System and method using differential loop gain for fault identification in line monitoring equipment

The present invention relates to a communication system, and more particularly to a system that uses differential loop gain for defect identification in a transmission line monitoring device.

In long-distance fiber optic optical communication systems, it is important to monitor the health of the system. For example, monitoring can be used to detect defects or breaks in fiber optic cables, repeater or amplifier failures, or other problems with the system.

Known monitoring techniques include the use of line monitoring devices that generate test signals that represent pseudo-random bit sequences. The line monitoring device is, for example, a wavelength division multiplexing system, and can transmit a test signal together with an information signal. The test signal can be looped back to the line monitoring device via a high loss loopback (HLLB) path in the amplifier or repeater. The line monitoring device then separates the folded test signal from the data signal and is applied to the test signal during propagation back from the line monitoring device to the line monitoring device via the HLLB and each intervening optical path or amplifier. The folded test signal can be processed to obtain data representing the HLLB loop gain. Significant deviations in HLLB loop gain may indicate a system defect.

<p> In submarine optical communication systems, repeater excitation power loss and large fiber span loss may be the main failure mechanisms that result in large deviations in HLLB loop gain from normal values. In known systems, large deviations in HLLB loop gain, such as deviations above a predetermined alarm threshold, will trigger a system alarm. Selection of alarm thresholds in such systems will require discrimination between normal system fluctuations, measurement errors, and actual communication path defects. Unfortunately, HLLB loop gain measurements are generally physical in the communication path, partly because of the repeater amplifier gain mechanism, eg gain self-regulation, as well as the output-output structure of the repeater loopback. This identification would be difficult as it is not sensitive to change. Therefore, real-world path changes that result in non-destructive defects within such changes may alter the HLB loop gain, which results in only slightly detectable typical measurement errors and system variation.</p>

<p> Systems and methods for using differential loop gain for defect identification in optical transmission line monitoring equipment are provided as follows. According to one aspect of the disclosure, in a line monitoring system of an optical communication system, a test signal transmitter configured to supply a test signal transmitted by the optical communication system, the optical communication system receives the test signal. , A first optical fiber path that transmits the test signal in the first direction, a second optical fiber path that transmits the signal in the second direction opposite to the first direction, and a second optical path, respectively. A test signal transmitter having a plurality of loopback paths that give the test signal to the fiber path as a related feedback test signal, and a differential loop gain data related to the loopback path are calculated from the feedback test signal, and a difference is obtained. A line monitoring system is provided with a correlator configured to receive the results of dynamic loop gain data and provide an output that identifies defects in the optical communication system.</p><p> According to another aspect of the present disclosure, a test signal transmitter configured to supply a test signal; a first optical fiber path that receives the test signal and transmits the test signal in a first direction; said first. A second optical fiber path that transmits a signal in the direction opposite to one direction; a plurality of loopback paths, each feeding the test signal as an associated feedback test signal to the second fiber path; and said related. From the feedback test signal, the differential loop gain data related to each of the loopback paths is calculated, and the result of the differential loop gain data is received to output a signal for identifying the defect of the optical communication system. A line monitoring system with configured correlators is provided.</p><p> According to yet another aspect of the present disclosure, each transmits a signal in a first optical fiber path that transmits the signal in the first direction and a second direction that transmits the signal in the second direction opposite to the first direction. A method of monitoring an optical communication system having multiple loopback paths connecting to a fiber optic path: a step of transmitting a signal on the first fiber optic path; feedback back from each of the loopback paths. The step of receiving the test signal from the second optical fiber path; the step of calculating the differential loop gain data associated with each of the loopback paths from the feedback test signal; and receiving the differential loop gain data. A method having a step of identifying a defect in an optical communication system is provided.</p><p> See the detailed description below that should be read in conjunction with the drawings below. In the drawings, similar symbols represent similar parts.</p>

