Source: https://patents.google.com/patent/EP1914849A1/en
Timestamp: 2019-07-23 14:04:30
Document Index: 239825934

Matched Legal Cases: ['art 23', 'art 23', 'art 23', 'art 23', 'arts 1', 'arts 1', 'art 4', 'art 1', 'art 1', 'art 4', 'art 1', 'art 1', 'art 1', 'art 1', 'art 1', 'arth 1']

EP1914849A1 - Optical amplifier and a transmission system using the same - Google Patents
Optical amplifier and a transmission system using the same Download PDF
EP1914849A1
EP1914849A1 EP07121344A EP07121344A EP1914849A1 EP 1914849 A1 EP1914849 A1 EP 1914849A1 EP 07121344 A EP07121344 A EP 07121344A EP 07121344 A EP07121344 A EP 07121344A EP 1914849 A1 EP1914849 A1 EP 1914849A1
EP07121344A
EP1914849B1 (en
1997-02-18 Priority to JP3406797 priority Critical
1997-09-03 Priority to JP9238672A priority patent/JPH1184440A/en
1998-02-18 Application filed by Nippon Telegraph and Telephone Corp filed Critical Nippon Telegraph and Telephone Corp
1998-02-18 Priority to EP98904367A priority patent/EP0911926B1/en
2008-04-23 Publication of EP1914849A1 publication Critical patent/EP1914849A1/en
2011-06-29 Publication of EP1914849B1 publication Critical patent/EP1914849B1/en
The invention concerns an optical amplifier A, comprising:
- a Raman amplifier A1 which is provided with an internal Raman amplifier medium and carries out Raman amplification by said Raman amplification medium; and
- a rare-earth doped fiber amplifier A2 in which a rare-earth doped fiber is used as an amplification medium.
The structure of an optical amplifier of the related technology used in an optical fiber transmission system is shown in Figs. 23 ~ 25. Figs. 23, 24, and 25 show respectively the first, second, and third structures of the optical amplifiers of the related technology.
In Fig. 23, the optical amplifier 23 - 1 comprises an amplifier 23-2 and a gain equalizer 23-3. This optical amplifier 23 - 1 is connected to transmission fibers 23-4 and 23-5. Signal beams with a plurality of wavelengths are incident on this optical amplifier 23-1, and amplified. This amplifier 23 - 2 comprises a gain medium 23 - 6 (a rare-earth element doped fiber or waveguide), an excitation light source 23-7, and an optical part 23 - 8 (multiplexer for excitation light and signal beam, a light isolator, etc.) disposed on the pre-stage of a gain medium 23 - 6, and an optical part 23 - 9 (optical isolator, etc.) disposed on the post-stage of the gain medium 23 - 6 (see Citation Massicott et al., Electron. Lett., vol. 26, No. 20, pp. 1645 - 1646, 1990).
The gain characteristics of the optical amplifier 23 - 1 whose structure is shown in Fig. 23 are shown in Figs. 26A ~ 26C. Fig. 26A shows the wavelength dependency of the gain of the gain medium 23 - 6. In Fig. 26A, the peak value of the gain is 30 dB, the gain-flattened bandwidth (for example, the 3 dB gain-reduction bandwidth) is 10 nm. The loss of the gain equalizer 23 - 3 is shown in Fig. 26B. The peak value of this loss is about 10 dB. The value obtained by subtracting the loss of Fig. 26B from the gain of Fig. 26A is the gain of the optical amplifier 23 - 1, and this is shown in Fig. 26C. For simplification, the loss of the optical part 23 - 8 and the optical part 23 - 9 are ignored. By using the gain equalizer 23 - 3, the gain-flattened bandwidth is increased by about 30 nm. In this manner, as long as the signal beam wavelength intervals are equal, if the gain-flattened bandwidth is widened, it is an advantage that signal beams of more wavelengths (and therefore more channels) can be amplified with an identical gain.
