WO2022099552A1

WO2022099552A1 - System and method for real-time fiber performance monitoring

Info

Publication number: WO2022099552A1
Application number: PCT/CN2020/128445
Authority: WO
Inventors: Chongjin Xie; Sai CHEN; Liang Dou; Huan ZHANG
Original assignee: Alibaba Group Holding Limited
Priority date: 2020-11-12
Filing date: 2020-11-12
Publication date: 2022-05-19
Also published as: CN116349163A

Abstract

One embodiment described herein provides a system for monitoring performance of fibers in an optical transport network. The system can include a plurality of optical time-domain reflectometer (OTDR) modules and an OTDR control-and-management module coupled to the plurality of OTDR modules. A respective OTDR module is embedded in a network element of the optical transport network and is coupled to an optical fiber span. The OTDR control-and-management module configures the respective OTDR module to monitor, in real time, performance of the coupled optical fiber span, which can include detecting a fault in the coupled optical fiber span and identifying a location of the detected fault.

Description

SYSTEM AND METHOD FOR REAL-TIME FIBER PERFORMANCE MONITORING

Inventors: Chongjin Xie, Sai Chen, Liang Dou, and Huan Zhang

BACKGROUND Field

This disclosure is generally related to real-time monitoring of fiber performance. More specifically, this disclosure is related to a system that monitors optical fibers using optical time-domain reflectometer (OTDR) -based technologies.

Related Art

An optical transport network (OTN) includes a set of optical network elements (NEs) connected by optical fiber links, and is able to provide functionality of transport, multiplexing, switching, management, supervision, and survivability of optical channels carrying client signals. The optical fiber links connecting the NEs play an important role in the OTN. Performance degradation (either caused by intrusion or the degradation of fiber quality) of the optical fiber links often leads to the degradation of the entire OTN.

Conventionally, only after a system failure or noticeable performance degradation are fiber links inspected to identify faulty fibers. Such a process can be time-consuming and can sometimes result in prolonged service disruption.

SUMMARY

In a variation on this embodiment, the OTDR control-and-management module resides on a network control-and-management platform of the optical transport network.

In a variation on this embodiment, the OTDR control-and-management module configures the respective OTDR module to operate in one of: a fiber-characterization mode for characterizing the coupled optical fiber span, a fiber-failure-detection mode for detecting a fault in the coupled optical fiber span, and a fiber-failure-identification mode for identifying a location of the detected fault.

In a further variation, while operating in the fiber-characterization mode, the respective OTDR module is configured to inject optical pulses having a first pulse width into the coupled optical fiber span; while operating in the fiber-failure-detection mode, the respective OTDR module is configured to inject optical pulses having a second pulse width into the coupled optical fiber span, the second pulse width being greater than the first pulse width; while operating in the fiber-failure-identification mode, the respective OTDR module is configured to inject optical pulses having a third pulse width into the coupled optical fiber span, the third pulse width being greater than the first pulse width but smaller than the second pulse width.

In a further variation, while operating in the fiber-characterization mode, the respective OTDR module is configured to generate an output by averaging a first number of measurements; while operating in the fiber-failure-detection mode, the respective OTDR module is configured to generate an output by averaging a second number of measurements, the second number being less than the first number; and while operating in the fiber-failure-identification mode, the respective OTDR module is configured to generate an output by averaging a third number of measurements, the third number being less than the first number but greater than the second number.

In a further variation, the OTDR control-and-management module configures the respective OTDR module to operate in the fiber-characterization mode after an initial installment of the coupled fiber span and before the coupled fiber span is put into service.

In a further variation, the OTDR control-and-management module is configured to receive OTDR measurement results from the respective OTDR module while the respective OTDR module operates in the fiber-characterization mode, extract information associated with characteristics of the coupled fiber span based on the received OTDR measurement results, and store the information associated with characteristics of the coupled fiber span in a fiber database.

In a further variation, the OTDR control-and-management module configures the respective OTDR module to operate in the fiber-failure-detection mode after the coupled fiber span is put into service.

In a further variation, the OTDR control-and-management module switches the respective OTDR module from operating in the fiber-failure-detection mode to operating in the fiber-failure-identification mode in response to detecting a fault in the coupled fiber span.

In a variation on this embodiment, the OTDR control-and-management module is configured to determine optimal operating parameters of the respective OTDR module for operating in different modes.

In a further variation, the OTDR control-and-management module is configured to store the determined optimal operating parameters in a lookup table, and the lookup table is indexed using unique identifiers assigned to the plurality of OTDR modules.

In a variation on this embodiment, the optical fiber span is coupled to an additional OTDR module embedded in an adjacent network element.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 presents a diagram illustrating an exemplary optical transport network (OTN) with embedded optical time-domain reflectometer (OTDR) modules, according to one embodiment.

FIG. 2A illustrates an exemplary unidirectional fiber-monitoring scenario, according to one embodiment.

FIG. 2B illustrates an exemplary bidirectional fiber-monitoring scenario, according to one embodiment.

FIG. 2C illustrates an exemplary OTDR measurement result, according to one embodiment.

