Shared OTDR resources

Abstract

A shared OTDR resource is disclosed that utilizes a combination of pluggable OTDRs and merged 1 * N optical switches to allow OTDR measurement and monitoring functionality to be shared between a number N of individual optical fibers that function as communication paths between a pair of optical nodes (e.g., multiple individual fiber spans for interconnecting a pair of data centers). The ability to maintain OTDR functionality within a small pluggable housing (e.g., QSFP, OSFP, etc.) in combination with a switch results in a shared OTDR resource that remains pluggable and allows for increased flexibility in how the resource is shared between various optical fibers.

Description

Technical Field

[0001] Disclosed herein is an optical time domain reflectometer (OTDR) that enables the OTDR function to be provided as a pluggable module, e.g., in the form of a small form factor pluggable (SFP) combined with an optical switch, such that the OTDR function can be shared among multiple individual fiber spans. Background

[0003] OTDRs are widely used to determine fiber characteristics such as attenuation, reflection, etc., in order to optimize the operating levels of associated transmitter and receiver devices. An OTDR module typically includes a light source for generating a probe light wave coupled into the fiber span being analyzed, and a photoreceiver for detecting the reflected light attributable to the probe light wave that re-enters the OTDR from the fiber span being evaluated. A processing module utilizes information associated with the probe light wave (e.g., in the case of using a probe pulse, timing information associated with a pulse train) and the optical power in the returned back-reflected light to create an output that defines the total loss along the fiber span (commonly referred to as an OTDR trace), as well as the identification of any physical changes / reflection points (e.g., connectors, splices, etc.) that may exist along the measured span.

[0004] One problem with many conventional OTDR devices is the overall size of the unit, which significantly affects its ability to be formed as a "pluggable" component (for the purposes of this disclosure, the term "pluggable" refers to an optical component that can be located within a device assembly along with other components). In one example, a device assembly in the form of a router can be configured to include a backplane connection for an exemplary OTDR and one or more optical transceivers, thereby providing a flexible network design.

[0005] Additionally, there is a motivation to control costs by sharing the OTDR function among a defined set of transceivers. While there are some configurations for connecting conventional OTDR components to an optical switch, the resulting devices are relatively large, typically taking the form of a daughter board on an embedded line card or a full rack in an equipment bay. Thus, conventional designs for implementing a switchable OTDR are not consistent with the desire to provide a compact, pluggable solution.

[0006] Summary of the Disclosure

[0007] A shared OTDR resource is proposed, which is based on the utilization of pluggable OTDR components and meets the requirement of using small modules. The 1×N optical switch is integrated with the pluggable OTDR component (specifically, coupled to the output of the pluggable OTDR component) and is controlled to select a specific fiber span from among multiple individual fiber spans for OTDR testing. Each fiber span only requires an optical coupler (e.g., a wavelength division multiplexer (WDM)) to provide coupling between the shared OTDR resource and the fiber span.

[0008] The process controller within the pluggable OTDR component is preferably used to control the operation of the 1×N switch in a manner that maintains the identity of the selected fiber span under test. In one example process, the conventional data transmission along the selected fiber span can be "paused" by the controller, and the generated OTDR trace can be stored in association with the identity identification information of the fiber span under test. Alternatively, the OTDR measurement can be performed while data is being transmitted along the selected span.

[0009] In one embodiment, the 1×N switch can be coupled to an existing pluggable OTDR component, and then the OTDR component is configured to provide switch control. Alternatively, the 1×N switch can be incorporated within the module of the pluggable OTDR during the pluggable OTDR assembly; specifically, incorporated within a designated "passive" module that includes components for guiding the signal flow between the OTDR and the fiber span.

[0010] An example of the disclosed shared OTDR resource can take the form of a pluggable OTDR component, a 1×N optical switch, and a controller module. The pluggable OTDR component is used to generate an optical probe beam that is subsequently directed into the fiber to be evaluated, and an OTDR trace is generated based on the light reflection returned from the fiber to the pluggable OTDR component. The 1×N optical switch is coupled to the output of the pluggable OTDR component, where each of the N individual output paths from the 1×N optical switch is coupled to a separate one of the N individual fiber spans. The controller module is used to provide a fiber span selection control signal to the 1×N optical switch to determine the specific fiber span for OTDR testing according to time.

