WO2001011735A1

WO2001011735A1 - Optical amplifier

Info

Publication number: WO2001011735A1
Application number: PCT/JP2000/005233
Authority: WO
Inventors: Hisashi Sawada; Minoru Yoshida; Kazuo Imamura
Original assignee: Mitsubishi Cable Industries, Ltd.
Priority date: 1999-08-04
Filing date: 2000-08-03
Publication date: 2001-02-15
Also published as: JP2001044551A; JP3787045B2

Abstract

An optical amplifier comprises an amplifier element including a fiber optic amplifier that directly amplifies signal light by stimulated emission. For amplification in the L-band (1570 nm to 1610 nm), a large gain is obtained for all signal light included in the L-band, while the difference in gain between wavelengths of the signal light is decreased. The optical amplifier is composed of a front-stage (2a) and a final stage (2b), which include fiber optic amplifiers (6a, 6b) for amplification of signal light by stimulated emission. The product of the Er dose and fiber length is 4 to 8 kppm-m for the fiber optic amplifier (6a) in the front stage (2a), and 80 to 100 kppm-m for the fiber optic amplifier (6b) in the final stage (2b).

Description

Specification

Optical amplifier

Technical field

The present invention relates to an optical amplifier provided with an amplifying optical fiber for directly amplifying signal light by the stimulated emission effect as an amplifying element, and particularly to a technique for smoothly performing amplification in wavelength division multiplex communication.

Background art

Generally, in an optical communication system, an optical amplifier is used to amplify the power of signal light attenuated in the middle of a transmission line and send the amplified signal light to the optical transmission line again.

Conventionally, as an amplifying element in such an optical amplifier, one using an amplifying optical fiber for directly amplifying signal light without photoelectric conversion by an stimulated emission effect has been provided. On the other hand, the effectiveness of wavelength division multiplexing has been pointed out to efficiently transmit multiple pieces of information over a single optical fiber transmission line.

In such wavelength-division multiplexing communication, when the signal light that has been wavelength-multiplexed is collectively amplified using an optical amplifier that uses the above-described amplification optical fiber as an amplifying element, amplification doped with A1 together with Er Optical fibers are effective because the amplification gain wavelength band has a relatively wide range (1531ηπ! ~ 156 nm) centered at 150 nm. Academic Fall Meeting (see 199 2) C-263.

In wavelength-division multiplexing communication, especially when using a dispersion-shifted fiber (DSF) in which the zero dispersion is shifted to the 1550 nm band as a silica-based optical fiber for transmission, so-called light wave mixing is used. Light of an unnecessary wavelength component is generated, which becomes noise and signal degradation easily occurs. Therefore, in wavelength division multiplexing communication, 157 ηπ !, which is slightly longer than the 1550 nm band! The use of a wavelength range of up to 16 1 O nm (hereinafter referred to as L-band) has been studied to suppress the degradation of transmission characteristics due to light wave mixing as described above. Therefore, in order to amplify a signal whose wavelength range is multiplexed, it is necessary to extend the amplifiable range of the amplification optical fiber to the L-band.

In order to amplify the signal light including L-band,

, A large gain is obtained in the wavelength band including L-band, • have gain characteristics that are flattened in the wavelength band including the L band so that no gain difference (hereinafter, referred to as wavelength gain difference) occurs in the amplification output of each signal light;

Is required.

However, the fact is that a conventional optical amplifier that can satisfy these requirements has not been provided yet.

Therefore, the present invention has been made to solve the above problems, and when performing amplification in the L-band, a large gain is obtained for each signal light included in the L-band, and The purpose is to reduce the wavelength gain difference of each signal light.

Disclosure of the invention

In the optical amplifier of the present invention, a front-stage amplifier and a rear-stage amplifier are connected in cascade, and each of the front-stage and rear-stage amplifiers includes an amplification optical fiber as an amplification element for amplifying signal light by the stimulated emission effect. The product of the concentration length, which is the product of the doping amount of Er and the length of the optical fiber for amplification of the preamplifier, is 4 to 8 kppm · m. As a result, the range that can be amplified is extended to the L-band, and each signal light included in the L-band can be amplified with great gain.

According to the present invention, in the improved optical amplifier described above, the concentration length product of the amplification optical fiber of the post-amplification section is set to 80 to 10 Oppm · m. Thereby, the wavelength gain difference of each signal light can be reduced.

In the improved optical amplifier described above, it is preferable that the preamplifier and the postamplifier are connected via an isolator, and the preamplifier and the postamplifier are each provided with the amplifying optical fiber. It is preferable to provide an excitation light source for bombing.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a configuration diagram of an optical amplifier according to an embodiment of the present invention.

