Detecting seismic disturbances using optical fiber

Abstract

Embodiments of the present application relate to detecting seismic disturbances using optical fibers. In an example embodiment, a WDM optical transmitter of a network node operates to transmit a CW optical signal and an optical signal carrying original data. At another network node, a low-complexity, low-latency coherent optical receiver is used to obtain time-resolved measurements of the Stokes parameters of the CW optical signal. The signal processing chain of the optical receiver uses digital filtering to select frequency components in the measurement stream corresponding to the seismic disturbance of the optical fiber cable connecting the node. The selected frequency components are then used to calculate the value of the earthquake indicator and report the value to the network controller. Based on such reports from three or more nodes, the network controller can determine the epicenter and magnitude of the earthquake, and can generate a tsunami forecast if necessary.

Description

Technical Field

[0001] Various example embodiments relate to seismic dating and, more particularly, but not exclusively, to detecting seismic disturbances using terrestrial and / or submarine optical fibers. Background Art

[0002] This section introduces aspects that may help to better understand the present disclosure. Therefore, the statements in this section should be read in this light, and should not be understood as an admission about what is and is not the prior art.

[0003] The scarcity of seismic instruments in the ocean limits earthquake detection capabilities. For example, most seismic stations are located on land, with only a few on the ocean floor. As a result, many underwater earthquakes remain undetected, for example, because onshore seismic stations are often too far from the epicenter of the earthquake. Similarly, most tsunami detection equipment is onshore, which may not be optimal in generating adequate tsunami warnings for affected coastal communities. Summary of the invention

[0004] Various embodiments of optical communication systems are disclosed herein that enable any deployed (e.g., long-haul, terrestrial, or submarine) optical fiber cable to act as an earthquake detection sensor. In an example embodiment, a wavelength division multiplexing (WDM) optical transmitter of one network node is configured to transmit an optical detection signal together with an original data-carrying optical signal. At another network node, a low-complexity, low-latency coherent optical receiver is used to obtain time-resolved measurements of the Stokes parameters of the optical detection signal. The signal processing chain of the optical receiver uses digital filtering to select frequency components in the measurement stream corresponding to seismic disturbances of the optical fiber cable connecting the node. The selected frequency components are then used to calculate the value of the earthquake indicator and report the value to the network controller. Based on such reports from three or more nodes, the network controller can determine the epicenter and magnitude of the earthquake and generate a tsunami forecast if necessary.

[0005] Example embodiments may advantageously be implemented at relatively little additional cost, requiring only minor modifications to some of the network's WDM transceivers, without requiring any modifications to existing fiber optic cable plant.

[0006] According to an example embodiment, a device is provided that provides information about an earthquake, the device comprising: an electronic analyzer connected to receive measurements of polarization states of light beam pairs, light beams in each of the light beam pairs traveling in opposite directions between corresponding network node pairs via corresponding optical fiber cables whose ends are connected to corresponding network node pairs, different light beam pairs in the light beam pairs traveling in different ones of the corresponding optical fiber cables; and wherein the electronic analyzer has a circuit system that is configured to characterize one of the earthquakes based on the measurements of polarization states of a plurality of the light beam pairs.

[0007] According to another example embodiment, a machine-implemented method is provided for providing information about an earthquake, the machine-implemented method comprising the following steps: (A) receiving measurements of polarization states of light beam pairs, light beams in each of the light beam pairs traveling in opposite directions between corresponding network node pairs via corresponding optical fiber cables whose ends are connected to corresponding network node pairs, different light beam pairs in the light beam pairs traveling in different ones of the corresponding optical fiber cables; and (B) processing in an electronic circuit system the measurements of polarization states of a plurality of the light beam pairs to characterize one of the earthquakes.

[0008] According to yet another example embodiment, an apparatus is provided, comprising: an optical wavelength demultiplexer having a plurality of passbands for demultiplexing optical signals received through an optical fiber; a first optical receiver connected to the optical wavelength demultiplexer to receive a data modulated optical signal; and a second optical receiver connected to the optical wavelength demultiplexer to obtain time-resolved measurements of Stokes parameters of an optical detection signal, the data modulated optical signal and the optical detection signal both passing through one passband of the optical wavelength demultiplexer; and wherein the second optical receiver comprises a digital bandpass filter to filter the stream of the time-resolved measurements to select frequency components in the stream corresponding to seismic disturbances of the optical fiber. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Other aspects, features, and benefits of the various disclosed embodiments will become more fully apparent, for example, from the following detailed description and accompanying drawings, in which:

[0010] Figure 1 A block diagram showing an optical fiber line of an optical communication system in which some embodiments may be practiced;

[0011] Figure 2 Demonstrate that according to the embodiment, Figure 1 Block diagram of a wavelength division multiplexing (WDM) optical transceiver used in optical communication systems;

[0012] Figure 3 The following diagrams illustrate the Figure 2 Some spectral characteristics of WDM optical transceivers;

[0013] Figure 4 Demonstrate that according to the embodiment, Figure 2 A block diagram of an optical receiver used in a WDM optical transceiver;

[0014] Figure 5 Shows graphical representation of the state of polarization (SOP) using the Poincare sphere;

[0015] Figure 6 Demonstrate that according to the embodiment, Figure 4 A block diagram of a digital signal processor (DSP) used in an optical transceiver;

[0016] Figure 7 A block diagram showing a fiber optic network in which some embodiments may be practiced; and

[0017] Figure 8 Demonstrate that according to the embodiment, Figure 7 Flowchart of an example signal processing method used in an optical fiber network. DETAILED DESCRIPTION

[0018] Some embodiments may benefit from the use of the apparatus, methods, and certain features disclosed in U.S. patent application Ser. No. 16 / 988,874, filed on Aug. 10, 2020, which is incorporated herein by reference in its entirety.

[0019] Although some example embodiments are described below with reference to submarine optical fibers and / or submarine optical fiber cables, persons of ordinary skill in the art will readily understand how to make and use embodiments that employ terrestrial optical fibers and / or terrestrial optical fiber cables based on the description provided.

[0020] Some embodiments may be used to detect earthquakes and / or predict tsunami waves.

[0021] Figure 1 A block diagram showing a portion of an optical communication system 100 in which some embodiments may be practiced. System 100 is a long-distance submarine communication system that includes landing stations 102 connected by means of underwater (wet) cable equipment 104. 1 and 102 2 Landing Station 102 1 and 102 2 Usually further connected to the corresponding terrestrial network ( Figure 1In alternative embodiments, the system 100 may have one or more additional landing stations connected to different underwater cable equipment (i.e., having a form similar to the underwater cable equipment 104), as is known in the related art, such as using one or more branching units and / or completely different submarine optical fiber cables ( Figure 1 (not explicitly shown) for connection.

[0022] In the example embodiment, the underwater cable equipment 104 comprises a submarine cable system including, among other things, submersible optical repeaters 150 connected in series via an optical fiber span 140. 1 -150 L ,For example Figure 1 Indicated in , where L is a positive integer. In the embodiment shown, each span 140 i Contains 140 ia and 140 ib , where i=1, 2, ..., L+1. The number L of optical repeaters 150 used in the underwater cable equipment 104 depends on the specific embodiment and can range from 1 to 200, for example. 1 and 102 2 The distance between the fiber spans is 140 i The typical length of the underwater cable equipment 104 may be in the range of 50 km to 150 km. 1 With 102 2 There may not be any optical repeaters in between.

