JPH05294670A - Production of rare earth-doped core fiber - Google Patents

Abstract

PURPOSE:To obtain rare earth-doped core fiber in which the core is doped with a rare earth element and aluminum at high concentrations. CONSTITUTION:Core raw material powder 8 containing a rare earth element in a desired proportion is introduced into the interior of a glass pipe 4 connected to a quartz-based glass pipe 1 composed of F-doped SiO2, heated in the presence of a chlorine-containing gas and dehydrated. A through-hole 2 of the quartz- based glass pipe 1 is then filled with the raw material powder 8 and the glass pipe 1 is drawn to afford the objective rare earth-doped core fiber.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an optical fiber having a core doped with a rare earth compound such as erbium or neodymium and aluminum, which is suitable for a fiber type optical amplifier.

[0002]

2. Description of the Related Art As a fiber type optical amplifier, a rare earth-doped core fiber having a core doped with a rare earth element such as erbium or neodymium is known. Furthermore, in addition to the rare earth element, aluminum is co-doped into the cores of these fibers to flatten the gain wavelength characteristics of optical amplification of these fibers. This kind of rare earth-doped core fiber is manufactured by a method such as MCVD method, VAD method + immersion method, and plasma method.

[0003]

At present, there is a demand for a method capable of doping a core with a higher concentration of a rare earth element in order to improve the efficiency, quality and shorten the length of a fiber type optical amplifier. However, in the conventional manufacturing method,
If the concentration of erbium added to the core exceeds 1000 ppm, the problem of concentration quenching occurs due to the interaction between adjacent erbium ions, making it difficult to obtain a high gain proportional to the concentration of erbium added.

As a measure against the above-described concentration quenching, co-addition of aluminum is effective. Therefore, if the doping amount of the rare earth element into the core is increased, the co-addition amount of aluminum is reduced to the addition amount of the rare earth element of 5 to eliminate the concentration quenching.
It is necessary to increase it by 0 times or more. However, it is difficult to dope a large amount of aluminum by the conventional method.

Furthermore, the above-mentioned conventional method has a problem that it requires a lot of steps and requires skill. For example, in the external attachment of a core material highly doped with aluminum,
The core material may crystallize, foam, or crack. The present invention has been made in view of the above circumstances, and provides a method for easily doping a core with a high concentration of a rare earth element and aluminum.

[0006]

A method for producing a rare earth-doped core fiber according to the present invention comprises a raw material powder containing a rare earth element, aluminum oxide, and silicon oxide, which are cores, inside a silica glass pipe, which is a cladding. Filling and melt-spinning this were the means for solving the above problems.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to the drawings. 1 and 2 show one embodiment of the fiber manufacturing method of the present invention. In FIG. 1, reference numeral 1 is a silica-based glass pipe serving as a clad. The quartz glass pipe 1 has an outer diameter of several tens of centimeters, and is a tubular pipe having a through hole 2 formed in the center in the longitudinal direction. The material of the quartz glass pipe 1 is SiO _{2 which} is usually used as a cladding material, and more preferably F-doped S.
iO ₂ is used. When F-doped SiO ₂ is used,
By appropriately selecting the F doping amount, the cladding of the finished fiber can be set to a desired low refractive index.

In the silica glass pipe 1, the core / cladding ratio of the finished fiber can be set by appropriately selecting the ratio of the diameter of the through hole 2 to the thickness of the silica glass pipe 1. The diameter of one end of the quartz glass pipe 1 is narrowed, and an exhaust port 3 is formed. The silica-based glass pipe 1 having the above structure can be produced by a known method such as OVD.

A glass pipe 4 having an outer diameter equal to the outer diameter of the quartz glass pipe 1 is hermetically sealed at the end of the quartz glass pipe 1 opposite to the exhaust port 3 by a method such as heat fusion. They are connected in a state to form the connection object 5. The composition of the glass forming the glass pipe 4 is not particularly limited. The inside of the glass pipe 4 is hollow,
A sample reservoir 6 is formed. Further, the diameter of the open end of the glass pipe 4 to which the quartz glass pipe 1 is not connected is narrowed to form a supply port 7.

First, the raw material powder 8 to be the core is dehydrated using such an apparatus. First, the raw material powder 8 serving as a core is put into the sample reservoir 6 of the glass pipe 4 through the supply port 7. This raw material powder 8 has a desired finished composition of the core, is preliminarily blended, and contains silicon oxide, aluminum oxide and a rare earth element compound as essential components. A mixture of the system and sodium oxide,
A multi-component mixture in which calcium oxide, potassium oxide, etc. are added, or a mixture in which a dopant for adjusting the refractive index such as germanium oxide is further added is used. In order to achieve a high gain of optical amplification and elimination of concentration quenching for the purpose of the present invention, a rare earth element of about 0.2 to 5 wt%,
It is preferable that aluminum oxide is mixed in an amount of about 5 to 75 wt%.

