JP2010226499A - Optical signal quality-monitoring system, optical signal quality monitor, optical signal transmitter, and method of monitoring optical signal quality - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical signal quality-monitoring system, device, and method, and an optical signal transmitter, which can monitor a polarized state of each polarization channel without performing optical polarization separation of data modulated light. <P>SOLUTION: An optical signal quality monitor has a transmitter 10 and an optical signal quality monitor 30. The transmitter 10 includes a modulating section 11 for modulating a carrier light at a different frequency for each polarization channel and a polarization multiplexing section 12 that performs polarization multiplexing of the polarization channels and outputs them to an optical transmission line 20. The optical signal quality monitor 30 includes a polarization component detecting section 31 that extracts a light intensity component of each unit light frequency over the entire modulation bandwidth of a received data-modulated light signal and detects four kinds of polarization components for each light intensity component at each unit light frequency, a Stokes vector-calculating section 32 for calculating a Stokes vector by calculating the intensity of four kinds of light intensity polarization components, and an intensity extracting section 33 for extracting, from the Stokes vector, the intensity of a frequency modulation component added to each polarization channel. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an optical signal quality monitoring technique in an optical communication system, and performs polarization dispersion monitoring in service without polarization separation by modulating the carrier frequency of an optical signal to be polarization multiplexed at an appropriate frequency. The present invention relates to an optical signal quality monitoring system, an optical signal quality monitoring device, an optical signal transmission device, and an optical signal quality monitoring method.

  In recent years, polarization multiplexing technology that multiplexes two optical signals in two orthogonal polarization states has been spotlighted. This is because if the transmission symbol rate per channel is the same, the transmission throughput is doubled compared to the case where polarization multiplexing is not performed.

  For example, when realizing a 100 Gb / s optical communication system, when polarization multiplexing is not performed, since 100 Gb / s communication is performed with one channel, it is necessary that the optical components and electrical components constituting the system operate at 100 Gb / s. is there. On the other hand, in the case of polarization multiplexing, since 100 Gb / s communication is performed with two channels, the optical components and electrical components constituting the system only need to operate at 50 Gb / s, and the system speed can be easily increased. There is.

  However, even if the symbol rate per channel is halved by polarization multiplexing, in order to realize an optical transmission system with a throughput exceeding 100 Gb / s, the symbol rate per channel still exceeds 10 Gb / s. There are almost no cases.

  In a large-capacity optical communication system in which the symbol rate per channel exceeds 10 Gb / s, even if slight waveform deterioration due to optical transmission has a large effect on signal quality during reception, as in the case where polarization multiplexing is not performed. Become.

  Physical phenomena that cause waveform degradation include chromatic dispersion, polarization dispersion, and nonlinear phenomena. Among these, regarding chromatic dispersion, there is currently no decisive workaround.

  Therefore, it is important to monitor polarization dispersion with high accuracy and use it as a control signal for dynamic waveform distortion compensation and as a trigger signal for fault recovery. Are disclosed in Patent Documents 1 and 2, Non-Patent Document 1, and the like.

  Further, in the case of a polarization multiplexed signal, there are cases where optical signal deterioration factors peculiar to the polarization multiplexed signal such as crosstalk between polarization channels caused by polarization dependent loss cannot be ignored.

Japanese Patent Laid-Open No. 2005-304048 JP 2003-270097 A

K. E. Cornick, S.M. D. Dods, M.M. Boroditsky and P.M. M.M. Farrel, "All-Order PMD Penalty Prediction Usage SOP String Lengths", LEOS 2005. , WEE3, pp. 702-703, Oct. 2005.

  In a polarization multiplexed signal, since two different polarization states exist simultaneously in one optical signal optical frequency component, the methods disclosed in Patent Documents 1 and 2 and Non-Patent Document 1 are not suitable. One of the major challenges is the inability to represent wave conditions.

  That is, in the methods disclosed in these documents, four polarization components are extracted for each optical frequency, a Stokes vector is calculated from the light intensity, a polarization state is specified, and polarization dispersion monitoring is performed. It has become. This Stokes vector calculation method assumes that there is only one polarization state for each optical frequency. In the case of a polarization multiplexed signal, since two different polarization states are included in the same optical frequency component, when the same method is adopted, the polarization information calculated for the two multiplexed polarization signals Therefore, the state change to be detected for each polarization cannot be detected. Therefore, the Stokes vector calculation method cannot be applied to polarization multiplexed signals.

