JP2013055679A - Device and method of monitoring polarization scrambler, and optical transmission device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect (monitor) an operation state of a polarization scrambler in a simple manner.SOLUTION: A device of monitoring a polarization scrambler has: a polarization passing device 14 that passes light with specific polarization among output light of the polarization scrambler; a photoelectric converter 15 generating an electric signal depending on a receiving intensity of light that has passed through the polarization passing device 14; and a detector 16 detecting from the electric signal a modulation component depending on a frequency of a polarization control signal. The detector 16 has: a wavelength filter 161 passing signals of components in a predetermined band among frequency components included in the electric signal; and an amplifier circuit 163 detecting from the signal a signal having the same frequency component as a modulation frequency signal that is given to the polarization scrambler by a polarization controller to detect the modulation component from an output from the wavelength filter.

Description

  The present invention relates to a polarization scrambler monitoring apparatus and method, and an optical transmission apparatus. This case may be used for an optical transmission apparatus provided with a polarization scrambler.

  In recent years, there is a case where wavelength extension (upgrade) of an optical transmission system such as an existing submarine cable system is performed as means for increasing a transmission amount to cope with an increase in communication amount. For example, when increasing the number of wavelengths in a one-wavelength optical transmission system or a narrow-band wavelength division multiplexing (WDM) system, the wavelength is set by narrowing the wavelength interval (grid) in a predetermined signal band. May multiplex at high density. In addition, an error correction method or encoding method with better characteristics may be required.

When signal light is transmitted through an optical transmission line with a poor optical signal to noise ratio (OSNR), the influence of the polarization of the signal light is large, and when the polarization of the signal light changes, the gain dependence of the optical amplifier depends on the polarization. In some cases, the signal light level fluctuates and the characteristics deteriorate due to polarization, polarization dependency of transmission loss, polarization hole burning, and the like. A polarization scrambler that randomizes the polarization state of signal light may be used to reduce the influence of such signal quality degradation due to polarization dependency.
JP 2003-60576 A

  One of the purposes of this case is to make it possible to easily detect (monitor) the operating state of the polarization scrambler.

  In addition, it is positioned as one of the other purposes of the present invention that is not limited to the above-mentioned purpose but is an effect that is derived from each configuration shown in the embodiments described later, and that cannot be obtained by conventional techniques. Can do.

For example, the following means are used.
(1) A polarization scrambler monitoring device that scrambles the polarization state of input light in accordance with a polarization control signal provided from a polarization control unit, wherein a specific polarization of the output light of the polarization scrambler A polarization passing device that passes light, a photoelectric converter that generates an electrical signal according to the received light intensity of the light that has passed through the polarization passing device, and a frequency corresponding to the frequency of the polarization control signal from the electrical signal. A detection unit that detects a modulation component, wherein the detection unit includes a wavelength filter that passes a signal of a component in a predetermined band among frequency components included in the electrical signal, and the polarization control signal from the signal. A polarization scrambler comprising: an amplifier circuit for detecting the modulation component from the output from the wavelength filter by detecting a signal having the same frequency component as the modulation frequency signal of It can be used to monitor device.

  (2) A polarization scrambler that scrambles the polarization state of the input light, a polarization control unit that provides a polarization control signal to the polarization scrambler to control the scramble, and output light of the polarization scrambler A polarization passing device that passes light of a specific polarization, a photoelectric converter that generates an electrical signal according to the received light intensity of the light that has passed through the polarization passing device, and the polarization from the electrical signal A detection unit that detects a modulation component corresponding to a frequency of the control signal, and the detection unit includes a wavelength filter that passes a signal of a component in a predetermined band among frequency components included in the electrical signal, and the signal And an amplification circuit that detects the modulation component from the output from the wavelength filter by detecting a signal having the same frequency component as the modulation frequency signal of the polarization control signal. That may be provided by an optical transmission device.

  (3) A polarization scrambler monitoring method that scrambles the polarization state of input light in accordance with a polarization control signal provided from a polarization control unit, wherein a specified polarization of the output light of the polarization scrambler Light is passed through a polarization passing device, an electrical signal is generated according to the received light intensity of the light that has passed through the polarization passing device, and a signal of a predetermined band component of the frequency components included in the electrical signal is wavelength The modulation component is detected from the output from the wavelength filter by detecting a signal having the same frequency component as the modulation frequency signal of the polarization control signal from the signal by passing through a filter, A polarization scrambler monitoring method can be used.

  According to the disclosed technology, it is possible to easily detect (monitor) the operating state of the polarization scrambler.

