JP3504902B2 - Optical signal quality evaluation method, optical signal quality evaluation device, and storage medium - 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 signal quality evaluation method, an optical signal quality evaluation apparatus, and a storage medium in digital optical fiber transmission, and particularly in a photonic network in which different bit rates and different signal formats coexist. The present invention relates to a technique for monitoring optical signal quality deterioration such as noise deterioration and waveform distortion with a single circuit regardless of the bit rate and signal format of the optical signal to be measured.

[0002]

2. Description of the Related Art Conventionally, synchronous digital high arrakey (Sy
In the nchronous Digital Hierarchy (SDH) transmission system, bit interleaved parity
By performing a parity check called "ved Parity" between the repeaters and between the multiplexed terminal stations, the fault section is identified and the switching start signal is obtained.

However, in these signal quality monitoring systems, the bit rate, signal format and modulation format (N
RZ (Non Return to Zero) or RZ
(Return to Zero) corresponding to the receiving system (clock extraction circuit, receiving circuit, frame detection circuit, parity check circuit or error detection circuit consisting of matching circuit) is required. Therefore, there is a point that a single receiving system cannot support signals of arbitrary bit rates, signal formats, and modulation formats.

As a method for solving this point, reference document 1
There is an optical signal quality monitor described in (Reference 1: Japanese Patent Laid-Open No. 11-223575). This optical signal quality monitor is a receiving system (clock extraction circuit, receiving circuit, frame detection circuit, which corresponds to the bit rate, signal format and modulation format,
An error detection circuit consisting of a parity check circuit or a matching circuit is not required, and a single reception system can handle signals of arbitrary bit rates, signal formats, and modulation formats.

[0005]

However, when an amplitude histogram obtained from an asynchronous eye pattern is evaluated using the above conventional optical signal quality monitor, a cross point (between level 1 and level 0 of the optical signal) is evaluated. Since the inaccuracy of quality evaluation due to (part) remains, it is one of the problems to be solved to provide an evaluation method in which this influence is reduced.

Optical signal quality evaluation algorithms in the conventional optical signal quality monitor are shown in FIGS.

FIG. 13A: An intensity distribution within a certain average time is obtained by optical sampling or electrical sampling.

FIG. 13 (B): An amplitude histogram is obtained from the obtained intensity distribution.

FIG. 14 (A): m0 'is the maximum value when the amplitude histogram is examined from the smaller intensity level.
Stipulate.

FIG. 14B: Integrating the number of sampling points from the sampling point with the maximum intensity level toward the smaller intensity level,

[0011]

## EQU00003 ## N (middle) = N (total) .times.D.times.M (1) (where N (total) is the total number of sampling points, D is the duty ratio of the optical signal (ratio of pulse width and time slot), M
Is the minimum level of the integrated sampling points when the number of sampling points N (middle) obtained by the mark rate (probability of occurrence of level 1 in digital transmission) and the integral value are equal to m (middle).

FIG. 15A:

[0013]

[Equation 4]     m1 ′ = 2 × {m (middle) −m0 ′} (2) Determine m1 'found in.

FIG. 15B:

[0015]

[Equation 5]     A = m1'-alpha (m1'-m0 ') (3) The strength level obtained by

[0016]

[Equation 6] B = m0 ′ + alpha (m1′−m0 ′) (4) The intensity level obtained by (4) is a threshold value B (where alpha is 0 <
alpha <a real number of 0.5), and a distribution having an intensity level equal to or higher than the threshold value A is a level 1 distribution, and a distribution having an intensity level equal to or lower than the threshold value B is a level 0 distribution.

FIG. 16A: Average values m1 and m0 and standard deviations s1 and s0 are obtained in the level 1 and level 0 distributions determined in FIG. 15B, respectively.

FIG. 16B: From the average values m1 and m0 and standard deviations s1 and s0 obtained in FIG.

[0019]

[Expression 7] Q = | m1-m0 | / (s1 + s0) The Q value obtained by (5) is used as a quality evaluation parameter as a signal-to-noise coefficient.

In this conventional example, as shown in the above equations (2) to (4), there is a problem to be solved that the influence of the cross point always remains and the quality evaluation accuracy is lowered.

The present invention has been made in view of the above points, and an object thereof is to be measured in a photonic network of digital optical fiber transmission in which signals of different bit rates, signal formats and modulation formats are mixed. Optical signal quality evaluation method, optical signal quality evaluation device, and storage medium capable of monitoring optical signal quality deterioration such as noise deterioration and waveform distortion with a single circuit, regardless of the signal bit rate, signal format, and modulation format To provide.

A further object of the present invention is to reduce the influence on the SNR (Signal to Noise Ratio) of the optical signal on the digital optical fiber transmission line and improve the quality evaluation accuracy.

