EP3881452A1 - Secured fiber link system - Google Patents
Secured fiber link systemInfo
- Publication number
- EP3881452A1 EP3881452A1 EP19884210.6A EP19884210A EP3881452A1 EP 3881452 A1 EP3881452 A1 EP 3881452A1 EP 19884210 A EP19884210 A EP 19884210A EP 3881452 A1 EP3881452 A1 EP 3881452A1
- Authority
- EP
- European Patent Office
- Prior art keywords
- optical
- signal
- fiber
- otdr
- chaff
- 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.)
- Pending
Links
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]
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- 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
- H04B10/80—Optical aspects relating to the use of optical transmission for specific applications, not provided for in groups H04B10/03 - H04B10/70, e.g. optical power feeding or optical transmission through water
- H04B10/85—Protection from unauthorised access, e.g. eavesdrop protection
Definitions
- the present disclosure relates generally to optical fiber cables, and more particularly to detecting and preventing tapping of optical fiber cables.
- Intruders can tap into optical fiber transmission lines and steal information by either bending a segment or segments of the fiber or by stretching, e.g., tapering, a segment or segments of the fiber via application of heat. Doing so may enable reading and interpreting the signal energy escaping from the bent or stretched fiber. While there are other methods of tapping information out of optical fibers, taps based on fiber bending or stretching are easy to implement, effective, and can be hard to detect. Tapping valuable data transmitted over the world wide optical fiber infrastructure is a threat to every major industry and government organization and, in particular, to larger organizations utilizing multiple facilities. While these organizations may be able to secure optical fiber cables within their own facilities, they generally have much less control over the optical fiber cable links between those facilities.
- An optical time domain reflectometer is a known tool for characterizing, monitoring, and troubleshooting a fiber.
- An OTDR typically operates by sending laser pulses of different widths and monitoring their refection as received at the pulse-transmitting end of the fiber.
- An OTDR can pinpoint the location of faults in a fiber link, and OTDRs find and characterize both reflective and non-reflective events in optical fiber.
- an OTDR can be used to detect a bend introduced in a fiber link after the fiber link is established by comparison with an earlier OTDR trace prior to the fiber having been bent, e.g., a trace made when the link is first installed.
- An OTDR can be used for testing an in-service fiber, i.e., one carrying data intended to be delivered to a destination, by running the test pulses on a different wavelength channel than the one used to carry the data intended for delivery.
- an optical data signal not be modified by a transceiver.
- Such a preference when made a requirement, means that the fiber carrying the secure communication cannot also carry the pulses required by the OTDR.
- the techniques used by an OTDR suffer from so-called“dead zones”, which are areas after a reflective event takes place that cannot be seen by the OTDR. Such a dead zone often occurs for a large distance at the beginning of the fiber when trying to look at a very long length optical fiber. This is because when trying to look at a very long optical fiber, it is necessary to launch a lot of power to be able to see the conditions at the end of the fiber. When a lot of optical power is launched, the pulse width of the launched optical signal is increased. Use of a large pulse width decreases the resolution of the measurement that can be made by an OTDR the result of the reduced resolution can extend as far as several hundred meters.
- faults near the launch end are masked because of the hundreds of meters between the launch pulse and the receiver being able to see the reflected pulse.
- This length of fiber is also called a“dead zone” because the faults are masked in the length close to the OTDR.
- the receiver requires an amount of time to recover from the saturation.
- the OTDR may take up to, for example, 500 meters or more to fully recover from such faults near the launch point.
- launch fibers are fibers of a prescribed length that are placed between the OTDR and the actual fiber that is being measured and thereby provides time for the receiver to settle and also for the pulse width dependent resolution to be overcome.
- launch fibers When launch fibers are used, faults close to the end of the fiber being measured can be seen by the OTDR. They do not interfere with the actual fiber being measured and are a proven technique for identifying faults in the total length of fiber being tested from its first interface to its last.
- Such launch fibers are thus located on a spool or within a“launch box” in between the OTDR and the fiber under test so as to create the proper conditions for testing the optical fiber for faults.
- the disclosed embodiments include a system for securing communication over an optical fiber.
- the system comprises a transmit spatial multiplexer configured to couple ones of a plurality of optical signals into ones of a plurality of spatial paths of an optical fiber, each of the spatial paths being able to carry an optical signal, wherein at least a first one of the plurality of optical signals is an optically modulated version of a desired sequence of information that is intended to be transferred over the optical fiber, the at least first one of the plurality of optical signals being coupled into a first one of the plurality of spatial paths; wherein at least a second one of the plurality of optical signals is an optical chaff signal, the at least second one of the plurality of optical signals being coupled into a second one of the plurality of spatial paths different from the first one; and wherein at least a third one of the plurality of optical signals is an optical signal for use by an optical time domain reflectometer (OTDR); whereby a tap along the fiber cannot determine the transmitted desired sequence of information.
- OTD optical time domain reflectometer
- the disclosed embodiments also include a method for securing information transmitted over an optical fiber having a plurality of spatial paths.
