JP2004006634A - Light amplifier - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light amplifier which is improved in noise properties (Noise Figure) and power conversion efficiency. <P>SOLUTION: The light amplifier is equipped with an amplifying optical fiber 2 which is loaded with an erbium element and amplifies signal light having an L wavelength band (1565 to 1625nm) as using exciting light; forward exciting light feeders 3 and 6 which supply exciting light to the amplifying optical fiber 2 from forward in the transmitting direction of the signal light; and backward exciting light feeders 4 and 7 which supply exciting light to the amplifying optical fiber 2 from backward in the transmitting direction of the signal light. The forward exciting light feeders 3 and 6 supply the forward exciting light having a wavelength of 1480 nm to the amplifying optical fiber 2. The backward exciting light feeders 4 and 7 supply the backward exciting light having a wavelength of 1555 nm to the amplifying optical fiber 2. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an optical amplifying device that amplifies signal light using an optical fiber for amplification.
[0002]
[Prior art]
Generally, in order to amplify an optical signal in the L band (1565 to 1625 nm) with high efficiency, it is necessary to maintain a relatively low population inversion state long along the longitudinal direction of the amplification optical fiber (erbium-doped optical fiber). Becomes effective.
[0003]
On the other hand, when excitation light of 1520 nm to 1560 nm is supplied to the amplification optical fiber, a high population inversion state cannot be obtained, but a relatively low population inversion state is maintained long along the longitudinal direction of the amplification optical fiber. It becomes possible.
[0004]
This is because an emission band is generated in a wavelength band very close to the signal light (L band (1565 to 1625 nm)), so that the upper level energy of erbium ions is induced and emitted before a sufficient population inversion state is achieved. It is caused by that.
[0005]
2. Description of the Related Art Conventionally, in an optical amplifying device that amplifies an optical signal in the L band (1565 to 1625 nm), pump light having a wavelength of 1520 nm to 1560 nm is used to enhance power conversion efficiency by utilizing the above-described characteristics. (See Patent Document 1)
[0006]
[Patent Document 1]
JP-A-10-294510
[0007]
[Problems to be solved by the invention]
However, even in the conventional optical amplifying apparatus having the increased power conversion efficiency, there is a problem that the noise characteristic (NF) is degraded and a long fiber length is required as the amplifying optical fiber. This will be described below.
[0008]
In an optical amplifying device, the smaller the signal input power, the higher the population inversion state is required to lower the noise characteristic (NF). On the other hand, the conventional configuration using the excitation light of 1520 nm to 1560 nm has a feature that a high population inversion state cannot be obtained as described above. Therefore, especially when the signal input power is small, the noise characteristic is low. (NF) is greatly deteriorated.
[0009]
Further, in the conventional configuration using the excitation light of 1520 nm to 1560 nm, the excitation light having a very large power and the signal light coexist in the emission band. The gain obtained in the optical amplifier having such a configuration is not the gain for the signal light power but the gain for (pumping light power + signal light power). In an optical amplifying device, the gain decreases as the power of the light to be amplified increases. Therefore, in comparison with the case where pumping light having a wavelength other than 1520 nm to 1560 nm is used, the conventional configuration using pumping light having a wavelength of 1520 nm to 1560 nm has an amplification required to satisfy a gain required for signal light. The fiber length of the optical fiber must be long.
[0010]
As described above, in the conventional configuration using the pump light of 1520 nm to 1560 nm, the fiber length is inevitably long, so that it is necessary to further increase the power conversion efficiency as compared with the configuration using the pump light in other wavelength regions. Is increasing.
[0011]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the present invention provides an amplification optical fiber comprising an optical fiber doped with an erbium element and amplifying an L-band wavelength band (1565 nm to 1625 nm) signal light using pump light; A forward pumping light supplier for supplying the pumping light to the amplification optical fiber from the front side in the propagation direction of the signal light, and a backward pumping light supply for supplying the pumping light to the amplification optical fiber from the rear side in the propagation direction of the signal light. And a container. The forward pump light supplier supplies forward pump light in the 1480 nm wavelength band to the amplification optical fiber. The backward pumping light supplier supplies backward pumping light in a wavelength band of 1555 nm to the amplification optical fiber.
