Power transient event detection in optical communication systems

Abstract

A power transient event detection system includes a first set of photodetectors (PDs) located within a first node of an optical communication system. Each PD in the first group of PDs has a different response time. The system also includes an output signal monitor that monitors a signal output from each PD of the PDs in the first group and records power transient event detection information. The transient event characterizer identifies, based on the recorded event detection information, a subset of the PDs in the first set where the power transient event was observed, and determines a duration of the power transient event based on an amount of time that the signal output meets a low signal criterion for at least one PD in the subset.

Description

Background Art

[0001] Currently, optical communication networks provide a substantial amount of infrastructure that facilitates long - distance communication for telephone signals, cable television signals, and Internet communication. These networks convert electrical signals into optical pulses and transmit the light along optical fibers that physically connect communication endpoints.

[0002] In an optical communication system, various environmental factors can cause power transient events, which are characterized by a temporary reduction in signal power and can affect communication. For example, vibrations caused by construction work can introduce noise to nearby optical fiber lines. Signal noise can also be introduced by direct physical forces, such as tree roots hitting underground cables, wind, or other inclement weather. In all of these scenarios, the optical signal may become indistinguishable, resulting in a link outage (communication interruption) and / or data loss.

[0003] When a power transient event occurs, effective troubleshooting depends on the ability to quickly identify the characteristics of the power transient event and use device information to identify appropriate corrective actions. Specifically, the duration of the power transient event can provide important clues that allow identification of the most likely cause of the power transient event. Additionally, being able to identify the physical source (location) of the power transient event is also important so that, if necessary, personnel can be deployed to perform line maintenance, such as improving protection of the line with respect to the surrounding environment or replacing a damaged optical fiber segment. Summary of the Invention

[0004] According to one implementation, a power transient event detection system includes a first set of photodetectors (PDs) located within a first node in an optical communication system. Each PD within the first set of PDs has a different response time. The system further includes an output signal monitor configured to monitor the signal output from each PD in the first set, and a transient event characterizer that, based on the monitored signal output for each PD, identifies a subset of the PDs in the first set where a power transient event is observed. The transient event characterizer also determines the duration of the power transient event based on the amount of time the signal output meets a low - signal criterion for at least one PD in the subset.

[0005] This Summary of the Invention is intended to provide an introduction to some concepts in a simplified form that will be further described in the Detailed Description below. This Summary of the Invention is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to limit the scope of the claimed subject matter.

[0006] Other implementations are also described and recited herein. Brief Description of the Drawings

[0007] Figure 1Illustrates aspects of an optical communication network implementing a power transient detection system for determining the location and duration of short-term power transient events.

[0008] Figure 2 Illustrates an example plot of the optoelectronic detector signal outputs of a set of optoelectronic detectors with variable response times located within a node of an optical communication system.

[0009] Figure 3 Illustrates Figure 2 a modified version of the plot in, where some data has been removed to clarify certain concepts.

[0010] Figure 4 Illustrates a trend plot that depicts the known monotonic relationships among the response times, alarm interval times, and event durations of the PDs in a PD group.

[0011] Figure 5 Illustrates aspects of an exemplary technique for determining the physical source of a power transient event along an optical fiber cable in a communication network.

[0012] Figure 6 Illustrates an example operation for determining the duration of a short-term power transient event within an optical communication network.

[0013] Figure 7 Illustrates an example schematic diagram of a processing device suitable for implementing aspects of the disclosed technology. Detailed Description

[0014] A particular challenge in the operation of an optical communication network is how to effectively diagnose power transient events with a duration of less than a few minutes. In many cases, noise introduced by the external environment may attenuate the optical signal to a sufficient extent to cause the link to be temporarily interrupted (such as for a few seconds). Such events may affect large portions of the network and impose a burden on customers using the network, such as video stream interruptions, mobile phone call interruptions, and point-to-point Internet connection interruptions (which must be re-established once the network link is restored).

[0015] Existing diagnostic tools generally cannot effectively diagnose the characteristics of these shorter power transient events. One existing diagnostic method provides injecting a signal at a network node using an optical time domain reflectometer (OTDR) and measuring the characteristics of the reflected signal, thereby effectively mapping how the signal varies along the optical fiber with distance. However, a single OTDR signal trace may take several minutes to complete, and if a localized power transient event is shorter than the entire duration of the signal trace, this method generally cannot detect the event.

[0016] The techniques disclosed herein provide tools and techniques for effectively characterizing short-term power transient events in optical communication systems. As used herein, a power transient event refers to a signal interruption that causes a temporary reduction in the signal power received at a particular system node. The techniques disclosed herein are designed to detect short-term power transient events, meaning events that typically last less than one minute, such as on the order of seconds to fractions of a second. Although these short-term power transient events are brief, they can cause large-scale communication outages.

[0017] According to one implementation, the systems and methods disclosed herein facilitate accurate measurement of the duration of short-term power transient events. This ability to accurately measure allows an operator to quickly determine the most likely cause of such an event. For example, sub-second events may indicate vibrations caused by a nearby construction project, while multi-second events (e.g., 2 - 3 seconds) are more likely due to strong winds.

[0018] According to another implementation, the disclosed systems and methods facilitate accurate identification of the physical source of a short-term power transient event along the length of an optical fiber, between the network nodes that detect the event. Accurately locating the physical source of a short-term power transient event can also help an operator quickly determine the cause of the event transient, such as by allowing the operator to evaluate publicly available information related to the conditions and / or characteristics of the identified location that may affect the optical line. Similarly, the ability to accurately locate the position of a short-term power transient event permits a team maintaining the optical fiber network to quickly deploy maintenance personnel to the identified location.

