JPH09145545A - Method and apparatus for measuring polarization mode dispersion utilizing four polarization incidenttype fixed analyzer method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To correctly measure and evaluate a polarization mode dispersion, by distinguishing a mode-coupling state of an optical fiber to be measured. SOLUTION: A spectrum of an emitted light (first spectrum) penetrating from one side to the other side of an optical fiber to be measured and, a spectrum of a emitted light (second spectrum) penetrating from the other side to the one side of the optical fiber are measured. A first and a second polarization mode dispersion values (PMD values) are obtained from the corresponding spectrums. Whether or not waveforms of the first and second spectrums, and the first and second PMD values agree with each other within a preset range is detected by a reversibility judgment part 15. When the waveforms and PMD values agree respectively with each other, it is judges as a strong/weak mode- coupled state. If the waveforms and PMD values do not agree, it is judged as an intermediate mode-coupled state, whereby a PMD evaluation is discarded. In the strong/weak mode-coupled state, whether it is a strong mode or weak mode is distinguished from whether the waveform of each spectrum is a sine. The PMD is evaluated correspondingly to each mode.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention, in the field of optical communication, uses a four polarization incident type fixed analyzer method for accurately measuring polarization mode dispersion which limits transmission characteristics of an optical fiber. The present invention relates to a method of measuring modal dispersion and an apparatus thereof.

[0002]

2. Description of the Related Art With the development of optical fiber amplifiers and dispersion-controlled single-mode optical fiber technology, polarization mode dispersion (hereinafter referred to as PMD), which has never been a problem when performing long-distance and large-capacity optical communication, It has attracted attention as one of the important parameters that limit the transmission characteristics of optical fibers. Under such a background, accurate measurement of PMD of a single mode optical fiber is currently one of the important problems. Until now, as a method of measuring PMD, (i) polarimetric method, (ii) interferometric method, (iii)
Several methods have been proposed, represented by the fixed analyzer method. A list of reference documents related to the present specification is shown in Tables 1 and 2, and will be described below with reference to these documents.

[0003]

[Table 1]

[Table 2]

Among the methods for measuring PMD, the fixed analyzer method (1) makes it easy to set up a measuring instrument in a laboratory. (2) Since the measurement time is short, it is unlikely to be affected by the change over time of mode coupling. Therefore, it is considered to be superior to other methods (Reference [1]).

Among the measurement methods called the fixed analyzer method, the four polarization incident type fixed analyzer method is known as shown in the document [13], and a PMD measuring apparatus using this method is known. As shown in FIG. 8B, the phase compensator main body 8 is provided on the incident side (one side 30 in the figure) of the optical fiber 4 to be measured. The phase compensator body 8 is provided with a quarter wave plate 6 and a half wave plate 7. In the figure, 1 indicates a light source, which is a white light source or an ASE (Amplifier) of an optical amplifier.
It is a light source with a sufficiently wide wavelength width of emitted light, such as ified Spontaneous Emission. Further, 2 is an incident side polarizer, 3 is an emission side polarizer, and 5 is an optical spectrum analyzer.

This four-polarization incident type fixed analyzer method (hereinafter referred to as the fixed analyzer method (b)) is a quarter wavelength plate after the light emitted from the light source 1 passes through the incident side polarizer 2. 6 and a half wave plate 7, and by adjusting the angle of each of these wave plates 6 and 7, four types of light with different polarization states as shown in Table 3 below. Is incident on the optical fiber 4 to be measured.

[0007]

[Table 3]

The incident side polarizer 2 and the output side polarizer (analyzer) 3 shown in FIG. 8B are each about a tentative principal axis.
It is tilted at 45 °. Then, this four polarization incident type fixed analyzer method measures each of the above four types (called Cnt.1 to Cnt.4) in combination, and as shown in Table 4, the PMD is evaluated by the average value thereof. .

[0009]

[Table 4]

As shown in the literature [11],
In addition to the fixed analyzer method (b), the measurement methods called the fixed analyzer method include the fixed analyzer methods (a) and (c) shown in Table 4 depending on the difference in the hardware part. A measuring device using the fixed analyzer method (a) is shown in FIG.
A measuring device using the fixed analyzer method (c) is shown in FIG. At first glance, it can be seen from these devices that the polarization state of the light being measured is different depending on each measurement method.

When measuring the PMD of an optical fiber using the fixed analyzer method as described above, the handling of data in the measurement is classified as shown in Table 5 depending on whether the optical fiber has mode coupling or not. It is known that this is the case (Reference [11]).

[0012]

[Table 5]

In Table 5, the definition and spectral characteristics of weak mode coupling are properly determined, whereas the definition of strong mode coupling and spectral characteristics only deny the description in weak mode coupling. And
Not well defined. In addition, the numerical value of 0.82 in the evaluation method appears firmly for that.

Then, there arises a question of whether the proposition: "all things that are not weak mode coupling are strong mode coupling" is correct. In Ref. [16], consideration and experiments were conducted under such a problem awareness. As a result, it turns out that the above proposition is not correct. In other words, as shown by Poole and Favin, the numerical value of 0.82 called the correction coefficient is obtained under the hypothesis that mode coupling is sufficiently random over the longitudinal direction of the optical fiber (Reference) [3]), the correction coefficient 0.82 is a numerical value that can be applied only when the optical fiber length is sufficiently long and mode coupling is sufficiently random. Therefore, it is considered that Table 5 should be rewritten as Table 6.

[0015]

[Table 6]

By the way, the fixed analyzer method is a measurement method that does not use the concept of "principal polarization state" (reference [2]). Therefore, when the mode coupling of the optical fiber to be measured can be regarded as sufficiently random, the measured value Cannot be considered as the value of PMD. Then, as shown in Tables 5 and 6, the value corrected by multiplying the measured value by the correction coefficient k = 0.82 is P
It is known to support MD. (Reference [3]).

Aso et al. Measured PMD while cutting a dispersion-shifted optical fiber having a total length of 90 km, and investigated the distance dependence of the correction coefficient (reference [4]). According to their experimental report, the correction factor is at least 50 km if the optical fiber length is not more than 50 km.
It has been shown to be unstable above and below 0.82. The result is that the fiber length is 50
If it is less than km, it can be interpreted that the mode coupling is not sufficiently random. Naturally, the length of 50 km is not always a general property, but depending on the optical fiber to be measured, it is unclear how long the optical fiber can be considered that the mode coupling is sufficiently random.

According to the research reports so far, the conditions shown in Table 7 below are listed as sufficient conditions for the long single mode optical fiber to be in the random mode coupling state.

[0019]

[Table 7]

[0020]

However, of these sufficient conditions shown in Table 7, only the condition 1 can be determined only by the fixed analyzer method. However, for condition 1, the PMD measured with one optical fiber was measured.
It is not obvious whether is proportional to the square root of the distance. Moreover, as is clear from Table 6, when the optical spectrum is in the intermediate mode coupling state, it is unknown whether or not the measurement spectrum is sinusoidal. Therefore, when the measurement spectrum is sinusoidal, all are in the weak mode coupling state. If the PMD is determined to be the measured value, and if the measured spectrum is not sinusoidal, it is determined that all are in strong mode coupling, and the PMD is set to the measured value × 0.82, the accurate value of the PMD cannot be determined. .

Therefore, the applicant of the present invention has made a study for clarifying the difference between strong mode coupling, weak mode coupling, and intermediate mode coupling of an optical fiber when measuring PMD using the four polarization incident type fixed analyzer method. Variously, and the approach is to measure the spectrum and PMD of the optical fiber under test.
Whether or not the measurement depends on the direction through which light passes, ie P
Focusing on the presence or absence of the direction dependence of the MD and the spectrum waveform, experiments were conducted using various optical fibers shown in Table 8.

[0022]

[Table 8]

Tables 9 to 11 below show the measurement of PMD and spectrum waveforms of the optical fibers A to C shown in Table 8 by the four polarization incident type fixed analyzer method (fixed analyzer method (b)). The results are shown. Table 9 shows the measurement result of the optical fiber A, and Table 10 shows the measurement result of the optical fiber B.
Table 11 shows the measurement results of the optical fiber C. In addition, in each of Tables 9 to 11, for reference, each measurement result by the fixed analyzer methods (a) and (c), and
Polari known as a measurement method based on the theory of main polarization state
The measurement results by the metric method (Reference [17]) are added.

Further, in these tables, the direction 1 indicates that the light from the light source 1 or the variable wavelength light source 9 is directed to one side of the measured optical fiber 4 (optical fibers A to C) as shown in FIG.
The direction in which the light is incident from 30 and transmitted to the opposite side 31 of the optical fiber 4 to be measured is shown, and the direction 2 is such that the optical fiber 4 to be measured is connected to the light source 1 etc. The direction in which light is transmitted from the opposite side 31 to the one side 30 is shown.

[0025]

[Table 9]

[0026]

[Table 10]

[0027]

[Table 11]

Further, FIGS. 9 to 12 show spectrum waveforms measured for each of the optical fibers B and C shown in Table 8 by using the fixed analyzer method (b),
As is clear from these figures, in the optical fiber B, as shown in Tables 10 and 11, Cnt. The spectrum waveforms other than 1 are different between the directions 1 and 2, and in the optical fiber C, all the spectrum waveforms are different between the directions 1 and 2.

As is apparent from the above results, when the optical fiber 4 to be measured has mode coupling like the optical fibers B and C, the measurement result by the fixed analyzer method (b) is the direction 1 It has been found that the same spectral waveform and PMD characteristics are not obtained in and (direction 2) (they do not have reversibility or have direction dependence).・ We wondered if it could be distinguished from weak mode coupling and conducted further experiments. As a result, when the PMD and the spectrum waveform were obtained using the fixed analyzer method (b), that is, the four polarization incident type fixed analyzer method, the following was found.

