JP6135068B2 - Optical transmission system, optical amplifier for relay, and optical transmission method - Google Patents

Description

  The present invention relates to an optical transmission system, a repeater optical amplifier, and an optical transmission method that multiplex and transmit light of different wavelengths, and particularly to a technique for realizing good transmission characteristics.

Currently, an optical wavelength division multiplexing (WDM) transmission system is used as a method for multiplexing and transmitting a plurality of signal lights having different wavelengths on one optical fiber transmission line. A large-capacity transmission technology using WDM using modulated optical signals of several tens of wavelengths has been put into practical use in land transmission systems and submarine transmission systems such as access network systems, metro network systems, and long-distance network systems.
In the future, in order to further increase the transmission capacity, it is desirable to close the wavelength interval between channels. However, it is known that if the wavelength interval between channels is made dense, reception characteristics deteriorate due to the influence of four-wave mixing (FWM), which is one type of nonlinear optical effect.

  Here, four-wave mixing will be described. When three types of light having different frequencies are input into the optical fiber, minute non-linear polarization is also generated in the optical fiber medium in addition to polarization mainly proportional to each photoelectric field. Such a phenomenon that the fourth type of light is generated from the three types of input light is referred to as four-wave mixing (FWM), and the newly generated light is referred to as four-wave mixing light.

  In optical fiber transmission, how to reduce FWM is important. Since the degree of the influence of the nonlinear optical effect such as FWM has a correlation with the fiber incident intensity (power), it is effective to suppress the fiber incident intensity in order to suppress the deterioration of the reception characteristics due to the nonlinear optical effect. However, if the fiber incident intensity is suppressed, the signal intensity after fiber transmission is also reduced. When the S / N ratio (signal-to-noise ratio) becomes small, the influence of noise becomes large, and as a result, the transmittable distance becomes short.

  In many optical transmission systems, the transmission distance or the optical repeat interval is limited in terms of facilities or economy, and there are often no degrees of freedom when designing an optical transmission system. Therefore, in order to increase the wavelength spacing between channels while maintaining the transmittable distance, it is necessary to take another means for suppressing the nonlinear optical effect.

  Therefore, as one of means for suppressing the nonlinear optical effect, there is a method of arranging wavelengths at unequal intervals (see Patent Document 1). This unequal arrangement of wavelengths is a system in which the wavelengths are not arranged at equal intervals, and the wavelengths are arranged so that no noise is generated on the wavelength to be used even when four-wave mixed light is generated. Patent Document 1 proposes a four-wave mixed light suppressing means for suppressing the four-wave mixed light generated in the transmission line optical fiber at the relay part of the transmission line optical fiber by setting the frequency interval of the main signal as unequal intervals. As the means, an arrayed waveguide grating and a fiber grating are used.

  However, the unequal interval arrangement requires a larger average wavelength interval than the equal interval arrangement, and the number of usable wavelengths is reduced. Also, from the viewpoint of high-density wavelength arrangement, when the wavelength interval for unequal interval arrangement is narrowed, the occupied band per wavelength is reduced, and it is difficult to increase the transmission speed. In general, it is known that in the four-wave mixing, the power of noise is larger as the wavelength interval used is narrower.

  Further, if the wavelength arrangement is changed from the equidistant arrangement, the system becomes complicated and the cost increases. This is because wavelength arrangements and wavelength intervals are defined by international standardization organizations, and various optical components used in optical transmission systems are manufactured on the assumption that they operate with the specified wavelength arrangements and wavelength intervals. Because it is normal.

  Patent Document 2 proposes a countermeasure for a four-wave mixing phenomenon in a wavelength division multiplexing optical transmission system. Specifically, while setting the optical frequency arrangement of each optical signal in the wavelength division multiplexing optical transmission system at equal intervals, the intensity of the optical signal having a large interference wave due to the four-wave mixing is set large, and the interference wave due to the four-wave mixing is small. It proposes to reduce the degradation of the dynamic range due to four-wave mixing by setting the optical signal intensity of the wavelength small.

  Patent Document 3 proposes a cross-phase modulation suppressing device that suppresses cross-phase modulation between channels and improves the transmission characteristics of wavelength-multiplexed signal light in a wavelength division multiplexing optical transmission system.

