Patent Description:
According to a first aspect, there is provided a computer implemented method according to any one of accompanying Claims <NUM> to <NUM>.

Features of the present disclosure are illustrated by way of examples shown in the following figures. In the following figures, like numerals indicate like elements, in which:.

For simplicity and illustrative purposes, the present disclosure is described by referring mainly to examples thereof. In the following description, details are set forth in order to provide an understanding of the present disclosure. It will be readily apparent however, that the present disclosure may be practiced without limitation to these details.

An optical time-domain reflectometer (OTDR) is an optoelectronic instrument used to characterize an optical fiber. The OTDR may inject a series of optical pulses into an optical fiber under test. Based on the injected optical pulses, the OTDR extracts, from the same end of the optical fiber in which the optical pulses are injected, light that is scattered or reflected back from points along the optical fiber. The scattered or reflected light that is gathered back may be used to characterize the optical fiber. For example, the scattered or reflected light that is gathered back may be used to detect, locate, and measure events at any location of the optical fiber. The events may include faults at any location of the optical fiber. Other types of features that may be measured by the OTDR include temperature distribution along a fiber, attenuation uniformity and attenuation rate, segment length, and location and insertion loss of connectors, splices, or any other optical components such as splitters or multiplexers.

With respect to temperature distribution measurement by an OTDR, an OTDR may include distributed temperature sensing (DTS). For DTS, Raman distributed temperature sensing may encounter different attenuations at different test wavelengths. For example, the different test wavelengths may include the Anti-Stokes (AS) wavelength, the Rayleigh wavelength, the Stokes wavelength, etc. In order to implement distributed temperature sensing, interrogation of an optical fiber may be performed by using several laser sources. Alternatively or additionally, the interrogation of the optical fiber may be dual-ended (e.g., on both ends of the optical fiber). For an interrogation that includes several laser sources, the distributed temperature sensing results may include inconsistencies in that differing spectral shapes of the various test signals used may result in different mean-weighted-average wavelengths and non-matching attenuation compensations. For an interrogation that is dual-ended, the need to access both ends of an optical fiber may add additional technical complexities, for example, with respect to a downhole end of the optical fiber.

Distributed temperature sensing utilizes the temperature sensitivity of an anti-Stokes Raman band in order to derive temperature. Since the transient Raman OTDR signal may also decay with attenuation, the signal may be normalized to the Stokes-OTDR trace. In this regard, a Rayleigh OTDR trace may also be utilized.

In order address the aforementioned technical challenges, a temperature distribution sensor as disclosed herein may utilize two spectral slices of the Anti-Stokes Raman to implement distributed temperature sensing. In this regard, the coefficient of the Anti-Stokes power variation versus temperature depends on the exact wavelength. As disclosed herein, this dependency may be evident from the literal equation of the anti-Stokes power derived from Bose-Einstein statistics. Further, the differential response at closely spaced wavelengths may be utilized as a new mechanism in distributed temperature sensing, with an inherently reduced differential loss, while also offering new means for differential losses compensation.

<FIG> illustrates an architecture of a temperature distribution sensor <NUM> (hereinafter referred to as "sensor <NUM>").

Referring to <FIG>, the sensor <NUM>, which is an OTDR, includes a laser source <NUM> to emit a laser beam that is tunable over a wavelength range. The wavelength range is less than a Raman bandwidth in a device under test (DUT) <NUM>, or of-the-order-of the Raman bandwidth in the DUT <NUM>. According to examples, the DUT <NUM> may include an optical fiber.

A pulsed source <NUM> applies a pulse drive signal to the laser beam or to a modulator to modulate the laser beam that is to be injected into the DUT <NUM>.

A bandpass filter <NUM> is operatively disposed between the laser source <NUM> and the DUT <NUM>. The bandpass filter <NUM> is configured to an anti-Stokes wavelength that is narrower than the Raman bandwidth.

