JP5223585B2 - Optical signal quality monitoring apparatus and optical signal quality monitoring method - Google Patents

Description

  The present invention relates to an optical signal quality monitoring apparatus and an optical signal quality monitoring method for detecting a polarization state fluctuation by monitoring a polarization state fluctuation amount.

  In recent years, with an increase in communication capacity, a transmission rate per optical signal channel of over 10 Gb / s has been put into practical use, and research and development of over 100 Gb / s has become active. In such an optical communication system, even a slight waveform deterioration due to optical transmission has a large effect on signal quality during reception.

  Physical phenomena that cause waveform degradation include chromatic dispersion, polarization dispersion, and nonlinear phenomena. Of these, chromatic dispersion and nonlinear phenomena can be avoided by transmission line design technology and signal compensation technology.

  However, there is currently no decisive workaround for polarization dispersion. For this reason, it has been important to monitor polarization dispersion with high accuracy and use it as a control signal for dynamic waveform distortion compensation or as a trigger signal for failure recovery.

  As an optical signal quality monitoring method, for example, as described in Non-Patent Document 1, a method has been proposed in which an optical frequency-resolved Stokes vector is measured and the trajectory length on the Poincare sphere is used as a scale (for example, non-patent document 1). Patent Document 1). Since this method can take into account even higher-order components of polarization dispersion, it is effective to apply to an optical transmission line having a large polarization dispersion and ultrahigh-speed optical signal transmission with a symbol rate exceeding 100 Gb / s.

  Further, Patent Document 1 discloses that a polarization mode dispersion failure is obtained by measuring the polarization of an optical signal using a heterodyne polarimeter, determining a related polarization state from the measured polarization parameter, and calculating the parameter from the polarization state. The technique which calculates | requires is disclosed.

  Further, Patent Document 2 discloses a coupler that generates a heterodyne signal having a radio frequency component by mixing a deflection scramble signal with an optical signal, and transmits polarization and frequency from a radio frequency (RF) component through a fixed polarization component. A technique for quickly and accurately measuring a polarization mode dispersion of a working channel is disclosed.

In Patent Document 3, a polarization scrambler that randomly changes the polarization state of the optical signal is provided between the optical amplification unit and the optical fiber transmission line, and the polarization state of the wavelength multiplexed optical signal is changed from the optical transmission device. Randomly change the transmission and average the bit error rate (BER) fluctuation due to the time fluctuation of the polarization mode dispersion (PMD) in the optical receiver, thereby reducing the influence of PMD and high-precision wavelength. Distributed control is realized.
JP 2004-138615 A Japanese Patent No. 2005-304048 Japanese Patent No. 2007-329558 JP-A-11-271143 KE Cornick, SD Dods, M. Boroditsky and PM Farrel, "All-Order PMD Penalty Prediction Using SOP String Lengths", LEOS 2005, WEE3, pp.702-703, Oct.2005.

  However, regarding the technique described in Non-Patent Document 1, since it is difficult to speed up the optical frequency-resolved Stokes vector measurement within the modulation band, if the polarization state changes during the measurement, the Stokes vector measurement value itself, And the amount of polarization dispersion estimated from it becomes inaccurate.

  That is, in order to perform optical frequency-resolved Stokes vector measurement, it is necessary to measure four different polarization components with respect to the optical spectrum of the optical signal to be measured. There are several combinations of what four different polarization components are measured. For example, for each optical frequency, a vertical linear polarization component Iv, a 45-degree linear polarization component Iq, and a clockwise circular polarization component There is a method for measuring Ir and the transmitted light component It.

  The Stokes vector is calculated from the four types of polarization component measurement values, but it is assumed that there is no polarization state fluctuation during measurement. Therefore, if polarization state fluctuation occurs during measurement, the Stokes vector measurement value cannot be obtained correctly. The amount of polarization dispersion can be estimated from the Stokes vector measurement value. When considering even higher-order components, it is necessary to perform optical frequency-resolved Stokes vector measurement with high optical frequency resolution. If the Stokes vector measurement value is inaccurate, the polarization dispersion amount estimation value will be inaccurate as well. End up.

  The polarization state fluctuation speed is fast and is on the order of msec. Therefore, the four types of polarization component measurements must be completed within a shorter time.

  By the way, the four types of polarization component measuring methods are roughly divided into two types. One is a method in which the polarization component is changed four times by a polarization controller or the like, and the other is a method in which a desired polarization component is simultaneously measured by dividing the optical signal into four.

  At first glance, since four types of polarization components are measured simultaneously, the four-branch method seems to be more advantageous for polarization state fluctuations, but it is necessary to perform optical frequency sweep within the modulation band with high resolution. Currently, high speed measurement is very difficult.

