JPH0380133A - Distributed refractive index type optical device and its production - Google Patents

Abstract

PURPOSE:To obtain the optical device capable of permitting a greater latitude in material design and in which refractive indexes can be widely varied by allowing the independent presence of the refractive index distributions due to the concn. gradients of the glass forming oxide constituent elements and glass modifying oxide constituent ions in the same optical device. CONSTITUTION:The concns. of the metallic elements such as Ti and Nb being the glass forming oxide constituents for varying the refractive indexes are distributed in the sol-gel method as the first stage. An univalent ion such as Na<+> and K<+> is then uniformly incorporated into the treated material to obtain a gel, and the gel is dried and sintered to obtain a glass base material. The base material is dipped in a molten salt contg. another univalent ion, and another concn. distribution is imparted by ion exchange. As a result, the desired distributed refractive index type optical element having independently a glass forming oxide constituent element concn. distribution and a glass modifying oxide constituent cation concn. distribution (imparted by ion exchange in second stage) in one glass base material is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a gradient index optical element and a method for manufacturing the same.

[Conventional technology]

Gradient index optical elements are attracting attention as optical elements indispensable for next-generation optical systems because of their excellent aberration correction ability.

There are various graded refractive index optical elements that are being researched and developed by many companies and research institutes, including 5ELFOC (registered trademark) lenses and slab lenses that are currently on the market.

A refractive index gradient optical element is one in which the medium itself has power (refractive power) by imparting a refractive index distribution to the medium. The power is determined by the refractive index distribution, and in order to increase the power, it is sufficient to increase the difference in slope of the refractive index n (hereinafter referred to as Δn). Therefore, increasing Δn is currently a major challenge in the research and development of gradient index optical elements.
Many researchers are conducting research to increase Δn.

By the way, the development of gradient index optical elements to date has been as follows:
As described above, there are many approaches to increasing Δn and increasing the outer diameter, but efforts to reduce the chromatic aberration of optical elements are lagging behind.

Moreover, the refractive index gradient optical element has excellent aberration correction ability.
This makes it possible to drastically reduce the number of lenses, but there is a paradox in that the smaller the number of lenses, the more difficult it becomes to correct chromatic aberration. Therefore, in order to create a lens system that includes a gradient index optical element and sufficiently corrects chromatic aberration, it may be necessary to add an achromatic lens or other means. The advantage of using a gradient index optical element is halved.

Therefore, in order to create a lens system in which chromatic aberration is also corrected using a small number of lenses, it is important to reduce the chromatic aberration itself that occurs between the lenses. The characteristics required of the medium of the gradient index optical element for this purpose are that the medium changes from high refractive index-low dispersion to low refractive index-high dispersion. And, patent application No. 11112 filed by the same applicant as this case.
According to No. 92, a glass base material containing 5 mo1% or more of L i 20 and having an Atsube number of 50 or more is Na'', +.

Immersion in a molten salt containing at least one of Rh+, or Na2O+ K2O, Rb2O
It is stated that a gradient index optical element having the above characteristics can be obtained by immersing a glass base material containing 5 mo1% or more of at least one of the above and having an Atsube number of 50 or more in a molten salt containing Li+. It is being That is, L1
Focusing on the fact that a graded index optical element with better chromatic dispersion characteristics than those using T1+ can be obtained by ion exchange between + and Na+ and +, we systematically performed ion exchange experiments on various Li-based glasses. I did this. In this experiment, the nd of the glass base material was used as the optical property of the material. ,ν,. (value at the center) and ndex+vdex (value at the outermost periphery) after ion exchange were measured, and Δn and Δν were determined and studied.

As a result, we have come to know that the properties of the glass base material are greatly involved in the properties obtained as a gradient index optical element. In particular, it has become clear that Δν is almost determined by the Atsube number ν of the glass base material.

By further organizing this relationship, Li”!K.

In a composition system in which a refractive index distribution is obtained by an equal concentration gradient of Li+ such as 1i+Q, in order to achieve the above-mentioned refractive index distribution optical properties, an important condition has been discovered that the Atsube number of the glass base material should be 50 or more. The technology was perfected.

[Problem to be solved by the invention]

However, few of the currently developed graded index optical elements have such characteristics, and even in those that do, Δn remains at a very small value.

