JP2012141264A - Apparatus and method for measuring wavelength resolved stokes vector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To evaluate the accuracy of a measurement result of a wavelength resolved Stokes vector.SOLUTION: An apparatus for measuring a wavelength resolved Stokes vector includes: wavelength sweeping means for resolving an inputted optical signal in a specific wavelength band width into a plurality of wavelength components by a wavelength band width narrower than the specific wavelength band width and outputting the wavelength components; four-polarized component intensity extraction means for inputting optical signals of the respective wavelength components and extracting and outputting four mutually different polarized component intensity values of the respective optical signals; and arithmetic means for performing operation based on the four mutually different polarized component intensity values of the optical signals of the respective wavelength components, executing the measurement of wavelength resolved Stokes vectors of the optical signals of the respective wavelength components and the calculation of polarization degrees based on the operation results, evaluating the measurement accuracy of the wavelength resolved Stokes vectors based on differential values between the calculation values of polarization degrees of the optical signals of the respective wavelength components and logical values of the polarization degrees of the optical signals of the respective wavelength components, and outputting the evaluated result.

Description

  The present invention relates to a wavelength-resolved Stokes vector measurement apparatus and method for optical signals, and more particularly to a wavelength-resolved Stokes vector measurement apparatus and method for evaluating measurement accuracy based on the degree of polarization calculated from a wavelength-resolved Stokes vector measurement result.

  High-speed digital transmission technology is being researched to meet the need for high-speed and large-capacity communications. In optical digital communication, optical communication having a transmission rate per optical signal channel exceeding 10 Gbps has been put into practical use, and research and development of optical communication having a transmission rate exceeding 100 Gbps has become active. In an ultra-high-speed optical digital communication system exceeding 40 Gbps, signal waveform degradation due to polarization mode dispersion occurring in a transmission path, which has not been a problem so far, has a large effect on received signal quality. It is like that.

  Polarization mode dispersion (PMD) is dispersion caused by the occurrence of a group delay difference between two orthogonal polarization modes due to unintended minute birefringence of a single mode optical fiber. Single mode optical fibers used for long-distance transmission are designed as isotropic fibers having no birefringence. However, in the process of manufacturing, cabling, cable laying and system operation, the core is subjected to elliptical or lateral stress, and is also affected by partial temperature changes. The single mode optical fiber has a slight unintentional birefringence due to the ovalization of the core, side pressure, partial temperature change, and the like, and its size and direction randomly change in the transmission direction. As a result, the light propagating in such an optical fiber reaches the output end at a time when each polarization component is different under the influence of the birefringence.

  It is important to monitor this PMD with high accuracy and to use the monitoring result as a control signal for dynamic waveform distortion compensation and as a trigger signal for failure recovery.

  In order to discuss the behavior of the polarization state of light, it is effective to express the polarization state by a vector called a Stokes vector. That is, the Stokes vector is a physical quantity that expresses the polarization state of an optical signal, and is used for measuring and evaluating PMD. The Stokes vector is composed of four Stokes parameters, and the Stokes vector is measured by calculating these parameters. The Stokes vector can represent various polarization states.

  For example, Patent Documents 1 to 3 disclose techniques for monitoring and evaluating the quality of optical signals related to PMD by measuring Stokes parameters and Stokes vectors.

  Patent Document 1 discloses a Stokes parameter device and a measurement method that accurately measure a Stokes parameter with high accuracy without causing polarization fluctuation or PDL (Polarization dependent loss) when splitting incident light. . The Stokes parameter device disclosed in Patent Document 1 has at least one or more prisms in an optical branching section, and the prism has an angle formed between its ridge (incident optical surface) and the optical axis of signal light from 45 degrees. It is also characterized by being formed large. In other words, this Stokes parameter device can suppress the occurrence of PDL when the incident signal light is divided by reducing the incident angle. As a result, DOP (Degree of Polarization) can be increased in a wide wavelength band.

  Patent Document 2 discloses an optical signal quality monitoring apparatus that monitors optical signal quality using a value estimated from a polarization state in an optical communication system. This optical signal quality monitoring device can accurately monitor optical signal quality fluctuations caused by polarization components even when higher-order components of polarization components cannot be ignored. The optical signal quality monitoring device disclosed in Patent Document 2 evaluates the quality of a transmission optical signal using a quality judgment value estimated from a measurement value based on a measurement value measured from the transmission optical signal. That is, the Stokes vector of the transmission optical signal is measured over the optical signal modulation frequency band, and the length of the locus drawn on the Poincare sphere by the measured Stokes vector in the optical signal modulation frequency band is acquired as a measurement value. At the same time, a DGD (Differential Group Delay, group delay time difference) value, which is the primary component of polarization dispersion of the transmitted optical signal, is acquired. The quality determination value is estimated using the acquired length of the trajectory and the acquired DGD value.

  If polarization state fluctuation occurs during measurement, the Stokes vector measurement value cannot be obtained correctly. Therefore, Patent Document 3 discloses an optical signal quality monitoring device that monitors polarization state fluctuations and measures Stokes vectors in a short time and with high accuracy. This optical signal quality monitoring device includes an optical frequency-resolved Stokes vector monitor and an optical frequency average Stokes vector monitor. The optical frequency average Stokes vector monitor extracts the polarization component from the average light intensity and measures the Stokes vector, and determines the occurrence of polarization state fluctuation from the measurement result. Then, in accordance with the occurrence of the detected polarization state fluctuation, the optical frequency-resolved Stokes vector monitor determines the reliability of the measurement result of the Stokes vector measured by extracting the polarization component from the light intensity for each unit optical frequency.

JP 2006-308286 JP 2009-260875 A JP 2010-096632 A

  Polarization mode dispersion (PMD) is often broadly classified into a primary component having no wavelength dependency and a secondary or higher order component having a wavelength dependency. Therefore, in order to measure and evaluate PMD including higher-order components, it is essential to obtain a wavelength-dependent Stokes vector (hereinafter, wavelength-resolved Stokes vector).

  Patent Document 1 discloses a Stokes parameter device and a measurement method for accurately measuring Stokes parameters with high accuracy, and this suppresses polarization fluctuations and PDL (polarization dependent loss) that occur when incident light is branched. This technology focuses on Therefore, Patent Document 1 does not consider obtaining the wavelength-resolved Stokes vector.

  The wavelength-resolved Stokes vector can be obtained by first decomposing an optical signal to be measured into wavelength components and measuring the Stokes vector for each wavelength component. The measurement accuracy of the wavelength-resolved Stokes vector depends on the wavelength resolution of the measuring device.

