Patent Description:
During operation of an aircraft, numerous on-board components and sub-systems are continuously or periodically monitored. Various methods for monitoring these components and sub-systems of the aircraft have been used. For example, sensors and/or transducers can be affixed to an aircraft at specific locations so as to produce signals indicative of various physical phenomena experienced at those specific locations. These signals can then be transmitted to an analyzer that interprets the signals received by the analyzer. These signals can be processed to generate parametric data that can be correlated to measurements of physical phenomena. Some of the specific locations where it would be desirable to affix a sensor and/or transducer might be locations that have harsh environments. For example, some such locations might expose any affixed sensor to high temperatures, high pressures, high levels of exposure to electromagnetic interference, etc..

In many of these harsh environment locations, optical transducers have found use. Optical sensors and/or transducers can produce optical signals indicative of various physical phenomena. For example, optical sensors and/or transducers can produce optical signals indicative of stress, strain, temperature, tilt, rotation, vibration, pressure, etc. Various sensors and/or transducers employ various types of technologies. For example, some sensors use Fabry-Pérot Interferometry (FPI), while others use fiber Bragg grating (FBG) technologies. Some of these technologies and techniques produce optical signals having a spectrum that is indicative of the measured parameter. Spectrum analysis and/or spectral measurement of such signals is performed to determine a measure of the physical phenomena causing the specific spectrum of the optical signal.

<CIT> discloses a fibre optic cable forming a temperature sensor to detect overheating and fire conditions. <CIT> discloses methods and apparatus for interrogating sets of optical elements having characteristic wavelengths spanning a sweep range.

The present invention provides a method for identifying an anomaly pulse response signal of an optical sensing system as defined in claim <NUM>.

Existing FBG interrogation systems are based on either wavelength division multiplexing (WDM), or time division multiplexing (TDM). In WDM, the number of FBGs to be interrogated is limited by the availability of wavelength range supported by hardware, i.e. laser sources and photodetectors; while in TDM, the spacing between FBGs is limited by the period of the optical pulse. There is a need to interrogate an array of FBGs with nominally identical center wavelength, serially coexisting in a single fiber with a large number of FBGs (e.g., greater than <NUM>) and dense spacing between adjacent FBGs (e.g., less than <NUM>). Temperature or strain changes on one or a few FBGs will cause changes to its/their reflection spectrum, and the changes, if successfully detected, can be used to measure temperature/strain. Such temperature or strain change events are referred to as anomaly events, and the corresponding FBGs located at these events are likewise called anomaly FBGs. Nevertheless, spectral shadowing by the rest of FBGs often masks small spectrum changes and makes measurement only applicable for very large changes in temperature/strain. Neither a direct application of existing TDM and WDM nor a combination of them will be able to address the need.

Existing WDM based systems illuminate FBGs with a continuous wave light source, either with a broadband or a scanning narrowband, and use a reflection spectrum to interrogate temperature/strain of the optical fiber. The interrogation assumes that the reflection spectrums from individual FBGs include different wavelengths such that the peak or shape of an individual spectrum can be used. An aggregated reflection spectrum from FBGs with overlapping spectra with respect to wavelength, however, is complicated by spectral shadowing and multiple reflections, which are challenges in determining if one or more FBGs in such an array are subject to elevated temperature or strain.

Existing TDM based systems illuminate FBGs with a short pulse, and use time domain windows to multiplex and interrogate FBGs. The interrogation requires FBGs with weak reflectivity to minimize crosstalk among FBGs in the round trip pulse travel. Also, the spacing between adjacent FBGs needs to be larger than the product of pulse time and light speed in order to avoid overlapping of reflection in the time domain.

In this disclosure, pulse based interrogation of a fiber optic sensor system includes sending a pulse with a specific wavelength down the optical fiber and monitoring return pulses reflected by (FBGs) in the optical fiber. The reflection spectra of two or more FBGs can overlap, and the spacing between adjacent FBGs does not need to be larger than the product of pulse time and light speed. The wavelength of the source pulse is adjusted in order to sweep a wavelength band that is correlated to an anomaly or anomalies of interest. At each discrete wavelength, a time domain response signal is measured, and a reflection intensity triggering threshold is applied to the time domain response signal in order to determine time-of-flight at which the intensity of the response signal are above the reflection intensity triggering threshold. After sweeping through the entire wavelength band, a two-dimensional time-of-flight versus wavelength map can be constructed. A two dimensional window can be applied to and moved through the map to measure density of time-of-flight points. Anomalies, or overheat conditions are then identified based on the density measure and the locations of anomalies can be derived by the position of the window. In the examples discussed herein, the term "anomaly" generally refers and/or relates to the occurrence or presence of an overheat condition or temperature, such as can be experienced by an optical fiber network (shown in <FIG>). Put another way, the term "anomaly" refers to a shift in the reflected wavelength of a FBG due to elevated strain or temperature.

