JPH07149525A - Production of optical element having refractive index distribution - Google Patents

Abstract

PURPOSE:To easily produce a refractive index distributed optical element having high reproducibility and reliability of optical characteristics such as refractive index, refractive index difference and dispersion characteristics by accurately controlling the profile of a metal component distribution in a porous material. CONSTITUTION:In the production of a refractive index distributed optical element, a porous material (gel) is intermittently contacted with a solution (distribution-imparting solution) containing at least one component selected from metal salt or metal alkoxide, acid, organic solvent and water. The term 'contact' means the contact of a part of the porous material with the above solution and the term 'intermittent' means the change of the contacting part by rotating the porous material in contact with the above solution and a process comprising the contact of the porous material with the solution and the separation of the material from the solution.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a gradient index optical element used in various micro optical systems such as an endoscope.

[0002]

2. Description of the Related Art In recent years, a new optical area called a micro optical system has been actively researched and many uses thereof have been studied. A lens used in the area of a micro optical system is called a micro lens, and its necessity is increasing. In order to manufacture such a microlens, there is a limit to the size and cost that can be processed by the conventional polishing process, and therefore a completely new lens manufacturing method has been proposed. As one of them, a method of manufacturing a microlens by the sol-gel method has been studied. Since the sol-gel method can synthesize a multi-component glass having various optical properties by adjusting the chemical composition of the sol in a low temperature process, it has various properties (refractive index, Abbe number, color, etc.).
It is expected that a microlens will be obtained.

As a typical example of the method of manufacturing a gradient index optical element by the sol-gel method, first, a method of introducing a metal component as a metal alkoxide and imparting a distribution with an acid or the like (Elect. Lett. 22). (198
6), p1108), and second, a method of introducing a metal component as a water-soluble metal salt and imparting distribution with an aqueous solution (J.
of Non-cryst. Solids 85 (19
86) and p244) are known.

Japanese Patent Publication No. 5-27575 discloses a method of manufacturing a gradient index optical element by a sol-gel method, in which a sol obtained by hydrolyzing a solution mainly containing silicon alkoxide is provided with a refractive index distribution. After obtaining a gel-like porous body by adding a solution containing a water-soluble metal salt for imparting a distribution of the metal component in the radial direction, it is fired to obtain a glass body having the desired refractive index distribution A method is disclosed. Further, JP-A-4-260608 discloses a method of increasing the difference in refractive index between the central portion and the outer peripheral portion of a gradient index optical element. In this method, a step of eluting a metal component from a wet gel obtained from a sol containing a silicon alkoxide and a metal alkoxide which is a component for increasing the refractive index is performed a plurality of times, and in the first concentration distribution giving step, the solution to be dipped is a gel. An appropriate time for reaching the center and dissolving the metal component and diffusing the dissolved component outside the gel is defined as the distribution imparting time. After fixing the metal concentration distribution once, in the second and subsequent concentration distribution applying steps, the time for which the solution to be dipped does not reach the center of the gel is adjusted so that the concentration of the metal component in the center of the gel is maintained. Estimate from the diffusion rate and immerse in a new distribution-imparting solution.

[0005]

At present, in a micro optical system, as one of high-performance optical elements, it is necessary to downsize the optical element and to correct various aberrations as in a normal optical system. Has become. When manufacturing such an optical element, not only the shape of the optical element but also precise control of the refractive index distribution is indispensable as the size is reduced. For example, a lens having an outer diameter of about 0.5 to 3 mm is used for the endoscope. Here, when an attempt is made to obtain a lens having an outer diameter of 0.5 mm in which a lead component is distributed by the method disclosed in Japanese Patent Publication No. 5-27525, the time for distribution distribution is approximately the square of the radius. Since it is proportional, it is a very short time of about 30 seconds.