- the method comprises coupling each of a set of optical signals into at least one of the plurality of spatial paths; wherein at least one of the set of optical signals is an optically modulated version of a desired sequence of information that is intended to be transferred over the optical fiber, the at least first one of the plurality of optical signals being coupled into a first one of the plurality of spatial paths; wherein at least a second one of the set of optical signals is an optical chaff signal, the at least second one of the plurality of optical signals being coupled into a second one of the plurality of spatial paths different from the first one; and wherein at least a third one of the plurality of optical signals is an optical signal for use by an optical time domain reflectometer (OTDR).
- OTD optical time domain reflectometer
- the disclosed embodiments also include a terminal equipment for securing communication over an optical fiber.
- the terminal equipment comprises a transmit spatial multiplexer configured to couple a plurality of optical signals into respective ones of a plurality of spatial paths of an optical fiber, each of the spatial paths being able to carry an optical signal; wherein at least one of the plurality of optical signals is an optically modulated version of a desired sequence of information that is intended to be transferred over the optical fiber; and wherein at least one of the plurality of optical signals is an optical chaff signal multiplexed with an optical signal for use by an optical time domain reflectometer (OTDR); whereby a tap along the fiber cannot determine the transmitted desired sequence of information.
- OTDR optical time domain reflectometer
- the disclosed embodiments also include a system for securing communication over an optical fiber.
- the system comprises a receive spatial demultiplexer couplable to a plurality of spatial paths of the optical fiber at one end thereof, at least two spatial paths of the plurality of spatial paths carrying optical signals; wherein an optical signal on a first of the at least two spatial paths includes at least an optically modulated version of a desired sequence of information that is intended to be received from the optical fiber; wherein an optical signal on a second of the at least two spatial paths different from the first of the at least two spatial paths includes an optical chaff signal; and wherein the receive spatial demultiplexer is configured to receive from at least one of the plurality of spatial paths a signal for use by an optical time domain reflectometer (OTDR) and to supply the received signal for use by an OTDR to an OTDR.
- OTDR optical time domain reflectometer
- FIG. 1 is a block diagram of a secured fiber link system according to an embodiment
- FIGs. 2A, 2B and 2C are block diagrams of illustrative embodiments of chaff sources using amplified spontaneous emission (ASE);
- FIG. 2D shows an illustrative embodiment of a chaff generator using copies of a chaff signal and optional delay lines
- FIG. 3 is an illustrative plot of the spectrum of the ASE source with optional filter as compared to the spectrum of the data channels according to an embodiment
- FIG. 4 shows an illustrative embodiment in which a terminal is contained in which within a secure box.
- the terms“true signal”,“true data”,“information signal”,“true data signal” and“data signal” are used interchangeably to refer to a desired sequence of information that is intended to be transferred between legitimate users at the ends of a link.
- a chaff signal is a signal that does not carry true data.
- the secured fiber link system is configured to allow transmission of data to the intended user while simultaneously making the signal opaque or uninterpretable to a tapper who makes a tap anywhere along the entire link other than at the intended receiver by overwhelming the information signal with interfering signal energy at such tapping point and also enabling detection of tapping, moving, or similar such interference with the optical cable through the use of an optical time domain reflectometer (OTDR).
- OTDR optical time domain reflectometer
- the secured fiber link system sends on a first spatial path of a fiber cable, e.g., a core of a multicore fiber, a desired sequence of information in the form of a first “legitimate” or true signal, or a set of true signals, that is typically intended to be transferred between legitimate users located at the ends of a link.
- a fiber cable e.g., a core of a multicore fiber
- at least one other spatial path of the fiber cable e.g., a different core of the multicore fiber
- the OTDR signal may be carried on a dedicated core or may be wavelength multiplexed with either one or more true signals or with one or more chaff signals. This enables detection of tapping or tampering at the terminals of the fiber optic link system.
- Chaff signals which are interfering signals not needed for conveying the true signal, may be applied to the link at one or both ends of the link.
- OTDR signals may be applied at one or both ends of the link.
- the secured fiber link system is configured to provide physical security of a data signal propagating over at least one of a plurality of spatial paths of an optical fiber in parallel with at least one chaff signal propagating over another of the plurality of spatial paths of the optical fiber, in combination with, e.g., multiplexed with, such as using frequency division multiplexing, a signal for use by the OTDR at least some of the time.
- more than one of the spatial paths that carry a chaff signal may carry a multiplexed OTDR signal.
- an OTDR signal may be carried continuously on one or more of the spatial paths carrying chaff signals or an OTDR signal may be time multiplexed amongst the various spatial paths carrying chaff signals, or a combination of both may be employed.
- the spatial paths carrying the data signal and the chaff signals may be cores of a multicore fiber.
- the system is configured to ensure that the intended recipient at the other end of the link receives the true data.
- tapping of a fiber link may be an act of changing a fiber such as by putting physical force on a fiber cable, e.g., by bending the fiber, or by modifying the fiber, e.g., applying heat to allow a segment or segments of the fiber to be axially stretched but without breaking the fiber.
- Such techniques causes the energy propagating within the fiber to leak out therefrom so that it may be detected, e.g., a hacker attempting to steal the information that is being transmitted on the cable.