<figref num="1">A simplified block diagram of a system according to an embodiment of the present disclosure.</figref><figref num="2">The graph which shows the relationship between the distance of the exemplary transmission system which concerns on this disclosure, and the maximum value and the minimum value of the differential loop gain.</figref><figref num="3">The graph which shows the relationship between the loopback repeater number and the differential loop gain which is related to the decrease of the repeater excitation power of 3dB in the exemplary system which concerns on this disclosure.</figref><figref num="4">The graph which shows the relationship between the loopback repeater number and the change of the differential loop gain which is related to the excess fiber loss of 3dB in the exemplary system which concerns on this disclosure.</figref><figref num="5">The graph showing the relationship between the loopback repeater number and the differential loop gain deflection associated with the excess fiber loss condition shown in FIG.</figref><figref num="6">In the present disclosure, a graph showing the relationship between the wavelength coefficient and the relative power exemplifies the impulse response of the wavelet function corresponding to the low-pass filter.</figref><figref num="7">The graph which shows the relationship between the wavelength coefficient and the relative power which exemplifies the impulse response of the wavelet function corresponding to the high region passing filter which concerns on this disclosure.</figref><figref num="8">FIG. 8A shows the relationship between the loopback repeater number and the change in the differential loop gain related to the decrease in the repeater excitation power of 3 dB, which is shown together with the graph of the impulse response of the wavelet function in the high frequency pass filter according to the present disclosure. Graph to show. Figure 8B is a graph showing the response of the lowpass filter to changes in the differential loop gain shown in Figure 8A. Figure 8C is a graph showing the response of the high pass filter to changes in the differential loop gain shown in Figure 8A.</figref><figref num="9">FIG. 9A is a graph showing the relationship between the loopback repeater number and the change in the differential loop gain related to the fiber loss of 3 dB, which is shown together with the graph of the impulse response of the wavelet function in the low-pass filter according to the present disclosure. Figure 9B is a graph showing the response of the lowpass filter to changes in the differential loop gain shown in Figure 9A. Figure 9C is a graph showing the response of the high pass filter to changes in the differential loop gain shown in Figure 9A.</figref><figref num="10">A block-like flowchart showing an example of the process according to the present disclosure.</figref><figref num="11">The flowchart which shows another example of the process which concerns on this disclosure.</figref>

FIG. 1 is a simplified block diagram illustrating an exemplary embodiment of a WDM transmission system 10 including a line monitoring device (LME) 12 according to the present disclosure. System 10 as a whole can be configured to calculate the differential loop gain value associated with each repeater / amplifier. Changes in differential loop gain can be used to generate system alarms that indicate system defects. An automatic signature analysis (ASA) algorithm can be applied to the differential loop gain to identify the type of defect.

Those skilled in the art will recognize that System 10 was drawn in the form of a highly simplified two-point system for ease of explanation. It will be appreciated that the systems and methods according to the present disclosure may be incorporated into various network elements and network configurations. The exemplary embodiments presented herein are provided solely for illustration purposes, not for limitation purposes.

In the illustrated exemplary embodiment, the transmission system 10 comprises a laser transmitter 30 and an optical fiber pair that includes fibers 28 and 29 to transmit an optical signal. Fibers 28 and 29 can be, for example, long-distance optical fiber lines deployed on the seabed. Optical fibers 28 and 29 are unidirectional fibers and can transmit signals in opposite directions. Fibers 28 and 29 together establish a bidirectional path for transmitting signals. Although the exemplary monitoring system herein is described as monitoring a transmission system that includes two unidirectional fibers 28 and 29, the system according to the present disclosure employs a single bidirectional fiber for transmission. Can be used to monitor the system.

The laser transmitter 30 may be an optical wavelength division multiplexing (WDM) transmitter configured to transmit optical data to the WDM receiver 60 via a fiber 29 on a plurality of channels (or wavelengths). Transmitters and receivers are, of course, presented in a very simplified format for ease of explanation. The laser transmitter 30 combines a plurality of laser transmitters, each of which transmits an optical data signal using a different channel or wavelength, and a plurality of data signals, and a combined wave transmitted via a fiber 29. It can have a multiplexer as a signal. The receiver can detect the transmitted data signal by demultiplexing it. Similarly, WDM data signals can be transmitted from transmitter 62 to receiver 64, i.e., in the opposite direction of the signal on fiber 29, via fiber 28. Alternatively, data from a single channel can be transmitted over fiber 28 and / or 29.