Next, the quartz glass pipe 1 and the glass pipe 4 are installed so that the axial directions thereof are horizontal, and while rotating them around this axis, a chlorine-containing gas such as SOCl ₂ and He, He, A mixed gas consisting of O ₂ etc.
It is introduced at a flow rate of about 70 to 100 cc / min. The proportion of chlorine-containing gas in this mixed gas is preferably about 0.3 to 1.0%, and the proportion of oxygen gas is preferably about 40 to 60%. Then, while continuing the above state, the raw material powder 8 is heated from below the sample reservoir 6 using a burner 9 at 900 to 1050 ° C.
The raw material powder 8 is dehydrated by heating for about 6 to 12 hours.

After the dehydration step of the raw material powder 8 is completed, the exhaust port 3 is melt-sealed, and the connecting material 5 of the quartz glass pipe 1 and the glass pipe 4 is rotated 90 degrees to make the axial direction vertical and quartz. The system glass pipe 1 is installed so as to face downward. As a result, the raw material powder 8 becomes the through hole 2 of the quartz glass pipe 1.
Filled inside. In this way, the raw material powder 8 does not come into contact with the outside air, so that it can be filled in the through hole 2 in a dehydrated state.

Further, another glass tube 10 is melted in the supply port 7 to form a T-shaped passage as shown in FIG. Then,
Flow rate of He gas from the supply port 11 of the glass tube 10 is 100 cc
/ min, and while sucking the gas generated from the raw material powder that becomes the core during melt spinning, the heaters 12, 1 on both sides
2, the quartz glass pipe 1 is 1700-1800
Rare earth-doped core fiber 1 heated to about ℃ and drawn
Get 3.

The rare earth-doped core fiber 13 produced by the above method is a fiber having the same composition as the raw material powder 8 as the core and the same composition as the silica glass pipe 1 as the clad. Therefore, by mixing the core material raw material powder 8 with a high concentration of a rare earth element and aluminum, a rare earth-doped core fiber 13 in which the core is highly doped with these elements can be obtained. Further, as described above, since the raw material powder to be the core is heated in the presence of the chlorine-containing gas, the finished fiber 13 does not contain water in the core, and there is no light absorption loss. Therefore, since such a rare earth-doped core fiber 13 has both high gain characteristics and low wavelength dependence, it can be used as a high quality fiber type optical amplifier, and the length of the optical amplifier can be shortened.

Further, in the above-described erbium or neodymium doping example, if other desired elements such as erbium or neodymium are substituted, those elements can be similarly doped into the core. That is, not only rare earth elements, but also when the core is doped with other elements, as long as it is a compound containing the element and in the form of a powder, the raw material powder may be prepared as a powder regardless of the type. The method of the invention can also be applied when doping a dopant such as germanium or phosphorus for increasing the refractive index.

(Example) A rare earth element-doped core fiber was prepared by the above-mentioned method using the apparatus shown in FIGS. The composition of the raw material powder to be the core is SiO ₂ 1
1.9 wt%, Al ₂ O ₃ 47.8 wt%, CaO 40.
3 wt% and Er4000 wtppm. The fiber thus obtained has a cutoff wavelength of 0.94 μm,
MFD is 4.6 μm, pumping power = 23 mW, signal light wavelength = 1552 nm, input signal light power = −40 d
A maximum gain of 37 dB was obtained at Bm.

[0017]

According to the method for producing a rare earth-doped core fiber of the present invention, a raw material powder containing a rare earth element to be a core, aluminum oxide and silicon oxide as essential components is filled in a silica glass pipe to be a clad. Is melt-spun. Therefore, the core can be easily and surely doped with a high concentration of a rare earth element by a simple method of mixing a desired rare earth element in a raw material powder at a desired ratio. Further, by appropriately selecting the ratio of the diameter of the through hole to the thickness of the silica glass pipe, the fiber core /
The clad ratio can be controlled easily and reliably. Moreover, since the number of steps is small, it is possible to mass-produce the rare earth-doped core fiber.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a step of dehydrating a raw material powder according to an embodiment of a manufacturing method of the present invention.

FIG. 2 is a cross-sectional view showing a drawing process of an example of the manufacturing method of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Quartz glass pipe, 2 ... Through hole, 4 ... Glass pipe, 5 ... Connection object 6 ... Sample reservoir, 7 ... Supply port, 8 ... Raw material powder, 9 ... Burner,
10 ... Glass tube 11 ... Supply port, 12 ... Heater, 13 ... Rare earth-doped core fiber

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Ryozo Yamauchi 1440 Rokuzaki, Sakura City, Chiba Prefecture Fujikura Electric Cable Co., Ltd. Sakura Factory

Claims (3)

[Claims] 1. A rare earth-doped core characterized in that a raw material powder containing a rare earth element to be a core, aluminum oxide and silicon oxide as essential components is filled in a quartz glass pipe to be a clad and melt-spun. Fiber manufacturing method. 2. The method for producing a rare earth-doped core fiber according to claim 1, wherein the raw material powder to be the core is dehydrated in advance. 3. One end of a second glass pipe is joined to one end of a first silica-based glass pipe that serves as a clad, and a rare earth element, aluminum oxide, and silicon oxide serving as a core are essential in the second glass pipe. A first quartz glass pipe, in which a raw material powder to be a component is put, the raw material powder is heated and dehydrated while flowing a chlorine-containing gas from an open end of the second glass pipe, and the raw material powder serves as a clad. A method for producing a rare-earth-doped core fiber, which comprises moving the inside, filling the inside, and then melt-spinning this.