A photodiode <NUM> may be operatively disposed between the bandpass filter <NUM> and the DUT <NUM> to acquire, from the DUT <NUM>, anti-Stokes optical time-domain reflectometer traces for two preset wavelengths of the laser beam to determine (e.g., by a sensor controller) a temperature distribution <NUM> for the DUT <NUM>. In this regard, the temperature distribution <NUM> for the DUT <NUM> may be determined by determining a ratio of the anti-Stokes optical time-domain reflectometer traces for the two preset wavelengths of the laser beam. Further, with respect to the anti-Stokes optical time-domain reflectometer traces for the two preset wavelengths of the laser beam, a wavelength difference resulting from differing anti-Stokes spectral slices and a corresponding mean weighted average wavelength may be corrected.

A further photodiode <NUM> may be operatively disposed between the laser source <NUM> and the bandpass filter <NUM> to acquire Rayleigh optical time-domain reflectometer traces at the two preset wavelengths of the laser beam. In this regard, a differential attenuation between the two preset wavelengths of the laser beam may be corrected by determining a ratio of the Rayleigh optical time-domain reflectometer traces at the two preset wavelengths of the laser beam.

A fiber amplifier <NUM> may amplify the pulse drive signal applied to the laser beam or to the modulator to modulate the laser beam that is to be injected into the DUT <NUM>. The amplifier <NUM> may comprise a temporal gating element that may suppress the amplified spontaneous emission and associated power fluctuations in between pulses.

According to examples, for the laser source <NUM> that includes a narrow linewidth tunable laser, the sensor <NUM> may be operated, using the narrow linewidth tunable laser source, in a Rayleigh mode to record a distributed acoustic sensing signal over the DUT <NUM>.

Referring to <FIG>, an example of the sensor <NUM>, described to aid understanding, that includes two laser sources may be designated as sensor <NUM>. In this regard, the sensor <NUM>, which may be an OTDR, may include a first laser source <NUM> to emit a first laser beam, and a second laser source <NUM> to emit a second laser beam. The first and second laser beams may include wavelengths that differ by a quantity that is less than a Raman bandwidth in a DUT <NUM>, or of-the-order-of the Raman bandwidth in the DUT <NUM>.

A pulsed source <NUM> may apply a pulse drive signal to the first and second laser beams or to a modulator to modulate the first and second laser beams that are to be injected into the DUT <NUM>.

A bandpass filter <NUM> may be operatively disposed between the first laser source <NUM> and the second laser source <NUM> and the DUT <NUM>. The bandpass filter <NUM> may be configured to an anti-Stokes wavelength that is narrower than the Raman bandwidth.

A photodiode <NUM> may be operatively disposed between the bandpass filter <NUM> and the DUT <NUM> to acquire, from the DUT <NUM>, anti-Stokes optical time-domain reflectometer traces for two preset wavelengths of the first and second laser beams to determine a temperature distribution <NUM> for the DUT <NUM>. The photodiode <NUM> may be connected to the passing port of the bandpass filter <NUM>. The first laser source <NUM> and the second laser source <NUM> may be connected to the reflective port of the bandpass filter <NUM> (complementary of the passband function), and the DUT <NUM> to the common port of the bandpass filter <NUM>.

A further photodiode <NUM> may be operatively disposed between the first laser source <NUM> and the second laser source <NUM> and the bandpass filter <NUM> to acquire Rayleigh optical time-domain reflectometer traces at the two pre-set wavelengths of the first and second laser beams.

Operation of the sensor <NUM> (and the sensor <NUM>) is described in further detail with reference to <FIG>.