- Embodiments of the secured fiber link system may be compatible with contemporary data rates, formats, and telecommunications protocols, as well as signal wavelength provisioning, such as wavelength division multiplexing (WDM).
- WDM wavelength division multiplexing
- the disclosed embodiments may also be agnostic to equipment and protocols developed in the future.
- Fig. 1 shows a block diagram of an illustrative secured fiber link system 100 according to an embodiment.
- System 100 includes transceiver terminals 1 10-1 and 1 10-2 connected via an optical link, e.g., optical fibers 150-1 and 150-2, each of which may be, for example, a multicore fiber, a multimode fiber or a few mode fiber, which preferably allow for spatial division multiplexing.
- optical fibers 150-1 and 150-2 although shown as separate fibers for explanatory purposes, may be implemented as different spatial paths that are part of the same physical optical fiber. As such, they may, for example, represent different optical cores within a multicore fiber.
- Each terminal 1 10-1 or 1 10-2, collectively terminals 1 10, may each include at least one transmitter, e.g., transmitters 121 -1 or 121 -2, at least one receiver, e.g., receivers 130-1 or 130-2, at least one chaff generator, e.g., chaff generators 140-1 or 140-2, and at least one OTDR, e.g., OTDR 151 -1 or 151 -2.
- transmitters 121 -1 or 121 -2 the transmitters e.g., transmitters 121 -1 or 121 -2
- receivers 130-1 or 130-2 at least one chaff generator, e.g., chaff generators 140-1 or 140-2
- OTDR e.g., OTDR 151 -1 or 151 -2.
- FIG. 1 shows an embodiment in which terminal 1 10-1 is supplied with electrical input data signal 101 -1 , and in particular, electrical input data signal 101 -1 is received at transmitter 121 -1. Electrical input data signal 101 -1 is converted into optical input data signal 102-1 by transmitter 121 -1 which acts as optical-electronic-optical (OEO) converter. In other embodiments of the invention, instead of an electrical input data signal
- optical input data signal 102-1 may be directly supplied to terminal 1 10-1 as the input data source, i.e., as the true signal, and will, in particular, be supplied to spatial multiplexer 180-1.
- terminal 1 102-1 e.g., per a requirement or preference, will not be modified by terminal 1 10-1 , and hence transmitter 121 -1 will not be employed.
- Terminal 1 10-1 transmits and receives signals via optical fibers 150-1 and 150-2, respectively.
- chaff signals which are signals used as explained herein to cause interference at a tap with respect to the true signals, are generated within the terminal 1 10-1 and are transmitted via the optical fiber 150-1 along with the true optical input data signal 102-1 as described above.
- a chaff signal may be generated by chaff generator 140-1 , or a chaff signal received from terminal 1 10-2 via fiber 150-2 may be re-used for propagation along optical fiber 150-1.
- the output connections of chaff re-use module 141 -1 take the place of the output connections of chaff generator 140-1 which are shown as dashed lines in Fig.
- chaff generators 140- 1 or 140-2 are shown in FIG. 2 and described further hereinbelow.
- an OTDR e.g., OTDR 151 -1 within terminal 110-1 , generates a signal for use in detecting issues with the one of optical fibers 150 to which it is coupled, e.g., optical fiber 150-1 , and the location of such issues.
- One such issue may be a tap.
- OTDR may pinpoint the location of a tap.
- the OTDR signal may be transmitted via one of transmitters 152, e.g., transmitter 152-1 which is typically incorporated within OTDR 151 -1.
- Coupler 154-1 is typically arranged such that in a first direction it couples the signal from transmitter 152-1 to a launch cable 155, e.g., launch cable 155-1 , while in a second direction it couples signal received from launch cable 155-1 to receiver and signal processor 153-1. In the second direction coupler 155-1 may also act as a filter to block reflections of the chaff signal.
- Transmitter 152-1 is typically a high power laser transmitter that transmits a pulse of light to be sent down one of optical fibers 150. Back-scattered light and reflected light return to each OTDR 151 from one of optical fibers 150. In terminal 1 10-1 such back- scattered light and reflected light are directed to receiver and signal processor 153-1 by coupler 154-1.
- the OTDR signal from transmitter 152-1 may be split or directed by splitter 158 and then further split or directed by splitters 156-1 or 157-1 to enable substantially simultaneous launching of copies of the same OTDR signal into multiple spatial paths of optical fibers 150.
- the various splitters may, but need not, be passive splitters.
- splitters 156-1 or 157-1 may be replaced by switches that can successively route OTDR pulses to different ones of the spatial paths and direct their corresponding reflections to receiver 153-1.
- OTDR launch cable 155-1 may be coupled to either fiber 150-1 or 150-2 or to both simultaneously via either spatial or wavelength multiplexers or both.
- the OTDR signal supplied by OTDR 151 -1 may be wavelength multiplexed with one or more true data signals, one or more chaff signals, any desired combination of true data signals and chaff signal, or may be supplied to its own spatial path without being multiplexed with any other signal.
