Patent Description:
A submarine optical cable system is becoming more open, and greater importance is placed for a system owner to recognize performance of a transmission path in order to maximize an expansion capacity of the system. <CIT> relates to a formula of optical transmission path monitoring for monitoring the states of optical fibers and optical amplifier-repeaters constituting optical transmission paths in a wavelength division multiplexing optical transmission system by utilizing an optical time domain reflectometer. <CIT> relates to an optical time domain reflectometry signal detection method and apparatus. <CIT> relates to a system and method for wavelength dependent measurement in optical signal transmission systems. This patent teaches obtaining the gain response of an optical transmission link (or a part of the link, e.g. a block of repeaters) by measuring the gain flatness, i.e. the amplifier gain at different wavelengths. A Coherent Optical Time Domain Reflectometry (COTDR) technique is employed for this purpose. <CIT> relates to a method and system for measuring a gain profile in the middle of an optical transmission line and a gain profile controlling method and system for controlling a gain profile in an optical transmission line by utilizing the gain profile measuring method and system. <CIT> relates to the use of an arrangement to allow coherent optical time domain reflectometry (COTDR) to be used to detect faults in the optical transmission path of an optical transmission system consisting of multiple spans of fiber and optical amplifiers.

In a submarine optical cable system, a light transmission path, a repeater constituting the light transmission path, a cable, and the like are laid on a sea bottom, and thus spectrum acquisition in the light transmission path is difficult. A spectrum inclination and a deviation occurring in the light transmission path due to various factors affect main signal transmission quality in each wavelength of a wavelength band of the light transmission path. However, it is difficult to analyze a spectrum in the light transmission path only with a spectrum measurement in a reception unit of the light transmission path.

An object of the present disclosure is to solve the problem described above, and provide a light-transmission-path-spectrum measurement device, a light-transmission-path-spectrum measurement method and a light-transmission-path-spectrum measurement program, being able to acquire detailed spectrum information in a light transmission path.

A light-transmission-path-spectrum measurement device according to the invention is defined in appended claim <NUM>.

One example embodiment is able to provide a light-transmission-path-spectrum measurement device, a light-transmission-path-spectrum measurement method and a light-transmission-path-spectrum measurement program, being able to acquire detailed spectrum information in a light transmission path.

First, before description of a light-transmission-path-spectrum measurement device and a light-transmission-path system according to an example embodiment, a light-transmission-path-spectrum measurement device and a light-transmission-path system according to a comparative example will be described. In this way, the present example embodiment is made more clear.

<FIG> is a diagram illustrating a configuration of the light-transmission-path system including the light-transmission-path-spectrum measurement device according to the comparative example, and <FIG> is a graph illustrating a cable loss trace received by the light-transmission-path-spectrum measurement device according to the comparative example, where a horizontal axis indicates reception time and a vertical axis indicates a signal level. As illustrated in <FIG>, a light-transmission-path system <NUM> according to the comparative example includes a coherent optical time domain reflectometry (COTDR) measurement unit <NUM>. The COTDR measurement unit <NUM> is used for a measurement of a cable loss trace in the light-transmission-path system <NUM> laid on a sea bottom. The light-transmission-path system <NUM> is formed of a light transmission path <NUM> including light transmission path fibers <NUM> and <NUM> in both transmission and reception directions and a repeater <NUM>, and a light transmission/reception device <NUM> connected to a land station at both ends of the light transmission path <NUM>.

In the comparative example, a transmission unit and a reception unit of the COTDR measurement unit <NUM> are connected to a monitoring measurement port of the light transmission/reception device <NUM>. COTDR measurement light is transmitted from the COTDR measurement unit <NUM> to the light transmission path fiber <NUM> via the light transmission/reception device <NUM>, and a part of the COTDR measurement light returns to a direction opposite to a transmission direction by Rayleigh scattering and the like in the light transmission path fiber <NUM>. The COTDR measurement light moving backward in the transmission fiber returns to a light transmission path fiber <NUM> in an opposite direction due to a loopback path mounted on the repeater <NUM>, and the COTDR measurement unit <NUM> receives the COTDR measurement light. Then, a cable loss trace illustrated in <FIG> is acquired.

