Abstract: Methods and apparatus for the active control of a wavelength-swept light source used to interrogate optical elements having characteristic wavelengths distributed across a wavelength range are provided.

Abstract: Methods and apparatus for discrete point temperature sensing include a temperature sensor that can be part of an array of temperature sensors for location in a wellbore. A single unitary ribbon-like structure can form the temperature sensor that has separate optical cores possessing different characteristics such that one core is unique from another core. Each core has a reflective grating disposed therein such that the wavelength of light reflected by the gratings is in response to temperature and any strain applied to the sensor from a surrounding environment. For some embodiments, the responses to strain from each of the gratings are similar while the responses from each of the gratings to temperature are dissimilar due to the different characteristics of the cores. These responses provided separately by each grating therefore enable compensation for strain in order to provide an accurate temperature measurement at the sensor.

Abstract: Methods and apparatus allowing distributed temperature sensing (DTS) measurements to be compensated for differential and/or varying loss between Raman Stokes and anti-Stokes signals are provided. By irradiating an optical waveguide with signals at wavelengths at or near the Raman Stokes and anti-Stokes bands, a distributed loss profile for the waveguide may be generated. This distributed loss profile may be used to adjust the amplitudes or amplitude ratios of Raman Stokes and anti-Stokes signals used in DTS measurements, which may lead to more accurate DTS profiles.

Abstract: Methods and apparatus for distributed temperature sensing (DTS) include marking one or more points at known locations along a waveguide or fiber of a distributed temperature sensing (DTS) system and applying position information from such marked locations to DTS measurements. A Bragg grating in the waveguide or fiber may provide a discrete marker for identification of the position information. Application of the position information from such marked locations to the DTS measurements avoids ambiguous interpretations of other inherent features to assess location and enables data analysis referenced by the known locations to correlate the DTS measurements in space.

Abstract: Methods and apparatus enable compensation of source light wavelength fluctuations due to instability of a broadband source within an optical sensing system. Tapping off two or more portions of the light output from the source at specific wavelength bands enables power based measurements of these portions. The measurements provide compensation ability by either use as feedback to control the source or for determination of the central wavelength so that adjustments can be applied to sensor response signals received at a receiver.

Abstract: Methods and apparatus for distributed temperature sensing (DTS) along a single mode or multimode optical waveguide or fiber include a calibration of initial Brillouin-based DTS measurements using Raman-based DTS measurements to enable accurate subsequent Brillouin-based DTS measurements. Such calibration may occur while the fiber is deployed in the environment in which temperature is to be sensed and thereby corrects influences on Brillouin scattered light from stress or strain along the fiber. Further, calibration may utilize one or more discrete temperature sensors to correct errors in one or both of the Brillouin-based DTS measurements and the Raman-based DTS measurements.

Abstract: Methods and apparatus for discrete point temperature sensing include a temperature sensor that can be part of an array of temperature sensors for location in a wellbore. A single unitary ribbon-like structure can form the temperature sensor that has separate optical cores possessing different characteristics such that one core is unique from another core. Each core has a reflective grating disposed therein such that the wavelength of light reflected by the gratings is in response to temperature and any strain applied to the sensor from a surrounding environment. For some embodiments, the responses to strain from each of the gratings are similar while the responses from each of the gratings to temperature are dissimilar due to the different characteristics of the cores. These responses provided separately by each grating therefore enable compensation for strain in order to provide an accurate temperature measurement at the sensor.

Abstract: Methods and apparatus enable compensation of source light wavelength fluctuations due to instability of a broadband source within an optical sensing system. Tapping off two or more portions of the light output from the source at specific wavelength bands enables power based measurements of these portions. The measurements provide compensation ability by either use as feedback to control the source or for determination of the central wavelength so that adjustments can be applied to sensor response signals received at a receiver.

Abstract: Methods and apparatus for sampling techniques can constantly monitor a spectral output from a broadband source in order to control a central wavelength of interrogation light supplied by the source for input to a sensor. A first portion of light output from the broadband source passes through a controller module for spectral analysis and referencing to provide measurements that can be used as feedback to actively modify a second portion of the light from the source. This modified second portion thereby controls the central wavelength to ensure accurate determination of sensor response signals received at a receiver.

