JP2007300465A - Optical signal quality evaluation apparatus and method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical signal quality evaluation apparatus and a method for evaluating the quality of an NRZ phase modulation optical signal at an optional bit rate within a wavelength dispersion range wider than that of a conventional art. <P>SOLUTION: The optical signal quality evaluation apparatus receives an NRZ optical signal subjected to phase modulation as an optical signal, obtains a parameter F<SB>dis</SB>representing the quality of the optical signal as a quality deterioration coefficient of the NRZ phase modulation optical signal caused by wavelength dispersion so as to inspect the quality of the optical signal, wherein the parameter F<SB>dis</SB>is made F<SB>dis</SB>=μ<SB>h</SB>/μ<SB>m</SB>, μ<SB>m</SB>is a level at which the number of sampling points is a maximum value, and μ<SB>h</SB>is a level when the number of sampling points is equal to the number of sampling points N<SB>high</SB>obtained by N<SB>high</SB>=N<SB>total</SB>×k (0.5<k<1), when N<SB>total</SB>is all the number of sampling points by integrating the number of sampling points from a level minimum value of a histogram. The value k is desirably 0.6<k<1. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention is used in an apparatus for evaluating the quality of a phase-modulated optical signal. In particular, the present invention relates to a technique for evaluating the quality of a non-return to zero (NRZ) phase modulated optical signal.

  Optical transmission systems that have been put into practical use have been intensity modulation methods that modulate the intensity of light, but in recent years, optical transmission systems have been aiming for higher frequency efficiency, higher capacity, and longer distances. Research and development of a phase modulation method for modulating the phase is being actively promoted (for example, see Non-Patent Document 1).

  Conventionally, as a method for evaluating the quality of a phase-modulated optical signal, a method of converting a phase-modulated signal into an intensity-modulated signal and then converting it into an electric signal as shown in FIG. 5 is mainly used. It was. Here, a Mach-Zehnder interferometer 8 having a 1-bit delay is specifically used as the phase modulation / intensity modulation conversion means.

  This is because, when the delay difference between the two optical paths of the Mach-Zehnder interferometer 8 is set to 1 bit and the interference with the adjacent bits passes through the two optical paths, the intensity after interference is caused by the phase difference between the bits. Take advantage of changing. Specifically, error rate measurement, Q value measurement, and the like are used as the intensity modulation signal evaluation means 9.

  The phase-modulated optical signal includes a non-return-to-zero (NRZ) phase-modulated optical signal generated by phase-modulating CW light and a return-to-zero generated by phase-modulating light that has been intensity-modulated in a sine wave or pulse shape. There is a zero (RZ) phase modulation signal, and the method using the phase modulation / intensity modulation conversion means described above can be applied to both NRZ and RZ type phase modulation optical signals.

  However, the above method requires a phase modulation / intensity modulation conversion means, and there is a problem that the configuration of the reception system becomes complicated. In addition, since the 1-bit delay Mach-Zehnder interferometer 8 has a fixed bit delay, the bit rate that can be handled is fixed, and it is impossible to evaluate the quality of a signal having an arbitrary bit rate.

  Therefore, as a method for evaluating the quality of an NRZ phase-modulated optical signal that does not depend on the bit rate, a method has been devised in which a light intensity histogram is obtained by asynchronous sampling, and a specific parameter is extracted from the histogram to obtain a quality evaluation. (For example, refer nonpatent literature 2). FIG. 6 shows a configuration of a conventional optical signal quality evaluation apparatus.

In FIG. 6, a phase-modulated NRZ optical signal having a bit rate N · f ₀ (bit / s) (N = 1, 2,...) That is an integral multiple of the basic clock frequency f ₀ (Hz) is input. The optical signal is converted into an electrical signal by the photoelectric conversion means 10 and input to the electrical sampling means 2. The sampling clock generation means 4 has a frequency f ₀ / n ₁ −Δf obtained by adding or subtracting an offset frequency Δf (Hz) from an integer of the basic clock frequency f ₀ (Hz).
A sampling clock of (Hz) or f ₀ / n ₁ + Δf (Hz) is generated. The electrical sampling means 2 samples an electrical signal using this sampling clock. The electrical signal processing means 3 measures a histogram of light intensity using the sampling electrical signal obtained by sampling by the electrical signal sampling means 2.

