JP3367624B2 - Optical fiber - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical glass component, for example, a low scattering optical fiber used for an optical fiber for transmission, a fiber laser, a fiber amplifier and the like.

[0002]

2. Description of the Related Art Among the factors that govern the loss of an optical fiber, the ones attributed to the inherent properties of glass are absorption due to molecular vibration in the infrared light region and light scattering in the ultraviolet and visible light region (Rayl).
eigh scattering). An optical fiber made of a fluoride glass having excellent infrared light transmissivity has been studied for the purpose of obtaining a loss characteristic lower than that of a silica optical fiber currently used for optical communication.

However, it has been revealed that in the fluoride glass, fine crystals are likely to precipitate during the production, and it becomes a light scattering center to increase the loss, and the loss characteristics of silica glass have not been exceeded (JBMacChesney and DJDiGiova).
nni, J. Am. Ceram. Soc., 1990, Vol.73, 3537-3556).

The silicate-based multi-component oxide glass is superior to the fluoride glass in that crystals are less likely to precipitate than the fluoride glass. However, since the infrared transmissivity is not as great as that of fluoride glass, it is necessary to select glass that has small light scattering in the ultraviolet and visible range in order to realize a low loss optical fiber.

In the alkali-alkaline earth silicate glass, a composition having a smaller Rayleigh scattering than that of quartz glass has been clarified (J. Schroeder; "Light Scatteri
ng of glass "in M.Tomozawa and RHDoremus," Treat
ise on materials science and technology ", Academic
Press, New York, 1977, vol.12, p199 [Na ₂ O-MgO-SiO
₂ type glass] and GACMSpierings and TPMMe
euwsen; J. Non-Cryst. Solids, 1984, Vol.66, p.494 [K
₂ O-MgO-SiO ₂ system glass]).

[0006] We have further studied, silicon oxide (S
iO ₂ ) and a divalent metal oxide (M ^II O and M ^II represent divalent cations) and a monovalent metal compound (M ₂ ^I O and M ^I represent monovalent cations) An oxide glass composition, wherein the SiO ₂ is 50 to 80 mol% and the M ^II O is 0 to 20 mol.
It has been clarified that the silicate-based glass composition characterized by having 1% and M ₂ ^I O of 15 to 40 mol% has smaller light scattering than that of pure SiO ₂ glass and is vitrified stably.
The above M ^II is from at least one of Mg, Ca, Sr, Ba and Zn, and the above M ^I is L
It can be selected from at least one of i, Na and K.

The reason for limiting the composition of the above-mentioned silicate glass composition is that the content of SiO ₂ is less than 50 mol% or M
_{When 2} ^I O is more than 40 mol%, crystals are likely to precipitate in the glass, and SiO ₂ is more than 80 mol%, or M ^II O is 20 mol%.
This is because if the amount is larger or the amount of M ₂ ^I O is smaller than 15 mol%, light scattering becomes large.

However, no attempt has been made to make an optical fiber using this silicate glass composition. That is, there is no known glass for use in the core or the clad, which has a slightly different refractive index, has low scattering, and is thermally stable enough to form a fiber.

When an optical fiber is manufactured by using this glass, two kinds of glass for core and clad having similar thermal characteristics and different in refractive index must be prepared in order to form a waveguide structure. . In order to obtain the same thermal characteristics, it is good to make the glass composition as close as possible. For that purpose, there are generally the following two methods. (1) Dope the glass for the core with a component that increases the refractive index. (2) Dope the glass for cladding with a component that reduces the refractive index. In the case of (1), an increase in refractive index leads to an increase in Rayleigh scattering. That is, the Rayleigh scattering intensity peculiar to glass increases in proportion to the 8th power of n as described by the following equation (DAPinnow et al .; Appl. Phys. Lett., Vol. 22, p. 52).
7 (1973)).

[0010]

[Equation 1]

Here, n is the refractive index, p is the elastic optical constant, K _T (T _F ) is the static isothermal compressibility, T _{F is the} fictive temperature, and the glass transition temperature Tg. In fact, increased scattering of Pb-doped glass has been reported (GACMSpierings and TPM Meeuwsen; J. Non-
Cryst. Solids, 1984, Vol.66, p.494).

In the case of (2), it is considered that doping with boron (B) and fluorine (F) is effective for reducing the refractive index. That is, in quartz glass, B
It is known that Tg and n are reduced by doping with F (T. Izawa and S. Sudo, "Optical fibers:
materials and fabrication ", KTK Scientific Publieh
ers (1987), p.27). However, the doping of B causes an increase in infrared absorption, and is not effective in reducing the loss. Therefore, it is considered that introduction of fluorine is effective.

On the other hand, it is known that when a silicate glass is doped with fluoride, phase separation and crystallization occur (H. Sc
holze, "Glass-Nature, Structure and Properties", Sp
ringer-Verlag, New York, 1991). This significantly increases light scattering and also reduces glass stability. The degree of phase separation and crystallization tendency is closely related to the glass composition.