[0023] In the illustrated embodiment, the optical repeater 150 j Including optical amplifier (OA) 160 ja and 160 jb , where j = 1, 2, ..., L. Optical amplifier 160 ja Configured to zoom in toward landing station 102 2 The optical signal is traveling. Optical amplifier 160 jb Similarly configured to zoom in toward landing station 102 1 In the example embodiment, the optical amplifier 160 j This can be implemented as known in the art, for example, using erbium-doped fiber, gain flattening filters, and one or more laser diode pumping. The laser diodes can be powered by power from a corresponding shore feed equipment (PFE, Figure 1 The DC current is fed through the electrical conductors of the corresponding submarine cable, which usually also contains an optical fiber 140. ia and 140 ibIn some embodiments, the electrical conductor (eg, wire) may be located near the center of the submarine cable. In some other embodiments, the electrical conductor may have a generally tubular shape, for example, having an annular cross-section in a plane orthogonal to the longitudinal axis of the submarine cable.

[0024] In alternative embodiments, the optical repeater 150 may be designed for use with two, three, four, or more pairs of optical fibers 140 connected thereto on each side. i For example, an optical repeater 150 designed to be compatible with a four-fiber pair submarine cable typically includes eight optical amplifiers 160 arranged in four amplifier pairs, each pair being similar to the pair of optical amplifiers 160. ja and 160 jb .

[0025] Optical Repeater 150 j It may also include a supervisory optical circuit ( Figure 1 The supervision optical circuit is located at the landing station 102 respectively. 1 and 102 2 Monitoring equipment (ME) unit 120 at 1 and 120 2 The operating status of the optical repeater can be monitored.Some embodiments of supervising optical circuits are disclosed, for example, in European Patent Application Nos. EP17305569.0 and EP17305570.8, which are incorporated herein by reference in their entirety.

[0026] In an example embodiment, ME unit 120 1 and 120 2 Each of the 1 and λ 2 ) for corresponding supervisory signals, which can be sent toward the remote landing station 102 via the corresponding optical fiber 140. Each optical repeater 150 j The supervisory optical circuit of the ME unit 120 is configured to send back at least a portion of the supervisory optical signal in the reverse direction. 1 The optical signal may be received by the optical repeater 150. 1 -150 N The different supervisory optical circuits return portions of the original supervisory optical signal to the ME unit. Similarly, the ME unit 120 2 The optical signal may be received by the optical repeater 150. 1 -150 N The ME unit 120 returns the corresponding supervision optical signal to the ME unit. 1 and 1202 The received loopback supervisory optical signal may be processed and analyzed to determine whether at least some or all of the optical repeaters 150 in the underwater cable device 104 are connected to the optical repeater 150. 1 -150 N The parameters determined may include, but are not limited to: (i) input and output signal levels and some or all of the individual optical amplifiers (OAs) 160 ja and 160 jb (ii) individual optical fibers 140 i non-catastrophic failures in, for example, any progressive loss therein; and (iii) individual optical repeaters 150 j and / or optical fiber 140 i Catastrophic failure in.

[0027] Landing Station 102 1 Including by means of an optical wavelength multiplexer (MUX) 130 1 and optical wavelength demultiplexer (DMUX) 136 1 A subsea line terminal equipment (SLTE) unit 110 connected to the underwater cable equipment 104 1 and ME unit 120 1 ,like Figure 1 In the example embodiment, SLTE unit 110 1 comprising a carrier wavelength λ configured to use 3 -λ n Wavelength division multiplexing (WDM) transceivers that transmit and receive optical data signals carrying payloads Figure 1 Not explicitly shown in Figure 2 ), where n generally represents the number of WDM channels in the system 100. The number n may range, for example, from ˜10 to ˜150.

[0028] In an example embodiment, the carrier wavelengths λ1-λ may be selected according to a frequency (wavelength) grid, such as a frequency grid in accordance with ITU-T G.694.1 Recommendation, which is incorporated herein by reference in its entirety. n The frequency grid used in system 100 may be defined, for example, in a frequency range of about 184 THz to about 201 THz, with channels spaced 100, 50, 25, or 12.5-GHz. Although typically defined in units of frequency, the parameters of the grid may equally be expressed in units of wavelength. For example, a 100-GHz spacing between the centers of adjacent WDM channels is equivalent to about 0.8-nm spacing in a wavelength range of about 1528 nm to about 1568 nm. In alternative embodiments, other fixed or flexible (elastic) frequency grids may also be used.

[0029] In operation, MUX 130 1 SLTE unit 110 1 The generated wavelength is λ 3 -λ n The optical signal with wavelength λ 1 and λ 2 The one or more supervisory optical signals are multiplexed and the resulting multiplexed optical signal is applied to the optical fiber 140 1a DMUX 136 1 From the optical fiber 140 1b The received multiplexed optical signal is demultiplexed into two parts. The first part has a wavelength of λ 3 -λ n The optical signal is directed to the SLTE unit 110 1 The second portion has one or more wavelengths λ 1 and λ 2 The return supervision optical signal is guided to the ME unit 120 1 .

[0030] In an example embodiment, ME unit 120 1 Including optical time domain reflectometer (OTDR, Figure 1 ), the optical time domain reflectometer is configured to use a wavelength λ 1 and λ 2 The underwater cable device 104 is optically detected. For example, the ME unit 120 1 It can be designed to detect and process the 1 -150 N The received loopback supervision optical signal is used to perform OTDR measurement. 1 Can be configured to use any suitable OTDR method.

[0031] Landing Station 102 2 Generally similar to Landing Station 102 1 , and includes an SLTE unit 110 2 、ME unit 120 2 、MUX 130 2 and DMUX 136 2 Similar elements / components of both landing stations are Figure 1 The same numerical labels are used in the above description, but with different corresponding subscripts. 1 SLTE Unit 110 1 、ME unit 120 1 、MUX 130 1 and DMUX1361 The description of 2 SLTE Unit 110 2 、ME unit 120 2 、MUX 130 2 and DMUX136 2 , which will not be repeated here.

[0032] In various embodiments, each landing station 102 1 and 102 2 It may also include one or more of the following conventional elements / components: (i) power feeding equipment; (ii) system supervision equipment; (iii) network management equipment; (iv) cable terminal box; (v) network protection equipment; and (vi) various interface circuits.

[0033] When an earthquake occurs relatively close to the system 100, mechanical disturbances 190 (e.g., shock waves and seismic waves caused thereby) travel from the epicenter through the Earth's crust and eventually reach the underwater cable equipment 104. Assuming a sufficiently strong earthquake occurs close enough to at least some of the optical fibers 140, the mechanical disturbances 190 may cause the landing station 102 to 1 and 102 2 The optical signal disturbance can be detected, for example as described below. Appropriate signal processing can then be used to accurately estimate the time from the point where the mechanical disturbance 190 first arrives at the corresponding optical fiber 140 to the landing station 102. 1 and 102 2 The distance D 1 and D 2 .

[0034] Figure 2 The SLTE unit 110 according to the embodiment is shown 1 1 is a block diagram of a WDM optical transceiver 200 for use in FIG. The transmit and receive optical channels corresponding to the transceiver 200 are illustratively referred to as "uplink" (or U) channels and "downlink" (or D) channels, respectively. Figure 2 The index of the optical channel is Figure 1 The index used in the SLTE unit 110 is consistent with 1 Use wavelength λ 3 -λ n , and ME unit 120 1 Use wavelength λ 1 -λ 2 By exchanging Figure 2 The U and D symbols in the SLTE unit 110 can be obtained to indicate 2 Block diagram of an embodiment of a WDM optical transceiver for use in.

