JP2825109B2 - Optical soliton transmission method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical soliton transmission method, and more particularly, to a long-distance, ultra-high-speed, large-capacity optical system by compensating for frequency modulation of optical soliton pulses due to optical transmission loss in an optical soliton transmission line. The present invention relates to an optical soliton transmission method capable of performing communication economically.

[0002]

2. Description of the Related Art When performing large-capacity optical communication, it is necessary to increase the transmission capacity by narrowing the pulse width of an optical pulse used for communication. Has a group velocity dispersion characteristic and an optical loss wavelength characteristic in which a zero dispersion region exists near a 1.32 μm wavelength band. Therefore, when a linear optical pulse is used, the effect of the group velocity dispersion existing in the optical fiber is obtained. The pulse width of the light pulse is widened, and the degree of the spread becomes more remarkable as the pulse width becomes narrower. With the current technology, it is difficult to further increase the transmission capacity, and there is a limit to increasing the capacity of optical communication.

In order to increase the transmission capacity of the optical pulse, it is necessary to overcome the waveform spread due to the effect of group velocity dispersion and the waveform distortion due to higher-order dispersion.
ppert theoretically showed in 1973 that optical soliton transmission becomes possible by balancing the group velocity dispersion and the self-phase modulation effect in an optical fiber (Ref. 1: A. Hasegawa and F. A.). Tappert, Appl. Phys. Let
t.23 (1973) 142.).

An optical soliton formed in the anomalous dispersion wavelength region of an optical fiber has no transmission loss (optical loss) due to the optical fiber because the spread due to the group velocity dispersion and the compression due to the nonlinear optical effect (optical Kerr effect) are balanced. In this case, there is a characteristic that the light propagates through the optical fiber without changing the waveform. For this reason, the transmission method using the optical soliton is a very promising method for realizing long-distance, large-capacity optical communication.

However, practically used optical fibers have a slight optical loss (0.25 μm in a wavelength band of 1.55 μm).
2 dB / km, the light is weakened by about 5% at a distance of 1 km), the amplitude of the light pulse is reduced even in the case of the optical soliton, and the pulse width is widened accordingly, and the waveform changes.

Heretofore, in order to compensate for the change in the waveform of the optical soliton due to the optical loss, an amplifying effect is provided in the optical transmission line in a distributed manner by using stimulated Raman scattering, and an equivalently lossless optical transmission is performed. A method of making a path and propagating an optical soliton has already been proposed (Reference 2: A. Hasegawa, Appl.
Opt. 23, P. 3302 (1984). Reference 3: LF Mollena
uer, JP Gordon, and MN Islam, IEEE J. Qu
antum Electron. QE22, p.157 (1986).).

This method can provide an ideal optical soliton transmission line, and is an optical transmission method particularly suitable for long-distance propagation.

Further, the optical transmission line does not have an amplifying function,
A method has been proposed in which an optical amplifier is inserted into the optical transmission line at a certain interval and the optical soliton is propagated over a long distance by a method of compensating for the loss of the optical fiber in a lumped manner (Reference 4: Kubota, Nakazawa, Suzuki, Japanese Patent Application No. 1-68619, Reference 5: H. Kubota and
M. Nakazawa, IEEE J. Quantum Electron. QE2
6, p. 692 (1990).).

This method is a highly feasible optical transmission method because a region having an amplifying action can be localized and the configuration is simple.

[0010]

By the way, the optical soliton transmission method using stimulated Raman scattering can provide an ideal optical soliton transmission line, and is suitable for long-distance optical soliton pulse propagation. However, since the configuration of the entire system is complicated, and it is difficult to have a uniform amplification gain over the entire optical transmission line, it is necessary to obtain a lossless optical soliton transmission line at any place. There was a disadvantage that it could not be done. Another disadvantage is that the gain of stimulated Raman scattering is relatively small.