[0014]

SUMMARY OF THE INVENTION Thus, Rayleigh
There is no known cladding glass that has a low refractive index, is low in scattering, and is thermally stable, which is necessary for producing an optical fiber having a core of silicate glass having low scattering. An object of the present invention is to provide an optical fiber using a low-scattering silicate glass by combining a low-refractive index and low-scattering glass composition as a raw material.

[0015]

Means for Solving the Problems The constitution of the present invention which achieves the above object is silicon oxide (SiO ₂ ), a divalent metal compound (M ^II X _x , M ^II is a divalent cation, and X is an anion). Ion, x
Represents the number of anions) and monovalent metal compounds (M
^I X ′ _y , M ^I is a monovalent cation, X ′ is an anion, and y is the number of anions), and a silicate glass composition is used as a core, and at least silicon (Si), An oxyfluoride glass composition composed of a divalent metal (M ^II ), a monovalent metal (M ^I ), oxygen (O) and fluorine (F), which satisfies all of the following conditions 1 to 3 concerning the composition: The clad is characterized in that its composition satisfies at least one of the following conditions as compared with the glass composition for the core, and the refractive index of the glass for the clad is smaller than that of the glass for the core.

Conditions: 40% of the total number of cations is silicon
Above, 75% or less Condition The above divalent metal is 30% or less of the total number of cations The above monovalent metal is 18% or more and 60% or less of the total number of cations Fluorine Is less than 20% of the total number of anions, that is, z atom% of F with respect to the total number of anions is
Then, the condition that z <20 is satisfied. The condition that the glass for clad has a higher SiO ₂ content. The glass composition for clad replaces a part of the components other than SiO ₂ contained in the core glass with a fluoride. The above M ^II is at least one of Mg, Ca, Sr, Ba and Zn, and the above M ^I is Li,
It can be selected from at least one of Na and K.

[0017]

In an oxyfluoride glass composition composed of silicon, a divalent metal, a monovalent metal, oxygen and fluorine, silicon is less than 40% of the total number of cations, or 1
If the valent metal is more than 60% of the total number of cations or the fluorine is more than 20% of the total number of anions, crystals are likely to precipitate in the glass and silicon is more than 75% of the total number of cations. Light scattering increases when the divalent metal is more than 30% of the total number of cations or the monovalent metal is less than 18% of the total number of cations. That is, as shown in FIG.
It is easy to vitrify in the area above the curve α, and
In the region below the curve β, at a scattering angle of 90 °
The relative value R <1 of the Rayleigh scattering intensity with respect to pure SiO ₂ is obtained. In FIG. 2, the range surrounded by the curves α and β (indicated by hatching in the figure) is the auxiliary straight lines ₁ , ₂ ,
It is defined by ₁ and ₂ .

Here, the auxiliary straight lines ₁ and ₂ are 40% and 75% of the total number of cations of silicon, respectively.
The area surrounded by the auxiliary straight lines ₁ and ₂ is the area corresponding to the above condition. Further, the auxiliary straight line shows 30% of the total number of cations of divalent ions, and therefore, the region above the auxiliary straight line is the region corresponding to the above condition. In addition, the auxiliary straight lines ₁ and ₂ have 18 monovalent ions, which is the total number of positive ions.
%, 60%, and therefore the area surrounded by the auxiliary straight lines ₁ and ₂ is the area corresponding to the above conditions. Unless the condition that fluorine is less than 20% of the total number of anions is satisfied, a glass having a relative value R <1 of Rayleigh scattering intensity with respect to pure SiO ₂ at a scattering angle of 90 ° could not be obtained.

After all, when the range of fluorine defined by the auxiliary straight lines ₁ , ₂ , ₁ , ₂ is less than 20% of the total number of anions, Ra
It is possible to obtain a low-scattering glass composition having a small yleigh scattering and stably forming glass. Further, in an optical fiber having a silicate-based glass composition as a core and an oxyfluoride glass composition as a clad, the glass composition for clad is compared with the glass composition for core, and SiO ₂
If the content is large or a part of the components other than SiO ₂ is replaced with fluoride, the refractive index becomes small.

[0020]

EXAMPLES The present invention will now be described in detail with reference to examples, but the present invention is not limited to these examples.

Example 1 Glass was synthesized by the following procedure. As starting materials, SiO ₂ , Na ₂ CO ₃ ,
Powders of MgO and MgF ₂ (purity 99.9% or more) were used.
These are weighed and mixed so as to have a predetermined component ratio, the mixed raw material is put into a platinum crucible, and an electric furnace is used to raise the heating rate 1
It was heated at 0 ° C / min and melted at 1300 to 1500 ° C for 1 hour. After melting, it was cooled at a rate of 20 ° C / min. At this time, at a temperature of approximately 800 ° C or lower, due to the heat capacity of the furnace,
The cooling rate was smaller than the above, and the glass was in a furnace-cooled state. After cooling, the crucible was taken out and visually inspected for vitrification.