Fig. 24 has the same gain characteristics as Fig. 23, but compared to Fig. 23, this structure of an optical amplifier has lower noise. The difference between this figure and Fig. 23 is that in this figure two excitation light sources 23 - 7 and 24 - 3 with different excitation light wavelengths are used. The wavelength of the excitation light which is output by excitation light source 24 - 3 is shorter than the wavelength of the excitation light output by excitation light source 23 - 7, and the upper part of the gain medium 23 - 6 (with respect to the input direction of the signal beam) is excited to a higher population inversion state in comparison to Fig. 23 (see Citation Massicott et al., Electron. Lett., vol. 28, No. 20, pp. 1924 - 1925, 1992).
Fig. 25 is an optical amplifier with a structure analogous to the structure of the present invention, although the widening of the bandwidth of the gain was not planned. The amplifier is divided into a pre-stage (amplifier 25 - 2) and a post-stage (amplifier 25 - 3), and a band restricting optical filter or a dispersion compensator is disposed therebetween. The signal beam is generally a single wavelength. When a band limiting optical filter is used, because the gain medium is divided into two stages, degradation of the amplification characteristics due to laser oscillation or amplified spontaneous emission light is not incurred, and a high gain is possible. When using a dispersion compensator, it is possible to eliminate degradation of the signal to noise ratio due to loss in the dispersion compensator (see Citation Masuda et al., Electron. Lett., vol. 26, No. 10, pp. 661 - 662, 1990).
In order to obtain the above-described object, the present invention provides an optical amplifier provided with a split gain medium wherein a long gain medium using a rare-earth doped fiber as the gain medium is partitioned into two or more stages, two or more amplifiers which include excitation light sources which output excitation light such that the effective excitation wavelength of this gain medium is 1.53 µm, and a gain equalizer which is effective for a wide wavelength band of a gain medium disposed between each amplifier. In this manner, compared to the related technologies, the effect is obtained that the gain-flattened band is wide, and it is possible to realize a high saturation output, low noise optical amplifier.
Fig, 10 is a graph of the characteristics of the third structure of this invention.
Figs. 26 A ~ C are graphs showing the characteristics of the optical amplifier having the structure in Fig. 23.
Fig. 1, which is the first structure, differs markedly from Fig. 23 of the related technology in that the amplifier is divided into two stages: a pre-stage (amplifier 1 - 2) and a post-stage (amplifier 1 - 3). In addition, Fig. 1 differs markedly from Fig. 25 of the related technology in that the optical part disposed between the pre-stage of the amplifier 1 - 2 and the post-stage of the amplifier 1 - 3 is a gain equalizer 1 - 4, and that the input signal beam is a wide band multiple wavelength beam.
The gain characteristics of this first structure are shown in Figs. 7A, 7B, and 7C. Fig. 7A shows the wavelength dependency of the gain of the gain medium. In Fig. 7A, the peak value of the gain is about 40 dB, and in comparison to the related technology, because there is no degradation of the amplifier characteristics due to laser oscillation and amplified spontaneous light emission, a high value can be obtained. The typical value of the gain of the pre-stage amplifier 1 - 2 is 25 dB, and the typical value of the gain of the post-stage amplifier 1 - 3 is 15 dB. In addition, the gain increases at or above a constant value (for example, 10 dB or 20 dB). Fig. 7B shows the loss of the equalizer 1-4. The peak value of this loss is about 10 dB and 20 dB.
The value derived by subtracting the loss in Fig. 7B from the gain in Fig. 7A is the gain of optical amplifier 1 - 1, and this is shown in Fig. 8. For the sake of simplification, the loss of optical parts 1 - 8 and 1-10, and optical parts 1-12 and 1 - 14 has been ignored. The gain-flattened bandwidth with the 10 dB loss peak value is 30 nm, and the gain-flattened bandwidth with the 20 dB loss peak value is 50 nm. The gain-flattened bandwidth with a 20 dB flattened-gain value in the related technology is 30 nm as shown in Fig.26C, and the gain-flattened bandwidth with a 20 dB flattened-gain value in the present invention is 50 nm as shown in Fig.8. Due to the structure of the present invention, we can understand that the gain-flattened bandwidth has been remarkably widened
The dependency of the flattened-gain bandwidth upon the flattened-gain in the present invention is shown in Fig. 9A. In comparison to the related technology, we understand that the gain-flattened bandwidth has been remarkably increased. Fig. 9B shows the dependency of the optical amplifier saturation output upon the equalizer loss in the present invention. In the present invention, because there is an optical amplifier (amplifier 1 - 3) following the gain equalizer 1 - 4, we understand that the saturated output of the optical amplifier does not depend very much on the equalizer loss. In comparison with the related technology, we understand that the saturated output of the optical amplifier has remarkably increased. As shown above, in the first structure of the present invention, it is possible to guarantee a wide gain-flattened bandwidth while maintaining the high optical amplifier saturation output as-is.
