Optical time domain reflectometer (OTDR) apparatus and methods

Abstract

An optical time domain reflectometer (OTDR) apparatus and method includes an optical transmitter, an optical receiver having a plurality of operational settings, an optical coupler, and a processor. The light emitter generates a probe signal comprising a train of pulses. The optical receiver generates a time-varying measurement of a back-reflected signal resulting from injecting respective pulses of the probe signal into an optical fiber link. The optical coupler injects the probe signal from the optical transmitter into the optical fiber link and directs the back-reflected signal from the optical fiber link to the optical receiver. The processor generates a probe trace of an optical fiber link from a first time-varying measurement of the back reflection signal, identifies an internal scan first transition point from the probe trace, and generates a range extension trace of the optical fiber link from a second time-varying measurement of the back reflection signal, wherein the light receiver transitions from a first operational setting to a second operational setting at an internally scanning first transition point.

Description

Technical Field

[0001] Aspects of the present disclosure relate to optical time domain reflectometer (OTDR) devices and methods for generating OTDR traces of optical fibers. Background Art

[0002] OTDR equipment can determine the optical characteristics of a fiber link, such as attenuation, reflection, etc., in order to optimize the operating levels of associated transmitter and receiver equipment. OTDR equipment generally includes: a light source for generating a large number of light pulses that are injected into the optical fiber under test; and an optical receiver for detecting light emitted from the light source that is back-reflected by the optical fiber. An associated processor can process the back-reflected signal detected by the optical receiver to create an OTDR trace that defines the total loss along the fiber span and identifies physical changes / reflection points (e.g., connectors, joints, etc.) along the measurement segment.

[0003] Although OTDR traces are useful tools for assessing the operational health of a fiber optic link, the operating range of an OTDR device is limited by various factors such as the amount of optical power that can be launched into a given fiber optic link, the length of the fiber optic link, and the duration a user is willing to wait for the OTDR device to generate an OTDR trace.

[0004] Further limitations and disadvantages of conventional and traditional approaches will become apparent to those skilled in the art by comparing such systems with certain aspects of the present disclosure as set forth in the remainder of this application with reference to the accompanying figures. Summary of the invention

[0005] Shown in at least one of the drawings and / or described in conjunction with at least one of the drawings, and more fully set forth in the claims, is an optical time domain reflectometer (OTDR) apparatus and associated processing for generating an OTDR trace of a fiber link under test. For some embodiments, the OTDR apparatus and processing can effectively generate an OTDR trace with an extended dynamic range with only a slight increase in the time required to generate such an OTDR trace when compared to conventional OTDR apparatus and techniques.

[0006] These and other advantages, aspects and novel features of the present disclosure, as well as details of illustrated embodiments thereof, will be more fully understood from the following description and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] The various features and advantages of the present disclosure may be more readily understood by reference to the following detailed description taken in conjunction with the accompanying drawings, wherein like reference numerals represent like structural elements.

[0008] Figure 1 Depicted is a block diagram of an example OTDR device coupled to a fiber optic link.

[0009] Figure 2A Depicted is an example OTDR probe trace of a fiber optic link having one or more "clear" ranges.

[0010] Figure 2B An example OTDR range extension trace is depicted in which the OTDR device increases the sensitivity level of the optical receiver at the inner scan transition point associated with the clear range.

[0011] Figure 3A Depicted is an example OTDR probe trace of a fiber optic link lacking a clear range for transition optical receivers.

[0012] Figure 3B A first example OTDR trace is depicted in which the OTDR device transitions an optical receiver at a first internal scan transition point.

[0013] Figure 3C A second example OTDR trace is depicted in which the OTDR device transitions the optical receiver at a second internal scan transition point.

[0014] Figure 3D A third example OTDR trace is depicted in which the OTDR device transitions the optical receiver at a third internal scan transition point.

[0015] Figure 3E A fourth example OTDR trace is depicted in which the OTDR device transitions the optical receiver at a fourth internal scan transition point.

[0016] Figure 3F Describes the basis FIG. 3B to FIG. 3E An example OTDR range extension trace constructed by a first OTDR trace, a second OTDR trace, a third OTDR trace, and a fourth OTDR trace.

[0017] FIG. 4A to FIG. 4C Depicted by Figure 1 A flowchart of an example OTDR process implemented by an embodiment of an OTDR device, wherein Figure 4A Depicts the OTDR probe trace processing, Figure 4B Depicts OTDR clear trace processing, and Figure 4C OTDR opaque trace processing is depicted. DETAILED DESCRIPTION

[0018] The following discussion provides various examples of optical time domain reflectometer (OTDR) equipment and associated processes for generating OTDR traces. These examples are non-limiting, and the scope of the appended claims should not be limited to the specific examples disclosed. In the following discussion, the terms "example" and "for example" are non-limiting.