- FIG. 1 shows the case where the signal from OTDR launch cable 155-1 is split using splitter 158-1 to eventually be supplied to both fibers 150-1 and 150-2 via wavelength multiplexing with the chaff signals in wavelength multiplexers 143-1 and 143- 2, followed by spatial multiplexing in spatial multiplexers 180-1 and 181 -1.
- optical fibers 150-1 and 150-2 may be structured as multicore cables.
- Each core of a multicore fiber may be capable of independently guiding a light signal along the entire length of the multicore fiber.
- the individual cores may be single mode or multimode at the signal wavelengths transmitted.
- the combined optical chaff signal and OTDR signal are supplied to at least one spatial path of optical fiber 150-1 , e.g., one core thereof when optical fiber 150-1 is a multicore fiber, while the true signal is supplied to a different spatial path of optical fiber 150-1.
- a device in terminal 1 10-1 may be used to determine that there is interference with the optical fiber 150-2.
- This may be achieved through the use of optional splitter 157-1.
- splitter 157-1 can duplicate an OTDR signal supplied by OTDR 151 -1 of terminal 1 10-1 and supply it to fiber 150-2 attached to terminal 1 10-1.
- splitter 157-2 can duplicate an OTDR signal supplied by OTDR 151 -2 of terminal 1 10-2 and supply it to fiber 150-1 attached to terminal 1 10-2 for processing, e.g., by receiver and signal processor 153-2.
- detecting interference with optical fiber 150- 1 may be by a combined effort of OTDR 151 -1 and an OTDR-type device, e.g., OTDR 151 -2, in terminal 1 10-2.
- At least one chaff signal which is multiplexed with the OTDR signal, as well as the at least one data signal are coupled into respective cores, or channels, of the optical fiber at the transmitter end.
- Couplers for use in embodiments of the invention may be, for example, 1 ) a lensed fiber based coupler, 2) a tapered glass fiber coupler, 3) a free space bulk optics coupler, or 4) any other known or developed coupler.
- the couplers may also include fiber and free space paths.
- Couplers amount to a transmit spatial multiplexer, e.g., one of transmit spatial multiplexers 180-1 and 180-2, in that they couple a plurality of optical signals into respective ones of a plurality of spatial paths of one of optical fibers 150.
- the true data signal or any chaff signal desired to be extracted may be obtained similarly, e.g., by using a receive spatial demultiplexer, such as one of spatial demultiplexers 190-1 and 190-2, which can be made up of individual decouplers.
- a receive spatial demultiplexer such as one of spatial demultiplexers 190-1 and 190-2, which can be made up of individual decouplers.
- Such decouplers may be a coupler operating in reverse for this purpose or may be of any other known or developed decoupler.
- Such couplers may be operated bidirectionally so as to also couple signals into the one of optical fibers 150 to which they are coupled. Alternatively, the fiber core carrying the true data signal may simply be extended alone into the receiver.
- the generated chaff signals are uncorrelated with the true data signals.
- the bandwidth of chaff signals may be at least as wide as the bandwidth used for the true data signals.
- the chaff signal may be arranged to be of sufficient optical strength to reduce the optical signal-to-noise-ratio (OSNR), or equivalently raise the bit error rate (BER), that would be observed by a tapper at a tap placed at any location along one of optical fibers 150 to a level such that the information obtained by the tapper is un-interpretable, e.g., the information that is carried in the data signals cannot be recovered at the tap.
- OSNR optical signal-to-noise-ratio
- BER bit error rate
- the true signal need be recovered.
- only the core carrying the true signal may be coupled into receiver 130-2, which may include an optical to electrical converter, e.g., one or more photodiodes.
- the true signal may be passed on for further processing in optical form.
- the intended recipient will be able to obtain the data carried by the true signals regardless of the chaff signals.
- the OTDR signals may be available at the one or both ends of the optical fiber to detect tampering with the optical fiber, e.g., to detect a tap and the location thereof.
- the properties of the chaff signal thus provides protection for the optical fiber from tampering. Such properties, discussed in more detail below, prevent separating the true data signal from the resulting combined signal, which is a combination of the true data and chaff signals, that is obtained at a tap of the optical fiber.
- the secured fiber system provides protection along the entire length of the optical fiber without the need for expensive guards or encasements along the optical fibers. This makes installation and security maintenance less expensive, especially for use with a long optical fiber.
- encryption may be employed for the true signal, there is no need to do so.
- not employing encryption increases the bandwidth available for transmitting data which is often otherwise consumed by the data encryption.
- FIG. 1 shows only two terminals 1 10 and two optical fibers 150 merely for simplicity purposes and without limitation on the disclosed embodiments. Additional terminals and/or optical fibers may be utilized without departing from the scope of the disclosure. Wavelength-division multiplexing may also be used both for data signals and chaff signals as needed, as long as each data signal to be protected is accompanied by one or more co-propagating chaff signals preferably occupying at least essentially the same wavelength range as the data signal.
- Fig. 2A shows illustrative chaff source 200-A implemented according to an embodiment.
