JP5064619B2 - Optical transmission equipment - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical transmission equipment provided with optical amplifiers in the transmission path between the transmitter and receiver.
[0002]
[Prior art]
EDFA (Erbium Doped Fiber Amplifier) is a 1R (Regeneration) repeater for loss compensation in optical fiber communications because it has high output and low noise characteristics at 1.55μm, which is a low loss of transmission line fiber. Has been widely used so far. Recently, due to the demand for transmission capacity expansion, wavelength division multiplexing (WDM) transmission technology that multiplexes and transmits signal light in a plurality of wavelength bands is generally used, and wavelength multiplexed signals are transmitted to EDFAs arranged in the transmission line. Often done.
[0003]
Assuming a point-to-point system, when an EDFA is placed between both points and signals are transmitted, the number of signals passing through the transmission path and EDFA is usually the number (number of signals) and the arrangement (wavelength) Arrangement) is constant. For this reason, the EDFA is usually designed optimally for all signals passing through the transmission line, and the output, NF (Noise Figure), amplification characteristics (gain deviation), etc. fall within the range according to the system requirements. It is designed to work.
[0004]
[Problems to be solved by the invention]
As described above, in a point-to-point system, when signals are transmitted with an EDFA placed between both points, the number of signals and the wavelength arrangement of signals passing through the transmission line and the EDFA are usually constant. However, when some signal in the signal band is cut off due to some trouble, or when a system in which a path is freely selected according to wavelength, such as a system using XC (cross connect) in the future, is realized. The number of signals passing through the transmission line and the EDFA and the wavelength arrangement are not constant. Particularly in XC, the wavelength arrangement of signals changes from moment to moment.
[0005]
In the EDFA, the inversion distribution is formed differently depending on the number of input signals and the wavelength arrangement, and the output, gain deviation, NF, amplification characteristic (gain deviation), and the like change remarkably. If the number of signals to be transmitted is slightly decreased on average over the entire wavelength range with respect to the total number of signals passing through the transmission line, there is no effect on the amplification characteristics. If it is less than half or unevenly distributed at a certain wavelength, the gain flatness cannot be maintained, and the gain deviation that can be established as an optical transmission system increases beyond the allowable range. In the worst case, the signal power excess exceeds the power at which the nonlinear optical effect of the transmission line fiber is generated, and conversely, the decrease causes a great influence on the transmission quality such that the signal cannot be received due to SN degradation. there is a possibility. Since conventional EDFAs and optical communication systems do not cope with the occurrence of the above situation, there is a concern when such a situation occurs.
[0006]
[Means for Solving the Problems]
An optical amplifier, in particular in the EDFA, since the amplifying operation dictated by the inversion state of formation of the EDF is amplified medium, if it is possible to maintain a constant within a desired range in a state of population inversion, a constant increase Fu properties It is possible to obtain. Based on this principle, the present invention locks the operational state of the optical amplifier within a certain range by the inverted distribution fixed signal, and keeps the amplification characteristic (gain deviation) constant with respect to changes in the number of signals and wavelength arrangement. An object of the present invention is to provide an optical transmission apparatus that can flexibly cope with such changes.
[0007]
The optical transmission device of the present invention has an inversion distribution state of an EDFA in any device or part of an optical transmission device including an EDFA in a transmission path between a transmission device and a reception device that transmits a plurality of signals having different wavelengths. An optical transmission apparatus comprising an inverted distribution fixed signal light source for generating an inverted distribution fixed signal for fixing, wherein the inverted distribution fixed signal light source is in the vicinity of a signal band passing through an optical amplifier and other than the excitation wavelength of EDFA of a plurality of wavelengths, 1530nm ± 3nm, 1555nm + 5 / der which generates a population inversion fixed signal of one wavelength in each of -10nm is, the population inversion of the EDFA by controlling the power of their inversion fixed signal It can be fixed .
[0008]
The optical transmission device of the present invention is the optical transmission device described above , wherein the wavelength of the inverted distribution fixed signal is set near the peak of the gain coefficient of the EDF.
[0009]
The optical transmission device of the present invention is the above optical transmission apparatus, and has a inverted distribution fixed signal removing means.
[0010]
An example of the present invention will be described below. In the C-band EDFA that amplifies the region near the wavelength of 1528 nm to 1563 nm, for example, 1ch in any of 1530nm ± 3nm, 1555nm + 5 / -10nm, or 2ch at the same time, and Nch (N> 1), respectively. The inverted distribution formation state can be fixed. By providing an inverted distribution fixed signal light source that generates an inverted distribution fixed signal of this wavelength in the amplifier, the transmitter, or both, a constant amplification characteristic (gain) even if the number of input signals or wavelength arrangement changes Deviation).