[0019] The accompanying drawings illustrate the overall manner of construction, and descriptions and details of well-known features and techniques may be omitted to avoid unnecessarily obscuring the present disclosure. In addition, the elements in the accompanying drawings are not necessarily drawn to scale. For example, the size of some elements in the drawings may be enlarged relative to other elements to help improve the understanding of the examples discussed in the present disclosure. The same reference numerals in different drawings represent the same elements.

[0020] The term "and / or" means any one or more of the items in the list connected by "and / or". As an example, "x and / or y" means any element in the three-element set {(x), (y), (x, y)}. In other words, "x and / or y" means "one or both of x and y". As another example, "x, y and / or z" means any element in the seven-element set {(x), (y), (z), (x, y), (x, z), (y, z), (x, y, z)}. In other words, "x, y and / or z" means "one or more of x, y and z".

[0021] The terms “comprising,” “including,” “includes,” and / or “comprising” are “open” terms and specify the presence of the feature, but do not preclude the presence or addition of one or more other features.

[0022] The terms "first", "second", etc. may be used herein to describe various elements, and these elements should not be limited by these terms. These terms are only used to distinguish one element from another element. Thus, for example, a first element discussed in the present disclosure may be referred to as a second element without departing from the teachings of the present disclosure.

[0023] Unless otherwise specified, the term "coupled" can be used to describe two elements that are in direct contact with each other or to describe two elements that are indirectly coupled by one or more other elements. For example, if element A is coupled to element B, then element A can be directly in contact with element B or indirectly coupled to element B through an intermediate element c. Similarly, the terms "above" or "on" can be used to describe two elements that are in direct contact with each other or to describe two elements that are indirectly coupled by one or more other elements.

[0024] Aspects of the present disclosure relate to OTDR devices and processes for generating OTDR traces. In various embodiments, the OTDR device may generate an OTDR probe trace before generating an OTDR range extension trace. Specifically, the OTDR device may generate an OTDR probe trace using an operational setting that avoids a saturation effect of the entire trace based on measurements acquired during an initial interrogation period (e.g., 10 seconds). Based on the OTDR probe trace, the OTDR device may identify one or more transition points corresponding to a time period or distance range, in which the operational setting of the OTDR device may be transformed during a single pulse or scan of a fiber link. During a longer interrogation period (e.g., 180 seconds), the OTDR device may inject an optical pulse into the fiber link and generate a scanned measurement of an optical pulse reflected back to the OTDR device by the fiber link. During the time-varying measurement of the back reflection signal of a single pulse is generated, the OTDR device may transform the operational setting of the OTDR device at the identified transition point. Such a transition may extend the effective range of the OTDR device, thereby permitting the OTDR device to output an OTDR range extension trace containing the characteristics of the fiber link at a greater distance from the OTDR device.

[0025] Now turn to Figure 1 , shows an OTDR device 10 coupled to an optical fiber link 20. The OTDR device 10 may interrogate the optical fiber link with a probe signal and may generate an OTDR trace based on the portion of the probe signal reflected back from the optical fiber link 20 to the OTDR device 10. Figure 1 Although shown as a standalone device in FIG. 1 , the OTDR device 10 may be integrated into an optical node of optical communication equipment.

[0026] As shown, the OTDR device 10 may include an optical transmitter 12, an optical receiver 14, an optical coupler 16, a processor 18, and an output device 19. The optical transmitter 12 may generate an optical detection signal coupled to the near end of the optical fiber link 20 via the optical coupler 16. Injecting the optical detection signal into the optical fiber link 20 may create a back reflection signal. In various embodiments, the optical detection signal may include a series or a series of optical pulses. Specifically, the optical pulses may be spaced apart so that each optical pulse has enough time to travel from the near end of the optical fiber link 20 to the far end of the optical fiber link 20 and return to the near end of the optical fiber link 20 before the next optical pulse is injected into the near end of the optical fiber link 20.

[0027] The optical receiver 14 (e.g., a photodetector and a transimpedance amplifier) ​​can generate an electrical signal based on the back-reflected optical signal of each pulse of the detection signal. Specifically, each scan of the optical fiber link 20 can include the optical transmitter 12 injecting a pulse into the optical fiber link 20 and the optical receiver 14 generating a time-varying measurement value based on the back-reflected signal. Therefore, by injecting a string or series of pulses into the optical fiber link 20, the OTDR device 10 can generate a separate scanning measurement of the optical fiber link for each pulse of the detection signal. In addition, the optical receiver 14 can have a plurality of sensitivity levels from which the processor 18 can select. Specifically, the processor 18 can generate a first control signal that causes the optical receiver 14 to operate at a first sensitivity level and can generate a second control signal that causes the optical receiver 14 to operate at a second sensitivity level.

