JP2002141586A - Telluride optical fiber for optical amplification or optical waveguide or optical amplifier - Google Patents

Abstract

PROBLEM TO BE SOLVED: To connect an erbium added telluride glass optical fiber (EDTF) with an optical fiber for communication without inserting a mode field diameter converting part in an erbium added optical fiber amplifier (EDFA). SOLUTION: Mode field diameter of an EDTF is set larger than 6.3 μm. Consequently, the EDTF can be connected with an optical fiber for communication while matching the mode field diameter within 10%. Today, the EDFA is commonly used in saturated region and energy conversion efficiency, dependent on connection loss, is more important than gain coefficient. Since the EDTF is connected directly with the optical fiber for communication in the invention, loss, reliability and yield in manufacturing are enhanced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber, an optical waveguide or an optical amplifying medium (optical amplifier) using tellurite glass for optical amplifying. Applicable to light sources.

[0002]

2. Description of the Related Art In order to expand the transmission capacity and improve the function of an optical communication system, optical signals of a plurality of wavelengths are multiplexed and transmitted in one optical fiber. Multiplexing transmission technology (WDM: Wavelength Div.) That separates optical signals of a plurality of wavelengths transmitted through
research and development of ision Mutiplexing is currently underway.
In this transmission method, it is necessary to transmit a plurality of optical signals of different wavelengths with one optical fiber and to repeat and amplify the signals according to the transmission distance as in the conventional case. Therefore, in order to increase the wavelength of an optical signal and increase the transmission capacity, an optical amplifier having a wide amplification wavelength band is required. In addition, the wavelength of a system for maintaining and monitoring an optical communication system ranges from 1.61 μm to 1.66 μm.
With wavelengths between m and m being considered, the development of light sources and optical amplifiers for maintenance and monitoring systems is desired.

In recent years, for the purpose of application to the optical communication field,
Research and development of an optical fiber amplifier using an optical fiber in which a core is doped with a rare earth element as an optical amplification medium, for example, an Er (erbium) -doped optical fiber amplifier (EDFA),
Applications to optical communication systems are being actively pursued. This EDFA minimizes the loss of a silica-based optical fiber.
It is known that it operates in the 5 μm band, and has excellent features such as high gain of 30 dB or more, low noise, a wide gain band, polarization independence, and high saturation output.

[0004] One of the performances required when the EDFA is applied to WDM transmission is that the amplification band is wide as described above. A fluoride ED using fluoride glass or tellurite glass as a host of an Er-doped optical fiber amplifier as an EDFA having a wide amplification band.
FA or Tellurite EDFA has been developed.

By the way, when tellurite EDFA is used, 1.5% of conventional quartz EDFA or fluoride EDFA is used.
Batch amplification in the wavelength band from 1.53 μm to 1.61 μm, which is at least twice as wide as the wavelength band from 3 μm to 1.56 μm, becomes possible (A. Mori et al., OFC'9).
7, PD1). Further, in the tellurite EDFA, the gain at the long wavelength side can be obtained by 7 to 9 nm wider than that of the silica-based EDFA and the fluoride EDFA, so that an amplifier at a wavelength of 1.6 μm band which cannot be used conventionally is realized. (A. Mori et al., ECOC '97, vol. 3,
pp. 135-138). Therefore, future ultra-large capacity WDM
It is receiving attention as an EDFA for systems.

The Er-doped tellurite fiber (tellurite EDF) used as the amplifying medium of tellurite EDFA has a high relative refractive index difference (Δn) of 1% or more in order to increase the gain coefficient, and has a tellurite difference. Since the glass itself has a large refractive index (n _D ) of 2 or more, the mode field diameter is largely different from that of a silica-based optical fiber having Δn of 1% or less, which is usually used for communication. If these fibers are directly connected, a large loss will occur. Conventionally, TEC (Thermally Expanded Core)
) Technology (H. Hanafusa et al., Electron. Lett., Vol.
27, pp. 1968-1969, 1991), it is possible to connect with low loss by providing a mode field diameter converter. At that time, the core diameter is 2
In order to realize low reflection and low loss characteristics, a diagonal V-groove connection (Japanese Patent Application No. 10-31874) is used for connecting a tellurite EDF of about 3 μm to a quartz optical fiber having a high Δn.

