WO2013176505A1

WO2013176505A1 - Optical line monitoring device, optical line monitoring system including the optical line monitoring device, and method of controlling the optical line monitoring system

Info

Publication number: WO2013176505A1
Application number: PCT/KR2013/004540
Authority: WO
Inventors: Eun Jeong Yang; Lae Hyuk Park; Ki Yeul Kim; Ji Sang Park
Original assignee: Ls Cable & System Ltd.
Priority date: 2012-05-25
Filing date: 2013-05-23
Publication date: 2013-11-28

Abstract

An optical line monitoring device includes an OTDR for selectively transmitting monitoring light by an optical line for connecting a supplier-side terminal with an ONT and receiving monitoring light reflected by the optical line and an analysis unit for analyzing a trace of the monitoring light, wherein the analysis unit sets two or more types of reflection peak factor threshold values in a OTDR reference trace of the monitoring light, measures two or more types of reflection peak factors corresponding to the reflection peak factor threshold values in the OTDR reference trace of the monitoring light, compares values of the measured reflection peak factors with the set reflection peak factor threshold value, and determines a reflection peak in the OTDR reference trace of the monitoring light; the analysis unit measures two or more types of reflection peak factors in a measured trace of the monitoring light, compares the measured reflection peak factors with the set reflection peak factor threshold values, and determines a reflection peak in the measured trace of the monitoring light; and the analysis unit compares a reflection peak factor of the reflection peak of the measured trace with a reflection peak factor of the reflection peak of the OTDR reference trace and determines whether a fault has occurred in the optical line.

Description

OPTICAL LINE MONITORING DEVICE, OPTICAL LINE MONITORING SYSTEM INCLUDING THE OPTICAL LINE MONITORING DEVICE, AND METHOD OF CONTROLLING THE OPTICAL LINE MONITORING SYSTEM

The present invention relates to an optical line monitoring device, an optical line monitoring system including the optical line monitoring device, and a method of controlling the optical line monitoring system.

In general, optical fiber has advantages, such as a low energy loss ratio when sending data, a wide bandwidth, light weight, and impossibility of external wire tapping as compared with existing copper line. If an optical network is constructed using an optical line utilizing this optical fiber, the optical network is being widely used because infinite data communication is theoretically possible along with the above advantages.

Meanwhile, optical fiber has a variety of advantages, such as those described above, but has a disadvantage in that it has weaker mechanical characteristics than an existing copper line. That is, if an optical line includes optical fiber, a fault, such as the bending or break of the optical line, can occur while the optical line is installed or after the optical line is installed because the optical line is relatively less reliable than an existing copper line. Accordingly, a monitoring system for detecting a fault in this optical line is being developed.

Monitoring systems are disclosed in Japanese Patent Publication No. 4902213 (hereinafter referred to as 'Prior Art Document 1'), Korean Patent Publication No. 672023 (hereinafter referred to as 'Prior Art Document 2'), and Japanese Patent Laid-Open Publication No. 2011-154001 (hereinafter referred to as 'Prior Art Document 3').

Prior Art Document 1 discloses a method of determining a reflection peak based on a power of a peak and determining whether a fault is occurred based on the power. If only the poweres are simply compared with each other and a reflection peak of monitoring light is determined based on a result of the comparison, noise or fluctuation can be included in the reflection peak or an actual reflection peak can be determined as noise or fluctuation. That is, if a reflection peak is determined using one type of a Reference value, it is difficult to determine the reflection peak precisely. In addition, it is also difficult to determine a fault precisely in case where the fault is determined using the reflection peak.

Furthermore, Prior Art Document 2 discloses a method of comparing a OTDR reference trace and a measured trace of monitoring light with each other and determining a fault based on a result of the comparison, but does not disclose a detailed method of determining a fault.

Furthermore, Prior Art Document 3 discloses a monitoring system for determining a fault using two types of monitoring light having different wavelengths. However, Prior Art Document 3 separately includes an optical line along which signal light is transmitted and an optical line along which monitoring light is transmitted. Therefore, also there is a problem in that the construction of the monitoring system is very complicated and analysis of two types of monitoring light is very difficult because the two types of monitoring light having different wavelength are used.

An object of the present invention is to provide a monitoring system and a method of controlling the monitoring system which can detect a fault, such as a break or bending occurring in each line, easily and precisely.

In particular, an object of the present invention is to provide a monitoring system and a method of controlling the monitoring system which can easily detect a fault occurring in each optical line even in an optical line using a P2MP method.

To accomplish the above objects, according to a first aspect of the present invention, there is provided an optical line monitoring device, comprising an Optical Time Domain Reflectometery (OTDR) for selectively transmitting monitoring light by an optical line for connecting a supplier-side terminal and an Optical Network Terminal (ONT) together and receiving the monitoring light reflected and an analysis unit for analyzing a trace of the monitoring light, wherein the analysis unit sets two or more types of reflection peak factor threshold values in a OTDR reference trace of the monitoring light, measures two or more types of reflection peak factors corresponding to the reflection peak factor threshold values in the OTDR reference trace of the monitoring light, compares values of the measured reflection peak factors with the set reflection peak factor threshold value, and determines a reflection peak in the OTDR reference trace of the monitoring light based on a result of the comparison, the analysis unit measures two or more types of reflection peak factors in a measured trace of the monitoring light, compares the measured reflection peak factors with the set reflection peak factor threshold values, and determines a reflection peak in the measured trace of the monitoring light based on a result of the comparison and the analysis unit compares the reflection peak factors of the reflection peak of the measured trace with the reflection peak factors of the reflection peak of the OTDR reference trace and determines whether or not a fault has occurred in the optical line based on a result of the comparison.

The analysis unit partitions the optical line into at least two sections, and the sections are determined depending on an optical splitter provided along the optical line.

If two or more optical splitters are provided along the optical line, the analysis unit sets an ONT, located at a longest distance from the supplier-side terminal, as an end point of an end section and sets a predetermined point adjacent to a peak due to a first optical splitter as an end point of a first section.

The analysis unit sets a predetermined point between a first peak due to the first optical splitter and a second peak subsequent to the first peak as the end point of the first section.

If a first optical splitter and one or more second optical splitter connected to the first optical splitter are provided along the optical line, the analysis unit sets an optical splitter located at a longest distance from the supplier-side terminal, from among the second optical splitters, as an end point of a second section.

The analysis unit differently sets at least one of the two or more types of reflection peak factor threshold values in the partitioned sections.

The analysis unit sets a first reflection peak factor threshold value Th_level and a second reflection peak factor threshold value Th_height and differently sets the second reflection peak factor threshold value Th_height in each partitioned section.

The analysis unit sets the second reflection peak factor threshold value Th_height to be sequentially increased as the section proceeds from the supplier-side terminal to the ONT.

The analysis unit sets the second reflection peak factor threshold value Th_height to be equal to or higher than noise occurring in each partitioned section.

The analysis unit sets the second reflection peak factor threshold value Th_height to be a greatest in a section adjacent to the ONT.

The analysis unit calculates a Root Mean Square (RMS) value and a standard deviation of the OTDR reference trace of the monitoring light in a section after an ONT located at a longest distance from the supplier-side terminal, sets a first noise upper limit value by adding a first predetermined value to the RMS value, sets a second noise upper limit value by adding a second predetermined value to the first noise upper limit value, sets a third noise upper limit value by adding a value, obtained by multiplying the standard deviation by the predetermined coefficient, to the RMS value, and sets any one of the first noise upper limit value, the second noise upper limit value, and the third noise upper limit value as the first reflection peak factor threshold value Th_level.

The analysis unit calculates a first average and a first standard deviation of noise in the OTDR reference trace including a peak and a second average and a second standard deviation of noise in the OTDR reference trace without the peak in each partitioned section, and the analysis unit sets a value obtained by adding the first standard deviation to the first average or a value obtained by adding the second standard deviation to the second average as the second reflection peak factor threshold value Th_height in each partitioned section.

The analysis unit measures two reflection peak factors in peaks of the OTDR reference trace of the monitoring light, compares the measured reflection peak factors with the first and the second reflection peak factor threshold values, and determines a reflection peak based on a result of the comparison, and the analysis unit measures two reflection peak factors in peaks of the measured trace of the monitoring light, compares the measured reflection peak factors with the first and the second reflection peak factor threshold values, and determines a reflection peak based on a result of the comparison.

The analysis unit measures a peak value Peak_level and a peak height Peak_height of each of the peaks in the OTDR reference trace of the monitoring light, sets the measured peak value Peak_level and the measured peak height Peak_height as the first reflection peak factor and the second reflection peak factor, respectively, and the analysis measures a peak value Peak_level and a peak height Peak_height of each of the peaks in the measured trace of the monitoring light, and sets the measured peak value Peak_level and the measured peak height Peak_height as the first reflection peak factor and the second reflection peak factor, respectively.

The analysis unit compares a value of the first reflection peak factor Peak_level of each of the peaks with the first reflection peak factor threshold value Th_level in the OTDR reference trace or the measured trace of the monitoring light and determines whether or not each of the peaks in the OTDR reference trace or the measured trace of the monitoring light corresponds to noise based on a result of the comparison. If, as a result of the determination, it is determined that each of the peaks in the OTDR reference trace or the measured trace of the monitoring light does not correspond to noise, the analysis unit compares a value of the second reflection peak factor Peak_height with the second reflection peak factor threshold value Th_height in each partitioned section and determines a reflection peak based on a result of the comparison.

When a reflection peak factor of the reflection peak of the measured trace is compared with a reflection peak factor of the reflection peak of the OTDR reference trace and whether or not a fault has occurred in the optical line is determined based on a result of the comparison, the analysis unit determines whether or not a break has occurred in the optical line and then determines whether or not bending has occurred in the optical line.

When a reflection peak factor of the reflection peak of the measured trace is compared with a reflection peak factor of the reflection peak of the OTDR reference trace and whether or not a fault has occurred in the optical line is determined based on a result of the comparison, the analysis unit compares a number and locations of the reflection peaks of the measured trace with a number and locations of the reflection peaks of the OTDR reference trace, determines whether or not a break has occurred in the optical line based on a result of the comparison, and determines that the optical line has been broken if, as a result of the comparison, at least one of the number and locations of the reflection peaks of the measured trace has been changed as compared with the reflection peaks of the OTDR reference trace.

When a reflection peak factor of the reflection peak of the measured trace is compared with a reflection peak factor of the reflection peak of the OTDR reference trace and whether or not a fault has occurred in the optical line is determined based on a result of the comparison, the analysis unit compares the first reflection peak factor Peak_level of the reflection peak of the measured trace with the first reflection peak factor Peak_level of the reflection peak of the OTDR reference trace and determines whether or not bending has occurred in the optical line based on a result of the comparison if the reflection peaks of the measured trace have an identical number and locations with the reflection peaks of the OTDR reference trace.

The analysis unit measures a third reflection peak factor of the reflection peak of the OTDR reference trace and a third reflection peak factor of the reflection peak of the measured trace, and if a difference between the first reflection peak factor of the reflection peak of the measured trace and the first reflection peak factor of the reflection peak of the OTDR reference trace is a predetermined value or higher, the analysis unit compares the third reflection peak factor of the reflection peak of the measured trace with the third reflection peak factor of the reflection peak of the OTDR reference trace and determines whether or not bending has occurred in the optical line based on a result of the comparison.

The analysis unit sets a value, obtained by subtracting an initial strength of the OTDR reference trace or the measured trace from the first reflection peak factor Peak_level of the monitoring light, as the third reflection peak factor, respectively.

If a difference between the third reflection peak factor of the reflection peak of the OTDR reference trace and the third reflection peak factor of the reflection peak of the measured trace is a predetermined value or higher, the analysis unit determines that bending has occurred in the optical line.