[0028] In one embodiment, the first sensitivity level is associated with a low gain level of the optical receiver 14 and the second sensitivity level is associated with a high gain level of the optical receiver 14. In another embodiment, the first sensitivity level is associated with a high attenuation level of the optical receiver 14 and the second sensitivity level is associated with a low attenuation level of the optical receiver 14. Although various embodiments of the optical receiver 14 are described as having two sensitivity levels (e.g., a low sensitivity level and a high sensitivity level) or two operating levels, the optical receiver 14 may be implemented with multiple operating levels, thereby permitting multiple transitions during a scanning measurement and / or providing the processor 18 with greater flexibility in selecting appropriate transition points and operating levels for the optical receiver 14.

[0029] Optical coupler 16 may control or direct the flow of optical detection signals from optical transmitter 12 to fiber link 20 and the flow of back reflection signals from fiber link 20 to optical receiver 14. Various other arrangements may be used to control the direction of propagating signals.

[0030] The processor 18 can process the measurements of the back reflection signal and construct one or more OTDR traces based on such measurements. In addition, the processor 18 can control the operation of the optical transmitter 12 and the optical receiver 14, as described below with respect to FIG. 4A to FIG. 4C The processing is explained in more detail.

[0031] To this end, the processor 18 may include a microprocessor, a microcontroller, and / or some other general processing unit configured to execute software, firmware, and / or other instructions and to perform tasks based on the execution of such instructions. These instructions may be embedded in the firmware of the processor 18, stored in the memory of the processor 18, and / or stored in a memory external to the processor 18. In some embodiments, in addition to or in place of a general processing unit, one or more application specific integrated circuit (ASIC) components, one or more analog circuit components, and / or one or more digital circuit components may be used to implement one or more tasks or aspects of the processor 18.

[0032] As further shown, the OTDR device 10 may include one or more output devices 19. For example, the output device 19 may include a display device, a network device, and / or a storage device. The processor 18 may use such an output device 19 to provide the generated OTDR trace and / or associated measurements to a person and / or another device. For example, the processor 18 may graphically present the generated OTDR trace via a display device in order to convey the operating characteristics of the optical fiber link 20 to the person operating the OTDR device 10.

[0033] Figure 2A An example OTDR detection trace that can be constructed by the processor 18 as a result of injecting a pulse signal into the optical fiber link 20 and generating a time-varying measurement of the back reflection signal is shown. Specifically, the OTDR trace can depict the optical power loss (in dB) of the back reflection signal as a function of time (e.g., microseconds) or distance (e.g., kilometers) along the optical fiber link 20. As shown, the OTDR trace can contain spikes, dips, or other events associated with various distances along the optical fiber link 20. In the absence of optical fiber link events along its length, the back reflection signal decreases exponentially as a function of time or distance (i.e., linearly on the logarithmic scale of the trace shown). The distance traveled by the back reflection signal is proportional to the time it takes for the pulse to travel in both directions along the optical fiber link 20 (i.e., from the optical transmitter 12 to the reflection location and back to the optical receiver 14). Likewise, time and distance can be used interchangeably with respect to the various OTDR traces presented or described herein.

[0034] In an attempt to increase the range of the OTDR device 10 and the OTDR traces it generates, the processor 18 may transition the optical receiver 14 to a higher sensitivity level. When operating at a higher sensitivity level, the optical receiver 14 may detect and generate time-varying measurements of portions of the back-reflected signal corresponding to greater distances of the optical fiber link 20. However, as Figure 2AAs further shown, if the optical receiver 14 is operated at a higher sensitivity level, the portion of the back reflection signal corresponding to the shorter distance of the optical fiber link 20 will exceed the saturation level of the optical receiver 14. Therefore, if the OTDR device 10 performs a scan with the optical receiver 14 operating at a lower sensitivity level, the OTDR device 10 may not be able to detect the back reflection signal associated with the longer distance. However, if the OTDR device 10 performs a scan with the optical receiver 14 operating at a higher sensitivity level, the back reflection signal associated with the shorter distance may saturate the optical receiver 14.

[0035] Since the measurement value provided by the optical receiver 14 does not accurately reflect the signal level of the back reflection when the optical receiver 14 is saturated, such saturation may cause the loss of OTDR information at a closer distance. In addition, the optical receiver 14 may need a stabilization period after saturation. During such a stabilization period, the measurement value provided by the optical receiver 14 may be inaccurate or otherwise unreliable. Therefore, even after the back reflection signal drops below the saturation level of the optical receiver 14, as the optical receiver 14 recovers from the saturation state during this stabilization period, the OTDR device 10 may also experience a loss of OTDR information. Therefore, in various embodiments, the OTDR device 10 may attempt to avoid saturation of the optical receiver 14 in order to increase the amount of OTDR information collected.

