JPH0735266B2 - Optical fiber and manufacturing method thereof - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] In the present invention, the core portion is made of GeO ₂ glass and has a long wavelength region (up to 2.
The present invention relates to an optical fiber capable of low-loss optical transmission up to 1 μm and having a large nonlinear optical effect, and a method for manufacturing the same.

[Conventional technology]

Conventionally, as an optical fiber using an oxide glass other than SiO ₂ glass and multi-component glass, as seen in the publication by Takahashi et al. (Electron Letter 1982, Vol. 18, pp. 398-399), it is used as a core member. using a glass material obtained by adding antimony (Sb) to increase the refractive index to GeO ₂ glass, there is an example of a multimode fiber using GeO ₂ glass as the cladding member. However, since this type of fiber uses GeO ₂ glass with antimony added to the core, there is a problem in that the loss cannot be reduced by the absorption loss caused by Sb ₂ O ₃ .

Further, there is a problem that the relative refractive index difference between the core layer and the clad layer cannot be made sufficiently large because the amount of antimony added is limited.

Such, in the manufacture of optical fiber comprising a GeO ₂ glass, porous nature due that the softening point of GeO ₂ is low (about 1050 ° C.) vapor pressure is high, as represented by the VAD method, the glass preform It is impossible to use a manufacturing method in which the material is formed as a material, and the material is made into transparent glass and drawn, and it is difficult to manufacture a single-mode optical fiber.

[Problems to be solved by the invention]

The present invention, the core portion of the optical fiber formed by pure GeO ₂ glass, the cladding portion does not become irregular in the structure of the GeO ₂ issues, and materials such as refractive index is less than GeO ₂ By using it, it is intended to realize an optical fiber which does not have unnecessary absorption and has low loss up to a long wavelength (up to 2.1 μm) as a characteristic of GeO ₂ .

In addition, by improving the VAD method, it becomes possible to deposit low-melting GeO ₂ glass or glass containing GeO ₂ as a main component in the form of fine particles, and an optical fiber preform of any diameter having a core / clad structure. Is what you are trying to get.

In the GeO ₂ core single mode optical fiber made possible by the manufacturing method of the present invention, highly efficient non-linear optical effect can be expected due to the concentration of optical power.

In order to deposit GeO ₂ having a lower softening temperature than SiO ₂ as a porous body by the flame method, it is necessary to lower the flame temperature. If the flame temperature is above a certain level, the temperature of the deposition part will be above the sublimation temperature of GeO ₂ , and deposition will not occur. The flame temperature of an oxyhydrogen flame can be lowered by reducing the flow rate of hydrogen, which is a combustible gas, but the flame becomes unstable and it becomes impossible to deposit a porous body with a constant diameter. . Therefore, in the present invention, a torch for synthesizing glass particles is supplied with a certain amount of an inert gas at the same time as a combustible gas and a combustion-supporting gas to lower the flame temperature and form an oxide having a low softening temperature in the flame. It is characterized by supplying a gas raw material to do so.

According to the method of the present invention, it is possible to lower the flame temperature by controlling the amount of inert gas, and, since it is possible to maintain a stable state of the flame, the glass containing GeO ₂ or GeO ₂ as the main component. It is possible to deposit fine particles with a constant diameter. Also SiO ₂
Glass in which an additive for lowering the melting point is added to the system glass can be deposited without any problem.

[Means and Actions for Solving Problems]

In the present invention, the selection of the cladding member is important because pure GeO ₂ is used as the core of the optical fiber.

The first candidate for the clad member is SiO ₂ glass. SiO ₂
In order to use the system glass as the cladding, the difference in the softening temperature and the difference in the coefficient of thermal expansion with GeO ₂ are problems. The refractive index is
GeO ₂ is about 1.6, whereas SiO ₂ is about 1.46 and G
eO ₂ is large enough to give a sufficient relative refractive index difference Where n ₀ and n ₁ are the refractive indices of the core and cladding, respectively.
Can be obtained.

