EP3928441A1 - Method for testing quality of optical network components - Google Patents
Method for testing quality of optical network componentsInfo
- Publication number
- EP3928441A1 EP3928441A1 EP20713069.1A EP20713069A EP3928441A1 EP 3928441 A1 EP3928441 A1 EP 3928441A1 EP 20713069 A EP20713069 A EP 20713069A EP 3928441 A1 EP3928441 A1 EP 3928441A1
- Authority
- EP
- European Patent Office
- Prior art keywords
- optical
- component
- fibre
- calibrated reflector
- otdr
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Withdrawn
Links
- 230000003287 optical effect Effects 0.000 title claims abstract description 74
- 238000000034 method Methods 0.000 title claims description 54
- 238000012360 testing method Methods 0.000 title description 12
- 239000013307 optical fiber Substances 0.000 claims abstract description 43
- 238000010998 test method Methods 0.000 claims abstract description 3
- 239000000835 fiber Substances 0.000 claims description 52
- 238000011144 upstream manufacturing Methods 0.000 claims description 6
- 238000007526 fusion splicing Methods 0.000 claims description 5
- 230000013011 mating Effects 0.000 claims description 2
- 230000001419 dependent effect Effects 0.000 claims 2
- 238000005259 measurement Methods 0.000 description 12
- 238000009434 installation Methods 0.000 description 10
- 230000005540 biological transmission Effects 0.000 description 5
- 239000011248 coating agent Substances 0.000 description 2
- 238000000576 coating method Methods 0.000 description 2
- 230000005693 optoelectronics Effects 0.000 description 2
- 238000012935 Averaging Methods 0.000 description 1
- 230000000295 complement effect Effects 0.000 description 1
- 238000012937 correction Methods 0.000 description 1
- 238000001514 detection method Methods 0.000 description 1
- 238000010892 electric spark Methods 0.000 description 1
- 230000007613 environmental effect Effects 0.000 description 1
- 230000004927 fusion Effects 0.000 description 1
- 239000003365 glass fiber Substances 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 238000010606 normalization Methods 0.000 description 1
- 238000013102 re-test Methods 0.000 description 1
Classifications
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
- H04B10/07—Arrangements for monitoring or testing transmission systems; Arrangements for fault measurement of transmission systems
- H04B10/071—Arrangements for monitoring or testing transmission systems; Arrangements for fault measurement of transmission systems using a reflected signal, e.g. using optical time domain reflectometers [OTDR]
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
- G01M11/00—Testing of optical apparatus; Testing structures by optical methods not otherwise provided for
- G01M11/30—Testing of optical devices, constituted by fibre optics or optical waveguides
- G01M11/31—Testing of optical devices, constituted by fibre optics or optical waveguides with a light emitter and a light receiver being disposed at the same side of a fibre or waveguide end-face, e.g. reflectometers
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
- H04B10/07—Arrangements for monitoring or testing transmission systems; Arrangements for fault measurement of transmission systems
- H04B10/073—Arrangements for monitoring or testing transmission systems; Arrangements for fault measurement of transmission systems using an out-of-service signal
- H04B10/0731—Testing or characterisation of optical devices, e.g. amplifiers
Definitions
- This invention relates to a method for characterising connections and components in an optical network.
- Telecommunications signals may be transmitted over optical fibres.
- Optical fibre transmission has been used for over 30 years for long links in the core of telecommunications networks.
- the access network connects customers' premises (houses, flats and offices) to the telecommunications company's equipment in a local exchange or central office building, also referred to herein as the head end of the network.
- the use of optical fibre in the access network is driven by the need for higher bandwidth for Internet-based services to customers.
- Optical fibre transmission systems consist of a transmitter which turns electrical pulses into pulses of light, then the optical fibre itself which carries the light from end to end, and finally a receiver which turns the pulses of light back into electrical pulses.
- the transmitter and receiver are called“opto-electronic” components because they convert signals from the optical to the electronic domain or vice versa.
- PON Passive Optical Network
- access networks are characterised by much larger numbers of end-points necessitating a larger and less specialised workforce, by the poor environmental conditions in which much of the equipment is housed (up poles and down holes), and by the need to minimise cost because of strong price competition in end-customer services.
- Optical fibres making up a PON cannot be installed in a single length from customer end to central office, so fibres must be connected together so that light can pass from one to the other. Ideally the connection has no loss so that light passes from one fibre to the other as if the fibres were continuous.