The method disclosed in Japanese Patent Laid-Open No. 4-260608 is to increase the difference in refractive index of the gradient index optical element manufactured by the method disclosed in Japanese Patent Publication No. 5-27525. However, the disadvantage that the distribution application time is short and it is difficult to keep the distribution application conditions constant has not been solved. As described above, according to the methods described in JP-B-5-27525 and JP-A-4-260608, when a minute gradient index optical element is produced, diffusion of ionic species in the porous body is prevented. A slight variation in the manufacturing conditions such as the temperature of the solution, the concentration of the solution, and the time for which the distribution is imparted causes the distribution shape of the composition of the metal species in the porous body to vary, and the sintered refractive index distribution type optical element Refractive index,
It has a drawback that it is inferior in reproducibility and reliability in optical characteristics such as refractive index difference and dispersion characteristics.

The present invention has been made in view of the above-mentioned conventional problems, and precisely controls the shape of the metal component distribution in the porous body to obtain optical characteristics such as refractive index, refractive index difference and dispersion characteristics. An object of the present invention is to provide a method for easily manufacturing a gradient index optical element having high reproducibility and reliability.

[0008]

In order to solve the above-mentioned problems, the present invention provides a porous body with a metal salt or a metal alkoxide, an acid, in producing a gradient index optical element.
A step of intermittently contacting with a solution containing at least one component selected from an organic solvent and water is provided. In addition, contact here means that a part of porous body is contacting the said solution. Further, the intermittent means that the porous body is brought into contact with the solution, and the contact portion is changed by rotating, and that it has a step of bringing the porous body into contact with the solution and a step of not bringing the porous body into contact with the solution. .

[0009]

In the following, the drawbacks of the conventional method will be clarified from the aspect of its operation, and then the operation of the present invention for solving the above drawbacks will be described. In the step of imparting distribution, the gel, which is a porous body, is completely immersed in the solution for imparting distribution, and the liquid phase is exchanged until the distribution imparting solution reaches the center of the gel, so it is immersed in the solution for imparting distribution. It goes without saying that the time to be performed, that is, the distribution giving time is an important parameter for controlling the distribution shape of the metal species of the gradient index optical element, and further, the optical characteristics such as the refractive index, the refractive index difference, and the dispersion characteristic. Therefore, if the distribution application time can be controlled easily (it is easy to operate in the actual manufacturing process), the distribution shape of the metal species of the gradient index optical element can be precisely controlled.

However, when a gradient index microlens is manufactured by a conventional method, the distribution component is too fast to diffuse, and the distribution imparting time is so short that it is difficult to actually operate. Was there. Therefore,
The present invention makes it possible to precisely control the concentration distribution of metal species by lengthening the apparent distribution application time and slowing the diffusion rate of the metal component. The detailed operation of the present invention will be described below.

The time for which the porous body is first contacted with the solution for imparting the refractive index distribution is set shorter than the time for the contacted solution to reach the center of the porous body. Then, the contact of the porous body with the distribution-imparting solution is once interrupted, and the distribution-imparting solution is contacted again after an appropriate time. By the first contact with the distribution-imparting solution, the liquid phase is formed to a certain position where the surface cannot reach the center. A distribution can be imparted by diffusing this liquid phase, but since a new distribution-imparting solution is not supplied from the surface layer by once pulling up the porous body, only the liquid phase remaining in the porous body Diffusion occurs, and distribution speed decreases. After a while, the porous body is again brought into contact with the distribution-imparting liquid, whereby the liquid phase is supplied to the surface layer again, and the distribution-imparting speed is improved. By repeating these steps, it is possible to lengthen the apparent distribution application time, so that it becomes possible to precisely control the distribution shape of the metal species.

The porous material used is a so-called gel obtained by gelling a sol obtained by hydrolyzing a silicon alkoxide, a soot produced by the CVD method or the VAD method, a porosity produced by a phase separation method, or the like. Quality glass, metal salts and acids include organic acid salts such as acetate, lactate, citrate, malate, maleate, oxalate, and their acids, as well as hydrochlorides, nitrates, and nitrites. Inorganic salts such as and the acid thereof can be used.

