JPS60186424A - Manufacture of glass rod having refractive index gradient - Google Patents

Abstract

PURPOSE:To produce a glass rod having adequate refractive index gradient, by unstuffing a stuffed porous glass rod with a dopant solution having low concentration, and precipitating the dopant in the pores. CONSTITUTION:A porous glass rod is stuffed with a dopant solution, and is unstuffed in a dopant solution containing the same kind of dopant as the above solution and having lower dopant concentration. The unstuffed rod is immersed in a solvent maintained at <=5 deg.C and having a dopant solubility of <=0.5g/100g (solvent) at 5 deg.C to effect the precipitation of the dopant in the pores. The glass is then dried and sintered to collapse the pores. The process gives a glass rod having almost ideal refractive index gradient and excellent axial aberration characteristics.

Description

[Detailed Description of the Invention] [Industrial Application Fields] The present invention is directed to optical transmission fiber materials (preforms).
The refractive index gradient is suitable as a material for rod-shaped lenses, particularly rod-shaped microlenses for microlens arrays, or microlenses for coupling optical communication fibers and light sources.

The present invention relates to a method for manufacturing a rod-shaped glass body having the following.

[Prior Art] A molecular stuff ink method is known as a method for manufacturing a glass body having a refractive index gradient. This method involves filling the pores of a porous glass body with a dopant (refractive index modifying component) so that the dopant (refractive index modifying component) forms a concentration gradient and is distributed within the porous glass body. )
A method of crushing by
The publication describes that after a dopant solution is infiltrated into the pores of a porous glass body (stuffing), a part of the dopant is eluted from the glass body (unstuffed ink), and the dopant is distributed within the pores. A glass having a refractive index gradient, which is obtained by forming a concentration gradient in 1 to 2, then precipitating a dopant into the pores, drying the glass body, and then subjecting it to a firing treatment to collapse the pores. A method of manufacturing the body is taught.

[Object of the invention] Microphone [rod-shaped microlens for collens array,
Alternatively, the rad-shaped glass body, which is used as a material for microlenses for coupling optical communication fibers and light sources, etc., with a right gradient of refractive index, must have small aberrations and good imaging characteristics. be.

In order to reduce lens aberrations, it is desirable to adjust the refractive index gradient to an ideal distribution. Let the refractive index on the central axis of a rod-shaped glass body with a refractive index gradient be no, and the refractive index at a radius of ``'' from the central axis be n (r).The refractive index over the entire radial direction of the rod is The ideal distribution is expressed by equation (1).

n(r) -no (1-(gr)) ...(1)
Here, q is a quadratic constant of the distribution.

However, according to the molecular stuffing method taught in the above-mentioned publication, the radius ro)
After immersing it in a cesium nitrate aqueous solution to perform stuffing, immersing it in a 40% by volume ethanol aqueous solution to perform unstuffing, and then immersing it in 0 °C ethanol for 3 hours to form dopane l = CS N O3. When a rod-shaped glass body A having a refractive index gradient is produced by depositing it in the pores, followed by drying and firing, the refractive index distribution in the radial direction of the glass rod is as shown in Figure 1. (
As shown by the broken line in a), it matches the ideal distribution curve shown by the solid line near the central axis, but at positions beyond about 60% of the radius, the slope becomes gentler as it approaches the periphery, and the ideal distribution curve The gap between them becomes larger. The degree of approximation of the refractive index distribution to the ideal distribution expressed by equation (1) is expressed by the size of the standard deviation S defined by equation (2) below,
Experience has shown that when the value of S exceeds iox io', aberrations increase, so it is preferable that the value of S be equal to or less than this value. In the glass rod A introduced above, the value of S is 4.4X 10' up to 60% of the radius, but it is 4.4X 10' up to 80% of the radius.
Since it exceeds 0x10', it cannot be used practically as a rod-shaped microlens.

Further, in a rod-shaped lens, it is necessary to consider the axial aberration characteristics, but in the glass rod A described above, the axial aberration worsens at the periphery of the rod, as shown in FIG. 1(b).

An object of the present invention is to improve the molecular stuff ink method to provide a method for producing a rod-shaped glass body that has a refractive index gradient that almost matches an ideal distribution and also has good axial aberration.

[Structure of the Invention] As a result of repeated research on a method for manufacturing a rod-shaped glass body that meets the above objectives, the present inventors have discovered a method for using stuffing ink when unstirring a stuffed rod-shaped porous glass body. By using a solution containing the same type of dopant (-) at a lower concentration as the dopant solution that was used, and by immersing the glass body in this dopant solution, the refractive index of the peripheral area of the glass body expected from the dopant concentration gradient can be idealized. If the glass body is unstuffed to be slightly higher than the distribution curve (see the solid line in Figure 2 (a)) and then immersed in a solvent with low dopant solubility at low temperature, the dopant in the glass body will be absorbed into the pores. At the same time as the precipitation, a part of the dopant in the periphery of the glass body is eluted from the glass body, so that the refractive index almost matches the ideal distribution up to the periphery of the rod, as shown in Figure 2 (b). It has been found that a glass body with a gradient can be obtained.