[0011] In some example embodiments, the controller module may be incorporated within a pluggable OTDR element. In particular, the controller module may be located within the "active" module portion of the pluggable OTDR element, which houses the probe beam source (and driver) and a photodetector for capturing the returned probe reflections. Similarly, a 1×N optical switch may be incorporated within the pluggable OTDR element. In particular, the 1×N optical switch may be located within the "passive" module portion of the pluggable OTDR element, which houses directional coupling elements for providing the signal direction into and out of the pluggable OTDR.

[0012] During the following discussion and by reference to the accompanying drawings, other and additional aspects of embodiments related to shared OTDR resources will become apparent. Brief Description of the Drawings

[0014] Now referring to the accompanying drawings, where like numerals may refer to like components in several views:

[0015] Figure 1 is a simplified diagram of an interconnection between a pair of optical nodes, the interconnection being based on a plurality of N individual fiber spans and showing a shared OTDR resource of the present disclosure, the shared OTDR resource being provided within one of the nodes and configured to individually monitor each of the plurality of N individual fiber spans;

[0016] Figure 2 is a diagram of a first embodiment of a shared OTDR resource formed in accordance with the present disclosure, in which a 1×N switch provided as a component separate from the pluggable OTDR element is utilized;

[0017] Figure 3 is Figure 2 an illustration of a shared OTDR resource of, the shared OTDR resource being provided with a set of four individual fiber spans, particularly showing the control of the 1×N switch to select a particular fiber span for an OTDR test; and

[0018] Figure 4 shows a second embodiment of the shared OTDR resource of the present disclosure, in which the function of the 1×N switch is incorporated within the pluggable OTDR element itself (particularly within the "passive module" portion of the pluggable OTDR element). Detailed Description

[0020] OTDR is becoming an essential component of optical communication networks in terms of being able to continuously monitor the health of the optical fiber spans of interconnected network nodes. For example, the measurements obtained by an OTDR can be used to improve routing algorithm capabilities (as a function of optical loss / gain fluctuations along individual spans) and to provide feedback to the network maintenance system regarding the quality of the optical fiber itself. The latest progress in the implementation of "pluggable" OTDRs is described in our co-pending application and allows the OTDR components to be compact enough such that they can be in the desired "small form-factor pluggable" (SFP) form.

[0021] As described below, the advantages of the pluggable OTDR configuration are now exploited to create an OTDR device that can be shared among multiple individual optical fiber spans; for example, shared among multiple individual optical fiber spans used to interconnect a pair of optical nodes.

[0022] In applications such as data centers where accurate data transmission needs to be ensured, the physical "health" of each optical fiber span supporting the data transmission is crucial. For example, OTDR measurements are a good metric of the quality of the optical fiber and can even be used to improve routing algorithm capabilities. Additionally, in cases where the installed fiber plant is owned by a third party (e.g., leased to the entity providing the data center) and not under the direct control of the data center entity, the ability to independently monitor the integrity of the optical fiber spans is important.

[0023] Figure 1 A device formed in accordance with the principles of the present disclosure is shown for providing an OTDR function that can be shared among multiple individual optical fiber spans in a compact and efficient manner. In particular, a shared OTDR resource 10 is provided that allows monitoring of each of a plurality of individual optical fiber spans used to interconnect a first optical node 1 and a second optical node 2 (where these nodes can be data center locations). The first optical node 1 is shown as including a plurality of individual optical transceivers 3 numbered N, and the second optical node 2 is shown as including a plurality of individual optical transceivers 5 numbered N, where a plurality of optical fiber spans 4 numbered N are used to provide communication between the identified transceiver 3-x in optical node 1 and the identified transceiver 5-x in optical node 2. In many applications, the optical fiber spans 4 can be relatively short (compared to the length of long-distance transmission cables) and are used to provide high-density, high-speed optical signal paths. Dense wavelength division multiplexing (DWDM) can be used to support the transmission of a large number of individual signals along a single optical fiber span 4. Thus, the ability to continuously monitor the quality of individual optical fiber spans is an important requirement.

