Long-distance distributed optical fiber sensing (DFOS) and WDM communications over repeated fiber spans using an all-Raman amplification and coding scheme

Abstract

Aspects of the present disclosure describe distributed optical fiber sensing (DFOS) systems, methods, and structures that advantageously provide DFOS and WDM communications over an amplified multi-span optical WDM optical communications facility using an all-Raman amplification and coding scheme. The all-Raman amplification operates stably without isolators and provides sufficient gain to simultaneously compensate for fiber span losses in both the DFOS signal and the WDM channel signal. Additionally, the inventive techniques employ signal coding such as MB-TGD-OFDR for DAS, which operates the DFOS operating power at much lower power levels compared to pulse interrogation. Using signal coding along with distributed Raman amplification to improve OSNR and reduce power allows DFOS systems to coexist with WDM communications channels on the same amplified multi-span optical fiber links over long distances.

Description

[Technical field]

[0001] The present disclosure relates generally to distributed optical fiber sensing (DFOS) and wavelength division multiplexing (WDM) communications over a common optical fiber over long distances, including repeated fiber spans, using an all-Raman amplification and coding scheme. [Background technology]

[0002] As will be understood and appreciated by those skilled in the art, distributed optical fiber sensing (DFOS) uses backscattering mechanisms in optical fibers, such as Rayleigh scattering, Brillouin scattering, and Raman scattering, to sense the environment around the optical fiber cable. To date, deployment of DFOS systems has primarily employed repeaterless single-span fiber links due to the difficulty of achieving the optical signal-to-noise ratio (OSNR) required for DFOS in multi-span fiber links with in-line amplification. Furthermore, the in-line amplifiers commonly used in optical fiber communication networks are only capable of unidirectional signal propagation. These in-line amplifiers are typically based on erbium-doped optical fiber amplifiers (EDFAs), but require costly redesign to return the DFOS signal to the interrogator node. Thus, systems, methods, and structures that facilitate the development of amplified multi-span optical fiber installations that provide DFOS and data communications over a common optical fiber would be a welcome addition to the art. Summary of the Invention

[0003] The advancement of the art is achieved by aspects of the present disclosure which relate to a coded DFOS system operating over an amplified multi-span optical WDM communications facility.

[0004] In contrast to the prior art, systems, methods, and structures according to aspects of the present disclosure employ distributed Raman amplification to amplify a DFOS signal across multiple amplified fiber spans. In further contrast to the prior art, the all-Raman amplification of the present invention operates stably without an isolator and provides sufficient gain to simultaneously compensate for fiber span losses of both the DFOS signal and the WDM channel signal.

[0005] Additionally, the inventive technique employs signal coding, such as MB-TGD-OFDR for DAS, to operate the DFOS operating power at much lower power levels compared to pulse interrogation. The operating power is directly related to the amount of crosstalk that affects the co-propagating WDM channel, which can result in burst errors even after forward error correction (FEC). Using signal coding along with distributed Raman amplification to improve OSNR and reduce power allows DFOS to coexist with WDM communication channels on the same amplified multi-span optical fiber link. [Brief description of the drawings]

[0006] A more complete understanding of the present disclosure may be realized by reference to the accompanying drawings.

[0007] [Figure 1] FIG. 1 is a schematic diagram illustrating a coded constant amplitude DFOS system with out-of-band signal generation, according to an aspect of the present disclosure.

[0008] [Diagram 2] FIG. 1 is a schematic diagram illustrating an all-Raman amplification scheme supporting DFOS and WDM optical fiber communications over multiple amplified fiber spans, according to an embodiment of the present disclosure.

[0009] [Diagram 3] FIG. 2 is a schematic diagram illustrating WDM multiplexing of a communication channel and a DFOS signal according to an embodiment of the present invention.

[0010] [Figure 4]1 is a series of graphs illustrating the generation of an example DFPS signal in an all-Raman amplified optical fiber link across a first span, a second span, and a third span, in accordance with an embodiment of the present disclosure.

