JPH0788224B2 - Method of manufacturing gradient index lens - Google Patents

Description

The present invention relates to a method of manufacturing a gradient index lens.

[Outline of Invention]

The present invention, a solution obtained by hydrolyzing an alkyl silicate under an acidic catalyst and a solution obtained by hydrolyzing an alkyl silicate under a basic catalyst are mixed to produce a sol,
Injecting sol into a cylindrical container, gelling in the cylindrical container to produce a wet gel, drying the wet gel to produce a dry gel, sintering the dry gel, baking with continuous pores Sintered gel (I) is produced by producing a binding gel (I).
Is immersed in a solution containing a dopant to produce a sintered gel (II) in which the dopant is deposited inside the pores, and the sintered gel (II) is immersed in a solution of a dopant to partially disperse the dopant. A gradient index lens that produces a refractive index distribution by eluting it to produce a sintered gel (III) having a dopant concentration distribution therein, and sintering the sintered gel (III) into a transparent glass. Is a manufacturing method.

[Conventional technology]

 Conventionally well known as gradient index lens
To SELFOC There is a (Nippon Sheet Glass trademark) lens. this is,
Ionize ions such as thallium, which has a large electronic polarizability, in advance.
Keep it in the glass rod and charge it with potassium.
Ions in a high temperature molten salt bath containing ions with a small polarizability.
Ion exchange reaction to cause thallium ion concentration distribution,
That is, a refractive index distribution is formed (ion exchange method).

Also, recently, a new method called "molecular stuffing method" has been devised (JP-A-51-126207, JP-B-60-2405).
7) This is because a refractive index adjusting agent (dopant) is deposited in the pores of a porous body using the phase separation phenomenon of glass, or a silica fine powder calcined porous body obtained by a flame hydrolysis method or the like. A method of forming a dopant concentration distribution, that is, a refractive index distribution by partially eluting the dopant by utilizing the difference in solubility of the dopant depending on the temperature.

[Problems to be solved by the invention]

Among the above-mentioned inventions, the ion exchange method requires a very long time for production even in view of reaction kinetics. For example, an outer diameter of several millimeters requires days for one week or more and high temperature. Further, regarding the molecular stuffing method, when a porous body using the phase separation phenomenon of glass is used as a precursor, the influence of impurities must be considered. Since the gradient index lens according to the present invention is used as an optical component as a matter of course, it is desirable that impurities that cause optical loss be as small as possible. In particular, considering the application for communication, it is inappropriate that impurities remain in the order of ppm. From that point of view, the use as an optical component is limited by the selection of the precursor porous body. On the other hand, it has been considered to use porous silica obtained by a flame hydrolysis method as a precursor, but it has a problem in terms of cost such as a low reaction yield and a complicated apparatus.

Therefore, an object of the present invention is to provide a large-sized gradient index lens of high purity at low cost by utilizing the sol-gel method.

[Means for solving problems]

In the method for producing a gradient index lens of the present invention, the porous body obtained by the sol-gel method is immersed in a solution containing a refractive index adjusting agent (hereinafter referred to as a dopant), and the dopant is deposited inside the pores (stuffing). Then, the dopant is partially eluted by further immersing the porous body in a dopant soluble solution (unstuffing) to generate a dopant concentration distribution inside the porous body, that is, a refractive index distribution, which is dried, Characterized by sintering.

According to the present invention, a highly pure porous body, which is one of the merits of the sol-gel method, can be obtained. Regarding the size, it has been difficult to produce a large bulk body by the conventional sol-gel method, but recently, a large bulk body has been obtained by dispersing fine particles in a hydrolyzed solution of a metal alkoxide with an acidic catalyst. Was devised (Japanese Patent Application Nos. 58-23757 and 60-26001). This invention relates to the production of quartz glass, and the outline thereof is as follows.
First, an acidic catalyst hydrolysis solution of an alkyl silicate is prepared, and silica fine particles obtained by the basic catalyst hydrolysis of an alkyl silicate are mixed with this to obtain a raw material sol. A gel obtained from such a raw material sol has a strong binding force even though it has relatively large pores, and can be said to be an epoch-making method for obtaining a large bulk.

By combining the sol-gel method for obtaining such a large gel and the molecular stuffing method, a large-sized gradient index lens can be obtained in a short time. In addition, the sol-gel method is also a useful method from the viewpoint of cost reduction since the raw material yield is high.