  The present invention has been made in view of such a problem, and the polarization of each polarization channel without optically polarization-separating the data-modulated light in which the frequency of the channel light is modulated at a different frequency for each polarization channel. An object of the present invention is to provide an optical signal quality monitoring system, an optical signal quality monitoring device, an optical signal transmission device, and an optical signal quality monitoring method capable of monitoring the state.

  In order to achieve the above object, the present invention provides, as a first aspect, means for modulating the frequency of the carrier light of the data modulated optical signal with a different frequency for each polarization channel, A light intensity component for each unit optical frequency is extracted over the entire area within the modulation bandwidth of the data-modulated optical signal received via the optical transmission path; Stokes vector by calculating means for detecting four different kinds of polarized light components for each light intensity component and calculating the intensity of the four light intensity polarized components for each frequency modulation component added for each polarization channel And a monitor device comprising means for calculating the intensity of the frequency modulation component added for each polarization channel from the Stokes vector. There is provided an optical signal quality monitoring system.

  In order to achieve the above object, according to a second aspect of the present invention, there is provided a data modulated optical signal modulated at different frequencies for each polarization channel, polarization multiplexed and transmitted via an optical transmission line. Means for extracting a light intensity component for each unit optical frequency over the entire area within the modulation bandwidth, detecting four different types of polarization components for each light intensity component for each unit optical frequency, and for each polarization channel Means for calculating the intensity of the four types of light intensity polarization components for each frequency modulation component added to, and means for extracting the intensity of the frequency modulation component added for each polarization channel from the Stokes vector; An optical signal quality monitoring device characterized by comprising:

  In order to achieve the above object, as a third aspect, the present invention provides means for modulating the frequency of the carrier light of the data modulated optical signal with a different frequency for each polarization channel, and polarization multiplexing the polarization channel. And an optical signal transmission device including means for outputting to an optical transmission line.

  In order to achieve the above object, according to a fourth aspect of the present invention, the frequency of the carrier light of the data modulated optical signal is modulated with a different frequency for each polarization channel, and the polarization channel is polarization multiplexed and optically multiplexed. The light intensity component for each unit optical frequency is extracted over the entire range within the modulation bandwidth of the data modulated optical signal, and four different types of polarized light different from each other for each light intensity component for each unit optical frequency. Detects the component, calculates the Stokes vector by calculating the intensity of the four types of light intensity polarization components for each frequency modulation component added for each polarization channel, and adds the frequency modulation component for each polarization channel from the Stokes vector It is an object of the present invention to provide an optical signal quality monitoring method characterized by extracting the intensity of light.

  According to the present invention, the optical signal quality monitor that can monitor the polarization state of each polarization channel without optically polarization-separating the data modulated light whose frequency of the channel light is modulated at a different frequency for each polarization channel. A system, an optical signal quality monitoring device, an optical signal transmission device, and an optical signal quality monitoring method can be provided.

It is a figure which shows the function structure of the optical signal quality monitor apparatus which concerns on suitable embodiment of this invention. It is a figure which shows the structure of the optical signal quality monitoring system which concerns on suitable embodiment of this invention. It is a figure which shows the relationship between FM modulation frequency, a variable optical bandpass filter optical frequency resolution, and the frequency resolution of RF analyzer. An example of implementation of an optical signal quality monitoring system is shown. It is a figure which displays and displays the Stokes vector of the monitored optical signal on a Poincare sphere.

A preferred embodiment of the present invention will be described.
FIG. 1 shows a functional configuration of an optical signal quality monitoring apparatus according to a preferred embodiment of the present invention. The optical signal quality monitoring apparatus includes a modulation unit 11 that modulates the frequency of carrier light at a different frequency for each polarization channel, and a polarization multiplexing unit 12 that polarization-multiplexes the polarization channel and outputs the polarization channel to the optical transmission line 20. The light intensity component for each unit optical frequency is extracted over the entire area within the modulation bandwidth of the received data-modulated optical signal, and four types of polarization components are obtained for each light intensity component for each unit optical frequency. Polarization component detection unit 31 to detect, Stokes vector calculation unit 32 that calculates the Stokes vector by calculating the intensity of the four types of light intensity polarization components, and the intensity of the frequency modulation component added for each polarization channel from the Stokes vector And an optical signal quality monitoring device 30 provided with an intensity extracting unit 33 for extracting.