[0023]

In order to achieve the above object, the invention of an optical signal quality evaluation method according to claim 1 is a step of converting an optical signal having a bit rate f0 (bit / s) into an electric intensity modulation signal. And clock frequency f1 (H
z) (f1 = (N / M) f0 + a, where a is an offset frequency and N and M are positive integers), the intensity distribution of the optical signal is measured by sampling the electrical intensity modulation signal intensity, Among the sampling points constituting the intensity distribution of the measurement optical signal, a point group (a-1) having an intensity higher than a predetermined intensity threshold value (A) and the point group (a
-1) The point cloud (a-2) that is line-symmetric with respect to the intensity threshold value (A) is set to "level 1" as a whole, and the point cloud (intensity lower than the separately determined intensity threshold value (B) ( b-1) and the
A step of setting the entire point group (b-2) line-symmetric with respect to the intensity threshold value (B) of the point group (b-1) to "level 0", the "level 1" and the "level 0" Signal-to-noise obtained as a ratio of the difference between the average value intensities within each averaging time and the sum of the standard deviation values of each of the "level 1" and the "level 0" within the averaging time. Evaluating the ratio coefficient.

In order to achieve the above object, the invention of an optical signal quality evaluation method according to claim 2 is the bit rate f0 (bit
/ S) and the repetition frequency f1 (H
z) (f1 = (N / M) f0 + a, a is an offset frequency, N and M are positive integers), and the pulse width is sufficiently narrower than the time slot of the optical signal. to generate a cross-correlation signals of different optical frequencies, the No. said phase SekiShin after photoelectric conversion, composing the steps of measuring the intensity distribution of the optical signal by performing electrical signal processing, the intensity distribution of the optical signal to be measured among the sampling points, with a predetermined intensity threshold (a) high strength point group than (a-1), line symmetry about the intensity threshold (a) of the point group (a-1) The entire point group (a-2) is set to "level 1", and the point group (b-1) having an intensity lower than a separately set intensity threshold value (B) and the point group (b-1)
A line group (b-
2) the step of setting the whole to “level 0”, the difference between the average value intensities of the “level 1” and the “level 0” within a certain average time, the “level 1” and the “level” Evaluating the signal-to-noise ratio coefficient obtained as a ratio with the sum of the standard deviation values of the respective "0" within the corresponding averaging time.

Here, for the intensity thresholds (A) and (B), two maximum values are obtained from the amplitude histogram obtained from the intensity distribution of the optical signal under measurement, and the one having the higher amplitude intensity is the intensity. The threshold value (A) may be used, and the lower one may be the intensity threshold value (B).

Further, the first maximum value of the amplitude histogram when the intensity level is larger is determined as the intensity threshold value (A), and the amplitude histogram is examined from the smaller intensity level. It is possible to define the first maximum value of the above as the intensity threshold value (B).

In addition, the first local maximum value of the amplitude histogram when the intensity level is smaller is determined as the intensity threshold value (B), and the intensity level is sampled from the maximum sampling point toward the smaller intensity level. , Integrate the sampling points,

[0028]

## EQU00008 ## N (middle) = N (total) .times.D.times.M (where N (total) is the total number of sampling points, D is the duty ratio of the optical signal (ratio of pulse width and time slot), M
Is the minimum level of the integrated sampling points when the integrated value is equal to the number of sampling points N (middle) obtained by the mark rate (the probability of occurrence of level 1 in digital transmission), and m (middle)

[0029]

The intensity threshold value (A) can be characterized in that the intensity threshold value (A) = 2 × {m (middle) −intensity threshold value (B)}.

Further, instead of the evaluation of the signal-to-noise ratio coefficient, it is possible to evaluate only the ratio of the average intensity and the standard deviation value of "level 1" or the standard deviation value.

In order to achieve the above object, the invention of an optical signal quality evaluation apparatus according to claim 7 is a bit rate f0 (bit /
photoelectric conversion means for converting an optical signal having s) into an electric intensity modulation signal, and a clock frequency f1 (Hz) (f1 = (N
/ M) f0 + a, a is an offset frequency, N and M are positive integers), and an optical signal quality evaluation device using an electrical sampling oscilloscope that measures the intensity distribution of the optical signal by sampling the intensity modulated signal intensity there is obtained in the electrical sampling oscilloscope, among the sampling points which constitute the intensity distribution of the optical signal to be measured, predetermined intensity threshold (a) high strength group of points than the (a-1) , In front of the point group (a-1)
Point group (a-2) line-symmetric with respect to the intensity threshold (A)
Is set as "level 1", and the point group (b-1) having an intensity lower than the intensity threshold value (B) separately defined and the point group (b
-1) intensity distribution estimating means for setting the entire line group (b-2) line-symmetric with respect to the intensity threshold value (B) to "level 0", and the "level 1" and the "level 0" A signal-to-noise ratio obtained as a ratio of the difference between the average value intensities within a certain average time and the sum of the standard deviation values of the "level 1" and the "level 0" within the respective average time. And an optical signal quality evaluation means for evaluating the coefficient.

