JP4044200B2 - Bismuth-doped quartz glass, manufacturing method thereof, optical fiber using the glass, and optical amplifier - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a technique for doping Bi (bismuth) into quartz glass.
[0002]
[Prior art]
In general, in an optical communication system, a single-mode silica-based optical fiber that is inexpensive and easily available is usually used for signal transmission. In addition, in order to amplify light attenuated during transmission through such an optical fiber, an amplification optical fiber that directly amplifies signal light without photoelectric conversion due to a stimulated emission effect may be used.
[0003]
By the way, the zero-dispersion wavelength of a normal silica-based optical fiber for signal transmission is in the 1.3 μm band.
[0004]
Therefore, there is a demand to use an optical fiber for amplification having amplification characteristics in the 1.3 μm band with little signal distortion.
[0005]
As such an optical fiber having amplification characteristics in the 1.3 μm band, conventionally, for example, a structure in which a fluoride glass is doped with Pr (praseodymium) is provided.
[0006]
[Problems to be solved by the invention]
However, such an optical fiber for amplification mainly composed of fluoride glass tends to be unreliable due to the deterioration of strength due to the influence of moisture. The fusion splicing is difficult due to the difference in the component composition, and is more expensive than the quartz-based one.
[0007]
For this reason, there is a demand to obtain a silica-based optical fiber having amplification characteristics in the 1.3 μm band.
[0008]
On the other hand, there is a demand for obtaining a laser medium that can generate high-intensity and high-power laser light in the 1.3 μm band as a laser medium used for nuclear fusion.
[0009]
Accordingly, an object of the present invention is to provide a quartz glass that can meet such a demand, an optical fiber using the glass, and an optical amplifier.
[0010]
[Means for Solving the Problems]
The present invention adopts the following configuration in order to solve the above problems.
[0011]
That is, the bismuth-doped quartz glass according to claim 1 is characterized in that zeolite is uniformly dispersed in the quartz glass, and bismuth is clustered and doped at the central site in the unit cell constituting the zeolite. And
[0012]
In the method for producing bismuth-doped quartz glass according to claim 2, a zeolite is mixed with an aqueous solution of bismuth nitrate, the aqueous solution is stirred at room temperature for a predetermined time, and then dried to produce a bismuth-doped zeolite. The bismuth-doped zeolite is mixed in a sol containing quartz as a main component, the sol is gelled, dried, sintered, and vitrified.
[0013]
An optical fiber according to a third aspect is constituted by using the bismuth-doped quartz glass according to the first aspect.
[0014]
The optical amplifier according to claim 4 uses the optical fiber according to claim 3 as an amplifying element.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
In the bismuth-doped quartz glass of the present invention, zeolite is uniformly dispersed in the quartz glass, and as shown in FIG. 1, bismuth is clustered and doped at the central site in the unit cell constituting the zeolite. .
[0016]
Moreover, the manufacturing method of the bismuth dope quartz glass of this invention mixes a zeolite with the aqueous solution of bismuth nitrate, after stirring this aqueous solution for a predetermined time at room temperature, this is dried and the bismuth dope zeolite is produced | generated. Next, by applying a sol-gel method, the bismuth-doped zeolite is mixed into a sol containing quartz as a main component, the sol is gelled, dried, sintered, and vitrified.
[0017]
The optical fiber of the present invention is configured using the bismuth-doped quartz glass according to claim 1.
[0018]
Furthermore, in the optical amplifier of the present invention, the optical fiber according to claim 3 is used as an amplifying element.
[0019]
FIG. 2 shows a configuration of an optical amplifier using such an optical fiber made of bismuth-doped quartz glass as an amplifying element.
[0020]
In FIG. 2, a is an optical fiber as an amplifying element, b is a laser diode as a pumping light source that generates pumping light for pumping the optical fiber a, c is an optical coupler for guiding the pumping light to the optical fiber a, and d is Polarization-independent isolators that allow only signal light to pass in only one direction, e ₁ and e _2, are an incident end and an output end of the signal light.
[0021]
A normal silica-based optical fiber is connected before and after the optical fiber a serving as an amplifying element.
[0022]
In this configuration, pumping light (for example, 0.81 μm) from the laser diode b is incident on the amplification optical fiber a via the optical coupler c and is pumped. .3 μm) passes through the isolator d and enters the optical fiber a, this signal light is amplified by the stimulated emission effect, and only the amplified signal light is emitted via the optical coupler c and isolator d. .
[0023]
2 is a so-called backward pumping type, but it may be a forward pumping type in which signal light and pumping light are incident from the same direction.
[0024]
【Example】
Next, a method for producing bismuth-doped quartz glass will be described with a specific example, and characteristics of the bismuth-doped quartz glass after production will also be described.
[0025]
(Production method)
1. Pretreatment process
Process a
First, a raw material zeolite (here, particularly type X) is charged into a saturated ammonium chloride aqueous solution.
