JP4663587B2 - Method and apparatus for measuring degradation factors - Google Patents

Description

  The present invention relates to a method for measuring a degradation factor of an optical signal and an optical repeater monitoring technique using the method.

  Currently, in optical networks, the quality of signal light is monitored using power measurement, spectrum measurement, parity check, and the like. However, the deterioration of the optical signal is caused by a mixture of various factors due to the speedup of the optical signal and the progress of the transparent optical network technology that passes through the node as it is. For example, SNR degradation, waveform distortion due to chromatic dispersion in the fiber, and waveform degradation due to deviation between the signal light wavelength and the transmission profile of the filter can be considered. In such an optical network in which various degradation factors coexist, it is important to use an optical relay monitoring technology that can quantitatively determine the degradation amount for each factor.

  As a conventional optical relay monitoring technique, a technique for identifying a degradation factor from the average Q value of signal light (see Non-Patent Document 1), or a technique for identifying a degradation factor by comparing with a known eye diagram (Non-Patent Document) 2) has been proposed. In the former method using the average Q value, it is possible to specify the deterioration factor transparently without depending on the bit rate or the modulation method by specifying the dispersion deterioration asynchronously. In the latter method of comparing with a known eye diagram, the eye diagram deteriorated by a known deterioration factor is stored in a database in advance, and the deterioration factor is specified by comparing with the eye diagram to be measured.

I. Shake and H. Takara, "Chromatic Dispersion Dependence of Asynchronous Amplitude Histogram Evaluation of NRZ Signal," J. Lightwave Technol. 21, pp. 2154-2161 (2003) IEICE Technical Report NS2003-249, OCS2003-133 Takeshita et al., "Optical signal monitoring method using eye pattern analysis", IEICE, IEICE Technical Report, NS003-249, OCS 2003-133 (2004-01) I. Shake and H. Takara, and S, Kawanishi, "Simple Q Factor Monitoring for BER Estimation Using Opened Eye Diagrams Captured by High-Speed Asynchronous Electrooptical Sampling" IEEE Photon. Technol. Lett. 15, pp. 620-622 (2003 ) Ohno, “Pattern Recognition for Character Recognition”, O plus E 25, pp. 1143-1149 (2003)

  However, in the above two methods, there is no report on the separation when the wavelength filter is deteriorated due to the shift of the transmission wavelength of the wavelength filter. In the latter method, it is necessary to compare with all the assumed eye diagrams, and the processing load is large.

  The present invention has been made in view of such problems, and an object of the present invention is to provide an optical signal monitoring technique for specifying a deterioration factor and / or measuring a deterioration amount from an eye diagram.

In order to achieve the above object, the present invention provides a method for measuring a degradation factor of an optical signal in an optical network including an optical fiber and an optical wavelength filter , the optical signal comprising: Obtaining an eye diagram from, extracting a parameter correlated with a deterioration factor from the eye diagram, and obtaining a deterioration amount of the deterioration factor from the parameter, and extracting the parameter, As characteristic points from the eye diagram, the left and right cross points X1 and X2 of the eye opening, the point of the mark level maximum value Y, the curve of the optical signal modulated by 100, and the point of the optical signal modulated by 001 intersect The step of extracting Z and modulated by 111 as a parameter correlated with the deterioration factor from the feature point The parameter α is defined such that the difference between the mark level of the signal and the space level of the optical signal modulated by 000 is a, and the difference between the maximum value Y of the mark level and the space level of the optical signal modulated by 000 is b. = B / a, the time difference between the midpoint of the straight line connecting the cross points X1 and X2 and the crossing point Z is c, and the time difference between the cross points X1 and X2 is given as d. Parameter β = d / extracting the degradation amount, the step of obtaining the deterioration amount, obtaining a chromatic dispersion in the optical fiber based on the parameter α, and the optical wavelength filter based on the obtained dispersion and the parameter β. And a step of obtaining an inclination of

The invention according to claim 2 is the method according to claim 1 , wherein the step of extracting the feature points is the step of making the eye diagram into an eye line, and the eye line with the eye diagram. And a step of extracting feature points from.