JP-A-10-322314 JP 2005-026910 A JP 2002-185402 A

  As described above, the four-wave mixing phenomenon occurs in the optical wavelength division multiplex transmission system, which is a method of multiplexing and transmitting signal lights having different wavelengths. The unequal interval arrangement described in Patent Document 1 requires a larger average wavelength interval than the equal interval arrangement, and the number of usable wavelengths is reduced. In addition, if the fiber incident power is suppressed in order to suppress the generation of four-wave mixed light, the transmission distance is shortened. Patent Documents 1 to 3 do not provide any solution to this problem.

  The present invention has been made to solve such problems, and an object thereof is to provide an optical transmission system, a repeater optical amplifier, and an optical transmission method capable of reducing four-wave mixing. .

In one aspect, an optical transmission system includes: an optical transmission unit that wavelength-multiplexes signal light having a plurality of wavelengths and sends the optical signal as an optical signal to an optical transmission line; and a relay unit that is provided in the optical transmission line and amplifies the optical signal An optical amplifier, an optical signal intensity adjusting unit provided in the optical transmission line for individually adjusting the intensity of the optical signal of each wavelength, and an optical receiving unit for demodulating the plurality of wavelength-multiplexed optical signals, The optical signal intensity adjusting means adjusts the optical signal intensity so that the wavelength interval between optical signals having relatively strong optical signal intensities is wider than the wavelength interval between optical signals having adjacent wavelengths. It is configured. With such a configuration, the occurrence of four-wave mixing can be suppressed.
In one aspect, the optical transmission system includes the optical signal intensity adjusting means in the repeater optical amplifier. With such a configuration, the system can be simplified and control of temperature change and the like is facilitated.

  In one aspect, the optical signal intensity adjusting means is configured to adjust the optical signal intensity so as to have a relatively strong optical signal intensity at every predetermined wavelength interval. With such a configuration, generation of four-wave mixing can be suppressed as compared with a case where a strong optical signal is incident for each wavelength.

  In one aspect, in the optical transmission system, after the optical signal is transmitted by means of amplifying and incident so that the incident intensity to the optical signal of each wavelength is increased at every predetermined wavelength interval, the optical signal is amplified by the incident intensity. The optical signal having a wavelength other than the optical signal is configured to be amplified and incident so that the incident intensity to the optical signal becomes higher at every predetermined wavelength interval. With such a configuration, the occurrence of four-wave mixing can be suppressed.

  In one aspect, a Fabry-Perot etalon filter is used as the optical signal intensity adjusting means. With such a configuration, it is possible to transmit light of a specific wavelength and suppress the occurrence of four-wave mixing.

  In one aspect, a repeater optical amplifier for relaying an optical signal in which a plurality of optical signals having different wavelengths is multiplexed has a wavelength interval between optical signals having relatively strong optical signal intensities. The optical signal intensity is adjusted so as to be wider than the wavelength interval between the optical signals. With such a configuration, the occurrence of four-wave mixing can be suppressed.

  In one aspect, in an optical transmission method in which a plurality of optical signals having different wavelengths are multiplexed and transmitted on an optical transmission line, wavelength intervals between optical signals having relatively strong optical signal intensities are adjacent on the optical transmission line. Adjusting the optical signal intensity so as to be wider than the wavelength interval between optical signals having wavelengths. By such a method, generation of four-wave mixing can be suppressed.

  In one aspect, an optical transmission method that multiplexes a plurality of optical signals having different wavelengths and transmits them on an optical transmission line is a method of combining optical signals having relatively strong optical signal strengths at a first point on the optical transmission line. Adjusting the optical signal intensity so that the wavelength interval is wider than the wavelength interval between optical signals having adjacent wavelengths, and at a second point different from the first point on the optical transmission line, The optical signal having the relatively strong optical signal intensity at the first point is an optical signal having a relatively strong optical signal intensity, and an optical signal having a relatively strong optical signal intensity. Adjusting the optical signal intensity so that the wavelength interval between the signals is wider than the wavelength interval between the optical signals having adjacent wavelengths. By such a method, generation of four-wave mixing can be suppressed.

  In one aspect, in the optical transmission method, the wavelength interval between the optical signals having relatively strong optical signal intensities includes a constant wavelength interval.