[0024] The shared OTDR resource 10 is in Figure 1is shown as including a pluggable OTDR element 12 used in conjunction with a 1×N optical switch 14 (N≥2). Time-based control of the 1×N switch 14 by a control element within the pluggable OTDR element 12 allows selection of a particular fiber span to be studied, where the 1×N switch 14 is used to direct an OTDR probe input to a designated fiber span 4-x. The returned reflections are similarly directed back into the pluggable OTDR element 12 for processing by the action of the 1×N switch 14. As shown, a WDM 6 is provided at the output of each transceiver 3 and is also coupled in the manner shown in the figure to a selected one of the N outputs from the 1×N optical switch 14. Using the pluggable OTDR element 12 to control the selection of the 1×N switch 14 allows the integrity of data communication along all non-selected fiber spans, while also ensuring that the OTDR trace information collected is only associated with the "selected" fiber span.

[0025] For example and with reference Figure 1 , a control signal C from the pluggable OTDR element 12 is applied to the 1×N switch 14 and indicates that the 1×N switch 14 is currently selecting fiber span 4-2 for study. Thus, the optical probe beam P generated by the pluggable OTDR element 12 will be directed into the WDM 6-2 and then coupled into the fiber span 4-2. The remaining fiber spans 4-1, 4-3, and 4-4 will continue to support data transmission between the transceiver 3 and the transceiver 5. Once the OTDR monitoring of the fiber span 4-2 is complete (which can be identified by the completion of the OTDR trace), the OTDR element 12 can send another control signal to the 1×N switch 14, thereby changing the selection of the fiber span for study. In this way, different time slots can be allocated to different fiber spans for performing OTDR monitoring.

[0026] Figure 2 A first embodiment 10A of the disclosed shared OTDR resource 10 is shown. In this embodiment, the pluggable OTDR element 12 and the 1×N optical switch 14 include separate components housed within a common package 30 to provide a compact final structure that retains the ability to be inserted into a device such as a router. As fully described in our co-pending application, the pluggable OTDR element 12 includes a first module 16 that houses electronic components and active optical components and a second module 18 that houses passive optical components. By this separation, the first module 16 can be configured as a compact, small component compatible with desired QSFP / OSFP requirements.

[0027] The first module 16 of the pluggable OTDR element 12 houses a light transmitter 20 for providing an optical probing light wave, which is coupled into a selected fiber span 4 (discussed in detail below) and used in a manner well known in the art to generate backscattered light in the return direction, where the reflected light is used to generate an OTDR trace of the selected fiber span 4 as an output from the pluggable OTDR element 12. In many cases, the optical probing takes the form of an optical pulse train, but other types of optical probing signals (e.g., continuous wave signals, digital signals with a specific coding scheme, etc.) can also be used. In this configuration, the light transmitter 20 includes a laser device 22 activated by an electrical drive circuit 24 that controls the laser device 22 to generate a pulsed or CW probing signal.

[0028] The first module 16 of the OTDR pluggable element 12 further includes a light receiver 30, which includes a photodetector 32 and a transimpedance amplifier 34. The photodetector 32 is used to receive the backscattered light, and the transimpedance amplifier 34 is used to convert the current from the photodetector 32 into a voltage waveform that can be used for further processing. A control / processor element 40 is included within the first module 16 and is used to control the operation of the electrical drive circuit 24 and also generate an OTDR trace output by analyzing the returned electrical signal from the transimpedance amplifier 34. As will be described in detail below, the control / processor element 40 is further used in accordance with the present disclosure to provide control of the 1×N optical switch 14 in a manner that allows sharing of the pluggable OTDR element 12 among multiple different fiber spans. An electrical interface 42 is included within the first module 16 and provides two-way communication between the pluggable OTDR element 12 and a remote monitoring device (not shown).

[0029] In this embodiment, the second module 18 of the pluggable OTDR element 12 is shown to house passive optical elements for controlling the signal propagation direction between the shared OTDR resource 10 and the selected fiber span 4 being analyzed. In this particular configuration, the second module 18 includes an optical circulator 50 and a bandpass filter 52. It should be understood that various other passive devices can be used in place of the optical circulator to control the direction of signal flow; for the sake of brevity, the following discussion is intended to generically describe all possibilities in terms of the phrase "optical circulator". As an example, some devices may not use a bandpass filter (so element 52 is considered optional). Additionally, in certain configurations, the bandpass filter 52 can be tunable to track a specific wavelength used as the OTDR probing beam.