Although the optical soliton transmission method using an optical amplifier can localize an area having an amplifying effect and simplifies the configuration of the entire system, it is extremely feasible.
Since the intensity of the optical soliton pulse decreases due to the optical loss of the optical fiber because the change in the waveform of the high-intensity optical soliton as a non-linear pulse is actively used, there is a limit on the relay distance of the optical transmission line. In addition, the distance between the optical amplifiers in the optical transmission line can be set to only about 50 km, and it is extremely difficult to further extend the distance between the optical amplifiers.

The present invention has been made in view of the above circumstances, and compensates for frequency modulation (phase change), which has conventionally focused only on compensating for a decrease in the intensity of an optical soliton pulse. Focusing on the point, by compensating the frequency modulation of the optical soliton pulse due to the optical transmission loss in the optical soliton transmission line using an optical dispersion compensator having the group velocity dispersion of the opposite sign to the single mode optical fiber, An object of the present invention is to provide an optical soliton transmission method capable of extending a transmission distance of an optical soliton or an installation interval of an optical repeater amplifier in optical soliton transmission and economically performing a long-distance, ultra-high-speed, large-capacity optical communication.

[0013]

In order to solve the above problems, the present invention employs the following optical soliton transmission method.

That is, the optical soliton transmission method according to the first aspect of the present invention is an optical soliton transmission method using an optical soliton formed in a wavelength region of negative group velocity dispersion of a single mode optical fiber. There is an optical transmission loss in a transmission optical fiber, and the nonlinearity associated with this optical transmission loss
And self-dispersion caused by nonlinearity
Causes nonlinear frequency modulation caused by self-phase modulation
In this case, it is characterized in that a non-linear frequency modulation of an optical soliton pulse due to the optical transmission loss is compensated by using an optical dispersion compensator having a group velocity dispersion of a sign opposite to that of the single mode optical fiber.

According to a second aspect of the present invention, there is provided an optical soliton transmission method according to the first aspect, wherein the optical soliton pulse after the nonlinear frequency modulation is compensated for by the optical dispersion compensator is transmitted to an optical amplifier. Amplify using
It is characterized in that the light receiving sensitivity of the optical soliton pulse is improved.

According to a third aspect of the present invention, there is provided an optical soliton transmission method using an optical soliton formed in a wavelength region of negative group velocity dispersion of a single mode optical fiber. Optical transmission loss in fiber
And the nonlinearity and dispersion of the optical transmission loss
Self-phase modulation caused by nonlinearity
When non-linear frequency modulation occurs due to, using one or more stages of optical repeaters comprising optical dispersion compensating means having a group velocity dispersion of the opposite sign to the single mode optical fiber and optical amplifying means, The method is characterized in that the nonlinear frequency modulation of the optical soliton pulse due to the optical transmission loss is compensated, and the optical soliton pulse is amplified to restore the intensity of the optical soliton pulse.

[0017]

According to the optical soliton transmission method according to the first aspect of the present invention, the effect of the optical soliton is used at the beginning of propagation.
Further, after the intensity of the optical soliton pulse is reduced due to the optical transmission loss of the transmission optical fiber, the pulse is propagated as a linear pulse. Then, during optical soliton transmission, optical soliton transmission
The transmission optical fiber has an optical transmission loss.
Non-linearity due to the loss of balance between accompanying non-linearity and dispersibility
Frequency caused by self-phase modulation caused by noise
If the resulting modulated, the spread of the frequency modulation and pulse width of the optical soliton pulses by group velocity dispersion occurring in the linear portion, the optical dispersion compensation having group velocity dispersion of said single-mode optical fiber and opposite sign By using a compensator, the pulse width of the optical soliton pulse being propagated is allowed to spread and the distance over which the optical soliton pulse can be transmitted without relay (the distance over which the optical signal can be transmitted without returning it to an electrical signal). To extend the installation interval of the optical repeater amplifier in optical soliton transmission. Also, as is well known, optical soliton transmission is transmission utilizing a non-linear effect, and the frequency modulation generated in that case is not linear, but non-linear frequency modulation caused by such non-linear transmission. Even so, in the present invention, a large compensation effect is achieved by utilizing the linear compensation effect of the optical dispersion compensator.