- the chaff source includes an optical amplifier (OA) 210 and operates as an amplified spontaneous emission (ASE) generator.
- OA optical amplifier
- ASE amplified spontaneous emission
- the OA 210 may be, for example, any of 1 ) a semiconductor amplifier, 2) a Raman amplifier, 3) a doped fiber optic amplifier, e.g. an Erbium doped amplifier, with no signal source as an input, and 4) the like.
- the spontaneous emission from the OA 210 may be amplified to a high intensity.
- Fig 2B shows illustrative chaff source 200-B implemented according to another embodiment.
- chaff source 200-B includes an optional optical filter 220 coupled to OA 225.
- Optical filter 220 is located at the output stage of chaff generator 200-B to flatten and limit the spectrum over a predefined frequency band.
- optical filter 225 flattens the output of chaff source 200-B to at least cover data signal spectrum 320.
- Fig. 2C shows illustrative chaff source 200-C implemented according to another embodiment.
- first optical amplifier 230 is coupled to optical filter 240 which is coupled to second optical amplifier 250.
- Optical amplifier 250 is the output stage of chaff generator 200-C and is utilized to amplify the output signal, i.e., the chaff signal, received from optical filter 240.
- a separate chaff source such as those shown in FIGs. 2A-2C, may be used within chaff generator 140 to generate each of the chaff signals that are supplied therefrom.
- the output of a master chaff source which may be one of chaff sources 200- A, 200-B, or 200-C, may be split, by means of splitter 260, into multiple copies to obtain the various chaff signals, as shown in FIG. 2D.
- These copies of the chaff signal may be delayed relative to one another using, e.g., optical fiber delay lines 270-1 through 270-N, so as to decorrelate them.
- the chaff signals can be made overwhelmingly strong so that the level of tapped optical energy exceeds the dynamic range of the detector in the tapper’s tapping equipment. In this case, there may not be any need to structure the format of the chaff signals as their total power will simply overwhelm the tapping equipment.
- the OSNR of the data channel seen by the intended recipient at one of receivers 130 is essentially not degraded by the presence of chaff signals in other cores of the multicore fiber so long as there is essentially no leakage into the core carrying the data channel.
- the OSNR seen by the intended recipient is given by the ratio of the signal intensity detected in the data channel to the total noise power detected where Psignai.Rx is the signal power received from the terminal equipment and ASEtotai is the total amplified spontaneous emission power generated over the link and detected at the receiver.
- Psignai.Rx is the signal power received from the terminal equipment
- ASEtotai the total amplified spontaneous emission power generated over the link and detected at the receiver.
- the two quantities are inversely related, the higher the OSNR the lower the BER and vice versa.
- the purpose of the chaff in combination with the multicore fiber is to make sure that the BER seen at a tap
- a monitoring signal from one of OTDRs 151 is combined, e.g., multiplexed with at least one of the chaff signals prior to the chaff signal being supplied to a core of optical fiber 150 when optical fiber 150 is a multicore fiber.
- a combined OTDR and chaff signal is supplied to at least one core of one of the multicore fibers 150.
- the OTDR signal may be used to detect tampering with the cable, such as a tap and the location thereof, either by reflection of the signal back to the one of OTDRs 151 that generated it or by being received by an OTDR or similar detector at the opposite end of the optical fiber.
- FIG. 4 shows an illustrative embodiment of the disclosure in which an embodiment of a terminal, e.g., terminal 1 10-1 (FIG. 1 ), is contained within secure box 400.
- the true data signal is supplied to input 460 as an optical signal.
- an optical chaff signal is generated by chaff source 41 1 , e.g., which may include one of chaff generators 200 (FIG. 2).
- the optical chaff signal is supplied as an output from chaff source 41 1 , e.g., via fiber 417, and is coupled to a first port 413 of 2:N optical coupler 459-1 , where N is an integer equal to or greater than 1 , although often N will be greater than 1.
- a monitoring signal 407 from an OTDR e.g., OTDR 151 -1 , such as may be supplied from transmitter 121 -N (FIG. 1 ), is coupled to second port 415 of 2:N optical coupler 459- 1 , e.g., via launch fiber 157-1 , which may be arranged as a fiber coil.
- OTDR 151 -1 such as may be supplied from transmitter 121 -N (FIG. 1 )
- second port 415 of 2:N optical coupler 459- 1 e.g., via launch fiber 157-1 , which may be arranged as a fiber coil.
- launch fiber 157-1 which may be arranged as a fiber coil.
- the transmitter, receiver and signal processor, and coupler which may be included in OTDR 151 -1 as shown in FIG. 1 are not shown in FIG. 4.
- optical coupler 459-1 combines the optical chaff signal and the OTDR monitoring signal and generates N copies of the combined, e.g., multiplexed, chaff and OTDR monitoring signal, each of which is provided to a respective one of each of its output ports 405-1 through 405-N.
- 2:N optical coupler 459-1 may be implemented using, for example, 1 ) fibers, 2) optical integrated circuits, 3) free space coupling, or 4) other methods as well as combinations thereof.