In addition, the structure of the case wherein the gain medium has been partitioned into three stages is shown in Fig. 27. The gain equalizers 1 - 4 and 1 - 4' have been disposed between the three-stage gain medium. Because two gain equalizers 1 - 4 and 1 - 4' are being used, the total peak value of the loss of the gain equalizer can be set at about 30 dB. The gain-flattened bandwidth at this time is 60 nm. Because the gain-flattened bandwidth is 50 nm when the gain medium is divided into two stages, it is possible to enlarge the gain-flattened bandwidth about 10 nm by partitioning into three stages. Moreover, in the figure, an example of a gain medium partitioned into three stages is shown, but it is possible to compose the optical amplifier in which the number of partitions is N (N is an integer equal to or greater than 2), and an N stage amplifier wherein a partitioned gain-medium is used as a structural component, and N - 1 stage gain equalizer is disposed between these amplifiers. Moreover, by increasing the number of partitions N, it is possible to gradually increase the gain-flattened bandwidth of the optical amplifier within the bandwidth range of the gain medium.
Fig. 2 shows the second structure of the present invention. In the second structure ofthe present invention, the amplifiers 1 - 2 and 1 - 3 having the structure (first structure) shown in Fig. 1 are respectively replaced with amplifiers having the structure shown in Fig. 2. Compared to Fig. 1, the amplifier further comprises one more excitation light source. In Fig. 2, for the sake of simplifying the figure, only the points of difference with Fig. 1 are shown for the amplifier 2 - 1 which corresponds to the amplifier 1 - 2 in Fig. 1. This point of difference is similar for the amplifier (not shown) corresponding to the amplifier 1 - 3 in Fig. 1. In comparison with Fig. 1, the present construction is a structure of a lower noise optical amplifier. The difference between Fig. 2 and Fig. 1 is that two excitation source lights 1 - 7 and 2-2 with different optical excitation wavelengths are used. The wavelength of the excitation light emitted from excitation light source 2 - 2 is shorter than the wavelength of the excitation light emitted from excitation light source 1 - 7, and in comparison with Fig. 1, the upper part of the gain medium 1 - 9 (with respect to the direction of input of the signal beam) is excited to a higher population inversion state.
Fig. 3 shows the third structure of the present invention. The difference between this figure and Fig. 23 (related technology) is that a transmission fiber 23 - 4 is used as an amplifier medium, and its excitation light source 3 - 3 is newly installed. The transmission fiber 23 - 4 carries out Raman amplification, and its gain has the characteristic of flattening the wavelength dependency of the gain medium such as a rare-earth doped fiber, etc., that is, equalizing the gain depending on wavelength. That is, the wavelength of the excitation light is set in the short-wave part only of the Raman shift amount (about 110 nm for silica fibers) of the wavelength which produces gain equalization. The gain characteristics of this third structure are shown in Fig. 10. The gain-flattened bandwidth of the total gain (gain medium gain - equalizer loss + Raman gain) is wider than the gain-flattened bandwidth of the gain (gain medium gain-equalizer loss) when Raman amplification is carried out.