Further, in the optical soliton transmission method according to claim 2, in the optical soliton transmission method according to claim 1, the optical soliton pulse after frequency modulation is compensated by the optical dispersion compensator is amplified using an optical amplifier. By doing so, the light receiving sensitivity of the optical soliton pulse is improved, the distance over which the optical soliton pulse can be transmitted without relay is further extended, and the installation interval of the optical repeater amplifier in the optical soliton transmission is extended.

According to a third aspect of the present invention, in the optical soliton transmission method, there is provided an optical repeater comprising an optical dispersion compensating means having a group velocity dispersion having a sign opposite to that of the single mode optical fiber, and an optical amplifying means. Optical soliton transmission optical fiber using more than one step
There is an optical transmission loss, and the nonlinearity and
Self caused by nonlinearity due to disparity in dispersibility
By compensating for the nonlinear frequency modulation of the optical soliton pulse caused by the phase modulation and amplifying the optical soliton pulse, the intensity of the optical soliton pulse is recovered, and the distance over which the optical soliton pulse can be transmitted without relay is further extended. And enables long-distance multi-relay optical soliton transmission.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows an optical soliton transmission system S as an embodiment of the optical soliton transmission method according to claim 1 of the present invention.
2A to 2C are diagrams schematically showing the waveforms of the optical soliton pulses in the portions A to C of the optical transmission line in FIG.

In FIG. 1, 1 is an optical soliton generator, 2
Denotes an optical fiber (optical fiber) for transmitting an optical soliton, 3 denotes an optical dispersion compensator, and 4 denotes a light receiver.

The optical soliton generator 1 generates an optical soliton pulse in a wavelength band of 1.55 μm. For example, a soliton laser composed of a mode-locked F center laser and a polarization maintaining single mode fiber is preferable. Used for

The optical fiber 2 is, for example, a silica-based single mode optical fiber having a group velocity dispersion characteristic and a light loss wavelength characteristic in which a zero dispersion region exists near a 1.32 μm wavelength band.

The optical dispersion compensator 3 has a group velocity dispersion having a sign opposite to that of the optical fiber 2, and performs frequency modulation of an optical soliton pulse due to group velocity dispersion generated in a linear portion thereof during optical soliton transmission. This is to compensate for the spread of the pulse width.

For example, when the wavelength band of the optical soliton pulse used is 1.5 μm, the optical dispersion compensator 3 is a silica-based dispersion shift in which the zero dispersion wavelength is shifted to a longer wavelength side than 1.5 μm. Fiber (having positive group velocity dispersion), GT interferometer, Fabry-Perot resonator, or lithium niobate (LiNbO ₃ ) or rutile titanium dioxide (TiO ₂ ; also known as “titania”), tellurium dioxide (TeO ₂₎ ), Or an optical fiber or an optical waveguide using them.

The optical receiver 4 receives the optical soliton pulse compensated by the optical dispersion compensator 3 and converts it into an electric signal. For example, an avalanche photodiode (AP)
D) and the like are preferably used.

Next, the operation of the optical soliton transmission system S will be described.

First, an electric signal is converted into an optical soliton pulse by the optical soliton generator 1, and the optical soliton pulse is incident on the optical fiber 2 and propagates through the optical fiber 2.

The optical soliton pulse has a high intensity and a narrow waveform when it first enters the optical fiber 2 (FIG. 2).
(A)), while propagating through the optical fiber 2, the intensity is reduced and the nonlinearity is weakened by the optical loss of the optical fiber 2, and the pulse width is reduced by the negative group velocity dispersion of the optical fiber 2. As it spreads, it has frequency modulation (chirping) (FIG. 2B).

In this state, since adjacent optical soliton pulses overlap each other, it becomes impossible to detect individual signals.