  The wavelength resolution required to maintain a certain measurement accuracy of the wavelength-resolved Stokes vector differs depending on the polarization state and the optical signal speed. The larger the PMD added to the optical signal, the smaller the wavelength resolution required to maintain the measurement accuracy of the wavelength-resolved Stokes vector. If there is not sufficient wavelength resolution, the PMD obtained from the measurement result of the wavelength-resolved Stokes vector includes a large error due to measurement accuracy degradation.

  For example, in the case of an optical signal with a PMD of zero (0) ps, the wavelength resolution can be allowed even in the order of nm, but the wavelength resolution required for an optical signal with an optical signal speed of 100 Gbps and a PMD of 5 ps is on the order of several tens of pm. Become. Here, it is assumed that the wavelength resolution of a certain wavelength-resolved Stokes vector measurement apparatus is 10 pm under a certain condition. With this wavelength-resolved Stokes vector measuring device, it can be said that the above-described optical signal with a PMD of 0 ps can be used with an optical signal with an optical signal speed of 100 Gbps and a PMD of 5 ps.

  However, the wavelength resolution of 10 pm of this measuring device is a value under a certain condition, and this value is not always maintained. This is because the wavelength resolution changes with time due to factors such as environmental temperature and optical system misalignment inside the measurement apparatus.

  The Stokes vector is generally measured by extracting four different polarization component intensities from the optical signal to be measured and calculating them. For this reason, the Stokes vector measurement apparatus includes a polarization component intensity extraction unit. For example, when branching an optical signal into four and extracting four polarization component intensities at a time, processing such as spectroscopy, polarization modulation, photoelectric conversion, A / D (analog / digital) conversion is performed. That is, in the measuring apparatus, a branching means composed of a beam splitter, a half mirror, a filter, etc., and a phase element such as a polarizing element and a quarter-wave plate are used as an optical system, and a photoelectric conversion circuit or AD converter is used. Circuitry is also used.

  Therefore, factors affecting the measurement accuracy of the wavelength-resolved Stokes vector include the accuracy of the polarization component intensity extraction unit of the measurement apparatus in addition to the accuracy of the wavelength resolution.

  In addition, the polarization component intensity extraction unit of the measurement apparatus is not configured to extract four polarization component intensities at a time as described above, but a polarization component intensity extraction unit having a structure in which measurement of the polarization component intensity is repeated four times. There may also be a measuring device provided. In such a case, there is an inherent deterioration factor inherent in each measuring apparatus.

  For example, when the measurement apparatus is provided with only one polarization component intensity extraction unit and the measurement of the polarization component intensity is repeated four times, the polarization state of the optical signal is changed over time during the four measurements. It can change. When the polarization state of the optical signal to be measured changes with time, an error due to time-varying accuracy deterioration occurs. Also, when the optical signal is branched into four and measured at the same time by the four polarization component intensity extraction units, if there is a difference in the extraction performance of each of the four polarization component intensity extraction units, an error due to fixed accuracy degradation will occur. Occurs. Further, when there is a temperature characteristic in the extraction performance of the polarization component intensity extraction unit, a measurement error due to time-varying accuracy deterioration due to time change of temperature occurs.

  As described above, the measurement accuracy of the wavelength-resolved Stokes vector is deteriorated due to various factors and may change with time. Accordingly, in order to maintain a measurement accuracy of a certain level or higher, it is essential to check the accuracy of the measurement device constantly or periodically.

  The optical signal quality monitoring device disclosed in Patent Document 2 is a technique whose main purpose is to be able to evaluate the quality of a transmitted optical signal even when higher-order components of polarization components cannot be ignored. This technique acquires the length of the locus drawn by the Stokes vector on the Poincare sphere as a measurement value, acquires the DGD (group delay time difference) value, which is the primary component of the polarization dispersion of the transmitted optical signal, and transmits the transmitted optical signal. Evaluate the quality. Therefore, Patent Document 2 does not consider evaluating the accuracy of the measuring device.

  The optical signal quality monitoring device disclosed in Patent Document 3 is a technique for determining the reliability of the Stokes vector measurement result by monitoring polarization state fluctuations. This technique determines the occurrence of polarization state fluctuation from the measurement result of the optical frequency average Stokes vector monitor. Then, the reliability of the measurement result of the Stokes vector measured by the optical frequency-resolved Stokes vector monitor is determined according to the occurrence of the polarization state fluctuation. That is, this technique can determine the reliability of the measurement result of the Stokes vector, but does not consider evaluating the accuracy of the measuring device itself.

  As described above, until now, there has been no method or index for simply evaluating whether the wavelength resolution of the measuring apparatus is sufficient. For this reason, the measurement accuracy (resolution) is evaluated by measuring the impulse response of the device after adjusting each factor individually in the measurement device. In addition, if there are many factors in the measuring apparatus that cause deterioration in measurement accuracy, the number of adjustments and evaluations increases accordingly. Furthermore, it is essential to periodically perform accuracy calibration of the measuring apparatus in order to cope with changes in measurement accuracy over time. Therefore, there is a problem that much time and labor are required for evaluating the measurement accuracy of the wavelength-resolved Stokes vector.

  An object of the present invention is to solve the above-described problems, measure a wavelength-resolved Stokes vector, and evaluate whether or not the accuracy of the measurement result is sufficient based on the measurement result. It is to provide a method.

  In order to achieve the above object, the wavelength-resolved Stokes vector measurement device according to one aspect of the present invention is configured to input an optical signal having a specific wavelength bandwidth with a wavelength bandwidth narrower than the specific wavelength bandwidth. Wavelength sweeping means for decomposing and outputting a plurality of wavelength components, and 4-polarization component intensity extraction for inputting and outputting four different polarization component intensities of the respective optical signals. And calculating the polarization-resolved Stokes vector of each optical signal of the wavelength component based on the calculation result and calculating the polarization The wavelength-resolved Stokes vector based on a difference value between a calculated value of the polarization degree of each optical signal of the wavelength component and a theoretical value of the polarization degree of the optical signal of the wavelength component. Characterized in that it comprises calculating means for outputting by evaluating measurement accuracy of Le, the.

  In addition, the wavelength-resolved Stokes vector measurement method according to another aspect of the present invention decomposes an input optical signal having a specific wavelength bandwidth into a plurality of wavelength components with a wavelength bandwidth narrower than the specific wavelength bandwidth. And extracting four different polarization component intensities of the respective optical signals of the wavelength components, calculating based on the four different polarization component intensities of the extracted optical signals of the wavelength components, and calculating the result. Measurement of the wavelength-resolved Stokes vector of each optical signal of the wavelength component and calculation of the degree of polarization based on the calculation of the degree of polarization of the optical signal of each wavelength component and the optical signal of the wavelength component The measurement accuracy of the wavelength-resolved Stokes vector is evaluated and output based on a difference value between the theoretical value of the degree of polarization and the theoretical value.