To accomplish the above objects, according to a second aspect of the present invention, there is an optical line monitoring system, comprising an optical line configured to connect a supplier-side terminal with a plurality of Optical Network Terminals (ONTs), an optical line monitoring device configured to comprise an Optical Time Domain Reflectometery (OTDR) for selectively transmitting monitoring light by the optical line and receiving the monitoring light reflected and an analysis unit for analyzing a trace of the monitoring light, an optical switching unit configured to selectively connect the optical line with the optical line monitoring device, a Wavelength Division Multiplexer (WDM) configured to combine signal light and the monitoring light and an optical splitter provided along the optical line, wherein the analysis unit sets two or more types of reflection peak factor threshold values in a OTDR reference trace of the monitoring light, measures two or more types of reflection peak factors corresponding to the reflection peak factor threshold values in the OTDR reference trace of the monitoring light, compares values of the measured reflection peak factors with the set reflection peak factor threshold value, and determines a reflection peak in the OTDR reference trace of the monitoring light based on a result of the comparison, the analysis unit measures two or more types of reflection peak factors in a measured trace of the monitoring light, compares the measured reflection peak factors with the set reflection peak factor threshold values, and determines a reflection peak in the measured trace of the monitoring light based on a result of the comparison and the analysis unit compares the reflection peak factors of the reflection peak of the measured trace with the reflection peak factors of the reflection peak of the OTDR reference trace and determines whether or not a fault has occurred in the optical line based on a result of the comparison.

To accomplish the above objects, according to a third aspect of the present invention, there is a method of controlling an optical line monitoring device, comprising an Optical Time Domain Reflectometery (OTDR) for selectively transmitting monitoring light by an optical line for connecting a supplier-side terminal and an Optical Network Terminal (ONT) together and receiving the monitoring light reflected and an analysis unit for analyzing a trace of the monitoring light, the method comprising steps of analyzing a OTDR reference trace of the monitoring light, analyzing a measured trace of the monitoring light and comparing the measured trace with the OTDR reference trace and determining whether or not a fault has occurred in the optical line, wherein the step of analyzing the OTDR reference trace of the monitoring light comprises steps of setting two or more types of reflection peak factor threshold values in the OTDR reference trace of the monitoring light, measuring two or more types of reflection peak factors corresponding to the reflection peak factor threshold values, comparing the measured reflection peak factors with the set reflection peak factor threshold values, and determining a reflection peak based on a result of the comparison, the step of analyzing the measured trace of the monitoring light comprises steps of measuring two or more types of reflection peak factors in the measured trace of the monitoring light, comparing the measured reflection peak factors with the set reflection peak factor threshold values, and determining a reflection peak based on a result of the comparison and the step of comparing the measured trace with the OTDR reference trace and determining whether or not a fault has occurred in the optical line comprises a step of comparing the reflection peak factors of the reflection peak of the measured trace with the reflection peak factors of the reflection peak of the OTDR reference trace and determining whether or not a fault has occurred in the optical line based on a result of the comparison.

The step of analyzing a OTDR reference trace of the monitoring light and the step of analyzing a measured trace of the monitoring light further comprise a step of partitioning the optical line into at least two sections depending on an optical splitter provided along the optical line.

The step of partitioning the optical line into at least two sections depending on an optical splitter provided along the optical line comprises steps of setting an ONT, located at a longest distance from the supplier-side terminal, as an end point of an end section and setting a predetermined point adjacent to a peak due to a first optical splitter as an end point of a first section.

The step of setting a predetermined point adjacent to a peak due to a first optical splitter as an end point of a first section comprises setting a predetermined point between a first peak due to the first optical splitter and a second peak subsequent to the first peak as the end point of the first section.

The step of partitioning the optical line into at least two sections depending on an optical splitter provided along the optical line further comprises a step of setting an optical splitter located at a longest distance from the supplier-side terminal, from among second optical splitters, as an end point of a second section, if a first optical splitter and one or more second optical splitter connected to the first optical splitter are provided along the optical line.

The step of setting two or more types of reflection peak factor threshold values in the OTDR reference trace of the monitoring light further comprises a step of differently setting at least one of the two or more types of reflection peak factor threshold values in the partitioned sections.

The step of differently setting at least one of the two or more types of reflection peak factor threshold values in the partitioned sections comprises steps of setting a first reflection peak factor threshold value Th_level and differently setting a second reflection peak factor threshold value Th_height in each partitioned section.

The step of differently setting a second reflection peak factor threshold value Th_height in each partitioned section comprises setting the second reflection peak factor threshold value Th_height to be sequentially increased as the section proceeds from the supplier-side terminal to the ONT.

The second reflection peak factor threshold value Th_height is set to be equal to or higher than noise occurring in each partitioned section.

The step of differently setting a second reflection peak factor threshold value Th_height in each partitioned section comprises setting the second reflection peak factor threshold value Th_height to be a greatest in a section adjacent to the ONT.

The step of setting a first reflection peak factor threshold value Th_level comprises calculating a Root Mean Square (RMS) value and a standard deviation of the OTDR reference trace of the monitoring light in a section after an ONT located at a longest distance from the supplier-side terminal, setting a first noise upper limit value by adding a first predetermined value to the RMS value, setting a second noise upper limit value by adding a second predetermined value to the first noise upper limit value, setting a third noise upper limit value by adding a value, obtained by multiplying the standard deviation by the predetermined coefficient, to the RMS value, and setting any one of the first noise upper limit value, the second noise upper limit value, and the third noise upper limit value as the first reflection peak factor threshold value Th_level.

The step of differently setting a second reflection peak factor threshold value Th_height in each partitioned section comprises calculating a first average and a first standard deviation of noise in the OTDR reference trace including a peak and a second average and a second standard deviation of noise in the OTDR reference trace without the peak in each partitioned section of the OTDR reference trace and setting a value obtained by adding the first standard deviation to the first average or a value obtained by adding the second standard deviation to the second average as the second reflection peak factor threshold value Th_height in each partitioned section.

The step of comparing the measured reflection peak factors with the set reflection peak factor threshold values in the OTDR reference trace of the monitoring light and determining a reflection peak based on a result of the comparison comprises a step of measuring two reflection peak factors in peaks of the OTDR reference trace of the monitoring light, comparing the measured reflection peak factors with the first and the second reflection peak factor threshold values, and determining a reflection peak based on a result of the comparison, and the step of comparing the measured reflection peak factors with the reflection peak factor threshold values in the measured trace of the monitoring light and determining a reflection peak based on a result of the comparison comprises a step of measuring two reflection peak factors in peaks of the measured trace of the monitoring light, comparing the measured reflection peak factors with the first and the second reflection peak factor threshold values, and determining a reflection peak based on a result of the comparison.

The step of measuring two reflection peak factors in the peaks of the OTDR reference trace of the monitoring light comprises measuring a peak value Peak_level and a peak height Peak_height of each of the peaks in the OTDR reference trace of the monitoring light and setting the measured peak value Peak_level and the measured peak height Peak_height as the first reflection peak factor and the second reflection peak factor, respectively, and the step of measuring the two reflection peak factors in the peaks of the measured trace of the monitoring light comprises measuring a peak value Peak_level and a peak height Peak_height of each of the peaks in the measured trace of the monitoring light and setting the measured peak value Peak_level and the measured peak height Peak_height as the first reflection peak factor and the second reflection peak factor, respectively.

The step of comparing the measured reflection peak factors with the first and the second reflection peak factor threshold values and determining a reflection peak based on a result of the comparison comprises comparing a value of the first reflection peak factor Peak_level of each of the peaks with the first reflection peak factor threshold value Th_level in the OTDR reference trace or the measured trace of the monitoring light, determining whether or not each of the peaks in the OTDR reference trace or the measured trace of the monitoring light corresponds to noise based on a result of the comparison, comparing a value of the second reflection peak factor Peak_height with the second reflection peak factor threshold value Th_height in each partitioned section, and determining a reflection peak based on a result of the comparison in the OTDR reference trace or the measured trace of the monitoring light.

The step of comparing a reflection peak factor of the reflection peak of the measured trace with a reflection peak factor of the reflection peak of the OTDR reference trace and determining whether or not a fault has occurred in the optical line based on a result of the comparison comprises steps of determining whether or not the optical line has been broken and determining whether or not bending has occurred in the optical line.

The step of comparing a reflection peak factor of the reflection peak of the measured trace with a reflection peak factor of the reflection peak of the OTDR reference trace and determining whether or not a fault has occurred in the optical line based on a result of the comparison comprises a step of comparing a number and locations of the reflection peaks of the measured trace with a number and locations of the reflection peaks of the OTDR reference trace, determining whether or not a break has occurred in the optical line based on a result of the comparison, and determines that the optical line has been broken if, as a result of the comparison, at least one of the number and locations of the reflection peaks of the measured trace has been changed as compared with the reflection peaks of the OTDR reference trace.

The step of comparing a reflection peak factor of the reflection peak of the measured trace with a reflection peak factor of the reflection peak of the OTDR reference trace and determining whether or not a fault has occurred in the optical line based on a result of the comparison comprises a step of comparing the first reflection peak factor Peak_level of the reflection peak of the measured trace with the first reflection peak factor Peak_level of the reflection peak of the OTDR reference trace and determining whether or not bending has occurred in the optical line based on a result of the comparison, when the reflection peaks of the measured trace have an identical number and locations with the reflection peaks of the OTDR reference trace.

The step of determining whether or not bending has occurred in the optical line comprises steps of measuring a third reflection peak factor of the reflection peak of the OTDR reference trace and a third reflection peak factor of the reflection peak of the measured trace, and if a difference between the first reflection peak factor of the reflection peak of the measured trace and the first reflection peak factor of the reflection peak of the OTDR reference trace is a predetermined value or higher, comparing the third reflection peak factor of the reflection peak of the measured trace with the third reflection peak factor of the reflection peak of the OTDR reference trace and determining whether or not bending has occurred in the optical line based on a result of the comparison.

The step of measuring a third reflection peak factor of the reflection peak of the OTDR reference trace and a third reflection peak factor of the reflection peak of the measured trace comprises setting a value, obtained by subtracting an initial strength of the OTDR reference trace or the measured trace from the first reflection peak factor Peak_level of the monitoring light, as the third reflection peak factor, respectively.

If a difference between the third reflection peak factor of the reflection peak of the OTDR reference trace and the third reflection peak factor of the reflection peak of the measured trace is a predetermined value or higher, it is determined that that bending has occurred in the optical line.

The optical line monitoring system in accordance with the present invention can precisely detect a fault, such as bending and/or a break in an P2MP optical line. That is, the optical line monitoring device in accordance with the present embodiment can precisely detect a fault because it compares a OTDR reference trace of monitoring light with a reflection peak of measured trace and detects a fault in an optical line based on a result of the comparison. Furthermore, if a reflection peak is detected in a OTDR reference trace or measured trace of monitoring light, one type of a Reference value is not used, but two or more types of reflection peak factor threshold values are set, two or more types of reflection peak factors corresponding to the reflection peak factor threshold values are measured, and the reflection peak is determined based on a result of the measurement. Accordingly, a reflection peak can be detected more precisely as compared with prior arts, and a problem in which fluctuation or noise is determined as a reflection peak can be solved.

Furthermore, when reflection peak factor threshold values are set, an optical line is partitioned into at least two sections and at least one reflection peak factor threshold value is differently set in each section. Accordingly, although noise is generated in each section, noise and a reflection peak can be precisely distinguished from each other. As a result, even when a fault is generated, the fault can be detected precisely and easily. Furthermore, when a fault, such as bending or a break, occurs, a point or section where the fault has occurred can be easily determined.

