JPH04260632A - Production of optical fiber containing rare earths added thereto - Google Patents

Abstract

PURPOSE:To improve addition efficiency by depositing a porous soot in the interior of a starting quartz tube, then impregnating the deposited soot with sublimed rare earths in the vapor phase, sintering the impregnated soot and transparently vitrifying the impregnated soot. CONSTITUTION:A soot deposited in the interior of a soot deposited quartz tube [13A (13B)] is dehydrated by heating with an oxyhydrogen torch 17 to provide a porous state. An additive of a rare earth compound such as ErCl3 in a sublimation chamber (14a) and an additive such as AlCl3 in a sublimation chamber (14b) are respectively heated with subliming burners (18a) and (18b), sublimed, converted into a vapor-phase state, fed into a soot quartz tube [13A (13B)] with a feeding gas such as He, impregnated into the soot and then heated with the oxyhydrogen torch 17. Thereby, the soot is sintered while moving the oxyhydrogen torch 17 in the direction of an arrow (B). As a result, a transparent quartz tube doped with the additives is obtained, further heated at a high temperature and collapsed to afford the objective preform for the optical fiber containing the rare earths added thereto.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a method for manufacturing rare earth-doped optical fibers containing rare earth elements such as erbium, which are applied to optical fiber technology such as direct amplification of light using optical fibers, and in particular to a method for manufacturing rare earth-doped optical fibers containing rare earth elements such as erbium. This is a fiber manufacturing method that improves the efficiency of adding additives.

0002

2. Description of the Related Art Direct amplification of light using optical fibers doped with rare earth metals is an optical fiber technology that has recently attracted attention. FIG. 9 shows an example of this amplification technology.
This is an erbium (Er) doped single mode fiber aimed at optical amplification in the 5 μm band. ), the excitation light from the excitation light source 3 and the signal light 4 are incident on the optical coupler 2, and the energy of the rare earth ions excited by the excitation light is given to the signal light by stimulated emission, and the amplified light is It is configured to be transmitted to a fiber communication path 5.

[0003] Conventionally, methods using the following CVD method and VAD method are known as methods for manufacturing the base material of the rare earth-doped optical fiber. For example, the method shown in FIG.
A halide of the metal to be added (for example, NdCl
Additives such as Nd and Er are deposited in the soot 7 while introducing a mixed gas of He and a gas obtained by sublimating 3 and ErCl3) into the CVD reaction zone inside the starting quartz tube 6. This is a method (CVD-vapor phase method) in which an optical fiber preform containing Nd or Er is added to the core and then solidified to produce an optical fiber preform containing Nd or Er in the core.

On the other hand, taking advantage of the fact that NdCl3 and ErCl3 are soluble in water and alcohol, these NdCl3 and ErCl3
An additive solution is prepared by dissolving Cl3 or ErCl3 in ethanol, etc., and this additive solution is poured into the soot 7 of the quartz tube 6.
There is also a known method (CVD-liquid phase method) in which Nd and Er are added to the soot 7 by impregnating the soot 7, drying it, and then sintering it with a burner 7.

Furthermore, in the VAD method, as shown in FIG. 11, for example, a soot-deposited portion 10 of a quartz glass rod 9 on which soot is deposited is heated with He and solid state NdCl3 or ErCl.
A method of sintering in a mixed atmosphere of gas obtained by sublimating No. 3 (VAD-vapor phase method) is known.

On the other hand, there is also a method (VAD - liquid phase method) in which the soot-deposited portion 10 of the quartz glass rod 9 on which soot is deposited is impregnated with an additive solution in which NdCl3 or ErCl3 is dissolved in ethanol, etc., and then dried and sintered. Are known.

[0007]

[Problem to be solved by the invention] However, the above C
In the former method (CVD-vapor phase method) of the VD methods, it takes a long time to deposit soot, and NdC in a solid state is used.
Since it is very difficult to control the amount of heat applied when sublimating l3 and ErCl3, it is extremely difficult to make the partial pressure of NdCl3 gas and ErCl3 gas in the mixed gas flowing into the CVD reaction zone uniform for a long time. For this reason, Nd
There was a problem in that it was not possible to obtain soot to which Er and Er were added uniformly. Additionally, as the soot deposition time increases, the frequency of the additive flowing into the CVD reaction zone as a solid increases.
There was a problem that caused bubbles to form.

In addition, in the latter method (CVD-liquid phase method), the amount of NdCl3 and ErCl3 that can be dissolved in a solvent such as ethanol naturally has a limit commensurate with its solubility; exceeding Nd and Er
It was not possible to add

[0009] Furthermore, among the above VAD methods, the former method (V
In AD-vapor phase method), it takes a long time to sinter the soot (2
However, during the sintering operation, it is extremely difficult to sublimate a constant amount of additives, so it is difficult to add additives uniformly in the longitudinal direction of the quartz rod. was there.