<FIG> is a schematic diagram of an exemplary system for monitoring health and usage of components on an aircraft wing using optical spectral analysis. In <FIG>, a portion of aircraft <NUM> is shown with fiber optic sensor system <NUM>. Fiber optic sensor system <NUM> includes control unit <NUM>, optical fiber network <NUM>, and sensors S<NUM>-SN.

In this example, aircraft <NUM> is an airplane. In other examples, aircraft <NUM> can be a helicopter, airship, glider, or other type of vessel capable of flight. In other examples, fiber optic sensor system <NUM> can be used in conjunction with a ground-based, subterranean, or water-based vehicle, building, or other structure. Fiber optic sensor system <NUM> is a system for detecting overheat events and/or specific temperature values throughout various areas of aircraft <NUM>. Control unit <NUM> is a digital computer and can include one or more electronic devices. In some examples, control unit <NUM> can include a microprocessor, a microcontroller, application-specific integrated circuit (ASIC), a digital signal processor (DSP), a field programmable gate-array (FPGA), or other equivalent discrete or integrated logic circuitry. As will be discussed in the examples shown in <FIG>, control unit <NUM> can also include an optical pulse generator, a coupler, a laser source, a photo-detector, a comparator, a timing detector, and/or a controller.

Optical fiber network <NUM> is a network of one or more fiber optic cables configured to communicate an optical signal. Optical fiber network <NUM> can include one or more optical fibers configured in a loop or single-ended arrangement. In this example, sensors S<NUM>-SN are fiber Bragg gratings ("FBGs") configured to sense a temperature or overheat condition along optical fiber network <NUM>. In this example, sensors S<NUM>-SN include twelve sensors (e.g., N=<NUM>). In other examples, N can be more or less than twelve.

Additional examples of fiber optic overheat detection systems can be found in the following co-pending applications: <CIT> and <CIT>.

Fiber optic sensor system <NUM> is disposed and mounted within portions of aircraft <NUM>. Control unit <NUM> is disposed within a portion of aircraft <NUM> near a cockpit of aircraft <NUM>. In this example, control unit <NUM> is in optical communication with optical fiber network <NUM>. Optical fiber network <NUM> is disposed in a portion of a wing of aircraft <NUM>. In other examples, fiber optic sensor system <NUM> can be disposed throughout any other portion of aircraft <NUM>, such as in a fuselage, wheel-well, cockpit, gearbox, engine, etc. Sensors S<NUM>-SN are disposed in optical fiber network <NUM> along portions of optical fiber network <NUM>. In this example, sensors S<NUM>-SN are located at various specific locations along optical fiber network <NUM>.

In this example, control unit <NUM> coordinates operation of a laser, a pulse generator, and a timing generator to generate a pulse of optical energy and to direct the generated pulse into optical fiber network <NUM>. For example, control unit <NUM> controls a laser source to sweep frequencies and controls an optical pulse generator to allow a pulse of light from the laser to pass through a coupler and into optical fiber network <NUM>. Optical fiber network <NUM> receives the generated pulse of optical energy and transmits the received pulse of optical energy to sensors S<NUM>-SN distributed along optical fiber network <NUM>. Sensors S<NUM>-SN are configured to generate a narrow-band optical signal in response to the transmitted light beam. As each of sensors S<NUM>-SN encounters the transmitted pulse of optical energy, a portion of the encountered pulse of optical energy is reflected by sensors S<NUM>-SN. The portion of the pulse of optical energy reflected by each sensor SX (e.g., X representing any number from <NUM> to N) is indicative of the physical parameter sensed by sensor SX. The portion of the pulse of optical energy reflected by some sensors can be of a narrow band of wavelengths and/or be characterized by a specific wavelength. That specific wavelength and/or narrow-band of wavelengths can be indicative of the sensed physical parameter, such as temperature of the optical fiber or an overheat condition. Control unit <NUM> then receives and processes the sequence of reflected pulses of optical energy, so as to determine the physical parameters sensed by sensors S<NUM>-SN.