The invention according to claim 3 is the method according to claim 1 or 2 , wherein the step of extracting the feature point includes a plurality of the feature points with the portion where the eye is open as the origin of coordinates. In some cases, the method includes a step of obtaining feature points by averaging the respective coordinates.

The invention according to claim 4 is the method according to any one of claims 1 to 3 , wherein the step of extracting the feature points obtains a histogram of an eye diagram when there are a plurality of feature points, It is characterized by comprising a step having a feature point where the distribution is large.

The invention according to claim 5 is the method according to any one of claims 1 to 4 , wherein when there are a plurality of feature points, the feature points are compared with known eye diagrams and feature point data. characterized in that it comprises the step of determining a.

The invention according to claim 6 is the method according to any one of claims 1 to 5 , wherein the step of acquiring the eye diagram includes the step of converting an optical signal into an electric signal, and the electric signal. Sampling.

The invention according to claim 7 is the method according to any one of claims 1 to 5 , wherein the step of acquiring the eye diagram includes a step of sampling an optical signal, and the sampled optical signal. Converting the signal into an electrical signal.

The invention according to claim 8 is the method according to any one of claims 1 to 7 , wherein the optical signal is converted into a medium having a variable deterioration amount before the step of acquiring the eye diagram. The method further includes the step of passing.

The invention according to claim 9 is the method according to any one of claims 1 to 7 , wherein the optical signal is converted into a plurality of signals having a known deterioration amount before the step of acquiring the eye diagram. The method further includes the step of passing through a medium and the step of changing the number of the plurality of media having the known deterioration amount.

The invention according to claim 10 is the method according to any one of claims 1 to 9 , wherein when the optical signal is phase-modulated, before the step of acquiring the eye diagram, The method further includes the step of converting the phase-modulated optical signal into an intensity-modulated optical signal.

The invention according to claim 11 is a method for improving the waveform of an optical signal in an optical network, and is based on parameters or feature points obtained by using the method according to any one of claims 1 to 10. And compensating for deterioration of the optical signal.

The invention according to claim 12 is the method according to claim 11 , wherein a modulation scheme or average optical power of the optical signal is obtained from the eye diagram, and based on the modulation scheme or average optical power. The method further comprises the step of shaping the waveform of the optical signal.

The invention according to claim 13 is an apparatus for measuring a degradation factor of an optical signal in an optical network including an optical fiber and an optical wavelength filter, and an eye diagram acquisition means for acquiring an eye diagram from the optical signal; A parameter extracting unit that extracts a parameter correlated with a deterioration factor from the eye diagram; and a deterioration amount calculating unit that calculates a deterioration amount of the deterioration factor from the parameter, wherein the parameter extracting unit is a feature point from the eye diagram. And means for extracting a cross point X1 and X2 at the left and right of the eye opening, a point Z at which the curve of the optical signal modulated with the maximum mark level Y, 100 and the curve of the optical signal modulated with 001 intersect As a parameter correlated with the deterioration factor from the feature point, the mark level of the optical signal modulated at 111 is used. And a space level of the optical signal modulated with 000 is a, and the difference between the maximum value Y of the mark level and the space level of the optical signal modulated with 000 is b. a, a parameter β = d / c is extracted, where c is the time difference between the midpoint of the straight line connecting the cross points X1 and X2 and the crossing point Z, and d is the time difference between the cross points X1 and X2. Means for determining the chromatic dispersion in the optical fiber based on the parameter α, and determining the slope of the optical wavelength filter based on the calculated dispersion and the parameter β. Means .

  According to the present invention, it is also possible to isolate degradation due to deviation of the transmission wavelength of the wavelength filter. Moreover, the load of calculation processing is small compared with the method compared with the conventional eye diagram. Furthermore, it is possible to identify and isolate the deterioration factor without extracting the clock.

