Bidirectional optical fiber auto-notifier test system

Optical fiber communication systems include monitor filters that permit OTDR or other monitoring signals to co-propagate or counter-propagate on link fibers. OTDR measurements are periodically triggered, and acquired OTDR signatures are compared with store signatures to locate faults. The monitor filter can be used in single direction, dual OTDR bidirectional, or signal OTDR bidirectional (loopback) monitoring.

BACKGROUND

Optical communication between data centers permits high data rate communication that can be used to satisfy user demands for both data storage and processing of stored or other data. In order to provide a satisfactory user experience, storage and processing outages must be infrequent and must be quickly identified and repaired. Unfortunately, in many cases, such outages are identified only when users encounter difficulties. In addition, repair is often unacceptably slow as it is difficult to identify a fiber location associated with an identified outage. Finally, even with an identified fiber location in a network topology, it is often time-consuming to find the corresponding physical location and determine who is responsible for repair. Accordingly, improved monitoring systems are needed that permit rapid identification and repair of fiber faults.

DETAILED DESCRIPTION

Filters that include fiber wavelength division multiplexers are situated to couple optical time domain reflectometers (OTDRs) to optical communication networks to provide built in fiber link testing. Using OTDRs, fiber links can be evaluated, even during operation, and network deterioration detected, and locations associated with deterioration identified for remediation. In one example, OTDR signals are coupled to a remote transceiver via a first link fiber and looped back via a second link fiber so that a single OTDR can interrogate a pair of link fibers with OTDR optical signals that are counter-propagating with respect to optical communication signals propagating in the first and second link fibers.

In some examples, values, procedures, or apparatus' are referred to as “lowest”, “best”, “minimum,” or the like. It will be appreciated that such descriptions are intended to indicate that a selection among many used functional alternatives can be made, and such selections need not be better, smaller, or otherwise preferable to other selections. In some cases, locations of data centers or transceivers or other network components are referred to as local or remote for convenient description. Typically, local or remote locations are interchangeable.

In the following description, representative optical filters and filter assemblies are used that combine and separate optical signals used for data or other communications and signals such as optical time domain reflectometer signals (typically, optical pulses) used to monitor network and fiber characteristics. Such optical filters are generally referred to below as “filters” or “monitor filters.” Optical fibers used to communication between data centers or between other different locations are referred to as “link fibers” to distinguish such fibers from short fibers and fiber segments used to form transmitters, receivers, and other optical communication components.

In some examples, optical fiber connectors are used to permit system reconfiguration. As shown in the accompanying drawings, angled physical contact (APC) or ultra physical contact (UPC) connectors are used. UPC connectors typically have slightly rounded end facets for direct contact to reduce coupling loss and in some drawings are noted as with a “U” in a box. APC connectors have end facets that are polished at an angle to reduce light reflects back into a fiber. For low return loss, APC connectors are generally preferred and are noted with an “A” in a box is some drawings. While UPC or APC connectors can be superior in some applications, either or both can generally be used. In other examples, fiber connections a made with splices such as fusion splices.

Fiber couplers or wavelength sensitive fiber couplers are used in some examples. Wavelength sensitive fiber couplers are referred to herein as fiber wavelength division multiplexers (FWDM). Such devices include one or more inputs and outputs, typically as lengths of optical fiber. For convenience, in some cases such fiber inputs and output are referred to as ports or fiber ports, as whether a particular fiber serves as an input or output depends on how the fiber coupler is arranged with respect to optical sources and detectors.

In typical examples, a wavelength sensitive fiber coupler or FWDM is selected to optically couple a first port to a second port at a first wavelength or wavelength range and optically couple a third port to the second port at a second wavelength or wavelength range that is different from the first wavelength or wavelength range. In some embodiments, the first wavelength range is associated with optical fiber communications such as a dense wavelength division multiplexing (DWDM) and the second wavelength or wavelength range is associated with probe pulse provided by an Optical Time Domain Reflectometers (OTDR).