<FIG> is a schematic block diagram of fiber optic sensor system <NUM> and shows control unit <NUM> (including laser source <NUM>, optical pulse generator <NUM>, coupler <NUM>, photodetector <NUM>, comparator <NUM>, timing detector <NUM>, and controller <NUM>), optical fiber <NUM>, and avionics controller <NUM>. Laser source <NUM> can be any suitable narrowband optical source for providing an optical signal. In one example, laser source <NUM> can be a light-emitting diode laser or a gas or solid laser. It should be further understood that laser source <NUM> can be configured to provide the optical signal in any suitable manner, such as through a single pulse at a fixed wavelength, a tunable swept-wavelength, a broadband signal, and/or a tunable pulse. Optical pulse generator <NUM> is a device that regulates the intensity and duration of optical signals produced by laser source <NUM>. Coupler <NUM> is an optical component with one or more optical inputs and one or more optical outputs, which are capable of splitting an optical signal into multiple channels. In another example, coupler <NUM> can be a circulator. Photodetector <NUM> and timing detector <NUM> are receivers configured to receive an optical signal. For example, photodetector <NUM> and/or timing detector <NUM> can be a photodiode, a photodiode array, a phototransistor, an optical circulator (e.g., a non-reciprocal optical device with three or four ports configured such that light entering any of the ports exits from the next port), or any other suitable optical receiving device.

Comparator <NUM> is a device that compares aspects of a detected optical signal with data from a second source such as stored data, threshold value(s), or data from a second optical signal. For example, comparator <NUM> can be an analog comparator. In another example, comparator <NUM> can be a digital controller configured to digitally process data. Timing detector <NUM> is a detector or timer configured to measure timing windows or periods of signal pulses received by timing detector <NUM>. For example, timing detector <NUM> can be an analog detector. In another example, timing detector <NUM> can be a digital detector configured to digitally process data. In yet another example, comparator <NUM> and/or timing detector <NUM> can include a digital-to-analog converter ("ADC") incorporated within or located externally to controller <NUM>. Controller <NUM> is an electronic device that is configured to control, monitor, analyze, and/or store electronic information during and after operation of aircraft <NUM>. In one example, controller <NUM> includes a computer-readable storage medium.

In one example, controller <NUM> can include a processor (or processors) configured to implement functionality and/or process instructions for execution within control unit <NUM>. For instance, the processor(s) can be capable of processing instructions stored in or received by control unit <NUM>. Examples of processor(s) can include any one or more of a microprocessor, a controller, a micro-controller, a digital signal processor(s) (DSP), an application specific integrated circuit (ASIC), a field-programmable gate array (FPGA), a Programmable Logic Device (PLD), or other discrete or integrated logic circuitry. Avionics controller <NUM> is an electronic device that is configured to control, monitor, analyze, and/or store electronic information during and after operation of aircraft <NUM>. In an example, avionics controller <NUM> can be located in an instrument panel of the cockpit or can be a component of a health management system of aircraft <NUM>.

Controller <NUM> is electrically connected to laser source <NUM> and timing detector <NUM> (the vice versa is also true, e.g., these components are each electrically connected to controller <NUM>). Laser source <NUM> is connected to optical pulse generator <NUM>. Optical pulse generator <NUM> is connected to coupler <NUM>. Coupler <NUM> is connected to optical pulse generator <NUM>, to photodetector <NUM>, and to optical fiber network <NUM>. Photodetector <NUM> is connected to coupler <NUM> and to comparator <NUM>. Comparator <NUM> is connected to photodetector <NUM> and to timing detector <NUM>. Timing detector <NUM> is connected to comparator <NUM> and to controller <NUM>. Avionics controller <NUM> is disposed externally from control unit <NUM> and is in electrical communication with controller <NUM>.