The measurement light output from the COTDR measurement unit <NUM> is normally an optical pulse, and a relationship between a reception power level and a distance can be acquired as a cable loss trace from reception time of return light. The acquired cable loss trace normally has the highest level at an output end of the repeater <NUM>, and has a lower level toward a farther end of a relay span. In the light-transmission-path system <NUM>, by the cable loss trace, the COTDR measurement is utilized for a use for determining a rupture position at a time of cable trouble, and the like.

Next, a light-transmission-path system including a light-transmission-path-spectrum measurement device according to a first example embodiment will be described. <FIG> is a configuration diagram illustrating the light-transmission-path system including the light-transmission-path-spectrum measurement device according to the first example embodiment. As illustrated in <FIG>, a light-transmission-path system <NUM> includes a light transmission/reception device <NUM> and a light-transmission-path-spectrum measurement device <NUM>. The light transmission/reception device <NUM> transmits a wavelength multiplexed signal to a light transmission path <NUM>, and also receives a wavelength multiplexed signal from a light transmission path <NUM>. Note that, the light transmission path <NUM> and the light transmission path <NUM> are relayed by a plurality of repeaters. The light-transmission-path-spectrum measurement device <NUM> includes a light transmission path interface unit <NUM>, a wavelength varying OTDR measurement unit <NUM>, a control unit <NUM>, and a measurement data processing unit <NUM>. The light-transmission-path-spectrum measurement device <NUM> is a device that acquires a cable loss trace.

The light transmission path interface unit <NUM> includes an optical signal multiplexing unit <NUM>, an optical signal branching unit <NUM>, a dummy light generation unit <NUM>, and a loopback circuit unit <NUM>. The light transmission path interface unit <NUM> includes an interface that transmits and receives a wavelength multiplexed signal to and from the light transmission paths <NUM> and <NUM>. The light transmission path interface unit <NUM> is connected to the light transmission paths <NUM> and <NUM> with the interface. Further, the light transmission path interface unit <NUM> includes an interface that transmits and receives a wavelength multiplexed signal to and from the light transmission/reception device <NUM>. Note that, a plurality of the interfaces may be provided. The light transmission path interface unit <NUM> includes a transmission port and a reception port of measurement light of the wavelength varying OTDR measurement unit <NUM>. The transmission port and the reception port each are connected to the optical signal multiplexing unit <NUM> and the optical signal branching unit <NUM> in the light transmission path interface unit <NUM>, respectively.

The optical signal multiplexing unit <NUM> includes an input port of a wavelength multiplexed signal, an input port of dummy light from the dummy light generation unit <NUM>, and an input port of OTDR measurement light from the wavelength varying OTDR measurement unit <NUM>. The optical signal multiplexing unit <NUM> may include a wavelength selective switch typified by a wavelength selectable switch (WSS). For example, the wavelength selective switch selects a wavelength of measurement light being generated by the wavelength varying OTDR measurement unit <NUM>. The optical signal multiplexing unit <NUM> can select a wavelength of input light from the input ports, multiplexes the input wavelength, and outputs the multiplexed wavelength to the light transmission path <NUM>. Specifically, for example, the optical signal multiplexing unit <NUM> selects a wavelength of measurement light being generated by the wavelength varying OTDR measurement unit <NUM>, and outputs the selected wavelength to the light transmission path <NUM>.

The dummy light generation unit <NUM> supplies dummy light disposed instead of a wavelength multiplexed signal. The dummy light generation unit <NUM> may not be needed depending on an arrangement or a number of wavelengths of a wavelength multiplexed signal, and a main signal transmission characteristic.

The loopback circuit unit <NUM> is applied when a cable trace of a transmission fiber in a first relay section of a light transmission path is acquired in an OTDR measurement. The loopback circuit unit <NUM> has a function of performing loopback, to a reception-side path, on Rayleigh scattered light in the same relay section of an OTDR measurement signal. The loopback circuit unit <NUM> may not be needed when the same section is not needed. Note that, a "relay section" refers to a section from an output end of a certain repeater to an input end of a next repeater.

The optical signal branching unit <NUM> has a function of branching a wavelength multiplexed signal from the light transmission path <NUM> into the light transmission/reception device <NUM> side and the wavelength varying OTDR measurement unit <NUM> side. A branching method may be wavelength branching, power branching, and the like, which is not limited here.