[0036] In view of this, the OTDR device 10 according to the present disclosure can generate an OTDR detection trace with an optical receiver 14 operating at a lower sensitivity level of the optical receiver OTDR device. The processor 18 can analyze this OTDR detection trace to identify one or more transition points, at which the sensitivity level of the optical receiver 14 is increased. Specifically, the processor 18 can select a transition point associated with a distance beyond which the back reflection signal will saturate the optical receiver 14 operating at a higher sensitivity level of the optical receiver. In addition, the processor 18 can select a transition point that exceeds the saturation distance associated with a "clear" range (i.e., a distance range of the optical fiber link 20 lacking discrete events such as Fresnel reflections, lumped losses, etc.). If the processor 18 cannot identify a clear range that exceeds the saturation distance, the processor 18 can select a set of transition points that exceed the saturation distance within an "opaque" range (i.e., a distance range of the optical fiber link 20 having discrete events such as Fresnel reflections, lumped losses, etc.). The processor 18 can then generate an OTDR range extension trace in which the optical receiver 14 transitions from a lower sensitivity level of the optical receiver to a higher sensitivity level at the identified transition point. In this way, the OTDR device 10 can generate an OTDR range extension trace that includes a combination of a near portion generated based on a lower sensitivity level of the optical receiver 14 and a far portion generated based on a higher sensitivity level of the optical receiver 14.

[0037] Reference now FIG. 4A to FIG. 4C , further details of the above process are addressed with respect to the depicted flowchart. Specifically, Figure 4A The process of the OTDR device 10 for generating an OTDR probe trace is depicted. Based on the results obtained from such OTDR probe trace, the OTDR device 10 may proceed to Figure 4B OTDR clear trace processing or Figure 4C OTDR opaque trace processing.

[0038] At 410, the processor 18 of the OTDR device 10 may prepare the optical receiver 14 for the OTDR detection trace. Specifically, the processor 18 may generate one or more control signals that configure the optical receiver 14 to operate at a lower sensitivity level of the optical receiver. For example, such signals may transition the optical receiver 14 to a higher attenuation level of the optical receiver and / or a lower gain level of the optical receiver. At 415, the processor 18 may initiate scanning of the OTDR detection trace of the optical fiber link 20 by generating one or more signals that cause the optical transmitter 12 to inject a pulse of the detection signal into the near end of the optical fiber link 20. In some embodiments, the processor 18 and / or the optical transmitter 12 may delay the transmission of the pulse until after the transition period when the optical receiver 14 stabilizes to the new operating level of the optical receiver. As a result of the injected pulse, the optical receiver 14 may receive a back reflection signal from the optical fiber link 20. When the back reflection signal is received, at 420, the optical receiver 14 may sample the back reflection signal and / or generate a time-varying measurement of the back reflection signal based on the lower sensitivity level of the optical receiver. In this manner, the OTDR device 10 can generate a probing scan of the fiber link 20 that contains time-varying measurements of the backreflected signal over at least a period of time sufficient for a pulse to travel to the far end of the fiber link 20 and return to the OTDR device 10 .

[0039] At 425, the processor 18 may determine whether to perform additional scans of the optical fiber link 20. Specifically, if the current scan of the optical fiber link 20 has been completed and additional scans for the OTDR probe trace remain, the processor 18 may determine that additional scans are performed. For example, if the length of the optical fiber link 20 is known, if a sufficient amount of time has passed for the transmitted pulse to travel to the far end of the optical fiber link 20 and back, the processor 18 may determine that the current scan has been completed. Additionally and / or alternatively, if the measured value of the back reflection signal has dropped below a threshold level, the processor 18 may determine that the current scan has been completed. In addition, if a predetermined time period (e.g., 10 seconds) allocated to generate the OTDR probe trace has not expired, or a predetermined number of scans for generating the OTDR probe trace have not been performed, the processor 18 may determine that additional scans remain.

[0040] If additional scans are to be performed, the processor 18 may return to 415 to generate one or more control signals that cause the optical transmitter 12 to transmit another pulse of the probe signal. Otherwise, the processor 18 may proceed to 430 to construct an OTDR probe trace based on multiple scans of the optical fiber link 20. For example, the processor 18 may perform various signal processing functions based on the time-varying measurements generated for each pulse of the probe signal to construct the OTDR probe trace. See Figure 2A and Figure 3A , such as an OTDR probe trace.

[0041] After constructing the OTDR probe trace, the processor 18 may perform event analysis on the OTDR probe trace at 432. Specifically, the processor 18 may utilize various signal processing techniques (such as Fresnel reflection, lumped loss, etc.) to identify discrete events in the OTDR trace.

