Optical transmission line monitoring device, optical transmission line monitoring system and optical transmission line monitoring method

Abstract

Provided are an optical transmission line monitoring device, an optical transmission line monitoring system, and an optical transmission line monitoring method capable of monitoring multiple optical transmission lines in parallel. A monitoring light output unit (1) outputs monitoring light (ML1-MLn) having different frequencies to an optical transmission line (LA1-LAn). A local oscillator light source (2) outputs local oscillator light (LO). An interference unit (3) to which return light (BL1-BLn) corresponding to the monitoring light (ML1-MLn) is input is configured to output output light generated by interference between the input light and the local oscillator light (LO). A conversion unit (4) converts the output light into an electrical signal (ED). A signal processing unit (5) extracts an intermediate frequency signal from the electrical signal (ED) based on each monitoring light (ML1-MLn), and generates a monitoring result of the optical transmission line (LA1-LAn) from the intermediate frequency signal.

Description

Technical Field

[0001] The present invention relates to an optical transmission line monitoring device, an optical transmission line monitoring system and an optical transmission line monitoring method. Background Art

[0002] In an optical network system connected by optical transmission lines, a fault such as a break in the optical transmission line may occur, and in order to detect such a fault, an optical transmission line monitoring device such as COTDR (Coherent Optical Time Domain Reflectometer) is used. Generally, such an optical transmission line monitoring device outputs an optical pulse (monitor light) to the optical transmission line, and obtains a relationship between a received power level and a distance as a cable loss trace from the reception time of a return light generated by scattering the monitor light.

[0003] For example, a COTDR device for use in a submarine cable system has been proposed (Patent Document 1). According to the COTDR device, uplink and downlink optical transmission lines are laid on the seabed, and the device outputs monitoring light to the uplink optical transmission line, and receives the monitoring light returned through the downlink optical transmission line by coherent detection, thereby obtaining the measurement result of the optical transmission line.

[0004] In addition, COTDR measurement capable of improving monitoring performance has been proposed (Patent Document 2). This technology outputs a plurality of monitoring lights having different frequencies to one optical transmission line and receives their return lights by coherent detection, which enables reduction of detection time.

[0005] Reference List

[0006] Patent Literature

[0007] PTL1: Japanese translation of PCT international patent application publication No. 2007-518365

[0008] PTL2: Japanese translation of PCT international patent application publication No. 2012-506651 Summary of the invention

[0009] Technical issues

[0010] Since a plurality of optical transmission lines (systems) composed of optical fibers are placed in a submarine cable, it is necessary to establish a technology for monitoring a plurality of optical transmission lines. In addition, since there may be a situation where a plurality of optical transmission lines are managed by different operators, or a plurality of optical transmission lines are managed by one operator but are managed separately in order to use different optical transmission lines according to the purpose, it is necessary to monitor the plurality of optical transmission lines independently of each other. Therefore, it is desirable to monitor the respective optical transmission lines in parallel. However, the above-mentioned COTDR device and COTDR measurement are designed to monitor one optical transmission line, and they are not intended to monitor a plurality of optical transmission lines in parallel.

[0011] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an optical transmission line monitoring device, an optical transmission line monitoring system, and an optical transmission line monitoring method capable of monitoring a plurality of optical transmission lines in parallel.

[0012] Technical Solutions

[0013] According to one aspect of the present invention, an optical transmission line monitoring device includes: a monitoring light output unit, which is configured to output a plurality of monitoring lights with different frequencies to a plurality of first optical transmission lines respectively; a local oscillator light source, which is configured to output local oscillator light; an interference unit, to which a plurality of return lights corresponding to the plurality of monitoring lights are input, and the interference unit is configured to output output light generated by interference between the input light and the local oscillator light; a conversion unit, which is configured to convert the output light into an electrical signal; and a signal processing unit, which is configured to extract signals with beat frequencies from the electrical signal respectively based on the plurality of monitoring lights, and generate monitoring results for each first optical transmission line from the signals with beat frequencies.

[0014] According to one aspect of the present invention, an optical transmission line monitoring system includes: an optical transmission device, which is configured to output optical signals to multiple first optical transmission lines; and an optical transmission line monitoring device, which is connected to the optical transmission device and configured to monitor the multiple first optical transmission lines, wherein the optical transmission line monitoring device includes: a monitoring light output unit, which is configured to output multiple monitoring lights with different frequencies to the multiple first optical transmission lines respectively; a local oscillator light source, which is configured to output local oscillator light; an interference unit, to which multiple return lights corresponding to the multiple monitoring lights are input, and the interference unit is configured to output output light generated by interference between the input light and the local oscillator light; a conversion unit, which is configured to convert the output light into an electrical signal; and a signal processing unit, which is configured to extract signals with beat frequencies from the electrical signals based on the multiple monitoring lights, and generate monitoring results for each first optical transmission line from the signals with beat frequencies.

[0015] According to one aspect of the present invention, a method for monitoring an optical transmission line includes: outputting a plurality of monitoring lights with different frequencies to a plurality of first optical transmission lines respectively; outputting output light generated by interference between a plurality of return lights corresponding to the plurality of monitoring lights and a local oscillator light; converting the output light into an electrical signal; and based on the plurality of monitoring lights, extracting a signal with a beat frequency from the electrical signal respectively, and generating a monitoring result for each of the first optical transmission lines from the signal with the beat frequency.

[0016] Beneficial Effects

[0017] According to the present invention, there are provided an optical transmission line monitoring device, an optical transmission line monitoring system, and an optical transmission line monitoring method capable of monitoring a plurality of optical transmission lines in parallel. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 : is a diagram showing connections when an optical network is monitored by the optical transmission line monitoring device according to the first exemplary embodiment.

[0019] Figure 2 is a view schematically showing the structure of an optical repeater.

[0020] Figure 3 is a view schematically showing the structure of an optical transmission line monitoring device according to a first exemplary embodiment.

[0021] Figure 4 is a view showing the structure of the optical transmission line monitoring device according to the first exemplary embodiment in more detail.

[0022] Figure 5 is a view schematically showing the structure of a monitor light output unit according to the first exemplary embodiment.

[0023] Figure 6 : is a diagram showing the relationship among the frequency of the return light, the frequency of the local oscillation light, and the intermediate frequency.

[0024] Figure 7 is a view schematically showing an example of the structure of an interference unit according to the first exemplary embodiment.

[0025] Figure 8 is a view schematically showing the structure of a conversion unit according to the first exemplary embodiment.

[0026] Fig. 9 is a view schematically showing the structure of a signal processing unit according to the first exemplary embodiment.

[0027] Fig.10 is a view schematically showing the relationship of an optical transmission line, monitor light, and return light according to the first exemplary embodiment.

[0028] Fig.11 is a view showing a return light generating mechanism according to the first exemplary embodiment.

[0029] Fig.12 is a diagram showing an example of a waveform of return light.

[0030] Fig.13 is a view schematically showing transmission of monitor light and return light according to the first exemplary embodiment.

[0031] Fig.14 : is a view showing a modified example of the optical transmission line monitoring device according to the first exemplary embodiment.

[0032] Fig.15 It is shown Fig.13 A view of an example of a waveform of return light in the structure shown.

[0033] Fig.16 is a view schematically showing a table in the control unit.

[0034] Fig.17 2 is a view schematically showing propagation paths of monitor light and return light according to the second exemplary embodiment.

[0035] Fig.18 2 is a view schematically showing propagation paths of monitor light and return light according to the third exemplary embodiment.

[0036] Fig.19 2 is a view schematically showing propagation paths of monitor light and return light according to the fourth exemplary embodiment.

[0037] Fig. 20 is a view schematically showing propagation of monitor light and return light according to the fifth exemplary embodiment.

[0038] Fig.21 : is a view showing connections when an optical network is monitored by the optical transmission line monitoring device according to the sixth exemplary embodiment.

[0039] Fig. 22 is a view schematically showing the structure of a monitor light output unit in a first modified example.

[0040] Fig.23 is a view schematically showing the structure of a monitor light output unit in a second modified example.

[0041] Fig.24 is a view schematically showing the structure of a monitor light output unit in a third modified example.

[0042] Fig.25 is a view schematically showing the structure of an interference unit in a modified example.

[0043] Fig.26 is a view schematically showing the structure of an interference unit and a conversion unit in a modified example. DETAILED DESCRIPTION

[0044] Hereinafter, exemplary embodiments of the present invention will be described with reference to the accompanying drawings. In the description of the accompanying drawings, the same elements will be denoted by the same reference numerals, and redundant description will be omitted when necessary.

