Devices and methods for protecting telecommunication infrastructure from optical signals

Abstract

An interface device connected between a telecommunication network and a distributed acoustic sensing (DAS) device. The interface device includes: a first signal splitter configured to receive a probe signal from the DAS device and split the probe signal into a first portion and a second portion; a signal analyzing module configured to receive the first portion of the probe signal and determine whether peak and / or average power of the probe signal is below predetermined peak and / or average power threshold values; and a delay device configured to receive the second portion of the probe signal and delay propagation of the second portion of the probe signal to the telecommunication network by an amount of time taken by the signal analyzing module to analyze the first portion of the probe signal.

Description

DEVICES AND METHODS FOR PROTECTING TELECOMMUNICATION INFRASTRUCTURE FROM OPTICAL SIGNALSTECHNICAL FIELD

[0001] Aspects of the present disclosure are generally directed to methods and / or systems for protecting submarine assets such as repeaters from optical signals.BACKGROUND

[0002] Reference to any prior art in the specification is not an acknowledgment or suggestion that this prior art forms part of the common general knowledge in any jurisdiction or that this prior art could reasonably be expected to be understood, regarded as relevant, and / or combined with other pieces of prior art by a skilled person in the art.

[0003] Fiber-optic submarine communication cables are often laid on the sea floor between land-based communication stations and are used to transmit digital data, such as telephone, Internet and private data, across spatially vast marine environments. Repeaters (e.g., two-way amplifiers) are placed at intervals along the fiber-optic submarine communication cable and are used to amplify the optical signal carrying digital data that would otherwise be attenuated during its transmission across the marine environment. The repeaters may be powered by electrical conductors located in the submarine communication cables and are typically connected to a land-based power source.

[0004] Although such cables and associated infrastructure are primarily used for communicating digital data, they can often also be used to detect incidents or events (such as wear and tear of the cables, exposure of cables to the marine environment, earthquakes, etc.) along the optical fibers or in the surrounding regions along the optical fibers. Information about such incidents or events can then be used to take actions, e.g., mitigate risks and hazards to the cables, thereby increasing the longevity of the cables, issuing warnings, etc.

[0005] One such technology that utilizes fiber optic communication cables to detect submarine incidents is distributed acoustic sensing (DAS). The principle of DAS relies on the occurrence of one or more acoustic event, from a stationary or moving object, causing a corresponding localized perturbation of the refractive index and / or geometry of an optical fiber. Due to the perturbed refractive index and / or geometry, an optical signal that istransmitted along the optical fiber and then backscattered in a distributed manner (e.g. via Rayleigh scattering or other similar scattering phenomena) along the length of the fiber includes fluctuations (e.g. in intensity and / or phase) over time. The magnitude of the fluctuations relates to the severity or proximity of the perturbing event. The timing of the fluctuations along the distributed back-scattering time scale relates to the location of the perturbing event.

[0006] Such DAS systems typically interact with the existing repeaters located along fiber-optic submarine communication cables. In particular, the DAS optical signals are combined with other signals carried by the fiber-optic submarine communications cable, for example using wavelength division multiplexing.

[0007] However, sometimes, the optical signals generated or transmitted by the DAS system may have a peak or average power of several watts that may damage the repeater or at least portions of the repeater. This may cause the entire telecommunications infrastructure to fail.

[0008] Accordingly, there is a desire for a mechanism to protect the fiber optic infrastructure and in particular the repeaters from damage that may be caused by DAS systems.SUMMARY

[0009] Disclosed herein is an interface device connected between a telecommunication network and a distributed acoustic sensing device. The interface device includes: a first signal splitter configured to receive a probe signal from the distributed acoustic sensing device and split the probe signal into a first portion and a second portion; a signal analyzing module configured to receive a first portion of the probe signal and determine whether a peak and / or average power of the probe signal is below a predetermined peak and / or average power threshold values; and a delay device configured to receive a second portion of the probe signal and delay propagation of the second portion of the probe signal to the telecommunication network by an amount of time taken by the signal analyzing module to analyze the first portion of the probe signal.