[0011] [Figure 5(A)] 1 is a pair of graphs illustrating post-FEC bit error rate (BER) for a communication channel subject to adjacent sensing signals at different peak power levels using a pulsed DAS, according to an embodiment of the disclosure. [Figure 5(B)] 1 is a pair of graphs illustrating post-FEC bit error rate (BER) for a communication channel subject to adjacent sensing signals at different peak power levels using coded DAS, according to an embodiment of the disclosure.

[0012] [Figure 6] FIG. 1 is a schematic diagram of an example architectural configuration of a correlation-based DAS interrogator including a generator that launches chirped pulses into a fiber under test (FUT) and detects Rayleigh backscattering by a coherent receiver, according to an aspect of the present disclosure.

[0013] [Figure 7] FIG. 2 is a schematic diagram of an exemplary DSP architecture for MB-DF-OFDR according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] The following merely illustrates the principles of the present disclosure, and it will thus be appreciated that those skilled in the art will be able to devise various arrangements which, although not explicitly described or shown herein, embody the principles of the present disclosure and are included within its spirit and scope.

[0015] Furthermore, all examples and conditional terms described herein are intended to be for educational purposes only to aid the reader in understanding the concepts contributed by the inventors to further the principles and techniques of the present disclosure, and should not be construed as being limited to such specifically recited examples and conditions.

[0016] Moreover, all statements herein reciting principles, aspects, and embodiments of the present disclosure, as well as specific examples thereof, are intended to encompass both structural and functional equivalents thereof. Additionally, such equivalents are intended to include both currently known equivalents as well as equivalents developed in the future, i.e., elements developed that perform the same function, regardless of structure.

[0017] Thus, for example, it will be appreciated by those skilled in the art that any block diagrams herein represent conceptual views of illustrative circuitry embodying the principles of the disclosure.

[0018] Unless otherwise specified herein, the figures making up the drawings are not drawn to scale.

[0019] As additional background, we begin by noting that Distributed Fiber Optic Sensing (DFOS) is an important and widely used technique for detecting environmental conditions (temperature, vibration, stretch levels, etc.) anywhere along a fiber optic cable which is in turn connected to an interrogator. As is known, a modern interrogator is a system that generates an input signal into the fiber and detects / analyzes the reflected / scattered and subsequently received signal. The signal is analyzed and an output is generated that is indicative of the environmental conditions encountered along the fiber. The signal thus received may result from reflections within the fiber such as Raman backscattering, Rayleigh backscattering, Brillion backscattering, etc. It may also be a forward signal utilizing multiple mode velocity differences. Without loss of generality, the following discussion assumes reflected signals, but the same approach can be applied to forward signals as well.

[0020] As will be appreciated, modern DFOS systems include an interrogator that periodically generates and injects a pulse of light (or any coded signal) into the optical fiber, which then transmits the pulsed light signal along the optical fiber.

[0021] At each location along the fiber, a small portion of the signal is reflected back to the interrogator. The reflected signal carries information that the interrogator uses to detect, for example, changes in power level that indicate mechanical vibrations.

[0022] The reflected signal is converted to the electrical domain and processed in the interrogator. Based on the time of pulse injection and the time the signal is detected, the interrogator can determine which location on the fiber the signal is coming from and sense the activity at each location on the fiber.

[0023] Those skilled in the art will understand and appreciate that by implementing signal coding on the interrogation signal, more optical power can be transmitted into the fiber, which can advantageously improve the signal-to-noise ratio (SNR) of Rayleigh scattering-based systems (e.g., distributed acoustic sensing, or DAS) and Brillouin scattering-based systems (e.g., Brillouin optical time domain reflectometry, or BOTDR).

[0024] As currently practiced in modern implementations, a dedicated fiber is allocated to the DFOS system in a fiber optic cable and is physically separated from existing optical communication signals carried on different fibers. However, given the exploding demand for bandwidth, it is becoming increasingly difficult to economically operate and maintain optical fiber just for DFOS operations. As a result, there is growing interest in integrating communication and sensing systems over a common fiber.