[0042] At 435, the processor 18 may determine whether the OTDR probe trace contains a range without events after the saturation level of the optical receiver 14. Specifically, the processor 18 may utilize the output of the event analysis to identify a clear range of the OTDR probe trace that lacks such identified events. The processor 18 may also compare the duration of each clear range with a transition period or stabilization time of the optical receiver 14, which is associated with the optical receiver 14 switching from a lower sensitivity level of the optical receiver to a higher sensitivity level of the optical receiver. That is, when the optical receiver 14 transitions from a lower sensitivity level of the optical receiver to a higher sensitivity level of the optical receiver, the optical receiver 14 may experience a period in which the optical receiver cannot generate or cannot reliably generate a measurement of the back reflection signal. Therefore, at 435, the processor 18 may search for a clear range long enough to allow the optical receiver 14 to complete the switch to the higher sensitivity level of the optical receiver and resume the generation of reliable measurements.

[0043] For example, Figure 2A The OTDR detection trace of FIG. 1 contains three clear ranges C1, C2, and C3. However, only the clear ranges C2 and C3 extend beyond the saturation level. Therefore, the processor 18 can identify the clear range C2 or C3 as a suitable period for the transition point. However, in the case of the clear range C2, the processor 18 can only utilize the portion of the clear range C2 that exceeds the saturation level to avoid saturating the optical receiver 14.

[0044] If the processor 18 is able to find such a clear range, the processor 18 may proceed to Figure 4B OTDR clear processing, wherein the internal scan transition occurs during the identified clear range. Conversely, if the processor 18 cannot find such a clear range, the processor 18 may continue to perform Figure 4C The OTDR is not transparent processing, where the internal scan transitions of multiple scans across the optical fiber link 20 occur at different transition points.

[0045] If the processor 18 identifies a suitable clear range that exceeds the saturation level associated with the higher sensitivity level of the optical receiver 14, then at 500, the processor 18 may select a transition point in the identified clear range (e.g., at the beginning of the identified clear range, but after the saturation level). At 510, the processor 18 of the OTDR device 10 may prepare the optical receiver 14 for an OTDR scan of the near portion of the optical fiber link 20. Specifically, the processor 18 may generate one or more control signals that configure the optical receiver 14 to operate at a lower sensitivity level of the optical receiver. For example, such signals may transition the optical receiver 14 to a higher attenuation level of the optical receiver and / or a lower gain level of the optical receiver. At 515, the processor 18 may initiate a scan of the OTDR clear trace of the optical fiber link 20 by generating one or more signals that cause the optical transmitter 12 to inject a pulse of a probe signal into the near end of the optical fiber link 20. In some embodiments, the processor 18 and / or the optical transmitter 12 may delay the transmission of the pulse until after a transition period suitable for the optical receiver 14 to stabilize to the new operating level of the optical receiver. As a result of the injection pulse, the optical receiver 14 may receive a back reflection signal from the optical fiber link 20. Upon receiving the back reflection signal, at 520, the optical receiver 14 may generate a time-varying measurement of the back reflection signal for a near portion of the optical fiber link 20 corresponding to a portion of the optical fiber link 20 prior to the transition period of the optical receiver 14 based on the lower sensitivity level of the optical receiver. For example, see Figure 2B The transition period T.

[0046] At 525, while the injected probe signal is still traversing the optical fiber link, the processor 18 may generate one or more control signals that configure the optical receiver 14 to operate at a higher sensitivity level of the optical receiver. For example, such signals may transition the optical receiver 14 to a lower attenuation level of the optical receiver and / or a higher gain level of the optical receiver. As a result of increasing the sensitivity level of the optical receiver 14, at 530, the optical receiver 14 may generate a time-varying measurement of the back reflection signal for a distant portion of the optical fiber link 20 corresponding to a portion of the optical fiber link 20 after the transition period. For example, see Figure 2B As described above, the optical receiver 14 may not be able to generate and / or may not be able to stabilize the transition period (e.g., Figure 2B The resulting scan may therefore contain gap periods or portions of the scan where reliable measurements are lacking.

[0047] At 535, the processor 18 may determine whether to perform additional scans of the fiber link 20. Specifically, if the current scan of the fiber link 20 has been completed and additional scans for an OTDR clear trace remain, the processor 18 may determine to perform additional scans. For example, if the length of the fiber link 20 is known, if a sufficient amount of time has passed for the transmitted pulse to travel to the far end of the fiber link 20 and back, the processor 18 may determine that the current scan has been completed. Additionally and / or alternatively, if the measured value of the back reflection signal has dropped below a threshold level, the processor 18 may determine that the current scan has been completed. Furthermore, if a predetermined time period (e.g., 180 seconds) allocated to generate an OTDR clear trace has not expired, or a predetermined number of scans for generating an OTDR clear trace have not been performed, the processor 18 may determine that additional scans remain.