  The present invention evaluates whether the measurement accuracy of the wavelength-resolved Stokes vector measurement device is sufficient by comparing the calculated value of the degree of polarization of the optical signal for each wavelength component with its theoretical value and identifying the difference value. be able to.

It is a block diagram which shows the structure of the wavelength-resolved Stokes vector measurement apparatus of 1st Embodiment. It is a flowchart which shows operation | movement of the wavelength-resolved Stokes vector measurement apparatus of 1st Embodiment. It is a block diagram which shows the structure of the wavelength-resolved Stokes vector measurement apparatus of 2nd Embodiment. It is a system block diagram which shows the connection form of the wavelength-resolved Stokes vector measurement apparatus of 2nd Embodiment. It is a flowchart which shows operation | movement of the wavelength-resolved Stokes vector measurement apparatus of 2nd Embodiment. It is a system block diagram which shows the connection form of the example of a measurement using the wavelength-resolved Stokes vector measuring apparatus. It is a block diagram which shows the structure of the wavelength-resolved Stokes vector measurement apparatus of 3rd Embodiment. It is a flowchart which shows operation | movement of a monitor part.

  According to the wavelength-resolved Stokes vector measurement apparatus and measurement method of the present invention, an index that can easily evaluate the measurement accuracy of a wavelength-resolved Stokes vector is determined, and a wavelength-resolved Stokes vector measurement result that is constantly highly reliable is obtained. Obtainable.

  The present invention uses DOP (Degree of Polarization) for each wavelength component calculated from the wavelength-resolved Stokes vector measurement result.

  The principle of the present invention is to calculate the DOP from the measurement result of the wavelength-resolved Stokes vector of the optical signal observed by dividing it into each sufficiently narrow wavelength band, and to determine how much the DOP deviates from the theoretical value. Evaluate whether the result is accurate enough. That is, an optical signal having a specific wavelength bandwidth is decomposed into a plurality of wavelength components with a wavelength bandwidth narrower than the specific wavelength bandwidth. Then, DOP is calculated from the measurement result of the wavelength-resolved Stokes vector of the decomposed optical signal of each wavelength component, and how much the DOP deviates from the theoretical value is identified. Whether the accuracy of the measurement result of the wavelength-resolved Stokes vector is sufficient according to the difference between the calculated value of DOP and the theoretical value is evaluated.

  The wavelength bandwidth of the wavelength resolution possessed by the wavelength-resolved Stokes vector measuring device is used as a narrow wavelength bandwidth for decomposing an optical signal having a specific wavelength bandwidth into wavelength components. This means that, regardless of the polarization state of an optical signal having a specific wavelength bandwidth, the DOP of each wavelength component decomposed with wavelength resolution is theoretically always “DOP = 1” if the wavelength resolution is sufficient. Take advantage of that.

  The polarization state represented by four polarization components described later varies depending on the wavelength component. Therefore, since a plurality of wavelength components are mixed in the optical signal having the wavelength bandwidth to be measured, a plurality of polarization states are mixed. If the optical signal having the wavelength bandwidth to be measured can be decomposed into a single wavelength component with a narrow wavelength bandwidth of Δλ, for example, it is separated into a single polarization state, so “DOP = 1”. Further, when the wavelength bandwidth of Δλ used for the decomposition is not sufficiently narrow, and other wavelength components are mixed in the decomposed optical signal, “DOP <1”.

  Note that the theory concerning polarization in optics includes the Jones method and the Mueller method.

  Polarization mode dispersion (PMD: Polarization Mode Dispersion) is caused by a difference in group delay generated between two orthogonal polarization modes for each wavelength component. That is, PMD is generated when the polarization state changes for each wavelength within the optical signal band. Therefore, even if there is PMD in the optical signal of the wavelength band to be measured, if the observation is made only within a sufficiently narrow wavelength band, it can be assumed that the polarization state is the same and the polarization state has not changed. The PMD within the observation range is zero (0). In other words, even if “DOP <1” as the entire optical signal band, when observation is performed by dividing into sufficiently narrow wavelength bands, the DOP for each wavelength component in the observation range is always “DOP = 1”. Become.

  In this case, “sufficient” has a different numerical value depending on the PMD to be measured, and if the PMD to be measured is large, the change in the polarization state for each wavelength within the optical signal band becomes large. Is required. However, roughly speaking, when an optical signal for basic transmission of optical digital communication is to be measured, it can be said to be “sufficient wavelength resolution” with a wavelength resolution of about several tens of pm.

  In addition, if the polarization component intensity extraction unit and the accuracy calibration of the part that causes the measurement accuracy are sufficiently performed and the measurement apparatus is in an ideal state with no error factor, Since DOP is output without error, DOP is always “DOP = 1”.

  Accordingly, if the degree of deviation of the DOP of each wavelength component resolved with the wavelength resolution from the theoretical value “1” is identified, it becomes a factor that affects the wavelength resolution insufficiency, the polarization component intensity extraction unit, and the measurement accuracy. It becomes possible to evaluate the accuracy deterioration due to the part.

  Decomposing an optical signal to be measured into a plurality of optical signals divided into sufficiently narrow wavelength bands is referred to as “decomposing into wavelength components”. An optical signal divided into sufficiently narrow wavelength bands that have been decomposed is referred to as “wavelength component” or “optical signal of wavelength component”.

  DESCRIPTION OF EMBODIMENTS Embodiments for carrying out the present invention will be described with reference to the drawings.

  FIG. 1 is a block diagram showing the configuration of the wavelength-resolved Stokes vector measurement apparatus according to the first embodiment of the present invention.

  The embodiments are examples, and the disclosed apparatus and system are not limited to the configurations of the following embodiments.

  The wavelength-resolved Stokes vector measuring apparatus 1 according to the first embodiment of the present invention includes a wavelength sweep unit 11, a four polarization component intensity extraction unit 12, and a calculation unit 13.