[0010] Also disclosed herein is a method for determining threshold peak power and average power signals for an interface device connected between a distributed acoustic sensing (DAS) unit and a telecommunication network. The method includes: identifying one or more optical paths in an infrastructure device of the telecommunication network connected to the DAS unit, determining maximum peak power and average power limits that can be handled by optical components of the infrastructure device in each optical path; determine critical optical paths for maximum peak power and maximum average power based on the maximum peak power and maximum average power limits of each optical path; determine allowable peak power and allowable average power based on the maximum peak power and maximum average power of the critical optical paths; and adjust threshold values of the interface device based on the allowable peak power and the allowable average power.

[0011] Further aspects of the present disclosure and further embodiments of the aspects described in the preceding paragraphs will become apparent from the following description, given by way of example and with reference to the accompanying drawings.BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Fig. l is a schematic of an example telecommunications infrastructure with a DAS unit and an interface device.

[0013] Fig. 2 is a block diagram of an interface device.

[0014] Fig. 3 is a block diagram of the signal analyzing module of the interface device.

[0015] Fig. 4 is a flowchart illustrating an example method for determining the allowable peak and average power for the DAS unit.DETAILED DESCRIPTION

[0016] As described previously, fiber-optic communication infrastructure includes fiber optic cables and repeaters. Repeaters typically include several components designed to amplify optical signals and ensure reliable long-distance communication of optical signals. The main components of a repeater include optical amplifiers that amplify weak optical signals transmitted through the fiber and monitoring units that are responsible for monitoring the health and performance of the repeater. The monitoring units typically includephotodiodes that monitor the traffic and collect data on various parameters such as signal strength, temperature, and power levels. If any of the parameters are not within threshold levels, the monitoring units can trigger alarms or corrective actions.

[0017] As telecommunication network repeaters generally receive weak optical signals and amplify them, they typically operate at low power levels, typically in the range of OdB or l-10mW. Accordingly, it is rare to add an optical amplifier in a fiber-optic communication network before a repeater. However, DAS systems typically include an amplifier (e.g., an Erbium-doped fiber amplifier EDFA) that amplifies optical signals before the signals are transmitted by the DAS system into the repeater. Although amplifiers within the DAS systems are operated such that the power of the optical signals is within the tolerance range of repeaters, these amplifiers nevertheless have the capability of boosting the power of the optical signals considerably, e.g., in the range of several watts, which is orders of magnitude higher than any typical power experienced in a telecommunication repeater.

[0018] If such high-powered signals inadvertently enter the repeater, they may damage the repeater as the repeaters are not equipped to handle such high-power levels. In particular, such high-powered optical signals may damage or blind the photodiodes in the monitoring units, thereby damaging the telecom infrastructure, which is often difficult to service or replace given its location (e.g., subsea or buried under cities).

[0019] Aspects of the present disclosure present systems and methods to prevent such damage to fiber-optic infrastructure. In particular, aspects of the present disclosure provide an interface device that protects telecommunication infrastructure from damage by optical signals transmitted from a DAS system. Other aspects of the present disclosure provide a method for using the interface device to analyze a critical path of the infrastructure to protect the telecommunication infrastructure from damage by optical signals.

[0020] The interface device disclosed herein is connected between a DAS system and the telecommunication infrastructure (such as repeaters, branching units, nodes, line terminating equipment, etc.) and it actively prevents the DAS optical output from reaching the telecommunication infrastructure if the optical output is above a threshold value in order to protect the telecommunication infrastructure. In particular, the interface device receives optical signals from the DAS system (referred to as probe signals herein) and analyzes the peak and / or average power of the probe signals. If the power of the probe signals is determined to be within threshold values, it transmits the probe signals to thetelecommunication infrastructure it is connected to. Alternatively, if the interface device determines that the peak and / or average power of the probe signals exceeds the threshold peak and / or average power levels, the interface device automatically actuates an optical switch to cutoff the DAS optical signal and prevents it from being transmitted to the telecommunication infrastructure it is connected to.

[0021] To inject the probe signal into the telecommunication infrastructure amid active data traffic, the interface device also includes a passive wavelength division multiplexer (WDM). The interface device is designed to be independent of the telecommunication data traffic. This way even if the interface device fails (i.e. a power supply failure), it does not impact on the telecommunication data traffic in any way. This is because the active components of the interface device are separate from the telecommunications traffic and only interact with the DAS optical path.