FIG. 1 is a schematic diagram showing the construction of an optical line monitoring system in accordance with an embodiment;

FIG. 2 is a graph showing a trace of monitoring light on which a smoothing task has been performed;

FIG. 3 is a graph showing a trace of monitoring light by the optical line monitoring system of FIG. 1;

FIG. 4 is a flowchart illustrating a method of controlling the optical line monitoring system in accordance with an embodiment;

FIG. 5 is a graph showing a comparison between a OTDR reference trace and a measured trace in a trace of monitoring light in accordance with an embodiment;

FIG. 6 is a graph showing a trace of monitoring light and a method of detecting reflection peaks in the optical line monitoring system of FIG. 1;

FIG. 7 is a graph illustrating a method of setting a first reflection peak factor threshold value;

FIG. 8 is a graph illustrating a method of setting a second reflection peak factor threshold value;

FIG. 9 is a flowchart illustrating a method of determining a fault in the optical line monitoring system; and

FIG. 10 is a graph showing a comparison between a OTDR reference trace and a measured trace in a trace of monitoring light in accordance with another embodiment.

FIG. 1 is a schematic diagram showing the construction of an optical line monitoring system 1000 in accordance with an embodiment.

Techniques in which an optical line is connected to a subscriber over an optical network are implemented in various kinds of ways, such as Fiber To The Home (FTTH), Fiber To The Office (FTTO), an Fiber To The Neighborhood (FTTN). Techniques for implementing FTTH, that is, one of the techniques, have been developed in various ways. For example, a Passive Optical Network (PON) is described below. The PON includes a supplier-side optical line terminal 120 (hereinafter referred to as a 'supplier-side terminal') installed in a Central Office (CO) and Optical Network Terminals (ONTs) 180, 182, 184, 190, 192, 194, and 196 to which an optical line 122 extended from the supplier-side terminal 120 is connected.

In this case, the PON can be divided into a Point to Point (P2P) method and a Point to Multi-Points (P2MP) method depending on the number of ONTs connected to the optical line of the supplier-side terminal 120. The P2P method is a method in which a single ONT is connected to a single optical line extended from the supplier-side terminal 120, and the P2MP method is a method in which a plurality of ONTs is connected to a single optical line extended from the supplier-side terminal 120. Accordingly, the P2MP optical line includes one or more

optical splitters

150 and 152 from which the single optical line is branched. For example, a first optical splitter and one or more second optical splitter connected to the first optical splitter are provided along the optical line.

The supplier-side terminal 120 is provided in a CO, such as a telephone office and is configured to generate pieces of signal light having different wavelengths, multiplex the pieces of signal light, and send the pieces of multiplexed signal light to the optical splitter 150. Furthermore, the supplier-side terminal 120 receives signals from one or more ONTs to the CO via the optical splitter. More particularly, the supplier-side terminal includes a plurality of light sources (not shown) for generating signal light having a predetermined wavelength, such as a laser, and outputting the generated signal light. The supplier-side terminal multiplexes pieces of signal light having different wavelengths outputted from the plurality of light sources, outputs the pieces of multiplexed signal light, and also demultiplexes received signals by the wavelength.

Each of the

optical splitters

150 and 152 branches multiplexed signal light provided by the supplier-side terminal 120 and sends the branched signal light to each ONT.

Meanwhile, optical fiber has advantages, such as a low energy loss ratio when sending data, a wide bandwidth, light weight, and impossible external wire tapping as compared with existing copper line, but has a disadvantage in that it has weaker mechanical characteristics than an existing copper line. That is, if an optical line is made of optical fiber, a fault, such as the bending or break of the optical line, can occur while the optical line is installed or after the optical line is installed because the optical line is relatively less reliable than the existing copper line. Accordingly, the optical line monitoring system 1000 for detecting a fault in the optical line is being included if an optical network is provided using an optical line.

The monitoring system 1000 includes the optical line 122 configured to connect the supplier-side terminal 120 with the plurality of ONTs, an optical line monitoring device 10 configured to include an Optical Time Domain Reflectometery (OTDR) 12 and an analysis unit 14 for analyzing the OTDR 12, an optical switching unit 30 configured to selectively connect the optical line 122 with the optical line monitoring device 10, a Wavelength Division Multiplexer (WDM) 140 configured to combine signal light and monitoring light, and the

optical splitters

150 and 152 provided along the optical line 122.

More particularly, the optical line monitoring device 10 includes the OTDR 12 for selectively transmitting monitoring light by the optical line 122 for connecting the supplier-side terminal 120 and the ONTs together and receiving reflected monitoring light and the analysis unit 14 for analyzing a trace of the monitoring light.

The OTDR 12 first generates monitoring light having a wavelength different from the signal light of the supplier-side terminal 120. That is, the OTDR 12 monitors the optical line 122 using the monitoring light having a different band from the signal light. Accordingly, the wavelengths of the signal light and the monitoring light are prevented from overlapping with each other, and thus the signal light is not influenced by the monitoring light.

For example, the wavelength of the signal light may be approximately 1600 nm or less. More particularly, the wavelength of the signal light may have a wavelength, such as 1490 nm or 1550 nm. In contrast, the wavelength of the monitoring light may be approximately 1600 nm or more. More particularly, the wavelength of the monitoring light may be approximately 1625 nm to 1650 nm. The OTDR 12 transmitts this monitoring light by the optical line 122 and receives the amount of light reflected and scattered from each point in the length direction of the optical line. Accordingly, the analysis unit 14 can measure a loss of the optical line, a distance up to the connection point of each ONT, a connection loss, the amount of reflection from a connection point, and a distance up to a point at which a fault has occurred when the fault was generated in the optical line by analyzing a distance distribution of pieces of reflected monitoring light.

Pieces of monitoring light outputted from the OTDR 12 are sequentially transmitted respective optical lines through the optical switching unit 30. The WDM 140 combines communication light generated from a communication light source and monitoring light generated from a monitoring light source, so that the combined light moves to each subscriber.

Meanwhile, if monitoring light transmitted by one optical line is scattered or reflected and then received, a peak according to the length of each branched optical line is shown in the OTDR 12 with a different distance. Accordingly, a worker can check that a peak is a peak from what optical line by checking the distance of the peak according to each optical line in the OTDR 12. This is described in detail later.

Meanwhile, reflection means, for example,

reflection filter units

160 and 170 for transmitting signal light, but reflecting only monitoring light can be provided in the respective input terminals of the ONTs. Each of the

reflection filter units

160 and 170 can be provided in an optical connector assembly (not shown) for connecting each ONT with the optical line. If the

reflection filter units

160 and 170 are provided as described above, the OTDR 12 can detect a peak more easily because a peak signal reflected from the end of the optical line, that is, the input terminal of the ONT, is further increased.

Meanwhile, the optical line monitoring system 1000 of FIG. 1 is configured using the P2MP method. That is, in an optical line section 100, the optical line 122 is extended from the supplier-side terminal 120, and the optical line 122 is connected to the

ONTs

180, 182, 184, 190, 192, 194, and 196 via the first optical splitter 150 and the second optical splitter 152. That is, in the optical line section 100, the optical line is connected to the ONTs via the two optical splitters.

An example in which the optical line monitoring device 10 including the OTDR 12 analyzes monitoring light is described below.

FIG. 2 is a graph showing that the optical line monitoring device 10 using the P2P method has mitigated fluctuation in an actual trace of monitoring light or has removed fluctuation from an actual trace of monitoring light through a smoothing task. In this graph, a horizontal axis denotes the distance km, and a vertical axis denotes the intensity of light (or the strength of light) dB.

Referring to FIG. 2, the intensity of monitoring light experiences a loss as the length of the optical line is increased, and the intensity of the monitoring light is reduced to a predetermined slope as shown in FIG. 2. Furthermore, when the monitoring light is reflected by the reflection filter unit provided in the input terminal of the ONT, the monitoring light has a predetermined peak P.

However, when an actual trace of the monitoring light is enlarged and viewed, it includes predetermined fluctuation or noise. In this case, the optical line monitoring device 10 may misunderstand that a corresponding optical line includes a fault due to the fluctuation or noise although the optical line is normal when analyzes the actual trace of the monitoring light. Accordingly, in order to prevent this misunderstanding, the analysis unit 14 performs a smoothing task for mitigating or removing the fluctuation or noise in the actual trace of the monitoring light.

Meanwhile, if a peak equal to or higher than a predetermined Reference value is generated, the optical line monitoring device 10 determines the peak as a peak reflected by the reflection filter unit included in the input terminal of the ONT (hereinafter referred to as a 'reflection peak') not noise. A method of determining a reflection peak in a trace of monitoring light is described in more detail below.

The optical line monitoring device 10 can determine a fault, such as a break or bending, by analyzing the reflection peak generated in the optical line and measure the distance up to the fault based on the time that the monitoring light is transmitted by the optical line and then reflected by and received from the reflection filter unit. That is, the optical line monitoring device 10 can compare a distance up to a point where the reflection peak P was generated with a previously stored length of the optical line and check that the optical line is what optical line based on a result of the comparison. Accordingly, the optical line monitoring device 10 can check that the optical line in which the fault was generated corresponds to what optical line.

Meanwhile, the trace of the monitoring light can be divided into a dynamic range D in which a trace of the monitoring light can be analyzed and a noise range N in which noise is generated. The dynamic range D can be defined as a range in which a trace of the monitoring light can be analyzed, and the noise range N can be defined as a range in which it is difficult to analyze a trace because the trace chiefly includes noise.

More particularly, the dynamic range D can be defined as a range between a virtual horizontal line S1 extended from an initial power of the monitoring light and a line S2 corresponding to 98% of the average size of noise in the noise range N. Here, the initial power of the monitoring light is set as follows. The trace of the monitoring light initially includes a saturation peak due to a light source, and then the strength of the monitoring light is reduced at an approximately predetermined slope according to the distance. Accordingly, the initial power can defined as the initial strength of the trace other than the saturation peak in the trace of the monitoring light, that is, the strength of an initial point L at which the dotted line of the trace meets the vertical line of the graph in FIG. 3.

Furthermore, the noise range N can be defined as a range between the line S2 corresponding to 98% of the average size of noise and the horizontal line of the graph of the initial point L.

If the dynamic range D is increased, it is advantageous when an optical line is monitored because a range in which the trace of the monitoring light can be recognized is widened. The dynamic range D has a relation with a pulse width of the monitoring light. That is, if the pulse width of the monitoring light is increased, the dynamic range D is increased. In contrast, if the pulse width of the monitoring light is increased, a dead zone in which the peaks of adjacent ONTs overlap with each other is also increased. Accordingly, if an optical loss due to the reflection of a peak or bending is generated in a plurality of ONTs included in the dead zone, it is impossible to precisely detect that the optical loss was generated in what ONT. As a result, since the characteristics of the dynamic range and the dead zone are traded off according to a pulse width of monitoring light, it is necessary to properly adjust the pulse width of the monitoring light.

Meanwhile, the trace of the monitoring light in the noise range N is shown as not being a predetermined pattern, but is shown so that a signal cannot be recognized. That is, in the noise range N, a predetermined pattern is not present and a noise signal is irregularly generated. Accordingly, if a trace of a reflection peak having a non-reflection event occurring in monitoring light or a small reflectance is located in the dynamic range D, the trace of the monitoring light can be analyzed relatively easily. If the trace of the reflection peak is located in the noise range N, it is difficult to analyze the trace.

A method in which the optical line monitoring system 1000, such as that shown in FIG. 1, monitors an optical line and determines a fault is described in detail below with reference to FIG. 3.

FIG. 3 is a graph showing a trace of monitoring light for the optical line section 100 by the optical line monitoring system 1000 shown in FIG. 1. The optical line section 100 includes two optical splitters, that is, the first optical splitter 150 and the second optical splitter 152.

Referring to FIG. 3, the strength of monitoring light is weakened at a predetermined slope as it becomes farther from the supplier-side terminal 120, and the monitoring light experiences a loss non-reflection event due to the first optical splitter 150 when the monitoring light passes through the first optical splitter 150. Accordingly, a peak S1 due to the first optical splitter 150 is generated, and a non-reflection event due to a loss is then generated. That is, if the optical line is branched by the first optical splitter 150, an optical line loss due to the first optical splitter 150 itself is generated. From the graph of FIG. 3, it can be seen that non-reflection events are generated in the trace before and after the first optical splitter 150.

