JPH04271329A - Partially erbium-added optical fiber coupler and production thereof - Google Patents

Abstract

PURPOSE:To provide the partially Er-added optical fiber coupler for optical amplification formed to a high gain by adopting the structure having an erbium(Er)-added region in a part of a clad. CONSTITUTION:The partially Er-added optical fiber coupler 11 is constituted of cores 12, 12 and a clad part 13 and the Er-added region 15 is formed in a part (clad fused part 14) of the clad part 13 between the cores 12 and 12. The optical amplifier having the extremely high gain efficiency is obtd. if the partially Er-added optical fiber coupler is used as the optical amplifier. The up-conversion effect of the clad fused part is suppressed by the added Al, by which the decrease of the gain of the partially Er-added optical fiber coupler is prevented. The refractive index is lowered by an added refractive index lowering agent and the increase in the transmission loss by an increase in the refractive index in the case of coaddition of the Al is prevented.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a partially erbium-doped optical fiber coupler that improves the gain efficiency of an optical fiber coupler used as an optical amplifier, a method of manufacturing the same, and a method of manufacturing the same.

0002

[Prior Art] Conventionally, an optical amplifier using an optical fiber coupler has been manufactured by fusing and stretching two optical fibers whose claddings are doped with erbium (hereinafter abbreviated as Er). Techniques using fiber couplers are known.

FIG. 10 shows the above-mentioned conventional optical fiber coupler for optical amplification, and reference numeral 1 in the figure indicates an Er-doped optical fiber coupler.

The Er-doped optical fiber coupler 1 includes a core 2 made of germanium-doped quartz glass with a diameter of 10 μm, and a cladding 3 made of quartz glass doped with 1500 ppm of erbium in addition to germanium (hereinafter abbreviated as Ge). 2 of 4 optical fibers configured
It was made by fusing and stretching a book.

The Er-doped optical fiber coupler 1 is used, for example, in an optical amplification system shown in FIG. This optical amplification system uses the optical fiber coupler 1 described above to connect pump light from a pump light source 6 and signal light 7 to an erbium (Er)-doped single mode fiber 5 aimed at optical amplification in the 1.55 μm wavelength band. The energy of the incident Er ions excited by the excitation light is given to the signal light by stimulated emission, and the amplified light is transmitted to the fiber communication path 8.

[0006]

However, in the above-mentioned conventional Er-doped optical fiber coupler, Er is not applied to the entire cladding area, that is, to the area where the optical power density is low.
is doped, and in such a region, the efficiency of population inversion due to optical power is poor, and therefore the optical amplification efficiency due to Er ions is reduced accordingly.

Furthermore, in an amplifier using the optical fiber coupler 1, the length of the Er-doped region is inevitably very short, so the Er-doped concentration is increased in order to obtain sufficient amplification. If the concentration exceeds 100 ppm,
This has the disadvantage of causing a phenomenon (up-conversion effect) in which the excitation energy that should originally be given to the signal light 7 by stimulated emission of Er ions is exchanged between Er ions, resulting in a decrease in gain.

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a partially Er-doped optical fiber coupler for optical amplification that has a structure in which a part of the cladding has an Er-doped region, thereby achieving a high gain. purpose.

[0009]

[Means for Solving the Problems] This problem is solved by an optical fiber coupler manufactured by fusing and stretching two rare earth-doped optical fibers consisting of a core and a cladding. This problem can be solved by adding a dopant containing Er to the cladding portion.

[0010] The optical fiber coupler also includes a first step of manufacturing a first glass rod having an Er-doped quartz glass portion in the center and a pure silica glass layer on the outside thereof; A part of the glass rod of Er
A second layer partially doped with Er protrudes in a cylindrical shape so as to include the boundary between the doped silica glass portion and the pure silica glass layer.
A second step of producing a glass rod, and forming a central hole by protruding the center of the second glass rod in a cylindrical shape, and forming a cylindrical light having a core-clad structure separately prepared in the central hole. A third step of inserting a fiber intermediate preform and heating and integrating them to produce an optical fiber preform, and then spinning the optical fiber preform to produce an optical fiber in which Er is added to a part of the cladding. It is preferable to prepare the two optical fibers, arrange the Er-doped portions of these optical fibers in contact with each other, and perform a fourth step of fusing and stretching them.