In order to achieve the above object, the invention of an optical signal quality evaluation apparatus according to claim 8 is the bit rate f0 (bit /
s) and the repetition frequency is f1 (Hz)
(F1 = (N / M) f0 + a, a is the offset frequency,
N, M is using a positive integer) narrow enough sampling optical pulse train pulse width than the time slot of the optical signal, these two light and to generate a cross-correlation signals of different optical frequencies, photoelectrically No. said phase SekiShin An optical signal quality evaluation device using an optical sampling oscilloscope, which measures the intensity distribution of an optical signal by performing electrical signal processing after conversion, wherein the intensity distribution of the measured optical signal obtained by the optical sampling oscilloscope is configured. Of the sampling points to be set, the point group (a-1) having a higher intensity than a predetermined intensity threshold value (A) and the intensity threshold value (A) of the point group (a-1 ) are line-symmetrical. The entire point cloud (a-2) is set to "level 1", and the point cloud (b-1) having an intensity lower than the intensity threshold (B) separately defined and the point cloud (b-1) For on the intensity threshold (B) And intensity distribution estimating means the overall axisymmetric point group of (b-2) to "Level 0", the difference between the average intensity within the average time each of certain of the said "level 1", "Level 0" And an optical signal quality evaluation unit for evaluating a signal-to-noise ratio coefficient obtained as a ratio of the sum of the standard deviation values of the "level 1" and the "level 0" within the average time. It is characterized by

In order to achieve the above object, the invention of a storage medium according to a tenth aspect of the invention is a photoelectric conversion means for converting an optical signal having a bit rate f0 (bit / s) into an electrical intensity modulation signal, and a clock frequency f1 (Hz. ) (F1 = (N / M)
f0 + a, a is the offset frequency, N and M are positive integers)
A storage medium storing a program for executing a light signal quality evaluation by a computer using an electric sampling oscilloscope that measures the intensity distribution of an optical signal by sampling the electric intensity modulated signal intensity at Is a point group (a-1) having a higher intensity than a predetermined intensity threshold value (A) among the sampling points constituting the intensity distribution of the measured optical signal obtained by the electric sampling oscilloscope to the computer. a) is the whole the point group for (a-1) of the intensity threshold (a) line-symmetrical point group of (a-2) a "level 1", separately determined intensity threshold (B Of the point group (b-1) having a lower intensity than that of (b-1) and the point group (b-2 ) which is line-symmetric with respect to the intensity threshold value (B) of the point group (b-1) . <br/> Body level 0 ”, and the difference between the average value intensities of the“ level 1 ”and the“ level 0 ”within a certain average time and the average time of the“ level 1 ”and the“ level 0 ”. It is characterized in that the signal-to-noise ratio coefficient obtained as a ratio with the sum of the standard deviation values in is evaluated.

In order to achieve the above object, the invention of a storage medium according to claim 11 is such that an optical signal having a bit rate f0 (bit / s) and a repetition frequency f1 (Hz) (f1
= (N / M) f0 + a, a is the offset frequency, N, M
The pulse width using well narrow sampling optical pulse train from the time slot of the optical signal at a positive integer), to generate a cross-correlation signal of the optical frequency different from these two light, correlation
Measuring the intensity distribution of the optical signal after photoelectric conversion of signals by performing an electrical signal processing, a storage medium storing a program for execution by a computer the optical signal quality evaluation using optical sampling oscilloscope, the The program instructs the computer to use the optical sampling oscilloscope to obtain a point cloud (a-) having a higher intensity than a predetermined intensity threshold value (A) among the sampling points constituting the intensity distribution of the measured optical signal. 1) and this point
An intensity that is lower than an intensity threshold (B) separately determined by setting the entire point group (a-2) line-symmetric with respect to the intensity threshold (A) of the group (a-1) to "level 1". Point cloud (b-
Wherein a 1), then the whole for the intensity threshold of the point group (b-1) (B) line-symmetrical point group of (b-2) and "Level 0", the "level 1", " It is obtained as a ratio of the difference between the average value intensities of each "level 0" within a certain average time and the sum of the standard deviation values of each of the "level 1" and the "level 0" within the corresponding average time. It is characterized in that the signal-to-noise ratio coefficient is evaluated.

(Operation) In the present invention, a certain bit rate f
An optical signal having 0 (bit / s) is converted into an electric intensity modulation signal, and this electric intensity modulation signal strength is converted to a clock frequency f1.
An electrical sampling method is used in which the intensity distribution of an optical signal is measured by sampling at (Hz) (f1 = (N / M) f0 + a, a is an offset frequency, and N and M are positive integers).

Further, in the present invention, the bit rate f0
An optical signal having (bit / s) and a repetition frequency of f
1 (Hz) (f1 = (N / M) f0 + a, a is an offset frequency, N and M are positive integers), and the pulse width is sufficiently narrower than the time slot of the optical signal. to generate a cross correlation signal light with different optical frequencies, the phase No. SekiShin after converting photoelectrically, using an optical sampling method for measuring the intensity distribution of the optical signal by performing electrical signal processing.