The wavelength varying OTDR measurement unit <NUM> has a function of being able to perform an OTDR measurement on the light transmission path <NUM> by varying a wavelength of measurement light across the entire wavelength band of the light transmission path <NUM>. Specifically, the wavelength varying OTDR measurement unit <NUM> varies and generates a wavelength of measurement light transmitted to the light transmission path <NUM>. Moreover, the wavelength varying OTDR measurement unit <NUM> measures return light acquired from the measurement light being returned by a repeater connected to the light transmission path <NUM>. In this way, the wavelength varying OTDR measurement unit <NUM> acquires a cable trace across the wavelength band in the light transmission path <NUM>. The wavelength varying OTDR measurement unit <NUM> includes a transmission port and a reception port of an OTDR measurement signal. Further, the wavelength varying OTDR measurement unit <NUM> can output an OTDR measurement result to the outside.

The control unit <NUM> has a function of selecting and controlling, by a control signal, a measurement wavelength of the wavelength varying OTDR measurement unit <NUM> and an output wavelength in the optical signal multiplexing unit <NUM>. In other words, the control unit <NUM> controls a wavelength of measurement light being generated by the wavelength varying OTDR measurement unit <NUM> and a wavelength of measurement light being selected by the optical signal multiplexing unit <NUM>. Specifically, for example, the control unit <NUM> controls the wavelength varying OTDR measurement unit <NUM> in such a way as to perform sweeping across a wavelength band of the light transmission path <NUM> while switching a wavelength of measurement light generated by the wavelength varying OTDR measurement unit <NUM>. Further, the control unit <NUM> controls the optical signal multiplexing unit <NUM> in such a way as to block a portion near a wavelength of measurement light in a wavelength multiplexed signal transmitted to the light transmission path <NUM>.

The measurement data processing unit <NUM> has a function of performing data processing on OTDR measurement data being measured by the wavelength varying OTDR measurement unit <NUM>. Further, the measurement data processing unit <NUM> extracts a reception level in each wavelength of measurement light for each position of the light transmission path <NUM>. Then, the measurement data processing unit <NUM> acquires a spectrum in a predetermined position in the light transmission path <NUM>. Furthermore, the measurement data processing unit <NUM> generates three-dimensional data about a level deviation of measurement light with, as an axis, a positional direction of the light transmission path <NUM> and a wavelength direction of the measurement light, based on the acquired spectrum.

Next, an operation of the light-transmission-path-spectrum measurement device <NUM> will be described. <FIG> is a diagram illustrating an operation under a normal condition of the light-transmission-path-spectrum measurement device according to the first example embodiment, and <FIG> is a diagram illustrating an operation during a measurement of the light-transmission-path-spectrum measurement device according to the first example embodiment.

Similarly to the comparative example, it is assumed that the wavelength varying OTDR measurement unit <NUM> according to the present example embodiment can acquire a cable trace. As illustrated in <FIG>, in the present example embodiment, the optical signal multiplexing unit <NUM> controls a wavelength of an optical signal to be transmitted from the light transmission path interface unit <NUM> to the light transmission path <NUM>. For example, a wavelength of wavelength multiplexed signal light from a transmission side or dummy signal light from the dummy light generation unit <NUM> spans, as a transmission signal to the light transmission path <NUM>, across a wavelength band of the light transmission path <NUM>.

As illustrated in <FIG>, the control unit <NUM> controls a wavelength arrangement state during a measurement of the light transmission path <NUM> in the present example embodiment. The control unit <NUM> sweeps a measurement wavelength and performs a measurement while controlling, in a manner indicated below, a wavelength of measurement light being generated by the wavelength varying OTDR measurement unit <NUM> and a wavelength of measurement light being output from the optical signal multiplexing unit <NUM>.

In other words, for the control, an OTDR measurement is performed by sweeping the entire wavelength band of the light transmission path <NUM> while switching a wavelength of measurement light of an OTDR signal. Further, the optical signal multiplexing unit <NUM> blocks a portion around a wavelength of OTDR measurement light to be measured in a wavelength multiplexed signal (or a dummy signal). By such an operation, the wavelength varying OTDR measurement unit <NUM> acquires a cable trace in the entire wavelength band of the light transmission path <NUM>. Then, the measurement data processing unit <NUM> extracts an OTDR measurement level in each wavelength of measurement light for each distance in the light transmission path <NUM>. Then, a spectrum in any distance position in the light transmission path <NUM> is acquired. Further, the measurement data processing unit <NUM> can generate three-dimensional data/graph information about a level deviation in a distance direction and a wavelength direction of the light transmission path, based on processed spectrum information, and provide the three-dimensional data/graph information to the outside.

