JP2006066620A - Optical amplifying method and optical amplifier - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical amplifying method that can be applied to optical amplification in a liquid crystal distribution system, such as CATV in the CWDM optical communications system and optical amplification for compensating a loss of a transmission fiber and a network device. <P>SOLUTION: A plurality of signal lights belong to a wavelength band of 1,540 to 1,620 nm with wavelengths, respectively different by Δλ nm or larger (Δλ is 15 or larger). The wavelengths of the signal lights are (1,571-0.5×Δλ) nm to (1,570+0.5×Δλ) nm, and a difference between the maximum wavelength and the minimum wavelength is 40 nm or shorter. The amplifying method is performed, by inputting the signal lights to an optical amplification fiber 1 in the presence of a stimulation light. The optically amplified fiber 1 is a Bi<SB>2</SB>O<SB>3</SB>group glass fiber; the signal lights are amplified in the fiber 1; and the optical amplifying method gives the signal lights to the optically amplified fiber 1, by decreasing the intensity of the signal lights whose wavelengths are (1,571-0.5×Δλ) nm to (1,570+0.5×Δλ) nm, to be lower than the intensity of other signal lights. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an optical amplification method and an optical amplifier suitable for a CWDM (Coarse WDM, coarse wavelength division multiplexing or low density wavelength division multiplexing) optical communication system.

The CWDM optical communication system has attracted attention as an optical communication system that can reduce the network costs of metro and access systems.
In the CWDM optical communication system (hereinafter simply referred to as “CWDM”), the wavelength interval of the signal light is as large as 20 nm, and therefore, for example, 3 channel transmission and 4 channel transmission require 40 nm and 60 nm wavelength regions, respectively.

In general, CWDM does not use an optical amplifier, but in recent years, an optical amplifier is generally used to compensate for a loss of a transmission fiber or a network device.
As an optical amplifier, an optical amplifier (EDFA) using an erbium-doped silica optical fiber is widely known, but the wavelength width capable of obtaining a flat gain characteristic is 40 nm at most. Therefore, if an EDFA is used to amplify signal light of 3 channels or more in CWDM, there is a possibility that a flat gain characteristic cannot be obtained with one unit in consideration of fluctuations in signal light wavelength (± 7 nm). There was a problem that required.
An optical amplifier (EDTFA) using an erbium-doped tellurite optical fiber is known as an optical amplifier that solves such a problem in the wavelength range of 1543 to 1617 nm (see Non-Patent Document 1).

Tadashi Sakamoto, 2 others, Rare-earth-doped fiber amplifier for eight-channel CWDM transmission systems, OFC 2004, Paper ThJ5, USA, February 2004

The EDTFA is excellent in that the gain fluctuation can be 2 dB in the wavelength range of 1543 to 1617 nm. The gain fluctuation is obtained when the intensity of each input signal light is −20 dBm (0.01 mW). is there. Since the gain is assumed to be 22.5 dB, the intensity of each output signal light is estimated to be 2.5 dBm (1.8 mW).
On the other hand, an optical amplifier used in an optical distribution system such as CATV in CWDM and an optical amplifier (booster amplifier) for compensating for the loss are required to have an intensity of each output signal light of 10 mW or more, EDTFA has a problem that it is difficult to apply to such applications.
It is an object of the present invention to provide an optical amplification method and an optical amplifier that can solve such problems.

The present invention is a plurality of signal lights belonging to a wavelength range of 1540 to 1620 nm and having a wavelength of Δλ of 15 or more and different from each other by Δλnm or more, and the difference between the maximum wavelength and the minimum wavelength is 40 nm or more, 0.5 × Δλ) nm to (1570 + 0.5 × Δλ) nm A plurality of signal light including signal light is input to an optical amplifying fiber in the presence of pumping light to amplify the optical amplifying fiber, Bi ₂ O ₃ glass fiber, the intensity of signal light having a wavelength of (1571−0.5 × Δλ) nm to (1570 + 0.5 × Δλ) nm is made smaller than any of the other signal light intensities. An optical amplification method for inputting to an optical amplification fiber is provided.
An optical amplifier having a plurality of input terminals, a pumping light source, one optical amplifying fiber, and an output terminal, wherein at least one input terminal and the optical amplifying fiber are connected via an optical attenuator. And an optical amplifier in which the optical amplification fiber is a Bi ₂ O ₃ glass fiber.