  The wavelength sweeping unit 11 decomposes and outputs the input optical signal having a specific wavelength bandwidth into a plurality of wavelength components with a wavelength bandwidth narrower than the specific wavelength bandwidth. The four-polarization component intensity extracting means 12 receives the respective optical signals of the wavelength components that have been decomposed into a plurality of components, and extracts and outputs four different polarization component intensities of the respective optical signals. The calculation means 13 inputs and calculates four different polarization component intensities of the respective optical signals of the wavelength components, and measures the wavelength-resolved Stokes vector of each optical signal of the wavelength components and the degree of polarization based on the calculation result. The calculation of is performed. In addition, the calculation means 13 evaluates the measurement accuracy of the wavelength-resolved Stokes vector based on the difference value between the calculated value of the polarization degree of each optical signal of the wavelength component and the theoretical value of the polarization degree of the optical signal of the wavelength component. And output.

  FIG. 2 is a flowchart showing the operation of the wavelength-resolved Stokes vector measurement apparatus according to the first embodiment. The wavelength-resolved Stokes vector measurement apparatus according to the first embodiment operates as follows.

  An optical signal is input (S101). The input optical signal having a specific wavelength bandwidth is decomposed into a plurality of wavelength components with a wavelength bandwidth narrower than the specific wavelength bandwidth (S102). Four different polarization component intensities of the respective optical signals of the wavelength components resolved into a plurality are extracted (S103). Calculation based on four different polarization component intensities of the extracted optical signals of the wavelength components, and measurement of wavelength-resolved Stokes vectors of the optical signals of the wavelength components and calculation of the degree of polarization based on the calculation results Execute (S104). The measurement accuracy of the wavelength-resolved Stokes vector is evaluated and output based on the difference value between the calculated value of the polarization degree of each optical signal of the wavelength component and the theoretical value of the polarization degree of the optical signal of the wavelength component (S105). .

  As described above, the wavelength-resolved Stokes vector measurement apparatus according to the first embodiment uses the wavelength sweeping unit 11 to generate a plurality of optical signals having a specific wavelength bandwidth with a wavelength bandwidth narrower than the specific wavelength bandwidth. Is divided into sufficiently narrow wavelength bands. Four different polarization component intensities are extracted by the four polarization component intensity extraction unit 12 from the optical signals of the respective wavelength components divided into sufficiently narrow wavelength bands. The calculation means 13 inputs the extracted four different polarization component intensities, performs calculation, and executes wavelength-resolved Stokes vector measurement and polarization degree calculation. Then, how much the calculated value of the degree of polarization deviates from the theoretical value is identified. Since the calculated value of the degree of polarization of the optical signal of each wavelength component is decomposed into a sufficiently narrow wavelength band, it becomes “1” which is a theoretical value when all the elements of the measuring apparatus are optimally adjusted. . Therefore, by identifying how much the calculated value of the degree of polarization deviates from the theoretical value “1”, the measurement accuracy of the measurement apparatus used can be evaluated.

  Next, a chromatic dispersion Stokes vector measuring apparatus according to the second embodiment will be described.

  FIG. 3 is a block diagram illustrating a configuration of the chromatic dispersion Stokes vector measurement apparatus 10 according to the second embodiment.

  The chromatic dispersion Stokes vector measuring apparatus 10 is an example in which a variable optical bandpass filter 101 is used as wavelength sweeping means, and a polarimeter (polarimeter) and an A / D converter are used as four-polarization component intensity extracting means 102. The chromatic dispersion Stokes vector measurement apparatus 10 includes a calculation unit 103 and a monitor unit 104 as calculation means.

  FIG. 4 is a system configuration diagram illustrating a connection form of the wavelength-resolved Stokes vector measurement apparatus according to the second embodiment.

  As shown in FIG. 4, the wavelength-resolved Stokes vector measuring apparatus 10 is connected to the optical signal source 2 through the optical fiber 3.

  The optical signal output from the optical signal source 2 passes through the optical fiber 3 and is added with polarization mode dispersion (PMD).

  In general, PMD is roughly divided into a group delay time difference that is a primary component and a secondary polarization mode dispersion that is a high-order component. The group delay time difference is called DGD (Differential Group Delay), and the second-order polarization mode dispersion is called SOPMD (Second Order Polarization Mode Dispersion). For the sake of simplicity, only DGD will be considered. Even when SOPMD exists, the operation does not change.

  It is assumed that DGD is added by τ (ps) by passing an optical signal having an optical spectrum width Λ that is a specific wavelength bandwidth output from the optical signal source 2 through the optical fiber 3. The optical signal having the optical spectrum width Λ and DGD = τ is input to the wavelength-resolved Stokes vector measuring apparatus 10.

  The optical signal having the optical spectrum width Λ is input to the variable optical bandpass filter 101 which is a wavelength sweeping unit of the wavelength-resolved Stokes vector measuring apparatus 10. The variable optical bandpass filter 101 uses the wavelength bandwidth of the wavelength resolution possessed by the measurement apparatus as a narrow wavelength bandwidth for decomposing the optical spectrum width Λ into a plurality of wavelength components. That is, the variable optical bandpass filter 101 is a bandpass filter that uses a wavelength bandwidth of Δλ corresponding to wavelength resolution as transmitted light, and can sequentially change the center wavelength of the transmitted light. Therefore, the optical signal having the optical spectrum width Λ is decomposed by the variable optical bandpass filter 101 into a plurality of optical signals divided into sufficiently narrow wavelength bands with a wavelength resolution of Δλ.

  The wavelength components resolved for each Δλ by the variable optical bandpass filter 101 are sequentially input to the 4-polarization component intensity extraction unit 102 in time series, and four different polarization component intensities of the optical signals of the respective wavelength components are extracted. The That is, the optical signal having the optical spectrum width Λ is decomposed into n (n is a positive integer) wavelength components having a wavelength bandwidth of Δλ. Then, the decomposed optical signal of each wavelength component is sequentially time-sequentially such that Δλ at time t1 is λ1 component, Δλ of t2 is λ2 component,. Input to the extraction unit 102. Then, four different polarization component intensities corresponding to the decomposed optical signals of the respective wavelength components are extracted. The wavelength bandwidth of the decomposed optical signal of each wavelength component is Δλ, and the relationship Δλ × n = Λ is established.

  The optical signal of the wavelength component decomposed for each Δλ input to the four-polarized component intensity extracting unit 102 is divided into four different polarized components by the polarimeter, and the respective polarized component intensities are extracted. The four-polarization component intensity extraction unit 102 is configured to extract four different polarization component intensities by repeating the measurement of the polarization component intensity four times without branching the input optical signal into four. Also good.

