JPH11204859A - Optical fiber amplifier - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical fiber amplifier of low noise and wide band width. SOLUTION: An optical fiber amplifier is composed of optical amplifying fibers which are loaded with rare earth ions and connected together in series or parallel, wherein the optical amplifying fiber is formed of fluoride optical fiber, tellurite fiber, chalcogenide fiber or quartz fiber. Or, a first amplifying optical fiber 11 and a second amplifying optical fiber 12 both loaded with rare earth ions are connected in series through the intermediary of an isolator 3, the first amplifying optical fiber 11 is positioned on the upper side of the isolator 3 in the traveling direction of signal light, and the second amplifying optical fiber 12 is positioned on the lower side of the isolator 3 in the traveling direction of signal light, the first amplifying optical fiber 11 is formed of chalcogenide fiber or tellurite fiber, and the second amplifying optical fiber 12 is formed of fluoride fiber.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber amplifier used in an optical communication system and the like, and more particularly to a 1.3 .mu.m band optical fiber amplifier excellent in a wide band and low noise characteristics.

[0002]

2. Description of the Related Art In recent years, research and development of optical devices for large-capacity and high-speed optical fiber communication have been vigorously conducted. Above all, an optical fiber amplifier is a device that can amplify an optical signal weakened during transmission through an optical fiber line as light, and the optical / electric or electric / optical conversion required by the conventional regenerative amplification repeater is required. In addition to being unnecessary, in the application to wavelength division multiplexing (WDM), which is currently being actively researched and developed, it is possible to amplify a large number of signal wavelengths at a time. As a result, it is possible to significantly improve the system and reduce the cost.

Here, in the 1.5 μm band, which is an important wavelength band for optical fiber communication, at present, an optical fiber amplifier using a silica-based optical fiber in which erbium (Er) is added as a rare earth ion to a core as an amplifying medium. (EDFA) is already in practical use.

However, in the 1.3 μm band which is another important wavelength band, an optical fiber amplifier (PDFA) using a fluoride optical fiber in which praseodymium (Pr) is added as a rare earth ion to the core as an amplification medium has been developed. Although it is in the stage, its practical use is behind in comparison with EDFA. This is because, since the quantum efficiency of 1.3 μm emission in Pr is low, an optical fiber having a low phonon energy, such as a fluoride optical fiber, must be used as an optical amplification fiber. The reason for this is that the size and cost of the module have not been reduced as compared with the EDFA due to the need for a high-output laser.

The present inventors aimed at improving this low quantum efficiency by using a PbF ₂ / InF ₃ -based fluorine as a new host glass instead of a ZrF ₄ -based fluoride glass conventionally used as a fluoride glass. We have succeeded in developing a new compound glass (Japanese Patent Application No. 9-15744).

The PbF ₂ / InF ₃ -based fluoride glass has a lower phonon energy than the conventional ZrF ₄ -based fluoride glass, and is therefore expected to improve the 1.3 μm emission quantum efficiency of Pr. Can be. actually,
The present inventors have succeeded in achieving twice the efficiency of a PDFA using a conventional ZrF ₄ -based fluoride optical fiber as an amplification medium in a PDFA using the optical fiber.

However, the wavelength band that can be amplified by the 1.3 μm-band optical fiber amplifier PDFA is about 80 nm when a ZrF ₄ -based fluoride optical fiber is used, and a PbF ₂ / InF ₃ -based fluoride optical fiber is used. Even in such a case, the amplification band is limited to about 90 nm (3 dB down), and a wider amplification band has been desired in order to further increase the capacity by applying the WDM communication system.

[0008] Apart from this, in a ZrF ₄ -based or PbF ₂ / InF ₃ -based fluoride optical fiber, P
Since a large ground state absorption (GSA) of the r from the ³ H ₄ level to the ³ F ₄ level exists around a wavelength of 1.5 μm, the base of the GSA overlaps with the long wavelength side of the 1.3 μm emission,
There is a problem that a noise figure in a wavelength region longer than 1.32 μm is deteriorated.

[0009]

SUMMARY OF THE INVENTION An object of the present invention is to provide a low-noise, wide-band optical fiber amplifier which has solved the above-mentioned drawbacks.

[0010]

According to a first aspect of the present invention, there is provided an optical fiber amplifier in which a plurality of optical amplification fibers doped with rare earth ions are connected in series or in parallel. Wherein the optical amplification fiber is made of any one of a fluoride optical fiber, a tellurite fiber, a chalcogenide sulfide, and a silica-based fiber.

Further, in the optical fiber amplifier according to a second aspect of the present invention, the first optical amplification fiber doped with rare earth ions and the second optical amplification fiber are connected in series via an isolator. The first optical amplification fiber is located at a stage before the isolator with respect to the traveling direction of the signal light, and the second optical amplification fiber is located at a stage following the isolator, and the first optical amplification fiber is Is made of a chalcogenide fiber or a tellurite fiber, and the second optical amplification optical fiber is made of a fluoride optical fiber.

In each of the optical fiber amplifiers, the rare earth ions to be added include Pr, Dy, and N, respectively.
d can be used.

[0013] Similarly, in each of the optical fiber amplifier, the glass composition of the fluoride optical fiber, in atomic mole fraction, InF ₃ 10 to 30 mol%, GaF ₃ is 7-30
Mol%, ZnF ₂ is 10 to 19 mol%, BaF ₂ is 4
30 mol%, SrF ₂ is 0 to 24 mol%, PbF ₂ 0
To 30 _{mol%, LaF 3, YF 3,} GdF 3, LuF 3
At least one selected from the group consisting of 1.5 to 10
Mol%, LiF 1.5 to 30 mol%, NaF 0 to 3
0 mol%, the additional component may be 0 to 15 mol%, and the total amount of these components may be 100 mol%.

Here, as the additional components, BeF ₂ is 0 to 10, MgF ₂ is 0 to 10, and C
aF ₂ a 0~10, CdF ₂ 0 to 4, 0 to the TlF ₄
5, MnF ₂ 0-5, SmF ₃ 0-5, ScF ₃ 0-5, HfF ₄ 0-5, ZrF ₄ 0-5, 0-10 and KF, 0-10 and RbF, CsF 0 to 10, Bi
The F ₃ may contain at least one of the group consisting 0-5, the AlF ₃ from 0 to 15.

