metal salts of contribution to the refractive index distribution, it is desirable to increase the metal salt concentration in the central portion as shown in a of FIG. In the figure, b indicates the conventional concave distribution. In order to impart a metal salt distribution such as a,
Increase the metal salt concentration in the metal salt solution used for distribution (hereinafter referred to as distribution application liquid) or increase the immersion time in the distribution application liquid (hereinafter referred to as distribution application time) to bring the metal salt to the gel center part. Methods such as permeation are possible.

[Procedure Amendment 6]

[Document name to be amended] Statement

[Correction target item name] 0015

[Correction method] Change

[Correction content]

However, there is a limit to the solubility in increasing the metal salt concentration in the distribution-imparting liquid, and there is also a limit to increasing the metal concentration in the center of the gel only by increasing the metal salt concentration. Further, when the distribution is imparted for a long time, the distribution-imparting liquid sufficiently penetrates into the gel central portion. In principle, the solvent of the distribution-imparting liquid must have a certain degree of solubility in the metal salt, so when this solution penetrates to the center of the gel, it precipitates once as fine crystals in the gel pores. The metal salts will gradually dissolve. Furthermore, since many metal salts are dissolved in the solution when the solvent is exchanged by immersing it in a solvent having a low solubility in the subsequent distribution fixing step,
Even during the fixing operation, the metal salt is likely to work in the pores together with the distribution-imparting liquid, and the distribution shape is likely to collapse.

[Procedure Amendment 7]

[Document name to be amended] Statement

[Correction target item name] 0018

[Correction method] Change

[Correction content]

The present invention is manufactured by the sol-gel method in view of these conventional problems, that is, the variation in the optical characteristics of the concave distribution GRIN is poor, and the base material porous body is easily cracked when immersed in a solution. In order to solve the problem that the fixed distribution tends to become unstable when the concentration of the metal species in the concave distribution pattern is increased by applying a suitable treatment to the wet gel and selecting the method of giving the concave shape. The concave distribution GRIN having a high concentration at the central position of the concavely distributed metal species and thus a high refractive index of the base.
It is an object of the present invention to provide a method for producing the same without disturbing the distribution shape of the desired metal salt concentration and its GRIN.

[Procedure Amendment 8]

[Document name to be amended] Statement

[Correction target item name] 0020

[Correction method] Change

[Correction content]

Further , in the above manufacturing method,
As a metal species distributed so as to increase toward the circumference,
GRI prepared by selecting a metal species that has a large contribution to the folding rate
N has a high refractive index from the center to the outer periphery in the glass medium.
Is becoming

[Procedure Amendment 8]

[Document name to be amended] Statement

[Name of item to be corrected] 0037

[Correction method] Change

[Correction content]

[0037]

EXAMPLE 2 0.01N H was added to a solution prepared by mixing 50 ml of tetramethoxysilane and 12 ml of triethoxyboron.
To the solution obtained by adding 25 ml of Cl aqueous solution and hydrolyzing for 1 hour, 134.5 ml of 2N potassium acetate aqueous solution, 1.2N
A solution in which 33.63 ml of a lead acetate aqueous solution and 61.4 ml of acetic acid were mixed was added, and the mixture was vigorously stirred for about 3 minutes and then left standing for 3 minutes to prepare a sol. This sol was dispensed into a polypropylene test tube having a diameter of 18 mm, gelled, subjected to the same immersion treatment as in Example 1, and dried at 30 ° C. to obtain a dry gel. The dry gel was sintered to 605 ° C. in a tubular furnace to obtain a colorless and transparent glass rod.

[Procedure Amendment 9]

[Document name to be amended] Statement

[Correction target item name] 0044

[Correction method] Change

[Correction content]

[0044]

Example 4 To a solution prepared by mixing 30 ml of tetramethoxysilane and 30 ml of tetraethoxysilane, 20 ml of 0.01N HCl aqueous solution and 3.2 g of boric acid were added to 5 ml of H ₂
A solution dissolved in O was added for hydrolysis, and a solution prepared by mixing 320 ml of a 0.5 N lanthanum acetate aqueous solution and 62.3 ml of a 2.5 N potassium acetate aqueous solution was added to prepare a sol. This sol was dispensed into a polypropylene test tube having a diameter of 18 mm and then gelled. The gel was dipped in a methanol / water mixed solution containing 0.6N lanthanum acetate and 0.6N potassium acetate for 24 hours and then dipped in acetone to give lanthanum acetate and potassium acetate microcrystals in the gel pores. Was generated.

[Procedure Amendment 10]

[Document name to be corrected] Drawing

[Name of item to be corrected] Figure 2

[Correction method] Change

[Correction content]

[Fig. 2]

[Procedure Amendment 11]

[Document name to be corrected] Drawing

[Name of item to be corrected] Figure 5

[Correction method] Change

[Correction content]

[Figure 5]

Claims (2)

[Claims] 1. A step of preparing a wet gel by introducing a salt of a metal species other than silicon into silica sol in the production of a gradient index optical element by the sol-gel method; A step of immersing in a solution containing a salt of at least one metal species, and distributing the concentration of the metal salt contained in the solution so as to increase from the center to the outer periphery of the wet gel; A method of manufacturing a characteristic gradient index optical element. 2. Produced by the manufacturing method according to claim 1,
A gradient index optical element having a refractive index distribution in which the refractive index increases from the center to the outer periphery in a glass medium.