[0012]
Hereinafter, the operation of the present invention will be described. There is a close relationship between the power conversion efficiency of signal light and the population inversion state in the amplification optical fiber. When amplifying the L-band wavelength band (1565 nm to 1625 nm) signal light, as described above, it is necessary to have a relatively low population inversion state as long as possible along the longitudinal direction of the amplification optical fiber. This is convenient for obtaining efficiency. Also, there is a close relationship between the noise characteristic (NF) and the population inversion state in the amplification optical fiber, and setting the signal input end of the amplification optical fiber to the high population inversion state can reduce the noise characteristic (NF). This is convenient for lowering.
[0013]
That is, when amplifying the L-band wavelength band (1565 nm to 1625 nm) signal light,
Maintaining a relatively low population inversion state as long as possible along the longitudinal direction of the amplification optical fiber;
-Only the signal input end of the amplification optical fiber is in a high inversion distribution state,
If these two conditions are satisfied, it is possible to achieve both high power conversion efficiency and low noise characteristics.
[0014]
FIG. 4 shows how the excitation light power attenuates along the longitudinal direction of the fiber when the excitation light of 1480 nm and the excitation light of 1555 nm are introduced into an erbium-doped optical fiber (hereinafter, referred to as EDF). FIG. In FIG. 4, the horizontal axis is the EDF length, and the vertical axis is the pump light power. In FIG. 4, the EDF length is normalized such that the fiber end on the pump light input side is 0 and the fiber end on the opposite side is 1. Similarly, the pumping light power is normalized by setting the pumping light input time to 1.
[0015]
As shown in FIG. 4, the excitation light of 1480 nm has a high attenuation rate, and attenuates substantially in a geometric series. On the other hand, the attenuation rate of the 1555 nm excitation light is low, is attenuated in an approximately arithmetic series, and the slope of the attenuation is relatively small.
[0016]
In view of such characteristics of the pumping light (1480 nm wavelength light, 1555 nm wavelength light), supplying a 1555 nm backward pumping light to the amplification optical fiber changes a relatively low population inversion state in the longitudinal direction of the amplification optical fiber. Along as long as possible. Further, by supplying the forward pumping light of 1480 nm to the amplification optical fiber, only the signal input end of the amplification optical fiber can be in a high inversion distribution state.
[0017]
FIG. 5 shows an attenuation state of each pumping light when the 1480 nm wavelength light is supplied as the forward pumping light and the 1555 nm wavelength light is supplied as the backward pumping light to the amplification optical fiber. In FIG. 5, the EDF length is normalized with the fiber end on the front pumping light input side as 0 and the fiber end on the rear pumping light input side as 1. Similarly, the pumping light power is normalized by setting the pumping light input time to 1.
[0018]
In the present invention, based on the above points, the forward pumping light supplier supplies forward pumping light in the 1480 nm wavelength band to the amplifying optical fiber, and the backward pumping light supplier supplies backward pumping light in the 1555 nm wavelength band to the amplifying light. As a result, the present invention achieves both high power conversion efficiency (thus shortening the fiber length) and low noise characteristics.
[0019]
When the signal light is amplified by the amplification optical fiber, part of the spontaneous emission light (Amplified \ Spotaneous \ Emission) generated inside the amplification optical fiber is not reabsorbed in the amplification optical fiber. The light is emitted along the signal propagation direction of the fiber together with the amplified signal light. Therefore, the spontaneous emission light emitted along the signal propagation direction becomes a noise component for the signal light and raises its background level.
[0020]
On the other hand, in the present invention, 1555 nm pump light is supplied to the amplification optical fiber along the direction opposite to the signal propagation direction. When the backward pumping light of 1555 nm is supplied to the amplification optical fiber in this manner, the energy at the excitation level in the amplification optical fiber is stimulated and emitted, and as a result, the excitation level of the excitation level that can become spontaneous emission light inside the optical fiber is obtained. Energy is consumed for the amplification of the 1555 nm backward pump light. As a result, noise is absorbed. That is, the spontaneous emission light remaining inside the optical fiber is absorbed by the backward pumping light of 1555 nm by the stimulated emission. Therefore, the output level of the spontaneous emission light emitted from the amplification optical fiber along the signal propagation direction is reduced, and the noise characteristic (NF) is further improved accordingly. Thus, in the present invention, the backward pumping light in the 1555 nm wavelength band also functions as noise suppression light.