[0010] Furthermore, the latter method (VAD-liquid phase method) has the problem that soot cracking may occur when the soot is immersed in the additive solution.

On the other hand, recently, A along with Er has been added to optical fibers.
A method of improving the wavelength characteristics of an optical fiber type optical amplifier by adding l is widely used. By this method, E
As is clear from the wavelength-gain characteristic graph shown in FIG. 12, the optical fiber doped with Er and Al has Er in the core.
Compared to optical fibers doped only with rare earth metals such as
It is known that the gain wavelength characteristics are better. Furthermore, when applying an optical fiber doped only with rare earth metals such as Er to the optical amplifier shown in FIG.
When using an optical fiber containing Er at a high concentration exceeding 00 ppm, a phenomenon occurs in which Er ions give and receive excitation energy that should originally be given to signal light 4 through stimulated emission of Er ions (co-operative up-conversion effect). ), but it is also known that this phenomenon does not occur if Al is co-added.

However, even when Al is added to the soot by the two CVD methods and the two VAD methods mentioned above, it is not possible to add Al at a high concentration and uniformly for the same reason as when adding rare earths. It was extremely difficult.

The present invention was made in view of the above circumstances, and
It is an object of the present invention to provide a method for manufacturing a rare earth-doped optical fiber that can uniformly add metals such as rare earth metals and Al that are solid at room temperature to soot deposited on a quartz tube at a high concentration.

[0014]

[Means for Solving the Problems] This problem is solved by depositing a porous silica glass soot in a starting quartz tube by CVD, adding a rare earth element to the soot, and then heating the starting quartz tube. In the method for manufacturing a rare earth-doped optical fiber, the soot is melted to form a transparent glass layer containing the rare earth element, and the starting quartz tube is further heated and solidified to form a preform. A tube with at least one additive sublimation chamber connected to one open side of the tube is prepared, and after porous soot is deposited on the inner part of the starting quartz tube, it is placed in the sublimation chamber. The problem is solved by heating the additive, impregnating the sublimated gas-phase additive into the soot, and then converting the soot impregnated with the additive into transparent vitrification.

An example of the method for manufacturing the rare earth-doped optical fiber of the present invention will be explained in detail below.

First, as shown in FIG. 1, pure quartz tubes 12 having the same outer diameter and inner diameter as the fluorine-doped quartz tube 11 are placed at both ends of a fluorine-doped quartz tube 11 doped with fluorine or the like.
A quartz tube 13 is produced by melting and joining the ends of each of the tubes 12 so that their outer diameters match.

Next, as shown in FIG. 2, two sublimation chambers 14a and 1 are connected to one opening of the quartz tube 13.
4b are installed in series. Note that ErCl3 is placed in the sublimation chamber 14a, and additives such as AlCl3 are placed in the sublimation chamber 14b in advance.

Next, the quartz tube 13 with the sublimation chambers 14a and 14b connected thereto is installed in a glass lathe 15 as shown in FIG. The etching gas is supplied with oxygen as a carrier gas, and at the same time, an oxyhydrogen torch 17 provided directly below the quartz tube 13 is installed at a portion of the quartz tube 13 that will become a soot deposition portion, along the length of the quartz tube 13 shown by arrow B. The inner surface of the quartz tube 13 is etched by heating while moving in the direction.

After the etching is completed, as shown in FIG. 4, the feeding of the etching gas is stopped, and then SiCl4 is injected into the quartz tube 13 by the gas feeding device 16 using oxygen as the carrier gas.
into the tube, and the surface of the quartz tube 13 reaches 1100 to 1300℃.
Move the oxyhydrogen torch 17 in the direction of arrow B while adjusting the firepower of the oxyhydrogen torch 17 so that the quartz tube 1
3. A quartz tube 13A with soot deposited therein is manufactured.

Next, as shown in FIG.
6, helium gas and Cl2 gas are poured into the soot-depositing portion in the quartz tube 13A, and the gas is directly below the sublimation chambers 14a and 14b so that the temperature inside the sublimation chambers 14a and 14b is approximately 190 to 210°C. Each of the sublimation chambers is heated with the provided heating burners 18a and 18b to dehydrate the additives inside each of the sublimation chambers.

Further, while performing the above additive dehydration operation, the oxyhydrogen torch 17 is moved in the direction of arrow B, and the quartz tube 13A is
Dehydrates the soot that has accumulated inside the pipe. The heating power of the oxyhydrogen torch 17 during this soot dehydration is adjusted so that the surface temperature of the quartz tube 13A is approximately 650 to 750°C.

