JP2001201401A - Optical signal quality evaluation method and optical signal quality evaluation device and recording media - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve quality evaluation accuracy with a single circuit, regardless of bit rate of measured signal, signal form or modulation form. SOLUTION: A signal process unit 1503 has a strength distribution estimation part 1505, which estimates axial symmetric points group (a-2) about threshold A from points group (a-1) with a strength higher than the strength threshold A and each (a-1), (a-2) points group makes to level '1', and also estimates axial symmetric points group (b-2) about threshold B fun points group (b-1) with a strength lower than the strength threshold B which is decided separate by, then each (b-1), (b-2) points group makes to level '0' among sampling points in signal strength distribution obtained with a sampling oscilloscope 1502 and It also has a light signal quality evaluation part 1506 for evaluating a signal to noise ration coefficient obtained as the ration of the difference between the average strengths of level '1' and level '0' obtained from the strength distribution in a certain averaging time and the sum of the standard deviation values of level '1' and level '0' in the averaging time.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an optical signal quality evaluation method, an optical signal quality evaluation device, and a storage medium in digital optical fiber transmission, and more particularly to 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 degradation such as noise degradation and waveform distortion with a single circuit regardless of the bit rate and signal format of an optical signal to be measured.

[0002]

2. Description of the Related Art Conventionally, synchronous digital hierarchies (Sy
In the nchronous Digital Hierarchy (SDH) transmission method, bit interleaved parity (Bit Interleaved Parity) is used.
By performing a parity check called "ved Parity" between repeaters and between multiplexing terminals, identification of a faulty section and a switching start signal are 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), a receiving system (an error detecting circuit including a clock extracting circuit, a receiving circuit, a frame detecting circuit, a parity checking circuit, or a matching circuit) is required. Therefore, there is a point that a single receiving system cannot cope with a signal of an arbitrary bit rate, a signal format, or a modulation format.

[0004] As a method for solving this problem, reference 1
(Ref. 1: Japanese Unexamined Patent Application Publication No. 11-223575). This optical signal quality monitor uses a reception system (clock extraction circuit, reception circuit, frame detection circuit,
An error detection circuit including a parity check circuit or a collation circuit) is not required, and a single reception system can handle signals of any bit rate, signal format, and modulation format.

[0005]

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

FIGS. 13 to 16 show an optical signal quality evaluation algorithm in the conventional optical signal quality monitor.

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

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

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

FIG. 14 (B): integrating the number of sampling points from the sampling point with the highest intensity level to the one with the smaller intensity level,

[0011]

N (middle) = N (total) × D × M (1) (where N (total) is the total number of sampling points, D is the duty ratio of the optical signal (ratio between 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 (probability of occurrence of level 1 in digital transmission).

FIG. 15A:

[0013]

M1 ′ = 2 × {m (middle) −m0 ′} (2) m1 ′ is determined.

FIG. 15B:

[0015]

A = m1′−alpha (m1′−m0 ′) (3)

[0016]

[Mathematical formula-see original document] B = m0 '+ alpha (m1'-m0') ... The intensity level determined by the following equation (4) is set to a threshold value B (where alpha is 0 <
alpha <0.5 real number), and a distribution whose intensity level is equal to or higher than the threshold value A is defined as a level 1 distribution, and a distribution whose intensity level is equal to or less than the threshold value B is defined as a level 0 distribution.

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

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

[0019]

Q = | m1−m0 | / (s1 + s0) (5) The Q value obtained as follows 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 reduced.

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and an object of the present invention is to provide a digital optical fiber transmission photonic network in which signals of different bit rates, signal formats, and modulation formats coexist. Optical signal quality evaluation method, optical signal quality evaluation device, and storage medium that can monitor optical signal quality degradation such as noise degradation and waveform distortion with a single circuit, regardless of the signal bit rate, signal format, and modulation format Is to provide.

A further object of the present invention is to reduce the influence on the SNR (signal-to-noise ratio) of an optical signal on a digital optical fiber transmission line and improve the quality evaluation accuracy.