[0035] The optical transceiver 200 includes a plurality of individual channel optical data transmitters 210 3 -210 n and an optical detection transmitter 220. The optical detection transmitter 220 includes a laser 222. In some embodiments, the laser 222 may be a directly modulated laser. In some other embodiments, the laser 222 may be a continuous wave (CW) laser. The optical transmitter 210 3 -210 n-1 directly connected to the corresponding optical input ports (labeled 3, ..., n-1) of the optical MUX 230. In the illustrated example, the optical transmitter 210 n The optical transmitter 220 and the optical transmitter 220 are connected to a common corresponding optical input port (labeled as n) of the optical MUX 230 via an optical combiner (e.g., a 3-dB optical coupler) 214, but in other embodiments, the optical transmitter 220 can be connected to a separate optical input port (not shown) of the corresponding optical MUX. The optical MUX 230 operates in a conventional manner to correspond to the optical signals 216 applied to its optical input ports 3, ..., n. 3 -216 n The wavelength multiplexing is performed to generate an optical output signal 232 at its optical output port 0. The optical output signal 232 may be directed to the optical MUX 130 1 And further to the uplink (also see Figure 1 In the example embodiment, all optical signals 216 3 -216 n In the spectrum, the optical repeater is 150 1 -150 N within the amplification band.

[0036] Figure 3 The spectral characteristics of the optical MUX 230 and the optical output signal 232 are graphically illustrated according to an embodiment. More specifically, the dashed line 310 3 -310 n The spectral passband of the optical MUX 230 is graphically illustrated. Spectral passband 310 3 Corresponds to the optical path between the optical input port 3 and the optical output port 0 of the optical MUX 230. Spectral passband 310 4 Corresponds to the optical path between the optical input port 4 and the optical output port 0 of the optical MUX 230, and so on. Spectral passband 310 n-1 Corresponds to the optical path between the optical input port n-1 and the optical output port 0 of the optical MUX 230. Spectral passband 310 n Corresponding to the optical path between the optical input port n and the optical output port 0 of the optical MUX 230 .

[0037] like Figure 3 Indicated, light signal 2163 -216 n In the spectrum, they are respectively 310 3 -310 n For example, for the optical signal 216 3 -216 n-1 In each of the above, the center frequency of the signal is spectrally aligned with the spectral passband 310. 3 -310 n-1 The center frequencies of the corresponding ones of are substantially aligned. In the example embodiment, the optical signal 216 3 -216 n-1 The center frequency f 3 ,…,f n-1 Corresponds to Figure 1 The wavelength λ 3 , ..., λ n-1 In some embodiments, the wavelength λ 3 , ..., λ n-1 It can be the carrier wavelength. In some other embodiments, for example, using carrier suppression modulation, the wavelength λ 3 , ..., λ n-1 It can be roughly the central wavelength of the corresponding spectral envelope.

[0038] Optical Signal 216 n It includes two components, respectively labeled 212 and 224 (see also Figure 2 ). The optical signal 212 is transmitted by the optical transmitter 210 n Generates, and is substantially similar to, the optical signal 216 described above 3 -216 n-1 The center frequency of the optical signal 212 is the frequency f n , which is spectrally consistent with the spectral passband 310 n In the example embodiment, optical signal 224 is a continuous wave (CW) signal generated by laser 222 and has a much narrower spectral width than optical signal 212. Figure 3 In the example, the optical signal 224 has a frequency of f s The spectral line at frequency f s close to the roll-off edge of the spectral envelope of the optical signal 212, but still within the spectral passband 310 n In other embodiments, a modulated optical signal may be used to implement optical signal 224 as long as the modulation does not cause one or more modulation sidebands to spectrally overlap with optical signal 212.

[0039] In the illustrated example embodiment, the frequency f s is shown as being in the last optical channel of the corresponding WDM channel multiplex. In various alternative embodiments, the frequency fs can be placed in any other selected optical channel in a similar manner. In some embodiments, the frequency f s can be located at any spectral position within the EDFA gain region, so that the frequency f s is also within the spectral passband of the corresponding MUX / DMUX. For example, if the selected payload channel is not used, the frequency f s It can be placed near the center frequency of the corresponding passband of the corresponding MUX / DMUX.

[0040] Return to reference Figure 2 The optical transceiver 200 further includes a plurality of separate channel optical data receivers 260 3 -260 n and a light detection receiver 270. Light receiver 260 3 -260 n-1 Directly connected to the corresponding optical output port (labeled 3, ..., n-1) of the optical DMUX 280. Optical receiver 260 n 2 and 270 are connected to a common corresponding optical output port (labeled n) of optical DMUX 280 via optical splitter 264, but in other (not shown) embodiments, may be connected to separate optical output ports of corresponding optical DMUXs. Optical DMUX 280 operates in a conventional manner to receive optical signals at its optical input port 0, such as from optical DMUX 136. 1 (See also Figure 1 ) receives the optical input signal 282 and performs wavelength demultiplexing. The demultiplexed optical signal 266 is obtained. 3 -266 n The optical output ports 3, ..., n of the DMUX 280 are respectively directed to the optical receiver 260. 3 -260 n-1 and optical splitter 264. Optical splitter 264 operates to split optical signal 266 n are then applied to the optical receiver 260 n and 270 of the optical signals 262 and 274 .

[0041] In the example embodiment, the optical DMUX 280, the optical input signal 282 and the optical signal 266 3 -266 n Can have similar Figure 3 Spectral characteristics shown. In some embodiments, optical DMUX 280 may be implemented using a nominal replica of optical MUX 230, but configured to send signals in the opposite direction, ie, from port 0 to port 3, ..., n.

[0042] Figure 4 2 shows a block diagram of an optical receiver 270 according to an embodiment. Figure 4As shown in FIG. 2 , the optical receiver 270 includes an optical local oscillator (OLO) source (eg, a laser) 406, a polarization beam splitter (PBS) 410, and a 1 and 410 2 , Optocoupler 420 1 and 420 2 , Photodiode 430 1 -430 4 , Transimpedance Amplifier (TIA) 440 1 and 440 2 、Analog / digital converter (ADC) 450 1 and 450 2 and a digital signal processor (DSP) 460. Each photodiode pair 430 1 / 430 2 and 430 3 / 430 4 The photodiodes in the embodiment are electrically connected in a differential (eg, balanced) configuration, such as Figure 4 As indicated in .

[0043] In operation, PBS 410 1 Received optical signal 274 (see also Figure 2 ) and divide the received light into 274 X and 274 Y Two relatively orthogonal polarization components of PBS 410 2 Receive an OLO signal 408 generated by an OLO source 406 and split the received light into X and 408 Y In an example embodiment, the OLO signal 408 may have a fixed linear polarization and an optical carrier frequency f LO CW optical signal. Frequency f LO and f s ( Figure 3 ) can be expressed as Δf = |f LO -f s In some embodiments, f LO Can be greater than f s In other embodiments, f LO Can be less than f s .

[0044] Optocoupler 420 1 Operation to mix optical signals 274 X and 408 X To generate a mixed optical signal 428 1 and 428 2 , the mixed optical signal is optical signal 274 Xand 408 X The mixed light has different relative phase shifts (e.g., about 180 degrees) between the photodiode pair 430. 1 / 430 2 The optical signal 428 1 and 428 2 Converted into corresponding electrical signal 432 1 . Electrical signal 432 1 Using TIA440 1 amplified and optionally filtered, for example low frequency filtering, and the corresponding amplified electrical signal is processed using ADC 450 1 Converted into digital electrical signal 452 1 .