[0025] As mentioned above, one of the biggest challenges in integrating sensing and communication signals on the same fiber is the nonlinear crosstalk that occurs between the sensing and communication signals. One of the reasons is that the instantaneous operating power of the DFOS signal is much larger than that of the communication signal (channel), so the communication performance is degraded by the nonlinearity of the fiber. Although the instantaneous operating power of the interrogation signal can be reduced by implementing signal coding in DFOS, there still exists a large power fluctuation at the starting and falling edges of the code sequence, which results in cross-phase modulation (XPM) distortion in the adjacent wavelength division multiplexing (WDM) communication channel.

[0026] Yet another problem when applying coding to DFOS systems is the amplification of the signals. As a well-known fact, erbium-doped fiber amplifiers (EDFAs) are the medium of choice for optical signal amplification and are widely used in communication optical fibers. However, for the possible signal coding mentioned above, as the length of the code sequence increases, it approaches the carrier recovery time of the erbium atoms. As a result, the amplified output signal exhibits a non-uniform amplitude profile, and the code sequence has a decreasing gain over the duration of the entire sequence. If not corrected, the non-uniform amplitude profile affects the autocorrelation function of the implemented code and causes signal crosstalk between different fiber segments of the DFOS system.

[0027] 1 is a schematic block diagram of a coded constant amplitude DFOS system with out-of-band signal generation according to an embodiment of the present disclosure. The illustrated block diagram exemplarily illustrates how out-of-band signal generation according to an embodiment of the present invention may be applied to a DFOS system.

[0028] Operationally, we assume that DFOS systems are Rayleigh scattering-based systems (e.g., distributed acoustic sensing, or DAS) and Brillouin scattering-based systems (e.g., Brillouin optical time-domain reflectometry, or BOTDR) with coding implementations. With such coding designs, these systems are more likely to be integrated with fiber communication systems because they operate at lower power and are more sensitive to the response time of optical amplifiers.

[0029] In the exemplary arrangement shown in the block diagram, it is assumed that the coded interrogation sequence is generated digitally and modulated onto the sensing laser via a digital-to-analog converter (DAC) and an optical modulator. The modulated interrogation sequence may be amplified to an optimal operating power before being sent to the fiber for interrogation.

[0030] Advantageously, DFOS operations can also be integrated with communication channels via WDM in the same fiber. Within the sensing fiber, the interrogation sequence and the returned sensing signal may be optically amplified. The returned sensing signal, after amplification and optical bandpass filtering, is sent to a coherent receiver. The coherent receiver detects the optical field in both polarizations of the signal and downconverts it to four baseband lanes for analog-to-digital conversion (ADC) sampling and digital signal processor (DSP) processing. As will be readily understood and appreciated by those skilled in the art, the decoding operation is performed in the DSP to generate the interrogation Rayleigh or Brillouin response of the fiber, after which changes in the response are identified and interpreted as sensor readings.

[0031] FIG. 2 is a schematic diagram illustrating an all-Raman amplification scheme supporting DFOS and WDM optical fiber communications over multiple amplified fiber spans, according to an embodiment of the present disclosure.

[0032] As shown in Figure 2, a multi-span fiber link is amplified by multiple distributed Raman amplifiers to support both DFOS operation and WDM communication channels. The DFOS system can be a coherent optical time-domain reflectometry (OTDR) using Rayleigh backscattering used for DAS, or a Brillouin-based OTDR for temperature or strain sensing. Signal coding can be used to provide sufficient optical signal-to-noise ratio (OSNR) gain to mitigate the optical fiber losses due to typical span distances of ~80 km and the additional asynchronous spontaneous emission (ASE) noise caused by multiple optical amplifiers.

[0033] At the interrogation node, the DFOS signal is multiplexed with the communication channel via WDM to support sensing and communication using the same fiber and amplification equipment, which can be easily done using a standard wavelength selective switch (WSS). The circulator required to return the sensing signal to the DFOS interrogator can be placed after the WSS to avoid the insertion loss of the WSS. An optical bandpass filter (OBF) is used to block reflections of all other WDM channels before the sensing signal is detected by the DFOS receiver. At the destination node, the DFOS signal is demultiplexed from the WDM channel using a WSS and can also be terminated to avoid high back reflections.