  Since the phase-modulated NRZ optical signal is modulated in the phase region and has a constant intensity, the light intensity histogram has a shape having one peak. However, according to Non-Patent Document 2, when a phase-modulated NRZ optical signal is affected by chromatic dispersion such as a transmission path, the histogram has a shape having three peaks as shown in FIG.

The level at the peak of the central mountain is μ ₁ and the standard deviation is σ ₁ . Further, when the maximum level first from the maximum level side is μ2, and the first maximum level from the minimum level side is μ3, parameters AQ and D indicating the quality of the optical signal are AQ = μ ₁ / Σ ₁ (1)
D = (μ2−μ3) / μ ₁ (2)
Asking. Of the above parameters, AQ is a signal-to-noise ratio coefficient of the NRZ phase modulation optical signal, and the parameter D is a quality degradation coefficient due to wavelength dispersion of the NRZ phase modulation optical signal, so that the quality of the NRZ phase modulation optical signal is Inspect. As described above, the optical signal quality evaluation apparatus shown in FIG. 6 has an advantage that there is no dependency on the bit rate because the optical signal quality is evaluated based on the histogram obtained by using asynchronous sampling.

Y. Miyamoto, “Advanced modulation formats for high-capacity optical transport network”, ECOC 2005, Th 1.2, 2005 Zhihong Li et al. , “In-Service Signal Quality Monitoring and Multi-Implementation Discrimination Based on Asynchronous Amplified Histogram Evaluation for NRZ-DPSK EON 17, NO. 9, SEPTEMBER 2005 M.M. J. et al. W. Rodwell, et al. "Active and Nonlinear Wave Propagation Devices in Ultrafast Electronics and Optical Electronics", Proceedings of the IEEE, vol. 82, no. 7, pp. 1037-1059, 1994

  However, the method of Non-Patent Document 2 has a drawback that the range of chromatic dispersion that can be evaluated is narrow. FIG. 7 shows the relationship between the D coefficient and chromatic dispersion reported in Non-Patent Document 2. In FIG. 7, the horizontal axis represents chromatic dispersion, and the vertical axis represents D coefficient.

  Normally, when an optical signal with a bit rate of 10 Gbit / s is subjected to chromatic dispersion of ± 1000 ps / nm, the waveform of the optical signal is distorted, resulting in a power penalty of about 1 dB. Therefore, it is necessary to evaluate the influence of chromatic dispersion in the range of at least ± 1000 ps.

  On the other hand, as can be seen from FIG. 7, the chromatic dispersion range reported in Non-Patent Document 2 was −180 to +330 ps / nm. FIG. 8 is a diagram showing a light intensity histogram of the NRZ phase modulation signal. In FIG. 8, the horizontal axis represents the sampling number (frequency), and the vertical axis represents the light intensity (voltage). As shown in FIG. 8, when the chromatic dispersion is not large, the light intensity histogram clearly has three peaks. Therefore, the quality due to the chromatic dispersion of the NRZ phase-modulated optical signal is calculated from the equation (2). The deterioration coefficient D can be obtained. However, when the chromatic dispersion increases, the peak at the high level of the light intensity histogram becomes unclear as described in FIG. 8, and the coefficient D cannot be obtained.

  In other words, there has been no optical signal quality evaluation device that can evaluate the influence of chromatic dispersion over a wide range of chromatic dispersion without using phase modulation / intensity modulation conversion means and without depending on the bit rate for an NRZ phase modulated optical signal. It was.

  The present invention has been made in view of the above points, and an object of the present invention is to provide an optical signal quality evaluation apparatus capable of evaluating the influence on the quality due to wavelength dispersion of an NRZ phase modulated optical signal having an arbitrary bit rate in a phase modulation method, and It is to provide a method. Another object is to reduce the cost of the apparatus by simplifying the configuration and using optical components that are easy to manufacture.