The above metal salt used as a distribution-imparting solution,
By appropriately changing the solution containing at least one component selected from metal alkoxide, acid, organic solvent and water, the concentration distribution shape of the metal species in the porous body is changed.
For example, by preliminarily containing a metal component to be distributed in the porous body, by contacting it with a solution for eluting the metal component containing acid, water, an organic solvent, etc. to elute the metal component from the porous body. The so-called convex distribution, in which the metal concentration distribution decreases from the central portion toward the outer peripheral portion, can be imparted to the porous body. On the other hand, by including a solution containing a metal salt or a metal alkoxide in the distribution-imparting solution and introducing a metal species from the outside into the porous body, the metal concentration distribution increases from the central portion toward the outer peripheral portion, a so-called concave distribution. Can be applied to the porous body. Further, when it is desired to give a concentration distribution to a plurality of metals, the first metal species is contained in the porous body, and a distribution in which a component for dissolving the first metal component and a second metal component are mixed is provided. By bringing them into contact with the solution, it is possible to impart a convex distribution to the first metal component and a concave distribution to the second metal component.

The distribution-imparting time is determined by roughly estimating the time of contact with the distribution-imparting solution in consideration of the diffusion rate of the metal species to be distributed, and then the composition and concentration of the solution, liquid temperature, contact time, and porosity. The parameters such as the pore size of the body, the diameter of the porous body, the amount of contact with the distribution-imparting solution, and the time interval of repeated contact with the distribution-imparting solution can be controlled with high accuracy.

By fixing the distribution of the porous material obtained by these operations, drying and firing, the refractive index distribution type optics having high reproducibility and reliability in optical characteristics such as refractive index, refractive index difference and dispersion characteristics. The device can be easily manufactured.

The effect of the present invention is particularly effective when the radius of the porous body used is small or when the diffusion rate of the metal species contained in the porous body is high. Even if the radius is large, there is an advantage that the distribution control can be performed more finely. Further, the porous body can be applied in a shape other than a simple rod shape, such as a spherical shape or an elliptic spherical shape, and can also be applied to a thick film having a thickness of several millimeters or more.

[0017]

Example 1 5 ml of tetramethoxysilane, 5 ml of tetraethoxysilane and 2.1 ml of triethylborate were mixed, 4.2 ml of 1 / 100N hydrochloric acid was added thereto, and the mixture was stirred at room temperature for 1 hour for partial hydrolysis. It was A solution prepared by mixing 17.9 ml of 1.25 mol / l acetic acid aqueous solution and 2.6 ml of acetic acid was added to this solution, stirred vigorously for 10 minutes, allowed to stand for 5 minutes, and then placed in a Teflon true round container having an inner diameter of 5 mm. The mixture was dispensed and allowed to stand in a constant temperature bath at 30 ° C. for 3 days for gelation and aging. The obtained gel having a diameter of 3 mm was brought into contact with a 0.61 mol / l lead acetate solution using a mixed solvent of 60 ° C. of isopropanol: water = 8: 2 (volume ratio, hereinafter solvent ratio is volume ratio), and acetic acid was added. Was removed and the gel was thermally aged. Isogel this gel with isopropanol:
By contacting with acetone = 8: 2, 5: 5, and then acetone for 6 hours each, fine crystals of lead acetate were deposited and fixed in the gel pores.