This is mainly due to the method of manufacturing the gradient index optical element. For example, in the ion exchange method, monovalent ions TI+, Na+, and A concentration gradient is imparted by ion exchange with TI+, but while Δn can be large when TI+ is used, the change characteristics of the Atsube number are from high refractive index - high dispersion to low refractive index - low dispersion,
Significant chromatic aberration will occur. Further, although Δn can be increased by replacing Ag+ with Na+, a large chromatic aberration occurs. Furthermore, as mentioned above, there are examples in which chromatic aberration is significantly improved by using Li+, but on the other hand, Δn becomes small, and the effect is not fully exhibited. That is, although it is possible to improve Δn by increasing the Li+ content, there is a limit due to the resistance of the glass base material and the difficulty in stably dissolving the easily volatile alkali component into the glass base material. We have not yet achieved a level that is sufficiently effective in reality. In the ion exchange method,
Since the exchange speed of divalent or higher ions is extremely slow, it is practically possible to create a concentration gradient only with monovalent cations, so variations in the ion concentration gradient for creating the distribution are extremely limited. As above, Δ
It has not been possible to obtain a lens in which n is large and chromatic aberration is small.

Also, development using the sol-gel method is progressing, and Ti and G
e. A method in which metal elements such as Zr, which increase the refractive index and constitute glass-forming oxides (those originally included in order to form glass) are eluted from a wet gel with an acid or the like to create a concentration gradient. However, although this method can obtain a somewhat large Δn, the change in the number is from high refractive index - high dispersion to low refractive index - low dispersion, which causes large chromatic aberration and changes the refractive index distribution. The characteristics of the type optical element are close to those obtained by ion exchange of the TI+, :Na+ type.

In view of the above-mentioned problems, the present invention has been developed to have a sufficiently large Δn for practical use, and to have various characteristics such as changes in Abbe number, high refractive index, low dispersion, low refractive index, high dispersion, and small chromatic aberration. An object of the present invention is to provide a gradient index optical element and a method for manufacturing the same.

[Means and effects for solving the problem] The refractive index distribution type optical element according to the present invention has a refractive index distribution due to the concentration gradient of elements constituting the glass-forming oxide and a concentration of cations constituting the glass-modifying oxide. The refractive index distribution according to the gradient exists in the same optical element, and the side refractive index distributions exist independently of each other.

Further, the method for manufacturing a gradient index optical element according to the present invention includes:
a first step of imparting a concentration gradient to the elements constituting the glass-forming oxide of the glass base material to give the glass base material a first refractive index distribution; and a first step of providing the glass base material with a first refractive index distribution; and a second step of imparting a concentration gradient to the ions to give the glass base material a second refractive index distribution, and further, the second step includes at least monovalent cations. It is characterized in that it is carried out by an ion exchange method in which the glass base material formed in the first step is immersed in a molten salt containing one or more types. These points will be explained in detail below.

The inventor of the present invention first creates a glass base material with a concentration distribution of metal elements that greatly contribute to the divalent refractive index by a sol-gel method, and then performs ion exchange on the glass base material to obtain TI'', etc. By providing a concentration distribution of monovalent ions and an ion concentration distribution independent of the concentration distribution of the divalent metal element, it is possible to create a gradient index optical element with a sufficiently large Δn for practical use and good chromatic aberration characteristics. In other words, when imparting concentration distributions of metal elements or ions independent of each other through these two steps, it is necessary to change the concentration of only the metal elements or ions for which the concentration distribution is desired in each step. Although the concentration of other metal elements or ions must be completely fixed, the inventor of the present invention, after various studies, found that
Focusing on the fact that in ion exchange, only monovalent ions are exchanged, and metal elements with a valence of 2 or more remain essentially fixed and unaffected, we developed a method to create a glass with a concentration gradient created by non-monovalent ions. I decided to use a handbag that exchanges ions with monovalent ions. That is, the sol-gel method is used as the first step, which is a process in which a concentration gradient can be imparted to metal elements that are not monovalent ions in advance, and monovalent ions can be introduced into the glass base material for ion exchange in the subsequent second step. was selected. It has also been found that elements constituting glass-forming oxides are suitable as metal elements that do not inhibit the exchange of monovalent ions in the ion exchange step and that provide a concentration gradient in the first step.

Based on these studies, first, as a first step, a metal element, such as Tl, which is a constituent of the crow-forming oxide and which changes the refractive index, is prepared using a sol-gel method.

Add concentration distribution to Nb, Zr, Ge, Na+,
K+, TI", Cs+, Li+, Rb+,
A gel body uniformly containing monovalent ions such as Ag+ is prepared and dried and sintered to obtain a glass base material.

Of course, this alone is sufficient to function as a gradient index optical element, but the glass matrix is further immersed in a molten salt containing other monovalent ions, that is, by ion exchange, the above-mentioned 1.
Gives a different concentration distribution to valence ions. In this way, one glass base material has a concentration distribution of elements constituting the glass-forming oxide (provided by the sol-gel method in the first step) and a concentration distribution of cations constituting the glass-modifying oxide (the ions in the second step). A gradient index optical element was obtained which independently had a gradient index (applied by exchange).