As disclosed herein, the sensor <NUM> (and the sensor <NUM>) may utilize two spectral slices of the Anti-Stokes Raman to implement distributed temperature sensing. In this regard, the coefficient of the Anti-Stokes power variation versus temperature may depend on the exact wavelength. This dependency may be evident from the literal expression of the number of optical phonons η generated by thermal agitation and derived from Bose-Einstein statistics. <MAT> Equation (<NUM>) represents the number of optical phonons generated by thermal agitation at frequency Δν, k represents the Boltzmann constant, and T represents the temperature of the DUT. The anti-Stokes power for each spectral component, each corresponding to a frequency shift Δν with regard to probe laser frequency, is directly proportional to this number of phonons. However, in certain implementations, a single mean-weighted-average Raman frequency shift of about <NUM>. 2THz may be retained. The same considerations may apply to the Stokes component. Calculations based on a mean wavelength may result in the following relationship between temperature and Anti-Stokes/Stokes ratio: <MAT> The expression for Equation (<NUM>) may account for the potentially different losses at the Stokes and anti-Stokes wavelengths. For Equation (<NUM>), R represents the power ratio of anti-Stokes and Stokes, z represents the position along the DUT, T represents the temperature, λS represents the mean-weighted average wavelength of the Stokes profile, λAS represents the mean-weighted average wavelength of the anti-Stokes profile, h represents the Planck's constant , k represents the Boltzmann constant, αAS represents the DUT attenuation coefficient at λAS, αS represents the DUT attenuation coefficient at λAS, ξ represents the position in the integral, and dξ represents an increment on position in the integral.

As disclosed herein, the spectral dependency of the phonon population within a single Raman anti-Stokes band may be utilized as the core mechanism for sensing. From Equation (<NUM>), the coefficient of variation of the Raman anti-Stokes power with temperature, as a function of frequency, may be determined. This coefficient may represent the derivative of the population with temperature, normalized to the population itself in order to express a sensitivity in %/K for Raman sensing, and may be expressed as follows: <MAT>.

<FIG> illustrates the sensitivity as a function of wavelength, when the DUT is illuminated at <NUM>, according to an example of the present disclosure. The sensitivity may vary substantially across the useful range of the Raman profile. The mean value of <NUM>%/K may be found at Raman resonance of <NUM>, but sensitivity may vary from <NUM> to <NUM>%/K for spectral components of <NUM> to <NUM> respectively. Thus, instead of making the ratio of the anti-Stokes to the Stokes and obtaining a final sensitivity of approximately <NUM>%/K, by taking the ratio of two spectral components of the anti-Stokes which are <NUM> apart, a <NUM>%/K sensitivity may be expected. This lower sensitivity value may increase the sensitivity to detection noises and lower the dynamic range. However, as will be described hereafter, several key advantages arise from the use of a reduced spectral range (e.g., <NUM> instead of <NUM> at <NUM>).

<FIG> illustrate examples of implementation of the temperature distribution sensors of <FIG> and <FIG>.

Referring to <FIG>, an implementation <NUM> of the sensor <NUM> (or the sensor <NUM>) includes the laser source <NUM> (or the first laser source <NUM> and the second laser source <NUM>) at section <NUM> of the sensor <NUM>. At section <NUM> of the sensor <NUM>, the bandpass filter <NUM> (or the bandpass filter <NUM>) are operatively disposed between the laser source <NUM> and the DUT <NUM>, and are configured to an anti-Stokes wavelength that is narrower than the Raman bandwidth. At section <NUM> of the sensor <NUM>, the photodiode <NUM> (or the photodiode <NUM>), designated as an avalanche photodiode (APD), may be operatively disposed between the bandpass filter <NUM> and the DUT <NUM> to acquire, from the DUT <NUM>, anti-Stokes optical time-domain reflectometer traces for two preset wavelengths of the laser beam to determine the temperature distribution <NUM> for the DUT <NUM>. At section <NUM> of the sensor <NUM>, the further photodiode <NUM> (or the further photodiode <NUM>) may be operatively disposed between the laser source <NUM> and the bandpass filter <NUM> to acquire Rayleigh optical time-domain reflectometer traces at the two preset wavelengths of the laser beam.

Referring to <FIG>, a tunable laser and a fixed bandpass filter may be utilized.