These deformed optical soliton pulses pass through the optical dispersion compensator 3 so that the pulse width is recovered and the frequency modulation is also compensated (FIG. 2C). The intensity of the optical soliton pulse is reduced (in this example, 1/100 or less).
However, the waveform is the same (similar shape) as that at the time of incidence. As a result, the optical soliton pulses overlapping each other are clearly separated, and the signal can be detected again. Also, as is well known, optical soliton transmission is transmission utilizing a nonlinear effect, that is, as described above , optical soliton transmission.
Is the spread due to group velocity dispersion and the nonlinear optical effect (optical
Effect) is balanced by the compression
If there is no transmission loss (light loss) due to
Although it has the characteristic of propagating without changing the waveform,
If there is a loss in the fiber, the nonlinearity and
The frequency modulation caused by the disperse imbalance does not become linear, but even in the case of nonlinear frequency modulation caused by such non-linear transmission, the linear dispersion of the optical dispersion compensator in the present invention. A large compensation effect is achieved using the compensation effect.

The optical soliton pulse whose pulse width has been recovered is
The light is converted into an electric signal again by the light receiver 4 and extracted as a signal.

FIG. 3 shows an example of the result of simulation analysis using a computer in order to confirm the effect of dispersion compensation of optical soliton pulses in the optical soliton transmission system S of the above embodiment.

This figure shows how the waveform of the optical soliton pulse changes when the dispersion compensation amount (ps / nm) of the optical dispersion compensator is used as a parameter.

Here, the half width τ of the optical soliton pulse
It was assumed that the _FWHM was 10 ps, the wavelength was 1.55 μm, the length of the optical fiber was 100 km, the optical transmission loss was 0.24 dB / km, and the group velocity dispersion was −2.0 ps / km / nm.

The broken line in the figure shows the waveform of the input undistorted optical soliton pulse for reference. As described above, since the pulse intensities differ by more than 100 times before and after propagation, they are shown in a reduced scale.

From these results, it can be seen that in the case of an optical pulse without dispersion compensation (when the dispersion compensation amount is 0 ps / nm), the pulse width is widened and the wave height is low, but the pulse width becomes narrower as the dispersion compensation amount is increased. And the dispersion compensation amount is 16
It can be seen that at 0 ps / nm, the waveform has been recovered to a waveform having substantially the same shape as the input optical soliton pulse. On the other hand, when the dispersion compensation amount is set to 180 ps / nm or more, the waveform is distorted, and it can be seen that dispersion compensation cannot be performed when the dispersion compensation amount exceeds a certain value.

FIG. 4 shows another example of the result of simulation analysis performed by a computer for confirming the effect of the present invention. The relationship between the pulse width of the optical soliton pulse and the dispersion compensation amount is shown. FIG.

In the figure, the horizontal axis is the amount of dispersion compensation (ps / nm),
The vertical axis is the pulse width (ps).

Here, the half width τ of the optical soliton pulse
_FWHM : 10 ps, wavelength: 1.55 μm, optical fiber transmission loss: 0.24 dB / km, group velocity dispersion: -2.0
ps / km / nm, and three types of optical fiber lengths (Z) of 60, 80, and 100 km were assumed.

From this result, even when the length (transmission distance) of the optical fiber is different, the optical soliton pulse whose pulse width has been changed by adjusting the dispersion compensation amount can be reduced to almost the same pulse width as the input optical soliton pulse. You can see that you can recover.

FIG. 5 is a diagram showing the result of a simulation analysis for confirming the effect of the present invention when an optical soliton pulse pair is made incident on an optical fiber and propagated, and corresponds to FIG. is there.

Here, the pulse interval of the optical soliton pulse pair is set to 50 ps, and the half width τ _FWHM of each pulse is set to 10 p.
s, wavelength 1.55μm, optical fiber length 100k
m, optical transmission loss 0.24 dB / km, group velocity dispersion-
2.0 ps / km / nm was assumed.