The line monitoring device (LME) 12 can be configured to monitor the health of system 10. In an exemplary embodiment, the LME 12 includes a code generator 14, a test signal transmitter 15 including a laser transmitter 16 and a polarization converter 70, a delay system 20, an ASA processor 72 and a correlation system 22 including computer readable memory. , And a filter 26. The LME 12 can be configured to supply an output 24, eg, an alarm, to the element management system 74 when a defect is detected in the system 10.

The code generator 14 can be configured to generate and output test code, such as a pseudo-random sequence of code (PRS). Various code generators and code configurations are known to those of skill in the art. The output of the code generator 14 can be coupled to the laser transmitter 16. As used herein, the term "linkage" refers to any term such as a connection, coupling, link, etc., such that a signal transmitted by a system element is given to the "linkage" element. Such "connected" devices need not be directly connected to each other and may be separated by intermediate components or devices that manipulate or modify such signals. The laser transmitter 16 may have a known configuration, such as a distributed feedback laser (DBF), and has a carrier wavelength λ that is different from the wavelengths of all data channels transmitted on the transmission system.₀Can be configured to generate light output with. Carrier wavelength λ₀Can be, for example, the wavelength of the edge of the spectral bandwidth of the system, or the wavelength between data channels. In one embodiment, the laser transmitter can be configured to provide optical output at a plurality of different carrier wavelengths. For example, a laser transmitter has a short LME wavelength at the short wavelength end of the data signal transmission band, that is, at a long LME wavelength adjacent to the shortest wavelength data channel and at the long wavelength end of the data signal transmission band. That is, the output can be supplied adjacent to the longest wavelength data channel. In one embodiment, the short LME wavelength may be 1537 nm and the long LME wavelength may be 1563 nm. The power of the laser output can be set below the power level of the data signals communicated on the fibers 28 and 29 to minimize interference with the data signals.

The laser transmitter 16 can generate an LME test signal indicating the code received from the code generator 14, for example, at both the long LME wavelength and the short LME wavelength. The LME test signal can be supplied as the LME test signal output 18 of the test signal transmitter 15. In one embodiment, the output of the code generator can directly modulate the amplitude of the laser output. Other configurations are known that add a code to the output light from the laser transmitter. For example, the code may be provided by an amplitude modulator or other modulator coupled to the output of the laser transmitter 16.

In the illustrated exemplary embodiment, an optional polarization transducer 70 is coupled to a laser transmitter 16 to convert the polarization of the LME test signal. The polarization transducer may have a known configuration. In one embodiment, the polarization transducer 70 can convert the polarization state of the LME test signal such that the mean value of the polarization state is reduced from 1 during the polarization modulation period. Therefore, it is considered that the LME test signal output 18 of the test signal transmitter 15 has a degree of polarization substantially equal to zero, and the polarization is converted.

In an exemplary embodiment, the coupler 34 can combine the WDM data 32 from the transmitter 30 with the LME test signal 18 and transmit the combined signal to the fiber 29. Multiple optical repeaters 36-1, 36-2, ..., 36-N can be connected to optical fibers 28 and 29. Each repeater receives via fiber 28 with first amplifiers 40-1, 40-2, ..., 40N that amplify the optical signal transmitted to receiver 60 via fiber 29, respectively. Second amplifiers 38-1, 38-2, ..., 38-N that amplify the optical signal transmitted to the device 64 may be provided. Each repeater also wraps a portion of the signal on fiber 29 or fiber 28 and sends it to the LME 12, accompanying loopback paths 42-1, 42-2, ..., 42N, eg, high loss loopback paths. To be equipped.