[0023]

According to a first aspect of the present invention, there is provided an optical signal quality evaluation method for converting an optical signal having a bit rate of f0 (bit / s) into an electric intensity modulated signal. And the clock frequency f1 (Hz) (f1
= (N / M) f0 + a, a is the offset frequency, N, M
Measuring the intensity distribution of the optical signal by sampling the intensity of the electric intensity modulation signal with a positive integer), and a predetermined intensity threshold among sampling points constituting the intensity distribution of the optical signal to be measured. From the point group (a-1) having an intensity higher than the value (A), a point group (a-2) that is line-symmetric with respect to the intensity threshold (A) is estimated, and the point group (a-1) and the point group (a-1) The whole point group (a-2) is "level 1"
From the point group (b-1) having an intensity lower than the separately determined intensity threshold (B), a point group (b-2) that is line-symmetric with respect to the intensity threshold (B) is estimated. Setting the whole of the group (b-1) and the point group (b-2) to “level 0”; and calculating the average intensity of the “level 1” and the “level 0” within a certain average time. Evaluating a signal-to-noise ratio coefficient obtained as a ratio between the difference and a sum of standard deviation values of the “level 1” and the “level 0” within the average time. I do.

In order to achieve the above object, the invention of the optical signal quality evaluation method according to the second aspect is directed to an optical signal having a bit rate f0 (bit / s) and a repetition frequency of f1 (Hz) (f1 =
(N / M) f0 + a, where a is an offset frequency, and N and M are positive integers), and using a sampling optical pulse train whose pulse width is sufficiently smaller than the time slot of the optical signal, a mutual optical frequency different from these two lights is used. Generating a correlation signal, photoelectrically converting the correlation optical signal, and then performing electrical signal processing to measure the intensity distribution of the optical signal; and, among the sampling points forming the intensity distribution of the optical signal to be measured, A point group (a-2) that is line-symmetric with respect to the intensity threshold (A) is estimated from the point group (a-1) having an intensity higher than the determined intensity threshold (A), and the point group (a) is estimated. -1) and the entire point group (a-2) is set to “level 1”, and the intensity threshold (B) is calculated from the point group (b-1) having an intensity lower than the intensity threshold (B) separately determined. ) Point group (b-2)
Estimating the point group (b-1) and the entire point group (b-2) as “level 0”; and within a certain average time of each of the “level 1” and the “level 0” Estimating a signal-to-noise ratio coefficient obtained as a ratio of a difference between the average intensity at the time and a sum of standard deviation values of the “level 1” and the “level 0” within the average time. It is characterized by having.

Here, with respect to the intensity thresholds (A) and (B), two local maximum values are obtained from an amplitude histogram obtained from the intensity distribution of the optical signal to be measured, and the one having the higher amplitude intensity is determined as the intensity intensity. The threshold value (A) may be used, and the lower one may be used as the intensity threshold (B).

Further, the first maximum value when the intensity level of the amplitude histogram is checked is determined as the intensity threshold value (A), and when the amplitude histogram is checked from the lower intensity level. Is defined as the intensity threshold (B).

In addition, the first maximum value when the intensity level is examined from the smaller intensity level in the amplitude histogram is defined as the intensity threshold (B), and the intensity level becomes smaller from the sampling point at the maximum intensity level. To integrate the sampling points

[0028]

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

[0029]

[Mathematical formula-see original document] The intensity threshold (A) may be obtained by the following expression: intensity threshold (A) = 2 * {m (middle) -intensity threshold (B)}.

Further, instead of the evaluation of the signal-to-noise ratio coefficient, it is characterized in that only the ratio of the average intensity of the "level 1" to the standard deviation or the standard deviation is evaluated.