In general, fiber optic sensor system <NUM> is configured to determine whether an overheat condition is present in aircraft <NUM>, to determine the location of the overheat condition, and to determine these two pieces of information at the same time. In one example, laser source <NUM> can be configured to provide the optical signal as at least one of a tunable swept-wavelength laser and a broadband laser. Optical pulse generator <NUM> controls the transmission of the optical signal from laser source <NUM> to optical fiber network <NUM>. For example, optical pulse generator can function as a modulator and/or a switch. Optical pulse generator <NUM> converts the optical signal from laser source <NUM> into an optical signal pulse based on instructions received from controller <NUM>. In this example, optical pulse generator <NUM> is configured to emit the optical signal pulse into optical fiber network <NUM>. In another example, optical pulse generator <NUM>, in combination with laser source <NUM>, is configured to produce a wavelength-tunable optical signal having an optical spectrum that is indicative of a measurement parameter such as a temperature of optical fiber network <NUM>. Optical pulse generator <NUM> is configured to send the optical signal into optical fiber network via coupler <NUM>.

Coupler <NUM> is configured to transmit an optical signal pulse from optical pulse generator <NUM> to optical fiber network <NUM>. Coupler <NUM> also receives and transmits reflected optical signals from sensors S<NUM>-SN to photodetector <NUM>. Photodetector <NUM> is configured to detect wavelengths and reflection intensities of the reflected optical signals from sensors S<NUM>-SN. In this example, photodetector <NUM> is configured to detect the wavelength and the amplitude of the anomaly optical signal reflected by an anomaly fiber Bragg grating. Under normal operating conditions (e.g., in the absence of an anomaly overheat condition) of aircraft <NUM>, there are no anomaly FBG sensors associated with an overheat condition and therefore there are also no anomaly reflected optical signals produced. In this example, the anomaly pulse response signal corresponds to a pulse response signal generated by the anomaly fiber Bragg grating, wherein a location of the anomaly fiber Bragg grating corresponds to a location of an overheat condition in aircraft <NUM>.

Comparator <NUM> is configured to apply a triggering threshold of reflection intensity to the reflected optical signals from sensors S<NUM>-SN to identify whether any of the reflected optical signal reflection amplitudes are above the triggering threshold. For example, comparator <NUM> identifies a reflected optical signal that is above the triggering threshold based upon a comparison of the reflection intensity of the reflected optical signal with the reflection intensity triggering threshold. In this example, comparator <NUM> is configured to determine whether a reflected optical signal has a reflection intensity that is equal to or greater than a triggering threshold. In one example, the triggering threshold applied by comparator <NUM> can be based on a system model that is associated with emitting pulse power, optical attenuations and reflectivity of sensors S<NUM>-SN. Timing detector <NUM> is configured to detect response times whenever the comparator changes its status. In this example, timing detector <NUM> is configured to identify a response time of the anomaly pulse response signal from the anomaly fiber Bragg grating.

Controller <NUM> is configured to control, send signals to, and receive signals from laser source <NUM>, optical pulse generator <NUM>, coupler <NUM>, photodetector <NUM>, comparator <NUM>, and timing detector <NUM>. In general, controller <NUM> of control unit <NUM> is configured to (i) identify the presence of an anomaly reflected optical signal, then (ii) determine which sensor Sx produced the anomaly reflected signal, then (iii) identify the sensor Sx that produced the anomaly reflected optical signal as an anomaly sensor Sa, and then (iv) determine the location of the overheat condition based upon a response time of the anomaly reflected optical signal. In one example, controller <NUM> is configured to convert the detected wavelengths, reflection intensities, and response times of the plurality of reflected optical signals to pulse response data and to transfer that data to a reflection intensity curve. In another example, controller <NUM> is configured to determine a triggering threshold of reflection intensity based on at least one of the pulse response data and the reflection intensity curve. In another example, the triggering threshold of reflection intensity is a preset or known value based on operational parameters of the system, e.g., reflectivity of sensors S<NUM>-SN, intensity of the optical signal, etc. In another example, controller <NUM> is configured to determine the location of the anomaly fiber Bragg grating that the anomaly pulse response signal was reflected from based on a total amount of time between when the optical signal is sent to the detection of the anomaly optical signal reflected by the anomaly fiber Bragg grating.