The difference between the combustion temperature and the coefficient of thermal expansion is solved by adding P ₂ O ₅ to SiO ₂ . The addition of P ₂ O ₅ increases the refractive index of SiO ₂ , but the increase rate is small and Δn with GeO ₂ is secured at 5% in a practical range. Figure 2 is a glass doped with P ₂ O ₅ to SiO ₂ (a) refractive index, (b) softening temperature, (c) the thermal expansion coefficient α
And the comparison with the value of GeO ₂ . For example, SiO ₂ glass containing 15 mol% P ₂ O ₅ has a refractive index of 1.47 and a softening temperature of 1050.
℃, the thermal expansion coefficient is 2.5 × 10 ^-6 , the difference between the characteristics and GeO ₂ glass is 10 ° C. softening temperature, about 3 times the thermal expansion coefficient, it is possible to form the core, clad structure. At this time, the relative refractive index difference Δn is 8.8%.

The second candidate for the clad material is GeO ₂ glass with fluorine added.

In the fluorine-added GeO ₂ glass, the softening temperature and the coefficient of thermal expansion of GeO ₂ glass are little changed from that of GeO ₂ glass. Therefore, it is necessary to secure the refractive index difference between the core and the cladding and to effectively add fluorine to GeO _2. The method of inclusion is a major issue.

FIG. 3 shows the change in the refractive index of GeO ₂ glass containing fluorine. A refractive index decrease of about 0.2 is observed with the addition of 1 mol% fluorine. The addition of fluorine to GeO ₂ is effectively performed by forming a porous glass body and treating this in a fluorine atmosphere to make the porous body transparent, as in the case of adding fluorine to SiO ₂ glass. It became clear that addition was possible. Also, even if the transparent glass body GeO ₂ glass is treated in a fluorine atmosphere, fluorine is not added, so the amount of fluorine added is controlled in the fiber radial direction by controlling the bulk density of the GeO ₂ porous body. It became clear that it could be done.

As described above, the behavior of fluorine is almost the same as the findings obtained for SiO ₂ -based glass, except that the deposition temperature of GeO ₂ -based porous glass is low and the heating temperature for vitrification is low. Is. However, in the case of GeO ₂ -based glass, if the deposition is performed so that fluorine is contained only in the limited part of the porous body, the fluorine may remain in the limited part due to the subsequent transparency. It was revealed. In SiO ₂ -based glass, fluorine cannot be localized in this way without controlling the bulk density of the porous body. It is considered that this difference is due to the fact that the diffusion of fluorine in the porous body is not so fast at the transparent vitrification temperature (about 900 ° C.) of the porous body of GeO ₂ glass.

The addition of fluorine is the primary candidate for the core member, SiO ₂ -P ₂
It is also effective when applied to O ₅ type glass.

〔Example〕

Example 1 FIG. 1 is a diagram showing an example of the optical fiber of the present invention, showing the dimensions of the core and cladding and the refractive index distribution in the fiber cross section. 21 is a core made of GeO ₂ glass, 22 is Si
This is a cladding part made of O ₂ -P ₂ O ₅ (15 mol%) glass. The lower part of FIG. 1 shows the refractive index distribution in the radial direction, and the relative refractive index difference Δ0 in this example is 8.8%. Core diameter D ₀
Is 0.8 μm and the fiber diameter D ₁ is 125 μm. At this time, determine the fiber transmission specification At a wavelength λ = 0.5 μm or more, V ≦ 2.405 is satisfied, resulting in a single-mode optical fiber. The loss of this optical fiber was 1 dB / Km or less in the wavelength range of 1.4 to 2.1 μm.

Further, when a semiconductor laser beam of 5 mV (λ = 1.3 μm) was made incident on the fiber, emitted light due to the stimulated Raman effect was generated in the wavelength range of λ = 1.36 to 1.54 μm. Since the relative refractive index is large, the intensity of the propagating light in the core portion is about 10 ² times as large as that of the optical fiber having Δn = 0.3%. Due to this strong confinement effect, the Kerr effect in which the refractive index changes depending on the light intensity is observed, and when a light pulse with a pulse width of 10 psec (wavelength 1.55 μm) is injected, self-focusing of the pulse with a pulse width of 5 psec at 1 km propagation. A phenomenon was seen.

Example 2 FIG. 4 shows a second example of the present invention, in which the core portion was formed of GeO ₂ and the clad portion was formed of GeO ₂ glass 22 'to which 0.2 mol% of F was added. At this time, the relative refractive index difference between the core and the clad was 0.31%, and when the core diameter D ₀ was 8 μm, V ≦ 2.405 was obtained at a wavelength of 1.29 μm or more, and a single mode optical fiber was obtained.