[0045] Optocoupler 420 2 Similar operation is performed to mix the optical signal 274 Y and 408 Y To generate a mixed optical signal 428 3 and 428 4 . Photodiode pair 430 3 / 430 4 The optical signal 428 3 and 428 4 Converted into corresponding electrical signal 432 2 . Electrical signal 432 2 Using TIA440 2 amplified and optionally filtered, for example low frequency filtering, and the corresponding amplified electrical signal is processed using ADC 450 2 Converted into digital electrical signal 452 2 .

[0046] Digital electrical signal 452 1 and 452 2 Apply to DSP 460, where these signals can be processed, for example, as described below with reference to Figure 6 and equations (3)-(16) to determine the state of polarization (SOP) of the optical signal 274. In response to certain SOP characteristics exhibited by the optical signal 274, the DSP 460 may further operate to generate an indication of the mechanical disturbance 190 (see also Figure 1 ) occurs.

[0047] In an alternative embodiment, optical receiver 270 may be implemented using a coherent optical receiver as disclosed in the aforementioned US Patent Application No. 16 / 988,874.

[0048] In optics, polarized light can be represented by a Jones vector, and a linear optical element acting on polarized light and its mixed light can be represented by a Jones matrix. When light passes through such an optical element, the Jones vector of the output light can be obtained by taking the product of the Jones matrix of the optical element and the Jones vector of the input light, for example, according to equation (1):

[0049]

[0050] in and are the x and y electric field components of the Jones vector of the input light, respectively; and are the x and y electric field components of the Jones vector of the output light, respectively; and J(θ,φ) is the Jones matrix of the optical element given by equation (2):

[0051]

[0052] where 2θ and φ are the elevation and azimuth polarization rotation angles, respectively, whose values ​​can be used to define the SOP. For clarity, the above example of the Jones matrix does not include the effects of light attenuation and / or amplification.

[0053] Figure 5 A graphical representation showing the SOP using the Poincare sphere. Here, the Poincare sphere is a sphere of radius P centered at the origin of a three-dimensional Cartesian coordinate system with mutually orthogonal axes S 1 , S 2 and S 3 represents the corresponding Stokes parameter of the light field. The radius P represents the light power and is expressed by equation (3):

[0054]

[0055] For a given optical power P, different SOPs can be mapped to different corresponding points on the Poincare sphere surface. For example, Figure 5 The vector S shown in represents one of such SOPs. Then, a SOP rotation can be visualized as a corresponding rotation of the vector S.

[0056] In some cases, it may be convenient to use a unit radius Poincare sphere, where P = 1. The unit radius Poincare sphere can be obtained by normalizing the Stokes parameters with respect to the optical power P. For the unit radius Poincare sphere, the angles θ and φ are related to the normalized Stokes parameters S 1 ′、S 2 ′ and S 3 ′ is related as follows:

[0057]

[0058]

[0059]

[0060] As used herein, the term "polarization tracking" refers to a time-resolved measurement of the SOP of an optical signal. In some embodiments, such polarization tracking may include the determination of angles θ and φ as a function of time. In some other embodiments, such polarization tracking may include the normalized Stokes vector S′=(1S 1 'S 2 'S 3 ′) T The Stokes parameter S 1 ′、S 2 ′ and S 3 ', where the superscript T indicates transposition. In some other embodiments, such polarization tracking may include a non-normalized Stokes vector S = (S 0 S 1 S 2 S 3 ) T Determination of Stokes parameters S0=P, S1, S2 and S3.

[0061] In an example embodiment, DSP 460 ( Figure 4 ) can be based on the system 100 (see also Figure 2-3 ) medium frequency f s The probe light corresponds to the following simplified model of the optical channel to be programmed.

[0062] For simplicity, it is assumed that the SLTE unit 110 2 ( Figure 1 ) The downlink optical signal 224 generated by the SLTE unit 110 has a fixed linear polarization, which can be labeled as X polarization. 2 The Jones vector of the downlink optical signal 224 at can be expressed as in Given by equation (5):

[0063]

[0064] where A is a constant amplitude; and is the phase of signal 224. After propagating through underwater cable equipment 104, downlink optical signal 224 is transmitted by SLTE unit 110 1 The optical receiver 270 receives the downlink optical signal 274 (see also Figure 2 ). Using equations (1)-(2), the Jones vector of this downlink optical signal 274 is It can be expressed as follows:

[0065]

[0066]

[0067] Jones vector of the OLO signal 408 It can be expressed as follows:

[0068]

[0069] Where B is the constant amplitude; δ is the phase of signal 408; Δf is the frequency f as indicated above LO With f s The frequency difference between them; and t is the time.

[0070] Using equations (6)-(7), the mixed optical signal 428 1 -428 4 The electric field E 1 -E 4 They can be expressed as follows:

[0071]

[0072]

[0073]

[0074]

[0075] Then, the electrical signal 432 1 and 432 2 It can be expressed as follows:

[0076] H x =|E 1 | 2 -|E 2 | 2 (9a)

[0077] H y =|E 3 | 2 -|E 4 | 2 (9b)

[0078] Among them, H x Indicates electrical signal 432 1 ;H y Indicates electrical signal 432 2 ; and E 1 -E 4The expressions for are given by equations (8a)-(8d), respectively. For simplicity, the photoelectric conversion coefficient is omitted (i.e., set to one). The expansion of equations (9a) and (9b) using equations (8a)-(8d) reveals: H x and H y Each of H has two spectral components located at frequencies +Δf and -Δf, respectively. x and H y The negative frequency components of Figure 6 610) is rejected, the SSB filter will only make the signal H x and H y The positive frequency component I x and I y Here, SSB means "single sideband". It can be verified using equations (8)-(9) x and I y It can be expressed as follows:

[0079]

[0080]

[0081] Using equations (4a)-(4c) and (10a)-(10b), it can be further verified that the non-normalized Stokes vector S of the optical signal 274 is equal to (S 0 S 1 S 2 S 3 ) T It can be calculated as follows:

[0082] S 0 =|I x | 2 +|I y | 2 (11a)

[0083] S 1 =|I x | 2 -I y | 2 (11b)

[0084] S 2 =2Re(I x ·(I y ) * ) (11c)

[0085] S 3 =-2Im(I x ·(I y ) * ) (11d)

[0086] The "*" symbol in the superscript represents the complex conjugate. Then, the normalized Stokes vector S' = (1S 1 'S 2 'S 3 ′) T The resulting unnormalized Stokes vector S can be obtained by dividing the components of the unnormalized Stokes vector S by the value S calculated using equation (11a) 0 to calculate.

[0087] In an example embodiment, ADC 450 1 and 450 2 can be clocked to sample at a relatively high rate (e.g., 10 9 Therefore, the Stokes parameters can be updated by the DSP 460 at a relatively fast rate to achieve polarization tracking with a relatively high time resolution, thereby providing a sufficient amount of SOP tracking data to accurately extract SOP dynamics and / or dynamics-related characteristics therefrom.

[0088] Mechanical disturbance 190 typically causes the SOP to be modulated with a characteristic frequency in a range between about 0.1 Hz and about 2 Hz. The amplitude of the corresponding frequency component may be related to the amplitude of the mechanical disturbance 190. For example, in one possible approximation, it may be assumed that within a fixed distance from the epicenter, the amplitude of such frequency component is linearly dependent on the magnitude of the corresponding earthquake. For example, as known in the related art, the attenuation of the mechanical disturbance 190 may also be incorporated into the signal processing as the distance to the epicenter increases.

[0089] Figure 6 A block diagram of a DSP 460 is shown according to an embodiment. Figure 6 The digital signal 452 is also shown 1 and 452 2 and control signal 462 to better illustrate Figure 4 and 6 The relationship between the circuits.