[0034] In the present invention, all accumulated losses in the fiber span are compensated by the all-Raman amplification technique. This is in contrast to erbium-doped fiber amplification, which is "ramp amplification" and unstable when operated without a directional separator, whereas Raman amplification is dispersive and can operate stably with bidirectional signal propagation. This feature is important for supporting DFOS in multi-span fiber links. All-Raman amplification is also suitable for integrated optical sensing and communication systems because it can provide sufficient gain for wide optical bandwidths for WDM communications.

[0035] If the span loss is low, then only a backward pumping Raman amplifier is needed to compensate for the span loss. If the span loss is higher than the gain provided by the backward pumping (typically ~20 dB), then a forward pumping Raman amplifier can also be used.

[0036] As with data transmission over optical fiber, the achievable range of DFOS is limited by the OSNR over long distances, and in-line amplification is required to achieve operation over multiple optical fiber spans. In-line amplification for long-distance optical fiber links typically uses EDFAs with isolators at the output to avoid undesirable effects from reflections, and therefore does not work with DFOS. In some designs, such as undersea communications cables, backscattered signals of certain wavelengths can be routed to another fiber that supports propagation in the opposite direction. In a previous IR, we detailed how to redesign EDFA-based repeaters to support DFOS operation over multi-span links, incorporating optical bandpass filters, optical multiplexers / demultiplexers, optical switches, and photodiodes. However, such repeater redesigns are costly to implement, even when the return route for the signal has a dedicated combining path.

[0037] As will be understood and appreciated by those skilled in the art, Raman amplification is commonly used in single-span DFOS systems. It is typically used in a forward-pumped configuration to maintain the OSNR of the signal at ~40 km, but is insufficient to provide sufficient OSNR gain to reach the 80 km length of typical fiber spans. Signal coding designs such as MB-TGD-OFDR (IR 20008) allow the OSNR gain to compensate for large fiber span link losses, making multi-span DFOS systems possible.

[0038] According to aspects of the present invention, all-Raman amplification offers two differentiated features. First, DFOS can be operated bidirectionally in multi-span fiber links, and Raman pump can be injected from the backward, forward, or both. Furthermore, Raman pump is shared among integrated systems that include both WDM communication channels and DFOS, thus reducing implementation costs. Such configurations do not require dedicated signal coupling paths or expensive amplifier redesigns.

[0039] An integrated multi-span fiber sensing and communication system amplified using an all-Raman scheme began with WDM multiplexing of the DFOS signal and the communication channel.

[0040] FIG. 3 is a schematic diagram illustrating WDM multiplexing of communication channels and DFOS signals according to an embodiment of the present disclosure. Here, an MB-TGD-OFDR signal at 1550.12 nm, a 200 Gb / s DP-16QAM data channel at 1550.52 nm, and an emulated WDM transmission signal band of 2.5 THz emulated using an ASE noise source are multiplexed together using a commercially available WSS using a standard 50 GHz grid. The multiplexed signals are launched onto the same fiber link with multiple spans, and the loss of each span is compensated by full Raman amplification. The multiplexed signal spectrum at the interrogator node and the signal spectrum after transmission over 13 spans of optical fiber are shown.

[0041] FIG. 4 is a series of graphs illustrating an exemplary DFPS signal generation in an all-Raman amplified optical fiber link across a first span, a second span, and a third span, according to an embodiment of the present disclosure. The figure shows a typical DFPS signal generation profile in a three-span fiber link supported by all-Raman amplification. The first and second spans contain 80 km of optical fiber with a span loss of ∼20 dB and are pumped by Raman amplifiers in both forward and backward directions. The third span is a shorter span section with a fiber length of 50 km and is pumped using only backward Raman amplifiers.

[0042] The use of coding schemes such as MB-TGD-OFDR for DFOS is important to suppress amplifier noise as well as OSNR degradation due to high fiber loss. The peak power operating point of DFOS with coding schemes is typically much lower than that of conventional pulse-based DFOS.