  According to the present invention, even if the length of the optical amplifying fiber is 3 m or less, the gain fluctuation is 1 dB or less or output for 2 to 4 channel signal lights belonging to the wavelength range of 1540 to 1620 nm and having a wavelength interval of 20 nm. Furthermore, optical amplification can be performed so that the output intensity fluctuation of the signal light of each channel is 1.3 or less, and the gain fluctuation or the output intensity fluctuation in the CWDM optical amplification can be reduced.

Further, even when the intensity of the signal light input to the optical amplifying fiber is as large as 1 mW or more, for example, a large gain can be obtained, and the intensity of the amplified signal light can be 10 mW or more. It can be used as a booster amplifier or an optical amplifier for an optical distribution system.
In addition, optical amplifiers based on the use of optical filters or gain equalizers have been proposed in the past, but in such cases, the signal light is assumed to have a substantially constant intensity. However, since the use thereof is not essential in the present invention, optical amplification with small gain fluctuation or output intensity fluctuation can be performed even if the intensity of the signal light changes.

The Bi ₂ O ₃ glass fiber has a feature that a large gain can be obtained even when the length is short, or has a wide amplification band, and is essential.
Bi ₂ O ₃ based core of glass fiber _Bi 2 _{O 3} 20 to 80 mol%, the SiO ₂ 5 to 70 mol%, the _Er 2 _{O 3} be a glass containing 0.05 to 4 mol% typically Is. Hereinafter, the component content in the glass is expressed in mol%.

The Er ₂ O ₃ content should be determined according to the transmission loss and the like of the Bi ₂ O ₃ glass fiber. For example, when the transmission loss is 0.2 dB / m, 0.10 to 0.20%, 0.7 dB. / M is preferably 0.23 to 0.27%.

The core of Bi ₂ O ₃ glass fiber is Bi ₂ O ₃ 20 to 80%, SiO ₂ 5 to 70%, Er ₂ O ₃ 0.05 to 4%, B ₂ O ₃ 0 to 30%, In ₂ O _{3 0~20%, Al 2 O 3} + Ga 2 O 3 0~45%, WO 3 0~30%, Ta 2 O 5 0~30%, TeO 2 0~30%, Y 2 O 3 + La 2 O 3 + Gd ₂ O ₃ + Yb ₂ O ₃ 0-15%, GeO ₂ 0-30%, TiO ₂ 0-30%, SnO ₂ 0-30%, CeO ₂ 0-2% Is preferred. More preferably, _Bi 2 _{O 3} is 30 to 55%, SiO ₂ is 25~45%, _Er 2 _{O 3} is _0.05~0.5%, B 2 _{O 3} is 0~5%, _In 2 _{O 3} 0 to 3%, Al ₂ O ₃ 1 to 5%, Ga ₂ O ₃ 10 to 25%, WO ₃ 0 to 1%, Ta ₂ O ₅ 0 to 1%, TeO ₂ 0 to 1 %, Y ₂ O ₃ is 0 to 1%, La ₂ O ₃ is 0.5 to 3%, Gd ₂ O ₃ + Yb ₂ O ₃ 0 to 1%, GeO ₂ 0 to 1%, TiO ₂ 0 to 1% SnO ₂ 0-0.5%, CeO ₂ 0-0.5%. This preferred glass may contain components other than the above components as long as the object of the present invention is not impaired. In that case, the total content of such components is preferably 10% or less. For example, “In ₂ O ₃ 0-20%” means that In ₂ O ₃ is not essential but may be contained up to 20%.