Similarly, in each of the above-described optical fiber amplifiers, the glass composition of the fluoride optical fiber is 5 to 25 mol% of InF _{3 and} 13 to 13 mol of GaF _{3 in} atomic mole fraction.
40 mol%, ZnF ₂ 4-25 mol%, PbF ₂ 3
0 to 46 mol%, CdF ₂ is 0 to 20 mol%, LaF
₃ , at least one member selected from the group consisting of YF ₃ , GDF ₃ and LuF ₃ is 1.5 to 12 mol%, and the additional component is 0%.
１５15 mol%, and the total of these composition amounts is 10
It may be 0 mol%.

Here, as the additional components, BeF ₂ is 0 to 10, MgF ₂ is 0 to 10, and C
aF ₂ a 0~10, BaF ₂ 0 to 15, the SrF ₂ 0
To 15, TlF ₄ 0-5, the MnF ₂ 0-5, SmF
₃ 0 to 5, ScF ₃ 0 to 5, HfF ₄ and 0 to 5, Z
rF ₄ 0 to 5, 0 the KF, 0~10 the RbF,
0 the CsF, BiF ₃ 0 to 5, the AlF ₃ 0~
At least one member of the group consisting of 15 can be contained.

Similarly, in each of the optical fiber amplifiers, the glass composition of the fluoride optical fiber is ZrF ₄
At least one selected from the group consisting of HfF ₄ and 4
3 to 60 mol%, ₆ to 28 mol% of BaF ₂ , LaF ₃
Is 1.5 to 6 mol%, ScF ₃ , YF ₃ , GdF ₃ , L
at least one member selected from the group consisting of uF ₃ is 1.5
6 mol%, AlF ₃ is 1.5 to 6 mol%, PbF ₂ is 0 to 25 mol%, of at least one 3 to 25 mol% was exposed, obtained from LiF and NaF, additional ingredients 0-15
Mol%, and the total of these composition amounts is 100 mol%
It may be.

Here, as the additional components, BeF ₂ is 0 to 10, MgF ₂ is 0 to 10, and C
aF ₂ a 0~10, SrF ₂ 0 to 15, the CdF ₂ 0
To 4, TlF ₄ to 0 to 5, MnF ₂ to 0 to 5, SmF ₃
The 0~5, ScF ₃ 0 to 5, 0 the KF, RbF
0-10, CsF 0-10, InF ₃ 0-5, G
aF ₃ 0-5, a BiF ₃ may contain at least one of the group consisting of 0-5.

Similarly, in each of the optical fiber amplifiers, the glass composition of the tellurite fiber is TeO ₂
55 to 90 mol%, ZnO, WO ₃ , Li ₂ O, Na
_At least two kinds selected from the group consisting of ₂ O, Al ₂ O ₃ and Bi ₂ O ₃ are each 0 to 35 mol%, and the total of these composition amounts may be 100 mol%.

Similarly, in each of the above optical fiber amplifiers, the glass composition of the chalcogenide fiber is Ga, Ge, In, La, Na, Li,
It may contain at least one selected from the group consisting of K and Cs, and may contain at least one selected from the group consisting of S, Cl, I and Br as anions.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION The emission spectrum of rare earth ions has different shapes depending on the type of host glass to which rare earth ions are added. This is because the appearance of the energy level splitting (Stark splitting) that determines the shape of the spectrum is different for each host glass due to the influence of the ligand field.

The present inventors have conducted intensive studies on the 1.3 μm emission spectral shape of Pr. As shown in FIG. 1, the 1.3 μm emission spectrum in the chalcogenide glass and the tellurite glass was changed to ZrF ₄ or P
It has been found that the spectrum is shifted to a longer wavelength side than the spectrum observed in the bF ₂ / InF ₃ -based fluoride glass. Here, the horizontal axis in FIG. 1 shows the wavelength, and the vertical axis shows the 1.3 μm emission intensity of each of the obtained glasses normalized to 1.

Further, chalcogenide glass or, in the tellurite glass, ³ H ₄ center defined state absorption to ³ F ₄ level by level (GSA) also ZrF ₄ system or PbF ₂ / InF ₃ based fluoride Since it is shifted to the longer wavelength side than that seen in the glass, the wavelength is longer at 1.32 μm than 1.32 μm, which has been a problem at the time of optical amplification of ZrF ₄ -based or PbF ₂ / InF ₃ -based fluoride glass. The present inventors have found that no degradation of the noise figure is observed.

On the other hand, as a construction method of an optical fiber amplifier for obtaining low noise and high output, there is a report example of a cascaded EDFA in which an isolator is arranged between two optical amplification optical fibers (Yamashita et al. “Improvement of e
rbium-doped fiber amplifier characteristics by ins
ertion of midway-isolator ”, In Proc. OEC'92, 17B
3-3, 1992). In this EDFA, the former 980n
The low-noise, high-gain signal obtained from the m-pumped EDFA is passed through the isolator to the subsequent 1480 nm-pumped EDF.
By inputting to A, low-noise, high-output optical amplification is realized.

This is because the value of the noise figure obtained by the cascaded optical fiber amplifier described above is

[0026]

## EQU1 ## Since the total noise figure (NF) = NF of the preceding stage + (NF of the succeeding stage) / (gain of the preceding stage), when a high gain is achieved in the preceding stage, the degradation of the noise figure in the following stage is reduced. That
Further, since the energy conversion efficiency from the pump light to the signal light is higher as the wavelengths of the pump light and the signal light (1550 nm) are closer to each other, the EDFA is more excellent in the high output characteristic when pumping at 1480 nm than at 980 nm. I use it.

Therefore, in the above-mentioned EDFA, low-noise and high-gain amplification characteristics are realized in the first stage by pumping at 980 nm, and degradation in noise characteristics due to 1480 nm pumping in the second stage is reduced by high gain in the first stage. To increase the output.

