JPH11322364A - Fluoride glass composition and waveguide for optical amplification and optical amplifier using the composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a fluoride glass composition used for optical communication, laser, etc., and provide an optical waveguide and optical amplifier using the glass composition. SOLUTION: In this fluoride glass composition, the molar percents (%) of cations constituting glass are each represented by the formulas 30<=In<=45%, 10<=M<=35%, 10<=T<=25%, 1<=Pb<=25%, 0<=α<=10%, 0<=L<=3%, 0<=Yb<=3%, 0.01<=R<=7 and 0.01<=A<=5% [M is Mg, Ca, Sr or Ba and T is Zn, Cd or Sn and α is Al or Ga and L is Sc or Y; R is La, Ce, Gd or Lu; A represents one or more kinds of rare earth elements selected from among Er, Pr, Nd, Ha and Tm] and total of the cations is 100% and the molar percent (%) of anions constituting glass is represented by the formula F=(100-Cl)% [0<=Cl<=10%]. This waveguide for optical amplification is obtained by using the fluoride glass composition as a core. This optical amplifier having a specific waveband is obtained by using the waveguide for optical amplification containing an active ion as a core part.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fluoride glass composition used for optical communications and lasers, an optical waveguide and an optical amplifier using the same.

[0002]

2. Description of the Related Art Er (1.5 μm
Band) and Pr (1.3 μm band) as active ions are being studied. Also,
Research has also been conducted on fluoride fiber lasers to which Er, Pr, Nd, Ho, and Tm are added. In particular, Er-doped fluoride glass has attracted attention as a medium for wavelength multiplex communication. In-based fluoride glass has been attracting attention as a medium having a higher quantum efficiency because its lattice vibration energy (phonon energy) is smaller than that of general fluoride glass, ZBLAN. It is difficult to make glass or fiber. For this reason,
Active development of stable compositions (for example, Japanese Patent Application Laid-Open
-10593).

[0003]

It is known that the optical waveguides and fibers of halide glass and chalcogenide glass to which Er is added have a flat gain band wider than that of currently used quartz fiber amplifiers. 5
It is expected as an amplification medium for wavelength-division multiplex communication in the μm band. Research on fluoride glass has been focused on Zr-based fluoride glass called ZBLAN.
Recently, an In-based fluoride glass that can be expected to have higher efficiency has been developed. In addition, even in 1.3 μm band amplification, Pr-doped In-based fluoride glass is expected to be used as an amplifier fiber because of its high quantum efficiency. In addition to these communication applications, Er, Pr, Nd, H
Research on fiber lasers to which o, Tm, etc. are added has been conducted. However, In-based fluoride glass is easily crystallized, and it is very difficult to form a large glass base material by melting and cooling, or to process it into fibers.

In order to improve amplification efficiency in a fiber type optical amplifier, it is preferable that the refractive index of the core portion of the amplification optical waveguide be increased and the relative refractive index difference (numerical aperture) from the cladding be larger. Are known. However, not only In-based but also fluoride glass has a low refractive index, and it is necessary to add heavy metal elements such as Pb and Cd in order to increase the refractive index. However, these additives significantly reduce the glass stability. Spoil.
Recently, Japanese Patent Application Laid-Open No. 7-10593 discloses a glass composition having a high refractive index and a relatively stable glass composition. However, compared to ZBLAN, which is the most stable fluoride glass, it is considerably unstable, and it is difficult to prepare a large glass base material. Therefore, further stabilization is required. Further, recently, for the purpose of downsizing the amplifier, the length of the amplification fiber has been required to be short, and it has been required that the stability is not deteriorated even when a large amount of active ions such as Er and Pr are added. Have been.

[0005] Although the In-based fluoride glass is a promising material for optical amplification as described above, its instability makes practical use difficult. In addition, the In-based fluoride glass has a relatively narrow vitrification range, and there is not much room for changing the composition. In addition, heavy elements such as Pb are contained in large amounts to increase the refractive index, and the active ions Er and P
Since r or the like must be added at a high concentration, the room for changing the composition is considerably limited.

[0006]

Means for Solving the Problems In view of such a difficult situation, the present inventors have made intensive studies, and as a result, a trace amount of rare earth or a combination of rare earth greatly influences the stability of In-based fluoride glass. This has led to the present invention.