[0019] Figure 1 Aspects of an optical communication network 100 that implements a power transient detection system 103 for determining the location and duration of short-term power transient events are illustrated. The optical communication network 100 includes a plurality of nodes (e.g., Node A and Node B) interconnected by an optical fiber 108. As used herein, a node refers to an optical line system. An optical line system can have different forms, such as an optical line terminal (OLT) and an optical line amplifier (OLA). An OLT is typically located at a terminal where a transmitter and a receiver are located (e.g., at a source endpoint and a destination endpoint where data is transmitted), and typically includes a frequency multiplexer / demultiplexer, an optical amplifier, an optical channel monitor (OCM), an optical service channel (OSC), and other optical time domain reflectometer (OTDR) components. In contrast to an OLT, an OLA is located at a position between terminals (data endpoints). In various optical networks, any number of OLAs may exist along a path between a pair of endpoints. For example, each pair of OLAs may be separated by dozens of kilometers to slightly more than one hundred kilometers. An OLA typically includes an optical amplifier, an OSC, and an OTDR.

[0020] The power transient detection system 103 includes groups of photodetectors (PDs) (e.g., PD groups 106 and 114), each group being positioned at a respective different system node for collecting data related to the signal quality observable at that node. In addition, the power transient detection system 103 includes at least an output signal monitor 110 and a transient event characterizer 112, which may be understood to be composed of software, or a collection of hardware and software, with the software elements stored in a memory and executable by one or more system processors. The output signal monitor 110 records power transient event detection information observed by respective PDs in the PD group 106, and the transient event characterizer 112 analyzes the recorded power transient event detection information to identify the characteristics of each observed short-term power transient event.

[0021] In Figure 1 , the functionality of the power transient detection system 103 is shown and described primarily with respect to node A. However, it should be understood that the optical communication network 100 may include additional PD groups at each of its multiple system nodes, with characteristics similar to those of the PD groups 106 and 114. Similarly, additional instances of the output signal monitor 110 and the transient event characterizer 112 may be implemented at other system locations to support the functionality at each of the multiple other system nodes in the same or similar manner as described below with respect to node A. The software elements for analyzing the data collected at each node may be networked for peer-to-peer communication to facilitate data analysis of the data sets collected from multiple nodes. In some implementations, instances of the transient event characterizer 112 are executed in association with each different PD group 102. In other implementations, the transient event characterizer 112 operates centrally, i.e., a single software component executes to determine the characteristics of event transients located at two or more nodes of the optical communication network 100.

[0022] In Figure 1 the photodetector (PD) group 106 is physically positioned within node A of the optical communication network 100. The PD group 106 includes a plurality of photodetectors (PDs), sometimes also referred to as optical sensors, which measure the intensity of incident light. Each PD in the PD group 106 has a different response time. As used herein, the response time of a PD refers to the time it takes for the photocurrent generated by the PD to rise to at least a certain threshold percentage (e.g., 63.2%) of its final value or steady-state value after a long time. For example, the PD group 106 is shown as including five PDs (e.g., PD1, PD2, PD3, PD4, and PD5) with respective response times of 1 microsecond (μs), 10 μs, 100 μs, 1 millisecond (ms), and 10 ms. In the illustrated example, the response times form a logarithmic distribution (e.g., 10 -6 10 -5 10-4 , 10 -3 and 10 -2 ). Although not necessary to implement the disclosed technology, using a PD group with a log - distributed PD response time can facilitate capturing a large number of transient events with capture durations roughly between the fastest PD response time and the slowest PD response time. In Figure 1 , the PD response times and the number of PDs in PD group 106 are intended to be exemplary, as various implementations can include groups with more or fewer PDs, whose response times span ranges different from the ranges shown.

[0023] PD group 106 includes circuitry (not shown) where the PDs are positioned in parallel with each other to ensure that each PD in PD group 106 measures the same portion of the optical signal simultaneously. The output signal monitor 110 monitors the signal output of the PDs in PD group 106, such as by continuously sampling the output signals of each PD in PD group 106. When a power transient event occurs, the event can be detected in the output signals of a subset of PDs whose response times are less than or approximately equal to the duration of the event. For example, a 2 - microsecond event can be detected by PD1 with a response time of 1 microsecond, but is less likely to be detected by PDs whose response times are significantly greater than the duration of the event (e.g., 1.3 times or greater), because the event time is not long enough to trigger a response in these photodetectors.

[0024] In one implementation, whenever the signal output of a given PD meets a "low - signal criterion" (e.g., whenever the signal output (power) drops below a predefined threshold), the output signal monitor 110 generates an alert for that given PD. When the signal output of the given PD no longer meets the low - signal criterion (e.g., when the signal output rises above the predefined threshold), the output signal monitor 110 clears the alert for that given PD at a subsequent time point.

[0025] In the following description, if a short - term power transient event causes the output signal monitor 110 to trigger an alert for a given PD and then clears the alert within a threshold time period (e.g., less than one minute), the event is said to be observed or detected by the given PD. Since the response times of the PDs in PD group 106 vary, a given event may be detected on less than all of the PDs in PD group 106. Additionally, the subset of PDs that detect a particular event may detect the event in different ways, i.e., there may be a difference in the elapsed time between the alert trigger and alert clearance on each PD that detects the event. This elapsed time during which the signal output meets the "low - signal criterion" is referred to below as the "alert interval time".

[0026] As mentioned above, each short-term power transient event is detectable in the output signals of the PDs in PD group 106 whose response time is less than or approximately equal to the duration of the event. When the response time of a PD is much less than the event duration (e.g., about 1 / 3 or less of the event duration), the alarm interval time of that PD will accurately map to the event duration (e.g., when the PD response time is less than 1 / 3 of the transient duration, the error is less than 1.7%). However, as the response time of the PD approaches the event duration, more errors are introduced in the measurement, resulting in a deviation between the alarm interval time for the PD and the actual event duration.