In order to achieve the above object, an optical signal quality evaluation apparatus according to a seventh aspect of the present invention comprises: a photoelectric conversion means for converting an optical signal having a bit rate f0 (bit / s) into an electric intensity modulation signal; f1 (Hz) (f1 = (N / M) f
An optical sampling quality oscilloscope that measures the intensity distribution of the optical signal by sampling the intensity of the electric intensity modulated signal at 0 + a, a is an offset frequency, and N and M are positive integers, Among the sampling points forming the intensity distribution of the optical signal to be measured obtained by the electric sampling oscilloscope, the intensity is calculated from a point group (a-1) having an intensity higher than a predetermined intensity threshold (A). A point group (a-2) that is line-symmetric with respect to the threshold (A) is estimated, and the point group (a-1)
In addition, the entire point group (a-2) is set to “level 1”, and the point group (b−2) having an intensity lower than the intensity threshold value (B) separately determined.
1), a point group (b-2) that is line-symmetric with respect to the intensity threshold (B) is estimated, and the point group (b-1) and the point group (b) are estimated.
-2) intensity distribution estimating means for setting the whole to “level 0”;
Difference between the average intensity of the “level 1” and the “level 0” within a certain average time, and the standard deviation value of the “level 1” and the “level 0” within the average time, respectively And an optical signal quality evaluation means for evaluating a signal-to-noise ratio coefficient obtained as a ratio to the sum of

In order to achieve the above object, the invention of the optical signal quality evaluating apparatus according to claim 8 is an optical signal having a bit rate f0 (bit / s) and a repetition frequency f1 (Hz) (f1 =
(N / M) f0 + a, where a is an offset frequency, and N and M are positive integers) and a cross-correlation between these two lights and different optical frequencies using a sampling light pulse train whose pulse width is sufficiently narrower than the time slot of the optical signal. An optical signal quality evaluation device that uses an optical sampling oscilloscope to generate a signal and measure the intensity distribution of the optical signal by performing electrical signal processing after photoelectrically converting the correlated optical signal, which is obtained by the optical sampling oscilloscope. Among the sampling points forming the intensity distribution of the measured optical signal, a point group (a-a) having an intensity higher than a predetermined intensity threshold (A).
1), a point group (a-2) that is line-symmetric with respect to the intensity threshold (A) is estimated, and the point group (a-1) and the point group (a) are estimated.
-2) The whole is set to "level 1", and the point group (b-1) having an intensity lower than the separately determined intensity threshold (B) to the point group (b) line-symmetric with respect to the intensity threshold (B) -2), an intensity distribution estimating means for estimating the point group (b-1) and the entire point group (b-2) as "level 0";
And the difference between the average intensity of the “level 0” within a certain average time, and the “level 1” and the “level 0”.
And an optical signal quality evaluation means for evaluating a signal-to-noise ratio coefficient obtained as a ratio with respect to each of the standard deviation values within the average time.

In order to achieve the above object, a storage medium according to a tenth aspect of the present invention provides a photoelectric conversion device 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) f0 + a,
(a is an offset frequency, N and M are positive integers), and an electric sampling oscilloscope for measuring the intensity distribution of the optical signal by sampling the intensity of the electric intensity modulated signal is used to perform optical signal quality evaluation by a computer. A storage medium storing the program of the present invention, the program instructs a computer to obtain a predetermined intensity threshold value (a predetermined threshold value) among sampling points constituting the intensity distribution of the measured optical signal obtained by the electric sampling oscilloscope. Point group (a-1) having higher intensity than A)
From the point group (a)
-2), the point group (a-1) and the point group (a-
2) The whole is set to “level 1”, and the point group (b-1) having an intensity lower than the separately determined intensity threshold (B) to the point group (b) line-symmetric with respect to the intensity threshold (B) -2), the point group (b-1) and the entire point group (b-2) are set to “level 0”, and a certain average time of each of the “level 1” and the “level 0” To evaluate the signal-to-noise ratio coefficient obtained as the ratio of the difference between the mean intensity values within the range and 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 the eleventh aspect provides an optical signal having a bit rate f0 (bit / s) and a repetition frequency of f1 (Hz) (f1 = (N /
M) f0 + a, a is an offset frequency, N and M are positive integers) and a pulse width of which is sufficiently narrower than the time slot of the optical signal is used to generate a cross-correlation signal having an optical frequency different from those of the two lights. A storage medium storing a program for performing an optical signal quality evaluation by a computer using an optical sampling oscilloscope for measuring the intensity distribution of the optical signal by performing electrical signal processing after photoelectrically converting the correlated optical signal. The program instructs the computer to select a point group having an intensity higher than a predetermined intensity threshold (A) among sampling points constituting an intensity distribution of the optical signal to be measured, obtained by the optical sampling oscilloscope. From (a-1), a point group (a-2) that is line-symmetric with respect to the intensity threshold (A) is estimated, and the point group (a- ) And the point group (a-2) the whole is the "Level 1", the intensity threshold from separately determined intensity threshold (B) low intensity point group than (b-1) (B)
Is estimated, a point group (b-2) that is axisymmetric with respect to is estimated, the point group (b-1) and the entire point group (b-2) are set to “level 0”, and the “level 1” and the “level 0, and a signal obtained as a ratio of the difference between the average intensity within a certain average time and the sum of the standard deviation values of the “level 1” and the “level 0” within the average time. It is characterized in that the noise 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 the electric intensity modulation signal intensity is converted to a clock frequency f1.
An electrical sampling method for measuring the intensity distribution of an optical signal by sampling at (Hz) (f1 = (N / M) f0 + a, where a is an offset frequency and N and M are positive integers) is used.