In this way, a light-transmission-path-spectrum measurement method as an operation of the light-transmission-path-spectrum measurement device <NUM> according to the present example embodiment includes: a step of varying and generating a wavelength of measurement light to be transmitted to the light transmission path <NUM>; a step of selecting the wavelength of the generated measurement light, and outputting the selected wavelength to the light transmission path <NUM>; a step of controlling the wavelength of the measurement light to be generated and the wavelength of the measurement light to be selected; a step of measuring return light acquired from the measurement light being returned, by a repeater connected to the light transmission path <NUM>, via the light transmission path <NUM>; and a step of processing measurement data about the measured return light. Then, the light-transmission-path-spectrum measurement method further includes performing sweeping across a wavelength band of the light transmission path <NUM> while switching the wavelength of the measurement light to be generated, and blocking a portion near the wavelength of the measurement light in a wavelength multiplexed signal transmitted to the light transmission path <NUM>, in the step of selecting the wavelength of the generated measurement light, and outputting the selected wavelength to the light transmission path <NUM>.

In the present example embodiment, a spectrum in any position in each relay section of a light transmission path can be acquired, and a spectrum at an output end of each repeater can be measured and extracted at a high speed by setting an average measurement number in one wavelength as minimum, and measuring only a peak level of each repeater at a high level. In this way, the light-transmission-path-spectrum measurement device <NUM> according to the present example embodiment performs an operation of scanning to a spectrum in any position in each relay section when time for scanning is spent. Further, the light-transmission-path-spectrum measurement device <NUM> performs, at a high speed, an operation of scanning spectrum acquisition at an output end of each repeater in a light transmission path. Hereinafter, the operation of the light-transmission-path-spectrum measurement device <NUM> is divided into <spectrum acquisition in normal state>, <acquired spectrum during cable loss increase>, <acquired spectrum during output decrease of repeater>, and <acquired spectrum when light transmission gain wavelength deviation is present>, and will be specifically described.

<FIG> is a diagram illustrating a light transmission path to be measured according to the first example embodiment. <FIG> only illustrates the light transmission path <NUM> on the transmission side for simplification, and illustrates, for example, the light transmission path <NUM> formed of <NUM> repeaters REP1 to REP10. In the present example embodiment, description is given on an assumption that the repeaters REP1 to REP10 constituting the light transmission path <NUM> perform an output constant operation for simplifying the description. Further, it is assumed that the light transmission path <NUM> is in a normal state without trouble and the like in each of the repeaters REP1 to REP10 and a cable, and a gain wavelength deviation in each relay section is extremely good (flat).

<FIG> are diagrams illustrating a cable trace acquired by measuring the light transmission path by a basic measurement operation (<FIG>) according to the first example embodiment. As a representative, <FIG> illustrates a signal level on a short wave side, <FIG> illustrates a signal level of a center wavelength, and <FIG> illustrates a signal level on a long wave side.

<FIG> is a diagram three-dimensionally illustrating an output spectrum of each repeater being acquired by plotting a peak level of a cable trace acquired by the basic measurement operation (<FIG>) according to the first example embodiment. <FIG> are diagrams acquired by extracting an output spectrum in a representative repeater from the three-dimensional data in <FIG>, <FIG> illustrates a case of a light transmission path input unit, <FIG> illustrates a case of the repeater REP4, <FIG> illustrates a case of the repeater REP5, and <FIG> illustrates a case of the repeater REP10.

As illustrated in <FIG>, <FIG>, and <FIG>, in the light transmission path <NUM> being in a normal state and having ideal flatness, a similar cable trace is acquired in the entire wavelength band regardless of a wavelength of OTDR measurement light. A trace level at each repeater end is constant similarly to an initial level. In an operation of acquiring a spectrum at an output end of each repeater, a cable trace in the entire span region does not need to be acquired. Thus, by sweeping an OTDR measurement of each wavelength at a high speed, spectrum acquisition in a relatively short time can be achieved. In this way, also in <FIG> and <FIG> of the acquired spectrum, a flat output spectrum can be acquired in the entire light transmission path <NUM>.

