JP3527462B2 - Transmission test method and transmission simulation device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transmission test method for an optical signal in an optical transmission system and an apparatus for simulating a transmission state, and particularly, a transmission test of an ultrahigh-speed optical transmission system under a condition close to an actual environment. The present invention relates to a transmission test method and a transmission simulation device that can be evaluated by performing the test.

[0002]

2. Description of the Related Art At present, the bit rate transmitted through an optical fiber is increasing with the explosive increase of traffic such as the Internet. Under these circumstances, Wavelength Division Multiplexing (WDM) that utilizes the wide band property of optical fibers.
Technology is drawing attention.

On the other hand, the time width of the optical pulse representing each 1 bit is shortened by time division multiplexing (TDM: Time Division Multiplexing).
Multiplexing) technology is also being actively used. At present, a commercial device allocates a bit rate of 10 Gbit / s to each wavelength, and in the near future 40 Gbit / s.
It is considered that the above optical channel technology will be realized.

Due to such an increase in bit rate, various transmission deterioration factors in the optical fiber can be considered. First, by shortening the pulse width, the number of photons in 1 bit becomes insufficient and the S / N deteriorates. Therefore, either the relay section must be shortened or high-power light must be transmitted into the fiber.

At this time, the waveform deteriorates due to the non-linear optical effect. Further, the frequency variation in 1 bit causes the waveform to deteriorate through the effect of group velocity dispersion. The other is that, depending on the manufacturing process of the optical fiber, the principal axis exists in the cross section of the fiber, and the propagation velocity between the principal axes is different.
The waveform also deteriorates due to the effect of MD: Polarization Mode Dispersion.

Among the above-mentioned three deterioration factors, S / N
The effects of deterioration and group velocity dispersion are stable deterioration that does not fluctuate over time, and error correction code and dispersion compensation techniques are applied, and the prospect of resolution is easy to make. However, the effect of PMD is random deterioration that fluctuates with time, and high-quality transmission cannot be realized without adaptive equalization during service (Reference 1 T. Takahashi et al., Electron. Lett., V01.30, No. .Four,
(See p.348, (1994))

Transmission deterioration is caused by DGD: Differential Group D
It strongly depends on the physical quantity called elay. Furthermore, the transmission deterioration is
In addition to this, SO that is the polarization state of the incident light of the fiber
P: State Of Polarization is also strongly dependent on PSP: Principal State of Polarization, which represents the principal axis in the fiber.

In the actually laid optical fiber, these three quantities, DGD, SOP, and PSP, are all complicated with time-varying. Therefore 4
When researching and developing ultra-high-speed optical transmission systems such as 0 Gbit / s and 100 Gbit / s or more, it is important how to simulate this complicated system and perform testing.

Particularly, DGD is around the average value, and Maxwel
It is reported that they are stochastically distributed by the l distribution (Reference 2: CDPoole et al., Opt. Lett., No.16., p.372,
(1991)), which has been reported to have an ergodic property in which the sample dependence when the wavelength is changed and the temporal variation have the same Maxwell distribution (Reference 3: S.DeAn.
gelis et al., J. Lightwave Technol., Vol.10, No.5, p.
552, (1992)).

[0010] Further, although there is a report that the temporal fluctuation period is about 20 minutes, there are also other reports and it depends on the laying condition of the fiber (Reference 3: S. De Angelis et al., J. Lightw.
aveTechnol., Vol.10, No.5, p.552, (1992), Reference 4: HB
ulow and G. Veith, ECOC'97, M03C, (1997)).

[0011]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention SOP. PS
The characteristics such as P depend on the manufacturing method of the optical fiber, the laying condition, etc., and it is difficult to uniquely simulate it. At present, a simulation device called a PMD emulator has been developed, but this device is far from simulating the actual fiber state, and the DGD amount representing the PMD can be set, but cannot be changed randomly. It was

The present invention focuses on DGD among the three fluctuation amounts of DGD, SOP, and PSP, and varies this value randomly and according to a specific distribution (for example, Maxwell distribution). The purpose is to realize a transmission simulation device that can do this.

[0013]

According to the invention, the aforesaid problems are solved by the means defined in the claims. That is, the invention of claim 1 is a transmission test method for simulating deterioration due to polarization mode dispersion of an optical transmission waveform between a transmission side and a reception side when transmitting an optical signal,
On the transmission side, an optical signal is distributed by polarization, a delay is given to one of the distributed branches, and a system is configured so that the delayed branch and the other distributed branch are multiplexed and received. However, it is a transmission test method in which the delay is set to an arbitrary value and the value of the delay is randomly changed.

