JPH08146472A - Optical soliton communication method - Google Patents

Abstract

PURPOSE: To provide a cost effective and practicable soliton communication system. CONSTITUTION: Optical fibers F1, F2, F3...Fn which respectively have lengths Z1, Z2, Z3...Zn and dispersion values D1, D2, D3...Dn and are connected serially are so selected that the average values by the distance of the values of their group velocity dispersion attain abnormal dispersion in order to enable soliton communication. Namely, the free selection of the lengths Z1 to Zn and dispersion values D1 to Dn of the respective optical fibers F1 to Fn is possible within the range satisfying these conditions. The yield in the production of the optical fibers F1 to Fn is thus greatly improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to optical communication, and more particularly to an optical soliton communication method.

[0002]

2. Description of the Related Art A single mode optical fiber is used as a transmission line for transmitting an optical soliton, and it has been conventionally said that its chromatic dispersion characteristic must have anomalous dispersion characteristic. Furthermore, for recent large-capacity optical communication, the value of group velocity dispersion (hereinafter referred to as dispersion value) is 1 ps / km / n.
It is necessary to make the value as small as about m or less, and to suppress the variation of the dispersion value as small as half or less. For this reason, conventionally, only the optical fibers satisfying the above conditions have been selected and used to create an optical fiber line for soliton transmission.

[0003]

By the way, when manufacturing an optical fiber which is a transmission line for optical communication, the dispersion value is distributed with a certain spread around the design value. In order to perform ideal soliton transmission, the width of its distribution is narrow and a transmission line with a constant value is preferable, but when selecting only optical fibers with a specific dispersion value, the yield of optical fibers is poor. turn into. This leads to a high cost of the optical soliton transmission line, which has been a major obstacle to practical use.

In order to solve this problem, the present invention is a new communication method capable of performing soliton transmission using optical fibers having various dispersion values, and realizes economical and practical soliton communication. Is intended.

[0005]

Optical solitons have a characteristic distance called a "soliton cycle", and solitons are stable against various fluctuations that occur over a shorter distance than the soliton cycle. . Utilizing this effect,
It has been reported that solitons can be stably transmitted when the dispersion fluctuates slightly in the anomalous dispersion (negative dispersion) region ([1] LFMollenauer, SGEvangelides, and HAHau.
s: "Long distance soliton propagation using lumped a
mplifiers and dispersion-shifted fiber ", IEEE J. Ligh
twave Technol.vol.9,1991, pp.194-197. [2] A. Hasegaw
a and Y. Kodama: "Guiding-center soliton in fibers w
ith periodically varying dispersion ", Opt. Lett., 199
1, vol.16, pp.1385-1387).

According to the present invention, the average dispersion is abnormal even when a transmission line having a normal dispersion (positive dispersion) region, which has been said that solitons cannot exist stably until now, is used. We take advantage of this effect by newly showing that solitons can propagate with dispersion (ie, negative dispersion).

[0007] Specifically, it is characterized in that optical fibers having a length shorter than the soliton period are spliced so that the average dispersion value has anomalous dispersion characteristics. In this way, an optical amplifier is inserted at an interval shorter than the soliton period in the optical transmission line in which the dispersion is largely changed between positive and negative and the average value thereof becomes a negative value, and soliton multi-repeater transmission is realized.

According to the second aspect of the invention, the average dispersion value is made to have a normal dispersion characteristic, and the dark soliton is propagated.

[0009]

By using the present invention, an optical fiber having various positive and negative dispersion values can be used as a transmission line for performing soliton transmission, so that a soliton transmission line can be economically produced, and therefore, it is economical. And practical soliton communication can be realized.

[0010]

Embodiments of the present invention will be described in detail below with reference to the drawings. <First Embodiment> FIG. 1 is a diagram showing a configuration example of a soliton transmission line using the present invention, in which F1, F
2, F3 ... Fn are optical fibers. The optical fibers F1 to Fn have lengths Z1, Z2, Z3 ... Zn, respectively.
And the dispersion values D1, D2, D3 ... Dn, and are serially connected.

Assuming that n fibers Fi (i = 1 to n) each have dispersion Di and length Zi, the average dispersion value D
ave is

[Equation 1] It is expressed as

In the present embodiment, the dispersion and length of each fiber Fi are selected so that this average value becomes anomalous dispersion. For example, Z1 = 60 km, D1 = -3 ps / k
m / nm fiber, Z2 = 30km, D2 = + 3ps
The average dispersion is -1 when connecting a fiber of / km / nm.
It becomes ps / km / nm.