Alternatively, in the present invention, a certain bit rate f
An optical signal having 0 (bit / s) and a repetition frequency of f1 (H
z) (f1 = (N / M) f0 + a, where a is an offset frequency and N and M are positive integers) and a sampling optical pulse train whose pulse width is sufficiently narrower than the time slot of the optical signal, is used for these two light beams. An optical sampling method is used in which a cross-correlation signal having an optical frequency different from the above is generated, the correlation optical signal is photoelectrically converted, and then the electric signal processing is performed to measure the intensity distribution of the optical signal.

In the present invention, a frame detecting circuit,
Instead of using an error detection circuit including a parity check circuit or a check circuit, the intensity distribution of an optical signal to be measured from a sampling point obtained by using the electrical sampling method or the optical sampling method in an asynchronous system not using a clock extraction circuit. Is measured, and among the sampling points constituting the intensity distribution of the measured optical signal, a point group (a-1) having an intensity higher than a predetermined intensity threshold (A) is used to determine the intensity threshold (A). ), A point group (a−
2) is estimated, and the point group (a-1) and the point group (a-
2) The whole is “level 1”, and a point group (b−) that is line-symmetric with respect to the intensity threshold (B) from a point group (b−1) having an intensity lower than the intensity threshold (B) separately determined. 2) is estimated, and when the point group (b-1) and the whole point group (b-2) are set to "level 0", "level 1" and "level 0"
Of the average intensity within a certain average time of each of
Evaluate the signal-to-noise ratio coefficient obtained as the ratio of the sum of the standard deviation values of the “level 1” and “level 0” within the average time, or the average intensity of the “level 1” Only the ratio of the standard deviation value or the standard deviation value is evaluated.

According to the present invention, according to the present invention, in a photonic network in which signals of different bit rates, signal formats, and modulation formats are mixed, the bit rate, signal format, and modulation format of the signal to be measured are changed. Instead, a single circuit can monitor optical signal quality degradation such as noise degradation and waveform distortion, reducing the effect on optical signal SNR (signal-to-noise ratio) on digital optical fiber transmission lines. Can also improve the quality evaluation system.
Further, the present invention can provide an evaluation method with less influence of cross points and higher quality evaluation accuracy than the conventional technology.

[0039]

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. This embodiment exemplifies a case in which the intensity distribution of an NRZ optical signal is evaluated using an electrical sampling method or an optical sampling method. For measuring the optical signal intensity distribution by the electric sampling method, a commercially available electric sampling device or the like can be used. In addition, the optical signal intensity distribution measurement by the optical sampling method can use the optical sampling or the like of Reference Document 2 (Reference Document 2: Takara et al .: “Ultrafast optical waveform measurement by optical sampling using sum frequency light generation” Law, IEICE Transactions, B-1, vol.J75-B-1,
No. 5, pp. 372-380, 1992).

When the optical sampling method is used, as shown in FIGS. 1A to 1C, the signal intensity is increased by using an optical sampling oscilloscope in a receiving system, an optical amplifying repeater system, or an optical regenerative repeater system. Get the distribution. The cross-correlation signal in this case can be obtained by utilizing second harmonic generation, sum frequency light generation, difference frequency light generation, four-wave mixing light generation, or the like.

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

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

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

FIG. 1C shows a photoelectric conversion circuit 1 having a photoelectric conversion circuit 112, an electric signal processing circuit 113, and a photoelectric conversion circuit 114.
12 shows a case where an optical sampling oscilloscope 105 is connected via an optical branching unit 111 coupled to a stage preceding the block 12.