[0021]
In addition, since the signal light is amplified using the 1555 nm backward pumping light in which the energy that can be spontaneous emission light is absorbed by stimulated emission, the power conversion efficiency is further improved. As described above, the power conversion efficiency is improved, so that the length of the amplification optical fiber can be reduced.
[0022]
In addition, in the amplification optical fiber targeted by the present invention, a population inversion state can be formed in the amplification optical fiber even if excitation light having a wavelength band of 980 nm other than 1480 nm is used. Moreover, a high population inversion state can be formed with the excitation light in the 980 nm wavelength band. Therefore, the forward pumping light supplier may supply forward pumping light in the 980 nm wavelength band to the amplification optical fiber instead of forward pumping light in the 1480 nm wavelength band.
[0023]
Here, also in the configuration of the present invention, in order to reduce the noise characteristic (NF) as much as possible, the light intensity P of the forward pumping light is required._fwdAnd the light intensity P of the backward excitation light_bwdIt is necessary to optimize the ratio. This is based on the following reasons.
[0024]
In order to keep the noise characteristic (NF) at the signal input end of the amplification optical fiber low, it is necessary to maintain the signal input end in a high inversion distribution as described above. On the other hand, as shown in the characteristic diagrams of FIGS. 4 and 5, the backward pumping light of 1555 nm easily passes through the amplification optical fiber. Therefore, there is a high possibility that the backward pump light reaches the input end of the amplification optical fiber. At the signal input end, if light is present in the erbium (Er) emission wavelength band (1510 nm to 1630 nm), the erbium (Er) light will be converted to the 1555 nm wavelength light, which is the pump light, before the fiber region at the signal input end is in a sufficiently inverted population state. The upper level energy is stimulated emitted. As a result, the signal input terminal does not enter the high inversion distribution state, and the noise characteristic (NF) may be degraded.
[0025]
In the configuration of the present invention having such characteristics, the following conditions are required to keep the noise characteristics (NF) low. That is, even if the backward pumping light (1555 nm) reaches the input end of the amplifying optical fiber, the forward pumping light (1480 nm) having a light amount (light intensity) of such a degree that a high population inversion can be obtained is output from the signal of the amplifying optical fiber. That is to supply to the light input end.
[0026]
The above condition is based on the light intensity P of the forward excitation light._fwdAnd the light intensity P of the backward excitation light_bwdAnd the ratio (P_fwd/ P_bwd) Can be satisfied by optimizing. Based on this, in the present invention, the light intensity P of the forward excitation light is_fwdAnd the light intensity P of the backward excitation light_bwdAnd the ratio (P_fwd/ P_bwd) With 1.4 ≦ P_fwd/ P_bwdBy setting ≦ 20, the noise characteristic (NF) is kept low.
[0027]
Further, as a condition for maintaining the noise characteristic at the lowest, the light intensity P of the forward pump light is_fwdAnd the light intensity P of the backward excitation light_bwdAnd the ratio (P_fwd/ P_bwd) With 1.6 ≦ P_fwd/ P_{b wd}≤ 7.5.
[0028]
Further, based on the above-described noise generation mechanism, if the backward pumping light (1555 nm) can be prevented from reaching the signal input terminal of the amplification optical fiber, the noise characteristic (NF) can be maintained low.
[0029]
Therefore, in the present invention, the amplification optical fiber is divided into a front end fiber portion to which the forward pumping light is supplied and a rear end fiber portion to which the backward pumping light is supplied, and between these fiber portions, A rear pump light blocker is provided for guiding the signal light amplified by the front fiber section to the rear fiber section and for preventing the rear pump light from entering the front fiber. Thereby, the noise characteristic (NF) can be kept low. Note that specific examples of the backward pumping light blocker include an isolator and a circulator.
[0030]
It is also conceivable to supply 1555 nm wavelength band light as forward pumping light and 1480 nm wavelength band light as backward pumping light. However, this configuration has the following disadvantages.