After the monitoring light passes through the first optical splitter 150, reflection peaks P1, P2, and P3 reflected by the reflection filter unit 160 included in the

ONTs

180, 182, and 184 directly connected to the first optical splitter 150 appear. The reflection peaks sequentially appear according to the distance between the

ONTs

180, 182, and 184 and the supplier-side terminal 120. That is, the reflection peak P1 of the ONT 180 located at the closest location from the supplier-side terminal 120 first appears, and the remaining reflection peaks then appear according to the distance up to the remaining ONTs. As a result, the reflection peak P3 of the ONT 184 located at the farthest location from the supplier-side terminal 120 appears finally.

When the monitoring light passes through the second optical splitter 152, likewise, a peak S2 and a loss non-reflection event due to the second optical splitter 152 are generated, and reflection peaks P4, P5, P6, and P7 due to the

ONTs

190, 192, 194, and 196 connected to the second optical splitter 152 are generated. Even in this case, the reflection peaks P4, P5, P6, and P7 are sequentially generated according to the distance between the supplier-side terminal 120 and the

ONTs

190, 192, 194, and 196.

Meanwhile, from the graph of FIG. 3, it can be seen that the reflection peaks of the trace are clearly distinguished from each other, but this is only an example. In an actual trace of monitoring light, reflection peaks may not be clearly distinguished from each other. This is because noises and fluctuations in addition to the reflection peaks may be included in the trace of the monitoring light. Accordingly, it is necessary to determine reflection peaks reflected by the reflection filter unit other than noise and simple fluctuation in a trace of monitoring light.

The reason why reflection peaks are determined in a trace of monitoring light is to determine a fault occurring in an optical line using the reflection peaks. That is, if at least one of the number, locations, and strength of reflection peaks is changed, it may be determined that a fault has occurred in the optical line. However, there is a need for a trace that becomes a criterion in order to perform a comparison on the number, locations, and strength of the reflection peaks. That is, a trace not including any fault in an optical line is stored, and a trace assumed to include a fault in the optical line is compared with the trace not including any fault. The trace that is a criterion for the comparison as described above is defined as a OTDR reference trace. The OTDR reference trace can be defined as a trace not including any fault in an optical line. A OTDR reference trace of actual monitoring light can be set as a trace that is first measured after an optical line is buried. That is, a trace of monitoring light without a fault in an optical line can be obtained by measuring a trace of monitoring light right after the optical line is buried. This trace is defined as a OTDR reference trace and stored in the storage unit (not shown) of the analysis unit 14. Next, a trace of the monitoring light is measured when a fault is assumed to be included in the optical line or periodically (hereinafter referred to as a 'measured trace'), the measured trace is compared with the stored OTDR reference trace, and whether or not a fault has occurred in the optical line is determined based on a result of the comparison.

A method of determining reflection peaks in a OTDR reference trace and measured trace of monitoring light is described in detail below with reference to FIG. 4. FIG. 4 is a flowchart illustrating a method of determining reflection peaks in a trace of monitoring light and determining a fault based on a result of the determination.

Referring to FIG. 4, the analysis unit 14 of the optical line monitoring device 10 determines a reflection peak in a OTDR reference trace of monitoring light at step S510, determines reflection peaks in a measured trace of the monitoring light at step S530, compares each of the reflection peaks of the measured trace with the OTDR reference trace of the monitoring light, and determines whether or a fault has occurred based on a result of the comparison at step S550.

First, the determination of the reflection peak in the OTDR reference trace of the monitoring light at step S510 is described below. The analysis unit 14 sets two or more types of reflection peak factor threshold values in the OTDR reference trace of the monitoring light at step S511, measures two or more types of reflection peak factors corresponding to the reflection peak factor threshold values in the OTDR reference trace of the monitoring light at step S513, compares the measured reflection peak factors with the respective set reflection peak factor threshold values, and determines the reflection peak based on a result of the comparison at step S515.

More particularly, the analysis unit 14 sets the two or more types of reflection peak factor threshold values in the OTDR reference trace of the monitoring light at step S511. The reflection peak factor threshold values function as reflection peak factor threshold values for determining the reflection peak. When a reflection peak is determined in a prior art, a peak equal to or higher than predetermined strength is simply determined as the reflection peak. However, the method of simply determining a peak equal to or higher than predetermined strength as a reflection peak is problematic in that simple fluctuation not an actual reflection peak can be recognized as a reflection peak.

For example, as in a graph of FIG. 5, a case where a general measured trace of monitoring light rises higher than a OTDR reference trace is described below. In this case, a power of a peak P10 in the OTDR reference trace of the monitoring light corresponds to level_1, and a power of a peak P10 in the measured trace of the monitoring light corresponds to level_2, which rises higher than the power of the peak of the OTDR reference trace. Furthermore, a criterion power for determining a reflection peak corresponds to level_S. Accordingly, in the OTDR reference trace, the peak P10 is not determined as a reflection peak because the power level_1 of the peak P10 is smaller than the criterion power. In contrast, in the measured trace, there is a problem in that the peak P10 is determined as a reflection peak because the power level_2 of the peak P10 is greater than the criterion power. That is, if a general measured trace simply rises higher than a OTDR reference trace, there is a problem in that a peak not a reflection peak can be determined as a reflection peak. Furthermore, if a general measured trace simply falls below a OTDR reference trace, there is a problem in that an actual reflection peak can be determined as noise even though the actual reflection peak is noise not a reflection peak. In order to solve the problems, in the present invention, factors that determine a reflection peak, that is, two or more reflection peak factor threshold values are set.

For example, the analysis unit 14 can set a first reflection peak factor threshold value Th_level and a second reflection peak factor threshold value Th_height. A method of determining reflection peak factor threshold values and reflection peaks is described below with reference to FIG. 6. FIG. 6 is a graph showing the method of determining reflection peak factor threshold values and reflection peaks.

Referring to FIG. 6, the first reflection peak factor threshold value Th_level can be defined as a reflection peak factor threshold value for the strength of a reflection peak, and the second reflection peak factor threshold value Th_height can be defined as a reflection peak factor threshold value for the height of a reflection peak for a trace of monitoring light.

That is, in the graph of FIG. 6, the first reflection peak factor threshold value Th_level can be set as predetermined strength Th_level dB in order to filter a peak having predetermined strength or lower. Furthermore, the second reflection peak factor threshold value Th_height functions as a reflection peak factor threshold value for selecting a peak having predetermined height or higher from a trace of monitoring light. That is, the second reflection peak factor threshold value Th_height can be set as a predetermined height in a trace right before a point at which a peak is generated in the trace. Accordingly, the second reflection peak factor threshold value Th_height functions as a reflection peak factor threshold value for selecting a peak having a predetermined height (or strength) or higher in the trace. A method of setting the first reflection peak factor threshold value Th_level and the second reflection peak factor threshold value Th_height is described in more detail below with reference to FIG. 7.

FIG. 7 is a graph illustrating a method of setting the first reflection peak factor threshold value Th_level.

Referring to FIG. 7, first, the analysis unit 14 calculates a Root Mean Square (RMS) value of noise present in the noise range N. The analysis unit 14 sets a first noise upper limit value by adding a first predetermined value Value_1 to the calculated RMS value and sets a second noise upper limit value by adding a second predetermined value Value_2 to the first noise upper limit value.

Here, the first noise upper limit value can be set identically with an IEC noise level, and the first noise upper limit value corresponds to a noise level corresponding to 98% of the size of noise in the noise range N. More particularly, if the first predetermined value Value_1 is set to approximately 1.5 dB and added to the RMS value, it results in the first noise upper limit value. As a result, a range between the first noise upper limit value and an initial power of the trace corresponds to an IEC dynamic range determined in IEC.

Meanwhile, the second noise upper limit value is calculated by adding the second predetermined value Value_2 to the first noise upper limit value. More particularly, a difference between a measurement range defined as a distance in which a 0.1 dB non-reflection event loss can be detected and the first noise upper limit value corresponds to the second predetermined value. For example, the second predetermined value can be set to approximately 6.6 dB.

After calculating the first noise upper limit value and the second noise upper limit value, the analysis unit 14 sets the first noise upper limit value or the second noise upper limit value as the first reflection peak factor threshold value Th_level.

As shown in FIG. 7, the second noise upper limit value is located higher than the first noise upper limit value in the graph. Accordingly, if the first noise upper limit value is set as the first reflection peak factor threshold value, it is easy to detect a reflection peak, but noise may be slightly included. In contrast, if the second noise upper limit value is set as the first reflection peak factor threshold value, noise can be effectively removed, but a reflection peak having a small power may not be detected.

Meanwhile, although not shown, the analysis unit 14 can set a third noise upper limit value as the first reflection peak factor threshold value Th_level. The third noise upper limit value can be obtained by adding a standard deviation to the RMS value of noise. For example, the third noise upper limit value can be calculated as in Math Figure 1.

MathFigure 1

That is, a standard deviation of noise is calculated, and the third noise upper limit value can be calculated by adding a value, obtained by multiplying the standard deviation by a predetermined coefficient A, to an RMS value of the noise. Here, the predetermined coefficient A can be an integer or a value other than the integer. In accordance with experiments performed by the applicant of the present invention, the predetermined coefficient can have a value of approximately 2 to 3 and can have a value of, for example, 2.4 to 2.6. Accordingly, the analysis unit 14 can set any one of the first noise upper limit value, the second noise upper limit value, and the third noise upper limit value as the first reflection peak factor threshold value Th_level.

The analysis unit 14 sets the first reflection peak factor threshold value by taking an overall construction of the optical line monitoring system 1000, a trace of monitoring light, the supplier-side terminal, and the ONTs into consideration.

As a result, when the first reflection peak factor threshold value is set, a first reflection peak factor of a peak is measured and compared with the first reflection peak factor threshold value. If the first reflection peak factor of the peak is smaller than the first reflection peak factor threshold value, it is determined that the first reflection peak factor of the peak is included in the noise range N and thus determined as noise. If the first reflection peak factor of the peak is greater than the first reflection peak factor threshold value, it is determined that the first reflection peak factor of the peak is not noise and subsequent processes are performed.

A method of setting the second reflection peak factor threshold value is described below with reference to FIG. 8.

Referring to FIG. 8, a trace of monitoring light appears as a smooth curve, but may include a plurality of fluctuations or noises when the trace is enlarged. A smoothing task can be performed as described above, but it is difficult to remove all fluctuations or noises by way of the smoothing task. Accordingly, the trace of the monitoring light can include a plurality of fluctuations or noises. Accordingly, it is necessary to distinguish the fluctuation and the reflection peak included in the trace, and the second reflection peak factor threshold value is necessary as a Reference value for this distinguishment.

The second reflection peak factor threshold value can be set as a threshold height in a trace right before a peak when the peak is generated, that is, right before the trace rises due to the peak. As a result, when the peak is generated, if the height of the highest point of the peak rises at the second reflection peak factor threshold value or higher in the trace, the corresponding peak is determined as a reflection peak.

The second reflection peak factor threshold value may be differently set depending on a method used in an optical line. For example, an P2P optical line is connected by means of a connector or splicing without being branched by an optical splitter because a single supplier-side terminal and a single ONT are connected by the P2P optical line. If an optical splitter is placed in the middle of the P2P optical line, an optical loss is generated through the optical splitter. As a result, in the case of the P2P optical line, an optical loss due to the branch of the P2P optical line is not generated because an optical splitter is not included. Accordingly, in the case of the P2P optical line, the optical line monitoring device 10 can set the second reflection peak factor threshold value having a single value over the entire range of monitoring light. As described above, a trace of monitoring light can include a predetermined noise or fluctuation, and the trace is compared with the second reflection peak factor threshold value in order to distinguish the noise (or fluctuation) from a reflection peak. However, the P2P optical line has a lower optical loss and a very smaller noise (or fluctuation) than a P2MP optical line because the P2P optical line does not experience a loss due to branch and it is connected by a connector. Accordingly, in the case of the P2P optical line, the second reflection peak factor threshold value having a single Reference value can be used over the entire range of the P2P optical line, and the single Reference value can be set to a relatively small value.