The present invention provides a photoelectric converter that converts an optical signal having a bit rate N · f ₀ (bit / s) that is an integral multiple of the basic clock frequency f ₀ (Hz) into an electrical signal, and the basic clock frequency f ₀ (Hz). ), A timing clock generating means for generating a timing clock having a repetition frequency f ₀ / n ₁ −Δf (Hz) or f ₀ / n ₁ + Δf (Hz) different from a fraction of an integer, and the timing signal Electrical signal processing for measuring a level using an electrical sampling means for sampling a level and a sampling electrical signal obtained by sampling by the electrical sampling means, and obtaining a coefficient indicating the quality of the optical signal from the sampling points constituting the histogram And an optical signal quality evaluation apparatus.

Here, a feature of the present invention is that the photoelectric converter inputs a non-return-to-zero (NRZ) optical signal that is phase-modulated as the optical signal, and the electrical signal processing means has a maximum number of sampling points. the level of the value and mu _m, and integrating the number of sampling points from the level minimum value of the histogram, the total number of sampling points when the N _total,
N _high = N _total × k (0.5 <k <1)
The level when the number of sampling points N _high obtained in step S is equal to μ _high is μ _h, and the parameter F _dis indicating the quality of the optical signal is F _dis = μ _h / μ _m
The parameter F _dis is obtained as a quality degradation coefficient due to wavelength dispersion of the NRZ phase modulation optical signal, and a means for inspecting the quality of the optical signal is provided.

Alternatively, according to the present invention, timing for generating a timing clock having a repetition frequency f ₀ / n ₁ −Δf (Hz) or f ₀ / n ₁ + Δf (Hz) that is different from an integer of the basic clock frequency f ₀ (Hz). Clock generating means, opto-electrical sampling means for sampling the level of an optical signal having a bit rate N · f ₀ (bit / s) that is an integral multiple of the basic clock frequency f ₀ (Hz) with the timing clock, A photoelectric converter for converting a sampling optical signal into a sampling electric signal, and an electric signal processing means for measuring a histogram of light intensity from the sampling electric signal and obtaining a coefficient indicating the quality of the optical signal from sampling points constituting the histogram Is an optical signal quality evaluation apparatus.

Here, a feature of the present invention is that the photoelectric converter inputs a non-return-to-zero (NRZ) optical signal that is phase-modulated as the optical signal, and the electrical signal processing means has a maximum number of sampling points. the level of the value and mu _m, and integrating the number of sampling points from the level minimum value of the histogram, the total number of sampling points when the N _total,
N _high = N _total × k (0.5 <k <1)
The level when the number of sampling points N _high obtained in step S is equal to μ _high is μ _h, and the parameter F _dis indicating the quality of the optical signal is F _dis = μ _h / μ _m
The parameter F _dis is obtained as a quality deterioration coefficient due to wavelength dispersion of the NRZ phase modulation optical signal, and means for inspecting the quality of the optical signal is provided.

  The k is preferably 0.6 <k <1.

  Further, as the optical-electrical sampling means, an electroabsorption optical modulator, an optical modulator utilizing an electro-optic effect, or a semiconductor optical amplifier can be used.

  Thereby, it is possible to provide an optical signal quality evaluation apparatus capable of evaluating the influence on the quality due to the wavelength dispersion of the NRZ phase modulation optical signal having an arbitrary bit rate in a wider wavelength dispersion range than conventional. In addition, the cost of the apparatus can be reduced by simplifying the configuration and using optical components that are easy to manufacture.