FIG. 2 shows a specific configuration of the optical signal quality monitoring system according to the present embodiment. An optical signal OPT-SIG1 linearly polarized in the X direction is output from the optical transmitter 1003. Further, OPT_SIG1 is intensity modulated (AM modulated) with the output frequency f1 from the frequency generator 1001. From the optical transmitter 1004, an optical signal OPT_SIG2 linearly polarized in the Y direction is output. OPT_SIG2 is AM-modulated at the output frequency f2 from the frequency generator 1002. Then, OPT_SIG1 and OPT_SIG2 are polarization multiplexed by the polarization multiplexer 1005 and transmitted to the optical transmission line 1006. The polarization multiplexed optical signal that has passed through the optical transmission line 1006 is input to the optical signal quality monitoring apparatus 1100. Inside the optical signal quality monitoring apparatus 1100, the polarization multiplexed optical signal is sequentially guided to the variable optical bandpass filter 1007, the polarimeter 1008, and the RF analyzer 1009. Finally, the CPU 1010 obtains an optical signal quality monitor result due to polarization dispersion.
The frequency generators 1001 and 1002 and the optical transmitters 1003 and 1004 correspond to the modulation unit 11 in FIG. The polarization multiplexer 1005 corresponds to the polarization multiplexing unit 12 in FIG. The optical transmission line 1006 corresponds to the optical transmission line 20 in FIG. A combination of the variable optical bandpass filter 1007 and the CPU 1010 corresponds to the polarization component detection unit 31 in FIG. A combination of the polarimeter 1008 and the CPU 1010 corresponds to the Stokes vector calculation unit 32 in FIG. A combination of the RF analyzer 1009 and the CPU 1010 corresponds to the intensity extraction unit 33 in FIG.

The operation will be described.
The optical transmitter 1003 outputs an optical signal OPT_SIG1 linearly polarized in the X direction in which AM modulation of a frequency f1 [Hz] slower than B is superimposed on the data modulation signal at a data modulation speed B [bps]. Similarly, an optical signal OPT_SIG2 linearly polarized in the Y direction in which AM modulation of f2 [Hz] is superimposed on the data modulation signal is output from the optical transmitter 1004 at the data modulation rate B [bps]. OPT_SIG1 and OPT_SIG2 are polarization multiplexed by the polarization multiplexer 1005 with the polarization states being orthogonal. This polarization multiplexed optical signal passes through the optical transmission line 1006 and is input to the optical signal quality monitoring apparatus 1100.

  Inside the optical signal quality monitoring apparatus 1100, the polarization multiplexed optical signal is sequentially guided to the optical bandpass filter 1007, the polarimeter 1008, and the RF analyzer 1009.

  The optical bandpass filter 1007 is controlled by the CPU 1010 and transmits an optical signal from Fc−B [Hz] to Fc + B [Hz] within a range of ± B [Hz] in the vicinity of the optical carrier frequency Fc [Hz]. A Stokes vector is measured for each optical frequency over Tres [sec] with a frequency resolution ΔF [Hz]. Therefore, the Stokes vector data of the number of samples 2B / ΔF [pts] can be obtained by one optical signal quality monitor. If the speed change of polarization dispersion is Tpmd [sec], the optical bandpass filter 1007 is controlled by the CPU 1010 so that Tres <Tpmd.

The polarimeter 1008 is controlled by the CPU 1010, and the Stokes vector is measured by the polarimeter 1008 for each light intensity data point of 2B / ΔF [pts]. In the polarimeter 1008, the Stokes vectors (S1, S2, S3) are measured by extracting the light intensity of four different polarization components from the input polarization multiplexed optical signal. Specifically, the voltage conversion value Vt [dBm] of the transmitted light intensity, the voltage conversion value Vh [dBm] of the linear horizontal polarization component intensity, the voltage conversion value Vq [dBm] of the 45 ° linear polarization component light intensity, a clockwise circle From the voltage conversion value Vr [dBm] of the polarized light intensity, it is obtained by the following formula (1).
S1 = (2Vh−Vt) / Vt
S2 = (2Vq-Vt) / Vt
S3 = (2Vr−Vt) / Vt (1)

  In the polarimeter 1008, the Stokes vector measurement is performed 2B / ΔF times within one optical signal quality monitor, that is, within a time when the variable wavelength bandpass filter sweeps the data modulation band 2B once. Therefore, Tres / (2B / ΔF ) It is controlled by the CPU 1010 to finish one Stokes vector measurement within [sec]. Since the polarization multiplexed optical signal that is FM-modulated with the carrier optical frequencies f1 and f2 is input to the polarimeter 1008, various frequency components are mixed in Vt, Vh, Vq, and Vr. . Therefore, in order to obtain the Stokes vector for each polarization channel, the f1 and f2 components may be extracted from S1 to S3 of Equation 1. The RF intensity is measured by the RF analyzer 1009 with the frequency resolution BW [Hz], and the RF intensity of the f1 and f2 components of S1 to S3 is obtained. The amount of polarization dispersion can be estimated from the Stokes vector measurement value.