[0022] Further, the threshold values in the interface device are predetermined and fixed in the hardware and therefore cannot be reprogrammed remotely or with physical access to the device. This improves security as the threshold values cannot be altered by a rogue entity that is able to hack into the telecommunication network or inadvertently from the outside of the device. These and other aspects of the interface device will be described in detail in the following sections with reference to Figs. 1-3.

[0023] Fig. 1 illustrates an example telecommunication infrastructure configuration including the interface device. As shown in Fig. 1, the configuration includes telecommunications infrastructure 102, a DAS unit 104, and an interface device 106.

[0024] The telecommunication infrastructure includes a line terminating equipment 108, a repeater 110 and two optical fibers 112, 114. The line terminating equipment 108 is connected to the repeater 110 via the two fiber optic cables - a transmission cable 112 and a receiver cable 114. The transmission cable carries data traffic from the line terminating equipment 108 to the repeater 110 and the receiver cable 114 carries data traffic from the repeater 110 to the line terminating equipment 108.

[0025] The interface device 106 is connected to the telecommunications infrastructure 102 via one of the optical fibers, namely, the receive fiber 114. In particular, it is connected between the line terminating equipment 108 and the repeater 110 via the receiver fiber 114. The interface device 106 may be spaced from the repeater 110 at any suitable distance for power and data communication purposes. In one example, the interface device 106 may be10-50 km from the repeater 110, with the data cable carrying the optical fibers 112, 114 being anchored to the seafloor / buried underground.

[0026] The DAS unit 104 is connected to the telecommunication infrastructure 102 via the interface device 106. That is, the DAS unit 104 is connected to the interface device and the interface device is connected to the telecommunication infrastructure. In some embodiments, the DAS unit 104 is designed to operate with its probe signals counter-propagating relative to the data transmission signals in the telecommunications infrastructure. That is, the probe signals cross the telecom traffic in a counter propagating fashion. In such cases, the DAS unit 104 is connected to interface device 106 and the interface device is connected to the receiver fiber 114. The DAS unit 104 transmits probe signals to the interface device 106 and the interface device 106 transmits these probe signals to the repeater via the receiver fiber 114, whereas data transmission signals travel along the receiver fiber 114 from the repeater 110 to the line terminating equipment 108. By counter-propagating the probe signals and the data transmission signals, crossover and / or leakage between the high-power probe signals and the data transmission signals can be prevented.

[0027] It will be appreciated that in other embodiments, the DAS unit 104 may be designed to operate with its probe signals co-propagating relative to the data transmission signals in the telecommunications infrastructure. That is, the probe signals and telecom traffic travel in the same direction. In such cases, the DAS unit 104 is connected to the interface device 106 and the interface device 106 is connected to the transmission fiber 112 and it transmits its probe signals from the DAS unit 104 to the repeater via the transmission fiber 114 in the same direction as the data transmission signals.

[0028] In one embodiment, the DAS unit 104 transmits probe signals to the interface device 106. The interface device 106 analyses these probe signals to determine whether the peak and / or average power output of the probe signals is below threshold values. If the interface device 106 determines that the peak and / or average power output of the probe signals is below the threshold values, it passes these probe signals onto the repeater 110 via fiber 112 or 114. The repeater 110 then transmits these probe signals along the optical fiber 112.

[0029] In some embodiments the communication is unidirectional, from the DAS unit 104 to the repeater 110. In other embodiments the communication is bidirectional allowing for example, control signals to be communicated from the repeater 110 to the DAS unit 104.

[0030] Although Fig. 1 depicts a line terminating equipment and a repeater as part of the telecommunications infrastructure, it will be appreciated that this is merely an example. The interface device of the present disclosure is not limited to protecting these devices. Instead, it can be used in conjunction with other telecommunication infrastructure such as branching units, nodes, etc., without departing from the scope of the present disclosure.

[0031] Further, the probe signal generated by the DAS unit 104 can be a square pulse, a chirped-frequency pulse, or any other suitable type of pulse without departing from the scope of the present disclosure.

[0032] Fig. 2 illustrates the interface device 106. As shown in Fig. 2, the interface device 106 includes a signal analyzing module 202, a delay device 204, and an optical switch 206. The interface device 106 also includes a signal splitter 208 and a wavelength division multiplexer 210.