In this case, when fibers having a core diameter of about 2 to 3 μm are connected to each other, the amount of change in the connection loss with respect to the misalignment of the fiber is large, and the connection loss also changes due to temperature fluctuation from room temperature. This is because, in the above connection method, since the connection is made as a composite of several kinds of materials, the expansion and contraction of each material with respect to the temperature change is various, and the optical axis is shifted. In the above connection method, there is a problem that the connection loss fluctuates about ± 0.5 dB with respect to a temperature change of −40 to + 75 ° C., and the characteristics of the device fluctuate according to the temperature fluctuation in the use environment. In addition, from the viewpoint of the production efficiency of the fiber module, it takes time to align fibers having a core diameter of about 2 to 3 μm and connect them with low reflection and low loss, and the production yield is low. Further, by providing a mode field diameter converter, one end of the mode field diameter converter is provided.
Due to the loss of about 2 dB, there is a problem that the noise figure, which is an important characteristic of the optical amplifier, is increased and the energy conversion efficiency is reduced.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to improve the reliability, operation stability, production efficiency, and reliability of a tellurite EDF module used as an amplifying medium for tellurite EDFA.
It is an object of the present invention to provide a fiber specification capable of improving the production yield and reducing the loss, and to provide an inexpensive broadband tellurite EDFA using the fiber as an optical amplification medium.

[0009]

SUMMARY OF THE INVENTION The present invention relates to a tellurite E
The most important feature is that the mode field diameter of the DF is set within 10% of the quartz optical fiber (single mode fiber, dispersion shift fiber, non-zero dispersion fiber, etc.) used for communication. Conventionally, in order to increase the gain coefficient of a silica-based EDF, it is general to increase the value of Δn to 1% or more. In this case, the mode field diameter is smaller than that of a quartz optical fiber for communication. When these two fibers are fusion-spliced, a thermal diffusion phenomenon similar to that in the case of producing a TEC occurs by performing additional discharge after fusion-splicing once, so that the mode field diameter is almost continuously increased. Since the connection can be made, a low-loss connection of 0.1 dB or less can be realized. On the other hand, in the case of tellurite EDF, since the V groove oblique polishing connection is used,
The difference in the mode field diameter results in a mode field gap at the connection plane, which causes a large connection loss.

[0010] The present inventors have devised that the mode field diameter of the tellurite EDF is set to a specification adapted to the communication optical fiber in order to reduce the connection loss without using the TEC technology. At this time, when the mode field diameter is increased and the cutoff wavelength is set to a shorter wavelength side than the 1.5 μm band, Δn becomes 0.6% or less, and the gain coefficient decreases.

Here, the background of increasing the gain coefficient of the EDFA will be considered. Initial development of EDFA (19
The output of the semiconductor LD of 0.98 μm and 1.48 μm used as the excitation light source in the late 80's and early 1990's was about several tens mW, and the number of signals to be amplified was one to several waves. Therefore, the gain coefficient at the small signal gain has been positioned as an important index indicating the characteristics of the EDFA. Energy has been devoted to increasing this value, and 11 dB / mW with 0.98 μm excitation (M. Shimizu et al. Electron. L
ett., vol. 26, pp. 1641-1642, 199
0), 6.3 dB / mW with 1.48 μm excitation (T. Kash
iwada et al. IEEE Photonics Technol. Lett., vol.
3, pp. 721-723, 1991).

[0012] However, the currently mainstream WD
In M transmission, since the number of wavelengths has increased from 32 to 170 waves, it is necessary to amplify a large incident signal and output it as a larger signal.
The output power of the semiconductor LD for excitation is 100 mW or more, which is available at low cost. Due to such a change in the use condition, the EDFA is generally used in a saturation region. In this case, the energy conversion efficiency is more important than the gain coefficient as an index indicating the characteristics of the EDFA. When the EDFA is used in the saturation region, the energy conversion efficiency does not depend on the specifications of the fiber but depends on energy loss such as connection loss.

Therefore, it is found that setting the mode field diameter of the tellurite EDF larger than that of the conventional one and lowering the connection loss in accordance with the quartz optical fiber for communication is also advantageous from the viewpoint of the energy conversion efficiency. Further, in order to make the tellurite EDF into a single mode in the 1.5 μm band, Δn needs to be 0.6% or less in order to set the cutoff wavelength to 1.5 μm or less,
Further, in order to prevent loss due to bending, it is necessary to set Δn to 0.1% or more.

The present invention is based on the above findings,
The tellurite optical fiber or optical waveguide for optical amplification according to claim 1 or 2 is an optical fiber or optical waveguide made of tellurite glass and doped with at least a core of erbium, and has a mode field diameter (MF).
D) is in the range of 6.3 <MFD (μm).

The tellurite optical fiber or optical waveguide for optical amplification according to claim 3 or 4 is preferably made of TeO.
Compositions consisting of _{2 -LO-M 2 O-N} 2 O 3 (L is Zn,
Ba is at least one kind, M is one or more kinds of alkali elements, N is Bi, La, Al, Ce, Yb, Lu.
Of at least one of the above, and an optical fiber or an optical waveguide in which erbium is added to at least the core, wherein the mode field diameter (MFD) is in the range of 6.3 <MFD (μm). It is characterized by being.