- 2:N optical coupler 459-1 may be constructed of a tree of 1 :2 and 2:2 couplers as is known in the art. Differential delays, e.g., as shown in FIG. 2D, may be introduced in the 2:N coupler output 405-1 through 405-N before sending the decorrelated combination of OTDR and chaff signals to individual cores 403- 1 through 403-N of a multi-core optical fiber.
- the data signal may be sent to the central core 403-N+1 , e.g., as an optical signal 460 directly provided to box 400 from the outside.
- At least one of the combined chaff and OTDR monitoring signals from output ports 405 is provided to at least one of cores 403, which includes cores 403-1 through 403-N, of multicore fiber 150.
- Core 403-N+1 is supplied with the true data signal that is received at the input data source 460.
- the received true signal is already in a suitable format for transmission via optical fiber 150, e.g., within core 403-N+1.
- optical fiber 150 e.g., within core 403-N+1.
- the arrangement shown in FIG. 4 is, advantageously, particularly suitable for such applications.
- the chaff signals are coupled into ones the individual channels of multicore fiber 150, e.g., using respective couplers 421 -1 through 421 -N.
- coupler 421 -N+1 provides an optical path coupling input data source 460 to core 403-N+1.
- Such couplers may be, for example, 1 ) a lensed fiber-based coupler, 2) a tapered glass fiber coupler, 3) a free space bulk optics coupler, or 4) any other known or developed coupler as well as combinations thereof.
- the couplers may also include fiber and free space paths. Collectively these couplers amount to a transmit spatial multiplexer in that they couple a plurality of optical signals into respective ones of a plurality of spatial paths of optical fiber 150.
- FIG. 4 shows the use of each of the cores not being used to carry a true data signal as carrying one of combined chaff and monitoring signals 405, it is only necessary that one of the cores carry one of combined chaff and monitoring signals output from one of output ports 405.
- the other cores could carry other signals or nothing at all.
- only chaff signals may be carried.
- the number of cores, the number of chaff and OTDR multiplexed signals, the number of true data signals, and the number of chaff only signals need not be directly related and are at the discretion of the implementer. All cores need not be used all chaff or chaff multiplexed with OTDR signals that are produced need not be used.
- the known OTDR so-called“dead zone” may be arranged to be substantially contained within secure box 400. This may be achieved, in one embodiment of the disclosure, by arranging for the length of launch fiber 155-1 to be long enough so that it extends substantially for the length of the OTDR dead zone. In another embodiment of the disclosure, the length of optical fiber 150 contained within secure box 400 is arranged to substantially contain the OTDR dead zone and the length of launch fiber 155-1 and the optical path to optical fiber 150 may be relatively short.
- the optical path including the combined length of launch fiber 155-1 , 2:N coupler 459-1 , the interconnects, and optical fiber 150 within secure box 400 is arranged to be long enough so as to extend substantially the length of the OTDR dead zone.
- the portion of optical fiber 150 that extends beyond secure box 400 falls with the zone that can be monitored for tampering by OTDR 151.
- the OTDR signal may be used to detect tampering such as a bend or tap and, e.g., the location thereof, at any point along substantially the entire portion of optical fiber 150 that is external to secure box 400 while those portions of the link from OTDR 151 to the exit point of optical fiber 150 that cannot be monitored by OTDR 151 because they are within the dead zone are safely within secure box 400 and so cannot be tampered with or otherwise tapped.
- tampering such as a bend or tap and, e.g., the location thereof, at any point along substantially the entire portion of optical fiber 150 that is external to secure box 400 while those portions of the link from OTDR 151 to the exit point of optical fiber 150 that cannot be monitored by OTDR 151 because they are within the dead zone are safely within secure box 400 and so cannot be tampered with or otherwise tapped.
- the length of the fiber length within secure box 400 may range from 10 meters to 100 meters so that the entire dead zone of OTDR 151 is contained within secure box 400.
- secure box 400 may be a secure enclosure that conforms to Committee on National Security Systems (CNSSI) 7003 for Protected Distribution Systems (PDS).
- CNSSI Committee on National Security Systems
- PDS Protected Distribution Systems
- separate fiber couplers e.g., 1 :2 and 2:2 fiber couplers
- Each of the individual chaff signals may be separately generated or they may be copies of a single chaff signal, e.g., through the use of a 1 :M coupler, M being an integer greater than or equal to 2, or a combination of such approaches, e.g., one or more individually generated and at least two that are copies produced by a coupler.
- 2:N coupler 459-1 may be a device configured such as to supply the OTDR signal multiplexed with the chaff signal to different ones of outputs 405 at different times.
- the OTDR signal may be multiplexed with the chaff signal so as to supply the combined signal to one of cores 403-1 to 403-N on a round robin basis.
- a S ignai and a C haff are the attenuations suffered by the data signal and chaff respectively between the terminal equipment and the position at which the optical fiber was tapped
- psignai and pchaff are the out-coupling coefficients for the signal and chaff at the tap location.
- Psignai, tc is the signal power transmitted from the terminal equipment and ASEchaff is the power in the chaff signal generated at the terminal equipment.
- the secured optical fiber system may utilize multicore optical fibers.