Here, the four different polarization components are transmitted light component (hereinafter t component), vertical linear polarization component (hereinafter v component), 45 ° linear polarization component (hereinafter q component), clockwise circular polarization component (hereinafter r). Component). The transmitted light component is a light component that has passed through the four-polarized component intensity extraction unit 102. Further, linearly polarized light is polarized light whose surface (electric field vector) including the vibration direction of the electric field of light is specified as one, and circularly polarized light is polarized light whose electric field vector rotates with time. A clockwise rotation of the electric field vector with respect to the light traveling direction is referred to as “clockwise”. Depending on the inclination of the electric field vector of the linearly polarized light with respect to the coordinate axis, it is referred to as vertical linearly polarized light or 45 ° linearly polarized light. More precisely, depending on the angle between the input light non-signal polarization axis and the polarization axis of the polarization component extraction device included in the four-polarization component intensity extraction unit 102, they are referred to as vertical linear polarization and 45 ° linear polarization.
That is, four polarization component intensities t, v, q, and r are output for each optical signal having a wavelength component of Δλ. Therefore, when measuring an optical signal having an optical spectrum width Λ by dividing it into n wavelength components with a wavelength resolution of Δλ, 4 × n pieces of data are input to the computing unit 103 in one measurement. become.

  That is, in the four-polarization component intensity extraction unit 102, the intensities of different polarization components (t, v, q, r components) of the optical signals of the respective wavelength components decomposed into Δλ are optically extracted by a polarimeter, and are subjected to photoelectric conversion. And output as an analog electrical signal. The analog electric signal output from the polarimeter is converted into a digital electric signal by the A / D converter, and the intensities of the t, v, q, and r components are output to the arithmetic unit 103 as digital voltage values.

  The calculation unit 103 inputs 4n pieces of data (digital voltage values indicating the intensity of each component of t, v, q, and r) output from the four-polarized component intensity extraction unit 102 and performs calculation. The calculation unit 103 performs measurement of the wavelength-resolved Stokes vector of the optical signal of each wavelength component and calculation of DOP based on the calculation result.

  The wavelength-resolved Stokes vectors (S0 (λ), S1 (λ), S2 (λ), S3 (λ)) of the optical signal of each wavelength component are measured as wavelength-resolved Stokes vectors based on the calculation result of Equation 1.

  In Equation 1, It (λ), Iv (λ), Iq (λ), and Ir (λ) represent the intensity of each polarization component of t, v, q, and r for each Δλ.

  Further, DOP (λ) which is the DOP of the optical signal of each wavelength component decomposed into Δλ is S0 (λ), S1 (λ), S2 (λ), S3 (λ) obtained from the above calculation result. And is calculated by Equation 2.

  The DOP (λ) calculated by Equation 2 has n data. The operation unit 103 extracts the minimum value of n DOP (λ) and outputs the extracted value to the monitor unit 104.

  The monitor unit 104 evaluates the measurement accuracy of the chromatic dispersion Stokes vector measurement apparatus 10 by comparing the minimum value of DOP (λ) output from the calculation unit 103 with a theoretical value. That is, the monitor unit 104 evaluates the measurement accuracy of the wavelength-resolved Stokes vector measured as described above by identifying how much the minimum value of DOP (λ) deviates from the theoretical value “1”. be able to.

  This means that, as described above, no matter what PMD is added to the optical signal input to the measuring device, if observation is performed by dividing the optical signal into sufficiently narrow wavelength bands, the polarization is within the observation range. The fact that the state has not changed is used.

  PMD caused by the difference in group delay generated between two orthogonal polarization modes for each wavelength component occurs when the polarization state changes for each wavelength in the optical signal band. That is, the optical signal to which PMD is added means that a plurality of polarization states are included in the optical spectrum width Λ. However, if the optical signal of the wavelength bandwidth to be measured with the optical spectral width Λ can be decomposed with a sufficiently high wavelength resolution Δλ and decomposed into a single wavelength component, the polarization state is single within the range of Δλ. Can be considered. For this reason, the n DOP (λ) calculated by the calculation unit 103 is theoretically all values always 1 regardless of the PMD of the input optical signal if the wavelength resolution Δλ of the measuring apparatus is sufficiently high. Become.

  Conversely, when the wavelength resolution Δλ of the measuring device is not sufficient, other wavelength components are mixed in the optical signal decomposed by Δλ, and the polarization state in the divided wavelength band cannot be regarded as single, The calculated DOP (λ) is smaller than 1.

  In addition, since DOP (λ) is calculated by the calculations according to Expressions 1 and 2, if the calculation is not accurate, an error occurs and becomes smaller than 1.

  DOP (λ) is the result of the calculation of Equation 1 using It (λ), Iv (λ), Iq (λ), Ir (λ), S0 (λ), S1 (λ), S2 ( λ) and S3 (λ) are obtained from Equation 2 based on the measured values. For this reason, DOP (λ) is smaller than 1 even when measurement for extracting It (λ), Iv (λ), Iq (λ), and Ir (λ) is not performed accurately.

  A case where the measurement for extracting It (λ), Iv (λ), Iq (λ), and Ir (λ) is not performed accurately is considered to be because the four-polarized component intensity extracting unit 102 is operating normally. This is the case. The detection sensitivity and detection efficiency of It (λ), Iv (λ), Iq (λ), and Ir (λ), and the loss amount of each component of t, v, q, and r should be essentially uniform. . However, it is considered that the cause is variation. In other words, the accuracy of the optical system of the polarimeter that constitutes the four-polarized component intensity extracting unit 102, the variation in the characteristics of the light receiving element, the photoelectric conversion circuit, and the A / D conversion circuit are affected.

  Therefore, the wavelength dispersion Stokes vector measurement apparatus of this embodiment can evaluate the measurement accuracy of the wavelength-resolved Stokes vector by identifying how much the calculated value of DOP (λ) deviates from the theoretical value 1. it can.

  This chromatic dispersion Stokes vector measurement apparatus does not need to know the wavelength resolution in advance. Even if the wavelength resolution of the measurement apparatus is not directly known, the use of DOP (λ) calculated from the measurement result of the wavelength-resolved Stokes vector that strongly depends on the wavelength resolution can be used to evaluate the wavelength resolution of the measurement apparatus. Can be estimated indirectly.

  Further, although there are n data items of DOP (λ), only the worst value, that is, the minimum value (min (DOP (λ))) may actually be used as the evaluation index. As described above, the calculation unit 103 extracts the minimum value of DOP for each resolved wavelength. Therefore, since min (DOP (λ)) is output from the calculation unit 103 without preparing a special external device and without disturbing the measurement, the monitor unit 104 can perform the evaluation in real time. .

  Of course, the extraction of the minimum value may be performed by the monitor unit 104 without being performed by the calculation unit 103.