Therefore, the method of the present invention involves stuffing a dopant solution inside a rod-shaped porous glass body, and then unstuffing a portion of the dopant within the pores to form a concentration gradient in the dopant distributed within the glass body. A method for producing a rod-shaped glass body having a refractive index gradient comprises: precipitating a dopant into the pores, drying the glass body, and then firing the glass body to collapse the pores. C. Unstuffed ink is carried out by immersing the stuffed glass body in a solution containing the same type of dopant at a lower concentration as the dopant solution used for the stuffed ink, and then unstuffed. Dopant solubility at 5℃ of stuffed glass body is 0.5g/loo
g (Solvent) Immerse in a solvent at a temperature of 5°C or less i!
? In particular, it is characterized in that dopanes 1 to 1 are precipitated within the J:TI pores.

The 11-point porous glass body used in the present invention can be easily manufactured from a borosilicate glass rod that can undergo phase separation, and can be made rich in SiO2 by, for example, heat-treating the glass rod under predetermined conditions. If the glass rod is separated into an acid-insoluble phase and an acid-easily soluble phase rich in alkali metal oxides and B203, and then treated with acid to elute the acid-easily soluble phase, it will have continuous pores. A rod-shaped porous glass body can be obtained.

In the present invention, any dopant known in the molecular stuffing method can be used, but among them, thallium nitrate (T
47NO3), cesium nitrate (CsNO3), and the like are preferred. In the step of stuffing the rod-shaped porous glass body with a solution of dopane 1-, a known molecular stuffing method is employed as is. However, unlike the conventional unstuffing process that uses only a dopant-free solvent, the unstuffed ink process of the present invention uses a solution containing the same type of dopant at a lower concentration as the dopant solution used in the stuffing process. use.

By immersing the stuffed rod-shaped porous glass body in this solution, the porous glass body has a second
A dopant concentration gradient is formed that provides a refractive index distribution curve as shown by the broken line in Figure (a). The solvent of the dopant solution used in the unstuffing process may be the same or different from the solvent of the dopant solution in the stuffing process, but typically p is , water is used as a solvent for the dopant in the stuffing process, and an aqueous solution of a lower alcohol is used in the unstuffing process. The temperature of the unstuffing process is usually lower than that of the stuffing process.

After the unstuffed ink process, the porous glass body in which a dopant concentration gradient has been formed as specified is then transferred to a precipitate process, where the dopant mWEW at 5°C is 0.5 g/ioo.

(Solvent) Immersed in a solvent below at a temperature of 5°C or below. As a result, the dopant within the porous glass body is precipitated into the pores, and a portion of the dopant present in the pores around the glass body is eluted out of the glass body, resulting in a rod-shaped porous glass. Figure 2 (b) is on the body.
) is provided with an *i gradient of the dopant that can provide a refractive index distribution as shown by the broken line (the solid line is the ideal distribution curve). The solvent used in this precipitation step, i.e., the solubility of the dopant at 5°C
, 5g/10(Ig (solvent) or less) 9
− Examples of lower − such as methanol, ethanol, etc.
In addition to using one or more types of alcohols and ketones such as acetone and methyl ethyl ketone, a mixture of these with water or any ether such as methyl ether, methyl ethyl ether, ethyl ether, etc. can be used as a solvent. It is. By the way, if a lifting platform uses a solvent with a dopant solubility higher than 0.50/1000 (solvent), the elution rate of the dopant around the glass body will be too fast, and the time required to precipitate the dopant into the pores will be too high. However, if the glass body is immersed in the solvent, the refractive index gradient around the glass body becomes steeper and deviates from the ideal distribution. The temperature at which the glass body is immersed in the solvent should be 5° C. or lower; immersion at a temperature higher than 5° C. is not preferred because the dopant concentration distribution within the glass body will be disturbed. The immersion is continued for a period of time necessary to precipitate the dopanes distributed within the glass body into the pores, but the immersion time is generally 25 to 1 hour. Range 1
0- Surrounded by.

The porous glass body that has undergone the precipitating process described in - is removed from the solvent, and then dried to volatilize the solvent in the pores in the usual manner of the molecular stuff ink method. By performing the firing process until it collapses, it is possible to obtain a rod-shaped glass body with a desired refractive index gradient.