[0045] First Exemplary Embodiment

[0046] Hereinafter, an optical transmission line monitoring device 100 according to a first exemplary embodiment is described. For example, the optical transmission line monitoring device detects a fault in an optical transmission line constituting various optical networks such as a submarine optical network. The optical transmission line monitoring device 100 detects a fault in an optical transmission line, for example, by outputting an optical pulse as monitoring light to an optical transmission line connected to an optical transmission device placed in a terminal station and measuring the intensity of its return light.

[0047] Figure 1 1 shows the connection when the optical network 1000 is monitored by the optical transmission line monitoring device 100 according to the first exemplary embodiment. The terminal station TS0 is connected to a plurality of terminal stations TS1 to TSn (n is an integer of 2 or more) through an optical transmission line. Note that the terminal stations TS1 to TSn are not limited to individual terminal stations, and some or all of the terminal stations TS1 to TSn may be regarded as a plurality of optical transmission devices installed in one terminal station.

[0048] The terminal station TS0 includes a plurality of optical transmission devices TR1 to TRn. The optical transmission devices TR1 to TRn include transmitters T1 to Tn and receivers R1 to Rn, respectively. The terminal stations TS1 to TSn include transmitters TT1 to TTn and receivers RR1 to RRn, respectively.

[0049] The optical signals output from the transmitters T1 to Tn are transmitted to the receivers RR1 to RRn of the terminal stations TS1 to TSn through the optical transmission lines LA1 to LAn (also referred to as the first optical transmission lines), respectively. The optical signals output from the transmitters TT1 to TTn of the terminal stations TS1 to TSn are transmitted to the receivers R1 to Rn of the terminal station TS0 through the optical transmission lines LB1 to LBn (also referred to as the second optical transmission lines), respectively. In other words, the optical transmission line LAk (k is an integer from 1 to n) and the optical transmission line LBk form a pair of optical transmission lines, which connect the terminal station TS0 and the optical transmission device TRk of the terminal station TSK.

[0050] One or more optical repeaters RP are inserted in the optical transmission line LAk and the optical transmission line LBk of the optical transmission line pair. Figure 2 The structure of the optical repeater RP is schematically shown. The optical repeater RP includes optical amplifiers A1 and A2 and couplers CP1 and CP2.

[0051] The optical amplifier A1 is inserted into the optical transmission line LAk, and amplifies an optical signal transmitted to the terminal station Tsk through the optical transmission line LAk.

[0052] For example, the coupler CP1 is configured as a directional coupler or an optical circulator. The coupler CP1 is inserted into the rear stage of the optical amplifier A1, and selectively branches an optical signal propagating in the opposite direction to the optical signal transmitted to the terminal station TS0 through the optical transmission line LAk (i.e., the return light BLk described later), and outputs the branched optical signal to the coupler CP2.

[0053] The optical amplifier A2 is inserted into the optical transmission line LBk, and amplifies an optical signal transmitted through the optical transmission line LBk.

[0054] For example, the coupler CP2 is configured as a directional coupler or an optical circulator. The coupler CP2 is inserted into the rear stage of the optical amplifier A2, and couples the optical signal output from the coupler CP1 (the return light BLk described later) to the optical transmission line LBk. The coupled optical signal (i.e., the return light BLk described later) is transmitted to the terminal station TS0 through the optical transmission line LBk. Note that the coupler CP2 can be inserted into the front stage of the optical amplifier A2, and the coupler CP2 can couple the optical signal output from the coupler CP1 (i.e., the return light BLk described later) to the optical transmission line LBk, thereby inputting the coupled light (feedback light BLk) to the optical amplifier A2. In this case, the optical amplifier A2 can amplify and output the input light (feedback light BLk).

[0055] The optical transmission line monitoring device 100 is connected to the terminal station TS0 in order to detect faults in the optical transmission lines LA1 to LAn. In the terminal station TS0, couplers CA1 to CAn are respectively inserted into the rear stage of the transmitters T1 to Tn. For example, the couplers CA1 to CAn are the connection ports of the optical transmission line monitoring device 100 and are configured as directional couplers or optical circulators. The couplers CA1 to CAn couple the monitoring lights ML1 to MLn having different frequencies output from the optical transmission line monitoring device 100 to the optical transmission lines LA1 to LAn, respectively. Thus, the monitoring lights ML1 to MLn are respectively transmitted through the optical transmission lines LA1 to LAn toward the terminal stations TS1 to TSn.

[0056] Furthermore, in the terminal station TS0, couplers CB1 to CBn are inserted in the preceding stages of the receivers R1 to Rn, respectively. The couplers CB1 to CBn are connection ports of the optical transmission line monitoring device 100, and are configured as directional couplers or optical circulators, for example.

[0057] As described above, when the monitor lights ML1 to MLn are output to the optical transmission lines LA1 to LAn, respectively, feedback lights BL1 to BLn propagating in the opposite direction to the monitor lights ML1 to MLn are generated due to Rayleigh scattering (backscattering) in the optical transmission lines LA1 to LAn. The feedback lights BL1 to BLn are branched from the optical transmission lines LA1 to LAn by the optical repeater RP, and then coupled to the optical transmission lines LB1 to LBn, and are transmitted to the couplers CB1 to CBn, respectively. Note that the feedback light may include not only scattered light generated by Rayleigh scattering, but also scattered light generated by another scattering such as Brillouin scattering or Raman scattering, or may include reflected light.

[0058] The couplers CB1 to CBn respectively branch the return lights BL1 to BLn having different frequencies and output them to the optical transmission line monitoring device 100 .

[0059] The optical transmission line monitoring device 100 according to the present exemplary embodiment detects the intensities of the received return lights BL1 to BLn having different frequencies, thereby detecting a fault in the optical transmission lines LA1 to LAn. Hereinafter, the optical transmission line monitoring device 100 is described in detail. Figure 3 The structure of an optical transmission line monitoring device 100 according to the first exemplary embodiment is schematically shown. The optical transmission line monitoring device 100 includes a monitoring light output unit 1, a local oscillation light source 2, an interference unit 3, a conversion unit 4, and a signal processing unit 5.

[0060] The monitoring light output unit 1 outputs monitoring lights ML1 to MLn having different frequencies to the optical transmission lines LA1 to LAn, respectively. The monitoring light output unit 1 may sequentially output the monitoring lights ML1 to MLn having different frequencies, or may output some or all of the monitoring lights ML1 to MLn simultaneously.

[0061] Note that the output operation of the monitor light output unit 1 that outputs the monitor lights ML1 to MLn may be controlled by a control unit included in the optical transmission line monitoring device 100 . Figure 4 The structure of the optical transmission line monitoring device 100 according to the first exemplary embodiment is shown in more detail. Figure 4 As shown, the optical transmission line monitoring device 100 may include a control unit 6. In this example, control signals C1 to Cn for controlling the frequency and output timing of the monitoring lights ML1 to MLn are applied to the control unit 6, respectively. Based on the control signals C1 to Cn, the control unit 6 outputs a control signal CON1 to the monitoring light output unit 1. Based on the control signal CON1, the monitoring light output unit 1 controls the frequency of the monitoring lights ML1 to MLn, and outputs the monitoring lights ML1 to MLn at a specified timing.

[0062] Figure 5The structure of the monitoring light output unit 1 according to the first exemplary embodiment is schematically shown. The monitoring light output unit 1 includes a light pulse generating unit 11 and a monitoring light generating unit 12. In this example, the control signal CON1 includes control signals CON11 and CON12, and the control signal CON11 is applied to the light pulse generating unit 11, and the control signal CON12 is applied to the monitoring light generating unit 12.

[0063] The optical pulse generating unit 11 includes a light source such as a laser element, and outputs an optical pulse OP to the monitoring light generating unit 12 based on a control signal CON11 .

[0064] Based on the control signal CON12, the monitoring light generating unit 12 converts the frequency of the optical pulse OP and generates monitoring light, and outputs the generated monitoring light to any one of the optical transmission lines LA1 to LAn. The monitoring light generating unit 12 can be configured as, for example, an acousto-optic element. The acousto-optic element can modulate the intensity of the received optical pulse OP and deflect the optical pulse OP (path control). In addition, the acousto-optic element can shift the frequency of the optical pulse OP according to the frequency of the applied sound wave (frequency conversion). Therefore, using the frequency f0 of the optical pulse OP as a reference, it is possible to convert the optical pulse OP having different frequencies f1 to f n The monitor lights ML1 to MLn are output to the optical transmission lines LA1 to LAn respectively. Note that the frequencies f1 to f n Any one of can be the same as frequency f0.

[0065] The local oscillator light source 2 includes a light source such as a laser element and has a frequency f LO The local oscillation light LO of the local oscillation light source 2 is output to the interference unit 3. The local oscillation light output operation of the local oscillation light source 2 can be controlled by a control signal provided from the control unit 6.