By the way, regarding the sol raw material, there is a degree of freedom depending on the intended use. For example, when the size is not so required, a porous body having a certain size can be obtained without mixing silica fine particles. In addition, silica fine particles to be used may be commercially available powders (for example, Aerosil OX-50: manufactured by deggusa) for those having a wide range of purity.

The porous body used for the stuffing is a gel obtained by the above method, but the so-called dry gel obtained by gelating and drying the sol is weak in strength, so some heat treatment is added to improve the strength of the gel. (Calcination). The heat treatment at this time is basically such that the pores of the gel do not become parallel, but if the pores become too small, the diffusion rate of the dopant solution afterwards becomes slow, so appropriate conditions should be adopted. You have to choose.

The type of dopant is oxidized by the principle of the molecular stuffing method and has the function of increasing the refractive index in glass.Therefore, there are compounds that exist as compounds whose solubility changes significantly depending on the temperature and solvent depending on the solution conditions during stuffing. Good. _{CsNO 3, Pb (NO 3)} 2, TlNO 3, such as Tl ₂ SO ₄ will become representative.

The dopant as described above is dissolved in water or a suitable solvent and uniformly dispersed in the gel at a high temperature. By cooling this, the dopant is deposited in the gel pores by the difference in solubility caused by the difference in height.

Next, as an unstuffing step, the gel is immersed in a solution in which the dopant is dissolved to some extent. As a result, the dopant is partially eluted from the outer peripheral portion of the gel, and a dopant concentration distribution based on the liquid-liquid diffusion principle is formed in the gel. However, at this time as well, the dopant concentration distribution changes greatly depending on the temperature, type, immersion time, etc. of the immersion liquid, and therefore it is necessary to strictly control the concentration distribution so as to obtain a desired concentration distribution.

In this way, after forming a gel having a dopant concentration distribution inside, it is dried and sintered, but in the sintering process, the problem of crystallization after the gel has been transformed into glass Care must be taken with respect to the sintering temperature as it contains. Also, the presence of air bubbles in the glass significantly reduces the performance as an optical component, so as a countermeasure, sintering in a helium atmosphere,
It is effective to carry out under reduced pressure.

The present invention is described in detail below with reference to examples.

[Example 1] Preparation of I gel Preparation of ammonia-synthesized silica (ammozil) 206 g of distilled ethyl silicate (Si (OEt) ₄ ) 347 g of ethanol, 9.5 g of ammonia water (29%), 72 g of water were mixed,
The mixture was stirred for 2 hours and left standing for 5 days. This was concentrated using a rotary evaporator until the silica concentration became 0.40 g / cc.

Binder preparation Distilled ethyl silicate 165g, tetrabutoxy germanium 72g and ethanol 146g mixed solution 0.2N hydrochloric acid
71 g was added dropwise for hydrolysis.

mixture. Gelation When the pH of the ammozil solution synthesized above was adjusted to 4.00 with 2N aqueous ammonia and then mixed with the binder prepared above, the pH of the solution became 3.80.
The pH of this solution was further adjusted to 4.50 with 0.2N ammonia water, and a polypropylene cylindrical container (inner diameter 10 mm x length 20
0 mm). Although it gelled after 2 hours, it was aged in a thermostatic chamber at 30 ° C. for 3 days in a sealed state.

Drying The above wet gel was transferred to a polypropylene box container (200 mm × 300 mm × 100 mm) having an opening ratio of 3% and dried in a thermostatic chamber at 60 ° C. After 10 days, a stable dry gel (outer diameter 6 mm x length 120 mm) that did not crack even at room temperature was obtained.

Calcination The above dry gel was heated from room temperature to 30 ° C / hour at a heating rate of 1000
The temperature was raised to ℃ and kept for 5 hours. At this time, calcination was performed in an oxygen atmosphere to remove organic substances and the like in the gel.

Through the above steps, a silica porous body as a precursor of the gradient index resistor glass was obtained.

II A saturated aqueous solution of stuffing CsNO ₃ at 100 ° C was prepared. The calcinated gel was immersed in this solution for 3 hours. At this time, the white gel body was in a semitransparent state before the immersion because the solution was uniformly dispersed in the pores.

III Unstuffing The above-mentioned stuffed gel is treated with ethanol at 70 ℃.
It was immersed in a vol% aqueous solution. After 30 minutes, take out the gel and
It was immersed in water at 0 ° C for 5 minutes.