Further, the tellurite optical fiber or optical waveguide for optical amplification according to claim 5 or 6 is an optical fiber or optical waveguide having at least a core doped with erbium, and has a mode field diameter (MFD) of communication. Mode 13 (ITU standard G.652)
8.6 μm to 9.5 which is the value of MFD at 10 nm
It is characterized by conforming to μm within 10%.

The tellurite optical fiber or optical waveguide for optical amplification according to claim 7 or 8 is an optical fiber or optical waveguide having at least a core doped with erbium, and has a mode field diameter (MFD) for communication. 1550nm of shift fiber (ITU standard G.653)
Of 7.8 μm to 8.5 μm, which is the MFD value of
It is characterized by conformity within 0%.

According to a ninth or tenth aspect of the present invention, the tellurite optical fiber or the optical waveguide for optical amplification is an optical fiber or an optical waveguide having at least a core doped with erbium, and has a non-zero mode field diameter (MFD) for communication. 1550 of dispersion fiber (ITU standard G.655)
10 to 8 μm to 11 μm which is the value of MFD in nm
% Or less.

The tellurite optical fiber or optical waveguide for optical amplification according to claim 11 or 12 is an optical fiber or optical waveguide having at least a core doped with erbium, and has a cutoff wavelength of 1.5 μm or less. It is characterized by the following.

The tellurite optical fiber or optical waveguide for optical amplification according to claim 13 or 14 is an optical fiber or optical waveguide having at least a core doped with erbium, and has a relative refractive index difference (Δn) of 0. 1 <Δn <0.
6 (%).

Claim 15 or Claim 1 based on the present invention
6. The optical amplifier according to 6, wherein an optical amplification medium comprising an optical fiber or an optical waveguide having a core glass and a clad glass; and input means for inputting excitation light and signal light for exciting the optical amplification medium to the optical amplification medium. Wherein the optical amplification medium comprising the optical fiber or the optical waveguide is the optical amplification tellurite optical fiber or the optical waveguide.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail, but the present invention is not limited thereto.

Example 1 (74) T was added to the core glass composition.
eO _2- (16) ZnO- (6) Na ₂ O- (4 mol%) Bi ₂ O ₃ , and cladding composition of (75) -TeO
₂ (17) ZnO- (6) Na ₂ O- (2 mol%) Bi
_{Using 2} O ₃ , tellurite fiber (EDTF) in which Er ³⁺ was added to the core glass at 1000 ppm was produced by a jacket stretching method. Core clad base material (outer diameter 5
mmφ, length 70 mm) was produced by a suction casting method. Separately from this, a jacket tube (outer diameter 15 mmφ, inner diameter 5.5 mmφ, length 150 mm) having the same composition as the clad glass was produced by using a rotational casting method. Insert the core / cladding base material into the produced jacket tube and hold it on the chuck,
An optical fiber was manufactured by inserting the inside of the heating furnace heated to 340 ° C. at a speed of 3 mm / min from the upper part with a reduced pressure to a diameter of 125 μm. ED manufactured
TF (EDTF1) is a single mode, having a relative refractive index difference of 0.4%, a core diameter of 6.5 μm, a cutoff of 1.4 μm,
The mode field diameter is 8 μm, and the loss value is wavelength 1.2.
It was 0.04 dB / m in μm.

Separately, (73) TeO _{2 was} added to the core glass composition.
- (15) ZnO- (6) Na 2 O- (6 mol%) Bi
₂ O ₃ , with cladding composition of (73) TeO _2- (18) Z
_{nO- (7) Na 2 O- (} 2 mol%) using a Bi ₂ O _3, was prepared an optical fiber in a similar manner. E manufactured
DTF (EDTF2) is a single mode, has a relative refractive index difference of 1.5%, a core diameter of 3 μm, a cutoff of 1.4 μm, a mode field diameter of 4.2 μm, and a loss value of wavelength 1.2.
It was 0.04 dB / m in μm.

Using the above two fibers, a fiber module (module 1: EDTF1, module 2:
EDTF2) was prepared. The outline of the modules 1 and 2 is shown in FIGS. E cut to 5m each
DTFs 01 and 01 'are wound around bobbins 02 and 02', and both ends are fixed by V-groove members 03 and 03 'and polished diagonally. 04 is a dispersion-shifted fiber connected to EDTF1 (mode field diameter 8 μm), 05 and 05 ′ are V-groove members, 06 ′ is TEC connected to EDTF2 (mode field diameter 4.2 μm / 8 μm), and 04 ′ is connected to TEC. Dispersion-shifted fiber (mode field diameter 8 μm)
It is.