[0043] 5(A) and 5(B) are a pair of graphs showing post-FEC bit error rate (BER) for a communication channel affected by adjacent sensing signals at different peak power levels, in accordance with an embodiment of the present disclosure, where FIG. 5(A) uses pulsed DAS and FIG. 5(B) uses coded DAS.

[0044] These figures show how the transmission performance of a 200G 16QAM system is affected by adjacent DAS signals. When a conventional pulsed DAS (with a typical reach of 50 km) is used on an 80 km fiber span, the high peak power at the normal operating point of the DAS results in burst errors that cannot be corrected by the transponder's FEC. When a DAS with MB-TGD-OFDR coding is used, the received channel still has errors even after 1000 km co-propagation with the 200G channel due to its low peak power operating point. Schemes such as out-of-band signal addition can also be employed to further reduce the impact of NL on adjacent WDM channels.

[0045] Those skilled in the art will understand and appreciate that time-gated digital optical frequency domain reflectometry (TGD-OFDR) is one encoding technique that can be used to increase the signal-to-noise ratio (SNR) in distributed acoustic sensing (DAS) through signal correlation.

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[0046] The same peak power (limited by fiber nonlinearity) and bandwidth, but with duration T and bandwidth B w =1 / T pulse

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[0047] FIG. 6 illustrates a schematic diagram of an example architectural configuration of a correlation-based DAS interrogator including a generator that launches chirped pulses into a fiber under test (FUT) and detects Rayleigh backscattering by a coherent receiver according to a further aspect of the present disclosure.

[0048] Consider the standard architecture of a correlation-based DAS shown in Figure 6, where a dual-polarized coherent receiver is used to detect Rayleigh backscattering. When applying TGD-OFDR in the absence of laser phase noise and phase modulation due to mechanical vibrations of the FUT, the received signal is

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[0049] Where:

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[0050] The Rayleigh impulse response can be estimated by correlating y(t) with the complex conjugate of the TGD-OFDR signal.

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[0051] This operation relies on the good autocorrelation properties of the chirped pulse.

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[0052] Long Chirp

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[0053] Therefore, the correlation output of equation (3) is the time domain Rayleigh impulse response g(t) filtered between frequencies ±1 / 2T with T c Thus, the energy delivered to the FUT increases, and the chirp duration T c It appears that by increasing , the SNR performance of TGD-OFDR can be linearly improved without limit.

[0054] In practice, however, when very long chirp durations are used, both the downstream interrogation signal and the upstream receive Rayleigh backscattering are susceptible to distortion due to phase modulation. First, we consider the effect of FUT vibrations on the downstream signal.

[0055]

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[0056] It can be seen that the original signal x(t) is phase modulated by the accumulated longitudinal strain. A Rayleigh reflection with amplitude h(z) at a position z contributes to the reflected signal:

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[0057] The total received signal (ignoring the contribution of noise) is the sum of all infinitesimal reflections y z (t)

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[0058] Compared to the simple convolution in equation (3), the received signal in equation (9) is distorted by two phase modulations in both the downstream signal and the upstream Rayleigh backscattering due to the time-varying longitudinal distortion. As a result,

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[0059] The effect of phase distortion on DAS is "spatial leakage" and z ν Vibration at fiber position z>z ν Leaks.

[0060] The spatial leakage was experimentally evaluated using the example of a DAS experiment carried out on an FUT in which a piezoelectric transducer (PZT) was inserted between two spools of standard single-mode fiber (SSFM) of 50 km and 25 km. In the experiment, c =50μs, chirp width 1 / T=10MHz (spatial resolution

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[0061] The PZT contains 12 m of fiber wrapped around a piezoelectric ring and has a gradient of 0.8 rad / V. In this experiment, the PZT is vib = 110Hz frequency with amplitude 10V (phase amplitude

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[0062] DAS is 1 / T f = 1,000Hz frame rate to sample the distributed vibrations,

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[0063] We note that the adverse effects of multiplicative phase noise interacting with the convolution with a linear impulse response are similar to the phenomenon of equalized enhanced phase noise (EEPN) previously observed in telecommunications. In EEPN, the multiplicative phase noise is the noise of the local oscillator laser, and the linear operator is the inverse chromatic dispersion (CD) of the fiber channel. It is known that the longer the duration of the CD, the more severe the effects of EEPN become.