Further, the present invention can be viewed from the viewpoint of the invention of the optical signal quality evaluation method. That is, the present invention is an optical signal quality evaluation method performed by an optical signal quality evaluation apparatus, and the present invention is characterized by a bit rate N · f ₀ (integer multiple of the basic clock frequency f ₀ (Hz). bit / s) is converted into an electrical signal, and a repetition frequency f ₀ / n ₁ −Δf (Hz) or f ₀ / n ₁ + Δf different from an integral fraction of the basic clock frequency f ₀ (Hz). When generating a timing clock of (Hz), sampling the level of the electric signal with the timing clock and measuring the histogram, and obtaining a coefficient indicating the quality of the optical signal from the sampling points constituting the histogram, the optical signal as inputs the phase-modulated non-return to zero (NRZ) optical signal, the level of sampling points is the maximum value and mu _m, histogram Integrates the number of sampling points from the level minimum, all sampling points when the N _total,
N _high = N _total × k (0.5 <k <1)
The level when the number of sampling points N _high obtained in step S is equal to μ _high is μ _h, and the parameter F _dis indicating the quality of the optical signal is F _dis = μ _h / μ _m
The parameter F _dis is obtained as a quality deterioration coefficient due to wavelength dispersion of the NRZ phase modulation optical signal, and the quality of the optical signal is inspected.

Alternatively, the optical signal quality evaluation method performed by the optical signal quality evaluation apparatus of the present invention is a repetition frequency f ₀ / n ₁ −Δf (Hz) or f ₀ // different from an integral fraction of the basic clock frequency f ₀ (Hz). A timing clock of n ₁ + Δf (Hz) is generated, and the level of an optical signal having a bit rate N · f ₀ (bit / s) that is an integral multiple of the basic clock frequency f ₀ (Hz) is sampled by the timing clock. Converting the sampling optical signal into a sampling electric signal, measuring a histogram of light intensity from the sampling electric signal, and obtaining a coefficient indicating the quality of the optical signal from the sampling points constituting the histogram. enter the phase modulated non-return to zero (NRZ) optical signal as the level of sampling points is the maximum value mu _m And integrates the number of sampling points from the level minimum value of the histogram, the total number of sampling points when the N _total,
N _high = N _total × k (0.5 <k <1)
The level when the number of sampling points N _high obtained in step S is equal to μ _high is μ _h, and the parameter F _dis indicating the quality of the optical signal is F _dis = μ _h / μ _m
The parameter F _dis is obtained as a quality deterioration coefficient due to wavelength dispersion of the NRZ phase-modulated optical signal, and the quality of the optical signal is inspected.

  The k is preferably 0.6 <k <1.

  Thereby, it is possible to provide an optical signal quality evaluation method capable of evaluating the influence on the quality due to the chromatic dispersion of the NRZ phase modulation optical signal having an arbitrary bit rate in a wider chromatic dispersion range than conventional.

  The present invention can provide an optical signal quality evaluation apparatus and method capable of evaluating the influence of chromatic dispersion on the quality of an NRZ phase modulated optical signal having an arbitrary bit rate in a wider chromatic dispersion range than before. In addition, the cost of the apparatus can be reduced by simplifying the configuration and using optical components that are easy to manufacture.

(First embodiment)
An optical signal quality evaluation apparatus according to a first embodiment of the present invention will be described with reference to FIG. FIG. 1 is a configuration diagram of an optical signal quality evaluation apparatus according to the first embodiment. An NRZ phase modulated optical signal (NRZ-DPSK) having a bit rate of N · f ₀ (bit / s) is incident on the photoelectric conversion means 1. On the other hand, the electrical sampling clock is generated from the sampling clock generating means 4 at a repetition frequency f ₁ (Hz) (f ₁ = [f ₀ / n] + a: n is a natural number, and a is an offset frequency). It reaches. The sampling electric signal sampled and output by the electric sampling means 2 is input to the electric signal processing means 3.

  As the sampling clock generation means 4, it is possible to use a synthesized signal generator + comb generator or a synthesized signal generator + electric short pulse generation by a non-linear transmission line (for example, see Non-Patent Document 3).

  The electric signal processing means 3 constructs an intensity histogram of an optical signal from sampling data obtained by analog / digital conversion (AD conversion) of the sampling electric signal and data fetching and storing operation using a buffer.

  A feature of the present invention is that the electrical signal processing means 3 extracts a quality deterioration coefficient due to wavelength dispersion of the NRZ phase modulated optical signal from the intensity histogram.