When the core of the Bi ₂ O ₃ glass fiber is the preferred glass, the cladding of the glass fiber is Bi ₂ O ₃ 20 to 80%, SiO ₂ 5 to 70%, B ₂ O ₃ 0 to 30%, In ₂ O ₃ 0-20%, Al ₂ O ₃ + Ga ₂ O ₃ 0-45%, WO ₃ 0-30%, Ta ₂ O ₅ 0-30%, TeO ₂ 0-30%, Y ₂ O ₃ + La ₂ A glass consisting essentially of O ₃ + Gd ₂ O ₃ + Yb ₂ O ₃ 0-15%, GeO ₂ 0-30%, TiO ₂ 0-30%, SnO ₂ 0-30%, CeO ₂ 0-2%. Preferably there is.

The refractive index (n ₁ ) at a wavelength of 1550 nm of the core of the Bi ₂ O ₃ based glass fiber is typically 1.8 to 2.2, and is usually between the same refractive index (n ₂ ) of the clad. The following relational expression holds.
0.0005 ≦ (n ₁ −n ₂ ) / n ₁ ≦ 0.1
The core diameter and clad diameter of the Bi ₂ O ₃ glass fiber are typically 2 to 10 μm and 100 to 200 μm, respectively.

When the intensity of the signal light input to the Bi ₂ O ₃ glass fiber (intensity per channel; the same applies hereinafter) is 0.1 to 10 mW, the long product peak of the Bi ₂ O ₃ glass fiber is 350 It is preferably ˜700 dB. Outside this range, a sufficient gain may not be obtained.
The length (L) of the Bi ₂ O ₃ based glass fiber is typically 1.5 to 2.2 m when the Er ₂ O ₃ content of the core is 0.23 to 0.27%.

Although light (excitation light) for exciting Er in the core is incident on the Bi ₂ O ₃ glass fiber, its wavelength is usually 1470 to 1490 nm.

Δλ is typically 20 nm in CWDM, and the wavelength interval between a plurality of signal lights to be amplified is usually 20 nm at regular intervals.
The optical amplification method of the present invention simultaneously amplifies 2, 3 or 4 channel signal light among 4 channel signal lights having wavelengths of 1550 ± 7 nm, 1570 ± 7 nm, 1590 ± 7 nm, 1610 ± 7 nm in CWDM. It is suitable for the case.

  The intensity of the signal light having a wavelength of (1571−0.5 × Δλ) nm to (1570 + 0.5 × Δλ) (hereinafter referred to as low-intensity signal light) is different from that of the gain fluctuation or output intensity fluctuation. Although it is smaller than the intensity of the signal light and is input to the optical amplifying fiber, it is typically 50% or less of the minimum value of the intensity of the other signal light.

  In a plurality of signal lights to which the optical amplification method of the present invention is applied, the intensity of low-intensity signal light is typically 50% or more of the minimum value of the intensity of other signal light, but more preferably 80% or more, more preferably If it is 90% or more, the effect becomes more remarkable.

  When the plurality of signal lights to be amplified include signal light having a wavelength of (1551−0.5 × Δλ) nm to (1550 + 0.5 × Δλ), in order to reduce gain fluctuation or output intensity fluctuation, It is preferable that the input intensity of the signal light to the optical amplifying fiber is the maximum of the input intensity of the plurality of signal lights to the optical amplifying fiber, that is, not lower than any of the input intensities of the other signal lights.

The difference between the maximum and minimum gains of each signal light obtained when a plurality of signal lights are amplified simultaneously, that is, the gain fluctuation with respect to the plurality of signal lights is preferably 1 dB or less.
Further, the value obtained by dividing the maximum value of the output intensity of each signal light by the minimum value, that is, the output intensity fluctuation with respect to the plurality of signal lights is preferably 1.3 or less, more preferably 1.26 or less, particularly Preferably it is 1.22 or less.