The present inventors diligently studied the configuration of an optical fiber amplifier for a 1.3 μm band with a low noise, a high gain, and a wide band. As a result, Pr having a gain peak near the wavelength of 1.34 μm in the preceding stage was obtained. By disposing a doped chalcogenide fiber or tellurite fiber and disposing a Pr-doped PbF ₂ / InF ₃ -based fiber or ZrF ₄ -based fiber having a gain peak at a wavelength of 1.30 μm after the isolator, It has been found that a high-gain, wide-band optical fiber amplifier can be constructed.

According to this configuration, by arranging optical amplification fibers having different gain peak positions in the front stage and the rear stage, the net amplification band is widened and PbF ₂ / I
The degradation of the noise figure on the longer wavelength side than 1.32 μm due to the influence of GSA, which has been a problem when using an nF ₃ -based or ZrF ₄ -based fluoride optical fiber, is explained by the chalcogenide in the front stage. Or higher gain in the wavelength range longer than 1.32 μm obtained using tellurite fiber,
Low noise characteristics are realized over the entire net amplification band.

Here, in order to realize a wide band optical fiber amplifier, either a group of tellurite or chalcogenide fiber and a group of PbF ₂ / InF ₃ or ZrF ₄ based fluoride optical fiber is placed at the front or rear stage. It may be configured to be arranged. However, in order to realize broadband and low-noise optical amplification, a tellurite or chalcogenide fiber is used in the preceding stage,
The arrangement of a PbF ₂ / InF ₃ -based or ZrF ₄ -based fluoride optical fiber at the subsequent stage is the same as the above described 1.32 μm.
This is preferable in terms of reducing the degradation of the noise figure at a wavelength longer than m. A wideband optical fiber amplifier can also be configured by arranging a tellurite or chalcogenide fiber and a PbF ₂ / InF ₃ -based or ZrF ₄ -based fluoride optical fiber in parallel via a filter or a WDM fiber coupler.

The configuration of the optical fiber amplifier according to the present invention is as follows.
The configuration of the optical fiber amplifier for low noise and high output by the cascade connection of the EDFAs described above is different in that different types of fibers are used in the first and second stages. Also, the amplification bands of the optical fibers for optical amplification at the front and rear stages used are different, and by superimposing these different amplification bands, the net amplification band of the optical fiber amplifier is expanded. different. Furthermore, the present invention has been made to expand the amplification band of the 1.3 μm band while maintaining low noise characteristics, and to realize the aforementioned low noise and high output characteristics in the 1.5 μm band. It should be noted that the configuration is essentially different in the wavelength band applied.

Further, the present inventors have studied the glass composition of a PbF ₂ / InF ₃ -based fluoride optical fiber for realizing the optical fiber amplifier of the present invention.
InF ₃ 10 to 30 mol% in atomic mole fraction, GaF ₃
7 to 30 mol%, the ZnF ₂ 10~19 mol%, Ba
F ₂ 4 to 30 mol%, the SrF ₂ 0-24 mol%, P
0 to 30 mol% of bF ₂ , LaF ₃ , YF ₃ , GdF
₃ and LuF ₃ , at least one selected from the group consisting of 1.5 to 10 mol%, LiF at 1.5 to 30 mol%, N
It has been found that a stable glass can be obtained in a composition range in which aF is 0 to 30 mol%, the additional component is 0 to 15 mol%, and the total is 100 mol%.

Here, InF ₃ and GaF ₃ are essential components forming the skeleton of glass. InF ₃ is desirably contain 10 to 30 mol%, 10 mol% or less, or in the 30 mol% or more can not be obtained a transparent glass by crystallization. GaF ₃ is 7-30.
If it is contained in the range of 7 mol% or less, or 30 mol% or more, stable glass cannot be obtained by crystallization.

ZnF ₂ and BaF ₂ are essential components for modifying the glass skeleton. Here, ZnF ₂ is 10 to
It is desirable that the content be in the range of 19 mol%, and if it is 10 mol% or less, or if it is 19 mol% or more, the tendency of crystallization becomes remarkable, so that a stable glass cannot be obtained. BaF ₂ is desirably contain 4 to 30 mol%, 4 mol% or less, or in the 30 mol% or more can not be obtained a stable glass by crystallization.

SrF ₂ is contained in the range of 0 to 24 mol% of Ba.
It can replace F ₂ and has the function of increasing the thermal stability of the glass.

PbF ₂ and NaF are components for improving the thermal stability of glass. By containing these components, a uniform glass melt can be obtained even at a low temperature, and the glass forming ability can be increased. Here, PbF ₂ is preferably be contained in the range of 0 to 30 mol%, it is difficult to increase in the volatility of the glass melt to obtain a stable glass in more than 30 mole%. NaF is desirably contained in an amount of 0 to 30 mol%, and if it is 30 mol% or more, crystallization becomes remarkable and a stable glass cannot be obtained.

LiF is a particularly important component for stabilizing the glass, and it is particularly desirable that LiF be contained in the range of 1.5 to 10 mol%. Furthermore, in order to obtain a stable glass in a system containing PbF ₂ , it is an essential condition to contain LiF.

LaF ₃ , YF ₃ , GdF ₃ , LuF ₃
Is an essential component for increasing the thermal stability of glass. At this time, at least one of these is set to 1.5
It is desirable that the content be from 10 to 10 mol%. At a content of 1.5 mol% or less, no increase in thermal stability can be confirmed, and at a content of 10 mol% or more, the tendency of crystallization is remarkable. As a result, stable glass cannot be obtained.

The present inventors also studied another embodiment of the PbF ₂ / InF ₃ -based fluoride optical fiber constituting the optical fiber amplifier of the present invention. As a result, the atomic mole fraction of InF ₃ was 5%. to 25 mol%, the GaF ₃ 13~4
0 mol%, ZnF ₂ is 4 to 25 mol%, and PbF ₂ is 30 mol%.
To 46 mol%, the CdF ₂ 0 to 20 mol%, LaF _3,
Alternatively, at least one selected from the group consisting of YF ₃ , GdF ₃ and LuF ₃ is 1.5 to 12 mol%, the additional component is 0 to 15 mol%, and the composition is stable in a composition range of 100 mol% in total. We found that a good glass could be obtained.