  Regarding the method of changing the polarization component four times, there is a method of increasing the measurement time by combining the method using the spectroscope and the light receiving element array and collectively measuring the optical frequency within the modulation band for each polarization component.

  However, for example, in a light-receiving element array using an InGaAs-based material, an accumulation time of several msec to several sec is required to ensure a sufficient S / N ratio, so that msec or less over the optical signal modulation band. Thus, it is difficult to measure four types of polarization components.

  In the case of optical frequency batch using a light receiving element array, for example, as described in Patent Document 4, it is difficult to arrange the light receiving elements at high density, so that it is difficult to realize high optical frequency resolution. There is also a problem that it is.

  In addition, with respect to the techniques described in Patent Documents 1 to 3, measurement is performed using a monitor alone. For example, in optical frequency-resolved Stokes vector measurement, high-precision measurement is realized. Measurement takes time. On the other hand, optical frequency average Stokes vector measurement has a problem of high speed but low accuracy.

  Therefore, the present invention has been made in view of the above problems, and an object thereof is to measure optical frequency-resolved Stokes vector in a short time and with high accuracy.

  In order to solve the above-described problems, the optical signal quality monitoring apparatus according to the present invention extracts light intensity components for each unit optical frequency over the entire area within the optical signal modulation bandwidth, and each of the light intensity components has a predetermined difference 4. Optical frequency-resolved Stokes vector measuring means that measures the Stokes vector by extracting four types of polarization components and calculating the four types of light intensity polarization components, and extracting four different types of polarization components from the average light intensity And an optical frequency average Stokes vector measuring means for measuring the Stokes vector by calculating four types of average light intensity polarization components, and a polarization for judging the occurrence of polarization state fluctuations from the measurement results by the optical frequency average Stokes vector measuring means. Wave state fluctuation determination means and the optical frequency component according to the occurrence of polarization state fluctuation detected by the polarization state fluctuation judgment means. Characterized in that it comprises an optical frequency decomposition Stokes vector reliability judging means for judging the reliability of the measurement result by the Stokes vector measurement means.

  The polarization state fluctuation determining means calculates a difference between a measurement value obtained by the optical frequency average Stokes vector measuring means and a predetermined reference value as a fluctuation amount, and the fluctuation amount is previously measured while the optical frequency-resolved Stokes vector measuring means is measuring. When a set threshold value is exceeded, occurrence of polarization state fluctuation is determined.

  The reference value is a value measured by the optical frequency average Stokes vector measuring unit at the time when the optical frequency-resolved Stokes vector measuring unit starts measurement.

  The optical frequency-resolved Stokes vector reliability determining means invalidates the measurement result of the optical frequency-resolved Stokes vector measuring means when the polarization state fluctuation occurs.

  The optical frequency-resolved Stokes vector reliability determining means replaces the measurement result of the optical frequency-resolved Stokes vector measuring means when the polarization state fluctuation occurs with the measurement result at the previous measurement.

  The optical frequency-resolved Stokes vector reliability determining means is characterized in that the measurement by the optical frequency-resolved Stokes vector measuring means is stopped when a polarization state fluctuation occurs.

  The optical frequency-resolved Stokes vector reliability determination unit is characterized in that when the polarization state fluctuation occurs, the measurement by the optical frequency-resolved Stokes vector measurement unit is performed again.

  SOP calculation means for calculating a one-dimensional quantity SOP (State of Polarization) from a measurement value by a multi-dimensional quantity optical frequency average Stokes vector measurement means, and using SOP instead of the optical frequency average Stokes vector And

  DOP calculating means for calculating DOP (Degree of Polarization), which is a one-dimensional quantity, from a value measured by an optical frequency average Stokes vector measuring means that is a multi-dimensional quantity, and using SOP instead of the optical frequency average Stokes vector And

  The length of the Stokes vector trajectory on the Poincare sphere is calculated from the measured value by the optical frequency-resolved Stokes vector measuring means, and the amount of quality degradation that the modulated signal light has received by the polarization dispersion in the transmission path is calculated from the length of the trajectory A first quality deterioration amount estimating means for estimating is provided.

  A second quality degradation amount estimation unit is provided that estimates a quality degradation amount received by the first-order polarization dispersion that the modulated signal light has received on the transmission path from a measurement value obtained by the optical frequency average Stokes vector measurement unit.

  A polarimeter is used as means for extracting four different types of polarized light components.

  A variable optical frequency bandpass filter is used as means for extracting the light intensity component for each optical frequency.