[0037] In the present invention, a frame detection circuit, instead of using such error detection circuit comprising a parity check circuit or matching circuit, electrical sampling method or optical sampling method utilized in an asynchronous system does not use a clock extraction circuit The intensity distribution of the measured optical signal is measured from the obtained sampling points, and among the sampling points constituting the intensity distribution of the measured optical signal, the point group having an intensity higher than a predetermined intensity threshold value (A). (A-1)
And the entire point group (a-2) line-symmetric with respect to the intensity threshold value (A) of the point group (a-1) is set to "level 1", and the intensity threshold value (B) defined separately is Low intensity point cloud (b
-1) and the point group (b-2) which is line-symmetric with respect to the intensity threshold value (B) of the point group (b-1) are referred to as "level 0" .
Then, the difference between the average value intensities of “level 1” and “level 0” within a certain average time and the standard deviation value of “level 1” and “level 0” within the corresponding average time of Evaluate the signal-to-noise ratio coefficient obtained as a ratio to the sum, or
Alternatively, only the ratio of the "level 1" average intensity and the standard deviation value or the standard deviation value is evaluated. That is, the present invention
Then, of the sampled point cloud, the threshold (A)
From the highest point group (a-1),
The point group (a
-2) can be directly obtained and used as the distribution of "level 1"
From the threshold (B) of the sampled point cloud,
From the lowest point group (b-1) to the threshold of that point group (b-1)
Point (b-
2) is directly obtained and the distribution of “level 0” is calculated as “level
Calculate the average strength and standard deviation of "1" and "level 0"
To evaluate the optical signal quality.

In the present invention, sampling is performed in this way.
The distribution of "level 1" and "level 0" directly from the point cloud
The sampled point cloud as a histogram
Need to find the envelope of the histogram
Instead, infer the histogram function from the envelope of the histogram.
There is no need to set. Therefore, the present invention has a very simple structure.
Optical signal quality evaluation with less influence of cross points
realizable.

[0039]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below in detail with reference to the drawings.

(First Embodiment) FIGS. 1 to 6 show a first embodiment of an optical signal quality monitoring method according to the present invention. The present embodiment exemplifies a case where the intensity distribution of the NRZ optical signal is evaluated using the electrical sampling method or the optical sampling method. A commercially available electric sampling device or the like can be used for measuring the optical signal intensity distribution by the electric sampling method. Further, the optical signal intensity distribution measurement by the optical sampling method can use the optical sampling of Reference 2 or the like (Reference 2: Takara et al .: “Ultrafast optical waveform measurement by optical sampling using sum frequency light generation” Law "The Institute of Electronics, Information and Communication Engineers, B-1, vol.J75-B-1,
No. 5, pp. 372-380, 1992).

In the case of using the optical sampling method, as shown in (A) to (C) of FIG. 1, in the receiving system, the optical amplification repeating system or the optical regenerating repeating system, the optical sampling oscilloscope is used to obtain the signal strength. Get the distribution. The cross-correlation signal in this case can be obtained by utilizing the second harmonic generation, the sum frequency light generation, the difference frequency light generation, the four-wave mixing light generation, or the like.

In FIGS. 1A to 1C, 100 is a photonic network for digital optical fiber transmission in which different bit rates and different signal formats are mixed, and 105 is an optical sampling oscilloscope.

FIG. 1A shows a receiving system unit 101 having a photoelectric conversion circuit 103 and an electric signal processing circuit 104.
The optical sampling oscilloscope 10 is connected to the optical sampling oscilloscope 10 via the optical branching unit 102 coupled to the front stage of the photoelectric conversion circuit 103.
The case where 5 is connected is shown.

FIG. 1B shows an optical amplification circuit 1 for an optical amplification repeater unit 106 having an optical amplification circuit 108.
A case where the optical sampling oscilloscope 105 is connected via the optical branching unit 107 coupled to the preceding stage of 08 is shown.

FIG. 1C shows the photoelectric conversion circuit 1 for the optical regeneration repeater unit 110 having the photoelectric conversion circuit 112, the electric signal processing circuit 113, and the photoelectric conversion circuit 114.
The case where the optical sampling oscilloscope 105 is connected via the optical branching unit 111 coupled to the preceding stage of 12 is shown.

When the electric sampling method is used, FIG.
As shown in (A) to (C), a signal intensity distribution is obtained by using an electric sampling oscilloscope in the receiving system, the optical amplification repeating system, or the optical regenerating repeating system.

In FIGS. 2A to 2C, 205 is an electric sampling oscilloscope.

FIG. 2A shows a reception system unit 201 having a photoelectric conversion circuit 203 and an electric signal processing circuit 204.
In contrast, the photoelectric conversion circuit 203 and the electric signal processing circuit 20
A case where an electrical sampling oscilloscope 205 is connected via a branching unit 202 coupled between four is shown.

FIG. 2B shows an optical amplification circuit 2 for an optical amplification repeater unit 206 having an optical amplification circuit 208.
The optical sampling oscilloscope 2 is connected to the optical sampling oscilloscope 2 via the optical branching unit 207 and the photoelectric conversion circuit 209, which are connected to the preceding stage of 08.
The case where 05 is connected is shown.

FIG. 2C shows the photoelectric conversion circuit 2 for the optical regeneration repeater unit 210 having the photoelectric conversion circuit 212, the electric signal processing circuit 213, and the photoelectric conversion circuit 214.
12 connected to the electrical signal processing circuit 213
1 shows a case where the electrical sampling oscilloscope 205 is connected via 1.