When the electrical signal processing means 3, the level of sampling points is the maximum value and mu _m, and integrating the number of sampling points from the level minimum value of the histogram, the total number of sampling points was N _total,
N _high = N _total × k (0.6 <k <1)
The level when the sampling point number N _high obtained in step S is equal to μ _h is set to μ _h, and the parameter F _dis indicating the quality of the optical signal is set to F _dis = μ _h / μ _m (3)
Asking. The parameter F _dis is obtained as a quality deterioration coefficient due to wavelength dispersion of the NRZ phase modulated optical signal, and the quality of the optical signal is inspected.

  As described in the prior art, in the optical signal quality evaluation apparatus using D calculated by the equation (2) reported in Non-Patent Document 2, as shown by the portion surrounded by the frame line in FIG. Increases (from 160 ps / nm to 240 ps / nm), the peak at the higher level of the light intensity histogram becomes unclear and the coefficient D cannot be obtained. This is because the energy of light is diffused as the spread of the high level increases due to the dispersion, and the peak value of the histogram gradually becomes unclear because the peak value of the high level in the histogram becomes low.

On the other hand, the present invention measures the high-level spread due to chromatic dispersion not by the peak value but by F _dis which is the ratio of the number of sampling points, so that the NRZ phase-modulated optical signal is deteriorated in quality such as waveform distortion caused by chromatic dispersion. Can be accurately evaluated in a wide wavelength dispersion region.

FIG. 2 shows calculation results obtained by the beam propagation method for the relationship between F _dis and chromatic dispersion. Here, the coefficient k is 0.9. By using this method as shown in FIG. 2, it becomes possible to evaluate in a wavelength dispersion range that is four times or more wider than that of the prior art. In addition, since this method uses asynchronous sampling, a light intensity histogram at an arbitrary bit rate can be created.

  Therefore, by using the present invention, it is possible to realize an apparatus that evaluates quality degradation due to wavelength dispersion of an NRZ phase-modulated optical signal having an arbitrary bit rate in a wider wavelength dispersion range than before.

The number of sampling points N _m from the level minimum value to the level μ _m where the number of sampling points is the maximum value is half of the total number of sampling points (N _m = N _total × 0.5). F _dis is because an index that represents the broadening due to the high level dispersion, level mu _h as the N _high must be in the high level in the intensity histogram. That is, the range of the coefficient k that determines N _high needs to be a value larger than 0.5. However, 0.5 around at hardly observed extent of high level due to the dispersion too large peak levels mu _m is. Therefore, the coefficient k is 0.6 <k <1
Is effective.

  In the above description, the asynchronous sampling optical signal waveform measurement and evaluation apparatus has been described. Of course, the present invention is also applied to an optical signal waveform measurement and evaluation apparatus provided with the clock extraction means 5 as shown in FIG. can do. In the example of FIG. 3A, a clock is extracted from an input optical signal, and the sampling clock generating means 4 generates a sampling clock based on the extracted clock.

(Second embodiment)
An optical signal quality evaluation apparatus according to a second embodiment of the present invention will be described with reference to FIG. FIG. 4 is a configuration diagram of the optical signal quality evaluation apparatus of the second embodiment. A feature of the present invention is that the quality of the optical signal can be evaluated with higher time resolution by using the optical signal electrical sampling means 7.

As the optical signal electrical sampling means 7, an electroabsorption optical modulator, an optical modulator utilizing an electro-optic effect, or a semiconductor optical amplifier can be used. Here, it is desirable that the repetition frequency f ₁ of the electrical sampling clock generated by the sampling clock generating means 4 is a high speed of about MHz to GHz. Similar to the configuration of FIG. 1, the sampling clock generation means 4 can use a synthesized signal generator + com generator or a synthesized signal generator + electric short pulse generation by a non-linear transmission line (for example, Non-Patent Document 3).