Next, a spectrum acquisition operation of a repeater output end in a cable loss increasing state will be described. <FIG> is a diagram illustrating a light transmission path to be measured according to the first example embodiment. <FIG> only illustrates the light transmission path <NUM> on the transmission side for simplification, and illustrates, for example, the light transmission path <NUM> formed of <NUM> repeaters REP1 to REP10. In the present example embodiment, description is given on an assumption that the repeaters REP1 to REP10 constituting the light transmission path <NUM> perform an output constant operation for simplifying the description. In <FIG>, a situation where a loss in a cable between the repeater REP4 and the repeater REP5 increases is assumed to be a cable loss increasing state.

<FIG> are diagrams illustrating a cable trace acquired by measuring the light transmission path by the basic measurement operation (<FIG>) according to the first example embodiment. As a representative, <FIG> illustrates a signal level on a short wave side, <FIG> illustrates a signal level of a center wavelength, and <FIG> illustrates a signal level on a long wave side.

<FIG> is a diagram three-dimensionally illustrating an output spectrum of each repeater being acquired by plotting a peak level of a cable trace acquired by the basic measurement operation (<FIG>) according to the first example embodiment. <FIG> are diagrams acquired by extracting an output spectrum in a representative repeater from the three-dimensional data in <FIG>, <FIG> illustrates a case of the light transmission path input unit, <FIG> illustrates a case of the repeater REP4, <FIG> illustrates a case of the repeaters REP5 to REP9, and <FIG> illustrates a case of the repeater REP10.

In a light transmission path in a cable loss increasing state, as in <FIG>, a loss increase (level decrease) is observed in a trouble position in a cable trace of each wavelength. A similar cable trace is acquired in the entire wavelength band regardless of an OTDR measurement wavelength. However, since output constant control is performed on the repeater used for the light transmission path <NUM>, a gain of the repeater REP5 in a next stage increases, and a gain inclination declining at a long wave occurs. At this time, a peak level of a cable trace of each repeater after the repeater REP5 does not change at the center wavelength, but is higher than an initial level on the short wave side, and is lower than the initial level on the long wave side. In <FIG> and <FIG> of the spectrum acquired above at the output end of each repeater, it is clear that occurrence of a level deviation in each relay section can be visualized. In the present example, it can be visually confirmed that the short wave side is susceptible to non-linear degradation of a main signal in each span after the repeater REP5, and OSNR degradation of a main signal is concerned on the long wave side.

Next, a spectrum acquisition operation of a repeater output end in a repeater output decreasing state will be described. <FIG> is a diagram illustrating a light transmission path to be measured according to the first example embodiment. <FIG> only illustrates the light transmission path <NUM> on the transmission side for simplification, and illustrates, for example, the light transmission path <NUM> formed of <NUM> repeaters REP1 to REP <NUM>. In the present example embodiment, description is given on an assumption that each of the repeaters other than the repeater REP5 constituting the light transmission path <NUM> performs an output constant operation for simplifying the description. In <FIG>, a situation where an EDF output of a repeater output of the repeater REP5 decreases is assumed to be a repeater output decreasing state.

<FIG> is a diagram three-dimensionally illustrating an output spectrum of each repeater being acquired by plotting a peak level of a cable trace acquired by the basic measurement operation (<FIG>) according to the first example embodiment. <FIG> are diagrams acquired by extracting an output spectrum in a representative repeater from the three-dimensional data in <FIG>, <FIG> illustrates a case of the light transmission path input unit, <FIG> illustrates a case of the repeater REP4, <FIG> illustrates a case of the repeater REP5, and <FIG> illustrates a case of the repeaters REP6 to REP10.

In the light transmission path <NUM> in the repeater output decreasing state, as in <FIG>, a repeater gain decreases in a repeater in which an output decrease occurs, and thus a gain inclination declining at a short wave occurs. At this time, a peak level of a cable trace of the repeater REP5 does not change at the center wavelength, but is lower than an initial level on the short wave side, and is higher than the initial level on the long wave side.

In the subsequent repeater REP6, input total power of the repeater REP5 decreases, but output total power does not change due to repeater output constant control. Thus, a gain increases as a result, and a gain inclination declining at a long wave occurs. This cancels out the gain inclination declining at the short wave that occurs in the previous stage, and a gain inclination hardly occurs at an output end of the repeater REP6.