The signal 52 will carry all the signals present on the fiber 28, including the WDM data 32 and the LME test signal given to the filter 26. The filter 26 is wavelength selective and will only pass the wavelength of the folded LME test signal 18 towards the correlator 22. The LME test signal returned to the LME 12 by each repeater via the fiber 28 is delayed from the original LME test signal 18 by a period proportional to the distance of the delay path of each repeater. For example, for the first repeater 36-1, the time delay t_slIs proportional to the distance of the delay path through the first repeater 36-1. Distance d via the first repeater₁From the code generator 14, via the transmitter 16, the polarization converter 70, the coupler 34, the first repeater 36-1, through the loopback path 42-1 to the optical fiber 28, the correlator 22. It can be calculated as a distance. Therefore, the time delay of the LME test signal folded back by the first repeater 36-1 t_slWith c as the speed of light, t_sl= d₁It can be calculated as / c. Similarly, the time delay of the LME test signal folded back by the second repeater 36-2 t_s2Is the known distance d of the delay path for the second repeater 36-2₂Can be calculated based on, t_s2= d₂It can be calculated as / c. Similarly, the time delays for repeaters added in the system can be calculated based on the known distances of those delay paths. To facilitate the correlation processing by the correlator 22, the delay system 20 can receive the code transmitted from the code generator 14 and output a plurality of related delay codes to the correlator 22. The delay system 20 corresponds to a time delay corresponding to each repeater, i.e. (eg, a time delay associated with the first repeater 36) t._s1, (Corresponding to the time delay for the second repeater 44) t_s2After, etc., each code can be output. In other words, the delay system 20 may delay the code based on the position of each repeater.

The correlator 22 then correlates the folded LME test signal with the delayed code from the delay system 20. The correlator 22 may correlate either an electrical signal or an optical signal. When the correlator 22 correlates the electrical signal, the LME 12 is a photoelectric converter connected between the filter 26 and the correlator 22 in order to convert the optical signal output to the filter 26 into an electrical signal. Can be provided.

In correlation processing, the correlator 22 may be configured to calculate loop gain data associated with each repeater 36-1, 36-2, ..., 36-N. The loop gain data for each receiver can be calculated by comparing the feedback LME test signal received from the repeater with the associated delay test code. In the illustrated exemplary embodiment, the loop gain for any of the repeaters 36-i is from the code generator 14 via the transmitter 16, the polarization transducer 70, the coupler 34, the repeater 36-i. It will represent the gain and loss applied to the test signal through the loopback path 42-i, through the optical filter 26 and to the correlator 22.

According to the present disclosure, the correlator 22 converts the loop gain data associated with each repeater into the differential loop gain data associated with each repeater 36-1, 36-2, ..., 36-N. Can be configured as follows. The differential loop gain of each repeater 36-i can be calculated by subtracting the loop gain associated with repeater 36- (il) from the loop gain associated with repeater 36-i. For example, the differential loop gain associated with repeater 36-2 can be calculated by subtracting the loop gain of repeater 36-1 from the loop gain of repeater 36-2. In the illustrated exemplary embodiment, the differential loop gain associated with repeater 36-2 is essentially because the losses associated with the HLLB path of the repeater essentially cancel each other out. Represents the gain given to the test signal by the amplifiers 40-2, 38-1 minus the loss given to the test signal in paths 39 and 37.

The differential loop gain can thus depend on only four random variables: two gain variables and two loss variables. Therefore, the differential loop gain will show a smaller maximum / minimum deviation than normal system variation compared to a simple loop gain and will be less sensitive to distance. These factors will allow reliable settings for gain change thresholds for which failure detection triggers can be set.

For example, FIG. 2 is a graph 80 showing the relationship between distance and maximum and minimum differential loop gains for an exemplary transmission system containing 140 repeaters, here between 20 independent measurements. Differential loop gain data is obtained. As shown, the maximum value of the differential loop gain in the graph 80 is about 0.08 dB. This relatively low maximum / minimum deviation value is a relatively low set value for the gain change threshold for which the failure detection trigger is set, compared to, for example, the maximum / minimum deviation value indicated by simple loop gain data. To facilitate the adoption of. In one embodiment, the correlator 22 alerts the element management system 74, for example, if the change in differential loop gain of any repeater exceeds the specified differential loop gain change threshold of 0.2 dB. Will supply.