Further, in the method for manufacturing a partially Er-doped optical fiber coupler according to claim 2, Er and aluminum (
It is desirable to co-dope a dopant containing a refractive index lowering agent (hereinafter abbreviated as Al) to a pure silica glass rod.

[0012] Further, the above optical fiber coupler is manufactured by fabricating an Er-doped quartz glass plate, and installing the Er-doped quartz glass plate between two optical fiber base materials consisting of a core and cladding prepared separately. , it is desirable to manufacture these three materials by fusing and stretching them.

In the method for manufacturing a partially Er-doped optical fiber coupler according to claim 3, a dopant containing Er, Al, and a refractive index additive is co-doped into a pure silica glass plate when the Er-doped quartz glass plate is produced. is desirable.

[0014]

[Function] As described above, in the partially Er-doped optical fiber coupler of the present invention, Er is doped only in the cladding fused portion where the optical power density is highest.
Er ions are excited extremely efficiently.

Further, as stated in claims 3 and 4, when producing the above-mentioned partial Er-doped optical fiber coupler, in addition to Er, Al is added to the Er-doped region of the cladding fused portion.
When a dopant containing a refractive index lowering agent and a refractive index lowering agent is co-doped, the added Al causes up-conversion of the clad fused portion (Er, Al, refractive index lowering agent added region) of the fabricated partially Er-doped optical fiber coupler. effect is suppressed, thereby preventing a decrease in the gain of the partially Er-doped optical fiber coupler. Furthermore, the refractive index is lowered by the added refractive index additive, thereby preventing an increase in transmission loss due to an increase in the refractive index when Al is co-doped.

The present invention will be explained in detail below with reference to the drawings. Figure 1 shows a partially Er-doped optical fiber coupler (
In the figure, reference numeral 11 indicates a partial EDF coupler.

The partial EDF coupler 11 has a core 12
, 12 and a cladding part 13, the core 1
An Er-added region 15 is formed in a part of the cladding part 13 (cladding fused part 14) between the cladding parts 2 and 12. This E
The amount of Er added to the r-added region is 2000 to 4
It is desirable to set it to about 000 wt·ppm.

Further, in order to prevent a decrease in gain due to the up-conversion effect caused by the above-mentioned high-concentration addition of Er, it is more preferable to co-dope Al to the Er-doped region. The amount of Al added at this time was 300
It is desirable to set it to about 0 to 10,000 wt·ppm.

Furthermore, when Al is added to the Er-doped region as described above, a refractive index lowering agent such as fluorine may be co-doped in order to prevent the refractive index from increasing and the loss from increasing. More preferred. Note that the amount of fluorine added at this time was 0 so that the relative refractive index decrease was 0.12%.
．． It is desirable to set it to about 4 to 0.6 wt%. Further, the refractive index lowering agent is not limited to the above-mentioned fluorine, and for example, boron or the like may be used.

Next, a first method of manufacturing the partial EDF coupler of the present invention will be explained.

[0021] This method can be roughly represented by four steps shown below.

(1) A first step of producing a first glass rod having an Er-doped quartz glass portion in the center and a pure silica glass layer on the outside thereof.

[0023] A part of the first glass rod is protruded in a cylindrical shape so as to include the boundary between the Er-doped quartz glass portion and the pure silica glass layer, and a second glass rod partially doped with Er is formed. The second step of producing a glass rod.

[0024] ■ A central hole is formed by protruding the center of the second glass rod in a cylindrical shape, and a separately prepared cylindrical optical fiber intermediate base material with a core-clad structure is inserted into the central hole. , a third step of heating and integrating these to produce an optical fiber preform, and then spinning the optical fiber preform to produce an optical fiber in which a part of the cladding is doped with Er.

■ Prepare two optical fibers obtained through the third step, and set the E of each of these two optical fibers to
A fourth step of arranging the r-added parts in contact with each other, fusing and stretching them.

[0026] In the first step, first, a normal VA
By method D, soot is formed on a quartz glass rod, and the obtained soot body is treated with Er chloride (ErCl3.1/2H2
O) is immersed in a hydrochloric acid solution to impregnate Er into the soot body to produce an Er-added soot body. Note that the raw material gas used when producing the soot body by the above-mentioned VAD method is Si
In addition to Cl4 and the like, a dopant for adjusting the refractive index such as GeCl4 may be used.