- Such a fiber is arranged to have a set of cores that extend in parallel along the length of the multicore fiber.
- An optical signal may propagate independently in each core.
- the cores may be sized so as to correspond to single mode, few mode, and multimode fibers.
- the multicore fiber thus allows for the use of spatial division multiplexing as well as wavelength division multiplexing and time division multiplexing.
- Multicore fibers can be made with a variety of core geometries including, but not limited to, concentric refractive index layers in a fiber creating concentric cores as well as individual cores arranged in a variety of cross sectional configurations. These configurations include, but are not limited to: linear, circular, hexagonal, rectangular, and the like.
- the individual cores of a multicore fiber used in the secured fiber link system can be identical to each other or can be different from one another.
- one or more of the cores may be bend sensitive while one or more of the cores may be bend insensitive.
- Bend insensitive cores may be made using refractive index trenches or rings of air-cores surrounding the signal carrying core that will limit the amount of light that can escape the fiber when it is bent.
- a center core of a multicore fiber carries the true signal and is a bend sensitive core while the one or more outer cores, at least one of which is carrying a chaff and at least one OTDR signal, are of the bend insensitive type.
- the energy in the signal channel will drop and is detectable by an OTDR at at least one of the terminals at the ends of the link. The location of the tap may also be detected.
- the M signal cores may be of the bend sensitive type and the N chaff cores may be of the bend insensitive type.
- the center core of the multicore fiber which is carrying the true signal, is bend insensitive and any outer cores carrying a chaff signal, at least one of which also carries an OTDR signal, are of the bend sensitive type. This will improve the OSNR advantage of the secured fiber link system when tapped by a tapper as more energy leaks out of the chaff cores than the true signal core.
- the M true signal carrying cores can be of the bend insensitive type and the N cores carrying chaff can be of the bend sensitive type.
- the chaff signals are uncorrelated with the true data signal and have a bandwidth at least as wide as that used for the data signals being transmitted over the fiber link.
- the chaff signals should also be of sufficient strength to reduce the OSNR or equivalently raise the BER for a tapper tapping the fiber link.
- any transmission medium in which multiple, independent information bearing optical signals can propagate simultaneously may be employed, e.g., few mode fibers and multimode fibers, so that spatial division multiplexing technology is employed.
- the chaff and true signal channels can each be coupled selectively into the chaff and true signal channels of the fiber at the transmitter end and selectively coupled out at the other end (receiver) of the link with an appropriate coupler.
- couplers include lensed fiber based couplers, tapered glass fiber couplers, polymer based couplers, and free space bulk optics couplers.
- the optical fiber medium should have properties that both maximize the effectiveness of the anti-tapping capability of the system and do not inhibit the legitimate information transfer between system users:
- the relevant properties of the fiber are out-coupling efficiency (dB) of the true and chaff channels via bending or stretching, attenuation of the chaff and true signal channels (dB/m) along the fiber link, and cross-talk between the chaff and true signal channels (dB).
- the various disclosed embodiments include involves the relative out-coupling of the chaff signal(s) energy as compared to the true signal(s) energy at the point of tapping along the link and the corresponding impact on the OSNR as seen by a tapper.
- the strength of the true and chaff signal(s) depends on the strength of the corresponding sources, the attenuation of the signals in the fiber from the source to the point along the fiber link where the tapping occurs and the out-coupling efficiency for each signal at the point of tapping.
- the essential point is that the total chaff energy extracted by a tapper from the fiber link at the point of tapping should be sufficiently strong compared to the true signal energy such that the OSNR observed by the tapper is sufficiently low so that the bit error rate will be sufficiently high to prevent the tapper from extracting useful information from the true signal.
- Simultaneously the OSNR observed by each intended receiver, e.g., one of receivers 130-1 or 130-2, to which a true signal is legitimately coupled should be sufficiently high so that the intended receiver can extract all information from the true signal.
- crosstalk in the fiber between the true data signal and chaff channels, some of which may be carrying an OTDR signal should be minimized.
- station reflectors may be used at the terminations of the multicore fiber cores that carry the chaff signals so that generated chaff generated signal at the central office can be“reused” in the cable. This may negate the need for to generate a chaff signal at the recipient’s premises, reducing the equipment needed at the customer’s premises. This may be advantageous for fiber-to-the-home, where this embodiment minimizes the equipment required at the customer’s home. This aids the network management in that all chaff signal generation can be at the central office making repairs easier and less invasive to a home customer.
- a reflector can be placed at the end of the multicore fiber link that only reflects the chaff channels and does not reflect the true signal core.
- An alternative is to use a multichannel fanout coupler and then to terminate the individual chaff fanout channels with connectors that have a reflector on them that will reflect the amplified spontaneous emission energy back through the multichannel fanout coupler and back into the multicore fiber.
- the signal channel(s) will not be terminated with a reflector.
- Such reflectors may be considered to be an implementation of a chaff generator, e.g., one of chaff generators 140.
- one or more of the non-true-signal carrying cores can be used to carry light that will be used to transmit power from the central office to the receive station where a photocell will convert the optical energy into electrical energy that can be used to run the receive station or be stored in a battery if one is used at the receiver.