Referring to <FIG>, an implementation <NUM> of the sensor <NUM> (or the sensor <NUM>) includes the laser source <NUM> (or the first laser source <NUM> and the second laser source <NUM>) at section <NUM> of the sensor <NUM>. At section <NUM> of the sensor <NUM>, the bandpass filter <NUM> (or the bandpass filter <NUM>) are operatively disposed between the laser source <NUM> and the DUT <NUM>, and are configured to an anti-Stokes wavelength that is narrower than the Raman bandwidth. At section <NUM> of the sensor <NUM>, a single photodiode <NUM> (or the photodiode <NUM>) may be operatively connected to a switch at section <NUM> of the sensor <NUM>. In this regard, the switch at section <NUM> of the sensor <NUM> may be operated so that the photodiode <NUM> (or the photodiode <NUM>) is operatively disposed between the bandpass filter <NUM> and the DUT <NUM> to acquire, from the DUT <NUM>, anti-Stokes optical time-domain reflectometer traces for two preset wavelengths of the laser beam to determine the temperature distribution <NUM> for the DUT <NUM>. Further, the switch at section <NUM> of the sensor <NUM> may be operated so that the photodiode <NUM> (or the photodiode <NUM>) is operatively disposed between the laser source <NUM> and the bandpass filter <NUM> to acquire Rayleigh optical time-domain reflectometer traces at the two preset wavelengths of the laser beam.

Referring to <FIG>, an implementation <NUM> of the sensor <NUM> includes the laser source <NUM> at section <NUM> of the sensor <NUM>. Laser pulses are be sent to the DUT. At section <NUM> of the sensor <NUM>, backscattered radiation may be directed towards bandpass filters linked via wavelength division multiplexing (WDM) to successively record the anti-Stokes Raman OTDR trace at two optical frequencies. Alternatively, the switch and fixed filters may be replaced by a tunable filter. With respect to the aspect of "Lambda laser minus (Raman Shift - Δλ)" versus "Lambda laser minus (Raman Shift + Δλ)", in this implementation where two bandpass filters would be used, for an example with a single laser at <NUM>, the Raman shift is ~<NUM>, and for the anti-Stokes at <NUM>, there may be a bandpass at <NUM>-<NUM> and a bandpass at <NUM>+<NUM>.

As disclosed herein, a differential attenuation between the two preset wavelengths of the laser beam may be corrected by determining a ratio of the Rayleigh optical time-domain reflectometer traces at the two preset wavelengths of the laser beam. In this regard, in case of a high differential loss profile, it may be technically challenging to measure and account for the differential attenuation between the two anti-Stokes wavelengths, irrespective of how closely spaced they the anti-Stokes wavelengths are. In this regard, a tunable laser (e.g., <NUM> at <NUM>) and a fixed bandpass filter, implemented as shown in <FIG> and <FIG> may be utilized. With respect to <FIG> and <FIG>, the two backward Raman wavelength losses may be virtually identical as they are selected by the same bandpass filter. The losses at forward pulse wavelengths (e.g., forward losses), may now be different, and may be measured in the Rayleigh OTDR mode.

For a nominal case where the two test wavelengths are separated by approximately the Raman bandwidth, the loss in sensitivity to temperature may be equivalent to a loss of dynamic range, for example, by <NUM>. This value may represent a default value. However, compared to a dual wavelength setup, the optics of the implementation may allow to spare approximately <NUM>. 4dB of dynamic range (e.g., <NUM> LOG).