  FIG. 5 is a flowchart showing the operation of the wavelength-resolved Stokes vector measurement apparatus 10 of the second embodiment. The wavelength-resolved Stokes vector measurement apparatus 10 according to the second embodiment operates as follows.

  An optical signal having an optical spectrum width Λ that is a specific wavelength bandwidth is input (S201). The input optical signal is decomposed into a plurality of wavelength components with wavelength resolution (S202). Four different polarization component intensities of the optical signals of the respective wavelength components resolved into a plurality are extracted (S203). Calculation is performed based on four different polarization component intensities of the extracted optical signals of the wavelength components, and wavelength-resolved Stokes vectors of the optical signals of the wavelength components are measured based on the calculation results (S204). Based on the measured wavelength-resolved Stokes vector, the degree of polarization of each optical signal of the wavelength component is calculated (S205). A minimum value is extracted from the degree of polarization calculated for each optical signal of the wavelength component (S206). A difference value between the calculated minimum value of polarization degree and the theoretical value of polarization degree is identified (S207). Based on the identified difference value, the measurement accuracy of the calculated wavelength-resolved Stokes vector is evaluated and output (S208).

  As described above, the chromatic dispersion Stokes vector measuring apparatus according to the present embodiment decomposes an optical signal having an optical spectrum width Λ into a plurality of wavelength components by wavelength resolution Δλ, and measures a wavelength-resolved Stokes vector for each wavelength component . DOP (λ) for each wavelength component is calculated from the measured wavelength-resolved Stokes vector. Then, by evaluating how much min (DOP (λ)), which is the minimum value of DOP (λ), deviates from the theoretical value “1”, the quality of the wavelength-resolved Stokes vector is evaluated. Can do.

  For example, if min (DOP (λ)), which is the minimum value of the calculated value, is 0.8, since the theoretical value of DOP (λ) is 1, the difference value between the calculated value and the theoretical value is 0.2. . Assuming that min (DOP (λ)), which is the minimum value of the calculated value, becomes 0.9 as a result of improving the wavelength resolution of the measuring device, the light intensity difference of the polarization component, circuit characteristics, etc., the calculated value and the theoretical value Is 0.1. The smaller the difference between the calculated value and the theoretical value, the better the measurement accuracy of the wavelength-resolved Stokes vector.

  Next, a measurement example using the chromatic dispersion Stokes vector measurement device according to the embodiment of the present invention will be described.

  FIG. 6 is a system configuration diagram showing a connection form of a measurement example using the wavelength-resolved Stokes vector measuring apparatus.

  This measurement example is an example in the case of evaluating the group delay time difference (DGD) measurement performance of the wavelength-resolved Stokes vector measurement device. In other words, an optical signal having a known polarization mode dispersion (PMD) is input, and PMD added to the optical signal is gradually increased in a state where the DOP for each wavelength component is monitored. That is, DGD is gradually increased. As a result, the monitored DOP decreases as the DGD increases. Then, a DOP reduction amount that can be measured within the allowable error is determined in advance as an allowable reduction amount, and the DGD when the DOP decreases to the allowable reduction amount is identified. Thereby, the measurement range of DGD measurable with this wavelength-resolved Stokes vector measurement device can be evaluated as DGD measurement performance.

  This will be described below with reference to FIG.

  As a device for adding a known PMD to an optical signal input to the wavelength-resolved Stokes vector measuring device 10, a variable group delay time difference (DGD) generator 4 (hereinafter, variable DGD generator 4) is connected to the optical signal source 2 and wavelength-resolved. It is installed between the Stokes vector measuring device 10.

  The variable DGD generator 4 includes a polarization controller 41, polarization beam splitters 43 and 44, and an optical delay adjuster 42.

  The polarization controller 41 converts the polarization state of the optical signal output from the optical signal source 2 into linear 45 ° polarized light and outputs it to the polarization beam splitter 43. The polarization beam splitter 43 decomposes the input optical signal into two orthogonally polarized components X and Y and outputs the result. For example, the X component is output to the polarization beam splitter 44 and the Y component is output to the optical delay adjuster 42, respectively. The optical delay adjuster 42 adds a delay of τ (ps) to the Y component of the input optical signal. The Y component of the optical signal to which the delay of τ is added and the X component of the optical signal without the delay are combined by the polarization beam splitter 44, and an optical signal of DGD = τ is generated.

  In the wavelength-resolved Stokes vector measuring apparatus 10, the minimum value (min (DOP (λ))) of DOP for each wavelength component resolved with wavelength resolution is monitored.

  As described above, when an optical signal is observed divided into each wavelength band of Δλ, when the observation range of Δλ is sufficiently narrow with respect to the added DGD, it can be considered that the polarization state has not changed. Is the theoretical value of 1 min (DOP (λ)) being monitored.

  Here, the DGD (value of τ) added by the variable DGD generator 4 is gradually increased.

  Then, when DGD exceeds a certain value, min (DOP (λ)) monitored by the wavelength-resolved Stokes vector measuring apparatus 10 decreases from the theoretical value 1.

  This is because the DGD becomes large and the observation range of Δλ cannot be regarded as a sufficiently narrow range with respect to the added DGD. In other words, the added DGD becomes large, and the polarization state contained in the observation range of Δλ is not single. If it becomes like this, the error of a measurement result will increase and a measurement precision will deteriorate.

  Therefore, it is added when DGD (τ value) is within a range in which min (DOP (λ)) = 1 can be maintained, or when min (DOP (λ)) value (allowable decrease value) can be measured within the allowable error. The measured DGD (value of τ) is measured. That is, the DGD is increased, and the value of DGD immediately before min (DOP (λ)) is less than 1 or the tolerance that min (DOP (λ)) can be measured within a predetermined allowable error. The value of DGD just before reaching the drop value is measured.

  Thereby, it is possible to determine that the DGD value measured immediately before min (DOP (λ)) is less than 1 is the maximum value of DGD that can be measured by the measurement apparatus without error. In addition, the value of DGD measured immediately before min (DOP (λ)) reaches a permissible drop value that can be measured within a predetermined tolerance can be measured with the measurement accuracy predetermined by the measurement device. The maximum value of the DGD can be determined. It can be said that the allowable decrease value of min (DOP (λ)) is the maximum allowable value of the difference value between the value of min (DOP (λ)) and the theoretical value 1.

  For example, it is evaluated that “This measuring device can measure DGD 0 to 8 ps without measurement error”, or “DOP allowable decrease value maintaining DGD measurement error 0.1 ps is 0.05, and measurement is possible under this condition. The maximum value of DGD is 10 ps ". The “DOP allowable decrease value 0.05” means “DOP allowable minimum value 0.95”.