[0090] like Figure 6 4, DSP 460 includes a 452 connected to receive digital signals respectively. 1 and 452 2 SSB filter 610 1 and 610 2 In the example embodiment, SSB filter 610 1 and 610 2 Each of the operations is to receive the real-valued digital signal 452 i Converted into the corresponding complex-valued digital signal 612 i, where i = 1, 2. For a real-valued time-dependent signal a(t), the transfer function L(·) of the SSB filter can be transformed with the Hilbert transform Related, as follows:

[0091]

[0092] SSB Filter 610 i The spectral transfer function of is approximately a Heaviside step function with its 0-1 transition at zero frequency.

[0093] DSP 460 also includes a squaring circuit 620 1 and 620 2 , a conjugation circuit 624 , a SOP circuit 630 , a bandpass filter 640 , and a signal analyzer 650 .

[0094] Square Circuit 620 i Operation to calculate the digital signal 612 i The square of the absolute value of each complex value provided thereby generates a corresponding real-valued digital signal 622 i .

[0095] The conjugation circuit 624 responds to the digital signal 612 2 Each complex-valued output conjugate value is provided, thereby generating a corresponding complex-valued digital signal 626 .

[0096] The SOP circuit 630 uses the received digital signal 612 1 ,622 1 ,622 2 and 624 to compute three digital value streams, the streams being Figure 6 Marked as S 1 ′、S 2 ′ and S 3 Each of these digital values ​​is related to the normalized Stokes vector S′=(1S 1 'S 2 'S 3 ′) T The Stokes parameter S 1 ′、S 2 ′ and S 3 ' is proportional to the corresponding one of '. In one example embodiment, this calculation can be performed in the SOP circuit 630 according to equations (4) and (11). In another example embodiment, this calculation can be performed in the SOP circuit 630 according to equations (11b)-(11d). The latter embodiment can be used, for example, when the laser 222 is a relatively stable CW laser that generates an optical signal 224 with a substantially constant output power.

[0097] The bandpass filter 640 operates to filter the digital signal S 1 ′、S 2 ′ and S 3 ' Digital filtering is performed to filter only the frequency components of those signals that are spectrally within the filter passband 642 1 -642 3 In an example embodiment, the passband of filter 640 may be between about 0.1 Hz and about 2 Hz. In some embodiments, bandpass filter 640 may be tunable, for example, being able to controllably vary one or both of the upper and lower boundaries of its passband.

[0098] Signal analyzer 650 operates to process digital signal 642 1 -642 3 To generate control signal 462. In an example embodiment, the signal processing implemented in signal analyzer 650 may include the following steps: (i) in response to digital signal 642 1 -642 3 (ii) comparing the seismic indicator to a threshold value; (iii) recording and time-stamping the moment when the seismic indicator P(t) exceeds the threshold value; (iv) determining the maximum value of the seismic indicator P(t) within a certain time interval; and (iv) providing a control signal 462 to an appropriate control entity (e.g., Figure 7 710) Report observations and measurements.

[0099] In an example embodiment, the signal analyzer 650 may be programmed to calculate the seismic index P(t) as follows:

[0100] P(t)=|F 1 (t)|+|F 2 (t)|+|F 3 (t)| (13)

[0101] where F 1 (t) represents the bandpass filtered digital signal S 1 ′; F 2 (t) represents the bandpass filtered digital signal S 2 ′; F 3 (t) represents the bandpass filtered digital signal S 3 '; and t is time. The maximum value of the earthquake indicator P(t) can be used, for example, to estimate the magnitude of the corresponding earthquake, for example, as described below with reference to Figure 7-8 described.

[0102] Assume that in the uplink optical receiver 270 (located Figure 1 Landing Station 102 2 ) at timestamp t U At (i.e., t = tU The earthquake index P calculated at U (t) reaches or exceeds the threshold P 0,U (i.e., P U (t)≥P 0,U ). Then, the time t0 when the mechanical disturbance 190 impacts the corresponding optical fiber span 140 can be estimated as follows:

[0103]

[0104] where n f is the effective refractive index of the optical fiber; D 2 It is landing station 102 2 The length of the optical fiber between the position where the mechanical disturbance 190 first impacts the optical fiber (see also Figure 1 ); and c is the speed of light. Similarly, at the downlink optical receiver 270 (located at Figure 1 Landing Station 102 1 ), time t 0 It can be estimated as follows:

[0105]

[0106] where t D is the seismic index P calculated at the downlink optical receiver 270 D (t) reaches or exceeds the threshold P 0,D (i.e., P D (t)≥P 0,D ); and D 1 It is landing station 102 1 The length of the optical fiber between the position where the mechanical disturbance 190 first impacts the optical fiber (see also Figure 1 ). Combining equations (14) and (15), we obtain the following equation:

[0107]

[0108] Where Z is a landing station 102 at a different or opposite end of the same optical fiber link 1 With 102 2 Since all quantities on the right side of equation (16) are observable or known, equation (16) can be used to determine t 0 Then, equations (14) and (15) can be used to determine the length D 1 and D 2 .

[0109] Figure 7A block diagram of a portion 700 of a fiber optic network in which some embodiments may be practiced is shown. The network 700 includes landing stations LS1, LS2, and LS3. Landing stations LS1 and LS2 are connected to each other via fiber optic links 740. A Landing stations LS2 and LS3 are connected via optical fiber link 740 B The network 700 also includes two control links 720 and 730, respectively. 1 ,720 2 and 720 3 Electronic (eg, digital) analyzers 710 connected to landing stations LS1, LS2, and LS3. In the event of an earthquake, network 700 may be used, for example, using method 800 ( Figure 8 ) determines the geographic location E of the epicenter of the earthquake and estimates the magnitude of the earthquake. For example, as illustrated, the resulting pressure wave or displacement wave may radiate from the epicenter in a spherical shape, but the land surface features may cause the radiated wave to have a wavefront of a different shape, which may be explained in method 800 ( Figure 8 In an example embodiment, each of the landing stations LS1, LS2, and LS3 may be similar to the above-described landing station 102. i ( Figure 1 ). In some embodiments, the electronic analyzer 710 may be located at a corresponding control entity (e.g., network controller) 708. In alternative embodiments, other locations of the electronic analyzer 710 are possible, including a distributed configuration in which different portions of the electronic analyzer are placed at two or more different, relatively remote locations.

[0110] In an example embodiment, the electronic analyzer 710 has appropriate circuitry, such as a digital processor 712, configured to process the received SOP measurements to characterize an earthquake.

[0111] In some embodiments, the corresponding fiber optic network may include additional landing stations LS and / or additional fiber optic links 740 ( Figure 7 For example, two or more fiber optic links used to sense earthquakes may not be as Figure 8 The landing stations are shared as in the example above so that the measurements from four or more landing stations can be used to characterize an earthquake using method 800 ( Figure 8 ). Depending on the relative location of the earthquake epicenter E and the network topology, a suitable subset of landing stations LS and fiber links 740 may be selected to perform method 800 or other suitable methods. For example, when the selected subset of fiber links 740 has three or more links, a triangulation method may be used.

[0112] Figure 8 A flow chart showing an example signal processing method 800 that can be used in the network 700 according to an embodiment. Figure 7Method 800 is described. The execution of method 800 may be performed, for example, by a mechanical disturbance 190 emitted by the epicenter E of a sufficiently strong earthquake (see also Figure 1 and 7 )trigger.