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 a receiving system, an optical amplifying repeater system, or an optical regenerative repeater system.

In FIGS. 2A to 2C, reference numeral 205 denotes an electric sampling oscilloscope.

FIG. 2A shows a receiving 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
4 shows a case where an electric sampling oscilloscope 205 is connected via a branch unit 202 coupled between the four.

FIG. 2B shows an optical amplification circuit 2 with an optical amplification repeater unit 206 having an optical amplification circuit 208.
08, via the optical branching unit 207 and the photoelectric conversion circuit 209 coupled to the previous stage of the electric sampling oscilloscope 2.
05 is connected.

FIG. 2C shows a photoelectric conversion circuit 2 having a photoelectric conversion circuit 212, an electric signal processing circuit 213, and a photoelectric conversion circuit 214.
Branch 21 coupled between the circuit 12 and the electric signal processing circuit 213
1 shows a case where an electric sampling oscilloscope 205 is connected via the oscilloscope 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 as shown in FIG. 1 or electrical sampling by the electric sampling oscilloscope 205 using the configuration as shown in FIG. Find the intensity distribution in time.

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

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

FIG. 4B: A threshold value B is determined as the first maximum value when the amplitude histogram is examined from the smaller intensity level.

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

FIG. 5B: A line is drawn between the sampling point group (b-1) having an intensity smaller than the intensity threshold value (B) and the intensity threshold value (B) of this point group (b-1). The whole of the symmetric point group (b-2) is set as the distribution of “level 0”, and the average value m0 and the 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]

Q = | m1−m0 | / (s1 + s0) (6) The Q value obtained as follows 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 the present embodiment, the threshold (A),
The part for obtaining (B) is different from the above-described first embodiment of the present invention.

The optical signal quality evaluation algorithm according to 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 by the optical sampling oscilloscope 105 using the configuration as shown in FIG. 1 or electrical sampling by the electric sampling oscilloscope 205 using the configuration as shown in FIG. Find the intensity distribution in time.

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

FIG. 8A: A threshold value (B) is defined as the first 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 highest intensity level toward the one with the smaller intensity level,

[0065]

N (middle) = N (total) × D × 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 to 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 (probability of occurrence of level 1 in digital transmission).

FIG. 9A:

[0067]

Threshold value (A) = 2 × {m (middle) −Threshold value (B)} (8)

FIG. 9 (B): A line is drawn between the sampling point group (a-1) having an intensity higher than the intensity threshold value (A) and the intensity threshold value (A) of this point group (a-1). The whole of the symmetric point group (a-2) is defined as a “level 1” distribution, and the level 1
The average value m1 and the standard deviation s1 are obtained. In addition, the sampling point group (b−) having an intensity smaller than the intensity threshold (B).
1) and the entire point group (b-2) that is line-symmetric with respect to the intensity threshold value (B) of the point group (b-1) has a distribution of "level 0", and the average value m0 of level 0 and the standard Find the deviation s0.

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

[0070]

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

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

When the electric sampling oscilloscope shown in FIG. 11 is used, the light intensity
The signal is converted into an electric intensity modulated signal by 501, and a signal intensity distribution of the electric intensity modulated signal for a predetermined time is obtained by an electric sampling oscilloscope 1502. Then, based on the signal intensity distribution, the signal processing unit 1503 performs The optical signal quality evaluation according to the present invention described in the second embodiment is performed.

The signal processing unit 1503 includes an intensity distribution estimating unit 1505 for estimating the “level 1” and “level 0” intensity distributions from the signal intensity distribution obtained by the electric sampling oscilloscope 1502, and The ratio of the difference between the average intensity 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 average time. And an optical signal quality evaluation unit 1506 that evaluates a signal-to-noise ratio coefficient obtained as

When using the optical sampling oscilloscope shown in FIG.
After obtaining the signal intensity distribution for a certain period of time by O2, the signal processing unit 1603 performs the optical signal quality evaluation according to the present invention described in the first and second embodiments.