Since the frequency band of the polarization multiplexed optical signal input to the polarimeter 1008 is limited to ΔF by the variable optical bandpass filter 1007, the band of the electrical frequency spectrum observed by the RF analyzer 1009 is also ΔF. Accordingly, the FM modulation frequencies f1 and f2 are set to fall within ΔF. Furthermore, since the frequency resolution of the RF analyzer 1009 is BW, the frequency interval between f1 and f2 is set to be equal to or greater than BW so that the f1 and f2 components can be separated.
FIG. 3 shows the relationship between the FM modulation frequencies f 1 and f 2, the variable optical bandpass filter optical frequency resolution ΔF, and the frequency resolution BW of the RF analyzer 1009. Since the band of width BW centered at f1 and the band of width BW centered at f2 are separated, it can be seen that the frequency interval between f1 and f2 is greater than or equal to BW. Further, as is apparent from the values on the horizontal axis, f1 and f2 <ΔF.

  In the above configuration, the optical center frequency of the transmission light source is frequency-modulated with a different frequency for each polarization channel, the light intensity for each optical frequency is monitored, and the light intensity for each modulated frequency component of the optical center frequency is extracted. This makes it possible to monitor the polarization state of each polarization channel without optically separating the polarization.

  When extracting the light intensity for each modulation frequency component of the polarization multiplexed optical signal, a frequency component analysis by a frequency analyzer or a synchronous detection method such as a lock-in detector is effective. For example, in the case of the lock-in detection method, the frequency resolution is determined by the time constant (measurement integration time), and the frequency resolution improves as the time constant increases. On the other hand, when polarization dispersion is fast, it changes in the order of msec. Therefore, in order to perform effective monitoring, the measurement time allowed for one monitor is also in the order of msec. Therefore, the frequency resolution in lock-in detection is limited by the allowable measurement time for one monitor. Therefore, it is necessary to select in advance the two intensity modulation frequency intervals added for each polarization channel so that they can be separated by lock-in detection. Polarization dispersion is performed by monitoring the light intensity for each optical frequency, but the frequency bandwidth in lock-in detection is limited by the optical bandpass filter when extracting the light intensity component for each optical frequency. It is necessary to note that. Therefore, the maximum value of the two modulation frequencies added for each polarization channel is also limited. In order to improve the polarization dispersion monitoring system, it is effective to improve the optical frequency resolution. Therefore, as the polarization dispersion monitoring system is improved, the maximum allowed for the two modulation frequencies added for each polarization channel is increased. The value drops.

  Based on the above, considering the optical bandpass filter bandwidth at the time of light intensity component extraction and the frequency resolution in lock-in detection to extract the polarization state for each polarization channel, the modulation frequency to be superimposed for each polarization channel is appropriate. If this is selected, the polarization state for each polarization channel can be monitored without optically polarization separation.

  FIG. 4 shows an example of implementation of the optical signal quality monitoring system. A configuration in which an LD 2003 and a data modulator 2005 are combined as an optical transmitter that outputs OPT_SIG1 is adopted. The same applies to OPT_SIG2. As the RF analyzer, a lock-in detector 2012 that operates at a frequency f1 and a lock-in detector 2013 that operates at a frequency f2 are employed.

  The polarization state of the output light of the LD 2003 is linearly polarized in the X direction. This is modulated at the modulation speed B by the data modulator 2005. On the data modulation signal of speed B, AM modulation of frequency f1 which is slower than B generated by frequency generator 2001 is superimposed. Thereby, OPT_SIG1 is generated. Similarly, OPT_SIG2 is generated using an LD 2004 that outputs light linearly polarized in the Y direction, a frequency generator 2002 having an output frequency f2, and a data modulator 2006 having a modulation speed B. The operations of the polarization multiplexer 2007, the optical transmission line 2008, the variable wavelength bandpass filter 2009, and the polarimeter 2010 are as described in FIG.

  The electrical output of the polarimeter 2010 branched into two by the distributor 2011 is guided to lock-in detectors 2012 and 2013, respectively. The lock-in detector 2012 extracts and outputs only the f1 component intensity from the input electrical signal.

  As in FIG. 2, it is assumed that the rate of change of polarization dispersion in the optical transmission line 2008 is Tpmd. When the optical frequency is swept by the control of the CPU 2018 with the optical frequency resolution ΔF from Fc−B to Fc + B around the carrier optical frequency Fc of the polarization multiplexed optical signal by the wavelength tunable filter 2009, it is 2B in one optical signal quality monitor. / ΔF Stokes vectors are measured.