By variously changing the combinations and quantitative relationships of components that provide concentration distribution, this gradient index optical element can have many characteristics. For example, the first
As shown in Figure (A), in the first step, a concentration distribution A is attached to the metal element a that greatly contributes to the refractive index, and in the second step, the concentration distribution A is added to the metal ion b that greatly contributes to the refractive index. When distribution B is attached, △n of the obtained refractive index gradient optical element
Since is the sum of Δn due to metal element a and metal ion b, a very large Δn is obtained as shown in FIG. In addition, C in the figure represents the concentration distribution of the exchanged metal ion C.
r indicates the radius of the optical element.

In addition, as shown in Figure 2 (A), by making the concentration distributions A and B1 of metal element a and metal ion b, which greatly contribute to the refractive index, to be in opposite directions, the characteristics of metal element a and metal ion b can be A refractive index gradient optical element with completely new dispersion characteristics that utilizes the difference in dispersion characteristics can be obtained. This time, the inventors of the present invention paid particular attention to this density distribution and discovered that an ideal gradient index optical element with excellent chromatic aberration can be obtained.

The refractive index distribution based on the concentration distribution in FIG. 2(A) is as shown in FIG. 2(B).

Furthermore, as an example of actively utilizing the fact that concentration distributions A and B are two independent distributions, if ion exchange in the second step is stopped for a short time, concentration distribution B in Figure 3 (A) will be obtained. Therefore, it is possible to correct the higher-order components of the refractive index distribution provided in the first step to obtain a refractive index distribution as shown in FIG. 3(B).

In particular, in order to achieve characteristics that take advantage of the higher-order terms of the refractive index, and in cases where aberrations are extremely degraded, errors in the refractive index distribution in the first step can be effectively corrected in the second step by correcting the higher-order components. It is also possible to do so. Furthermore, by appropriately selecting the composition and the ratio of the two concentration distributions, it is possible to obtain a refractive index distribution 9 that has an inflection point in the middle, which is called a W-type or M-type overall.

In this way, if two concentration distributions are independently controlled and imparted to one optical element by adjusting the compositional components and their contents completely separately, the interaction of these two concentration distributions will result in many Various types of refractive index distributions can be provided.

It goes without saying that the element imparting the concentration distribution in the first step may be a non-metallic element.

〔Example〕

Hereinafter, the present invention will be described in detail based on the illustrated embodiments.

1st Example Tetramethoxysilane (7MO3) 19.29ml
13.2 ml of methanol and 2.45 ml of 2N hydrochloric acid were mixed, heated to 60°C, covered with a timer, and stirred with a starch. After removing the heater for about 1 hour and returning the temperature to room temperature, 1.75 ml of n-butyl tetratitanate was added to 13.
A solution diluted with 20 ml of methanol was added slowly. Further stirring was continued, and 13.20 ml of methanol was added. A solution mixed with 17.24 ml of pure water and 9.78 ml of IN ammonia water was dropped at a rate of 1 drop/1 second. After stirring the dripped liquid for another hour at room temperature, it was poured into a Teflon tube, sealed, and left overnight.
It turned into a slightly cloudy gel. After aging, this gel is immersed in hydrochloric acid to give a titanium concentration distribution, and after being thoroughly washed with methanol, it is immersed again in a mixed solution of thallium nitrate and barium nitrate, dried and sintered to give a titanium concentration distribution. A silica-based glass base material having a uniform distribution of thallium ions and barium ions was obtained. This glass base material was immersed in a molten salt containing sodium nitrate as a main component to exchange thallium ions in the glass base material with sodium ions in the salt.

When the refractive index distribution of the glass base material thus obtained was measured, it was found that this was a refractive index distribution type optical element with the highest refractive index at the central portion where Δn=0.13.

The relationship between the refractive index and dispersion of this gradient index optical element was as shown in (2) in FIG. Before ion exchange treatment, Δn = 0.07, so by ion exchange, Δn
This means that the value has improved approximately twice. In addition, when a glass base material with no titanium concentration distribution was ion-exchanged, Δn
It was 006. In this way, it was found that a large Δn could be obtained by using two concentration distributions.

Second Example Tetramethoxysilane (TMOS) 16.46ml
and 19.1 ml of isopropanol and 1.88 ml of 2N-hydrochloric acid.
ml was mixed, heated to 600C, and stirred for 1 hour.

After cooling to room temperature, 4.375 g of niobium ethoxide was added to 19. ] mm of isopropanol dissolved in 2
It was dropped at a rate of about 1 drop/1 second. Furthermore, a solution prepared by combining 19.1 ml of isopropanol, 13.05 ml of pure water, and 25 ml of 1N ammonia water was slowly dropped at a rate not exceeding 1 drop/second.

