Apparatus and method for testing fiber optic communications network

Abstract

An apparatus (170) for performing diagnostics on an optical cable (180) in a fiber optic network (100), the apparatus comprising: a reflector (240); a dichroic filter (220) configured to output from input light emitted through the optical cable: a reflected component; and a transmission component; an optical switch (230) arranged to receive the transmission component and interface with the reflector, and configured to perform switching between optically connecting the reflector to the transmission component and disconnecting the reflector from the transmission component; and a photovoltaic PV power source (250) arranged to receive the reflected component and electrically connected with the optical switch to generate power from the reflected component and power the switching of the optical switch. A fiber optic network (100) and a method (300) of operating the network are also provided.

Description

Technical Field

[0001] This invention relates to an apparatus for testing fiber optic communication networks. Background Technology

[0002] Passive Optical Network (PON) is a fiber optic telecommunications technology used to provide broadband network access to end customers using a point-to-multipoint topology. In this technology, a single optical fiber serves multiple endpoints by using a powerless (i.e., passive) splitter to divide the fiber bandwidth between endpoints via the introduced fiber.

[0003] An optical time-domain reflectometer (OTDR) is an optoelectronic instrument used to characterize fiber optic networks. An OTDR works by sending short pulses of light into the fiber optic network and measuring the amount of light reflected back. The time it takes for the light to travel to the reflection point and return is used to calculate the distance to that point.

[0004] Using an OTDR can make it difficult to distinguish individual optical cables extending beyond the splitter towards the customer-side terminal, as these cables may lack distinguishing features. Furthermore, even effective OTDR measurements outside the splitter can be challenging because the optical loss caused by the splitter may be too great to detect drop fibers. Additionally, selective testing of individual such cables is challenging due to the passive nature of PONs and often requires expensive equipment such as fiber Bragg gratings.

[0005] The purpose of this invention is to at least alleviate some of the aforementioned problems. Summary of the Invention

[0006] According to a first aspect of the invention, an apparatus is provided for performing diagnostics on optical cables in an optical fiber network, the apparatus comprising: a reflector; a dichroic filter configured to output a reflected component and a transmitted component from input light emitted through the optical cable; an optical switch arranged to receive the transmitted component and interface with the reflector, and configured to perform switching between optically connecting the reflector to the transmitted component and disconnecting the reflector from the transmitted component; and a photovoltaic (PV) power supply arranged to receive the reflected component and electrically connected to the optical switch, thereby generating power from the reflected component and supplying power for switching of the optical switch.

[0007] Preferably, when the optical switch is not energized, the optical switch is biased to disconnect the reflector from the transmission component. Preferably, the PV power supply is therefore configured to supply power only for switching purposes to connect the reflector to the transmission component.

[0008] Preferably, the device includes a port for connecting a dichroic filter to an output of an optical cable via a band-drop filter, wherein input light is received from the band-drop filter via the port. Optionally, the device includes the band-drop filter. Optionally, the band-drop filter is configured to output light to the dichroic filter at a service signal wavelength and / or a diagnostic test signal wavelength. Preferably, the service signal wavelength is used to transmit telecommunications services to users. Preferably, the service signal operates at a service wavelength, and wherein the service wavelength is between 1200 nm and 1650 nm. Preferably, the diagnostic test signal wavelength does not carry the signal used to provide telecommunications services to users, and is therefore used only for testing and diagnostics, and operates at the diagnostic test wavelength. Preferably, the diagnostic test wavelength is within the U-band or C-band as defined by the ITU Telecommunication Standardization Sector. Preferably, the diagnostic test wavelength is between 1200nm and 1700nm, more preferably between 1500nm and 1650nm, and even more preferably between 1525nm and 1575nm.

[0009] Preferably, the fiber optic network includes: a plurality of optical network units; a splitter; and a plurality of distribution optical cables, each of which extends between the splitter and one of the plurality of optical network units; and wherein the device includes a connector for connection (and connectable to) one of the plurality of distribution optical cables and downstream of the splitter. Preferably, the plurality of distribution optical cables include drop cables and / or feeder cables. Preferably, the device is connected upstream of the optical network unit (ONU).