FIG. 3 presents a flowchart illustrating an exemplary process for real-time fiber-performance monitoring, according to one embodiment.

FIG. 4 illustrates a block diagram of an exemplary embedded OTDR module, according to one embodiment.

FIG. 5 illustrates a block diagram of an exemplary centralized OTDR control-and-management module, according to one embodiment.

FIG. 6 illustrates an exemplary computer system, according to one embodiment.

In the figures, like reference numerals refer to the same figure elements.

DETAILED DESCRIPTION

The following description is presented to enable any person skilled in the art to make and use the embodiments, and is provided in the context of a particular application and its requirements. Various modifications to the disclosed embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be applied to other embodiments and applications without departing from the spirit and scope of the present disclosure. Thus, the present invention is not limited to the embodiments shown, but is to be accorded the widest scope consistent with the principles and features disclosed herein.

Overview

The disclosed embodiments provide a fiber-monitoring system that can automatically monitor fiber performance in real time. The fiber-monitoring system can include a plurality of optical time-domain reflectometer (OTDR) modules distributed among various network elements (NEs) in an optical transport network (OTN) and an OTDR-management unit. In one embodiment, each NE in the network, including the edge NEs and the inline NEs, can be equipped with an OTDR module, such that each fiber span can be monitored/measured by at least one OTDR module. Depending on the measurement need, each OTDR can be configured (e.g., by the OTDR-management module) to operate in one of the three different operating modes: the fiber-characterization mode, the fiber-failure-detection mode, and the fiber-failure-identification mode. When operating in the fiber-characterization mode, the OTDR modules are configured to perform OTDR measurement at a higher spatial resolution but with a lower speed. When operating in the fiber-failure- detection mode, the OTDR modules are configured to perform OTDR measurement at a lower spatial resolution but with a higher speed. Based on the high-resolution OTDR measurement results, the system can determine the optimal OTDR parameters for each fiber span and store such parameters in a lookup table for future use. When operating in the fiber-failure-identification mode, the OTDR modules are configured to perform OTDR measurement at a spatial resolution between the higher and lower resolutions and with a speed between the higher and lower speeds. More specifically, subsequent to detecting failure or fault on a particular fiber span, the OTDR-management unit can perform a table lookup to retrieve optimal OTDR parameters for that particular span. The OTDR parameters can then be used to perform the OTDR measurement as well as OTDR data analysis.

Real-Time Fiber-Performance Monitoring System

Optical time-domain reflectometers (OTDRs) are instruments that measure the spatially resolved reflectivity and losses in optical fibers. An OTDR works by injecting a series of optical pulses into the fiber under test and extracts, from the same end of the fiber, light that is scattered (Rayleigh backscatter) or reflected back from points along the fiber. The scattered or reflected light that is gathered back is used to characterize the optical fiber. This is equivalent to the way that an electronic time-domain reflectometer measures reflections caused by changes in the impedance of the cable under test. The strength of the return pulses is measured and integrated as a function of time, and plotted as a function of fiber length.

In conventional approaches, OTDRs (which can include handheld units or benchtop units) are often used to diagnose the fibers (e.g., locating the faulty fiber) after the network experiences failure. Such approaches cannot meet the demand of the current telecommunication networks where network operators are expected to provide services to customers with minimal disruption. It is desirable to be able to detect and locate faults (e.g., fiber cuts) the instant they occur to expedite the service recovery. To facilitate real-time monitoring of fiber performance, in some embodiments, the OTN can include a plurality of OTDR modules embedded in NEs. Each embedded OTDR module can continuously monitor fiber span (s) interfacing with the corresponding NE (e.g., by performing OTDR measurements) . Therefore, any performance degradation of the optical fiber can be timely identified and reported to ensure minimal interruption to services caused by fiber failure.

FIG. 1 presents a diagram illustrating an exemplary optical transport network (OTN) with embedded optical time-domain reflectometer (OTDR) modules, according to one embodiment. In FIG. 1, OTN 100 includes a number of network elements (NEs) , including

terminal NEs

102 and 104, and

inline NEs

106, 108, and 110. Terminal NEs can include electrical layer devices, such as optical transponders, and optical layer devices, such as multiplexers/demultiplexers, terminal optical amplifiers (e.g., Erbium-doped fiber amplifiers (EDFAs) ) , and reconfigurable optical add-drop multiplexers (ROADMs) . Inline NEs can include inline optical amplifiers (e.g., EDFAs) and ROADMs. In some embodiments, each NE in OTN 100 can include an embedded OTDR module. For example,

terminals NEs

102 and 104 include embedded

OTDR modules

112 and 114, respectively. An OTDR module embedded in a terminal NE can be part of a terminal optical amplifier or ROADM module. Similarly,

inline NEs

106, 108, and 110 include embedded

OTDR modules

116, 118, and 120, respectively. An OTDR module embedded in an inline NE can be part of an inline amplifier or ROADM module. The embedded OTDR module can be designed to be compact to fit into the various optical layer devices.