[0027] The transient event characterizer 112 relies on the relationship between the PD response time and the PD alarm interval time to perform operations to determine the duration of each detected power transient event. Specifically, the transient event characterizer 112 identifies the subset of PDs that have observed a power transient event, and then performs further operations to determine which of these PDs (if any) have characteristics that meet an "accuracy criterion", which will be discussed in more detail below with respect to Figure 2 If the characteristics of a PD meet the accuracy criterion, the alarm interval time of the PD will be a reliable indicator of the event duration. If none of the PDs in PD group 106 have characteristics that meet the accuracy criterion, the transient event characterizer 112 can perform further analysis to estimate the event duration based on the alarm interval times of the PDs that detected the event. This analysis will be discussed at least with respect to Figure 5 below.

[0028] Figure 1 Illustrated is an exemplary data output generated by the output signal monitor 110 and the transient event characterizer 112 for a short-term power transient event that lasts 150 microseconds. In this example, the output signal monitor 110 creates an event detection log file 118 and records information indicating which PDs in PD group 106 detected the event. Although Figure 1 not explicitly shown, the event detection log file 118 can also include the specific alarm trigger and alarm clear times of the PDs that detected the event. In the illustrated example, PD4 and PD5 did not detect the 150-microsecond event because their respective response times were much longer than the event duration; however, PD1, PD2, and PD3 detected the event because these PDs had response times much shorter than the power transient event.

[0029] The transient event characterizer 112 compares the alarm interval times of three PDs that detected the event and extracts an estimate of the event duration - for example, 150 milliseconds - based on this comparison and the known correlations between the alarm interval times, response times, and event durations. Extracting an estimate of the event duration may involve using one of the alarm interval times as the event duration or, alternatively, performing calculations to estimate an event duration different from the recorded alarm interval times, such as when all of the PDs that detected the event have response times that are too close to the event duration to be reliable indicators of the event duration.

[0030] In some implementations, the transient event characterizer 112 performs further operations to identify the location of the observed power transient event. In the power transient detection system 103, this is accomplished by determining the delay in the detection of the power transient event on the same PDs within two nodes on either side of the location 120. In Figure 1 this, the location 120 represents the physical origin of the power transient event (e.g., the location where an environmental force physically acts on the optical fiber 108 and generates signal noise). When a power transient event occurs at the location 120 between node A and node B, a subset of the PDs in the PD group 106 and the corresponding subset of PDs in the PD group 114 with the same characteristics detect the event. For example, if PD1, PD2, and PD3 in the PD group 106 at node A observe the event, then these same PDs (with the same response times) in the PD group 114 at node B also observe the event. However, for each pair of PDs with the same response times at opposite ends of the optical fiber 108, there is a time offset in the observed alarm trigger and clear times, which varies based on the location 120 of the event transient.

[0031] For example, if the location 120 is exactly at the midpoint between node A and node B, the observed offset in the alarm trigger and clear times is zero, which means that the alarms are triggered and / or cleared simultaneously on the same PDs in different groups (e.g., on PD2 in the PD group 106 and on PD2 in the PD group 104). However, if the location 120 where the transient event occurs is closer to node B than to node A, then the event is detected faster in the PD group 114 than in the PD group 106. In this case, the difference between the alarm trigger and / or clear times on the same PDs in different groups represents the additional optical travel time required for the signal to travel the additional distance to node A (relative to node B). Therefore, based on this difference and the known speed of light, the location 120 of the power transient event can be identified (e.g., "66 kilometers from node A"). In Figure 1In this case, the transient event characterizer 112 generates an output 122 including an event duration and an event location to the display of the user equipment, thereby allowing the technician of the optical communication network 100 to quickly diagnose the cause of the transient event and, where applicable, deploy maintenance personnel to location 120. It should be noted that some implementations of the disclosed technology may provide for determining either the event duration or the location, but not both characteristics simultaneously.

[0032] Figure 2 An example plot 200 of the PD signal outputs of a set of PDs with variable response times located within a node of an optical communication system is illustrated. Plot 200 illustrates how the signal output on each PD changes during a short-term power transient event when the set of PDs is positioned as shown and described with respect to Figure 1 the optical communication network 100 in. In one implementation, plot 200 is generated by an output signal monitor (such as Figure 1 the output signal monitor 110 in). The y-axis of the plot shows the PD signal output in arbitrary units (a.u.), where "1" represents a full-strength signal and "0" represents no signal at all. The y-axis shows time (also in arbitrary units), increasing from left to right. The actual duration of the power transient event is shown as a solid line - for example, in the form of a square wave, with a start time of 1000 and an end time of 1001.

[0033] Plot 200 illustrates how each of the nine PDs in the set of PDs with different response times observes the power transient event. Each PD in the set of PDs is represented by a dashed line with a different style, and the legend 202 illustrates this mapping relationship. Specifically, legend 202 represents each different PD by the ratio of the response time (τ pd ) of each different PD to the duration (τ d ) of the power transient event. It should be noted that since the event duration τ d of the illustrated event is fixed, this ratio (τ pd / τ d ) increases proportionally with the PD response time. In legend 202, the PD response times increase from the top to the bottom of the page (the ratio 0.1 corresponds to the fastest PD response time, and the ratio 1000 corresponds to the slowest PD response time).

[0034] Plot 200 also includes a horizontal line representing a predefined threshold 204. When the power output of a given PD drops below the predefined threshold 204, it is said that the PD has detected the "start" of a power transient event. This is also referred to herein as the "alarm trigger time". When the power output of a given PD subsequently rises above the predefined threshold 204, it is said that the PD has detected the "end" of a power transient event. This is also referred to herein as the "alarm clear time". For each PD that detects an event, the alarm interval time is defined by the time between alarm trigger and alarm clear.

[0035] In the illustrated example, the power transient event is detected by a subset 206 of the PDs with the shortest response times.

[0036] In various implementations, the predefined threshold 204 can be set to different values. In one implementation, the predefined threshold 204 is set to be -3 dB lower than the expected (nominal) signal power. In this implementation, the subset of PDs that observe a given event with a duration of τ d includes PDs with a τ pd / τ d ratio lower than ~1.44. In this implementation, PDs with a τ pd / τ d ratio lower than ~0.33 have an alarm interval time that closely corresponds to the event duration, such as an error less than 1.7%.