  In addition, since the time resolution of the apparatus greatly depends on the pulse width of the sampling clock, it is desirable that the pulse width of the output clock from the comb generator or the nonlinear transmission line is short. Since the nonlinear transmission line can generate pulses of several ps or less, when it is used, optical signal waveform measurement and quality evaluation with time resolution of several ps or less (corresponding to a band of several tens of GHz or more) are realized. it can. Further, if necessary, an electric amplifier can be used before or after the comb generator or the nonlinear transmission line. Further, if necessary, a baseband clipper can be used in the subsequent stage of the comb generator or the nonlinear transmission line.

  Therefore, by using the optical signal electrical sampling means 7, it is possible to realize a device that evaluates quality degradation due to chromatic dispersion of an NRZ phase modulated optical signal having an arbitrary bit rate in a wider chromatic dispersion range than ever before with higher time resolution. Can do.

  In the above description, the asynchronous sampling optical signal waveform measurement and evaluation apparatus has been described. Of course, the present invention is also applied to an optical signal waveform measurement and evaluation apparatus provided with the clock extraction means 5 as shown in FIG. can do. In the example of FIG. 3A, a clock is extracted from an input optical signal, and the sampling clock generating means 4 generates a sampling clock based on the extracted clock.

  According to the present invention, it is possible to evaluate the influence on the quality due to the chromatic dispersion of the NRZ phase-modulated optical signal having an arbitrary bit rate in a wider chromatic dispersion range than the conventional one. In addition, the cost of the apparatus can be reduced by simplifying the configuration and using optical components that are easy to manufacture.

The block diagram of the optical signal quality evaluation apparatus of 1st embodiment. The figure which shows the calculation result calculated | required by the beam propagation method about the relationship between _Fdis and chromatic dispersion. The figure which shows the other structural example of 1st embodiment. The block diagram of the optical signal quality evaluation apparatus of 2nd embodiment. The figure for demonstrating the method of converting and evaluating to an electric signal, after converting a phase modulation signal into an intensity modulation signal. The block diagram of the conventional optical signal quality evaluation apparatus. The figure which shows the wavelength dispersion characteristic of a prior art. The figure which shows the light intensity histogram of a NRZ phase modulation signal.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 10 Photoelectric conversion means 2 Electrical sampling means 3 Electrical signal processing means 4 Sampling clock generation means 5 Clock extraction means 7 Optical signal electrical sampling means 8 1-bit delay Mach-Zehnder interferometer 9 Intensity modulation signal evaluation means

Claims (7)