OTN 100 can also include a control-and-management module 122, which can be coupled to each OTDR module. More specifically, each OTDR module can be equipped with a control interface, and control-and-management module 122 can transmit control signals to each OTDR module via the control interface to set the operating parameters of the OTDR module. In addition to receiving control signals, an embedded OTDR can also transmit the measurement results to control-and-management module 122 via the control interface.

Some OTDR modules can work in a unidirectional fashion, meaning that each fiber span has one coupled OTDR module and the OTDR module sends and receives test pulses from one end of the fiber span. The transmitted OTDR test pulses can co-propagate or counter-propagate with optical data signals carried by the fiber span. FIG. 2A illustrates an exemplary unidirectional fiber-monitoring scenario, according to one embodiment. In FIG. 2A, each fiber span is coupled to one OTDR module, and OTDR test pulses co-propagate with data signals in the fiber span. The OTDR module can be configured to monitor the performance of the coupled fiber span. For example, OTDR 202 embedded in NE 204 is only coupled to a fiber span 206, although NE 204 itself is coupled to both fiber spans 206 and 208. During operation, OTDR 202 can be configured to inject test pulses (as shown by the arrow) into fiber span 206 (the test pulses co-propagate with optical data signal carried by fiber span 206) and receive backscattered light from fiber span 206. By analyzing the backscattered light received by OTDR 202 (more specifically, by calibrating the speed of the pulse as it passes down the fiber, measuring time, calculating the pulse position in the fiber and correlating the intensity of the backscattered light with an actual location in the fiber) , one can infer the condition of the fiber, such as detecting loss distributed along the fiber span, fiber cut, or excessive stress resulting from a tight bend. In the example shown in FIG. 2A, NE 204 is an amplifier site and includes an inline amplifier 210. It is also possible that NE 204 is an ROADM site that includes a ROADM module.

Some OTDR modules can work in a bidirectional fashion, meaning that a single fiber span can be coupled to two OTDR modules, with each OTDR module injecting and receiving test pulses into and from one end of the fiber span, and the two OTDR modules work coordinately. FIG. 2B illustrates an exemplary bidirectional fiber-monitoring scenario, according to one embodiment. In FIG. 2B, each NE can include two OTDR modules, one for monitoring performance of a particular (downstream or upstream) fiber span. For example,

OTDRs

212 and 214 embedded in NE 216 can be respectively coupled to upstream fiber span 218 and downstream fiber span 220, both of which are interfacing with NE 216. During operation, OTDR 212 can be configured to inject test pulses into fiber spans 218 (as shown by the arrow next to fiber 218) and receive backscattered light from fiber span 218. Note that, in this scenario, the injected test pulses counter-propagate with data signal in fiber span 218. By analyzing the backscattered lights, one can obtain information regarding conditions of fiber span 218. Similarly, OTDR 214 can be configured to inject test pulses into fiber span 220 (as shown by the adjacent arrow) and receive backscattered light from fiber span 220. On the other hand, each fiber span can be monitored by two OTDR modules, one at each end. In the example shown in FIG. 2B, fiber span 220 is monitored by

OTDR modules

214 and 222, which are respectively embedded in

adjacent NEs

216 and 224. The measurement results from both OTDR modules can be combined (e.g., averaged) to provide more accurate information about fiber span 220. Such a bidirectional operation can be achieved by configuring the downstream OTDR module and the upstream OTDR module to use different wavelengths. Alternatively, one OTDR module can be used in one NE and a switch can be configured to alternate the OTDR module between monitoring the two fiber spans.

FIG. 2C illustrates an exemplary OTDR measurement result, according to one embodiment. In FIG. 2C, OTDR 222 injects test pulses into fiber 224 and receives backscattered light from fiber 224. The intensity of the backscattered light at different fiber locations can be plotted as a curve 226, which is also referred to as the OTDR trace. As one can see from FIG. 2C, the optical power of the received light decreases along the fiber length due to the roundtrip fiber attenuation. Moreover, the various components (e.g., connectors, splicers, etc. ) within fiber 224 can also cause a loss of light power. In addition, each connector can also generate a reflective peak because of Fresnel reflection, with the height of the peak indicating the amount of reflection at the connector site. The end of fiber usually produces a high reflective peak due to Fresnel reflection, as shown in FIG. 2C. By analyzing curve 226, one can obtain vital information regarding the status of fiber 224. For example, the overall slope of curve 226 indicates the attenuation coefficient of the fiber, and an abnormally high attenuation coefficient can indicate problems in fiber 224. If fiber 224 is broken, the peak indicating end of fiber will show up in curve 226 at a location much closer to OTDR 222 than the length of fiber 224. If excessive stress is placed on fiber 224 due to kinking or a tight bend, additional loss (e.g., a loss similar to a splicer loss) will show up in curve 226 at a location having no splicer.