According to a second aspect of the present invention, in the transmission test method according to the first aspect, the delay value is varied randomly so that the delay value probability distribution becomes a Maxwell distribution.

According to a third aspect of the present invention, in the transmission test method according to the second aspect, when setting a delay, an average delay value is input, and a sample of an arbitrary delay value is sampled from the average delay value and the Maxwell distribution. A configuration in which a number is calculated, an arbitrary delay value is weighted from the number of samples, a table of weighted arbitrary delay values is created, and a delay value is randomly selected from the table of the arbitrary delay values. Is.

According to a fourth aspect of the present invention, there is provided a device for simulating deterioration of an optical transmission waveform due to polarization mode dispersion, which is set in a light distribution means by polarization and one branch distributed by the light distribution means. According to the delay condition, means for giving a delay, means for combining the delayed branch with the other branch distributed by the optical distributing means, and setting the delay to an arbitrary value as the delay condition. , A transmission simulation device having means for randomly varying the delay value.

According to a fifth aspect of the present invention, in the transmission simulating device according to the fourth aspect, the means for randomly varying the delay value comprises means for setting a variation time interval. .

According to a sixth aspect of the present invention, in the transmission simulating apparatus according to the fourth aspect, the means for setting the delay condition changes the delay value randomly so that the delay value probability distribution becomes a Maxwell distribution. It is configured to include means.

According to a seventh aspect of the present invention, in the transmission simulating device according to the sixth aspect, the means for setting the delay condition comprises means for inputting an average delay value, and the input average delay value and Maxwell distribution. Means for calculating the number of samples of the arbitrary delay value, means for weighting the arbitrary delay value from the number of samples, means for creating a table of the weighted arbitrary delay values, and randomizing from the table of the arbitrary delay values And a means for selecting a delay value.

According to an eighth aspect of the present invention, in the transmission simulating device according to the sixth or seventh aspect, a unit for inputting an average delay value, and an arbitrary delay value based on the input average delay value and Maxwell distribution are selected. A module for calculating the number of samples and a means for weighting an arbitrary delay value based on the number of samples, and a means for creating a table of weighted arbitrary delay values; and the arbitrary delay value The means for randomly selecting the delay value from the table of FIG. 2 constitutes another module.

According to a ninth aspect of the present invention, in the transmission simulating apparatus according to the sixth or seventh aspect, a unit for inputting an average delay value, and an arbitrary delay value based on the input average delay value and Maxwell distribution are selected. Means for calculating the number of samples, means for weighting an arbitrary delay value from the number of samples,
The means for creating the table of the weighted arbitrary delay values and the means for randomly selecting the delay values from the table of the arbitrary delay values constitute the same module.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a diagram showing an example of the configuration of a system for implementing the present invention, showing the configuration of a PMD emulator. In the figure, numeral 1 is the transmitter side of the transmission device, and 2 is the abbreviated symbol of the splitter (Polarization Beam Splitter). Further, 3 is a variable delay device, 4 is a transmission device receiving side, 5 is a controller, and 6 is PM.
It represents a D emulator. Hereinafter, a first example of the embodiment will be described as a first example.

In this example, the hardware configuration is the same as the conventional one, but the present invention is different in the DGD changing means mounted in the controller 5 in the figure.
In the first embodiment, this DGD changing means is composed of three modules. One of them is a module that calculates the Maxwell distribution by inputting the average DGD value and obtains the number of samples of each DGD value from this probability distribution.

In this example, the case where the Maxwell distribution is used as the distribution has been described, but the present invention is not limited to this. For example, Poisson distribution or χ
(Chi) Square distribution may be used.

FIG. 2 is a diagram showing an example in which the number of DGD value samples is calculated from the Maxwell distribution. This module was created using a program called Mathematica by Addison-Wesley, but of course it does not have to be this program. As shown in FIG. 2, {x. x in y} represents a DGD value, and y represents the number of samples for that value. In this figure, the average DGD is 43 ps.

It can be seen that the number of samples having an extremely large or small DGD value is 0 as compared with the average DGD value. This DGD value and the number of samples are combined to create a weighted table. In this example,
For the combination of {x, y}, a table was created such that y values were included in the value of x (this example was created manually, but this may be done automatically).