  Here, the Stokes vector is converted into an electrical signal according to the above equation (1) and output. The Stokes vector measurement time Tres is controlled by the CPU 2018 to end at or below the polarization dispersion change rate Tpmd in order to perform accurate polarization dispersion measurement, and is set to satisfy the relationship Tres <Tpmd. Yes. Accordingly, the polarimeter 2010 outputs a Stokes vector of an optical signal obtained by cutting out a polarization multiplexed optical signal with an optical frequency resolution ΔF every Tres / (2B / ΔF). Since the output Stokes vector includes various frequency components, only the AM modulation frequencies f1 and f2 are extracted by the lock-in detectors 2012 and 2013.

Since the polarimeter 2010 outputs Stokes vectors corresponding to different optical frequency components in the polarization multiplexed optical signal data modulation band for each Tres / (2B / ΔF), the lock-in detectors 2012 and 2013 have the Tres / It is set to end the measurement at a speed of (2B / ΔF) or less. When the time constant of the operation of the lock-in detectors 2012 and 2013 is τ [sec], the frequency resolution BW [Hz] of the lock-in detectors 2012 and 2013 is given by the following equation (2).
BW = 1 / (2πτ) (2)

Since τ <(Tres / (2B / ΔF)) <(Tpmd / (2B / ΔF)), the relationship shown in the following formula (3) is established in combination with the above formula (2).
BW> B / (π · Tpmd · ΔF) (3)

When the frequency resolution of the lock-in detectors 2012 and 2013 is BW, different frequencies whose frequency interval is equal to or less than BW cannot be separated. Therefore, the AM modulation frequencies f1 and f2 satisfy the relationship of the following formula (4). It is necessary to set to.
f2> f1 + BW (4)

Therefore, the following formula (5) is derived from the above formulas (3) and (4).
f2> f1 + B / (π · Tpmd · ΔF) (5)

Furthermore, since the frequency band that can pass through the variable length bandpass filter 2009 is ΔF or less, the following equation (6) is finally derived.
ΔF>f2> f1 + B / (π · Tpmd · ΔF) (6)

  According to the above equation (6), the AM modulation frequencies f1 and f2 need to be determined in consideration of the polarization dispersion change rate Tpmd, the data modulation band B, and the optical frequency resolution ΔF of the variable frequency filter 2009.

  As described above, for example, when the data modulation rate B is defined, the polarization dispersion change rate Tpmd in the optical transmission line 2008 and the optical frequency resolution ΔF of the variable length bandpass filter 2009 required for calculating the Stokes vector are appropriately set. If set, the Stokes vector can be calculated for each polarization channel without optically polarization splitting, and the amount of polarization dispersion can be monitored.

An example of another operation of the optical signal quality monitoring system according to the present embodiment will be described.
The operation described here monitors polarization dispersion dependent loss (PDL) for each optical frequency in the optical transmission line 2008 from Stokes vectors monitored for each polarization channel, and reduces optical signal quality degradation caused by PDL. It is an operation to monitor.

  When the polarization multiplexed optical signal multiplexed with the polarization state orthogonalized by the polarization multiplexer 2007 is negligible in the optical transmission line 2008, the orthogonal relationship of the polarization state for each optical frequency is preserved. The When the PDL cannot be ignored, the orthogonal relationship is lost, and this causes a crosstalk between the polarization channels after polarization channel separation. Therefore, by monitoring the orthogonal relationship between the polarization states for each optical frequency, it is possible to monitor optical signal quality degradation caused by PDL.

In the optical signal quality monitor apparatus 2100, by appropriately setting the polarization dispersion change rate Tpmd in the optical transmission line 2008 and the optical frequency resolution ΔF of the variable length bandpass filter 2009 required for calculating the Stokes vector, Stokes vectors can be calculated around the polarization channel. Further, since the Stokes vector uses the visible light frequency bandpass filter 2009, it is calculated for each optical frequency. FIG. 5 shows a vector display on the Poincare sphere 3001 of the Stokes vector Sx of the polarization channel X and the Stokes vector Sy of the polarization channel Y at the monitored optical frequency Fs. θ is an angle formed by Sx3002 and Sy3002, and the relationship of the following formula (7) is established.
Sx · Sy = | Sx || Sy | cos (θ) = cos (θ) (7)
However, | Sx | = | Sy | = 1, Sx · Sy is a vector dot product.