[0031]
When this configuration is adopted, there is a high possibility that only the forward pumping light in the 1555 nm wavelength band exists at the signal input end. With the forward pumping light in the 1555 nm wavelength band, it is impossible to bring the signal input end of the amplification optical fiber into a high inversion distribution state. Therefore, it becomes impossible to improve the noise characteristics (NF).
[0032]
Further, as described above, the forward pumping light in the 1555 nm wavelength band has a high possibility of being emitted together with the signal light from the signal output end of the amplification optical fiber due to the low attenuation factor. The forward pumping light in the 1555 nm wavelength band output from the signal output end in this way becomes a noise component for the L-band wavelength band (1565 nm to 1625 nm) signal light.
[0033]
As described above, a configuration in which the 1555 nm wavelength band light is supplied as the forward pumping light and the 1480 nm wavelength band light is supplied as the backward pumping light cannot be adopted because the noise characteristics deteriorate.
[0034]
BEST MODE FOR CARRYING OUT THE INVENTION
Embodiment 1
FIG. 1 is a configuration diagram of the optical amplification device according to the first embodiment of the present invention. The optical amplifying device 1 is a bidirectional pumping type optical amplifying device, and includes an amplifying optical fiber 2, a forward pumping light source 3, a backward pumping light source 4, and a first multiplexer 6. , A second multiplexer 7 and isolators 9A and 9B.
[0035]
The amplification optical fiber 2 amplifies the L-band (1565 to 1625 nm) signal light input from the signal source A. In the present embodiment, the amplification optical fiber 2 is composed of EDF (optical fiber doped with erbium). In this embodiment, the optical fiber 2 for amplification uses a co-doped phosphorous (P).
[0036]
The forward excitation light source 3 is configured by a light source device such as a laser diode. The forward pumping light source 3 generates pumping light in the 1480 nm wavelength band (hereinafter, this pumping light is referred to as forward pumping light) supplied from the signal light input end to the amplification optical fiber 2. The light source 4 for backward pumping light is composed of a light source device such as a laser diode. The backward pumping light source 4 generates pumping light in the 1555 nm wavelength band (hereinafter, this pumping light is referred to as backward pumping light) supplied from the signal light output end to the amplifying optical fiber 2.
[0037]
The first multiplexer 6 is composed of, for example, a WDM multiplexer, and transmits the forward pumping light generated by the forward pumping light source 3 to a signal propagation path ( (Composed of a communication optical fiber and an amplification optical fiber 2) along the signal propagation direction. Thereby, the first multiplexer 6 supplies the forward pumping light to the amplifying optical fiber 2 from the signal input end thereof along the signal propagation direction.
[0038]
The second multiplexer 7 is composed of, for example, a WDM multiplexer, and applies the backward pump light generated by the backward pump light source 4 to a signal propagation path arranged on the output end side of the amplification optical fiber 2. On the other hand, they are multiplexed along the opposite direction of the signal propagation direction. Thus, the second multiplexer 7 supplies the backward pumping light to the amplifying optical fiber 2 from the signal output end thereof in the direction opposite to the signal propagation direction.
[0039]
In the present embodiment, the forward pumping light source 3 and the first multiplexer 6 constitute a forward pumping light supplier, and the backward pumping light source 4 and the second multiplexer 7 supply backward pumping light. Vessel is configured.
[0040]
Hereinafter, the operation of amplifying the signal light by the optical amplifying device 1 will be described. The forward excitation light source 3 generates forward excitation light having a wavelength of 1480 nm. The forward pumping light generated by the forward pumping light source 3 is supplied to the amplification optical fiber 2 through the first multiplexer 6 along the signal propagation direction. The amplifying optical fiber 2 amplifies the signal light of the L band (1565 to 1625 nm) by the stimulated emission using the forward pumping light supplied in this manner.
[0041]
At this time, the amplification of the signal light is mainly performed at the front end side portion of the amplification optical fiber 2 in the signal propagation direction. Therefore, the energy of the pumping level, which can become spontaneous emission light, is easily consumed in the amplification optical fiber 2 and the noise characteristic (noise figure: NF) is improved accordingly, but the amplified signal light is also amplified light. It is easily absorbed in the fiber 2, which slightly lowers the power conversion efficiency.