A signal processing unit 1603 includes an intensity distribution estimating unit 1605 for estimating the “level 1” and “level 0” intensity distributions from the signal intensity distribution obtained by the optical sampling oscilloscope 1602, and the intensity distribution estimating unit 1605 based on the obtained intensity distributions. The ratio of the difference between the average intensity 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 average time. And an optical signal quality evaluation unit 1606 for evaluating the signal-to-noise ratio coefficient obtained as

(Other Embodiments) An object of the present invention is to supply a storage medium storing software program codes for realizing the functions of the above-described embodiments to a system or an apparatus, and to provide the system or apparatus with the storage medium. It is needless to say that the present invention is also achieved when the computer (or CPU or MPU) of the apparatus reads out and executes 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 embodiment, and the storage medium storing the program code constitutes the present invention. As a storage medium for storing the program code and for storing 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,
In a photonic network where signals with different bit rates, signal formats, and modulation formats coexist, noise degradation and waveform distortion can occur with a single circuit regardless of the bit rate, signal format, and modulation format of the signal under test. Of the optical signal quality 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 with less influence of cross points and higher quality evaluation accuracy as compared with the prior art.

[Brief description of the 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 illustrating an initial stage of an optical signal quality evaluation algorithm according to the first embodiment of the present invention.

FIG. 4 is a conceptual diagram showing an optical signal quality evaluation algorithm according to the first embodiment of the present invention, following FIG. 3;

FIG. 5 is a conceptual diagram showing an optical signal quality evaluation algorithm according to the first embodiment of the present invention, following FIG. 4;

FIG. 6 is a conceptual diagram showing an optical signal quality evaluation algorithm according to the first embodiment of the present invention, following FIG. 5;

FIG. 7 is a conceptual diagram illustrating an initial stage of an optical signal quality evaluation algorithm according to the second embodiment of the present invention.

FIG. 8 is a conceptual diagram showing an optical signal quality evaluation algorithm according to the second embodiment of the present invention, following FIG. 7;

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

FIG. 10 is a conceptual diagram showing an optical signal quality evaluation algorithm according to the second embodiment of the present invention, following FIG. 9;

FIG. 11 is a block diagram illustrating 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 illustrating 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 an initial stage of a conventional optical signal quality evaluation algorithm.

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

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

FIG. 16 is a conceptual diagram showing a conventional example of an optical signal quality evaluation algorithm following FIG. 15;

[Explanation of symbols]

REFERENCE SIGNS LIST 100 photonic network 101 for digital optical fiber transmission 101, 201 receiving system unit 102, 107, 111 optical branching unit 103, 203 photoelectric conversion circuit 104, 204 electric signal processing circuit 105 optical sampling oscilloscope 106, 206 optical amplification relay system unit 108 , 208 Amplification circuit 110, 210 Optical regeneration repeater unit 112, 212 Photoelectric conversion circuit 113, 213 Electric signal processing circuit 114, 214 Photoelectric conversion circuit 205 Electric sampling oscilloscope 202, 211 Branch unit 207 Optical branch unit 1501 Photoelectric conversion circuit 1502 Electric Sampling oscilloscope 1503, 1603 Signal processing unit 1505, 1605 Intensity distribution estimating unit 1506, 1606 Optical signal quality evaluating unit 1602 Optical sampling oscilloscope Flop

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hidehiko Takara 2-3-1 Otemachi, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation (72) Inventor Yoshiaki Yamabayashi 2-chome Otemachi, Chiyoda-ku, Tokyo No. 1 Nippon Telegraph and Telephone Corporation (72) Inventor Koichi Fujisaki 20-1 Sakuragaoka-cho, Shibuya-ku, Tokyo NTT Electronics Corporation F-term (reference) 2G065 AA04 AA12 BA01 BB02 BC03 BC07 BC14 BC16 BC22 BC31 BC35 DA13 5K002 DA05 EA05 FA01 5K028 AA08 BB08 KK01 PP04 PP11 SS03 5K029 AA18 CC04 FF08 HH13 JJ01 KK01 KK28

Claims (11)