  When a plurality of signal lights including signal light having an intensity of 1 mW or more (typically 10 mW or less) are amplified by the optical amplification method of the present invention, the gain for the signal light having an intensity of 1 mW or more is 10 dB or more. It is preferable. Otherwise, it may be difficult to perform optical amplification required for an optical amplifier as a booster amplifier in CWDM or an optical amplifier of an optical distribution system.

  It is preferable that the minimum value of the intensity | strength of several amplified signal light is 10 mW or more. Otherwise, it may be difficult to perform optical amplification required for an optical amplifier as a booster amplifier in CWDM or an optical amplifier of an optical distribution system.

The optical amplifier of the present invention is an optical amplifier suitable for the optical amplification method of the present invention. The case where the optical amplifier of the present invention is applied to the amplification method of the present invention will be described below, but the present invention is not limited to this case.
FIG. 1 is a schematic diagram showing an example of the configuration of an optical amplifier according to the present invention.
Four-channel signal lights S ₁ , S ₂ , S ₃ , S ₄ (not shown) are input from input terminals 21, 22, 23, 24, respectively. When performing the optical amplification method of the present invention, one of the signal lights S ₂ and S ₃ is the intensity signal light.

The signal lights S ₁ and S ₄ are directly reduced, and the signal lights S ₂ and S ₃ are respectively reduced in intensity by the optical attenuators 31 and 32 and then combined to the optical multiplexer 40 to be combined, and a plurality of signal lights S _in It becomes.
The plurality of signal lights S _in are combined with the excitation light from the excitation light source 61 that is a laser diode (LD) by the optical coupler 51 and then input to the optical amplification fiber 1. Further, the pumping light from the pumping light source 62 which is an LD is also input to the optical amplifying fiber 1 through the optical coupler 52, that is, bidirectional pumping is performed.

The amplified signal light passes through the optical coupler 52 and is output to the output terminal 71 as the plurality of amplified signal lights _Sout .
The optical amplifying fiber 1 is a Bi ₂ O ₃ glass fiber, and is the same as described above with respect to the optical amplifying method of the present invention.

  FIG. 1 is a diagram in the case where two optical attenuators 31 and 32 are provided for four-channel signal light. However, the optical attenuator is optically attenuating when the output intensity fluctuation may be increased, for example. Only one unit 31 may be provided, or conversely, when it is desired to reduce the fluctuation in output intensity, an optical attenuator may be provided between the input terminal 24 and the optical multiplexer for a total of three units.

Bi ₂ O ₃ 42.7%, SiO ₂ 34.1%, Al ₂ O ₃ 3.6%, Ga ₂ O ₃ 17.8%, La ₂ O ₃ 1.4%, CeO ₂ 0 in terms of mol%. .2%, Er ₂ O ₃ 0.25% core glass, Bi ₂ O ₃ 42.8%, SiO ₂ 34.2%, Al ₂ O ₃ 7.1%, Ga ₂ O _{3 A} preform was prepared by compounding with a cladding glass composed of 14.3%, La ₂ O ₃ 1.4%, and CeO ₂ 0.2%, and the preform was stretched to have a core diameter of 5.1 μm. An optical fiber A having a cladding diameter of 125 μm was obtained. In the optical fiber A, n ₁ was 2.03, n ₂ was 2.02, and transmission loss was 0.7 dB / m.

An optical amplifier A having the configuration shown in FIG. 2 was manufactured using the optical fiber A (length product peak: 460 dB) having a length of 1.60 m as the optical amplification fiber 1. 21, 22, 23, and 24 are all input terminals, 31 and 32 are all ANDO optical attenuators AQ3140, 41, 42, and 43 are Anritsu optical couplers MN9604C, 51, and 52 are all optical couplers , 61 and 62 are excitation light sources, LD light source SELAM-130 (excitation light wavelength: 1480 nm) manufactured by System Engineering Co., Ltd., and 71 is an output terminal.
On the other hand, as a comparative example, the same optical amplifier B as the optical amplifier A was manufactured except that the attenuators 31 and 32 were not provided and the input terminals 22 and 23 were directly connected to the optical couplers 41 and 42, respectively.