[0066] The return lights BL1 to BLn (having frequencies f1 to f n ) are input from the optical transmission lines LB1 to LBn to the interference unit 3, and the interference unit 3 outputs output light generated by interference between the local oscillator light LO and the return light BL1 to BLn. Therefore, the light output from the interference unit 3 contains light having a beat frequency |f generated by interference between the return light BL1 to BLn and the local oscillator light LO. LO -f1|to|f LO -f n |The weight.

[0067] Figure 6 The frequencies of the return lights BL1 to BLn (frequencies f1 to f n ), the frequency f of the local oscillator light LO LO With |f LO -f1|to|fLO -f n |. When two lights with different frequencies interfere, a beat is generated. The frequency of the beat is the beat frequency. Figure 6 As shown, when the frequency f1 to f n The return light BL1 to BLn has a frequency f LO When the local oscillator light LO interferes, the beat frequency is |f LO -f1|to|f LO -f n |frequency component.

[0068] Since the return lights BL1 to BLn are not necessarily input to the interference unit 3 at the same time, depending on the frequency of the output monitor light, any one or some of the return lights BL1 to BLn interfere with the local oscillator light LO in the interference unit 3. However, all the return lights BL1 to BLn may of course interfere with the local oscillator light LO at the same time.

[0069] Figure 7 An example of the structure of the interference unit 3 according to the first exemplary embodiment is schematically shown. In order to simplify the description, hereinafter, an example in which four return lights and the local oscillation light LO are input to the interference unit 3 is described. The interference unit 3 includes couplers 31 to 34. The couplers 31 to 34 are configured as 2-input 1-output couplers. In order to multiplex the return lights BL1 to BL4 into one (guide them to one propagation path), the couplers 31 to 34 are cascaded.

[0070] The return light BL1 and the return light BL2 are input to the coupler 31, and the outputs thereof are connected to one input of the coupler 33. The return light BL3 and the return light BL4 are input to the coupler 32, and the outputs thereof are connected to the other input of the coupler 33. The output of the coupler 33 is connected to one input of the coupler 34. The other input of the coupler 34 is connected to the local oscillation light source 2, and the local oscillation light LO is input thereto, and the output thereof is connected to the conversion unit 4.

[0071] Although the case where return light having four different frequencies is input is described above, a structure resulting in return light having two, three, five or more different frequencies and local oscillation light LO can be realized by changing the number of couplers and the number of cascade connections.

[0072] The conversion unit 4 converts the output light output from the interference unit 3 into an analog electric signal EA, further converts the analog electric signal EA into a digital electric signal ED, and outputs the signal to the signal processing unit 5 . Figure 8The structure of the conversion unit 4 according to the first exemplary embodiment is schematically shown. The conversion unit 4 includes a photoelectric conversion unit 41 and an analog-to-digital (A / D) conversion unit 42 .

[0073] For example, the photoelectric conversion unit 41 can be configured using a photodiode and a transimpedance amplifier. The photodiode converts the output light output from the interference unit 3 into a current signal. The transimpedance amplifier converts the current signal into an analog electric signal EA as a voltage signal, amplifies the signal, and outputs the signal to the A / D conversion unit 42. The A / D conversion unit 42 converts the analog electric signal EA into a digital electric signal ED, and outputs the signal to the signal processing unit 5.

[0074] The signal processing unit 5 separates the signal having the beat frequency |f contained in the digital electrical signal ED LO -f1|to|f LO -f n | signal components and performs signal processing, and then outputs data signals D1 to Dn indicating the detection results thereof.

[0075] Fig. 9 The structure of the signal processing unit 5 according to the first exemplary embodiment is schematically shown. The signal processing unit 5 includes filters F1 to Fn and data processing units P1 to Pn. The digital electric signal ED is input to the filters F1 to Fn, and the filters F1 to Fn make the signal corresponding to the beat frequency |f LO -f1|to|f LO -f n The signal components of | pass therethrough respectively. The signals having passed through the filters F1 to Fn are processed by the data processing units P1 to Pn respectively, and are converted into data signals D1 to Dn and then output.

[0076] As described above, filters F1 to Fn are respectively used to make the filters have a specified beat frequency |f LO -f1|to|f LO -f n |The signal passes through this, ensuring that the data signals D1 to Dn correspond to the monitor lights ML1 to MLn, that is, the optical transmission lines LA1 to LAn.

[0077] In the case where the pass frequencies of the filters F1 to Fn are fixed, the data processing units P1 to Pn can appropriately output the data signals D1 to Dn corresponding to the optical transmission lines LA1 to LAn, respectively, by associating the pass frequencies of the filters F1 to Fn with the optical transmission lines LA1 to LAn. This can be achieved by providing the signal processing unit 5 with a table 51, which represents the association between the pass frequencies of the filters F1 to Fn and the optical transmission lines LA1 to LAn, so that the data processing units P1 to Pn refer to the table 51 as appropriate. In addition, when the frequency of the monitoring light to be assigned to each system is changed, the association defined by the table can be appropriately updated according to the change. Note that the data signals D1 to Dn are not necessarily output to one destination (e.g., one administrator terminal). Specifically, the data signals D1 to Dn can be output to any destination, such as multiple corresponding destinations (e.g., multiple administrator terminals), respectively.

[0078] When the frequencies f1 to f2 of the monitoring lights ML1 to MLn are n and the frequency f of the local oscillator LO LO If there is a possibility of change, the pass frequency of the filters F1 to Fn can be changed as appropriate. LO -f1|to|f LO -f n For example, the pass frequencies of the filters F1 to Fn can be adjusted as needed by applying control signals C1 to Cn to the control unit 6 and then applying a control signal CON2 from the control unit 6 to the signal processing unit 5 based on the control signals C1 to Cn.

[0079] As described above, even when some or all of the return lights BL1 to BLn having different frequencies are input to the interference unit 3 in a simultaneous or overlapping manner, the signal processing unit 5 is able to independently monitor the return lights based on the beat frequency, which allows the optical transmission lines LA1 to LAn to be monitored in parallel. Therefore, the return lights having different frequencies do not need to be discrete in time, which enables frequent and high-speed detection of faults in multiple optical transmission line pairs.

[0080] Fig.10 The relationship among the optical transmission line, the monitoring light, and the return light in the first exemplary embodiment is schematically shown. Fig.10 As shown, it will have frequencies from f1 to f n The monitoring lights ML1 to MLn are sequentially output to the optical transmission lines LA1 to LAn, and the return lights BL1 to BLn generated by the scattering of the monitoring lights ML1 to MLn are returned to the optical transmission line monitoring device 100 through the optical transmission lines LB1 to LBn. In this example, a communication system consisting of the optical transmission line LAk and the terminal station Tsk and the optical transmission line LBk corresponding thereto is referred to as a system Sk.

[0081] Fig.11 A return light generating mechanism in the system S1 according to the first exemplary embodiment is shown. Fig.11 An example is shown in which four optical repeaters RP1 to RP4 are sequentially inserted from the optical transmission line monitoring device 100 side in the optical transmission lines LA1 and LB1 of the system S1. Figure 2 As described above, the monitoring light ML1 transmitted to the terminal station TS1 through the optical transmission line LA1 is amplified each time it passes through the optical repeater RP. The return light generated by the scattering of the amplified monitoring light ML1 returns to the optical repeater, branches from the optical transmission line LA1 and is coupled to the optical transmission line LB1 through a loopback path formed by couplers CP1 and CP2, and then returns to the optical transmission line monitoring device 100.

[0082] As a result, it was observed that the intensity variation of the return light BL1 showed a sawtooth waveform in which the number of rises was the same as the number of the optical repeaters RP1. Fig.12 An example of the waveform of the return light BL1 is shown. Fig.12 In the process, the return light BL is at the timing T RP1～ T RP4 Increases sharply and rises. At the timing T RP1 To T RP4 The rise of corresponds to the amplification of the monitoring light ML by the optical repeaters RP1 to RP4. Fig.12 The intervals between adjacent rises are the same, but the intervals between the rises may vary depending on the distance between adjacent optical repeaters. It is expected that this technology for monitoring optical transmission lines will be effective in submarine optical networks where the transmission distance is long and multiple optical repeaters are inserted in the optical transmission line.

[0083] Fig.13 The transmission of the monitor light and the return light according to the first exemplary embodiment is schematically shown. It shows an example in which three pulses MLk_1 to MLk_3 are repeatedly output as the monitor light MLk, and three return lights BLk_1 to BLk corresponding to the respective pulses are fed back to the optical transmission line monitor device 100.