  In the optical signal quality monitoring method according to the present invention, the light intensity component for each unit optical frequency is extracted over the entire area within the optical signal modulation bandwidth, and four different types of polarization components different from each other for each light intensity component. An optical frequency-resolved Stokes vector measurement step for measuring the Stokes vector by extracting and calculating four types of light intensity polarization components, and extracting four different types of polarization components from the average light intensity, Optical frequency average Stokes vector measurement step for measuring the Stokes vector by calculating the average light intensity polarization component, and polarization state variation determination step for determining the occurrence of polarization state variation from the measurement result of the optical frequency average Stokes vector measurement step And the optical frequency according to the occurrence of the polarization state fluctuation detected in the polarization state fluctuation judgment step. And an optical frequency decomposition Stokes vector reliability determining step of determining the reliability of the measurement results by the solution Stokes vector measuring step, characterized in that it comprises a.

  According to the present invention, by monitoring the polarization state fluctuation during the low-speed optical frequency-resolved Stokes vector measurement, and determining whether the value of the optical frequency-resolved Stokes vector can be trusted by monitoring the optical frequency average Stokes vector measurement. It is possible to reduce the measurement time and measure with high accuracy.

  Next, the best mode for carrying out the invention will be described in detail with reference to the drawings.

  FIG. 1 is a configuration diagram of an optical signal quality measurement system according to an embodiment of the present invention. The present optical signal quality monitoring device includes an optical transmitter 1001, an optical transmission line 1002, an optical receiver 1003, an optical demultiplexer 1004, and an optical signal quality monitoring device 1100.

  An optical signal is output from the optical transmitter 1001, passes through the optical transmission line 1002, and is received by the optical receiver 1003. An optical demultiplexer 1004 is provided immediately before the optical receiver 1003, a part of the optical signal is branched for optical signal quality monitoring, and the optical signal branched for monitoring is sent to the optical signal quality monitoring apparatus 1100. It is guided.

  The optical signal quality monitoring apparatus 1100 includes an optical demultiplexer 1005, an optical frequency-resolved Stokes vector monitor 1006, an optical frequency average Stokes vector monitor 1007, and a CPU 1009.

  The optical signal guided from the optical demultiplexer 1004 is branched into two by the optical demultiplexer 1005, one is input to the optical frequency-resolved Stokes vector monitor 1006, and the other is input to the optical frequency average Stokes vector monitor 1007. The result of the input to each monitor is output to the CPU 1009.

  The CPU 1009 receives the monitoring results of the optical frequency-resolved Stokes vector monitor 1006 and the optical frequency average Stokes vector monitor 1008, and also performs operation control.

  Next, the operation of the optical signal quality monitoring apparatus 1100 will be described in detail with reference to FIG.

  An optical signal having a modulation rate of Bbps output from the optical transmitter 1001 passes through the optical transmission line 1002 and is received by the optical receiver 1003. The optical signal undergoes waveform distortion due to polarization dispersion while passing through the optical transmission line 1002, and when the waveform distortion increases, that is, the polarization dispersion increases, the code error rate in the optical receiver 1003 increases.

  An optical demultiplexer 1004 is provided immediately before the optical receiver 1003, and a part of the optical signal after transmission is guided to the optical signal quality monitoring apparatus 1100. The optical signal input to the optical signal quality monitoring apparatus 1100 is further split into two by an optical splitter 1005 inside the apparatus, one being an optical frequency-resolved Stokes vector monitor 1006 and the other being an optical frequency average Stokes vector monitor. 1007 is input.

  The optical frequency-resolved Stokes vector monitor 1006 is controlled by the CPU 1009, and the optical signal is changed from fc−B [Hz] to fc + B [Hz] within ± B [Hz] around the center optical frequency fc [Hz] of the optical signal. The Stokes vector is measured for each optical frequency over Tres [sec] in Δf steps.

  In the optical frequency-resolved Stokes vector monitor 1006, data of the number of samples 2B / Δf [pts] is obtained by one measurement, and the obtained measurement result is output to the CPU 1009. In order to correctly measure the optical frequency-resolved Stokes vector within the modulation band of the input optical signal, it is assumed that there is no change in the polarization state of the input optical signal during Tres.

  In the optical frequency average Stokes vector monitor 1007, since the optical frequency is not decomposed, the time Tavg [sec] required for one measurement is faster than Tres. The optical frequency average Stokes vector monitor device 1008 is always in a monitor state, and the monitor result is output to the CPU 1009.

  Since the CPU 1009 controls the optical frequency-resolved Stokes vector monitor 1006, the optical frequency sweep start time Ts and end time Te are known. here,

  The relationship is established. The CPU 1009 stores the optical frequency average Stokes vector Ss (avg) at the time Ts.