In order for the OTDR measurement to provide accurate results (e.g., curve 226 shown in FIG. 2C) , the operating parameters (e.g., test range, wavelength, pulse width, and the averaging times) of the OTDR need to be carefully selected. The test range is the distance the OTDR will measure. In general, the test range should be at least twice the length of the fiber under test. A longer range can result in a lower spatial resolution, and a shorter range may create distortions in the OTDR trace. The wavelength of the test pulses is often determined by the type of fiber under test. Multimode fibers are used to carry optical signals in the 850 nm and 1300 nm bands; hence, the OTDR measurement for a multimode fiber should be performed at the 850 nm or 1300 nm band. On the other hand, single-mode fibers are used to carry optical signals in the 1300 nm and 1550 nm bands and, hence, the OTDR measurement for a single-mode fiber should be performed at the 1300 nm or 1550 nm band. Note that a shorter wavelength (e.g., 850 or 1300 nm) can generate more backscatter and provide higher signal-to-noise ratio (SNR) . So one may wish to use a shorter wavelength to perform the initial OTDR measurement and then use a longer wavelength to perform additional OTDR measurement on the fiber. Results from both wavelengths can be used to evaluate the fiber condition.

The pulse width is the duration of each test pulse. A longer pulse can provide a larger dynamic range for the OTDR but a lower spatial resolution. The longer pulse also means that a larger amount of optical power will be injected into the fiber and therefore can travel further down the fiber. On the other hand, a shorter pulse can provide higher spatial resolution, but can require a longer time to obtain sufficient SNR due to reduced backscatter.

The data points obtained from a single test pulse may vary in level from one to the next even though there is little change in the pulse they came from. The resulting OTDR measurement result (e.g., the OTDR trace) can be noisy. To improve the SNR, an OTDR can send out thousands of test pulses every second. Every pulse provides a set of data points that are then averaged together with subsequent sets of points in order to improve the SNR of the measurement result. The parameter of averaging times refers to the number of measurements (i.e., pulses) used for averaging to improve the SNR. More averaging times can provide a better SNR but will take a longer time to finish.

Depending on the need (e.g., whether the test is used to characterize fiber or detect fault) and characteristics (e.g., type, length, number of bends, etc. ) of the fiber, different operating parameters are required for generating the optimal OTDR measurement result. In conventional settings, the operating parameters of an OTDR can be manually set by a human operator. However, such approaches cannot meet the demands of the real-time fiber-monitoring system. Automated parameter setting is needed.

In some embodiments, the control-and-management module can be configured to automatically set the operating parameters of each OTDR module. More specifically, an OTDR control-and-management module (which can be part of the network control-and-manage platform for the OTN) can determine, based on the testing scenario as well as the characteristics of the fiber under test, operating parameters of an embedded OTDR module. The OTDR control-and-management module can further send control signals to the embedded OTDR module to set its operating parameters.

In some embodiments, depending on the testing scenario, an embedded OTDR module can be configured to operate in one of the three operating modes: the fiber-characterization mode, the fiber-failure-detection mode, and the fiber-failure-identification mode. More specifically, the parameter space can be divided into three zones, with each zone corresponding to a particular operating mode.

When a fiber is first installed, it is desirable to discover the detailed characteristics of the fiber, including the length of the fiber, the loss coefficient, the various loss-inducing elements (e.g., connectors and splicers) , etc. Such information can be important for network administrators for evaluating the performance of the OTN and managing the power distribution within the OTN. Hence, when the fiber is first installed, the embedded OTDR module (s) coupled to the fiber is configured to operate in the fiber-characterization mode to obtain detailed information regarding the characteristics of the fiber. More specifically, while operating in the fiber-characterization mode, an embedded OTDR module is configured to perform OTDR measurement using a high spatial resolution. To configure the embedded OTDR module, the OTDR control-and-management module can send control signals to the embedded OTDR module to set the pulse width to a relatively small number. To obtain the highest resolution, the pulse width can be set to the lowest possible number, which can be a few nanoseconds. To ensure sufficient SNR, the averaging times will be set to a higher number (e.g., hundreds of times) . Note that, while operating in the fiber-characterization mode, the measurement speed is not critical. Therefore, the particular zone in the parameter space corresponding to the fiber-characterization mode can have smaller pulse widths but larger averaging times.

After the fiber is put into service, the embedded OTDR can be placed in the fiber-failure-detection mode in order to detect fault in the fiber as soon as it happens. In this operating mode, the measurement speed is the main concern, meaning that a small number of averaging times is desired. Consequently, the spatial resolution will be lower (i.e., longer pulses will be used) . When placing the embedded OTDR in the fiber-failure-detection mode, the OTDR control-and-management module can send control signals to set the pulse width to a relatively large value (e.g., tens or hundreds of nanoseconds) and the averaging times to a smaller number (e.g., a few times) . In general, the pulse width used in the fiber-failure-detection mode can be significantly larger (e.g., by a few orders of magnitude) than the pulse width used in the fiber-characterization mode. On the other hand, the number of averaging times used in the fiber-failure-detection mode can be significantly smaller (e.g., by a few orders of magnitude) than that used in the fiber-characterization mode. The particular zone in the parameter space corresponding to the fiber-failure-detection mode can have larger pulse widths but fewer averaging times. In one example, while operating in the fiber-failure-detection mode, the embedded OTDR can be configured to simply measure the end-to-end loss of a coupled fiber by injecting a single long pulse into the fiber and no averaging is needed.