  Hereinafter, embodiments will be described with reference to the drawings. However, the embodiment described below is merely an example, and there is no intention to exclude various modifications and technical applications that are not explicitly described below. That is, the present embodiment can be implemented with various modifications (combining the embodiments) without departing from the spirit of the present embodiment.

[1] First Embodiment In the WDM optical transmission apparatus, when the polarization of transmission signal light is scrambled, for example, as shown in FIG. A method of performing polarization scrambling by the scrambler 11 or, as shown in FIG. 2, performing polarization scrambling on the WDM signal after wavelength multiplexing by the wavelength multiplexing unit 40 by the common polarization scrambler 11 collectively. There is a way. 1 and 2, reference numeral 50 denotes an optical amplifier such as an EDFA that collectively amplifies WDM signals.

  FIG. 3 shows a configuration example for monitoring the polarization scrambler 11 for one wavelength in the WDM optical transmission apparatus shown in FIG. The WDM optical transmission apparatus shown in FIG. 3 is an example of a polarization scrambler 11, a control circuit (polarization controller) 12, an optical coupler (branching coupler) 13, a polarizer 14, and a light receiver. As a photodiode (PD) 15, a modulation component detection unit 16, and an alarm processing unit (determination unit) 29. The optical coupler 13, the polarizer 14, the PD 15, the modulation component detection unit 16, and the alarm processing unit 29 are used as an example of a monitoring device for the polarization scrambler 11.

  A polarization scrambler (polarization modulator) 11 scrambles (modulates or randomizes) the polarization (polarized light) of the input light. For example, the polarization scrambler 11 uses an electro-optic effect such as a lithium niobate (LiNbO3) crystal or an external force such as pressure, vibration, temperature, or magnetic field on the optical fiber at a level that does not cause loss. The thing using the birefringence change which arises by adding can be applied.

完全偏光、即ち、degree of polarization（ＤＯＰ、偏光度）＝１では、（Ｓ０）^１／２＝（Ｓ１）^１／２＋（Ｓ２）^１／２＋（Ｓ３）^１／２が成立する。 Here, the polarization state of light is represented by Stokes parameters S0 (polarization intensity), S1 (horizontal linear polarization component intensity), S2 (45 degree linear polarization component intensity), and S3 (clockwise circular polarization component intensity). be able to. For example, degree of polarization (DOP) can be defined by the following formula (1) using the Stokes parameters S0, S1, S2, and S3.

With perfect polarization, ie, degree of polarization (DOP) = 1, (S0) ^1/2 = (S1) ^1/2 + (S2) ^1/2 + (S3) ^1/2 holds.

  Therefore, the Stokes parameters S1, S2, and S3 representing the polarization state are located at one point on the spherical surface having the radius of the intensity S0. When focusing on the polarization state, considering the light of unit intensity (S0 = 1), the polarization state can be expressed by the position on the unit sphere with S1, S2, and S3 as the three axes of the orthogonal coordinate system. . Such a sphere is called a “Poincare sphere”.

  For example, the control circuit 12 performs control (polarization control signal) corresponding to rotating the Poincare sphere once in a fixed cycle so that the polarization state represented on the Poincare sphere is not biased. By giving to the bra 11, DOP can be brought close to 0% (non-polarized state).

  For example, the DOP is set to 0% (non-polarized state) by performing the control so that the polarization state of the optical signal changes at a speed (frequency) sufficiently faster than the operation speed (response frequency) of the optical amplifier 50. You can get closer. Therefore, it is possible to reduce the signal quality deterioration due to the polarization dependency of the gain of the optical amplifier 50, the polarization dependency of the transmission loss in the optical transmission line, the polarization hole burning, and the like. In this example, it is assumed that the frequency (modulation frequency) of the polarization control signal of the control circuit 12 is several hundred kHz, for example, 100 kHz.

  The branching coupler 13 branches a part of the light scrambled by the polarization scrambler 11 and inputs it to the polarizer 14. The remaining light is transmitted to the optical transmission line.

  The polarizer (polarized wave passing device) 14 passes light polarized in a specific direction out of the light input from the branch coupler 13. Therefore, when the polarization of the input light is not scrambled appropriately, the light whose polarization matches the polarization plane of the polarizer passes through the polarizer 14 in a direct current (DC) manner, and the other polarized light. Will not pass through the polarizer 14. Note that the polarizer 14 is an example of a polarization passing device that passes polarized light in a specific direction, and is not limited to this (the same applies hereinafter).

  On the other hand, when the polarization of the input light is appropriately scrambled, the input light includes light in an arbitrary polarization state on the average, and accordingly, according to the change in polarization by the polarization scrambler 11 Light in a specific polarization state periodically passes through the polarizer 14. That is, when the polarization scrambler 11 is operating properly, the polarizer 14 responds to the polarization control signal (modulation frequency: for example, 600 kHz) given to the polarization scrambler 11 by the control circuit 12. Light having a frequency component (modulation component), in other words, modulated light is output.