  Then, the CPU 1009 compares the optical frequency average Stokes vector St (avg) and Ss (avg) at a certain time T between the times Ts and Te, and calculates the fluctuation amount ΔSt (avg).

  The CPU 1009 compares this ΔSt (avg) with a preset fluctuation amount threshold value ΔSth (avg), and recognizes that the polarization state fluctuation occurrence state when ΔSt (avg) exceeds ΔSth (avg). . In this way, the CPU 1009 can recognize whether or not the polarization state fluctuation has occurred during one measurement by the optical frequency-resolved Stokes vector monitor 1006.

  When the polarization state fluctuation occurs, the time Ts when the optical frequency-resolved Stokes vector monitor 1006 starts one measurement at the time Ta when the polarization state fluctuation is recognized by the CPU 1009 and the input deviation to the optical signal quality monitoring apparatus 1100. Since the wave state has changed, the output optical frequency-resolved Stokes vector results from monitoring under different input conditions for Ts and Ta. For this reason, the optical frequency-resolved Stokes vector monitor 1006 cannot correctly measure the optical frequency-resolved Stokes vector, which contributes to errors and reduces the reliability of the optical signal quality monitor result.

  In order to prevent a decrease in the reliability of the optical signal quality monitor result, when the optical frequency-resolved Stokes vector monitor 1006 recognizes the polarization state fluctuation occurrence state in the CPU 1009 during one measurement, the light obtained at the end of the measurement. Disable frequency-resolved Stokes vector monitor. As a result, only the optical frequency-resolved Stokes vector monitor result determined to be valid by the CPU 1009 is guaranteed to have no polarization state fluctuation of the input optical signal being monitored. It will be measured correctly.

  Instead of invalidating, the previous optical frequency-resolved Stokes vector measurement value may be used as the measurement value at the time of occurrence of the polarization state fluctuation, or the measurement itself is repeated or the measurement of the optical frequency-resolved Stokes vector is stopped. You may do it. Further, the fluctuation amount ΔSt (avg) may be a difference between a predetermined reference value and the optical frequency average Stokes vector St (avg).

  The length of the Stokes vector locus on the Poincare sphere is calculated from the optical frequency-resolved Stokes vector measurement value measured by the above configuration, and the amount of quality degradation that the modulated signal light has received by the polarization dispersion in the transmission path from the locus length. The reliability can be improved by calculating. Note that it is possible to further improve the reliability by calculating the quality deterioration amount from the optical frequency average Stokes vector measurement value at the same time.

  According to the present embodiment configured as described above, the optical frequency average Stokes vector is measured during the measurement of the optical frequency-resolved Stokes vector within the modulation band, and the presence or absence of polarization state fluctuation is monitored. When the polarization state fluctuation exceeds a predetermined threshold value, it is determined that the optical frequency-resolved Stokes vector measurement value being measured is invalid. The optical frequency-resolved Stokes vector measurement requires N measurements when the light intensity is measured for each of N types of optical frequencies, whereas the optical frequency average Stokes vector measurement measures the optical intensity averaged once. 1 / N times of measurement is required.

  Therefore, the optical frequency average Stokes vector measurement is faster than the optical frequency resolved Stokes vector measurement, and can be said to be a measurement speed capable of detecting high-speed polarization state fluctuation during the optical frequency resolved Stokes vector measurement.

  During optical frequency-resolved Stokes vector measurement, since the optical frequency average Stokes vector measurement value can know the presence or absence of polarization state fluctuation by the presence or absence of fluctuations more than a predetermined threshold, which timing measurement result can be trusted, Judgment of untrustworthiness can be made. Therefore, the reliability of the optical frequency-resolved Stokes vector measurement result can be improved, and the reliability of the polarization dispersion amount estimated from the measurement result can be improved as well.

  FIG. 2 shows an optical frequency-resolved Stokes vector monitor using a variable optical bandpass filter (hereinafter referred to as variable optical BPF) 2006 having a transmission bandwidth Δf and a polarimeter 2007 in combination with a polarimeter 2008 as an optical frequency average Stokes vector monitor. It is an example using. Since other configurations are the same as those in FIG. 1, the description thereof is omitted.

  According to this configuration, the CPU 2009 can measure the optical frequency-resolved Stokes vector for each Δf within the modulation band of the input optical signal by controlling the variable optical BPF 2006.

  Next, the operation of the optical signal quality monitoring apparatus 2100 will be described in detail with reference to FIG.

  Operations in the optical transmitter 2001, the optical transmission line 2002, the optical receiver 2003, and the optical splitter 2004 are the same as those in FIG.