When the OTDR measurement from a particular embedded OTDR module indicates fault (e.g., excessive fiber loss or a fiber cut is detected) , the OTDR control-and-management module can be triggered to send control signals to the particular embedded OTDR module to switch its operating mode from the fiber-failure-detection mode to the fiber-failure-identification mode in order to obtain more detailed location information associated with the fault, thus facilitating the network operator to conduct fiber-repair operations at the identified fault location. To be able to identify the location of the fault in a timely manner, the OTDR module needs to take into consideration both the spatial resolution and the measurement speed. In other words, the pulse width cannot be too large to ensure sufficient spatial resolution and cannot be too small to ensure that a moderate number of averaging times is needed. When switching the embedded OTDR to operate in the fiber-failure-identification mode, the OTDR control-and-management module can send control signals to set the pulse width as well as the averaging times to values that are between the settings for the fiber-characterization mode and the fiber-failure-detection mode. That is, the pulse width is larger than what is used in the fiber-characterization mode but smaller than what is used in the fiber-failure-detection mode. On the other hand, the averaging times are less than what is used in the fiber-characterization mode but more than what is used in the fiber-failure-detection mode. Consequently, the particular zone in the parameter space corresponding to the fiber-failure-identification mode can be located between the zones corresponding to the fiber-characterization mode and the fiber-failure-detection mode. This can ensure the fast and accurate identification of the fault location.

In addition to the different operating modes, the operating parameters of an embedded OTDR can also depend on the characteristics of the fiber coupled to the OTDR. For example, fibers with different lengths require different settings for the test range. Although the length of a typical fiber span can be between 80 and 100 kilometers, depending on the practical scenario, shorter or longer spans of fibers can be possible. Fibers having different attenuation parameters may require different pulse widths and/or averaging times. To provide optimal settings for each OTDR in every operating mode, the OTDR control-and-management module can obtain the optimal operating parameters for each embedded OTDR module in each operating mode and store those optimal operating parameters in a lookup table indexed by the identifiers of the embedded OTDR modules. When an embedded OTDR module needs to have its parameters set (e.g., when it switches from one operating mode to a different operating mode) , the OTDR control-and-management module can perform the table lookup to obtain the optimal parameters for the embedded OTDR and send control signals to the embedded OTDR to set its operating parameters accordingly. In addition to the OTDR operating parameters, various data-processing parameters (e.g., filter parameters or particular algorithms used) used by the OTDR control-and-management module to process the raw OTDR data can also be specific to the fiber under test.

Various mechanisms can be used to determine the optimal OTDR measurement and data-processing parameters for each fiber span. In some embodiments, those parameters can be obtained through computation. More specifically, given known fiber characteristics (e.g., length, attenuation coefficient, etc. ) , one may compute optimal or sub-optimal OTDR measurement and/or data-processing parameters based on certain linear or non-linear relationships between the fiber characteristics and the parameters. In some embodiments, those parameters can be obtained through experimentation. For example, after a fiber is first installed, the OTDR control-and-management module can configure the coupled OTDR to scan the parameter space to obtain the optimal operating parameters of the OTDR in all three different modes. The data-processing parameters can be obtained using similar approaches.

FIG. 3 presents a flowchart illustrating an exemplary process for real-time fiber-performance monitoring, according to one embodiment. During operation, a fiber span is installed within an OTN and is coupled to an OTDR module embedded in an NE interfacing with the fiber span (operation 302) . The fiber span can be a newly expanded portion of the OTN or a replacement of a faulty fiber span. The NE can be a terminal NE or an inline NE, depending on its location of the fiber span in the OTN.

Prior to putting the fiber span into service, the system determines the optimal OTDR measurement and data-processing parameters (operation 304) and stores the determined parameters in a lookup table (operation 306) . As discussed previously, the optimal parameters can be determined by performing computation or scanning the parameter space. The optimal algorithms used for processing raw OTDR data can be determined based on previous experience. The lookup table can be indexed using the unique identifiers assigned to the individual OTDR modules. If an OTDR module is bidirectional, two sets of parameters will be stored in the table, one for each module at one end of a fiber span. The lookup table can be maintained by the OTDR control-and-management module, which can reside on the control-and-management platform of the OTN.

The OTDR control-and-management module can also place the OTDR module (s) coupled to the fiber span in a fiber-characterization mode to obtain detailed characteristics of the fiber (operation 308) and store the fiber characteristics in a fiber database (operation 310) . In some embodiments, the operation for determining the optimal parameters and the operation for determining the fiber characteristics can be performed in an iterative manner. In other words, the optimal parameters determined in operation 304 can be used in operation 308 to set the operating parameters of the OTDR, and fiber characteristics obtained in operation 308 can be used to update the optimal parameters determined in operation 304.

Subsequently, the fiber is put into normal service and the OTDR control-and-management module can also place the OTDR module (s) coupled to the fiber span in a fiber-failure-detection mode to continuously monitor the performance (more particularly the overall loss) of the fiber (operation 312) . Based on the OTDR measurement result, the OTDR control-and-management module can determine if fiber fault is detected (operation 314) . In some embodiments, the system detects fault if the loss on the fiber exceeds a predetermined threshold or if a fiber cut is detected (e.g., the end of fiber is closer to the OTDR than the fiber length) .