IV Sintering The above-mentioned gel after unstuffing was dried in a constant temperature room at 60 ° C for one day and then sintered in a diffusion furnace according to the following program.

First, raise the temperature from room temperature to 700 ° C at 60 ° C / hour and
Hold for 0 hours. Subsequently, while flowing helium gas at 0.5 / minute, the temperature was raised to 1100 ° C at 30 ° C / hour and kept at this temperature for 10 hours, and further raised to 1200 ° C at 30 ° C / hour and kept at this temperature.
It was held for 10 hours to complete the sintering.

By the above sintering, a transparent glass rod having an outer diameter of 5 mm and a length of 100 mm was obtained.

V analysis A part of the glass rod was cut out and the concentration distribution of cesium in the radial direction was measured. The distribution chart is shown in FIG. 1. The deviation from the square distribution was observed in the vicinity of the outer peripheral portion, but it was close to the square distribution in the central portion.

VI Optical measurement The optical characteristics of the rod lens were measured using the ordinary optical measurement method, and the relative refractive index difference was Δn = 0.01, the numerical aperture NA = 0.20, and the focusing constant g = 0.09 mm ⁻¹ . .

In addition, when the purity of the obtained glass rod was analyzed, impurities such as Fe, Ti, Cr, and other transition metals, which largely cause optical loss, were not detected.

[Example 2] I Preparation of gel A gel was prepared in the same manner as in Example 1.

II Stuffing A saturated aqueous solution of TlSO ₄ was prepared at 80 ° C, and the above gel was immersed for 2 hours.

III Unstuffing The gel after stuffing above was treated with ethanol 40 vo at 60 ° C.
After being immersed in a 1% aqueous solution for 40 minutes, it was immersed in water at 0 ° C. for 1 minute.

IV Sintering The above-mentioned gel after unstuffing was dried in a constant temperature room at 60 ° C. for one day and then sintered in a diffusion furnace according to the following program.

First, raise the temperature from room temperature to 700 ° C at 60 ° C / hour and
Hold for 0 hours. Next, when the temperature was raised to 1000 ° C. at 30 ° C./hour, the pressure inside the core tube was reduced by a rotary pump. The internal pressure was maintained at 100 mmHg. In this state, up to 1200 ℃, 30 ℃ /
The temperature was raised over time, and the temperature was maintained for 20 hours to complete the sintering.

By the above sintering, a transparent glass rod having an outer diameter of 5 mm and a length of 100 mm was obtained.

V. Analysis The thallium concentration distribution in the radial direction of the glass rod was measured in the same manner as in Example 1, and there was almost no difference in distribution shape from that in Example 1.

VI Optical Measurement The optical characteristics of the rod lens were measured in the same manner as in Example 1.

Δn = 0.02, NA = 0.29 g = 0.120.

[Example 3] Preparation of I gel In 500 g of purified commercially available ethyl silicate, 0.02 N hydrochloric acid was added.
165 g was added and stirred for hydrolysis. More water on this
After adding 165 g, commercially available silica fine powder (Aerosil OX-50
145 g (manufactured by Deggusa) was added and stirred for 2 hours and ultrasonic vibration was applied for 2 hours to obtain a silica sol solution having high dispersibility. 0.
After adjusting the pH to 4.50 with 1N ammonia water, pour it into a large number of polypropylene cylindrical containers (inner diameter 10 mm x length 200 mm) 50 minutes later, transfer the gelled material to a polypropylene box container, and open it. Cover with a 5% rate,
When dried in a thermostatic chamber at 60 ° C, the drying was completed in 10 days.

When the rod lens was manufactured using the above dry gel in the same process as in Example 1, almost the same optical characteristics were obtained.

Example 4 Up to the stuffing step was performed in exactly the same way as in Example 1, and the unstuffing step was changed as follows.

First, the gel after stuffing is treated with ethanol 40 vo at 50 ° C.
After soaking in l.% aqueous solution for 3 hours, quickly change to 20vol.% ethanol aqueous solution at 70 ℃ and soak for 20 minutes.
Immerse in 0 ° C. water for 2 minutes.

Sintering was also performed in the same manner as in Example 1, and the cesium concentration distribution in the radial direction of the obtained transparent glass rod was measured. As shown in FIG. 2, it can be seen that the deviation from the square distribution in the vicinity of the outer circumference is considerably improved as compared with that of Example 1 (FIG. 1).