[0042]
On the other hand, the backward pumping light source 4 generates backward pumping light having a wavelength of 1555 nm. The backward pumping light generated by the backward pumping light source 4 is supplied to the amplification optical fiber 2 through the second multiplexer 7 along the direction opposite to the signal propagation direction. The amplifying optical fiber 2 amplifies the signal light of the L band (1565 to 1625 nm) by the stimulated emission using the backward pumping light supplied in this manner.
[0043]
At this time, the amplification of the signal light is mainly performed at the rear end portion of the amplification optical fiber 2 in the signal propagation direction. Therefore, the amplified signal light is less likely to be absorbed in the amplification optical fiber 2, and the power conversion efficiency is improved accordingly. However, the energy of the excitation level, which can be spontaneous emission light, is less likely to be consumed in the amplification optical fiber 2, and the noise characteristic (NF) is degraded accordingly.
[0044]
On the other hand, the optical amplifying device 1 exhibits an effect of reducing noise by introducing light in a wavelength band of 1480 nm as forward pumping light, and an effect of improving power conversion efficiency by introducing backward pumping light of 1555 nm. Thereby, in the optical amplifying device 1, the power conversion efficiency is improved while maintaining the noise characteristics (NF).
[0045]
The reason why the power conversion efficiency is improved while maintaining the noise characteristics (NF) is as described in the section for solving the problem.
[0046]
However, in the optical amplifying device 1, the following conditions are required to keep the noise characteristic (NF) even lower. That is, even if the backward pumping light (1555 nm) arrives at the input end of the amplifying optical fiber 2, the forward pumping light (1480 nm) having such a light quantity (light intensity) that a high population inversion can be obtained. Is supplied to the signal light input terminal.
[0047]
The above condition is based on the light intensity P of the forward excitation light._fwdAnd the light intensity P of the backward excitation light_bwdAnd the ratio (P_fwd/ P_bwd) Can be satisfied by optimizing. Hereinafter, the light intensity P of the forward excitation light_fwdAnd the light intensity P of the backward excitation light_bwdAnd the ratio (P_fwd/ P_bwd) Will be described with reference to the characteristic diagram of FIG. In FIG. 2, the horizontal axis represents the light intensity P of the forward excitation light._fwdAnd the light intensity P of the backward excitation light_bwdAnd the ratio (P_fwd/ P_bwd), And the horizontal axis indicates noise figure (NF) and power conversion efficiency. Each characteristic is an L-band wavelength band (1565 nm to 1625 nm), and is data in the case of amplifying optical signals of −3 dBm, −7 dBm, and −10 dBm, respectively.
[0048]
First, the ratio (P_fwd/ P_bwd) Is focused on the fluctuation of the noise figure (NF). Generally, a noise figure (NF) of 6 dB or less is required for optical amplification in the L-band wavelength band (1565 nm to 1625 nm). In this regard, the ratio (P_fwd/ P_bwd) Is preferably 1.4 or more. Further, the noise figure (NF) is optimally required to be 5.8 dB or less. In this regard, the ratio (P_fwd/ P_bwd) Is optimally 1.6 or more.
[0049]
Next, the ratio (P_fwd/ P_bwdAttention is paid to the fluctuation of the power conversion efficiency in the case of changing the above. The conversion point at which the power conversion efficiency gradually increases is the ratio (P_fwd/ P_bwd) = 20. Further, the conversion point at which the power conversion efficiency sharply increases is the ratio (P_fwd/ P_bwd) = 7.5. Thus, from the viewpoint of the power conversion efficiency, the noise figure (NF) is preferably 20 or less. Furthermore, the ratio (P_fwd/ P_bwd) Is optimally 7.5 or less.
[0050]
Based on the above measurement results, in the optical amplifier 1, the light intensity P of the forward pump light is_fwdAnd the light intensity P of the backward excitation light_bwdAnd the ratio (P_fwd/ P_bwd) With 1.4 ≦ P_fwd/ P_bwdBy setting ≦ 20, the noise characteristic (NF) is kept low while improving the power conversion efficiency.