  According to the present invention, it is possible to identify a deterioration factor by image recognition from an eye diagram acquired in an optical monitoring device. Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(First embodiment)
FIG. 1 shows a configuration example of an optical signal monitoring apparatus according to the first embodiment of the present invention, and FIG. 2 shows a configuration example of an optical signal monitoring apparatus according to the second embodiment of the present invention. The eye diagram may be acquired by electrical sampling as shown in FIG. 1 or by optical sampling as shown in FIG.

  In FIG. 1, an optical signal is photoelectrically converted by a photoelectric conversion circuit 11. The photoelectrically converted electrical signal is sampled by the clock from the local clock 13 in the electrical sampling 12. The sampled electrical signal is acquired as an eye diagram by the eye diagram acquisition circuit 14, and a deterioration factor is specified from the eye diagram acquired by the parameter extraction circuit 15 and output.

  On the other hand, in FIG. 2, the optical signal is directly sampled by the electrical pulse from the local clock 22 in the photoelectric sampling 21. The sampled optical signal is converted into an electrical signal by the photoelectric conversion circuit 23. An eye diagram is acquired from the converted electrical signal by the eye diagram acquisition circuit 24, a deterioration factor is specified from the eye diagram acquired by the parameter extraction circuit 25, and output. In optical sampling, an eye diagram can be acquired without extracting the clock by sampling at high speed using a local clock, which makes it possible to acquire an eye diagram without depending on the bit rate / modulation method. (See Non-Patent Document 3).

  Next, FIG. 3 shows a flow for specifying the degradation factor of the optical signal from the eye diagram and measuring the degradation amount in the optical signal monitoring apparatus according to the first embodiment of the present invention. First, in step 31, an eye diagram of an optical signal is acquired by the eye diagram acquisition circuit of FIG. 1 or FIG. FIG. 4A shows an example of the acquired eye diagram. Next, in step 32, the acquired diagram is eyelined (thinned) by image processing (see Non-Patent Document 4). FIG. 4B shows an example of an eye diagram made into an eyeline. Next, in step 33, feature points such as cross points are extracted from the eyelinetized eye diagram. FIG. 4C shows an example of extracted feature points. In step 34, a parameter having a correlation with the deterioration factor is obtained from the extracted feature points. Finally, in step 35, a deterioration factor is specified from these parameters.

  Factors that degrade optical signals include chromatic dispersion, deviation between the wavelength of the signal light and the transmission profile of the filter (transmission wavelength deviation), polarization dispersion, and nonlinear crosstalk. However, in the transmission of intensity modulation schemes such as 10 Gb / s and 40 Gb / s, chromatic dispersion and transmission wavelength shift are the main deterioration factors. Degradation due to chromatic dispersion occurs due to the influence of chromatic dispersion inherent to quartz, and deterioration due to transmission wavelength shift is due to the influence of chromatic dispersion on the spectrum that is asymmetrical due to the deviation between the transmission profile of the filter and the signal light wavelength. appear.

  Here, as an example of the present invention, a case where signal light is deteriorated due to chromatic dispersion and transmission wavelength shift will be described. FIG. 5A is a diagram for explaining the inclination of the filter. In FIG. 5A, the dotted line indicates the transmission profile of the filter, and the solid line indicates the wavelength of the optical signal. As shown in the figure, the slope of the transmission profile of the filter at the center wavelength of the optical signal is defined as the slope of the filter.

  Next, with reference to FIG. 5B, a method of extracting feature points from the acquired eye diagram and obtaining a parameter correlated with the deterioration factor will be described. Here, as an example, the left and right crosspoints when viewed from the center of the eye opening are X1 and X2, the maximum mark level is Y, and the curve that intersects the lower part of the eye opening (the curves corresponding to digital 100 and 001) ) Is defined as Z. Next, parameters that correlate with the deterioration factors of the optical signal are obtained from these feature points. Α = b / a and β = d / c are defined as parameters indicating degradation due to chromatic dispersion and transmission wavelength deviation. a is a difference between a mark level corresponding to digital 111 and a space level corresponding to digital 000, b is a difference between a maximum value Y of the mark level and a space level corresponding to digital 000, and c is a cross point X1 and A time difference connecting X2 and d is a time difference between a midpoint of a straight line connecting the cross points X1 and X2 and a point Z intersecting at the lower stage in the eye opening. These parameters are independent of each deterioration factor, and are preferably parameters uniquely determined by the deterioration factor.