(1) The PMD value and the measured waveform are reversible when there is no mode coupling or can be ignored. At this time, the measured PMD value is polarimetric
It agrees with the PMD measurement value of the same sample by the method.
(2) If there is mode coupling but it is not random, P
The MD value and the measured waveform are not reversible. (3) When there is mode coupling but it is not random, the more randomness of mode coupling becomes, the more reversible the PMD value and the measured waveform become. In addition, the measured value by the fixed analyzer method is the PMD of the same sample by the polarimetric method.
It approaches the value obtained by multiplying the measured value by 0.82. (4) The PMD value and the measured waveform recover reversibility when there is mode coupling and is sufficiently random. At this time, the measured PMD value coincides with the PMD measurement value of the same sample multiplied by 0.82 by the polarimetric method. The item (4) has actually been confirmed by an experiment by Aso et al. (Reference [4]).

Then, in summary of the above, as shown in Table 12, in the case of weak mode coupling without mode coupling,
In the case of strong mode coupling in which the coupling between the polarization modes is sufficiently random, the PMD value and the spectral waveform in the direction 1 and the PMD value and the spectral waveform in the direction 2 are almost the same, in other words, the PMD value and the spectral waveform. Has reversibility and will not have this reversibility only in the case of intermediate mode coupling.

[0032]

[Table 12]

The present invention has been made by utilizing this result, and its purpose is to determine whether the coupling state of the optical fiber is strong mode coupling or weak mode coupling even if only one optical fiber is provided. Provided is a polarization mode dispersion measurement method and device using the four polarization incident type fixed analyzer method, which makes it possible to easily discriminate between intermediate mode couplings and accurately measure and evaluate polarization mode dispersion. To do.

[0034]

Means for Solving the Problems To achieve the above object, the present invention provides means for solving the problems by the following constitution. That is, in the polarization mode dispersion measuring method using the four polarization incident type fixed analyzer method of the first aspect of the invention, the light incident from one side of the measured optical fiber is transmitted through the measured optical fiber and emitted. The spectrum of the outgoing light to be measured is measured as the first outgoing light spectrum, and similarly the spectrum of the outgoing light emitted from the side opposite to the optical fiber under measurement is transmitted through the optical fiber under measurement and is emitted.
The first polarization mode dispersion value is obtained based on the first emission light spectrum, and the second polarization mode dispersion value is obtained based on the second emission light spectrum. After that, it is determined whether the first and second polarization mode dispersion values match within a predetermined error range, and the waveforms of the first and second emitted light spectra match within a predetermined allowable range. Whether or not the first and second polarization mode dispersion values match within the error range and the first and second emission light spectrum waveforms match within the allowable range. It is judged that the optical fiber is not in the intermediate mode coupling state, and it is judged whether or not the coincident emission light spectrum waveform is sinusoidal within the predetermined allowable range, and when the emission light spectrum waveform is sinusoidal. The optical fiber under test is in the mode of weak mode coupling. Then, the polarization mode dispersion value that agrees within the error range is evaluated as the polarization mode dispersion value of the measured optical fiber, and when the emitted light spectrum waveform is not sinusoidal, the measured optical fiber has a strong mode. It is configured to evaluate as the polarization mode dispersion value of the optical fiber under measurement by multiplying the correction value 0.82 by the polarization mode dispersion value that agrees within the error range by judging that it is in the coupled state. ing.

Further, in the polarization mode dispersion measuring method using the four polarization incident type fixed analyzer method of the second invention, the light incident from one side of the measured optical fiber is transmitted through the measured optical fiber. First, the spectrum of the emitted light
Of the outgoing light spectrum, and similarly, the spectrum of outgoing light in which the light incident from the opposite side of the optical fiber under measurement passes through the optical fiber under measurement and is output is measured as the second outgoing light spectrum. The first polarization mode dispersion value is obtained based on the emission light spectrum of the first polarization mode, the second polarization mode dispersion value is obtained based on the second emission light spectrum, and then the first and second polarization modes are obtained. It is determined whether the modal dispersion values match within a predetermined error range and whether the waveforms of the first and second emitted light spectra match within a predetermined allowable range. When the 1st and 2nd polarization mode dispersion values match within the error range and the 1st and 2nd outgoing light spectrum waveforms match within the allowable range, the measured optical fiber is not in the intermediate mode coupling state. Judging that the first and second less Also, one of the outgoing light spectrum waveforms is Fourier-transformed, and when the Fourier-transformed waveform is a vertical linear pattern waveform peculiar to the weak mode, it is judged that the optical fiber under measurement is in the weak mode coupling state, and they match within the error range. The polarization mode dispersion value to be evaluated as the polarization mode dispersion value of the optical fiber to be measured, and when the Fourier transform waveform is a Gaussian approximate waveform, the optical fiber to be measured is determined to be in a strong mode coupling state, and The characteristic is that the value obtained by multiplying the polarization mode dispersion value that matches within the error range by a correction coefficient of 0.82 is evaluated as the polarization mode dispersion value of the optical fiber to be measured.

Further, the measurement method of polarization mode dispersion using the four polarization incident type fixed analyzer method of the third invention is as follows:
The spectrum of the outgoing light emitted from the one side of the measured optical fiber after passing through the measured optical fiber was measured as the first outgoing light spectrum, and was similarly entered from the opposite side of the measured optical fiber. The spectrum of the outgoing light that the light transmits through the optical fiber under measurement and exits is measured as the second outgoing light spectrum, and the first polarization mode dispersion value and the first outgoing light spectrum are measured based on the first outgoing light spectrum. The first Fourier transform waveform obtained by Fourier transforming the waveform of the emitted light spectrum is obtained, and the second polarization mode dispersion value and the waveform of the second emitted light spectrum are Fourier transformed based on the second emitted light spectrum. The Fourier transform waveform is obtained, and after that, it is determined whether or not the first and second polarization mode dispersion values match within a predetermined error range, and the first and second Fourier transform waveforms are predetermined. Huh It is determined whether or not they match within the range, the first and second polarization mode dispersion values match within the error range, and the first and second Fourier transform waveforms match within the allowable range. When it is determined that the optical fiber to be measured is not in the intermediate mode coupling state, the Fourier transform waveform that matches within the allowable range is determined to be in the intermediate mode coupling state. In the case of a circular pattern waveform, the measured optical fiber is judged to be in the mode of weak mode coupling, and the polarization mode dispersion value that matches within the error range is evaluated as the polarization mode dispersion value of the measured optical fiber.
When the Fourier transform waveform that matches within the allowable range is a Gaussian approximate waveform, it is determined that the optical fiber under measurement is in the strong mode coupling state, and the correction coefficient 0.82 is added to the polarization mode dispersion value that matches within the error range. It is characterized in that the value multiplied by is evaluated as the polarization mode dispersion value of the optical fiber under measurement.

Further, when it is judged that the Fourier transform waveform is a Gaussian approximate waveform and the optical fiber to be measured is in a strong mode coupling state, it is considered that the Fourier transform waveform has a Gaussian distribution, and It is also possible to evaluate the standard deviation value of the Gaussian distribution as the polarization mode dispersion value of the optical fiber to be measured, or to measure the polarization mode dispersion using the four polarization incident type fixed analyzer method of the second and third inventions. It has a characteristic configuration of.

Further, the polarization mode dispersion field measuring apparatus using the four polarization incident type fixed analyzer method of the first invention is
The light emitted from one side of the optical fiber to be measured is transmitted through the optical fiber to be measured, and the first emitted light spectrum measured at the emission side and the light incident from the opposite side of the optical fiber to be measured are the measured light. An emission light spectrum storage unit for storing a second emission light spectrum transmitted through the fiber and measured on the emission side; a first polarization mode dispersion value calculated based on the first emission light spectrum; A polarization mode dispersion actual measurement calculation unit that calculates a second polarization mode dispersion value based on the emitted light spectrum; and first and second polarization mode dispersion actual values calculated by the polarization mode dispersion actual measurement calculation unit. It is determined whether or not they match within a predetermined error range, and whether or not the waveforms of the first and second emitted light spectra match within a predetermined allowable range. Polarization mode dispersion value is within the error range Match, and, when the first and second outgoing light spectrum waveform matches within an allowable range is judged that the measured optical fiber is not an intermediate mode coupling state,
In other cases, the reversibility determining unit determines that the optical fiber to be measured is in the intermediate mode coupling state; the reversibility determining unit receives the determination result that the optical fiber to be measured is not in the intermediate mode coupling state, and It is determined whether or not the output light spectral waveforms that match within the specified allowable range are sinusoidal, and when the output light spectral waveforms are sinusoidal, it is determined that the measured optical fiber is in the weak mode coupling state, A strong / weak mode coupling discriminating unit which judges that the optical fiber to be measured is in a strong mode coupling state when the emitted light spectrum waveform is not sinusoidal; When it is determined that the polarization mode dispersion value that agrees within the error range is evaluated as the polarization mode dispersion value of the optical fiber to be measured, and when it is determined to be the strong mode coupling state, And a polarization mode dispersion value definite evaluation unit that evaluates a value obtained by multiplying the polarization mode dispersion value that matches within the difference range by a correction coefficient of 0.82 as the polarization mode dispersion value of the optical fiber under test; Has been done.

Further, the polarization mode dispersion measuring apparatus using the four polarization incident type fixed analyzer method of the second invention is
The light emitted from one side of the optical fiber to be measured is transmitted through the optical fiber to be measured, and the first emitted light spectrum measured at the emission side and the light incident from the opposite side of the optical fiber to be measured are the measured light. An emission light spectrum storage unit for storing a second emission light spectrum transmitted through the fiber and measured on the emission side; a first polarization mode dispersion value calculated based on the first emission light spectrum; A polarization mode dispersion actual measurement calculation unit that calculates a second polarization mode dispersion value based on the emitted light spectrum; and first and second polarization mode dispersion actual values calculated by the polarization mode dispersion actual measurement calculation unit. It is determined whether or not they match within a predetermined error range, and whether or not the waveforms of the first and second emitted light spectra match within a predetermined allowable range. Polarization mode dispersion value is within the error range Match, and, when the first and second outgoing light spectrum waveform matches within an allowable range is judged that the measured optical fiber is not an intermediate mode coupling state,
In other cases, the reversibility determining unit determines that the optical fiber to be measured is in the intermediate mode coupling state; and the reversibility determining unit receives the determination result that the optical fiber to be measured is not in the intermediate mode coupling state. Fourier transform is performed on at least one of the first and second emission light spectrum waveforms, and when the Fourier transform waveform is a vertical linear pattern waveform peculiar to the weak mode, it is determined that the optical fiber to be measured is in the weak mode coupling state, A strong / weak mode coupling discriminating unit that judges that the optical fiber to be measured is in a strong mode coupling state when the converted waveform is a Gaussian approximate waveform; this strong / weak mode coupling discriminating unit judges that the optical fiber is in a weak mode coupling state. Occasionally, when the polarization mode dispersion value that matches within the error range is evaluated as the polarization mode dispersion value of the optical fiber under measurement, and it is determined that the strong mode coupling state And a polarization mode dispersion value definite evaluation unit for evaluating a value obtained by multiplying the polarization mode dispersion value that matches within the error range by a correction coefficient of 0.82 as the polarization mode dispersion value of the optical fiber under test. Is configured.