[0051]
Further, the light intensity P of the forward excitation light_fwdAnd the light intensity P of the backward excitation light_bwdAnd the ratio (P_{fw d}/ P_bwd) Is 1.6 ≦ P_fwd/ P_bwdBy setting ≦ 7.5, an optimum value of the power conversion efficiency and the noise characteristic (NF) can be obtained.
[0052]
Further, in the optical amplifying device 1, the backward pumping light of 1555 nm is supplied to the amplification optical fiber 2 via the second multiplexer 7 along the direction opposite to the signal propagation direction. When the backward pumping light of 1555 nm is supplied to the amplification optical fiber 2 in this manner, spontaneous emission light generated in the amplification optical fiber 2 during amplification is suppressed. That is, the energy at the excitation level that can be spontaneous emission light generated inside the amplification optical fiber 2 is used for amplifying the backward excitation light by the action of stimulated emission. Therefore, the output level of spontaneous emission light (noise) emitted from the amplification optical fiber 2 along the signal propagation direction is reduced.
[0053]
When the forward pumping light having a wavelength of 1480 nm and the backward pumping light having a wavelength of 1555 nm are supplied to the amplification optical fiber 2, light having a wavelength band of 1550 nm (specifically, a wavelength band of 1520 n to 1560 nm) is used as spontaneous emission light. appear. Of course, the spontaneous emission light is necessary for amplification of the signal light. However, the spontaneous emission light remaining after amplification becomes noise for a signal band of 1580 nm or less.
[0054]
The light of 1555 nm supplied as the backward pumping light in the optical amplifying device 1 has such a characteristic that it can consume the energy of the pumping level which can be the spontaneous emission light in the wavelength band of 1550 nm and absorb noise. ing. Therefore, the noise characteristic (NF) of the optical amplifying device 1 is improved accordingly.
[0055]
Further, the optical amplifying device 1 constitutes a bidirectional pump type amplifier. In such an optical amplifying device 1, in the present embodiment, backward pumping light of 1555 nm is supplied to the amplifying optical fiber 2 from the signal output end side.
[0056]
When the signal light is amplified by forward pumping, spontaneous emission light is unlikely to be emitted to the outside from the output end of the amplification optical fiber 2 as a noise component along the signal propagation direction. However, in this case, high power conversion efficiency cannot be obtained.
[0057]
On the other hand, when signal light is amplified by backward pumping, high power conversion efficiency is obtained. However, in this case, the energy of the excitation level, which can be spontaneous emission light, is unlikely to be completely consumed inside the amplification optical fiber 2. Therefore, the energy of such an excitation level becomes spontaneous emission light, and is easily emitted outside from the output end of the amplification optical fiber 2 as a noise component along the signal propagation direction.
[0058]
As described above, in the optical amplifier 1 of the bidirectional pump type, the spontaneous emission light emitted as a noise component to the outside from the output end of the amplification optical fiber 2 along the signal propagation direction is mainly used when performing backward pumping. At the rear end side of the amplification optical fiber 2.
[0059]
Therefore, in the optical amplifying device 1, light in the 1555 nm wavelength band is supplied to the amplifying optical fiber 2 from the signal output end side as backward pumping light. As a result, the energy of the pumping level, which can be noise light (spontaneous emission light) generated on the rear end side of the amplification optical fiber 2, can be efficiently consumed by the backward pumping light. Increase.
[0060]
As described above, the backward pumping light in the 1555 nm wavelength band supplied to the amplification optical fiber 2 in the optical amplifying device 1 also functions as noise suppression light. Therefore, in the optical amplifying device 1, the noise characteristic (NF) is further improved.
[0061]
In this way, the 1555 nm backward pumping light supplied to the amplification optical fiber 2 does not become noise for the L band wavelength band (1565 nm to 1625 nm) signal light. It is for the following reasons.
[0062]
In the optical amplifying device 1, backward pumping light having a wavelength of 1555 nm is supplied to the amplifying optical fiber 2 along the direction opposite to the signal propagation direction. Therefore, the backward pumping light having a wavelength of 1555 nm contributes to the amplification of the signal light and consumes the energy of the pumping level which can become spontaneous emission light while passing through the amplification optical fiber 2, and then the signal of the amplification optical fiber is consumed. It will be emitted from the input end along the opposite direction to the signal light. Therefore, unless the backward pumping light is reflected in the amplification optical fiber 2, the backward pumping light having the wavelength of 1555 nm is not emitted as noise light from the output end of the amplification optical fiber 2 along with the signal light.