  According to the present invention, it is possible to provide an optical transmission system, a relay optical amplifier, and an optical transmission method capable of reducing four-wave mixing.

It is a figure of the optical transmission system concerning this embodiment. It is a figure which shows the incident example of the incident power of the optical signal which concerns on this embodiment. It is a figure which shows the example which changed the incident power of the optical signal which concerns on this embodiment for every channel different from FIG. It is a figure which shows the example at the time of changing the incident power of the optical signal which concerns on this embodiment for every wavelength interval different from FIG. FIG. 5 is a diagram illustrating an example when the incident power of an optical signal according to the present embodiment is changed for each channel different from that in FIG. 4. It is a figure which shows the example at the time of changing the incident power of the optical signal which concerns on this embodiment for every channel different from FIG. It is the figure which showed the structural example of the optical transmission system which concerns on this embodiment. It is a figure explaining the Fabry-Perot etalon filter. It is the figure which showed the transmission intensity of the light of a specific wavelength with respect to the reflectance of a Fabry-Perot etalon filter.

Embodiment 1 FIG.
First, of the nonlinear optical effect, the mechanism that occurs in the four-wave mixing, which is the main deterioration factor of reception characteristics in the optical transmission system, will be described.

When three types of light having different frequencies are input into the optical fiber, in the optical fiber medium, polarization that is mainly proportional to each photoelectric field and minute nonlinear polarization also occur. For example, if the frequency of the input light is f _i , f _j , f _k , the nonlinear polarization due to this input light is not only the components of the original frequencies f _i , f _j , f _k , Contains frequency components. Such a phenomenon that the fourth type of light is generated from the three types of input light is called four-wave mixing, and light newly generated thereby is called four-wave mixing light. The frequency f _ijk of the four-wave mixed light is expressed by Expression (1).

The power P _ijk of the four-wave mixed light is expressed as shown in Equation (2) by the powers P _i , P _j , P _k and the like of the three types of frequency components that are the original.

Here, n is the refractive index of the core of the optical fiber, lambda is the wavelength, c is the speed of light in a vacuum, D _e is degenerate coefficients, chi ₁₁₁₁ the third-order nonlinear susceptibility, L _eff is effective length, A _eff is the effective The cross-sectional area, L is the length of the fiber, and η is the generation efficiency. From this equation, it can be seen that the amount of generated four-wave mixed light is proportional to the cube of the input optical power.

  Next, the generation efficiency is expressed as shown in Equation (3).

  Here, Δβ represents the amount of phase mismatch, and for simplification, the case of two-wavelength input is considered as shown in Equation (4).

  Here, Δf represents the frequency difference of the input light, and D represents chromatic dispersion. From the above equation, it can be seen that the generation probability of four-wave mixed light is inversely proportional to the fourth power of Δf in the region where D is large, and is inversely proportional to the sixth power of Δf in the region where D is small and can be ignored.

  From the above, in order to suppress the generation of the four-wave mixed light, it is conceivable to either reduce the incident intensity to the fiber or increase the frequency (wavelength) interval of the optical signal. It can be seen that the effect is particularly great when the frequency (wavelength) interval of the optical signal is increased.

Next, an optical transmission system according to an embodiment of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a block diagram showing the overall configuration of an optical transmission system according to an embodiment of the present invention. The optical transmission system 100 includes an optical transmitter 1, an optical multiplexer 2, a transmission optical amplifier 3, an optical transmission path 4, a relay optical amplifier 5, an optical demultiplexer 6, and an optical receiver 7.

  The optical transmitter 1 generates a plurality of signal lights (λ1, λ2,..., Λn) having different wavelengths and outputs them to the optical multiplexer 2. In the present embodiment, the wavelengths of the plurality of signal lights are equally spaced. The optical multiplexer 2 multiplexes the signal lights output from the optical transmitter 1 and outputs them to the transmission optical amplifier 3. The transmission optical amplifier 3 amplifies the signal light combined in the optical multiplexer 2 and outputs the amplified signal light to the optical transmission line 4.