Next, after dehydrating the additives and soot, as shown in FIG. 6, the gas supply device 16 is operated to stop the flow of Cl2 gas into the quartz tube 13A. Next, the heating power of the heating burner 18a is set to 930°C in the sublimation chamber 14a.
The heating temperature of the heating burner 18b is adjusted so that the temperature in the sublimation chamber 14b is about 240-260°C.
The temperature is adjusted to about 0° C., and Er in the sublimation chamber 14a and Al in the sublimation chamber 14b are sublimated into gaseous states, and these gaseous additives are added to the quartz tube 13A.
It is sent to the soot-accumulated area in the interior and impregnated. Furthermore, after that, the heating power of the oxyhydrogen torch 17 is adjusted so that the surface temperature of the quartz tube 13A is about 1700 to 1900°C,
Further, while moving the oxyhydrogen torch 17 in the longitudinal direction of the quartz tube 13A, the soot is sintered to produce a transparent quartz tube 13B doped with additives.

Next, as shown in FIG.
The quartz tube 13B is heated to a high temperature to shrink the quartz tube 13B, thereby making the quartz tube 13B solid, thereby producing an optical fiber preform 20 having a core 19 added with an additive.

In the method for manufacturing the rare earth-doped optical fiber of this example, as described above, two types of additives (ErCl3
and AlCl3) are placed in a sublimation chamber connected to one opening of the starting quartz tube, and sublimated into a gaseous state.The soot deposited area is doped with these gaseous additives, and then The soot impregnated with additives is made into transparent glass, and the resulting quartz tube is solidified to produce an optical fiber base material. Can be added. Therefore, the optical fiber preform manufactured by this rare earth-doped optical fiber manufacturing method has greatly improved wavelength-gain characteristics, and can be applied to an extremely wide band optical amplifier.

[0025] Furthermore, in the method for manufacturing the rare earth-doped optical fiber of this example, Er and Al are used as additives, so Al is co-doped into the optical fiber preform manufactured by this method. In an optical amplifier using an optical fiber made of an optical fiber base material, the co-operative up-conversion effect is suppressed.

[0026]

EXAMPLE An optical fiber was manufactured based on an example of the optical fiber manufacturing method of the present invention described above.

First, the outer diameter is 26 mm, the inner diameter is 20 mm, and the length is 2.
A quartz tube 13 is obtained by melting and joining one 00 mm fluorine-doped quartz tube 11 and pure quartz tubes 12, 12 having the same outer diameter and inner diameter as this fluorine-doped quartz tube 11, by aligning their outer diameters. was created.

Next, as shown in FIG. 2, two sublimation chambers 14a and 1 are connected to one opening of the quartz tube 13.
4b were installed in series. Note that 5 g of ErCl3 is placed in the sublimation chamber 14a, and 10 g of AlCl3 is placed in the sublimation chamber 14b.
I put it in.

Next, the quartz tube 13 with the sublimation chambers 14a and 14b connected thereto was installed in a glass lathe 15 as shown in FIG.
ml of SF6 and 2,000 ml of oxygen per minute are fed into this quartz tube 13, and at the same time, the oxyhydrogen torch 17 provided directly below the quartz tube 13 is connected to the portion of the quartz tube 13 that will become the soot accumulation section. The inner surface of the quartz tube 13 was etched by heating while moving it in the longitudinal direction of the quartz tube 13 shown in B.

After the etching is completed, as shown in FIG. 4, the feeding of the etching gas is stopped, and then the Si
A gas obtained by bubbling Cl4 with oxygen at a rate of 530 ml per minute was fed into the quartz tube 13 by the feeding device 16. Also, at this time, the oxyhydrogen torch 17 was moved in the direction of arrow B while adjusting the firepower of the oxyhydrogen torch 17 so that the surface of the quartz tube 13 reached about 1200° C., so that soot was deposited inside the quartz tube 13. 13A was produced.

Next, as shown in FIG.
6 to 2000ml helium gas per minute and 50ml per minute
of chlorine is poured into the soot deposited portion in the quartz tube 13A, and the sublimation chamber 14a is heated so that the temperature inside the sublimation chambers 14a and 14b is approximately 200°C.
, 14b, heating burners 18a,
Each of the sublimation chambers was heated in step 18b to dehydrate the additives inside each of the sublimation chambers.

Further, while performing the above additive dehydration operation, the oxyhydrogen torch 17 is moved in the direction of arrow B, and the quartz tube 13A is
The soot accumulated inside the pipe was dehydrated. The heating power of the oxyhydrogen torch 17 during this soot dehydration was adjusted so that the surface temperature of the quartz tube 13A was approximately 700°C.