If no fault is detected, the OTDR continues to monitor the fiber (operation 312) . If fault is detected, the OTDR control-and-management module can switch the operation mode of the OTDR module to fiber-failure-identification mode to identify the exact location of the fault (operation 316) . For example, if the fiber is cut, while operating in the fiber-failure-identification mode, the OTDR can determine the exact location of the fiber cut. In addition, if excessive stress (e.g., kinks or a tight bend) causes abnormal loss in the fiber, the OTDR can determine the exact location where the stress is occurring. Based on the identified location, the network operator can perform necessary repair on the faulty fiber (operation 318) . Note that the fiber characteristics may change after the fiber is repaired. Therefore, the optimal operating parameters will need to be re-calibrated (operation 304) .

FIG. 4 illustrates a block diagram of an exemplary embedded OTDR module, according to one embodiment. Embedded OTDR module 400 can include a control interface 402, a mode-configuration unit 404, a pulse generator 406, a transmitter 408, a receiver 410, and a signal-processing unit 412.

Control interface 402 allows a centralized OTDR control-and-management module to send control signals to embedded OTDR module 400. The control signals can be used to place OTDR module 400 in one of the three operating modes. In one embodiment, the control signals can further include various OTDR measurement parameters. Moreover, the OTDR measurement results (e.g., raw data) can also be sent to the centralized OTDR control-and-management module via control interface 402. Mode-configuration unit 404 can configure OTDR module 400 to operate in one of the three operating modes based on the received control signals. In one embodiment, mode-configuration unit 404 can set the various operating parameters of OTDR module 400. Standard techniques of communicating the control-and-management signals in an OTN can be used for communication between the centralized OTDR control-and-management module and the OTDR modules. For example, optical supervisory channel (OSC) signals can be used to carry the control signals as well as the OTDR measurement results.

Pulse generator 406 can be configured to generate test pulses. The width of the test pulses is determined based on the parameters provided by the centralized OTDR control-and-management module. Transmitter module 408 can transmit the test pulses to the fiber under test. In some embodiments, transmitter module 408 can include lasers of different wavelengths. Receiver module 410 can receive the backscattered light from the fiber under test. Signal-processing unit 412 can process the raw OTDR measurement data, including averaging the outputs of receiver 410 over a plurality of test pulses, performing fiber-loss calculations, and identifying reflection points. The number of averaging times is determined based on parameters provided by the centralized OTDR control-and-management module. The output of signal-processing unit 412 can be sent to the centralized OTDR control-and-management module via control interface 402.

FIG. 5 illustrates a block diagram of an exemplary centralized OTDR control-and-management module, according to one embodiment. Centralized OTDR control-and-management module 500 can include a control interface 502, an OTDR mode-determination unit 504, a data-processing unit 506, an OTDR parameter-optimization and fiber-characterization unit 508, a fiber-fault-detection unit 510, a fiber-fault-identification unit 512, a lookup table 514, and a fiber database 516.

Control interface 502 allows centralized OTDR control-and-management module 500 to interface with a plurality of OTDR modules embedded in a plurality of NEs within an OTN. Centralized OTDR control-and-management module 500 can send control signals to each embedded OTDR to configure its operating mode and setting its operating parameters. Moreover, centralized OTDR control-and-management module 500 can receive OTDR measurement results from the OTDR modules via control interface 502.

OTDR mode-determination unit 504 can determine the operating mode of an embedded OTDR based on the testing needs. If the OTDR is measuring a newly installed and not yet in-service fiber, OTDR mode-determination unit 504 can determine that the OTDR should be placed in the fiber-characterization mode. If the OTDR is monitoring a fiber carrying data, the OTDR should be placed in the fiber-failure-detection mode. If a fault is detected in the fiber, the OTDR should be placed in the fiber-failure-identification mode.

Data-processing unit 506 can be configured to process and analyze the OTDR data sent from the OTDR modules embedded in the various NEs in the OTN. The data can be raw data from OTDR modules or pre-processed data from OTDR modules. Pre-processing raw data at the OTDR module can reduce the amount of data sent from OTDR modules to the OTDR control-and-management module. On the other hand, to reduce the size or energy consumption of the OTDR module, it is possible that the OTDR module does not perform certain data-processing tasks (e.g., pre-processing the raw data) . By analyzing the OTDR data provided by a particular OTDR module, information regarding the fiber being measured by that particular OTDR can be determined, including the characteristics of the fiber or fault status of the fiber.

OTDR parameter-optimization and fiber-characterization unit 508 determines the optimal measurement and data-processing parameters for individual OTDR modules as well as the characteristics of the fibers under test. The optimal parameters can be determined based on either computation or measurement results. Fiber-fault-detection unit 510 can detect fault in a fiber based on the output of data-processing unit 506. For example, a sudden power loss can indicate fault. Similarly, fiber-fault-identification unit 512 can identify the location of the fault in a fiber based on the output of data-processing unit 506. For example, the location of a fiber cut can be identified based on the position of the end-of-fiber reflection.