Meanwhile, in the case of a P2MP optical line, a plurality of ONTs is connected to a single supplier-side terminal. That is, a single optical line extended from the single supplier-side terminal is connected to the plurality of ONTs through an optical splitter. For example, FIG. 8 shows a trace of monitoring light in a P2MP optical line and shows an example in which two optical splitters (i.e., the first optical splitter 150 and the second optical splitter 152) are included in the P2MP optical line.

If the first and the second optical splitters are included in an optical line section, the analysis unit 14 can partition the optical line section into two or more sections. For example, the analysis unit 14 can partition the optical line section based on the first and the second

optical splitters

150 and 152.

Referring to FIG. 8, the analysis unit 14 can partition the optical line section into three sections. That is, the optical line section can be partitioned into a first section Section 1, a second section Section 2, and a third section Section 3. Here, the analysis unit 14 can partition the optical line section based on the first and the second

optical splitters

150 and 152. For example, the first section corresponds to an optical line from the supplier-side terminal 120 to the first optical splitter 150, the second section corresponds to an optical line between the first optical splitter 150 and the second optical splitter 152, and the third section corresponds to an optical line after the second optical splitter 152.

More particularly, if two or more optical splitters are included along the optical line, the analysis unit 14 can set an ONT, located at the longest distance from the supplier-side terminal 120, as the end point F3 of an end section and set a predetermined point adjacent to a peak S1 due to a first optical splitter as the end point F1 of the first section Section 1. Assuming that two or more optical splitters are included, the first section corresponds to the first section, and the end section corresponds to the third section. It is hereinafter assumed that two optical splitters are included.

In a graph, such as the graph of FIG. 8, the end point F3 of an end section (i.e., the third section) is set as a reflection peak P7 due to an ONT located at the longest distance from the supplier-side terminal 120. In contrast, if the distance up to each ONT is previously stored in the analysis unit 14 before a reflection peak is determined in a trace of monitoring light, a distance up to a peak occurring in the trace can be measured and a reflection peak corresponding to the ONT located at the longest distance from the supplier-side terminal 120 can be detected based on the measured distance.

Meanwhile, when the end point F1 of the first section is set, the analysis unit 14 can set a predetermined point between the first peak S1 due to the first optical splitter and a subsequent second peak as the end point F1 of the first section. Here, the second peak subsequent to the first peak S1 may have any peak as well as a reflection peak. That is, a peak occurring in the trace is not included between the first peak S1 due to the first optical splitter and the end point F1 of the first section.

Furthermore, the analysis unit 14 can set an optical splitter located at the longest distance from the supplier-side terminal 120, from among second optical splitters, as the end point F2 of the second section. Here, the second optical splitters are defined as optical splitters connected to the first optical splitter 150 in FIG. 1. Only one optical splitter 152 is illustrated as being connected to the first optical splitter 150 in FIG. 1, but this is only an example. One or more optical splitters can be connected to the first optical splitter 150. If the optical splitters connected to the first optical splitter 150 are defined as the second optical splitters as described above, the end point F2 of the second section can be set as an optical splitter located at the longest distance from the supplier-side terminal 120, from among the second optical splitters.

A method of setting the second reflection peak factor threshold value when the optical line section is partitioned as described above is described below.

Referring to FIG. 8, in the first section Section 1, the intensity of monitoring light is decreased at a predetermined slope as described above. In the first section Section 1, noise is less generated as compared with the second section and the third section because the first section Section 1 is connected by a single optical line before it is connected to the first optical splitter.

When the optical line is connected to the first optical splitter, the predetermined peak S1 is generated, and a peak is generated and at the same time, an optical loss non-reflection event due to the first optical splitter is generated. This optical loss non-reflection event corresponds to an optical loss occurring in a process in which the optical line is split by the first optical splitter, and this optical loss is represented by a non-reflection event in the trace of the monitoring light. After the first optical splitter, reflection peaks P1, P2, and P3 are generated according to a distance from the supplier-side terminal 120. Although not shown, the size of noise or fluctuation is relatively greater in the second section after the first optical splitter than in the first section. This is because the second section is farther from the supplier-side terminal 120 than the first section and an optical loss is generated through the first optical splitter. Meanwhile, in the first section and the second section, a trace of the monitoring light can be analyzed relatively easily because the first section and the second section are located in a dynamic range D.

Likewise, when the optical line is connected to the second optical splitter via the first optical splitter, a predetermined peak S2 due to the second optical splitter is generated and an optical loss is also generated. Here, an optical loss according to the distance is generated as the distance of the optical line is increased, and an optical loss due to the second optical splitter is generated through the second optical splitter. As a result, in a trace of the monitoring light in the third section after passing through the second optical splitter, noise or fluctuation is relatively increased due to the optical loss. In the trace of the monitoring light in the third section, fourth to seventh reflection peaks P4 to P7 appear.

If it is sought to detect a reflection peak, however, when the second reflection peak factor threshold value for detecting the reflection peak in the third section is set to a value equal to or lower than noise, the analysis unit 14 recognizes all peaks, having strength equal to or higher than the second reflection peak factor threshold value, as the reflection peaks. Accordingly, the analysis unit 14 cannot distinguish a reflection peak reflected by an ONT from the noise if the size of the noise is the second reflection peak factor threshold value or higher.

In particular, a conventional optical line monitoring device simply compares the height of a peak with a Reference value, determines a reflection peak based on a result of the comparison, and also uses a Reference value having a single Reference value in the entire section of an optical line. Accordingly, there are problems in that a reflection peak can become smaller than a Reference value in the first section if the Reference value is increased in order to distinguish the reflection peak from noise or fluctuation and the nose is not distinguished from the reflection peak in the end section if the Reference value is reduced.

In order to solve the problems, the analysis unit 14 can differently set at least one of two or more types of reflection peak factor threshold values according to the partitioned sections. For example, if the analysis unit 14 sets two types of reflection peak factor threshold values, such as a first reflection peak factor threshold value Th_level and a second reflection peak factor threshold value Th_height, the analysis unit 14 can differently set the second reflection peak factor threshold value Th_height according to the partitioned sections.

If the optical line section is partitioned into a plurality of sections, the analysis unit 14 can differently set the second reflection peak factor threshold value Th_height in each section. For example, the second reflection peak factor threshold value Th_height can be differently set only in one section, or the second reflection peak factor threshold value Th_height can be differently set in all the sections.

As described above, as the length of an optical line is increased, a loss is generated in the intensity of light. In particular, when a trace passes through an optical splitter, a loss due to an optical splitter is generated. Furthermore, as a loss in the intensity of light is increased, noise or fluctuation is increased. Accordingly, if the optical line is partitioned into two or more sections and the second reflection peak factor threshold value Th_height is differently set in at least one section, a proper Reference value can be set depending on the characteristics of each section.

For example, in FIG. 8, the first section is relatively small in an optical loss and is rarely affected by noise or fluctuation because the first section is more adjacent to the supplier-side terminal 120 than other sections. Accordingly, the first reflection peak factor threshold value TH1 of the first section can be set to a value relatively smaller than that of other sections.

Meanwhile, the third section is located farther from the supplier-side terminal 120 than other sections. Accordingly, in the third section, it may be difficult to distinguish a reflection peak generated from an ONT from noise because an optical loss in the third section is greater than that in other sections and the size of the noise in the third section is relatively great. As a result, the third reflection peak factor threshold value TH3 of the third section can be set to a value relatively greater than that of other sections.

That is, the analysis unit 14 can set the second reflection peak factor threshold value Th_height at which a peak is detected so that the second reflection peak factor threshold value Th_height is sequentially increased as the optical line moves from the supplier-side terminal 120 to the ONTs. This is because as the optical line proceeds, an optical loss is increased, the size of noise is increased, and noise is frequently generated. Meanwhile, TH2 not described in FIG. 8 indicates the second reflection peak factor threshold value of the second section, and TH2 may have a value greater than the first reflection peak factor threshold value TH1 of the first section, but smaller than the third reflection peak factor threshold value TH3 of the third section.

Furthermore, if it is sought to set the second reflection peak factor threshold value Th_height in the third section, the second reflection peak factor threshold value Th_height is applied to a line S2 corresponding to 98% of the average size of noise in the noise range N. In the first section or the second section, the second reflection peak factor threshold value Th_height can be directly applied to the trace of the monitoring light because the trace of the monitoring light is decreased at a relatively constant slope. In the third section, however, it is difficult to apply the second reflection peak factor threshold value Th_height to the trace of the monitoring light because the noise range N is included in the third section and thus the trace of the monitoring light is irregularly changed. Accordingly, in the third section, a peak is detected by applying the second reflection peak factor threshold value Th_height to the line S2 corresponding to 98% of the average size of noise in the noise range N.

As a result, the analysis unit 14 can set the first reflection peak factor threshold value TH1 of the first section that comes into contact with the supplier-side terminal 120 to the smallest value or can set the third reflection peak factor threshold value TH3 of the third section that comes in contact with an ONT to the greatest value. Furthermore, if it is sought to set the second reflection peak factor threshold value Th_height in each section, the analysis unit 14 can set the second reflection peak factor threshold value Th_height to a value equal to or greater than the size of noise occurring in each section. In this case, noise can be distinguished from a reflection peak as described above.

A method of the analysis unit 14 setting the second reflection peak factor threshold value Th_height to a value equal to or greater than the size of noise occurring in each section can be implemented in various ways. For example, the analysis unit 14 can set a Reference value depending on the average size (i.e., the average) of noise in each partitioned section. In one embodiment, the analysis unit 14 can measure the average of noise in each section and set the second reflection peak factor threshold value Th_height by adding a predetermined ratio to the measured average. In another embodiment, the analysis unit 14 can calculate a standard deviation of noise along with the average of the noise in each section and set the second reflection peak factor threshold value Th_height of each section by adding the standard deviation to the average.

If the second reflection peak factor threshold value Th_height is set based on the average and standard deviation of noise in each section, a variety of embodiments are possible according to a peak value included in the corresponding section. For example, if the analysis unit 14 calculates the average of noise in each section, the analysis unit 14 can calculate the first average and first standard deviation of noise of a OTDR reference trace including a peak of each section and set a value, obtained by adding the first standard deviation to the first average, as the second reflection peak factor threshold value Th_height of a corresponding section. In some embodiments, the analysis unit 14 can calculate the average using an interpolation method. That is, if the analysis unit 14 calculates the average of noise in each section, the analysis unit 14 can calculate the second average and second standard deviation of noise of a OTDR reference trace other than a peak of each section and set a value, obtained by adding the second standard deviation to the second average, as the second reflection peak factor threshold value Th_height of the corresponding section.

A method of determining reflection peaks using the first reflection peak factor threshold value and the second reflection peak factor threshold value set as described above is described below with reference to FIGS. 4 and 6.

Referring to FIG. 4, the analysis unit 14 sets two or more types of reflection peak factor threshold values in a OTDR reference trace of monitoring light and measures two or more types of reflection peak factors in the OTDR reference trace of the monitoring light at step S513. The analysis unit 14 measures the reflection peak factor so that it corresponds to a predetermined reflection peak factor threshold value.

