JP3502546B2 - Optical amplification repeater transmission system - 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 amplification repeater transmission system for transmitting a wavelength division multiplexed optical signal through an optical fiber transmission line and an optical amplification repeater. In particular, the present invention relates to an optical amplification repeater transmission system in which a dispersion compensator is inserted in an optical fiber transmission line at a predetermined interval so that the average dispersion value of the entire transmission line becomes zero.

[0002]

2. Description of the Related Art In an optical transmission system using an optical fiber transmission line, an optical signal wavelength near a zero dispersion wavelength is used in order to suppress deterioration of an optical signal waveform due to group velocity dispersion of an optical fiber.

On the other hand, when transmitting a WDM optical signal,
If the wavelength is set near the zero-dispersion wavelength, the power of the four-wave mixing light generated by the non-linear effect of the optical fiber becomes large, which is a major factor that deteriorates the transmission characteristics.

In order to avoid this, a dispersion compensator is inserted in the optical fiber transmission line at a predetermined interval to set the average dispersion value of the entire transmission line to zero, and the wavelength of the wavelength division multiplexed optical signal is set to the wavelength of the entire transmission line. The method of setting near zero dispersion wavelength is effective. This is to suppress the generation of four-wave mixing light by making the dispersion value of the optical fiber transmission line sufficiently large, and suppress the waveform deterioration by setting the average dispersion value to zero in the entire transmission line.

FIG. 6 shows a configuration example of a conventional optical amplification repeater transmission system for performing dispersion compensation. In the figure, the transmitter 1
The optical fiber transmission lines 3 and the optical amplification repeaters 4 are alternately arranged between the receiver and the receiver 2, and the dispersion compensators 5 are inserted at appropriate intervals. Here, the interval at which the optical amplification repeater 4 is inserted is the repeater interval Za, and the interval at which the dispersion compensator 5 is inserted is the dispersion compensation interval Zcmp. In the figure, a dispersion compensator 5-1 compensates for group velocity dispersion in the optical fiber transmission lines 3-1 and 3-2 and the optical amplification repeaters 4-1 and 4-2. The group velocity dispersion within each dispersion compensation interval is compensated so that the average dispersion value of the entire transmission line becomes zero.

[0006]

The power of the four-wave mixing light becomes stronger as the wavelength interval of the optical signal becomes narrower. Therefore, if the wavelength spacing becomes narrower as the transmission capacity increases,
Even with the configuration of performing dispersion compensation as shown in FIG. 6, suppression of four-wave mixed light is insufficient.

Further, it is known that the power of the four-wave mixed light periodically increases and decreases along the transmission line as shown in FIG. For example, the period Zc1 in which the power of the four-wave mixing light in the non-zero dispersion wavelength region in the transmission system having a uniform dispersion value increases or decreases, the optical signal wavelengths are λ _i , λ _j , λ _k (λ _i ≠
λ _k , λ _j ≠ λ _k ), c is the light velocity in vacuum, and D is the dispersion value at the wavelength λ _k in the optical fiber transmission line.

[0008]

[Equation 3]

It is known that In addition, the cycle Zc2 at which the power of the four-wave mixing light near the zero-dispersion wavelength increases or decreases
Is a zero-dispersion wavelength λ ₀ and a dispersion slope at a wavelength λ _k is dD / dλ,

[0010]

[Equation 4]

It is known that The present invention focuses on the relationship between the optical signal wavelength, the transmission line dispersion value, the repeater interval, and the dispersion compensation interval in a wavelength-multiplexed repeater transmission system that performs dispersion compensation, and minimizes the generation of four-wave mixing light. It is an object of the present invention to provide an optical amplification repeater transmission system that can be performed.

[0012]

The optical amplification repeater transmission system of the present invention is a wavelength division multiplex repeater transmission system for performing dispersion compensation, by setting an optimum repeater interval or dispersion compensation interval, thereby It is characterized by minimizing the occurrence.

As shown in FIG. 2, the inventor of the present application has confirmed that the four-wave mixing optical power rapidly increases when the ratio of the repeater interval Za and the period Zc1 is an integer. Here, it is assumed that the four-wave mixed light is generated by an optical signal of wavelength λ _i (= λ _j ) and an optical signal of wavelength λ _k . The circles and squares in Fig. 2 are for compensation of dispersion, and the circles and squares are
Indicates the case where dispersion compensation is not performed. In FIG. 2, ◯ and ● have an optical signal wavelength difference Δλ of 0.4 nm, and □ and ■ have a Δλ of 0.6 nm. × is an experimental value.