  One of the optical signals branched into two by the optical branching device 2005 in the optical signal quality monitoring apparatus 2200 is input to the polarimeter 2007 via the variable optical BPF 2006, and the other is input to the polarimeter 2008.

  The variable optical BPF 2006 having a transmission bandwidth Δf performs the same optical frequency sweeping operation as the optical frequency-resolved Stokes vector monitor 1006 in FIG.

  Since the polarimeter 2008 receives an optical signal that is not swept by the optical frequency, the optical frequency average Stokes vector is monitored.

  The time Tstokes [sec] required for one monitoring of the polarimeter 2008 is shorter than the time polarimeter Tbpf [sec] required for the polarimeter 2007, and 2007 takes fc ± B [Hz] over Tbpf [sec]. ], The polarimeter 2008 can monitor the optical frequency average Stokes vector at least 2B / Δf times (2B / Δf times faster). The polarimeter 2008 is always in a state of monitoring the optical frequency average Stokes vector, and the monitoring result is output to the CPU 2009.

  The CPU 2009 performs optical frequency sweep control. here,

  The relationship is established. Further, the CPU 2009 calculates the polarization state fluctuation amount ΔSt (avg) at times Ts and T.

  Since the Stokes vectors (S0, S1, S2, S3) are four-dimensional quantities and multivariables, SOP (State of Polarization) is used instead to simplify processing. SOP is calculated by the following equation.

  That is, the SOP value calculated from the optical frequency average Stokes vector at time Ts is used as Ss (avg). The same applies to St (avg). Therefore, the fluctuation amount ΔSt (avg) is the fluctuation amount of the SOP value. Also, ΔSth (avg) is converted into an SOP value and used.

  The CPU 2009 compares ΔSt (avg) with a preset fluctuation amount threshold value ΔSth (avg) and recognizes whether or not the polarization state fluctuation has occurred during the optical frequency sweep of the variable optical BPF 2006. At this time, when the polarization state fluctuation occurs, the reliability of the optical signal quality monitor result is lowered as in FIG.

  Therefore, in order to prevent the reliability of the optical signal quality monitoring result from being lowered, when the polarization state fluctuation occurrence state is recognized by the CPU 2009 during the optical frequency sweep of the variable optical BPF 2006, the optical frequency resolution Stokes obtained at the end of the sweep. Invalidate vector monitor results.

  Further, DOP (Degree of Polarization) may be used as another one-dimensional quantity instead of SOP.

  Next, the operation when invalidating the optical frequency-resolved Stokes vector monitor result will be described in detail with reference to FIG. FIG. 3 is a flowchart of the optical signal quality monitoring apparatus in the present embodiment.

  When the optical signal is input to the optical signal quality monitoring device 2100, the CPU 2009 issues an optical frequency-resolved Stokes vector monitor start command (step S3001), and the variable optical BPF 2006 and the polarimeter 2007 prepare for starting the optical frequency sweep measurement operation. (Step S3002).

  The CPU 2009 sets fc-B as the transmission center optical frequency initial value f (0) in the variable light BPF 2006, and operates the variable light BPF 2006 (step S3003). At the same time, the CPU 2009 reads the optical frequency average Stokes vector monitor result from the polarimeter 2008 (step S3004) and stores it as the optical frequency average Stokes vector monitor result Ss (avg) at the start of the optical frequency sweep operation (step S3005).

  Then, the CPU 2009 reads the Stokes vector at the optical frequency f (0) from the polarimeter 2007 (step S3006). After the reading is completed, the CPU 2009 instructs the variable light BPF 2006 to move the transmission center optical frequency to f (i + 1) = f (i) + Δf (i = 0, 1, 2,...). The operation is repeated (step S3007) until f (i + 1) exceeds the modulation band fc + B of the optical signal (step S3008). If it has exceeded, it is determined that one optical frequency sweep operation has been completed, and then the next optical frequency sweep operation is started (step S3002).

  In step S3008, when f (i + 1) is equal to or less than fc + B within the modulation band of the optical signal, the CPU 2009 reads the optical frequency average Stokes vector monitor result from the polarimeter 2008 (step S3009) and sets it as the current value St (avg). Save (step S3010). Here, the CPU 2009 calculates a difference ΔSt (avg) between St (avg) and Ss (avg) (step S3011), and whether ΔSt (avg) exceeds a predetermined polarization state fluctuation threshold ΔSth (avg). It is determined whether or not (step S3012).

  When the CPU 2009 determines that ΔSt (avg) is equal to or smaller than ΔSth (avg), the Stokes vector at the optical frequency f (i + 1) is read from the polarimeter 2007 (step S3013), and the transmission center optical frequency of the variable optical BPF is further calculated by Δf. Only move (step S3007).