When Sx3002 and Sy3003 are orthogonal, θ = ± π. Therefore, if the following equation (8) is satisfied, the orthogonal relationship between the polarization channels is preserved, and PDL can be ignored.
| Sx · Sy | = 1 (8)

The vector components of Sx3002 and Sy3003 are obtained by voltage conversion from the above equation (1). Sx = (S1x, S2x, S3x), Sy = (S1y, S2y, S3y) when an arbitrary orthogonal coordinate system is set and the axial directions thereof are s1, s2, and s3. Equivalent to (9). Note that s1, s2, and s3 can be arbitrarily set without depending on the polarization directions x and y.
| S1xS1y + S2xS2y + S3xS3y | = 1 (9)

  Since | Sx · Sy | is obtained for each optical frequency, this is represented as Sxy (F). L = 1−Sum (Sxy (F)) is introduced as a PDL evaluation parameter. Here, Sum represents the sum of Sxy (F) in the data modulation band 2B. If L is 1, the PDL received by the polarization multiplexed optical signal through the optical transmission line 2008 is 0, and the PDL increases as L decreases from 1. Regarding the calculation of L, Vt (F) representing the light intensity at each optical frequency of the optical signal in the above formula (1) is used, and Sxy (F) is weighted by Vt (F), and L = 1−Sum ( Vt (F) Sxy (F)).

  When PDL is not negligible, crosstalk between polarization channels occurs, which is one factor that degrades the optical signal quality after polarization separation. However, as described above, PDL monitoring is performed for each optical frequency, and PDL causes It becomes possible to monitor the deterioration of the optical signal.

As described above, according to the above embodiment, since the electrical AM modulation frequency is used as the polarization separation channel separation means instead of using the optical polarization separation means, optical polarization separation control is unnecessary. It is.
In addition, since a method of monitoring polarization dispersion for each optical frequency that could not be applied to a polarization multiplexed optical signal is also applicable to a polarization multiplexed optical signal, each polarization channel includes a higher order polarization. Wave dispersion monitoring is possible.
Also, it is clear that under what conditions the AM modulation band should be set according to the optical frequency resolution, sweep speed, polarization change speed, and data modulation band of the variable wavelength bandpass filter in the monitor device.
PDL monitoring is possible by monitoring the Stokes vector for each optical frequency for each polarization channel and examining the orthogonal relationship. Therefore, it is possible to cope with the case where the PDL cannot be ignored and the polarization channel crosstalk and the optical signal quality after the polarization separation due to this are deteriorated.
Furthermore, since it does not depend on the main signal light velocity, the carrier light frequency, and the data modulation method, it can be applied as an optical signal quality monitoring system to various types of optical communication systems.

  In addition, the said embodiment is an example of suitable implementation of this invention, and various deformation | transformation are possible for this invention, without being limited to this.

DESCRIPTION OF SYMBOLS 10 Transmission apparatus 11 Modulation part 12 Polarization multiplexing part 20, 1006, 2008 Optical transmission path 30, 1100, 2100 Optical signal quality monitoring apparatus 31 Polarization component detection part 32 Stokes vector calculation part 33 Intensity extraction part 1001, 1002, 2001, 2002 Frequency generator 1003, 1004 Optical transmitter 1005, 2005 Polarization multiplexer 1007, 2009 Variable length band pass filter 1008, 2010 Polarimeter 1009 RF analyzer 1010, 2018 CPU
2003, 2004 LD
2005, 2006 Data modulator 2011 Divider 2012, 2013 Lock-in detector 3001 Poincare sphere 3002 Stokes vector of polarization channel X 3003 Stokes vector of polarization channel Y

Claims (25)