In <FIG> and <FIG> of the spectrum acquired above at the output end of each repeater, occurrence of a level deviation in each relay section in the state can be visualized. In the present example, the gain inclination declining at the short wave occurs only in the repeater REP5. A main signal on the long wave side is susceptible to non-linear degradation only between the repeater REP5 and the repeater REP6. OSNR degradation of a main signal is concerned on the short wave side. In the present example embodiment, such points can be visually confirmed. In a case of such an instance, a change is hardly observed in a spectrum measured at a reception end after light transmission. Thus, a state of a deviation of a spectrum in the light transmission path <NUM> cannot be observed. However, according to the light-transmission-path-spectrum measurement method in the present example embodiment in contrast to a measurement method at a reception end after light transmission, occurrence of a level deviation in each relay section can be measured.

Next, a spectrum acquisition operation of a repeater output end in a state where a gain wavelength deviation is present in each repeater output in a light transmission path will be described. <FIG> is a diagram illustrating a light transmission path to be measured according to the first example embodiment. <FIG> only illustrates the light transmission path <NUM> on the transmission side for simplification, and illustrates, for example, the light transmission path <NUM> formed of <NUM> repeaters REP1 to REP10. In the present example embodiment, description is given on an assumption that the repeaters REP1 to REP10 constituting the light transmission path <NUM> perform an output constant operation for simplifying the description. Further, a gain equalizer <NUM> is attached to the repeater REP5.

<FIG> is a diagram three-dimensionally illustrating an output spectrum of each repeater being acquired by plotting a peak level of a cable trace acquired by the basic measurement operation (<FIG>) according to the first example embodiment. <FIG> are diagrams acquired by extracting an output spectrum in a representative repeater from the three-dimensional data in <FIG>, <FIG> illustrates a case of the light transmission path input unit, <FIG> illustrates a case of the repeater REP4, <FIG> illustrates a case of the repeater REP5, and <FIG> illustrates a case of the repeater REP10.

In the example in <FIG>, an ideal example without gain wavelength dependence of each repeater is used for description in order to simplify the description, but an individual variation and an environmental variation such as temperature are present in the gain wavelength dependence of each repeater in the light transmission path <NUM> in a normal light-transmission-path system. Then, a deviation is more likely to be accumulated when a number of relays becomes a multistage due to gain wavelength dependence of an EDF itself in the repeater REP, and becomes a greater deviation.

In the present example, it is assumed that a gain wavelength deviation between the repeater REP1 to the repeater REP4 is generated and accumulated. The gain equalizer <NUM> attached to the repeater REP5 makes an accumulated deviation flat and equivalent. Hereinafter, a deviation is also accumulated in the repeater REP6 to the repeater REP10. <FIG> and <FIG> illustrate such an example. Also in the present example, it is difficult to specifically recognize a deviation at each place in a light transmission path only with spectrum information at a reception end after light transmission. According to the light-transmission-path-spectrum measurement method in the present example embodiment in contrast to a measurement method at a reception end after light transmission, a deviation at each place in the light transmission path <NUM> can be visualized and confirmed.

Next, an effect of the present example embodiment will be described. In the present example embodiment, the control unit <NUM> controls a wavelength of measurement light being generated by the wavelength varying OTDR measurement unit <NUM> and a wavelength of measurement light being selected by the optical signal multiplexing unit <NUM>. In this way, detailed spectrum information in the light transmission path <NUM> can be acquired.

The control unit <NUM> controls the optical signal multiplexing unit <NUM> in such a way as to block a portion near a wavelength of measurement light in a wavelength multiplexed signal transmitted to the light transmission path <NUM>. Further, the control unit <NUM> controls the wavelength varying OTDR measurement unit <NUM> in such a way as to perform sweeping across a wavelength band of the light transmission path <NUM> while switching a wavelength of measurement light to be generated. Thus, spectrum information in any distance of the light transmission path <NUM> can be acquired. Further, an output spectrum of each of the repeaters REP of the light transmission path <NUM> can be acquired in a short time.

The wavelength varying OTDR measurement unit <NUM> acquires a cable trace across the wavelength band of the light transmission path <NUM>. By measuring only a reception level of a peak portion of a cable trace, an output spectrum of the repeater REP can be acquired in a short time.

The measurement data processing unit <NUM> extracts a reception level in each wavelength of measurement light for each position of the light transmission path <NUM>, and acquires a spectrum in a predetermined position of the light transmission path <NUM>. In this way, three-dimensional data about a level deviation of measurement light with, as an axis, a positional direction of the light transmission path <NUM> and a wavelength direction of the measurement light can be acquired. Thus, more detailed design of main signal transmission performance in the light transmission path <NUM> can be achieved.