Here, InF ₃ and GaF ₃ are essential components forming a skeleton of glass. At this time, InF ₃ is 5
It is desirable that the content be in the range of from about 25 mol% to less than 5 mol%. Further, even at 25 mol% or more, the tendency of crystallization becomes remarkable, and a good glass cannot be obtained. GaF ₃ is 1
If it is contained in an amount of 3 to 40 mol% or less, it is difficult to obtain a transparent glass by crystallization, and if it is more than 40 mol%, the glass melt becomes turbid and transparent glass cannot be obtained.

PbF ₂ and ZnF ₂ are essential components for modifying the glass skeleton. By containing these ions, a uniform melt can be obtained even at a low temperature, and the glass forming ability is increased. Here, PbF ₂ is
If the content is 30 mol or less, it is difficult to obtain a transparent glass by crystallization, and if it is 46 mol% or more, the glass melt tends to volatilize, and a stable glass is obtained. I can't. Also,
ZnF ₂ is desirably contained in an amount of 4 to 25 mol%,
When the amount is less than 4 mol%, a transparent glass cannot be obtained by crystallization, and when the amount is more than 25 mol%, the tendency of crystallization becomes remarkable, and a transparent glass cannot be obtained. In addition, CdF ₂
Can be contained in the range of 0 to 20 mol in place of PbF ₂ or ZnF ₂ . Preferably, it is effective to increase the glass forming ability and obtain a stable glass by being contained in the range of 0 to 7 mol. Furthermore, LaF ₃ or YF ₃ , GdF ₃ , Lu
F ₃ is an essential component for improving the thermal stability against crystallization in the fluoride glass of the present invention. By containing at least one of these in an amount of 1.5 to 12 mol%, the thermal stability against reheating can be improved.

Further, the present inventors studied the glass composition of the ZrF ₄ -based fluoride optical fiber constituting the optical fiber amplifier of the present invention, and found that ZrF ₄ and HfF
_At least one selected from the group consisting of 43 to 60
Mol%, the BaF ₂ 6 to 28 mol%, the LaF ₃ 1.5
6 _{mol% ScF 3, YF 3, GdF} 3, at least one selected from the group consisting of LuF ₃ 1.5-6 mol%, AlF ₃ and 1.5 to 6 mol%, the PbF ₂ 0 to 25
Mol%, at least one selected from LiF and NaF is 3 to 25 mol%, and the additional component is 0 to 15 mol%.
And in a composition region whose total is 100 mol%,
It has been found that a stable glass can be obtained.

Here, ZrF ₄ and HfF ₄ are essential components forming a network structure which is a skeleton of glass.
It is desirable to contain it in the range of 0 mol%. 43 mol%
If the content is less or more than 60 mol%, crystals precipitate inside the glass, which is not suitable. BaF ₂ , LaF ₃ , AlF ₃ and LiF
F, NaF and at least one selected from ScF ₃ ,
At least one selected from YF ₃ , GdF ₃ , and LuF ₃ is an essential component for modifying the network structure of the glass and increasing the thermal stability of the glass, and is desirably contained in the above-described ranges. . Those outside the above-mentioned range are not suitable. BaF ₂ , LaF ₃ ,
AlF ₃ , at least one selected from LiF and NaF, and at least one selected from ScF ₃ , YF ₃ , GdF ₃ and LuF ₃ modify the network structure of the glass and increase the thermal stability of the glass Is an essential component, and it is desirable that each is contained in the above-mentioned range.
If the content is more than the above range, crystals are precipitated in the glass, which is not suitable. In addition, when the content is low, the effect of increasing the thermal stability cannot be confirmed.

PbF ₂ has a function of increasing the refractive index of glass by being contained in place of BaF ₂ . If the content exceeds the above range, crystals are precipitated in the glass, which is not suitable.

Further, the present inventors have studied the glass composition of the tellurite fiber constituting the optical fiber amplifier of the present invention. As a result, 55 to 90 mol% of TeO ₂ and Z
nO, WO ₃ , Li ₂ O, Na ₂ O, Al ₂ O ₃ , La
It is required that at least two types selected from the group consisting of ₂ O ₃ and Bi ₂ O ₃ are each contained in an amount of 0 to 35 mol%, and that a stable glass can be obtained in a composition range in which the total is 100 mol%. I found it.

Here, TeO ₂ is an essential component forming a network structure as a glass skeleton, and is desirably contained in the range of 55 to 90 mol%. In the region of less than 55 mol% or in the region of more than 90 mol%,
It is difficult to obtain a stable glass by crystallization.

Further, ZnO, Bi ₂ O ₃ , Li ₂ O, N
_{a 2 O, Al 2 O 3} , WO 3, La 2 O 3 is a component for modifying a network structure, at least two kinds of these, be contained in the range of 0 to 35 mol%, respectively desirable. If the content is more than 35 mol%, it becomes difficult to produce glass by crystallization.

Further, the present inventors studied the glass composition of the chalcogenide fiber constituting the optical fiber amplifier of the present invention, and found that Ga, Ge, and cation were used as cations.
It contains at least one selected from the group consisting of In, La, Na, Li, K, and Cs, and contains S, C as anions.
It has been found that a stable glass can be obtained in a composition range containing at least one selected from the group consisting of l, I, and Br.

Here, Ga ₂ S ₃ is an essential component constituting the skeleton of glass, and is desirably contained in the range of 38 to 75 mol%. La ₂ S ₃ , GeS ₂ , In ₂ S
₃ has a function of modifying the glass skeleton to enhance weather resistance and thermal stability, and is desirably contained in the range of 0 to 20 mol%. La ₂ S ₃ and In ₂ S ₃ are 20
When the content is higher by mol%, the liquidus temperature rises and G
When eS ₂ is contained in an amount of more than 20 mol%, the glass melt tends to volatilize, and it is difficult to obtain a stable state of the glass melt. Na ₂ S, Li ₂ S, K ₂
S, Cs ₂ S, NaCl, LiCl, KCl, CsC
1, NaI, LiI, KI, CsI, NaBr, LiB
r, KBr and CsBr have the function of modifying the glass skeleton to increase the glass-forming ability. However, when contained in an amount of more than 55 mol%, the glass-forming ability is significantly deteriorated, and the stable glass It becomes difficult to obtain.