Fiber end connected to EDTF and TEC
The ends are fixed by V-groove members 05 and 05 'similarly to the EDTF, and are polished obliquely. The loss of the module 1 is a fiber loss of 0.04 × 5 = 0.2 dB, the connection loss of the EDTF 01 and the dispersion shift fiber 04 is 0.2 × 2 = 0.4 dB, and the total loss of the module 2 is 0.6 dB. Fiber loss 0.04 × 5 = 0.2 dB, connection loss between EDTF01 ′ and TEC06 ′ 0.3 × 2 = 0.6 dB, TE
The C loss was 0.2 × 2 = 0.4 dB, and the total was 1.2 dB.

Using these two EDTF modules, the amplification characteristics were evaluated with the configuration shown in FIG. In the figure, 11a,
11b is an optical isolator, 12 is an optical coupler for introducing excitation light, 13 is an excitation light source, and 1
Reference numeral 4 denotes an EDTF module.

FIG. 3 shows the gain with respect to the amount of incident signal.
The signal light wavelength is 1550 nm and the excitation light quantity is 100 m
W. From this figure, it can be seen that module 2
Has a higher gain, but the difference decreases as the incident signal light amount increases, and is substantially equal in a saturation region of -10 dBm or more. This indicates that there is no difference between the gains of the two amplifiers when used in the saturation region. Also, the energy conversion efficiency and noise figure at the time of -5 dBm input are 42% and 5.6 dB in the module 2, respectively, and 46% and 5 dB in the module 1, respectively. The module 1 showed more excellent characteristics because of the lower loss.

[0029] In the present embodiment using the above tellurite glass composition, it is not limited thereto, TeO ₂ -
Compositions consisting of _{LO-M 2 O-N 2} O 3 (L is Zn, Ba
And M is at least one kind of alkali element, N is at least one kind of Bi, La, Al, Ce, Yb, and Lu). Can be obtained.

Example 2 (77) T was added to the core glass composition.
eO _2- (5) ZnO- (12) Li ₂ O- (6 mol%) Bi ₂ O ₃ , and cladding composition of (79) TeO _2-
(5) ZnO— (12) Na ₂ O— (4 mol%) Bi ₂
EDTF obtained by adding 1000 ppm of Er ³⁺ to a core glass using O ₃ was produced in the same manner as in Example 1. The manufactured EDTF (EDTF3) is a single mode, having a relative refractive index difference of 0.25%, a core diameter of 7 μm, a cutoff of 1.4 μm, a mode field diameter of 9 μm, and a loss value of 0.1 at a wavelength of 1.2 μm. 03 dB / m.

A fiber module 3 for connecting this fiber 5 m to a single mode fiber (mode field diameter 9 μm) was manufactured. The loss of the module 3 is 0.03 × 5 = 0.15 dB for the fiber loss, 0.15 × 2 = 0.3 dB for the connection loss between the EDTF and the single mode fiber, and a total of 0.45 dB. Lost.

The amplification characteristics of the module 3 were evaluated in the same manner as in the first embodiment. The gain with respect to the amount of the incident signal showed characteristics similar to those of the module 1. In addition, the energy conversion efficiency and the noise figure at the time of -5 dBm input were 48% and 4.7 dB, respectively, which were more excellent than the module 1.

(Example 3) EDTF produced in Example 1
Samples 1 and EDTF2 polished with V groove end faces
No EDTF1 was prepared, and the EDTF1 was connected to a dispersion-shifted fiber whose V-groove end face was polished. The time required for the alignment connection was 25 minutes and 15 seconds on average with EDTF2-TEC, whereas the time required for EDTF1-dispersion shift fiber was 15 minutes and 20 seconds on average, which was about 10 minutes shorter. In addition, since it takes about 3 hours to manufacture one TEC on average, the operation time of the EDTF1-dispersion shift fiber can be reduced to 1/10 or less as a whole. Splice loss is 0.2 average on EDTF1-dispersion shift fiber
EDTF2-TEC averages 0.1 dB while 1 dB.
It was 38 dB. A product having a connection loss exceeding 0.5 dB is out of the standard and is not commercialized. EDTF1-
In the connection of the dispersion-shifted fiber, all of the 100 out of 100 connections were 0.5 dB or less, but in the connection of the EDTF2-TEC, 23 out of 100 out-of-specification products exceeded 0.5 dB.

From the above, the EDTF1-dispersion shift fiber connection not only improves the working efficiency, the production accuracy, and the work yield than the EDTF2-TEC connection, but also
Since no TEC member was required, the connecting portion could be made inexpensively.

(Example 4) EDTF produced in Example 2
100 specimens each having the V-groove end face polished were prepared and connected to a single mode fiber having the V-groove end face polished. The time required for the alignment connection was 13 minutes and 38 seconds on average, which was shorter than that of the EDTF1-dispersion shift fiber. The connection loss was 0.19 dB on average, and was even lower than the average of 0.21 dB for the EDTF1-dispersion-shifted fiber. Also,
There were no nonstandard products during 100 connections. From the above,
The EDTF3-single mode fiber connection improves the work efficiency, the production accuracy, and the work yield similarly to the EDTF1-dispersion shift fiber connection.