Further, the measurement method of polarization mode dispersion using the four polarization incident type fixed analyzer method of the third invention is as follows:
The light emitted from one side of the optical fiber to be measured is transmitted through the optical fiber to be measured, and the first emitted light spectrum measured at the emission side and the light incident from the opposite side of the optical fiber to be measured are the measured light. An emission light spectrum storage unit for storing a second emission light spectrum transmitted through the fiber and measured on the emission side; a first polarization mode dispersion value calculated based on the first emission light spectrum; A polarization mode dispersion measurement calculating unit that calculates a second polarization mode dispersion value based on the emitted light spectrum; and Fourier transform the waveform of the first emitted light spectrum to obtain a first Fourier transformed waveform, and A Fourier transform unit that Fourier transforms the waveform of the outgoing light spectrum to obtain a second Fourier transform waveform; and the first and second polarization mode dispersion values obtained by the polarization mode dispersion measurement calculation unit in advance. Determination is made within the error range and whether the first and second Fourier transform waveforms obtained by the Fourier transform unit match within a predetermined allowable range. , The first and second polarization mode dispersion values match within the error range, and the first and second Fourier transform waveforms match within the allowable range, the measured optical fiber is not in the intermediate mode coupling state. And a reversibility determining unit that determines that the optical fiber to be measured is in the intermediate mode coupling state in other cases; and the reversibility determining unit determines the determination result that the optical fiber to be measured is not in the intermediate mode coupling state. When the Fourier transform waveform that matches within the allowable range under the received state is a vertical linear pattern waveform specific to the weak mode, it is determined that the optical fiber under measurement is in the weak mode coupling state, and the Fourier transform waveform is Gaussian. Approximation A strong / weak mode coupling discriminating unit that determines that the optical fiber under measurement is in a strong mode coupling state when the optical fiber is in a form; and within the error range when the strong / weak mode coupling discriminating unit determines that the optical fiber is in a weak mode coupling state. The polarization mode dispersion value that agrees with is evaluated as the polarization mode dispersion value of the optical fiber to be measured, and when it is judged that the strong mode coupling state is found, the polarization mode dispersion value that agrees within the error range is multiplied by the correction coefficient 0.82. And a polarization mode dispersion value definite evaluation unit that evaluates the measured value as the polarization mode dispersion value of the optical fiber to be measured.

Further, the polarization mode dispersion value definite evaluation section has a Gaussian distribution standard deviation calculation means, and when the optical fiber to be measured is judged to be in the strong mode coupling state by the strong / weak mode coupling discrimination section, it is Gaussian. It is also considered that the Fourier transform waveform determined as an approximate waveform has a Gaussian distribution, and the standard deviation value of the Gaussian distribution is evaluated as the polarization mode dispersion value of the optical fiber under measurement. It is a characteristic configuration of the polarization mode dispersion measuring apparatus using the four polarization incident type fixed analyzer method of the second and third inventions.

In the first aspect of the present invention having the above-mentioned structure, the first outgoing light spectrum which is incident from one side of the optical fiber to be measured and is emitted from the opposite side, and the optical spectrum which is incident from the opposite side of the optical fiber to be measured and is incident. The values of the first and second polarization mode dispersions (PMD) are respectively obtained based on the second outgoing light spectrum that passes through the measurement optical fiber and exits, and the first and second PMD values are obtained. It is determined whether or not they match within a predetermined error range, and whether or not the waveforms of the first and second emitted light spectra match within a predetermined allowable range. When the first and second PMD values match within the error range and the first and second emitted light spectrum waveforms match within the allowable range, the measured optical fiber is not in the intermediate mode coupling state. Judged as something.

By comparing the first and second PMD values and the first and second emitted light spectrum waveforms, the optical fiber under test is not in the intermediate mode coupling state, that is, the strong mode coupling state or the weak mode coupling state. When it is confirmed that the mode coupling state is one of the mode coupling states, a determination is then made as to whether the mode is the strong mode coupling state or the weak mode coupling state. This judgment is made based on whether or not the emission light spectrum waveforms that match within a predetermined allowable range are sinusoidal. When the emission light spectrum waveforms are sinusoidal, the measured optical fiber is in the weak mode coupling state. If the output light spectrum waveform is not sinusoidal, it is determined that the optical fiber under measurement is in the strong mode coupling state.

In the first aspect of the present invention, as described above, it is judged whether the optical fiber to be measured is in the intermediate mode coupling state,
Except when in the intermediate mode coupling state, the strong / weak mode coupling is distinguished, so even if only one optical fiber is given, whether the measured optical fiber is in the intermediate mode coupling state or not It is possible to accurately make a distinction between the mode coupling state and the weak mode coupling state.

When it is determined that the measured optical fiber is in the weak mode coupling state, the PMD value that matches within the error range is evaluated as the PMD value of the measured optical fiber, and the measured optical fiber is in the strong mode. When it is determined that the PMs are in the combined state, the PMs that match within the error range
When the measured optical fiber is in the intermediate mode coupling state as in the past, by evaluating the D value multiplied by the correction coefficient 0.82 or the standard deviation value of the Gaussian distribution as the PMD value of the measured optical fiber. Unlike the case where the PMD value is calculated without considering the above, it becomes possible to accurately evaluate the PMD value of the optical fiber to be measured, and the above problem is solved.

In the second aspect of the present invention, similarly to the first aspect of the present invention, the values of the first and second PMDs are obtained based on the respective spectra of the first and second emitted light. Based on the first and second PMD values and the first and second emission light spectra, the first and second PMD values match within the error range by the same judgment as in the first invention. ,
Moreover, when the first and second emission light spectrum waveforms match within the allowable range, it is determined that the optical fiber under measurement is not in the intermediate mode coupling state.

Then, in the same manner as in the first invention, the first
And the second PMD value and the comparison of the first and second emitted light spectrum waveforms, the measured optical fiber is not in the intermediate mode coupling state, that is, either the strong mode coupling state or the weak mode coupling state. If it is confirmed, then a distinction is made between the strong mode coupling state and the weak mode coupling state. In making this determination, the Fourier transform waveform of at least one of the first and second emitted light spectrum waveforms is obtained. When this Fourier transform waveform is a vertical linear pattern waveform peculiar to the weak mode, the measured optical fiber is weak. It is determined that the optical fiber to be measured is in the mode coupling state, and when the Fourier transform waveform has a Gaussian approximate waveform, it is determined that the optical fiber under measurement is in the strong mode coupling state. Then, thereafter, the same operation as in the first aspect of the invention is performed to obtain the PMD value.

Therefore, also in the second aspect of the invention, similarly to the first aspect of the invention, it becomes possible to accurately distinguish and judge the mode coupling state of the optical fiber to be measured and accurately evaluate the PMD value. The above problems are solved.

Further, in the third invention, the first Fourier transform waveform obtained based on the first emitted light spectrum and the second Fourier transform waveform obtained based on the second emitted light spectrum. And the first PMD and the second PMD
It is determined whether or not the values match within a predetermined error range.

When the Fourier transform waveform that matches within the allowable range is a vertical linear pattern waveform unique to the weak mode, it is determined that the optical fiber to be measured is in the weak mode coupling state, and the matched within the allowable range. When the Fourier transform waveform is a Gaussian approximate waveform, it is determined that the optical fiber to be measured is in the strong mode coupling state, and thereafter, the same operation as that of the second invention is performed.

Therefore, also in the third aspect of the invention, similarly to the first and second aspects of the invention, the PMD value can be accurately evaluated by accurately determining the mode coupling state of the optical fiber to be measured. Therefore, the above problem is solved.

[0052]

Embodiments of the present invention will be described below with reference to the drawings. In the description of this embodiment, the same reference numerals are given to the same names as those of the apparatus used in the above description, and the duplicated description will be omitted. FIG. 1 shows a main part configuration of an embodiment of a polarization mode dispersion measuring apparatus using a four polarization incident type fixed analyzer method according to the present invention. The apparatus shown in FIG. It is connected to the optical spectrum analyzer 5 shown in FIG.

As shown in FIG. 1, the apparatus for measuring the polarization mode dispersion of this embodiment includes an outgoing light spectrum storage unit 13, a polarization mode dispersion measurement calculation unit 14, a reversibility determination unit 15, a strong / weak mode. It is configured to have a coupling discriminating unit 20, a polarization mode dispersion value definite evaluation unit 23, the reversibility determination unit 15, the spectral waveform determination unit 16, a polarization mode dispersion determination unit 17, a memory unit 18,
An intermediate mode combination determination unit 19 is provided.

As shown in FIG. 8 (b), the outgoing light spectrum storage unit 13 has a structure in which the light incident from one side 30 of the measured optical fiber is transmitted through the measured optical fiber 4 and the outgoing side (opposite side). The output light spectrum measured in 31) is stored as the first output light spectrum, and similarly, the optical fiber 4 to be measured is connected to the light source 1 or the like and the light incident from the opposite side 31 of the optical fiber 4 to be measured is input. Of the emitted light spectrum transmitted through the measured optical fiber 4 and emitted on the emitting side (one side 30)
It is stored as the emission light spectrum of. In addition,
The first outgoing light spectrum is the outgoing light spectrum in the direction 1 shown in Tables 9 to 11, and the second outgoing light spectrum is the outgoing light spectrum in the direction 2 shown in Tables 9 to 11.