[0030] The optical circulator 50 is used to control / guide the signal flow between the optical transmitter 20, the optical receiver 30, and the fiber spans 4. More specifically, the optical circulator 50 is configured as a three-port device, including an input port 54 coupled to the output from the laser device 22, a bi-directional port 56, and an output port 58 coupled to the output of the bandpass filter 52. Thus, the optical probe beam generated by the laser device 22 will leave the first module 16 and be applied as an input to the second module 18, specifically coupled to the input port 54 of the optical circulator 50. Thereafter, this OTDR probe beam will propagate inside the optical circulator 50 and leave the device at the bi-directional port 56.

[0031] As Figure 2 specifically shown in, and in accordance with the principles of the disclosed ability to share the pluggable OTDR element 12 between multiple individual fiber spans 4, the bi-directional port 56 of the optical circulator 50 is coupled to the input signal path 60 of the 1×N optical switch 14. Thus, the probe beam output from the pluggable OTDR element 12 (i.e., the output from the laser device 22) will thereafter leave the 1×N switch 14 at a selected output signal path 62-x among the multiple output signal paths 62 of number N (shown as output signal path 62-2 in this example). The output signal path 62-2 is shown in Figure 2 the illustration as being coupled to the WDM 6-2, and is thus coupled into the fiber span 4-2, allowing the optical probe signal to leave the 1×N switch 14, pass through the WDM 6-2, and be coupled into the fiber span 4-2, where the probe beam is used to perform the OTDR measurement of that particular fiber span.

[0032] When the reflection from the propagating probe beam returns along the fiber span 4-2 and is guided back by the WDM 6-2 along the signal path 62-2 through the 1×N switch 14 and into the pluggable OTDR element 12, this connection between the input signal path 60 and the designated output signal path 62-x (here 62-2) in the 1×N optical switch 14 is maintained. Specifically, and as Figure 2 shown, the returned reflection enters the second module 18 of the pluggable OTDR element 12 and is guided into the bi-directional port 56 of the optical circulator 50. In this return direction, the reflection will propagate through the optical circulator 50 and leave at the output port 58, passing through the bandpass filter 52 before being applied as an input to the photodetector 32 of the receiver 30.

[0033] Further in accordance with the disclosed principles, the operation of the 1×N optical switch 14 is controlled by the control / processor element 40 of the pluggable OTDR element 12 (or any other suitable monitoring component) to select the particular fiber span 4-x for study. In Figure 2In the example, the "optical fiber span selection" control line 70 is shown as being coupled between the control output 44 of the control / processor element 40 and the control input C of the 1×N optical switch 14.

[0034] Thus, by enabling the ability to select a particular optical fiber span 4-x for study by controlling the 1×N optical switch 14, the pluggable OTDR element 12 can be used to perform OTDR measurements on each individual optical fiber span among the plurality of N optical fiber spans 4 used to connect a pair of optical nodes. By controlling the timing of the connection, a complete measurement cycle can be provided (and repeated as needed), thereby allowing the pluggable OTDR element 12 to be shared by the plurality of optical fiber spans 4.

[0035] Figure 3 This principle is further illustrated in terms of the ability to configure the OTDR resource 10 to share the pluggable OTDR element 12 among multiple individual optical fiber spans 4. Figure 3 The apparatus assumes an application where there is a set of four individual optical fiber spans 4-1 to 4-4 for connecting a pair of optical nodes (e.g., a pair of data centers). Figure 2 Comparing the apparatus with Figure 3 the apparatus, it is clear that the control / processor element 40 has transmitted the "optical fiber span selection" control signal C to the 1×N optical switch 14 (a 1×4 optical switch in this example) to connect the input signal path 60 to the output signal path 62-3 (i.e., changing the 1→2 signal path interconnection of the optical switch 14 to a 1→3 signal path interconnection). Thus, the same pluggable OTDR element 12 previously used to evaluate the optical fiber span 4-2 is used to evaluate the optical fiber span 4-3. Since the processor 40 maintains a record of the timing of the switch control, the generated OTDR trace will be paired with the appropriate designated optical fiber span 4.

[0036] Figure 4 Another embodiment of a shared OTDR resource formed in accordance with the present disclosure is shown, which is shown here as the shared OTDR resource 10B. This embodiment maintains the same ability to share the OTDR function among multiple individual optical fiber spans as Figure 2 the embodiment, but in this case, the configuration of the pluggable OTDR element 12 is modified to incorporate the 1×N optical switch 14 within a modified version of the second module 18 (referred to as the second module 18B in this embodiment). Thus, while Figure 2 the embodiment may be considered preferable when retrofitting an existing pluggable OTDR device to a "shared" OTDR, Figure 4 the configuration may be more suitable when initially assembling the pluggable OTDR components.