The Rayleigh scattering measurement was carried out on a cylindrical glass sample having the same composition as the glass composition obtained above and on a pure SiO ₂ glass sample prepared by a vapor phase axis (VAD) method. The relative value R of the Rayleigh scattering intensity at a scattering angle of 90 ° for pure SiO ₂ glass was determined. Table 1 is a table for explaining one embodiment of the present invention, in which the above M ^II X _x is MgF ₂
And MgO, and M ^I X ′ _y is NaO, the glass composition of the core and the cladding, the refractive index, the refractive index difference Δ and Ra.
It shows a relative value R of yleigh scattering with respect to pure SiO ₂ glass.

[0023]

[Table 1]

As can be seen from the above, regarding the refractive index,
It can be seen that the refractive index becomes smaller by increasing the amount of SiO ₂ or substituting a part of MgO with MgF ₂ . FIG. 1 is a diagram showing the results of measuring the Rayleigh scattering intensity of the glass samples shown in Table 1 obtained above with respect to angles. Also,
The measurement results for the pure SiO ₂ glass sample are also shown. In FIG. 1, the glass for core is indicated by a triangle symbol, the glass for clad is indicated by a symbol, and the pure SiO ₂ glass is indicated by a square symbol. As is clear from the figure, the Rayleigh scattering of both the glass samples of the compositions of this example is significantly smaller than that of the pure SiO ₂ glass sample, about 70% and about 40%, and the refractive index of the cladding glass is It can be made 1% smaller than the core glass.

Further, the results show that the cladding glass 1 can be used as the core and the cladding glass 2 can be used as the cladding. The above shows that when an optical fiber is manufactured using the glass in the composition range of this example, a lower value can be expected as the optical loss than that of the pure SiO ₂ optical fiber. in this way,
By combining glass in the composition range of this example, a waveguide structure can be formed in the fiber, and an optical fiber with small light scattering can be formed.

[0026] [Example 2] shown in the first embodiment, shown MgF ₂ other than M ^II X _x, the embodiment using the M ^I X _'y other than Na ₂ O in Table 2.

[0027]

[Table 2]

Further, as M ^II X _x and M ^I X _'y, it is needless to say that effective to use a plurality of components. Furthermore, the introduction of fluorine into the glass composition, M ^I F
It goes without saying that it is possible to use (monovalent metal fluoride).

[0029]

As described above in detail with reference to the examples, by using the silicate glass composition of the present invention in the core and the clad, Rayleigh scattering is small and a stable glass is obtained. It was possible to provide a glass composition for forming a low loss optical fiber.

[Brief description of drawings]

FIG. 1 Glass for core (60SiO ₂ -30Na ₂ O-10
MgO), glass for clad (65SiO ₂ -25Na ₂ O)
-5MgF ₂ -5MgO) and Rayleigh of pure SiO ₂ glass
It is a graph which shows the angle dependence of scattering intensity.

FIG. 2 is a ternary phase diagram showing the overlap of the vitrification range and the composition range with R> 1.

FIG. 3 is a diagram expressing an oxyfluoride glass composition using an xyz space.

[Explanation of symbols]

x a of M ^I (monovalent metal element) with respect to the total number of cations
tom% y of the total number of cations of M ^II (divalent metal element)
atom% z atom% of F with respect to the total number of anions

─────────────────────────────────────────────────── ─── Continuation of the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) C03C 1/00-14/00 WPI

Claims (2)

(57) [Claims] 1. A silicate glass composition comprising silicon oxide, a divalent metal compound and a monovalent metal compound as a core, and at least silicon, a divalent metal, a monovalent metal, oxygen and An oxyfluoride glass composition comprising fluorine, which satisfies all of the following conditions 1 to 4 as a clad, and the composition thereof is at least one of the following conditions as compared with the core glass composition: As a result, the refractive index of the glass for cladding is made smaller than that of the glass for core. Conditions Silicon is 40% or more of the total number of cations, 75%
The condition that the divalent metal is 30% or less of the total number of cations The condition of the monovalent metal is 18% or more and 60% or less of the total number of cations Fluorine is an anion It is less than 20% of the total number, that is, the atom% of F with respect to the total number of anions is z
Then, the condition that z <20 is satisfied. The condition that the glass for clad has a higher SiO ₂ content. The glass composition for clad replaces a part of the components other than SiO ₂ contained in the core glass with a fluoride. The composition should be 2. The divalent metal is Mg, Ca, Sr, B.
The optical fiber according to claim 1, wherein the optical fiber is at least one of a and Zn, and the monovalent metal is at least one of Li, Na, and K. .