The loss of the single mode optical fiber in the wavelength range of 1.3 to 2.1 μm is 1 dB / Km or less, and the 50 mW semiconductor laser light (λ =
1.3 μm) is incident on the fiber, λ = 1.36 ~
Emitted light was generated by the stimulated Raman effect in the wavelength range of 1.56 μm.

Example 3 In the fiber of Example 2 above, the cladding glass 21 '
The amount of fluorine added therein was increased to Δn = 3%. In this fiber, by setting the core diameter D ₀ to 2.0 μm,
The single mode condition was satisfied at a wavelength of 1 μm or more. When semiconductor laser light (λ = 1.3 μm) was incident on this fiber, stimulated Raman light was generated with an incident light amount of 5 mW, and a very high nonlinear optical effect was exhibited.

Example 4 FIG. 5 shows the structure of a glass particle synthesizing torch used in the method for producing an optical fiber of the present invention. 1 is a raw material nozzle,
2 is a combustion gas nozzle, 3 is an auxiliary combustion gas nozzle, 4 is a gas mixer, and 5 is a torch body. In the torch, the combustion gas and the inert gas are introduced into the gas mixer 4, mixed at a desired ratio, and then introduced into the combustion gas nozzle. The mixed gas from the combustion gas nozzle and the auxiliary gas form a flame at the tip of the torch, and the glass raw material such as GeCl ₄ supplied from the raw material nozzle 1 in the flame is flame-hydrolyzed into glass fine particles such as GeO _2. . The flame temperature can be lowered by mixing an inert gas with the combustion gas. FIG. 6 shows how the flame temperature changes with the flow rate ratio of H ₂ which is the combustion gas when He is used as the inert gas. The sum of the flow rates of He and H ₂ was constant at 5 / min. The flame temperature was measured at the center at a distance of 20 mm from the torch tip. By mixing 50% of He, the flame temperature decreased to 900 ℃. Since the total flow rate was constant, the fluid conditions of the flame flow did not change,
The shape of the flame was constant.

FIG. 7 shows a state in which a porous body of GeO ₂ is deposited using the torch of FIG. 32 is a flame flow formed, 33 is a glass fine particle flow formed in the flame flow, 35 is a reaction vessel, 36 is a starting rod, and 38 is an exhaust port. As a glass raw material
GeCl ₄ is 200 cc / min, H ₂ is 2.5 / min, H as combustion gas
E was supplied to the torch 5 at a rate of 2.5 / min and O ₂ as a co-firing gas at a rate of 10 / min. By blowing the fine glass particle stream 33 onto the tip of the starting rod 36 that rises while rotating, a porous glass body 34 of GeO ₂ was formed in the axial direction at a speed of 50 mm / min. The growth rate of the porous body increased with increasing the flow rate of He while keeping the total flow rate of He and H ₂ constant, and decreased with increasing H ₂ . As long as the total flow rate was constant, there was no significant change in the shape of the porous body.

However, when He is not introduced in the above synthesis and only H ₂ is reduced to lower the flame temperature, the flame becomes unstable as the flow rate of H ₂ is reduced, and a porous body of a certain shape is formed. Could not be formed.

The base material made of GeO ₂ porous glass formed in the above step was dehydrated and made into a transparent glass in an electric furnace into which chlorine and helium as dehydrating agents were introduced. The temperature of the electric furnace was set to 900 ° C. In the process, adding a trace amount of oxygen to the atmosphere gas in the electric furnace is the germanium monoxide (GeO).
It was effective in preventing the generation of. The effect was recognized when the amount of oxygen added was 1 mol% or more of the total gas amount.
Was not observed. When transparent vitrification was performed without adding oxygen, about 1 ppb GeO was observed.

In order to form the core and clad structure of an optical fiber, transparent vitrified or porous GeO ₂ base material is formed on the outer periphery of
The SiO ₂ -P ₂ O ₅ glass fine particles are deposited concentrically.

The SiO ₂ —P ₂ O ₅ glass fine particles were synthesized by introducing POCl ₃ in addition to SiCl ₄ into the raw material nozzle 1 of the glass fine particle synthesis torch shown in FIG. H ₂ gas mixed with He gas was introduced into the combustion gas nozzle in the same manner as in the synthesis of the GeO ₂ porous base material, and the flame temperature was set to 1000 ° C. SiCl ₄ and POCl ₃
About 15 mol% of P ₂ O ₅ was added to the synthesized clad layer by setting the ratio of the supply amount of P to 4: 1. Porous G
When depositing a SiO ₂ —P ₂ O ₅ porous body on the outer circumference of the eO ₂ base material, a plurality of torches are installed in the growth direction of the base material in FIG. 7, and GeCl ₄ is placed on the torch at the bottom. , SiCl ₄ and POCl ₃ can be introduced into the upper torch to synthesize the respective glass particles, and the core and clad can be deposited in a single process.