[0010] Preferably, the filter and / or another filter has a reflectivity that is substantially independent of temperature.

[0011] According to another aspect of the invention, an optical fiber network comprising the devices described above is provided. Optionally, the optical fiber network is a passive optical network (PON). Preferably, the optical fiber network comprises at least two of the devices, wherein: the at least two devices are connected to different distribution optical cables; and each dichroic filter of each of the at least two devices is configured to filter at a different wavelength.

[0012] Preferably, the at least two devices are connected to the same optical cable. Preferably, the different wavelengths do not overlap with each other partially or completely. Optionally, each bandstop filter associated with each distribution optical cable is configured to filter at a different wavelength.

[0013] According to another aspect of the present invention, a method for operating an optical fiber network is provided, the network comprising: an optical time domain reflectometer (OTDR); a plurality of ONUs; and at least one device as described above and / or below, wherein the at least one device is coupled to an optical cable serving at least one of the plurality of ONUs; the method comprising the steps of: sending a diagnostic signal from the OTDR to the plurality of ONUs, wherein the diagnostic signal is configured to switch the at least one device to optically connect the reflector to a transmission component; and measuring reflection from the reflector at the OTDR.

[0014] Preferably, when the network comprises at least two devices, and when the devices are connected to different ONUs and configured to perform optical switching at different (and more preferably, non-overlapping) wavelengths of the diagnostic signal (or "input light"), the OTDR is operated to send a diagnostic signal configured to perform optical switching on a subset (i.e., less than the whole) of the at least two devices, and more preferably only one of the devices. Preferably, the method includes an additional step of sending another diagnostic signal (optionally, after measuring reflections from the subset), which is configured to perform optical switching from a device that does not form part of the subset among the at least two devices.

[0015] A computer-readable carrier medium including a computer program, which, when executed by a computer, causes the computer to perform the above-described method.

[0016] Preferably, the reflector is a retroreflector or a bidirectional reflector. Preferably, the reflector is a broadband reflector. Optionally, the dichroic filter and / or another dichroic filter is: interferometric, holographic, or thin-film type. Preferably, the dichroic filter is a channel drop filter. Preferably, the dichroic filter is configured to have transmission and / or reflection wavelengths that are substantially independent of temperature, and more preferably has a response of less than 0.2 pm / ℃ in a temperature range of -40℃ to +85℃. Preferably, the PV power supply is arranged to receive only the reflected component and not the transmitted component. Preferably, the PV power supply is remotely powered from the input light via the reflected component. Preferably, the input light is provided by an optical time-domain reflectometer, an optical frequency-domain reflectometer, and / or an optical line terminal. Preferably, the PV power supply comprises or is composed of photovoltaic cells. Preferably, the device includes another dichroic filter disposed between the dichroic filter and the PV power supply, thereby intercepting the reflected component and outputting a portion of the reflected component to the PV power supply. Preferably, the dichroic filter and / or the other dichroic filter are channel-down filters. Preferably, the dichroic filter is configured to filter light of a first wavelength, and the other dichroic filter is configured to filter light of a second wavelength. Optionally, the first wavelength and the second wavelength may be the same or different. Optionally, the first wavelength may include all or part of the second wavelength. Preferably, the dichroic filter and the other dichroic filter are arranged in series, or in a daisy-chain configuration.

[0017] This invention includes any novel aspects described and / or illustrated herein. The invention also extends to methods and / or apparatus substantially as described herein and / or illustrated with reference to the accompanying drawings. The invention is also provided as computer programs and / or computer program products for performing any methods described herein and / or embodying any apparatus features described herein, and computer-readable media having thereon stored programs for performing any methods described herein and / or for specifically implementing any apparatus features described herein. Features described as hardware-implemented may alternatively be software-implemented, and vice versa.

[0018] Any device feature can also be provided as a corresponding step of the method, or vice versa. As used herein, device plus functional features can alternatively be expressed according to their corresponding structure, such as a suitably programmed processor.

[0019] Any feature in one aspect of the invention may be applied in any suitable combination to other aspects of the invention. Any, some, and / or all features in one aspect may be applied in any suitable combination to any, some, and / or all features in any other aspect. Specific combinations of the various features described and defined in any aspect of the invention may be implemented and / or provided and / or used independently.