Fig. 4 shows the fourth structure of the present invention. The gain and noise characteristics are similar to those of Fig. 2 (the second structure of the present invention), but the component parts are simpler, cheaper, and the construction becomes more stable. In order to guarantee low noise characteristics, a excitation light source 2 - 2 with a short excitation wavelength is used. Using optical part 4 - 2, a laser ring (optical part 1 - 8 ~ gain medium 1 - 9 ~ optical part 1 - 10 ~ optical part 4 - 2 ~ optical part 1 - 8) using gain medium 1 - 9 as a laser oscillation medium is formed. At this time, the optical part 1 - 8 and the optical part 1 - 10 have a multiplexer and demultiplexer respectively for laser oscillation. This laser oscillation light has an operation similar to the excitation light which the excitation light source 1 - 7 outputs in Fig. 2 (the second structure of the present invention), that is, an operation wherein the gain medium is excited to the desired population inversion state.
Fig. 5 shows the fifth structure of the present invention. The structure is analogous to that of Fig. 4 (the fourth structure of the present invention), but the propagation direction of the laser oscillation beam is reversed. At this time, the optical part 1 - 8 and optical part 1 - 10 have a multiplexer and demultiplexer respectively for the laser oscillation beam, but there is the new possibility that these are optical circulators, etc., which is a directional multiplexer-demultiplexer, and the efficiency is good. Because the laser oscillation beam is propagated in a direction reverse to that of the signal beam, is it possible to set the wavelength of the laser oscillation light irrespective of the wavelength of the signal beam, and degree of optionality of the components is increased, which is advantageous.
Above, the first through sixth structures of the present invention have been shown, but below, in order to clarify the differences with the related technology, the structure of a typical example of the related technology and the present invention and the gain characteristics when using these structures are explained referring to the figures. The gain medium is an erbium-doped fiber (Er3+ doped fiber: EDF). The erbium doping concentration is 1000 ppm, and the unsaturated absorption coefficient of the signal beam at 1550 nm is 1 dB / m.
Fig. 11A and Fig. 11B show a first and second structure of a typical example of the related technology. Fig. 11 A is a first typical example of the related technology wherein the excitation wavelength is 1.48 µm. The length of the EDF 11 - 6 is 50 m, the excitation light power is 100 mW, and the peak loss of the gain equalizer 11 - 3 is 10 dB or less. The wavelength dependency of the gain under these conditions is shown in Fig. 12A. The flattened-gain is 20 dB, and the flattened bandwidth is 30 nm (1535 ~ 1565 nm).
Fig. 11B is a second typical example of the related technology whose excitation wavelength is 1.55 µm. The length of the E.DF 12 - 4 is 150 m, the excitation light power is 200 mW, and the peak loss of the gain equalizer 11 - 3 is 10 dB or less. The wavelength dependency of the gain (the gain spectrum) under these conditions is shown in Fig. 12A. The flattened gain is 20 dB and the flattened bandwidth is 40 nm (1570 ~ 1610 nm).
Fig. 13 shows the structure of a typical example of the present invention. It is a two-stage amplifier structure, wherein the length of the pre-stage EDF 13 - 7 is 100 m, and the length of the post-stage EDF 13 - 11 is 70 m. In addition, the gain of the pre-stage EDF 13 - 7 is 25 dB, and the gain of the post-stage EDF 13 - 11 is 15 dB. The peak loss of the gain equalizer 13 - 4 disposed therebetween is 20 dB. The total gain spectrum is shown in Fig. 128. The flattened-gain is 20 dB, and the flattened-bandwidth is 50 nm (1550 - 1600 nm).
In this embodiment, an erbium doped fiber (Er3+ doped fiber: EDF) is used as a gain medium, and has the structure of a two-stage amplifier. The concentration of the erbium dopant is 1000 ppm, and the unsaturated absorption coefficient of the signal beam at 1550 nm is 1 dB / m. The length of the pre-stage EDF 14 - 8 is 100 m, and the length of the post-stage EDF 14 - 12 is 70 m. The excitation light sources 14 - 6 and 14 - 10 is a 1.53 µm semiconductor laser (LD), and the excitation light power is 100 mW. The excitation light and multiplexers 14 - 7 and 14 - 11 are an induction multilayer film filter, and the gain equalizer 14 - 4 is a split beam Fourier filter (Fourier filter). The peak loss of the gain equalizer (Fourier filter) 14 - 4 is 17 dB. The gain of the pre-stage EDF 14 - 8 is 25 dB, and the gain of the post-stage EDF 14 - 12 is 15 dB. Two optical isolator are installed in the pre-stage amplifiers and one optical isolator is installed in post-stage amplifier for preventing laser oscillation. Moreover, parameters, which makes flattened-gain bandwidth wide and is effective at the wide wavelength band of the gain medium, is set at the gain equalizer 14-4.