Furthermore, as the immersion liquid for immersing the soot body, ErCl3 and AlC were used instead of the above-mentioned Er hydrochloric acid solution.
By using an alcohol solution containing 13, Er and Al can be co-added into the soot body.

Next, the Er-added soot body obtained by the above operation is dried. This drying method is not particularly limited, but for example, the Er-added soot body is housed in a drying cylinder, and dry nitrogen gas is supplied from one end of the cylinder to the soot body in the cylinder at a rate of about 2000 cc/min. A method of spraying and drying at room temperature for about 60 hours is used. In addition, Er・Al obtained when an alcohol solution containing ErCl3 and AlCl3 is used as the soot body immersion liquid.
Co-added soot completely removes alcohol,
It was stored in a cylinder similar to that used for drying the Er-added soot body, and heated at 70 to 100°C in an inert gas (He, etc.) atmosphere.
A method of drying for 96 hours or more under the following conditions is used. Note that it is desirable to add a refractive index lowering agent such as fluorine to this Er/Al co-doped soot body, and the operation of adding fluorine, etc. is carried out by placing the Er-doped soot body after drying in a heating furnace, Furthermore, inside this heating furnace, SiF4, CF4, SF6,
1400 to 150 in an atmosphere of a gas such as C2Cl2F2 alone or as a mixture, or in a mixed atmosphere of these gases and argon, helium, etc.
This is done by heating at 0°C to make it transparent.

Next, the dried Er-doped soot body was inserted into a separately prepared pure quartz tube, and then heated and integrated to form an Er-doped quartz glass in the center as shown in FIG. A synthetic glass rod 23 (first glass rod) having a portion 21 and a pure silica glass layer 22 on the outside thereof is manufactured.

Next, in a second step, a part of the synthetic glass rod 23 is shaped into a column so as to include the boundary between the Er-doped quartz glass portion 21 and the pure silica glass layer 22, as shown in B in FIG. A partially Er-doped glass rod 25 protrudes and has an Er-doped region 24 in a portion as shown in FIG.
2nd glass rod) is produced.

Next, in a third step, the center of the Er-doped glass rod 25 is pierced in a cylindrical shape to form a center hole 26 as shown in FIG. 4A. Furthermore, the center hole 2
A cylindrical optical fiber intermediate preform 27 having a core 12 and a cladding 13 as shown in FIG.
A partial Er-doped optical fiber 28 having an Er-doped region 24 in a part of the cladding is fabricated as shown in FIG.

Next, in the fourth step, the two Er-doped optical fibers 28 are arranged with their Er-doped regions 24 in contact with each other as shown in FIG. Partial EDF coupler 1 shown in Figure 1b
1 is produced.

Next, a second method of manufacturing the partial EDF coupler of the present invention will be explained. In this method, an Er-doped quartz glass plate is produced, and this Er-doped quartz glass plate is installed between two separately prepared optical fiber base materials consisting of a core and cladding to fuse these three materials. This is a method of manufacturing a partially Er-doped optical fiber coupler by depositing and stretching the fiber.

[0035] First, soot was formed on the surface of a pure silica glass plate using the usual VAD method, and the obtained soot body was immersed in a hydrochloric acid solution of Er chloride (ErCl3.1/2H2O). to impregnate the soot body with Er,
An r-added soot body is prepared. In addition, the raw material gas used when producing the soot body by the above-mentioned VAD method is SiCl4.
In addition to the above, a dopant for adjusting the refractive index such as GeCl4 may be used.

Furthermore, as the immersion liquid for immersing the soot body, ErCl3 and AlC were used instead of the above-mentioned Er hydrochloric acid solution.
By using an alcohol solution containing 13, Er and Al can be co-added into the soot body.

Next, the Er-added soot body obtained by the above operation is dried. This drying method is performed in the same manner as the soot drying operation in the first step of the first method described above. Note that it is desirable to add a refractive index lowering agent such as fluorine to this Er/Al co-doped soot body, as in the first method, and the operation for adding fluorine, etc. is also the same as in the first method. The same is true. By the above operations, the plate shape E shown in Fig. 7 is created.
An r-added soot body 31 is produced.