The polarization mode dispersion measurement calculation unit 14 calculates the first polarization mode dispersion value (first PMD value) based on the first emission light spectrum stored in the emission light spectrum storage unit 13.
Value) and calculates the second value based on the second emission spectrum.
The polarization mode dispersion value (second PMD value) of is calculated. The polarization mode dispersion actual measurement calculating unit 14 adds the calculated first and second PMD values to the polarization mode dispersion determining unit 17 of the reversibility determining unit 15.

The polarization mode dispersion determination unit 17 determines whether or not the first and second polarization mode dispersion values (PMD values) obtained by the polarization mode dispersion measurement calculation unit 14 match within a predetermined error range. Is to be determined. In making this determination,
The memory unit 18 is provided with a predetermined error range of the difference between the first and second polarization mode dispersion values, and the polarization mode dispersion determination unit 17 determines this error range and the first and second polarization mode dispersion values. PMD
The difference between the values is compared, and the comparison result is added to the intermediate mode combination determination unit 19.

The spectrum waveform determining section 16 determines whether or not the waveforms of the first and second emitted light spectra match within a predetermined allowable range. In making this determination,
An allowable range of the difference between the waveforms of the first and second outgoing light spectra is given in advance to the memory unit 18, and the spectral waveform determination unit 16 stores this allowable range and the outgoing light spectrum storage unit 13. The difference between the waveforms of the first and second emitted light spectra that have been recorded is compared, and the comparison result is added to the intermediate mode coupling determination unit 19.

The intermediate mode coupling judgment unit 19 compares the comparison result of the first and second emitted light spectrum waveforms added from the spectrum waveform judgment unit 16 with the first and second additions from the polarization mode dispersion judgment unit 17. The first and second PMD values match within the error range and the first PMD value is
And the second output light spectrum waveform match within the allowable range, the output light spectrum of the measured optical fiber 4 is reversible, and it is determined that the measured optical fiber 4 is not in the intermediate mode coupling state. In other cases, the output light spectrum of the measured optical fiber 4 does not have reversibility, and the measured optical fiber 4 is determined to be in the intermediate mode coupling state. The intermediate mode coupling determination unit 19 adds this reversibility determination result to the strong / weak mode coupling determination unit 20.

The strong / weak mode coupling discriminating unit 20 receives the reversibility judgment result added from the intermediate mode coupling judging unit 19 of the reversibility judging unit 15, and the outgoing light spectrum of the measured optical fiber 4 has reversibility. However, when the judgment result that the measured optical fiber 4 is not in the intermediate mode coupling state is added, the at least one of the first and second emission light spectrum waveforms is read from the emission light spectrum storage unit 13, and When the emitted light spectrum is sinusoidal as shown in, for example, FIG. 7A, it is determined that the measured optical fiber 4 is in the weak mode coupling state, and the emitted light spectrum waveform is, for example, as shown in FIG. When it is not sinusoidal as shown in b), it is determined that the optical fiber 4 to be measured is in the strong mode coupling state.
The result of this determination is added to the polarization mode dispersion value confirmation evaluator 23.

The polarization mode dispersion value deciding and evaluating unit 23 receives the discrimination result by the strong / weak mode coupling discriminating unit 20, and when it is determined that the optical fiber 4 to be measured is in the weak mode coupling state, within the error range. Is evaluated as the polarization mode dispersion value of the optical fiber 4 to be measured, while the optical fiber 4 to be measured has a strong mode coupling. When it is determined that the state is the same, the polarization mode dispersion value of the optical fiber 4 to be measured is evaluated by multiplying the polarization mode dispersion value that matches within the error range by the correction coefficient 0.82.

The example of the present embodiment is configured as described above. Next, the measurement method of polarization mode dispersion using the four polarization incident type fixed analyzer method performed by using this measurement apparatus will be described with reference to FIG. It will be described based on the flowchart shown in FIG. First, as shown in FIG. 8 (b), the measured optical fiber 4 is used for the measurement system of the four polarization incident type fixed analyzer method.
Connect. As shown in the figure, one side 30 of the optical fiber 4 to be measured is connected to the light source 1 side and the other side 31 is connected to the optical spectrum analyzer 5 side so that the incident light from the light source 1 is measured light. The optical fiber 4 is made incident from one side 30 of the fiber 4, transmitted through the optical fiber 4 to be measured, emitted from the opposite side 31, and received by the optical spectrum analyzer 5. This connection state is called direction 1.

Then, in step 102, the spectrum of the outgoing light emitted from the opposite side 31 of the optical fiber 4 to be measured is measured by the optical spectrum analyzer 5 to obtain the first outgoing light spectrum (spectrum 1). The first emitted light spectrum is stored in the emitted light spectrum storage unit 13.

Next, in step 103, the incident direction of the light to the optical fiber 4 to be measured is reversed with respect to the direction 1, and the optical fiber 4 to be measured is connected to the measurement system of the four polarization incident type fixed analyzer method. . That is, the opposite side 31 of the optical fiber 4 to be measured is connected to the light source 1 side of FIG. 8B, and the one side 30 of the optical fiber 4 to be measured is connected to the optical spectrum analyzer 5 side. The light incident from the opposite side 31 of the optical fiber 4 passes through the optical fiber 4 to be measured, and one side thereof
The light is emitted from 30 and received by the optical spectrum analyzer 5. This is called direction 2.

Then, the measurement in this direction 2 is performed, that is, the light enters from the opposite side 31 of the measured optical fiber 4 and passes through the measured optical fiber 4, and the one side 30 of the measured optical fiber 4 enters.
The emitted light emitted from is measured by the optical spectrum analyzer 5 to obtain the second emitted light spectrum (spectrum 2). This second outgoing light spectrum is also stored in the outgoing light spectrum storage unit 13 in the same manner as the first outgoing light spectrum.

Next, at step 105, the polarization mode dispersion actual measurement calculating section 14 obtains the first polarization mode dispersion value (first PMD value) based on the first outgoing light spectrum, and the second polarization mode dispersion value is calculated. The second polarization mode dispersion value (second PMD value) is obtained based on the emitted light spectrum, and these values are added to the polarization mode dispersion determination unit 17 of the reversibility determination unit 15, and the first and second The PMD value of is evaluated. On the other hand, the reversibility judgment unit
The spectrum waveform determination unit 16 of 15 reads out the first and second emission light spectra stored in the emission light spectrum storage unit 13 and evaluates these spectrum waveforms.

Then, in step 106, it is determined whether or not the spectral waveform and the PMD value match regardless of the direction. The determination of the spectrum waveform is performed by the spectrum waveform determination unit 16, and the spectrum waveform determination unit 16 determines that the waveforms of the first and second emitted light spectra are within the allowable range given in advance in the memory unit 18. It is determined whether or not they match, and this determination result is added to the intermediate mode combination determination unit 19. The polarization mode dispersion determination unit 17 determines whether the PMD values match, and the polarization mode component determination unit 17 determines that the first and second PMD values are stored in the memory. It is determined whether or not they match within an error range given in advance to the unit 18, and this determination result is added to the intermediate mode combination determination unit 19.

Then, when the first and second PMD values match within the error range and the first and second emitted light spectrum waveforms match within the allowable range, PMD and Since the spectral waveform is determined to be reversible, the intermediate mode coupling determination unit 19 determines that the optical fiber 4 under measurement is in the strong mode coupling state or the weak mode coupling state, and the process proceeds to step 108. .

On the other hand, in step 106, the first and second PM
When the condition that the D values match within the error range and the first and second emitted light spectrum waveforms match within the allowable range is not satisfied, that is, the first and second PMD values fall within the error range. , And the first and second emitted light spectrum waveforms do not match within the allowable range, or the first and second
Even if the PMD values of the two match within the error range, the first and second emitted light spectrum waveforms do not match within the allowable range, or the first and second emitted light spectrum waveforms match within the allowable range. Also, when the first and second PMD values do not match within the error range, it is determined that the PMD and the spectrum waveform are not reversible. Then, when the PMD and the spectral waveform are not reversible in this way, step 10
At 7, the intermediate mode coupling determination section 19 determines that the optical fiber 4 to be measured is in the intermediate mode coupling state.

In step 108, the strong / weak mode coupling discriminating unit 20 determines whether or not the spectrum waveforms matching within the allowable range are sinusoidal. Then, when the waveform of the emission light spectrum (first emission light spectrum or second emission light spectrum or both) that matches within the allowable range is sinusoidal, the process proceeds to step 109, and the measured optical fiber 4 is Determined to be in weak mode coupling,
Go to step 110.

In step 110, the polarization mode dispersion value definite evaluation unit 23 measures the PMD values that match within the error range (PMD values obtained by the polarization mode dispersion measurement calculation unit 14).
Is evaluated as the PMD value of the measured optical fiber 4.
The PMD measurement value may be, for example, the first PMD value, the second PMD value, or the average value of the first and second PMD values. .

On the other hand, when the strong / weak mode coupling discriminating unit 20 determines in step 108 that the emitted light spectral waveforms that match within the allowable range are not sinusoidal, in step 111, the measured optical fiber 4 Is determined to be in strong mode coupling. Then, this determination result is added to the polarization mode dispersion value confirmation and evaluation unit 23, and in step 112,
By the polarization mode dispersion value confirmation and evaluation unit 23, the value of PMD is
A value obtained by multiplying the matching PMD value (measured value) within the error range by a correction coefficient of 0.82 is evaluated as the PMD value of the optical fiber 4 to be measured. In addition, this PMD measurement value
As with 110, it can be the first PMD value,
It can be the second PMD value or the first and second P
It may be an average value of MD values.

Next, a specific example in which the polarization mode dispersion is actually measured using the polarization mode dispersion measuring method using the four polarization incident type fixed analyzer method of the present embodiment will be described. In this specific example, the device configuration shown in FIG. 8B is used as the measurement system, and the optical fiber C to be measured is the optical fiber C shown in Table 8. The first outgoing light spectrum Cnt. In the direction 1 obtained by the operations of steps 101 to 102 in FIG. 1, Cnt. 2, Cnt. 3,
Cnt. 4 are (a), (b), (c), and FIG. 11 respectively.
(D), and steps 103 to 103 in FIG.
The second output light spectrum Cnt. 1, Cnt. 2, Cnt. 3, Cnt.
4 are (a), (b), (c), and (d) of FIG. 9, respectively.
It became as shown in.