  Therefore, by monitoring the output light of the polarizer 14, it can be determined whether or not the polarization scrambler 11 is operating properly. For example, with reference to a modulation component observed (detected) when the polarization scrambler 11 is operating properly, if a modulation component within a predetermined allowable range with respect to the reference is detected, the polarization It can be determined that the scrambler 11 is operating properly.

  On the other hand, if the modulation component outside the allowable range is detected or the modulation component itself is not detected, it can be determined that the polarization scrambler 11 is not operating properly (occurrence of abnormality or performance degradation). If it is determined that the polarization scrambler 11 is not operating properly, the alarm processing unit 29 can generate an alarm or record a log.

  Therefore, in this example, the output light of the polarizer 14 is monitored using the PD 15 and the modulation component detector 16. That is, the PD 15 generates an electrical signal corresponding to the received light intensity of the light that has passed through the polarizer 14 as a monitor value of the output light of the polarization scrambler 11, and the modulation component detector 16 receives the monitor obtained by the PD 15. The modulation component is detected from the value.

  A configuration example of the modulation component detector 16 is shown in FIG. 4 includes, for example, a band pass filter (BPF) 161 and an integration circuit 162.

  The BPF 161 passes a signal component in a predetermined band centered on the modulation frequency among frequency components included in the electrical signal obtained by the PD 15 according to the output light power of the polarizer 14.

  The integration circuit 162 integrates (averages) the signal that has passed through the BPF 161. Thereby, a constant direct current (DC) voltage is obtained as a detection voltage (average value) of the modulation component.

  In order to increase the detection accuracy of the modulation component, the modulation component detection unit 16 may be configured as illustrated in FIG. 5 includes, for example, a BPF 161 and a lock-in amplifier 163 having a multiplier 164 and a low-pass filter (LPF) 165.

  4, the BPF 161 has a predetermined frequency component centered on the modulation frequency out of the frequency components included in the electrical signal obtained by the PD 15 in accordance with the output light power of the polarizer 14. Pass the signal component of the band.

  The lock-in amplifier 163 detects a signal having the same frequency component as the reference signal from the input signal to be measured. Therefore, the input signal is a passing signal of the BPF 161, and the reference signal is a signal of the modulation frequency (for example, the oscillation frequency of a local oscillator not shown) provided to the polarization scrambler 11 by the control circuit 12. (For example, see the dotted arrow in FIG. 3). Thereby, the modulation component can be detected from the output of the BPF 161.

  More specifically, the multiplier 164 multiplies the output signal of the BPF 161 and the signal of the modulation frequency to convert a component equal to the modulation frequency that is a reference signal in the output signal of the BPF 161 into a DC signal. . At this time, other frequency components are converted into AC signals.

  The LPF 165 passes a low frequency signal (DC signal) including the modulation frequency among the output signals of the multiplier 164. Therefore, only the modulation component converted into a DC signal by the multiplier 164 can pass through the LPF 165, and other frequency components converted into the AC signal are removed by the LPF 165. As a result, a constant direct current (DC) voltage is obtained as the detection voltage (average value) of the modulation component at the output of the LPF 165.

  Even if the cutoff frequency of the LPF 165 is slightly shifted, the lock-in amplifier 163 does not greatly affect the measurement result as long as it can pass a DC signal. In addition, a narrow band LPF is easier to realize than a BPF. Therefore, by using the lock-in amplifier 163 as in this example, the detection accuracy of the modulation component can be easily increased.

  The lock-in amplifier 163 may be a phase sensitive detector (PSD) using a switching element instead of the multiplier 164.

  The alarm processing unit 29 includes a comparator (comparator) 291 as shown in FIG. The comparator 291 compares the detection result (constant DC voltage) by the modulation component detection unit 16 with a predetermined alarm threshold voltage. As a result of the comparison, when the detection result is equal to or lower than the alarm threshold voltage, it is determined that the polarization scrambler 11 is not operating properly, and the comparator 291 outputs, for example, an alarm signal. This alarm signal can be notified to an operator of the optical transmission apparatus, for example. Also, an alarm log can be recorded.

  When the performance of the polarization scrambler 11 deteriorates and the polarization cannot be changed sufficiently (scrambled), the signal quality may be rapidly deteriorated depending on the polarization state. May not lead to degradation of signal quality. For this reason, it is not easy to detect the performance deterioration of the polarization scrambler 11 from the error state of the optical signal. Therefore, it is difficult to determine whether the signal quality degradation is caused by the polarization scrambler 11 or an abnormality of another device.