Next, as shown in FIG. 8, the plate-shaped Er-doped soot body 31 is installed between two optical fiber preforms 34, 34 consisting of a core 32 and a cladding 33 prepared separately. Furthermore, these three members are fused and stretched to produce a partially Er-doped optical fiber coupler 11 as shown in FIG.

[0039]

EXAMPLE A partially Er-doped optical fiber coupler was fabricated using the first method described above.

First, in the first step, 0.5wt of fluorine
.%, Al1wt.%, and Er5000ppm were co-added to produce a soot body. Next, this soot body has a diameter of 1
It was stretched to 4 mm and inserted into a separately prepared quartz tube with an outer diameter of 40 mm and an inner diameter of 22 mm, and then heated and integrated to form an Er in the center as shown in Figure 2.
A synthetic glass rod 23 having a doped silica glass portion 21 and a pure silica glass layer 22 on the outside thereof was produced.

Next, in a second step, a part of the synthetic glass rod 23 is shaped into a column so as to include the boundary between the Er-doped quartz glass portion 21 and the pure silica glass layer 22, as shown by reference numeral B in FIG. It pierces through and there is an E
A partially Er-doped glass rod 25 having an outer diameter of 15 mm and having an r-doped region 24 was produced.

Next, in a third step, the center of the Er-doped glass rod 25 was pierced in a cylindrical shape to form a center hole 26 having a diameter of 8 mm as shown in FIG. 4A. Furthermore, a cylindrical optical fiber intermediate preform 27 having a core 12 and a cladding 13 as shown in FIG. 4B is inserted into the center hole 26, and the optical fiber preform obtained by heating and integrating the preform is spun. Thus, a partial Er-doped optical fiber 28 having an Er-doped region 24 in a part of the cladding was fabricated as shown in FIG.

Next, in the fourth step, the two Er-doped optical fibers 28 are arranged so that their Er-doped regions 24, 24 are in contact with each other as shown in FIG. Then, a partial EDF coupler 11 shown in FIG. 1b was manufactured.

When signal light and pumping light are input from one input port of the partial EDF coupler 11 fabricated as described above, the gain with respect to the sum of the signals at both output ports with respect to the pumping light intensity is as shown in FIG. The conventional E mentioned earlier
It was confirmed that higher gain amplification was achieved compared to r-doped optical fiber couplers.

Furthermore, as mentioned above, the portion ED of this embodiment
In the partial EDF coupler 11 manufactured by the F coupler manufacturing method, 1 wt.% of Al is co-doped in the Er-doped region 15, so that a decrease in gain due to the up-conversion effect caused by high-concentration addition of Er is prevented. be done.

Similarly, in the Er doped region 15, 0.
Since 5 wt.% of fluorine was co-doped, this caused Al
This prevents an increase in transmission loss due to an increase in refractive index in the case of co-doping.

[0047]

Effects of the Invention As described above, in the partially Er-doped optical fiber coupler of the present invention, Er is doped only in the fused cladding portion where the optical power density is highest, so that the excitation of Er ions is reduced. is carried out extremely efficiently. Therefore, when the partially Er-doped optical fiber coupler described above is used as an optical amplifier, it becomes an optical amplifier with extremely high gain efficiency.

Further, as stated in claims 3 and 4, when producing the above-mentioned partial Er-doped optical fiber coupler, in addition to Er, Al is added to the Er-doped region of the cladding fused portion.
When a dopant containing a refractive index lowering agent and a refractive index lowering agent is co-doped, the added Al causes up-conversion of the clad fused portion (Er, Al, refractive index lowering agent added region) of the fabricated partially Er-doped optical fiber coupler. effect is suppressed, thereby preventing a decrease in the gain of the partially Er-doped optical fiber coupler. Furthermore, the refractive index is lowered by the added refractive index lowering agent, thereby preventing an increase in transmission loss due to an increase in the refractive index when Al is co-doped.

[0049]

[Description of drawings]

FIG. 1 is a diagram showing an example of a partially Er-doped optical fiber coupler of the present invention, in which a is a plan view of the partially Er-doped optical fiber coupler, and b is a sectional view taken along line AA' of the same coupler shown in a.