Means for modulating the frequency of the carrier light of the data modulated optical signal with a different frequency for each polarization channel;
A transmission device comprising means for polarization-multiplexing the polarization channel and outputting it to an optical transmission line;
A light intensity component for each unit optical frequency is extracted over the entire area within the modulation bandwidth of the data modulated optical signal received via the optical transmission path, and a predetermined difference is obtained for each light intensity component for each unit optical frequency. Means for detecting four types of polarization components;
Means for calculating a Stokes vector by calculating the intensity of four types of light intensity polarization components for each frequency modulation component added for each polarization channel;
An optical signal quality monitoring system comprising: a monitoring device including means for extracting the intensity of a frequency modulation component added for each polarization channel from the Stokes vector. The means for extracting the intensity of the frequency modulation component added for each polarization channel extracts the intensity of the frequency modulation component using lock-in detection,
The lock-in detection speed is set to be equal to or higher than the polarization dispersion change speed,
The modulation frequency interval when modulating the frequency of the carrier light of the data modulation signal light with a different frequency for each polarization channel is set to be equal to or higher than the lock-in detection frequency resolution determined from the time constant of the lock-in detection,
The maximum value of the modulation frequency added for each polarization channel is determined by the resolution at the time of extracting the light intensity component for each unit optical frequency over the entire area within the modulation bandwidth of the data modulated optical signal. 2. The optical signal quality monitoring system according to claim 1, wherein the optical signal quality monitoring system is set so as to be within a bandwidth.   The monitor device calculates the length of the locus of the Stokes vector on the Poincare sphere for each polarization channel from the measured value of the Stokes vector, and the data modulated optical signal is polarization-dispersed in the transmission path. 3. The apparatus according to claim 2, further comprising means for monitoring the amount of quality degradation received by each of the polarization channels based on the length of the trajectory without optically polarization splitting the data modulated light. The optical signal quality monitoring system described. The transmitter multiplexes two orthogonally polarized data modulated optical signals as polarization multiplexed signals,
The monitor device monitors a polarization dependent loss generated in the optical transmission line by calculating a deviation from the orthogonal relationship between the polarization channels for each unit optical frequency from a Stokes vector obtained for each polarization channel. 3. The optical signal quality monitoring system according to claim 2, further comprising:   The monitor device optically polarizes the data-modulated optical signal based on the degree of polarization obtained from the Stokes vector, based on the amount of quality degradation that the data-modulated optical signal receives due to polarization dispersion in the transmission path. 3. The optical signal quality monitoring system according to claim 2, further comprising means for monitoring each polarization channel without separation. When the maximum value of the polarization dispersion change rate is Tpmd [sec] and the measurement point is estimated as N [pts] when extracting the light intensity component for each unit optical frequency, the frequency resolution BW of the lock-in detection is 1 / (2π · Tpmd · N) [Hz], and the modulation frequency interval when modulating with a different frequency for each polarization channel is BW [Hz] or more,
By estimating the optical frequency resolution required for the polarization dispersion monitor for each polarization channel as ΔF [Hz], the frequency different for each polarization channel is changed to any two frequencies equal to or less than ΔF and the frequency interval equal to or greater than the BW. 6. The optical signal quality monitor system according to claim 2, wherein the optical signal quality monitor system is set.   The said transmission apparatus outputs the said data modulation optical signal by carrying out the intensity modulation of the signal light intensity | strength of the carrier light of a data modulation optical signal with a different frequency for every polarization channel. The optical signal quality monitoring system according to any one of the preceding claims.   The optical signal quality monitoring system according to any one of claims 1 to 6, wherein the transmission device superimposes intensity modulation at a different frequency for each polarization channel on the data-modulated optical signal. The light intensity component for each unit optical frequency is extracted over the entire area within the modulation bandwidth of the data-modulated optical signal that has been modulated at a different frequency for each polarization channel, multiplexed by polarization, and transmitted via the optical transmission line. Means for detecting four different types of polarized light components for each light intensity component for each unit optical frequency;
Means for calculating a Stokes vector by calculating the intensity of four types of light intensity polarization components for each frequency modulation component added for each polarization channel;
Means for extracting the intensity of a frequency modulation component added for each polarization channel from the Stokes vector. The means for extracting the intensity of the frequency modulation component added for each polarization channel extracts the intensity of the frequency modulation component using lock-in detection,
The lock-in detection speed is set to be equal to or higher than the polarization dispersion change speed,
The modulation frequency interval when modulating the frequency of the carrier light of the data modulation signal light with a different frequency for each polarization channel is set to be equal to or higher than the lock-in detection frequency resolution determined from the time constant of the lock-in detection,