[0084] exist Fig.13 In the example of , the return lights BL1_1 to BLn_1 corresponding to the monitoring lights ML1_1 to MLn_1 respectively overlap in time. As described above, even when the return lights BL1_1 to BLn_1 with different frequencies overlap, the signal processing unit 5 is able to separate the frequencies of the return lights and detect the intensity changes thereof in parallel. Therefore, the return lights with different frequencies do not need to be discrete in time, which enables frequent and high-speed detection of faults in multiple optical transmission line pairs.

[0085] Furthermore, a coupler may be placed inside the terminal station TS0 or between the terminal station TS0 and the closest optical repeater, so that return light generated between the optical transmission line monitoring device 100 and the closest optical repeater can be detected. Fig.14 FIG. 2 shows a modified example of the optical transmission line monitoring device 100 according to the first exemplary embodiment. Fig.14 As shown, in the terminal station TS0, a coupler CP3 is inserted in the optical transmission lines LA1 to LAn, and a coupler CP4 is inserted in the optical transmission lines LB1 to LBn. The couplers CP3 and CP4 are configured as directional couplers or optical circulators.

[0086] exist Fig.14 In the structure shown, the return light from a position closer than the closest optical repeater RP1 is selectively branched from the optical transmission line LA1 to Lan through the coupler CP3, and coupled to the optical transmission lines LB1 to LBn through the coupler CP4. In other words, the couplers CP3 and CP4 form a loopback path, just like the couplers CP1 and CP2 of the optical repeaters RP1 to RPn.

[0087] like Fig.14 As shown, by placing couplers CP3 and CP4 in the terminal station TS0, the optical repeater ( Fig.14 The monitoring of the optical transmission line is performed when an optical repeater RP1 to RPn in the optical transmission line is inserted into the optical transmission line. As described above, when the monitoring lights ML1 to MLn are output to the optical transmission lines LA1 to LAn, respectively, return lights BL1 to BLn propagating in the opposite direction to the monitoring lights ML1 to MLn are generated due to Rayleigh scattering (backscattering) in the optical transmission lines LA1 to LAn. The return lights BL1 to BLn arrive at the coupler CP3 of the terminal station TS0 without being branched by the optical repeater. The return lights BL1 to BLn that have arrived at the coupler CP3 are selectively branched from the optical transmission lines LA1 to LAn through the coupler CP3, and are coupled to the optical transmission lines LB1 to LBn through the coupler CP4. This makes it possible to monitor the optical transmission line even when an optical repeater is not inserted in the optical transmission line.

[0088] Fig.15 Shows Fig.14 An example of the waveform of the return light BL1 in the structure shown. Fig.11 Compared with the structure shown in FIG. 1 , this structure enables the optical repeater RP1 (timing T RP1 ) by detecting changes in the intensity of the returning light at a position closer to the optical transmission line, thereby detecting a nearby optical transmission line fault.

[0089] As described above, in this structure, light having different frequencies (monitor light, return light) is respectively assigned to multiple paths, and a beat frequency corresponding to the frequency of the return light is identified in the signal processing unit 5, which enables multiple paths to be independently monitored in parallel.

[0090] Note that the control signals C1 to Cn may be assigned to different users. Therefore, there may be a case where the control signals C1 to Cn are randomly applied to the control unit 6. For example, in a case where a certain user uses some of the above-mentioned systems S1 to Sn and another user uses other parts of the systems S1 to Sn, each user instructs the control unit 6 to detect a fault in the system being used by the user at an arbitrary timing by using some of the control signals C1 to Cn. When commands from a plurality of users arrive at the control unit 6 at substantially the same time, the control unit 6 may arbitrate between the plurality of commands, and may autonomously determine the output timing of the monitoring lights ML1 to MLn based on the commands. For example, the output timing and interval of the monitoring lights ML1 to MLn may be determined based on the length of the optical transmission lines LA1 to LAn and the propagation speed of the monitoring lights ML1 to MLn through the optical transmission lines LA1 to MLn.

[0091] The control unit 6 may comprise a table 61 defining the association of users, control signals, systems and monitoring lights. Fig.16 The table 61 included in the control unit 6 is schematically shown. Fig.16 As shown, in Table 61, the control signal C1, the system S1, and the monitoring light M1 are associated with the user U1, while the signals C2 and C3, the systems S2 and S3, and the monitoring lights M2 and M3 are associated with the user U2. Therefore, the control signal C2 is assigned to the user U1, and the user U1 applies the control signal C1 to the control unit 6, thereby using the system S1 and controlling the monitoring light M1. In addition, the control signals C2 and C3 are assigned to the user U1, and the user U1 applies the control signals C2 and C3 to the control unit 6, thereby using the systems S2 and S3 and controlling the monitoring lights M2 and M3.

[0092] Note that, in order to simplify the drawing, Table 61 represents the association of certain users, control signals, systems, and monitoring lights, and may of course include the association of other users, control signals, systems, and monitoring lights.

[0093] In addition, there may be a case where users are not assigned to all the monitoring lights ML1 to MLn according to the usage of the optical transmission line monitoring device 100. In this case, the new user can request that the monitoring light be assigned to the control unit 6 by using the control signals C1 to Cn. In response to the request, the control unit 6 can assign the unused monitoring light to the new user. In addition, the control unit 6 can determine the frequency of the assigned monitoring light. In this case, the control unit 6 can notify the signal processing unit 5 of the determined frequency of the monitoring light by using the control signal CON2, and the signal processing unit 5 can select the corresponding filter according to the notified frequency by, for example, referring to the above-mentioned table, and adjust the passing frequency of the corresponding filter.

[0094] Second Exemplary Embodiment

[0095] In the first exemplary embodiment, it is described that the n An example in which the monitoring lights ML1 to MLn are sequentially output to the optical transmission lines LA1 to LAn. However, the order of outputting the monitoring lights ML1 to MLn is not limited thereto. Hereinafter, a damage detection operation of the optical transmission line monitoring device 100 according to the second exemplary embodiment is described.

[0096] Fig.17 The propagation paths of the monitoring light and the return light according to the second exemplary embodiment are schematically shown. Fig.13 Compared with the example of FIG. 1 , the order of outputting the monitor light ML1 and the monitor light ML2 is interchanged. Therefore, the return light BL2 is fed back to the optical transmission line monitoring device 100 at an earlier timing than the return light BL1.

[0097] In this case as well, the return lights BL1_1 to BLn_1 corresponding to the monitor lights ML1_1 to MLn_1 respectively overlap in time. However, even when the monitor lights ML1_1 to MLn_1 having different frequencies are output in any order and the corresponding return lights overlap in time, the signal processing unit 5 is able to separate the frequencies of the return lights and detect their intensity changes in parallel.

[0098] Note that since the return lights may overlap in time, even if the monitor light output unit 1 simultaneously outputs monitor lights having different frequencies, the signal processing unit 5 can separate the frequencies of the return lights and detect intensity changes thereof in parallel.

[0099] Third Exemplary Embodiment

[0100] In the first exemplary embodiment, it is described that the transistors having different frequencies f1 to f1 are sequentially and at the same intervals. nThe example of outputting the monitoring lights ML1 to MLn of the optical transmission lines LA1 to LAn. However, there may be a case where it is necessary to control the output timing of the monitoring lights having different frequencies according to the needs. For example, in the case where the users of a system having a plurality of optical transmission line pairs are different and the users of the system are different, it is necessary to allow each user to perform a function of fault detection of the optical transmission line at a desired timing.

[0101] Hereinafter, the operation of the optical transmission line monitoring device 100 that performs fault detection of the optical transmission line at a desired timing is described. Fig.18 The propagation paths of the monitor light and the return light according to the third exemplary embodiment are schematically shown. The monitor light ML1 is repeatedly output at intervals of ΔT1. On the other hand, the monitor lights ML2 to MLn are output at intervals and timings different from those of the monitor light ML1. In this example, the first pulse of the monitor light ML2 is output after the second pulse of the monitor light ML1, and the first pulse of the monitor light MLn is output after the first pulse of the monitor light ML1.

[0102] In this structure, for example, by applying control signals C1 to Cn to the control unit 6 as needed, and then applying the control signal CON1 from the control unit 6 to the monitor light output unit 1 based on the control signals C1 to Cn, the output timing of each monitor light ML1 to MLn can be controlled.

[0103] Also in this case, the return lights BL1 to BLn corresponding to the monitor lights ML1 to MLn respectively sometimes overlap in time. As with the above-described exemplary embodiment, the signal processing unit 5 can separate the frequencies of the return lights and detect their intensity changes in parallel.

[0104] Therefore, as with the first exemplary embodiment, return lights having different frequencies do not need to be discrete in time, which enables frequent and high-speed detection of faults in a plurality of optical transmission line pairs.