[0063]
Embodiment 2
FIG. 3 is a configuration diagram of the optical amplification device according to the second embodiment of the present invention. The basic configuration of the optical amplifier 10 is the same as that of the first embodiment. Therefore, in FIG. 3, the same or similar parts as those in FIG. 1 are denoted by the same reference numerals, and description thereof is omitted.
[0064]
The amplifying optical fiber 2 'of the optical amplifying device 10 is characterized in that it has a multistage configuration in which a front end fiber section 2A and a rear end fiber section 2B are connected in series. Further, the optical amplifying device 10 includes an isolator 11 which is a backward pumping light blocker.
[0065]
The isolator 11 is provided on a connection optical path 12 that connects the front end fiber section 2A and the rear end fiber section 2B. The isolator 11 has a function of allowing light to pass along the propagation direction of the signal light, but blocking the passage of light along the direction opposite to the propagation direction.
[0066]
This optical amplifier 10 operates as follows. That is, in the optical amplifying device 10, signal light amplification with high power conversion efficiency is performed using the 1555 nm backward pump light in the rear end fiber section 2B. On the other hand, in the front end fiber section 2A, signal light amplification with good noise characteristics (NF) is performed using the forward pumping light of 1480 nm.
[0067]
In the optical amplifying device 10 that performs such an amplifying role sharing, all of the backward pumping light having a wavelength of 1555 nm supplied to the rear end fiber section 2B is not used for amplifying the signal light, and the remaining backward pumping light is not used. Is emitted from the input end of the rear end fiber section 2B toward the front end fiber section 2A along the direction opposite to the signal propagation direction.
[0068]
If the backward pumping light emitted toward the front end fiber section 2A is left in this way, there is a high possibility that the backward pump light will reach the input end of the front end fiber section 2A. When pumping light having a wavelength range of 1555 nm substantially equivalent to the signal light (L band wavelength band (1565 nm to 1625 nm)) is present at the signal input end, the pumping light is used before the fiber region at the signal input end becomes in a sufficiently inverted distribution state. The upper level energy of erbium is stimulatedly emitted into a certain 1555 nm wavelength light. As a result, the signal input terminal does not enter the high inversion distribution state, and the noise characteristic (NF) may be degraded.
[0069]
Therefore, in the optical amplifying device 10, by providing the isolator 11 between the front end fiber section 2A and the rear end fiber section 2B, the backward pumping light of 1555 nm wavelength is prevented from entering the front end fiber section 2A. As a result, in the optical amplifying device 10, the backward pumping light having the wavelength of 1555 nm does not enter the front end fiber portion 2A, and the noise characteristic (NF) is improved.
[0070]
In the optical amplifying device 10, in order to further improve the noise characteristic (NF), it is preferable to set the concentration length product of the front end fiber portion 2A to 4 kppm · m or more. Further, in the optical amplifying device 10, the light intensity P of the forward pumping light having a wavelength of 1480 nm to be supplied to the front end fiber portion 2A._fwdAnd the backward pump light intensity P of 1555 nm wavelength supplied to the rear end fiber portion 2B._fwdAnd the ratio (P_fwd/ P_bwd) Is P_fwd/ P_bwdIt is preferable to set ≦ 7.5 in order to maintain high power conversion efficiency. This is the same as P described in Embodiment 1 with reference to FIG._fwd/ P_bwd≦ 7.5 is for the same reason as the preferable reason for maintaining high power conversion efficiency.
[0071]
In the optical amplifying device 10, the isolator 11 is used as the post-excitation blocker. Alternatively, the circulator may be used to configure the rear-excitation light blocker. Further, the backward pumping light blocker can be constituted by a long-period fiber grating that selectively gives a loss to light having a wavelength of 1555 nm. Further, a rear pumping light blocker can be constituted by a wavelength demultiplexer that transmits the front pumping light and the signal light (L band), but separates the 1555 nm wavelength band light.