Based on these spectra, in step 105 of FIG. 2, the first and second PMD values were obtained by the polarization mode dispersion actual measurement calculating section 14. The first PMD value (PMD1) is obtained from the spectrum shown in FIG. 11, and the second PMD value (PMD2) is obtained from the spectrum shown in FIG. As a result, PMD1 = 0.327 ps, PMD2
= 0.355 ps. And the relative measurement error between both averages was 6.57%.

In this specific example, as the error range between PMD1 and PMD2, the memory unit 18 is provided with a measurement accuracy of 5% by the polarization analyzer HP8509B manufactured by Applied Photonics Laboratory Inc. If the error range of 5% is compared with the relative measurement error of 6.57% between PMD1 and PMD2 in step 106 of FIG.
1 and PMD2 are larger than the range of measurement accuracy of the device,
It is judged that they do not match within the given error range.
Therefore, it is found that this PMD measurement is not reversible, and in step 107, the intermediate mode coupling determination unit 19 determines that the measured optical fiber 4 (optical fiber C) is in the intermediate mode coupling state. And in this case,
Since the correlation between the value of PMD calculated from the spectrum and the value of PMD based on the theory of the main polarization state cannot be obtained, the value of PMD calculated from the measured spectrum has no physical meaning, It was rejected.

As a specific example of this embodiment, Table 8
When an experiment similar to the above-mentioned specific example was conducted by using the optical fiber A shown in FIG. 2 as the optical fiber 4 to be measured, as shown in Table 9, the first output light spectrum waveform and the second output light spectrum waveform were Almost the same waveform, PMD1 = PMD2
= 1.24ps, and the spectrum waveform and P
Since it was confirmed that the MD values were the same, the process proceeded from step 106 to step 108 in FIG. 2 to evaluate the emitted light spectrum waveform. As a result, since it was determined that this emitted light spectrum waveform is sinusoidal, it is determined in step 109 of FIG. 2 that the measured optical fiber 4 (optical fiber A) is in the weak mode coupling state, and step At 110 PM
The value of D was evaluated as 1.24 ps.

According to this embodiment, the above-mentioned operation results in
The first and second PMs obtained by measuring the first and second emission spectrums of the optical fiber 4 to be measured in the directions 1 and 2 respectively, and calculating from the first and second emission spectrums.
By determining whether the values of D match within the error range and whether the first and second spectral waveforms match within the allowable range, the reversibility of the emitted light spectrum is determined. , Even if only one optical fiber 4 to be measured is provided, it can be easily and accurately determined whether the optical fiber 4 to be measured is in a strong mode or weak mode coupling state or in an intermediate mode coupling state. You can judge.

Therefore, the measured optical fiber 4 is in the intermediate mode coupling state, and P calculated from the outgoing light spectrum is obtained.
Although the correlation between the MD value and the PMD value based on the principle of the main polarization state cannot be obtained, the erroneous PMD evaluation is performed by performing the PMD evaluation based on the theory of the main polarization state.
It is possible to solve the conventional problem of making an evaluation. Then, after accurately determining that the measured optical fiber 4 is not in the intermediate mode coupled state but in the strong mode coupled state or the weak mode coupled state, it is determined from the emitted light spectrum waveform that the measured optical fiber 4 is in the strong mode coupled state. The PMD value can be accurately measured and evaluated by determining the weak mode coupling state and evaluating the PMD value based on the determination result.

FIG. 3 shows a second embodiment of the polarization mode dispersion measuring apparatus using the four polarization incident type fixed analyzer method according to the present invention. The example of the present embodiment is configured almost similarly to the example of the first embodiment described above, and
The redundant description with the embodiment example will be omitted. The feature of the present embodiment different from the first embodiment is that the strong / weak mode coupling discriminating unit 20 is provided with a Fourier transform unit 21, and the Fourier transform waveform obtained by the Fourier transform unit 21 is used. This is to distinguish between strong mode coupling and weak mode coupling.

Specifically, the strong / weak mode coupling discrimination unit 20
Is determined by the reversibility determination unit 15 that the output light spectrum of the measured optical fiber 4 is reversible and the measured optical fiber 4 is not in the intermediate mode coupling state, and the determination result is strong. When at least one of the first and second emission light spectrum waveforms is read from the emission light spectrum storage unit 13 when added to the weak mode coupling determination unit 20, the Fourier transform unit 21 Fourier transforms the emission light spectrum. Convert. As shown in (a ′) of FIG. 7, this Fourier transform waveform is a vertical linear pattern waveform peculiar to the weak mode in which a region where the time t spreads near 0 and a loss peak is formed at Δτ. When it is, it is judged that the optical fiber 4 to be measured is in the weak mode coupling state, and when the Fourier transform waveform is a Gaussian approximate waveform as shown in FIG. 7B, the optical fiber 4 to be measured is Judge as being in the strong mode coupling state.

Then, this judgment result is added to the polarization mode dispersion value definite evaluation section 23, and the polarization mode dispersion value definite evaluation section 23 makes the polarization mode dispersion values corresponding to the strong and weak mode coupling states. Is evaluated in the same manner as in the first embodiment. In the vertical linear pattern waveform peculiar to the weak mode shown in (a ′) of FIG. 7, Δτ corresponds to the PMD value. Therefore, the polarization mode dispersion value deciding and evaluating unit 23 uses the weak mode coupling. Instead of evaluating the PMD value obtained by the polarization mode dispersion measurement calculation unit 14 as the polarization mode dispersion value of the measured optical fiber 4 when obtaining the polarization mode dispersion value of the measured optical fiber 4 that is determined to be in the state In addition, the value of Δτ obtained from the Fourier transform waveform can be evaluated as the PMD value.

The measuring apparatus of the present embodiment is configured as described above. Next, using this apparatus, the polarization mode dispersion of the polarization mode dispersion using the four polarization incident type fixed analyzer method of the present embodiment is used. The measuring method will be described. The measurement of the polarization mode dispersion of this embodiment is performed according to the flowchart shown in FIG. 4, and in FIG. 4, the same operation as the step number of the operation of the first embodiment shown in FIG. 2 is performed. The same step number is attached to the step number for performing.

In FIG. 4, from step 101 to step
The operation up to 107 is the same as that of the first embodiment, so the duplicated description will be omitted. In the present embodiment, when it is determined in step 106 that the two spectral waveforms and the PMD value match regardless of the direction and the optical fiber 4 to be measured is in the strong mode coupling state or the weak mode coupling state, Proceed to step 108a. And step 108a
Then, the Fourier transform unit 21 of the strong / weak mode coupling discrimination 20 obtains the Fourier transform waveform of the outgoing light spectrum waveform on at least one of the first and second sides, and step 108
Proceed to b.

In step 108b, the strong / weak mode combination discriminating unit 20 judges whether the Fourier transform waveform is a vertical linear pattern waveform peculiar to the weak mode or a Gaussian approximate waveform. When the Fourier transform waveform is a vertical linear pattern waveform peculiar to the weak mode as shown in FIG. 7A, for example, the process proceeds to step 109, and the operation from step 109 to step 110 It is performed in the same manner as the embodiment. On the other hand, when it is determined in step 108b that the Fourier transform waveform is not the vertical linear pattern waveform peculiar to the weak mode, that is, the Fourier transform waveform has a Gaussian approximate waveform as shown in FIG. 7B '. If so, the process proceeds to step 111, and the operations from step 111 to step 112 are performed in the same manner as in the first embodiment.

According to the present embodiment, the above-mentioned operation results in
Similar to the first embodiment, the measured optical fiber 4 is set to the strong mode or weak mode coupling state based on the first and second outgoing light spectra in the direction 1 and the direction 2 of the measured optical fiber 4. Since it is possible to easily and accurately determine whether the optical fiber 4 is in the intermediate mode coupling state or the intermediate mode coupling state, the measured optical fiber 4 is in the intermediate mode coupling state, as in the first embodiment. Nevertheless, the PMD evaluation based on the theory of the main polarization state was performed, and the false P
It is possible to solve the conventional problem of performing MD evaluation.

Also in this embodiment, after accurately determining that the optical fiber 4 to be measured is not in the intermediate mode coupling state but in the strong mode coupling state or the weak mode coupling state, the Fourier transform waveform of the outgoing light spectrum is obtained. Therefore, the PMD value can be accurately measured and evaluated by discriminating between the strong mode coupling state and the weak mode coupling state of the optical fiber 4 to be measured and evaluating the PMD based on the discrimination result.

FIG. 5 shows a third embodiment of the polarization mode dispersion measuring apparatus using the four polarization incident type fixed analyzer method according to the present invention. This example of the embodiment is constructed almost in the same way as the example of the second embodiment, and
The redundant description with the embodiment example will be omitted. The characteristic of this embodiment is different from the second embodiment is that the Fourier transform unit 21 is provided independently of the strong / weak mode coupling discrimination unit 20, and the Fourier transform waveform obtained by this Fourier transform unit 21. That is, the reversibility determination unit 15 determines the reversibility of the measured spectrum based on the above.

Specifically, the Fourier transform unit 21 reads the first and second outgoing light spectra stored in the outgoing light spectrum storage unit 13 and Fourier transforms the waveform of the first outgoing light spectrum. Find the first Fourier transform waveform,
The waveform of the second outgoing light spectrum is Fourier transformed to the second
The Fourier transform waveform of is obtained. And this first and second
The Fourier transform waveform of is added to the spectrum waveform determination unit 16 of the reversibility determination unit 15 and the strong / weak mode coupling determination unit 20.

Then, the spectrum waveform judging section 16 determines whether or not the first and second Fourier transform waveforms added from the Fourier transform section 21 match within a predetermined allowable range in the memory section 18. A determination is made and the determination result is added to the intermediate mode combination determination unit 19.

The intermediate mode combination determining section 19 determines that the first and second Fourier transform waveforms match within the allowable range and that the first and second Fourier transform waveforms are obtained in the same manner as in the first and second embodiments.
And the second PMD value match within the error range, it is determined that the optical fiber 4 to be measured is not in the intermediate mode coupled state, and in other cases, the optical fiber 4 to be measured is determined to be in the intermediate mode coupled state. Then, this determination result is added to the strong / weak mode coupling determination unit 20.