[0105] Fourth Exemplary Embodiment

[0106] In the above exemplary embodiments, the case where the system having multiple optical transmission line pairs has the same structure is described. However, in reality, the system may have different structures, such as different lengths of the optical transmission lines LA1 to LAn, different numbers of inserted optical repeaters, or different distances between optical repeaters.

[0107] Hereinafter, the operation of the optical transmission line monitoring device 100 that performs fault detection of the optical transmission line according to the structure of each system will be described. Fig.19The propagation paths of the monitoring light and the return light according to the fourth exemplary embodiment are schematically shown. In this example, the optical transmission line LA2 is shorter than the optical transmission line LA1, and the number of optical repeaters inserted is smaller. In addition, the optical transmission line LAn is longer than the optical transmission line LA1, and the number of optical repeaters inserted is larger.

[0108] In this exemplary embodiment, the output interval of each monitoring light is controlled according to the difference in the structure of each system. In this example, the output interval ΔT2 of the monitoring light ML2 output to the shorter optical transmission line LA2 is shorter than the output interval ΔT1 of the monitoring light ML1 output to the optical transmission line LA1 (ΔT2<ΔT1). The output interval ΔTn of the monitoring light MLn output to the longer optical transmission line LAn is longer than the output interval ΔT1 of the monitoring light ML1 output to the optical transmission line LA1 (ΔTn>ΔT1).

[0109] At a timing corresponding to the output timing of the monitoring lights ML1 to MLn, the length of the optical transmission lines LA1 to LAn, etc., the return lights BL1 to BLn are fed back to the optical transmission line monitoring device 100. Also in this case, the return lights BL1 to BLn corresponding to the monitoring lights ML1 to MLn, respectively, sometimes overlap in time. As in the above exemplary embodiment, the signal processing unit 5 is capable of separating the frequencies of the return lights and detecting their intensity changes in parallel.

[0110] Also in this structure, for example, by applying control signals C1 to Cn to the control unit 6 as needed, and then applying the control signal CON1 from the control unit 6 to the monitor light output unit 1 based on the control signals C1 to Cn, the output timing of each monitor light ML1 to MLn can be controlled.

[0111] Therefore, as with the first exemplary embodiment, return lights having different frequencies do not need to be discrete in time, which enables frequent and high-speed detection of faults in a plurality of optical transmission line pairs.

[0112] Fifth Exemplary Embodiment

[0113] In the above exemplary embodiment, it is described that the n In this exemplary embodiment, an example in which at least two of the monitor lights ML1 to MLn are output to at least one of the optical transmission lines LA1 to LAn is described.

[0114] Fig. 20 The propagation of the monitor light and the return light according to the fifth exemplary embodiment is schematically shown. Fig. 20An example is shown in which the monitor lights ML1 and ML2 are sequentially output to the optical transmission line LA1. In this case, the return lights BL1 and BL2 corresponding to the monitor lights ML1 and ML2 are sequentially fed back to the optical transmission line monitoring device 100 through the optical transmission line LB1.

[0115] Also in this structure, the output timing of each monitoring light ML1 to MLn is controllable, and the optical transmission line to which the monitoring light ML1 to MLn is output can be appropriately selected, for example, by applying control signals C1 to Cn to the control unit 6 as needed, and then applying the control signal CON1 from the control unit 6 to the monitoring light output unit 1 based on the control signals C1 to Cn.

[0116] In this case, the beat frequency f corresponding to the monitor lights ML1 and ML2 can be obtained by converting the beat frequency f corresponding to the monitor lights ML1 and ML2 into the signal processing unit 5. L0 -f1 and f L0 -f2 is associated with the optical transmission line LA1 and detects intensity changes of the return lights BL1 and BL2 to detect a fault in the optical transmission line LA1.

[0117] For example, the return lights BL1_1 and BL2_1 corresponding to the monitor lights ML1_1 to ML2_1 overlap in time. Also in this case, the signal processing unit 5 can separate the frequencies of the return lights and detect their intensity changes in parallel.

[0118] Note that since the return light corresponding to the monitoring light with different frequencies output to an optical transmission line can overlap in time, even if the monitoring light output unit 1 simultaneously outputs monitoring light with different frequencies, the signal processing unit 5 is able to separate the frequencies of the return light and detect its intensity changes in parallel.

[0119] Therefore, as with the above-described exemplary embodiment, return lights having different frequencies do not need to be discrete in time, which enables frequent and high-speed detection of faults in a plurality of optical transmission line pairs.

[0120] Generally, the intensity of the return light generated by Rayleigh scattering is low, and the signal-to-noise ratio (S / N ratio) of the return light detected by the optical transmission line monitoring device 100 is relatively low. Therefore, the monitoring light can be output multiple times to one monitoring light, and the signal processing unit 5 can obtain the time change of the return time and average it. The influence of the noise is thereby averaged and eliminated, which improves the accuracy of fault detection. In this case, the averaging process is completed at high speed by outputting monitoring lights with different frequencies to one optical transmission line as in this structure.

[0121] Sixth Exemplary Embodiment

[0122] Hereinafter, an optical transmission line monitoring device according to a sixth exemplary embodiment is described. In the above exemplary embodiments, an example is described in which the optical transmission line monitoring device 100 is connected to one terminal station TS0. However, the optical transmission line monitoring device 100 may be connected to a plurality of terminal stations. Fig.21 Connections when the optical network 2000 is monitored by the optical transmission line monitoring device according to the sixth exemplary embodiment are shown.

[0123] The optical network 2000 is an improved example of the optical network 1000, and refers to Figure 1 The optical transmission devices TR1 to TRn are placed in different terminal stations TS0_1 to TS0_n respectively. The other structures of the optical network 2000 are the same as those of the optical network 1000.

[0124] like Fig.21 As shown, the number of terminal stations to which the optical transmission line monitoring device 100 is connected is not limited to one, but may be greater than one. This makes it possible to detect faults in an optical transmission line through which a plurality of terminal stations transmit optical signals by one optical transmission line monitoring device 100. Therefore, even when a plurality of terminal stations TS0_1 to TS0_n are located at a certain distance from each other, by connecting the optical transmission line monitoring device 100 to each of the terminal stations TS0_1 to TS0_n using an optical transmission line such as an optical fiber, a structure in which faults in an optical transmission line through which a plurality of terminal stations transmit optical signals by one optical transmission line monitoring device 100 can be easily realized.

[0125] Although a structure in which terminal stations TS0_1 to TS0_n are connected to one optical transmission line pair is described in this exemplary embodiment, terminal stations TS0_1 to TS0_n may be connected to two optical transmission line pairs, and the number of connections between terminal stations TS0_1 to TS0_n and the optical transmission line monitoring device 100 may be increased according to the number of optical transmission line pairs.

[0126] Seventh Exemplary Embodiment

[0127] In this exemplary embodiment, a modified example of the monitor light generating unit of the monitor light output unit is described. Fig. 22 The structure of a monitoring light output unit 1A as a first improved example of the monitoring light output unit 1 is schematically shown. The monitoring light output unit 1A has a structure in which the optical pulse generating unit 11 and the monitoring light generating unit 12 of the monitoring light output unit 1 are replaced by an ITLA (Integrated Tunable Laser Assembly) wavelength tunable laser module 11A and an optical switch 12A, respectively. Note that the ITLA wavelength tunable laser is an example of a wavelength tunable laser, and of course another wavelength tunable laser different from the ITLA wavelength tunable laser may be used.

[0128] The ITLA wavelength tunable laser module 11A outputs the monitor lights ML1 to MLn having the frequencies f1 to f2 corresponding to the frequencies f1 to f3 corresponding to the monitor lights ML1 to MLn based on the control signal CON11 included in the control signal CON12. n The optical switch 12A is configured as a WSS (wavelength selective switch), for example, and switches the laser beam having the frequencies f1 to f2 based on the control signal CON12. n Laser light of any one of the frequencies is output as monitor light ML1 to MLn to the optical transmission lines LA1 to LAn.

[0129] In other words, when the frequency of the laser light output from the ITLA wavelength tunable laser module 11A is f k When the optical switch 12A has a frequency f k The monitor light MLk is output to the optical transmission line LAk.

[0130] Next, a second modified example of the monitor light output unit is described. Fig.23 The structure of the monitoring light output unit 1B is schematically shown, which is a second improved example of the monitoring light output unit. The monitoring light output unit 1B includes an ITLA wavelength tunable laser module 11A, an optical coupler 123, and interrupters BR1 to BRn. The ITLA wavelength tunable laser module 11A is the same as the wavelength tunable laser module of the monitoring light output unit 1A, so its description is omitted.