  However, according to this example, it is possible to detect whether or not the polarization scrambler 11 is operating properly with a simple configuration. It is possible to easily monitor, and the cause of signal quality degradation can be easily identified. Further, an expensive measuring device for monitoring the polarization state is not required.

[2] Second Embodiment FIG. 7 is a block diagram illustrating an example of a WDM optical transmission apparatus according to a second embodiment. FIG. 7 illustrates a configuration for monitoring the polarization scrambler 11 that collectively scrambles the WDM light illustrated in FIG. 2.

  The WDM optical transmission apparatus shown in FIG. 7 exemplarily has a point that the input light to the polarization scrambler 11 is WDM light as compared with the configuration shown in FIGS. The difference is that an optical bandpass filter (BPF) 17 is provided between the polarizer 14 and the polarizer 14. In FIG. 7, elements denoted by the same reference numerals as those described above are the same or similar elements as those described above unless otherwise specified. In this example, the optical coupler 13, the BPF 17, the polarizer 14, the PD 15, the modulation component detection unit 16, and the alarm processing unit 29 are used as an example of a monitoring device for the polarization scrambler 11.

  The polarization scrambler 11 receives the WDM signal from the wavelength multiplexing unit 40 shown in FIG. 2 as an input, and applies polarization scramble to the WDM signal collectively under the control of the control circuit 12.

  The BPF 17 passes an optical signal of any wavelength (channel) out of the output (WDM signal) of the polarization scrambler 11 branched by the branch coupler 13. The passing wavelength of the BPF 17 may be fixed or variable.

  As a result, either of the wavelengths included in the WDM signal output from the polarization scrambler 11 corresponds to the modulation frequency given to the polarization scrambler 11 by the control circuit 12 in the same manner as in the first embodiment. The presence / absence of the modulation component can be detected by the polarizer 14, the PD 15, and the modulation component detection unit 16.

  Therefore, according to this example, it is possible to easily monitor the polarization scramble state of the WDM light that is difficult to monitor even with an expensive measuring device that monitors the polarization state.

[3] Third Embodiment FIG. 8 is a block diagram illustrating an example of a WDM optical transmission apparatus according to a third embodiment. FIG. 8 also illustrates a configuration for monitoring the polarization scrambler 11 that collectively polarization scrambles the WDM light illustrated in FIG.

  In the WDM optical transmission apparatus shown in FIG. 8, the input light to the polarization scrambler 11 is a WDM signal, as compared with the configuration shown in FIGS. A difference is that a tracking filter 18 and an optical coupler (branching coupler) 19 are provided between the polarizer 14 and a light receiver (PD) 20 and a tracking filter control unit 21 are provided.

  In FIG. 8, elements indicated by the same reference numerals as those already described are the same as or similar to the elements described above unless otherwise specified. In this example, the optical coupler 13, the tracking filter 18, the optical coupler 19, the PD 20, the tracking filter control unit 21, the polarizer 14, the PD 15, the modulation component detection unit 16, and the alarm processing unit 29 are included in the polarization scrambler 11 monitoring device. Used as an example.

  The polarization scrambler 11 receives the WDM signal from the wavelength multiplexing unit 40 shown in FIG. 2 as an input, and applies polarization scramble to the WDM signal collectively under the control of the control circuit 12.

  The tracking filter 18 is a wavelength tunable filter and sets a passing wavelength (monitoring wavelength) to one of wavelengths (channels) included in the WDM signal by setting (control) from the tracking filter control unit 21. Can do.

  The branch coupler 19 splits the optical signal that has passed through the tracking filter 18 into two, and outputs one to the PD 20 and the other to the polarizer 14.

  The PD 20 generates an electrical signal corresponding to the received light intensity of the optical signal input from the branch coupler 19 and outputs the electrical signal to the tracking filter control unit 21.

  The tracking filter control unit (wavelength filter control unit) 21 controls the passing wavelength (monitoring wavelength) of the tracking filter 18. For example, when the electrical signal level generated by the PD 20 is less than a predetermined threshold, for example, the tracking filter control unit 21 uses the modulation component detection unit 16 to convert the light having a wavelength that passes through the tracking filter 18 into the modulation component described above. It is determined that the light intensity is not sufficient for detection, and the passing wavelength of the tracking filter 18 is set to another wavelength.

  As a result, in the WDM optical transmission apparatus of this example, when an optical signal having a part of the wavelength included in the WDM signal is damaged, the received light intensity sufficient for detecting the modulation component cannot be obtained. Can adaptively switch the channel (monitoring channel) to be detected (monitored) to another channel.