[0033] The signal splitter 208 receives probe signals from the DAS unit 104 and splits the probe signals such that one portion of the probe signal is passed to the signal analyzing module 202 and the other portion of the probe signal is passed to the delay device 204. In some embodiments, the splitter divides the probe signal in such a way that a significant portion of the probe signal is passed to the delay device 204 and a small portion of the probe signal is passed to the signal analyzing module 202. In one example, the splitting ratio of the splitter 208 may be 98:2, such that 98% of the signal is passed to the delay device 204 and only 2% of the signal is passed to the signal analyzing module 202.

[0034] In some embodiments, the signal splitter is a passive optical splitter that enables the optical signal to be distributed to the two locations without the need for electrical conversion, thereby maintaining the integrity of the original signal. Examples of optical splitters that can be used include fused biconical taper (FBT) splitters and planar Lightwave circuit (PLC) splitters.

[0035] The signal analyzing module 202 is configured to receive a portion of the probe signal from the signal splitter 208 and determine whether the peak and / or average power of the probe signal is below predetermined peak and / or average power threshold values.

[0036] The delay device 204 receives a majority of the probe signal from the signal splitter 208 and is configured to delay the propagation of the probe signal by a controlled amount oftime. This delay can be achieved by routing the optical signal through a longer optical path, such as a loop of optical fiber before it can exit the delay device 204. Any suitable delay device 204 may be utilized as long as it is able to delay propagation of the probe signal for the amount of time it takes the signal analyzing module 202 to analyze the signal and complete its analysis. The delay also considers the time taken to actuate the optical switch.

[0037] This timing relationship is achieved through careful design and calibration of the delay device 204. The optical path length within the delay device 204 is calculated and adjusted based on the known processing time of the signal analyzing module 202. For example, if the signal analyzing module 202 requires 100 nanoseconds to complete its analysis, the delay device 204 is designed with an optical path length that introduces a 100 nanosecond delay to the second portion of the probe signal.

[0038] To ensure this precise timing, the delay device 204 may incorporate adjustable elements, such as variable optical delay lines or tunable optical buffers. These adjustable elements allow fine-tuning of the delay time to match any variations in the processing time of the signal analyzing module 202. Additionally, the delay device 204 may include monitoring and feedback mechanisms to continuously measure and adjust the delay time, ensuring it remains synchronized with the signal analyzing module's processing time even under changing operational conditions.

[0039] This synchronized delay ensures that the second portion of the probe signal, which includes the majority of the signal power, does not reach the optical switch 206 until the signal analyzing module 202 has completed its analysis of the first portion and determined whether the signal power exceeds the threshold values. This timing coordination allows the optical switch 206 to be actuated, if necessary, before the potentially harmful portion of the probe signal can pass through to the telecommunication network.

[0040] Examples of delay devices include optical delay lines (ODLs), optical coherence tomography systems, microelectromechanical systems, optical buffers such as loops or integrated optical memory devices. These devices offer various advantages and trade-offs in terms of complexity, precision, and integration, allowing for flexible and efficient optical signal delay management. In one embodiment, the delay device 204 is a delay loop that has an optical path length that delays propagation of the probe signal for the amount of time it takes the signal analyzing module to analyze the probe signal.

[0041] The optical switch 206 is typically a device that selectively switches optical signals from one path to another. In the present case, the optical switch 206 connects the output of the delay device to the WDM 210. However, upon receiving a signal from the signal analyzing module 202 (in case the signal analyzing module 202 determines that the peak and / or average signal power exceeds one of the thresholds), the optical switch 206 prevents the probe signal from the delay device 204 reaching the WDM 210. Instead, it may redirect the probe signal back to the delay device in a way trapping the probe signal between the delay device 204 and the optical switch 206.

[0042] Any known optical switch may be utilized including MEMs switches, electro-optic switches, thermos-optic switches, opto-mechanical switches, magneto-optic switches, etc. In a preferred embodiment, the optical switch is a high-speed electro-optic switch that offers a 100ns actuation time.

[0043] The WDM device 210 combines or multiplexes optical signals onto a single optical fiber using different wavelengths of laser light or separates / demultiplexes combined signals into individual channels. In the embodiment shown in Fig. 2, the WDM operates on two channels. One of the channels is a long band (L-band) channel that has a wavelength range of approximately 1565 nm to 1625 nm and the other is a conventional band (C-band) channel that has a wavelength range of approximately 1530 nm to 1565 nm. The probe signals from the DAS unit 104 are communicated to the repeater over the L-band channel, whereas signals from the repeater 110 may be received at the line terminating equipment 108 over the C-band channel.