FIGS. 3 to 6 show an optical signal quality evaluation algorithm in the optical signal quality monitor according to the first embodiment of the present invention.

FIG. 3A: First, a certain average is obtained by optical sampling by the optical sampling oscilloscope 105 using the configuration shown in FIG. 1 or electrical sampling by the electrical sampling oscilloscope 205 using the configuration shown in FIG. Find the intensity distribution in time.

FIG. 3B: An amplitude histogram is obtained from the obtained intensity distribution.

FIG. 4A: A threshold value A is defined as the first maximum value when the amplitude histogram is examined from the one having the largest intensity level.

FIG. 4 (B): The threshold B is defined as the first local maximum value when the amplitude histogram is checked from the smaller intensity level.

FIG. 5A: A sampling point group (a-1) having an intensity greater than the intensity threshold value (A) and a line regarding the intensity threshold value (A) of this point group (a-1). The entire symmetric point group (a-2) is set as the distribution of "level 1", and the average value m1 and standard deviation s1 of this "level 1" are obtained.

FIG. 5 (B): a sampling point group (b-1) whose intensity is smaller than the intensity threshold value (B) and a line regarding the intensity threshold value (B) of this point group (b-1). The entire symmetric point group (b-2) is set to the distribution of "level 0", and the average value m0 and standard deviation s0 of this "level 0" are obtained.

FIG. 6: From the average values m1 and m0 and the standard deviations s1 and s0 obtained in FIGS. 5A and 5B.

[0059]

[Expression 10] Q = | m1-m0 | / (s1 + s0) (6) The Q value obtained by (6) is used as an optical signal quality evaluation parameter as a signal-to-noise coefficient. (Second Embodiment) FIGS. 7 to 10 show a second embodiment of the optical signal quality monitoring method of the present invention. In this embodiment, in the optical signal quality evaluation algorithm, the threshold value (A),
The part for obtaining (B) is different from that of the above-described first embodiment of the present invention.

The optical signal quality evaluation algorithm of the second embodiment of the present invention will be described with reference to FIGS.

FIG. 7A: First, a certain average is obtained by optical sampling with the optical sampling oscilloscope 105 having the configuration shown in FIG. 1 or electrical sampling with the electrical sampling oscilloscope 205 having the configuration shown in FIG. Find the intensity distribution in time.

FIG. 7B: An amplitude histogram is obtained from the obtained intensity distribution.

FIG. 8A: The threshold value (B) is defined as the first local maximum value when the amplitude histogram is examined from the smaller intensity level.

FIG. 8B: Integrating the number of sampling points from the sampling point with the maximum intensity level toward the smaller intensity level,

[0065]

## EQU00009 ## N (middle) = N (total) .times.D.times.M (7) (where, N (total) is the total number of sampling points, D is the duty ratio of the optical signal (ratio of pulse width and time slot), M
Is the minimum level of the integrated sampling points when the number of sampling points N (middle) obtained by the mark rate (probability of occurrence of level 1 in digital transmission) and the integral value are equal to m (middle).

FIG. 9A:

[0067]

[Equation 12]     Threshold value (A) = 2 × {m (middle) -threshold value (B)} (8) The threshold value (A) is calculated with.

FIG. 9B: Sampling point group (a-1) whose intensity is larger than the intensity threshold value (A) and a line regarding the intensity threshold value (A) of this point group (a-1). The entire symmetric point group (a-2) is set to the distribution of "level 1", and the level 1
The average value m1 and the standard deviation s1 are calculated. In addition, a sampling point group (b-
1) and the entire point group (b-2) line-symmetric with respect to the intensity threshold value (B) of the point group (b-1) are set as the distribution of "level 0", and the average value m0 of the level 0 and the standard The deviation s0 is calculated.

FIG. 10: Average value m obtained in FIG. 9B
From 1, m0 and standard deviation s1, s0

[0070]

[Expression 13] Q = | m1-m0 | / (s1 + s0) ... The Q value obtained by (9) is used as an optical signal quality evaluation parameter as a signal-to-noise coefficient.

The first embodiment of the present invention described above has the advantage that it is the simplest method, but the scope of application is N
Limited to RZ signals. On the other hand, the second embodiment is more complicated than the first embodiment, but has an advantage that it can be applied not only to the NRZ signal but also to the RZ signal.
However, as shown in the above equation (7), it is necessary to know the duty ratio D of the signal pulse and the mark ratio M in advance. (Hardware Configuration Example in Each Embodiment) FIG. 11 and FIG. 12 are configuration examples of an optical signal quality evaluation apparatus in the case of using an electrical sampling oscilloscope and in the case of using an optical sampling oscilloscope in each embodiment of the present invention. Show.

When the electric sampling oscilloscope shown in FIG. 11 is used, the light intensity modulation signal is converted into the photoelectric conversion means 1.
After converting into an electric intensity modulation signal by 501 and obtaining a signal intensity distribution of the electric intensity modulation signal at a constant time by the electric sampling oscilloscope 1502, based on the signal intensity distribution, the above-mentioned first, in the signal processing unit 1503, The optical signal quality evaluation according to the present invention described in the second embodiment is performed.

