JPS6215492B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of manufacturing a light transmitting glass article as a material for a light transmitting glass fiber or as a material for a rod lens. This glass fiber is required to have characteristics such as low optical transmission loss, a predetermined refractive index distribution in its cross section, and high strength. Many manufacturing methods are currently being considered for this glass fiber, and examples of those that have been put into practical use include the M-CVD method, the O-CVD method, and the VAD method.
However, unlike those methods, a molecular stacking method has been proposed as a method for making preforms that is easy to mass produce and is inexpensive. On the other hand, a rod lens with a square distribution in the radial direction has no disturbance in its refractive index distribution, has a center portion with a high refractive index, and has small changes in the refractive index distribution with respect to wavelength. characteristics are required.

The above-mentioned molecular stuffing method can be used as a method for manufacturing such a rod lens with good environmental resistance and at low cost. However, the glass made by the conventional molecular stacking method had the following drawbacks.

Previously, dopants such as Cs ₂ O were distributed. On the other hand, when making a fiber from a glass preform, it is necessary to melt it at a high temperature, spin it, and rapidly cool it to make it strong. However, Cs ₂ O
is an oxide that easily decomposes at high temperatures and generates bubbles during spinning, which causes a decrease in the transmission loss and strength of the optical fiber.

Since the refractive index dispersion (dn/dλ) of glass containing distributed dopants such as Cs ₂ O and Tl ₂ O is large, chromatic aberration becomes large when used as a lens.

The present invention is a glass material manufacturing method using the above-mentioned molecular stuffing method. By strictly selecting dopants, the present invention suppresses the generation of bubbles during spinning, increases strength, reduces transmission loss, and produces a glass material with small chromatic aberration. The structure is such that a dopant compound that changes the refractive index is stuffed into the micropores of a porous glass body, then the dopant compound is precipitated, and after further thermal decomposition, In the method for producing a glass body having a predetermined refractive index distribution by melting and solidifying the porous glass body to make it transparent, at least one compound of Nb, Ta, Sc, Y, La, or Th is used as the dopant compound. It is characterized by

The present invention will be explained in detail below along with examples.

Here, to explain the outline of the molecular stuffing method, first, as a starting material, for example, a porous glass rod of SiO ₂ containing several percent of B ₂ O ₃ made using phase separation, and other materials such as CVD Porous glass with continuous air bubbles inside, such as porous glass obtained by aggregating and semi-sintering powders made by Use glass. This porous glass rod is immersed in a stuffing liquid to allow the stuffing liquid to penetrate into the micropores of the glass rod. This stuffing liquid uses a solution of a dopant compound that changes the refractive index. When the glass rod is pulled up from the stuffing liquid, the stuffing liquid containing the dopant compound remains in the micropores. Then, the glass rod is immersed again in the solution for depositing the dopant compound, and the dopant compound is deposited on the inner surface of the micropores. In this case, by repeatedly dipping into solutions with different dopant concentrations as necessary, that is, by repeating stuffing and unstuffing, the dopant concentration deposited on the inner surface of the micropores can be adjusted stepwise or continuously. The concentration distribution can be adjusted so that the concentration changes over time. Thereafter, when the glass rod is dried and heated, the dopant compound precipitated in the micropores is thermally decomposed into oxides. Of course, the dopant compound remaining in the pores will precipitate during the drying process, so drying and heating may be performed immediately after the glass rod is pulled out of the stuffing liquid. After the above thermal decomposition, when the temperature continues to rise, the glass rod gradually melts, and the fine pores inside are soaked, resulting in a transparent glass rod.