A photoelectric converter that converts an optical signal having a bit rate N · f ₀ (bit / s) that is an integral multiple of the basic clock frequency f ₀ (Hz) into an electrical signal;
Timing clock generation means for generating a timing clock having a repetition frequency f ₀ / n ₁ −Δf (Hz) or f ₀ / n ₁ + Δf (Hz) different from an integral fraction of the basic clock frequency f ₀ (Hz);
Electrical sampling means for sampling the level of the electrical signal with the timing clock;
An electrical signal quality evaluation comprising: an electrical signal processing means for measuring a histogram using a sampling electrical signal obtained by sampling by the electrical sampling means, and obtaining a coefficient indicating the quality of the optical signal from a sampling point constituting the histogram In the device
The photoelectric converter inputs a non-return-to-zero (NRZ) optical signal phase-modulated as the optical signal,
When the electrical signal processing means, a level at which the number of sampling points is the maximum value and mu _m, and integrating the number of sampling points from the level minimum value of the histogram, the total number of sampling points was N _total,
N _high = N _total × k (0.5 <k <1)
The level when the number of sampling points N _high obtained in step S is equal to μ _high is μ _h, and the parameter F _dis indicating the quality of the optical signal is F _dis = μ _h / μ _m
An optical signal quality evaluation apparatus comprising: means for obtaining the parameter F _dis as a quality degradation coefficient due to wavelength dispersion of the NRZ phase modulation optical signal and inspecting the quality of the optical signal. Timing clock generating means for generating a timing clock having a repetition frequency f ₀ / n ₁ −Δf (Hz) or f ₀ / n ₁ + Δf (Hz) different from an integral fraction of the basic clock frequency f ₀ (Hz);
Opto-electrical sampling means for sampling the level of an optical signal having a bit rate N · f ₀ (bit / s) which is an integral multiple of the basic clock frequency f ₀ (Hz) with the timing clock;
A photoelectric converter that converts the sampling light signal into a sampling electrical signal;
In an optical signal quality evaluation apparatus comprising: an electrical signal processing means for measuring a histogram of light intensity from the sampling electrical signal and obtaining a coefficient indicating the quality of the optical signal from sampling points constituting the histogram;
The photoelectric converter inputs a non-return-to-zero (NRZ) optical signal phase-modulated as the optical signal,
When the electrical signal processing means, a level at which the number of sampling points is the maximum value and mu _m, and integrating the number of sampling points from the level minimum value of the histogram, the total number of sampling points was N _total,
N _high = N _total × k (0.5 <k <1)
The level when the number of sampling points N _high obtained in step S is equal to μ _high is μ _h, and the parameter F _dis indicating the quality of the optical signal is F _dis = μ _h / μ _m
An optical signal quality evaluation apparatus comprising: means for obtaining the parameter F _dis as a quality deterioration coefficient due to wavelength dispersion of the NRZ phase modulation optical signal and inspecting the quality of the optical signal.   3. The optical signal quality evaluation apparatus according to claim 1, wherein 0.6 <k <1.   3. The optical signal quality evaluation apparatus according to claim 2, wherein an electroabsorption optical modulator, an optical modulator using an electro-optic effect, or a semiconductor optical amplifier is used as the optical-electrical sampling means. An optical signal quality evaluation method performed by an optical signal quality evaluation device,
An optical signal having a bit rate N · f ₀ (bit / s) that is an integral multiple of the basic clock frequency f ₀ (Hz) is converted into an electrical signal;
Generating a timing clock having a repetition frequency f ₀ / n ₁ −Δf (Hz) or f ₀ / n ₁ + Δf (Hz) different from an integral fraction of the basic clock frequency f ₀ (Hz);
When the level of the electrical signal is sampled with the timing clock and the histogram is measured, and when obtaining a coefficient indicating the quality of the optical signal from the sampling points constituting the histogram,
A non-return-to-zero (NRZ) optical signal that is phase modulated as the optical signal is input,
The level at which the number of sampling points is the maximum value and mu _m, and integrating the number of sampling points from the level minimum value of the histogram, the total number of sampling points when the N _total,
N _high = N _total × k (0.5 <k <1)
The level when the number of sampling points N _high obtained in step S is equal to μ _high is μ _h, and the parameter F _dis indicating the quality of the optical signal is F _dis = μ _h / μ _m
And determining the parameter F _dis as a quality degradation coefficient due to wavelength dispersion of the NRZ phase-modulated optical signal and inspecting the quality of the optical signal. An optical signal quality evaluation method performed by an optical signal quality evaluation device,
Generating a timing clock with a repetition frequency f ₀ / n ₁ −Δf (Hz) or f ₀ / n ₁ + Δf (Hz) different from an integral fraction of the basic clock frequency f ₀ (Hz);
The level of an optical signal having a bit rate N · f ₀ (bit / s) that is an integral multiple of the basic clock frequency f ₀ (Hz) is sampled by the timing clock,
Converting the sampling light signal into a sampling electrical signal;
When measuring a histogram of light intensity from the sampling electrical signal and obtaining a coefficient indicating the quality of the optical signal from the sampling points constituting the histogram,
A non-return-to-zero (NRZ) optical signal that is phase modulated as the optical signal is input,
The level at which the number of sampling points is the maximum value and mu _m, and integrating the number of sampling points from the level minimum value of the histogram, the total number of sampling points when the N _total,
N _high = N _total × k (0.5 <k <1)
The level when the number of sampling points N _high obtained in step S is equal to μ _high is μ _h, and the parameter F _dis indicating the quality of the optical signal is F _dis = μ _h / μ _m
And determining the parameter F _dis as a quality degradation coefficient due to wavelength dispersion of the NRZ phase-modulated optical signal, and inspecting the quality of the optical signal.   7. The optical signal quality evaluation method according to claim 5, wherein 0.6 <k <1.

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