Generally, when manufacturing an optical fiber, the average dispersion value is distributed around the design value D0. That is, since the dispersion value of each fiber is distributed symmetrically with respect to the design value D0, a fiber having a dispersion value larger than D0 and a fiber having a dispersion value smaller than D0 are made to have substantially the same length.

Therefore, if the design value D0 is set in advance so as to have anomalous dispersion, it is easy to combine the fibers obtained as a result to create a transmission line having an anomalous average value, and The yield in fiber production can be dramatically improved.

On the other hand, the fiber length Zi is preferably equal to or shorter than the soliton period Zsp. Here, the soliton period Zsp is given by the following equation.

[Equation 2] Where c is the speed of light in vacuum, λ is the wavelength of the optical signal, and t is the full width at half maximum of the pulse. Thus, the soliton period Zsp
Is defined by the absolute value of the average variance value | Dave |.

In this embodiment, since the transmission line is prepared by combining the respective fibers, the transmission line having a very small absolute value of the average dispersion value within 0.2 ps / km / nm can be easily constructed. can do. For example, when the average dispersion value is -0.2 ps / km / nm for a soliton having a pulse width of 20 ps, the soliton period is 793 km.

<Second Embodiment> FIG. 2 is a diagram showing a configuration example of a multi-relay transmission system to which the present invention is applied. In this figure, 1 is a transmitter, 3 is an optical amplifier, and 4 is a receiver. Reference numerals 2, 2 ', 2 "are soliton transmission lines, respectively, which are configured by optical fibers having anomalous dispersion characteristics as an average as shown in FIG. 1. Further, in FIG. The thick solid line shows the part with normal dispersion and the thin solid line shows the part with anomalous dispersion.However, combinations other than those shown in this figure can be used as long as they satisfy the condition that the average variance value becomes anomalous dispersion. Good.

The transmitter 1 produces an optical soliton signal,
It is guided to the transmission line 2 and transmitted. The optical amplifiers 3 ... Amplify the signals transmitted through the respective transmission lines 2, 2 ', 2''..., and compensate for the attenuation. After repeating transmission and amplification in this way, a desired distance is obtained. At, the signal is restored by the receiving device 4.

Next, the input soliton power of multi-repeater transmission will be described. If the dispersion value is Dave, the power P1 of N = 1 soliton is

(Equation 3) Given in. Here, n ₂ is the nonlinear refractive index of the optical fiber, and Aeff is the effective area of the optical fiber.

The equation for describing the propagation of such a soliton is as follows, where the distance between the optical amplifiers 3 is La and the electric field of the soliton is u.

[Equation 4] Given in. Here, Γ is a standardized loss of the optical fiber, and when converted into a loss of optical power α, α = 2Γ.

The power Pin to be coupled to the optical fiber is calculated from the equations (3) and (4).

(Equation 5) Is. For example, La = 90 km, loss 0.25 dB
/ Km (α = 0.058 km ⁻¹ ), A = 2.29
Becomes | Dave | = 0.2 ps / km / nm, t = 2
When 0 ps and Aeff = 50 μm ² , P1 = 3.8 mW, so that the optical soliton transmission power of this embodiment is Pin = 20 mW at the time of sending. What I would like to note here is P
1 is determined by the average dispersion | Dave |, but the amplitude A is determined only by the repeater interval La and the loss α of the optical fiber.

FIG. 3 is a diagram showing signal waveforms after optical soliton transmission in a multi-repeater transmission system (see FIG. 2) obtained by computer simulation. The dispersion value of the transmission line and 2 ⁵ -1 for the input signal are shown. 3 shows the relationship with the eye pattern after transmission, which is obtained when the pseudo-random signal of is used.

Of these, FIG. 3A shows the dispersion value +2.0 ps / k as the transmission lines 2, 2 ', 2 "... Of FIG.
m / nm fiber 30 km and dispersion value -1.75 ps /
An average dispersion value over a repeating interval (interval La of the optical amplifier 3) of 90 km is set to -0.5 ps / km / nm by connecting a fiber of 60 km of km / nm, and optical amplification is performed every 90 km to propagate 1170 km in total. It is the figure which showed the signal waveform.

FIG. 3A shows the transmission lines 2, 2 ',
2 ″ ..., a fiber 30 km having a dispersion value of +2.0 ps / km / nm and a fiber 60 km having a dispersion value of −1.3 ps / km / nm are connected, and an average dispersion value of 90 km is −0.2 ps / km / FIG. 3 is a diagram showing a signal waveform after the optical amplification is performed every 90 km and the total wavelength is 1170 km after propagation for 1170 km.

