JP2003060273A - Optical transmission apparatus and optical communication method using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem of an optical amplifier cannot maintain gain flatness properties, gain deviation is generated over a system tolerance, and hence transmission quality is affected greatly, when the number of signals to be transmitted is equal to or less than half the sum for passing through a transmission path, or the wavelength arrangement of the signals to be transmitted is distributed unevenly, while WDM transmission is made in the transmission path having the optical amplifier. SOLUTION: An inverting distribution fixing signal light source is provided in either equipment or places of an optical transmission apparatus, having an optical amplifier in the transmission line between a transmitter and a receiver, and the operation state of the optical amplifier is locked within the range for maintaining amplification characteristics to a fixed state by an inverting distribution fixing signal generated from the light source, thus flexibly coping with the change in the number of signals and the uneven distribution of wavelength arrangement.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical transmission device provided with an optical amplifier in a transmission line between a transmission device and a reception device, and an optical communication method using the optical transmission device.

[0002]

2. Description of the Related Art EDFA (Erbium Doped Fiber Amplifie)
r) is 1.55μ, which is the band where the transmission line fiber loss is small.
Since high output and low noise can be obtained at m,
1R (Regenerati for loss compensation in optical fiber communication
on) It has been widely used as a repeater. In addition, recently, due to a demand for expansion of transmission capacity, a wavelength division multiplexing (WDM) transmission technique for multiplexing and transmitting signal light in a plurality of wavelength bands is generally used, and a wavelength division multiplexing signal is transmitted to an EDFA arranged in a transmission line. It is often done.

Assuming a point-to-point system, when an EDFA is arranged between both points to transmit a signal, the number of signals (number of signals) passing through the transmission line and the EDFA is usually within a wavelength band. The arrangement (wavelength arrangement) is constant. Therefore, the EDFA is usually designed optimally for all signals passing through the transmission line, and the output and NF (Noise Figu
re), amplification characteristics (gain deviation), etc. are set within the range according to the requirements of the system.

[0004]

[Problems to be Solved by the Invention] As described above, Point
In a to-point system, when an EDFA is arranged between both points to transmit a signal, the number of signals and the wavelength arrangement of signals passing through the transmission line and the EDFA are usually constant. However, when some of the signals in the signal band are blocked due to some failure, or when a system in which a path is freely selected according to wavelength, such as a system using XC (cross connect), is realized in the future, The number of signals passing through the transmission line and the EDFA and the wavelength arrangement are not constant. Especially X
In C, the wavelength arrangement of signals changes from moment to moment.

In the EDFA, the formation state of the population inversion differs depending on the number of input signals and the wavelength arrangement, so that the output,
Gain deviation, NF, amplification characteristics (gain deviation), etc. change significantly. If the number of signals to be transmitted decreases slightly on average with respect to the total number of signals passing through the transmission line, the amplification characteristics will not be affected, but with respect to the total number of signals passing through the transmission line. In the case of less than half or uneven distribution in 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, if the signal power exceeds, the power reaches the power at which the nonlinear optical effect of the transmission line fiber is generated, and conversely, if the signal power decreases, it becomes impossible to receive due to SN deterioration, which causes a great influence on the transmission quality. there is a possibility. Conventional EDFA
Since the optical communication system does not cope with the occurrence of such a situation as described above, there is concern when such a situation occurs.

[0006]

Optical amplifiers, especially EDFAs
Then, the amplification operation is determined by the population inversion formation state in the EDF, which is the radiation increasing medium. Therefore, if the population inversion distribution can be kept constant within a desired range, it is possible to obtain a constant enhancement characteristic. is there. Based on this principle, the present invention locks the operating state of an optical amplifier within a certain range by a fixed population inversion signal, and keeps the amplification characteristic (gain deviation) constant with respect to changes in the number of signals and wavelength allocation. In addition, an optical transmission device capable of flexibly coping with such changes and an optical transmission method using the same are provided.

In the optical transmission device of the present invention, the inverted distribution state of the optical amplifier is fixed to a certain state in any device or part of the optical transmission device provided with the optical amplifier in the transmission line between the transmission device and the reception device. Or a population inversion fixed signal light source capable of generating a population inversion fixed signal of wavelength and power that can be kept within a certain range.

According to the optical communication method of the present invention, optical transmission is performed using the optical transmission device, and in order to fix the population inversion state of the optical amplifier to a certain state, the wavelength of the population inversion fixed signal is controlled and the power is adjusted. It is a method of controlling or controlling both power and wavelength.

In another optical communication method of the present invention, optical transmission is performed using the optical transmission device, and the population inversion state of the optical amplifier is fixed to a certain state, or is kept within a certain range. This is a method of setting the wavelength of the population inversion fixed signal near the peak of the gain coefficient.

