JPS6227012B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention is suitable for use as a material for optical transmission fibers (preforms) and rod-shaped lenses, particularly for rod-shaped microlenses for microlens arrays, or for coupling fibers for optical communication with light sources. The present invention relates to a method of manufacturing a rod-shaped glass body having a refractive index gradient suitable as a material for microlenses and the like. [Prior Art] A molecular stuffing 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 certain concentration gradient and is distributed within the porous glass body, and then heat-treating the pores ( JP-A-51-12607 discloses a method in which a dopant solution is infiltrated into the pores of a porous glass body (stuffing), and then the dopant is crushed from the glass body. A portion of the dopant is eluted (unstuffed) to form a concentration gradient in the dopant distributed within the pores, and then the dopant is precipitated within the pores, the glass body is dried, and then subjected to a firing process. A method of manufacturing a glass body with a refractive index gradient is taught, which comprises collapsing the pores by applying a refractive index gradient. [Object of the Invention] A rod-shaped glass body with a refractive index gradient used as a material for rod-shaped microlenses for microlens arrays or microlenses for coupling optical communication fibers and light sources, etc.
The requirements are that the aberrations are small and the imaging characteristics are good. In order to reduce lens aberrations, it is desirable to adjust the refractive index gradient to an ideal distribution. The refractive index on the central axis of a rod-shaped glass body with a refractive index gradient is n ₀ , and the refractive index at a position at a radius r from the central axis is n
(r), the ideal distribution of refractive index over the entire radial area of the rod is expressed by equation (1). n(r) ² =n ₀ ² {1-(gr) ² } ...(1) Here, g is a quadratic constant of the distribution. However, according to the molecular stuffing method taught in the above-mentioned publication, a rod-shaped porous glass body (radius r ₀ ) was immersed in an aqueous cesium nitrate solution for stuffing, and then 40% by volume of the material was stuffed. The rod is immersed in an ethanol aqueous solution for unstuffing, then immersed in 0°C ethanol for 3 hours to precipitate the dopant CsNO ₃ into the pores, and then dried and fired to form a rod with a refractive index gradient. When a shaped glass body A is manufactured, the refractive index distribution in the radial direction of the glass rod A is as shown by the broken line in FIG. , at a position beyond about 60% of the radius, the slope becomes gentler as it approaches the periphery, and the gap from the ideal distribution curve becomes larger. The degree of approximation of the refractive index distribution to the ideal distribution expressed by equation (1) is the standard deviation S defined by equation (2) below.
From experience, the value of S is 10×10 ^-5
If the value exceeds this value, the aberration becomes large, so it is preferable that the value is less than this value. In the glass rod A introduced above, the value of S is 4.4×10 ^-5 up to 60% of the radius.
However, up to 80%, it exceeds 40×10 ^-5 and cannot be used practically as a rod-shaped microlens. In addition, with rod-shaped lenses, it is necessary to consider the axial aberration characteristics, but with the glass rod A mentioned above,
As shown in FIG. 1b, the axial aberration worsens at the periphery of the rod. An object of the present invention is to provide a method for manufacturing a rod-shaped glass body which has a refractive index gradient that substantially matches an ideal distribution and also has good axial aberration by improving the molecular stuffing method. [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 that can be used for stuffing when unstuffing a rod-shaped porous glass body that has been stuffed. 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 at the periphery 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 2a) and then immersed in a solvent with low dopant solubility at low temperature, the dopant in the glass body will precipitate into the pores. At the same time, some of the dopants around the glass body are eluted from the glass body again, so
It was finally found that a glass body having a refractive index gradient almost matching the ideal distribution up to the periphery of the rods could be obtained, as shown in FIG. 2b. 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 create a concentration gradient in the dopant distributed within the glass body. In a method for producing a rod-shaped glass body having a refractive index gradient, the process comprises forming a dopant, then precipitating a dopant into the pores, drying the glass body, and then firing it to collapse the pores. ,