  The optical transmission line 4 transmits the signal light output from the transmission optical amplifier 3. A plurality of relay optical amplifiers 5 are inserted in the middle of the optical transmission line 4. In this example, since N repeating optical amplifiers 5 (5-1, 5-2,..., 5-N) are inserted, the optical transmission path 4 has (N + 1) transmission sections ( 4-1, 4-2,..., 4- (N + 1)). The number and interval of the inserted repeater optical amplifiers 5 are determined by the design of the optical transmission system. In FIG. 1, it is assumed that N stages of repeater optical amplifiers 5 are inserted, and the repeater optical amplifiers are designated as 5-1, 5-2,. It is assumed that transmission sections divided by the optical amplifiers for relay are 4-1, 4-2, ... 4- (N + 1), respectively.

  The plurality of relay optical amplifiers 5 perform amplification processing so that a predetermined amplification degree is obtained for each of the plurality of optical signals included in the signal light transmitted on the transmission path 4. Specifically, it has a control unit that performs amplification processing to increase or decrease the wavelength interval between optical signals having high intensities by adding strength to the optical signals of adjacent channels. In order to perform processing so that the amplification degree differs for each channel, the relay optical amplifier 5 uses, for example, an optical filter set to have a different transmittance for each channel.

  Each of the plurality of relay optical amplifiers 5 has an amplification degree set so as to change the intensity distribution of the optical signal of each channel for each transmission section. For example, the optical signal of the channel amplified with the low amplification degree in the first repeating optical amplifier 5 is amplified with the high amplification degree in the next repeating optical amplifier 5. On the other hand, the optical signal of the channel amplified with high amplification in the first relay optical amplifier 5 is amplified with low amplification in the next relay optical amplifier 5.

By setting the amplification degree in this way, the average incident intensity in the entire optical transmission line can be increased over all channels. As a result, the influence of noise can be reduced while increasing the S / N ratio of the optical signal input to the optical receiver 7.
In this way, a system that is simpler than installing the optical signal intensity adjusting means at a place other than the optical amplifier for relay by setting the means for individually adjusting the optical signal intensity of each wavelength as the optical amplifier for relay. It can be. Even when the means for individually adjusting the optical signal intensity of each wavelength has temperature dependence, the relay optical amplifier 5 has a power supply, and therefore, temperature control can be performed relatively easily.
The optical signal intensity adjusting means may be provided at a position on the optical transmission line 4 that is separated from the relay optical amplifier 5.

The optical demultiplexer 6 receives the optical signal transmitted through the optical transmission path 4 and demultiplexes it into signal light of each wavelength.
The optical receiver 7 inputs each signal light (λ1, λ2,..., Λn) demultiplexed by the optical demultiplexer 6 and performs a reception process on these signal lights.

  Note that an optical demultiplexer 6 that does not have a wavelength filter function may be used. In that case, since the optical signal input to each optical receiver 7 (λ1, λ2,..., Λn) includes all wavelength components, each optical receiver 7 (λ1, λ2,. , Λn) has a function of extracting a target wavelength component.

  In the optical transmission system of FIG. 1, when the wavelength interval of the signal light is Δλ, if the optical fiber incident intensity of the signal light is constant for all channels and less than Pin, the generation of the four-wave mixed light can be sufficiently suppressed. Suppose it is designed. The Pin is designed to have a margin against the performance limit of the optical transmission system.

  2 and 3 are diagrams illustrating examples of the optical signal intensity of the optical signal incident on each transmission section. In each transmission section, the optical signal attenuates according to the transmission distance, but is transmitted to the end of the transmission section while maintaining substantially the same intensity ratio.

  As shown in FIG. 2, the incident intensity of the optical signal of each channel incident on the optical transmission path 4-2, 4-4, 4-6,... (That is, even-numbered optical transmission path) of each channel. Among them, the incident intensity of the signal corresponding to λ2, λ4, λ6,... (That is, the even-numbered channel when arranged in order from the shortest wavelength) is increased by ΔP. In the odd-numbered repeater optical amplifiers 5-1, 5-3, 5-5,..., The amplification degree for the optical signals of the even-numbered channels of λ2, λ4, λ6,. This can be realized by adjusting so that the optical signal intensity of the optical signal output to the transmission line 4 can be increased so as to increase by ΔP as compared with other odd-numbered channels.

  In this case, the wavelength interval FSR between the increased optical signals is 2Δλ, and the increase in the generation efficiency of the four-wave mixed light is 1/16 of the simple calculation as compared with the case where the incident intensity of all the channels is increased. It becomes the following.