Optical Time Domain Reflectometers (OTDRs) include a beam source that directs a beam along a fiber under test. Portions of the beam returned to the OTDR are detected at a receiver, and based on a propagation time in the fiber under test, fiber faults, breaks, poor connections, and other characteristics can be located for service. In most OTDRs, a very large return signal at a particular location can cause a blind spot or otherwise limit fault detection for a distance beyond the very large reflection, although in some cases optical switches are used to attenuate large reflections at particular locations. Optical fibers also return portions of OTDR signals throughout a fiber length due to Rayleigh scattering. Such scattering is weak, but most OTDRs are arranged to measure scattering, and a fiber break even absent a reflection back to an OTDR is apparent due to loss of a scattering signal.

As used herein, signal or optical signal such as an OTDR signal or communication signal refers to a time varying optical beam that is generally contained in and guided by a waveguide such as an optical fiber. OTDR signals are typically pulses, but sophisticated OTDRs using more complex signals (such as coded signals) can be used. Communication signal generally refers to an optical signal modulated to communicate data. For convenient explanation, DWDM multiplexed signals are used for illustration. Various types of faults can be detected using the disclosed approaches such as fiber breaks and excessive connector losses.

With reference toFIG. 1, a monitor filter100includes an optical fiber connector102that is coupled to a fiber port103of a first fiber wavelength division multiplexer (FWDM)104. An optical fiber connector106is coupled to a reflective optical filter108that is coupled to a fiber port114of the first FWDM104. The reflective optical filter108is configured to reflect at wavelengths associated with OTDR pulses and transmit at communication signal wavelengths. In typical embodiments for use with dense wavelength division multiplexing (DWDM) or other communication standards, optical signals at wavelengths associated with such communications are transmitted (typically in a band from 1290 nm to 1580 nm) and optical signals in a band from 1600 nm to 1670 nm are reflected. Typically, an OTDR probe pulse wavelength at or about 1625 nm is used. However, different bands can be used, and the selection of bands is generally limited only by the transmission bandwidth of the optical fibers used. For convenience in the following description, λcomor λdwdmrefers one or more communication wavelengths (or bands) such as DWDM wavelengths, and λOTDRrefers to a wavelength (or band) used for OTDR fiber link assessment.

The first FWDM104is coupled via fiber port112to a fiber connector110that is provided for coupling to an OTDR or to a loopback fiber as discussed below. The first FWDM104is configured to couple an OTDR beam between the fiber ports103,112and couple a communication beam between the fiber ports103,114. For example, a combined communication beam/OTDR beam received from the connector102at the fiber port103is coupled so that an OTDR beam portion is coupled to the connector110and a communication beam portion is coupled to the connector106. Portions of the OTDR beam coupled by the first FWDM104to the fiber port114are reflected by the filter108and do not reach the connector106or are substantially attenuated.

In the arrangement ofFIG. 1, the first FWDM104permits an OTDR beam from the connector110and a communication beam from the connector106to combined and directed to the connector102. In addition, the first FWDM104permits a combined communication/OTDR beam received from the connector102to be separated into an OTDR beam directed to the connector110and a communication beam directed to the connector106. In most examples, OTDR beams and communication beams are arranged to counter-propagate due to interference effects and nonlinearities that can arise with co-propagation. Thus, it is generally preferable to situate the filter100to couple an OTDR beam from the connector102to the first FWDM104and to couple a communication beam received at the connector106to the connector102. The reflective filter108then attenuates OTDR beam portions that might otherwise arrive at the connector102.

A second fiber connector132is coupled to a fiber port133of a second FWDM134that is coupled by the second FWDM134to a fiber port142and to the connector130at an OTDR wavelength (or wavelength range) and to a fiber port144and the connector136at a communication wavelength (or wavelength range). In order to avoid co-propagating OTDR and communication beams, the second FWDM134is generally used to couple a communication beam to the connector136and to direct an OTDR beam from the connector136to the connector132.

InFIG. 1, an example configuration in which communication beams and OTDR beams counter-propagate is indicated with DWDM beam inputs at the connectors106,132, DWDM beam outputs at the connectors102,136, and OTDR beam outputs at the connector132and OTDR beam input at the connector102. The connectors102,132are generally coupled to link fibers so as to connect the filter to one or more remote optical transmitters, receivers, and/or OTDRs.