[0037] Figure 3 An example plot 300 is illustrated, which is a modified version of the Figure 2 shown plot 200. Specifically, plot 300 is identical to the Figure 2 plot 200 except that some data has been removed for clarity. Here, the lines on plot 300 specifically correspond to the subset of PDs that detected the power transient event. For ease of reference, these PDs (corresponding to Figure 2 the subset 206 in

[0038] Annotations are added to Plot 300 to illustrate the alarm interval times (as defined above) for each of the three PDs, where "A" corresponds to the alarm interval time for PD1, "B" corresponds to the alarm interval time for PD2, and "C" corresponds to the alarm interval time for PD3. Generally, when the PD response time is significantly shorter than the duration of the power transient event, the alarm interval time and the PD response time are substantially equal. When the PD response time approaches the event duration, the alarm interval time begins to deviate from the event duration. The exact time point at which this deviation begins to occur varies for each implementation based on the value of the predefined threshold 304.

[0039] After determining that PD1, PD2, and PD3 have observed an event, the next step is to determine which of these PDs meet the "accuracy criteria" and can be used to measure the event duration. The accuracy criteria for a given PD are said to be "met" when it is determined that the alarm interval time (A, B, and / or C) for the given PD can represent the event duration within a predefined acceptable error margin. According to one implementation, this determination involves comparing the alarm interval times for "nearest neighbor" pairs of PDs, where a nearest neighbor pair refers to a pair of PDs that are consecutive in the sequence of response times of the PDs arranged continuously in the PD group. For example, the alarm interval time for PD1 is compared with the alarm interval time for PD2, and then the alarm interval time for PD2 is compared with the alarm interval time for PD3.

[0040] For a given event, if the ratio of the alarm interval times for two nearest neighbor PDs is approximately equal to 1, meaning equal within the defined + / - 1% error margin, this indicates that both PDs meet the "accuracy criteria", in which case it is known that the alarm interval times for these PDs match the event duration (within the defined error margin).

[0041] When this ratio of the alarm interval times for two nearest neighbor PDs is not approximately equal to 1, this indicates that the alarm interval time for one or both of the PDs is not as accurate as the measured value of the event time, and further analysis is required to estimate the event duration. It should be noted that in all cases, the relative accuracy of the alarm interval time as an estimate of the event duration can be obtained by constructing a curve with a monotonic first derivative (as illustrated in Figure 4 and by identifying the position of each PD on the curve. As discussed further below, this method essentially depends on the comparison of the alarm interval times for nearest neighbor PDs and on the known relationship between PD response times.

[0042] Figure 4FIG. 400 illustrates a trend plot that illustrates the known relationship between the response time, alarm interval time, and event duration of PDs in a PD group. The data points shown on the plot (e.g., the points labeled PD1, PD2, PD3) correspond to the PDs in a PD group that is part of a transient event detection system in an optical communication network. The PD group includes an array of PDs with variable response times. In some implementations, the response times of the PDs in the PD group are characterized by a logarithmic relationship. Regarding Figure 4 Other characteristics of the PD group, transient event detection system, and optical communication network that are not explicitly described are assumed to be the same or similar to those described in other implementations herein.

[0043] In trend plot 400, the x-axis illustrates the ratio of the PD response time (τ pd ) to the event duration (τ d ) (increasing from left to right). The y-axis indicates the ratio of the PD alarm interval time to the event duration (τ d ) (increasing from bottom to top). Each point shown on trend plot 400 (e.g., point 402) represents an individual photodetector that has a corresponding response time (τ d ) and alarm interval time for the same power transient event of a fixed duration (τ pd ).

[0044] In a scenario where the PD response times are known (and different from each other) and two or more PDs in the PD group detect a power transient event, due to the potential correlation illustrated by curve 404, the duration of the power transient event can be determined based on the known response times and known alarm interval times. Specifically, the event duration can be determined by fitting the data points representing the PD response times and alarm interval times to curve 404, which is a monotonic first derivative (e.g., independent of the alarm interval time and event duration) and is described by a known function. Thus, if two of the three related variables (alarm interval time, response time, and event duration) are known for at least two data points, curve 404 can be derived.

[0045] It is known that when the PD response time is much shorter than the event duration, the alarm time for that PD represents an accurate measurement of the event duration. For example, region A of trend plot 400 includes PDs with response times ranging from 1 to 1 / 3 of the event duration. For these PDs, the recorded alarm time represents an accurate measurement of the event duration with an error of less than + / - 1.7%. This corresponds to a scenario where the alarm threshold is set 3 dB below the nominal signal level. However, as the PD response time approaches and exceeds the event duration (e.g., region B of trend plot 400, which includes PDs with response times ranging from 33% to 144% of the event duration), the corresponding alarm time deviates from the event duration.

[0046] For example, trend plot 400 illustrates three points that correspond to three PDs that detected a short-term power transient event. In this example, due to the power transient event, PD1, PD2, and PD3 each experienced a temporary drop in signal output, which caused an alarm trigger, as described above with respect to Figure 3 In this example, it is further assumed that the alarm interval time has been recorded for each of the three PDs, where the alarm interval time (as described above) indicates the elapsed time between the alarm trigger (when the PD output drops below the threshold) and the alarm clearance (when the PD output rises above the threshold). In this example, PD1 has a faster response time than PD2, and PD2 has a faster response time than PD3.

[0047] In general, the y-axis spacing between any two PDs in the group that observed a power transient event can be determined by comparing (e.g., subtracting) two associated alarm interval times. For example, if the difference between the alarm interval time for PD1 and the alarm interval time for PD2 is zero, this indicates that the y-axis spacing is also zero, as shown. Similarly, the difference in the alarm times for PD2 and PD3 is approximately 2.2 a.u., which translates to the y-axis spacing shown between PD2 and PD3.