(Example 5) EDTF produced in Example 1
1 and Module 2 using EDTF2 were subjected to a reliability temperature cycle test of 11 samples each (−40 to 75 ° C., 500 cycles: Telcodia GR-
1312-CORE). FIG. 4 shows loss fluctuation in the temperature cycle of the module 1 and the module 2.
The loss fluctuation of the module 1 was ± 0.1 dB, while the loss fluctuation of the module 2 was ± 0.5 dB. Also,
In the module 1, the loss variation was ± 0.5 dB or less during 500 cycles in all 11 samples.
Module 2 has a standard of ± 0.5d for 4 samples.
B has been exceeded. That is, the use of the fiber specification of the present invention was able to satisfy the Telcodia standard for long-term reliability for the first time.

(Example 6) EDTF produced in Example 2
Eleven fiber modules for connecting non-zero dispersion fiber (mode field diameter 9 μm) using 5 m of No. 3 were prepared. The average loss of this module was 0.03 × 5 = 0.15 dB for fiber loss, 0.17 × 2 = 0.34 dB for connection loss between EDTF and non-zero dispersion fiber, and 0.49 dB in total. This module is used in Example 5
In the same manner as above, 11 samples were subjected to a temperature cycle test for reliability.
As a result, for all 11 samples for 500 cycles,
The loss fluctuation was ± 0.3 dB or less, and, as in the case of the module 1 of the fifth embodiment, the Telcodia standard of long-term reliability could be satisfied.

(Example 7) EDTF produced in Example 1
The fiber module 4 and the fiber module 5 were manufactured using 10 m of each of 1 and EDTF2. Along with these fiber modules, a silica-based EDF (EDSF, Δ
n: 1.8%, Er concentration: 1000 ppm, cutoff: 1.2 μm, length: 150 m) were measured using a system as shown in FIG. In the figure, reference numerals 21a and 12b denote optical isolators.
2a and 22b are optical couplers for introducing excitation light, 23a and 23b are excitation light sources, and 24 is EDSF.
Or an EDTF module.

When the small signal gain was measured by bi-optical pumping at 100 mW at a wavelength of 1480 nm, the EDTF of EDTF was increased from 1560 nm to 1610 nm.
For SF, a gain of 20 dB or more was obtained on average in a long wavelength band (L-band) from 1570 nm to 1600 nm.

Next, 1590.0 nm, 1590.8 n
m, 1592.4 nm, 1593.2 nm 4-wave WDM
When a signal was incident at a signal light amount of −10 dBm / ch and the output spectrum was observed, FIG. 6 ((a) EDSF,
(B) EDTF2, (c) EDTF1).

As shown in FIG. 6A, in the amplifier using EDSF, an output signal of 15 dBm per one wave is obtained, and at the same time, Four Wave Mixing (FWM).
, A new signal light was generated, and the maximum FWM signal light amount was −13 dBm at a wavelength of 1591.6 nm. Therefore, the ratio of signal light to FWM generated light is -28 dB.
m.

Next, in the amplifier using the EDTF2 shown in FIG. 6B, an output signal light of 15 dBm per wave
The WM generated light was -10 dBm at a wavelength of 1591.6 nm, and the signal ratio was -25 dBm.

On the other hand, in the amplifier using the EDTF1 shown in FIG. 6C, the output signal light of 15 dBm per wave is also emitted, while the FWM generated light has a wavelength of 1591.6 nm and is -20.
It was less than dBm, and could not be accurately observed because it was buried in spontaneous emission light. The signal ratio was -35 dBm or less.

From the above observation of the output spectrum, by using the EDTF2 having the specifications specified in the present invention, it is possible to suppress the occurrence of FWM, which has been a problem in the conventional EDF, and to transmit a high-quality WDM signal. It became.

(Example 8) EDTF produced in Example 2
The fiber module 6 connected to the non-zero dispersion shift fiber was manufactured using 16 m of No.3. Using the same EDSF as that used in Example 7 together with this fiber module at 250 m, measurement was carried out in the system shown in FIG. Wavelength 1480nm
The small signal gain due to both optical excitations at 100 mW was measured at 1700 nm.
In the long wavelength band (L-band) from 1570 nm to 1608 nm, 2
A gain of 5 dB or more was obtained.

Next, a gain equalizer using a fiber black grating was inserted into both amplifiers, and flattened at a gain of 25 dB. A 40-wave WDM signal is applied to the band of 1575.0 nm to 1591.0 nm at an interval of 50 GHz by -20d.
When the light was incident at a signal light amount of Bm / ch and the output spectrum was observed, FIG. 7 ((a) EDSF, (b) EDTF
In an amplifier using EDSF as in 3), 5
The FWM generated light has a wavelength of 157 with respect to the output signal light of dBm.
It was -15 dBm at 4.6 nm and 1591.4 nm, and the signal ratio was -20 dBm.