The gain spectrum of the first embodiment of the present invention is shown in Fig. 15. A flattened gain of 17 dB and a gain-flattened bandwidth of 50 nm are obtained. In addition, the saturation output with a multiple wavelength signal output (for example, 20 channels, or 100 channels) at 1.54 ~ 1.61 µm is 15 dBm, which is sufficiently high. However, the insertion loss ofthe multiplexers 14 - 7 and 14 - 11, optical isolators 14 - 9 and 14 - 13, and the gain equalizer (Fourier filter) 14-4 are each 1 dB.
The excitation light sources are different from those in Fig. 14 (the first embodiment). The excitation light sources 16 - 4 and 16 - 8 are LDs having a wavelength of 1.48 µm and an output power of 100 mW, and the excitation light sources 16 - 6 and 16 - 10 are LDs having a wavelength of 1.55 µm, and an output optical power of 1 mW. The excitation light of 1.48 µm input into the EDFs 14 - 8 and 14 - 12 is absorbed by each EDF 14 - 8 and 14 - 12, and the 1.55 µm excitation light is amplified by each EDF 14 - 8 and 14 - 12. As a result, in the upper part of each EDF 14 - 8 and 14 - 12, a 1.48 µm excitation light power is dominant, while in the lower part, a 1.55 µm excitation light power is dominant. In total, it is possible to obtain the same gain as the first embodiment with the excitation light having 1.53 µm wavelength.
Furthermore, because the population inversion at the upper part was raised by the excitation light having 1.48 µm wavelength, the noise characteristics increased. Specifically, the noise index lowered. Fig. 17 shows the dependency ofthe noise index upon the signal beam wavelength in the second and first embodiments. It is clear that the noise index of the second embodiment has become lower.
Compared to Fig. 14 (the first embodiment), the present embodiment further comprises a Raman amplifier. The transmission fiber (silica fiber) 18 - 4 is excited by an excitation light source (LD) with a wavelength of 1.51 µm and an output optical power of 200 mW The transmission fiber 18 - 4 is a 60 km dispersion-shifted fiber. The Raman gain at 1.61 µm is 10 dB. Fig. 19 shows the gain spectrum according to the present embodiment. Compared to the first embodiment, the flattened gain is raised 5 dB and the gain bandwidth is raised 25 nm.
Moreover, an optical circulator, which is a directional coupler, can be used as a multiplexer 18 - 5. The reason is that because the directions of the excitation wavelength (1.51 µm) and the signal beam are different with respect to the transmission fiber, the multiplexing of light by an optical circulator can be easily carried out. In addition, compared to using a wavelength division multiplexing coupler as a multiplexer 18 - 5, by using an optical circulator, it is possible to amplify a signal beam near the excitation wavelength, and it is also possible to broaden the bandwidth which optically amplifies.
Compared to Fig. 16 (the second embodiment), the present embodiment has the structure of the excitation unit of the EDF in the pre-stage and post-stage. Therefore, in Fig. 20, only the pre-stage amplifier 20 - 1 is shown. The structure of the post-stage (not shown) is the same as the structure of the pre-stage amplifier 20 - 1. The excitation light source 16 - 4 is an LD with a wavelength of 1.48 µm and an output light power 100 mW. Instead of using an LD with a wavelength of 1.55 µm, a high power laser oscillation beam with a wavelength of 1.55 µm is oscillated in the ring laser. A ring laser comprises EDF 14 - 8, ring laser multiplexer (multiplexers 20 - 2 and 20 - 3), a narrow bandwidth transmission optical filter 20 - 6, a tunable attenuator 20 - 5, and an optical isolator 20 - 4. The multiplexers 20 - 2 and 20 - 3 can use wavelength division multiplex coupler which only multiplexes and demultiplexes a laser oscillator optical wavelength in a narrow bandwidth. The obtained amplification characteristics are the same as those in the second embodiment. In the present structure, because there is only one excitation light source (LD), it has the advantages that the structure is simple and stable.