[0020] As used throughout the text, unless otherwise stated, the word "or" may be interpreted in an exclusive and / or inclusive sense.

[0021] The present invention extends to apparatuses, telecommunication networks, and methods of operating telecommunication networks as described herein and / or substantially as shown with reference to the accompanying drawings. The invention will now be described by way of example only, with reference to the accompanying drawings, in which: Figure 1 An exemplary fiber optic communication network including diagnostic devices is schematically illustrated. Figure 2 Schematic details of the diagnostic device are shown; Figure 3 The process of operating a fiber optic communication network is illustrated; and Figure 4 shows a schematic example of an optical time domain reflectometer (OTDR) trace. Detailed Implementation

[0022] Figure 1 This is a schematic diagram of a fiber optic communication network 100, such as one used to provide wide-area fixed access broadband network services.

[0023] Network 100 includes: an optical line terminal (OLT) 110; an optical time domain reflectometer (OTDR) 120; an OTDR switch 130; a WDM splitter 140; a broadband splitter (or power splitter) 150; multiple optical network units (ONUs) 160, including a first ONU 160-1, a second ONU 160-2, a third ONU 160-3, and a fourth ONU 160-4; and multiple diagnostic devices 170, including a first diagnostic device 170-1, a second diagnostic device 170-2, a third diagnostic device 170-3, and a fourth diagnostic device 170-4 associated with each corresponding numbered ONU.

[0024] The aforementioned components are interconnected using optical links provided by at least optical cables (indicated by arrow lines) to provide telecommunications services between at least OLT110 and each ONU 160, and to provide diagnostic testing services between at least OTDR 120 and each of the same ONU 160 and / or multiple diagnostic devices 170.

[0025] OLT 110 is located at the head end of network 100, such as where the local switch is located, and is connected to multiple ONUs 160 via WDM splitter 140 and power splitter 150 (where the former is downstream of the latter, i.e., sequentially closer than the latter). Each ONU is connected to power splitter 150 via a dedicated corresponding distribution (also called "drop" or "feeder") optical cable 180; that is, a first optical cable 180-1 for connecting ONU 160-1, a second optical cable 180-2 for connecting ONU 160-2, a third optical cable 180-3 for connecting ONU 160-3, and a fourth optical cable 180-4 for connecting ONU 160-4.

[0026] The OLT 110 and OTDR 120 are operatively connected to a high-level network management software application (not shown), including a component management system (not shown) and / or a network management system (not shown). For example, via the network management software application, a user or network 100 can trigger diagnostic tests to be performed by the OTDR 120.

[0027] The OTDR 120 is an optical reflectance measurement device for Network 100. The OTDR 120 enables the detection of physical discontinuities in optical links (i.e., breaks, faulty connections and splices in optical fibers, excessive fiber bending and other structural deformations).

[0028] The OTDR 120 is operated by sending diagnostic signals along network 100. Discontinuities in the fiber optic structure cause backscattering and reflections. By measuring the time it takes for the signal to return to the OTDR (from which distance can be inferred) and the amplitude of the received signal relative to the transmitted signal, a properly configured OTDR can help determine the location, nature, and extent of physical discontinuities. For example, a sudden drop in backscattering to noise floor can indicate a complete break, while small reflections can indicate a connector with an air gap.

[0029] exist Figure 1 In the example, OTDR 120 is a separate device from OLT 110, and the OTDR is connected to multiple ONUs 160 using at least the same backbone network as the OLT (i.e., via WDM splitter 140 and power splitter 150).

[0030] Each diagnostic device 170 is connected to one of the fiber optic cables 180.

[0031] Figure 2 The first diagnostic device 170-1 is illustrated in detail, which is connected to the first optical cable 180-1 serving the first ONU 160-1 via a bandstop filter 210.

[0032] A bandstop filter 210, in the form of a dichroic filter, is arranged in a straight line with the first optical cable 180-1. The bandstop filter 210, as part of a direct-through branch, allows a specific frequency band to pass through (e.g., for delivering service signals) to the associated first ONU 160-1, while also reflecting another frequency band (e.g., for diagnostic signals) as part of a reflection branch (in...). Figure 2 (The dashed line shown is emanating from the bandstop filter 210).