Avionics controller <NUM> is configured to receive information from controller <NUM>. In one example, avionics controller <NUM> is configured to communicate information relating to a location of an overheat condition to a health management system (not shown in <FIG>) of aircraft <NUM>. Avionics controller <NUM> can be used to communicate information between controller <NUM> and aircraft <NUM>. In some examples, such information can include aircraft conditions, flying conditions, and/or atmospheric conditions. In some examples, such information can include data processed by controller <NUM>, such as, for example, alert signals. Avionics controller <NUM> can also include a communications module (not shown). Avionics controller <NUM>, in one example, utilizes the communications module to communicate with external devices via one or more networks, such as one or more wireless or wired networks or both. The communications module can be a network interface card, such as an Ethernet card, an optical transceiver, a radio frequency transceiver, or any other type of device that can send and receive information. Other examples of such network interfaces can include Bluetooth, <NUM>, <NUM>, and Wi-Fi devices as well as Universal Serial Bus (USB). In some examples, communication with aircraft <NUM> can be performed via a communications bus, such as, for example, an Aeronautical Radio, Incorporated (ARINC) standard communications protocol. In another example, aircraft communication with aircraft <NUM> can be performed via a communications bus, such as, for example, a Controller Area Network (CAN) bus.

Existing fiber optic sensor systems are often limited by their capacity to separately determine whether the overheat condition is present and the location of that overheat condition. This is an issue because to scan the fiber optic sensor system to determine the presence of an overheat condition and then to scan the fiber optic sensor system again to separately determine the location of the overheat condition creates a lot of addition processing time with respect to recordation and analysis of signal data. As will be further discussed with respect to <FIG>, fiber optic sensor system <NUM> and the related operation thereof allows for the determination of whether the overheat condition is present and the determination of the location of the overheat condition to occur simultaneously. This simultaneous determination decreases the amount of time for determining the location of an overheat condition as compared to existing WDM, TDM, and combination WDM/TDM based sensor systems.

<FIG> shows method <NUM> as a data collection process and includes steps <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>. In step <NUM>, during a first scan or stepping of fiber optic sensor system <NUM>, the wavelength is set by optical pulse generator <NUM> and by laser source <NUM> to an initial wavelength λ<NUM> such that the scan is started at wavelength λ<NUM>. In step <NUM>, a wavelength of fiber optic sensor system <NUM> is set. In step <NUM>, an optical pulse is emitted by optical pulse generator <NUM> via coupler <NUM> into optical fiber <NUM>. In step <NUM>, pulse reflections from optical fiber <NUM> are received by coupler <NUM> and are sent to photodetector <NUM>. In step <NUM>, the time-of-flights for the received pulse reflections are measured by timing detector <NUM>. In step <NUM>, the time-of-flights and corresponding wavelength for the received pulse reflections are logged. These steps are repeated for an N amount of cycles. For example, step <NUM> includes determining whether a cycle count equals N. If the cycle count does not equal N, steps <NUM>-<NUM> are repeated. If the cycle count equals N, the wavelength is set to a new, different wavelength λ in step <NUM>. Once a pre-determined range of wavelengths λ are scanned or stepped through, the process ends at step <NUM>.

<FIG> includes graph <NUM> of reflection intensity as a function of time and shows intensity axis <NUM>, time axis <NUM>, reflection intensity curve <NUM>, triggering threshold <NUM>, point <NUM> (located at time ta), points <NUM>, up-crossing <NUM>, and down-crossing <NUM>.

In this example, graph <NUM> is an anomaly reflection intensity curve created by controller <NUM> that includes data from the anomaly response signal (e.g., reflected optical signal ROSa measured at wavelength λa. Intensity axis <NUM> is a vertical axis indicative of reflection intensity "I. " Time axis <NUM> is a horizontal axis indicative of time-of- flight, or response time, "t. " Reflection intensity curve <NUM> is representative of an amount of reflection intensity as a function of response time, or time-of-flight, as detected by control unit <NUM> and its components of optical fiber network <NUM>. In this example, reflection intensity curve <NUM> is pulse response data of a plurality of reflected optical signals (e.g., of reflected optical signals ROS<NUM>-ROSN) created by controller <NUM>.