Unstuffing is carried out by immersing the above-mentioned unstuffed glass body in a solution containing a lower concentration of the same type of dopant as the dopant solution used for stuffing, and then the unstuffed glass body is It is characterized in that the dopant is precipitated within the pores by immersing it in a solvent whose dopant solubility at 5°C is 0.5g/100g (solvent) or less at a temperature of 5°C or less. The rod-shaped porous glass body used in the present invention can be easily manufactured from a phase-separable borosilicate glass rod, and can be produced by, for example, heat-treating the glass rod under predetermined conditions to form an SiO ₂ -rich acid. If the glass rod is separated into an insoluble phase and an acid-easily soluble phase rich in alkali metal oxides and B ₂ O ₃ , 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 (TlNO ₃ ), cesium nitrate (CsNO ₃ ), etc. are preferred. In the step of stuffing the rod-shaped porous glass body with a dopant solution, a known molecular stuffing method is directly adopted. However, unlike the conventional unstuffing process that uses only a dopant-free solvent, the unstuffing process of the present invention contains a lower concentration of the same type of dopant as the dopant solution used in the stuffing process. Use a solution that By immersing the rod-shaped porous glass body that has been stuffed into this solution, the dopant concentration gradient that gives the porous glass body a refractive index distribution curve as shown by the broken line in Figure 2a is created. It is formed. 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 unstuffing process, but typically, as shown in the Examples below, 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 completing the unstuffing process, the porous glass body in which a dopant concentration gradient has been formed in a predetermined manner is then transferred to a precipitation process.
It is immersed in a solvent whose dopant solubility at °C is 0.5 g/100 g (solvent) or less at a temperature of 5 °C or less. As a result, the dopant in the porous glass body is precipitated into the pores, and a part of the dopant present in the pores around the glass body is eluted out of the glass body, so that the rod-shaped porous glass body A concentration gradient of the dopant that can provide a refractive index distribution as shown by the broken line in FIG. 2b (the solid line is the ideal distribution curve) is given to the dopant. The solvent used in this precipitation process, i.e. the dopant solubility at 5°C, is
As a solvent that is 0.5g/100g (solvent) or less,
One or more types of lower monohydric alcohols such as methanol and ethanol, and ketones such as acetone and methyl ethyl ketone can be used, as well as combinations thereof with water or methyl ether, methyl ethyl ether, ethyl ether, etc. Mixtures with ethers can also be used as solvents. By the way, the dopant solubility is
If a solvent larger than 0.5g/100g (solvent) is used, the elution rate of the dopant around the glass body will be too fast, and the glass body will be evacuated from the solvent for the time necessary to precipitate the dopant in the pores. If the glass body is immersed in water, the refractive index gradient at the periphery of the glass body becomes steeper and deviates from the ideal distribution. The temperature when immersing the glass body in the solvent should be 5°C or less,
If the glass body is immersed at a temperature higher than 5° C., the dopant concentration distribution within the glass body will be disturbed, which is not preferable. The immersion is continued for a time necessary to precipitate the dopant distributed within the glass body into the pores, and the immersion time is generally in the range of the square of the porous glass rod diameter (mm) x 0.25 to 1 hour. After the porous glass body that has undergone the above precipitation process is removed from the solvent, it is dried to volatilize the solvent in the pores, and then the pores are collapsed, as is the usual method of molecular stuffing. A rod-shaped glass body having the desired refractive index gradient can be obtained by performing the firing process up to the desired temperature. [Example] In weight%, SiO ₂ ...54.50, B ₂ O ₃ ...34.30,
Glass having a composition of Na ₂ O...5.20 and K ₂ O...6.00 was melted at 1450℃ for 3 hours, stirred for 1 hour during melting, poured into a mold, kept at 480℃ for 2 hours, and then placed in a furnace. A glass block was obtained by cooling in a chamber.
Cut out multiple glass rods with a diameter of 4 to 6 mm and a length of 100 mm from this block, and heat each rod to 540°C.
They were heat-treated for 120 hours to separate the phases, and then treated in 1.5N sulfuric acid at 100°C for 12 to 24 hours to obtain porous glass rods. Next, for each of these porous glass rods,
After performing stuffing treatment, unstuffing treatment, and precipitation treatment under the conditions shown in the table below, each rod is dried in an atmosphere with a relative temperature of 20% or less, and then each rod is heated and fired to a temperature that collapses the pores. A glass rod with a refractive index gradient was obtained. still,
Comparative Examples 1 and 2 in the table correspond to those in which unstuffing was performed by the method taught in Japanese Patent Application Laid-Open No. 126207/1983. For each glass rod thus obtained, D
The refractive index distribution in the radial direction was measured by interference microscopy under the line, and the axial aberration was measured by ray tracing with a 633 nm He-Ne laser beam. The results are shown in Tables 1 and 2.