That is, the present invention relates to InF ₃ and MF ₂ (where M represents at least one element selected from Mg, Ca, Sr and Ba), TF ₂ (where T is Zn, Cd, At least one element selected from Sn), PbF ₂ as a main component, and Er, Pr,
In an In-based fluoride glass composition containing at least one or more rare earth elements selected from Nd, Ho, and Tm as active ions for amplification, when the cation of the component constituting the glass is represented by mol%, 30 ≦ In ≤ 45%, 10 ≤ M ≤ 35%, 10 ≤ T ≤ 25%, 1 ≤ Pb ≤ 25%, 0 ≤ α ≤ 10%, 0 ≤ L ≤ 3%, 0 ≤ Yb ≤ 3%, 0.01 ≤ R ≦ 7%, 0.01 ≦ A ≦ 5% (where α represents at least one or more elements selected from Al and Ga, L represents at least one or more elements selected from Sc and Y, R is La, Ce, Gd,
A represents at least one element selected from Lu, and A represents at least one or more rare earth elements selected from Er, Pr, Nd, Ho, and Tm. ) And the total amount of cations is 100%, and when the anions of the constituents of the glass are represented by mol%, F = (100−Cl)% (where 0 ≦ Cl ≦ 10%) An optical amplification waveguide using the fluoride glass composition for the core and using the all-fluoride glass or the halogen oxide glass for the clad. An optical amplifier in a specific wavelength band is provided by exciting light with a specific wavelength by using an optical amplification waveguide containing a specific rare earth element as an active ion in a core portion.

Hereinafter, the contents of the present invention will be described in detail, and all percentages are mol%. As an amplification medium for optical communication,
It is effective to increase the refractive index to improve the efficiency, and studies on glasses to which Pb or Cd is added have been conducted. As shown in JP-A-7-10593, a high refractive index and relatively stable In-based fluoride glass is disclosed. Has been developed. Various methods have been proposed as a measure of the stability of the glass. Stability parameters: S = (Tp-Tc) (Tc-Tg) / T
g [Tp: crystallization peak temperature, Tc: crystallization onset temperature,
Tg: glass transition temperature] [M. Saad and M. Poulain. Mat
er.Sci.Forum. 19-20 (1987) 11] is simple and suitable.
When evaluated by this method, in the composition disclosed in JP-A-7-10593, S = about 12, and ZBL
It is much more unstable than AN (S = approximately 14 to 16), and the stability of the glass is insufficient. In addition, Japanese Patent Application Laid-Open No. 7-1059
In Japanese Patent Publication No. 3, Yb is indispensable. However, Yb also has an effect of promoting the loss of excited state absorption (ESA) in addition to the sensitizing effect, and thus the addition of a high concentration may not be preferable.

Further, in recent years, from the viewpoint of miniaturization of an amplifier,
Short fiber materials capable of adding active ions such as Er and Pr at a high concentration have been required. Therefore, the purpose of the present invention is to greatly improve the stability of a fluoride glass capable of containing a large amount of a rare earth element as an active ion with a high refractive index without making a major change to the main component. Study was carried out.

Heretofore, in fluoride glass, it has been considered that rare-earth elements, such as rare-earth elements, having almost the same ionic radius and chemical properties have almost no effect on glass stability due to the exchange of rare-earth elements. Further, it has been thought that increasing the types of constituent elements in the rare earth elements increases the stability of the glass. However, unlike ZBLAN, which is a general composition, in In-based glass, not only the stability greatly changes depending on the rare earth element species, but also the stability changes depending on the combination of rare earth elements to be co-added. (FIG. 1).

Active ions (Pr, Nd, Ho, Er, T
m, etc.) are found to be La, Ce, Gd, Yb, and Lu. On the other hand, when La is co-added, the stability is deteriorated,
It became clear that there was a large difference depending on the rare earth ion species. La, Ce, Gd, and Lu are effective at low concentrations. However, when the content is less than 0.01%, little effect is observed. When the content is more than 7%, the solubility of rare earth elements approaches the limit, and on the other hand, the amount of crystals increases. The range is preferably from 0.01 to 7%, since it promotes the formation of the catalyst. Also, depending on the combination of rare earth elements, to improve stability,
More preferably, it is in the range of 0.1 to 7%. Among these elements, Yb has the effect of promoting ESA as described above, and high-concentration addition is not preferable, and the range of 0 ≦ Yb ≦ 3% is preferable. More preferably, the upper limit of the addition concentration of Yb is 0%. It must be kept at .5%. La, Ce, Gd, Y
Among b and Lu, Ce, which is most effective for improving the stability, is preferable (see Table 2). The addition amount of Sc and Y which does not contribute to the improvement of stability should be kept at most 3% or less, and if it exceeds this range, the stability of the glass is remarkably deteriorated.