On the other hand, in the amplifier using the EDTF3 shown in FIG. 7B, the output signal light of 5 dBm per wave, the FWM generated light has wavelengths of 1574.6 nm and 159
It was -30 dBm or less at 1.4 nm, and could not be accurately observed because it was buried in spontaneous emission light. Signal ratio is -35 dBm
Met.

From the above observation of the output spectrum, by using the EDTF3 having the specifications specified in the present invention, it is possible to suppress the generation of FWM, which has been a problem in the conventional EDF, and to transmit a high-quality WDM signal. It became.

(Example 9) EDTF produced in Example 1
1 and 5 m, an optical isolator and a WDM coupler integrated gain module as shown in FIG. 8 ((a) front, (b) rear) were manufactured. In the figure, 31a, 31b,
31c and 31d are dispersion shift fibers, 32 is EDT
F, 33a, 33b, 33c, 33d, 33e, 33f
Is an aspheric lens, 34a and 34b are polarization-independent isolators, 35a and 35b are mirrors, 36a, 36b, and 3
6c, 36d, 36e and 36f are AR coats.

The EDTF 32 was embedded in a suspension ferrule and the end face was obliquely polished to 12 degrees. Then, AR coats 36b and 36d using SiO ₂ were deposited on the end face to form a collimator using an aspherical lens. Similarly, the end faces of the dispersion-shifted fibers 31a, 31b, 31c, 31d are 1
Polish diagonally twice, and use AR coats 36a, 36c,
36e and 36f were deposited to form a collimator using an aspheric lens. Polarization independent isolator 34a,
Reference numeral 34b is a submodule composed of a magnet, a Faraday rotator, and the like. After these components were arranged and aligned as shown in the figure, each device was fixed by YAG welding.

The signal light passes through the dispersion-shifted fiber 31a, the polarization-independent isolator 34a, and the mirror 35a.
The light is focused on the TF 32. The loss was 0.6 dB. The excitation light passes through the dispersion shift fiber 31b and passes through the mirror 35a.
And is condensed on the EDTF 32. Coupling loss was 0.4 dB. Fig. 8 (a) in front of the EDTF
As shown in FIG. 8B, the rear side was connected as shown in FIG. 8B to produce a gain module. The total loss is 1.4 dB, and the loss is 2.1 d when a fiber module, an optical isolator, and a WDM coupler are separately manufactured and connected.
As compared with B, not only the loss can be reduced by 0.7 dB, but also the noise figure of the amplification characteristics, the energy conversion efficiency, and the like can be improved.

Example 10 When 100 gain modules were manufactured in Example 9, the average loss was 1.42 dB. Also, none of the nonstandard products having a loss of 2 dB or more were produced. Eleven modules were extracted at random and subjected to the same reliability test as in Example 5. The average of the loss variation is ± 0.2 dB and 1
The loss variation was ±
It was 0.5 dB or less. Therefore, the gain module of the present embodiment was able to satisfy the Telcodia standard of long-term reliability.

(Embodiment 11) Using the fiber modules 1 and 2 manufactured in Embodiment 1, the AS shown in FIG.
An E light source was configured. In the figure, reference numeral 41 denotes an oblique end face of the fiber;
2 is a fiber module, 43 is a WDM coupler, 44
Is an excitation light source and 45 is an isolator. When the output spectrum of the light source when the fiber module 41 was excited at 200 mW was observed,
An output of -10 dBm / nm was obtained over a wide band up to nm. When the energy conversion efficiency was determined from the measurement of the output power, the efficiency was 26% when the fiber module 2 was used, whereas it was 35% and 9% when the fiber module 1 was used. Improved.

(Example 12) Using the fiber modules 1 and 2 manufactured in Example 1, a wavelength tunable laser was configured with a configuration as shown in FIG. In the figure, 51 is a tunable filter, 52 is a fiber module, 53 is a WDM coupler, 54 is an excitation light source, 55 is a coupler, 56a, 56
b is an isolator. When the output spectrum of the laser when the fiber module 1 was excited at 200 mW was observed, it was found that the output spectrum was 1025 from 1525 nm to 1628 nm.
An output of 1 mW or more was obtained over a 3 nm band. On the other hand, when the fiber module 2 is used, 1530 n
1 m over a 90 nm band from m to 1620 nm
An output of W or more was obtained. Therefore, oscillation was possible in a wider band when the fiber module 1 was used.

By applying the fiber module manufactured using the EDTF described in the above embodiments to an optical amplification medium, an optical amplifier using the optical amplification medium, a laser device, or a light source, a low-power WDM optical transmission system can be realized. It can contribute to cost increase, high reliability and high performance.