  As long as the condition is satisfied in the determination in step S3012, the optical frequency-resolved Stokes vector is read into the CPU 2009 for each Δf by the variable optical BPF 2006 and the polarimeter 2007, that is, the condition is satisfied in the determination in step S3008, that is, f (i + 1) When> fc + B is satisfied, one optical frequency sweep operation is completed.

  If the condition of step S3012 is not satisfied during the above-described optical frequency sweep operation, all the optical frequency-resolved Stokes vector monitor results measured in step S3013 are invalidated and the optical frequency sweep operation is repeated (step S3002). ).

  When the optical frequency-resolved Stokes vector monitor realized by the variable optical BPF 2006 and the polarimeter 2007 and the optical frequency average Stokes vector monitor realized by the polarimeter 2008 operate in synchronization, the optical frequency-resolved Stokes vector monitor results are valid. A method of invalidation will be described in detail with reference to FIG.

  It is assumed that the optical frequency-resolved Stokes vector measurement value at a certain time T1 is P1. At time T1 to T2, the CPU 2009 detects the occurrence of polarization state fluctuation from the optical frequency average Stokes vector measured by the polarimeter 2008.

  The CPU 2009 continues to instruct the variable optical BPF 2006 to redo the optical frequency sweep until time T2 when the state of occurrence of the polarization state fluctuation is canceled. That is, the variable light BPF 2006 remains fixed at the optical frequency fc-B between the times T1 and T2.

  When the CPU 2009 cancels the state of occurrence of polarization state change at time T2, the variable optical BPF restarts the optical frequency sweep from fc-B in Δf steps. When the occurrence of a change in polarization state is detected again at time T3 (however, T3-T2 <Tbpf), the CPU 2009 continues to instruct the variable optical BPF 2006 again to repeat the optical frequency sweep from T3 to T4. .

  At time T3, since the optical frequency sweep started from time T2 has not been completed, the optical frequency-resolved Stokes vector measurement value measured in the Δf step from time T2 to T3 is discarded.

  When the occurrence of the polarization state fluctuation is canceled at time T4, the optical frequency sweep is resumed. Since the optical frequency sweep resumed at time T4 ends normally at time T5, the optical frequency-resolved Stokes vector monitor value is updated from P1 to P3.

  Similarly, since normal optical frequency sweep is performed at times T5 to T6, the optical frequency-resolved Stokes vector monitor value is updated from P3 to P2 at time T6. Similarly, the optical frequency-resolved Stokes vector monitor value is updated only when the occurrence of polarization state fluctuation is not detected by the CPU 2009 while the variable optical BPF 2006 sweeps the optical frequency within the input optical signal band.

  Although the optical frequency-resolved Stokes vector monitor realized by the variable optical BPF 2006 and the polarimeter 2007 and the optical frequency average Stokes vector monitor realized by the polarimeter 2008 have been described as operating synchronously, the synchronous operation is not necessarily performed. It is not necessary, and the optical frequency average Stokes vector monitor can be always operated, and thereafter the optical frequency resolved Stokes vector monitor can be started and stopped at a timing desired by the user.

  According to the above embodiment, only the optical frequency decomposition Stokes vector monitor result determined to be valid by the CPU 2009 is guaranteed to have no polarization state fluctuation of the input optical signal being monitored. The Stokes vector monitor is correctly measured.

  As described above, it is possible to improve the reliability of the optical frequency-resolved Stokes vector and the estimated polarization dispersion amount obtained therefrom.

  FIG. 5 is a configuration diagram of an optical signal quality monitoring device 4100 according to another embodiment of the present invention. In this embodiment, a polarization controller 4006, a spectroscope 4007, and a photodetector array 4010 are used in combination as an optical frequency-resolved Stokes vector monitor. A polarimeter 4008 is used as an optical frequency average Stokes vector monitor. Note that description of other components similar to those in FIG. 1 is omitted.

  In the optical signal quality monitor device 4100, the CPU 4009 controls the polarization controller 4006 to switch the polarization state of the input optical signal, and the spectroscope 4007 and the photodetector array 4010 measure the optical spectrum for each polarization state. It is possible to monitor the optical frequency-resolved Stokes vector.

  The polarization controller 4006 can output the vertical linear polarization component Sv, 45 degree linear polarization component Sq, clockwise circular polarization component Sr, and transmitted light component St of the input light. Since the spectroscope 4007 changes the traveling direction of the output light according to the optical frequency of the input light, the optical spectrum intensity of the input light of the spectroscope 4007 is measured by measuring the position and intensity of the input light in the photodetector array 4010. can do. Therefore, the optical frequency-resolved Stokes vector can be monitored by measuring the optical spectrum intensities Iv, Iq, Ir, It corresponding to Sv, Sq, Sr, St.