More particularly, in a graph, such as the graph of FIG. 6, the analysis unit 14 detects a peak in a trace by differentially analyzing a OTDR reference trace of monitoring light and measures the reflection peak factor of the detected peak. More particularly, the analysis unit 14 measures a first reflection peak factor Peak_level and a peak height Peak_height of each peak in the OTDR reference trace of the monitoring light and defines the measured first reflection peak factor Peak_level and peak height Peak_height as a first reflection peak factor and a second reflection peak factor. In the graph, the peak value can be calculated by measuring strength dB of the peak, and the peak height value can be calculated by measuring the height of the peak in the trace. That is, the peak height value can be calculated by measuring a height up to the highest point of the peak in a trace right before a point at which the peak has occurred in the trace. Here, the first reflection peak factor Peak_level corresponds to the first reflection peak factor threshold value Th_level, and the second reflection peak factor Peak_height corresponds to the second reflection peak factor threshold value Th_height.

Next, the analysis unit 14 compares the two or more types of set reflection peak factor threshold values with the two or more types of measured reflection peak factors and determines a reflection peak based on a result of the comparison at step S515.

As shown in FIG. 6, if a plurality of peaks is present in a predetermined section (Here, the second section is described as an example), a method of determining a reflection peak in a first peak P1 and a second peak E is described below. Here, the first peak P1 and the second peak E correspond to peaks on which the analysis unit 14 determines whether or not a peak is a reflection peak by differentially analyzing a trace.

First, the analysis unit 14 compares the first reflection peak factor of each peak Peak_level with the first reflection peak factor threshold value Th_level and determines whether each of the peaks of the monitoring light corresponds to noise based on a result of the comparison. For example, the analysis unit 14 can measure the first reflection peak factor Peak_level of the first peak P1 as a level A Th_level_A and compare a value of the measured first reflection peak factor Peak_level with the first reflection peak factor threshold value Th_level. The analysis unit 14 determines that the first peak P1 is not noise because the value of the first reflection peak factor Peak_level of the first peak P1 is greater than the first reflection peak factor threshold value Th_level.

Furthermore, the analysis unit 14 determines the second peak E likewise. That is, the analysis unit 14 also determines that the second peak E is not noise because a value of the first reflection peak factor Peak_level of the second peak E corresponds to a level B Th_level_B and the value of the first reflection peak factor Peak_level is greater than the first reflection peak factor threshold value Th_level.

Meanwhile, if a value of the first reflection peak factor Peak_level is smaller than the first reflection peak factor threshold value Th_level, the analysis unit 14 determines that the value is located in the noise range N, does not determine a corresponding peak as a reflection peak, and omits a subsequent process of comparing a value of the second reflection peak factor Peak_height with the second reflection peak factor threshold value Th_height.

The analysis unit 14 compares a value of the first reflection peak factor Peak_level with the first reflection peak factor threshold value Th_level, compares a value of the second reflection peak factor Peak_height with the second reflection peak factor threshold value Th_height, and determines a reflection peak based on a result of the comparison.

As described above, the analysis unit 14 determines that a corresponding peak is not noise because the first reflection peak factor of the first peak P1 has a value greater than the first reflection peak factor threshold value. Next, the analysis unit 14 compares a second reflection peak factor of the first peak P1 with the second reflection peak factor threshold value and determines a reflection peak based on a result of the comparison. In this case, the second reflection peak factor threshold value can have a different value in each section partitioned along the optical line as described above. This has been described above, and thus a redundant description thereof is omitted.

Referring to a partially enlarged part of FIG. 6, the analysis unit 14 measures a second reflection peak factor of the first peak P1 and stores a height value A Th_height_A as the second reflection peak factor of the first peak P1. Next, the analysis unit 14 compares the second reflection peak factor of the first peak P1 with the second reflection peak factor threshold value of a section (i.e., in the present embodiment, the second section) to which the first peak P1 belongs. As shown, the height value A Th_height_A is greater than the second reflection peak factor threshold value Th_height. Accordingly, the first reflection peak factor of the first peak P1 has a value greater than the first reflection peak factor threshold value, and the second reflection peak factor of the first peak P1 has a value greater than the second reflection peak factor threshold value. Accordingly, the analysis unit 14 determines the first peak P1 as a reflection peak.

Meanwhile, in the case of the second peak E, the analysis unit 14 measures a second reflection peak factor of the second peak E and stores a height value B Th_height_B as the second reflection peak factor of the second peak E. Next, the analysis unit 14 compares the second reflection peak factor of the second peak E with the second reflection peak factor threshold value of a section (i.e., in the present embodiment, the second section) to which the second peak E belongs. As shown, the height value B Th_height_B is smaller than the second reflection peak factor threshold value Th_height. Accordingly, the first reflection peak factor of the second peak E has a value greater than the first reflection peak factor threshold value, but the second reflection peak factor of the second peak E has a value smaller than the second reflection peak factor threshold value. Accordingly, the analysis unit 14 does not determine the second peak E as a reflection peak. In the graph of FIG. 6, the analysis unit 14 detects a total of the seven reflection peaks P1 to P7 in the OTDR reference trace of the monitoring light using the above-described method.

Next, the analysis unit 14 measures two or more types of reflection peak factors in the measured trace of the monitoring light at step S531, compares the measured reflection peak factors with the two or more types of determined reflection peak factor threshold values, and determines reflection peaks based on a result of the comparison at step S533.

If it is assumed that a fault has occurred in the optical line section or periodically, the analysis unit 14 determines a reflection peak in the measured trace of the monitoring light and determines whether or not a fault is present based on a result of the determination. A method of determining the reflection peak in the measured trace of the monitoring light is similar to the method of determining a reflection peak in the OTDR reference trace of the monitoring light other than the step of determining a reflection peak factor threshold value. That is, the analysis unit 14 measures two reflection peak factors in the measured trace of the monitoring light, compares the measured reflection peak factors with the first reflection peak factor threshold value and the second reflection peak factor threshold value, respectively, and determines reflection peaks based on a result of the comparison. In this case, the analysis unit 14 determines the reflection peaks in the measured trace of the monitoring light using the reflection peak factor threshold value set in the OTDR reference trace of the monitoring light. As a result, although the measured trace of the monitoring light is repeatedly measured, a value set in the OTDR reference trace is used as a reflection peak factor threshold value.

A method of the analysis unit 14 measuring a peak value Peak_level and a peak height Peak_height of a peak in the measured trace of the monitoring light and storing the peak value Peak_level and the peak height Peak_height as a first reflection peak factor and a second reflection peak factor, respectively, and a method of the analysis unit 14 comparing a value of the first reflection peak factor Peak_level with the first reflection peak factor threshold value Th_level in the measured trace of the monitoring light, determining whether or not the peak is noise, comparing the second reflection peak factor Peak_height with the second reflection peak factor threshold value Th_height in each partitioned section, and determining a reflection peak based on a result of the comparison are the same as the method of determining the OTDR reference trace, and thus a redundant description thereof is omitted.

Next, the analysis unit 14 compares each of the reflection peak factors of the reflection peaks of the measured trace with the reflection peak factor of the reflection peak of the OTDR reference trace and determines whether or not a reflection peak is a fault based on a result of the comparison at step S550. FIG. 9 is a flowchart illustrating a method of the analysis unit 14 determining a fault.

Referring to FIG. 9, if the reflection peak factor of the reflection peak of a measured trace is compared with the reflection peak factor of the reflection peak of a OTDR reference trace and whether or not a reflection peak is a fault is determined based on a result of the comparison, the analysis unit 14 determines whether or not a break has occurred in the optical line and then determines whether or not bending has occurred in the optical line.

More particularly, the analysis unit 14 compares the number and locations of reflection peaks in a measured trace of monitoring light with the number and locations of reflection peaks in a OTDR reference trace of the monitoring light at step S1010 and determines whether or not a break has occurred in the optical line based on a result of the comparison. If, as a result of the comparison, at least one of the number and locations of the reflection peaks is different, the analysis unit 14 determines that a break has occurred in the optical line at step S1015. That is, if the number of reflection peaks of the measured trace is smaller than the number of reflection peaks of the OTDR reference trace or the location of a reflection peak of the measured trace are different from the location of a reflection peak of the OTDR reference trace, the analysis unit 14 determines that a break has occurred in the optical line. If the optical line is broken at a predetermined position, reflection peaks generated from ONTs after the predetermined point do not appear in a graph or breaks appear irregularly at points not the original point. Accordingly, if at least one of the number and locations of the reflection peaks of the measured trace is changed as compared with the OTDR reference trace, the analysis unit 14 determines that a break has occurred in the optical line at step S1015.

In contrast, if, as a result of the determination at step S1010, the number and locations of the reflection peaks of the measured trace are identical with those of the reflection peaks of the OTDR reference trace, the analysis unit 14 determines whether or not a first reflection peak factor Peak_level of a reflection peak of the measured trace is less than a first reflection peak factor Peak_level of a reflection peak of the OTDR reference trace in order to determine whether or not bending has occurred in the optical line at step S1030.

If, as a result of the determination at step S1030, the first reflection peak factor Peak_level of the reflection peak of the measured trace is equal to or greater than the first reflection peak factor Peak_level of the reflection peak of the OTDR reference trace, the analysis unit 14 determines that the optical line is normal at step S1035. That is, if the first reflection peak factor Peak_level of the reflection peak of the measured trace is equal to or greater than the first reflection peak factor Peak_level of the reflection peak of the OTDR reference trace, the analysis unit 14 determines that an optical loss has not occurred in the optical line and thus determines that the optical line is normal.

Meanwhile, if the first reflection peak factor Peak_level of the reflection peak of the measured trace is less than the first reflection peak factor Peak_level of the reflection peak of the OTDR reference trace and a difference between the first reflection peak factor Peak_level of the reflection peak of the measured trace and the first reflection peak factor Peak_level of the reflection peak of the OTDR reference trace is a predetermined value or higher, the analysis unit 14 can determine that bending has occurred in the optical line.

The first reflection peak factor used to determine whether or not bending has occurred in the optical line corresponds to the strength (level) of a peak. As described above with reference to FIG. 5, a general trace of the measured trace may be higher or lower than that of the OTDR reference trace. In this case, although a fault has not occurred in the measured trace, it may be determined that the fault has occurred because the strength of a reflection peak has changed, that is, the first reflection peak factor has changed. As a result, if the first reflection peak factor of the reflection peak of the measured trace is simply compared with the first reflection peak factor of the reflection peak of the OTDR reference trace and whether or not bending has occurred based on a result of the comparison, a normal optical line may be determined as an optical line in which a fault, such as bending, has occurred.

In order to solve this problem, in the present embodiment, if a difference between the first reflection peak factor Peak_level of the reflection peak of the measured trace and the first reflection peak factor Peak_level of the reflection peak of the OTDR reference trace is a predetermined value or higher, the analysis unit 14 compares a third reflection peak factor of a reflection peak of the measured trace with a third reflection peak factor of a reflection peak of the OTDR reference trace at step S1050 and determines whether or not bending has occurred in the optical line. Here, the analysis unit 14 may previously measures the third reflection peak factor of the reflection peak of the OTDR reference trace and the third reflection peak factor of the reflection peak of the measured trace and store them in the storage unit (not shown).

Here, the third reflection peak factor can be defined as a value obtained by subtracting an initial power of the OTDR reference trace from the first reflection peak factor Peak_level of the reflection peak of the OTDR reference trace or the measured trace. The initial power in the trace of the monitoring light has been described with reference to FIG. 2, and thus a redundant description thereof is omitted. As a result, a value of the third reflection peak factor is defined as a difference between the virtual straight line S1 extended from the initial point and the highest point of a reflection peak in FIG. 2.

That is, if a general trace in the measured trace of the monitoring light becomes higher than that in the OTDR reference trace in a graph, a power of a peak of the measured trace also rises. That is, if a general trace rises or falls although the optical line is normal, there is a change in the peak strength of a reflection peak. Accordingly, it is difficult to precisely determine whether or not a fault has occurred in the optical line by simply comparing the poweres of peaks (i.e., the first reflection peak factors) with each other. It is also difficult to precisely determine whether or not a fault has occurred in the optical line if the second reflection peak factor includes noise or fluctuation in its trace. In order to solve the problems, in the present embodiment, a third reflection peak factor is used to precisely a fault.