[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 +
measuring the intensity distribution of the optical signal by sampling the intensity of the electric intensity modulated signal at a and a, where a and a are offset frequencies, and N and M are positive integers; and sampling that constitutes the intensity distribution of the optical signal to be measured. Among the points, a point group (a-2) that is line-symmetric about the intensity threshold (A) is estimated from a point group (a-1) having an intensity higher than a predetermined intensity threshold (A), The point cloud (a-
1) The entire point group (a-2) is set to “level 1”, and the point group (b) having an intensity lower than the intensity threshold value (B) separately determined.
-1), a point group (b-2) which is line-symmetric with respect to the intensity threshold (B) is estimated, and the point group (b-1) and the entire point group (b-2) are regarded as "level 0". And the difference between the average intensity of the “level 1” and the “level 0” within a certain average time, and the difference of the “level 1” and the “level 0” within the average time, respectively. Evaluating a signal-to-noise ratio coefficient obtained as a ratio with a sum of the standard deviation values in the optical signal quality evaluation method. 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)
Using a sampling optical pulse train whose pulse width is sufficiently narrower than the time slot of the optical signal, a cross-correlation signal having an optical frequency different from those of the two lights is generated, and after the correlation optical signal is photoelectrically converted, the electric signal processing is performed. And measuring the intensity distribution of the optical signal; and selecting a point group (a-1) having an intensity higher than a predetermined intensity threshold (A) among the sampling points constituting the intensity distribution of the measured optical signal. ), A point group (a-2) that is line-symmetric with respect to the intensity threshold (A) is estimated, and the point group (a-
1) The entire point group (a-2) is set to “level 1”, and the point group (b) having an intensity lower than the intensity threshold value (B) separately determined.
-1), a point group (b-2) which is line-symmetric with respect to the intensity threshold (B) is estimated, and the point group (b-1) and the entire point group (b-2) are regarded as "level 0". And the difference between the average intensity of the “level 1” and the “level 0” within a certain average time, and the difference between the “level 1” and the “level 0” within the average time. Evaluating a signal-to-noise ratio coefficient obtained as a ratio with a sum of the standard deviation values in the optical signal quality evaluation method. 3. For the intensity thresholds (A) and (B), two maximum values are obtained from an amplitude histogram obtained from an intensity distribution of the optical signal under measurement, and the higher one of the amplitude intensities is determined as the intensity threshold. The value (A), and the lower one is the intensity threshold (B).
The optical signal quality evaluation method described in 1. 4. The method according to claim 1, wherein the first maximum value when the intensity level is checked from the higher intensity level in the amplitude histogram is defined as the intensity threshold value (A), and when the intensity level is checked from the lower intensity level in the amplitude histogram. 4. The first maximum value of is defined as the intensity threshold (B).
The optical signal quality evaluation method described in 1. 5. An amplitude histogram, wherein the first local maximum value when examined from the smaller intensity level is defined as the intensity threshold (B), and the sampling point at which the intensity level is maximum is directed toward the smaller intensity level. N (middle) = N (total) × D × M (where N (total) is the total number of sampling points, and D is the duty ratio (pulse width and time slot) of the optical signal. M is the minimum level of the integrated sampling points when the integrated value is equal to the number of sampling points N (middle) determined by the mark rate (probability of occurrence of level 1 in digital transmission). The intensity threshold value (A) is obtained 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 of the “level 1” to the standard deviation or the standard deviation 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) f0 + a, a
An electrical sampling oscilloscope for measuring the intensity distribution of the optical signal by sampling the electrical intensity modulated signal intensity at an offset frequency, and N and M are positive integers. Among the sampling points forming the intensity distribution of the optical signal to be measured obtained by an oscilloscope, a point group (a-1) having an intensity higher than a predetermined intensity threshold (A) is selected from its intensity threshold ( Estimate a point group (a-2) that is axisymmetric with respect to A) and calculate the point group (a-1)
In addition, the entire point group (a-2) is set to “level 1”, and the point group (b−2) having an intensity lower than the intensity threshold value (B) separately determined.
1), a point group (b-2) that is line-symmetric with respect to the intensity threshold (B) is estimated, and the point group (b-1) and the point group (b) are estimated.