FIG. 3 is a diagram showing a module for arbitrarily (randomly) selecting a value from the created table. The display of S-3 to S-10 in the figure shows the steps of the process and corresponds to the display in FIG. This module was created using a VEE program from HP, but of course it does not have to be this program.

It was created by using weighting in the description of globall = [8,9,10,11,12,13, ...] in the top submodule of Formula 3 in FIG. The table is stored (S-3). The sub-module called Random (low, high) has a function of randomly giving a value by allocating a random number (S-6), which is also included in ordinary software. In addition, the lower sub-module, Formula, randomly selects D from the weighted table.
A GD amount is selected (S-7).

The sub module called PMD emulator has a function to actually set hardware (S-8),
(S-10). De connected to this submodule
A module called lay is used to set how often the DGD value is changed (S-4). In this example, 1
Seconds The above flow is shown as a flowchart in FIG.

In FIG. 4, numeral 11 indicates module 1, numeral 12 indicates module 2, and numeral 13 indicates module 3. In addition, S-1 to S- in the figure
The display of 10 indicates the step of the process and corresponds to the display in FIG. 3 described above. Here, the dotted line represents the module to be mounted.

First, the module 1 indicated by numeral numeral 11
At, the average DGD value is input (S-1). Next, the DGD value-the number of samples is calculated from the specific distribution (S-
2). Although this example shows the case where the distribution is the Maxwell distribution, the present invention is not limited to this, and for example, a Poisson distribution, a χ square distribution, or the like may be used.

Next, in module 2, a table in which the DGD value appears by the number of samples is created (S-3),
In module 3, input the fluctuation cycle (S-4),
The total number of samples (x) is input (S-5). Then, a random number is assigned (S-6), and the element of the number obtained by the random number is selected from the table (S-7).

Next, the hardware is set (S-
8). It is checked whether or not the processing after the above (S-6) has reached x times (S-9). If it has not reached x times (S-
6) to (S-8) are repeated. When the processing reaches x times, the hardware is set to 0 and the processing ends (S-10).

The DG is actually used by the above-mentioned changing means.
FIG. 5 shows how D changed. The horizontal axis of FIG. 5 is time and the vertical axis is the DGD value. As can be seen from this figure, the DGD value fluctuates randomly. FIG. 6 shows a probability distribution of DGD values which are randomly changed.

The mountain-shaped solid line in the figure shows the theoretical Maxwell distribution with an average value of 43 ps, and the bar chart shows the probability distribution when the DGD value of the emulator is changed by the present invention. From FIG. 6, the distribution obtained according to the present invention substantially matches the Maxwell distribution. Therefore, it can be seen that the polarization mode dispersion simulator according to the present invention can simulate an actual field environment.

Next, a second example of the embodiment of the present invention will be described as a second embodiment. Unlike the first embodiment, the present embodiment realizes a desired function in one module. Figure 7
9 shows the changing means of the second embodiment. Since FIGS. 7 to 9 are one module, they should be originally shown as one diagram. However, if this is done, the diagrams become very fine and difficult to see, so they are displayed separately for each process.

FIG. 7 shows Maxwellian calculation processing, FIG. 8 shows weighting table creation processing, and FIG. 9 shows random number generation and fluctuation period input processing. The sub-module group shown on the upper side of FIG. 7 is the setting input means and the average DG.
The D value, the fluctuation period, the total number of samples, and the maximum DGD value are shown. The meaning of the maximum DGD value is to reflect up to what probability the designer of the optical transmission system considers.

For example, when a designer wants to consider the probability up to 10 ^ -5, that is, the designer considers 20 in 1 year.
When considering the effect of minutes, the maximum DGD value is set to three times the average value. This module is a program in which the maximum value comes once. Along with the total number of samples, the desired worst value design is possible.

The feature of the second embodiment is that it is easy to operate because there is no transfer between software, it is easy to carry in the laboratory or on-site environment because it can be installed in the device, and the average value, maximum value, number of samples, etc. It is possible for the transmission system designer to arbitrarily change the setting items that change (without creating a corresponding table in advance).