FIG. 2 is a cross-sectional view of a synthetic glass rod 23 manufactured in the first step of the first manufacturing method of the partially Er-doped optical fiber coupler according to the present invention.

FIG. 3: Part E manufactured in the second step of the first manufacturing method of the partial Er-doped optical fiber coupler according to the present invention.
3 is a cross-sectional view of an r-doped glass rod 25. FIG.

FIG. 4 is a diagram for explaining the third step of the first manufacturing method of the partially Er-doped optical fiber coupler according to the present invention;
4 is a diagram showing the partially Er-doped glass rod after forming the center hole 26, which is indicated by reference numeral 25 in FIG.
6 is a diagram illustrating an optical fiber intermediate preform to be inserted into FIG.

FIG. 5: Part E manufactured in the third step of the first manufacturing method of the partial Er-doped optical fiber coupler according to the present invention.
FIG. 2 is a cross-sectional view of an r-doped optical fiber.

FIG. 6 is a diagram for explaining the fourth step of the first manufacturing method of the partially Er-doped optical fiber coupler according to the present invention.

FIG. 7 is a diagram showing a plate-shaped Er-doped soot body used in a second manufacturing method of a partially Er-doped optical fiber coupler according to the present invention.

FIG. 8 is a diagram for explaining a second manufacturing method of a partially Er-doped optical fiber coupler according to the present invention.

FIG. 9 is a graph showing the amplification characteristics of the partially Er-doped optical fiber coupler manufactured in the example.

FIG. 10 is a cross-sectional view showing a conventional optical fiber coupler.

FIG. 11 is a diagram showing an example of an optical amplification system using an optical fiber coupler.

[Explanation of symbols]

11 Partial Er-doped optical fiber coupler 12 Core 13 Clad 14 Clad fusion part 15 Er addition area 21 Er-doped quartz glass part 22 Pure silica glass layer 23 Synthetic glass rod 25 Partial Er doped glass rod 26 Center hole 27 Optical fiber intermediate base material 28 Partial Er-doped optical fiber 31 Plate-shaped Er-doped soot body 32 core 33 Clad 34 Optical fiber base material

Claims (5)

[Claims] 1. An optical fiber coupler manufactured by fusing and stretching two rare earth-doped optical fibers each having a core and a cladding, wherein a dopant containing erbium is contained in at least the cladding portion of the fused portion of the optical fiber coupler. A partially doped optical fiber coupler characterized by being doped with erbium. 2. A first step of producing a first glass rod having an erbium-doped quartz glass portion in the center and a pure silica glass layer on the outside thereof, and further comprising a part of the first glass rod. a second step of producing a second glass rod partially doped with erbium by protruding it in a cylindrical shape so as to include the boundary between the erbium-doped quartz glass portion and the pure silica glass layer; A central hole is formed by piercing the center of the glass rod in a cylindrical shape, and
A separately prepared cylindrical optical fiber intermediate preform with a core-clad structure is inserted into the center hole, and after heating and integrating them to produce an optical fiber preform, the optical fiber preform is spun to form a cladding. A third step is to prepare an optical fiber in which erbium is added to a part of the optical fiber, and a third step is to prepare the two optical fibers mentioned above, arrange the erbium-doped parts of each optical fiber in contact with each other, and fuse and stretch them. A method for manufacturing a partially erbium-doped optical fiber coupler, characterized by comprising four steps. 3. The part according to claim 2, wherein a dopant containing erbium, aluminum, and a refractive index lowering agent is co-doped into the pure silica glass rod during the production of the erbium-doped quartz glass rod in the first step. A method for manufacturing an erbium-doped optical fiber coupler. [Claim 4] An erbium-doped quartz glass plate is produced, and the erbium-doped quartz glass plate is installed between two separately prepared optical fiber base materials consisting of a core and a cladding. A method for manufacturing a partially erbium-doped optical fiber coupler, which comprises fusing and stretching. 5. The partially erbium-doped optical fiber according to claim 4, wherein a dopant containing erbium, aluminum, and a refractive index additive is co-doped into the pure quartz glass plate when the erbium-doped quartz glass plate is produced. How to manufacture a coupler.