[0048] Since curve 404 is described by a known function, any pair of data points can be fit to curve 404 based on the known y-axis spacing (e.g., determined by comparing alarm interval times) and based on the corresponding known PD response times. This curve fitting operation relies on mathematical methods known in the art.

[0049] Consistent with the above logic, an implementation of the disclosed technology provides for fitting data points corresponding to different PDs to a known function curve. Based on the resulting fit curve, it is possible to quickly determine which PDs (if any) have alarm intervals that accurately represent the event duration, within a predefined error margin threshold. As explained above, if the data points for a particular PD fall within region A of the trend plot 400 (where the slope of the region is substantially flat), then it is known that the event duration is approximately equal to the alarm interval for that PD.

[0050] On the other hand, if it is determined that the event was not observed for any of the PDs in region A, then additional steps are performed to estimate the event duration. Specifically, curve 404 and the fitted data points (e.g., in region B) can be used to infer that if included in the PD group, the alarm times for PDs that would fall within region A—e.g., response times less than about 32% of the event duration. In accordance with this method, ideal data points are identified on curve 404 (e.g., data points that have been fitted to the known PD distribution that detected the event as described above). An “ideal data point” is a data point located within region A, which is the region of curve 404 with zero slope. Then, the Y-axis coordinate of this ideal data point (e.g., the alarm interval) is used as the event duration estimate. The above analysis can be implemented using mathematical methods that are readily understandable in the art.

[0051] Based on the above technology, the duration of a power transient event can be determined based on: (1) the known distribution between the response times for the set of PDs that detected the event; and (2) the known (measured) relationship between the alarm intervals for these PDs, even if the event duration is much shorter than the duration for all PDs in the group (e.g., in scenarios where the alarm interval cannot be accurately estimated based on the alarm interval for any one of the PDs that detected the event).

[0052] Note that there are event scenarios where the PD with the fastest response time can be used alone to determine the duration of an event, especially if the fastest PD has a very fast response time (e.g., 1 microsecond) and the event is known to be several orders of magnitude larger (e.g., because it was detected by another PD with a response time of a higher order of magnitude), such as on the order of 10 milliseconds. However, relying on a single fastest PD results in a single point of failure, meaning that if the PD fails, the system's ability to detect power transient events also fails. Additionally, PDs with faster response times tend to be more costly to manufacture and are more sensitive to electrostatic discharge (ESD) events that can cause catastrophic component failures. For the reasons above, it is actually more cost-effective to use an array of PDs with slower response times relative to the fastest transient events to determine the event duration. In one implementation, the group of PDs utilized in the disclosed diagnostic system includes the PD with the fastest response time, which has a response time of about 0.3 - 0.5 times that of the fastest transient event (e.g., typically about 75 microseconds), which has a response time of about 20 - 40 microseconds.

[0053] Figure 5 Aspects of an exemplary technique 500 for determining the physical source (location) of a power transient event along an optical fiber cable in a communication network are illustrated. Exemplary technique 500 relies on a physical architecture that is the same as or similar to the physical architecture discussed with respect to Figure 1 wherein each of two nodes (e.g., node A and node B) has a group of PDs (e.g., PD groups 506 and 508) adjacent opposite ends of a section of optical fiber cable 502. At least one PD in PD group 506 has the same response time as the corresponding PD in PD group 508. In one implementation, PD groups 506 and 508 are identical, and each PD in PD group 506 has the same response time as the corresponding PD in PD group 508.

[0054] Although Figure 5 not shown, each group of PDs is coupled to an output signal monitor that monitors the output signals of each individual PD in the PDs. When the output signal of any one PD drops below a defined threshold, an alarm is triggered for that PD. The alarm remains active until the moment when the output signal of the PD rises above the threshold (at which point the alarm is cleared).

[0055] Note that most power transient events are two-way, i.e., the event affects a portion of the fiber optic cable and equally affects signals traveling in both directions along the cable. In such a scenario, an event detected by a PD in PD group 506 at node A (e.g., in the receiver at node A) will also be seen by a corresponding PD in PD group 508 at node B (e.g., in the receiver at node B) with the same response time. View 508 illustrates an example of how a pair of PDs with the same response time observe the same power transient event from their respective positions at opposite ends of the fiber optic cable 502. In this example, the alarm interval time 510 for the PD (PD1) in node A is the same as the alarm interval time 512 for the corresponding (identical) PD in node B (also referred to as PD1), but there is a delay between the time when PD1 in node A detects the event and the time when PD1 in node B detects the event. The magnitude of this delay (denoted by the variable t’) fluctuates proportionally with the spacing (d) between the midpoint 514 of the fiber optic cable 502 and the physical origin of the event (e.g., the transient event location 516).

[0056] If the transient event location 516 is aligned with the midpoint 514, the delay t’ will be zero (which means the same PDs observe the event at the same time). However, in the scenario illustrated, where the transient event location 516 is closer to node A than to node B, the PD in node A will detect the event before the same PD in node B due to the increased path distance (d) traversed in routing the interrupted signal to node B. This increased travel time can generally be expressed as (y - x) divided by the speed of light (c), where y is the distance between node B and the transient event location 516, and where x is the distance between node A and the transient event location 516.

[0057] Based on the above relationship, the distance “d” can be solved for based on the measured delay time t’. In one implementation, this technique is performed by software in a transient power event detection system (e.g., Figure 2 the transient event characterizer 112 in

[0058] In the case of a unidirectional transient (less common), the transient event affects the signal traveling in a single direction. For example, the PD group in the receiver (RX) component of node A detects a transient event, but it is not detected at the RX component of node B. However, in this case, as long as the transmitter (TX) components of both nodes also include additional PD groups, the location of the power transient event can still be determined. Specifically, the location of the transient event can be determined by comparing the actual signal detected with the OSC signal continuously transmitted in the opposite direction. For example, if the PD group in the RX component of node A detects a transient event, and the OSC signal is also continuously transmitted from the RX component of node A towards the TX component of node B (e.g., essentially sending a test signal in the direction opposite to the real signal but along the same line), then the two signals can be compared and analyzed. In this example, the TX component in node B receives the test signal, and the received test signal includes the same characteristics as the unidirectional transient event detected in the real signal in the RX component of node A. Here, the location of the transient event can be determined by determining the delay time between (1) the alarm triggered by the PD in the group of the RX component of node A (e.g., based on the observation of the real signal) and (2) the alarm triggered by the PD in the group of the TX component of node B with the same response time (e.g., based on the observation of the test signal).