With reference toFIG. 2A, a communication system200includes a DWDM transceiver202coupled to a filter204such as the filter100ofFIG. 1so as to transmit a DWDM communication signal to an FWDM206that couples the DWDM communication signal to a link fiber208. The DWDM transceiver202is coupled to an FWDM210to receive a communication signal from a link fiber212. In addition, an OTDR214is coupled to transmit an OTDR signal on the link fiber212. The OTDR234directs an ODTR signal to the filter220.

The filter220is coupled to the link fiber212and couples the OTDR signal from the OTDR214to a FWDM216that directs the OTDR signal to a reflection filter222and a transmitted communication signal from the DWDM transceiver230to a receiver of the DWDM transceiver202. A receiver of the DWDM transceiver230is couple to receive a communication signal from the link fiber208with an FWDM232that couples an OTDR signal from an OTDR234to the link fiber208.

The OTDRs214,234are coupled to the filters204,220, respectively, via fiber assemblies215,235that include fibers that permit OTDR dead zones produced at OTDR connectors and components to be displaced in time from optical circuit features of interest. Fiber lengths of between 100 m and 5 km are typical, and in some examples, lengths of 500 m, 100 m, 1500 m, or 2000 m are used. Each of the filters204,220includes an unused input/output (connectors240,241) that can be omitted if desired, or used as shown in some examples below.

FIG. 2Billustrates a representative filter260that is similar to the filters204,220but includes a single FWDM262and a reflective or other OTDR wavelength filter264so that a communication beam is coupled through the filter264to a connector266. An OTDR signal from a remote OTDR can be coupled into the filter260at the connector266, and blocked from a transmitter by the reflective filter264.

Referring toFIG. 3A, a communication system includes a first data center300and a second data center302that are coupled via optical fibers304,306. DWDM or other communication transceivers308,310of the data centers300,302are coupled to monitor filters312,314, respectively, that are similar to the filter shown inFIG. 1, and then to the optical fibers304,306. An OTDR transmitter/receiver320is coupled to a fiber assembly324that includes a fiber length326so that reflections of OTDR pulses at the OTDR transmitter/receiver320such as internal reflections of reflections at an input/output connector (for example, a connector328) do not result in “blind spots” due to large reflections obscuring fiber features of interest.

The OTDR transmitter/receiver320directs an OTDR signal to the filter314so that the OTDR signal is coupled to the optical fiber304and the filter312. A portion of the OTDR signal is then coupled by an FWDM330to a fiber bypass334. The OTDR signal returned to the OTDR320by an OTDR reflective filter332can be associated with the filter312, and receipt of such a signal portion by the OTDR320can be used to verify or evaluate an optical connection between the first filter312and the second filter314. Typically, any breaks, misaligned connections, or other optical losses between the first filter312and the second filter314are associated with relatively large return (reflected) optical signals and/or changes in Rayleigh backscattering signals returned to the OTDR320. For example, a broken link fiber may be associated with a reflection at a fiber break or with disappearance (or reduction) of received Rayleigh backscatter beyond the fiber break. Communication signals can be coupled between the second filter314(and the second transceiver310) and the first filter312(and the first transceiver308) and the fiber304can transmit both OTDR signals and communication signals.

At the fiber bypass334, the OTDR signal is directed to an FWDM336and then via the fiber306to an FWDM338of second filter314. A portion of the OTDR signal is directed to a reflective filter340and returned to the OTDR transmitter/receiver320and another portion directed to an unused port342that is available for coupling to an additional OTDR situated at the filter302or at the filter312. Communication signals can be coupled between the second filter314(and the second transceiver310) and the first filter312(and the first transceiver308) and the fiber306can transmit both OTDR signals and communication signals.