Compared to Fig. 20 (fourth embodiment), the present embodiment has optical circulators 21 - 2 and 21 - 3 in the ring laser instead of an optical isolator 20 - 4 and ring laser multiplexers (multiplexers 20 - 2 and 20 - 3). It is advantageous to use the optical circulators 21-2 and 21-3, because the number of optical parts is decreased and the structure is simplified.
First, referring to Fig. 29, the seventh embodiment of the optical amplifier will be explained. Moreover, this seventh embodiment relates to a most basic structure of an optical amplifier provided with a Raman amplifier using a high nonlinear fiber as a Raman amplifier medium. As shown in this figure, the optical amplifier A of the present embodiment comprises a Raman amplifier A1 and a rare-earth doped fiber amplifier A2. In the optical amplifier A structured in this manner, a transmission fiber B1 (transmission path) for inputting an optical signal and a transmission fiber B2 (transmission path) for outputting an amplified optical signal are connected together.
In addition, the above-described Raman amplifier A1 comprises a nonlinear fiber a1 which is the Raman amplifying medium, an excitation light source 2a which generates an excitation light for exciting the high nonlinear fiber a1, and a multiplexer a3. To one end of the high nonlinear fiber a1, the above transmission fiber B 1 is connected, and the optical signal is incident thereupon, and to the other end the multiplexer a3 is connected so that the excitation light supplied from the excitation light source a2 is incident thereupon.
In this manner, in using a high nonlinear fiber al as a Raman amplifier medium, the present embodiment is very different from the optical amplifier which uses an optical transmission fiber shown in the third embodiment as the Raman amplifier medium. Generally, a high nonlinear fiber has a mode radius which is small in comparison to the transmission fiber usually used, and in addition, because the concentration of the dopant is high, the efficiency of the nonlinear effects of the light are high, and thus it is possible to carry out highly efficient Raman amplification even in a comparatively short fiber length and low excitation light power. By such a high nonlinear fiber, a rate of Raman amplification proportionate to the square of the core diameter and the concentration of the dopant can be obtained. Therefore, because it is possible, for example, to have a fiber length of several kilometers with in-line optical amplifiers, it is possible to construct the lumped parameter optical amplifier, and at the same time, it is possible to construct the optical amplifier having an efficient Raman amplifier.
For example, as typical values for the parameters of the Raman amplifier A1 structured from this kind of high nonlinear fiber a1, the mode diameter and fiber length of the high nonlinear fiber a1 are respectively 4 µm and 1 km, and the power of the excitation light from the excitation source a2, which is a 1.51 µm excitation semiconductor laser, is 200 mW.
As shown in the figure, the rare-earth doped fiber amplifier A3 in the present embodiment comprises a pre-stage amplifier 1, a post-stage amplifier 2, and a Fourier filter (split beam Fourier filter) 3 interposed therebetween. In addition, the pre-stage amplifier 1 comprises isolators 1a and 1d, a multiplexer 1b, a rare-earth doped fiber 1c, and an excitation light source 1e (a semiconductor laser); the post-stage amplifier 2 comprises a multiplexer 2a, a rare-earth doped fiber 2b, an isolator 2c, and an excitation light source 2d (a semiconductor laser).
The optical signal output from the Raman amplifier A1 is incident on the isolator 1a, and output to the Fourier filter 3 from the isolator 1d via the multiplexer 1b and then the rare-earth doped fiber 1c. In addition, the excitation light output from the excitation light source 1e is incident on the rare-earth doped fiber 1c via the multiplexer 1b. The Fourier filter 3 acts as a gain equalizing means, and the optical signal input from the pre-stage amplifier 1 is gain-equalized and output to the post-stage amplifier 2.
In addition, the optical signal emitted from Fourier filter 3 in this manner is incident on the multiplexer 2a of the post-stage amplifier 2, and emitted from the isolator 2c via the rare-earth doped fiber 2b. Additionally, in the rare-earth doped fiber 2b, the excitation light generated in the excitation light source 2d is output via the multiplexer 2a.