In the illustrated exemplary embodiment, the correlator 22 comprises an ASA processor 72 and a computer-readable memory 71. The ASA processor 72 can be configured to apply one or more ASA algorithms to the differential loop gain data calculated by the correlator 22 to reveal the types of defects that occur in transmission system 10. The ASA process may be triggered by an alarm that occurs when the differential loop gain in the repeater exceeds the specified differential loop gain change threshold. As a result of the ASA process, the correlator will provide output 24, which indicates the type of defect, to the element management system 74.

For example, the ASA algorithm can take various configurations and may be run as one or more computer programs or applications running on a computer system such as the ASA processor 72. A computer program or application, such as the ASA algorithm, is stored in memory 71, or other computer-readable medium (eg, hard disk, CDRom, system memory, optical memory, etc.) and by a processor such as ASA processor 74. , All or part of the functions described herein by correlators can be performed. Such computer program products are distributed as computer-readable removable media (eg, diskettes, CD-ROMs), pre-installed in the system (eg, in system ROMs or fixed disks), or , Is expected to be distributed from servers or electronic bulletin boards on networks (eg, the Internet or the Worldwide Web). Those skilled in the art will recognize that the functionality of the correlator is performed to provide such functionality using any combination of hardware, software, and / or firmware.

In one embodiment, the ASA processor 72 is configured to compare the current differential loop gain data with a defined differential loop gain defect signature that corresponds to the differential loop gain due to defects in the optical communication system. be able to. The comparison of the differential loop gain data with the specified differential loop gain defect signature may be made using a known signal processing technique such as a matching filter. Specified defect signatures can be constructed for system defects such as excessive excitation loss and excessive fiber loss. Of course, other defects may be detected and examined.

Excessive excitation loss will be characterized by total or partial defects in the amplified excitation laser in the repeater. For example, in the exemplary embodiment of Figure 1, excessive excitation loss of repeater 36-2 would lead to a total or partial reduction in the gain imparted by the amplifiers 38-2 and 40-2. .. In general, optical amplifiers in communication lines are operated in a loosely compressed state, and changes in the output signal power of repeaters tend to self-correct by adjusting the gain after a few amplifiers. For example, if the excitation power of amplifiers 38-2 and 40-2 in Figure 1 is reduced, the output power of repeater 36-2 is reduced, resulting in the gain provided by amplifiers 38-1 and 40-3. Increases as a result of the gain control function within repeaters 36-1 and 36-3.

FIG. 3 shows the relationship between the loopback repeater number associated with a 3 dB reduction in repeater excitation power in the system, that is, excessive excitation loss, and the change in differential loop gain in an exemplary system according to the present disclosure. Includes graphs 82 and 84 shown. Graph 82 shows the relationship between the loopback repeater number associated with the short LME wavelength, that is, the short wavelength end of the transmission band, and the change in differential loop gain. Graph 84 also shows the relationship between the long LME wavelength, that is, the loopback repeater number associated with the long wavelength end of the transmission band and the change in differential loop gain. As shown, a 3 dB reduction in repeater excitation power results in a differential loop gain reduction of more than 0.2 dB at the defective repeater for both short and long LME wavelengths.

Excessive fiber loss occurs, which results in additional or total loss to transmission over the fiber path in the fiber path, eg, in the path between the amplifier 40-1 and the amplifier 40-2 in FIG. In general, when excessive fiber loss appears in the fiber path, gain control algorithms in other system repeaters will cause adjustment of the gain imparted by the other repeaters. For example, if excess fiber loss appears in the path between amplifier 40-1 and amplifier 40-2 in Figure 1, the gain provided by amplifier 40-2 is the gain in repeater 36-2. It will increase automatically as a result of control functions.