[Example weight% FS i 02-54.50, B203 ・-
34,3fINa20・-5,20 and 2(>-6,
A glass having a composition of 00(71) was melted at 1450°C for 3 hours, stirred for 1 hour during the melting, and poured into a mold.
After being held at 480°C for 2 hours, it was allowed to cool in a furnace to obtain Galazub 1]. From this block, the diameter is 4 to 6 mm,
A plurality of glass rods each having a length of 100 mm were cut out, and each rod was heat treated at 540°C for 120 hours to separate the phases, and then they were heated in 15N IlIIM at 100°C for 12 to 2 hours.
After treatment for 4 hours, a porous glass rod was obtained.

Next, each of these porous glass rods was subjected to stuff ink treatment, unstuffing treatment, and precipitation treatment under the conditions shown in the table below, and then dried in an atmosphere at a relative temperature of 20% or less, and then each [ A glass rod having a refractive index gradient was obtained by heating and firing one rod to a temperature at which the pores collapsed. In addition, Comparative Examples 1 and 2 in the table are
This corresponds to unstuffed ink processing performed by the method taught in Japanese Patent No. 126207.

For each glass rod obtained in this way, the refractive index distribution in the radial direction was measured by interference microscopy under the D line.
The axial aberration was measured by a ray tracing method using a 3 nml-1e-Ne laser beam. The results are shown in Tables 1 and 2. (
As is clear from the previous two tables, the glass rods of Examples 1 to 10 obtained by the method of the present invention have a difference with respect to the ideal distribution (radial distribution) of refractive index expressed by the above formula (1). , the standard deviation S becomes 2 up to 90% of the rod radius. 5 x 10-5
However, in the glass rods of Comparative Examples 1 and 2 according to the prior art, the standard deviation S already exceeds 10×10 −5 at 80% of the rod radius.

Furthermore, the measurement results of the axial aberrations of the glass rods obtained in Examples 1 to 5 and Comparative Examples are shown in FIG.
As is clear from FIGS. 3(f) and 3(q), the axial aberrations of glass rods No. 2 and 2 rapidly worsen on the peripheral side from a light incident radius ratio of 0.6. This means that the effective area as a rod-shaped lens is approximately 36 mm around the optical axis.
It means only up to %. On the other hand,
The glass rods of Examples 1 to 5 are shown in FIG. 3(a), respectively.
As shown in ~(e), the ray incident radius ratio is 0 in both cases.
．． It can be seen that the axial aberration up to 9 is within ±50 μm, and that almost the entire Rondo can be used as a lens.

[Effects] As described in detail above, according to the method of the present invention, a [lrad-shaped glass body] which has a refractive index gradient that almost matches the ideal distribution and has excellent axial aberration characteristics. can be manufactured. Therefore, the present invention has extremely great industrial value as a method for manufacturing a rond-shaped glass body that can be used as a lens for various rod-shaped lenses.

[Brief explanation of drawings]

FIG. 1(a) shows the refractive index distribution in the radial direction of glass [Irad A] manufactured by a conventional method, and FIG. 1(b) similarly shows the axial aberration of glass [Irad A]. FIG. 2(a) shows the radial refractive index distribution obtained when the porous glass rod that has undergone the unstuffed ink process of the present invention is dried and fired as it is, and FIG. 2(b) shows the refractive index distribution of the present invention. The refractive index distribution in the radial direction obtained by drying and firing the porous glass that has undergone the precivitation process according to the method
゛. Figures 3(a) to (e) show the axial aberrations of the glass rods obtained in Examples 1 to 5, respectively, and Figures 3(f) and (g) show the axial aberrations of the glass rods obtained in Comparative Examples 1 and 2. Glass rod axis
Shows no L aberration. Applicant Yasutani Glass Co., Ltd. Managing Director Masayuki Asakura 17- ((IJ/J) U kwy JP-A-Sho GO-186424 (7)

Claims (1)

[Claims] 1 After infiltrating (stuffing) the solution of dopant 1 to inside the rond-like porous glass body, a part of the dopant in the pores is eluted from the glass body (unstuffed ink).
A refractive index gradient is created by allowing the dopant distributed within the glass body to form a concentration gradient, then precipitating the dopant into the pores, drying the glass body, and then firing it to collapse the pores. In the method for manufacturing a rod-shaped glass body, unstuffing is performed by immersing the stuffed glass body in a solution containing the same type of dopant at a temperature lower than the dopant solution used for stuffing, and then unstuffed. When the inked glass body is heated to 5°C, the dopant solubility is 0.5.
q / 100G (solvent) or less by immersing in r8 medium at a temperature of 5°C or less, dopan 1~
1. A method for producing a rod-shaped glass body having a refractive index gradient as described above, which comprises causing the precipitation of.