Distribution of the obtained homogeneous gel was carried out in an experimental apparatus as shown in FIG. The inside of the glove box 1 is preliminarily made to have an alcohol atmosphere, and as shown in FIG.
Book 2 gel 30 r. p. m. 1 while rotating with
250 m of ethanol solution of potassium acetate 0.305 mol / l and acetic acid 0.153 mol / l as in (b)
The liquid level of 1 (distribution-imparting solution 3) was raised by the pump 4 until the gel 2 was completely contacted and kept in contact for 10 minutes, and then the liquid level was once lowered, rotated in an alcohol atmosphere for 30 minutes, and again the same. The solution 3 was brought into contact with it for 10 minutes to give a lead component a convex distribution and a potassium component a concave distribution. This gel was brought into contact with isopropanol, isopropanol: acetone = 8: 2, 5: 5, and acetone in this order for 6 hours each to fix the distribution. As the gel rotates, the contacting part is intermittently immersed. Further, a step of contacting the solution, a step of not contacting the solution, a step of further contacting, and a step of intermittently contacting are provided. 30 of these gels
After being dried at ℃ for 3 days, the temperature is raised to 570 ℃ and sintered to obtain a crack-free diameter of 1.1 mm.
A colorless and transparent glass body was obtained.

When the refractive index of these glass bodies was measured, as shown in FIG. 2, it has a refractive index distribution in which the refractive index monotonically decreases from the central portion toward the outer peripheral portion, and there is no inflection point. It had the optical characteristics shown in. There was almost no difference in the refractive index distribution between the five rods, and it was possible to obtain a gradient index optical element having the same optical characteristics in each glass body. In addition, as a result of performing experiments under the same conditions later, it was possible to obtain a gradient index optical element having the same optical characteristics with good reproducibility.

[0020]

[Table 1]

[Comparative Example 1] A gel was prepared in the same manner as in Example 1, and the gel was used in an amount of 0.305 mol of potassium acetate.
25 ml of an ethanol solution containing 1 / l of acetic acid and 0.153 mol / l of acetic acid was contacted for 20 minutes to give a lead component a convex distribution and a potassium component a concave distribution. This gel is used as isopropanol, isopropanol: acetone = 8: 2,
The mixture was contacted with each other for 5 hours in the order of 5: 5 and acetone to fix the distribution, and then fired. Four crack-free glass bodies were obtained, and one was broken. When the refractive index of the crack-free glass body was measured, there were variations in the refractive index difference and dispersion characteristics from rod to rod as shown in Table 2, and a refractive index distribution type optical element having the same optical characteristics in each glass body was used. I couldn't get it.

[0022]

[Table 2]

[0023]

Example 2 A gel was prepared in the same manner as in Example 1, and the gel was given a distribution in an experimental apparatus as shown in FIG. The glove box 1 was previously placed in an alcohol atmosphere, and while the five gels 2 were rotated, potassium acetate 0.
An ethanol solution of 5 mol / l and an acid acid of 0.2 mol / l (distribution-imparting solution 3) was pulled up by a pump 4 and sprayed onto the gel from the distribution-imparting solution jet port 5 for 10 minutes, and then the spraying was stopped once and the mixture was placed in an alcohol atmosphere at After spinning for a minute, the same solution 3 was again sprayed on the gel 2 for 5 minutes. By fixing the distribution of the obtained gel, drying and sintering, it was possible to obtain a colorless and transparent glass body having a crack-free diameter of 1.1 mm. When the radial distribution of this glass body was measured, a gradient index optical element having the same optical characteristics as each glass body could be obtained.

[0024]