In the molecular stuffing method described above, conventionally, as a solution of a dopant compound,
Alkali metals, alkaline earth metals, nitrate compounds of the aluminum group, etc. are used. This is because these are compounds that become aqueous solutions and whose solubility changes greatly with changes in temperature. In the present invention, a compound of a lanthanum-based or actinide-based element is used in place of the above dopant compound. The first condition for selecting a dopant is that it is difficult to decompose at high temperatures when glass is spun at high temperatures. Examples of substances that meet this condition include Sc ₂ O ₃ , Y ₂ O ₃ ,
Rare earth element oxides such as La ₂ O ₃ , TiO ₂ , ZrO ₂ ,
In addition to titanium group element oxides such as _{HfO2 , Nb2O5} ,
Examples include Ta ₂ O ₅ and WO ₂ . Next, regarding the dopant, it is necessary to take into account the second condition that when the dopant is added to the glass, no transmission loss occurs due to absorption, scattering, etc. From this condition, for example
TiO ₂ , Ce ₂ O ₃ or those that produce colored ions such as CeO ₂ , Nd ₂ O ₃ and WO ₂ are excluded. Furthermore, as a third condition, it is necessary to have a high refractive index and a small dispersion. This point is generally explained as follows. The refractive index and dispersion values for one-component, two-component, three-component, and four-component systems are given in the book by Morey. The relationship between the periodic table and refractive index or dispersion is given by Young and Finn, KHSun, Izumiya et al. Qualitatively, the refractive index generally increases as the number of modified oxides increases. Regarding the types of modified oxides, the ionic radius of the cation of the modified oxide becomes larger and the valence becomes higher, but it decreases when it becomes pentavalent or hexavalent.
On the other hand, the dispersion increases with the radius of the cation in the case of low valences such as mono- or divalent ions, and the dispersion increases as the ionic radius becomes smaller in the case of high-valence ions. Therefore, La ³⁺ , Th ⁴⁺ , Ta ⁵⁺ give high refraction and low dispersion, while Ti ⁴⁺ , V ⁵⁺ , W ⁶⁺ etc. give low refraction and high dispersion. Tl ⁺ , Pb ²⁺ , and Bi ³⁺ ions have a non-rare gas type outer shell electron arrangement and high polarizability, so they give high refraction and low dispersion, and are used as dopants that satisfy the first, second, and third conditions above. Lanthanum series such as La ₂ O ₃ or
actinides such as ThO ₂ and Sc ₂ O ₃ , Y ₂ O ₃
Rare earth elements and vanadium group element compounds such as Nb ₂ O ₅ and Ta ₂ O ₅ can be selected.

Previously, the above-mentioned oxides were not used in the molecular stuffing method, but by combining boric acid glass containing a small amount of the above-mentioned oxides with a low-refractive-index, high-dispersion glass as a high-refractive index, low-dispersion glass. It is only used to make lenses with little chromatic aberration. However, in this case, it is not possible to obtain a predetermined refractive index distribution inside the glass because the raw material powder is put into a platinum crucible or the like and melted to make glass with a uniform composition.

The present invention enables the use of the above-mentioned oxides in the molecular stuffing method. When the above-mentioned oxide is used as a dopant, unlike conventional dopants such as alkali metal salts, it is necessary to carry out stuffing and unstuffing methods as follows.

For example, when La ₂ O ₃ is used as a dopant and La(NO ₃ ) ₃ is used as a dopant compound, stuffing is performed as follows.

The porous glass body is stuffed by immersing it in water, alcohol, or acetone containing lanthanum nitrate, etc., and then unstuffed with water, alcohol, or acetone to obtain a predetermined concentration distribution, and then vacuum-dried. The precipitates of lanthanum nitrate are precipitated on the inner surface of the micropores, and are then decomposed and thermally solidified to form transparent glass. Alternatively, the porous glass body may be made of ethyl nitrate containing lanthanum nitrate or the like.
Stuffing with alcohol or acetone, followed by immersion in ethyl ether to precipitate the dopant compound, followed by unstuffing with immersion in ethyl alcohol + ethyl ether or acetone + ethyl ether, followed by immersion in ethyl ether. The dopant compound is reprecipitated by soaking to obtain a predetermined concentration distribution, and then vacuum-dried to precipitate lanthanum nitrate on the inner surface of the micropores, and further heated to decompose the lanthanum nitrate,
After turning it into lanthanum oxide, it is thermally solidified to form a transparent glass body. Still another method is to stuff the porous glass body with an aqueous solution containing lanthanum nitrate or the like, and then immerse it in one of an inorganic aqueous solution such as aqueous ammonia, aqueous alkaline solution, perchloric acid, or sulfuric acid for precipitation. Next, unstuffing is performed with water or a dilute aqueous solution of the above-mentioned inorganic aqueous solution, and the dopant compound is further immersed in one of the inorganic aqueous solutions to re-precipitate to obtain a predetermined concentration distribution, followed by vacuum drying and nitric acid. Lanthanum is precipitated on the inner surface of the micropores, and the temperature is further increased to decompose the lanthanum nitrate into lanthanum oxide, which is then thermally solidified to form a transparent glass body. Furthermore, in order to make the glass uniform and to obtain a high NA by co-doping an alkali metal, the following may be done.