Triggering threshold <NUM> is a value of reflection intensity representative of a minimum level of reflection intensity above which reflected optical signals can be identified as anomaly reflected optical signals. In an example, triggering threshold <NUM> can be chosen to discriminate (or identify) reflected optical signal ROSa reflected from sensor Sa (e.g., an anomaly FBG, or an FBG sensor located at an overheat condition). Triggering threshold <NUM> is determined by controller <NUM> and is applied by comparator <NUM>. Point <NUM> is a local maximum of reflection intensity curve <NUM> that is representative of a maximum reflection intensity within a given region or portion of optical fiber network <NUM> that is greater than triggering threshold <NUM>. Point <NUM> illustrates a maximum reflection intensity which is dependent upon a length of the pulse, locations of the FBG sensors, and the characteristics of photodetector <NUM>.

Time ta is a measure of response time, or time-of-flight, corresponding to one of point <NUM>, up-crossing <NUM>, or down-crossing <NUM>. In another example, time ta can also be estimated from an average of up-crossing <NUM> and down-crossing <NUM>, which can improve the accuracy of the measurement of time ta. Points <NUM> are values of reflection intensities along reflection intensity curve <NUM> that are less than triggering threshold <NUM>. Up-crossing <NUM> is an intersection point of reflection intensity curve <NUM> with triggering threshold <NUM> along a positively-sloped portion of reflection intensity curve <NUM>. For example, up-crossing <NUM> is a triggering point for an up-crossing of reflection intensity curve <NUM> with triggering threshold <NUM>. Down-crossing <NUM> is an intersection point of reflection intensity curve <NUM> with triggering threshold <NUM> along a negatively-sloped portion of reflection intensity curve <NUM>.

From graph <NUM>, point <NUM> is identifiable and/or identified due to the reflection intensity of reflection intensity curve <NUM> at time ta being greater than triggering threshold <NUM>. The delta (or difference) between up-crossing <NUM> and down-crossing <NUM> is a combined result of pulse length in time domain and the actual length of the anomaly FBG (e.g., sensor Sa).

In this example, after point <NUM> is identified based on triggering threshold <NUM>, time ta (e.g., response time of the anomaly pulse response signal) is identified by timing detector <NUM>. Based on the identified response time (e.g., time ta) of the anomaly pulse response signal, the location of sensor Sa (e.g., the anomaly fiber Bragg grating that the anomaly pulse response signal was reflected from) is determined by controller <NUM>. In another example, an extent of an overheat condition is determined by controller <NUM> based upon the detected wavelength (e.g., wavelength λa) of the anomaly pulse response signal.

<FIG> shows method <NUM> as an overheat detection and location determination process and includes steps <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>. In step <NUM>, time-of-flight and wavelength data, such as that collected in steps <NUM>-<NUM> of method <NUM> shown in <FIG>, is applied to a graph (see e.g., graphs 78B and 78C shown in <FIG>, respectively). In step <NUM>, a 2D (i.e., two dimensional) window defined by range Δλ and range Δt that are based on a design of the system. In step <NUM>, the 2D window is applied to the graph of time-of- flight and wavelength data. In step <NUM>, the position of the 2D window is changed. In step <NUM>, the density of time-of-flight points in the 2D window is determined. If the density of time-of-flight points in the 2D window is greater than (or equal to) a threshold value, an overheat condition is detected in step <NUM>. In step <NUM>, the temperature and location of the overheat condition is obtained. If the density of time-of- flight points in the 2D window is less than a threshold value, the position of the 2D window is set to a new position in step <NUM>. If the new position, or subsequently new positions, of the 2D window do not exhibit a density of the time-of-flight points as having a density greater than (or equal to) a threshold value, then no overheat condition is detected and the process ends in step <NUM>.

<FIG> includes graph 78B of time-of-flight as a function of wavelength corresponding to FBG sensors of fiber optic sensor system <NUM> and shows wavelength axis 80B, time-of-flight axis 82B, points 84B, set 86B of triggered points 88B, wavelength λ<NUM>, wavelength λa, range Δt, and range Δλ. In this example, graph 78B represents the resultant graph from step <NUM> shown in method <NUM>.

Wavelength axis 80B is an independent, horizontal axis indicative of wavelength "λ" and includes demarcations of wavelengths λ<NUM> and λa. Time-of-flight axis 82B is a dependent, vertical axis indicative of time-of-flight, or response time, "t. " Points 84B are data points of reflection intensities that are less than a triggering threshold of reflection intensity. Set 86B is a group or grouping of one or more of triggered points 88B with wavelengths outside an interested wavelength band, which is related to the measurement parameter or overheat temperature. In this example, set 86B is shown as a rectangle. In other examples, set 86B can include a circular, rectangular, parallelogram, or other geometric shape.

