JP2012165287A - Optical signal quality monitoring apparatus and method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide monitoring of optical signal quality by measuring the quality of each polarization signal against a signal with the same frequency and using a simple configuration without need of an external modulator.SOLUTION: The present invention includes: training signal generation means that generates a different periodic training signal at each polarization and transmission means that transmits a polarization multiplexed signal with a training signal given, which are installed on the transmission side. The present invention further includes: polarization separation means that separates the signal received from the transmission means into specific polarization and first and second power measurement means that measures the power of the polarization-separated signal, which are installed on the reception side.

Description

  The present invention relates to an optical signal quality monitoring apparatus and method for performing quality control of polarization multiplexed optical signals, and in particular, between OSNR (Optical Signal Noise Ratio) or X-Y polarization of X and Y polarization. The present invention relates to an optical signal quality monitoring apparatus and method for monitoring PDL (Polarization Dependent Loss).

  In recent years, with the spread of multimedia services and the expansion of the use of ICT (Information and Communication Technology) services, traffic flowing through backbone networks has been increasing year by year. Digital coherent technology is currently attracting attention as the next generation optical communication technology that drives the ever-increasing traffic. In a 40 Gbps WDM (Wavelength Division Multiplexing) system that has already been commercialized, dispersion management, a dispersion compensator, and the like are widely used to correct distortion of an optical signal generated in a transmission path. However, since the time slot becomes narrow and the relative influence becomes large in a system exceeding 100 Gbps, the conventional dispersion compensation technique has a limit in the compensation amount and the compensation accuracy. Therefore, by introducing the digital coherent technology, it is possible to perform dispersion compensation with high accuracy and wide range by estimating and correcting distortion in the transmission path due to digital signal processing. In addition, phase estimation and polarization separation can be performed by signal processing by using the digital coherent technology, so that technologies such as multilevel modulation and polarization multiplexing, which have been difficult to realize in the past, are widely used. became. The next 100 Gbps system uses a combination of multi-level modulation and polarization multiplexing, such as DP-QPSK (Dual Polarization Quadrature Phase Shift Keying) and DP-DQPSK (Dual Polarization Differential Quadrature Phase Shift Keying), to reduce the symbol rate. Gbps class transmission is possible. In the case of DP-QPSK, since the 2-bit information indicated by the four-phase phase state is transmitted on orthogonal polarization, the symbol rate is 25 Gbps, reducing the bandwidth required for optical and electrical components, and reducing the wavelength It is possible to improve the tolerance to various transmission limiting factors such as dispersion and polarization mode dispersion.

  On the other hand, when signals are transmitted with two orthogonal polarizations, a loss (PDL: Polarization Dependent Loss) depending on the polarization state occurs in the transmission path. Since signals are superimposed on the orthogonal carrier light having the same frequency and transmitted, it is difficult to measure the PDL received by each polarization in the light region. However, it is necessary to isolate transmission quality degradation and failure caused by PDL for practical application of 100 Gbps systems in the future.

  In the prior art, by modulating the frequency of the carrier light at a different frequency for each polarization channel, the receiving side extracts the intensity for each unit optical frequency over the entire area within the modulation bandwidth of the data modulated optical signal. The quality of each polarization is monitored. Also, there is a method of measuring the intensity of each polarization by applying tone modulation to each polarization at a different frequency and cutting out the spectrum component corresponding to the frequency of tone modulation after O / E conversion by a receiving device. Yes (see, for example, Patent Document 1).

JP 2010-135937 JP

  In the prior art, since the frequency of the carrier light is modulated with a different frequency for each polarization channel, a modulator capable of modulating with a different frequency for each polarization channel is required. Further, since each polarization channel is modulated at the same frequency in a normal polarization multiplexed signal, the proposed configuration cannot be applied to a normal system as it is. Further, in the technique disclosed in Patent Document 1, since the tone modulation is superimposed on the signal transmitted on the transmission side, a penalty occurs in the transmission signal. Here, the penalty indicates how much the signal after tone modulation is degraded as compared with the Back-to-Back signal. Further, since the optical signal quality monitor of Patent Document 1 described above needs to be provided with a modulator for tone modulation separately for each polarization, problems remain in terms of miniaturization and power saving.

  The present invention has been made in view of the above points, measures the quality of each polarization signal for signals having the same frequency carrier light and the same symbol rate, and requires an external modulator. It is an object of the present invention to provide an optical signal quality monitoring apparatus and method capable of monitoring the optical signal quality with a simple configuration.