For example, as shown in a graph of FIG. 10, although the optical line normally operates, a general trace of a measured trace of monitoring light may fall below a OTDR reference trace of the monitoring light. In this case, the general trace of the measured trace falls below that the OTDR reference trace, and thus a first reflection peak factor of a reflection peak of the measured trace has a value smaller than a first reflection peak factor of the OTDR reference trace. In contrast, a third reflection peak factor of the OTDR reference trace may have an approximately similar value to a third reflection peak factor of the measured trace. That is, the third reflection peak factor F1 of the OTDR reference trace and the third reflection peak factor F2 of the measured trace may have an approximately identical value. As a result, if the optical line is normal, a difference between an initial power of the OTDR reference trace and the highest point of a reflection peak (i.e., the third reflection peak factor of the reflection peak of the OTDR reference trace, F1 in FIG. 10) and a difference between an initial power of the measured trace and the highest point of a reflection peak (i.e., the third reflection peak factor of the reflection peak of the measured trace, F2 in FIG. 10) have an approximately similar or identical value.

As a result, if a difference between the third reflection peak factor of the reflection peak of the OTDR reference trace and the third reflection peak factor of the reflection peak of the measured trace is a predetermined value or higher, the analysis unit 14 determines that bending has occurred in the optical line at step S1070. More particularly, the analysis unit 14 subtracts a value of the third reflection peak factor of the reflection peak of the measured trace from a value of the third reflection peak factor of the reflection peak of the OTDR reference trace and compares the absolute value of the difference value with a Reference value. If, as a result of the comparison, the absolute value of the difference value is greater than the Reference value, the analysis unit 14 determines that bending has occurred in the optical line at step S1070. In contrast, if the absolute value of the difference value is equal to or less than the Reference value, the analysis unit 14 determines that the optical line is normal at step S1055.

Meanwhile, if it is determined that a fault has occurred, it is necessary to check a point or section where the fault has occurred. For example, if a reflection peak of a measured trace fully disappears as compared with a reflection peak of a OTDR reference trace, the analysis unit 14 may determine that a break has occurred in the first section of an optical line, such as that of FIG. 1, that is, in an optical line that connects the supplier-side terminal 120 with the first optical splitter 150. Furthermore, if the number of reflection peaks of the measured trace is decreased by the positive number times the number of optical lines branched from an optical splitter as compared with the number of reflection peaks of the OTDR reference trace, the analysis unit 14 may determine that a break has occurred in the second section, that is, in an optical line that connects the first optical splitter 150 with the second optical splitter 152. Furthermore, if the number of reflection peaks of the OTDR reference trace is different from the number of reflection peaks of the measured trace irrespective of the number of optical lines branched from one optical splitter, the analysis unit 14 may determine that a break has occurred in the third section, that is, in a section after the second optical splitter.

Furthermore, if bending has occurred, a section where the bending has occurred can be checked using the aforementioned method. In this case, if bending occurs, the number of reflection peaks is not decreased, but a value of the peak strength (i.e., the first reflection peak factor) of a reflection peak is decreased or a value of the third reflection peak factor of the reflection peak is decreased. Accordingly, a section where bending has occurred can be checked by comparing the number of reflection peaks in which a value of the peak strength (i.e., the second reflection peak factor) of a reflection peak of a measured trace has been decreased or the number of reflection peaks in which a value of the third reflection peak factor has been decreased with the number of reflection peaks of a OTDR reference trace, like in the check of a section where a break has occurred.

For example, if a value of each of the first reflection peak factors (or the third reflection peak factors) of all reflection peaks of a measured trace is smaller than that of the reflection peaks of a OTDR reference trace, the analysis unit 14 may determine that bending has occurred in the first section of an optical line, such as that of FIG. 1, that is, in an optical line that connects the supplier-side terminal 120 with the first optical splitter 150. Furthermore, if the number of reflection peaks in which a value of the first reflection peak factor (or the third reflection peak factor) of the measured trace has been decreased as compared with the reflection peaks of the OTDR reference trace corresponds to a positive number times the number of optical lines branched from an optical splitter, the analysis unit 14 may determine that bending has occurred in the second section, that is, in an optical line that connects the first optical splitter 120 with the second optical splitter 152. Furthermore, if the number of reflection peaks in which a value of the first reflection peak factor (or the third reflection peak factor) of the measured trace has been decreased is different from the number of reflection peaks of the OTDR reference trace irrespective of the number of optical lines branched from an optical splitter, the analysis unit 14 may determine that bending has occurred in the third section, that is, in a section after the second optical splitter.

In an optical line using the P2MP method in accordance with the present invention, a fault, such as bending and/or a break, can be detected precisely. That is, the optical line monitoring device in accordance with the present embodiment can precisely detect a fault because it compares the OTDR reference trace of the monitoring light with a reflection peak of measured trace and detects a fault in an optical line based on a result of the comparison. Furthermore, if a reflection peak is detected in a OTDR reference trace or measured trace of monitoring light, one type of a Reference value is not used, but two or more types of reflection peak factor threshold values are set, two or more types of reflection peak factors corresponding to the reflection peak factor threshold values are measured, and the reflection peak is determined based on a result of the measurement. Accordingly, a reflection peak can be detected more precisely as compared with a prior art, and a problem in which simple fluctuation or noise is determined as a reflection peak can be solved.

Furthermore, when reflection peak factor threshold values are set, an optical line is partitioned into at least two sections and at least one reflection peak factor threshold value is differently set in each section. Accordingly, although noise is generated in each section, noise and a reflection peak can be detected precisely. As a result, even when a fault is generated, the fault can be detected precisely and easily. Furthermore, when a fault, such as bending or a break, occurs, a point or section where the fault has occurred can be easily determined.

Claims

An optical line monitoring device, comprising:

an OTDR for selectively transmitting monitoring light by an optical line for connecting a supplier-side terminal with an ONT and receiving the monitoring light reflected; and

an analysis unit for analyzing a trace of the monitoring light,

wherein the analysis unit sets two or more types of reflection peak factor threshold values in a OTDR reference trace of the monitoring light, measures two or more types of reflection peak factors corresponding to the reflection peak factor threshold values in the OTDR reference trace of the monitoring light, compares values of the measured reflection peak factors with the set reflection peak factor threshold values, and determines a reflection peak in the OTDR reference trace of the monitoring light;

the analysis unit measures two or more types of reflection peak factors in a measured trace of the monitoring light, compares the measured reflection peak factors with the set reflection peak factor threshold values, and determines a reflection peak in the measured trace of the monitoring light; and

the analysis unit compares the reflection peak factors of the reflection peak of the measured trace with the reflection peak factors of the reflection peak of the OTDR reference trace and determines whether a fault has occurred in the optical line.
The optical line monitoring device of claim 1, wherein:

the analysis unit partitions the optical line into at least two sections, and

the sections are determined depending on an optical splitter provided along the optical line.
The optical line monitoring device of claim 2, wherein if two or more optical splitters are provided along the optical line, the analysis unit sets an ONT, located at a longest distance from the supplier-side terminal, as an end point of an end section and sets a predetermined point adjacent to a peak due to a first optical splitter as an end point of a first section.
The optical line monitoring device of claim 3, wherein the analysis unit sets a predetermined point between a first peak due to the first optical splitter and a second peak subsequent to the first peak as the end point of the first section.
The optical line monitoring device of claim 3, wherein if a first optical splitter and one or more second optical splitter connected with the first optical splitter are provided along the optical line, the analysis unit sets an optical splitter located at a longest distance from the supplier-side terminal, from among the second optical splitters, as an end point of a second section.
The optical line monitoring device of claim 2, wherein the analysis unit differently sets at least one of the two or more types of reflection peak factor threshold values in each partitioned section.
The optical line monitoring device of claim 6, wherein the analysis unit sets a first reflection peak factor threshold value Th_level and a second reflection peak factor threshold value Th_height and differently sets the second reflection peak factor threshold value Th_height in each partitioned section.
The optical line monitoring device of claim 7, wherein the analysis unit sets the second reflection peak factor threshold value Th_height to be sequentially increased as the section proceeds from the supplier-side terminal to the ONT.
The optical line monitoring device of claim 8, wherein the analysis unit sets the second reflection peak factor threshold value Th_height to be equal to or higher than noise occurring in each partitioned section.
The optical line monitoring device of claim 7, wherein the analysis unit sets the second reflection peak factor threshold value Th_height to be a greatest in a section adjacent to the ONT.
The optical line monitoring device of claim 7, wherein the analysis unit calculates a Root Mean Square (RMS) value and a standard deviation of the OTDR reference trace of the monitoring light in a section after an ONT located at a longest distance from the supplier-side terminal, sets a first noise upper limit value by adding a first predetermined value to the RMS value, sets a second noise upper limit value by adding a second predetermined value to the first noise upper limit value, sets a third noise upper limit value by adding a value, obtained by multiplying the standard deviation by the predetermined coefficient, to the RMS value, and sets any one of the first noise upper limit value, the second noise upper limit value, and the third noise upper limit value as the first reflection peak factor threshold value Th_level.
The optical line monitoring device of claim 7, wherein:

the analysis unit calculates a first average and a first standard deviation of noise in the OTDR reference trace including a peak and a second average and a second standard deviation of noise in the OTDR reference trace without the peak in each partitioned section, and

the analysis unit sets a value obtained by adding the first standard deviation to the first average or a value obtained by adding the second standard deviation to the second average as the second reflection peak factor threshold value Th_height in each partitioned section.
The optical line monitoring device of claim 7, wherein:

the analysis unit measures two reflection peak factors in peaks of the OTDR reference trace of the monitoring light, compares the measured reflection peak factors with the first and the second reflection peak factor threshold values, and determines a reflection peak, and

the analysis unit measures two reflection peak factors in peaks of the measured trace of the monitoring light, compares the measured reflection peak factors with the first and the second reflection peak factor threshold values, and determines a reflection peak.
The optical line monitoring device of claim 13, wherein the analysis unit measures a peak value Peak_level and a peak height Peak_height of each of the peaks in the OTDR reference trace of the monitoring light, sets the measured peak value Peak_level and the measured peak height Peak_height as the first reflection peak factor and the second reflection peak factor, respectively, and

the analysis measures a peak value Peak_level and a peak height Peak_height of each of the peaks in the measured trace of the monitoring light, and sets the measured peak value Peak_level and the measured peak height Peak_height as the first reflection peak factor and the second reflection peak factor, respectively.
The optical line monitoring device of claim 14, wherein the analysis unit compares a value of the first reflection peak factor Peak_level of each of the peaks with the first reflection peak factor threshold value Th_level in the OTDR reference trace or the measured trace of the monitoring light and determines whether each of the peaks in the OTDR reference trace or the measured trace of the monitoring light corresponds to noise.
The optical line monitoring device of claim 15, wherein if it is determined that each of the peaks in the OTDR reference trace or the measured trace of the monitoring light does not correspond to noise, the analysis unit compares a value of the second reflection peak factor Peak_height with the second reflection peak factor threshold value Th_height in each partitioned section and determines a reflection peak.
The optical line monitoring device of claim 1, wherein when a reflection peak factor of the reflection peak of the measured trace is compared with a reflection peak factor of the reflection peak of the OTDR reference trace and whether a fault has occurred in the optical line is determined, the analysis unit determines whether a break has occurred in the optical line and then determines whether bending has occurred in the optical line.
The optical line monitoring device of claim 1, wherein when a reflection peak factor of the reflection peak of the measured trace is compared with a reflection peak factor of the reflection peak of the OTDR reference trace and whether a fault has occurred in the optical line is determined, the analysis unit compares a number and locations of the reflection peaks of the measured trace with a number and locations of the reflection peaks of the OTDR reference trace, determines whether a break has occurred in the optical line, and determines that the optical line has been broken if, as a result of the comparison, at least one of the number and locations of the reflection peaks of the measured trace has been changed as compared with the reflection peaks of the OTDR reference trace.
The optical line monitoring device of claim 14, wherein when a reflection peak factor of the reflection peak of the measured trace is compared with a reflection peak factor of the reflection peak of the OTDR reference trace and whether a fault has occurred in the optical line is determined,