The signal processing unit 1503 estimates the respective intensity distributions of “level 1” and “level 0” from the signal intensity distribution obtained by the electrical sampling oscilloscope 1502, and from the obtained intensity distribution. The ratio of the difference between the average value intensities of "Level 1" and "Level 0" within a certain average time and the sum of the standard deviation values of "Level 1" and "Level 0" within the corresponding average time. The optical signal quality evaluation unit 1506 for evaluating the signal-to-noise ratio coefficient obtained as

When the optical sampling oscilloscope shown in FIG. 12 is used, the optical sampling oscilloscope 16
After obtaining the signal intensity distribution in a fixed time by 02, the signal processing unit 1603 performs the optical signal quality evaluation according to the present invention described in the above first and second embodiments.

The signal processing unit 1603 estimates the respective intensity distributions of “level 1” and “level 0” from the signal intensity distribution obtained by the optical sampling oscilloscope 1602, and from the obtained intensity distribution. The ratio of the difference between the average value intensities of "Level 1" and "Level 0" within a certain average time and the sum of the standard deviation values of "Level 1" and "Level 0" within the corresponding average time. The optical signal quality evaluation unit 1606 that evaluates the signal-to-noise ratio coefficient obtained as

(Other Embodiments) The object of the present invention is to supply a storage medium storing a program code of software for implementing the functions of the above-described embodiments to a system or apparatus, and It is needless to say that it is also achieved by the computer (or CPU or MPU) of the device reading and executing the program code stored in the storage medium. In this case, the program code itself read from the storage medium realizes the functions of the above-described embodiments, and the storage medium storing the program code constitutes the present invention. As a storage medium that stores the program code and variable data such as a table, for example, a floppy disk, a hard disk, or the like can be used.

[0077]

As described above, according to the present invention,
"Level 1" and "Level" directly from the sampled point cloud
Since the distribution of "0" is obtained, the sampled point cloud is
Histogram envelope without the need to histogram
It is not necessary to calculate
There is also no need to estimate the Gram function. Therefore, according to the present invention
If so, the configuration is very simple and the influence of cross points is small.
It is possible to realize an optical signal quality evaluation that does not exist. Also according to the invention
For example, in a photonic network in which signals with different bit rates, signal formats, and modulation formats coexist, noise degradation and waveforms can be generated with a single circuit regardless of the bit rate, signal format, and modulation format of the signal under measurement. Optical signal quality deterioration such as distortion can be monitored.

Further, according to the present invention, it is possible to provide a quality inspection means in which the influence on the SNR of the optical signal on the transmission line is reduced.

Further, according to the present invention, it is possible to provide an evaluation method in which the influence of cross points is less and the quality evaluation accuracy is higher than in the prior art.

[Brief description of drawings]

FIG. 1 is a block diagram showing a connection configuration example of an optical sampling oscilloscope suitable for the present invention.

FIG. 2 is a block diagram showing a connection configuration example of an electric sampling oscilloscope suitable for the present invention.

FIG. 3 is a conceptual diagram showing a first stage of an optical signal quality evaluation algorithm in the first exemplary embodiment of the present invention.

FIG. 4 is a conceptual diagram showing an optical signal quality evaluation algorithm in the first embodiment of the present invention following FIG.

FIG. 5 is a conceptual diagram showing an optical signal quality evaluation algorithm in the first embodiment of the present invention following FIG.

FIG. 6 is a conceptual diagram showing an optical signal quality evaluation algorithm in the first embodiment of the present invention following FIG.

FIG. 7 is a conceptual diagram showing a first stage of an optical signal quality evaluation algorithm in the second exemplary embodiment of the present invention.

FIG. 8 is a conceptual diagram showing an optical signal quality evaluation algorithm in the second embodiment of the present invention following FIG.

FIG. 9 is a conceptual diagram showing an optical signal quality evaluation algorithm in the second embodiment of the present invention following FIG.

FIG. 10 is a conceptual diagram showing an optical signal quality evaluation algorithm in the second embodiment of the present invention following FIG.

FIG. 11 is a block diagram showing a configuration example of an optical signal quality evaluation device when an electric sampling oscilloscope is used in each embodiment of the present invention.

FIG. 12 is a block diagram showing a configuration example of an optical signal quality evaluation device when an optical sampling oscilloscope is used in each embodiment of the present invention.

FIG. 13 is a conceptual diagram showing the first stage of a conventional optical signal quality evaluation algorithm.

FIG. 14 is a conceptual diagram showing a conventional optical signal quality evaluation algorithm following FIG.

FIG. 15 is a conceptual diagram showing a conventional optical signal quality evaluation algorithm following FIG.

16 is a conceptual diagram showing a conventional optical signal quality evaluation algorithm following FIG.