FIG. 2 is a diagram showing experimental results obtained by examining gain characteristics using the optical amplifier having the configuration of FIG.

FIG. 3 is a diagram showing an experimental result obtained by examining a gain characteristic using the optical amplifier having the configuration of FIG. BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, the best embodiment of the present invention will be described in detail with reference to FIG.

FIG. 1 is a diagram illustrating an overall configuration of an optical amplifier according to an embodiment of the present invention.

The optical amplifier 1 of this embodiment has a two-stage amplification configuration. That is, the optical amplifier 1 has a front-stage amplifier 2a and a rear-stage amplifier 2b, and the front and rear amplifiers 2a and 2b are connected to each other via the isolator 4.

The preamplifier 2a includes an amplification optical fiber 6a as an amplification element for amplifying signal light by the stimulated emission effect, an excitation light source 7a such as a laser diode for pumping the amplification optical fiber 6a, and An optical power bra 8a for introducing the excitation light from the excitation light source 7a to the amplification optical fiber 6a is provided. The preamplifier 2a is of a forward pump type in which the signal light and the pump light enter the amplification optical fiber 6a from the same direction.

In the amplification optical fiber 6a, Er and A1 are co-doped in the core or on the outer periphery thereof. The amplification optical fiber 6a is set such that the product of the concentration and the product of the doping amount of Er and the length of the optical fiber 6a is 4 to 8 kppmm. . The post-amplifying unit 2b includes an amplification optical fiber 6b as an amplification element for amplifying signal light by the stimulated emission effect, an excitation light source 7b such as a laser diode for pumping the amplification optical fiber 6b, and an excitation light source 7b. An optical power bra 8b for introducing the excitation light from the light source 7b into the amplification optical fiber 6b. The post-amplifier 2b is of a post-pump type in which pump light is incident on the amplification optical fiber 6b from the opposite direction with respect to the signal light. In the amplification optical fiber 6b, Er and A1 are co-doped in the core or in the outer periphery thereof. The amplification optical fiber 6b is set so that the concentration length product, which is the product of the Dop amount of Er in the optical fiber 6b and the length of the optical fiber 6b, is 80 to 10 Oppm ppm. It has been done.

As described above, since the amplification products of the amplification optical fibers 6a and 6b are different from each other in the front and rear amplification sections 2a and 2b, the pump light sources 7 that bomb both optical fibers 6a and 6b are used. Appropriate conditions for the pump light powers of a and 7b are also different from each other. For this reason, there is a concern that the excitation light and the fluorescence from the excitation light source 7b of the rear amplification unit 2b may affect the front amplification unit 2a. However, since the isolator 4 is provided between the two amplifying sections 2a and 2b, the excitation light and the fluorescent light from the excitation light source 7b of the subsequent amplifying section 2b are not separated by the isolator 4. It is cut off at Ray 4 and does not affect the preamplifier 2a. Therefore, the adjustment of the pump light power in the preamplifier 2a becomes easy. Also, in the latter-stage amplifier 2b, the pump light of the former-stage amplifier 2a passes through the isolator 4 and enters, so that the power of the pump light source 7b of the latter-stage optical fiber 6b is changed from the former-stage amplifier 2a. The setting may be made in consideration of the power of the exciting pump light.

In addition, 10a and 1 Ob are polarization-independent isolators that pass signal light only in one direction to suppress parasitic oscillation and reduce noise, and 12a and 12b are input / output connectors. Numeral 14 denotes a coupling optical fiber for coupling these elements. In the optical amplifier with the configuration shown in Fig. 1, in order to properly set the concentration length products CL1 and CL2 of the front and rear amplification fibers 6a and 6b, respectively, the gain wavelength for the front and rear wavelength bands including the L-band is determined. The results of examining the characteristics are shown below.

(Experiment 1)

Here, as the amplification optical fiber 6a in the pre-amplifier 2a, the Er doping amount of 90 0ρρπκ A1 is 10000 ppm, the power-off wavelength is 0.92 ζπκ, and the mode field diameter is 4.5 m. Three types with special features are used. In these three types of optical fibers 6a, the concentration length product CL1 is set to 4 kppm'm, 6 kppm · m, and 8 kppm · m, respectively. Also, the pumping light wavelength of the preamplifier 2a is set to 1.48 / m, and the pumping light power is set to 5 OmW.

The amplification optical fiber 6b in the rear amplification section 2b has the same characteristics as the amplification optical fiber 6a in the front amplification section 2a. However, the length of the optical fiber 6b is lengthened, and the concentration length product CL 2 is fixedly set to 4 Okppm · m. Also, the pumping light wavelength of the post-amplifier 2 b is set to 1.48

And the pump light power is 15 OmW.

