JP3497598B2 - Optical fiber transmission line - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [0001] BACKGROUND OF THE INVENTION The present invention relates generally to optical fiber transmission.
Path, especially for nonlinear optical fiber suitable for long-distance transmission of signal light.
Related to fiber transmission lines. [0002] 2. Description of the Related Art Long-distance single-mode optical fiber transmission
When the modulated light propagates through the path, first, the wavelength component of the optical fiber
Dispersion causes waveform distortion, resulting in large transmission characteristics
to degrade. To prevent this, use a zero-dispersion fiber
To reduce the fiber chromatic dispersion to zero by using
There is a way. However, the chromatic dispersion of an optical fiber transmission line is zero.
, The transmission characteristics deteriorate due to four-photon mixing.
Instead, light with small negative dispersion
Fiber and compensating optical fiber with positive dispersion
Are connected alternately to avoid local variance of zero.
It is known how to make the variance zero as a whole.
Have been. According to this method, the light intensity of the signal light is low.
In this case, it is possible to prevent degradation of transmission characteristics due to chromatic dispersion.
it can. However, since the light intensity of the signal light is low,
Requires a large number of transmission lines and increases the cost of transmission lines.
You. [0005] SUMMARY OF THE INVENTION An optical filter having a positive dispersion
Fiber and negative dispersion optical fiber are connected alternately.
The transmission distance is long and the light intensity
If the phase is not low enough,
The tonal effect (Kerr effect) broadens the light spectrum,
As a result, the effect of chromatic dispersion is magnified, resulting in poor transmission characteristics.
Will be caused. [0006] By solving this problem, long-distance signal transmission
As a method of changing the phase conjugate,
A wavelength converter generated before and after the converter.
Methods for canceling scattering and non-linear effects are known. However, the optical filters on both sides of the phase conjugate converter
The light intensity of the transmission line is not symmetric with respect to the phase conjugate converter.
For this reason, ordinary singles without special control of the core diameter
In the conventional method using multimode optical fiber, the ideal
There is a problem that cancellation is impossible. The present invention has been made in view of the above points.
The purpose is to use an optical fiber transmission line.
A phase conjugate converter in the middle of
Optical distortion that cancels out waveform distortion due to
Light intensity change in optical fiber transmission line
Optical fiber transmission line that makes the cancellation more complete in consideration of
It is to provide. [0009] According to the present invention, one end has
The other end is connected to the transmitter and the other end is connected to the phase conjugate converter.
One single-mode optical fiber and one end
A second sing connected to the second converter and the other end connected to the receiver
Optical fiber transmission line consisting of multimode optical fiber
And moving the second optical fiber forward from the phase conjugate converter.
Tentatively in the first, second,.
And splitting the first optical fiber into the position.
The second optical fiber is transmitted from the phase conjugate converter to the transmitter.
The first, second,.
When the optical fiber is virtually divided into n minute sections, the first optical fiber
In each of the first to nth minute sections of Iva, the light intensity and
The wavelength component of these small sections for the product of the Kerr effect constant
The ratios of the scattered values correspond to the corresponding first to n-th optical fibers.
For the product of the light intensity and the constant of the Kerr effect in a minute section
Make it equal to the ratio of the chromatic dispersion values of these minute sections.
The first and second optical filters in each of the minute sections
Iva core diameter, light intensity, Kerr effect constant, wavelength dispersion
Which parameters are determined, and the length of each minute section is
For each two corresponding minute sections, the light intensity and the car
Proportional to the reciprocal of the product of the effect constants or the reciprocal of the chromatic dispersion valueAnd
And the first or second optical fiber is a polarization-maintaining light.
Consisting of fiber,Optical fiber transmission line characterized by the following:
Is provided. [0010] According to the present invention, the first and second optical fibers are
Parameters such as core diameter, light intensity, Kerr effect constant, and chromatic dispersion
Parameters are defined as above, and the length of each minute section
Is calculated for each two corresponding minute sections by the light intensity of the minute section.
Proportional to reciprocal of product of Kerr effect constant or reciprocal of chromatic dispersion value
The chromatic dispersion of the optical fiber transmission line.
And the waveform distortion due to the Kerr effect can be almost completely canceled
it can. [0011] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, the principle of the present invention will be described with reference to FIG.