From these results, when dispersion compensation is not performed,
Although optical pulses overlap each other and cannot detect individual signals, the amount of dispersion compensation is 160 ps / nm.
Thus, optical soliton pulse pairs are clearly separated, and individual signals can be clearly identified. Further, it can be seen that when the dispersion compensation amount is increased to 180 ps / nm or more, the waveform is distorted and dispersion compensation cannot be performed.

As described above, according to the optical soliton transmission system S of this embodiment, the optical soliton due to the optical transmission loss is used by using the optical dispersion compensator 3 having the group velocity dispersion of the opposite sign to the optical fiber 2. Since the frequency modulation of the pulse is compensated, the optical soliton pulse compensates for the frequency modulation of the optical soliton pulse and the spread of the pulse width due to the group velocity dispersion generated in the linear part during transmission, and It is possible to extend the pulse width of the soliton pulse and extend the distance over which the optical soliton pulse can be transmitted without relay. Therefore, the length of the optical fiber can be set to 100 km or more.

In the optical soliton transmission system S, the optical soliton pulse has a higher signal-to-noise ratio (S / N ratio) after propagation because the pulse is higher in intensity than a linear pulse. If the S / N ratio is taken, the light can be propagated over a longer distance. Furthermore, while the effect of the soliton is maintained even partially, the change in waveform and the amount of frequency modulation (chirping) generated are smaller than those of a linear pulse (the waveform does not change in an ideal optical soliton). And there is no frequency modulation), and the amount of optical dispersion compensation required after propagating the same distance may be smaller than that using propagation using linear pulses.

Also, the optical soliton transmission system S can be combined with a lumped optical amplifier. In multi-repeater optical soliton transmission using this combination, the installation interval of the optical amplifier can be extended. In addition, it is possible to extend the distance in which relayless transmission can be performed as compared with a case where the present method is not used. In this case, as the optical amplifier, a semiconductor laser amplifier, an erbium (Er) -doped optical fiber amplifier, or the like is preferable.

As described above, it is possible to provide an optical soliton transmission method that can extend the transmission distance of optical solitons and economically perform long-distance, ultra-high-speed, large-capacity optical communication.

FIG. 6 is a schematic diagram showing the configuration of a multi-repeater optical soliton transmission system M which is an embodiment of the optical soliton transmission method according to the third aspect of the present invention.

This multi-repeater optical soliton transmission system M
An optical repeater 5 is connected after the optical fiber 2, and the optical repeater 5 is used to perform a series of operations of compensating the frequency modulation of the optical soliton pulse due to the optical transmission loss and amplifying the light intensity in a plurality of stages (N is obtained by the n _n until stage) repeating it from _one stage.

In this multi-repeater optical soliton transmission system M, an optical soliton generator 1, an optical fiber 2, a light receiver 4
Are exactly the same as the components of the optical soliton transmission system S, so that the description of these components will be omitted, and only the optical repeater 5 different from the components will be described.

The optical repeater 5 includes an optical dispersion compensator 6 and an optical amplifier 7.

The optical dispersion compensating means 6 has a group velocity dispersion having a sign opposite to that of the optical fiber 2, and performs frequency modulation of an optical soliton pulse due to group velocity dispersion generated in a linear portion thereof during optical soliton transmission. This is to compensate for the spread of the pulse width.

As the optical dispersion compensating means 6, as in the optical dispersion compensator 3 of the above embodiment, for example, when the wavelength band of the optical soliton pulse used is 1.5 μm, the zero dispersion wavelength is set to 1.5 μm. Silica-based dispersion-shifted fiber (having a positive group velocity dispersion) shifted to a longer wavelength side, GT
Interferometer, Fabry-Perot resonator, or lithium niobate (LiNbO ₃ ) or rutile titanium dioxide (Ti
O ₂ ; also known as “titania”), a crystal such as tellurium dioxide (TeO ₂ ), or an optical fiber or an optical waveguide using them is preferably used.