An example of the present invention will be described below. Wavelength 1528nm ~ 15
In the C-band EDFA that amplifies the region around 63 nm, for example,
The population inversion formation state can be fixed by the population inversion fixed signal of 1ch for 1530 nm ± 3 nm, 1555 nm + 5 / -10 nm, or 2 channels at the same time, and Nch (N> 1) each. By providing a population inversion fixed signal light source that generates a population inversion fixed signal of this wavelength in the amplifier, the transmitter, or both, a constant amplification characteristic (gain Deviation) can be obtained.

As described above, the amplification characteristic of an optical amplifier, especially an EDFA, is determined by the formation state of population inversion. In the case of EDFA, formation of population inversion in EDF which is an amplification medium is determined by EDF length, signal light power, and pumping light power. Further, the amplification characteristics differ depending on the number of signals input to the amplifier and the wavelength arrangement. This is due to the wavelength dependence of absorption cross section and emission cross section peculiar 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 minute cross section with EDF.

Generally, if a signal is inputted in advance to a wavelength region having a large gain coefficient calculated by the following equation (1) from the absorption cross section / emission cross section and the population inversion distribution formation state, the signal is inputted to the wavelength band having a small gain coefficient. It is a well-known fact that the change is relatively small as compared with the case where the signal is input or the case where the signal is added to the wavelength band other than this. g (λ, z, T) = Γ [σe (λ, T) ・ N2 (z) -σa (λ, T) ・ N1 (z)] (1) σe (λ, T): emission cross sections σa ( λ, T): absorption cross sections atomic population densities N1 (ground level) and N2
(excited level)

Since the optical transmission apparatus of the present invention is a system in which an optical distribution fixed signal source for generating an inverted distribution fixed signal of a wavelength having a large gain coefficient is provided in an optical amplifier or an optical communication system, the optical amplifier is an inverted distribution. Is fixed (or is kept within a certain range), and a signal that increases or decreases thereafter operates in a desired range regardless of the number of signals and the wavelength arrangement. Therefore, no matter how the number of signals or the wavelength arrangement changes, it is possible to obtain the characteristics that the gain deviation and the output are not much different from those before the change.

In the above description, the case of using the C-band is taken as an example, but also for the L-band, from the same viewpoint, the wavelength of the population inversion fixed signal is selected, and the population inversion fixed signal light source for generating the signal is amplified. If it is provided inside, the same effect can be expected. Further, this population inversion fixed signal light source does not necessarily have to be mounted in the amplifier, and there is no difference in operation even if it is provided in the transmitter and then supplied to the optical amplifier.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS (Embodiment 1) FIG. 1 shows a first embodiment of the present invention. This embodiment is a two-stage E in the transmission line.
In this example, the population inversion fixed signal light source is input to the DFA from the input side of the optical amplifier. From the input side of the signal light, the optical multiplexing means 1,
A pre-stage amplification section 2, a post-stage amplification section 3, and a population inversion fixed signal removal means 4 are provided, and a population inversion fixed signal light source 5 is connected to the optical multiplexing means 1. For example, a forward-pumped EDFA is used for the front-stage amplifier 2. A bidirectionally pumped EDFA or the like is used for the post-stage amplification section 3, for example. In the blocks of the front-stage amplification unit 2 and the rear-stage amplification unit 3, the isolator, the TAP coupler, the WDM, the EDF, and the P that are the constituent elements of the EDFA are included.
D, excitation LD, etc. are included. A coupler or the like is used as the population inversion fixed signal removing means 4. For the population inversion fixed signal light source 5, for example, a DFB-LD and an LD drive circuit are used. This block includes various circuits having a function for driving the LD, such as a temperature stabilizing circuit, a drive current adjusting circuit, and a monitor circuit for these.

The wavelength of the population inversion fixed signal is selected by the amplification wavelength band of the amplification section connected after the optical multiplexing means 1. The wavelength is usually near the signal band that passes through the amplification section and is a wavelength other than the excitation wavelength of the amplifier. For example, C-band amplifier is 1530nm ± 3nm, 1555nm ＋ 5 / -10nm
1ch to either of them, or 2ch at the same time, and Nchs respectively
(N> 1) signal is provided.

As the means for guiding the population inversion fixed signal to the optical amplifier, for example, the optical multiplexing means 1 such as an optical coupler can be used. Although the configuration of the two-stage EDFA is shown in this embodiment, the configuration of the optical amplifier in the present invention is not limited to a single stage, but is not limited to only two stages.
The present invention can also be applied to a configuration in which an optical component is included between the stages of the optical amplifier as shown in FIG. In this case, an optical component 6 such as a gain equalizing filter, an optical attenuator, a DCF, an OADM, an SMF, etc. is provided between the pre-stage amplification section 2 and the post-stage amplification section 3.
Is inserted. Furthermore, in this embodiment, the population inversion fixed signal is introduced from the input side of the amplifier, but the population inversion fixed signal can also be introduced between the stages of the amplifier or inside the amplifier.