The strong / weak mode coupling discriminating unit 20 may be in a state in which the intermediate mode coupling discriminating unit 19 of the reversibility discriminating unit 15 receives the determination result that the optical fiber 4 to be measured is not in the intermediate mode coupling state. With, it is determined whether the Fourier transform waveform, which is added from the Fourier transform unit 21 and matches within the allowable range, is a vertical linear pattern waveform peculiar to the weak mode or a Gaussian approximate waveform, and the Fourier transform is performed. When the waveform is a vertical linear pattern waveform peculiar to the weak mode, it is judged that the optical fiber 4 to be measured is in the weak mode coupling state,
When the Fourier transform waveform is Gaussian approximation,
The measured optical fiber 4 is determined to be in the strong mode coupling state.

The measuring apparatus of the present embodiment is constructed as described above. Next, using this apparatus, the polarization mode dispersion of the polarization mode dispersion using the four polarization incident type fixed analyzer method of the present embodiment is used. The measuring method will be described. The measurement of the polarization mode dispersion of this embodiment is performed according to the flowchart shown in FIG. 6, and in FIG. 6, the step numbers of the operations of the first and second embodiments shown in FIGS. The same step number is attached to the step number for performing the same operation as.

In FIG. 6, step 101 to step
Operations up to 102 are performed in the same manner as in the first and second embodiments, and then, in step S1, the Fourier transform unit 21 causes the first outgoing light spectrum (spectrum) stored in the outgoing light spectrum storage unit 13 to be stored. The first Fourier transform waveform is obtained from 1). Further, as in the first and second embodiments, the polarization mode dispersion measurement calculation unit 14 calculates the first PMD value from the first emission light spectrum stored in the emission light spectrum storage unit 13. Ask.

Next, the operations from step 103 to step 104 are performed in the same manner as in the first and second embodiments described above, and thereafter, in step S2, the Fourier transform unit 21 stores them in the outgoing light spectrum storage unit 13. A second Fourier transform waveform is obtained from the generated second outgoing light spectrum (spectrum 2). Also, by the polarization mode dispersion measurement calculation unit 14,
The second PMD value is obtained from the second emitted light spectrum, and the process proceeds to step S3.

In step S3, the reversibility determining unit 15 determines whether the Fourier transform waveform and the PMD value match regardless of the direction. Specifically, this judgment operation is
The spectrum waveform determination unit 16 determines whether or not the first Fourier transform waveform and the second Fourier transform waveform added from the Fourier transform unit 21 match within an allowable range given in advance to the memory unit 18. Whether the first and second PMD values calculated by the polarization mode dispersion measurement calculating unit 14 by the polarization mode dispersion determining unit 17 match within the error range given to the memory unit 18. It is performed by determining whether or not.

These determination results are the intermediate mode combination determination unit.
In addition, if one or both of the Fourier transform waveform and the PMD value do not match, the intermediate mode coupling determination unit 19 causes the same as in the first embodiment.
It is determined that the measured spectrum of the measured optical fiber 4 is not reversible, and in step 107, the measured optical fiber 4 is determined to be in the intermediate mode coupling state. On the other hand, in step S3, when it is determined that the first and second PMD values match within the error range and the first and second Fourier transform waveforms match within the allowable range, the intermediate mode coupling determination is performed. The section 19 judges that the measured spectrum of the optical fiber 4 to be measured is reversible, and the optical fiber 4 to be measured is not in the intermediate mode coupling state, and the process proceeds to step 108b in FIG.

Then, the operations from step 108b to step 112 in FIG. 4 are performed in the same manner as in the second embodiment.

According to the present embodiment, the above operation causes
First and second PMD values and first and second Fourier transform waveforms are obtained from the first and second emitted light spectra, respectively, and the first and second PMD values are given in advance. The optical fiber 4 to be measured is in a strong mode coupling state or a weak mode coupling state by judging whether it is within the error range and judging whether the first and second Fourier transform waveforms are within a predetermined allowable range. It is possible to easily and accurately determine whether it is in a state or in an intermediate mode coupling state, and then easily and accurately distinguish between a strong mode coupling state and a weak mode coupling state. Therefore, the same effects as those of the first and second embodiments can be obtained.

The present invention is not limited to the above-mentioned embodiments, but can take various modes. For example,
In the second and third embodiments, the Fourier transform waveform of the outgoing light spectrum has a Gaussian approximate waveform shape, and the strong / weak mode coupling determining unit 20 determines that the optical fiber 4 to be measured is in the strong mode coupling state. In this case, the polarization mode dispersion value definite evaluation unit 23 evaluates the value obtained by multiplying the measured value of PMD by the correction coefficient 0.82 as the polarization mode dispersion value of the measured optical fiber 4. 4 is in a strong mode coupling state, it is considered that the Fourier transform waveform of the measurement spectrum (first and second emitted light spectra) has a Gaussian distribution, and, for example, FIGS. As shown by the broken line, the standard deviation calculating means 28 for the Gaussian distribution is provided to obtain the standard deviation of the Gaussian distribution, and the standard deviation value of the Gaussian distribution is evaluated as the polarization mode dispersion value of the optical fiber 4 to be measured. You may make it.

When the optical fiber 4 to be measured is subjected to random mode coupling (strong mode coupling), the Fourier transform waveform obtained by Fourier transforming the measured spectrum waveform has a property of approaching a Gaussian normal distribution. Is apparent from the literature [15], the measured optical fiber 4
When is determined to be the strong mode coupling state, the standard deviation value of the Gaussian distribution can be evaluated as the polarization mode dispersion value of the optical fiber 4 to be measured, as described above.

In the above embodiment, the reversibility judgment unit
Reference numeral 15 is a spectrum waveform determination unit 16, a polarization mode dispersion determination unit
Although the configuration including the memory unit 17, the memory unit 18, and the intermediate mode combination determination unit 19 is adopted, the configuration of the reversibility determination unit 15 is not particularly limited, and for example, the memory unit 18 may be a first memory unit and a second memory unit. The error range given to the memory section 18 may be stored in the first memory section, and the allowable range given to the memory section 18 may be stored in the second memory section.

As described above, the reversibility determining section 15 determines whether or not the first and second PMD values match within a predetermined error range, and determines the waveforms of the first and second emitted light spectra. It is determined whether or not the first and second Fourier transform waveforms match within a predetermined allowable range, and based on this determination,
Similar to the above-described embodiment, the first and second PMD values match within the error range, and the first and second emitted light spectrum waveforms or the first and second Fourier transform waveforms are within the allowable range. When the values coincide with each other, it is determined that the measured optical fiber 4 is not in the intermediate mode coupled state, and in other cases, the measured optical fiber 4 is determined to be in the intermediate mode coupled state.

[0102]

According to the first and second aspects of the present invention, the first outgoing light spectrum which is incident from one side of the optical fiber to be measured and is emitted from the other side thereof, and from the opposite side of the optical fiber to be measured. The second emitted light spectrum that is incident and emitted from the one side is measured, and the first and second emitted light spectrum waveforms match within a predetermined allowable range, and the first and second emitted light spectra are When the first and second polarization mode dispersion values (PMD values) respectively obtained from the light emission spectra match within a predetermined error range, it is determined that the measurement spectrum is reversible and this condition is not satisfied. Since it is sometimes determined that there is no reversibility, the reversibility and the irreversibility of the measurement spectrum can be easily discriminated and determined. Then, when the measurement spectrum is reversible, it is determined that the measured optical fiber is in the strong mode coupling state or the weak mode coupling state, while when the measurement spectrum is not reversible, the measured optical fiber is In order to judge that the optical fiber is in the intermediate mode coupling state, even if only one optical fiber under measurement is provided, whether the optical fiber under measurement is in the strong / weak mode coupling state or in the intermediate mode coupling state. It is possible to easily and accurately discriminate whether or not there is.

Therefore, the measured optical fiber is in the intermediate mode coupling state, and the polarization mode dispersion value calculated from the measurement spectrum cannot be correlated with the polarization mode dispersion value based on the theory of the main polarization state. Nevertheless, by obtaining the polarization mode dispersion value based on the theory of the main polarization state, it is possible to solve the conventional problem that the polarization mode dispersion value is erroneously evaluated.

After confirming that the measured optical fiber is not in the intermediate mode coupling state but in the strong mode coupling state or the weak mode coupling state based on the reversibility of the measurement spectrum, the first In the present invention, when the measured emitted light spectrum waveform is sinusoidal, weak mode coupling is used, and when the measured emitted light spectrum waveform is not sinusoidal, strong mode coupling is performed to distinguish between strong mode coupling and weak mode coupling. According to the second aspect of the invention, when the Fourier transform waveform of the measured outgoing light spectrum is a vertical linear pattern waveform peculiar to the weak mode, weak mode coupling is performed, and when the Fourier transform waveform is a Gaussian approximate waveform, strong mode coupling is performed to make the distinction determination. Thus, in both the first and second inventions, it is possible to accurately distinguish between strong mode coupling and weak mode coupling. . Then, based on the theory of the main polarization state, by evaluating the polarization mode dispersion value of the measured optical fiber from the polarization mode dispersion value obtained from the measurement spectrum, the measured optical fiber in the weak mode coupling state It is possible to accurately evaluate the PMD value and the PMD value of the measured optical fiber in the strong mode coupling state.

As described above, according to the first and second aspects of the present invention, the optical fiber to be measured has strong mode coupling, weak mode coupling,
Even if it is in any coupling state of intermediate mode coupling,
The mode coupling states can be accurately distinguished and determined, and the polarization mode dispersion can be accurately measured and evaluated in correspondence with each mode coupling state.

In the third invention, the first
And the first and second Fourier transform waveforms obtained from the second emitted light spectrum match within a predetermined allowable range, and the first and second Fourier transform waveforms obtained from the first and second emitted light spectra are obtained. When the polarization mode dispersion values match within a predetermined error range, it is determined that the measurement spectrum is reversible, otherwise it is determined that the measurement spectrum is not reversible. According to the presence or absence of reversibility, the mode coupling state of the optical fiber to be measured is discriminated whether it is the intermediate mode coupling state or the strong or weak mode coupling state, as in the first and second inventions. Therefore, it is possible to accurately judge whether or not the mode coupling state is the same as in the first and second inventions. Then, after that, by performing the discrimination between the strong mode coupling state and the weak mode coupling state in the same manner as in the second invention, the discrimination between the strong mode and the weak mode can be easily and accurately performed. The same effects as those of the first and second inventions can be obtained.