[0131] The optical coupler 123 is configured as a 1-input n-output coupler, and branches the laser light output from the ITLA wavelength tunable laser module 11A to each of the interrupters BR1 to BRn. The interrupters BR1 to BRn transmit the laser light having frequencies f1 to f2 based on the control signal CON12. n The monitor lights ML1 to MLn are output to the optical transmission lines LA1 to LAn, respectively.

[0132] In other words, when the frequency of the laser light output from the ITLA wavelength tunable laser module 11A is f k When , only the breaker BRk is open, and the other breakers are closed, so that the frequency f k The monitor light MLk is output to the optical transmission line LAk.

[0133] A third modified example of the monitor light output unit is described hereinafter. Fig.24The structure of the monitoring light output unit 1C is schematically shown, which is a third improved example of the monitoring light output unit. The monitoring light output unit 1C has a structure in which the monitoring light generating unit 12 of the monitoring light output unit 1 is replaced with a monitoring light generating unit 12C. The monitoring light generating unit 12C includes a phase modulator 13 and an optical switch 14. The optical switch 14 is the same as the optical switch 12A, so its description is omitted.

[0134] The phase modulator 13 can modulate the phase of the optical pulse OP output from the optical pulse generating unit 11, and control the frequency of the optical pulse OP based on the control signal CON121 included in the control signal CON12. The optical switch 14 switches the optical pulse OP having the frequency f1 to f2 based on the control signal CON122 included in the control signal CON12. n An optical pulse of any frequency is output as monitor light ML1 to MLn to the optical transmission lines LA1 to LAn.

[0135] In other words, when the frequency of the laser light output from the phase modulator 13 is f k When the optical switch 14 has a frequency f k The monitor light MLk is output to the optical transmission line LAk.

[0136] As mentioned above, using Figures 22 to 24 The illustrated monitoring light output unit also makes it possible to provide an optical transmission line monitoring device capable of detecting a fault in an optical transmission line, similar to the optical transmission line monitoring device according to the above-described exemplary embodiments.

[0137] Eighth Exemplary Embodiment

[0138] In this exemplary embodiment, a modified example of the interference unit is described. Fig.25 The structure of the interference unit 3A is schematically shown, which is an improved example of the interference unit. The interference unit 3A is configured as an optical wavelength multiplexer. The interference unit 3A is configured as an optical wavelength multiplexer with (n+1) inputs and 1 outputs. The return light BL1 to BLn is input to the interference unit 3A through the optical transmission lines LB1 to LBn, and the local oscillation light LO is also input to the interference unit 3A. Even when the return light BL1 to BLn overlaps in time, some or all of the return light BL1 to BLn are multiplexed with the local oscillation light LO, so that they interfere with each other.

[0139] Therefore, the interference unit 3A can output output light generated by interference of the return lights BL1 to BLn input through the different optical transmission lines LB1 to LBn with the local oscillation light to the conversion unit 4 through the same path as the interference unit 3 .

[0140] Ninth Exemplary Embodiment

[0141] In this exemplary embodiment, improved examples of the interference unit and the conversion unit are described. Fig.26 The structures of the interference unit 3B and the conversion unit 4A are schematically shown, which are improved examples of the interference unit and the conversion unit. The interference unit 3A includes optical wavelength multiplexers 35A and 35B and optical intensity multiplexers 36A to 36D. In the following description, it is assumed that the number of monitoring lights ML1 to MLn is an even number (i.e., k=2m, where m is an integer greater than or equal to).

[0142] The optical wavelength multiplexers 35A and 35B are configured as k / 2 input and 1 output optical wavelength multiplexers. The wavelengths are f1, f3, ..., f k-1 The return lights BL1, BL3, ..., BLk-1 of the optical wavelength multiplexer 35A are input, and their monitoring lights are multiplexed and output to the optical intensity multiplexer 36B. k The return lights BL2, BL4, ..., BLk are input to the optical wavelength multiplexer 35B, and their monitor lights are multiplexed and output to the optical intensity multiplexer 36B.

[0143] The optical intensity multiplexers 36A to 36D are configured as 2-input 2-output optical intensity multiplexers. One input of the optical intensity multiplexer 36A is connected to the local oscillator light source 2, and a frequency f is input thereto. LO1 The other input of the optical intensity multiplexer 36A is connected to the local oscillator light source 2, and the frequency f is input thereto. LO2 Note that the local oscillator light LO1 and the local oscillator light LO2 may be output from the same local oscillator light source, or may be output from different local oscillator light sources.

[0144] One output of the optical intensity multiplexer 36A is connected to one input of the optical intensity multiplexer 36C, and the other output is connected to one input of the optical intensity multiplexer 36D.

[0145] One input of the optical intensity multiplexer 36B is connected to the output of the optical wavelength multiplexer 35A, and the other input is connected to the output of the optical wavelength multiplexer 35B. One output of the optical intensity multiplexer 36B is connected to the other input of the optical intensity multiplexer 36C, and the other output is connected to the other input of the optical intensity multiplexer 36D. Therefore, the return light BL1 to BLk interferes with each of the local oscillation lights LO1 and LO2, and the output light is output from the interference unit 3B.

[0146] Next, the conversion unit 4A is described. The conversion unit 4A includes balanced receivers 43A and 43B and A / D conversion units 44A and 44B.

[0147] The balanced receiver 43A includes two photoelectric conversion units OE1 and OE2. The input of the photoelectric conversion unit OE1 is connected to one input of the optical intensity multiplexer 36C, and it converts the light input from the optical intensity multiplexer 36C into an analog electric signal EA1, and outputs it to the A / D conversion unit 44A. The input of the photoelectric conversion unit OE2 is connected to the other input of the optical intensity multiplexer 36C, and it converts the light input from the optical intensity multiplexer 36C into an analog electric signal EA2, and outputs it to the A / D conversion unit 44A.

[0148] The balanced receiver 43B includes two photoelectric conversion units OE3 and OE4. The input of the photoelectric conversion unit OE3 is connected to one input of the optical intensity multiplexer 36D, and converts the light input from the optical intensity multiplexer 36D into an analog electrical signal EA3, and outputs it to the A / D conversion unit 44B. The input of the photoelectric conversion unit OE4 is connected to the other input of the optical intensity multiplexer 36D, and converts the light input from the optical intensity multiplexer 36C into an analog electrical signal EA4, and outputs it to the A / D conversion unit 44B.

[0149] The A / D conversion unit 44A converts a signal combining analog electric signals EA1 and EA2 into a digital electric signal ED1 and outputs it to the signal processing unit 5. The A / D conversion unit 44B converts a signal combining analog electric signals EA3 and EA4 into a digital electric signal ED2 and outputs it to the signal processing unit 5.

[0150] In this structure, two local oscillation lights having different frequencies interfere with the return light, and thereby double the beat frequency contained in the digital electrical signal converted by the A / D conversion unit, thereby doubling the dynamic range of the acquired beat frequency compared to the case where only one local oscillation light is used. Note, however, that the frequency f of the local oscillation light LO1 is LO1 and the frequency f of the local oscillator LO2 LO2 Not necessarily different, but they can be the same.

[0151] In addition, by using an optical intensity multiplexer and a balanced receiver, all wavelength demultiplexed signals are photoelectrically converted. This allows all wavelength demultiplexed signals to be used without wasting them, which eliminates the loss due to demultiplexing splitting and enables efficient signal processing.

[0152] Furthermore, since two optical wavelength multiplexers that multiplex the wavelength of the return light are provided, the wavelength interval of each optical wavelength multiplexer is larger than the case with only one optical wavelength multiplexer.

[0153] Other Exemplary Embodiments

[0154] The present invention is not limited to the above exemplary embodiments, and can be appropriately modified without departing from the spirit and scope of the present invention. For example, in the above exemplary embodiments, each terminal station can be installed on land, and the optical transmission device can be installed not only on land, but also in offshore or submarine facilities.

[0155] Although each system includes a pair of two optical transmission lines in the above exemplary embodiments, the monitor light may be output to one optical transmission line, and the return light may be fed back through the same optical transmission line.

[0156] Although in the above exemplary embodiment, the optical transmission line monitoring device monitors the optical transmission line of the submarine optical network system, this is only an example. The optical transmission line monitoring device can monitor any optical network system other than the submarine optical network system, such as a land-based optical network system. In addition, it can be applied to other purposes, such as sensing, without being limited to monitoring optical networks.

[0157] For example, the whole or part of the exemplary embodiments disclosed above may be described as, but not limited to, the following supplementary notes.