[0059] Figure 6 Example operation 600 for determining the duration of a short-term power transient event in an optical communication network is illustrated. Monitoring operation 602 monitors the signal output of each of a plurality of photodetectors in a first group of photodetectors located in a first node of an optical communication system. Each PD in the first group has a different response time. In one implementation, the distribution of the response times of the PDs in the PD group ranges from 30% - 50% (e.g., ~75 microseconds) of the fastest transient event the system is targeted for, up to approximately 100% or more of the fastest transient event.

[0060] Recording operation 604 records power transient event information based on the monitored signal output. In one implementation, the recorded power transient event information includes at least the alarm trigger time and the alarm clear time for each PD in the PD group that observed a particular transient event. The alarm trigger time corresponds to the time when the output signal for a given PD exceeds a threshold when the output signal strength decreases, and the alarm clear time corresponds to the time when the output signal for a given PD exceeds the threshold again when the output signal strength increases.

[0061] Identification operation 606 identifies a subset of the PDs in the first group of photodetectors that observed a power transient event based on the power transient information.

[0062] Determine operation 608 determines the duration of the power transient event based on the amount of time that the signal output meets the low signal criteria for one or more PDs in the subset. In one implementation, determine operation 608 includes comparing the alert interval times (e.g., the time between alert trigger and alert clear) for each PD in the subset, then identifying two other PDs in the subset with the same alert interval time, and the alert interval times of these PDs are within a predefined threshold error margin. In this scenario, the same alert interval time indicates that these two PDs have a response time significantly faster than the event duration. Thus, the alert interval time is determined based on the alert interval times of the two compared PDs (e.g., taking one of the alert interval times alone as the event duration, or averaging or otherwise combining the alert interval times to obtain the event duration).

[0063] In another implementation, the determine operation includes comparing the alarm interval times of different PDs in the subset as part of a curve fitting operation that fits the data points corresponding to the PDs to a curve of a known form (e.g., Figure 4 curve 404 in, which illustrates the correlation between response time, transient event duration, and alarm interval time). After the curve fitting operation, ideal data points are identified on the flat portion of the curve (e.g., the zero slope region known to correspond to PDs with a response time significantly faster than the event duration), and the coordinates of the ideal data points are used to provide an estimate of the event duration.

[0064] Figure 7 Exemplary schematic diagram of a processing device 700 suitable for implementing aspects of the disclosed technology is illustrated. Processing device 700 includes one or more processor units 702, (multiple) memory devices 704, a display 706, and other interfaces 708 (e.g., buttons). Each of the (multiple) processor units 702 may include one or more CPUs, GPUs, etc.

[0065] Memory 704 generally includes volatile memory (e.g., RAM) and non-volatile memory (e.g., flash memory). An operating system 710 (e.g., Microsoft operating system, Microsoft Phone operating system, or a dedicated operating system designed for gaming devices) may reside in memory 704 and be executed by the (multiple) processor units 702, but it should be understood that other operating systems may also be employed.

[0066] One or more applications 712 (e.g., Figure 1The output signal monitor 110 or the transient event characterizer 112) is loaded into the memory 704 and executed by the (multiple) processor units 702 on the operating system 710. The applications 712 can receive inputs from each other or from various local input devices, such as the microphone 734, the input accessory 735 (e.g., keyboard, mouse, stylus, touchpad, gamepad, racing wheel, joystick), and the camera 732. In addition, the applications 712 can receive inputs from one or more remote devices (such as remote smart devices) by using the more communication transceivers 730 and antennas 738 for providing network connections (e.g., mobile phone network, ) to communicate with such devices. The processing device 700 may also include one or more storage devices 728 (e.g., non-volatile storage). Other configurations may also be employed.

[0067] The processing device 700 further includes a power supply 716, which is powered by one or more batteries or other power sources and powers the other components of the processing device 700. The power supply 716 may also be connected to an external power supply (not shown), which covers or charges the built-in battery or other power source.

[0068] The processing device 700 may include various tangible computer-readable storage media and intangible computer-readable communication signals. Tangible computer-readable storage can be embodied by any available medium accessible to the processing device 700, and the available medium includes volatile and non-volatile storage media, removable and non-removable storage media. Tangible computer-readable storage media do not include intangible and transient communication signals, and include volatile and non-volatile, removable and non-removable storage media implemented by any method or technology for storing information, such as computer-readable instructions, data structures, program modules, or other data. Tangible computer-readable storage media include, but are not limited to, RAM, ROM, EEPROM, flash memory or other memory technologies, CD-ROM, digital versatile disk (DVD) or other optical disk storage devices, magnetic cassettes, magnetic disk storage devices or other magnetic storage devices, or any other tangible medium that can be used to store the required information and can be accessed by the processing device 700. In contrast to the tangible computer-readable storage media, intangible computer-readable communication signals can embody computer-readable instructions, data structures, program modules, or other data residing in a modulated data signal (such as a carrier wave or other signal transmission mechanism). The term "modulated data signal" means a signal in which one or more characteristics are set or changed to encode information into the signal. For example, intangible communication signals include wired media (such as wired networks or direct connections) and wireless media (such as acoustic waves, radio frequency, infrared, and other wireless media).