[0064] In equation (9), for the phase distortion in TGD-OFDR, the variable to be detected is g(t'), while the multiplicative phase noise exceeds x(t). Nevertheless, the same reasoning applies that the longer the duration of x(t), the worse the phase distortion becomes. This is true for the longest usable chirp duration T c It appears that limitations are imposed on the vibration-induced phase distortion, favoring the use of shorter chirp durations.

[0065] We use a multiband digitally fragmented signal processing architecture to reduce the effects of spatial leakage in DAS caused by vibration-induced phase modulation on long chirp pulses. By chopping the transmitted chirp pulse into a series of shorter pulses and processing them as separate frequency channels, we reduce spatial leakage at the expense of reduced spatial resolution. However, we also propose that spatial resolution can be recovered by speeding up the chirps and using a wider bandwidth receiver.

[0066] One particularly distinctive aspect of the systems, methods, and structures according to the present disclosure includes an innovative digital signal processing architecture, where instead of processing the transmitted chirp pulses as a single sequence, a parallel, fragmented, multi-band architecture is used, where each tributary correlates the received signal with a truncated chirp pulse to obtain a Rayleigh impulse response across its frequency band. Advantageously, by shortening the duration of the chirps processed by each tributary, spatial leakage is reduced across all tributaries, so that even after combining all interference products from all tributaries using a rotating vector sum, the resulting signal is much less affected by spatial leakage than when using the prior art TGD-OFDR method.

[0067] As an additional advantage, the DSP architecture of the present invention is very flexible because the number of fragmented tributaries used at the receiver does not depend on the chirp pulse generator, i.e., the generator can always transmit the same signal, and it is up to the receiver how to process the Rayleigh backscattered output to trade off between good spatial resolution and low spatial leakage.

[0068] To mitigate the vibration-induced phase distortion of long chirp pulses, our multiband digitally fragmented OFDR (MB-DF-OFDR) decomposes the chirp sequence x(t) into N b Short chirp sequences x b(t) ...

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[0069] Duration T c and bandwidth αT c long chirp sequences of duration αT c / N b and duration T c / N b N b It is divided into short chirp sequences, -T c / 2≦t<+T c About / 2

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[0070] In this regard, each x b (t) is duration T c / N b With delay

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[0071] Therefore, first divide the received signal y(t) by -f b Shift the frequency by x tr After correlating with (t), the delay τ b By restoring the frequency band f b Rayleigh impulse response for each

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[0072] Next,

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[0073] Next, these 4N b interference product terms

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[0074] Preserving spatial resolution

[0075] x(t) to N b The drawback of splitting into short chirp sequences is that each

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[0076] One way to maintain the original spatial resolution is to reduce the chirp rate to N b The aim is to increase the frequency of the interrogation signal by a factor of 1 so that the interrogation signal has a determined instantaneous frequency profile. To keep the envelope of the transmitted signal constant and avoid problems with amplifier gain transients, the remainder of the frame is filled with an out-of-band chirp so that the following signal is transmitted in each frame:

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[0077] In each frame, T c ≦t <T f In the case of N, the instantaneous frequency f(t) is outside the receiver bandwidth, so the out-of-band chirp has no effect on the signal processing of the received signal. b By chirping with an increasing rate of α, the truncated chirped pulse x trThe bandwidth covered by (t) is αT c = 1 / T, and the spatial resolution is therefore

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[0078] One drawback of the MB-DF-OFDR approach is that the coherent receiver optics and ADC are required for all N b The problem is that the bandwidth required to recover N bands is also large. b This increases the complexity of the DSP.