FIG. 4 is an exemplary system according to the present disclosure, with Graph 86 showing the relationship between loopback repeater numbers and differential loop gain changes associated with an excess fiber loss of 3 dB in the system in the outward direction. Includes 88. Graph 86 shows the relationship between the loopback repeater number and the change in differential loop gain associated with the short LME wavelength. Graph 88 also shows the relationship between the loopback repeater number and the change in differential loop gain associated with the long LME wavelength. As shown, excess fiber loss makes a large difference between the differential loop gains of short LME wavelengths and long LME wavelengths. The difference between the differential loop gains of the short LME wavelength and the long LME wavelength is referred to herein as differential loop gain deflection.

FIG. 5 includes Graph 90 showing the relationship between the loopback repeater number and the differential loop gain deflection associated with the excess fiber loss condition shown in FIG. As shown, the differential loop gain deflection associated with excess fiber loss may be about -1.5 dB. On the other hand, the differential loop gain deflection associated with excessive excitation loss may be on the order of about 0.1 dB, as shown in FIG. In general, this difference in differential loop gain deflection will be related to the output-output HLLB structure. For example, in the presence of excitation loss, differential loop gain will be caused by the use of two amplifiers with reverse gain change and reverse gain deflection. The gain deflections in the opposite directions will substantially cancel each other out. If excess fiber loss is present in only one outward and inward direction, differential loop gain will be caused by only one amplifier with a gain change that causes gain deflection. If the excess fiber loss is in both outward and inward directions within the same repeater span, the differential loop gain can be caused by two amplifiers with gain changes in the same direction and gain deflection in the same direction. There will be. Therefore, according to the present disclosure, gain deflection can be used to distinguish between excessive fiber loss and excessive excitation loss.

Excessive excitation loss defects and excess fiber loss defects, for example, as shown in Figure 3-Figure 5, produce distinctly different differential loop gain defect signatures. These defect signatures are generally independent of system type or system location, as differential loop gain is essentially dependent only on the four variables: the gain of the two amplifiers and the loss of the two input fibers. There will be. Excessive excitation loss and excess fiber loss in the system can be detected and identified by comparing the specified loop gain defect signature with the differential loop gain data. Although this specification describes the ASA as relating to comparing a defined loop gain defect signature with differential loop gain data, the ASA according to the present disclosure refers to the defect signature in addition to the differential loop gain data. Alternatively, in addition to this, it may be compared with the gain data.

In one embodiment, the defined loop gain defect signatures are orthogonal to each other and have an impulse response function that approximates the changes in the differential loop gain data represented by excessive excitation loss and excess fiber loss. It can be configured by a set of matching filters. The response from the low pass filter within the matching filter, or the response from the high pass fill within the matching filter, will indicate excessive excitation loss or excessive defect loss.

The matching filter can be represented by the associated wavelet function, and the differential loop gain data can be analyzed for the wavelet function by the ASA processor 72. 6 and 7 show exemplary impulse responses 92 and 94 of separate Koif stationary wavelet transform (SWT) functions useful in the embodiments according to the present disclosure. Specifically, FIG. 6 shows the impulse response 92 of the wavelet function corresponding to the lowpass filter that approximates the change in the differential loop gain data resulting from, for example, the excess fiber loss shown in FIG. FIG. 7 shows the impulse response 94 of the wavelet function corresponding to the high frequency pass filter that approximates the change in the differential loop gain data resulting from, for example, the excessive excitation loss shown in FIG.

The ASA processor 72 continuously compares the calculated differential loop gain data with the wavelet function, and the excessive fiber loss wavelet function or the excessive excitation loss wavelet function is combined with the calculated differential loop gain data. If they match, they will provide an output 24 that indicates either excessive fiber loss or excessive excitation loss. In one embodiment, in order to match the differential loop gain data with the wavelet function, the differential loop gain data can be extended by inserting zeros, and then sampled and extracted by convolution integration with a lowpass filter. it can. The static wavelet transform can then be performed and the partial band of the wavelet coefficient can be used as the defect signature.