Further, when it is determined that the optical fiber to be measured is in the strong mode coupling state, a value obtained by multiplying the polarization mode dispersion value that matches within the error range by the correction coefficient 0.82 is used. In addition to evaluating the polarization mode dispersion value, when the measured optical fiber is determined to be in the strong mode coupling state, the standard deviation value of the Gaussian distribution of its Fourier transform waveform is used to determine the polarization of the measured optical fiber. By adding the method of evaluating the mode dispersion value, the polarization mode dispersion value can be evaluated very accurately when the measured optical fiber is in the strong mode coupling state.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of essential parts showing a first embodiment of a polarization mode dispersion value measuring apparatus using a four polarization incident type fixed analyzer method according to the present invention by a block diagram.

FIG. 2 is a flow chart showing a method of measuring polarization mode dispersion using the four polarization incident type fixed analyzer method performed by using the apparatus of the above embodiment.

FIG. 3 is a main part configuration diagram showing a second embodiment of a polarization mode dispersion measuring apparatus using a four polarization incident type fixed analyzer method according to the present invention by a block diagram.

FIG. 4 is a flow chart showing a method of measuring polarization mode dispersion using a four polarization incident type fixed analyzer method performed by using the apparatus of the second embodiment.

FIG. 5 is a main part configuration diagram showing, by a block diagram, a third embodiment example of the polarization mode dispersion measuring apparatus using the four polarization incident type fixed analyzer method according to the present invention.

FIG. 6 is a flowchart showing a method of measuring polarization mode dispersion using the four polarization incident type fixed analyzer method performed by using the apparatus of the third embodiment.

FIG. 7 is a graph showing an output light spectrum waveform and a Fourier transform waveform thereof using the four polarization incident type fixed analyzer method, which are different depending on whether the optical fiber under test is in a weak mode coupling state or a strong mode coupling state. Is.

FIG. 8 shows a configuration (b) of a polarization mode dispersion measuring apparatus using the four polarization incident type fixed analyzer method, together with polarization mode dispersion measuring apparatuses (a) and (c) using another fixed analyzer method. FIG.

FIG. 9 is a diagram showing the measured optical fiber 4 (optical fiber B in Table 8) from one side 30 to the other side using the device shown in FIG. 8 (b).
It is a graph which shows the 1st outgoing-light spectrum which measured the transmitted light to 31 by the four polarization incident type fixed analyzer method.

[FIG. 10] Using the device of FIG. 8B, the transmitted light from the opposite side 31 to the one side 30 of the measured optical fiber 4 (optical fiber B in Table 8) is measured by the four polarization incident type fixed analyzer method. It is a graph which shows the 2nd emitted light spectrum measured by.

FIG. 11 is a diagram illustrating an optical fiber 4 to be measured (optical fiber C in Table 8) from one side 30 to the other side using the device shown in FIG. 8 (b).
It is a graph which shows the 1st outgoing-light spectrum which measured the transmitted light to 31 by the four polarization incident type fixed analyzer method.

[FIG. 12] Using the device of FIG. 8B, the transmitted light from the opposite side 31 to the one side 30 of the optical fiber 4 to be measured (optical fiber C of Table 8) is measured by the four polarization incident fixed analyzer method. It is a graph which shows the 2nd emitted light spectrum measured by.

[Explanation of symbols]

 4 Optical fiber under test 5 Optical spectrum analyzer 13 Emitted light spectrum storage unit 14 Polarization mode dispersion measurement calculation unit 15 Reversibility determination unit 18 Memory unit 19 Intermediate mode coupling determination unit 20 Strong / weak mode coupling determination unit 21 Fourier transform unit 23 Polarization mode dispersion value determination evaluation unit 28 Standard deviation calculation means

────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] February 9, 1996

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0004

[Correction method] Change

[Correction contents]

Among the methods for measuring PMD, the fixed analyzer method (1) can easily set up a measurement system in a laboratory. (2) Since the measurement time is short, it is unlikely to be affected by the change over time of mode coupling. It is considered to be superior to other methods in terms of the above (Reference [1]).

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0016

[Correction method] Change

[Correction contents]

By the way, the fixed analyzer method is "main polarization state" concept (Reference [2]) Ru assay der using no <br/> for the mode coupling of the measured optical fiber is sufficiently random If it can be regarded, the measured value cannot be considered as the PMD value as it is. Then, as shown in Tables 5 and 6, the value corrected by multiplying the measured value by the correction coefficient k = 0.82 is P
It is known to support MD. (Reference [3]).

[Procedure 3]

[Document name to be amended] Statement

[Correction target item name] 0017

[Correction method] Change

[Correction contents]

Aso et al. Measured PMD while cutting a dispersion-shifted optical fiber having a total length of 90 km, and investigated the distance dependence of the correction coefficient (reference [4]). According to their experimental report, the correction factor is at least 50 km if the optical fiber length is not more than 50 km.
It has been shown to be unstable above and below 0.82. The result is that the fiber length is 50
If it is less than km, it can be interpreted that the mode coupling is not sufficiently random. Naturally, the length of 50 km is not always a general property, but it is generally unknown how long the optical fiber can be considered that the mode coupling is sufficiently random depending on the optical fiber to be measured.

[Procedure amendment 4]

[Document name to be amended] Statement

[Correction target item name] 0020

[Correction method] Change

[Correction contents]

[0020]

However, of these sufficient conditions shown in Table 7, only the condition 1 can be determined only by the fixed analyzer method. However, even for condition 1, if one optical fiber is given and the measurement is performed,
In that case , it is not obvious whether the measured PMD is proportional to the square root of the distance. Moreover, as is clear from Table 6, when the optical spectrum is in the intermediate mode coupling state, it is unknown whether or not the measurement spectrum is sinusoidal. Therefore, when the measurement spectrum is sinusoidal, all are in the weak mode coupling state. PMD is used as a measured value, and when the measured spectrum is not sinusoidal, it is judged that all are in strong mode coupling and PMD
According to the method so far, which is measured value x 0.82, PMD
The exact value of could not be determined.

[Procedure Amendment 5]

[Document name to be amended] Statement

[Correction target item name] 0030

[Correction method] Change

[Correction contents]

(1) The PMD value and the measured waveform are reversible when there is no mode coupling or can be ignored. At this time, the measured PMD value is polarimetric
It agrees with the PMD measurement value of the same sample by the method.
(2) If there is mode coupling but it is not random, P
The MD value and the measured waveform are not reversible. (3) When there is mode coupling but it is not random, the more randomness of mode coupling becomes, the more reversible the PMD value and the measured waveform become. In addition, the measured value by the fixed analyzer method is the PMD of the same sample by the polarimetric method.
It approaches the value obtained by multiplying the measured value by 0.82. (4) The PMD value and the measured waveform recover reversibility when there is mode coupling and is sufficiently random. At this time, the measured PMD value coincides with the PMD measurement value of the same sample multiplied by 0.82 by the polarimetric method. It should be noted that, with regard to the item actually (4), that has been confirmed by Aso our experiments.

[Procedure correction 6]

[Document name to be amended] Statement

[Correction target item name]

[Correction method] Change

[Correction contents]

[0074] In this embodiment, as the error range of the PMD1 and PMD2, which gives 5% which is the measurement accuracy of the measurement in the memory unit 18, at step 106 of FIG. 2, and 5% The error range, Relative measurement error between PMD1 and PMD2 6.
Comparing with 57%, it is judged that PMD1 and PMD2 are larger than the range of the measurement accuracy of the device and do not match within the given error range. Therefore, it is found that this PMD measurement is not reversible, and in step 107, the intermediate mode coupling determination unit 19 determines that the measured optical fiber 4 (optical fiber C) is in the intermediate mode coupling state. In this case, since the correlation between the PMD value calculated from the spectrum and the PMD value based on the theory of the main polarization state cannot be obtained, the PMD value calculated from the measured spectrum is physically It was rejected as having no meaning.

Claims (8)