[0050]

EXAMPLES The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples.

(Embodiment 1) In this embodiment, an optical fiber amplifier in which an isolator is arranged between the first and second optical amplification optical fibers as shown in FIG.
In the figure, 1 is a first optical amplification fiber, 2 is a second optical amplification fiber, 3 is an isolator, 4 is a WDM fiber coupler, and 5 is an excitation light source.

In this embodiment, a Pr-doped chalcogenide fiber is used as the first optical amplification fiber.
An optical fiber amplifier was configured using a Pr-doped ZrF ₄ -based fluoride optical fiber as the second optical amplification fiber.

The ZrF ₄ -based fluoride optical fiber used as the optical amplification fiber was manufactured by a jacket stretching method. First, 51ZrF ₄ -18BaF ₂ -11PbF
₂ -3.5LaF ₃ -2YF ₃ -4.5AlF ₃ -10
Using LiF as a core glass composition, 49ZrF ₄ -21Ba
_{F 2 -3.5LaF 3 -2YF 3 -4.5AlF 3} -2
A fluoride optical fiber preform (outer diameter 5 mmφ, length 50 mm) using 0NaF as a cladding glass was produced by a suction casting method. Separately from this, a jacket tube having the same composition as the clad glass (external 15
mmφ, length 140 mm) using a rotation casting method. Insert the fiber preform into the produced jacket tube, hold it on the chuck, and insert it into the heating furnace heated to 320 ° C at a rate of 2 mm / min from the upper part while evacuating the inside to produce a 125 μm optical fiber. did. The manufactured ZrF ₄ -based fluoride optical fiber is a single mode, having a relative refractive index difference of 3.7% and a core diameter of 1.8 μm.
m, the cut-off wavelength is 1.0 μm, the concentration of Pr added is 1000 ppm, and the loss value is
dB / m.

On the other hand, chalcogenide fibers were produced by a rod-in-tube method. First, 65Ga ₂ S
The ₃ -14La ₂ S ₃ -21Na ₂ core glass batch composition consisting of S, melted in a glassy carbon crucible, by casting a stainless steel mold, core preform (outer diameter 5 mm.phi, length 140 mm) Produced. Apart from this _{50Ga 2 S 3 -15Ge 2 S 3} -
Jacket tube composed of 14La ₂ S ₃ -21Na ₂ S (inner diameter 5 mmφ, outer diameter 15 mmφ, length 140 m
m) was prepared, and the surface of the previously prepared core preform was optically polished and then inserted into a jacket tube. After holding the jacket tube in a vacuum chuck, the inside is evacuated and sent into a heating furnace heated to 450 ° C. at a rate of 2 mm per minute from the upper portion, and the lower portion of the jacket tube is held by another chuck and moved downward. By lowering at a speed of 30 mm per minute, a stretched base material having an outer diameter of 5 mmφ and a core diameter of 50 μm was prepared, and the stretched base material was inserted again into the jacket tube.
The jacket tube was fed at a feed rate of 3 mm / min into a drawing furnace heated to produce a fiber having an outer diameter of 125 μm. The manufactured optical fiber is a single mode fiber having Δn = 1.5%, a core diameter of 2.2 μm, and a cut-off wavelength of 1.0 μm. The additive concentration of Pr is 1000 ppm, and the loss is 1 dB / at a wavelength of 1.2 μm. m.

FIG. 3 shows a signal gain spectrum of the optical fiber amplifier of this embodiment with respect to an incident signal light amount of -30 dBm. As an excitation light source, an LD with an oscillation wavelength of 1.017 μm
, And the excitation light quantity of the chalcogenide fiber in the previous stage is 1
00mW, the amount of excitation light of the subsequent ZrF ₄ fiber is 25
0 mW. In the figure, the left vertical axis indicates the value of the signal gain, and the horizontal axis indicates the signal wavelength. The ZrF ₄ -based optical amplification fiber used is 20 m, and the chalcogenide fiber is 8 m. FIG. 3 also shows, for comparison, the gain spectrum (dotted line) of the conventional ZrF ₄ -based fluoride optical fiber and the gain spectrum (dot-dash line) of the chalcogenide fiber. From the figure, it is found that the wavelength is 1.29 to 1.35.
It can be seen that a gain of 20 dB or more was obtained over μm, and the amplification band was expanded with respect to the conventional spectrum. The noise index is shown on the right vertical axis of FIG. As for the noise figure, a low noise of 5 dB is realized over the measured wavelength range, and the noise figure is longer in a wavelength range longer than 1.32 m as observed when the aforementioned ZrF ₄ -based fluoride optical fiber is used. It can be seen that the noise figure is not deteriorated.

In addition, when a chalcogenide fiber having a core glass composition shown in Tables 1 to 5 or a ZrF ₄ -based fluoride optical fiber having a core glass composition shown in Table 6 is used, the same amplification is performed. Characteristics could be obtained.

[0057]

[Table 1]

[0058]

[Table 2]

[0059]

[Table 3]

[0060]

[Table 4]

[0061]

[Table 5]

[0062]

[Table 6]

(Comparative Example 1) An optical fiber amplifier having the same configuration as that of Example 1 was constructed. However, in this comparative example, the first and second optical amplification fibers used were both ZrF ₄ -based fluoride optical fibers. FIG. 4 shows a gain spectrum obtained by the optical fiber amplifier of this comparative example.
The incident signal light amount is -30 dBm, and the excitation wavelength is 1.01.
7 μm, and the amount of excitation light was 300 mW for both the front and rear stages. In the figure, the left vertical axis represents the signal gain, and the horizontal axis represents the signal wavelength. The amplification band of 3 dB down is 1.29-
It is found that the thickness is 20 nm up to 1.31 μm, which is narrower than the configuration of the first embodiment. Also, in the figure, it can be seen that the noise figure shown on the right vertical axis also increases in the wavelength region longer than 1.33 μm. From the above, it can be seen that the optical fiber amplifier having the configuration of the first embodiment has excellent wideband characteristics and noise characteristics.