[0011]
In an optical amplifier, in particular, an EDFA, as described above, the amplification characteristic is determined by the formation state of the inversion distribution. In the case of the EDFA, the formation of the inversion distribution in the EDF that is the amplification medium is determined by the EDF length, the signal light power, and the excitation light power. Further, the amplification characteristics vary depending on the number of signals input to the amplifier and the wavelength arrangement. This is due to the wavelength dependence of the absorption cross section and emission cross section inherent to EDF. FIG. 3 shows an example of the absorption cross section and the emission cross section, and FIG. 4 shows the gain coefficient in a micro cross section with EDF.
[0012]
In general, when a signal is input in advance to a wavelength region with a large gain coefficient calculated by the following equation (1) from the absorption cross-section area, emission cross-section area, and inverted distribution formation state, the signal is input to a wavelength region with a small gain coefficient. It is a well-known fact that there is relatively little change compared to cases where signals are added to other wavelength ranges.
g (λ, z, T) = Γ [σ _e (λ, T) · N2 (z) −σ _a (λ, T) · N1 (z)] (1)
σ _e (λ, T): emission cross sections
σ _a (λ, T): absorption cross sections
atomic population ranges N1 (ground level) and N2 (excited level)
[0013]
Since the optical transmission apparatus of the present invention is a system equipped with an inverted distribution fixed signal light source that generates an inverted distribution fixed signal having a large gain coefficient in an optical amplifier or an optical communication system, the optical amplifier has an inverted distribution fixed. A signal that is in a state of being (or within a certain range) and subsequently increasing or decreasing operates in a limited range regardless of the number of signals or wavelength arrangement. Therefore, regardless of how the number of signals and the wavelength arrangement change, characteristics with little difference in gain deviation and output compared to before the change can be obtained.
[0014]
In the above explanation, the case of using C-band is taken as an example, but for L-band, the wavelength of the inverted distribution fixed signal is selected from the same point of view, and an inverted distribution fixed signal light source for generating the signal is provided in the amplifier. If this is the case, the same effect can be expected. Further, the inverted distribution fixed signal light source does not necessarily need to be mounted in the amplifier. For example, there is no difference in operation even when the inverted distribution fixed signal light source is provided in the transmission device and then supplied to the optical amplifier.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Example 1
FIG. 1 shows a first embodiment of the present invention. In this embodiment, an inverted distribution fixed signal light source is input from the input side of an optical amplifier to a two-stage EDFA in a transmission line. An optical multiplexing unit 1, a pre-stage amplification unit 2, a post-stage amplification unit 3, and an inverted distribution fixed signal removal unit 4 are provided from the signal light input side, and an inverted distribution fixed signal light source 5 is connected to the optical multiplexing unit 1. For example, a forward excitation EDFA is used for the pre-amplifier 2. For example, a bidirectional excitation EDFA is used for the post-amplifier 3. The blocks of the pre-amplifier 2 and the post-amplifier 3 include EDFA components such as an isolator, a TAP coupler, WDM, EDF, PD, and excitation LD. A coupler or the like is used for the inverted distribution fixed signal removing means 4. For the inverted distribution fixed signal light source 5, for example, a DFB-LD and an LD driving circuit are used. This block includes various circuits having a function for driving the LD, such as a temperature stabilization circuit, a drive current adjustment circuit, and a monitor circuit thereof.
[0016]
The wavelength of the inverted distribution fixed signal is selected according to the amplification wavelength band of the amplification unit connected after the optical multiplexing means 1. The wavelength is usually near the signal band that passes through the amplifying unit and other than the excitation wavelength of the amplifier. For example, the C-band amplifier is configured to include one channel at 1530 nm ± 3 nm, 1555 nm + 5 / −10 nm, or two channels at the same time, and Nch (N> 1) signals, respectively.
[0017]
As means for guiding the inverted distribution fixed signal to the optical amplifier, for example, optical multiplexing means 1 such as an optical coupler can be used. In this embodiment, the configuration of the two-stage EDFA is shown. However, in the present invention, the configuration of the optical amplifier is not limited to only two stages as well as a single stage. The present invention can also be applied to a configuration in which an optical component is included between optical amplifier stages as shown in FIG. In this case, an optical component 6 such as a gain equalization filter, an optical attenuator, DCF, OADM, or SMF is inserted between the pre-amplifier 2 and the post-amplifier 3. Furthermore, in this embodiment, the inverted distribution fixed signal is guided from the input side of the amplifier. However, the inverted distribution fixed signal can also be guided between amplifier stages or from inside the amplifier.