[0044] To account for this, the WDM device 210 includes three ports - an L-band port, a C- band port, and a common port. It receives probe signals from the optical switch 206 on the L-band port and communicates these probe signals onto the common port, which is connected to the repeater 110 (via receiver cable 114). It may also receive signals at the common port from the repeater 110. Typically, it receives live telecom signals in the C-band at the common port and passes these on to the C-band port, which is connected to the line terminating equipment 108.

[0045] By doing so, the WDM device 210 facilitates the counter-propagation of the probe signals relative to the data transmission signals. In particular, the WDM 210 is configured tocommunicate the probe signals from the DAS unit 104 onto the common port in a direction opposite to that of the data transmission signals.

[0046] When the probe signals enter the WDM 210 through the L-band port, they are directed onto the common port and transmitted towards the repeater 110 via the receiver cable 114. Conversely, data transmission signals from the repeater 110 enter the WDM 210 through the common port and are directed to the C-band port, which is connected to the line terminating equipment 108. This arrangement ensures that the probe signals and data transmission signals travel in opposite directions within the same fiber, effectively implementing counter-propagation. By configuring the WDM 210 in this manner, the interface device 106 enables the separation and counter-propagation of the probe signals and data transmission signals, which helps prevent interference and potential damage to the telecommunication infrastructure.

[0047] A few different failure states can happen to the DAS unit 104. One of these failure states is that the peak pulse power can get too high. This may happen, for example, if the DAS unit 104 is compromised or hacked by a bad actor who gets access to a control interface of the DAS system. The bad actor may turn down the attenuation of the DAS unit 104 and would be able to send a large amount of power into the telecommunication network in an attempt to bring down the entire network. Another way this can occur is if some circuitry within the DAS unit 104 fails. This could also fail the attenuator within the DAS unit 104 and send a large amount of pulse power into the telecommunication infrastructure. Another failure state is that the average power can get too high. This may happen, for example, if the DAS unit 104 is compromised or hacked by a bad actor. The bad actor may turn up the pump currents that charge the erbium doped fiber amplifier (EDFA). This causes a larger pump current to flow into the EDFA and the EDFA may start amplifying the probe signals a lot more than usual. Alternatively, the modulation of the probe signal may fail altogether, and the DAS unit 104 may start transmitting continuous wave (CW) light. This CW light could potentially damage the telecommunication infrastructure by blinding its monitoring channels. The signal analyzing module 202 is designed to address both these potential failure states.

[0048] Fig. 3 illustrates the signal analyzing module 202. The signal analyzing module 202 includes a signal splitter 302, two receiver assemblies - a pulse receiver assembly 303A and a DC receiver assembly 303B, and a combiner device 310. Each receiver assembly includes anoptical receiver 304A, 304B, an amplifier 306A, 306B, and a comparison circuitry 308A, 308B.

[0049] The signal splitter 302 receives a portion of the probe signals from the signal splitter 208 and further splits that portion of the probe signals such that one portion of the probe signal is passed to the pulse receiver assembly 303 A, and the other portion is passed to the DC receiver assembly 303B.

[0050] In some embodiments, the splitter divides the probe signal in such a way that substantially half of the probe signal is passed to the pulse receiver assembly 303 A, and the other half is passed to the DC receiver assembly 303B. In one example, the splitting ratio of the splitter 208 may be 50:50.

[0051] In some embodiments, the signal splitter is a passive optical splitter that enables the optical signal to be distributed to the two locations without the need for electrical conversion, thereby maintaining the integrity of the original signal. Examples of optical splitters that can be used include fused biconical taper (FBT) splitters and planar Lightwave circuit (PLC) splitters.

[0052] The receiver assemblies receive their respective portions of the probe signal and determine whether the probe signal power is within threshold values. The pulse receiver assembly 303 A is configured to determine whether the peak power of the probe signal is below a threshold value and addresses the failure state that results in high peak power. The DC receiver assembly 303B is configured to determine whether the average power of the probe signal is below a threshold value and addresses the failure state that results in a high average power.