  Next, a wavelength-resolved Stokes vector measurement apparatus according to the third embodiment will be described.

  FIG. 7 is a block diagram illustrating the configuration of the wavelength-resolved Stokes vector measurement apparatus according to the third embodiment.

  The chromatic dispersion Stokes vector measurement apparatus 20 includes a variable optical bandpass filter 201, a four-polarization component intensity extraction unit 202 using a polarimeter and an A / D converter, a calculation unit 203, a monitor unit 204, and a calibration control unit 205. Is done.

  The variable optical bandpass filter 201, the four polarization component intensity extraction unit 202, and the calculation unit 203 have the same configuration as the variable optical bandpass filter 101, the four polarization component intensity extraction unit 102, and the calculation unit 103 in the second embodiment. I will omit the explanation.

  The wavelength-resolved Stokes vector measurement apparatus 20 according to the third embodiment is different from the second embodiment in that it has a feature in the monitor unit 204 and includes a calibration control unit 205 that operates by its control.

  The monitor unit 204 is a polarization degree input unit that inputs the minimum value of DOP calculated and extracted by the arithmetic unit 203, a comparison unit that compares the minimum value of DOP with various threshold values, and a control based on the comparison results in the comparison unit. A monitor control unit to be executed is included.

  Note that the calculation unit 203 may simply be configured to output the calculated DOP value for each calculated wavelength component, and the monitor unit 204 may extract the minimum value. In this case, the polarization degree input unit extracts the minimum value from the calculated DOP value for each wavelength component input from the calculation unit 203, and sends the minimum value of the DOP to the comparison unit.

  The comparison unit includes a first threshold value and a second threshold value that define an allowable value of the minimum value of DOP, and compares the first threshold value and the second threshold value. The first threshold value is an allowable minimum value of DOP determined in the measurement example described with reference to FIG. 6. When the minimum value of DOP is lower than this value, the measurement accuracy is deteriorated by exceeding the allowable value. This is the threshold value for determining that the The second threshold value is an arbitrarily set threshold value that determines that the minimum value of DOP does not reach the first threshold value, but that the minimum value of DOP is lower than the theoretical value and deterioration in measurement accuracy is recognized. is there.

  The comparison unit outputs, to the monitor control unit, a comparison result of a value at which the minimum value of DOP has not reached any threshold value, a value that has reached the first threshold value, or a value that has reached the second threshold value. . And a monitor control part performs the process based on the comparison result information which the comparison part output. The first threshold value and the second threshold value may be threshold values based on a difference value between the minimum value of DOP and the theoretical value 1 on the basis of the allowable decrease value of DOP. That is, the first threshold value is the allowable maximum value of the difference value (or the maximum value of the allowable decrease value), and the second threshold value has not reached the allowable maximum value, but it is determined that the measurement accuracy is deteriorated. The difference value between the minimum value of DOP and the theoretical value 1 can be arbitrarily set.

  The operation of the monitor unit 204 will be described with reference to FIG.

  FIG. 8 is a flowchart showing the operation of the monitor unit 204.

  The monitor unit 204 inputs the minimum value of DOP from the calculation unit 203 (S301). Note that, as described above, the calculation unit 203 may simply be configured to output the calculated DOP value for each calculated wavelength component, and the monitor unit 204 may extract the minimum value.

  S302 will be described later.

  It is compared whether or not the minimum value of DOP has reached the first threshold value and the second threshold value described above (S303). The information output from the comparison unit is a comparison result of “not reaching any threshold”, “having reached the first threshold”, or “having reached the second threshold”.

  If the comparison result “has not reached any threshold value”, it indicates that the measurement accuracy is maintained, and therefore the monitor control unit outputs valid information indicating that the measurement result is valid (S304).

  If the comparison result “has reached the first threshold”, it is an abnormal state in which it can be determined that the measurement accuracy has deteriorated, so preparations are made to output an alarm. That is, in order to confirm that this abnormal state is not an accidental factor, the continuity of occurrence is confirmed (S305). If this abnormal state occurs continuously for a predetermined number of times (S305, YES), an alarm is output to notify the outside of the device abnormality.

  When the comparison result “has reached the second threshold”, it indicates a state in which the measurement accuracy has deteriorated although the abnormal state has not been reached. Therefore, a calibration control unit 205 configured to calibrate a part that causes deterioration of the wavelength-resolved Stokes vector measurement apparatus 20 so as to maintain a constant measurement accuracy is controlled. For example, the calibration control unit 205 includes an actuator for adjusting the alignment deviation of the optical system and a sensor for detecting the deviation, and the monitor control unit 204 feedback-controls the calibration control unit 205 to automatically achieve a certain measurement accuracy. To be able to maintain.

  In order to perform this feedback control, 1 is set to the calibration control flag (S307). “Calibration control flag = 1” means that feedback control for calibration is being performed. The monitor control unit 204 sends a control signal to the calibration control unit 205 to perform a control operation for calibration (S308). Since the minimum value of DOP input after starting feedback control for calibration is “calibration control flag = 1”, the process proceeds to S309. In the processing of S309, it is confirmed whether or not the input minimum value of DOP shows a certain improved value. When the input minimum value of DOP shows a certain improved value (S309, YES), the calibration control flag is set to 0 (S310) and the control is terminated. On the other hand, when the input minimum value of DOP does not indicate a certain improved value (S309, NO), the monitor control unit 204 sends a control signal to the calibration control unit 205 again to perform a control operation for calibration. (S308).

  It should be noted that whether or not the minimum value of DOP based on the calibration control of the calibration control unit 205 shows a certain improved value is the third value in which the minimum value of DOP has not decreased to the second threshold value. You may determine by setting a threshold value. That is, in this case, the calibration control is performed with the minimum value of DOP lowered to the second threshold, and as a result, the minimum value of DOP has been improved to the third threshold. The minimum value of the DOP based showed a certain improved value ".

  As described above, the chromatic dispersion Stokes vector measurement apparatus 20 according to the third embodiment uses the DOP reduction allowable value determined in the measurement example described with reference to FIG. 6 to obtain the DOP value that is constantly monitored. Various types of control can be executed. In the above description, it has been described that the feedback control of the calibration control unit 205 is performed when the comparison result “has reached the second threshold”. However, without providing the calibration control unit 205, when the comparison result “has reached the second threshold”, a message notifying the necessity of calibration may be output.