[0069] Some implementations may include a manufactured article. The manufactured article may include a tangible storage medium (memory device) for storing logic. Examples of storage media may include one or more processor-readable storage media capable of storing electronic data, including volatile memory or non-volatile memory, removable memory or non-removable memory, erasable memory or non-erasable memory, writable memory or rewritable memory, and so on. Examples of logic may include various software elements, such as software components, programs, applications, computer programs, application programs, system programs, machine programs, operating system software, middleware, firmware, software modules, routines, subroutines, operational segments, methods, processes, software interfaces, application interfaces (APIs), instruction sets, computing code, computer code, code segments, computer code segments, words, values, symbols, or any combination thereof. For example, in one implementation, the manufactured article may store executable computer program instructions that, when executed by a computer, cause the computer to perform methods and / or operations according to the described implementation. The executable computer program instructions may include any suitable type of code, such as source code, compiled code, interpreted code, executable code, static code, dynamic code, and so on. The executable computer program instructions may be implemented according to a predefined computer language, manner, or syntax for instructing a computer to perform a specific operational segment. These instructions may be implemented using any suitable high-level, low-level, object-oriented, visual, compiled, and / or interpreted programming language.

[0070] The example power transient event detection system disclosed herein includes a first set of photodetectors (PDs) located at a first node in an optical communication system and an output signal monitor configured to monitor the signal output of each PD from the first set of PDs and record power transient event information. Each PD in the first set of PDs has a different response time. The system further includes a transient event characterizer configured to identify a subset of the PDs in the first set that observed a power transient event based on the power transient event information recorded in association with each PD in the first set, and further configured to determine the duration of the power transient event based on the amount of time the signal output meets a low-signal criterion for at least one PD in the subset.

[0071] In another example system of any of the foregoing systems, the transient event characterizer identifies a subset of the PDs in the first set that observed a power transient event by identifying a particular PD in the first set that detected a signal interruption that meets the low-signal criterion. The low-signal criterion is characterized by the signal output of the PD dropping below a threshold and then the signal output of the PD rising above the threshold.

[0072] In another example system of any of the foregoing systems, the transient characterizer determines the duration of a power transient event by determining an alarm interval time corresponding to the amount of time for which the signal output of a PD meets a low-signal criterion associated with the power transient event for a plurality of PDs that observe a power transient event in a subset.

[0073] In another example system of any of the foregoing systems, the transient event characterizer determines the duration of a power transient event based on the alarm interval times of at least one PD in a subset having a response time less than or equal to the duration of the power transient event.

[0074] In another example system of any of the foregoing systems, the transient event characterizer is further configured to identify pairs of PDs in the subset having PDs that meet an accuracy criterion based on a comparison of the alarm interval times determined for each PD in the subset; and determine the duration of the power transient event based on the alarm interval times of the PD pairs.

[0075] In another example system of any of the foregoing systems, a PD is determined to have a characteristic that meets an accuracy criterion when the ratio of the alarm interval times for a PD pair is approximately equal to 1.

[0076] In another example system of any of the foregoing systems, the transient characterizer is further configured to fit data points corresponding to each PD in a subset of PDs to a curve defined by a known function that depends on the PD response time and the alarm interval time; identify an ideal data point on the curve within a region of zero slope; and estimate the duration of the power transient event based on the coordinates of the ideal data point.

[0077] In another example system of any of the foregoing systems, a power transient event occurs between a first node and a second node. The power transient detection system further includes a second group of photodetectors (PDs) located at the second node, and a first distribution of the response times for the PDs in the second group is the same as a second distribution of the response times for the PDs in the second group.

[0078] In another example system of any of the foregoing systems, the transient characterizer is further configured to identify the location of a power transient event between the first node and the second node based on a time delay between observations of the power transient event by a first PD in a first group and a second PD in a second group. The second PD has the same response time as the first PD.

[0079] Example methods disclosed herein include: monitoring a signal output of each of a plurality of photodetectors (PDs) in a first set located at a first node in an optical communication system, and recording power transient event information based on the monitored signal output for each of the plurality of PDs in the first set. Each PD in the first set has a different response time. The method further includes identifying a subset of the PDs in the first set in which a power transient event is observed based on the recorded power transient event information for each of the plurality of PDs in the first set, and determining a duration of the power transient event based on an amount of time that the signal output meets a low signal criterion for at least one PD in the subset.

[0080] In another example method of any of the foregoing methods, identifying a subset of the PDs in the first set in which a power transient event is observed further includes identifying a particular PD in the first set in which a signal interruption that meets the low signal criterion is detected. The low signal criterion is characterized by: the signal output of the PD drops below a threshold and then the signal output of the PD rises above the threshold.

[0081] In another example method of any of the foregoing methods, determining a duration of the power transient event further includes: determining an alarm interval time corresponding to an amount of time that the signal output of the PDs in the subset in which a power transient event is observed meets the low signal criterion associated with the power transient event.

[0082] In another example method of any of the foregoing methods, determining a duration of the power transient event is based on the alarm interval time of at least one PD in the subset having a response time less than or equal to the duration of the power transient event.

[0083] In yet another example method of any of the foregoing methods, determining a duration of the power transient event further includes: identifying a pair of PDs in the subset having characteristics that meet an accuracy criterion based on a comparison of the alarm interval times determined for each of the PDs in the subset, and determining a duration of the power transient event based on the alarm interval time of the pair of PDs.

[0084] In yet another example method of any of the foregoing methods, when the ratio of the alarm interval times for a pair of PDs is approximately equal to 1, the PDs are determined to have characteristics that meet the accuracy criterion.

[0085] In yet another example method of any of the foregoing methods, the method further includes: fitting data points corresponding to each of the PDs in the subset to a curve, the curve being defined by a known function that depends on the PD response time and the alarm interval time; identifying an ideal data point on the curve in a region of zero slope; and estimating the event duration based on the coordinates of the ideal data point.

[0086] In yet another example method of any of the foregoing methods, a power transient event occurs between a first node and a second node, and the method further includes monitoring the signal output of each PD in a second set of PDs located at the second node. In an implementation, a first distribution of the response times of the PDs in the second set is the same as a second distribution of the response times of the PDs in the second set.