[0053] The optical receivers 304 A, and 304B of each receiver assembly receive respective portions of the probe signal and convert these optical signals into electrical signals. In one example, the optical receivers 304 A and 304B are photodetectors that convert the optical probe signals into electrical signals. Any suitable photodetectors may be utilized including photodiodes, avalanche photodiodes, and phototransistors.

[0054] Next, the amplifiers 306A, 306B receive the electrical signals generated by the optical receivers and amplify these electrical signals. Any suitable amplifier such as anoperational amplifier or a transimpedance amplifier may be utilized. Transimpedance amplifiers convert small current signals into more substantial voltage signals.

[0055] The amplified voltage signals from the amplifiers 306A and 306B are then fed to the respective comparison circuitry 308A, 308B. A suitable comparison circuitry may be employed without departing from the scope of the present disclosure. One particular comparison circuit is a comparator. Comparators are electronic devices that compare two voltage or current signals and output a digital signal indicating which of the two signals is larger. The comparator has two inputs, and the two voltage or current signals are applied to these two inputs. The comparator then measures the voltages at the two inputs and outputs a binary output - high or low.

[0056] In comparator 308 A, the amplified current or voltage signal (corresponding to the probe signals) from the amplifier 306A is applied to one of the inputs and a threshold peak power signal is applied to the second input as a reference signal. If the probe signal exceeds the threshold peak power signal, the output may be high, providing a clear indication that the probe signal is higher than the threshold peak power signal. Alternatively, if the probe signal is lower than the threshold peak power signal, the output may be low, indicating that the peak power of the probe signal is lower than the threshold peak power signal.

[0057] In comparator 308B, the amplified current or voltage signal (corresponding to the probe signals) from the amplifier 306B is applied to one of the inputs and a threshold average power signal is applied to the second input as a reference signal. If the probe signal exceeds the threshold average power signal, the output may be high, providing a clear indication that the probe signal is higher than the threshold average power signal. Alternatively, if the probe signal is lower than the threshold average power signal, the output may be low, indicating that the average power of the probe signal is lower than the threshold average power signal.

[0058] In one example, the threshold values for the two comparators may be set using trimming potentiometers (or “trim pots”). A trim pot is an adjustable resistor. By varying the position of the trim pot’s wiper, the exact voltage that the comparator uses as its threshold for switching can be set. The reference or threshold peak power signal and threshold average power signal can be set at the time of manufacturing.

[0059] The outputs from the comparators 308 A, 308B are provided to the combiner device310. In some embodiments, the combiner device is an OR gate. It receives a 1 or 0 signalfrom each comparator 308 A, 308B. A 1 signal indicates that the probe signal compared by the corresponding comparator is higher than the threshold signal and a 1 signal indicates that the probe signal compared by the corresponding comparator is lower than the threshold signal.

[0060] If both of the comparators 308 A, 308B output a 0, it means that the peak and average power of the probe signal is below the corresponding threshold values. The combiner device 310 also generates a 0 output in this case. Alternatively, if either one of the comparators 308 A, 308B outputs a 1, it means that the peak or average power of the probe signal is above the corresponding threshold value. The combiner device 310, in this case, generates a 1 output. If both the comparators 308 A, 308B output a 1, it means that the peak and average power of the probe signal is above the corresponding threshold values. In this case also the combiner device 310 generates a 1 output.

[0061] The output from the combiner device 310 is provided to the switch 206. If the output is 0, the switch does nothing. However, if the output is 1, the switch opens (breaking the connection of the optical path), thereby blocking the probe signal from the delay device 204 to reach the WDM 210.

[0062] If the switch flips, it does not reset it. This means that it switches, and it stays switched until the system is manually reset. The manual reset flips the polarity of the signal to the switch in a manual fashion, and it resets the switch. This manual reset makes the system safe and tamper free. There is no way to compromise or hack the interface device through network connections as the switch cannot be reset using any electronic signals.

[0063] Further, the peak power and average power thresholds are set on the electronic devices on the circuit - e.g., the physical resistor value is set using the trim pot. There are no microprocessors or on-board memory. All components of the interface device 106 are nonnetworked - making it independent and secure. This is relevant given any weakness of the interface device 106 can be used to try and damage the telecommunication infrastructure by bad actors.