  Therefore, the characteristics of the polarization scrambler 11 can be reliably monitored even in a state where light of some channels of the WDM signal is missing or in a state where the light intensity is not sufficient.

  The tracking filter control unit 21 can also change the passing wavelength of the tracking filter 18, that is, the monitoring channel, at an arbitrary timing. For example, it is possible to periodically change the passing wavelength (monitoring channel) of the tracking filter 18 according to a predetermined rule such as polling.

[4] Fourth Embodiment FIG. 9 is a block diagram illustrating an example of a WDM optical transmission apparatus according to a fourth embodiment. FIG. 9 also illustrates a configuration for monitoring the polarization scrambler 11 that collectively polarization scrambles the WDM light illustrated in FIG.

  The WDM optical transmission apparatus shown in FIG. 9 exemplarily has a light source 22 that outputs light of wavelength λs and an optical signal on the input side of the polarization scrambler 11 as compared with the configuration shown in FIGS. The difference is that a coupler (multiplexing coupler) 23 is provided, and a bandpass filter (BPF) 17 is provided between the branch coupler 13 and the polarizer 14.

  In FIG. 9, elements indicated by the same reference numerals as those described above are the same or similar elements as those described above unless otherwise specified. In this example, the light source 22, the optical coupler 23, the optical coupler 13, the BPF 17, the polarizer 14, the PD 15, the modulation component detection unit 16, and the alarm processing unit 29 are used as an example of a monitoring device for the polarization scrambler 11.

  For example, the light source 22 generates light having a wavelength (λs) other than the wavelength (channel) included in the WDM signal input to the polarization scrambler 11. As the light source 22, a light emitting element such as a laser diode can be used. The light generated by the light source 22 may be a light emission amount smaller than the light emission amount of the light source used for generating the signal light. Therefore, the light source 22 can improve the reliability such that the life can be longer than the light source for signal light.

  The multiplexing coupler 23 combines the WDM signal, which is the transmission signal light, and the direct current light from the light source 22 and inputs them to the polarization scrambler 11.

  The polarization scrambler 11 collectively applies polarization scramble to the WDM light input from the multiplexing coupler 23 under the control of the control circuit 12.

  The polarization-scrambled WDM light is branched into two by the branch coupler 13, one being transmitted to the BPF 17 and the other being transmitted to the optical transmission line.

  The BPF 17 has a passband characteristic that allows light of the light emission wavelength λs of the light source 22 to pass, and allows the light of the wavelength λs to pass through the WDM light input from the branch coupler 13 as light of the monitoring channel.

  The light that has passed through the BPF 17 is input to the polarizer 14. Thereby, it is possible to detect whether or not the light of the wavelength λs of the monitoring channel includes a modulation component according to control (modulation frequency) by the control circuit 22 by the polarizer 14, the PD 15, and the modulation component detection unit 16. It becomes.

  As described above, according to this example, light with a highly reliable wavelength (monitoring channel) λs is wavelength-multiplexed with WDM light and input to the polarization scrambler 11, and the light with wavelength λs is controlled among the output light. The characteristic of the polarization scrambler 11 can be monitored by detecting whether or not the modulation is performed according to the control by the circuit 22. Therefore, the characteristics of the polarization scrambler 11 can be monitored more stably for a longer period than in the embodiment described above.

  Even if signal light of some wavelengths (channels) of WDM light may be lost, it is not necessary to change the monitoring channel separate from the channel of WDM light. It is possible to avoid the trouble of resetting the monitoring channel each time.

[5] Fifth Embodiment FIG. 10 is a block diagram illustrating an example of a WDM optical transmission apparatus according to a fifth embodiment. FIG. 10 also illustrates a configuration for monitoring the polarization scrambler 11 that collectively polarization scrambles the WDM light illustrated in FIG.

  In the WDM optical transmission apparatus shown in FIG. 10, the input light to the polarization scrambler 11 is a WDM signal, as compared with the configuration shown in FIGS. A difference is that a filter 24 and an optical coupler (branching coupler) 25 are provided between the polarizer 14 and a light receiver (PD) 26 and an AC / DC comparison unit 27 are provided.

  In FIG. 10, elements indicated by the same reference numerals as those described above are the same or similar elements as those described above unless otherwise specified. In this example, the optical coupler 13, the filter 24, the optical coupler 25, the PD 26, the polarizer 14, the PD 15, the modulation component detection unit 16, the AC / DC comparison unit 27, and the alarm processing unit 29 are included in the polarization scrambler 11 monitoring device. Used as an example.

  The polarization scrambler 11 collectively applies polarization scramble to the input WDM light under the control of the control circuit 12.