Next, a second example embodiment will be described. <FIG> is a configuration diagram illustrating a light-transmission-path system including a light-transmission-path-spectrum measurement device according to the second example embodiment. Since measurement light is performed loopback to a light transmission path <NUM> in a reception direction in an OTDR measurement in a light transmission path <NUM> and the light transmission path <NUM> in two ways, an acquired spectrum may be affected by a state of the light transmission path <NUM> in the reception direction. Therefore, as illustrated in <FIG>, the light-transmission-path-spectrum measurement device <NUM> according to the first example embodiment may also be installed on an opposite station side of the light transmission paths <NUM> and <NUM>, and a function of acquiring spectrum information measured at the opposite station and correcting spectrum information measured at an own station may be provided.

Specifically, a light-transmission-path system <NUM> according to the present example embodiment includes the light transmission path <NUM> relayed by a plurality of repeaters REP, the light transmission path <NUM> relayed by the plurality of repeaters REP, a light transmission/reception device <NUM> that transmits a wavelength multiplexed signal to the light transmission path <NUM>, a light transmission/reception device <NUM> that transmits a wavelength multiplexed signal to the light transmission path <NUM>, a light-transmission-path-spectrum measurement device 2a disposed on the light transmission/reception device <NUM> side, and a light-transmission-path-spectrum measurement device 2b disposed on the light transmission/reception device <NUM> side. The light transmission/reception device <NUM> transmits a wavelength multiplexed signal to the light transmission/reception device <NUM> via the light transmission path <NUM>, and receives a wavelength multiplexed signal from the light transmission/reception device <NUM> via the light transmission path <NUM>. Meanwhile, the light transmission/reception device <NUM> transmits a wavelength multiplexed signal to the light transmission/reception device <NUM> via the light transmission path <NUM>, and receives a wavelength multiplexed signal from the light transmission/reception device <NUM> via the light transmission path <NUM>.

The light-transmission-path-spectrum measurement device 2a is similar to the light-transmission-path-spectrum measurement device <NUM> described above. The light-transmission-path-spectrum measurement device 2b has a configuration similar to that of the light-transmission-path-spectrum measurement device 2a except for that the light-transmission-path-spectrum measurement device 2b outputs measurement light to the light transmission path <NUM> and has return light being returned via the light transmission path <NUM>.

Then, when a measurement data processing unit <NUM> of the light-transmission-path-spectrum measurement device 2a processes measurement data about return light being measured by a wavelength varying OTDR measurement unit <NUM>, the measurement data processing unit <NUM> of the light-transmission-path-spectrum measurement device 2a refers to measurement data being processed by a measurement data processing unit <NUM> of the light-transmission-path-spectrum measurement device 2b. In this way, an influence of a state of the light transmission path <NUM> can be reduced. Similarly, the measurement data processing unit <NUM> of the light-transmission-path-spectrum measurement device 2b refers to measurement data being processed by the measurement data processing unit <NUM> of the light-transmission-path-spectrum measurement device 2a.

The light-transmission-path-spectrum measurement devices 2a and 2b and the light-transmission-path system <NUM> according to the present example embodiment can reduce an influence of a light transmission path through which return light passes. A configuration and an effect other than that are included in the description of the first example embodiment.

When a WDM signal on an opposite side is present in <FIG>, at a time of an OTDR measurement at an own station, a function of communicating with a control unit <NUM> at an opposite station, controlling an optical signal multiplexing unit <NUM> in a light transmission path interface unit <NUM> at the opposite station, and blocking an OTDR measurement wavelength peripheral wavelength of the own station may be provided.

When a wavelength multiplexed signal on a transmission side is not present in <FIG>, a wavelength selection function of output dummy light may be provided in a dummy light generation unit <NUM>. In this way, dummy light switching of a wavelength multiplexed signal may be achieved in the dummy light generation unit <NUM>.

In <FIG>, an optical signal multiplexing unit <NUM> may have a function of measuring an OTDR by changing a measurement level of each of a wavelength multiplexed signal, dummy light, and an OTDR measurement. Specifically, the following function is achieved. In other words, a function of measuring a spectrum in a light transmission path <NUM> by making a transmission peak level of a wavelength multiplexed signal or dummy light flat may be provided. Further, for a purpose of reception OSNR equalization, reception signal quality equalization, and the like, a function of measuring a spectrum in a state where a transmission peak level of a wavelength multiplexed signal or dummy light has a pre-emphasis (intentional level deviation) may be provided. Furthermore, a function of performing suppression control of a wavelength multiplexed signal or dummy light for a purpose of increasing a speed of an OTDR measurement and securing a high dynamic range may be provided. Specifically, control is performed in such a way as to change a power distribution of a wavelength multiplexed signal and OTDR measurement light and raise an OTDR measurement light level in the light transmission path <NUM>.