That is, in the wavelength division multiplexing transmission system for dispersion compensation, most of the transmission line is an optical fiber of non-zero dispersion, and therefore, when the dispersion value at the wavelength λ _k in the optical fiber transmission line is D. When the repeater spacing Za becomes a multiple of the cycle Zc1, the power of the four-wave mixing light increases. Therefore, if m is an integer, Za / Zc1 ≠ m, that is,

[0015]

[Equation 5]

So that the optical signal wavelengths λ _i , λ _j , λ
Set _k , variance value D, or repeater spacing Za. For example, optical signal wavelengths λ _i , λ _j , λ that generate four-wave mixing light
_{When k} and the dispersion value D are determined, the period Zc1 is obtained and the repeater interval Za is set to be unequal to the period Zc1, so that the generation of the four-wave mixed light can be suppressed. . When the number of optical signal wavelengths is large, a combination of three waves or λ _i = λ _{j is used} for each of 2 waves.
It suffices to find the respective cycles Zc1 by the combination of waves and set the repeater interval Za so as to make them unequal times.

Further, as shown in FIG. 3, the dispersion compensation interval Z
It was confirmed that when the ratio of cmp to the above-mentioned period Zc2 is an integer, the four-wave mixing light power sharply increases. Here, the four-wave mixed light is an optical signal of wavelength λ _i (= λ _j ) and a wavelength λ _i (= λ _j ).
_It is assumed to be generated by an optical signal of _k . ○ in Figure 3
Indicates that the optical signal wavelength difference Δλ is 0.4 nm, and □ indicates that Δλ is 0.6 nm.
and Δ indicates a Δλ of 0.388 nm. Further, the average zero-dispersion frequency of the transmission line is f ₀ , the optical signal frequency is f ₁ ,
When f ₂ is set, ◯ and □ are the case of f ₀ = (f ₁ + f ₂ ) / 2, and ● is the case of f ₀ = f ₂ −6 (f ₂ −f ₁ ). × is an experimental value.

That is, since the dispersion value of the entire transmission line is zero in the wavelength division multiplexing transmission system for performing dispersion compensation, the average zero dispersion wavelength in the entire transmission line is λ ₀ , and the dispersion slope at λ _k in the entire transmission line is Is dD / dλ, and the dispersion compensation interval Zcmp becomes a multiple of the period Zc2, the power of the four-wave mixing light increases. Therefore, if n is an integer, Zcmp / Zc2 ≠ n, that is,

[0019]

[Equation 6]

So that the optical signal wavelengths λ _i , λ _j , λ
_k , the average zero-dispersion wavelength λ ₀ in the entire transmission line, or the dispersion compensation interval Zcmp is set. For example, when the optical signal wavelengths λ _i , λ _j , and λ _k that generate the four-wave mixed light and the average zero-dispersion wavelength λ ₀ in the entire transmission line are determined, the cycle Zc2
And the dispersion compensation interval Zcmp is set to be unequal to the period Zc2, the generation of four-wave mixed light can be suppressed. Further, when the number of optical signal wavelengths is large, the respective periods Zc2 in the combination of each of the three waves or in the combination of each of the two waves with λ _i = λ _j are obtained and dispersed so as to be unequal times thereof. The compensation interval Zcmp may be set.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an embodiment of an optical amplification repeater transmission system of the present invention. In the figure, an optical fiber transmission line 3 and an optical amplification repeater 4 are alternately arranged between a transmission device 1 and a reception device 2, and a dispersion compensator 5 is inserted at an appropriate interval so that the entire transmission line is The average variance value is set to zero. Here, the interval at which the optical amplification repeater 4 is inserted is the repeater interval Za, and the interval at which the dispersion compensator 5 is inserted is the dispersion compensation interval Zcmp. The above configuration is the same as the conventional configuration.

The feature of this embodiment is that the period Zc1 is obtained from the input optical signal wavelength and the dispersion value of the optical fiber transmission line 3, and the repeater interval Za is an unequal multiple of the period Zc1, that is, Za / Zc1 ≠ m (conditional expression It is in the place of setting so as to be 1).

Further, the period Zc2 is obtained from the input optical signal wavelength, the average zero-dispersion wavelength of the entire transmission line and the dispersion slope, and the dispersion compensation interval Zcmp is an unequal multiple of the period Zc2, that is, Zcmp / Zc2 ≠ n (conditional expression 2 ) Is to be set. By satisfying conditional expressions 1 and 2 at the same time, the four-wave mixed light can be suppressed most effectively.

FIG. 4 shows an arrangement example of the input optical signal wavelengths λ _i , λ _j and λ _k and the average zero dispersion wavelength λ ₀ of the entire transmission line.
For example, λ ₀ = 1553.0 nm, λ _i = λ _j = 1553.1 nm,
λ _k = 1552.7 nm, the dispersion value D of the optical fiber transmission line 3 is −
At 1.5 ps / km / nm, the cycle Zc1 is 33.5 km and the cycle Zc2 is
Will be 2400 km and 7200 km. At this time, by setting the repeater interval Za to 50 km and the dispersion compensation interval Zcmp to 3500 km, it is possible to make the periods Zc1 and Zc2 unequal times, and it is possible to suppress the generation of excessive four-wave mixing light. it can.

When the number of wavelengths increases, the number of cycles Zc1 and Zc2 increases in accordance with the combination of three waves or the combination of two waves with λ _i = λ _j .
In this case, the cycle Zc1 and the cycle Zc2 in each combination are obtained, and the repeater interval or the dispersion compensation interval is set so that the integral multiples thereof and the repeater interval and the dispersion compensation interval do not match. Can be effectively suppressed.