  The polarization-scrambled WDM light is branched into two by the branch coupler 13, one being transmitted to the filter 24 and the other being transmitted to the optical transmission line.

  The filter 24 has a pass wavelength characteristic that allows any one of the wavelengths included in the WDM light to pass, and is, for example, a BPF with a fixed or variable pass wavelength.

  The branch coupler 25 splits the light that has passed through the filter 24 into two, and outputs one to the polarizer 14 and the other to the PD 26.

  The PD 26 generates, as a monitor value, an electric signal corresponding to the intensity (DC component) of the branched light from the branch coupler 25, that is, the light that has passed through the filter 24 before passing through the polarizer 14. The monitor value is input to the AC / DC comparison unit 27.

  On the other hand, the polarizer 14, the PD 15, and the modulation component detection unit 16 detect the presence or absence of the modulation component with respect to the light that has passed through the filter 24. The detection result (modulation component (AC component) after passing through the polarizer 14) is input to the AC / DC comparison unit 27.

  The AC / DC comparison unit 27 compares the DC component from the PD 26 with the AC component from the modulation component detection unit 16 to detect the degree of modulation of the polarization scrambler 11, and uses the detected information as the polarization scrambler 11. To give feedback.

  In general, the DOP of the polarization scrambler 11 changes depending on the voltage applied to the polarization scrambler 11, whether it is a type that uses an LN modulator or a type that applies pressure to an optical fiber.

  Therefore, a stable control for making DOP constant is realized by applying feedback to the control circuit 12 of the polarization scrambler 11 so that the ratio of the AC component to the DC component (AC / DC) is constant. Can do.

  That is, the AC / DC comparison unit 27 of the present example allows the control circuit 12 to control the polarization scrambler so that the ratio between the direct current component of the output light of the polarization scrambler 11 and the modulation component that is an alternating current component is constant. This is used as an example of an adjustment unit that adjusts a control signal given to the bra 11.

[6] Sixth Embodiment FIG. 11 is a block diagram illustrating an example of a WDM optical transmission apparatus according to a sixth embodiment. FIG. 11 illustrates a configuration for monitoring the polarization controller for one wavelength illustrated in FIG.

  The WDM optical transmission apparatus shown in FIG. 11 exemplarily includes polarization scramblers 11A and 11B connected in series, control circuits 12A and 12B for the polarization scramblers 11A and 11B, an optical coupler ( A branch coupler) 13, a polarizer 14, a light receiver (PD) 15, a modulation component detector 16, and an ON / OFF switching controller 28 are provided. In this example, the optical coupler 13, the polarizer 14, the PD 15, the modulation component detection unit 16, the ON / OFF switching control unit 28, and the alarm processing unit 29 are used as an example of a monitoring device for the polarization scrambler 11.

  The polarization scramblers 11A and 11B (hereinafter referred to as the polarization scrambler 11 if not distinguished from each other) are the same as or similar to the polarization scrambler 11 described above, and the corresponding control circuit 12A. , 12B, the input light polarization is scrambled. The polarization scrambler 11A and the polarization scrambler 11B may be of the same type (LN type, pressure type, etc.), or may be of different types.

  The control circuits (polarization controllers) 12A and 12B are the same as or similar to the control circuit 12 described above, for example, so that the polarization state expressed on the Poincare sphere described above is not biased. By applying the control equivalent to rotating the Poincare sphere once at a constant period to the corresponding polarization scramblers 11A and 11B, the DOP of the input light can be brought close to 0% (non-polarized state).

  Also in this example, the control circuits 12A and 12B each perform the control so that, for example, the polarization state of the optical signal changes at a speed (frequency) sufficiently higher than the operation speed (response frequency) of the optical amplifier 50. By doing so, DOP can be brought close to 0% (average polarization state). The frequency at that time can also be set to several hundred kHz, for example, 100 kHz, as in the above-described embodiment.

  The control circuits 12A and 12B may be a control circuit common to the polarization scramblers 11A and 11B.

  Based on the detection result of the modulation component detection unit 16, the ON / OFF switching control unit 28 performs control to set one of the control circuits 12 </ b> A and 12 </ b> B to an operation (ON) state and the other to a non-operation (OFF) state. Do.

  For example, when the control circuit 12A is in the ON state and the control circuit 12B is in the OFF state, the modulation component detection unit 16 does not detect the appropriate modulation component (the detection result by the detection unit is a predetermined value). It is below the threshold). In this case, the ON / OFF switching control unit 28 switches the polarization scrambler 11B to be operated to a different polarization scrambler 11B by setting the control circuit 12A to the OFF state and the control circuit 12B to the ON state.