[0087] In yet another example method of any of the foregoing methods, the method further includes identifying the location of a power transient event between the first node and the second node based on a time delay between an observation of the power transient event by a first PD in a first set and an observation of the power transient event by a second PD in a second set, wherein the second PD has the same response time as the first PD.

[0088] In another aspect, some implementations include a computer-readable storage medium for storing computer-readable instructions. The computer-readable instructions, when executed by one or more hardware processors, perform any of the methods described herein.

[0089] The example systems disclosed herein include means for monitoring the signal output of each PD in a first set of photodetectors (PDs) located at a first node in an optical communication system, and means for recording power transient event information based on the signal output monitored for each PD in the first set of a plurality of PDs. Each PD in the first set of PDs has a different response time. The system further includes means for identifying a subset of the PDs in the first set in which a power transient event is observed based on the power transient event information recorded for each PD in the first set of a plurality of PDs, and means for determining the duration of the power transient event based on the amount of time the signal output satisfies a low-signal criterion for at least one PD in the subset.

[0090] The logical operations described herein are implemented as logical steps in one or more computer systems. These logical operations can (1) be implemented as a series of processor-implemented steps executed in one or more computer systems, and (2) be implemented as machine or circuit modules interconnected within one or more computer systems. The particular implementation depends on the performance requirements of the computer systems utilized. Accordingly, the logical operations constituting the implementations described herein are sometimes referred to as operations, steps, objects, or modules. Further, it should be understood that unless explicitly stated otherwise or the language of the claims themselves requires a particular order, the logical operations can be performed in any order. The foregoing specification, examples, and data, as well as the appended appendix, provide a complete description of the structure and use of the exemplary implementations.

Claims

1. A power transient event detection system, comprising: a first set of photodetectors PD located at a first node in an optical communication system, each PD in the first set of PDs having a different response time; an output signal monitor configured to monitor the signal output from each PD in the first set and record power transient event information; and a transient event characterizer configured to identify a subset of the PDs in the first set in which a power transient event is observed, based on the power transient event information recorded in association with each PD in the first set; and determine a duration of the power transient event based on an amount of time during which the signal output satisfies a low signal criterion for at least one PD in the subset.

2. The power transient event detection system according to claim 1, wherein the transient event characterizer identifies the subset of the PDs in the first set in which the power transient event is observed by identifying a particular PD in the first set that detects a signal interruption that satisfies the low signal criterion, the low signal criterion being characterized by: the signal output of the PD drops below a threshold, and subsequently the signal output of the PD rises above the threshold.

3. The power transient event detection system according to claim 2, wherein the transient characterizer: determines the duration of the power transient event by determining an alarm interval time corresponding to an amount of time during which the signal output of the PD satisfies the low signal criterion associated with the power transient event, for a plurality of PDs in the subset in which the power transient event is observed.

4. The power transient event detection system according to claim 3, wherein the transient event characterizer determines the duration of the power transient event based on the alarm interval time of at least one PD in the subset having a response time less than or equal to the duration of the power transient event.

5. The power transient event detection system according to claim 3, wherein the transient event characterizer is further configured to: identify pairs of PDs in the subset having characteristics that satisfy an accuracy criterion, based on a comparison of the alarm interval times determined for each PD in the subset; and determine the duration of the power transient event based on the alarm interval times of the pairs of PDs.

6. The power transient detection system according to claim 5, wherein a PD is determined to have the characteristics that satisfy the accuracy criterion when the ratio of the alarm interval times for the pair of PDs is approximately equal to 1.

7. The power transient detection system according to claim 5, wherein the transient characterizer is further configured to: fit data points corresponding to each PD in the subset to a curve defined by a known function that depends on PD response time and alarm interval time; identify an ideal data point on the curve in a region of zero slope; and estimate the duration of the power transient event based on the coordinates of the ideal data point.

8. The power transient event detection system according to claim 1, wherein the power transient event occurs between a first node and a second node, and the power transient detection system further comprises: a second group of photodetectors PD located at the second node, wherein a first distribution of response times for the PDs in the second group is the same as a second distribution of response times for the PDs in the second group.

9. The power transient event detection system according to claim 8, wherein the transient characterizer is further configured to: identify a location of the power transient event between the first node and the second node based on a time delay between observations of the power transient event by a first PD in the first group and a second PD in the second group, the second PD having the same response time as the first PD.

10. A method, comprising: monitoring a signal output of each of a plurality of PDs in a first group of photodetectors PD located at a first node in an optical communication system, each PD in the first group of PDs having a different response time; recording power transient event information based on the monitored signal output for each of the plurality of PDs in the first group; identifying a subset of the PDs in the first group that observed the power transient event based on the recorded power transient event information for each of the plurality of PDs in the first group; and determining a duration of the power transient event based on an amount of time the signal output satisfies a low signal criterion for at least one PD in the subset.

11. The method according to claim 10, wherein identifying the subset of PDs in the first group that observed the power transient event further comprises: identifying a particular PD in the first group that detected a signal interruption that satisfies the low signal criterion, the low signal criterion being characterized by: the signal output of the PD drops below a threshold and then the signal output of the PD rises above the threshold.

12. The method according to claim 10, wherein determining the duration of the power transient event further comprises: determining an alarm interval time corresponding to an amount of time the signal output of the PD satisfies the low signal criterion associated with the power transient event for a plurality of PDs in the subset that observed the power transient event.

13. The method according to claim 12, wherein determining the duration of the power transient event is based on the alarm interval time of at least one PD in the subset having a response time less than or equal to the duration of the power transient event.

14. The method according to claim 12, wherein determining the duration of the power transient event further comprises: identifying pairs of PDs in the subset having characteristics that satisfy an accuracy criterion based on a comparison of the alarm interval times determined for each of the PDs in the subset; and determining the duration of the power transient event based on the alarm interval times of the PD pairs.

15. The method according to claim 14, wherein when the ratio of the alarm interval times for the PD pair is approximately equal to 1, the PD is determined to have the characteristic that meets the accuracy criterion.

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