Since the power of the four-wave mixing light is higher as the wavelength interval of the optical signals is narrower, even if the period Zc1 and the period Zc2 are obtained only for the combination of the optical signals whose wavelength differences are relatively close to each other. Good.

[0027]

As described above, according to the present invention, in the wavelength division multiplex transmission system for dispersion compensation, even if the wavelength interval of each optical signal is narrow and the influence of the four-wave mixing light cannot be avoided, By appropriately setting the wavelength, the dispersion value of the optical fiber transmission line, the repeater interval, and the dispersion compensation interval, it is possible to suppress the generation of excessive four-wave mixing light.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of an optical amplification repeater transmission system of the present invention.

FIG. 2 is a diagram showing a relationship between a repeater interval Za, a cycle Zc1, and four-wave mixing light power.

FIG. 3 is a diagram showing the relationship between the dispersion compensation interval Zcmp, the period Zc2, and the four-wave mixing light power.

FIG. 4 is a diagram showing an arrangement example of input optical signal wavelengths λ _i , λ _j , and λ _k and an average zero-dispersion wavelength λ ₀ of a transmission line.

FIG. 5 is a diagram showing a cycle in which the power of four-wave mixing light increases and decreases.

FIG. 6 is a diagram showing a configuration example of a conventional optical amplification relay transmission system that performs dispersion compensation.

[Explanation of symbols]

1 transmitter 2 Receiver 3 Optical fiber transmission line 4 Optical amplification repeater 5 Dispersion compensator

Continuation of the front page (56) References JP-A-7-1007069 (JP, A) JP-A-7-74699 (JP, A) JP-A-9-23187 (JP, A) Toshiya Matsuda et al., High-density WDM Distributed Allocation Method for Suppressing Four-Wave Mixing in Japan, Proceedings of the 1998 IEICE Communications Society Conference 2, Japan, The Institute of Electronics, Information and Communication Engineers, September 7, 1998, B-10- 165, p. 487 T.I. Matsuda, et al. , Dispersion Management Scheme for Suppressing FWM in DWDM Transmisson, Lasers and Electro-Optics Society Anniversary, 1998 Enematic Meeting, 1998. 1, References cited 6, pp. 372-373 (58) Fields investigated (Int.Cl. ⁷ , DB name) H04B 10/00-10/28 H04J 14/00-14/08 JISST file (JOIS)

Claims (4)

(57) [Claims] 1. An optical fiber transmission line having a dispersion value D at a wavelength λ _k , and a predetermined interval (repeater interval) Za between the optical fiber transmission lines.
And an optical amplifier repeater inserted in the optical fiber transmission line, and a predetermined interval (dispersion compensation interval) Z in the optical fiber transmission line.
It is equipped with a dispersion compensator that is inserted at cmp and that compensates the group velocity dispersion of the optical fiber transmission line so that the average dispersion value at wavelength λ ₀ in the entire transmission line becomes zero, and transmits wavelength multiplexed optical signals. In the optical amplification repeater transmission system, the optical signal wavelengths are λ _i , λ _j , λ _k (λ _i ≠ λ _k , λ _j ≠
λ _k ), the speed of light in vacuum is c, and m is an integer, An optical amplification repeater transmission system characterized in that signal light wavelengths λ _i , λ _j , λ _k , dispersion value D, and repeater interval Za are set so as to satisfy 2. When transmitting a wavelength-multiplexed optical signal of three or more waves, a combination of three waves or two each with λ _i = λ _j.
2. The optical amplification repeater transmission system according to claim 1, wherein the repeater interval Za satisfying conditional expression 1 is set according to the combination of waves. 3. An optical fiber transmission line having a dispersion value D at a wavelength λ _k , and a predetermined spacing (repeater spacing) Za between the optical fiber transmission lines.
And an optical amplifier repeater inserted in the optical fiber transmission line, and a predetermined interval (dispersion compensation interval) Z in the optical fiber transmission line.
It is equipped with a dispersion compensator that is inserted at cmp and that compensates the group velocity dispersion of the optical fiber transmission line so that the average dispersion value at wavelength λ ₀ in the entire transmission line becomes zero, and transmits wavelength multiplexed optical signals. In the optical amplification repeater transmission system, the optical signal wavelengths are λ _i , λ _j , λ _k (λ _i ≠ λ _k , λ _j ≠
λ _k ), the speed of light in vacuum is c, the dispersion slope at the wavelength λ _k in the entire transmission line is dD / dλ, and m is an integer, An optical amplification repeater transmission system characterized in that the signal light wavelengths λ _i , λ _j , λ _k , the average zero-dispersion wavelength λ ₀ , and the dispersion compensation interval Zcmp are set so as to satisfy 4. When transmitting a wavelength-division-multiplexed optical signal of three or more waves, a combination of three waves or two each with λ _i = λ _j.
The optical amplification repeater transmission system according to claim 3, wherein the dispersion compensation interval Zcmp that satisfies the conditional expression 2 is set according to the combination of waves.