[0064] An example method for setting the peak power and average power thresholds for the two comparators 308A, 308B is now described. As part of installing the interface device 106, the allowable peak pulse power and the average power from the DAS unit 104 is determined. The allowable power levels depend on the architecture of thetelecommunications infrastructure and the attenuation in the cables. To make this determination, an analysis of the optical components in the repeater 110 and / or in other telecom infrastructure that could be impacted by the probe signal is performed. The result of this analysis determines the limiting threshold values set for the comparators.

[0065] An example analysis to determine the allowable output peak power and allowable output average power from a DAS unit given a specific subsea repeater configuration and architecture is described next. The resulting values are set as hardware thresholds in the comparators 308 A, 308B to ensure safe optical levels are not exceeded.

[0066] The particular limiting threshold values will depend on the configuration of the telecom infrastructure, the direction of the probe signal with respect to the traffic signals, etc.

[0067] The first step in the analysis is to determine the critical optical path for both peak and average power which are the paths where damage or adverse impacts would occur at lowest counter-propagating peak and average power levels at the output of the repeater, which is where the probe signal would enter from.

[0068] There are two limiting factors to consider when analyzing each optical path. First, the threshold where hardware damage would occur. This would most likely be damage to monitoring photodiodes caused by high peak power from the pulsed, low-duty-cycle DAS unit. Secondly, the threshold where repeater system performance would be adversely impacted by interfering with the signals measured by the monitoring / supervisory receivers within a repeater.

[0069] Based on the analysis, the maximum peak power (Pm-pp) and the maximum average power (Pm-ave) for the DAS unit 104 can be calculated. These values are both subsequently reduced to determine the allowable peak power (Pa-pp) and the allowable average power (Pa- ave ) according to Eq. 1 -Pa-pp, P a-ave=Pm-pp, Pm-ave ~ Fs (Eq. 1)

[0070] Where Fsis a safety factor in dB. A typical conservative value for Fsis 10 dB.

[0071] The DAS unit 104 is configured to output less than these values during normal operation conditions. In the case of a hardware fault or compromise, the interface device 106 acts as a redundant, non-networked backup protection mechanism that detects power inexceedance of these pre-set values and activates the optical switch before any potentially problematic probe signals escapes into the telecommunications cable network.

[0072] Fig. 4 illustrates an example method for determining the allowable peak and average power outputs of the DAS unit 104. The method 400 commences at step 402, where the optical paths for the probe signal into a telecommunication infrastructure are determined. The telecommunication infrastructure may be any device that is connected to the output of the DAS unit 104 and may be e.g., a repeater, a line termination terminal, a branch, etc. As the DAS unit 104 is connected to the telecommunication infrastructure such that the probe signal is counter-propagating with respect to the data signals, the optical paths for the probe signal are generally any optical paths within the telecommunication infrastructure that connect the optical output of the telecommunication infrastructure with other elements of the telecommunication infrastructure.

[0073] Next, at step 404, the maximum peak and average power that can be handled by the elements within the identified optical paths is determined. This analysis can be performed as described above.

[0074] At step 406, the critical optical paths for maximum peak power and maximum average power are determined. The critical optical paths may be identified as the paths that have the lowest maximum peak power and the lowest maximum average power handling capabilities. In some embodiments, the same optical path may be a critical optical path for maximum peak power and maximum average power. In other embodiments, different optical paths may be the critical optical path for maximum peak power and maximum average power.

[0075] Next, at step 408, the allowable peak and average power are computed, for example, using equation 1.

[0076] Finally, at step 410, the threshold values for the comparators 308A, 308B are set based on the calculated allowable peak and average power values. In one example, a 5-volt input is fed to each of the trim pots and then the wiper of each trim pot is adjusted so that the voltage drop from the 5-volt input can be changed to the allowable values. In the case of the comparator 308A, this is set to the allowable peak power value and in the case of the comparator 308B, this is set to the allowable average power value.

[0077] Although the invention has been discussed with respect to various embodiments, it should be recognized that the invention comprises the novel and non-obvious claims supported by this disclosure.

[0078] As used herein, except where the context requires otherwise, the term "comprise" and variations of the term, such as "comprising", "comprises" and "comprised", are not intended to exclude further additives, components, integers or steps.