[0048] If additional scans are to be performed, the processor 18 may return to 510 to prepare the optical receiver 14 for another scan. Otherwise, the processor 18 may proceed to 540 to construct an OTDR range extension trace based on multiple scans of the optical fiber link 20. For example, the processor 18 may perform various signal processing functions based on the time-varying measurements generated for the near portion of each pulse of the detection signal to construct the near portion of the OTDR range extension trace. In addition, the processor 18 may perform various signal processing functions based on the time-varying measurements generated for the far portion of each pulse of the detection signal to construct the far portion of the OTDR range extension trace. In addition, the processor 18 may linearly extrapolate between the near portion and the far portion to fill in the gap portion associated with the transition period T of the optical receiver 14. See, for example, constructing an OTDR range extension trace. Figure 2B In some embodiments, at 435, the processor 18 can further add an OTDR range extension trace and / or fill gap portion based on the measurements used to construct the OTDR probe trace. In various embodiments, the processor 18 can zoom in on the near portion and / or zoom out on the far portion such that the near portion and far portion of the OTDR extension trace measurement of received power are normalized to represent the measured loss of the optical fiber link 20.

[0049] At 545, the processor 18 may output the complete OTDR range extension trace via the output device 19. For example, the processor 18 may display a graphical depiction of the OTDR range extension trace (e.g., a 2B graph) via a display device, and / or transmit the OTDR range extension trace and / or associated measurements to another device for further processing and / or presentation.

[0050] like Figure 3AAs shown in , the OTDR probe trace may lack a clear range after the optical receiver 14 transitions from the low sensitivity level of the optical receiver to the saturation level of the high sensitivity level of the optical receiver for a sufficient length. Therefore, if the processor 18 cannot identify a suitable clear range, then at 600, the processor 18 may select a set of transition points for the plurality of OTDR opaque scans. In one embodiment, the processor 18 selects the transition points such that each transition point exceeds the saturation level associated with the higher sensitivity level of the optical receiver 14 and is within the dynamic range of the optical receiver 14 when the optical receiver 14 is operating at the lower sensitivity level of the optical receiver. In addition, the processor 18 selects each transition point such that the resulting transition periods of the optical receiver 14 do not overlap. See, for example, FIG. 3B to FIG. 3F , FIG. 3B to FIG. 3F Depicted are non-overlapping transition periods T1 , T2 , T3 , T4 after a saturation level and within the dynamic range when the optical receiver 14 is operating at a lower sensitivity level of the optical receiver.

[0051] At 610, the processor 18 of the OTDR device 10 may prepare the optical receiver 14 for an OTDR opaque scan of the near portion of the optical fiber link 20. Specifically, the processor 18 may generate one or more control signals that configure the optical receiver 14 to operate at a lower sensitivity level of the optical receiver. For example, such signals may transition the optical receiver 14 to a higher attenuation level of the optical receiver and / or a lower gain level of the optical receiver.

[0052] At 615, the processor 18 may select the next transition point Tx from the set of transition points. In one embodiment, the processor 18 may cycle through each of the transition points Tx in sequence. For example, if there are four transition points corresponding to FIG. 3B to FIG. 3F If the processor 18 selects the transition point Tx at the beginning of the transition period T1, T2, T3, T4 of the first scan, the processor 18 can select the transition point T1 for the first scan, the transition point T2 for the second scan, the transition point T3 for the third scan, the transition point T4 for the fourth scan, and loops back to the transition point T1 for the fifth scan, etc. However, the processor 18 can use other algorithms to select the next transition point Tx. In some embodiments, the processor 18 can select the transition points so that each transition point and its associated transition period are selected for a roughly equal percentage (e.g., ±5%) of the scan. For example, if there are four transition points, the processor 18 can select each transition point for 25% ± 5% of the scan.

[0053] At 620, the processor 18 may initiate a scan of the optical fiber link 20 by generating one or more signals that cause the optical transmitter 12 to inject a pulse of the detection signal into the near end of the optical fiber link 20. In some embodiments, the processor 18 and / or the optical transmitter 12 may delay the transmission of the pulse until after a transition period suitable for the optical receiver 14 to stabilize to the new operating level of the optical receiver. As a result of the injected pulse, the optical receiver 14 may receive a back reflection signal from the optical fiber link 20. Upon receiving the back reflection signal, at 625, the optical receiver 14 may generate a time-varying measurement of the back reflection signal for a near portion of the optical fiber link 20 corresponding to the portion of the optical fiber link 20 before the selected transition point Tx based on the lower sensitivity level of the optical receiver.