In order to solve the above problems, the present invention is an optical signal quality monitoring apparatus for monitoring the quality of a polarization multiplexed signal,
On the sending side,
Training signal generating means for generating different periodic training signals for each polarization;
Transmitting means for transmitting a polarization multiplexed signal to which the training signal is attached;
Have
On the receiving side,
Polarization separation means for separating the signal received from the transmission means into a specific polarization;
First and second power measuring means for measuring the power of the polarization separated signal;
Have

  With the above configuration, the quality of each polarization signal is measured for signals having the same frequency carrier light and the same symbol rate, and no external modulator is required. The quality of the optical signal can be monitored by the configuration.

It is a block diagram of the optical signal quality monitoring apparatus in the 1st Embodiment of this invention. It is a figure which shows the spectrum of the 10G NRZ modulation signal in the 1st Embodiment of this invention. It is a figure which shows the bit number dependence of CSR in the 1st Embodiment of this invention. It is a figure which shows the polarization normal state before and behind the transmission line in the 1st Embodiment of this invention, and the relationship of power. It is a block diagram (reception side) of the optical signal quality monitoring apparatus in the 2nd Embodiment of this invention. It is a block diagram (reception side) of the optical signal quality monitoring apparatus in the 3rd Embodiment of this invention. It is a block diagram (reception side) of the optical signal quality monitoring apparatus in the 4th Embodiment of this invention. It is a block diagram (reception side) of the optical signal quality monitoring apparatus in the 5th Embodiment of this invention. It is a block diagram (reception side) of the optical signal quality monitoring apparatus in the 6th Embodiment of this invention. It is a block diagram (reception side) of the optical signal quality monitoring apparatus in the 7th Embodiment of this invention.

  Embodiments of the present invention will be described below with reference to the drawings.

[First Embodiment]
FIG. 1 shows a configuration of a light quality monitoring apparatus according to the first embodiment of the present invention.

  The optical quality monitoring apparatus shown in the figure includes a training signal generation unit 10 and a transmission unit 20 on the transmission side, and a polarization separation unit 30, a first power measurement unit 41, and a second power measurement unit 42 on the reception side. It has been.

  The transmission-side training signal generation unit 10 generates a training signal having a different period for each signal that is polarization multiplexed. The transmission unit 20 adds the training signal to the polarization multiplexed signal, and transmits an optical signal. On the receiving side that performs monitoring, the polarization multiplexed optical signal is separated into specific polarization components by the polarization separation unit 30, and the power of the separated polarization components is first and second power measurement units, respectively. Measured at 41 and 42. Since the training signal has patterns with different periods for the X polarization and the Y polarization, the OSNR of each polarization can be measured in real time by observing the power in a specific frequency band.

  Details of the principle will be described.

  FIG. 2 shows the spectrum of a 10G NRZ signal in one embodiment of the present invention. In the figure, the signal spectrum when the 10G NRZ signal is Fourier-transformed at 80 GS / s is shown.

  The training signal generator 10 inserts 512 bits of a repeated bit pattern of 001100110011... And 000011000111... Into the training signal, and a PN11 stage pseudo-random signal is inserted into the payload. In the first and second power measuring units 41 and 42, since the signal having the repetition period of 001100110011... Includes a spectral component having a quarter period of the symbol rate, a spectral component of 2.5 GHz when the symbol rate is 10 Gbps. Is detected (a in FIG. 2). Further, when the repetition pattern of the training signal is 000011000111..., A spectral component of 1.67 GHz is detected because it includes a spectral component of 1/6 period of the symbol rate (b in FIG. 2).

  FIG. 3 is a diagram showing the bit number dependency of CSR (Carrier to Signal Ratio) in the first embodiment of the present invention.

The horizontal axis is the number of payload bits 2 ⁿ , and the vertical axis is CSR. The training signal uses 512 bits of the repeating pattern of 001100110011... And 000011000111... And the payload uses a PNn-stage pseudo-random signal. CSR is the ratio of signal power (P _s ) to carrier light power (P _c )

を表したものである。ペイロード長がトレーニング信号長に対して長くなるにつれCSRは低下していく。これは、トレーニング信号による特定の周波数成分がキャリアのパワーに埋もれてしまうためである。しかしながら512ビットのトレーニング信号に対して2¹⁵ビット (32768ビット)のペイロード信号を用いた場合で約5 dBのCSRが得られており、ペイロードに対して1〜2パーセントのトレーニング信号を用いることで特定周波数帯域の信号光パワーをキャリア光成分と分離して、第１、第２のパワー測定部４１，４２で測定することは可能である。

It represents. CSR decreases as the payload length becomes longer than the training signal length. This is because a specific frequency component due to the training signal is buried in the power of the carrier. However, when using a ^15- bit (32768-bit) payload signal for a 512-bit training signal, a CSR of about 5 dB has been obtained. By using 1-2% of the training signal for the payload, It is possible to separate the signal light power in the specific frequency band from the carrier light component and measure it with the first and second power measuring units 41 and 42.