Triggered points 88B are local maxima or crossings (e.g., up-crossing <NUM> or down-crossings <NUM>) of reflection intensities within a given region or portion of optical fiber network <NUM> that include reflection intensities greater than the triggering threshold of reflection intensity. In this example, four triggered points 88B are shown. In other example, more or less than four triggering points can be included in graph 78B and/or in set 86B. Wavelength λ<NUM> is a starting nominal wavelength of optical fiber network <NUM>. Wavelength λa is a wavelength set by controller <NUM> and that is associated with a determined overheat temperature. In this example, wavelength λa is indicative if a wavelength corresponding to a defined maximum ambient temperature. Range Δt is a range of times determined by controller <NUM> that define the size of the vertical dimension of the rectangular shape of set 86B shown in graph 78B. Range Δλ is a range of wavelengths determined by controller <NUM> that define the size of the horizontal dimension of the rectangular shape of set 86B shown in graph 78B.

In this example, a value of the wavelength at which the wavelength-time plane shown in <FIG> is taken can be an identified triggering threshold of reflection intensity. In this example, points 84B and triggered points 88B represent single up-crossing points of intersection with the triggering threshold (similar to up-crossings <NUM> shown in <FIG>). As optical fiber network <NUM> is scanned at a first wavelength, when a reflected optical signal is received at the first wavelength, the up-crossing of that FBG's intensity level is indicated and the time-of-flight is recorded. Then, the scanning wavelength is set to a second wavelength, and optical fiber network <NUM> is scanned again at the second wavelength to determine the presence of an up-crossing occurring at the second wavelength. This process of identifying and collecting time-of-flight data for just the first detected up-crossing continues throughout a range of wavelength scans. Once the range of wavelengths is completely scanned, all of the up-crossings are then indicated in a graph such as graph 78B to determine if there is a grouping to the right of wavelength λa (as shown in <FIG>) indicating a grouping of triggered points 88B in an overheat condition zone of optical fiber network <NUM>.

In this example, range Δλ is a function of the triggering threshold (e.g., triggering threshold <NUM>) and points 84B. In this example, range Δλ spans <NUM> picometers to <NUM> picometers. In another example, set 86B can include <NUM> to <NUM> triggered points 88B with a wavelength of the scanning optical pulse set to <NUM> picometers. Range Δt is dependent on a quality of the optical pulse and a resolution of photodetector <NUM>. The resolution of photodetector <NUM> is typically quantified and specified in the design of controller <NUM> and can be adjusted by controller <NUM> to set range Δt to accommodate various design parameters such as FBG reflection variation. In one example, a one nanosecond timing resolution design which satisfies a <NUM> meter location requirement would provide range Δt at <NUM> nanoseconds.

In one example, a density of triggered points 88B can be calculated by controller <NUM> and applied by controller <NUM> in a portion of graph 78B to the right of wavelength λa as part of a moving two-dimensional window (e.g., an additional set of range Δt and range Δλ) to develop additional indicators for anomaly (e.g., overheat condition or temperature) detection. In another example, a two-dimensional Gaussian filter, such as is used in image processing, can be utilized by controller <NUM> to identify areas with concentrations of triggered points 88B. In another example, an overheat temperature can be related to measured wavelengths of set 86B or of triggered points 88B. The use of time-of-flight measurements as discussed herein can eliminate the need of scanning wavelengths lower than wavelength λa which saves processing time. In another example with a multi-zone, multi-wavelength λ<NUM> setup, multiple wavelength band limited scanning can be used to determine time-of-flight measurements of fiber optic sensor system <NUM>.

As such, fiber optic sensor system <NUM> and the above discussed analysis of graphs <NUM>, <NUM>, <NUM>, <NUM>, 78B, and 78C by controller <NUM> provides the benefit of reducing an amount of false alarms and improving the accuracy in determining time-of-flight. These two benefits can be viewed from the two dimensionalities of time-of-flight and wavelength. For example, in the wavelength dimension, singular time-of-flight triggering can isolate the effect of various instantaneous signal noises. Whereas in the time-of-flight dimension, averaging over multiple times-of-flight will reduce a variance in the measurement of range Δt. With respect to false alarm identification, if only a single triggered point <NUM> is detected, then a false alarm condition is likely to have occurred. However, if there are multiple triggered points <NUM> that are closely related together, then an overheat condition can be more accurately declared. Additionally, fiber optic sensor system <NUM> allows for detection of relatively low overheat temperatures.