In <FIG>, an optical signal multiplexing unit <NUM> may have a function of intentionally changing a wavelength arrangement of a wavelength multiplexed signal and dummy light, and measuring an OTDR. Specifically, the following function is achieved. In other words, a wavelength band is previously blocked at a regular interval in a wavelength arrangement of a wavelength multiplexed signal or dummy light, and an OTDR measurement is performed at a blocked wavelength. In this way, shortening of control time, shortening of measurement time, and simplification of a control sequence can be achieved.

In <FIG>, an optical signal branching unit <NUM> may be provided with a wavelength selection function by a WSS and the like. Further, control according to filtering of output light of an OTDR measurement unit <NUM> other than measurement light and a change in OTDR measurement wavelength may be added.

Note that, the present invention is not limited to the example embodiments described above, and may be appropriately modified without departing from the scope of the present disclosure. For example, an example embodiment acquired by combining each of the configurations of the first to seventh example embodiments is also included within the scope of a technical idea. Further, the following light-transmission-path-spectrum measurement program for causing a computer to execute the light-transmission-path-spectrum measurement method in the present example embodiment is also included within the scope of a technical idea of the example embodiment.

A non-transitory computer-readable medium that stores a light-transmission-path-spectrum measurement program causing a computer to execute:.

Although the present invention has been described above as a configuration of hardware in the example embodiments described above, the present invention is not limited to the example embodiments. The present invention can also achieve any processing by causing a central processing unit (CPU) to execute a computer program.

Further, the program described above is stored by using a non-transitory computer-readable medium of various types, and can be supplied to a computer. The non-transitory computer-readable medium includes a tangible storage medium of various types. Examples of the non-transitory computer-readable medium include a magnetic recording medium (for example, a flexible disk, a magnetic tape, and a hard disk drive), a magneto-optical recording medium (for example, a magneto-optical disk), a CD-read only memory (CD-ROM), a CD-R, a CD-R/W, and a semiconductor memory (for example, a mask ROM, a programmable ROM (PROM), an erasable PROM (EPROM), a flash ROM, and a random access memory (RAM)). Further, a program may be supplied to a computer by a transitory computer-readable medium of various types. Examples of the transitory computer-readable medium include an electric signal, an optical signal, and an electromagnetic wave. The transitory computer-readable medium can supply a program to a computer via a wired communication path such as an electric wire and an optical fiber or a wireless communication path.

Claim 1:
A light-transmission-path-spectrum measurement device (<NUM>), compri sing:
wavelength varying OTDR measurement means (<NUM>) for varying and generating a wavelength of measurement light to be transmitted to a first light transmission path (<NUM>), and also measuring return light acquired from the measurement light being returned, by a plurality of repeaters (REP) connected to the first light transmission path (<NUM>), via a second light transmission path (<NUM>) connected to the repeaters (REP);
optical signal multiplexing means (<NUM>) for selecting the wavelength of the measurement light being generated by the wavelength varying OTDR measurement means (<NUM>), and outputting the selected wavelength to the first light transmission path (<NUM>);
control means (<NUM>) for controlling the wavelength of the measurement light being generated by the wavelength varying OTDR measurement means (<NUM>) and the wavelength of the measurement light being selected by the optical signal multiplexing means (<NUM>); and
measurement data processing means (<NUM>) for processing measurement data about the return light being measured by the wavelength varying OTDR measurement means (<NUM>),
wherein the control means (<NUM>) controls the wavelength varying OTDR measurement means (<NUM>) in such a way as to perform sweeping across a wavelength band of the first light transmission path (<NUM>) while switching the wavelength of the measurement light to be generated,
wherein the wavelength varying OTDR measurement means (<NUM>) acquires a cable trace across a wavelength band of the first light transmission path (<NUM>),
wherein the measurement data processing means (<NUM>) extracts peak level of cable trace in each wavelength of the measurement light for each position of the first light transmission path (<NUM>) and acquires the peak level in each position of the first light transmission path (<NUM>) over different wavelengths.