[0033] Furthermore, the first diagnostic device 170-1 includes: a channel pull-down filter 220; an optical switch 230; a reflector 240; and a photovoltaic (PV) power supply 250.

[0034] The channel pull-down filter 220 is optically connected to the band-stop filter 210 to receive the reflection branch as input.

[0035] The channel-down filter 220 is also a dichroic filter. Therefore, using an input in the appropriate spectral band (described in more detail below), the channel-down filter outputs: the reflection component (in... Figure 2 (shown as dashed lines); and the transmission component (in...) Figure 2 (Shown as dashed lines). The channel pull-down filter 220 is optically connected to the optical switch 230 and the PV power supply 250 to output the transmitted component to the optical switch and the reflected component to the PV power supply.

[0036] The PV power supply 250 includes a photovoltaic cell and a battery (not shown separately for simplicity). The PV power supply 250 is configured to generate and then store electrical energy from the reflection component as input from the channel pull-down filter 220. The PV power supply 250 is electrically connected to the optical switch 230, such that the switching of the optical switch (discussed in more detail below) is powered by the PV power supply.

[0037] Optical switch 230 is configured to perform switching powered by PV power supply 250 to connect and disconnect the optical path between channel pull-down filter 220 and reflector 240. Thus, when the optical path is connected, the transmitted component received from the channel pull-down filter at the optical switch is emitted onto the reflector, and when the optical path is disconnected, the transmitted component is not emitted onto the reflector. Optical switch 230 can be a thin-film switch, a micro-electromechanical system (MEMS) switch, an acousto-optical switch, or an electro-optical switch. When not powered, optical switch 230 is biased to disconnect the optical path to reflector 240. However, when powered, and simultaneously, the optical switch connects the optical path to the reflector.

[0038] Reflector 240 is a broadband retroreflector. Optical switch 230, channel-down filter 220, and channel-down filter 210 are all bidirectional. In this way, when the optical switch connects the optical path to the reflector, the light incident on the reflector (i.e., the transmitted component) is reflected back through the optical switch, channel-down filter, and band-stop filter, and then reaches OTDR 120. In this way, the OTDR can be used to interact with reflector 240 when performing diagnostic measurements.

[0039] The aforementioned components of the diagnostic device 170-1 are configured to operate using diagnostic signals from the OTDR 120 (i.e., switching reflectors in and out of the path). In this example, the diagnostic signals have at least the following characteristics: 1. Includes a wavelength range, wherein the wavelength range is: a. The light is reflected by the band-stop filter 210, thereby creating a reflection branch that is input into the channel pull-down filter 220; b. Subsequently, the light is reflected by the channel pull-down filter 220, thereby generating a reflected component that is input into the PV power supply 250; c. The light is emitted by the channel pull-down filter 220, thereby generating a transmission component that is input to the reflector 240 via the optical switch 230; d. Within the spectral response of the PV power supply 250, so as to excite the components; and e. Reflected by reflector 240; and 2. It has sufficient intensity to excite the PV power supply 250 and can be detected by an OTDR that has traveled to and from the reflector 240.

[0040] The diagnostic signal is also configured not to carry the signal used to provide telecommunications services to the ONU 160, but only for testing and diagnostics; this contrasts with the service signal used to transmit telecommunications services to the ONU 160. The diagnostic and service signals do not overlap in the spectrum.

[0041] By matching the diagnostic signal to the filtered wavelength of the band-stop filter 210, the service signal is output entirely and solely as the transmit branch, while the diagnostic signal is output solely as the reflect branch. Therefore, by connecting one of the diagnostic devices 170-1 to the distribution optical cable 180-1 via the band-stop filter 210, the diagnostic device 170-1 can receive input light (i.e., the reflect branch) while also allowing light to be transmitted to the associated ONU 160-1 (i.e., via the transmit branch).

[0042] For example, the service signal uses wavelengths between 1575 nm and 1650 nm, while the diagnostic test signal uses wavelengths between 1500 nm and up to 1575 nm. When the bandstop filter 210 is configured to filter out wavelengths below 1575 nm and transmit wavelengths above 1575 nm, the service signal and diagnostic signal can be separated and used in parallel to activate the diagnostic device and transmit telecommunications services.