As disclosed herein, with respect to the anti-Stokes optical time-domain reflectometer traces for the two preset wavelengths of the laser beam, a wavelength difference resulting from differing anti-Stokes spectral slices and a corresponding mean weighted average wavelength may be corrected. In this regard, a relatively small difference of a few nm may remain in the mean-weighted-average anti-Stokes wavelength due to the Raman spectral shape. In this regard, <FIG> illustrates a <NUM> bandpass filtered anti-stokes Raman spectra with test wavelengths at min-max of Erbium/C-band, according to an example of the present disclosure. Referring to <FIG>, with respect to the relatively small difference of a few nm that may remain in the mean-weighted-average anti-Stokes wavelength, this aspect may be evaluated in the graphic of <FIG> of the expected filtered spectra with two test wavelengths, for example, at <NUM> and <NUM>, and a bandpass of <NUM>. With respect to the two curves at <NUM> and <NUM>, these curves may represent the two Raman spectra of backscattered radiation that is obtained when sending laser light at <NUM> and <NUM>, respectively. The spectra for the example of <FIG> may be windowed by the bandpass rectangular profile. The test wavelengths may be at the extremes of the C-band of fiber telecommunications, where sources and erbium doped fibers may be utilized. In order to mitigate any issues pertaining to the relatively small difference, scaling may be based on the width of bandpass (e.g., <NUM> for a <NUM> bandwidth for the following example), so that the difference may be reduced, at the cost of a lower signal power and therefore a lower dynamic range. Secondly from the knowledge of the origin of the losses (e.g., bending or darkening), the knowledge of the fiber attenuation at the two precisely defined laser wavelengths, and the knowledge of the test wavelengths including the two calibrated mean-weighted average anti-Stokes wavelengths, a differential loss may be extrapolated at those latter wavelengths to produce a further correction on the fiber losses.

Reducing the bandwidth of the Stokes band by use of a bandpass filter may provide for the reduction of the chromatic dispersion induced spatial spread and associated loss of spatial resolution, for example, in monomode fiber applications. In this regard, multimode applications may be primarily affected by modal dispersion.

<FIG> illustrates a table of various consequences of bandpass filter width, as a guideline for the determination of an optimal value, according to an example of the present disclosure.

Referring to the table <NUM> of <FIG>, a lower bandwidth may improve the wavelength definition (remaining differential loss problem) and the potential to reach longer distances while maintaining spatial resolution (CD problem). Further, a larger bandwidth may be utilized to maintain the dynamic range of an instrument (e.g., proportionally higher power). The columns of <FIG> may include bandpass filter width (nm), lambda error (nm), spread due to backward chromatic dispersion (CD) at <NUM> (m), sensitivity, power, losses, and bill. For the table <NUM>, bill may represent the sum of the various contributions to dynamic range (e.g., for row <NUM>, <NUM> + <NUM> - <NUM> = <NUM>. With respect to the CD impact, the delay corresponding to the two extremes of the bandpass may be determined, for example, using 10ps/nm/km at <NUM> and 10ns/m correspondence on an OTDR curve. For example, for row <NUM>, 10ps/nm/km x <NUM> x <NUM> / 10ns/m=<NUM>.

In order to recover the temperature information, the two anti-Stokes powers at the two spectral slices, centered at Δϑ<NUM> and Δϑ<NUM> respectively, may follow Bose-Einstein statistics as follows: <MAT> Referring to Equation (<NUM>), IAS represents the intensity detected, a quantity proportional to the anti-Stokes power, T represents the temperature, Δϑ<NUM>,<NUM> represents the mean-weighted average frequency shift for the anti-Stokes spectral slice considered, h represents the Planck's constant, and k represents the Boltzmann constant.

As disclosed herein, the temperature distribution <NUM> (or the temperature distribution <NUM>) for the DUT may be determined by determining a ratio of the anti-Stokes optical time-domain reflectometer traces for the two preset wavelengths of the laser beam. The ratio of the two Stokes may be derived from OTDR traces for every point of the link. Further, the ratio may be normalized to the ratio measured in a reference section at a known temperature T<NUM> as follows (this may provide for elimination of the constants of proportionality disregarded in Equation (<NUM>)): <MAT> Referring to Equation (<NUM>), R represents the anti-Stokes to Stokes ratio, Δϑ<NUM> represents the mean-weighted average frequency shift for spectral slice <NUM>, and Δϑ<NUM> represents the mean-weighted average frequency shift for spectral slice <NUM>. Equation (<NUM>) may be solved numerically to derive T all along the fiber from a measured ratio.