  FIG. 4 shows the relationship between the polarization state before and after the transmission line and the power in the first embodiment of the present invention.

Before transmission, as shown in FIG. 4A, both the X polarization and the Y polarization are orthogonal and the power is the same. Due to the loss and refractive index difference depending on the polarization in the transmission path, the polarization states of the X polarization and the Y polarization input to the polarization separation unit 30 are not always orthogonal to each other, and power Are also different (FIG. 4B). For example, when a polarization beam splitter is used for the polarization separation unit 30, after passing through the polarization beam splitter, the X polarization and the Y polarization are on the optical axis of the polarization beam splitter as shown in FIG. Separated into an X-axis component and a Y-axis component. The angle formed by the X polarization with respect to the optical axis of the polarization beam splitter is θ, the power is X _O , the angle formed by the Y polarization is γ, the power is Y _O, and the X polarization X immediately after the polarization beam splitter If the power of the axial component is X _{O_X} , the power of the Y-axis component is X _{O_X} , the power of the X-axis component of the Y polarization is Y _{O_X} , and the power of the Y-axis component is Y _{O_Y} , the following relational expression is established.

X_{O_X}、X_{O_Y}、Y_{O_X} 、Y_{O_Y}は既知であるため直交性を示すθ及びγは算出可能であり、また各偏波のパワーX_O 、Y_Oも算出することが可能である。

Since X _{O_X} , X _{O_Y} , Y _{O_X} , and Y _{O_Y} are known, θ and γ indicating orthogonality can be calculated, and the powers X _O and Y _{O of} each polarization can also be calculated.

  The bit pattern used for the training signal is not limited to the described pattern, and other bit patterns may be used as long as they have periodicity. The polarization separation unit 30 is not limited to this as long as it can be separated into a specific polarization, such as the polarization beam splitter or the polarization separation fiber.

[Second Embodiment]
FIG. 5 is a configuration diagram (receiving side) of the optical signal monitoring apparatus according to the second embodiment of the present invention.

  On the receiving side of the optical signal monitoring apparatus shown in the figure, the polarization separation unit 30, the first branching unit 51, the second branching unit 52, the first filter 61, the second filter 62, and the third filter 63, a fourth filter 64, a first power measurement unit 71, a second power measurement unit 72, a third power measurement unit 73, and a fourth power measurement unit 75 are provided.

After the polarization-multiplexed signal is separated into a specific polarization component by the polarization separating section 30, first, the spectrum of a specific frequency band F _x where X polarized wave branched by the second branching unit 51 has The first filter 61 and the third filter 63 are used to cut out. The second filter 62 and the fourth filter 64 are used to cut out the spectrum of the specific frequency band F _Y that Y polarization has. After cutting out only a specific frequency band with each filter, the power measurement is performed by the first, second, third, and fourth power measuring units 71 to 74, thereby the power X of each polarization and the power X of the Y component. _{O_X} , X _{O_Y} , Y _{O_X} , and Y _{O_Y} can be obtained.

[Third Embodiment]
FIG. 6 is a configuration diagram (receiving side) of the optical signal monitoring apparatus according to the third embodiment of the present invention.

  On the receiving side of the optical signal monitoring apparatus shown in the figure, a polarization separation unit 30, a first optical spectrum measurement unit 81, and a second optical spectrum measurement unit 82 are provided.

  The difference from the second embodiment is that optical spectrum measuring units 81 and 82 are used on the receiving side of the optical signal quality monitoring apparatus.

Similarly to the second embodiment, after the polarization multiplexed signal is separated into specific polarization components by the polarization separation unit 30, the optical spectrum measurement units 81 and 82 each have a specific frequency band F that each polarization has. Observe the power of _x and F _Y. Since F _x ≠ F _x , the power X _{O_X} , X _{O_Y} , Y _{O_X} , and Y _{O_Y} of the X component and Y component of each polarization can be obtained on the optical spectrum measurement units 81 and 82.

[Fourth Embodiment]
FIG. 7 is a configuration diagram (receiving side) of the optical signal monitoring apparatus according to the fourth embodiment of the present invention.