[Claims] 1. A spectrum of outgoing light, which is the light incident from one side of the optical fiber to be measured and which is transmitted through the optical fiber to be measured and is emitted, is measured as a first outgoing light spectrum. The spectrum of the outgoing light, which is the light entering from the opposite side and transmitted through the optical fiber under measurement, is measured as the second outgoing light spectrum, and the first polarization mode dispersion value is calculated based on the first outgoing light spectrum. Seeking
A second polarization mode dispersion value is obtained based on the second outgoing light spectrum, and thereafter, it is determined whether the first and second polarization mode dispersion values match within a predetermined error range. , It is determined whether or not the waveforms of the first and second emitted light spectra match within a predetermined allowable range, and the first and second polarization mode dispersion values match within an error range, When the first and second emission light spectrum waveforms match within the allowable range, it is determined that the optical fiber under measurement is not in the intermediate mode coupling state, and the emission light spectrum waveforms match within the predetermined allowable range. Is sinusoidal, and when the output light spectrum waveform is sinusoidal, it is judged that the optical fiber under measurement is in the weak mode coupling state, and the polarization mode dispersion value that agrees within the error range. Is the polarization mode dispersion value of the measured optical fiber. Evaluation, when the emitted light spectrum waveform is not sinusoidal, the measured optical fiber was determined to be in a state of strong mode coupling, and the polarization mode dispersion value that matched within the error range was multiplied by a correction coefficient 0.82. A method for measuring polarization mode dispersion using the four polarization incident type fixed analyzer method in which the value is evaluated as the polarization mode dispersion value of the optical fiber under test. 2. The spectrum of the outgoing light, which is the light incident from one side of the optical fiber to be measured and which is transmitted through the optical fiber to be measured and is emitted, is measured as a first outgoing light spectrum. The spectrum of the outgoing light, which is the light entering from the opposite side and transmitted through the optical fiber under measurement, is measured as the second outgoing light spectrum, and the first polarization mode dispersion value is calculated based on the first outgoing light spectrum. Seeking
A second polarization mode dispersion value is obtained based on the second outgoing light spectrum, and thereafter, it is determined whether the first and second polarization mode dispersion values match within a predetermined error range. , It is determined whether or not the waveforms of the first and second emitted light spectra match within a predetermined allowable range, and the first and second polarization mode dispersion values match within an error range, Further, when the first and second emission light spectrum waveforms match within the allowable range, it is judged that the optical fiber under measurement is not in the intermediate mode coupling state, and at least one of the first and second emission light spectrum waveforms. Fourier transform, and when the Fourier transform waveform is a vertical linear pattern waveform peculiar to the weak mode, it is determined that the optical fiber to be measured is in the weak mode coupling state, and the polarization mode dispersion value that matches within the error range is determined. Polarization mode of the optical fiber under test Evaluated as a dispersion value, when the Fourier transform waveform is a Gaussian approximate waveform, it is determined that the optical fiber under measurement is in a state of strong mode coupling, and a correction coefficient of 0.82 for the polarization mode dispersion value that matches within the error range. A method of measuring polarization mode dispersion using the four polarization incident type fixed analyzer method, which evaluates the value multiplied by as the polarization mode dispersion value of the optical fiber under test. 3. A spectrum of outgoing light, which is incident from one side of the optical fiber to be measured and is transmitted through the optical fiber to be measured and is emitted, is measured as a first outgoing light spectrum. The spectrum of the outgoing light, which is the light entering from the opposite side and transmitted through the optical fiber under measurement, is measured as the second outgoing light spectrum, and the first polarization mode dispersion value is calculated based on the first outgoing light spectrum. And a first Fourier transform waveform obtained by Fourier transforming the waveform of the first outgoing light spectrum, and the second polarization mode dispersion value and the waveform of the second outgoing light spectrum are Fourier-transformed based on the second outgoing light spectrum. The converted second Fourier transform waveform is obtained, and after that, it is determined whether or not the first and second polarization mode dispersion values match within a predetermined error range, and the first and second
Whether the Fourier transform waveforms of the first and second polarization mode dispersion values match within an error range, and whether the first and second polarization mode dispersion values match each other. When the Fourier transform waveforms match within the permissible range, it is determined that the optical fiber under measurement is not in the intermediate mode coupling state. When the converted waveform is a vertical linear pattern waveform peculiar to the weak mode, it is determined that the optical fiber under measurement is in the weak mode coupling state, and the polarization mode dispersion value that agrees within the error range is set to the polarization of the optical fiber under measurement. It is evaluated as a modal dispersion value, and when the Fourier transform waveform that matches within the allowable range is a Gaussian approximate waveform, it is determined that the optical fiber under measurement is in a strong mode coupling state, and the deviation that matches within the error range is determined. Polarization mode dispersion measurement method that utilizes a four polarization incidence type fixed analyzer method for evaluating a value obtained by multiplying the correction coefficient 0.82 to mode dispersion value as polarization mode dispersion value of the optical fiber under test. 4. When the Fourier transform waveform has a Gaussian approximate waveform and it is determined that the optical fiber under measurement is in a strong mode coupling state, the Fourier transform waveform is regarded as having a Gaussian distribution, and the Gaussian distribution is obtained. The polarization mode dispersion measuring method using the four polarization incident type fixed analyzer method according to claim 2 or 3, wherein the standard deviation value of the distribution is evaluated as the polarization mode dispersion value of the optical fiber to be measured. 5. The first outgoing light spectrum of the light incident from one side of the measured optical fiber, which is transmitted through the measured optical fiber and measured on the outgoing side, and the light which is incident from the opposite side of the measured optical fiber. An emission light spectrum storage unit for storing a second emission light spectrum which is transmitted through the optical fiber to be measured and is measured on the emission side; and a first polarization mode dispersion value based on the first emission light spectrum. A polarization mode dispersion actual measurement calculation unit that calculates and calculates a second polarization mode dispersion value based on the second outgoing light spectrum; first and second polarizations obtained by the polarization mode dispersion actual measurement calculation unit It is determined whether the modal dispersion values match within a predetermined error range and whether the waveforms of the first and second emitted light spectra match within a predetermined allowable range. 1st and 2nd polarization mode dispersion value Are within the error range, and the first and second emitted light spectrum waveforms are within the allowable range, it is determined that the optical fiber under measurement is not in the intermediate mode coupling state. The reversibility determining unit that determines that the measurement optical fiber is in the intermediate mode coupling state; the reversibility determining unit determines that the optical fiber to be measured is not in the intermediate mode coupling state, and agrees within the predetermined allowable range. It is determined whether or not the emitted light spectrum waveform is sinusoidal. When the emitted light spectrum waveform is sinusoidal, it is determined that the measured optical fiber is in the weak mode coupling state, and the emitted light spectrum waveform is sinusoidal. A strong / weak mode coupling discriminating unit which judges that the optical fiber under measurement is in a strong mode coupling state when it is not wavelike; When it is determined that the polarization mode dispersion value that matches within the error range is evaluated as the polarization mode dispersion value of the optical fiber to be measured, and when it is determined that the strong mode coupling state exists, the polarization mode dispersion value that matches within the error range. Polarization mode dispersion value evaluation unit that evaluates the value obtained by multiplying the value by the correction coefficient 0.82 as the polarization mode dispersion value of the optical fiber to be measured; Measuring device. 6. The first outgoing light spectrum of the light incident from one side of the measured optical fiber, which is transmitted through the measured optical fiber and measured on the outgoing side, and the light which is incident from the opposite side of the measured optical fiber. An emission light spectrum storage unit for storing a second emission light spectrum which is transmitted through the optical fiber to be measured and is measured on the emission side; and a first polarization mode dispersion value based on the first emission light spectrum. A polarization mode dispersion actual measurement calculation unit that calculates and calculates a second polarization mode dispersion value based on the second outgoing light spectrum; first and second polarizations obtained by the polarization mode dispersion actual measurement calculation unit It is determined whether the modal dispersion values match within a predetermined error range and whether the waveforms of the first and second emitted light spectra match within a predetermined allowable range. 1st and 2nd polarization mode dispersion value Are within the error range, and the first and second emitted light spectrum waveforms are within the allowable range, it is determined that the optical fiber under measurement is not in the intermediate mode coupling state. A reversibility determining unit that determines that the measurement optical fiber is in an intermediate mode coupling state; and at least one of the first and the second upon receiving a determination result that the measurement optical fiber is not in the intermediate mode coupling state by the reversibility determining unit. Fourier transform of the output light spectrum waveform of
When the Fourier transform waveform is a vertical linear pattern waveform peculiar to the weak mode, it is judged that the optical fiber to be measured is in the weak mode coupling state, and when the Fourier transform waveform is Gaussian approximate waveform, the optical fiber to be measured is the strong mode coupling. A strong / weak mode coupling discriminating unit that judges that the state is in the state;
When it is determined that the weak mode coupling state by the weak mode coupling determination unit, the polarization mode dispersion value that matches within the error range is evaluated as the polarization mode dispersion value of the measured optical fiber,
When it is judged to be the strong mode coupling state, the value obtained by multiplying the polarization mode dispersion value that matches within the error range by the correction coefficient 0.82 is evaluated as the polarization mode dispersion value of the optical fiber under test. Device for measuring polarization mode dispersion using a four-polarization incident type fixed analyzer method having a section. 7. The first outgoing light spectrum of the light incident from one side of the measured optical fiber which is transmitted through the measured optical fiber and measured on the outgoing side and the light which is incident from the opposite side of the measured optical fiber. An emission light spectrum storage unit for storing a second emission light spectrum which is transmitted through the optical fiber to be measured and is measured on the emission side; and a first polarization mode dispersion value based on the first emission light spectrum. A polarization mode dispersion measurement calculating unit that calculates and calculates a second polarization mode dispersion value based on the second emission light spectrum; and a first Fourier transform waveform by Fourier transforming the waveform of the first emission light spectrum. And a Fourier transform unit for Fourier transforming the waveform of the second outgoing light spectrum to obtain the second Fourier transform waveform;
The first obtained by the polarization mode dispersion measurement calculation unit
And whether the second polarization mode dispersion values match within a predetermined error range, and the first and second Fourier transform waveforms obtained by the Fourier transform unit are within a predetermined allowable range. It is determined whether or not they match, the first and second polarization mode dispersion values match within an error range, and the first and second polarization mode dispersion values match.
When the Fourier transform waveforms of 1 and 2 match within the allowable range, it is determined that the optical fiber under measurement is not in the intermediate mode coupling state, and in other cases, the reversibility determining unit determines that the optical fiber under measurement is in the intermediate mode coupling state. A vertical linear pattern waveform, which is unique to the weak mode, has a Fourier transform waveform that matches within the allowable range under the condition that the reversibility determining unit determines that the optical fiber under test is not in the intermediate mode coupling state. When, the measured optical fiber is judged to be in the weak mode coupling state, and when the Fourier transform waveform is Gaussian approximate waveform, it is judged that the measured optical fiber is in the strong mode coupling state. And; this strength
When it is determined that the weak mode coupling state by the weak mode coupling determination unit, the polarization mode dispersion value that matches within the error range is evaluated as the polarization mode dispersion value of the measured optical fiber,
When it is judged to be the strong mode coupling state, the value obtained by multiplying the polarization mode dispersion value that matches within the error range by the correction coefficient 0.82 is evaluated as the polarization mode dispersion value of the optical fiber under test. Device for measuring polarization mode dispersion using a four-polarization incident type fixed analyzer method having a section. 8. The polarization mode dispersion value definite evaluation section has a standard deviation calculation means of Gaussian distribution, and when the optical fiber to be measured is judged to be in strong mode coupling state by the strong / weak mode coupling discrimination section, Gaussian approximation is performed. 7. The Fourier transform waveform determined to be corrugated is regarded as having a Gaussian distribution, and the standard deviation value of the Gaussian distribution is evaluated as the polarization mode dispersion value of the optical fiber under measurement. Item 7. A measurement device for polarization mode dispersion using the four polarization incident type fixed analyzer method according to Item 7.