[0113] At step 802 of method 800, optical receivers 270 located at landing stations LS1, LS2, and LS3 respond to mechanical disturbance 190 to reach optical fiber link 740. A and 740 B Events are detected in which the corresponding seismic indicator P(t) (see, for example, equation (13)) exceeds the relevant threshold.

[0114] In step 804, landing stations LS1, LS2 and LS3 use control link 720 respectively. 1 ,720 2 and 720 3 The relevant measurements of the event are provided to the electronic analyzer 710. In an example embodiment, the landing stations LS1, LS2 and LS3 may collectively provide the following measured parameters to the electronic analyzer 710: (i) the optical fiber link 740 A The corresponding timestamp t U and t D (ii) for optical fiber link 740 A The maximum value P of the earthquake index P(t) observed in the uplink direction UA (iii) for optical fiber link 740 A The maximum value P of the earthquake indicator P(t) observed in the downlink direction DA (iv) with optical fiber link 740 B The corresponding timestamp t U and t D ; (v) for optical fiber link 740 B The maximum value P of the earthquake index P(t) observed in the uplink direction UB ; and (vi) for optical fiber link 740 B The maximum value P of the earthquake indicator P(t) observed in the downlink direction DB .

[0115] At step 806, electronic analyzer 710 uses the timestamps provided to the electronic analyzer at step 804 to determine the timestamps along optical fiber link 740. A and 740 B The positions of points A and B (see also Figure 7 ). More specifically, point A is along the optical fiber link 740 A The location that is first impacted by the mechanical disturbance 190. Similarly, point B is along the optical fiber link 740 BThe location that is first impacted by the mechanical disturbance 190 can be used, for example, using equations (14)-(16) and the corresponding optical fiber link 740 A The received timestamp t U and t D The position of point A can be determined by using equations (14)-(16) and the corresponding optical fiber link 740. B The received timestamp t U and t D To determine the location of point B.

[0116] At step 808, electronic analyzer 710 uses the geographic locations of points A and B inferred from the processing performed at step 806 and the map of network 700 to determine the geographic location of epicenter E. In the example shown, the geographic location of epicenter E is determined as line 702. A and 702 B The intersection of line 702 A At point A, it is locally orthogonal to the optical fiber link 740. A , and line 702 B At point B, it is locally orthogonal to the optical fiber link 740. B .

[0117] In an alternative embodiment of step 808 , electronic analyzer 710 may use the geographic locations of points A, B, and one or more similar points corresponding to additional fiber optic links 740 to determine the geographic location of epicenter E by triangulation.

[0118] At step 810, the electronic analyzer 710 uses the maximum value P of the seismic indicator P(t) DA , P UA , P DB and P UB To estimate the Richter scale magnitude of the earthquake. In an example embodiment, step 810 may include the following sub-steps: (i) scaling the maximum value P by a corresponding scaling factor DA , P UA , P DB and P UB , wherein the scaling factor represents the estimated attenuation of the seismic wave along the respective propagation paths from the epicenter E determined in step 808 to the occurrence points A and B determined in step 806; (ii) averaging the scaled maximum values ​​calculated in sub-step (i); and (iii) converting the average value calculated at sub-step (ii) into a corresponding Richter scale magnitude. In an example embodiment, sub-step (iii) may be performed, for example, using a lookup table compiled based on previous earthquake observations, for which the Richter scale magnitude is also measured by conventional seismological methods.

[0119] At step 812, the expected tsunami magnitude for affected coastal communities is forecast in a conventional manner using the geographic location of epicenter E determined at step 808 and the Richter scale magnitude determined at step 810. If a significant tsunami wave is forecast, an appropriate tsunami warning may be issued, for example, by network controller 708.

[0120] According to the above, for example in the Summary section and / or reference Figures 1 to 8 According to an example embodiment disclosed in any one or any combination of some or all of the embodiments, there is provided a device for providing information about an earthquake, the device comprising: an electronic analyzer (e.g., Figure 7 710), which is connected (e.g., via Figure 7 720) to receive a measurement of the polarization state of a pair of beams, each of which is connected to a corresponding network node (e.g., Figure 7 LS1, LS2) pair of corresponding optical fiber cables (for example, Figure 7 740) travel in opposite directions between the respective pairs of network nodes, different ones of the pairs of light beams travel in different ones of the respective fiber optic cables; and wherein the electronic analyzer has a circuit system (e.g., Figure 7 712), wherein the circuit system is configured to characterize one of the earthquakes based on measurements of polarization states of a plurality of the light beam pairs.

[0121] In some embodiments of the above apparatus, the electronic analyzer is configured to detect the presence of a signal between two network nodes (e.g., Figure 7 The measured value of the polarization state of the light beam received at LS1, LS2) is used to estimate the polarization state of a fiber optic cable (for example, Figure 7 of 740 A ) is the first time that seismic waves from an earthquake are received (e.g. Figure 7 190) of the area (for example, Figure 7 A).

[0122] In some embodiments of any of the above apparatus, first reception is identified by a measure of a polarization state (eg, P(t) of equation (13)) having a frequency component above a threshold spectrally below about 1 Hz.

[0123] In some embodiments of any of the above apparatus, the electronic analyzer is configured to estimate the time when the seismic wave of the earthquake was first received at one of the optical fiber cables (e.g., t 0 ).

[0124] In some embodiments of any of the above apparatus, the electronic analyzer is configured to generate a plurality of optical fiber cables (e.g., Figure 7 of 740 A ,740 B ) to estimate the region where the seismic waves of an earthquake are first received at two or more optical fiber cables (e.g., Figure 7 A, B) to identify the epicenter of the earthquake (for example, Figure 7 E).

[0125] In some embodiments of any of the above-described devices, the electronic analyzer is configured to estimate the time when seismic waves of an earthquake are first received at one of the fiber optic cables based on measurements of the polarization state of light beams received at two network nodes connected by the ends of one of the fiber optic cables.

[0126] In some embodiments of any of the apparatus described above, each of the measurements of a particular one of the received light beams measures a difference between the particular one of the light beams and an optical local oscillator (e.g., Figure 4 408) of light mixing.

[0127] In some embodiments of the above apparatus, the apparatus further comprises one or more filters (e.g., Figure 6 640) to remove spectrally frequency components above about 1 Hz from the measurements.

[0128] In some embodiments of any of the apparatus above, each particular pair of network nodes is configured to optically communicate data therebetween via an optical wavelength channel that is different from a wavelength channel carrying an optical beam between the particular pair of optical nodes.

[0129] In some embodiments of any of the above apparatus, the light beam is not modulated to carry the data stream.

[0130] According to the above, for example in the Summary section and / or reference Figures 1 to 8 Another example embodiment disclosed in accordance with any one or any combination of some or all of the foregoing, provides a machine-implemented method for providing information about an earthquake, the machine-implemented method comprising: (A) receiving (e.g., Figure 8 804) of the measured value of the polarization state of the beam pair, each beam in the beam pair being connected via the end to the corresponding network node pair (e.g., Figure 7 LS1, LS2) of the corresponding optical fiber cable (for example, Figure 7 740) travel in opposite directions between the corresponding network node pairs, different pairs of the light beams in the light beam pairs travel in different ones of the corresponding optical fiber cables; and (B) in the electronic circuit system (e.g., Figure 7712) in processing (for example, in Figure 8 806-812) of the polarization states of multiple pairs of the light beams to characterize an earthquake in the earthquake.