As for optical characteristics, △ n = 0.018, numerical aperture NA = 0.025, g
= 0.095, which is considerably higher than that of Example 1.

Example 5 I Preparation of gel A sol similar to that of Example 1 was poured into a polypropylene cylindrical container having an outer diameter of 30 mm and a length of 200 mm to cause gelation, and the gel was dried to obtain a large dry gel. This was similarly calcined.

II Stuffing Prepare a saturated aqueous solution of TlNO ₃ at 100 ° C and
Soak for hours.

III Unstuffing After soaking in an aqueous solution of 40 vol.% Ethanol at 70 ℃ for 1 hour,
Further, it was dipped in warm water of 90 ° C. for 5 minutes and dipped in water of 0 ° C. for 30 seconds.

IV Sintering Sintering was performed as in Example 1.

From the above, a large glass rod having an outer diameter of 15 mm and a length of 100 mm was obtained.

The concentration distribution shape of thallium was almost the same as that shown in FIG. 2, and was close to a square distribution up to the outer periphery.

[Example 6] The outer periphery of the rod lens obtained in Example 1 was optically polished,
After thorough washing, jacketing with a commercially available quartz glass tube and drawing the optical loss to an outer diameter of 125 μm by the usual method and measuring the optical loss showed that it was 10 dB / km in the 0.85 μm wavelength band.
And low loss.

Similarly, the optical loss of the rod lens obtained in Example 3 was measured and found to be as high as 500 dB / km, which means that it cannot be used for at least communication.

〔The invention's effect〕

As described above, a sol obtained by mixing a solution obtained by hydrolyzing an alkyl silicate under an acidic catalyst and a solution obtained by hydrolyzing an alkyl silicate under a base catalyst is used as a raw material sol, and the sol liquid is a gel. Immersing the porous body, which has been dried and dried and, if necessary, subjected to heat treatment, in a solution containing the dopant, stuffing the dopant inside the pores (stuffing), and then immersing the porous body in a solution containing a dopant. To partially elute the dopant (unstuffing) to generate a dopant concentration distribution, that is, a refractive index distribution inside the porous body, and by sintering this, a high-purity large-sized gradient index lens can be manufactured at low cost. Can be obtained at. That is, the effects of the present invention are as follows.

Obtained by mixing a solution obtained by hydrolyzing an alkyl silicate under an acidic catalyst with a solution obtained by hydrolyzing an alkyl silicate under a basic catalyst in the steps of claims A) to D). Since the sol is used, since particles of high purity are dispersed in the sol, it is possible to manufacture a glass body having a small amount of impurities with a high yield and at a low cost.

In the steps E) to F) of the claims, since the sintered gel having continuous pores inside is used, the strength of the porous body to be immersed in the solution containing the dopant becomes large. Therefore, a large gradient index lens can be manufactured with high yield. Although the gradient index lens made of silica-based glass has been described in the present invention, it is needless to say that the same effect can be obtained by using other metal alkoxide, metal oxide fine particles and the like. In addition, optical components with various refractive index distributions, such as optical couplers in optical communication, slab lenses for optical demultiplexers, various optical waveguides, and microlenses, can be obtained by slightly changing the shape of the porous body and the stuffing method. Arrays can be produced, and various developments as optoelectronic device parts in the future,
Applications could be considered.

[Brief description of drawings]

 Figure 1 is a Cs concentration distribution map. The solid line indicates the measured value in the present invention. The broken line shows the optimum square distribution curve. Figure 2 is a Cs concentration distribution chart. The solid line indicates the measured value in the present invention. The broken line shows the optimum square distribution curve.

Claims (1)

[Claims] 1. A step of preparing a sol by mixing a solution obtained by hydrolyzing an alkyl silicate under an acidic catalyst with a solution obtained by hydrolyzing an alkyl silicate under a basic catalyst, and B). Injecting the sol into a cylindrical container and gelling in the cylindrical container to produce a wet gel; C) drying the wet gel to produce a dry gel; and D) baking the dry gel. And a step of producing a sintered gel (I) having continuous pores, and E) immersing the sintered gel (I) in a solution containing a dopant to deposit the dopant inside the pores. And (F) a sintered gel having the concentration distribution of the dopant inside, by immersing the sintered gel (II) in a dopant-solvable solution to partially elute the dopant. Manufacture (III) Degree and, G) production method of the sintered gel (III) a step of transparent vitrification by sintering, a gradient index lens, characterized in that it comprises in that order.