An optical fiber preform having a core / clad structure can be obtained by transparentizing the clad layer or core and clad layer made of porous glass deposited as described above in the presence of a dehydrating agent in the same manner as described above. It was This base material was drawn at a heating temperature of 1200 ° C. to obtain an optical fiber. The relative refractive index difference in this fiber was about 8.8%.

Example 5 A cylindrical GeO ₂ porous body was deposited using the process of the first stage of Example 4, and this was dehydrated and heated to obtain a GeO ₂ transparent glass body. Centering around the GeO ₂ transparent glass body,
A GeO ₂ porous body was deposited. The deposition conditions were the same as when GeO ₂ was deposited in the central part. The center part formed in this way is transparent Ge
A base material composed of O ₂ glass and a peripheral portion of porous GeO ₂ was heated in a vitreous atmosphere during or immediately before the vitrification. By this treatment, fluorine diffused into the porous glass and was incorporated into the glass during transparent vitrification. No diffusion of fluorine was observed in the center of the base material, which was transparent glass before the treatment. Fluorine has a function of lowering the refractive index of the added portion, and is about 1
% By heat treatment at 900 ℃ in a fluorine atmosphere,
A relative refractive index difference of 0.31% between the core and the clad was obtained. It was possible to increase the relative refractive index difference to about 3% by increasing the fluorine content in the atmosphere and raising the temperature to about 1100 ° C.

In Examples 4 and 5, the ratio of the dimensions of the core and cladding of the fiber finally obtained was adjusted by controlling the diameter of the porous body during deposition. The bulk density of the deposited porous material has a constant value depending on the glass composition and the flame temperature of the synthetic torch. If this value is experimentally obtained, the reduction in diameter in the subsequent transparent vitrification treatment can be sufficiently predicted. It is possible to The control of the fiber diameter by drawing the base material is performed by controlling the heating temperature and the drawing speed, and is achieved with high accuracy by optically reading the fiber diameter immediately after drawing and feeding back the furnace temperature and the drawing speed.

Example 6 In the production condition of the GeO ₂ porous body shown in FIG. 7, a cladding layer was formed on the side surface of the cylindrical porous body using the torch of FIG. At this time, a fluorine compound was mixed into the raw material, and fluorine was directly added to the porous glass. Specifically as a glass raw material for forming a clad layer torch min 500cc of GeCl _4, and supplies min 10cc of SF _6, also the H ₂ 2.5 / min as the combustion gas, the the He 2.5 / min, as supporting gas O ₂ was supplied at a rate of 10 / min to form a clad layer containing fluorine, and then vitrified into transparent glass at 800 ° C. to 900 ° C. in an electric furnace to obtain an optical fiber preform. This base material core,
The relative refractive index difference Δn of the clad was 0.4%. Further, when the amount of fluorine mixed in the raw material was increased, Δn could be improved up to about 2% at the maximum. This is because in the case of GeO ₂ glass, the transparent vitrification temperature is as low as 800 to 900 ° C, so the fluorine contained in the porous body of the clad layer does not diffuse to the core part, and the fluorine does not easily volatilize in the glass. It is thought that it is easy to mix. It is also effective to use CF ₄ or the like as the fluorine source.

〔The invention's effect〕

INDUSTRIAL APPLICABILITY The present invention is an optical fiber having a pure GeO ₂ glass as a core, and is capable of propagating light with low loss up to a wavelength range of 1.4 to 2.1 μm as a characteristic peculiar to a material.

In addition, GeO ₂ -P ₂ O ₅ or fluorine-doped GeO ₂ can be used as a clad to form a core / clad structure. At this time, a significantly large relative refractive index difference ( Can be achieved up to 10%). As an effect, a remarkable concentration of propagating light can be achieved, and a Kerr effect and a stimulated Raman effect can be realized with high efficiency.