First, as a comparative example for the optical amplification method of the present invention, the following optical amplification was performed (Example 1B).
1550nm wavelengths respectively, 1570 nm, 1590 nm, a 1610 nm, the signal light _{S 1, S 2, S 3} , S 4 input terminals 21, 22, 23 of the optical amplifier B having an intensity respectively shown in the first _{P i} Table, type 24, measuring the output intensity P _o of as intensity P _f of the signal light becomes a plurality of signal light S _in are both 1 mW (0dBm) inputted each signal light in the optical amplifying fiber 1 did. The intensity of excitation light from the excitation light sources 61 and 62 was 300 W.

Next, the following optical amplification was performed by the optical amplification method of the present invention (Example 1A).
The optical amplifier A is used in place of the optical amplifier B, the signal light S ₂ (wavelength: 1570 nm) is attenuated by 6 dB by the optical attenuator 31, and the signal light S ₃ (wavelength: 1590 nm) is attenuated by 1 dB by the optical attenuator 32. Measured the output intensity _Po of each signal light in the same manner as in Example 1B.

Wavelength (unit: nm) of input signal light, intensity P _i (unit: mW) of signal light at the input terminal, intensity P _f (unit: mW) of signal light input to the optical amplification fiber 1, optical amplification fiber 1 Table 1 shows the intensity P _o (unit: mW) of the signal light output from P and the gain (unit: dB) calculated from P _o / P _f .
Incidentally, in the column of variation in Table 1 P _o indicates a value obtained by dividing the maximum value of P _o at the minimum value, the value in the column obtained by subtracting the minimum from the maximum G _f of variations in G _f respectively.

The optical couplers 41, 42, and 43 used in the optical amplifier A all have a loss of 2 to 3 dB. However, if the optical amplifier is changed to the one having the configuration shown in FIG. Amplification characteristics are obtained. In fact, when calculated based on data shown in Table 1, using an optical amplifier A ₀ is an optical fiber A of the optical amplification fiber 1 length 1.60m have the configuration shown in Figure 1 of the signal light P _When a plurality of signal lights having _i of 1.4 mW are amplified, P _{o of} each signal light is as shown in P _o (unit: mW) of Example 1A _{0 in} Table 2 (Example 1A ₀ ).

Incidentally, the signal light _{S 2} by the optical attenuator 31 and 5.4dB attenuation, the signal light _{S 3} by the optical attenuator 32 and 0.4dB attenuation, the OVA-20M (loss manufactured Suntec Inc. optical attenuator 0. 6 dB or less), and an optical multiplexer, Sun-Tech's Metro-X (loss is 1.6 dB or less) was used. Further, G in Table 2 is a gain (unit: dB) calculated from P _o / P _i .
For comparison, the optical amplifier A _{0 from} which the optical attenuators 31 and 32 are removed is used as an optical amplifier B ₀ , and _Po is also calculated for the case where the same amplification as in Example 1A ₀ is performed using this (example) 1B ₀ ).

  Further, the same optical amplifier B ′ as the optical amplifier B was prepared as a comparative example except that the optical fiber A (strand product peak: 530 dB) having a length of 1.85 m was used as the optical amplifying fiber 1, and the same as in Example 1B. Was measured (Example 2B).