  In the optical transmission system according to the present embodiment, it is allowed to exceed a part of the operation margin of each channel as compared with the system in which all channels are aligned with the maximum input intensity when the operation margin is considered. Consider increasing the intensity of a strong intensity channel. Since the increase in the generation efficiency of four-wave mixing light is 1/16 because the wavelength interval is doubled, the intensity of a strong channel can be effectively increased. As an example, the margin is set to 2 dB, for example, and it is assumed that the influence is slight even if the strength of the strong channel is increased by 10% (0.2 dB) of the margin. In this case, the strength of the strong channel can be increased by 3.2 dB. This is because 1/16 of 3.2 dB is 0.2 dB. In this example, the above numerical value is used. However, the setting amount of the size of the operation margin and the size of the portion of the margin that can be excluded because the influence is slight is not limited to the above numerical value.

  Also, as shown in FIG. 3, among the incident intensities on the optical transmission lines 4-2, 4-4, 4-6,... Of each channel, incident intensities of signals corresponding to λ1, λ3,. Is increased by ΔP.

  Further, as shown in FIG. 3, the light of each channel incident on the optical transmission lines 4-3, 4-5, 4-7,... (That is, odd-numbered optical transmission lines) of each channel. Among the incident intensities of the signals, the incident intensities of the signals corresponding to λ1, λ3, λ5,... (That is, odd-numbered channels when arranged in order from the shorter wavelength) are increased by ΔP. In the even-numbered repeater optical amplifiers 5-2, 5-4, 5-6,..., The amplification degree for the optical signals of the odd-numbered channels of λ1, λ3, λ5,. This can be realized by adjusting the optical signal output to the transmission line 4 so that the optical signal intensity can be increased so as to increase by ΔP as compared with other even-numbered channels.

  The optical signals incident on the even-numbered repeater optical amplifiers 5-2, 5-4, 5-6,... Are odd-numbered repeater optical amplifiers 5-1, 5-3, 5. Since the optical signal intensity is output in a state in which the intensity is increased or decreased by −5,..., The optical signal intensity differs for each channel. Therefore, it is necessary to set the amplification degree for the optical signal of each channel in consideration of the difference in the optical signal intensity at the time of incidence.

  As shown in FIG. 2 and FIG. 3, by increasing the amplification factor of alternately different channels, the increase in average incident intensity when viewed in the entire optical transmission line 4 becomes ΔP / 2, and the optical receiver The S / N ratio of the input optical signal can be improved.

  In this way, four-wave mixing (FWM) can be reduced by adding strength to the optical signals of adjacent channels and widening the wavelength interval between the optical signals having high strength. In the optical amplification, the wavelength arrangement shown in FIGS. 2 and 3 can be alternately used for each transmission section by the relay optical amplifier 5. In that case, it is effective for FWM reduction.

  As described above, according to the optical transmission system according to the present embodiment, adjacent channels among the optical signals propagating through the optical transmission line in each section divided by the relay optical amplifier inserted in the optical transmission line. By adjusting the control unit for adding or decreasing the intensity of the optical signal, the wavelength interval between the optical signals having high intensity can be increased, and the occurrence of the nonlinear optical effect can be suppressed. Also, by changing the intensity distribution of the signal light intensity of each channel for each transmission section, the average incident intensity in the entire optical transmission path is increased over all channels, and the S / N ratio of the optical signal input to the optical receiver is increased. Can be increased, that is, the influence of noise can be reduced.

Embodiment 2. FIG.
In the optical transmission system according to the second embodiment, the process of amplification in each relay optical amplifier 5 is different from that in the first embodiment. Since other configurations are the same as those in the first embodiment, description thereof is omitted.

  As shown in FIG. 4, among the incident intensities of the optical signals of the respective channels incident on the optical transmission lines 4-2, 4-5, 4-8,. ,... Is increased by ΔP. In this case, the amplification degree of the optical signals of the channels λ2, λ5, λ8,... Is output to the optical transmission line 4 in the optical amplifiers 5-1, 5-4, 5-7,. This can be realized by adjusting so that the optical signal intensity of the optical signal to be output can be increased so as to increase by ΔP compared to other channels.