EXAMPLE 3 Silicon tetrachloride, SiCl ₄ , zirconium tetrachloride, and barium nitrite Ba (NO ₂ ) ₂ .2H are used as raw materials for silicon, zirconium, barium, and sodium, respectively.
₂ O, sodium acetate NaOCOCH ₃ was used. Flame hydrolysis of silicon tetrachloride and zirconium tetrachloride,
Five soots having an outer diameter of 2 mm of zirconia silica were prepared. The obtained soot was brought into contact with a mixed solution of barium nitrite, ethanol and water, and microcrystals of barium nitrite were fixed to the soot. Distribution of the soot was performed in an experimental apparatus as shown in FIG. Reference numeral 6 is a gear connected to a drive source (not shown) for rotating the soot 7. The inside of the glove box 1 was previously made into an alcohol atmosphere. As shown in FIG. 4A, a solution in which sodium acetate is dissolved in methanol is prepared as the distribution-imparting solution 3, and
While rotating the soot 7 of the book, a part of the soot 7 is brought into contact with the liquid surface for 10 minutes as shown in FIG. The component was given a concave distribution. Then, the soot was again brought into contact with a solution of ethanol mixed with lactic acid to fix microcrystals of barium nitrate and potassium nitrate, followed by drying and firing to obtain a transparent gas body having a diameter of 1.2 mm. When the radial distribution of this glass body was measured, a gradient index optical element having the same optical characteristics as each glass body could be obtained.

[0025]

Example 4 20 ml of tetraethoxysilane, 9 ml of ethanol and 1.6 ml of 2N hydrochloric acid were mixed to partially hydrolyze a silicon alkoxide. Next, a solution of 4.5 g of zirconium tetraisopropoxide dissolved in 10 ml of isopropanol was added and stirred. Then, a mixed solution of sodium nitrate, water, isopropanol, dimethylformamide, and ammonia water was dropped into this solution to prepare a sol. The obtained sol has an inner diameter of 4 m.
Dispense into a Teflon round container of 3 m and put in a constant temperature bath at 30 ° C.
It was left to stand for a day to be aged for gelation.

The obtained gel was subjected to distribution in the same experimental apparatus as shown in FIG. Ethanol was used as the distribution-imparting solution, and the solution was added at 15 r. p. m. The solution was brought into contact with the solution for 5 minutes while being rotated by, and was pulled up and left for 10 minutes, and then contacted again for 5 minutes and pulled up and left for 10 minutes. This was immersed in isopropanol to fix the distribution. By fixing the distribution of this gel, drying it, and sintering it, the crack-free diameter is 0.6 m.
It was possible to obtain a colorless and transparent gas body of m. When the distribution in the radial direction of this glass body was measured, the zirconia component,
A glass body having the same convex distribution for both sodium components was obtained.
When the optical characteristics of each glass body were measured, a gradient index optical element having the same optical characteristics could be obtained.

[Comparative Example 2] The gel produced in the same manner as in Example 4 was immersed in an ethanol solution for 10 minutes to give a distribution. This was immersed in isopropanol to fix the distribution. By subjecting this gel to distribution fixing, drying and sintering, a colorless and transparent glass body having a diameter of 0.8 mm, which is all crack-free, was obtained. However, when the radial distribution of each gas body was measured, the zirconia component could be given a similar convex distribution, but the sodium component had a convex distribution with a different distribution shape for each rod, It was not possible to obtain a gradient index optical element having the same optical characteristics.

[0028]

As described above, according to the method of manufacturing the gradient index optical element of the present invention, the shape of the metal distribution in the porous body is precisely controlled, and the refractive index, the refractive index difference and the dispersion characteristics are controlled. It is possible to easily manufacture a gradient index optical element having high reproducibility and reliability in optical characteristics such as.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an experimental device used in Example 1 of the present invention.

FIG. 2 is a diagram showing a refractive index distribution in a radial direction of the gradient index optical element manufactured in Example 1.

FIG. 3 is a schematic configuration diagram showing an experimental device used in Example 2 of the present invention.

FIG. 4 is a schematic configuration diagram showing an experimental device used in Example 3 of the present invention.

[Explanation of symbols]

 1 glove box 2 gel 3 distribution-imparting solution 4 pump 5 distribution-imparting solution jet 6 gear 7 soot 8 cage 9 motor

Claims (1)

[Claims] 1. A refractive index characterized by comprising a step of intermittently contacting a porous body with a solution containing at least one component selected from a metal salt or metal alkoxide, an acid, an organic solvent and water. Manufacturing method of distributed optical element.