In the arrangement ofFIG. 3A, a single OTDR is used, and can be situated at filters associated with either of the transceivers308,310. For example, by situating a single OTDR at each of the filters312,314, OTDR optical signals and communication optical signals can be arranged to counter-propagate. In addition, each of the data centers300,302can be identically arranged, and a common filter/OTDR configuration can be used throughout a network. In other examples, unused ports (such as port342) can be coupled to an additional OTDR such as optional OTDR375as shown inFIG. 3Bso that a single data center can interrogate both link fibers304,306, although OTDR optical signals and communication optical signals might then co-propagate on the link fiber306. Alternatively, a single OTDR such as the OTDR320can be coupled to the port342as well as shown inFIG. 3C. Received OTDR signals may then exhibit overlapping features but these features would still permit link assessments. Such overlap can be avoided with additional optical delay between OTDR signals introduced into the link fiber304and the link fiber306. Such delay can be provided with one or more additional fiber delays, or by selecting a suitable length for the fiber length326. As shown inFIG. 3C, a fiber assembly378is coupled to the OTDR320and includes the fiber length326that couples OTDR optical signals to a connector379and to a fiber coupler380which in turn couples portions of the OTDR optical signals to a fiber length382. As a result, OTDR measurements of the link fibers304,306are displaced. A network supervisor350is coupled to the OTDR320to compare OTDR signatures to determine possible faults and fault locations. Based on the fault location, an appropriate notification can be sent for fault remediation.

Referring toFIG. 4A, a transceiver402at a first data center402is coupled to a filter403as illustrated above that is in turn coupled to link fibers414to communicate with a transceiver405at a second data center404or other location. An OTDR408is coupled to the filter403to evaluate one or both of the fibers414and communicate OTDR evaluations to a network supervisor410. The network supervisor410is coupled to one or more tangible storage devices412,414that store OTDR signatures and OTDR control and communication instructions. Based on changes in OTDR signatures, the network supervisor410can send requests for fault correction to dark fiber vendors or the data center operators. In an example shown inFIG. 4B, an initial OTDR signature488includes a portion490associated with a reflection and a portion491associated with Rayleigh backscatter. A subsequently measured OTDR signature489includes a portion494associated with an additional reflection and a portion495associated with Rayleigh backscatter having a significantly reduced amplitude with respect to Rayleigh backscatter in the OTDR signature488, indicating a coupling loss. In this example, this coupling loss is noted as internal to a data center, and can be reported as such. Typically, OTDR signatures are periodically acquired and evaluated for the changes in reflectance at one or more locations, and changes (especially decreases) in Rayleigh backscatter. OTDR signatures are generally acquired at rates of between about 10 mHz to about 100 Hz, but other rates can be used.

The network supervisor (or the OTDR408) can control OTDR pulse power, pulse repetition rate, pulse duration (and thus OTDR resolution), averaging, or other OTDR measurement parameters. ODTR signals can be produced relatively infrequently to assess link condition, and rates of 10 OTDR signal pulses per second is sufficient, but higher or lower rates can be used. As discussed above, OTDR measurements can be used to detect changes in reflectance for fault assessment, but detection of Rayleigh scattering can also be used, particularly in fiber portions that in which reflectance is otherwise low.

FIG. 5illustrates a method500of evaluating a fiber network. At502, OTDR pulse characteristics and repetition rate are selected, and at504, an OTDR is energized accordingly, and the OTDR pulses are launched into a filter that couples the OTDR pulses into at least one link fiber. OTDR pulse repetition rate is generally selected to avoid multiple pulses propagating in links under test and to avoid interference with communication signals. OTDR pulse width is generally selected based on an intended combination of range and resolution. Fiber signatures are acquired at506that typically include signature portions associated with link fibers and data center/local fibers and other components, and are compared with stored signatures at508. At510, status is reported based on the comparison, and fault correction can be initiated, or stored signatures updated.

A representative method600shown inFIG. 6includes placing filters and assigning OTDRs to selected filters at602. For example, multiple OTDRs can be provided for bidirectional monitoring (e.g., similar to the arrangement ofFIG. 2A), or a loopback configuration (similar to the arrangement ofFIG. 5) can be selected. At608, OTDR signatures are acquired and compared with stored signatures at610. Fiber status is reported at612based on the comparison. In some examples, stored signature are not required and reflections larger than a predetermined threshold are reported as faults, along with Rayleigh scattering that is less than a predetermined value. The predetermined value is scaled with OTDR pulse length as Rayleigh scattering is a function of OTDR pulse width.

FIG. 7illustrates representative exemplary embodiments of signature events for use in monitoring. Reflectance at various propagation distances (and associated GPS coordinates) is recorded, and distances associated with vendors or with data center operators are noted for use in error notification.