You. The optical signal that has exited the optical transmitter 6 has a first single mode
Propagating through an optical fiber (for example, a polarization-maintaining optical fiber) 2
Then, it enters the phase conjugate converter 8. The phase conjugate converter 8 has undergone phase conjugate conversion.
The optical signal propagates through the second single mode optical fiber 4
Received by the receiver 10. Where the second optical fiber
Consider the wavelength change that occurs in 4 and the waveform change due to the Kerr effect
The light amplitude is based on the nonlinear Schrodinger equation
To develop. That is, if the amplitude is A, the fiber transmission
The change in the carrying direction is idA / dx = (Dd^Two/ Dt^Two+ Κ | A |^Two) A Becomes Here, x is the propagation direction of the second optical fiber 4.
Distance, D is the magnitude of chromatic dispersion of the second optical fiber 4, κ
Is the coefficient of the Kerr effect. D and κ are equal in the optical fiber.
It may be constant or may change. The light in the second optical fiber 4 is subjected to phase conjugate conversion.
, The amplitude is actually A ^*Phase conjugate wave
And therefore the spatial development is idA^*/ Dx = (Dd^Two/ Dt^Two+ Κ | A |^Two) A^* Becomes Here, the second optical fiber 4 is subjected to phase conjugate conversion.
First minute section 4 from the receiver 8 to the receiver 10₁, Second fine
Subsection 4_Two... j-th minute section 4_j, ... n-th minute section
Interval 4 _nIs virtually divided into In each minute section, the wave
The long dispersion value D, the Kerr effect coefficient κ and the light intensity A are constant.
And Then, in the first optical fiber 2, D, κ and
The light intensity A corresponds to each minute area in the second optical fiber 4.
Suppose there is a corresponding minute interval equal to the interval.
That is, the first optical fiber 2 is transmitted from the phase conjugate converter 8
First minute section 2₁, 2nd minute section 2_Two
... j-th minute section 2_j..., N-th minute section 2_nTemporarily
And split each minute section of the first optical fiber 2 into a second section.
Corresponding to each minute section of the optical fiber 4. That is, the first minute section of the first optical fiber 2
2₁To the first minute section 4 of the second optical fiber 4₁Compatible with
And the second minute section 2 of the first optical fiber 2_TwoThe second light
Second minute section 4 of fiber 4_Two... 1st
N-th minute section 2 of the optical fiber 2_nThe second optical fiber
N-th minute section 4 of 4_nTo correspond to. Light intensity in each minute section of the first optical fiber 2
Change in degree A idA / dx = (Dd^Two/ Dt^Two+ Κ | A |^Two) A And its complex conjugate   -IdA^*/ Dx = (Dd^Two/ Dt^Two+ Κ | A |^Two) A^* In consideration of this, in this minute section of the second optical fiber 4,
The change occurs in the light in the corresponding minute section of the first optical fiber 2.
Fiber 2 retrograde change, i.e., replaced x with -x
Equal to change in case. Up to this point, the first and second optical fibers 2,
The light intensity, dispersion and Kerr effect of each corresponding minute section of 4
Was based on the assumption of equality, but in practice
The light intensity in the second optical fiber 4 decreases along the fiber
However, since it becomes an increasing form with the inserted amplifier, the second
A change in light intensity symmetrical to the optical fiber 4 is caused by the first optical fiber 2
It is difficult to make inside. To solve this problem, the first optical fiber
Fiber 2 and corresponding minute section in second optical fiber 4
Standardized nonlinear light, assuming that the light intensity of
So that the Schrodinger equations have the same shape
Just fine. Specifically, the first optical fiber 2 and the second optical fiber 2
Light intensity | A in the corresponding minute section of the optical fiber 4
|^TwoFor κ | A |^TwoAnd D have the same ratio
The value in the first optical fiber 2 is
Make it a constant multiple of the value. Κ and D are, for example, functions of the core diameter of the optical fiber.
Therefore, the first optical fiber 2 or the second optical fiber
This condition can be satisfied by controlling the core diameter of No. 4.
Can be. Thus, Schrodinger of spatial development
The right side of the equation, except for a constant multiple, is the first optical fiber 2
The same in the minute section and the corresponding minute section of the second optical fiber 4.
It becomes one form. Next, this constant multiple is the speed of spatial development of the amplitude.