  Note that the detection operation of the modulation component by the polarizer 14, the PD 15, and the modulation component detection unit 16 is the same as the detection operation described in the above-described embodiment.

  In general, the scramble function of the polarization scramblers 11A and 11B is realized by using passive components such as optical fibers, so that one of the polarization scramblers 11A and 11B connected in series causes a failure or performance degradation. However, the signal light is not cut off.

  Therefore, as described above, a plurality of polarization scramblers 11 are connected in series and made redundant, and the polarization component scrambler 11 in the ON state is detected when the modulation component detection unit 16 does not detect an appropriate modulation component. Is controlled to be in an OFF state, and any one of the other polarization scramblers 11 in the OFF state is controlled to be in an ON state, so that the polarization can be appropriately operated without stopping the operation of the WDM optical transmission apparatus. Switching to the scrambler 11 can be performed.

  Regarding the embodiment described in the items [1] to [6], the following additional notes are disclosed.

[7] Appendix (Appendix 1)
A polarization scrambler monitoring device that scrambles the polarization state of input light according to a polarization control signal,
A polarization passing device that passes light of a specific polarization out of the output light of the polarization scrambler,
A detection unit that detects a modulation component according to the frequency of the polarization control signal from light that has passed through the polarization passing device;
A polarization scrambler monitoring device characterized by comprising:

(Appendix 2)
The polarization according to claim 1, further comprising a determination unit that determines that the polarization scrambler is not operating normally when a detection result by the detection unit is equal to or less than a predetermined threshold value. Scrambler monitoring device.

(Appendix 3)
The input light is a wavelength multiplexed light in which a plurality of wavelengths of light are wavelength multiplexed,
The monitoring device
The supplementary note 1 or 2, further comprising a wavelength filter that passes through any one of the plurality of wavelengths of the output light of the polarization scrambler and inputs the light to the polarization passing device. Polarization scrambler monitoring device.

(Appendix 4)
The wavelength filter is a filter whose pass wavelength is variable,
The monitoring device
4. The polarization scrambler monitoring apparatus according to claim 3, further comprising a wavelength filter control unit that changes the passing wavelength when a detection result by the detection unit is equal to or less than a predetermined threshold.

(Appendix 5)
A light source that generates light having a monitoring wavelength different from the wavelength of the input light;
A wavelength multiplexing unit that wavelength-multiplexes the light generated by the light source with the input light;
The polarization scrambler according to appendix 1 or 2, further comprising: a wavelength filter that passes the monitoring wavelength light among the output light of the polarization scrambler and inputs the light to the polarization passing device. Bra monitoring device.

(Appendix 6)
The apparatus further includes an adjustment unit that adjusts the polarization control signal so that a ratio between a direct current component of the output light of the polarization scrambler and the modulation component that is an alternating current component is constant. The polarization scrambler monitoring apparatus according to any one of 1 to 5.

(Appendix 7)
A plurality of the polarization scramblers connected in series;
The monitoring device
Any one of Supplementary notes 1 to 6, further comprising: a switching control unit that switches a polarization scrambler to be operated to a different polarization scrambler when a detection result by the detection unit is equal to or less than a predetermined threshold value. The polarization scrambler monitoring device described in the paragraph.

(Appendix 8)
The polarization scrambler monitoring apparatus according to any one of appendices 1 to 7, wherein the polarization passing device is a polarizer.

(Appendix 9)
A polarization scrambler that scrambles the polarization state of the input light;
A polarization controller for controlling the scramble by giving a polarization control signal to the polarization scrambler;
A polarization passing device that passes light of a specific polarization out of the output light of the polarization scrambler,
A detection unit that detects a modulation component according to the frequency of the polarization control signal from light that has passed through the polarization passing device;
An optical transmission device characterized by comprising:

(Appendix 10)
A polarization scrambler monitoring method that scrambles the polarization state of input light according to a polarization control signal,
Pass the light of a specific polarization out of the output light of the polarization scrambler by a polarization passing device,
Detecting a modulation component corresponding to the frequency of the polarization control signal from the light passing through the polarization passing device;
A method for monitoring a polarization scrambler.

It is a block diagram which shows the structural example of the transmission system of a WDM optical transmission apparatus. It is a block diagram which shows the other structural example of the transmission system of a WDM optical transmission apparatus. It is a block diagram which shows an example of the monitoring apparatus of the polarization scrambler which concerns on 1st Embodiment. FIG. 4 is a block diagram illustrating a configuration example of a modulation component detection unit illustrated in FIG. 3. FIG. 4 is a block diagram illustrating another configuration example of the modulation component detection unit illustrated in FIG. 3. It is a figure which shows the structural example of the alarm process part illustrated in FIG. It is a block diagram which shows an example of the monitoring apparatus of the polarization scrambler which concerns on 2nd Embodiment. It is a block diagram which shows an example of the monitoring apparatus of the polarization scrambler which concerns on 3rd Embodiment. It is a block diagram which shows an example of the monitoring apparatus of the polarization scrambler which concerns on 4th Embodiment. It is a block diagram which shows an example of the monitoring apparatus of the polarization scrambler which concerns on 5th Embodiment. It is a block diagram which shows an example of the monitoring apparatus of the polarization scrambler which concerns on 6th Embodiment.