Then, for two types of signal light input of —l OdBm and —4 OdBm, the gain wavelength characteristics were examined with the position of the symbol X in FIG. 1 as the signal light input and the position of the code Y as the signal light output. The results are shown in Figure 2, Table 1 and Table 2.

For reference, instead of the two-stage amplification configuration shown in Fig. 1, a single-stage amplification configuration with a single amplification optical fiber having the same characteristics as in Fig. 1 was used. The gain wavelength characteristics when the strip length product was set to 2 Okppm'm were examined. The result Also shown in Figure 2, Table 1 and Table 2,

【table 1】

As can be seen from Fig. 2, the concentration-length product CL1 of the amplification optical fiber 6a in the preamplifier 2a in Fig. 1 was set to 4 kppmm, 6 kppm-m, and 8 kppmm. In this case, as compared with the conventional example, the band where the gain is larger spreads to the longer wavelength _side.t Also, when the concentration-length product CL 1 is increased, the rising part of the characteristic curve is slightly shifted to the longer wavelength side. However, the maximum gain is almost unchanged regardless of the signal light input of 1 OdBm, -40 dBm, regardless of the concentration length product CL1. For example, when the signal light input is 1 OdBm, the portion where the gain is flat is in the range of 1550 to 158 Onm, and the gain in that case is about 3 ldB.

The maximum gain does not change even if CL 1 is changed even if the concentration length product CL 1 of the amplification optical fiber 6 a in the pre-amplification section 2 a is changed by the concentration length product of the amplification optical fiber 6 b in the post-amplification section 2 b. The reason is that because the CL 2 is large and has a sufficient amplification factor, the amplification effect of the amplification optical fiber 6a in the pre-amplification section 2a does not appear significantly to the gain. Conceivable.

Table 1 shows the wavelength band where the amount of decrease in the gain from its maximum value is less than 1 dB when the signal light input is -1 OdBm. As shown in Table 1, the wavelength band in this case is approximately 28 nm when the concentration-length product CL 1 of the amplification optical fiber 6 a is 4 kppmm, 6 kppm-m, or 8 kppnim. Has a width of

Table 2 shows the wavelength band where the gain is 30 dB or more when the signal light input is 11 OdBm. As shown in Table 2, the wavelength band in this case is approximately equal when the concentration-length product CL1 of the amplification optical fiber 6a is 4 kppmm, 6 kppm-m, or 8 kppmm. It has a width of 32 nm.

As can be seen from Experiment 1, regardless of whether the concentration of the amplification optical fiber 6a in the preamplifier 2a is 1 kppm-m, 6 kppm-m, or 8 kppm The wavelength band where the gain is flat compared to the conventional example is shifted to the longer wavelength side, and the range that can be amplified is extended to L-band, and each signal light included in L-band is amplified with a large gain. You can see that it is possible.

However, as long as the concentration-length product CL 2 of the amplification optical fiber 6 b in the post-amplifying section 2 b is set to 4 Okppm · m, the gain is L—band (1570 M! ~ 16 1 Onm) It is hard to say that it is flat throughout. Therefore, it can be understood that the above conditions alone are not enough to obtain sufficient gain flatness for the L-band.

(Experiment 2)

Here, as the amplification optical fiber 6a in the pre-amplifier 2a, the doping amount of Er is 900 Opm, the doping amount of A1 is 100 Oppm, and the cut-off wavelength is 0.92 ΠΚ mode field diameter 4.5. It has the features of 1 and uses the product of concentration length product CL 1 of 8 kppm · m. The pump light wavelength of the preamplifier 2a is 1.48 // m, and the pump light power is 5 OmW.

The amplification optical fiber 6b in the rear amplification unit 2b has the same characteristics as the amplification optical fiber 6b in the front amplification unit 2a. However, for the optical fiber 6b, use four types of optical fiber 6b whose length is made longer and the concentration length product CL2 is 4 Okppmm, 80 kppm-m, 90 kppm-m, 10 Okppm-m. ing. Also, the pump light of the post-amplifier 2b The wavelength is 1.48 zm and the pump light power is 15 OmW.

Then, for two types of signal light input of —l OdBm and —4 OdBm, the gain wavelength characteristics were examined with the position of the symbol X in FIG. 1 as the signal light input and the position of the code Y as the signal light output. The results are shown in Figure 3, Table 3, Table 4, and Table 5.