Lookup table 514 stores the optimal OTDR measurement and data-processing parameters for each embedded OTDR module. In some embodiments, each embedded OTDR module can be assigned a unique identifier and lookup table 514 can be indexed using these identifiers. In some embodiments, each direction of a bidirectional OTDR module can be assigned different identifiers. Fiber database 516 can store the measured characteristics of each fiber span.

FIG. 6 illustrates an exemplary computer system, according to one embodiment. Computer system 600 includes a processor 602, a memory 604, and a storage device 606. Furthermore, computer system 600 can be coupled to peripheral input/output (I/O) user devices 610, e.g., a display device 612, a keyboard 614, and a pointing device 616. Storage device 606 can store an operating system 618, a real-time fiber-monitoring system 620, and data 640.

Real-time fiber-monitoring system 620 can include instructions, which when executed by computer system 600, can cause computer system 600 or processor 602 to perform methods and/or processes described in this disclosure. Specifically, real-time fiber-monitoring system 620 can include instructions for operating a control interface (control-interface module 622) , instructions for determining the operating mode of an embedded OTDR (OTDR mode-determination module 624) , instructions for processing OTDR measurement results (OTDR data-processing module 626) , instructions for determining the optimal measurement and data-processing parameters and fiber characteristics (OTDR parameter-optimization and fiber-characterization module 628) , instructions for detecting fault in a fiber based on processed OTDR data (fiber-fault-detection module 630) , and instructions for identifying the location of a detected fault (fiber-fault-identification module 632) .

In general, embodiments of the present application provide a solution for accurate real-time monitoring of fiber performance. By embedding compact OTDR modules in individual NEs of an OTN, the disclosed embodiments allow the OTDR modules to continuously monitor the performance of data-carrying fibers. A centralized OTDR control-and-management module residing on the network control-and-management platform can remotely configure the individual OTDRs to ensure that those OTDRs are operating in desired modes. By storing the optimal operating parameters of the individual OTDR modules in a lookup table, the centralized OTDR control-and-management module can ensure fast and accurate OTDR measurement, thus facilitating rapid fiber fault diagnosis and repair. Note that the operating modes of the OTDR modules are not limited to the three modes disclosed in this application. In practice, the OTDR module can have fewer or more operating modes.

The methods and processes described in the detailed description section can be embodied as code and/or data, which can be stored in a computer-readable storage medium as described above. When a computer system reads and executes the code and/or data stored on the computer-readable storage medium, the computer system performs the methods and processes embodied as data structures and code and stored within the computer-readable storage medium.

Furthermore, the methods and processes described above can be implemented in digital electronic circuitry; or in computer software, firmware or hardware. The hardware modules or apparatus can include, but are not limited to, application-specific integrated circuit (ASIC) chips, field-programmable gate arrays (FPGAs) , dedicated or shared processors that execute a particular software module or a piece of code at a particular time, and other programmable-logic devices now known or later developed. When the hardware modules or apparatus are activated, they perform the methods and processes included within them.

The techniques described above can be implemented using one or more computer program products. Programmable processors and computers can be included in or packaged as mobile devices. The processes and logic flows can be performed by one or more programmable processors or by one or more programmable logic circuitries. General and special purpose computing devices and storage devices can be interconnected through communication networks.

The foregoing descriptions of various embodiments have been presented only for purposes of illustration and description. They are not intended to be exhaustive or to limit the present invention to the forms disclosed. Accordingly, many modifications and variations will be apparent to practitioners skilled in the art. Additionally, the above disclosure is not intended to limit the present invention.

Claims

A system for monitoring performance of fibers in an optical transport network, comprising:

a plurality of optical time-domain reflectometer (OTDR) modules, wherein a respective OTDR module is embedded in a network element of the optical transport network and is coupled to an optical fiber span; and

an OTDR control-and-management module coupled to the plurality of OTDR modules;

wherein the OTDR control-and-management module configures the respective OTDR module to monitor, in real time, performance of the coupled optical fiber span, which comprises detecting a fault in the coupled optical fiber span and identifying a location of the detected fault.
The system of claim 1, wherein the OTDR control-and-management module resides on a network control-and-management platform of the optical transport network.
The system of claim 1, wherein the OTDR control-and-management module configures the respective OTDR module to operate in one of:

a fiber-characterization mode for characterizing the coupled optical fiber span,

a fiber-failure-detection mode for detecting a fault in the coupled optical fiber span, and

a fiber-failure-identification mode for identifying a location of the detected fault.
The system of claim 3, wherein:

while operating in the fiber-characterization mode, the respective OTDR module is configured to inject optical pulses having a first pulse width into the coupled optical fiber span;

while operating in the fiber-failure-detection mode, the respective OTDR module is configured to inject optical pulses having a second pulse width into the coupled optical fiber span, the second pulse width being greater than the first pulse width; and