[0037] It should be understood that various other pluggable configurations of the OTDR function can be combined with a 1×N optical switch to allow sharing of the OTDR measurement function among several separate fiber spans. While finding a particular use in the data center interconnect environment, the applicability of the shared pluggable OTDR is not limited thereto. In fact, any architecture that utilizes a multi-slot device to support pluggable modules of QSFP or OSFP size can benefit from a pluggable OTDR of such size that is capable of sharing among separate fibers. Adding additional functionality in QSFP (OSFP) format allows for the use of more optical functions in the same span; the OTDR is generally considered to be an essential optical function that can be easily accommodated in such a pluggable device.

[0038] Although the disclosed principles have been illustrated and described herein with reference to certain preferred embodiments and specific examples thereof, it will be readily apparent to those of ordinary skill in the art that other embodiments and examples can perform similar functions and / or achieve similar results. All such equivalent embodiments and examples are within the spirit and scope of this disclosure and are hereby contemplated and intended to be covered by the appended claims.

Claims

1. An optical time domain reflectometer (OTDR) resource configured to be shared between a plurality of individual optical fiber spans, the OTDR resource comprising: A pluggable OTDR element, wherein the pluggable OTDR element is used to generate an optical detection beam; a 1×N optical switch coupled to an output of the pluggable OTDR element, wherein each of a number N of separate output paths from the 1×N optical switch is coupled to a separate one of the number N of separate optical fiber spans; and A controller module is used to provide a fiber span selection control signal to the 1×N optical switch, so as to perform an OTDR test on a specific fiber span according to a time marker.

2. The OTDR resource according to claim 1, wherein: The controller module is incorporated into the pluggable OTDR element.

3. The OTDR resource according to claim 1, wherein: The 1xN optical switch includes discrete components coupled to an output port of the pluggable OTDR element.

4. The OTDR resource according to claim 1, wherein: The 1×N optical switch is integrated with the pluggable OTDR element and includes a signal path formed between an output end of the pluggable OTDR element and an input end of the 1×N optical switch.

5. The OTDR resource according to claim 1, wherein: The pluggable OTDR element comprises: a first module for housing electrical components and active optical components utilized in performing OTDR measurements; and A second module is provided for accommodating passive optical components for guiding optical signals between the pluggable OTDR element and the optical fiber span under test.

6. The OTDR resource according to claim 5, wherein: The first module also includes a controller module for controlling the selection of optical fiber spans for OTDR testing.

7. The OTDR resource according to claim 5, wherein: The second module includes a three-port optical circulator having an input port responsive to an optical probe beam generated by an active optical device within the first module, a bidirectional optical port coupled to an input end of the 1×N optical switch, and an output port responsive to back reflections of the optical probe beam passing through the 1×N optical switch in a reverse direction, the output port being used to direct the returned reflections toward a photoelectric detection device in the first module.

8. The OTDR resource according to claim 7, wherein: The second module also includes a bandpass filter disposed in a signal path from an output port of the optical circulator.

9. The OTDR resource according to claim 8, wherein: The bandpass filter comprises a wavelength tunable bandpass filter.

10. The OTDR resource according to claim 5, wherein: The 1×N optical switch is arranged in the second module.

11. The OTDR resource according to claim 1, further comprising: A plurality of wavelength division multiplexers (WDM) of number N are provided, each WDM being coupled between a separate output signal path of the 1×N optical switch and a separate optical fiber span of the plurality of optical fiber spans.

12. The OTDR resource according to claim 1, wherein: The pluggable OTDR element comprises: An active OTDR module, the active OTDR module comprising: a light emitter configured to generate the optical probe beam; an optical receiver configured to receive an incoming reflected light wave associated with the optical detection signal; and electrical processing and control circuitry for energizing the optical transmitter and converting received reflected light waves into data for generating an OTDR output trace; and A passive OTDR module, the passive OTDR module comprising: A directional optical coupling device is coupled to the active OTDR module and is configured to direct the propagation of the optical probe beam toward the optical fiber span under test and to direct reflected light waves attributed to the optical probe beam into the active OTDR module.

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