  As described above, in the chromatic dispersion Stokes vector measurement apparatus of the present embodiment, the degree of polarization used as an evaluation index for measurement accuracy is a physical parameter calculated from the wavelength-resolved Stokes vector. Therefore, the chromatic dispersion Stokes vector measurement apparatus of this embodiment does not require a special device only for accuracy monitoring, and can evaluate measurement accuracy at low cost. Moreover, since the measurement accuracy can be evaluated in real time without interfering with the original measurement, the chromatic dispersion Stokes vector measurement device of this embodiment can easily check the accuracy.

DESCRIPTION OF SYMBOLS 1, 10, 20 Wavelength-resolved Stokes vector measuring apparatus 2 Optical signal source 3 Optical fiber 4 Variable group delay time difference (DGD) generator 11 Wavelength sweep means 12 4 Polarization component intensity extraction means 13 Calculation means 41 Polarization controller 42 Optical delay Adjusters 43 and 44 Polarizing beam splitters 101 and 201 Variable optical bandpass filters 102 and 202 4 Polarization component intensity extraction units 103 and 203 Calculation units 104 and 204 Monitor unit 205 Calibration control unit

Claims (9)

Wavelength sweeping means for decomposing and outputting a plurality of wavelength components of an input optical signal having a specific wavelength bandwidth with a wavelength bandwidth narrower than the specific wavelength bandwidth;
4-polarized component intensity extracting means for inputting the respective optical signals of the wavelength components, extracting and outputting four different polarized component intensities of the respective optical signals;
Calculation is performed by inputting four different polarization component intensities of the optical signals of the wavelength components, and measuring the wavelength-resolved Stokes vectors of the optical signals of the wavelength components and calculating the degree of polarization based on the calculation results. The measurement accuracy of the wavelength-resolved Stokes vector is calculated based on the difference value between the calculated value of the polarization degree of each optical signal of the wavelength component and the theoretical value of the polarization degree of the optical signal of the wavelength component. A computing means for evaluating and outputting;
A wavelength-resolved Stokes vector measuring apparatus comprising: 2. The wavelength-resolved Stokes vector measurement device according to claim 1, wherein the wavelength sweeping unit is a variable optical bandpass filter that transmits light having a wavelength bandwidth of wavelength resolution possessed by the wavelength-resolved Stokes vector measurement device. . The computing means is
The wavelength-resolved Stokes vector of each optical signal of the wavelength component is measured by performing an operation based on the four different polarization component intensities of the optical signals of the wavelength component, and the measured wavelength-resolved Stokes vector A calculation unit for calculating the degree of polarization of each optical signal of the wavelength component based on,
The measurement accuracy of the wavelength-resolved Stokes vector is evaluated based on the difference value between the minimum calculated value of the polarization degree of each optical signal of the wavelength component and the theoretical value of the polarization degree of the optical signal of the wavelength component. A monitor unit that outputs the difference value, and the monitor unit does not reach the first threshold value of the difference value that determines that the measurement accuracy has deteriorated beyond an allowable value, and the first threshold value. 3. The wavelength-resolved Stokes vector measurement apparatus according to claim 2, wherein the measurement accuracy is evaluated using a second threshold value that is arbitrarily set, which is determined to be a deterioration in measurement accuracy. The monitor unit is
A degree of polarization input unit for inputting a calculated value of the degree of polarization of each optical signal of the wavelength component calculated by the arithmetic unit;
A comparison unit that compares a difference value between a minimum value of the calculated value of the degree of polarization and a theoretical value of the degree of polarization with the first threshold value and the second threshold value, and outputs a comparison result;
When the difference value reaches the first threshold value, the comparison result outputs an alarm notifying the outside of measurement accuracy deterioration, and the comparison result indicates that the difference value reaches the second threshold value. 4. The wavelength-resolved Stokes vector measurement according to claim 3, further comprising: a monitor control unit that outputs a signal for instructing externally calibration of a part that causes deterioration of the wavelength-resolved Stokes vector measurement device. apparatus. A calibration control unit that calibrates a site that causes deterioration by including an actuator that adjusts the alignment deviation of the optical system of the wavelength-resolved Stokes vector measurement device and a sensor that detects the deviation;
When the comparison result indicates that the difference value has reached the second threshold value, the monitor control unit transmits a control signal to the calibration control unit to execute calibration control, and the calibration control unit performs the calibration control. 5. The feedback control is performed until the difference value reaches an arbitrarily set third threshold value, which is determined that an improvement in measurement accuracy is recognized from the comparison result after the control execution. Wavelength-resolved Stokes vector measurement device. The input optical signal of a specific wavelength bandwidth is decomposed into a plurality of wavelength components with a wavelength bandwidth narrower than the specific wavelength bandwidth,
Extracting four different polarization component intensities of the respective optical signals of the wavelength components,
Based on the four different polarization component intensities of the optical signals of the extracted wavelength components,
Based on the calculation result, measurement of the wavelength-resolved Stokes vector of each optical signal of the wavelength component and calculation of the degree of polarization,
The measurement accuracy of the wavelength-resolved Stokes vector is evaluated and output based on the difference value between the calculated value of the polarization degree of each optical signal of the wavelength component and the theoretical value of the polarization degree of the optical signal of the wavelength component. And a wavelength-resolved Stokes vector measurement method. The wavelength bandwidth narrower than the specific wavelength bandwidth for decomposing the optical signal of the specific wavelength bandwidth into a plurality of the wavelength components is a wavelength bandwidth of wavelength resolution possessed by the wavelength-resolved Stokes vector measurement device. The wavelength-resolved Stokes vector measurement method according to claim 6. The difference value is a difference value between a minimum value of the calculated value of the polarization degree and a theoretical value of the polarization degree,
Evaluation of the measurement accuracy of the wavelength-resolved Stokes vector is:
A first threshold value of the difference value for determining that the measurement accuracy has deteriorated beyond an allowable value, and an arbitrary setting for determining that the measurement accuracy has been deteriorated although the first threshold value is not reached. Set a second threshold to
The wavelength-resolved Stokes vector measurement method according to claim 7, wherein the measurement accuracy is evaluated by comparing the difference value with the first threshold value and the second threshold value. When the comparison result between the difference value and the first threshold value and the second threshold value reaches the first threshold value, an alarm is output to notify the outside of measurement accuracy degradation. In the comparison result, when the difference value reaches the second threshold value, a signal instructing the outside to calibrate a portion that becomes a deterioration factor of the wavelength-resolved Stokes vector measurement device is output. The wavelength-resolved Stokes vector measurement method according to claim 8.

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