the analysis unit compares the first reflection peak factor Peak_level of the reflection peak of the measured trace with the first reflection peak factor Peak_level of the reflection peak of the OTDR reference trace and determines whether bending has occurred in the optical line if the reflection peaks of the measured trace have an identical number and locations with the reflection peaks of the OTDR reference trace.
The optical line monitoring device of claim 19, wherein:

the analysis unit measures a third reflection peak factor of the reflection peak of the OTDR reference trace and a third reflection peak factor of the reflection peak of the measured trace, and

if a difference between the first reflection peak factor of the reflection peak of the measured trace and the first reflection peak factor of the reflection peak of the OTDR reference trace is a predetermined value or higher, the analysis unit compares the third reflection peak factor of the reflection peak of the measured trace with the third reflection peak factor of the reflection peak of the OTDR reference trace and determines whether bending has occurred in the optical line.
The optical line monitoring device of claim 20, wherein the analysis unit sets a value, obtained by subtracting an initial strength of the OTDR reference trace or the measured trace from the first reflection peak factor Peak_level of the monitoring light, as the third reflection peak factor, respectively.
The optical line monitoring device of claim 21, wherein if a difference between the third reflection peak factor of the reflection peak of the OTDR reference trace and the third reflection peak factor of the reflection peak of the measured trace is a predetermined value or higher, the analysis unit determines that bending has occurred in the optical line.
An optical line monitoring system, comprising:

an optical line configured to counnect a supplier-side terminal with a plurality of ONTs;

an optical line monitoring device configured to comprise an OTDR for selectively transmitting monitoring light by the optical line and receiving the monitoring light reflected and an analysis unit for analyzing a trace of the monitoring light;

an optical switching unit configured to selectively connect the optical line with the optical line monitoring device;

a WDM configured to combine signal light and the monitoring light; and

an optical splitter provided along the optical line,

wherein the analysis unit sets two or more types of reflection peak factor threshold values in a OTDR reference trace of the monitoring light, measures two or more types of reflection peak factors corresponding to the reflection peak factor threshold values in the OTDR reference trace of the monitoring light, compares values of the measured reflection peak factors with the set reflection peak factor threshold value, and determines a reflection peak in the OTDR reference trace of the monitoring light;

the analysis unit measures two or more types of reflection peak factors in a measured trace of the monitoring light, compares the measured reflection peak factors with the set reflection peak factor threshold values, and determines a reflection peak in the measured trace of the monitoring light; and

the analysis unit compares the reflection peak factors of the reflection peak of the measured trace with the reflection peak factors of the reflection peak of the OTDR reference trace and determines whether a fault has occurred in the optical line.
A method of controlling an optical line monitoring device, comprising an OTDR for selectively transmitting monitoring light by an optical line for connecting a supplier-side terminal with an ONT and receiving the monitoring light reflected and an analysis unit for analyzing a trace of the monitoring light, the method comprising steps of:

analyzing a OTDR reference trace of the monitoring light;

analyzing a measured trace of the monitoring light; and

comparing the measured trace with the OTDR reference trace and determining whether a fault has occurred in the optical line,

wherein the step of analyzing the OTDR reference trace of the monitoring light comprises steps of setting two or more types of reflection peak factor threshold values in the OTDR reference trace of the monitoring light, measuring two or more types of reflection peak factors corresponding to the reflection peak factor threshold values, comparing the measured reflection peak factors with the set reflection peak factor threshold values, and determining a reflection peak;

the step of analyzing the measured trace of the monitoring light comprises steps of measuring two or more types of reflection peak factors in the measured trace of the monitoring light, comparing the measured reflection peak factors with the set reflection peak factor threshold values, and determining a reflection peak; and

the step of comparing the measured trace with the OTDR reference trace and determining whether a fault has occurred in the optical line comprises a step of comparing the reflection peak factors of the reflection peak of the measured trace with the reflection peak factors of the reflection peak of the OTDR reference trace and determining whether a fault has occurred in the optical line.
The method of claim 24, wherein the step of analyzing a OTDR reference trace of the monitoring light and the step of analyzing a measured trace of the monitoring light further comprise a step of partitioning the optical line into at least two sections depending on an optical splitter provided along the optical line.
The method of claim 25, wherein the step of partitioning the optical line comprises steps of setting an ONT, located at a longest distance from the supplier-side terminal, as an end point of an end section and setting a predetermined point adjacent to a peak due to a first optical splitter as an end point of a first section.
The method of claim 26, wherein the step of setting a predetermined point comprises setting a predetermined point between a first peak due to the first optical splitter and a second peak subsequent to the first peak as the end point of the first section.
The method of claim 26, wherein the step of partitioning the optical line further comprises a step of setting an optical splitter located at a longest distance from the supplier-side terminal, from among second optical splitters, as an end point of a second section, if a first optical splitter and one or more second optical splitter connected to the first optical splitter are provided along the optical line.
The method of claim 25, wherein the step of setting two or more types of reflection peak factor threshold values in the OTDR reference trace of the monitoring light further comprises a step of differently setting at least one of the two or more types of reflection peak factor threshold values in the partitioned sections.
The method of claim 29, wherein the step of differently setting at least one of the two or more types of reflection peak factor threshold values comprises steps of:

setting a first reflection peak factor threshold value Th_level; and

differently setting a second reflection peak factor threshold value Th_height in each partitioned section.
The method of claim 30, wherein the step of differently setting a second reflection peak factor threshold value Th_height in each partitioned section comprises setting the second reflection peak factor threshold value Th_height to be sequentially increased as the section proceeds from the supplier-side terminal to the ONT.
The method of claim 31, wherein the second reflection peak factor threshold value Th_height is set to be equal to or higher than noise occurring in each partitioned section.
The method of claim 30, wherein the step of differently setting a second reflection peak factor threshold value Th_height in each partitioned section comprises setting the second reflection peak factor threshold value Th_height to be a greatest in a section adjacent to the ONT.
The method of claim 30, wherein the step of setting a first reflection peak factor threshold value Th_level comprises calculating a Root Mean Square (RMS) value and a standard deviation of the OTDR reference trace of the monitoring light in a section after an ONT located at a longest distance from the supplier-side terminal, setting a first noise upper limit value by adding a first predetermined value to the RMS value, setting a second noise upper limit value by adding a second predetermined value to the first noise upper limit value, setting a third noise upper limit value by adding a value, obtained by multiplying the standard deviation by the predetermined coefficient, to the RMS value, and setting any one of the first noise upper limit value, the second noise upper limit value, and the third noise upper limit value as the first reflection peak factor threshold value Th_level.
The method of claim 30, wherein the step of differently setting a second reflection peak factor threshold value Th_height in each partitioned section comprises calculating a first average and a first standard deviation of noise in the OTDR reference trace including a peak and a second average and a second standard deviation of noise in the OTDR reference trace without the peak in each partitioned section of the OTDR reference trace and setting a value obtained by adding the first standard deviation to the first average or a value obtained by adding the second standard deviation to the second average as the second reflection peak factor threshold value Th_height in each partitioned section.
The method of claim 30, wherein:

the step of comparing the measured reflection peak factors with the set reflection peak factor threshold values in the OTDR reference trace of the monitoring light and determining a reflection peak comprises a step of measuring two reflection peak factors in peaks of the OTDR reference trace of the monitoring light, comparing the measured reflection peak factors with the first and the second reflection peak factor threshold values, and determining a reflection peak based on a result of the comparison, and

the step of comparing the measured reflection peak factors with the reflection peak factor threshold values in the measured trace of the monitoring light and determining a reflection peak comprises a step of measuring two reflection peak factors in peaks of the measured trace of the monitoring light, comparing the measured reflection peak factors with the first and the second reflection peak factor threshold values, and determining a reflection peak.
The method of claim 36, wherein:

the step of measuring two reflection peak factors in the peaks of the OTDR reference trace of the monitoring light comprises measuring a peak value Peak_level and a peak height Peak_height of each of the peaks in the OTDR reference trace of the monitoring light and setting the measured peak value Peak_level and the measured peak height Peak_height as the first reflection peak factor and the second reflection peak factor, respectively, and

the step of measuring the two reflection peak factors in the peaks of the measured trace of the monitoring light comprises measuring a peak value Peak_level and a peak height Peak_height of each of the peaks in the measured trace of the monitoring light and setting the measured peak value Peak_level and the measured peak height Peak_height as the first reflection peak factor and the second reflection peak factor, respectively.
The method of claim 37, wherein the step of comparing the measured reflection peak factors with the first and the second reflection peak factor threshold values and determining a reflection peak comprises comparing a value of the first reflection peak factor Peak_level of each of the peaks with the first reflection peak factor threshold value Th_level in the OTDR reference trace or the measured trace of the monitoring light, determining whether each of the peaks in the OTDR reference trace or the measured trace of the monitoring light corresponds to noise, comparing a value of the second reflection peak factor Peak_height with the second reflection peak factor threshold value Th_height in each partitioned section, and determining a reflection peak in the OTDR reference trace or the measured trace of the monitoring light.
The method of claim 24, wherein the step of comparing a reflection peak factor of the reflection peak of the measured trace with a reflection peak factor of the reflection peak of the OTDR reference trace and determining whether a fault has occurred in the optical line comprises steps of:

determining whether the optical line has been broken; and

determining whether the optical line has been bended.
The method of claim 24, wherein the step of comparing a reflection peak factor of the reflection peak of the measured trace with a reflection peak factor of the reflection peak of the OTDR reference trace and determining whether a fault has occurred in the optical line comprises a step of comparing a number and locations of the reflection peaks of the measured trace with a number and locations of the reflection peaks of the OTDR reference trace, determining whether a break has occurred in the optical line, and determines that the optical line has been broken if, as a result of the comparison, at least one of the number and locations of the reflection peaks of the measured trace has been changed as compared with the reflection peaks of the OTDR reference trace.
The method of claim 24, wherein the step of comparing a reflection peak factor of the reflection peak of the measured trace with a reflection peak factor of the reflection peak of the OTDR reference trace and determining whether a fault has occurred in the optical line comprises a step of comparing the first reflection peak factor Peak_level of the reflection peak of the measured trace with the first reflection peak factor Peak_level of the reflection peak of the OTDR reference trace and determining whether bending has occurred in the optical line, when the reflection peaks of the measured trace have an identical number and locations with the reflection peaks of the OTDR reference trace.
The method of claim 41, wherein the step of determining whether bending has occurred in the optical line comprises steps of:

measuring a third reflection peak factor of the reflection peak of the OTDR reference trace and a third reflection peak factor of the reflection peak of the measured trace, and

if a difference between the first reflection peak factor of the reflection peak of the measured trace and the first reflection peak factor of the reflection peak of the OTDR reference trace is a predetermined value or higher, comparing the third reflection peak factor of the reflection peak of the measured trace with the third reflection peak factor of the reflection peak of the OTDR reference trace and determining whether bending has occurred in the optical line.
The method of claim 42, wherein the step of measuring a third reflection peak factor of the reflection peak of the OTDR reference trace and a third reflection peak factor of the reflection peak of the measured trace comprises setting a value, obtained by subtracting an initial strength of the OTDR reference trace or the measured trace from the first reflection peak factor Peak_level of the monitoring light, as the third reflection peak factor, respectively.
The method of claim 43, wherein if a difference between the third reflection peak factor of the reflection peak of the OTDR reference trace and the third reflection peak factor of the reflection peak of the measured trace is a predetermined value or higher, it is determined that that bending has occurred in the optical line.