The temperature distribution sensor <NUM> as disclosed herein may include a single source or a single-band solution. In this regard, the temperature distribution sensor <NUM> may include a relatively small tuning range or in an embodiment included to aid understanding dual source, <NUM> broad/apart at <NUM>, <NUM> broad/apart at <NUM>.

The temperature distribution sensor <NUM> as disclosed herein may include a single source as disclosed herein. In this regard, at <NUM>, C-Band components, fiber lasers, and fiber amplifiers based on Erbium dopant may be utilized. At <NUM>, for example, Y-Band components and their capacity at producing <NUM>-<NUM> light may be utilized.

The temperature distribution sensor <NUM> as disclosed herein may provide for compensation of differential slope (e.g., with bending or bleaching). This may be associated with the same wavelength band in the anti-Stokes range (e.g., a power slope within band which create differing mean wavelengths anti-Stokes-<NUM> (AS1) and anti-Stokes-<NUM> (AS2), and two different probe wavelengths (e.g., <NUM> compared to the <NUM> of the dual-laser solution of <FIG>). Differential fiber losses may be measured in Rayleigh mode at these two test probe wavelengths. The four slopes may provide for the quantification of the whole link (e.g., Rayleigh <NUM> (lambda <NUM> forward and lambda <NUM> backward), Rayleigh <NUM> (lambda <NUM> forward and lambda <NUM> backward), AS1 (lambda <NUM> forward and AS1 backward) and AS2 (lambda <NUM> forward and AS2 backward).

The temperature distribution sensor <NUM> as disclosed herein may provide for a single-ended test for temperature distribution. Thus, the temperature distribution sensor <NUM> as disclosed herein may eliminate the need for a dual-ended test, which may include installation constraints which may not be possible to implement.

The temperature distribution sensor <NUM> as disclosed herein may provide for an intrinsic tolerance to nonlinearity. The two test probes and backscattered signals may be considered as equal with regard to non-linearity given the very similar wavelengths, power levels, and fiber attenuation profiles. In other techniques with dual lasers or three bands, the nonlinearity may affect each measure differently (e.g., Anti-Stokes retrofitting energy to forward pulse, Rayleigh depleted by co-propagating forward Stokes pulses, Stokes band increased by Rayleigh scattering of the same forward Stokes pulse, etc.).

As disclosed herein, for the temperature distribution sensor <NUM>, the laser source may include a narrow linewidth tunable laser. Thus, the sensor <NUM> may be operated using the narrow linewidth tunable laser source in a Rayleigh mode to record a distributed acoustic sensing signal over the DUT. In this regard, use of a narrow linewidth laser may provide for compatibility with a distributed acoustic sensing option. The Rayleigh section of the new distributed temperature sensing scheme previously described may include a direct-detection acquisition line that is also compatible with an intensity based distributed acoustic sensing. In this regard, a coherent detection scheme may provide a suitable mean for the differential slope compensations at source wavelengths, while also providing a higher sensitivity for an intelligent distributed acoustic sensor and the potential for a Phase-distributed acoustic sensing analysis. For example, in oil and gas applications, a distributed temperature sensing and a distributed acoustic sensing interrogator may be used alternatively and even simultaneously on the same sensing fiber with added value when crossing the respective information for these interrogators. Disposal of a tunable laser in the distributed acoustic sensing application with respect to wavelength diversity may provide for the reduction of the fading of the sensor response at locations of destructive interferences.

For the temperature distribution sensor <NUM> as disclosed herein, the narrow linewidth laser and narrow-filtered Raman signal may reduce the chromatic dispersion effect, which may limit the spatial resolution in long-distance monomode applications.

The temperature distribution sensor <NUM> as disclosed herein may be applicable to multimode applications. In this regard, the temperature distribution sensor <NUM> may require limited tunability (e.g., <NUM> @<NUM>) and a narrower bandpass.