The production method of the present invention is characterized by mixing an inert gas with the combustion gas, the flame temperature can be controlled in a wide range, and a low softening temperature glass such as GeO _{2 in} order to not change the flame shape. It is possible to deposit the porous body in a constant shape. By solving this technical problem, it has become possible to manufacture an optical fiber made of glass having a low melting point and having sufficiently controlled dimensions and refractive index. In addition, the method of forming core and clad structures by utilizing the difference in the diffusion rate of fluorine between transparent glass and porous glass has become applicable to the production of optical fibers made of low melting glass. Due to the low transparent vitrification temperature in the addition of fluorine,
It has become possible to manufacture an optical fiber in which fluorine is added to any part.

[Brief description of drawings]

FIG. 1 is a diagram showing a first embodiment of an optical fiber of the present invention,
Fig. 2 shows (a) glass refractive index change, (b) softening temperature change, (c) thermal expansion coefficient change by addition of P ₂ O ₅ to SiO ₂ glass, and Fig. 3 shows GeO. ₂ Diagram showing changes in refractive index when fluorine is added to glass, FIG. 4 is a diagram showing a second embodiment of the optical fiber of the present invention, and FIG. 5 is glass used in the method for producing an optical fiber of the present invention. FIG. 6 is a diagram showing the structure of a torch for synthesizing fine particles, FIG. 6 is a diagram showing a change in flame temperature depending on a flow rate ratio with H ₂ which is a combustion gas when He is used as an inert gas, and FIG. it is a diagram showing a state of depositing a porous body of GeO ₂ using the torch of FIG.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Internal reference number FI Technical display location G02B 6/16 321 7036-2K // C03C 3/32 (72) Inventor Shoji Horiguchi Naka-gun, Ibaraki Prefecture Tokai-mura, Oita, Shirahoji, 162, Shirane, Nippon Telegraph and Telephone Corporation, Ibaraki Research Institute of Telecommunications (56) Reference JP-A-56-72404 (JP, A) JP-A-55-144446 (JP, A) JP 57-11839 (JP, A)

Claims (11)

[Claims] 1. An optical fiber comprising a core part made of GeO ₂ glass and a clad part having a refractive index smaller than that of the core part. 2. The optical fiber according to claim 1, wherein the cladding portion is made of SiO ₂ —P ₂ O ₅ glass. 3. The optical fiber according to claim 1, wherein the cladding portion is made of SiO ₂ —P ₂ O ₅ —F glass. 4. The optical fiber according to claim 1, wherein the cladding portion is made of GeO ₂ -F glass. 5. A glass raw material which forms a single or a plurality of flames by a combustion gas and an auxiliary combustion gas, decomposes into the flames to become an oxide, and glass fine particles produced by a reaction in the flame are formed into a columnar shape. A porous optical fiber preform is deposited, and a method for producing an optical fiber in which this is made transparent and then drawn to form an optical fiber, in which a combustion gas, an auxiliary gas is mixed with an inert gas to lower the flame temperature, A glass raw material that forms an oxide with a low softening temperature is supplied into the flame, and the core is Ge
A method for manufacturing an optical fiber, which comprises O ₂ glass. 6. The glass particles of different composition are concentrically deposited by forming a plurality of flames in the growth direction of the base material and supplying raw materials of different compositions. A method for manufacturing an optical fiber according to the item. 7. The production of an optical fiber according to claim 5, wherein the fine glass particles are synthesized within different flame temperatures by adjusting the flow rate of the inert gas depending on the glass raw material supplied. Method. 8. The method according to claim 5, wherein the flow rate of the combustion gas is reduced as the amount of the inert gas is increased, and the sum of the flow rates of the inert gas, the combustion gas and the co-firing gas is made constant.
Item 6. A method for manufacturing an optical fiber according to Item 6 or 7. 9. A raw material having a composition containing fluorine is supplied to at least one flame among a plurality of flames formed in a growth direction of a base material.
Item 7. A method for manufacturing an optical fiber according to Item 7 or 8. 10. A porous optical fiber preform is prepared by depositing glass particles in a columnar shape, and when the porous optical fiber preform is made transparent, the atmosphere gas contains 1 mol% or more oxygen gas. Claim 5 characterized by the following:
Item 6. A method for manufacturing an optical fiber according to item 7, item 7, item 8 or item 9. 11. A transparent vitrification at a temperature of 1000 ° C. or less in an atmosphere gas containing fluorine at the time of making it transparent, claims 5, 6, 7 and 8. A method for manufacturing an optical fiber according to item 8, item 9, item 10 or item 11.