Stuffing the porous glass body with an aqueous solution containing lanthanum nitrate and at least one alkali metal nitrate, followed by immersion in ethyl alcohol to precipitate the alkali metal nitrate compound and simultaneously co-precipitate the lanthanum nitrate; Afterwards, the mixture is unstuffed with an aqueous solution containing a nitrate compound of water or water + alcohol or water + an alkali metal, and further precipitated with the solution used for the precipitation to obtain a predetermined concentration distribution, and then vacuum dried to form a nitrate compound. is precipitated on the inner surface of the micropores, and further heated to decompose and thermally solidify to form a transparent glass body. Note that the method described above is not limited to these, and several conditions may be combined. The reagents used therein are not limited to water, ethyl alcohol, diethyl ether, acetone, etc., but also heavy water, other alcohols such as propanol, other ethers such as methyl ethyl ether, methyl ether, etc. - It is also possible to use other ketones such as ketones. Dry decomposition and thermal solidification are performed under vacuum, in He gas, He + O ₂ gas, He + O ₂ +X ₂
Conditions such as gas may be combined.

Next, an embodiment of the present invention will be described.

First, a porous glass rod (8 mmφ) with a porosity of about 50% as shown in JP-A-51-126207.
was prepared and immersed in a solution of La(NO ₃ ) ₃ .6H ₂ O saturated in ethyl alcohol at 25° C. and left for one week. Next, take it out and heat it at 25℃.
When immersed in an ethyl ether solution, a white precipitate formed within the porous glass. This was also left for one week, then immersed again in a stream of ethyl alcohol at 25°C for 8 hours, and then again in a solution of ethyl ether at 25°C. As a result, a thick white precipitate was observed in the middle 4 mm diameter, and a slightly white precipitate was observed on the outside. Next, it was removed from the liquid and gradually evacuated at 0°C over 24 hours, and then heated to 900°C at 15°C/hr, resulting in a transparent glass rod (6.5φ). Of these, 3.2φ had a high refractive index in the core. When this glass rod preform was drawn to make a fiber with a diameter of 150 μmφ, λ
= 0.85 μm and the value was less than 100 dB/Km. In addition, the preform was completely free of air bubbles during drawing. In addition, the refractive index dispersion was determined from band measurements and was approximately 1/2 that of conventional fibers.

Claims (1)

[Claims] 1. A dopant compound that changes the refractive index is stuffed into the micropores of a porous glass body, the dopant compound is then precipitated, and after further thermal decomposition, the porous glass body is melted and solidified to make it transparent. In the method of vitrifying and producing a glass body having a predetermined refractive index distribution, the dopant compound is Nb,
A method for producing optical transmission glass, characterized in that at least one compound of Ta, Sc, Y, La or Th is used. 2 The porous glass body is made of Nb, Ta, Sc, Y, La.
Alternatively, it is immersed in water, alcohol, or acetone containing at least one type of Th nitrate, then stuffed, and then unstuffed with water, alcohol, or acetone to obtain a predetermined concentration distribution, and then vacuum dried. 2. The method of manufacturing a light transmission glass according to claim 1, wherein the nitrate is precipitated on the inner surface of the micropores, and then decomposed and thermally solidified to form transparent glass. 3 The porous glass body is made of Nb, Ta, Sc, Y, La.
Alternatively, stuffing with ethyl alcohol or acetone containing at least one of the nitrates of Th, followed by immersion in ethyl ether to precipitate the dopant compound, followed by ethyl alcohol + ethyl ether or ascent + ethyl ether. The optical transmission glass according to claim 1, characterized in that the glass is immersed in ether to perform unstuffing, and further immersed in ethyl ether to redeposit the dopant compound to obtain a predetermined concentration distribution. manufacturing method. 4 The porous glass body is made of Nb, Ta, Sc, Y, La.
Alternatively, stuffing is performed with an aqueous solution containing at least one of the nitrates of Th, followed by immersion in one of an inorganic aqueous solution such as aqueous ammonia, aqueous alkaline solution, perchloric acid, or sulfuric acid, followed by precipitation with water or the inorganic aqueous solution mentioned above. Claim 1, characterized in that a predetermined concentration distribution is obtained by performing unstuffing with a dilute aqueous solution and then immersing it in one of the inorganic aqueous solutions to re-precipitate the dopant compound. A method for manufacturing optical transmission glass. 5. Stuffing the porous glass body with an aqueous solution containing lanthanum nitrate and at least one alkali metal nitrate, followed by immersion in ethyl alcohol to precipitate the alkali metal nitrate compound and co-precipitate the lanthanum nitrate at the same time; After that, it is unstuffed with water or an aqueous solution containing water + alcohol or water + an alkali metal nitric acid compound,
2. The method of manufacturing optical transmission glass according to claim 1, wherein a predetermined concentration distribution is obtained by further precipitating with the solution used for the precipitation.