  On the receiving side of the optical signal monitoring apparatus shown in the figure, the polarization separation unit 30, the first optical / electrical conversion unit 91, the second optical / electrical conversion unit 92, the first electrical spectrum measurement unit 101, the first Two electrical spectrum measuring units 102 are provided.

  The difference from the second and third embodiments is that the spectrum after conversion into an electric signal is measured.

  As in the second and third embodiments, after the polarization multiplexed signal is separated into specific polarization components by the polarization separation unit 30, in this embodiment, the first and second optical / electrical components are used. The optical signals are converted into electric signals by the converters 91 and 92, and the converted electric signals are observed by the electric spectrum measuring units 101 and 102.

Generally, the electrical spectrum measurement unit has a wider dynamic range and higher frequency resolution than the optical spectrum measurement unit, so it is easy to separate the spectrum of the specific frequency of the X polarization and the spectrum of the specific frequency of the Y polarization. Is possible. The first electric spectrum measuring unit 101 measures the X-axis component power X _{O_X} and Y _{O_X} of the X polarization and Y polarization, and the second electric spectrum measurement unit 102 measures the X polarization and Y polarization. By measuring the powers X _{O_Y} and Y _{O_Y} of the Y-axis component, it is possible to calculate the power and orthogonality of each polarization.

[Fifth Embodiment]
FIG. 8 is a configuration diagram (reception side) of the optical signal quality monitoring apparatus according to the fifth embodiment of the present invention.

  On the receiving side of the optical signal quality monitoring apparatus shown in the figure, the polarization separation unit 30, the first delay interference system 111, the second delay interference system 112, the first filter 61, the second filter 62, the first 1 power measurement unit 71, second power measurement unit 72, third power measurement unit 73, and fourth power measurement unit 74 are provided.

  The difference from the second, third, and fourth embodiments is an optical signal quality monitoring apparatus when the polarization multiplexed signal is phase modulated. As in the previous embodiment, after the polarization multiplexed signal is separated into specific polarization components by the polarization separator 30, the first and second delay interference systems 111 and 112 are used in this embodiment. The phase modulation signal is converted into an intensity modulation signal. After conversion to intensity modulation, the power of the X component and Y component of each polarization is measured by the filters 61 to 64 and the power measuring units 71 to 74 in order to observe the power in a specific frequency band. The modulation format is not limited to phase modulation, and can be any ASK (Amplitude Shift Keying), PSK (Phase Shift Keying), QPSK (Quadrature Phase Shift Keying), or QAM (Quadrature Amplitude Modulation) modulation format. is not. Further, instead of the filters 61 to 64 and the power measuring units 71 to 74, it is possible to observe the power of each polarization in combination with the delay interference system and the optical spectrum measurement unit, or the delay interference system and the electric spectrum measurement unit. The combination is not limited to this.

[Sixth Embodiment]
FIG. 9 is a configuration diagram (reception side) of the optical signal quality monitoring apparatus according to the sixth embodiment of the present invention.

  On the receiving side of the optical signal quality monitoring apparatus shown in the figure, the polarization separation unit 30, the first amplification unit 121, the second amplification unit 122, the first power measurement unit 71, and the second power measurement unit 72 are provided. A control unit 130 is provided.

  The difference from the above-described embodiment is that the signal light power of the X polarization and the Y polarization can be compensated. The signal light of each polarization has different power when it reaches the receiving side due to PDL received in the transmission path. In the present embodiment, the power of each polarization is detected by the method described in the first to fifth embodiments, and the detected power is notified to the control unit 130. The control unit 130 determines the amplification factors of the first amplification unit 121 and the second amplification unit 122 based on the notified power of each polarization. The amplification factor of the first amplification unit 121 is

として表すことができるため、下記の式が成り立つよう前記増幅率を制御する。

Therefore, the amplification factor is controlled so that the following equation is established.

前記増幅部１２１、１２２にはファイバ増幅器、半導体光増幅器などを用いることができるが、これらに限定されるものではない。
［第７の実施の形態］
図１０は、本発明の第７の実施の形態における光信号品質監視装置の構成図（受信側）である。

The amplifiers 121 and 122 may be fiber amplifiers or semiconductor optical amplifiers, but are not limited thereto.
[Seventh Embodiment]
FIG. 10 is a configuration diagram (reception side) of the optical signal quality monitoring apparatus according to the seventh embodiment of the present invention.