FIG. 8A shows the impulse response of the high frequency pass filter wavelet function to help provide the excess excitation loss loop gain defect signature in the exemplary system according to the present disclosure, in addition to the repeater excitation in the system. Includes Graph 96 showing the relationship between loopback repeater numbers and differential loop gain changes associated with a 3 dB reduction in power, or excessive excitation loss. FIG. 9A shows the impulse response of the lowpass filter wavelet function to help provide the excess excitation loss loop gain defect signature in the exemplary system according to the present disclosure, plus a 3 dB fiber in the system. Includes Graph 100 showing changes in loopback repeater number and differential loop gain associated with loss, or excess fiber loss. A comparison of the data associated with Graph 96 with the impulse response of Graph 98, such as the convolution integral, will result in the output shown in Graph 104 of FIG. 8C, which indicates the presence of excess excitation loss. A comparison of the data associated with Graph 96 with the impulse response of Graph 102 would result in the output shown in Graph 108 of FIG. 9B, which indicates the presence of excess fiber loss. A comparison of the data associated with Graph 100 with the impulse response of Graph 98 would result in the smallest response shown in Graph 110 of FIG. 9C, as there is no excessive excitation loss.

FIG. 10 is a block flow chart of one exemplary process 120 according to the present disclosure. The blocky flowcharts used herein to describe various embodiments include a specific set of steps. However, it is understandable that the sequence of steps merely provides an example of how common functionality can be achieved. Moreover, unless otherwise noted, each sequence of steps need not be performed in the order in which they are written.

In the exemplary embodiment shown in FIG. 6, loop gain data can be calculated from a comparison of the transmitted LME signal with the folded LME signal (122). The loop gain data can be converted into differential loop gain data associated with each repeater in the system (124). The differential loop gain data is compared to one or more predefined differential loop gain defect thresholds associated with different system defect types, such as excess fiber loss or excessive excitation loss. Can be (126). The LME system output will be supplied in response to the results of the comparison to identify the type of system defect (128).

FIG. 11 is a block flow chart of another exemplary process 150 according to the present disclosure, configured to distinguish between excess fiber loss and excess excitation loss. In the illustrated exemplary embodiment, short LME wavelength and long LME wavelength loop gain data can be calculated for each repeater by comparing the transmitted LME signal with the folded LME signal (152). .. The loop gain data can be converted into differential loop gain data for short and long LME wavelengths associated with each repeater in the system (154). In one embodiment, the differential loop gain deflection can be analyzed to determine if the gain deflection exceeds a predetermined deflection threshold (eg 0.2 dB) (156).

Exceeding the gain deflection threshold can provide an output indicating the presence of excess fiber loss (158). The change in differential loop gain can optionally be compared to the defect signature corresponding to the fiber loss, eg, the low pass filter of the pair of matching filters described above (160). If the differential loop gain data matches the defect signature of the fiber loss (160), it can provide an output indicating the presence of excess fiber loss (158). Otherwise, the process proceeds to step 162.

In one embodiment, if the gain deflection threshold is not exceeded, the differential loop gain for the short LME wavelength is analyzed and the differential loop gain exceeds the specified differential loop gain threshold, eg 0.2 dB. It can be determined whether or not (162). If the specified differential loop gain threshold is exceeded, it can provide an output indicating the presence of excess excitation loss (164). Optionally, the change in differential loop gain can be compared to the defect signature corresponding to the excitation loss, eg, the high pass filter of the pair of matching filters described above (166). If the differential loop gain data matches the high frequency pass filter of the above pair of matching filters (166), it is possible to supply the output 164 indicating the presence of excessive excitation loss. Otherwise, the process proceeds to step 168.

If the specified loop gain threshold is not exceeded and the analysis of all repeaters has not been completed (168), the process returns to step 156 to continue the process for each repeater in the system. Once all repeaters have been analyzed (168), the process returns to the step of continuously analyzing system defects (152).

The embodiments described herein and some of which use the present invention have been described for illustrative purposes only and are not intended to be limiting. Many other embodiments that will be immediately apparent to those of skill in the art will be developed without departing from the principles and scope of the invention.

12: Line monitoring system 14: Code generator 16: Laser transmitter 20: Delay system 22: Correlation system 26: Filter 34: Coupler 70: Polarization transducer 71: Memory 72: ASA processor 74: Element management system