In the above embodiment, the mode field diameter of the erbium-doped tellurite glass optical fiber (EDTF) is matched with the mode field diameter of the communication single mode fiber and the communication dispersion shift fiber to be connected. However, even if the mode field diameter of the EDTF is somewhat smaller than the mode field diameter of the communication fiber, connection with sufficiently low loss can be realized. Specifically, the mode field diameter of the EDTF may be about 15% smaller than the mode field diameter of the communication fiber.
%, Most preferably within 8%.

[0057]

As described above, according to the present invention, the EDTF used as the optical amplifying medium has a specification matching the mode field diameter of the ordinary optical transmission fiber, so that the mode field conversion by the TEC can be performed. Since the V-groove diagonally polished connection can be made directly between the EDTF and the optical communication fiber without any intervening steps, the loss, reliability, and production yield have been improved compared to the conventional connection using TEC. Not only improves the noise figure and energy conversion efficiency of optical amplifiers using
Due to the increased mode field diameter of DTF, FW
The generation efficiency of M can also be suppressed, and cost reduction, high reliability, and high performance of the optical amplifier for a WDM optical transmission system can be realized.

[Brief description of the drawings]

FIG. 1 is a configuration diagram schematically showing a module.

FIG. 2 is a configuration diagram showing a fiber amplifier used in Embodiment 1 of the present invention.

FIG. 3 is a characteristic diagram showing a signal gain with respect to an incident signal light amount.

FIG. 4 is a characteristic diagram showing loss fluctuation in a temperature cycle of the module 1 and the module 2;

FIG. 5 is a configuration diagram showing a fiber amplifier used in Embodiment 7 of the present invention.

FIG. 6 is a characteristic diagram showing output spectra from an optical amplifier using various fibers.

FIG. 7 is a characteristic diagram showing an output spectrum from an optical amplifier using various fibers.

FIG. 8 is a configuration diagram of a gain module manufactured in Embodiment 9 of the present invention.

FIG. 9 is a configuration diagram showing an ASE light source used in Embodiment 11 of the present invention.

FIG. 10 is a configuration diagram showing a wavelength tunable laser used in Embodiment 12 of the present invention.

[Explanation of symbols]

01,01 'EDTF 02,02' Bobbin 03,03 'V-groove member 04,04' Dispersion shift fiber 05,05 'V-groove member 06' TEC 11a, 11b Optical isolator 12 Optical coupler 13 Excitation light source 14 EDTF module 21a, 21b Optical isolator 22a, 22b Optical coupler 23a, 23b Excitation light source 24 EDSF or EDTF module 31a, 31b, 31c, 31d Dispersion shift fiber 32 EDTF 33a, 33b, 33c, 33d, 33e, 33f Aspheric lens 34a, 34b No polarization Dependent isolators 35a, 35b Mirrors 36a, 36b, 36c, 36d, 36e, 36f A
R coated surface 41 Fiber oblique end surface 42 Fiber module 43 WDM coupler 44 Excitation light source 45 Isolator 51 Wavelength tunable filter 52 Fiber module 53 WDM coupler 54 Excitation light source 55 Coupler 56a, 56b Isolator

Continued on the front page (51) Int.Cl. ⁷ Identification FI FI Theme Court II (Reference) H01S 3/17 G02B 6/12 N (72) Inventor Makoto Shimizu 2-3-1 Otemachi, Chiyoda-ku, Tokyo Japan Inside Telegraph and Telephone Corporation (72) Koji Kano, Inventor 2-3-1 Otemachi, Chiyoda-ku, Tokyo Japan Inside Telegraph and Telephone Corporation (72) Tadashi Sakamoto 2-3-1, Otemachi, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation (72) Inventor Yoshiki Nishida 1-1-12 Dogenzaka, Shibuya-ku, Tokyo NTT Electronics Corporation (72) Inventor Yasutake Oishi 1-12-1 Dogenzaka, Shibuya-ku, Tokyo F term (reference) in NTT Electronics Corporation 2H047 QA04 RA00 2H050 AB37Z AC03 AC76 AD00 4G062 AA06 BB11 CC10 DA01 DB01 DC01 DD01 DE03 DE04 DF01 EA04 EB03 EB04 EC01 ED01 EE01 EF01 EG01 FA01 FA10 F01 FF01 FF01 FF01 GA03 GB01 GC01 GD07 GE01 HH01 HH0 3 HH05 HH07 HH09 HH11 HH13 HH15 HH17 HH20 JJ01 JJ03 JJ05 JJ07 JJ10 KK01 KK03 KK05 KK06 KK07 KK10 MM04 NN01 5F072 AB07 AB09 AK06 JJ05 JJ08 KK07 KK26 RR01 YY17

Claims (16)