[Explanation of symbols]

100 Photonic network 101, 201 receiving system unit 102, 107, 111 for performing digital optical fiber transmission Optical branching unit 103, 203 Photoelectric conversion circuit 104, 204 Electric signal processing circuit 105 Optical sampling oscilloscope 106, 206 Optical amplification repeater unit 108 , 208 amplifier circuit 110, 210 optical regeneration relay system unit 112, 212 photoelectric conversion circuit 113, 213 electric signal processing circuit 114, 214 photoelectric conversion circuit 205 electrical sampling oscilloscope 202, 211 branching unit 207 optical branching unit 1501 photoelectric conversion circuit 1502 electrical Sampling oscilloscopes 1503 and 1603 Signal processing units 1505 and 1605 Intensity distribution estimation units 1506 and 1606 Optical signal quality evaluation unit 1602 Optical sampling oscilloscope

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Yumei Yamabayashi 2-3-1, Otemachi, Chiyoda-ku, Tokyo Inside Nippon Telegraph and Telephone Corporation (72) Koichi Fujisaki 20-1 Sakuragaoka-cho, Shibuya-ku, Tokyo (NTT Electronics Co., Ltd.) (56) Reference JP-A-2001-194267 (JP, A) I. Shake et al., 3 persons, Optical signal quality monitoring method based on opticals sampling, ELECTRONIC S LETTERS, October 29, 1998, Vol. 3, No. 22, pp. 2152-2154 (58) Fields surveyed (Int.Cl. ⁷ , DB name) G01J 1/00-1/60 G01J 11/00 JISST file (JOIS)

Claims (11)