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[0079] As mentioned above, our multi-band DF-OFDR scheme uses the same physical hardware as conventional TGD-OFDR, and is shown in Figure 6. A low linewidth continuous wave (CW) laser is modulated with x(t) using standard methods, such as an arbitrary waveform generator (AWG) driving a Mach-Zehnder I / Q modulator. The modulated signal is amplified to the correct power level and sent to the FUT via a circulator. The Rayleigh backscatter is received at the third port of the circulator, amplified and filtered, and then coherently detected using the same CW laser as the local oscillator (LO), which generated the downstream interrogation signal. We assume a standard coherent receiver front-end consisting of a dual-polarized 90° optical hybrid, followed by a balanced photodetector (BPD), followed by anti-aliasing filtering to remove out-of-band chirp, followed by sampling and digitization by an analog-to-digital converter (ADC). The ADC sampling rate T adc is N b The value must be sufficient to recover all of the frequency bands without aliasing.

[0080] 7 shows a schematic diagram of an exemplary DSP architecture for MB-DF-OFDR according to an embodiment of the present invention. With reference to this figure, the recovered digitized waveform from the coherent receiver

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[0081] In tributary b, the received signal is first

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[0082] Interrogator is T f =N f T s A chirp sequence with a frame rate of

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[0083] 4N bThe time-aligned interference product of

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[0084]

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[0085]

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[0086] Our experiments show that the 5-band MP-DF-OFDR experiment improves over TGD-OFDR.

[0087] To demonstrate the superior performance of the multi-band DF-OFDR (MB-DF-OFDR) method, we b Repeated experiments were performed using a =5 band implementation. Truncated chirped pulse x tr (t) is a time period of T c / N b = 10μs, 1 / N b It is swept over a bandwidth of T = 10 MHz.

[0088] Thus, the total bandwidth of x(t) is 50 MHz compared to 10 MHz for conventional TGD-OFDR. It can be seen that the spatial leakage is significantly reduced as evidenced by the lack of tail after the PZT at 50 km. Defining the signal-to-interference ratio (SINR) as the power difference between the peak at 50 km and the average power after 50 km, the MB-DF-DFDR achieves a SINR of 34 dB compared to 18 dB for conventional TGD-OFDR.

[0089] While the present disclosure has been presented using some specific examples, those skilled in the art will recognize that the present teachings are not so limited. Accordingly, the present disclosure should be limited only by the scope of the claims appended hereto.

Claims

1. 1. A long-haul distributed fiber optic sensing (DFOS) and wavelength division multiplexing (WDM) communication system, comprising: a fiber optic sensor including a plurality of fiber optic cable spans, each of the plurality of fiber optic cable spans including at least one Raman excitation; a DFOS interrogator system in optical communication with the fiber optic sensor, the DFOS interrogator system having a code sequence generator for generating a coded interrogation sequence, the DFOS interrogator system being configured to generate the coded interrogation sequence, inject the generated coded interrogation sequence into the fiber optic sensor, and receive scattered sensing data in response to the injected generated coded interrogation sequence; an intelligent analyzer configured to analyze the scattered sensing data received by the DFOS interrogator system; a WDM transmitter configured to generate and inject an unsensed WDM communication signal into the optical fiber sensor; A system in which the DFOS coded interrogation sequence and the undetected communication signal are simultaneously injected into the fiber optic sensor.

2. The system of claim 1 , wherein one or more of the plurality of fiber optic cable spans exhibit both forward and backward Raman amplification.

3. 3. The system of claim 2, wherein the one or more of the plurality of optical fiber cable spans exhibiting both forward and backward Raman amplification includes at least two Raman pumps, one for the forward Raman amplification and another for the backward Raman amplification.

4. 4. The system of claim 3, further comprising a wavelength selective switch (WSS) in optical communication with said DFOS interrogator system, said WDM transmitter, and said fiber optic sensor, said WSS being interposed between said DFOS interrogator system and said fiber optic sensor, and said WSS being interposed between said WDM transmitter and said fiber optic sensor.

5. The system of claim 4 , further comprising an optical circulator interposed between the WSS and the fiber optic sensor.

6. The system of claim 5 , wherein the forward and backward Raman amplifications are provided without optical separation.

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