[0131] According to the above, for example in the Summary section and / or reference Figures 1 to 8 According to another example embodiment disclosed in any one or any combination of some or all of the above, there is provided an apparatus comprising: an optical wavelength demultiplexer (e.g., Figure 2 280), which has a function to demultiplex the signals transmitted through the optical fiber (e.g., Figure 1 140 Figure 7 of 740 A ) multiple passbands of the received optical signal (e.g., Figure 3 310); a first optical receiver (eg, Figure 2 of 260 n ), which is connected to the optical wavelength demultiplexer to receive the data modulated optical signal (e.g., Figure 2 262); and a second optical receiver (eg, Figure 2 270), which is connected to the optical wavelength demultiplexer to obtain an optical detection signal (e.g., Figure 2 274), the data modulated optical signal and the optical detection signal both pass through a passband of the optical wavelength demultiplexer; and wherein the second optical receiver includes a digital bandpass filter (e.g., Figure 6 640) to filter the stream of time-resolved measurements to select frequency components in the stream that correspond to seismic disturbances in the optical fiber.

[0132] In some embodiments of the above device, the device further comprises a plurality of third optical receivers (eg, Figure 2 of 260 3 -260 n-1 ), the plurality of third optical receivers are connected to receive corresponding data modulated optical signals (eg, Figure 2 of 266 3 -266 n-1 ).

[0133] In some embodiments of any of the apparatus described above, each of the first optical receiver and the third optical receiver is configured to recover data encoded in a corresponding one of the data modulated optical signals.

[0134] In some embodiments of any of the above apparatus, the carrier frequency of the optical detection signal (e.g., Figure 3 f s ) is different from the center frequency of the data modulated optical signal (e.g., Figure 3 f n ).

[0135] In some embodiments of any of the above apparatus, the carrier frequency of the optical detection signal (e.g., Figure 3 f s ) is spectrally located at the edge of the spectrum of the data modulated optical signal (e.g., Figure 3 (shown in the).

[0136] In some embodiments of any of the above apparatus, the carrier frequency of the optical detection signal (e.g., Figure 3 f s ) is spectrally located within the spectral envelope of the data modulated optical signal (e.g., Figure 3 212) (for example, Figure 3 (shown in the).

[0137] In some embodiments of any of the above apparatus, the second optical receiver includes an optical local oscillator (eg, Figure 4 406).

[0138] In some embodiments of any of the above devices, the second optical receiver is configured to: calculate a seismic indicator (e.g., P(t) of equation (13)) based on selected frequency components of the stream; and record and timestamp the value of the seismic indicator if it exceeds a fixed threshold.

[0139] In some embodiments of any of the above devices, the device further comprises an electronic analyzer (e.g., Figure 7 710), the electronic analyzer is connected (e.g., via Figure 7 of 720 1 ) to receive a time-stamped value of a seismic indicator from a second optical receiver, and further connected to receive (e.g., via Figure 7 of 720 2 ) from network nodes (e.g. Figure 7 LS2) of another time-stamped value of a seismic indicator; and wherein the optical wavelength demultiplexer and the network node are connected to the opposite end of the optical fiber via the end (e.g., Figure 7 of 740 A ).

[0140] In some embodiments of any of the above apparatus, the electronic analyzer is configured to determine (e.g., Figure 8 808) The geographical location of the earthquake epicenter (e.g. Figure 7 E).

[0141] In some embodiments of any of the above apparatus, the electronic analyzer is configured to estimate (e.g., Figure 8 810) earthquake on the Richter scale.

[0142] In some embodiments of any of the above apparatus, the electronic analyzer is configured to generate (e.g., based on the received time-stamped value of the seismic indicator) Figure 8 812) Tsunami wave forecast.

[0143] In some embodiments of any of the above apparatus, the optical detection signal is a continuous wave optical signal.

[0144] In some embodiments of any of the apparatus above, the passband of the digital bandpass filter is between 0.1 Hz and 1 Hz.

[0145] In some embodiments of any of the above apparatus, the digital bandpass filter is tunable.

[0146] Although the present disclosure includes references to illustrative embodiments, this description is not intended to be understood in a limiting sense. It is apparent to those skilled in the art that various modifications of the described embodiments to which the present disclosure relates and other embodiments within the scope of the present disclosure are considered to be within the principles and scope of the present disclosure, such as expressed in the appended claims.

[0147] Unless expressly stated otherwise, each numerical value and range should be interpreted as approximations as if the word "about" or "approximately" preceded the stated value or range.

[0148] It will be further understood that various changes may be made by those skilled in the art to the details, materials and arrangements of the parts which have been sequentially described and illustrated to explain the nature of the disclosure without departing from the scope of the disclosure, such as expressed in the appended claims.

[0149] The use of figure numbers and / or figure reference signs in the claims is intended to identify one or more possible embodiments of the claimed subject matter in order to facilitate the interpretation of the claims. Such use should not be construed as necessarily limiting the scope of those claims to the embodiments shown in the corresponding figures.

[0150] Although elements in the accompanying method claims (if any) are recited in a specific order by corresponding labels, those elements are not necessarily intended to be limited to being implemented in that specific order unless the claim recitation otherwise implies a specific order for implementing some or all of those elements.

[0151] References herein to "one embodiment" or "an embodiment" mean that a particular feature, structure, or characteristic described in connection with the embodiment may be included in at least one embodiment of the present disclosure. The phrase "in one embodiment" appearing in various places in this specification does not necessarily all refer to the same embodiment, nor are separate embodiments or alternative embodiments necessarily mutually exclusive of other embodiments. The same applies to the term "implementation".

[0152] Unless otherwise specified herein, the use of the ordinal adjectives "first," "second," "third," etc. to refer to objects among a plurality of identical objects merely indicates that different instances of such identical objects are mentioned, and is not intended to imply that the identical objects so mentioned must be in a corresponding order or sequence in time, space, sequencing, or in any other manner.

[0153] Unless otherwise specified herein, in addition to its ordinary meaning, the conjunction "if" may also or alternatively be understood to mean "when" or "upon..." or "in response to determining" or "in response to detecting", and its interpretation may depend on the corresponding specific context. For example, the phrase "if it is determined" or "if [the condition] is detected" may be understood to mean "upon determining..." or "in response to determining" or "upon detecting [the condition or event]" or "in response to detecting [the condition or event]".

[0154] Also for the purposes of this description, the terms "couple", "coupling", "coupled", "connect", "connecting", "connected" refer to any means known in the art or later developed that allow energy to be transferred between two or more elements, and encompasses the insertion of one or more additional elements, but is not required. Conversely, the terms "directly coupled", "directly connected", etc. imply the absence of such additional elements.

[0155] As used herein with reference to components and standards, the term compliant means that the component communicates with other components in a manner specified in whole or in part by the standard and will be considered by other components as sufficiently capable of communicating with other components in a manner specified by the standard. Compliant components are not required to operate internally in a manner specified by the standard.

[0156] The described embodiments should be considered in all respects as illustrative only and not restrictive. Specifically, the scope of the present disclosure is indicated by the appended claims rather than the description and drawings herein. All changes that exist within the equivalent meaning and scope of the claims will be included within the scope of the claims.

[0157] This specification and the accompanying drawings illustrate only the principles of the present disclosure. It should therefore be understood that a person of ordinary skill in the art will be able to design various arrangements that embody the principles of the present disclosure and are included in the spirit and scope of the present disclosure but are not explicitly described or shown herein. In addition, all examples described herein are primarily and explicitly intended for teaching purposes to assist the reader in understanding the principles and concepts of the present disclosure provided by the inventors, thereby deepening the field, and all examples should be understood as not being limited to such specifically described examples and conditions. In addition, all statements describing the principles, aspects, and embodiments of the present disclosure herein and their specific examples are intended to cover their equivalents.