(57) [Claims] 1. A step of converting an optical signal having a bit rate f0 (bit / s) into an electric intensity modulation signal, and a clock frequency f1 (Hz) (f1 = (N / M) f0 +
a, a is an offset frequency, N and M are positive integers, and the intensity distribution of the optical signal is measured by sampling the electric intensity modulation signal intensity; and sampling for configuring the intensity distribution of the optical signal under measurement. among the points, with a predetermined intensity threshold (a) high strength point group than (a-1), wherein the strong <br/> degree threshold of the point group (a-1) (a) The whole of the point group (a-2) that is line-symmetrical with respect to is set as "level 1", and the intensity threshold value (B) is determined separately.
Lower intensity point group (b-1) and the point group (b-1)
Of the point group (b-
2) the step of setting the whole to “level 0”, the difference between the average value intensities of the “level 1” and the “level 0” within a certain average time, the “level 1” and the “level” 0 ", and evaluating the signal-to-noise ratio coefficient obtained as a ratio with the sum of the standard deviation values within each averaging time. 2. An optical signal having a bit rate f0 (bit / s) and a repetition frequency f1 (Hz) (f1 =
(N / M) f0 + a, a is an offset frequency, N and M are positive integers, and the pulse width is sufficiently narrower than the time slot of the optical signal. Generate a correlation signal,
The No. SekiShin after photoelectric conversion, and measuring the intensity distribution of the optical signal by performing electrical signal processing, among the sampling points which constitute the intensity distribution of the optical signal to be measured, predetermined intensity threshold ( A point group (a-1) having a higher intensity than that of A) and a point group (a-2) line-symmetric with respect to the intensity threshold value (A) of the point group (a-1) . The whole is set as "Level 1", and the intensity threshold value (B) is determined separately.
Lower intensity point group (b-1) and the point group (b-1)
Of the point group (b-
2) the step of setting the whole to “level 0”, the difference between the average value intensities of the “level 1” and the “level 0” within a certain average time, the “level 1” and the “level” 0 ", and evaluating the signal-to-noise ratio coefficient obtained as a ratio with the sum of the standard deviation values within each averaging time. 3. For the intensity thresholds (A) and (B), two maximum values are obtained from an amplitude histogram obtained from the intensity distribution of the measured optical signal, and the one having a higher amplitude intensity is the intensity threshold. 3. The value (A) and the lower one is the intensity threshold value (B).
The optical signal quality evaluation method described in. 4. The intensity threshold (A) is defined as the first maximum value of the amplitude histogram when the intensity level is larger, and when the amplitude histogram is examined from the smaller intensity level. 4. The first local maximum value of is defined as the intensity threshold value (B).
The optical signal quality evaluation method described in. 5. The intensity maximum (B) is defined as the first maximum value of the amplitude histogram when it is examined from the smaller intensity level, and the sampling point having the maximum intensity level is followed by the smaller intensity level. Then, the sampling points are integrated, and N (middle) = N (total) × D × M (where N (total) is the total number of sampling points, and D is the duty ratio of the optical signal (pulse width and time slot). , M is the minimum level of the integrated sampling points when the number of sampling points N (middle) obtained by the mark rate (the probability of occurrence of level 1 in digital transmission) and the integrated value are equal to m (middle) 4. The intensity threshold value (A) is calculated by the following equation: intensity threshold value (A) = 2 × {m (middle) -intensity threshold value (B)}. Optical signal quality evaluation method. 6. The method according to claim 1, wherein instead of the evaluation of the signal-to-noise ratio coefficient, only the ratio of the average intensity and the standard deviation value of “level 1” or the standard deviation value is evaluated. An optical signal quality evaluation method according to any one of the above. 7. A photoelectric conversion means for converting an optical signal having a bit rate f0 (bit / s) into an electric intensity modulation signal, and a clock frequency f1 (Hz) (f1 = (N / M) f
0 + a, a is an offset frequency, N and M are positive integers, and an optical sampling oscilloscope that measures the intensity distribution of the optical signal by sampling the electrical intensity modulation signal intensity is used. Of the sampling points constituting the intensity distribution of the measured optical signal obtained by the electric sampling oscilloscope, a point group (a-1) having an intensity higher than a predetermined intensity threshold value (A), and the point The whole point group (a-2) which is line-symmetric with respect to the intensity threshold value (A) of the group (a-1) is defined as "level 1", and the intensity of the intensity is lower than the intensity threshold value (B) defined separately. Before the point group (b-1) and the point group (b-1)
Point group (b-2) which is line-symmetric with respect to the intensity threshold (B)
Of intensity distribution estimating means for setting the whole as “level 0”, the difference between the average value intensities of the “level 1” and the “level 0” within a certain average time, and the “level 1” and the “level 1”. And an optical signal quality evaluation means for evaluating a signal-to-noise ratio coefficient obtained as a ratio with the sum of standard deviation values of the respective "level 0" within the averaging time. . 8. An optical signal having a bit rate f0 (bit / s) and a repetition frequency f1 (Hz) (f1 =
(N / M) f0 + a, a is an offset frequency, and N and M are positive integers, and the pulse width is sufficiently narrower than the time slot of the optical signal. signal is generated, the correlation
After converting photoelectrically signals by performing the electric signal processing to measure the intensity distribution of the optical signal, an optical signal quality evaluation device using an optical sampling oscilloscope, obtained by said optical sampling oscilloscope, of the optical signal to be measured Among the sampling points constituting the intensity distribution, a point group (a-1) having a higher intensity than a predetermined intensity threshold value (A) and the intensity threshold value (A-1) of the point group (a-1). ), The entire point-symmetrical point group (a-2) is defined as "level 1", and the point group (b-1) having an intensity lower than the intensity threshold value (B) separately defined and the point group (b) Before -1)
Point group (b-2) which is line-symmetric with respect to the intensity threshold (B)
Of intensity distribution estimating means for setting the whole as “level 0”, the difference between the average value intensities of the “level 1” and the “level 0” within a certain average time, and the “level 1” and the “level 1”. And an optical signal quality evaluation means for evaluating a signal-to-noise ratio coefficient obtained as a ratio with the sum of standard deviation values of the respective "level 0" within the averaging time. . 9. The intensity distribution estimating means obtains two maximum values from the amplitude histogram obtained from the intensity distribution of the measured optical signal, and sets the one having a higher amplitude intensity as the intensity threshold value (A), 9. The optical signal quality evaluation device according to claim 7, wherein a lower one is set as the intensity threshold value (B). 10. A photoelectric conversion means for converting an optical signal having a bit rate f0 (bit / s) into an electric intensity modulation signal, and a clock frequency f1 (Hz) (f1 = (N / M) f
0 + a, a is an offset frequency, N and M are positive integers, and the optical signal quality evaluation is performed by a computer using an electrical sampling oscilloscope that measures the intensity distribution of the optical signal by sampling the electrical intensity modulation signal intensity. A storage medium storing a program for storing the program, the program causing a computer to obtain a predetermined intensity threshold value among sampling points constituting the intensity distribution of the measured optical signal obtained by the electric sampling oscilloscope. The entire point group (a-1) having a higher intensity than the value (A) and the point group (a-2) line-symmetric with respect to the intensity threshold value (A) of the point group (a-1) are represented by " Of the point group (b-1) having an intensity lower than a separately determined intensity threshold value (B) and the point group (b-1).
A line group (b-
The whole of 2) is set to “level 0”, the difference between the average value intensities of the “level 1” and the “level 0” within a certain average time, and the “level 1” and the “level 0”. A storage medium storing an optical signal quality evaluation program, which evaluates a signal-to-noise ratio coefficient obtained as a ratio with a sum of standard deviation values within the respective average times. 11. An optical signal having a bit rate f0 (bit / s) and a repetition frequency f1 (Hz) (f1 =
(N / M) f0 + a, a is an offset frequency, and N and M are positive integers, and the pulse width is sufficiently narrower than the time slot of the optical signal. to generate, said phase SekiShin <br/> No. measuring the intensity distribution of the optical signal by performing electric signal processing after converting photoelectrically, an optical sampling oscilloscope for execution by a computer the optical signal quality evaluation using A storage medium storing a program, the program causing a computer to determine a predetermined intensity threshold value (A) among sampling points constituting the intensity distribution of the measured optical signal obtained by the optical sampling oscilloscope. ) high strength group of points than the (a-1), the intensity threshold (a) for line-symmetrical point group of the point group (a-1) (a- 2 The whole is the "Level 1", separately determined intensity threshold (B) low intensity point group than the (b-1), the point group (b-1) of
A line group (b-
The whole of 2) is set to “level 0”, the difference between the average value intensities of the “level 1” and the “level 0” within a certain average time, and the “level 1” and the “level 0”. A storage medium storing an optical signal quality evaluation program, which evaluates a signal-to-noise ratio coefficient obtained as a ratio with a sum of standard deviation values within the respective average times.