  The receiving side of the optical signal quality monitoring apparatus shown in the figure has a polarization separation unit 30, a first power measurement unit 71, a second power measurement unit 72, a polarization state notification unit 150, and a signal processing unit 141. A signal receiving unit 140 is provided.

  The difference from the above-described embodiment is that the polarization state notifying unit 150 notifies the signal processing unit 141 of the signal receiving unit 140 of the signal light power and the polarization state of the X polarization and the Y polarization. This is a point that can be reflected in the parameter setting 141.

  In a 100 Gb / s class large-capacity optical communication system, dispersion and phase fluctuation received in the transmission path are compensated in the signal processing unit 141. The signal processing unit 141 performs signal compensation using an adaptive equalizer, but in order to optimize the compensation according to the phase and polarization state of each polarization, the number of taps and tap coefficients of the adaptive equalizer are set. It is necessary to update accordingly. Therefore, in the present embodiment, it is possible to notify the power and polarization state of each polarization when updating the parameters of the adaptive equalizer, thereby improving the compensation accuracy of the adaptive equalizer. Moreover, it is necessary to set the initial value of the adaptive equalizer at the time of starting the system. By setting the initial value based on the polarization state and power of each polarization signal notified, the convergence of the signal processing unit 141 is set. It is also possible to shorten the time.

  Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the specific embodiments described above, and various modifications can be made within the scope of the gist of the present invention described in the claims. Variations and changes are possible.

DESCRIPTION OF SYMBOLS 10 Training signal production | generation part 20 Transmission part 30 Polarization separation part 41 1st power measurement part 42 2nd power measurement part 51 1st branch part 52 2nd branch part 61 1st filter 62 2nd filter 63 3rd filter 64 4th filter 71 1st power measurement part 72 2nd power measurement part 73 3rd power measurement part 74 4th power measurement part 81 1st optical spectrum measurement part 82 2nd light Spectrum measurement unit 91 First optical / electrical conversion unit 92 Second optical / electrical conversion unit 101 First electrical spectrum measurement unit 102 Second electrical spectrum measurement unit 111 First delay interference system 112 Second delay interference System 121 First amplification unit 122 Second amplification unit 130 Control unit 140 Signal reception unit 141 Signal processing unit 150 Polarization state notification unit

Claims (9)

An optical signal quality monitoring device for monitoring the quality of a polarization multiplexed signal,
On the sending side,
Training signal generating means for generating different periodic training signals for each polarization;
Transmitting means for transmitting a polarization multiplexed signal to which the training signal is attached;
An optical signal quality monitoring device comprising: On the receiving side,
Polarization separation means for separating the signal received from the transmission means into a specific polarization;
First and second power measuring means for measuring the power of the polarization separated signal;
The optical signal quality monitoring apparatus according to claim 1, comprising: The first and second power measuring means include
First and second branching means for branching the signal light power;
First, second, third, and fourth filters that pass only frequencies in a specific band;
The optical signal quality monitoring apparatus according to claim 2, comprising: The first and second power measuring means include
The optical signal quality monitoring apparatus according to claim 2, further comprising an optical spectrum measuring unit that measures a spectrum of a specific frequency band of the signal light. The first and second power measuring means include
First and second optical / electrical conversion means for converting signal light from light to electricity;
Electrical spectrum measurement means for measuring a spectrum of a specific frequency band of the converted electrical signal;
The optical signal quality monitoring apparatus according to claim 2, comprising: The first and second power measuring means include
6. The optical signal quality monitoring apparatus according to claim 2, further comprising first and second delay interferometers that convert the phase-modulated signal into intensity modulation. An optical amplification means for amplifying the optical signal polarized by the polarization separation means;
Control means for determining an amplification factor of the optical amplification means;
The optical signal quality monitoring apparatus according to any one of claims 2 to 6, further comprising: Polarization state notifying means for calculating the polarization state of each polarization from the measured power of each polarization on the receiving side, and notifying the polarization state of each polarization and the power of each polarization;
Signal processing means for compensating a received signal based on the notified polarization state and power;
The optical signal quality monitoring apparatus according to any one of claims 2 to 7, further comprising: An optical signal quality monitoring method for monitoring the quality of a polarization multiplexed signal,
On the sending side,
Training signal generating means for applying a different periodic training signal to each polarization;
Transmitting means for transmitting a polarization multiplexed signal to which the training signal is attached;
On the receiving side,
A step of polarization separating means for separating the received signal into a specific polarization;
A power measuring means measuring the power of each of the polarization separated signals;
An optical signal quality monitoring method comprising:

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