-2) an intensity distribution estimating means that sets the whole to “level 0”; a difference between average values of the “level 1” and the “level 0” within a certain average time; Optical signal quality evaluation means for evaluating a signal-to-noise ratio coefficient obtained as a ratio of each of the “level 0” to a sum of standard deviation values within the average time. Evaluation device. 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, N and M are positive integers)
By using a sampling optical pulse train whose pulse width is sufficiently narrower than the time slot of the optical signal, a cross-correlation signal having an optical frequency different from those of the two lights is generated, and the correlated optical signal is photoelectrically converted and then subjected to electrical signal processing. An optical signal quality evaluation device that uses an optical sampling oscilloscope to measure the intensity distribution of an optical signal, wherein the sampling points constituting the intensity distribution of the optical signal to be measured obtained by the optical sampling oscilloscope are predetermined. From the point group (a-1) having an intensity higher than the intensity threshold (A), a point group (a-2) that is line-symmetric about the intensity threshold (A) is estimated, and the point group (a-1) is estimated. )
In addition, the entire point group (a-2) is set to “level 1”, and the point group (b−2) having an intensity lower than the intensity threshold value (B) separately determined.
1), a point group (b-2) that is line-symmetric with respect to the intensity threshold (B) is estimated, and the point group (b-1) and the point group (b) are estimated.
-2) an intensity distribution estimating means that sets the whole to “level 0”; a difference between average values of the “level 1” and the “level 0” within a certain average time; Optical signal quality evaluation means for evaluating a signal-to-noise ratio coefficient obtained as a ratio of each of the “level 0” to a sum of standard deviation values within the average time. Evaluation device. 9. The intensity distribution estimating means obtains two local maximum values from the amplitude histogram obtained from the intensity distribution of the optical signal under measurement, and determines a maximum amplitude intensity as the intensity threshold (A), 9. The optical signal quality evaluation device according to claim 7, wherein a lower one is set as the intensity threshold (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) f0 + a,
(a is an offset frequency, N and M are positive integers), and an electric sampling oscilloscope for measuring the intensity distribution of the optical signal by sampling the intensity of the electric intensity modulated signal is used to perform optical signal quality evaluation by a computer. A storage medium storing the program, wherein the program instructs the computer to select a predetermined intensity threshold value from among sampling points constituting the intensity distribution of the measured optical signal, which are obtained by the electric sampling oscilloscope. A point group (a-2) that is line-symmetric with respect to the intensity threshold (A) is estimated from a point group (a-1) having a higher intensity than A), and the point group (a-
1) The entire point group (a-2) is set to “level 1”,
A point group (b-2) that is line-symmetric with respect to the intensity threshold (B) is estimated from a point group (b-1) having an intensity lower than the intensity threshold (B) separately determined, and the point group ( b-1) and the entire point group (b-2) is set to “level 0”, and the difference between the average intensity of the “level 1” and the “level 0” within a certain average time, and A program for evaluating an optical signal quality characterized by evaluating a signal-to-noise ratio coefficient obtained as a ratio of a “level 1” and a sum of standard deviation values of the “level 0” within the average time. A storage medium that stores the information. 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, N and M are positive integers) and a pulse width of which is sufficiently narrower than the time slot of the optical signal is used to generate a cross-correlation signal having an optical frequency different from those of the two lights. A storage medium storing a program for performing an optical signal quality evaluation by a computer using an optical sampling oscilloscope for measuring the intensity distribution of the optical signal by performing electrical signal processing after photoelectrically converting the correlated optical signal. The program instructs a computer to select a point group having an intensity higher than a predetermined intensity threshold (A) among sampling points constituting an intensity distribution of the optical signal to be measured, obtained by the optical sampling oscilloscope. From (a-1), a point group (a-2) that is line-symmetric with respect to the intensity threshold (A) is estimated, and the point group (a-
1) The entire point group (a-2) is set to “level 1”,
A point group (b-2) that is line-symmetric with respect to the intensity threshold (B) is estimated from a point group (b-1) having an intensity lower than the intensity threshold (B) separately determined, and the point group ( b-1) and the entire point group (b-2) is set to “level 0”, and the difference between the average intensity of the “level 1” and the “level 0” within a certain average time, and A program for evaluating an optical signal quality characterized by evaluating a signal-to-noise ratio coefficient obtained as a ratio of a “level 1” and a sum of standard deviation values of the “level 0” within the average time. A storage medium that stores the information.