[0158] (Supplementary Note 1)

[0159] An optical transmission line monitoring device, comprising:

[0160] a monitoring light output unit configured to output a plurality of monitoring lights having different frequencies to the plurality of first optical transmission lines respectively;

[0161] A local oscillator light source configured to output local oscillator light;

[0162] an interference unit to which a plurality of return lights corresponding to the plurality of monitor lights are input, the interference unit being configured to output output light generated by interference between the input light and the local oscillation light;

[0163] a conversion unit configured to convert the output light into an electrical signal; and

[0164] A signal processing unit is configured to extract signals having a beat frequency from the electrical signal based on the plurality of monitor lights, respectively, and generate a monitoring result of each of the first optical transmission lines from the signals having the beat frequency.

[0165] (Supplementary Note 2)

[0166] The optical transmission line monitoring device according to Supplementary note 1, wherein each of the return lights is input to the interference unit through the second optical transmission line paired with each of the first optical transmission lines.

[0167] (Supplementary Note 3)

[0168] The optical transmission line monitoring device according to Supplementary Note 2, wherein:

[0169] inserting at least one optical repeater in the first optical transmission line and the second optical transmission line, and

[0170] Return light generated by scattering of monitor light having passed through one of the optical repeaters is branched from the first optical transmission line and coupled to the second optical transmission line through the optical repeater.

[0171] (Supplementary Note 4)

[0172] The optical transmission line monitor device according to any one of Supplementary Notes 1 to 3, further including a control unit configured to control a timing of outputting each of the plurality of monitor lights from the monitor light output unit.

[0173] (Supplementary Note 5)

[0174] The optical transmission line monitoring device according to Supplementary note 4, wherein the control unit determines a timing of outputting the monitor light based on a length of the first optical transmission line and a propagation speed of each monitor light passing through the first optical transmission line.

[0175] (Supplementary Note 6)

[0176] The optical transmission line monitoring device according to Supplementary note 4 or 5, wherein the control unit controls the frequency of each monitoring light based on a given command.

[0177] (Supplementary Note 7)

[0178] The optical transmission line monitoring device according to any one of Supplementary Notes 1 to 6, wherein the signal processing unit includes:

[0179] a plurality of filters configured to extract signals having a plurality of beat frequencies from the electrical signal based on the plurality of monitor lights; and

[0180] A plurality of processing units are configured to generate monitoring results of the plurality of first optical transmission lines from signals having a plurality of beat frequencies.

[0181] (Supplementary Note 8)

[0182] The optical transmission line monitoring device according to any one of Supplementary Notes 1 to 5, further comprising a control unit configured to control the frequency of each of the monitoring lights based on a given command and notify the signal processing unit of the frequency of each of the monitoring lights, wherein:

[0183] The signal processing unit comprises:

[0184] a plurality of filters configured to extract signals having a plurality of beat frequencies from the electrical signal based on the plurality of monitor lights; and

[0185] a plurality of processing units configured to generate monitoring results of the plurality of first optical transmission lines from signals having a plurality of beat frequencies, and

[0186] Based on the notified frequency of the monitor light, the frequency of the signal extracted by each filter is adjusted.

[0187] (Supplementary Note 9)

[0188] An optical transmission line monitoring system, comprising:

[0189] an optical transmission device configured to output an optical signal to a plurality of first optical transmission lines; and

[0190] an optical transmission line monitoring device connected to the optical transmission device and configured to monitor the plurality of first optical transmission lines, wherein:

[0191] The optical transmission line monitoring device comprises:

[0192] a monitoring light output unit configured to output a plurality of monitoring lights having different frequencies to the plurality of first optical transmission lines respectively;

[0193] A local oscillator light source configured to output local oscillator light;

[0194] an interference unit to which a plurality of return lights corresponding to the plurality of monitor lights are input, the interference unit being configured to output output light generated by interference between the input light and the local oscillation light;

[0195] a conversion unit configured to convert the output light into an electrical signal; and

[0196] A signal processing unit is configured to extract signals having a beat frequency from the electrical signal based on the plurality of monitor lights, respectively, and generate a monitoring result of each of the first optical transmission lines from the signals having the beat frequency.

[0197] (Supplementary Note 10)

[0198] The optical transmission line monitoring system according to Supplementary note 9, wherein each of the return lights is input to the interference unit through the second optical transmission line paired with each of the first optical transmission lines.

[0199] (Supplementary Note 11)

[0200] The optical transmission line monitoring system according to Supplementary Note 10, wherein

[0201] inserting at least one optical repeater in the first optical transmission line and the second optical transmission line, and

[0202] Return light generated by scattering of monitor light having passed through one of the optical repeaters is branched from the first optical transmission line and coupled to the second optical transmission line through the optical repeater.

[0203] (Supplementary Note 12)

[0204] The optical transmission line monitoring system according to any one of Supplementary Notes 9 to 11, further comprising a control unit configured to control a timing of outputting each of the plurality of monitor lights from the monitor light output unit.

[0205] (Supplementary Note 13)

[0206] The optical transmission line monitoring system according to Supplementary note 12, wherein the control unit determines a timing of outputting the monitor light based on a length of the first optical transmission line and a propagation speed of each monitor light passing through the first optical transmission line.

[0207] (Supplementary Note 14)

[0208] The optical transmission line monitoring system according to Supplementary note 12 or 13, wherein the control unit controls the frequency of each monitoring light based on a given command.

[0209] (Supplementary Note 15)

[0210] The optical transmission line monitoring system according to any one of Supplementary Notes 9 to 14, wherein the signal processing unit includes:

[0211] a plurality of filters configured to extract signals having a plurality of beat frequencies from the electrical signal based on the plurality of monitor lights; and

[0212] A plurality of processing units are configured to generate monitoring results of the plurality of first optical transmission lines from signals having a plurality of beat frequencies.

[0213] (Supplementary Note 16)

[0214] The optical transmission line monitoring system according to any one of Supplementary Notes 9 to 13, further comprising a control unit configured to control the frequency of each of the monitoring lights based on a given command and notify the signal processing unit of the frequency of each of the monitoring lights, wherein:

[0215] The signal processing unit comprises:

[0216] a plurality of filters configured to extract signals having a plurality of beat frequencies from the electrical signal based on the plurality of monitor lights; and

[0217] a plurality of processing units configured to generate monitoring results of the plurality of first optical transmission lines from signals having a plurality of beat frequencies, and

[0218] Based on the notified frequency of the monitor light, the frequency of the signal extracted by each filter is adjusted.

[0219] (Supplementary Note 17)

[0220] A method for monitoring an optical transmission line, comprising:

[0221] outputting a plurality of monitoring lights having different frequencies to a plurality of first optical transmission lines respectively;

[0222] outputting output light generated by interference between a plurality of return lights corresponding to the plurality of monitor lights and the local oscillation light;

[0223] converting the output light into an electrical signal; and

[0224] A signal having a beat frequency is extracted from the electric signal based on the plurality of monitor lights, respectively, and a monitoring result of each of the first optical transmission lines is generated from the signal having the beat frequency.

[0225] (Supplementary Note 18)

[0226] The optical transmission line monitoring method according to Supplementary Note 17, wherein the output light is output from a second optical transmission line paired with the first optical transmission line by interference between the local oscillator light and a plurality of return lights corresponding to the plurality of monitor lights.

[0227] (Supplementary Note 19)

[0228] The optical transmission line monitoring method according to Supplementary Note 18, wherein:

[0229] inserting at least one optical repeater in the first optical transmission line and the second optical transmission line, and

[0230] Return light generated by scattering of the monitor light having passed through one of the optical repeaters is branched from the first optical transmission line and coupled to the second optical transmission line through the optical repeater.

[0231] (Supplementary Note 20)

[0232] The optical transmission line monitoring method according to any one of Supplementary Notes 17 to 19, wherein the timing of outputting the monitor light is determined based on the length of the first optical transmission line and a propagation speed of each monitor light passing through the first optical transmission line.

[0233] (Supplementary Note 21)

[0234] The optical transmission line monitoring method according to any one of Supplementary Notes 17 to 20, wherein the frequency of each monitoring light is controlled based on a given command.

[0235] (Supplementary Note 22)

[0236] The optical transmission line monitoring method according to any one of Supplementary Notes 17 to 20, comprising:

[0237] determining a frequency of each of the monitoring lights based on a given command;

[0238] extracting a signal having a plurality of beat frequencies from the electrical signal based on the plurality of monitor lights; and

[0239] generating monitoring results of the plurality of first optical transmission lines from a signal having a plurality of beat frequencies,

[0240] Here, based on the determined frequency of the monitoring light, the frequency of the signal to be extracted is determined.

[0241] Although the present invention has been particularly shown and described with reference to exemplary embodiments thereof, the present invention is not limited to these exemplary embodiments. It will be understood by those skilled in the art that various changes in form and details may be made without departing from the spirit and scope of the present invention.