According to the above-described rare-earth doped fiber amplifier A3, the optical signal, which is Raman-amplified by the high nonlinear fiber a1 in the Raman amplifier A1, is optically amplified by the rare-earth doped fiber 1c, and then it is gain-equalized by the Fourier filter 6, and it is further amplified by the rare-earth doped fiber 2b.
Moreover, in Fig. 30, the rare-earth doped fiber amplifier A3 can be constructed from N amplifiers, explained in the first through sixth embodiments, and (N - 1) gain equalizers provided therebetween (N being an integer equal to or greater than 2).
Here, in the present embodiment, the excitation light for Raman amplification is multiplexed using a multiplexer a3, but in place of the multiplexer a3 a directional coupler such as a light circulator can also be used. In this case, the isolator 1a of the pre-stage amplifier 1 is unnecessary, and it is possible to decrease the loss of the optical signal in this isolator 1a.
Generally, because a dispersion compensation fiber is, like a high nonlinear fiber, etc., characterized in having a small core diameter and a high concentration of dopant, it is possible to use one as a Raman amplifying medium. By using this kind of dispersion compensation fiber, it is possible to compensate transmission path dispersion which accumulates in during signal propagation. In this state, a dispersion compensation of about -200 ~ +200 ps / nm / dB is possible by using a dispersion compensation fiber, it can also sufficiently compensate the accumulated dispersion not only in the transmission system using a dispersion-shifted fiber as a transmission path, but also in a transmission system using a single mode fiber as a transmission path.
First, referring to Figs. 36A and 36B, the first embodiment of an optical transmission system will be explained. As shown in Fig. 36A, the optical transmission system of the present embodiment comprises a transmitter 9, a dispersion-shifted fiber 10 having a zero-dispersion wavelength in the 1.5 µm band, an optical amplifier 11, and a receiver 12.
For example, as shown in Fig. 36B, in the case of a dispersion value of the above-described dispersion-shifted fiber 10 of a certain signal beam wavelength being 2 ps / nm / km, and the repeater interval being 100 km, dispersion compensation is possible by setting the dispersion value of the dispersion compensation fibers (a10 or a11) in the optical amplifier 11 and the fiber length to -100 ps / nm / km and 2 km, respectively. That is, as shown in the figure, because the area of the transmission by the dispersion-shifted fiber 10 and the area of the transmission of the dispersion-shifted fibers (a10 and a11) in the optical amplifier 11 are equal, dispersion is compensated.
Next, referring to Figs. 37A and B, the second embodiment of the optical transmission system of the present invention will be explained. This embodiment, as shown in Fig. 37A, is characterized in using a single mode fiber 13 having a zero dispersion wavelength in the 1.3 µm wavelength band as a transmission path instead of the dispersion-shifted fiber 10 of the above first embodiment. In addition, each parameter of dispersions compensation fibers (a10 and a11) are set so as to compensate the dispersion of the transmission path, that is to say, the single mode fiber 13.
As shown in Fig. 37B, when, for example, the dispersion value of a single mode fiber is at a certain signal beam wavelength is 15 ps / nm / km, and the repeater interval is 100 km, by setting the dispersion value of the dispersion compensation fibers (a10 and a11) in the optical amplifier 11 and the fiber length to 150 pa /nm/ km and 10 km respectively as shown in the figure, the dispersion is compensated because the area of the transmission by the single mode fiber 13 and the area of the transmission of the dispersion compensation fibers (a10 and a11) become the identical. In addition, as described above, by making an inverse relationship between the dispersion slope of the single mode fiber 13 and the dispersion slope of the dispersion compensation fibers (a10 and a11) in the optical amplifier 11, high order dispersion compensation is possible.
An optical amplifier A, comprising:
a Raman amplifier A1 which is provided with an internal Raman amplifier medium and carries out Raman amplification by said Raman amplification medium; and
a rare-earth doped fiber amplifier A2 in which a rare-earth doped fiber is used as an amplification medium.