The optical amplification means 7 amplifies the light intensity of the optical soliton pulse whose intensity has been reduced due to the optical transmission loss of the optical fiber 2. For example, for a pulse in the wavelength band of 1.5 μm, a semiconductor laser amplifier, erbium An (Er) -doped optical fiber amplifier or the like is preferably used.

The optical amplifying means 7 does not need to limit the type of the optical amplifier when a high-level function is not required. The optical amplifier provided before the light receiver 4 is preferably a preamplifier type, and the optical amplifier provided before the optical fiber 2 to obtain a large optical soliton pulse is preferably a main amplifier type.

Next, the operation of the multi-repeater optical soliton transmission system M will be described.

The optical soliton pulse incident on the optical fiber 2 of the first stage (N ₁ ) by the optical soliton generator 1 has its pulse width recovered by the optical dispersion compensating means 5 of the optical repeater 5 and the frequency modulation is also compensated. The light intensity is amplified by the light amplifying means 6 to recover the intensity of the optical soliton pulse reduced by the optical loss of the optical fiber 2.

The optical soliton pulse whose intensity has been recovered is thereafter incident on the optical fiber 2 of the second stage (N ₂ ), and the pulse width is recovered by the optical dispersion compensating means 5 of the optical repeater 5 and the frequency The modulation is also compensated, and the light intensity is amplified by the light amplification means 6, and the reduced intensity of the optical soliton pulse is restored.

Thereafter, optical dispersion compensation and optical amplification are repeatedly performed by the optical repeater 5 at each stage, and after the light enters the optical fiber 2 at the final stage (N _n ), the pulse width is recovered in the same manner as described above. The frequency modulation is also compensated, and the light intensity is also recovered, and is again converted into an electric signal by the light receiver 4 and extracted as a signal.

FIG. 7 shows an example of the result of simulation analysis using a computer to confirm the effects of optical dispersion compensation and optical amplification of optical soliton pulses in the multi-repeater optical soliton transmission system M of the above embodiment. It shows.

FIG. 7 shows how a pulse waveform changes on the output side of the optical repeater 5 at each stage in FIG. 6 using an optical soliton pulse pair as an input.

Here, the half width τ of each optical soliton pulse
_FWHM 10ps, wavelength 1.55μm, pulse interval 5
0 ps, the length of each optical fiber is 100 km, each optical transmission loss is 0.24 dB / km, and the group velocity dispersion is-
2.0 ps / km / nm, dispersion compensation amount 160 ps / n
m. This dispersion compensation amount is the same as the optimum value in FIG.

FIG. 8 shows, by way of comparison, a waveform of a pulse transmitted by multi-repeating transmission according to a conventional method using an optical soliton pulse pair under the same conditions as in FIG. 7 for comparison. . However, the length of each optical fiber is 25 km
It is.

From these results, while the conventional method has a short transmission distance and remarkably saves the waveform, the method of the present embodiment clearly separates the optical soliton pulse pairs and clearly identifies individual signals. It can be seen that it is possible to propagate a clear optical soliton pulse pair at a high information transmission rate (high bit rate) over 2000 km or more as a whole.

The distance between the optical fibers (the installation interval of the optical amplifiers) is more than doubled (four times in this example) by using this method, and long-distance transmission is possible with a small number of optical amplifiers. Economical optical soliton communication is possible.

As described above, according to the multi-repeater optical soliton transmission system M of this embodiment, the optical dispersion compensating means 6 having the group velocity dispersion of the opposite sign to the optical fiber 2 and the optical amplifying means 7 are provided. By using a plurality of optical repeaters 5 provided to compensate for the frequency modulation of the optical soliton pulse due to the optical transmission loss and to amplify the optical soliton pulse to recover the reduced intensity of the optical soliton pulse. The distance over which the optical soliton pulse can be transmitted without relay can be further extended, and the installation interval of the optical repeater 5 in the optical soliton transmission can be extended. Therefore, a high information transmission rate (high bit rate) over 2000 km or more can be achieved. This makes it possible to perform multi-repeater optical soliton transmission.