[Claims] 1. An optical fiber made of tellurite glass and doped with at least erbium in a core, wherein a mode field diameter (MFD) is 6.3 <MFD (μ
m), a tellurite optical fiber for optical amplification, characterized by being in the range of m). 2. An optical waveguide made of tellurite glass and doped with at least erbium in a core, wherein a mode field diameter (MFD) is 6.3 <MFD (μm).
A tellurite optical waveguide for optical amplification, characterized in that: _{3. A} composition comprising TeO ₂ —LO—M ₂ O—N ₂ O ₃ (L is at least one kind of Zn and Ba, M is one or more kinds of alkali elements, N is Bi, La,
(At least one of Al, Ce, Yb, and Lu)
An optical fiber made of tellurite glass having the following formula, and having at least a core doped with erbium, wherein a mode field diameter (MFD) is in a range of 6.3 <MFD (μm). Tellurite optical fiber. 4. A composition comprising TeO ₂ —LO—M ₂ O—N ₂ O ₃ (L is at least one kind of Zn and Ba, M is at least one kind of alkali element, N is Bi, La,
(At least one of Al, Ce, Yb, and Lu)
An optical waveguide made of tellurite glass having the following formula, and at least erbium added to the core, wherein the mode field diameter (MFD) is in the range of 6.3 <MFD (μm). Tellurite optical waveguide. 5. An optical fiber having at least a core doped with erbium and having a mode field diameter (MFD) of 8.6 μm or more at 1310 nm of a single mode fiber for communication (ITU standard G.652) at 1310 nm.
The tellurite optical fiber for optical amplification according to claim 1 or 3, which conforms to 9.5 µm within 10%. 6. An optical waveguide having at least a core doped with erbium, wherein a mode field diameter (MFD) is one of a communication single mode fiber (ITU standard G.652).
8. The value of the MFD at 310 nm of 8.6 μm to 9.
The tellurite optical waveguide for optical amplification according to claim 2, wherein the optical waveguide is adapted to 5 μm within 10%. 7. An optical fiber having at least a core doped with erbium and having a mode field diameter (MFD) of 7.8 μm or more at 1550 nm of a communication dispersion-shifted fiber (ITU standard G.653) at 1550 nm.
The tellurite optical fiber for optical amplification according to claim 1 or 3, wherein the optical fiber is adapted to 8.5 µm within 10%. 8. An optical waveguide having at least a core doped with erbium, wherein a mode field diameter (MFD) is one of a communication dispersion-shifted fiber (ITU standard G.653).
The value of MFD at 550 nm is 7.8 μm to 8.
The tellurite optical waveguide for optical amplification according to claim 2, wherein the optical waveguide is adapted to 5 μm within 10%. 9. An optical fiber having at least a core doped with erbium and having a mode field diameter (MFD) non-zero dispersion fiber for communication (ITU standard G.655).
8 μm to 11 which are MFD values at 1550 nm
The tellurite optical fiber for optical amplification according to claim 1 or 3, wherein the optical fiber conforms to μm within 10%. 10. An optical waveguide having at least a core doped with erbium and having a mode field diameter (MFD) of non-zero dispersion fiber for communication (ITU standard G.655).
8 μm to 11 which are MFD values at 1550 nm
The tellurite optical waveguide for optical amplification according to claim 2, wherein the optical waveguide is adapted to a μm within 10%. 11. The tellurite optical fiber for optical amplification according to claim 1, wherein the optical fiber has at least a core doped with erbium and has a cutoff wavelength of 1.5 μm or less. 12. The tellurite optical waveguide for optical amplification according to claim 2, wherein the optical waveguide has at least a core doped with erbium and has a cutoff wavelength of 1.5 μm or less. 13. An optical fiber having at least a core doped with erbium, wherein a relative refractive index difference (Δn) is 0.1 <.
The tellurite optical fiber for optical amplification according to claim 1 or 3, wherein Δn <0.6 (%). 14. An optical waveguide having at least a core doped with erbium, wherein a relative refractive index difference (Δn) is 0.1 <Δ.
The tellurite optical waveguide for optical amplification according to claim 2, wherein n <0.6 (%). 15. An optical amplifier comprising: an optical amplifying medium comprising an optical fiber having a core glass and a clad glass; and input means for inputting excitation light and signal light for exciting the optical amplifying medium to the optical amplifying medium. 4. An optical amplifier, wherein the optical amplification medium comprising the optical fiber is the tellurite optical fiber for optical amplification according to claim 1 or 3. 16. An optical amplifier comprising: an optical amplifying medium comprising an optical waveguide having a core glass and a cladding glass; and input means for inputting excitation light and signal light for exciting the optical amplifying medium to the optical amplifying medium. 5. An optical amplifier, wherein the optical amplifying medium comprising the optical waveguide is the tellurite optical waveguide for optical amplification according to claim 2 or 4.