[0242] This application is based upon and claims the benefit of priority from Japanese patent application No. 2018-215319, filed on November 16, 2018, the entire contents of which are incorporated herein by reference.

[0243] Reference designator list

[0244] 100 Optical transmission line monitoring device

[0245] 1, 1A, 1B, 1C Monitor light output unit

[0246] 2 Local oscillator light source

[0247] 3, 3A, 3B Interference Unit

[0248] 4 Conversion unit

[0249] 4A conversion unit

[0250] 5 Signal Processing Unit

[0251] 6 Control unit

[0252] 11. Optical pulse generation unit

[0253] 11A ITLA wavelength tunable laser module

[0254] 12 Monitoring light generation unit

[0255] 12A, 14 Optical switch

[0256] 13 Phase Modulator

[0257] 31~34 Coupler

[0258] 35A, 35B Optical Wavelength Multiplexer

[0259] 36A~36D Light Intensity Multiplexer

[0260] 41 Photoelectric conversion unit

[0261] 42, 44A, 44B A / D conversion unit

[0262] 43A, 43B Balanced Receiver

[0263] 123 Optocoupler

[0264] 1000, 2000 optical network

[0265] A1, A2 Optical Amplifier

[0266] BL1~BLn Return light

[0267] BR1~BRn breaker

[0268] CP1~CP4、CA1~CAn、CB1~CBn coupler

[0269] C1~Cn control signal

[0270] CON1, CON2, CON11, CON12, CON121, CON122 control signals

[0271] D1~Dn data signal

[0272] EA, EA1~EA4 analog electrical signal

[0273] ED, ED1, ED2 digital electrical signal

[0274] F1~F n filter

[0275] LA1~LAn、LB1~LBn optical transmission lines

[0276] LO, LO1, LO2 Local oscillator

[0277] ML1~MLn Monitoring light

[0278] OE1~OE4 Photoelectric conversion unit

[0279] P1~Pn Data processing unit

[0280] R1~Rn、RR1~RRn Receiver

[0281] RP, RP1~RPn optical repeaters

[0282] S1~Sn system

[0283] T1~Tn、TT1~TTn Transmitter

[0284] TR0~TRn Optical transmission device

[0285] TS0~TSn terminal station

Claims

1. An optical transmission line monitoring device, comprising: a monitoring light output unit configured to output a plurality of monitoring lights having different frequencies to the plurality of first optical transmission lines respectively; A local oscillator light source configured to output local oscillator light; an interference unit to which a plurality of return lights corresponding to the plurality of monitor lights are input, the interference unit being configured to guide the plurality of return lights to a single propagation path so that the plurality of return lights guided to the single propagation path interfere with the local oscillator light, and output output light including a beat frequency generated by interference between the plurality of return lights guided to the single propagation path and the local oscillator light; a conversion unit, the conversion unit being configured to convert the output light into an electrical signal; as well as A signal processing unit configured to extract signals having the beat frequency from the electrical signal based on the plurality of monitor lights, respectively, and generate a monitoring result of each of the first optical transmission lines from the signals having the beat frequency.

2. The optical transmission line monitoring device according to claim 1, wherein: Each of the return lights is input to the interference unit through the second optical transmission line paired with each of the first optical transmission lines.

3. The optical transmission line monitoring device according to claim 2, wherein: inserting at least one optical repeater in the first optical transmission line and the second optical transmission line, and The return light generated by scattering of the monitor light having passed through one of the optical repeaters is branched from the first optical transmission line and coupled to the second optical transmission line through the one optical repeater.

4. An optical transmission line monitoring device, comprising: a monitoring light output unit configured to output a plurality of monitoring lights having different frequencies to the plurality of first optical transmission lines respectively; A local oscillator light source configured to output local oscillator light; an interference unit to which a plurality of return lights corresponding to the plurality of monitor lights are input, the interference unit being configured to output output light generated by interference between the input light and the local oscillation light; a conversion unit, the conversion unit being configured to convert the output light into an electrical signal; a signal processing unit configured to extract signals having a beat frequency from the electrical signal based on the plurality of monitoring lights, respectively, and generate a monitoring result of each of the first optical transmission lines from the signals having the beat frequency; as well as A control unit configured to control a timing of outputting each of the plurality of monitor lights from the monitor light output unit.

5. The optical transmission line monitoring device according to claim 4, wherein: The control unit determines a timing to output the monitor light based on a length of the first optical transmission line and a propagation speed of each monitor light passing through the first optical transmission line.

6. The optical transmission line monitoring device according to claim 4, wherein: The control unit controls the frequency of each monitoring light based on a given command.

7. The optical transmission line monitoring device according to claim 1 or 2, wherein: The signal processing unit comprises: a plurality of filters configured to extract signals having a plurality of beat frequencies from the electrical signal based on the plurality of monitor lights; and A plurality of processing units are configured to generate monitoring results of the plurality of first optical transmission lines from the signals having the plurality of beat frequencies.

8. The optical transmission line monitoring device according to claim 1 or 2, further comprising a control unit configured to control the frequency of each of the monitoring lights based on a given command and notify the signal processing unit of the frequency of each of the monitoring lights, wherein: The signal processing unit comprises: a plurality of filters configured to extract signals having a plurality of beat frequencies from the electrical signal based on the plurality of monitor lights; and a plurality of processing units configured to generate monitoring results of the plurality of first optical transmission lines from the signals having the plurality of beat frequencies, and Based on the notified frequency of the monitor light, the frequency of the signal extracted by each filter is adjusted.

9. An optical transmission line monitoring system, comprising: an optical transmission device configured to output an optical signal to a plurality of first optical transmission lines; as well as an optical transmission line monitoring device connected to the optical transmission device and configured to monitor the plurality of first optical transmission lines, wherein: The optical transmission line monitoring device comprises: a monitoring light output unit configured to output a plurality of monitoring lights having different frequencies to the plurality of first optical transmission lines respectively; A local oscillator light source configured to output local oscillator light; an interference unit to which a plurality of return lights corresponding to the plurality of monitor lights are input, the interference unit being configured to guide the plurality of return lights to a single propagation path so that the plurality of return lights guided to the single propagation path interfere with the local oscillator light, and output output light including a beat frequency generated by interference between the plurality of return lights guided to the single propagation path and the local oscillator light; a conversion unit configured to convert the output light into an electrical signal; and A signal processing unit configured to extract signals having the beat frequency from the electrical signal based on the plurality of monitor lights, respectively, and generate a monitoring result of each of the first optical transmission lines from the signals having the beat frequency.

10. A method for monitoring an optical transmission line, comprising: outputting a plurality of monitoring lights having different frequencies to a plurality of first optical transmission lines respectively; guiding a plurality of return lights corresponding to the plurality of monitor lights to a single propagation path, causing the plurality of return lights guided to the single propagation path to interfere with local oscillator light, and outputting output light including a beat frequency generated by interference between the plurality of return lights guided to the single propagation path and the local oscillator light; converting the output light into an electrical signal; as well as A signal having the beat frequency is extracted from the electric signal based on the plurality of monitor lights, respectively, and a monitoring result of each of the first optical transmission lines is generated from the signal having the beat frequency.

11. An optical transmission line monitoring system, comprising: an optical transmission device configured to output an optical signal to a plurality of first optical transmission lines; as well as an optical transmission line monitoring device connected to the optical transmission device and configured to monitor the plurality of first optical transmission lines, wherein The optical transmission line monitoring device comprises: a monitoring light output unit configured to output a plurality of monitoring lights having different frequencies to the plurality of first optical transmission lines respectively; A local oscillator light source configured to output local oscillator light; an interference unit to which a plurality of return lights corresponding to the plurality of monitor lights are input, the interference unit being configured to output output light generated by interference between the input light and the local oscillation light; a conversion unit configured to convert the output light into an electrical signal; and a signal processing unit configured to extract signals having a beat frequency from the electrical signal based on the plurality of monitoring lights, respectively, and generate a monitoring result of each of the first optical transmission lines from the signals having the beat frequency; and A control unit configured to control a timing of outputting each of the plurality of monitor lights from the monitor light output unit.

12. A method for monitoring an optical transmission line, comprising: outputting a plurality of monitoring lights having different frequencies to a plurality of first optical transmission lines respectively; outputting output light generated by interference between a plurality of return lights corresponding to the plurality of monitor lights and the local oscillation light; converting the output light into an electrical signal; as well as extracting signals having a beat frequency from the electrical signal based on the plurality of monitoring lights, respectively, and generating a monitoring result of each of the first optical transmission lines from the signals having the beat frequency; as well as The timing of outputting each of the plurality of monitor lights is controlled.

Images