[0043] Therefore, by appropriately switching the optical switch 230 using diagnostic signals, the reflector 240 can selectively enter and exit the path of the OTDR 120. Thus, each diagnostic device 170 provides a passive device to aid in the selective testing of the fiber optic network 100, and said passive device is remotely powered by light emitted from the headend.

[0044] Unless otherwise stated, the second diagnostic device 170-2, the third diagnostic device 170-3 and the fourth diagnostic device 170-4 have an arrangement and configuration corresponding to the first diagnostic device 170-1.

[0045] In one example, a plurality of diagnostic devices 170 are formed into at least two distinct groups, wherein each group is configured and / or arranged to have different responses to different spectral ranges of diagnostic signals, and in particular to be activated by different spectral ranges of diagnostic signals; this is achieved by each group having a diagnostic device having a filter 220 and / or a PV power supply 250 having different spectral responses and / or being respectively coupled to bandstop filters 210, each having different spectral responses.

[0046] In a specific example, four different groups are provided, each configured to be activated using a channel pull-down filter 220 with different filtering wavelengths. All other things being equal, the first diagnostic device 170-1, the second diagnostic device 170-2, the third diagnostic device 170-3, and the fourth diagnostic device 170-4 are equipped with channel pull-down filters 220, which are tuned to output reflection components only between 1500nm and 1518nm; between 1519nm and 1537nm; between 1538nm and 1555nm; and between 1556nm and 1574nm, respectively.

[0047] Therefore, diagnostic signals including wavelengths only at 1500 nm and 1518 nm will cause only the first diagnostic device 170-1 to be activated, thereby bringing the associated reflector 240 into the path, and subsequently only the first diagnostic device 170-1 (and the optical cable to it) can be detected by the OTDR (as described in more detail below). In this way, with proper tuning of the diagnostic signals, testing of only the first distribution optical cable 180-1 can be performed.

[0048] Furthermore, a wider bandwidth diagnostic signal (e.g., at 1500nm to 1518nm and 1556nm to 1574nm) can be used simultaneously to activate at least two of the diagnostic devices 170 (e.g., the first diagnostic device 170-1 and the fourth diagnostic device 170-4), and thus simultaneously to test the associated fiber optic cables 180 (e.g., the first fiber optic cable 180-1 and the fourth fiber optic cable 180-4).

[0049] Figure 3 The process 300 for operating a telecommunications network 100 to identify and test the distribution optical cable 180 is shown.

[0050] In the first step 310, the optical fiber cable 180 is selected for testing, and the corresponding diagnostic device 170 is identified. For example, the first optical fiber cable 180-1 associated with the first diagnostic device 170-1 is to be tested. In this example, the diagnostic signal used to activate only the first diagnostic device 170-1 is known in advance (e.g., 1500nm to 1518nm).

[0051] In the next step 320, the OTDR 120 is operated to transmit diagnostic signals capable of operating the identified diagnostic device (i.e., diagnostic signals spanning from 1500 nm to 1518 nm).

[0052] In the subsequent step 330, the OTDR 120 is operated to monitor the response from the reflector 240 of the identified diagnostic device. Having detected a response from the reflector of the identified diagnostic device (as described in more detail below with reference to FIG4), it can be determined that the identified diagnostic device has been activated. With each of the diagnostic devices activated at a different and non-overlapping wavelength, the resulting OTDR trace is a diagnostic test result specific to the selected cabling cable (e.g., the first cabling cable 180-1).

[0053] Figure 4 illustrates an exemplary schematic OTDR trace 400 that can be retrieved using process 300.

[0054] Figure 4a A first OTDR trace 400-1 is shown retrieved from an OTDR test performed using a signal (e.g., a service signal) that does not activate any diagnostic device 170. Therefore, the first OTDR trace 400-1 includes reflections 410 from all the cabling optical cables and has a high loss rate exceeding that of the power divider 150, causing the reflections to attenuate to the measurement noise floor 420.