[0054] At 630, while the injected probe signal is still passing through the optical fiber link, the processor 18 may generate one or more control signals that cause the optical receiver 14 to perform an internal scanning transition from a lower sensitivity level to a higher sensitivity level at the selected transition point. For example, such a signal may transition the optical receiver 14 to a lower attenuation level of the optical receiver and / or a higher gain level of the optical receiver. As a result of increasing the sensitivity level of the optical receiver 14, at 635, the optical receiver 14 may generate a time-varying measurement of the back reflection signal for a distant portion of the optical fiber link 20 corresponding to a portion of the optical fiber link 20 after the selected transition point Tx. As described above, the optical receiver 14 may be unable to generate and / or unable to reliably generate a measurement of the transition period in which the optical receiver 14 switches to a high sensitivity level. Therefore, the resulting scan may include scanning a gap portion where reliable measurements are lacking.

[0055] At 640, the processor 18 may determine whether to perform additional scans of the optical fiber link 20. Specifically, if the current scan of the optical fiber link 20 has been completed and additional scans for the OTDR opaque trace remain, the processor 18 may determine to perform additional scans. For example, if the length of the optical fiber link 20 is known, if a sufficient amount of time has passed for the transmitted pulse to travel to the far end of the optical fiber link 20 and back, the processor 18 may determine that the current scan has been completed. Additionally and / or alternatively, if the measured value of the back reflection signal has dropped below a threshold level, the processor 18 may determine that the current scan has been completed. Furthermore, if a predetermined time period (e.g., 180 seconds) allocated to generate the OTDR opaque trace has not expired, or a predetermined number of scans for generating the OTDR opaque trace have not been performed, the processor 18 may determine that additional scans remain.

[0056] If additional scans are to be performed, the processor 18 may return to 610 to prepare the optical receiver 14 for another scan at the next transition point in the set of transition points. Otherwise, the processor 18 may proceed to 645 to construct an OTDR range extension trace based on multiple opaque scans of the optical fiber link 20. For example, the processor 18 may perform various signal processing functions based on the time-varying measurements generated for the near and far portions of each pulse of the probe signal to construct the near portion of the OTDR range extension trace. In some embodiments, at 435, the processor 18 may further augment the OTDR range extension trace based on the measurements used to construct the OTDR probe trace. However, unlike Figure 4B Unlike the OTDR clean trace processing, the time-varying measurements encompass the entire range (i.e., there are no gaps due to each scan transitioning at the same single point). Figure 4C The processing lacks the gap part, but the processor 18 performs a process for each transition period (for example, FIG. 3B to FIG. 3F Assuming non-overlapping transition periods and four transition periods associated with four transition points, each transition period may contain fewer time-varying measurements for each fiber link distance than those obtained for fiber link distances associated with non-transition periods. In addition, each transition period may contain measurements obtained when the optical receiver 14 is operating at a low sensitivity level and measurements obtained when the optical receiver 14 is operating at a high sensitivity level. Therefore, the processor 18 may appropriately scale the measurements and consider fewer measurements to construct an OTDR range extension trace from an opaque scan.

[0057] At 650, the processor 18 may output the complete OTDR range extension trace via the output device 19. For example, the processor 18 may display a graphical depiction of the OTDR range extension trace via a display device (e.g., Figure 3F ), and / or transmitting the OTDR range extension trace and / or associated measurements to another device for further processing and / or presentation.

[0058] The present disclosure includes references to certain examples, however, it will be appreciated by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the scope of the present disclosure. In addition, modifications may be made to the disclosed examples without departing from the scope of the present disclosure. Therefore, it is intended that the present disclosure is not limited to the disclosed examples, but that the present disclosure will include all examples falling within the scope of the appended claims.

Claims

1. An optical time domain reflectometer device, comprising: an optical transmitter configured to generate a detection signal including a train of pulses; an optical receiver configured to generate a time-varying measurement of a back-reflected signal resulting from injecting corresponding pulses of the probe signal into the optical fiber link; an optical coupler configured to inject the probe signal from the optical transmitter into the optical fiber link and direct the back-reflected signal from the optical fiber link to the optical receiver; as well as a processor configured to generate a probe trace of the optical fiber link based on a first time-varying measurement of the back-reflection signal, identify an internal scan first transition point based on the probe trace, and generate a range extension trace of the optical fiber link based on a second time-varying measurement of the back-reflection signal, wherein the optical receiver transitions from a first operating setting to a second operating setting at the internal scan first transition point.

2. The optical time domain reflectometer device according to claim 1, wherein: The processor is configured to: identifying one or more ranges of the detection trace that are free of events; and The internal scan first transition point is selected such that the optical receiver transitions from the first operating setting to the second operating setting during a range without events in one or more identified ranges.

3. The optical time domain reflectometer device according to claim 1, wherein: The processor is configured to: identifying one or more ranges of the detection trace that are free of events; and The inner scan first transition point is selected such that the back reflection signal does not saturate the optical receiver after the optical receiver transitions from the first operating setting to the second operating setting at the inner scan first transition point.