As described above, it is possible to provide an optical soliton transmission method capable of extending the installation intervals of optical amplifiers in optical soliton transmission and economically performing long-distance, ultra-high-speed, large-capacity optical communication. become.

In the multi-repeater optical soliton transmission system M, the position where the optical dispersion compensator is inserted may be either (1) the output end of the optical fiber or (2) the output end of the optical amplifier. The same effect can be shown.

The optical dispersion compensator does not need to be an independent device. For example, the optical amplifier may have a dispersion characteristic and also serve as the optical dispersion compensator.

In all of the above embodiments, the amplitude of the input optical soliton pulse is set to 1.
Reference 5, which takes about 5 times to extend the transmission distance
Method 5 is used in combination.

Further, the intensity of the output optical soliton pulse from the optical soliton generator or optical repeater can be set to the amplitude A = 1 or the amplitude A> 1 (references 4 and 5 described above). If A> 1, a further effect of extending the relay distance can be expected.

[0074]

As described above in detail, according to the optical soliton transmission method according to the first aspect of the present invention, the optical soliton formed in the wavelength region of the negative group velocity dispersion of the single mode optical fiber is provided. In the optical soliton transmission method used, when the optical fiber for optical soliton transmission has an optical transmission loss, an optical soliton transmission line is provided by using an optical dispersion compensator having a group velocity dispersion having a sign opposite to that of the single mode optical fiber. Optical transmission loss
There is a nonlinearity and dispersion fishing due to this optical transmission loss.
Self-phase modulation caused by nonlinearity
The optical soliton pulse caused by the nonlinear frequency modulation is compensated for, so that the optical soliton pulse frequency modulation and pulse width spread due to group velocity dispersion generated in the linear part during transmission To compensate for
It is possible to extend the pulse width of the optical soliton pulse during propagation and extend the distance over which the optical soliton pulse can be transmitted without relay. Further, the optical soliton transmission, as is known a transmission utilizing a nonlinear effect, i.e. optical soliton
Is the spread due to group velocity dispersion and the nonlinear optical effect (optical
Effect) is balanced by the compression
If there is no transmission loss (light loss) due to
Although it has the characteristic of propagating without changing the waveform,
If there is a loss in the fiber, the nonlinearity and
The frequency modulation caused by the disperse imbalance does not become linear, but even in the case of nonlinear frequency modulation caused by such non-linear transmission, the linear dispersion of the optical dispersion compensator in the present invention. A large compensation effect is achieved using the compensation effect.

Therefore, it is possible to provide an optical soliton transmission method capable of economically performing long-distance, ultra-high-speed, large-capacity optical communication.

According to the optical soliton transmission method according to the second aspect, in the optical soliton transmission method according to the first aspect, the optical soliton pulse after frequency modulation is compensated by the optical dispersion compensator using an optical amplifier. As a result, the light receiving sensitivity of the optical soliton pulse can be improved, and the distance over which the optical soliton pulse can be transmitted without relay can be further extended.

Therefore, it is possible to provide an optical soliton transmission method that can extend the installation interval of optical amplifiers in optical soliton transmission and economically perform long-distance, ultra-high-speed, large-capacity optical communication. .

According to a third aspect of the present invention, there is provided an optical soliton transmission method using an optical soliton formed in a wavelength region of negative group velocity dispersion of a single mode optical fiber. When there is an optical transmission loss in the optical fiber, the optical dispersion compensating means having the group velocity dispersion of the opposite sign to the single-mode optical fiber, and an optical repeater having an optical amplifying means using one or more stages, Optical soliton transmission
There is an optical transmission loss in the path, and the nonlinear
Due to non-linearity due to loss of balance between dispersiveness and dispersibility
Compensating the nonlinear frequency modulation of the optical soliton pulse caused by the self-phase modulation and amplifying the optical soliton pulse and restoring the intensity of the optical soliton pulse, it is possible to restore the intensity of the optical soliton pulse. Thus, the distance over which the optical soliton pulse can be transmitted without relay can be further extended, and multi-relay optical soliton transmission can be performed at a high information transmission rate (high bit rate).