- a photocell will convert the optical energy into electrical energy that can be used to run the receive station or be stored in a battery if one is used at the receiver.
- chaff re-use modules 141 may be employed in this context to convert such received light, which may be in the form of received chaff signals with or without OTDR signals multiplexed therewith, to power.
- chaff re-use modules 141 may reuse the chaff signals in the form of power, as chaff signals as described hereinabove, or in a combination power and chaff signals.
- the power required to power the terminal 1 10 may simply be reduced by the amount of power generated from converting the chaff signals.
- the chaff signals multiplexed with OTDR signals may be provided directly to a chaff reuse module 141 for conversion to electrical power.
- a single optical fiber may be employed while achieving bidirectional transmission.
- one or more of the cores of the single optical fiber could be employed for transmitting a true signal in one direction while others of the cores of the single optical fiber could be employed for transmitting a true signal in the opposite direction.
- Ones of the remaining cores of the single optical fiber may be employed for carrying chaff signals, one or more of which may be multiplexed with a signal for use by an OTDR.
- the disclosed embodiments may be utilized in conjunction with existing or future arrangements for preventing tapping or other tampering with optical fibers.
- other measures for protecting transmitted data such as data encryption, patrolling of data lines by guards, intrusion detection monitor sensors, and hardening of data lines by encasing them in concrete or steel conduits may be employed in addition to the techniques disclosed herein.
- use of the disclosed embodiments may reduce or eliminate the need for some or all of those measures.
- the software may be implemented as a program tangibly embodied on a program storage unit or computer readable medium.
- the program may be uploaded to, and executed by, a machine comprising any suitable architecture.
- a computer platform having hardware such as one or more central processing units (“CPUs”), a memory, and input/output interfaces may be suitably employed.
- the computer platform may also include an operating system and microinstruction code.
- a non-transitory computer readable medium is any computer readable medium except for a transitory propagating signal.
- any reference to an element herein using a designation such as“first,”“second,” and so forth does not generally limit the quantity or order of those elements. Rather, these designations are generally used herein as a convenient method of distinguishing between two or more elements or instances of an element. Thus, a reference to first and second elements does not mean that only two elements may be employed there or that the first element must precede the second element in some manner. Also, unless stated otherwise a set of elements comprises one or more elements.
- terminology of the form“at least one of A, B, or C” or“one or more of A, B, or C” or“at least one of the group consisting of A, B, and C” or“at least one of A, B, and C” used in the description or the claims means“A or B or C or any combination of these elements.”
- this terminology may include A, or B, or C, or A and B, or A and C, or A and B and C, or 2A, or 2B, or 2C, and so on.
Abstract
Description
Claims
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US16/190,801 US10784969B2 (en) | 2016-02-18 | 2018-11-14 | Secured fiber link system |
PCT/US2019/060465 WO2020102020A1 (en) | 2018-11-14 | 2019-11-08 | Secured fiber link system |
Publications (2)
Publication Number | Publication Date |
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EP3881452A1 true EP3881452A1 (en) | 2021-09-22 |
EP3881452A4 EP3881452A4 (en) | 2022-08-24 |
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Application Number | Title | Priority Date | Filing Date |
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EP19884210.6A Pending EP3881452A4 (en) | 2018-11-14 | 2019-11-08 | Secured fiber link system |
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EP (1) | EP3881452A4 (en) |
JP (1) | JP2022507482A (en) |
WO (1) | WO2020102020A1 (en) |
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CN113654639B (en) * | 2021-07-16 | 2023-11-17 | 太原理工大学 | Phase-sensitive optical time domain reflectometer with active frequency shift differential pulse modulation |
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US4217488A (en) * | 1977-01-21 | 1980-08-12 | Bell Telephone Laboratories, Incorporated | Secure optical communication components, method, and system |
US5712937A (en) * | 1994-12-01 | 1998-01-27 | Asawa; Charles K. | Optical waveguide including singlemode waveguide channels coupled to a multimode fiber |
US8693865B2 (en) * | 2010-01-11 | 2014-04-08 | Hewlett-Packard Development Company, L.P. | Network security using optical attenuation data |
CN107408982B (en) | 2015-03-16 | 2019-09-27 | 华为技术有限公司 | Device, method and computer-readable memory for the compensation of OTDR transmitter noise |
US10763962B2 (en) | 2016-02-18 | 2020-09-01 | Apriori Network Systems, Llc. | Secured fiber link system |
US20190222309A1 (en) * | 2016-08-09 | 2019-07-18 | Macquarie University | System and a method for detecting the installation of an optical tap and a method of securing an optical signal in an optical fiber |
-
2019
- 2019-11-08 EP EP19884210.6A patent/EP3881452A4/en active Pending
- 2019-11-08 WO PCT/US2019/060465 patent/WO2020102020A1/en unknown
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WO2020102020A1 (en) | 2020-05-22 |
EP3881452A4 (en) | 2022-08-24 |
JP2022507482A (en) | 2022-01-18 |
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