[Table 3]

As can be seen from FIG. 3, when the concentration length product CL 2 of the amplification optical fiber 6 b in the post-amplifier 2 b is set to 40 kppm-m, the signal light wavelength exceeds 158 58ηπι. The gain of the characteristic curve gradually decreases, which is insufficient for flattening the gain over the entire L-band (1570 nm to 1610M).

On the other hand, the signal light input is -1 OdBm, and the concentration length product CL 2 of the amplification optical fiber 6b is 8 Okppm · π! When Ok10 Okppm · m, the gain is flat over the entire L-band, and the gain in that case is about 3 I dB.

Table 3 shows the wavelength band where the amount of decrease in the gain from its maximum value is less than 1 dB when the signal light input is 11 OdBm. As shown in Table 3, the wavelength band in this case is as follows: The concentration-length product CL2 of the optical fiber 6b for amplification is 8 Okppm · m, 90 kppm-in, and 100 kppm · m. It has a width of about 46 nm including the band.

Table 4 shows the wavelength band where the gain is 30 dB or more when the signal light input is 11 OdBm. As shown in Table 4, the wavelength band in this case is either when the concentration length product CL2 of the optical fiber for amplification 6b is 80 kppm · m, 90 kppm-m, or 100 kppm · m. Also has a width of about 48 nm including the L-band. Table 5 shows the wavelength band where the gain is 30 dB or more when the signal light input is 4 OdBm. As shown in Table 5, in this case, the concentration band product of the optical fiber for amplification 6b, CL2, is 8 Okppm · m, 90 kppm-m, and 100 kppm-m. —It has a width of about 56 nm including the band.

In addition, when the signal light input was 11 OdBm, the conversion efficiency from pump light to signal light in a wavelength band in which the amount by which the gain decreased from the maximum value was less than 1 dB was examined. It was 50-60%. Although this conversion efficiency does not reach the conversion efficiency of 74% in the case of the conventional example, it is a practically sufficient value.

As can be seen from Experiment 2, the concentration length product CL of the amplification optical fiber 6a in the front amplification unit 2a is set to 8 kppmm, and the concentration length product CL of the amplification optical fiber 6b in the rear amplification unit 2b. When 2 was set to 4 Okppm · m, gain flattening over the entire L-band (570-161 Onm) was insufficient. However, it was confirmed that when the concentration-length product CL 2 was set to 80 to 10 Okppm · m, the gain over the entire L-band could be sufficiently flattened. In Experiment 2, the concentration-length product CL1 of the amplification optical fiber 6a in the preamplifier 2a was fixed at 8 kppmm, and CL1 was set to 4 kppmm or 6 kppmm and CL2 was set to 6 kppmm. Were not changed to 8 Okppm · m, 90 kppm-in, 100 kppm · m. However, as described above, the flattening of the gain requires more than the influence of the concentration-length product CL1 of the amplification optical fiber 6a in the pre-amplification section 2a, rather than the influence of the amplification optical fiber 6b in the post-amplification section 2b. Since the influence of CL 2 is greater than that of CL 2, the CL 1 force is 8 kppm · m even if (: 1 is set to 41 ^ 111 '111 ぁIt is considered that a curve having a gain characteristic similar to that of is obtained.

In the optical amplifier shown in FIG. 1, the preamplifier 2a is a forward pump type, and the rear amplifier 2b is a backward pump type.However, the present invention is not limited to this. It is also possible to use an excitation type, the rear amplification unit 2b is a forward excitation type, or both the front and rear amplification units 2a and 2b are both a forward excitation type, or both are a backward excitation type.

Industrial applicability

According to the present invention, when amplification is performed in the L-band (l 570 nn! To 1610 nm), a large gain can be obtained for the signal light of each wavelength included in the L-band. Further, the wavelength gain difference of the signal light can be reduced.

Claims

The scope of the claims

1. The front-stage and rear-stage amplifiers are connected in cascade, and each of the front-stage and rear-stage amplifiers has an amplification optical fiber as an amplification element for amplifying signal light by the stimulated emission effect.

The concentration, which is the product of the Er doping amount and the strip length of the amplification optical fiber of the preamplifier, was set to 4 to 8 kppmm.

Optical amplifier.

2. The optical amplifier according to claim 1, wherein

The concentration length product of the amplification optical fiber of the post-amplification unit was 80 to 10 Okppm * m.

Optical amplifier.

3. The optical amplifier according to claim 1, wherein

An optical amplifier, wherein the preamplifier and the postamplifier are connected via an isolator.

4. The optical amplifier according to claim 1, wherein

Each of the pre-stage and post-stage amplification units includes an excitation light source that bombs the amplification optical fiber.

Optical amplifier.