  FIG. 6 shows the correlation between the parameters α and β and the deterioration factors. As can be seen from the figure, within the effective range, the parameters α and β are correlated with the deterioration factors. FIG. 7 shows a flow for specifying the degradation factor of the optical signal from the parameters α and β and measuring the degradation amount. In step 71, the parameters α and β are calculated. In step 72, the variance is obtained based on the calculated parameter α from the correlation shown in FIG. In step 73, the filter inclination is obtained from the correlation shown in FIG. 6B based on the calculated parameter β and the obtained variance. In step 74, the degradation amount of the dispersion and the inclination of the filter is specified as the degradation factor of the optical signal.

  Next, an example in which the parameters α and β are calculated from the actually deteriorated eye diagram and the deterioration factor is specified will be described. FIG. 8 is a deteriorated eye diagram obtained from the simulation. This eye diagram is degraded with a dispersion of −400 ps / nm and a filter inclination of ± 0 dB / Hz. Here, a modulator having a chirp parameter α = −0.7 is used. According to the present embodiment, feature points are extracted from this eye diagram, and the parameters α and β are calculated. As a result, the dispersion is −440 to −280 ps / nm, and the filter inclination is −0.23 to 0.20 dB / Hz. I was able to.

  As described above, according to the present invention, the deterioration factor can be specified by acquiring the eye diagram from the optical signal to be measured and extracting the parameters α and β. Here, although two parameters α and β are used, it is possible to specify a deterioration factor with higher accuracy by using more parameters.

(Second Embodiment)
As an extension of the first embodiment, it is possible to monitor the optical waveform with higher accuracy by passing a medium having a variable deterioration amount before sampling the optical signal to be measured. As a specific example, as shown in the first embodiment, a case of deterioration due to wavelength dispersion and deterioration due to transmission wavelength shift will be examined. Degradation due to transmission wavelength deviation may be difficult to isolate using only the parameters of the first embodiment. For example, when the chirp parameter α = 0 of the modulator and the variance is 0, the slope of the graph of FIG. 6B is 0, and the slope of the filter cannot be obtained. Therefore, by passing a medium having a known dispersion amount before acquiring the eye diagram, the influence of the transmission wavelength shift of the filter can be accurately obtained.

  FIG. 9 shows a configuration example of an optical signal monitoring apparatus according to the second embodiment of the present invention. In FIG. 9, after the optical signal passes through the medium 81 having a variable dispersion amount, the optical signal is directly sampled by the electric pulse from the local clock 83 in the photoelectric sampling 82. The sampled optical signal is converted into an electrical signal by the photoelectric conversion circuit 84. An eye diagram is acquired from the converted electrical signal by the eye diagram acquisition circuit 85, and a deterioration factor is specified from the eye diagram acquired by the parameter extraction circuit 86, and is output. Note that this embodiment can be similarly applied to a configuration for acquiring an eye diagram by electrical sampling (configuration in FIG. 1).

  As the medium 81 having a variable dispersion amount, a variable dispersion circuit (fiber Bragg grating, VIPA (Virtually Imaged Array), or the like) may be used, or a plurality of known dispersion media may be switched by an optical switch. Thereby, it is possible to accurately detect the transmission wavelength shift of the filter with zero dispersion.