<FIG> includes graph 78C of reflection intensity as a function of wavelength corresponding to FBG sensors of fiber optic sensor system <NUM> and shows wavelength axis 80C, time axis 82C, points 84C, set 86C of triggered points 88C, wavelength λ<NUM>, wavelength λa, range Δt, and range Δλ.

In the example shown in <FIG>, graph 78C depicts set 86C of triggered points 88C as being larger in size than 86B of triggered points 88B shown in graph 78B of <FIG>. A portion of set 86C is shown as having a larger range Δλ than range Δλ of set 86B. Additionally, set 86C is shown as overlapping across wavelength λa.

Once the values of time t of trigger points <NUM>, 88B, and/or 88C, as well as for range Δt and range Δλ, are determined, controller <NUM> determines the locations of any anomaly fiber Bragg gratings based on the time-of-flight values. For example, the speed of the optical pulse (i.e., the speed of light in optical fiber network <NUM>) is known, and so once the time-of-flight value is determined, controller <NUM> can calculate a distance of an anomaly fiber Bragg grating from control unit <NUM> by multiplying the speed of the optical pulse by the one half of the time-of-flight. Controller <NUM> can also determine an extent of an overheat condition based upon a position of a window defined by range Δt and rangeΔλ. For example, specific amounts of change in wavelength λ can correlate to known temperature changes, such that a change of X nanometers (or picometers) in wavelength equates to a change of Y degrees in the temperature at the anomaly fiber Bragg grating.

In some examples, there can be a need to further lower the triggering threshold due practical constraints of fiber optic system <NUM> and/or optical fiber network <NUM>. In such an example, a multiple-crossing time-of-flight detector can be implemented such that there can be multiple time-of-flight points determined with a scan of a single wavelength. For example, the triggering threshold of reflection intensity is set by controller <NUM> at a lower value (e.g., less than triggering threshold <NUM> shown in <FIG>) in the pulse response data of the reflected optical signals from sensors S<NUM>-SN that is created by controller <NUM>.

Claim 1:
A method of identifying an anomaly pulse response signal of an optical sensing system, the method comprising:
i. setting, with an optical pulse generator (<NUM>), a wavelength of a wavelength-tunable optical signal pulse;
ii. emitting, with the optical pulse generator (<NUM>), the wavelength-tunable optical signal pulse into an optical fiber (<NUM>), wherein the optical fiber comprises a plurality of fiber Bragg gratings at spaced locations;
iii. receiving, with a photodetector (<NUM>), a plurality of reflected optical signals from the plurality of fiber Bragg gratings;
iv. measuring, with a timing detector (<NUM>), times-of-flight of the plurality of reflected optical signals;
v. logging the times-of-flight of the plurality of reflected optical signals and the wavelength of the wavelength-tunable optical signal pulse;
vi. determining whether a cycle count is equal to a preset amount of cycle steps, wherein:
a. when the cycle count is less than the preset amount of cycle steps, then repeat steps ii through vi; or
b. when the cycle count reaches the preset amount of cycle steps, then go to step vii;
vii. graphing the measured times-of-flight;
viii. creating a two-dimensional window, wherein a first dimension of the two-dimensional window is defined by a wavelength range Δλ and a second dimension of the two-dimensional window is defined by a time range Δt;
ix. applying the two-dimensional window to the times-of-flight;
x. changing a position of the two-dimensional window;
xi. determining whether a density of time-of-flight points in the two-dimensional window is greater than (or equal to) a threshold value; wherein
c. when the density of time-of-flight points in the two-dimensional window is greater than (or equal to) a threshold value, then:
detection of an overheat condition is declared; and
a temperature and a location of the overheat condition is obtained; or
d. when the density of time-of-flight points in the two-dimensional window is less than a threshold value, then:
a position of the two-dimensional window is set to a new position; and
steps x through xi are repeated.