Next, an optical amplifier A is used except that an optical fiber A having a length of 1.85 m is used as the optical amplifying fiber 1 and a third optical attenuator 33 is provided between the input terminal 24 and the optical coupler 42. The same optical amplifier A ′ was prepared, and the optical amplification as described below was performed using the optical amplifier A ′ by the optical amplification method of the present invention (Example 2A).
Based on Example 2B, the signal attenuator 31 attenuates the signal light S ₂ (wavelength: 1570 nm) by 9 dB, and the optical attenuator 32 attenuates the signal light S ₃ (wavelength: 1590 nm) by 3.7 dB. The output intensity of each signal light was measured in the same manner as in Example 2B except that the signal light S ₄ (wavelength: 1610 nm) was attenuated by 2.7 dB by 33.
Table 3 shows the measurement results of Examples 2A and 2B.

The optical couplers 41, 42, and 43 used in the optical amplifier A ′ all have a loss of 2 to 3 dB. However, if the optical amplifier is changed to the one having the configuration shown in FIG. 1, it is even better than Example 2A. Amplification characteristics can be obtained. In fact, when calculated based on data shown in Table 3, using the optical amplifier A _{0 'is} an optical fiber A of the optical amplification fiber 1 length 1.85m have the configuration shown in Figure 1 of the signal lights P _{i P o} of the amplifying each signal light is more than the signal light is 1.4mW is _{P o} example 2A ₀ Table 4 (unit: mW) as shown in (example _2A 0).

The optical attenuator 31 attenuates the signal light S ₂ by 8.4 dB, the optical attenuator 32 attenuates the signal light S ₃ by 3.1 dB, the optical attenuator 33 attenuates the signal light S ₃ by 2.1 dB, As the optical attenuator, OVA-20M manufactured by Suntech (loss is 0.6 dB or less), and as the optical multiplexer, Metro-X manufactured by Suntech (loss is 1.6 dB or less) is used. G in Table 4 is a gain (unit: dB) calculated from P _o / P _i .
_'The minus the optical attenuator 31, 32, 33 in the optical amplifier B _0' optical amplifier A ₀ for comparison as the P _o also when subjected to the same amplification as in Example 2A ₀ using this Calculated (Example 2B ₀ ).

  An optical amplifier B ″ that is the same as the optical amplifier B ′ except that an optical fiber A (length product peak: 600 dB) having a length of 2.11 m is used as the optical amplifying fiber 1 is produced as a comparative example, and Example 2B The same measurement as in Example 3B was performed.

Next, an optical amplifier A ″ that is the same as the optical amplifier A ′ is manufactured except that the optical fiber A having a length of 2.11 m is used as the optical amplifying fiber 1, and the optical amplifier A ″ is used to produce the optical amplifier A ″. The following optical amplification was performed by the optical amplification method (Example 3A).
The optical attenuator 31 attenuates the signal light S ₂ (wavelength: 1570 nm) by 10 dB, the optical attenuator 32 attenuates the signal light S ₃ (wavelength: 1590 nm) by 6.5 dB, and the optical attenuator 33 attenuates the signal light S ₄ ( The output intensity of each signal light was measured in the same manner as in Example 3B except that the wavelength was attenuated by 4.7 dB.
Table 5 shows the measurement results of Examples 3A and 3B.

The optical couplers 41, 42, and 43 used in the optical amplifier A ″ all have a loss of 2 to 3 dB. However, when the optical amplifier is changed to the one having the configuration shown in FIG. Good amplification characteristics can be obtained. In fact, when calculated based on the data shown in Table 5, each signal light is obtained using an optical amplifier A ₀ ″ having the configuration shown in FIG. 1 and the optical amplifying fiber 1 being an optical fiber A having a length of 2.11 m. When a plurality of signal lights having P _i of 1.4 mW are amplified, P _{o of} each signal light is as shown in P _o (unit: mW) of Example 3A _{0 in} Table 6 (Example 3A ₀ ).