  Further, as shown in FIG. 5, among the incident intensities of the optical signals of the respective channels incident on the optical transmission lines 4-3, 4-6, 4-9,. , Λ9,... Is increased by ΔP. In this case, in the repeater optical amplifiers 5-2, 5-5, 5-8,..., The amplification degree with respect to the optical signals of the channels λ 3, λ 6, λ 9,. This can be realized by adjusting so that the optical signal intensity of the optical signal to be output can be increased so as to increase by ΔP compared to other channels.

  Further, as shown in FIG. 6, among the incident intensities of the optical signals of the respective channels incident on the optical transmission lines 4-4, 4-7, 4-10,. , Λ10,... Is increased by ΔP. In this case, in the repeater optical amplifiers 5-3, 5-6, 5-9,..., The amplification degree with respect to the optical signals of the channels λ4, λ7, λ10,. This can be realized by adjusting so that the optical signal intensity of the optical signal to be output can be increased so as to increase by ΔP compared to other channels.

  In the optical transmission system according to the second embodiment, the increased wavelength interval FSR between the optical signals is 3Δλ, and the average incident intensity increment when viewed in the entire optical transmission line 4 is ΔP / 3. Accordingly, it is possible to reduce the generation of four-wave mixed light while reducing the incident intensity and widening the wavelength interval.

  Similarly, the incident intensity of the optical signal of each channel may be adjusted so that the wavelength interval is 4Δλ or more.

Embodiment 3 FIG.
There is a method of using an optical filter for adjusting the light intensity of each channel. For example, an optical filter whose light transmittance has periodicity with respect to frequency (or wavelength). An example of the filter is a Fabry-Perot etalon filter. A Fabry-Perot etalon is a Fabry-Perot interferometer with a fixed inter-interference distance. FIG. 7 shows an example of the configuration. The light propagated through the optical transmission line 8 is amplified by the optical amplifier 9. In the optical filter 10a, the incident intensity of the odd-numbered channel light is increased and emitted to the next transmission path 8. In the next filter 10b, the incident intensity of even-channel light is increased and emitted to the next transmission path 8. The filter is not necessarily installed for each optical amplifier, and may be installed every several stages.

  FIG. 8 is an example of a solid etalon among Fabry-Perot etalon filters. When the filter thickness is T = λ / 2, at other wavelengths other than λ, interference between the transmitted component wavefronts is canceled and transmitted light is reduced to near zero. That is, almost all light is reflected towards the light source. The incident light having the wavelength λ is subjected to multiple reflections between the two coated surfaces. The wavefront of the transmitted light is a superposition of the component wavefronts that are transmitted after receiving an even number of reflections. The transmitted light becomes maximum when there is no phase difference between the component wavefronts. The distance between the mirrors can vary from a fraction of a millimeter to several centimeters. FIG. 9 explains the reflection dependence of the transmission intensity spectrum of the Fabry-Perot etalon filter. The higher the reflectivity, the stronger the property of passing light of a specific wavelength.

  On the other hand, examples of the optical amplifier include a Raman amplifier and an erbium-doped optical fiber amplifier (EDFA). FIG. 7 shows an example. When WDM transmission is performed at a channel interval of 50 GHz, the intensity of light intensity for each channel can be increased most when the FSR (free spectral region) of the optical filter is 100 GHz.

Note that the present invention is not limited to the above-described embodiment, and can be changed as appropriate without departing from the spirit of the present invention.
For example, the present invention may be applied to a method in which the intensity of incident light to the optical transmission line is amplified and input at unequal intervals.

  Further, in the above-described embodiment, the signal is adjusted to one of two types of intensity having a difference in ΔP. However, the adjustment is not limited to this, and the signal is further adjusted to have three or more types of intensity. May be. Further, the intensity of incident light may be non-uniform for each channel.

  Further, an optical signal intensity adjusting means for individually adjusting the optical signal intensity of each wavelength may be provided in the optical transmission means such as the transmission optical amplifier 3.

  Further, as described above, it is preferable to provide a plurality of optical signal intensity adjusting means for individually adjusting the optical signal intensity of each wavelength on the optical transmission line, but only one optical signal intensity adjusting means may be provided. Further, even when a plurality of optical transmission lines are provided, the same channel may be adjusted so as to have a relatively strong optical signal intensity.