[0055] Figure 4bA second OTDR trace 400-2 retrieved from an OTDR test is shown. This OTDR test is performed using a diagnostic signal that activates only one of the diagnostic devices (e.g., the first diagnostic device 170-1), thereby introducing reflector 240 into the path of the OTDR test. Consequently, a high-intensity reflection 430 exceeding the measurement noise floor 420 is detected, allowing for better observation outside the power divider 150 compared to the first OTDR trace 400-1, and improving isolation of reflections associated only with the first distribution cable 180-1.

[0056] Replacement and modification

[0057] In an alternative example, each of the bandstop filter 210 and the diagnostic device 170 is identical in its responsiveness to the same diagnostic signal. In this way, the same diagnostic signal will operate all diagnostic devices, and thus the distribution network of all ONUs can be tested simultaneously, while still allowing for selective (and remotely powered) introduction of the reflector 240.

[0058] In an alternative, the channel pull-down filter 220 comprises a plurality of dichroic filters connected in series, wherein each of the filters is configured to power 250 and / or another PV power source and transmit a diagnostic signal to 240 and / or another reflector. However, each of the filters is tuned to operate under different and progressively narrower frequency bands of diagnostic signals. In this way, unique and different wavelengths can be selectively tested.

[0059] In one example, the bandstop filter 210 and the channel pull-down filter 220 are configured to have a low wavelength shift (~0.1 pm / °C) with temperature, such that only a very small change in spectral response exists at typical operating temperatures (-40°C to 85°C). Furthermore, each of the filters can be in the form of a thin-film filter comprising layers of optical materials with different refractive indices.

[0060] Referring to step 310, it should be understood that the wavelength that activates the diagnostic device does not need to be known, but can be identified based on experience.

[0061] Each feature disclosed herein and (where appropriate) as part of the claims and drawings may be provided independently or in any suitable combination.

[0062] Any reference numerals appearing in the claims are for illustrative purposes only and should not limit the scope of the claims.

Claims

1. An apparatus for performing diagnostics on optical cables in an optical fiber network, the apparatus comprising: Reflector; A dichroic filter, configured to output light emitted from the input light transmitted through the optical cable: Reflection component; as well as Transmission component; An optical switch is arranged to receive the transmitted component and interface with the reflector, and is configured to perform switching between optically connecting and disconnecting the reflector from the transmitted component; as well as A photovoltaic (PV) power source is arranged to receive the reflected component and is electrically connected to the optical switch, thereby generating power from the reflected component and supplying power for switching of the optical switch.

2. The apparatus according to claim 1, wherein, When the optical switch is not powered on, the optical switch is biased to disconnect the reflector from the transmission component.

3. The apparatus according to claim 1 or 2, the apparatus comprising a port for connecting the dichroic filter to the output of the bandstop filter connected to the optical cable, wherein, The input light is received via the port and from the bandstop filter.

4. The apparatus according to any of the preceding claims, wherein, The fiber optic network includes: Multiple optical network units; splitter; and Multiple distribution optical cables, each of which extends between the splitter and one of the multiple optical network units; and The device includes a connector for connection to one of the plurality of distribution optical cables and downstream of the splitter.

5. The apparatus according to any of the preceding claims, wherein, The filter and / or another filter have a reflectivity that is substantially independent of temperature.

6. An optical fiber network comprising the means according to any of the preceding claims.

7. The optical fiber network of claim 6, wherein the optical fiber network comprises at least two of the devices of claim 6, and wherein: The at least two devices are connected to different optical cables; and Each dichroic filter in each of the at least two devices is configured to filter at different wavelengths.

8. A method of operating an optical fiber network, the optical fiber network comprising: Optical Time Domain Reflectometer (OTDR); Multiple ONUs; as well as At least one device, said at least one device being the device according to any one of claims 1 to 7, wherein said at least one device is connected to an optical cable serving at least one of the plurality of ONUs; The method includes the following steps: The OTDR transmits diagnostic signals to the plurality of ONUs, wherein the diagnostic signals are configured to switch at least one device to optically connect the reflector to the transmission component; and The reflection from the reflector is measured at the OTDR.

9. A computer-readable carrier medium comprising a computer program that, when executed by a computer, causes the computer to perform the steps of claim 8.

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