(Comparative Example 2) In this comparative example, in the configuration of the optical fiber amplifier of Example 1, a ZrF ₄ -based fluoride optical fiber was used as the first optical amplification fiber, and a second optical amplification fiber was used. An optical fiber amplifier having a configuration in which a chalcogenide fiber is arranged as the optical fiber was constructed. FIG. 5 shows a gain spectrum obtained by the configuration of this comparative example. The incident signal light amount was −30 dBm, and the excitation wavelength was 1.017 μm. In the figure, the left vertical axis shows the gain and the horizontal axis shows the wavelength. From the figure, the wavelength is 1.295 to 1.3.
A gain of 20 dB is obtained over 55 μm, and it can be seen that the amplification band is expanded as compared with the conventional spectrum. The noise index is shown on the right vertical axis of FIG. The noise figure deteriorates on the longer wavelength side than the wavelength of 1.32 μm, and it can be seen that the noise figure is not improved by this configuration.

(Embodiment 2) In this embodiment, in the same configuration as in Embodiment 1, Pr-doped tellurite fiber is used as the first optical amplification fiber, and Pr-doped fiber is used as the second optical amplification fiber. An optical fiber amplifier using a PbF ₂ / InF ₃ -based fluoride optical fiber was manufactured.

The tellurite fiber used as the first optical amplification fiber was produced by a jacket stretching method.
_{First, 70TeO 2 -10ZnO 2 -5Bi 2 O} 3 -1
0Na ₂ O as a core glass composition, 70 TeO ₂ -10
A fluoride optical fiber preform (outside diameter 5 mmφ, length 50 mm) using ZnO ₂ -15Na ₂ O as a clad glass was produced by a suction casting method. Separately from this, a jacket tube (outer diameter 15 mmφ, length 140 mm) having the same composition as the clad glass was produced by using a rotational casting method. Insert the fiber preform into the manufactured jacket tube, hold it on the chuck,
By inserting the inside of the heating furnace heated to 350 ° C. from the upper part at a speed of 2 mm / min while evacuating the inside and extending the lower part of the jacket tube held by another chuck at a speed of 30 mm / min. , The second with a reduced core diameter
Was obtained. A jacket tube (70TeO ₂ -10ZnO) prepared separately from the obtained second fiber preform.
₂ -15Na ₂ O, an outer diameter having a diameter of 15 mm, length 140 mm)
While holding the upper part of the jacket tube with a chuck and evacuating the inside while inserting the fiber into a drawing furnace heated to 380 ° C. at a rate of 3 mm per minute, and drawing an optical fiber having an outer diameter of 125 μm. Manufactured. The manufactured tellurite fiber is single mode and has a relative refractive index difference of 1.
5%, the core diameter was 2.2 μm, the cut-off wavelength was 1.0 μm, the concentration of Pr added was 1000 ppm, and the loss value was 0.06 dB / m at a wavelength of 1.2 μm.

On the other hand, a PbF ₂ / InF ₃ -based fluoride optical fiber used as a second optical amplification optical fiber was produced by the same jacket stretching method. 25.5InF ₃
-11.5GaF ₃ -15ZnF ₂ -18PbF ₂ -1
2BaF ₂ -8SrF ₂ -2.5YF ₃ -2.5LaF
The ₃ -5LiF the core glass composition, 25.5InF ₃
-11.5GaF ₃ -14ZnF ₂ -2.5PbF ₂ -
19BaF ₂ -8SrF ₂ -2.5YF ₃ -2.5La
F ₃ -7.5NaF-7LiF a fluoride optical fiber preform for the cladding glass (outer diameter 5 mm.phi, length 50m
m) was prepared by a suction casting method.
Separately, a jacket tube (49ZrF4-21Ba)
_{F 2 -3.5LaF 3 -2YF 3 -4.5AlF 3} -2
0NaF, an outer diameter of 15 mmφ, and a length of 140 mm) were produced using a rotation casting method. The fiber preform is inserted into the produced jacket tube and held by a chuck, and while the inside is evacuated, inserted into a heating furnace heated to 320 ° C. at a rate of 2 mm per minute from the top and held by another chuck. The lower portion of the jacket tube was stretched downward at a speed of 30 mm per minute to obtain a second fiber preform having a reduced core diameter. The obtained second fiber preform was inserted into a separately prepared jacket tube (outer diameter: 12 mm, length: 140 mm), and heated to 350 ° C. while vacuum-evacuating the inside while holding the upper portion of the jacket tube with a chuck. An optical fiber having an outer diameter of 125 μm was manufactured by inserting the wire into a drawing furnace at a speed of 3 mm per minute and drawing. The manufactured PbF ₂ / InF ₃ -based fluoride optical fiber has a single mode, a relative refractive index difference of 3.7%, a core diameter of 1.8 μm, a cutoff wavelength of 1.0 μm, a Pr concentration of 1000 ppm, The loss value is at a wavelength of 1.2 μm.
0.04 dB / m.

FIG. 6 shows a signal gain spectrum of the optical fiber amplifier according to the present embodiment with respect to an incident signal light amount of -30 dBm. As an excitation light source, an LD with an oscillation wavelength of 1.017 μm
And the amount of excitation light of the preceding tellurite fiber is 300
The excitation light quantity of the PbF ₂ / InF ₃ -based fluoride optical fiber at the subsequent stage was 200 mW. In the figure, the left vertical axis indicates the value of the signal gain, and the horizontal axis indicates the signal wavelength. The used PbF ₂ / InF ₃ optical amplification fiber is 15 m
And the tellurite fiber is 5 m. FIG.
In FIG. _2, the gain spectrum (dotted line) of a conventional PbF ₂ / InF ₃ -based fluoride optical fiber and the gain spectrum (dot-dash line) of a tellurite fiber are also shown for comparison. From the figure, it can be seen that 2 from wavelength 1.285 to 1.345 μm.
It can be seen that a gain of 0 dB or more was obtained, and the amplification band was expanded with respect to the conventional spectrum. The noise figure is shown on the right vertical axis of FIG. As for the noise figure, low noise of 5 dB is realized over the measured wavelength range, and the noise figure is longer in the wavelength range of 1.32 μm than the wavelength 1.32 μm observed when the above-described PbF ₂ / InF ₃ -based fluoride optical fiber is used. It can be seen that the noise figure is not deteriorated. In addition, Table 7
In the case where a tellurite fiber having a core glass composition shown in Table 9 or a PbF ₂ / InF ₃ -based fluoride optical fiber having a core glass composition shown in Tables 10 and 11 is used, the same amplification is performed. Characteristics could be obtained.