11, 11A, 11B Polarization scrambler 12, 12A, 12B Control circuit (polarization controller)
13 Optical coupler (branch coupler)
14 Polarizer (Polarization passing device)
15 Receiver (PD)
16 Modulation component detector 161 Band pass filter (BPF)
162 Integration circuit 163 Lock-in amplifier 164 Multiplier 165 Low-pass filter (LPF)
17 Bandpass filter (BPF)
18 Tracking filter 19 Optical coupler (branch coupler)
20 Receiver (PD)
21 Tracking filter control unit 22 Light source 23 Optical coupler (multiplexing coupler)
24 filter 25 optical coupler (branch coupler)
26 Light receiver (PD)
27 AC / DC comparison unit (adjustment unit)
28 ON / OFF switching control unit 29 Alarm processing unit (determination unit)
291 Comparator
40 Wavelength multiplexing unit 50 Optical amplifier

Claims (7)

A polarization scrambler monitoring device that scrambles the polarization state of input light according to a polarization control signal given from a polarization controller,
A polarization passing device that passes light of a specific polarization out of the output light of the polarization scrambler,
A photoelectric converter that generates an electrical signal according to the received light intensity of the light that has passed through the polarization passing device;
A detection unit for detecting a modulation component corresponding to the frequency of the polarization control signal from the electrical signal;
With
The detection unit detects a signal having the same frequency component as the modulation frequency signal of the polarization control signal from the wavelength filter that passes a signal of a component in a predetermined band among frequency components included in the electrical signal. An amplifier circuit for detecting the modulation component from the output from the wavelength filter;
A polarization scrambler monitoring device characterized by comprising:   The deviation according to claim 1, further comprising a determination unit that determines that the polarization scrambler is not operating normally when a detection result by the detection unit is equal to or less than a predetermined threshold. Wave scrambler monitoring device. The input light is a wavelength multiplexed light in which a plurality of wavelengths of light are wavelength multiplexed,
The monitoring device
3. The apparatus according to claim 1, further comprising a wavelength filter that passes any one of the plurality of wavelengths of the output light of the polarization scrambler and inputs the light to the polarization passing device. Polarization scrambler monitoring device. The wavelength filter is a filter whose pass wavelength is variable,
The monitoring device
4. The polarization scrambler monitoring apparatus according to claim 3, further comprising a wavelength filter control unit that changes the passing wavelength when a detection result by the detection unit is equal to or less than a predetermined threshold value. A light source that generates light having a monitoring wavelength different from the wavelength of the input light;
A wavelength multiplexing unit that wavelength-multiplexes the light generated by the light source with the input light;
The polarization filter according to claim 1, further comprising: a wavelength filter that passes light of the monitoring wavelength out of output light of the polarization scrambler and inputs the light to the polarization passing device. Scrambler monitoring device. A polarization scrambler that scrambles the polarization state of the input light;
A polarization controller for controlling the scramble by giving a polarization control signal to the polarization scrambler;
A polarization passing device that passes light of a specific polarization out of the output light of the polarization scrambler,
A photoelectric converter that generates an electrical signal according to the received light intensity of the light that has passed through the polarization passing device;
A detection unit for detecting a modulation component corresponding to the frequency of the polarization control signal from the electrical signal;
With
The detection unit detects a signal having the same frequency component as the modulation frequency signal of the polarization control signal from the wavelength filter that passes a signal of a component in a predetermined band among frequency components included in the electrical signal. An amplifier circuit for detecting the modulation component from the output from the wavelength filter;
An optical transmission device characterized by comprising: A polarization scrambler monitoring method for scrambling the polarization state of input light according to a polarization control signal given from a polarization controller,
Pass the light of a specific polarization out of the output light of the polarization scrambler by a polarization passing device,
Generate an electrical signal according to the received light intensity of the light that has passed through the polarization passing device,
Among the frequency components included in the electrical signal, a signal of a predetermined band component is passed through a wavelength filter,
Detecting the modulation component from the output from the wavelength filter by detecting a signal having the same frequency component as the modulation frequency signal of the polarization control signal from the signal;
A method for monitoring a polarization scrambler.

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