- optical fibres in core networks have been connected by fusion splicing.
- the two fibre ends to be connected are first cleaved to leave a precise perpendicular end face on each fibre.
- the ends are aligned mechanically to very high precision.
- the ends are fused together by an electric spark.
- the new splice is sealed into a tube for mechanical protection.
- the fusion splicing process is now partly automated but still requires highly skilled operators and preferably very clean conditions. Both these requirements are hard to meet in the access network environment.
- fibres are by the use of mechanical connectors.
- the end of each fibre is held in a ferrule inside a rigid plastic or metal housing, and the fibre end is polished flush with the end of the ferrule.
- the two housings can be pushed together and locked. This holds the two fibre ends in very close physical contact so that light can pass from one fibre to the other with sufficiently low loss.
- Fibre optic patch cables of various standard lengths (about 0.1 m to about 100 m) with a connector at each end are mass-produced for use in data centres and office buildings.
- connections between the long transmission fibre and the terminating opto-electronic equipment at each end are usually made with mechanical connectors.
- Patch cables of standard lengths are often not suitable for installation in access networks where the length required varies widely. Use of an over-length patch cable is wasteful and it may be difficult to hide the excess length.
- FFCs Field Fit Connectors
- a newly cleaved fibre end can be fitted into a Field Fit Connector and locked in place. Internally, the Field Fit Connector holds the cleaved end of the external fibre in very close physical contact with one end of a short internal fibre. The other end of the internal fibre is held in a ferrule similar to the ferrule of a standard mechanical connector.
- the connector provides one of the standard mechanical-connector interfaces, for example, the SC connector of IEC61754-4.
- the junction between the new external fibre and the short fibre inside the connector is treated with an optical index-matching gel with refractive index close to that of the glass fibre, to minimise back-reflection and loss.
- Optical Time Domain Reflectometers are widely used to measure connection loss in point-to-point networks. The measurement compares the power received due to Rayleigh back-scattering from the region just upstream of the connection with the back-scattered power from the region just downstream of the connection. If the optical fibre structure is the same on both sides of the connection, the reduction in back-scattered power leads directly to the connection loss.
- the present invention seeks to address the above issues by providing a method for measuring loss in an optical network using a comparison between two calibrated reflections measured in successive tests.
- the method may be used even where no Rayleigh back-scattered signal is detectable by the OTDR.
- the method is applicable to, but is not restricted to, branches of a PON beyond the splitter.
- the present invention is provided particularly, though not exclusively, to measure the quality (loss and reflectance) of a Field Fit Connector during installation of the connector. This allows the engineer to rework the connection, or install a replacement connector, if necessary, and re-test. In this way the engineer can ensure that the installation is correct before leaving the site.
- a method of testing the quality of a component in an optical network comprising the steps of:
- the loss Lc is calculated by the expression:
- Step (e) preferably further comprises measuring the reflection Ri from the component.
- the second calibrated reflector preferably has a known optical return loss Pre fi , and the method may thus preferably comprise further the step of:
- the reflectance of the first calibrated reflector may be equal to, less than, or greater than, the reflectance of the second calibrated reflector.
- Step (a) may comprise cleaving the optical fibre at the location, and the first calibrated reflector may therefore comprise a cleaved face of the optical fibre end formed thereby.
- the first calibrated reflector is preferably a naturally-calibrated reflector due to Fresnel reflection, and comprises a substantially plane cleaved face whose normal lies in substantially the same direction as the axis of the optical fibre.
- the step (c) of replacing the first calibrated reflector with the component preferably comprises fusion splicing or mechanically mating the cleaved optical fibre end to the component.
- the reflection measured in the first test in step (b) is obtained by fitting, in step (a), a first calibrated reflector terminating the upstream optical fibre, in place of the section of network which constitutes the component whose loss is to be measured.
- the first calibrated reflector is removed, and replaced in step (c) by the section of network.
- a second calibrated reflector is then placed in step (d) at the downstream end of the section of network.
- the loss of the section of network is found in step (f) by comparison of the two reflection heights, after performance of step (e).
- the reflection measured in the first test in step (b) is obtained as the natural Fresnel reflection from the perpendicular face of the freshly cleaved fibre end which is formed in step (a), and which constitutes the first calibrated reflector.
- the reflection measured in the second test in step (e) may be obtained by connecting, in step (d), a short patch cable ending in second a calibrated reflector to the newly-fitted connector fitted in step (c). The loss of the connector is found in step (f) by comparison of the two reflection heights.