The optical attenuator 31 attenuates the signal light S ₂ by 9.4 dB, the optical attenuator 32 attenuates the signal light S ₃ by 5.9 dB, the optical attenuator 33 attenuates the signal light S ₃ by 4.1 dB, As the optical attenuator, OVA-20M manufactured by Suntech (loss is 0.6 dB or less) and Metro-X manufactured by Suntech (loss is 1.6 dB or less) are used as the optical multiplexer. G in Table 6 is a gain (unit: dB) calculated from P _o / P _i .
For comparison, the optical amplifier A ₀ ″ obtained by removing the optical attenuators 31, 32, and 33 is used as the optical amplifier B ₀ ″, and this is used to perform amplification similar to Example 3A _{0. o} was calculated (Example 3B ₀ ).

It is the schematic which shows the structure of the optical amplifier of this invention. It is the schematic which shows the structure of the optical amplifier of this invention used in the Example.

Explanation of symbols

1: Optical amplification fiber 21, 22, 23, 24: Input terminal 31, 32: Optical attenuator 40: Optical multiplexer 41, 42, 43, 51, 52: Optical coupler 61, 62: Excitation light source 71: Output terminal S _in : A plurality of signal lights input to the optical amplifying fiber S _out : a plurality of amplified signal lights

Claims (10)

A plurality of signal lights belonging to a wavelength range of 1540 to 1620 nm and having a wavelength Δλ of 15 or more and different from each other by Δλ nm or more, and a difference between the maximum wavelength and the minimum wavelength is 40 nm or more, and the wavelength is (1571−0.5 × Δλ) nm~ (1570 + 0.5 × Δλ) a plurality of signal light including signal light in nm is a method of amplifying is inputted to the optical amplifying fiber in the presence of the excitation light, the optical amplifying fiber is Bi ₂ O ₃ An optical amplifying fiber having a wavelength of (1571−0.5 × Δλ) nm to (1570 + 0.5 × Δλ) nm less than any of the other signal lights. Amplifying method to input to.   Among the plurality of signal lights input to the optical amplification fiber, the intensity of the signal light having a wavelength of (1571−0.5 × Δλ) nm to (1570 + 0.5 × Δλ) nm is the minimum of the intensity of the other signal light. The optical amplification method according to claim 1, which is 50% or less of the value.   The plurality of signal lights include signal light having a wavelength of (1551−0.5 × Δλ) nm to (1550 + 0.5 × Δλ) nm, and the plurality of signal lights input to the optical amplification fiber have a wavelength 3. The optical amplification method according to claim 1, wherein the intensity of the signal light having a wavelength of (1551−0.5 × Δλ) nm to (1550 + 0.5 × Δλ) nm is not smaller than any of the other signal lights. .   The optical amplification method according to claim 1, wherein the plurality of signal lights are signal lights having wavelengths of 1550 ± 7 nm, 1570 ± 7 nm, 1590 ± 7 nm, and 1610 ± 7 nm.   The optical amplification method according to any one of claims 1 to 4, wherein a gain fluctuation with respect to the plurality of signal lights is 1 dB or less.   The optical amplification method according to claim 1, wherein the plurality of signal lights include signal light having an intensity of 1 mW or more, and a gain with respect to the signal light is 10 dB or more.   The optical amplification method according to any one of claims 1 to 6, wherein a minimum value of the intensity of the plurality of amplified signal lights is 10 mW or more. Bi ₂ O ₃ based core of glass fiber with _Bi 2 _{O 3} 20 to 80 mol%, the SiO ₂ 5 to 70 mol%, of the preceding claims containing _Er 2 _{O 3} 0.05 to 4 mol% The optical amplification method according to any one of the above. An optical amplifier having a plurality of input terminals, a pumping light source, one optical amplification fiber, and an output terminal, wherein at least one input terminal and the optical amplification fiber are connected via an optical attenuator, An optical amplifier in which the optical amplification fiber is a Bi ₂ O ₃ glass fiber. Bi ₂ O ₃ based core of glass fiber with _Bi 2 _{O 3} 20 to 80 mol%, the SiO ₂ 5 to 70 mol%, of claim 9 containing _Er 2 _{O 3} 0.05 to 4 mol% Optical amplifier.

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