Is determined, the length of the corresponding minute section is κ | A |^Twoof
It is determined to be proportional to the reciprocal or the reciprocal of D. That is,
The length of the minute section in one optical fiber 2 is
It will be a constant fraction of the length of the corresponding minute section in bar 4.
Decide. Thus, the first optical fiber 2 and the
The relationship between the characteristics of the two optical fibers 4 is determined. Next, referring to FIG. 2, an embodiment of the present invention will be described.
Such an optical fiber transmission line will be described. For example, the second
Optical fiber 12 includes a plurality of optical amplifiers 16 in the middle.
Given as a transmission path, the light intensity in the second optical fiber 12
Suppose the degree was determined as a function of location. Second optical fiber
Since the bus 12 constitutes a main transmission path, a single mode optical fiber is provided.
And its core diameter is uniform. At this time, the direction from the phase conjugate converter 8
Thus, the characteristics of the second optical fiber 12 for each minute section
In order to match the characteristics of the first optical fiber 14, the first
Adjust the core diameter of the optical fiber 14 and the length of its minute section
I do. Of course, light loss occurs depending on the length of each minute section.
Therefore, as the light goes up the first optical fiber 14, the light intensity becomes
Will increase. In this way, the first optical fiber 14
Is higher than the light intensity of the second optical fiber 12
For example, the light intensity in the second optical fiber 12 which is the actual transmission line
The information of the degree change is compressed in the length direction, and the fiber core diameter
The first optical fiber 14 transferred to the
The optical transmitter 6 and the phase conjugate converter 8 are connected by a bus 14. An example
For example, the length of the first optical fiber 14 is 100 km.
The length of the second optical fiber 12 is 5000 km.
You. The first optical fiber described with reference to FIG.
The control of the core diameter of 14 is, of course, a logical case.
Changes stepwise without continuously changing the core diameter in the length direction
Even so, there are some effects. In the embodiment shown in FIG. 2, the phase conjugate converter
Through the second optical fiber 12 connecting the receiver 8 and the receiver 10.
I explained the case of using as a transmission route, but this is
Conversely, the first light connecting the transmitter 6 and the phase conjugate converter 8
The fiber 14 is used as a main transmission line having a constant core diameter,
The core diameter and the length of the minute section of the second optical fiber 12 are controlled.
You may control it. [0030] According to the present invention, an optical fiber transmission line is provided.
A phase conjugate converter is placed in the
Optical fiber that cancels out waveform distortion due to the
In the transmission line, the core diameter of the fiber and its partial length
Adjustments were made, so the chromatic dispersion and Kerr effect of the transmission line
The effect is that the waveform distortion due to
I do.

[Brief description of the drawings] FIG. 1 is a diagram illustrating the principle of the present invention. FIG. 2 is an explanatory view of one embodiment of the present invention. [Explanation of symbols] 2,14 first optical fiber 4,12 second optical fiber 6 Optical transmitter 8 Phase conjugate converter 10 Receiver 16 Optical amplifier

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Claims (1)

(57) [Claim 1] A first single mode optical fiber having one end connected to a transmitter and the other end connected to a phase conjugate converter, and one end connected to the phase conjugate converter. An optical fiber transmission line comprising a second single mode optical fiber having the other end connected to a receiver, wherein the second optical fiber is directed from the phase conjugate converter to the receiver by first, second, and third optical fibers. .. While virtually dividing into nth minute sections, the first optical fiber is directed from the phase conjugate converter to the transmitter so as to correspond to each minute section of the second optical fiber. When virtually divided into 1, 2,..., N-th minute sections, each of the first to n-th minute sections of the first optical fiber has a small value corresponding to the product of the light intensity and the constant of the Kerr effect. The ratio of the chromatic dispersion values of the section is the second optical fiber. The first and second sections in each of the minute sections are set to be equal to the ratio of the chromatic dispersion value of the minute sections to the product of the light intensity and the constant of the Kerr effect in the corresponding first to nth minute sections. Optical fiber core diameter, light intensity, Kerr effect constant,
A parameter such as a chromatic dispersion value is determined, and the length of each of the minute sections is proportional to the reciprocal of the product of the light intensity and the Kerr effect constant or the reciprocal of the chromatic dispersion value for each of the two corresponding minute sections. And the first or second optical fiber is a polarization-maintaining light.
Made from the fiber, the optical fiber transmission path, characterized in that.