Referring toFIG. 8, a communication device800includes a housing that includes a connector slot802for coupling an OTDR to a fiber delay806(internal to the device800) as discussed above with two APC type connectors. A connector slot804accommodates connector pairs810(APC),812(UPC),814(UPC) for coupling to an OTDR, line fibers, and communication transceivers/transmitters/receivers, respectively.

In the examples above, filters that permit use of OTDR and communication signals are coupled to communication transceivers. In some examples, a particular filter is coupled to receivers and transmitters associated with different transceivers, or with individual transmitters and receivers. In some cases, a single filter is coupled to two, three, or more data centers.

FIG. 9is an example communication system900in which transceivers902,904are coupled to respective filters906,920and link fibers932,934. As shown, a single OTDR914couples OTDR pulses to the link fiber934, while the link fiber932is not coupled to an OTDR at all. Such an arrangement can be referred to as a single OTDR, unidirectional monitoring system.

FIG. 10illustrates a representative single OTDR, unidirectional, cascaded monitoring system1000. An OTDR1014is coupled to a first filter1002that is in turn coupled to a second filter1004via link fibers1010. The second filter1004is coupled to a third filter1006that is coupled to link fibers1012. As shown, an OTDR pulse is delivered so as to counter-propagate with communication signals in the filters1002,1004,1006; in the filters1002,1004the communication signal is a receiver-side signal and in the filter1004, the communication signal is a transmitter-side signal. Only one of the link fibers is coupled for OTDR testing, but in other examples, both are.

With reference toFIG. 1100, a computing environment1100for network monitoring and management includes one or more processing units1110,1115and memory1120,1125. InFIG. 11, this basic configuration1130is included within a dashed line. The processing units1110,1115execute computer-executable instructions. A processing unit can be a general-purpose central processing unit (CPU), processor in an application-specific integrated circuit (ASIC) or any other type of processor. In a multi-processing system, multiple processing units execute computer-executable instructions to increase processing power. For example,FIG. 11shows a central processing unit1110as well as a graphics processing unit or co-processing unit1115. The tangible memory1120,1125may be volatile memory (e.g., registers, cache, RAM), non-volatile memory (e.g., ROM, EEPROM, flash memory, etc.), or some combination of the two, accessible by the processing unit(s). The memory1120,1125stores software1080implementing one or more innovations described herein, in the form of computer-executable instructions suitable for execution by the processing unit(s). For example, control procedures, signature comparisons, signatures, and fault thresholds can be stored.

A computing system may have additional features. For example, the computing environment1100includes storage1140, one or more input devices1150, one or more output devices1160, and one or more communication connections1170. An interconnection mechanism (not shown) such as a bus, controller, or network interconnects the components of the computing environment1100. Typically, operating system software (not shown) provides an operating environment for other software executing in the computing environment1100, and coordinates activities of the components of the computing environment1100.

The tangible storage1140may be removable or non-removable, and includes magnetic disks, magnetic tapes or cassettes, CD-ROMs, DVDs, or any other medium which can be used to store information in a non-transitory way and which can be accessed within the computing environment1100. The storage1140stores instructions for the software1080implementing one or more innovations described herein.

The input device(s)1150may be a touch input device such as a keyboard, mouse, pen, or trackball, a voice input device, a scanning device, or another device that provides input to the computing environment1100. The output device(s)1160may be a display, printer, speaker, CD-writer, or another device that provides output from the computing environment1100.

FIG. 12illustrates an alternative coupling assembly1200that includes fiber couplers1202,1204and not FWDMs. Couplers generally increase total loss, and need not be wavelength sensitive. Dual input couplers for single mode fibers (such as the couplers1202,1204) generally have four ports, but only three are shown for clarity. Because the coupler1204is not wavelength sensitive, significant portions of OTDR signals can be directed toward a connector1206, and an OTDR filter1208can be situated to block or attenuate at OTDR wavelengths. In addition, a DWDM filter1210is situated to block or attenuate communication signals directed to a loopback fiber1212. The coupling assembly can be used in single direction or bidirectional measurements, or loopback measurements.

In the above examples, fiber components such as FWDMs and couplers are used to combine and direct OTDR and communication signals. In other examples, prisms, mirrors, gratings, thin film coatings, holographic elements, or other optical components can be used to route communication and OTDR signals. In addition, planar waveguide components such as waveguides and components defined on or in silicon or other materials can be used.