The maximum value of the modulation frequency added for each polarization channel is determined by the resolution at the time of extracting the light intensity component for each unit optical frequency over the entire area within the modulation bandwidth of the data modulated optical signal. 10. The optical signal quality monitoring apparatus according to claim 9, wherein the optical signal quality monitoring apparatus is set so as to be within a bandwidth.   The quality degradation caused by calculating the length of the locus of the Stokes vector on the Poincare sphere for each polarization channel from the measured value of the Stokes vector, and the data modulated optical signal being polarized and dispersed in the transmission line 11. The optical signal according to claim 10, further comprising means for monitoring the quantity for each polarization channel based on the length of the trajectory without optically polarization splitting the data modulated optical signal. Quality monitoring device.   Based on the degree of polarization obtained from the Stokes vector, the amount of quality degradation that the data modulated optical signal has received by polarization dispersion in the transmission path can be obtained without optically polarization-separating the data modulated optical signal, 11. The optical signal quality monitoring apparatus according to claim 10, further comprising means for monitoring each polarization channel. When the maximum value of the polarization dispersion change rate is Tpmd [sec] and the measurement point is estimated as N [pts] when extracting the light intensity component for each unit optical frequency, the frequency resolution BW of the lock-in detection is 1 / (2π · Tpmd · N) [Hz], and the modulation frequency interval when modulating with a different frequency for each polarization channel is BW [Hz] or more,
By estimating the optical frequency resolution required for the polarization dispersion monitor for each polarization channel as ΔF [Hz], the frequency different for each polarization channel is changed to any two frequencies equal to or less than ΔF and the frequency interval equal to or greater than the BW. 13. The optical signal quality monitoring device according to claim 10, wherein the optical signal quality monitoring device is set.
Means for modulating the frequency of the carrier light of the data modulated optical signal with a different frequency for each polarization channel;
An optical signal transmitting apparatus comprising: means for polarization multiplexing the polarization channel and outputting the result to an optical transmission line.   15. The optical signal transmitting apparatus according to claim 14, wherein two orthogonally polarized data modulated optical signals are multiplexed as the polarization multiplexed signal.   16. The optical signal transmitter according to claim 14, wherein the data modulated optical signal is output by modulating the optical intensity of the carrier light of the data modulated optical signal at a different frequency for each polarization channel. .   16. The optical signal transmitter according to claim 14, wherein intensity modulation is superimposed on the data modulated optical signal at a different frequency for each polarization channel. Modulate the frequency of the carrier light of the data modulated optical signal with a different frequency for each polarization channel,
The polarization channel is polarization multiplexed and output to an optical transmission line,
Extracting the light intensity component for each unit optical frequency over the entire area within the modulation bandwidth of the data modulated optical signal, detecting four different types of polarized light components different from each other for each light intensity component for each unit optical frequency;
A Stokes vector is calculated by calculating the intensity of four types of light intensity polarization components for each frequency modulation component added for each polarization channel,
An optical signal quality monitoring method, wherein the intensity of a frequency modulation component added for each polarization channel is extracted from the Stokes vector. Using lock-in detection as means for extracting the intensity of the frequency modulation component added for each polarization channel,
Set the lock-in detection speed to be equal to or higher than the polarization dispersion change speed,
Set the modulation frequency interval when modulating the frequency of the carrier light of the data modulation signal light at a different frequency for each polarization channel to be equal to or higher than the resolution of the lock-in detection frequency determined from the time constant of the lock-in detection,
The band at the time of lock-in detection determined by the resolution at the time of extracting the light intensity component for each unit optical frequency over the entire area within the data modulation optical signal modulation bandwidth, the maximum value of the modulation frequency added for each polarization channel 19. The optical signal quality monitoring method according to claim 18, wherein the optical signal quality is set so as to be within the width.   The quality degradation caused by calculating the length of the locus of the Stokes vector on the Poincare sphere for each polarization channel from the measured value of the Stokes vector, and the data modulated optical signal being polarized and dispersed in the transmission line 20. The optical signal quality monitoring method according to claim 19, wherein the quantity is monitored for each polarization channel based on the length of the trajectory without optically polarization splitting the data modulated light. Multiplex the data modulation optical signal of two orthogonal polarization states as a polarization multiplexed signal,
The polarization dependent loss generated in the optical transmission line is monitored by calculating the deviation from the orthogonal relationship between the polarization channels for each unit optical frequency from the Stokes vector obtained for each polarization channel. The optical signal quality monitoring method according to claim 19.   Based on the degree of polarization obtained from the Stokes vector, the amount of quality degradation that the data modulated optical signal receives due to polarization dispersion in the transmission line can be determined without optical polarization separation of the data modulated light. 20. The optical signal quality monitoring method according to claim 19, wherein monitoring is performed for each wave channel. When the maximum value of the polarization dispersion change rate is Tpmd [sec] and the measurement point is estimated as N [pts] when extracting the light intensity component for each unit optical frequency, the frequency resolution BW of the lock-in detection is 1 / (2π · Tpmd · N) [Hz], and the modulation frequency interval when modulating at different frequencies for each polarization channel is set to BW [Hz] or more,
By estimating the optical frequency resolution required for the polarization dispersion monitor for each polarization channel as ΔF [Hz], the frequency different for each polarization channel is changed to any two frequencies equal to or less than ΔF and the frequency interval equal to or greater than the BW. 23. The optical signal quality monitoring method according to claim 18, wherein the optical signal quality monitoring method is set.   24. The data modulated optical signal according to claim 18, wherein the data modulated optical signal is output by modulating the intensity of carrier light of the data modulated optical signal at a different frequency for each polarization channel. Optical signal quality monitoring method.   The optical signal quality monitoring method according to any one of claims 18 to 23, wherein intensity modulation is superimposed on the data modulated optical signal at a different frequency for each polarization channel.

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