[0158] The functions of the various elements including any functional blocks marked as "processors" and / or "controllers" shown in the figure can be provided by using dedicated hardware and hardware capable of executing software associated with appropriate software. When provided by a processor, the functions can be provided by a single dedicated processor, by a single shared processor, or by multiple individual processors, some of which can be shared. In addition, the explicit use of the term "processor" or "controller" should not be interpreted as referring only to hardware capable of executing software, but may implicitly include but is not limited to digital signal processor (DSP) hardware, network processors, application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), read-only memories (ROMs), random access memories (RAMs) and non-volatile storage devices for storing software. Other conventional and / or customized hardware may also be included. Similarly, any switches shown in the figure are only conceptual. The functions of the switches can be implemented by the operation of program logic, by dedicated logic, by the interaction of program control and dedicated logic, or even manually, and specific techniques can be selected by the implementer, as more specifically understood according to the context.

[0159] As used in this application, the term "circuitry" may refer to one or more or all of the following: (a) a hardware-only circuit implementation (e.g., an implementation in analog and / or digital circuits only); (b) a combination of hardware circuits and software, such as (where appropriate): (i) a combination of analog and / or digital hardware circuits and software / firmware and (ii) any portion of a hardware processor and software (including a digital signal processor, software, and memory that work together to enable a device such as a mobile phone or server to perform various functions); and (c) a hardware circuit and or processor, such as a microprocessor or a portion of a microprocessor, which requires software (e.g., firmware) for operation, but the software may not be present when it is not required for operation. This definition of circuitry applies to all uses of this term in this application (including in any claims). As another example, as used in this application, the term circuitry also covers implementations of only a hardware circuit or processor (or multiple processors) or a portion of a hardware circuit or processor and its accompanying software and / or firmware. The term circuitry also covers, for example and where applicable to a particular claim element, a baseband integrated circuit or processor integrated circuit for a mobile device, or a similar integrated circuit in a server, cellular network device, or other computing or networking device.

[0160] It should be appreciated by those of ordinary skill in the art that any block diagrams herein represent conceptual views of illustrative circuit systems embodying the principles of the present disclosure. Similarly, it should be appreciated that any flow charts, flow diagrams, state transition diagrams, pseudo-codes, etc. represent various processes that can be substantially represented in a computer-readable medium and thus executed by a computer or processor, whether or not such computer or processor is explicitly shown.

[0161] The Summary of the Invention in this specification is intended to introduce some example embodiments, and additional embodiments are described in the Detailed Description and / or with reference to one or more figures. The Summary of the Invention is not intended to identify essential elements or features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter.

Claims

1. A device for providing information about an earthquake, the device comprising: Multiple network nodes connected by fiber optic cables; an electronic analyzer connected to receive measurements of polarization states of pairs of light beams, the light beams in each of the pairs of light beams traveling in opposite directions between the respective pairs of network nodes via respective ones of the fiber optic cables terminated between the respective pairs of network nodes, different ones of the light beam pairs of light beams traveling in different ones of the respective fiber optic cables; and wherein the electronic analyzer has circuitry configured to characterize one of the earthquakes based on the measurements of the polarization states of a plurality of the light beam pairs; and Wherein each of the plurality of network nodes is configured to transmit one of the light beams by wavelength division multiplexing a data-carrying optical signal with the one of the light beams, so that a carrier frequency of the one of the light beams is located at a spectrum edge of one of the data-carrying optical signals.

2. An apparatus according to claim 1, wherein the electronic analyzer is configured to estimate the region where the seismic waves of an earthquake are first received at one of the optical fiber cables based on the measured values ​​of the polarization state of the light beam received at two network nodes connected by the ends of one of the optical fiber cables.

3. An apparatus according to claim 2, wherein the electronic analyzer is configured to estimate the time when the seismic waves of the earthquake are first received at one of the optical fiber cables based on the measured values ​​of the polarization state of the light beam received at the two network nodes.

4. An apparatus according to claim 2, wherein the electronic analyzer is configured to identify the epicenter of the earthquake by estimating the region where the seismic waves of the earthquake were first received at two or more of the optical fiber cables based on the measured value of the polarization state of the light beam traveling through the two or more of the optical fiber cables.

5. An apparatus according to claim 1, wherein the electronic analyzer is configured to estimate the time when the seismic waves of an earthquake are first received at one of the fiber optic cables based on the measured values ​​of the polarization state of the light beam received at two network nodes connected by the ends of one of the fiber optic cables.

6. The apparatus of claim 1, wherein each measurement of a particular one of the received light beams measures mixing of the particular one of the light beams with light of an optical local oscillator.

7. The apparatus of claim 1, further comprising one or more filters to remove frequency components spectrally above 1 Hertz from the measurements.

8. The apparatus of claim 1, wherein each particular pair of the network nodes is configured to optically transmit data therebetween via an optical wavelength channel, wherein the optical wavelength channel is different from a wavelength channel that carries the optical beam between the particular pair of optical nodes.

9. The apparatus of claim 1, wherein the light beam is not modulated to carry a data stream.

10. A machine-implemented method of providing information about an earthquake, the machine-implemented method comprising: receiving the pair of light beams at each network node pair of a plurality of network node pairs; receiving a measurement of a polarization state of a pair of light beams, the light beams in each of the pairs of light beams traveling in opposite directions between a respective one of the plurality of network node pairs via a respective fiber optic cable terminated between the respective one of the plurality of network node pairs, different ones of the light beam pairs traveling in different ones of the respective fiber optic cables; as well as processing said measurements of said polarization states of a plurality of said light beam pairs in an electronic circuit system to characterize one of said earthquakes, and Wherein each of the plurality of network nodes is configured to transmit one of the light beams by wavelength division multiplexing a data-carrying optical signal with the one of the light beams, so that a carrier frequency of the one of the light beams is located at a spectrum edge of one of the data-carrying optical signals.

11. A device comprising: an optical wavelength demultiplexer having a plurality of passbands for demultiplexing optical signals received through the optical fiber; a first optical receiver connected to the optical wavelength demultiplexer to receive a data modulated optical signal; as well as a second optical receiver connected to the optical wavelength demultiplexer to obtain time-resolved measurements of Stokes parameters of an optical detection signal, the data modulated optical signal and the optical detection signal both passing through one of the passbands of the optical wavelength demultiplexer, wherein a carrier frequency of the optical detection signal is at an edge of a spectrum of the data modulated optical signal; and Wherein the second optical receiver comprises a digital bandpass filter to filter the stream of time resolved measurements so as to select frequency components in the stream corresponding to seismic disturbances in the optical fiber.

12. The apparatus of claim 11, further comprising a plurality of third optical receivers connected to receive respective data modulated optical signals that pass through different respective ones of the passbands of the optical wavelength demultiplexer.

13. The apparatus of claim 11, wherein the second optical receiver is configured to: calculating seismic indicators based on selected frequency components in the flow; and If the value of the seismic indicator exceeds a fixed threshold, the value is recorded and time-stamped.

14. The apparatus of claim 13, further comprising an electronic analyzer connected to receive a time-stamped value of the seismic indicator from the second optical receiver and further connected to receive another time-stamped value of the seismic indicator from a network node; wherein the optical wavelength demultiplexer and the network node end are connected to opposite ends of the optical fiber; and wherein the electronic analyzer is configured to generate at least one estimate of: an estimate of a geographical location of an earthquake epicenter based on said received time-stamped value of said earthquake indicator; an estimate of the Richter scale magnitude of the earthquake based on the received time-stamped value of the earthquake indicator; and A forecast of tsunami waves based on the received time-stamped value of the earthquake indicator.

Images