The concentration of the active ions depends on the glass composition and the design of the fiber, waveguide, laser, etc.
0.01 ≦ A ≦ 5% (A is Er, Pr, Nd, Ho, T
m represents at least one or more rare earth elements). If the concentration is below this range, the required fiber length and waveguide length become too long, which is practically inconvenient. Concentrations above this range are not suitable because losses such as so-called concentration quenching and absorption in the excited state increase. More preferably, the range of 0.05 ≦ A ≦ 5% is preferable.

When the fluoride glass is applied to an optical amplifier or a laser, it is required to increase the refractive index as described above. Therefore, Pb effective for increasing the refractive index
Need to be added. The amount of Pb added is suitably in the range of 1 ≦ Pb ≦ 25% in terms of mole% of cation. Below this range, the refractive index (nd) is 1.5 or less, and improvement in the efficiency of the optical amplifier or laser cannot be expected. On the other hand, if it is 25% or more, the stability of the glass is deteriorated, and the glass tends to be crystallized by heating, which is not suitable. More preferably, the range of 1 ≦ Pb ≦ 20% is preferable.

The cation composition range other than the rare earth element and Pb is 30 ≦ In ≦ 45%, 10 ≦ M ≦ 35%,
0 ≦ T ≦ 25%, 0 ≦ α ≦ 10% (where M is Mg,
T represents at least one or more elements selected from Ca, Sr, and Ba; T represents at least one or more elements selected from Zn, Cd, and Sn; and α represents at least one or more elements selected from Al and Ga. Is shown. If the ratio is out of this range, the effect of stabilization by the rare earth element is not recognized, and the stability of the glass deteriorates. In order to lower the phonon energy and increase the refractive index of the glass, it is advantageous to add a heavy element, and it is preferable to select Sr and Ba from the element group of M, and particularly, 5 ≦ Ba ≦ 25%, 5 ≦ Sr ≦
It is preferable that 20% and 10 ≦ (Ba + Sr) ≦ 35%. From the group of elements of T, it is preferable to select Zn and Sn which have relatively little influence on the environment.
n is preferably 10 ≦ Zn ≦ 25%.

Further, as a result of an investigation on anions, it was found that replacing F in the fluoride glass with Cl significantly improved the glass stability and the refractive index. The replacement amount of Cl depends on the glass composition, but should be at most 10% or less. Substitution of more than 10% is not preferable because problems such as deterioration of glass stability, phase separation of glass, and deterioration of weather resistance occur.

According to the composition of the present invention, a stable In-based fluoride glass having a high refractive index and containing a large amount of a rare earth element as an active ion can be obtained. Therefore, a highly efficient and short fiber amplifier or fiber laser can be used. Easy application.

[0017]

EXAMPLES Examples using the present invention will be shown below, but the present invention is not limited to these examples.

Example 1 In order to clarify the relationship between the Pb content and the refractive index, raw materials having the compositions shown in Table 1 were prepared, and a high-purity carbon crucible was used under an inert gas atmosphere at 800 to 1000 ° C. Melting was performed for 1 hour. Thereafter, the crucible was taken out, and the whole crucible was quenched on a metal plate to obtain 30 g of glass. These glasses are kept at 280-320 ° C. (20
(Temperature higher by 1 ° C.) for 1 hour and cooled to room temperature over 6 hours. The refractive index (nd) at the sodium-d line of the obtained glass was measured by the Abbe method. The relationship with the Pb content is shown in FIG. It can be seen that as the Pb content increases, the refractive index increases, and that Pb needs to be 1% or more in order to satisfy nd ≧ 1.5. When 10% PbF ₂ glass is used for the core and 2% PbF ₂ glass is used for the cladding, a high numerical aperture fiber having a numerical aperture of 0.25 can be produced. Similarly, using a glass of 15% PbF ₂ for the core,
When 2% PbF ₂ glass is used for the cladding, a high numerical aperture fiber having a numerical aperture of 0.33 can be produced. Similarly, by using 10% PbF ₂ glass for the core and using HB-doped ZBLAN (nd 1.485) for the cladding, a high numerical aperture fiber having a numerical aperture of 0.33 can be produced.