- the reflection measured in the first test in step (b) is obtained as the natural Fresnel reflection from the perpendicular face of the freshly cleaved fibre end formed in step (a) and constituting the first calibrated reflector.
- the reflection measured in the second test in step (e) may be obtained by connecting in step (d) a second calibrated reflector to the connector at the end of the downstream fibre connected by splicing in step (c), and correcting for the expected loss due to the length of the downstream fibre.
- the loss of the splice is found in step (f) by comparison of the two reflection heights.
- the method of the present invention can be used to detect very poor splices. Flowever, it may not be sufficiently precise to prove that the splice loss is less than the typically very tight specification applied to splices in core networks.
- the component to be tested may comprise one or more components connected by optical fibre.
- Said component to be tested may preferably have an optical input and an optical output, each provided with mechanical connectors for connection to adjacent optical components.
- the optical input may preferably be a fibre end suitable for splicing to upstream optical fibre, and the optical output may preferably be provided with a mechanical connector.
- the component to be tested comprises a Field Fit Connector (FFC) suitable for forming an adaptor between a cleaved fibre end and a mechanical connector.
- FFC Field Fit Connector
- step (c) preferably comprises a Field Fit Connector (FFC).
- the present invention is primarily intended to provide a method to characterise the FFC, that is, to measure the loss through the FFC and the reflectance of the FFC. Accordingly, Ri now represents the reflection from the FFC, and step (f) now comprises calculating the loss LFFC through the FFC, by comparison of the reflections Ro and R ⁇ .
- the loss LFFC is calculated by the expression:
- step (g) now comprises calculating the optical return loss ORLFFC of the FFC, where:
- ORLFFC Prefl+2(Ro-Rl).
- Steps (b) and (e) of the method are preferably carried out using an Optical Time Domain Reflectometer (OTDR). Accordingly, step (b) comprises carrying out a first OTDR trace of the optical network, and step (e) comprises carrying out a second OTDR trace of the optical network.
- the method thus uses two measurements of the reflection from the region of the FFC, taken with an optical time domain reflectometer (OTDR) located at the other end of the optical fibre.
- Steps (b) and/or (e) may further comprise measuring the level of Rayleigh scattering So from the start of the trunk fibre nearest the OTDR.
- the optical fibre preferably has a known Rayleigh scattering coefficient CR, whilst the OTDR preferably is configured to emit optical pulses having a known pulse width w.
- the method can thus also be used to yield the network loss from the location of the OTDR to a point immediately beyond the FFC.
- the method may further comprise the step of:
- the optical network therefore preferably is a Passive Optical Network (PON).
- the OTDR may be located at the head end of the PON, and the PON may further comprises one or more splitters between the OTDR and the component.
- FIG. 1 is a schematic representation of a Passive Optical Network (PON) in which a component is to be characterised by a method according to the present invention, and an Optical Time Domain Reflectometer (OTDR) trace for that network, with signals in the trace aligned with the corresponding physical components in the network schematic;
- PON Passive Optical Network
- OTDR Optical Time Domain Reflectometer
- FIG. 2 is a schematic representation of the PON of Figure 1 , now having added thereto a second calibrated reflector and a Field Fit Connector (FFC) to be characterised by the method of the present invention, and the corresponding OTDR trace, with signals in the trace aligned with the corresponding physical components in the network schematic;
- FFC Field Fit Connector
- Figure 3 is a representation of the reflection measurements made in the OTDR traces carried out in the method of the present invention.
- FIG 4 is a cross-sectional detailed view of the Field Fit Connector (FFC) of Figure 2;
- FIG 5 is a cross-sectional view of the Field Fit Connector (FFC) of Figure 4, having a patch cable connected thereto; and
- Figure 6 is a more detailed schematic representation of the Passive Optical Network (PON) and Optical Time Domain Reflectometer (OTDR) of Figure 1.
- PON Passive Optical Network
- OTDR Optical Time Domain Reflectometer
- the PON 10 comprises an Optical Time Domain Reflectometer (OTDR) 11 connected via a first length of optical fibre 12, also referred to herein as trunk fibre, to a splitter 13, to which is connected a second length of optical fibre 14.
- the splitter 13 is characterised as a 1 xN splitter, where N is the number of optical fibre lines 14 emanating from the splitter 13.
- Figure 1 shows only one such second length of optical fibre 14.