Claims

CLAIMS1. An interface device connected between a telecommunication network and a distributed acoustic sensing device, the interface device comprising: a first signal splitter configured to receive a probe signal from the distributed acoustic sensing device and split the probe signal into a first portion and a second portion; a signal analyzing module configured to receive the first portion of the probe signal and determine whether peak and / or average power of the probe signal is below predetermined peak and / or average power threshold values; and a delay device configured to receive the second portion of the probe signal and delay propagation of the second portion of the probe signal to the telecommunication network by an amount of time taken by the signal analyzing module to analyze the first portion of the probe signal.

2. The interface device of claim 1 further comprising: an optical switch connected between the delay device and the telecommunication network, the optical switch also connected to an output of the signal analyzing module, the optical switch configured to pass the second portion of the probe signal to the telecommunication network under normal operation and configured to open upon receiving an output signal from the signal analyzing module to prevent the second portion of the probe signal from reaching the telecommunication network.

3. The interface device of claim 2, wherein the delay device is configured to delay propagation of the second portion of the probe signal by the amount of time taken by the signal analyzing module to analyze the first portion of the probe signal and a time taken by the optical switch to respond.

4. The interface device of any one of claims 1-3, wherein the first splitter is substantially a 2:98 ratio splitter that splits the probe signal such that 2% of the probe signal is in the first portion of the probe signal and 98% of the probe signal is in the second portion of the probe signal.

5. The interface device of any one of claims 2-4 further comprising a wavelength division multiplexer (WDM) connected between the optical switch and the telecommunication network, the WDM configured to receive the second portion of the probe signal on a first port and communicate the second portion of the probe signal onto a common port connected to an infrastructure device of the telecommunication network.

6. The interface device of claim 5, wherein the WDM is configured to communicate the second portion of the probe signal onto the common port such that the second portion of the probe signal is counter-propagating in respect of data traffic on the telecommunication network.

7. The interface device of any one of claims 1-6, wherein the signal analyzing module comprises: a second signal splitter that splits the first portion of the probe signal into a third portion and a fourth portion, a pulse receiver assembly that receives the third portion of the probe signal and is configured to determine whether a peak power of the third portion of the probe signal exceeds a threshold peak power; a DC receiver assembly that receives the fourth portion of the probe signal and is configured to determine whether an average power of the fourth portion of the probe signal exceeds a threshold average power; and a combiner device connected to an output of the pulse receiver assembly and the DC receiver assembly and configured to combine outputs from the pulse receiver assembly and the DC receiver assembly.

8. The interface device of claim 7, wherein the pulse receiver assembly comprises: an optical receiver to convert the third portion of the probe signal into an electrical signal; and a comparison circuitry to:1006070682 compare the electrical signal with a reference signal that corresponds to the peak power threshold value, and generate an output signal if the electrical signal exceeds the reference signal.

9. The interface device of claim 7, wherein the DC receiver assembly comprises: an optical receiver to convert the fourth portion of the probe signal into an electrical signal; and a comparison circuitry to: compare the electrical signal with a reference signal that corresponds to the average power threshold value, and generate an output signal if the electrical signal exceeds the reference signal.

10. The interface device of any one of claims 7-9, wherein the combiner device is an OR gate, and is configured to generate an output signal if any one or more of the pulse receiver assembly or the DC receiver assembly generate an output signal.

11. The interface device of any one of claims 7-10 wherein the output of the combiner device is connected to the optical switch.

12. The interface device of claim 11, wherein the output signal of the combiner device causes the optical switch to open thereby preventing the second portion of the probe signal from reaching the telecommunication network.

13. The interface device of any one of claims 2-12 wherein once the optical switch is opened it is reset manually.

14. The interface device of any one of claims 7-11, wherein the second splitter has a 1 : 1 ratio such that half of the first portion of the probe signal is split into the third portion and the other half of the first portion of the probe signal is split into the fourth portion.100607068215. A method for determining threshold peak power and average power signals for an interface device connected between a distributed acoustic sensing (DAS) unit and a telecommunication network, the method comprising: identifying one or more optical paths in an infrastructure device of the telecommunication network connected to the DAS unit, determining maximum peak power and average power limits that can be handled by optical components of the infrastructure device in each optical path; determining critical optical paths for maximum peak power and maximum average power based on the maximum peak power and maximum average power limits of each optical path; determining allowable peak power and allowable average power based on the maximum peak power and maximum average power of the critical optical paths; and adjusting threshold values of the interface device based on the allowable peak power and the allowable average power.

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