[0072]
In Embodiments 1 and 2 described above, the forward pumping light source 3 generates forward pumping light in the 1480 nm wavelength band and supplies it to the amplification optical fiber 2. However, in the configurations of the first and second embodiments, the population inversion state can be formed in the amplifying optical fiber 2 even if pumping light having a wavelength band of 980 nm other than 1480 nm is used. Moreover, a high population inversion state can be formed with the excitation light in the 980 nm wavelength band. Therefore, the forward pumping light source 3 may supply the forward pumping light in the 980 nm wavelength band to the amplification optical fiber 2 instead of the forward pumping light in the 1480 nm wavelength band. However, when the forward pumping light in the 980 nm wavelength band is used, the light intensity P of the forward pumping light implemented in the first embodiment is used._fwdAnd the light intensity P of the backward excitation light_bwdAnd the ratio (P_fwd/ P_bwd) Optimization conditions (1.4 ≦ P_fwd/ P_bwd≦ 20 or 1.6 ≦ P_fwd/ P_bwd≤ 7.5) is not applicable. These conditions are conditions in the case where the forward pumping light in the 1480 nm wavelength band is supplied to the amplification optical fiber 2.
[0073]
【The invention's effect】
As described above, according to the present invention, it is possible to obtain high power conversion efficiency (thus shortening the fiber length) by maintaining good noise characteristics (NF).
[Brief description of the drawings]
FIG. 1 is a block diagram illustrating a configuration of an optical amplifying device according to a first embodiment of the present invention.
FIG. 2 is a diagram illustrating characteristics of the optical amplifying device according to the first embodiment.
FIG. 3 is a block diagram illustrating a configuration of an optical amplifying device according to a second embodiment of the present invention.
FIG. 4 is a diagram showing characteristics of forward excitation and characteristics of backward excitation.
FIG. 5 is a diagram showing characteristics when forward excitation and backward excitation are combined.
[Explanation of symbols]
A signal source 1 optical amplifier 2 optical fiber for amplification
2A {Front end fiber section} 2B} Rear end fiber section {3} Light source for forward pumping light
4 {light source for backward pumping} 6 {first multiplexer} 7} second multiplexer
9A, 9B Isolator 10 Optical amplifier 11 Isolator
12 connection optical path

Claims (5)

An amplification optical fiber comprising an optical fiber doped with an erbium element and amplifying signal light in an L-band wavelength band (1565 nm to 1625 nm) using excitation light;
A forward pumping light supplier that supplies the pumping light from the propagation direction front side of the signal light to the amplification optical fiber,
A backward pumping light supplier that supplies the pumping light from the propagation direction rear side of the signal light to the amplification optical fiber,
With
The forward pumping light supplier supplies forward pumping light in a 1480 nm wavelength band to the amplification optical fiber,
The backward pumping light supplier supplies backward pumping light in a wavelength band of 1555 nm to the optical fiber for amplification.
An optical amplifying device characterized by the above-mentioned. The optical amplifying device according to claim 1,
The forward pumping light supplier supplies forward pumping light in a 980 nm wavelength band to the amplification optical fiber instead of forward pumping light in a 1480 nm wavelength band.
An optical amplifying device characterized by the above-mentioned. The optical amplifying device according to claim 1,
The ratio (P _fwd / P _bwd ) between the light intensity P _fwd of the forward pump light and the light intensity P _bwd of the rear pump light was set to 1.4 ≦ P _fwd / P _bwd ≦ 20,
An optical amplifying device characterized by the above-mentioned. The optical amplifying device according to claim 1,
The ratio (P _fwd / P _bwd ) between the light intensity P _fwd of the forward pumping light and the light intensity P _bwd of the backward pumping light was set to 1.6 ≦ P _fwd / P _bwd ≦ 7.5,
An optical amplifying device characterized by the above-mentioned. The optical amplifying device according to any one of claims 1 to 4,
The amplifying optical fiber is divided into a front end fiber section to which the forward pumping light is supplied and a rear end fiber section to which the backward pumping light is supplied. A backward pumping light blocker that guides the signal light to the rear end fiber portion and prevents the rear pumping light from entering the front end fiber is provided.
An optical amplifying device characterized by the above-mentioned.

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