- the second length of optical fibre 14 terminates in a cleaved face 15, constituting a first calibrated reflector, which the installation technician has prepared for installation of a Field Fit Connector (FFC), according to step (a) of the method of the present invention.
- FFC Field Fit Connector
- Figure 1 further shows an OTDR trace, generally indicated 20, measured for this PON 10.
- the OTDR trace plots the signal to noise ratio (SNR) in dB against distance from the OTDR.
- SNR signal to noise ratio
- Rayleigh scattered light So is observable over the length of the trunk fibre 12 before the splitter 13. After the splitter 13, the Rayleigh scattered light So is not visible in the OTDR trace 20 against the OTDR detection noise, so the bottom of the trace 21 represents the OTDR noise level.
- the large reflection Rofrom the first calibrated reflector formed by the cleaved face 15 of the fibre 14, as prepared for fitting a Field Fit Connector is clearly visible, as is a reflection 22 from the splitter 13. Measurement of the reflection Reconstitutes step (b) of the method of the present invention.
- FIG. 2 there is shown the PON 10 after fitting a Field Fit Connector (FFC) 16 to the cleaved face 15 of the fibre 14, and so replacing the first calibrated reflector with the component to be tested, according to step (c) of the present invention.
- a patch cable 17, typically having a length of 10m, is connected at the newly installed FFC 16 via a patch cable connector 18, and terminates in a second calibrated reflector 19, according to step (d) of the present invention.
- the second calibrated reflector 19 might be as simple as a Physical Contact connector (not angled) giving a 4% reflectance (14 dB Optical Return Loss, ORL).
- the corresponding OTDR trace 20 in Figure 2 shows a reduced reflection Ri at the position of the FFC 16 where the previous trace 20 in Figure 1 showed a large reflection /3 ⁇ 4 from the first calibrated reflector formed by the cleaved face 15. There is a new large reflection R2 from the second calibrated reflector 19 at the end of the patch cable 17. Measurement of the reflections Ri and R ⁇ constitute step (e) of the method of the present invention.
- FIG 3 there is shown a representation of the respective heights of the three reflection measurements, namely: the reflection Ro from the first calibrated reflector formed by the newly-cleaved end face 15 of the fibre 14, measured in step (b) before installation of the FFC 16; the reflection Ri from the FFC 16 mated with the connector 18 of the patch cable 17, as measured in step (e) after installation; and the reflection k from the second calibrated reflector 19 at the end of the patch cable 17, as also measured in step (e).
- p is the measured optical power and p 0 is a normalisation which is often taken as the standard deviation of the measured baseline noise 21 .
- the factor 5 (rather than the usual 10) is used to arrange that the OTDR 1 1 reports losses correctly, because its optical pulse traverses the lossy component twice.
- ORLFFC 14 + 2(Ro - Ri).
- step (f) of the method of the present invention where the factor 2 comes from the use by the OTDR 1 1 of the factor 5 rather than 10 in its calculation of levels in dB.
- Calculation of the loss LFFC constitutes step (f) of the method of the present invention.
- the OTDR measurement trace 20 gives a level So for Rayleigh scattering from the start of the trunk fibre 12 nearest the OTDR 1 1 , network loss LN from the start of the trunk fibre 12 to the calibrated reflector 19. If the transmission power of the OTDR 1 1 is PT dBm, then:
- K is a calibration factor for the OTDR 1 1 , involving the baseline noise 21 of the OTDR detector, which is the same in the two measurements made in steps (b) and (e).
- the initial factor 1/2 comes from the use by the OTDR 1 1 of the factor 5, rather than 10, when calculating power in dB.
- p re n is the Optical Return Loss (ORL) of the calibrated reflector 19 giving rise to the reflection R ⁇ .
- w is the optical pulse width emitted by the OTDR 1 1 in ns.
- FIGs 4, 5 and 6, are included by way of background explanation only, and illustrate examples of Field Fit Connector 16 and Passive Optical Network 10 for which use of the method of the present invention is particularly, but not exclusively, intended.
- a Field Fit Connector 16 installed on the optical fibre 14.
- the coating 24 of the fibre 14 is in place at the point at which the fibre 14 enters the FFC 16, but as can be seen in Figure 4 has been stripped from the fibre 14 further along its length by the technician prior to installation.
- the coated fibre 24 is held against the connector body 23 by a coating clamp 25, and the stripped fibre 14 is then held against the connector body 23 further along its length by a fibre clamp 26.