  In the present embodiment, it is also possible to specify a deterioration factor by comparing a signal passing through a known dispersion medium and an input signal under measurement. FIG. 10 shows another configuration example of the optical signal monitoring apparatus according to the second embodiment of the present invention. In FIG. 10, the optical signal is branched, one is input to the photoelectric sampling 92-1 and the other is input to another photoelectric sampling 92-2 after passing through the medium 91 having a known dispersion amount. The respective optical signals are directly sampled by the electrical pulses from the local clock 93 in the photoelectric samplings 92-1 and 92-2, and converted into electrical signals by the photoelectric conversion circuits 94-1 and 94-2, respectively. Eye diagrams are acquired from the converted electrical signals by the eye diagram acquisition circuits 95-1 and 95-2, and deterioration factors are specified from the eye diagram acquired by the parameter extraction circuit 96 and output. The measurement can be performed by directly comparing the parameter obtained from the eye diagram passed through the medium having a known dispersion amount and the parameter obtained from the input signal under measurement.

  In this way, by combining with a medium having a known dispersion amount, it is possible to measure a deterioration factor that is difficult to measure only by the signal under measurement.

(Third embodiment)
In the current optical network, an intensity-modulated signal such as RZ is the mainstream, but in the future optical network, an optical network using a phase modulation system such as DPSK is also being studied in order to improve dispersion tolerance. . For such signals, deterioration factors can be specified by converting intensity modulation and phase modulation.

  FIG. 11 shows a configuration example of an optical signal monitoring apparatus according to the third embodiment of the present invention. In FIG. 11, a phase-modulated optical signal is converted into an intensity-modulated optical signal by a modulation system conversion circuit 101 typified by a Mach-Zehnder interferometer. The converted optical signal is directly sampled by the electrical pulse from the local clock 103 in the photoelectric sampling 102. The sampled optical signal is converted into an electrical signal by the photoelectric conversion circuit 104. An eye diagram is acquired from the converted electrical signal by the eye diagram acquisition circuit 105, a deterioration factor is specified from the eye diagram acquired by the parameter extraction circuit 106, and is output. Thus, the principle of the present invention can be applied not only to intensity modulation but also to phase modulation.

(Fourth embodiment)
According to the present invention, the quality of an optical signal can be constantly monitored by installing the optical signal monitoring device as described above in an optical network. When deterioration is recognized by the optical signal monitoring device, the network operator can be notified of the deterioration by issuing a warning from OpS (Operation System), NMS (Network Management System), or the like. Furthermore, in OADM (Optical Add / Drop Multiplexer), OXC (Optical Cross Connector), etc., narrowing the spectrum by multiple stages of filters is an important issue, but the optical signal immediately after passing through each filter is monitored and automatically adjusted. As a result, the problem of narrowing the spectrum can be solved.

  Further, it can be used as an apparatus for improving the optical waveform by combining the principle of the present invention with deterioration compensation, optical waveform shaping, and the like. FIG. 12 shows a configuration example of an optical waveform improving apparatus according to the fourth embodiment of the present invention.

  In FIG. 12, the optical signal is optically branched, one is input to the optical signal monitoring device 111, and the other is input to the degradation compensation circuit 112 and the optical waveform shaping circuit 113. In the optical signal monitoring device 111, the cause and amount of deterioration of the optical signal are specified, and the information is fed forward to the deterioration compensation circuit 112.

  Alternatively, in FIG. 12, the optical signal may be optically branched after passing through the deterioration compensation circuit 112 and the optical waveform shaping circuit 113, and one of them may be input to the optical signal monitoring device 111. In this case, the deterioration factor and the deterioration amount from the optical signal monitoring apparatus 111 are fed back to the deterioration compensation circuit 112.

  As a typical example of the chromatic dispersion degradation compensation, VIPA or the like can be cited as the degradation compensation circuit. The optical waveform shaping circuit uses nonlinear characteristics to improve SNR degradation. However, in order to operate transparently, information on the optical signal modulation scheme and average power is required. In this case, the modulation method and average power can be obtained from the difference between the mark level and the space level from the eye diagram obtained by the optical signal monitoring device. The optical signal monitoring apparatus obtains a modulation method such as NRZ and RZ and average power, and feedforward / feedback to the optical waveform shaping circuit 113, thereby improving the transparent optical signal waveform.