The sol prepared in this way was dispensed into a Teflon tube with a diameter of 16 mm, and the tube was sealed and allowed to gel. This gel was given a concentration distribution of niobium in the same manner as in the first example, and then sodium was introduced, followed by drying and sintering to obtain a glass base material with a diameter of just under 6 mm. Then, this glass base material was immersed in a molten salt containing a large amount of thallium nitrate to perform ion exchange treatment.

When the properties of the glass base material obtained in this way were measured, Δ
n=0.04, and the change in Atsbe's number was Δc6. However, as shown by ■ in Figure 4, the central part of the glass has a high refractive index and low dispersion, and as it moves toward the periphery, the refractive index does not decrease and the Abbe number decreases (dispersion increases). . This is a very effective distribution for correcting chromatic aberration.

Third Example In a solution partially hydrolyzed with 12.58 ml of tetramethoxysilane, 18.31 ml of n-butanol, and 5 ml of 2N-HCI, 5.73 g of zirconium n-butoxide was dissolved in 18.3 ml of n-butanol. Add the solution dropwise and add 13.73ml of n-butanol.
．． A mixture of 16.49 ml of pure water, 3.9 ml of N-N dimethylformacide, and 6 ml of IN-ammonia water was added dropwise to form a gel, and after ripening, a concentration distribution of zirconium was given, and then 40% sodium was added. A glass base material was obtained by immersing the glass in a methanol solution of methoxide, then drying and sintering. When this glass base material was subjected to 165 br ion exchange in molten thallium nitrate salt, as shown in ■ in Figure 4, Δn=0.02 and Δν■0 high refractive index - low dispersion to low refractive index - It was found to be a gradient index optical element with dispersion distribution characteristics in the high dispersion direction.

In this manner, it has been found that by selecting two directions of density distribution, etc., it is possible to obtain an extremely large Δn and an excellent chromatic aberration.

In the third example, the ion exchange time in the second step was 15
When the refractive index distribution was measured after stopping at hr, it was confirmed that only the outer peripheral portion deviated from the parabolic distribution and had a slightly higher refractive index distribution, as shown in FIG.

In this way, higher order components can be controlled. Since the two concentration distributions are completely independent, by changing the ion exchange time and salt composition, the shape of the refractive index distribution in the outer periphery can be changed in various ways without changing the shape of the refractive index distribution in the center at all. It is possible to create a refractive index gradient optical element.

〔Effect of the invention〕

As described above, according to the present invention, the degree of freedom in material design is increased by allowing the metal ions constituting the glass-forming oxide and the glass-modifying oxide to have independent distributions.
Many variations of refractive index distribution were obtained. For example, three types with large Δn and those that take advantage of higher-order components were easily obtained, but among them, two distributions of high refractive index components were made opposite to the unevenness, and metal ions constituting the glass modification oxide were obtained. By using TI+ or Ag+, a gradient index optical element with excellent chromatic aberration, in which the number changes from high refractive index and low dispersion to low refractive index and high dispersion, and has a practical Δn can be obtained. I was able to do that.

[Brief explanation of drawings]

1(A), CB) to FIG. 3(A), (B) respectively show the concentration distribution of metal elements or metal ions provided by each step of the method for manufacturing a gradient index optical element of the present invention. Diagram 4 showing the refractive index distribution of the optical element obtained by these methods.
The figure is a diagram showing the relationship between the refractive index and the number of squares in the first to third embodiments, and FIG. 5 is a diagram showing the refractive index distribution in the fourth embodiment. O-procedural amendment (voluntary) Mr. Commissioner of the Patent Office■. Indication of the case Patent Application No. 1999-214733 2゜Name of the invention Gradient index optical element and its manufacturing method 4゜Agent: 5-195 Shinbashi, Minato-ku, Tokyo 105, Details of the invention in the specification subject to amendment Description field. 6. Contents of the amendment (1) "K" on page 5, line 6 of the specification is corrected to "ni+". (2) Correct rNaJ on page 5, line 7 as [lNa+, i. (3) “Tetramethkin run” on page 3, line 14 of the same page
is corrected to "tetramethoxysilane". (4) Delete "This is" on page 14, line 16.

Claims (3)

[Claims] (1) A refractive index distribution due to the concentration gradient of the elements constituting the glass-forming oxide and a refractive index distribution due to the concentration gradient of the cations constituting the glass-modifying oxide exist in the same optical element, and A gradient index optical element in which index distributions exist independently of each other. (2) A first step of imparting a concentration gradient to the elements constituting the glass-forming oxide of the glass base material to give the glass base material a first refractive index distribution; and a second step of imparting a concentration gradient to the constituent cations to give the glass base material a second refractive index distribution. (3) The second step removes at least one monovalent cation.
The method for manufacturing a gradient index optical element according to claim 2, characterized in that the method is carried out by an ion exchange method in which the glass base material formed in the first step is immersed in a molten salt containing at least one type of molten salt. .