while operating in the fiber-failure-identification mode, the respective OTDR module is configured to inject optical pulses having a third pulse width into the coupled optical fiber span, the third pulse width being greater than the first pulse width but smaller than the second pulse width.
The system of claim 3, wherein:

while operating in the fiber-characterization mode, the respective OTDR module is configured to generate an output by averaging a first number of measurements;

while operating in the fiber-failure-detection mode, the respective OTDR module is configured to generate an output by averaging a second number of measurements, the second number being less than the first number; and

while operating in the fiber-failure-identification mode, the respective OTDR module is configured to generate an output by averaging a third number of measurements, the third number being less than the first number but greater than the second number.
The system of claim 3, wherein the OTDR control-and-management module configures the respective OTDR module to operate in the fiber-characterization mode after an initial installment of the coupled fiber span and before the coupled fiber span is put into service.
The system of claim 6, wherein the OTDR control-and-management module is configured to:

receive OTDR measurement results from the respective OTDR module while the respective OTDR module operates in the fiber-characterization mode;

extract information associated with characteristics of the coupled fiber span based on the received OTDR measurement results; and

store the information associated with characteristics of the coupled fiber span in a fiber database.
The system of claim 3, wherein the OTDR control-and-management module configures the respective OTDR module to operate in the fiber-failure-detection mode after the coupled fiber span is put into service.
The system of claim 3, wherein the OTDR control-and-management module switches the respective OTDR module from operating in the fiber-failure-detection mode to operating in the fiber-failure-identification mode in response to detecting a fault in the coupled fiber span.
The system of claim 1, wherein the OTDR control-and-management module is configured to determine optimal operating parameters of the respective OTDR module for operating in different modes.
The system of claim 10, wherein the OTDR control-and-management module is configured to store the determined optimal operating parameters in a lookup table, and wherein the lookup table is indexed using unique identifiers assigned to the plurality of OTDR modules.
The system of claim 1, wherein the optical fiber span is coupled to an additional OTDR module embedded in an adjacent network element.
A method for monitoring performance of fibers in an optical transport network, comprising:

embedding a plurality of optical time-domain reflectometer (OTDR) modules in a plurality of network elements of the optical transport network, wherein a respective OTDR module is embedded in a network element and is coupled to a fiber span; and

configuring, by an OTDR control-and-management module, the plurality of OTDR modules, which comprises configuring the respective OTDR module to monitor, in real time, performance of the coupled optical fiber span, wherein monitoring the performance comprises detecting a fault in the coupled optical fiber span and identifying a location of the detected fault.
The method of claim 13, wherein the OTDR control-and-management module resides on a network control-and-management platform of the optical transport network.
The method of claim 13, wherein the respective OTDR module is configured to operate in one of:

a fiber-characterization mode for characterizing the coupled optical fiber span,

a fiber-failure-detection mode for detecting a fault in the coupled optical fiber span, and

a fiber-failure-identification mode for identifying a location of the detected fault.
The method of claim 15, wherein:

while operating in the fiber-characterization mode, the respective OTDR module is configured to inject optical pulses having a first pulse width into the coupled optical fiber span;

while operating in the fiber-failure-detection mode, the respective OTDR module is configured to inject optical pulses having a second pulse width into the coupled optical fiber , the second pulse width being greater than the first pulse width; and

while operating in the fiber-failure-identification mode, the respective OTDR module is configured to inject optical pulses having a third pulse width into the coupled optical fiber span, the third pulse width being greater than the first pulse width but smaller than the second pulse width.
The method of claim 15, wherein:

while operating in the fiber-characterization mode, the respective OTDR module is configured to generate an output by averaging a first number of measurements;

while operating in the fiber-failure-detection mode, the respective OTDR module is configured to generate an output by averaging a second number of measurements, the second number being less than the first number; and

while operating in the fiber-failure-identification mode, the respective OTDR module is configured to generate an output by averaging a third number of measurements, the third number being less than the first number but greater than the second number.
The method of claim 15, wherein configuring the respective OTDR module comprises configuring the respective OTDR module to operate in the fiber-characterization mode after an initial installment of the coupled fiber span and before the coupled fiber span is put into service.
The method of claim 18, further comprising:

receiving OTDR measurement results from the respective OTDR module while the respective OTDR module operates in the fiber-characterization mode;

extracting information associated with characteristics of the coupled fiber span based on the received OTDR measurement results; and

storing the information associated with characteristics of the coupled fiber span in a fiber database.
The method of claim 15, wherein configuring the respective OTDR module comprises configuring the respective OTDR module to operate in the fiber-failure-detection mode after the coupled fiber span is put into service.
The method of claim 15, further comprising switching the respective OTDR module from operating in the fiber-failure-detection mode to operating in the fiber-failure-identification mode in response to detecting a fault in the coupled fiber span.
The method of claim 13, further comprising determining optimal operating parameters of the respective OTDR module for operating in different modes.
The method of claim 20, further comprising storing the determined optimal operating parameters in a lookup table, wherein the lookup table is indexed using unique identifiers assigned to the plurality of OTDR modules.
The method of claim 13, further comprising embedding an additional OTDR module in the network element, wherein the additional OTDR module is coupled to a second fiber span.