[0026]
Then, the aqueous solution mixed with the zeolite is stirred for a sufficient time and left to stand, and then the supernatant is discarded.
[0027]
Thereby, a zeolite in which Na ⁺ in the zeolite is replaced with NH ₄ ⁺ is obtained.
[0028]
Step b
The zeolite obtained in step a is mixed in an aqueous solution of bismuth nitrate [Bi (NO) ₃ ] and stirred for a sufficient time (for example, about 1 hour) at room temperature (around 25 ° C.).
[0029]
In this case, the mixing ratio of zeolite, bismuth nitrate, and water is set to a ratio of (zeolite), (bismuth nitrate) :( water) = 2: 1: 10, for example, in a weight ratio.
[0030]
Thereby, a bismuth-doped zeolite in which N ₄ ⁺ in the zeolite is replaced with Bi ³⁺ is obtained. In addition, as shown in FIG. 1, the bismuth-doped zeolite in this case is present in a state where bismuth is clustered at a central site (super cage) in the unit cell constituting the zeolite.
[0031]
Process c
Next, the bismuth-doped zeolite is filtered to remove moisture, and further dried sufficiently using a drier or the like.
[0032]
It is also possible to omit the step a and start from the step b, that is, the step of directly mixing the raw material zeolite in the aqueous solution of bismuth nitrate.
[0033]
Moreover, it can replace with the process a and can also perform the following process.
[0034]
First, the raw material zeolite (here, particularly type X) is put into a 100 ° C. aqueous solution of yttrium chloride [YCl ₃ ], and this aqueous solution is stirred for a sufficient time (for example, 2 weeks) and left to stand. After that, discard the supernatant. Thereby, a zeolite in which Na ⁺ is completely substituted with Y ⁺ is obtained. Subsequently, the zeolite is mixed in an aqueous solution of saturated ammonium chloride, and the aqueous solution is stirred for a sufficient time (for example, 4 hours). After allowing to stand, the supernatant is discarded. As a result, most of the Y ⁺ existing in the central site (Super cage) in the unit cell constituting the zeolite is extracted. Thereafter, the process proceeds to step b.
[0035]
When the treatment using yttrium chloride is performed in this way, sodium in the zeolite can be further reduced, so that improvement in characteristics such as improvement in water resistance can be achieved.
[0036]
2. Main Step In this main step, a so-called sol-gel method (for example, written by Sakuo Sakuo: published by Agne Sefu Co., Ltd., see “Science of Sol-Gel Method”) is applied. This will be specifically described below.
[0037]
Process d
Silicon alcoholate and water are mixed at a predetermined ratio, and the acidity is adjusted with hydrochloric acid (for example, adjusted to pH = 1.5), and then stirred for a predetermined time (for example, about one week).
[0038]
In this case, tetraethylorthosilicate (TEOS), tetramethylorthosilicate (TMOS), or the like can be used as the silicon alcoholate. Further, the mixing ratio with water when TEOS is used is, for example, set to a ratio of (TEOS) :( water) = 208: 180≈10: 9 by weight ratio.
[0039]
Process e
On the other hand, commercially available Tegusa OX50, etc., TEOS, quartz particles produced by mixing ethanol and aqueous ammonia (pH≈11.5) and water are mixed at a predetermined ratio, and this is mixed for a predetermined time (for example, about 2 hours). Is stirred.
[0040]
Process f
The aqueous solution obtained in step d and the aqueous solution obtained in step e are mixed at a predetermined ratio and stirred.
[0041]
The mixing ratio of the aqueous solutions obtained in steps d and e is set to 1: 1 in terms of the amount of SiO ₂ , for example.
[0042]
Process g
The bismuth-doped zeolite obtained in the previous step a to step c is dissolved with 5 times the weight ratio of water.
[0043]
Process h
Subsequently, the aqueous solution obtained in the previous step f and the aqueous solution obtained in the previous step g are mixed so as to meet the desired equivalent bismuth concentration, and then added to the 0.1N ammonia solution. Is added to gel.
[0044]
Process i
The gel is sufficiently dried to remove moisture and the like. For example, the gel is dried at 80 ° C. for 24 hours, followed by drying at 110 ° C. for 2 weeks.
[0045]
Process j
Next, the gel is pre-sintered at a relatively low temperature for a predetermined time (for example, 1200 ° C. for 4 hours) to be in a porous soot state, and subsequently, is heated at a relatively high temperature for a predetermined time (for example, 1750). It is sintered at 1.5 ° C for 1.5 hours to form a transparent glass.
[0046]
In the bismuth-doped quartz glass obtained in this way, the zeolite becomes amorphous, but the bismuth present in the central site (Superer cage) in the unit cell of the zeolite remains in a clustered state without much diffusion. It has become.