- the cleaved end 15 of the fibre 14 is held by the fibre clamp 26 in exact alignment with the end 28 of a stub fibre 27, and refractive index matching gel is applied over this boundary 15/28.
- the remainder of the stub fibre 27 is held in a ferrule connector 29 and terminates in a factory polished angled face 31.
- FIG. 5 there is shown the Field Fit Connector 16 of Figure 4, connected to a patch cable 17 as hereinbefore described.
- the ferrule connector 29 of the FFC 16 is mated with a complementary ferrule connector 18 of the patch cable 17 so that the respective fibres 27, 17 are in exact alignment.
- This connection 29/18 may be an Angled Physical Contact (APC) connection for low reflectance.
- the length of the patch cable 17 is pre-determined and selected such that reflectance and loss events in the OTDR trace 20 can be resolved and differentiated according to distance.
- the distal end of the patch cable 17 has a second ferrule connector 18 terminating in the second calibrated reflector 19.
- This second calibrated reflector 19 may simply be a perpendicular polished face of the cable 17, or alternatively a separate reflector may be connected to the ferrule 18.
- FIG. 6 there is shown an illustration of how a single OTDR 1 1 can be used to test multiple PONs 10.
- the OTDR 1 1 is housed within a central office or exchange building 32.
- the OTDR 1 1 is connected via switches 33 to Wavelength Division Multiplexors (WDMs) 34, which are also connected to the Optical Line Terminal (OLT) 35.
- WDMs Wavelength Division Multiplexors
- OLT Optical Line Terminal
- Multiple trunk fibres 12 thus emanate from the central office 32, each said trunk fibre 12 thus defining a separate PON 10.
- Each PON 10 may comprise a 1 xN splitter 13, at which the PON 10 is split into multiple (N) customer fibres 14, each having a different length so as to be identifiable in the OTDR trace
- Each customer fibre 14 terminates at an Optical Network Terminal (ONT) 36.
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- Physics & Mathematics (AREA)
- Electromagnetism (AREA)
- Engineering & Computer Science (AREA)
- Computer Networks & Wireless Communication (AREA)
- Signal Processing (AREA)
- Optics & Photonics (AREA)
- Chemical & Material Sciences (AREA)
- Analytical Chemistry (AREA)
- General Physics & Mathematics (AREA)
- Optical Communication System (AREA)
Abstract
Description
Claims
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
GB1902331.6A GB2582895B (en) | 2019-02-20 | 2019-02-20 | Method for testing quality of optical network components |
PCT/GB2020/050390 WO2020169964A1 (en) | 2019-02-20 | 2020-02-19 | Method for testing quality of optical network components |
Publications (1)
Publication Number | Publication Date |
---|---|
EP3928441A1 true EP3928441A1 (en) | 2021-12-29 |
Family
ID=65998512
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
EP20713069.1A Withdrawn EP3928441A1 (en) | 2019-02-20 | 2020-02-19 | Method for testing quality of optical network components |
Country Status (3)
Country | Link |
---|---|
EP (1) | EP3928441A1 (en) |
GB (1) | GB2582895B (en) |
WO (1) | WO2020169964A1 (en) |
Families Citing this family (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
EP4136425A4 (en) * | 2020-04-14 | 2023-09-27 | Jabil Inc. | Optical back reflection diagnostics for micro optical components |
CN115514412A (en) * | 2021-06-22 | 2022-12-23 | 中兴通讯股份有限公司 | Optical fiber testing system, method, electronic device and storage medium |
Family Cites Families (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
WO2005071380A1 (en) * | 2004-01-21 | 2005-08-04 | Agilent Technologies Inc. | Determination of an optical property of a device under test (dut) by otdr measurement |
GB2564697B (en) * | 2017-07-20 | 2021-12-08 | British Telecomm | Optical fibre |
-
2019
- 2019-02-20 GB GB1902331.6A patent/GB2582895B/en not_active Expired - Fee Related
-
2020
- 2020-02-19 EP EP20713069.1A patent/EP3928441A1/en not_active Withdrawn
- 2020-02-19 WO PCT/GB2020/050390 patent/WO2020169964A1/en unknown
Also Published As
Publication number | Publication date |
---|---|
WO2020169964A1 (en) | 2020-08-27 |
GB2582895B (en) | 2022-12-14 |
GB201902331D0 (en) | 2019-04-03 |
GB2582895A (en) | 2020-10-14 |
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