Accordingly, it is possible to provide an optical soliton transmission method that can extend the installation interval of optical repeaters in optical soliton transmission and can economically perform long-distance, ultra-high-speed, large-capacity optical communication with multiple relays. Becomes possible. In particular,
Depending on transmission conditions, high information transmission over 2000 km
It is possible to propagate a beautiful soliton pulse at the feed speed
It will work.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a configuration of an optical soliton transmission system S of an embodiment of an optical soliton transmission method according to claim 1 of the present invention.

FIG. 2 is a diagram schematically showing a waveform of an optical soliton pulse in each of the portions A to C of the optical transmission line in FIG.

FIG. 3 is an optical soliton transmission system S according to one embodiment of the present invention;
FIG. 6 is a diagram showing a relationship between the amount of dispersion compensation and the optical soliton pulse waveform.

FIG. 4 is an optical soliton transmission system S according to an embodiment of the present invention;
FIG. 4 is a diagram showing a relationship between a pulse width of an optical soliton pulse and a dispersion compensation amount.

FIG. 5 is an optical soliton transmission system S according to an embodiment of the present invention.
FIG. 6 is a diagram showing a relationship between the dispersion compensation amount of the above and the waveform of an optical soliton pulse pair.

FIG. 6 is a schematic diagram showing a configuration of a multi-repeater optical soliton transmission system M according to an embodiment of the optical soliton transmission method according to claim 3 of the present invention.

FIG. 7 is a diagram showing a state of a change in a pulse waveform on the output side of the optical amplifier in each stage of the multi-repeater optical soliton transmission system M according to one embodiment of the present invention.

FIG. 8 is a diagram showing a state of a change in a pulse waveform on the output side of an optical amplifier in each stage of a conventional multi-relay optical soliton transmission system.

[Explanation of symbols]

S Optical soliton transmission system 1 Optical soliton generator 2 Optical fiber for optical soliton transmission (optical fiber) 3 Optical dispersion compensator 4 Optical receiver M Multi-repeater optical soliton transmission system 5 Optical repeater 6 Optical dispersion compensation means 7 Optical amplification means N _{1 to} N _n stages

Claims (3)

(57) [Claims] 1. An optical soliton transmission method using an optical soliton formed in a wavelength region of negative group velocity dispersion of a single mode optical fiber, wherein the optical fiber for optical soliton transmission has an optical transmission loss.
Breaking the balance between nonlinearity and dispersion due to optical transmission loss
Non-linearity caused by self-phase modulation due to more nonlinearity
Compensating for nonlinear frequency modulation of an optical soliton pulse due to the optical transmission loss by using an optical dispersion compensator having a group velocity dispersion of a sign opposite to that of the single mode optical fiber when linear frequency modulation occurs. An optical soliton transmission method comprising: 2. The optical soliton transmission method according to claim 1, wherein the optical soliton pulse after the nonlinear frequency modulation is compensated for by the optical dispersion compensator is amplified using an optical amplifier. Method. 3. An optical soliton transmission method using an optical soliton formed in a wavelength region of negative group velocity dispersion of a single mode optical fiber, wherein the optical fiber for optical soliton transmission has an optical transmission loss.
Breaking the balance between nonlinearity and dispersion due to optical transmission loss
Non-linearity caused by self-phase modulation due to more nonlinearity
In the case where linear frequency modulation is generated , the light is transmitted using one or more optical repeaters each including an optical dispersion compensating unit having a group velocity dispersion having a sign opposite to that of the single mode optical fiber and an optical amplifying unit. An optical soliton transmission method, comprising compensating for nonlinear frequency modulation of an optical soliton pulse due to transmission loss and amplifying the optical soliton pulse.