[0040]

According to the present invention, in an ultrahigh-speed optical transmission system of 40 Gbit / s or the like, transmission deterioration due to PMD, which may cause a serious problem, can be simulated in the same manner as in the field environment. Therefore, it is possible to measure the performance of the transmitting device and the receiving device under conditions close to the actual environment. This also has the advantage of being able to obtain important information for research and development, such as the design of an optical transmission system or the identification of required functions, which is suitable for the actual environment.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of the configuration of a system for carrying out the present invention.

FIG. 2 is a diagram showing an example in which the number of DGD value samples is calculated from the Maxwell distribution.

FIG. 3 DGD randomly from a DGD weighting table
It is a figure which shows the module which selects a value.

FIG. 4 is a flowchart showing an algorithm of the first embodiment.

FIG. 5 is a diagram showing an example of time variation of a DGD value.

FIG. 6 is a diagram showing a probability distribution of DGD values.

FIG. 7 is a diagram illustrating a Maxwellian calculation process.

FIG. 8 is a diagram showing a process of creating a weighting table.

FIG. 9 is a diagram showing a process of random number generation and variation period input.

[Explanation of symbols]

1 transmitter side 2 distributor 3 variable delay device 4 Transmission device receiving side 5 controller 6 PMD emulator 11 Module 1 12 Module 2 13 Module 3

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁷ Identification code FI H04B 17/00 (72) Inventor Yoshiaki Kisaka 2-3-1, Otemachi, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation (56 ) References JP-A-11-215521 (JP, A) Special Table 2000-510573 (JP, A) International Publication 99/028723 (WO, A1) (58) Fields investigated (Int.Cl. ⁷ , DB name) H04B 10/00 G01M 11/00 H04B 17/00

Claims (9)

(57) [Claims] 1. A transmission test method for simulating deterioration of an optical transmission waveform between a transmission side and a reception side due to polarization mode dispersion when transmitting an optical signal, wherein the transmission side uses an optical signal by polarization. Is divided into two, a delay is given to one of the distributed branches, and a system is configured so that the delayed branch and the other distributed branch are combined and received, and the delay is set to an arbitrary value. The transmission test method is characterized in that the delay value is randomly changed while being set to. 2. The transmission test method according to claim 1, wherein the delay value is varied randomly and the probability distribution of the delay values is changed to a Maxwell distribution. 3. When setting the delay, an average delay value is input, the number of samples of the arbitrary delay value is calculated from the average delay value and the Maxwell distribution, and the arbitrary delay value is weighted from the number of samples. The transmission test method according to claim 2, wherein a table of weighted arbitrary delay values is created, and the delay values are randomly selected from the table of arbitrary delay values. 4. A device for simulating deterioration of an optical transmission waveform due to polarization mode dispersion, comprising: an optical distribution means by polarization and one branch distributed by the optical distribution means according to a delay condition set. A means for giving a delay, a means for multiplexing the delayed branch and the other branch distributed by the optical distributing means, and setting the delay to an arbitrary value as the delay condition,
A transmission simulation device comprising means for randomly varying a delay value. 5. The means for randomly varying the delay value comprises means for setting a variation time interval.
The transmission simulation device described in. 6. The transmission simulating device according to claim 4, wherein the means for setting the delay condition comprises means for varying the value of the delay randomly so that the probability distribution of the delay values becomes the Maxwell distribution. 7. A means for setting a delay condition, a means for inputting an average delay value, a means for calculating the number of samples of an arbitrary delay value from the input average delay value and Maxwell distribution, and the number of samples 7. The method according to claim 6, further comprising: means for weighting the arbitrary delay values, means for creating a table of the weighted arbitrary delay values, and means for randomly selecting a delay value from the table of the arbitrary delay values. Transmission simulator. 8. A means for inputting an average delay value, a means for calculating the number of samples of an arbitrary delay value from the inputted average delay value and Maxwell distribution, and weighting of the arbitrary delay value from the number of samples. And a means for forming a table of weighted arbitrary delay values and a means for randomly selecting a delay value from the table of the arbitrary delay values constitute another module. The transmission simulation device according to claim 6 or claim 7. 9. A means for inputting an average delay value, a means for calculating the number of samples of an arbitrary delay value from the inputted average delay value and Maxwell distribution, and weighting of the arbitrary delay value from the number of samples. The means, the means for creating the table of the weighted arbitrary delay values, and the means for randomly selecting a delay value from the table of the arbitrary delay values constitute the same module. Transmission simulator.