  In order to measure the optical spectrum intensity with high optical frequency resolution, a photon accumulation time of at least several milliseconds is required in the photodetector array 4010. However, if the polarization fluctuation occurs during the photon accumulation time, the measurement result becomes inaccurate. Therefore, the polarimeter 4008 monitors whether or not the polarization state fluctuation of the input light occurs during the accumulation time. Determine whether.

  If it is determined that the measurement result is inaccurate due to polarization state fluctuations during measurement, the measurement result is invalidated, and the effective measurement result obtained from the optical frequency-resolved Stokes vector monitor is invalidated. Since the reliability can be confirmed, the reliability of the polarization dispersion amount estimation value obtained therefrom can be improved.

  The first effect of the embodiment of the present invention is that high reliability can be obtained. The reason is that only effective optical frequency-resolved Stokes vector measurement values are adopted as monitoring results.

  The second effect is that realization of high reliability is easy. The reason is that in order to achieve high reliability with the conventional method, it is indispensable to realize a high-speed and high-precision optical frequency-resolved Stokes vector. However, since speed and accuracy are in a trade-off relationship, While this is difficult to achieve, in the present embodiment, by combining a low-speed optical frequency-resolved Stokes vector monitor that is easy to realize and a high-speed optical frequency average Stokes vector monitor that is easy to realize, it is highly reliable as a whole. This is because a monitor can be realized.

  The third effect is high versatility. The reason for this is that with respect to the optical frequency-resolved Stokes vector monitor method, a method of taking out the polarization component after sweeping the optical frequency, a method of sweeping the optical frequency after switching the polarization component can be applied. Instead, it is possible to perform optical frequency batch measurement by combining a spectroscope and a photodetector array, and a plurality of optical frequency-resolved Stokes vector monitoring methods can be used.

  The fourth effect is low cost. The reason for this is that if a method of measuring optical frequency-resolved Stokes vectors that is faster than the polarization state variation is adopted as a means to increase the reliability of monitoring results, the optical frequency batch measurement method is very expensive, even if it can be realized. It is predicted that This is because, in this embodiment, even if the optical frequency-resolved Stokes vector monitor is low speed, it is possible to achieve high reliability of the monitor result only by assisting the high-speed optical frequency average Stokes vector monitor.

  The fifth effect is that the application range is wide. This is because the present invention does not depend on the signal light speed or the signal center optical frequency.

  The present invention has been described above by the preferred embodiments of the present invention. While the invention has been described with reference to specific embodiments thereof, various modifications and changes can be made to these embodiments without departing from the broader spirit and scope of the invention as defined in the claims. is there.

It is a lineblock diagram of the light quality measuring system concerning the embodiment of the present invention. It is a block diagram of the optical quality measurement system which concerns on other embodiment of this invention. It is a flowchart figure of the optical signal quality monitor apparatus in embodiment of this invention. It is a figure explaining the method to validate / invalidate the result of optical frequency decomposition Stokes vector monitor. It is a block diagram of the optical quality measurement system which concerns on other embodiment of this invention.

Explanation of symbols

1001 Optical Transmitter 1002 Optical Transmission Line 1003 Optical Receiver 1004 Optical Demultiplexer 1005 Optical Demultiplexer 1006 Optical Frequency Resolved Stokes Vector Monitor 1007 Optical Frequency Average Stokes Vector Monitor 1009 CPU
DESCRIPTION OF SYMBOLS 1100 Optical signal quality monitor apparatus 2001 Optical transmitter 2002 Optical transmission line 2003 Optical receiver 2004 Optical demultiplexer 2005 Optical demultiplexer 2006 Variable optical band-pass filter 2007 Polarimeter 2008 Polarimeter 2009 CPU
2100 Optical signal quality monitoring device 4001 Optical transmitter 4002 Optical transmission line 4003 Optical receiver 4004 Optical demultiplexer 4005 Optical demultiplexer 4006 Polarization controller 4007 Spectrometer 4008 Polarimeter 4009 CPU
4010 Photodetector array 4100 Optical signal quality monitoring device

Claims (14)