DESCRIPTION OF SYMBOLS 1 Optical transmitter 2 Optical multiplexer 3 Transmission optical amplifier 4 Optical transmission line 5 Relay optical amplifier 6 Optical demultiplexer 7 Optical receiver 8 Optical transmission line 9 Optical amplifier 10 Filter 100 Optical transmission system

Claims (7)

An optical transmission system for multiplexing and transmitting a plurality of signal lights having different wavelengths,
Optical transmission means for wavelength-multiplexing signal lights of a plurality of wavelengths and sending them to the optical transmission line as optical signals;
An optical amplifier for relay provided in the optical transmission line for amplifying the optical signal;
An optical signal intensity adjusting means that is provided in the optical transmission line and individually adjusts the intensity of the optical signal of each wavelength;
Optical receiving means for demodulating the plurality of wavelength-multiplexed optical signals,
The optical signal intensity adjusting means adjusts the optical signal intensity so that the wavelength interval between optical signals having relatively strong optical signal intensity is wider than the wavelength interval between optical signals having adjacent wavelengths,
The optical signal intensity adjusting means adjusts the optical signal intensity so as to have a relatively strong optical signal intensity at every predetermined wavelength interval ,
In the optical transmission system, after the optical signal is transmitted by means for amplifying and incident so that the incident intensity to the optical signal of each wavelength becomes higher at every fixed wavelength interval, the optical signal other than the optical signal amplified by the incident intensity an optical transmission system, characterized in that with respect to the optical signal of the wavelength, the incident intensity of the optical signal to have a means for entering is amplified so as to be higher for each predetermined wavelength interval.   The optical transmission system according to claim 1, wherein the optical amplifier for relay includes the optical signal intensity adjusting means. The optical transmission system according to claim 1 or 2, wherein the optical signal intensity adjusting means is a Fabry-Perot etalon filter. A relay optical amplifier for relaying an optical signal in which a plurality of optical signals having different wavelengths are multiplexed,
Adjust the optical signal intensity so that the wavelength interval between optical signals having relatively strong optical signal intensity is wider than the wavelength interval between optical signals having adjacent wavelengths,
The optical signal intensity is adjusted so as to have a relatively strong optical signal intensity at a certain wavelength interval ,
After the optical signal that has been amplified and transmitted so that the incident intensity to the optical signal of each wavelength becomes higher at every constant wavelength interval, the optical signal having a wavelength other than the optical signal amplified by the incident intensity is transmitted. An optical amplifier for relaying that is amplified and incident so that the incident intensity to the optical signal becomes higher at every predetermined wavelength interval . An optical transmission method for multiplexing a plurality of optical signals having different wavelengths and transmitting them on an optical transmission line,
Adjusting the optical signal intensity so that the wavelength interval between optical signals having relatively strong optical signal intensity on the optical transmission line is wider than the wavelength interval between optical signals having adjacent wavelengths;
The wavelength spacing of the optical signals respectively having the relatively strong light signal intensity, Ri constant wavelength interval der,
After the optical signal that has been amplified and transmitted so that the incident intensity to the optical signal of each wavelength becomes higher at every constant wavelength interval, the optical signal having a wavelength other than the optical signal amplified by the incident intensity is transmitted. Then, the optical transmission method is characterized in that the incident intensity to the optical signal is amplified and incident so as to increase at every predetermined wavelength interval . An optical transmission method for multiplexing a plurality of optical signals having different wavelengths and transmitting them on an optical transmission line,
At the first point on the optical transmission line, the optical signal intensity is set so that the wavelength interval between optical signals having relatively strong optical signal intensities is wider than the wavelength interval between optical signals having adjacent wavelengths. Adjusting steps,
At a second point that is different from the first point on the optical transmission line, an optical signal having a different wavelength is relatively stronger than the optical signal having the relatively strong optical signal intensity at the first point. Adjust the optical signal intensity so that the wavelength interval between optical signals having optical signal strengths and relatively strong optical signal strengths is wider than the wavelength interval between optical signals having adjacent wavelengths. And an optical transmission method. The optical transmission method according to claim 6 , wherein a wavelength interval between the optical signals having relatively strong optical signal intensities is a constant wavelength interval.

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