【table】

【table】

【table】

[Table] 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 the formula (1) shown above.
Ideal distribution of refractive index (radial distribution) expressed by
In contrast, the standard deviation S is 2 to 90% of the rod radius.
In the range of 6×10 ^-5 , the glass rods of Comparative Examples 1 and 2 match well with the ideal distribution, whereas the standard deviation S of the glass rods of Comparative Examples 1 and 2 according to the prior art already exceeds 10×10 ^-5 at 80% of the rod radius. exceed. 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. 3, and as is clear from FIG. , ray incidence radius ratio
Axial aberration worsens rapidly on the peripheral side from 0.6. This means that the effective area as a rod-shaped lens is only up to 36% of the area centered on the optical axis. In contrast, Examples 1-
As shown in FIGS. 3a to 3e, each of the glass rods No. 5 has an axial aberration within ±50 μm up to a light beam incidence radius ratio of 0.9, and it can be seen that almost the entire area of the rod can be used as a lens. [Effects] As detailed above, according to the method of the present invention, the refractive index gradient almost matches the ideal distribution,
Moreover, a rod-shaped glass body with excellent axial aberration characteristics can be manufactured. Therefore, the present invention has extremely great industrial value as a method for manufacturing rod-shaped glass bodies that can be used as materials for various rod-shaped lenses.

[Brief explanation of the drawing]

FIG. 1a shows the radial refractive index distribution of glass rod A manufactured by the conventional method, and FIG. 1b also shows the axial aberration of glass rod A. Figure 2a shows the radial refractive index distribution obtained when the porous glass rod that has undergone the unstuffing process of the present invention is dried and fired as it is, and Figure 2b shows the refractive index distribution in the radial direction obtained when the porous glass rod is dried and fired in accordance with the method of the present invention. This figure shows the radial refractive index distribution obtained by drying and firing a porous glass rod that has undergone a recipe process. 3A to 3E show the axial aberrations of the glass rods obtained in Examples 1 to 5, respectively, and FIGS. 3F and 3G show the axial aberrations of the glass rods obtained in Comparative Examples 1 and 2.

Claims (1)

[Claims] 1. After a dopant solution is infiltrated into the rod-shaped porous glass body (stuffing), a part of the dopant in the pores is eluted from the glass body (unstuffing) and becomes the dopant distributed within the glass body. In a method for producing a rod-shaped glass body having a refractive index gradient, the method comprises forming a concentration gradient, then precipitating the dopant into the pores, drying the glass body, and then firing it to collapse the pores. The unstuffed glass body is then unstuffed by immersing it in a solution containing the same kind of dopant at a lower concentration than the dopant solution used for stuffing, and then the unstuffed glass body is The above-mentioned refractive index characterized in that the dopant is precipitated in the pores by immersion in a solvent whose dopant solubility at 5°C is 0.5g/100g (solvent) or less at a temperature of 5°C or less. A method for manufacturing a rod-shaped glass body with a gradient.