(Embodiment 2) FIG. 2 shows a second embodiment of the present invention. This is an example in which a population inversion fixed signal is input from the second optical multiplexing means 1 in the transmitting device, and the transmitting device 7 for transmitting a plurality of signals having different wavelengths, the first optical multiplexing means 8, and the second optical multiplexing means. The wave means 1 are connected in this order. Usually, a preamplifier or transmission line fiber is connected to this end,
These are not shown in FIG. The signal transmitted from the transmitter 7 is, for example, a signal in the 1550 nm band, a signal in the 1580 nm band, or a signal having a wavelength exhibiting a relatively small loss in the loss characteristics of the silica fiber. The block of the transmitter 7 includes functions generally required for the transmitter, such as a modulator and an LD drive circuit.

A population inversion fixed signal light source 5 is connected to the second optical multiplexing means 1 of FIG. The wavelength selection of the population inversion 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 population inversion fixed signal to the optical amplifier. First optical multiplexing means 8
The same as the above, or one in which the population inversion fixed signal is connected to one end of the input of the first optical multiplexing means 8 may be used.
An AWG, a coupler or the like is usually used for the first optical multiplexing means 8. Depending on the method, a temperature adjustment function is also included. The population inversion fixed signal is introduced into the optical amplifier through the transmission line. In FIG. 2, the population inversion fixed signal is applied to the second optical multiplexing means 1. However, the position to which the population inversion fixed signal is applied is not limited to this position, and it is inverted to the optical amplifier provided in the transmission line. The configuration does not matter as long as the fixed distribution signal can be introduced.

(Embodiment 3) In Embodiments 1 and 2, an example of the optical amplifier is an EDFA, but the optical amplifier of the present invention is not limited to the EDFA, and the same optical amplification as the EDFA is performed or the same. Any optical amplifier equipped with the optical amplification principle of can be used.

[0021]

According to the optical transmission device of the present invention, an inversion distribution fixed signal light source for generating an inversion distribution fixed signal for fixing the inversion distribution of the optical amplifier or keeping it within a certain range is used as an optical amplifier or an optical communication system. Therefore, the optical amplifier operates within a desired range regardless of the number of signals and wavelength allocation, and no matter how the number of signals or wavelength allocation changes, gain deviation and output will be smaller than before change. A characteristic with no great difference can be obtained.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a first embodiment of an optical communication system of the present invention.

FIG. 2 is an explanatory diagram showing a second embodiment of the optical communication system of the present invention.

FIG. 3A is an explanatory diagram showing an example of an absorption cross section of EDF, and FIG. 3B is an explanatory diagram showing an example of an emission cross section of EDF.

FIG. 4 is an explanatory diagram showing a gain coefficient in a minute cross section having an EDF.

[Explanation of symbols]

1 Optical multiplexing means 2 Pre-stage amplifier 3 Second stage amplifier 4 Inversion distribution fixed signal removal means 5 Inversion distribution fixed signal light source 6 Optical parts 7 transmitter 8 Optical multiplexing means

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Claims (7)

[Claims] 1. An inversion distribution state of an optical amplifier is fixed to a certain state in any device or place of an optical transmission apparatus having an optical amplifier in a transmission line between a transmitter and a receiver, or
An optical transmission device comprising a population inversion fixed signal light source that generates a population inversion fixed signal of wavelength and power that can be kept within a certain range. 2. An optical amplifier of an optical transmission device having an optical amplifier in a transmission line between a transmission device and a reception device, wherein an inverted distribution state of the optical amplifier is fixed to a certain state or is kept within a certain range. An optical transmission device comprising a population inversion fixed signal light source for generating a population inversion fixed signal of wavelength and power capable of controlling. 3. An inverted distribution state of an optical amplifier is fixed to a certain state or is kept within a certain range in a transmitting apparatus of an optical transmission apparatus having an optical amplifier in a transmission line between a transmitting apparatus and a receiving apparatus. An optical transmission device comprising a population inversion fixed signal light source for generating a population inversion fixed signal of wavelength and power capable of controlling. 4. The wavelength of a population inversion fixed signal for performing optical transmission using the optical transmission device according to claim 1 and fixing the population inversion state of an optical amplifier to a certain state. An optical communication method characterized by controlling the. 5. The power of a population inversion fixed signal for performing optical transmission using the optical transmission apparatus according to claim 1 and fixing the population inversion state of an optical amplifier to a certain state. An optical communication method characterized by controlling the. 6. The power of a population inversion fixed signal for performing optical transmission using the optical transmission device according to claim 1 and fixing the population inversion state of an optical amplifier to a certain state. And an optical communication method characterized by controlling the wavelength. 7. Optical transmission using the optical transmission device according to claim 1, wherein the population inversion distribution of the optical amplifier is fixed to a certain state, or is kept within a certain range. Therefore, the wavelength of the population inversion fixed signal is set near the peak of the gain coefficient of the EDF.