Next, differential calorimetry (DSC) was performed to clarify the Pb content and the stability of the glass. The results are shown in FIG. The thermal stability required for forming glass into a fiber is represented by a stability parameter represented by a glass transition temperature (Tg), a crystallization onset temperature (Tc), and a crystallization peak temperature (Tp): S = (Tp−Tc) ) (Tc-Tg) /
It was evaluated by Tg. For reference, Table 1 also shows the value of ZBLAN, which is known as a stable fluoride glass. As a result,
It can be seen that when the Pb content increases, the thermal stability of the glass rapidly deteriorates, and when the Pb content is 10% or more, it becomes very easy to crystallize.

[0020]

[Table 1]

Example 2 When the active ion species was Er, in order to clarify the change in stability of the glass due to the co-added rare earth species, raw materials having the compositions shown in Table 2 were prepared. It was created. The results of differential calorimetry (DSC) were analyzed in the same manner as in Example 1 and are shown in Table 2. No. As shown in 9 to 13, L
It can be seen that the stability parameter S was increased by adding a, Ce, Gd, Yb, and Lu, and the glass was stabilized.
These glasses contain 15% Pb and nd =
Since the refractive index is as high as 1.543, a high numerical aperture fiber can be produced as in the first embodiment. Also, Er is 2%
And a high concentration, an optical amplifier or a laser can be manufactured using a short fiber or a waveguide having a length of 20 cm or less.

[0022]

[Table 2]

Example 3 In order to know the high-temperature stability necessary for heat processing of glass, etc.,
5 in a nitrogen atmosphere at a temperature 50 ° C. higher than the glass transition temperature
The glass was heated for a period of time and the state of crystallization was compared. Table 3 shows the results. The composition numbers of the glass are the same as those in Example 1 and Example 2.
Corresponds to the sample number used in the above. ○ indicates that no crystal was observed, △ indicates that part of the crystal was crystallized, and X indicates that the whole was crystallized. In Examples 1 and 2, La, Ce, Gd,
It can be seen that the glass composition stabilized by Yb and Lu does not crystallize at all and is a stable glass.

[0024]

[Table 3]

Example 4 A glass was prepared in the same manner as in Example 1 with the composition shown in Table 4 in which the co-addition concentration of the rare earth was changed, and the heating stability was evaluated in the same manner as in Example 3. As a result, crystallization occurred in some glass compositions. The crystallized composition has a rare earth content outside the scope of the present invention.

[0026]

[Table 4]

Example 5 The same stability confirmation experiment as in Example 4 was conducted for the compositions shown in Table 5. As a result, partial or complete crystallization occurred in some compositions. Even if the glass composition is Δ or ×, it can be vitrified by rapid cooling in some cases, but it is found that it is not suitable for heating processing such as fiberization. Further, all the glass compositions of △ and × are compositions outside the scope of the present invention.

[0028]

[Table 5]

Example 6 In order to examine the effect of anion substitution, glass was prepared in the same manner as in Example 1 for the compositions shown in Table 6, and the refractive index was measured in the same manner as in Example 1. The stability was evaluated. Table 6 shows the results. Substitute some of the raw materials for chloride,
It can be seen that the stability is improved by introducing chlorine as an anion. However, if the introduced amount of chlorine is too large, phase separation occurs, and the stability during heating decreases. The contribution of chlorine to the refractive index is almost the same as that of Pb.

[0030]

[Table 6]

Embodiment 7 The amplifier shown in FIG. 4 is constructed, and Er + shown in Embodiment 2
A high-numerical-aperture fiber (amplifying fiber 4) having an NA of 0.22 was prepared by using a glass co-doped with Ce as a core, and excited with a semiconductor laser 3 having a wavelength of 0.974 μm.
The incident light 1 having a signal wavelength of 5 μm was amplified. The pump light and the signal light were multiplexed by the optical multiplexer 2 and introduced into the amplification fiber 4. Since the Er concentration is as high as 2%, the length of the amplification fiber 4 is as short as 15 cm. Both ends of the amplification fiber 4 were connected by obliquely polishing a high numerical aperture quartz fiber 5. The gain of the amplified signal light was measured by an optical spectrum analyzer 7 through an isolator 6. Pump light power is 100 mW and signal light power is -30 dBm
At this time, it was found that the gain was 25 dB, high-efficiency amplification was performed, and there was no loss such as crystallization.

Comparative Example 1 A fiber was prepared using the glass of Er + Yb co-added shown in Example 2 as a core, and an amplification experiment was performed under the same conditions as in Example 7. As a result, no gain was obtained. The fiber under measurement glowed strongly with green up-conversion fluorescence, indicating a very high ESA loss.