[0018]
(Example 2)
FIG. 2 shows a second embodiment of the present invention. This is an example in which an inverted distribution fixed signal is input from the second optical multiplexing means 1 in the transmission apparatus. The transmission apparatus 7, the first optical multiplexing means 8, the second optical multiplexing, which transmit a plurality of signals having different wavelengths. The wave means 1 are connected in this order. Usually, a preamplifier or a transmission line fiber is connected to this point, but these are not shown in FIG. The signal transmitted from the transmission device 7 is, for example, a signal having a wavelength exhibiting a relatively small loss in the loss characteristics of a 1550 nm band signal, a 1580 nm band signal, or a silica-based fiber. The block of the transmission device 7 generally includes functions necessary for the transmitter, such as a modulator and an LD drive circuit.
[0019]
An inverted distribution fixed signal light source 5 is connected to the second optical multiplexing means 1 in FIG. The wavelength selection of the inverted distribution fixed signal is the same as that of the first embodiment, and an optical multiplexer such as an optical coupler is used as the means (second optical multiplexing means) for guiding the inverted distribution fixed signal to the optical amplifier. The same one as that of the first optical multiplexing unit 8 or one having an inverted distribution fixed signal connected to one end of the input of the first optical multiplexing unit 8 may be used. For the first optical multiplexing means 8, an AWG, a coupler or the like is usually used. Depending on the system, a temperature adjustment function is also included. The inverted distribution fixed signal is guided into the optical amplifier through the transmission line. In FIG. 2, the inverted distribution fixed signal is added to the second optical multiplexing means 1, but the position where the inverted distribution fixed signal is added is not limited to this position, but is inverted to the optical amplifier provided in the transmission line. Any configuration can be used as long as a fixed distribution signal can be introduced.
[0020]
(Example 3)
In the first and second embodiments, an example of the optical amplifier is an EDFA. However, the optical amplifier of the present invention is not limited to the EDFA, and all optical amplifiers that perform optical amplification similar to the EDFA or have the same optical amplification principle. An optical amplifier can be used.
[0021]
【Effect of the invention】
The optical transmission apparatus of the present invention includes an inverted distribution fixed signal light source that generates an inverted distribution fixed signal for fixing an inverted distribution of an optical amplifier or keeping it within a certain range in an optical amplifier and an optical communication system. The optical amplifier operates within a desired range regardless of the number of signals and wavelength arrangement, and no matter how much the number of signals or wavelength arrangement changes, there is no significant difference in gain deviation or output compared to before the change. can get.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram showing a first embodiment of an optical communication system according to the present invention.
FIG. 2 is an explanatory view showing a second embodiment of the optical communication system of the present invention.
3A is an explanatory view showing an example of an absorption cross-sectional area of EDF, and FIG. 3B is an explanatory view showing an example of an emission cross-sectional area of EDF.
FIG. 4 is an explanatory diagram showing a gain coefficient in a micro cross section with an EDF.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Optical multiplexing means 2 Preamplifier 3 Subsequent amplifier 4 Inversion distribution fixed signal removal means 5 Inversion distribution fixed signal light source 6 Optical component 7 Transmitter 8 Optical multiplexing means

Claims (3)

Inversion distribution fixed signal for fixing the inversion distribution state of the EDFA in any device or part of the optical transmission apparatus having an EDFA in the transmission path between the transmission apparatus and the reception apparatus for transmitting a plurality of signals having different wavelengths. An optical transmission device equipped with an inverted distribution fixed signal light source that generates
The inverted distribution fixed signal light source has a plurality of wavelengths other than the excitation wavelength of the EDFA in the vicinity of the signal band passing through the optical amplifying unit, and generates an inverted distribution fixed signal of one wavelength for each of 1530 nm ± 3 nm and 1555 nm + 5 / −10 nm. der which is, an optical transmission device, characterized in that as it can fix the state of population inversion of the EDFA by controlling the power of their inversion fixed signal. An optical transmission apparatus according to claim 1 Symbol placement,
An optical transmission apparatus characterized in that the wavelength of the inverted distribution fixed signal is set near the peak of the gain coefficient of the EDF. The optical transmission device according to claim 1 or 2 ,
The optical transmission apparatus characterized by having inverted distribution fixed signal removing means.

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