An optical amplifier according to claim 1, wherein said Raman amplifier A1 medium is a high nonlinear fiber.
An optical amplifier according to claim 1, wherein said Raman amplifying medium is a dispersion compensation fiber.
An optical amplifier according to claim 2, wherein said Raman amplifier A1 comprises:
a high nonlinear fiber a1 into one terminal of which an optical signal is input via a transmission fiber B1;
an excitation light source a2 which generates an excitation light; and
a multiplexer a3 which is connected to the other terminal of said high nonlinear fiber, and which makes the excitation light input into said high nonlinear fiber, and outputs an optical signal input form said high nonlinear fiber into said rare-earth doped fiber amplifier A2.
An optical amplifier according to claim 3, wherein said Raman amplifier comprises:
a dispersion compensation fiber a10 into one terminal of which an optical signal is input via a transmission fiber;
a multiplexer a3 which is connected to the other terminal of said dispersion compensation fiber a10, and which makes the excitation light input into said dispersion compensation fiber, and outputs an optical signal input from said high nonlinear fiber into said rare-earth doped fiber amplifier.
An optical amplifier according to claim 4, wherein said Raman amplifier further comprises:
a second excitation light source 1e which generates excitation light; and
a second multiplexer 1b which makes the excitation light input into said one terminal of the Raman amplifying medium.
An optical amplifier according to claim 6, wherein said Raman amplifier comprises:
a rare-earth doped fiber 1c inserted between said second multiplexer and said Raman amplifying medium.
an isolator 2c which is installed at the terminal of said Raman amplifying medium and prevents leakage of the excitation light into the transmission fiber.
An optical amplifier according to claim 1, wherein said rare-earth 1c doped amplifier comprises:
a gain equalizing means inserted between said post-stage amplifier and said pre-stage amplifier.
An optical amplifier according to claim 3, wherein the dispersion slope of said dispersion compensation fiber has a reverse relationship with the dispersion slope of the transmission fiber.
An optical amplifier according to claim 4, wherein said Raman amplifier uses a directional coupler instead of said multiplexer.
An optical amplifier according to claim 3, wherein said dispersion compensation fiber has parameters which: are set to compensate a dispersion-shifted fiber which is a transmission path.
EP07121344A 1997-02-18 1998-02-18 Optical amplifier and a transmission system using the same Expired - Lifetime EP1914849B1 (en)
JP3406797 1997-02-18
JP9238672A JPH1184440A (en) 1997-09-03 1997-09-03 Optical amplifier and optical transmission system using the same
EP98904367A EP0911926B1 (en) 1997-02-18 1998-02-18 Optical amplifier and transmission system using the same
EP98904367A Division EP0911926B1 (en) 1997-02-18 1998-02-18 Optical amplifier and transmission system using the same
EP98904367.4 Division 1998-08-20
EP1914849A1 true EP1914849A1 (en) 2008-04-23
EP1914849B1 EP1914849B1 (en) 2011-06-29
ID=26372868
EP98904367A Expired - Lifetime EP0911926B1 (en) 1997-02-18 1998-02-18 Optical amplifier and transmission system using the same
EP07121344A Expired - Lifetime EP1914849B1 (en) 1997-02-18 1998-02-18 Optical amplifier and a transmission system using the same
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EP (2) EP0911926B1 (en)
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EP1914849B1 (en) 2011-06-29
EP0911926A4 (en) 2007-04-25
EP0911926A1 (en) 1999-04-28
EP0911926B1 (en) 2011-12-07
US6172803B1 (en) 2001-01-09
WO1998036479A1 (en) 1998-08-20
EP0734105B1 (en) 2004-09-29 Optical fiber amplifier and dispersion compensating fiber module for optical fiber amplifier
EP0944190B1 (en) 2010-07-28 Gain and signal level adjustments of cascaded optical amplifiers
EP1746745A2 (en) 2007-01-24 Optical amplifier with pump light source control for Raman amplification
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Inventor name: SUZUKI, KEN-ICHI
Inventor name: MASUDA, HIROJI
Inventor name: AIDA, KAZUO
Inventor name: KAWAI, SHINGO
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