Example 8 A fiber having the composition shown in Table 7 was prepared based on the core composition used in Example 7, and the fluorescence spectrum intensity in the 1.55 μm band when excited by a 0.974 μm semiconductor laser was prepared. Was measured. The experimental arrangement was the same as in Example 7, but no signal light was input. The fluorescence intensity is Er: 0.5%, Y
b: 0.5%, La: 3%, and normalized by fluorescence intensity and absorbed excitation light power. The results are summarized in Table 7. When the addition amount of Yb is 0.5% or more, the normalized fluorescence intensity decreases, and it is understood that the addition of less than 0.5% is appropriate.

[0034]

[Table 7]

[0035]

As described above, the fluoride glass of the present invention has a high refractive index, is stable against crystallization, and can provide a glass that is stable against heating such as fiberization. In addition, by using the optical amplifier, the medium for laser, or the core glass of the fiber amplifier or the fiber laser, the performance thereof can be dramatically improved.

[Brief description of the drawings]

FIG. 1 shows the change in glass stability due to the addition of rare earth elements.

FIG. 2 shows the relationship between the Pb content and the refractive index in Example 1.

FIG. 3 shows the relationship between Pb content and thermal stability in Example 1.

FIG. 4 is a configuration diagram of an optical amplifier used in the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Incident light of a signal wavelength 2 Optical multiplexer 3 Semiconductor laser 4 Optical amplification fiber 5 High numerical aperture silica fiber 6 Isolator 7 Optical spectrum analyzer

Claims (10)

[Claims] 1. InF ₃ , MF ₂ (where M is Mg, C
It represents at least one element selected from a, Sr, and Ba. ), TF ₂ (where T is Zn, Cd, Sn
At least one element selected from the group consisting of: ),
PbF ₂ as a main component, Er, Pr, Nd, Ho, Tm
In In-based fluoride glass compositions containing at least one or more rare earth elements selected from the group consisting of active ions for amplification, the cations of the components constituting the glass are represented by mol%, and 30 ≦ In ≦ 45%, 10 ≤ M ≤ 35%, 10 ≤ T ≤ 25%, 1 ≤ Pb ≤ 25%, 0 ≤ α ≤ 10%, 0 ≤ L ≤ 3%, 0 ≤ Yb ≤ 3%, 0.01 ≤ R ≤ 7%, 0.01 ≦ A ≦ 5% (where α represents at least one or more elements selected from Al and Ga, L represents at least one or more elements selected from Sc and Y, and R represents La and Ce , Gd,
A represents at least one element selected from Lu, and A represents at least one or more rare earth elements selected from Er, Pr, Nd, Ho, and Tm. ) And the total of the cations is 100%. When the anions of the components constituting the glass are expressed in terms of mol%, F = (100−Cl)% (where 0 ≦ Cl ≦ 10%). Fluoride glass composition characterized by the following. 2. The method according to claim 1, wherein 0.1 ≦ Ce ≦
The fluoride glass composition according to claim 1, wherein the content is 7%. 3. The fluoride glass composition according to claim 1, wherein the anion is a total fluoride glass comprising only F. 4. An optical amplification waveguide using the fluoride glass composition according to any one of claims 1 to 3 for a core and using all fluoride glass or halogen oxide glass for a clad. 5. The optical amplification waveguide according to claim 4, wherein the core is made of a fluoride glass composition containing at least Er as an active ion in the core.
Characterized by being excited by light of 0.99 μm.
1.6 μm band optical amplifier. 6. The optical amplifying waveguide according to claim 4, wherein a fluoride glass composition containing at least Er as an active ion in a core portion is used for the core, and a wavelength of 1.4 to 1.
1.5 to 1 characterized by being excited by 49 μm light.
6 μm band optical amplifier. 7. A 1.3 μm band optical amplifier using the optical amplification waveguide according to claim 4, wherein a fluoride glass composition containing at least Pr as active ions in a core portion is used for the core. 8. The optical amplification waveguide according to claim 4, wherein a fluoride glass composition containing at least Tm as an active ion in a core portion is used for the core. 65 μm band and 2 μm band optical amplifier. 9. A 1 μm band optical amplifier using the optical amplification waveguide according to claim 4, wherein a fluoride glass composition containing at least Nd as active ions in a core portion is used for the core. 10. A 2 μm band optical amplifier using the optical amplification waveguide according to claim 4, wherein a fluoride glass composition containing at least Ho as active ions in the core portion is used for the core.