FIG. 3C shows the transmission lines 2, 2 ',
2 ″ ..., a fiber 30 km having a dispersion value of +7.4 ps / km / nm and a fiber 60 km having a dispersion value of −4.0 ps / km / nm are connected, and an average dispersion value of 90 km is −0.2 ps / km / FIG. 3 is a diagram showing a signal waveform after the optical amplification is performed every 90 km and the total wavelength is 1170 km after propagation for 1170 km.

As shown in FIGS. 3 (a), 3 (a) and 3 (c), even if the optical fiber in the normal dispersion region is frequently used in the transmission line, the average dispersion value Dave is satisfied so as to satisfy the above-mentioned condition.
By setting, it can be seen that solitons can be transmitted stably. Further, as shown in FIG. 3C, the soliton can be stably propagated even when the dispersion is largely changed.

Here, if the optical signal wavelength is set to the wavelength at which Dave = 0, this soliton transmission line can be directly used as a linear transmission line. Therefore, the normal soliton (also referred to as a bright soliton) described above is transmitted by the signal light set to the wavelength of Dave <0, and at the same time, Dave = 0
It becomes possible to perform wavelength division multiplexing transmission in which a linear signal is transmitted by the signal light set to the wavelength of In this way, the interaction between solitons, which is a problem in soliton wavelength division multiplexing transmission, can be eliminated.

Furthermore, it is also possible to transmit dark solitons (also called dark solitons) by the signal light set to the wavelength of Dave> 0. In addition, by changing the wavelength of the signal light, it is possible to convert from linear transmission to soliton transmission with one transmission line. FIG. 4 shows how the above transmission setting wavelength and dispersion change.

[0029]

As described above, the present invention enables soliton transmission by an optical fiber having various positive and negative dispersion values, which has heretofore been impossible. Therefore, the yield in producing an optical soliton line is improved. Can be dramatically improved and economical soliton transmission can be realized.

The average dispersion value is -0.2 ps / km.
A transmission line with a very small value such as within / nm,
Since it can be easily constructed by combining fibers having various dispersion values, the soliton period can be lengthened, and the relay interval of soliton transmission, which was conventionally about 50 km, can be extended to about 100 km. As a result, the number of repeaters can be reduced and economical and practical soliton transmission can be realized.

Furthermore, Gordon-House Jitter ([3] JPGordon and HA which is a problem in the case of soliton transmission.
Haus: "Random walk of coherently amplified solitons
inoptical fiber transmission ", Opt. Lett., 1986, Vol.
11, pp.665-667.), The average dispersion value of the transmission line can be made small, so that it can be greatly reduced and transmission over a longer distance becomes possible.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration example of a soliton transmission line using the present invention.

FIG. 2 is a diagram showing a configuration example of a multi-relay transmission system to which the present invention is applied.

FIG. 3 is a diagram showing a relationship between a dispersion value of a transmission line and a waveform after soliton transmission.

FIG. 4 is a diagram for explaining wavelength multiplexing transmission of bright solitons, dark solitons, and linear signals.

[Explanation of symbols]

 F1 to Fn optical fiber Z1 to Zn optical fiber length D1 to Dn optical fiber dispersion value 1 transmitter 2,2 ', 2 "soliton transmission line 3 optical amplifier 4 receiver

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Claims (5)

[Claims] 1. In an optical communication method using an optical soliton, the dispersion characteristics of an optical fiber are largely changed from a normal dispersion region to an abnormal dispersion region, and the average value of the group velocity dispersion values over distance is regarded as the abnormal dispersion. Optical soliton communication method characterized in that a normal soliton is transmitted by using the soliton transmission line. 2. In an optical communication method using an optical soliton, the dispersion characteristics of an optical fiber are largely changed from a normal dispersion region to an abnormal dispersion region, and the average value of the group velocity dispersion values over distance is regarded as normal dispersion. Optical soliton communication method, characterized in that a dark soliton is transmitted using the soliton transmission line. 3. An optical communication method using an optical soliton, in which the dispersion characteristic of an optical fiber is largely changed from a normal dispersion region to an abnormal dispersion region, and the average value of the group velocity dispersion values depending on the distance is the abnormal dispersion. The normal soliton at the wavelength, the dark soliton at the wavelength at which the average value of the group velocity dispersion values becomes normal dispersion, and the linear at the wavelength at which the average value of the group velocity dispersion value at the distance becomes zero An optical soliton communication method characterized in that signals are simultaneously propagated by wavelength division multiplexing. 4. The optical soliton communication method according to claim 3, wherein a combination of any two signals of a normal soliton, a dark soliton, and a linear signal is used. 5. The optical soliton communication method according to any one of claims 1 to 4, wherein multi-relay transmission is performed by compensating for a loss of an optical fiber by an optical amplifier.