(Fifth embodiment)
In the first to fourth embodiments, an eyeline is formed from an eye diagram and a cross point is extracted by image processing. In addition, it is possible to extract the cross point directly from the eye diagram. This is a method of obtaining the histogram by cutting the acquired eye diagram and obtaining the position of the cross point from the histogram. By this method, it is possible to calculate feature points such as cross points directly from the eye diagram.

(Sixth embodiment)
If the waveform of the eye diagram is disturbed due to deterioration, the feature points cannot be recognized and it is difficult to extract the feature points. Therefore, if a plurality of feature points cannot be recognized, the feature points are recognized by the following method. The feature point can be extracted by averaging the coordinates of a plurality of feature points from the center where the eye is open. In addition, it is possible to recognize a known eye diagram and a portion that is likely to be a feature point compared to a feature point as a feature point. It is also possible to obtain a histogram of an eye diagram and recognize a point with a large distribution as a feature point.

  Although the present invention has been specifically described based on some embodiments, the embodiments described herein are merely illustrative in view of many possible embodiments to which the principles of the present invention can be applied. However, it does not limit the scope of the present invention. The configuration and details of the embodiment exemplified here can be changed without departing from the spirit of the present invention. Further, the illustrative components and procedures may be changed, supplemented, or changed in order without departing from the spirit of the invention.

It is a block diagram which shows the structural example of the optical signal monitoring apparatus by the 1st Embodiment of this invention. It is a block diagram which shows the other structural example of the optical signal monitoring apparatus by the 1st Embodiment of this invention. 5 is a flowchart for specifying a degradation factor of an optical signal according to the first embodiment of the present invention. It is a figure for demonstrating the process of the eye diagram of the optical signal by the 1st Embodiment of this invention, (a) shows the acquired eye diagram, (b) shows the thinned eye diagram, (c ) Indicates the characteristic points of the eye diagram. It is a figure which shows the inclination of the filter by the 1st Embodiment of this invention, the feature point of an eye diagram, and a parameter, (a) shows the inclination of a filter, (b) shows the relationship between the feature point of an eye diagram, and a parameter. Show. It is a graph which shows the correlation of a parameter and a degradation factor, (a) is a graph which shows the correlation of parameter (alpha) and chromatic dispersion, (b) is a graph which shows the correlation of parameter (beta) and a transmission wavelength shift. It is a flowchart for the specification of the degradation amount of the optical signal by the 1st Embodiment of this invention. It is a figure which shows the deteriorated eye diagram acquired by simulation. It is a block diagram which shows the structural example of the optical signal monitoring apparatus by the 2nd Embodiment of this invention. It is a block diagram which shows the other structural example of the optical signal monitoring apparatus by the 2nd Embodiment of this invention. It is a block diagram which shows the structural example of the optical signal monitoring apparatus by the 3rd Embodiment of this invention. It is a block diagram of the optical waveform improvement apparatus by the 4th Embodiment of this invention.

Explanation of symbols

11, 23, 84, 94-1, 94-2, 104 Photoelectric conversion circuit 12 Electrical sampling 13, 22, 83, 93, 103 Local clock 14, 24, 85, 95-1, 95-2, 105 Eye diagram Acquisition circuit 15, 25, 86, 96, 106 Parameter extraction circuit 21, 82, 92-1, 92-2, 102 Photoelectric sampling 81, 91 Medium having variable dispersion amount 101 Modulation system conversion circuit 111 Optical signal monitoring device 112 Various deterioration compensation devices 113 Optical waveform shaping device

Claims (13)