Next, after dehydrating the additives and soot, the gas supply device 16 was operated to stop the flow of Cl2 gas into the quartz tube 13A, as shown in FIG. Next, the heating power of the heating burner 18a is set to 950°C in the sublimation chamber 14a.
The heating power of the heating burner 18b is adjusted so that the temperature inside the sublimation chamber 14b is about 250°C, and Er in the sublimation chamber 14a and Al in the sublimation chamber 14b are sublimed. The additives in the gaseous state were then sent into the soot deposited portion of the quartz tube 13A to impregnate it. After that, the heating power of the oxyhydrogen torch 17 is adjusted so that the surface temperature of the quartz tube 13A is about 1800°C, and the soot is sintered and added while moving the oxyhydrogen torch 17 in the longitudinal direction of the quartz tube 13A. A transparent quartz tube 13B doped with the agent was prepared.

Next, as shown in FIG.
The quartz tube 13B was heated at a high temperature to shrink the quartz tube 13B, thereby making the quartz tube 13B solid, thereby producing an optical fiber preform 20 having a core 19 to which an additive was added.

The core 19 of the optical fiber preform 20 is coated with EP
As a result of measuring the Al concentration distribution using the MA method, this core 19
It was found that the addition was uniform at a concentration of 4 wt.% in both the radial and longitudinal directions. Incidentally, FIG. 8 shows the wavelength gain characteristics of the optical amplification optical fiber manufactured using the optical fiber preform 20 manufactured in this example.

[0036]

As described above, in the method of manufacturing a rare earth-doped optical fiber of the present invention, soot is deposited inside the starting quartz tube, and then the deposited soot of the soot-deposited quartz tube is used for sublimation. The soot is impregnated with the gaseous additive by sublimating it in the chamber and making it into a gaseous state.The soot is then sintered to produce a transparent quartz tube, and the soot is then sintered to produce a transparent quartz tube. Since the optical fiber preform is manufactured by solidifying the quartz tube, a high concentration of additive can be added to the core of the optical fiber preform. Therefore, the optical fiber manufactured by the method for manufacturing a rare earth-doped optical fiber of the present invention has greatly improved wavelength-gain characteristics, and can be applied to an extremely wide band optical amplifier.

Furthermore, since the time for doping the additive is short, the time for sublimating the additive is also short, making it easy to maintain a uniform amount of sublimation of the additive. Therefore, the concentration of additives added into the soot is made uniform. In addition, if the time for sublimating the additive is short, the frequency of the additive being fed into the CVD reaction zone in a solid state is extremely low, making it difficult for air bubbles to be generated during soot clarification.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal cross-sectional view of a starting quartz tube used in an example of the method for producing a rare earth-doped optical fiber according to the present invention.

2 is a diagram showing a state in which sublimation chambers 14a and 14b are connected to one opening of a quartz tube indicated by reference numeral 13 in FIG. 1. FIG.

FIG. 3 is a schematic diagram showing an apparatus suitably used in the rare earth-doped optical fiber manufacturing method of the present invention.

FIG. 4 is a diagram for explaining a soot deposition operation in the rare earth doped optical fiber manufacturing method of the present invention.

5 is a diagram for explaining the dehydration operation of the soot deposited in the quartz tube indicated by 13A in FIG. 4 and the additives in the sublimation chamber indicated by 14a and 14b; FIG.

FIG. 6 is a diagram for explaining the operation of sublimating the additive and impregnating it into soot.

7 is a diagram for explaining an operation of solidifying a quartz tube indicated by reference numeral 13B in FIG. 6. FIG.

FIG. 8 is a graph showing wavelength gain characteristics of an optical amplification optical fiber manufactured using the optical fiber preform 20 manufactured in the example.

FIG. 9 is a diagram showing an example of a conventional direct amplification technology of light using a rare earth-doped optical fiber.

FIG. 10 is a diagram for explaining a method of manufacturing a rare earth-doped optical fiber using a conventional CVD-vapor phase method.

FIG. 11 is a diagram for explaining a method of manufacturing a rare earth doped optical fiber using the conventional VAD-vapor phase method.

FIG. 12 is a graph for comparing the wavelength-gain characteristics of an optical fiber whose core is doped with Er and an optical fiber whose core is doped with Er and Al.

[Explanation of symbols]

11 Fluorine-doped quartz tube 12 Pure quartz tube 13 Quartz tube 13A soot deposited quartz tube 14a sublimation chamber 14b sublimation chamber 20 Optical fiber base material

Claims (1)

[Claims] 1. Depositing a porous silica glass soot in a starting quartz tube by a CVD method, adding a rare earth element to the soot, and then heating the starting quartz tube to melt the soot, In the method for manufacturing a rare earth-doped optical fiber, the transparent glass layer containing a rare earth element is formed, and the starting quartz tube is further heated and solidified to form a preform. A series of additive sublimation chambers is prepared, and after depositing porous soot on the inner part of the starting quartz tube, the additive contained in the sublimation chamber is heated. . A method for producing a rare earth-doped optical fiber, comprising impregnating the soot with a sublimated gas-phase additive, and then converting the soot impregnated with the additive into transparent glass.