A light intensity component for each unit optical frequency is extracted over the entire area within the optical signal modulation bandwidth, and four different kinds of polarized light components are extracted for each of the light intensity components, and the four kinds of light intensity polarizations are extracted. Optical frequency-resolved Stokes vector measurement means for measuring a Stokes vector by calculating components;
Optical frequency average Stokes vector measurement means for extracting four different types of polarization components from the average light intensity and measuring the Stokes vector by calculating the four types of average light intensity polarization components;
Polarization state fluctuation determining means for determining the occurrence of polarization state fluctuation from the measurement result by the optical frequency average Stokes vector measuring means;
An optical frequency-resolved Stokes vector reliability determination unit that determines the reliability of the measurement result by the optical frequency-resolved Stokes vector measurement unit according to the occurrence of the polarization state variation detected by the polarization state variation determination unit; An optical signal quality monitoring device comprising:   The polarization state fluctuation determining means calculates a difference between a measurement value obtained by the optical frequency average Stokes vector measurement means and a predetermined reference value as a fluctuation amount, and the optical frequency resolved Stokes vector measurement means 2. The optical signal quality monitoring apparatus according to claim 1, wherein occurrence of the polarization state fluctuation is determined when the fluctuation amount exceeds a preset threshold value.   3. The optical signal quality monitoring apparatus according to claim 2, wherein the reference value is a measurement value obtained by the optical frequency average Stokes vector measurement unit at the time when measurement is started by the optical frequency-resolved Stokes vector measurement unit.   4. The optical frequency-resolved Stokes vector reliability determination unit invalidates a measurement result of the optical frequency-resolved Stokes vector measurement unit when the polarization state fluctuation occurs. 2. An optical signal quality monitoring apparatus according to item 1.   2. The optical frequency-resolved Stokes vector reliability determining means replaces the measurement result of the optical frequency-resolved Stokes vector measuring means when the polarization state fluctuation occurs with the measurement result at the previous measurement. 4. The optical signal quality monitoring device according to any one of items 1 to 3.   4. The optical frequency-resolved Stokes vector reliability determining unit stops measurement by the optical frequency-resolved Stokes vector measuring unit when the polarization state fluctuation occurs. The optical signal quality monitoring device according to the item.   4. The optical frequency-resolved Stokes vector reliability determination unit re-measures the optical frequency-resolved Stokes vector measurement unit again when the polarization state fluctuation occurs. The optical signal quality monitoring device according to the item.   SOP calculation means for calculating a one-dimensional quantity SOP (State of Polarization) from a measurement value by a multi-dimensional quantity optical frequency average Stokes vector measurement means, and using SOP instead of the optical frequency average Stokes vector The optical signal quality monitoring apparatus according to any one of claims 1 to 7. DOP calculating means for calculating DOP (Degree of Polarization), which is a one-dimensional quantity, from a value measured by the optical frequency average Stokes vector measuring means, which is a multidimensional quantity, and using DOP instead of the optical frequency average Stokes vector The optical signal quality monitoring apparatus according to any one of claims 1 to 7.
  The length of the Stokes vector trajectory on the Poincare sphere is calculated from the measured value by the optical frequency-resolved Stokes vector measuring means, and the amount of quality degradation that the modulated signal light has received by the polarization dispersion in the transmission path from the length of the trajectory 10. The optical signal quality monitoring apparatus according to claim 1, further comprising first quality deterioration amount estimation means for estimating   2. A second quality deterioration amount estimating means for estimating a quality deterioration amount received by the first-order polarization dispersion that the modulated signal light received in the transmission line from a measurement value obtained by the optical frequency average Stokes vector measuring means. Item 11. The optical signal quality monitoring device according to Item 10.   The optical signal quality monitoring apparatus according to any one of claims 1 to 11, wherein a polarimeter is used as means for extracting the four different kinds of polarized components different from each other.   The optical signal quality monitoring apparatus according to any one of claims 1 to 12, wherein a variable optical frequency bandpass filter is used as means for extracting a light intensity component for each optical frequency. A light intensity component for each unit optical frequency is extracted over the entire area within the optical signal modulation bandwidth, and four different kinds of polarized light components are extracted for each of the light intensity components, and the four kinds of light intensity polarizations are extracted. An optical frequency-resolved Stokes vector measurement step for measuring a Stokes vector by computing components;
An optical frequency average Stokes vector measuring step of extracting a predetermined four different polarization components from the average light intensity and measuring a Stokes vector by calculating the four types of average light intensity polarization components;
A polarization state fluctuation determining step for determining occurrence of a polarization state fluctuation from a measurement result of the optical frequency average Stokes vector measurement step;
An optical frequency-resolved Stokes vector reliability determination step for determining reliability of a measurement result obtained by the optical frequency-resolved Stokes vector measurement step according to the occurrence of the polarization state variation detected by the polarization state variation determination step; An optical signal quality monitoring method comprising:

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