A method for measuring a degradation factor of an optical signal in an optical network including an optical fiber and an optical wavelength filter ,
Obtaining an eye diagram from the optical signal;
Extracting a parameter correlated with a deterioration factor from the eye diagram;
Obtaining a deterioration amount of the deterioration factor from the parameter ,
Extracting the parameter comprises:
As a feature point from the eye diagram,
Left and right cross points X1 and X2 of the eye opening,
Maximum mark level Y,
Extracting a point Z where the curve of the optical signal modulated at 100 and the curve of the optical signal modulated at 001 intersect;
As a parameter correlated with the deterioration factor from the feature point,
The difference between the mark level of the optical signal modulated at 111 and the space level of the optical signal modulated at 000 is defined as a, and the difference between the maximum value Y of the mark level and the space level of the optical signal modulated at 000 is defined as a. parameter α = b / a given as b,
A step of extracting a parameter β = d / c given as a time difference between a midpoint of a straight line connecting the cross points X1 and X2 and the crossing point Z and c as a time difference between the cross points X1 and X2. And
The step of obtaining the deterioration amount includes
Obtaining chromatic dispersion in the optical fiber based on the parameter α;
Obtaining the slope of the optical wavelength filter based on the obtained dispersion and the parameter β . The method according to claim 1 , wherein the step of extracting the feature points includes:
Converting the eye diagram into an eyeline;
Extracting feature points from the eyelined eye diagram. The method according to claim 1 or 2 , wherein the step of extracting the feature points includes:
A method comprising: obtaining a feature point by averaging each coordinate when there are a plurality of the feature points with a portion where an eye is open as a coordinate origin. The method according to any one of claims 1 to 3, the step of extracting the feature point, a histogram of the eye diagram when the feature points are multiple steps of feature points the place of distribution greater A method characterized by comprising. The method according to any one of claims 1 to 4, and the known eye diagrams when feature points are multiple, method characterized by comprising the step of obtaining feature points as compared to the data of the feature points . The method according to any one of claims 1 to 5 , wherein the step of acquiring the eye diagram comprises:
Converting an optical signal into an electrical signal;
Sampling the electrical signal. The method according to any one of claims 1 to 5 , wherein the step of acquiring the eye diagram comprises:
Sampling an optical signal;
Converting the sampled optical signal into an electrical signal. A method according to any of claims 1 to 7 , comprising
Passing the optical signal through a medium having a variable amount of degradation before the step of acquiring the eye diagram. A method according to any of claims 1 to 7 , comprising
Passing the optical signal through a plurality of media having a known amount of degradation prior to obtaining the eye diagram;
Changing the number of a plurality of media having the known degradation amount. A method according to any of claims 1 to 9 , comprising
Converting the phase-modulated optical signal into an intensity-modulated optical signal before obtaining the eye diagram if the optical signal is phase-modulated. . A method for improving the waveform of an optical signal in an optical network, comprising:
Method characterized by comprising the step of compensating the degradation of the optical signal on the basis of claims 1 to be parameters or feature points obtained using the method according to any one of 10. The method of claim 11 , comprising:
The method further comprising: obtaining a modulation scheme or average optical power of the optical signal from the eye diagram, and shaping a waveform of the optical signal based on the modulation scheme or average optical power. An apparatus for measuring a degradation factor of an optical signal in an optical network including an optical fiber and an optical wavelength filter ,
Eye diagram acquisition means for acquiring an eye diagram from the optical signal;
Parameter extraction means for extracting a parameter correlated with a deterioration factor from the eye diagram;
A deterioration amount calculating means for obtaining a deterioration amount of the deterioration factor from the parameter ,
The parameter extraction means includes
As a feature point from the eye diagram,
Left and right cross points X1 and X2 of the eye opening,
Maximum mark level Y,
Means for extracting a point Z where the curve of the optical signal modulated at 100 and the curve of the optical signal modulated at 001 intersect;
As a parameter correlated with the deterioration factor from the feature point,
The difference between the mark level of the optical signal modulated at 111 and the space level of the optical signal modulated at 000 is defined as a, and the difference between the maximum value Y of the mark level and the space level of the optical signal modulated at 000 is defined as a. parameter α = b / a given as b,
Means for extracting a parameter β = d / c, where c is the time difference between the midpoint of the straight line connecting the cross points X1 and X2 and the intersecting point Z, and d is the time difference between the cross points X1 and X2. And
The deterioration amount calculating means includes
Means for determining chromatic dispersion in the optical fiber based on the parameter α;
Apparatus characterized by comprising a means for determining the inclination of the optical wavelength filter based on the parameter β and the dispersion obtained said.

Images