[0047]
This can be determined to some extent from the appearance. That is, in the case of bismuth-doped quartz glass containing zeolite as in the present invention, the whole is light pink when it does not contain zeolite, whereas the whole is light pink. The difference in characteristics can also be determined.
[0048]
In addition, the various conditions in said manufacturing process are an example to the last, Comprising: It is not necessarily limited to such conditions.
[0049]
For example, in this embodiment, it is assumed that the zeolite (here, particularly type X) contains sodium ions, but the present invention can also be applied to different types of zeolite containing other elements such as calcium ions.
[0050]
Further, instead of the above embodiment, the following modification can be considered.
[0051]
1. About Zeolite Zeolite is usually a crystal having ion exchange characteristics, and when natural and synthetic substances are included, it has been confirmed that several hundred or more kinds exist. All of them have applicability. That is, it can be used instead of the X type. In particular, the Y, A type and the like have the same crystal structure, and can be used in the same manner as the X type.
[0052]
Most of the zeolite is composed of Si and Al, but there is also a special material composed of P and Al (aluminoline zeolite), so if you need to mix P, It is also possible to use such a zeolite.
[0053]
2. Manufacture of zeolite with less Na ions By replacing with Y ions as described above, it is possible to manufacture zeolite with less Na ions mixed in, but the same effect can be obtained with La ions.
[0054]
(Characteristics of bismuth-doped quartz glass)
FIG. 3 shows the results of examining the fluorescence characteristics of the bismuth-doped quartz glass obtained based on the above manufacturing method, and FIG. 4 shows the results of examining the absorption characteristics.
[0055]
In these figures, the solid line shows the bismuth-doped quartz glass according to the present invention doped with bismuth using zeolite (hereinafter referred to as the present invention), and the broken line simply shows bismuth in the quartz glass without using zeolite. 1 shows what is doped (hereinafter referred to as conventional product).
[0056]
The measurement conditions for the fluorescence characteristics are as follows: excitation light source: Xe lamp (peak wavelength 500 nm, full width at half maximum 50 nm), light receiver: Ge semiconductor, spectrometer resolution is about 1 nm, and sample size is 5 × 5 × 1 mm. I used something.
[0057]
In addition, the measurement conditions of the absorption characteristics are those obtained by measuring the light transmitted through a halogen lamp. The photoreceiver uses a photomultiplier tube, the resolution of the spectrometer is about 1 nm, and the thickness of the sample is about 1 to 2 mm. It is.
[0058]
As can be seen from FIG. 3, in the conventional product, no fluorescence is observed in the 1.3 μm band, whereas in the product of the present invention, the fluorescence intensity is large in the 1.3 μm band. Moreover, it has a long lifetime (τrad = 650 μs), a wide width (Δλ = 250 nm), and a moderate stimulated emission cross section (≈1.0 × 1.0 ⁻²⁰ cm ² ).
[0059]
This makes it possible to manufacture quartz-based amplification optical fibers that can be amplified in the low dispersion region (λ = 1.3 μm band), and can also be used as laser media for high brightness, high heat resistance, and high output. is there.
[0060]
As can be seen from FIG. 4, BandX and BandY are products of the present invention, and there are two absorption peaks, 500 nm and 700 nm. In particular, when used as an optical fiber amplifying medium, it can be excited by a semiconductor laser having a wavelength of about 680 nm, and as a laser medium for fusion, it can sufficiently cope with excitation of a conventional flash lamp.
[0061]
【The invention's effect】
The present invention has the following effects.
[0062]
(1) It is possible to manufacture a silica-based amplification optical fiber capable of amplification in a low dispersion region (λ = 1.3 μm band).
[0063]
(2) Application as a laser medium for high brightness, high heat resistance, and high output is possible.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing the structure of a unit cell of bismuth-doped zeolite obtained in the course of the production of bismuth-doped quartz glass of the present invention.
FIG. 2 is a configuration diagram of an optical amplifier using an optical fiber composed of bismuth-doped quartz glass of the present invention as an amplifying element.
FIG. 3 is a graph showing fluorescence characteristics of the bismuth-doped quartz glass of the present invention.
FIG. 4 is a graph showing the absorption characteristics of the bismuth-doped quartz glass of the present invention.

Claims (4)

A bismuth-doped quartz glass, wherein zeolite is uniformly dispersed in quartz glass, and bismuth is clustered and doped at a central site in a unit cell constituting the zeolite. Zeolite is mixed with an aqueous solution of bismuth nitrate, and this aqueous solution is stirred for a predetermined time at room temperature, and then dried to produce bismuth-doped zeolite. This bismuth-doped zeolite is mixed in a sol mainly composed of quartz. A method for producing bismuth-doped quartz glass, characterized in that the sol is gelled and then dried, sintered and vitrified. An optical fiber configured using the bismuth-doped quartz glass according to claim 1. An optical amplifier, wherein the optical fiber according to claim 3 is used as an amplifying element.

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