4. The optical time domain reflectometer device according to claim 1, wherein: The processor is configured to: identifying one or more ranges of the detection trace that are free of events; and The internal scan first transition point is selected such that it is within a dynamic range of the optical receiver when operating in accordance with the first operating setting.

5. The optical time domain reflectometer device according to claim 1, wherein: The optical receiver includes one or more gain levels; and The processor is configured to cause the optical receiver to transition to a gain level higher than a current gain level of the optical receiver at the inner scan first transition point.

6. The optical time domain reflectometer device according to claim 5, wherein: The processor is configured to cause the optical receiver to transition to one of the optical receiver's lower gain levels prior to each pulse of the detection signal.

7. The optical time domain reflectometer device according to claim 1, wherein: The optical receiver includes one or more attenuation levels; as well as The processor is configured to cause the optical receiver to transition to an attenuation level lower than a current attenuation level of the optical receiver at the inner scan first transition point.

8. The optical time domain reflectometer device according to claim 7, wherein: The processor is configured to cause the optical receiver to transition to one of the optical receiver's higher attenuation levels prior to each pulse of the detection signal.

9. The optical time domain reflectometer device according to claim 1, wherein: The processor is configured to: In response to determining that the detection trace lacks a suitable range without events, selecting an inner scan second transition point; as well as The range extension trace is generated based on a first scan in which the optical receiver transitions to the second operating setting at the internal scan first transition point and a second scan in which the optical receiver transitions to the second operating setting at the internal scan second transition point.

10. The optical time domain reflectometer device according to claim 9, wherein: The processor is configured to select the inner scan second transition point such that the back reflection signal does not saturate the optical receiver after the optical receiver transitions from the first operating setting to the second operating setting at the inner scan second transition point.

11. A method for an optical time domain reflectometer device, the method comprising: generating a probe signal comprising a train of pulses with the optical time domain reflectometer device and injecting the probe signal into an optical fiber link; generating, with the optical time domain reflectometry device, time-varying measurements of back-reflected signals resulting from injecting corresponding pulses of the probe signal into the optical fiber link; generating, with the optical time domain reflectometer device, a detection trace of the optical fiber link based on a first time-varying measurement of the back reflection signal; identifying an internal scan first transition point based on the detection trace using the optical time domain reflectometry device; as well as A range extension trace of the optical fiber link is generated based on second time varying measurements of the back reflection signal using the optical time domain reflectometer device, wherein the optical time domain reflectometer device transitions from a first operating setting to a second operating setting at the inner scan first transition point.

12. The method according to claim 11, comprising: identifying, with the optical time domain reflectometry device, one or more ranges of the detection trace that are free of events; as well as The internal scan first transition point is selected with the optical time domain reflectometer device such that the optical time domain reflectometer device transitions from the first operating setting to the second operating setting during a range without events in one or more identified ranges.

13. The method according to claim 11, comprising: identifying, with the optical time domain reflectometry device, one or more ranges of the detection trace that are free of events; as well as The internal scan first transition point is selected with the optical time domain reflectometer device such that the back reflection signal does not saturate the optical time domain reflectometer device after the optical time domain reflectometer device transitions from the first operating setting to the second operating setting at the internal scan first transition point.

14. The method according to claim 11, comprising: identifying, with the optical time domain reflectometry device, one or more ranges of the detection trace that are free of events; as well as The internal scan first transition point is selected with the optical time domain reflectometry device such that the internal scan first transition point is within a dynamic range of the optical time domain reflectometry device when operating according to the first operating setting.

15. The method of claim 11, comprising transitioning the optical time domain reflectometer device to a gain level higher than a current gain level of the optical time domain reflectometer device at the inner scan first transition point.

16. The method of claim 15, comprising switching the optical time domain reflectometry device to a lower gain level prior to each pulse of the probe signal.

17. The method of claim 11, comprising transitioning the optical time domain reflectometer device to an attenuation level lower than a current attenuation level of the optical time domain reflectometer device at the inner scan first transition point.

18. The method of claim 17, comprising switching the optical time domain reflectometry device to a higher attenuation level prior to each pulse of the probe signal.

19. The method according to claim 11, comprising: In response to the optical time domain reflectometry device determining that the detection trace lacks a suitable range without events, selecting an inner scan second transition point with the optical time domain reflectometry device; as well as The range extension trace is generated with the optical time domain reflectometer device according to a first scan in which the optical time domain reflectometer device transitions to the second operating setting at the internal scan first transition point and a second scan in which the optical time domain reflectometer device transitions to the second operating setting at the internal scan second transition point.

20. The method according to claim 19, comprising: The inner scan second transition point is selected such that the back reflection signal does not saturate the optical time domain reflectometry device after transitioning from the first operating setting to the second operating setting at the inner scan second transition point.

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