In addition, when the ZrF ₄ -based fluoride optical fiber used in Embodiment 1 is used as the second optical amplifying fiber (tellurite fiber + ZrF ₄ -based fiber), or the first optical amplifying fiber is used. In the case where the chalcogenide fiber used in Example 1 was used (chalcogenide fiber + PbF ₂ / InF ₃ system fiber), an optical fiber amplifier having a low noise and an expanded amplification band could be similarly formed.

[0070]

[Table 7]

[0071]

[Table 8]

[0072]

[Table 9]

[0073]

[Table 10]

[0074]

[Table 11]

Comparative Example 3 In this comparative example, in the configuration of the optical fiber amplifier of Example 2, a PbF ₂ / InF ₃ -based fluoride optical fiber was used as a first optical amplification fiber, and a _second optical amplification fiber was used. An optical fiber amplifier having a configuration in which a tellurite fiber was arranged as an optical amplification fiber was configured. When a gain spectrum was measured by the configuration of this comparative example, a gain of 20 dB was obtained over a wavelength of 1.285 to 1.345 μm, and it was confirmed that the amplification band was expanded as compared with the conventional spectrum. The noise figure deteriorated on the longer wavelength side than the wavelength of 1.32 μm, and the improvement of the noise figure by this comparative example was not recognized.

Example 3 In this example, an optical fiber amplifier having a configuration in which first, second, and third optical amplification fibers were connected in series as shown in FIG. 7 was manufactured. In the figure, 11 is a first optical amplification fiber, 12 is a second optical amplification fiber.
13 is a third optical amplification fiber,
3 is an isolator, 4 is a fiber type WDM coupler, 4 '
Is a bulk type WDM coupler, and 5 is an excitation light source.

In this embodiment, a tellurite fiber is used as the first optical amplification fiber, a chalcogenide fiber is used as the second optical amplification fiber, and a ZrF ₄ -based fluoride light is used as the third optical amplification fire. Fibers were used, and the specifications of each fiber were as described in Examples 1 and 2.
The same fiber specifications as those used in the above were used. When the gain spectrum of the optical fiber amplifier was measured, a gain of 20 dB or more and a low noise figure of 5 dB could be confirmed over a wavelength of 1.28 to 1.345 μm.
In addition, the same amplification band and noise figure could be confirmed when the first and second optical amplification fibers were replaced. Further, as a third optical amplification fiber, PbF
_When using a ₂ / InF ₃ -based fluoride optical fiber, (tellurite fiber + chalcogenide fiber + PbF ₂
/ InF ₃ -based fiber) or (chalcogenide fiber + tellurite fiber + PbF ₂ / InF ₃ -based fiber), the same amplification band and noise figure could be confirmed.

Embodiment 4 In this embodiment, an optical fiber amplifier having a configuration in which first and second optical amplification optical fibers as shown in FIG. 8 are connected in parallel was developed. Here, 11 is a first optical amplification fiber, 12 is a second optical amplification fiber, 3 is an isolator, and 4 is a fiber type W
The DM coupler, 4 'is a bulk type WDM coupler, 5 is an excitation light source, and 6 is an attenuator.

In this embodiment, a Pr-doped chalcogenide fiber is used as a first optical amplification optical fiber,
-Doped PbF ₂ / InF ₃ as an optical amplification fiber
A system fiber was used. In this embodiment, the filter used for the bulk type WDM coupler 4 'shown in the figure is a dielectric multilayer filter, and the signal light having a wavelength of 1.28 to 1.32 .mu.m passes through the second optical amplification fiber and passes through the second optical amplification fiber. 1.32 ~
The 1.36 μm signal light was configured to pass through the first optical amplification fiber. Further, in order to make the gain values of the first and second optical amplification fibers equal, the attenuator 7 is arranged at the subsequent stage of each of the optical amplification fibers.

FIG. 9 shows a gain spectrum obtained when the incident signal light amount is -30 dBm. In the figure, the left vertical axis shows the gain, and the horizontal axis shows the wavelength. From the figure, it can be seen that the gain decreases around 1.32 μm where the loss of the used filter increases, but that a flat gain characteristic is obtained in the wavelength range from 1.29 to 1.35 μm. The noise figure is shown on the right vertical axis in FIG. It can be seen that the noise figure increases around 1.32 μm where the loss of the filter increases, but a noise figure of 5 dB is obtained in other wavelength ranges.

(Embodiment 5) In this embodiment, in the configuration of the optical fiber amplifier used in Embodiment 1, a Pr-doped chalcogenide fiber is used as a first optical amplification fiber, and a second optical amplification optical fiber is used. An optical fiber amplifier was manufactured using a Dy-doped chalcogenide fiber. When the gain spectrum was measured for the incident signal light amount of −30 dBm, the gain could be confirmed over a wavelength of 1.25 to 1.4 μm. As the second optical amplification fiber, Dy-doped tellurite fiber, Zr
A similar wide amplification band could be confirmed in the case of using the F ₄ system fiber and the PbF ₂ / InF ₃ system fiber.