For the temperature distribution sensor <NUM> as disclosed herein, a narrow bandpass filter may be used for the purpose of reducing the chromatic-dispersion-related loss of spatial resolution. This loss may be overcome with relatively large pulse power, and a higher power compared to all existing solutions that are affected by nonlinearity issues. The temperature distribution sensor <NUM> as disclosed herein may include a fiber amplifier and utilize larger peak powers than otherwise possible, which may result in a net gain on the dynamic range.

<FIG> shows a computer system <NUM> that may be used with the examples described herein. The computer system may represent a generic platform that includes components that may be in a server or another computer system. The computer system <NUM> may be used as part of a platform for the sensor controller of <FIG> and/or <FIG>. The computer system <NUM> may execute, by a processor (e.g., a single or multiple processors) or other hardware processing circuit, the methods, functions and other processes described herein. These methods, functions and other processes may be embodied as machine readable instructions stored on a computer readable medium, which may be non-transitory, such as hardware storage devices (e.g., RAM (random access memory), ROM (read only memory), EPROM (erasable, programmable ROM), EEPROM (electrically erasable, programmable ROM), hard drives, and flash memory).

The computer system <NUM> may include a processor <NUM> that may implement or execute machine readable instructions performing some or all of the methods, functions and other processes described herein. Commands and data from the processor <NUM> may be communicated over a communication bus <NUM>. The computer system may also include a main memory <NUM>, such as a random access memory (RAM), where the machine readable instructions and data for the processor <NUM> may reside during runtime, and a secondary data storage <NUM>, which may be non-volatile and stores machine readable instructions and data. The memory and data storage are examples of computer readable mediums. The memory <NUM> may include the sensor controller of <FIG> and/or <FIG> including machine readable instructions residing in the memory <NUM> during runtime and executed by the processor <NUM>.

The computer system <NUM> may include an I/O device <NUM>, such as a keyboard, a mouse, a display, etc. The computer system may include a network interface <NUM> for connecting to a network. Other known electronic components may be added or substituted in the computer system.

The processor <NUM> may be designated as a hardware processor. The processor <NUM> may execute operations associated with various components of the sensor <NUM>. For example, the processor <NUM> may execute operations associated with the sensor controller of <FIG> and/or <FIG>, etc..

What has been described and illustrated herein is an example along with some of its variations. The terms, descriptions and figures used herein are set forth by way of illustration only and are not meant as limitations. Many variations are possible within the scope of the subject matter, which is intended to be defined by the following claims -- and their equivalents -- in which all terms are meant in their broadest reasonable sense unless otherwise indicated. Referring to Equation (<NUM>), R represents the anti-Stokes to Stokes ratio, Δϑ<NUM> represents the mean-weighted average frequency shift for spectral slice <NUM>, and Δϑ<NUM> represents the mean-weighted average frequency shift for spectral slice <NUM>. Equation (<NUM>) may be solved numerically to derive T all along the fiber from a measured ratio.

The temperature distribution sensor <NUM> as disclosed herein may include a single source or a single-band solution. In this regard, the temperature distribution sensor <NUM> may include a relatively small tuning range or dual source, <NUM> broad/apart at <NUM>, <NUM> broad/apart at <NUM>.

Claim 1:
A computer implemented method comprising:
emitting, from a laser source (<NUM>), a laser beam that is tunable over a wavelength range, characterized in that the wavelength range is
less than a Raman bandwidth in a device under test (<NUM>), DUT, or of-the-order-of the Raman bandwidth in the DUT (<NUM>);
applying a pulse drive signal to the laser beam or to a modulator to modulate the laser beam that is to be injected into the DUT (<NUM>);
configuring a bandpass filter (<NUM>) that is operatively disposed between the laser source (<NUM>) and the DUT (<NUM>) to an anti-Stokes wavelength that is narrower than the Raman bandwidth; and
determining a temperature distribution for the DUT (<NUM>) by acquiring, from the DUT (<NUM>), anti-Stokes optical time-domain reflectometer traces for two preset wavelengths of the laser beam.