(Embodiment 6) In this embodiment, in the configuration of the optical fiber amplifier used in Embodiment 1, an Nd-doped chalcogenide fiber is used as the first optical amplification fiber, and the second optical amplification fiber is used. An optical fiber amplifier was manufactured using a Dy-doped chalcogenide fiber as the optical fiber. When the gain spectrum was measured for the incident signal light amount of −30 dBm, the gain could be confirmed over a wavelength of 1.2 to 1.4 μm. As a second optical amplification fiber, a Dy-doped tellurite fiber,
ZrF ₄ -based fiber, PbF ₂ / InF ₄ based fiber or Pr added ZrF ₄ -based fibers,, PbF ₂ /
When using an InF ₃ -based fiber and using an Nd-doped tellurite fiber, a quartz-based fiber, and a quartz-based crystallized fiber as the first optical amplification fiber, the same wide amplification band should be confirmed. Was completed.

[0083]

As described in the above embodiments, according to the present invention, a low-noise and wide-band optical fiber amplifier can be constructed, so that the 1.3 .mu.m band optical communication system can be advanced and reduced in cost. There are advantages.

[Brief description of the drawings]

FIG. 1 shows a Pr-doped chalcogenide fiber, tellurite fiber, and PbF constituting an optical fiber amplifier of the present invention.
₂ / InF ₃ based fiber is a diagram showing the fluorescence spectra of ZrF ₄ system fiber.

FIG. 2 is a diagram illustrating a configuration of an optical fiber amplifier according to a first embodiment of the present invention.

FIG. 3 is a diagram illustrating a gain spectrum of the optical fiber amplifier according to the first embodiment of the present invention.

FIG. 4 is a diagram showing a gain spectrum of the optical fiber amplifier according to Comparative Example 1 of the present invention.

FIG. 5 is a diagram showing a gain spectrum of an optical fiber amplifier according to Comparative Example 2 of the present invention.

FIG. 6 is a diagram illustrating a gain spectrum of the optical fiber amplifier according to the second embodiment of the present invention.

FIG. 7 is a diagram illustrating a configuration of an optical fiber amplifier according to a third embodiment of the present invention.

FIG. 8 is a diagram illustrating a configuration of an optical fiber amplifier according to a fourth embodiment of the present invention.

FIG. 9 is a diagram illustrating a gain spectrum of the optical fiber amplifier according to the fourth embodiment of the present invention.

[Explanation of symbols]

11, 12, 13 First, second, and third optical amplification fibers 3 Isolator 4, 4 'WDM fiber coupler 5 Excitation light source 6 Attenuator

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Jun Mori, 3-19-2 Nishi-Shinjuku, Shinjuku-ku, Tokyo Japan Telegraph and Telephone Corporation (72) Inventor Yasutake Oishi 3-192, Nishi-Shinjuku, Shinjuku-ku, Tokyo No. Nippon Telegraph and Telephone Corporation

Claims (8)

[Claims] 1. An optical fiber amplifier having a configuration in which a plurality of optical amplification fibers doped with rare earth ions are connected in series or in parallel, wherein the optical amplification fiber is a fluoride optical fiber, a tellurite fiber, An optical fiber amplifier comprising a chalcogenide sulfide or a quartz fiber. 2. A first optical amplification fiber to which rare earth ions are added and a second optical amplification fiber are connected in series via an isolator, and the first optical amplification fiber travels through a signal light. The second optical amplification fiber is located after the isolator, and the first optical amplification fiber is made of a chalcogenide fiber or a tellurite fiber. 2. The optical fiber amplifier according to 2, wherein the optical fiber for optical amplification comprises a fluoride optical fiber. 3. The optical fiber amplifier according to claim 1, wherein said rare earth ions are composed of Pr, Dy, and Nd. 4. The fluoride optical fiber according to claim 1, wherein the glass composition is 10 to 30 mol% of InF _{3 in} atomic mole fraction.
aF ₃ is 7 to 30 mol%, ZnF ₂ is 10 to 19 mol%, BaF ₂ is 4 to 30 mol%, SrF ₂ is 0 to 24 mol%, PbF ₂ is 0 to 30 mol%, LaF _3, YF ₃ ,
GdF _3, at least one selected from the group consisting of LuF ₃ is 1.5 to 10 mol%, LiF is 1.5 to 30 mol%, NaF 0 to 30 mole%, an additional component is 0 to 15 mol% 3. The optical fiber amplifier according to claim 1, wherein the total amount of these components is 100 mol%. 5. The fluoride optical fiber according to claim 1, wherein the glass composition is 5 to 25 mol% of InF ₃ ,
F ₃ is 13 to 40 mol%, ZnF ₂ is 4 to 25 mol%,
PbF ₂ is 30 to 46 mol%, CdF ₂ is 0 to 20 mol%, at least one selected from the group consisting of LaF ₃ , YF ₃ , GDF ₃ and LuF ₃ is 1.5 to 12 mol%, and the additional component is 3. The optical fiber amplifier according to claim 1, wherein the amount is 0 to 15 mol%, and the total amount of these components is 100 mol%. 6. The glass composition of said fluoride optical fiber is such that at least one selected from the group consisting of ZrF ₄ and HfF ₄ is 3 to 60 mol%, BaF ₂ is 6 to 28 mol%, and LaF ₃ is 1. 5-6 mol%, ScF ₃ , YF ₃ ,
At least one selected from the group consisting of GdF ₃ and LuF ₃ is 1.5 to 6 mol%, AlF ₃ is 1.5 to 6 mol%, PbF ₂ is 0 to 25 mol%, and LiF and NaF are selected. At least one is 3 to 25 mol%, the additional component is 0 to 15 mol%, and the total of these composition amounts is 1
3. The optical fiber amplifier according to claim 1, wherein the amount is 00 mol%. 7. The glass composition of the tellurite fiber is such that the content of TeO ₂ is 55 to 90 mol%, ZnO, WO ₃ , L
_{i 2 O, Na 2 O,} Al 2 O 3, Bi 2 at least two selected from the group consisting of O _3, respectively 0 to 35 mol%
3. The optical fiber amplifier according to claim 1, wherein the total amount of these components is 100 mol%. 8. The glass composition of the chalcogenide fiber is such that Ga, Ge, In, La, Na,
2. The composition according to claim 1, wherein the anion contains at least one selected from the group consisting of Li, K, and Cs, and contains at least one selected from the group consisting of S, Cl, I, and Br as an anion. 3. The optical fiber amplifier according to any one of 2.