Abstract: A method and apparatus for mitigating the effects of polarization on wavelength determinations is disclosed. An optical source produces light across an optical spectrum, while a polarization element changes the polarization of the light at a first rate. The resulting light is applied to an optical element that produces a spectral response with a feature of interest from the polarization changed light. The optical element and the polarization element are such that the bandwidth of the feature of interest of the optical element is significantly greater than the first rate. A receiver network produces received signals from the received spectrum; and a data processing unit calculates a wavelength that is insensitive to ripple in the received signal and/or the received signals are low-pass filtered to reduce the ripple resulting from the polarization change.

Abstract: Methods and apparatus for distributed temperature sensing (DTS) along a single mode or multimode optical waveguide or fiber include a calibration of initial Brillouin-based DTS measurements using Raman-based DTS measurements to enable accurate subsequent Brillouin-based DTS measurements. Such calibration may occur while the fiber is deployed in the environment in which temperature is to be sensed and thereby corrects influences on Brillouin scattered light from stress or strain along the fiber. Further, calibration may utilize one or more discrete temperature sensors to correct errors in one or both of the Brillouin-based DTS measurements and the Raman-based DTS measurements.

Abstract: Method and apparatus enable optical evanescent sensing utilizing a waveguide with an annular core. The annular core can provide detectable sensitivity to a measurand due to optical interactions with contents along an inside surface of the annular core since optical properties of the contents vary with changes in the measurand.

Abstract: Methods and apparatus enable monitoring conditions in a well-bore using multiple cane-based sensors. The apparatus includes an array of cane-based Bragg grating sensors located in a single conduit for use in the well-bore. For some embodiments, each sensor is located at a different linear location along the conduit allowing for increased monitoring locations along the conduit.

Abstract: Methods and apparatus for discrete point temperature sensing include a temperature sensor that can be part of an array of temperature sensors for location in a wellbore. A single unitary ribbon-like structure can form the temperature sensor that has separate optical cores possessing different characteristics such that one core is unique from another core. Each core has a reflective grating disposed therein such that the wavelength of light reflected by the gratings is in response to temperature and any strain applied to the sensor from a surrounding environment. For some embodiments, the responses to strain from each of the gratings are similar while the responses from each of the gratings to temperature are dissimilar due to the different characteristics of the cores. These responses provided separately by each grating therefore enable compensation for strain in order to provide an accurate temperature measurement at the sensor.

Abstract: Methods and apparatus enable monitoring conditions in a well-bore using multiple cane-based sensors. The apparatus includes an array of cane-based Bragg grating sensors located in a single conduit for use in the well-bore. For some embodiments, each sensor is located at a different linear location along the conduit allowing for increased monitoring locations along the conduit.

Abstract: Methods and apparatus for the active control of a wavelength-swept light source used to interrogate optical elements having characteristic wavelengths distributed across a wavelength range are provided.

Abstract: A method and apparatus for improving the sensing of a physical parameter using a distributed optical waveguide and scattering. The optical waveguides have improved scattering efficiency and/or improved light capturing capability provided by multi-cladding layers and a tightly confining core waveguide. The core can be highly doped with a material such as germanium to improve scattering. The cladding layers provide a multi-mode waveguide for capturing scattered light. Such optical waveguides are useful in systems that rely on Rayleigh, Raman and Brillouin scattering.

Abstract: A method and apparatus for mitigating the effects of polarization on wavelength determinations is disclosed. An optical source produces light across an optical spectrum, while a polarization element changes the polarization of the light at a first rate. The resulting light is applied to an optical element that produces a spectral response with a feature of interest from the polarization changed light. The optical element and the polarization element are such that the bandwidth of the feature of interest of the optical element is significantly greater than the first rate. A receiver network produces received signals from the received spectrum; and a data processing unit calculates a wavelength that is insensitive to ripple in the received signal and/or the received signals are low-pass filtered to reduce the ripple resulting from the polarization change.

Abstract: Methods and apparatus allowing distributed temperature sensing (DTS) measurements to be compensated for differential and/or varying loss between Raman Stokes and anti-Stokes signals are provided. By irradiating an optical waveguide with signals at wavelengths at or near the Raman Stokes and anti-Stokes bands, a distributed loss profile for the waveguide may be generated. This distributed loss profile may be used to adjust the amplitudes or amplitude ratios of Raman Stokes and anti-Stokes signals used in DTS measurements, which may lead to more accurate DTS profiles.

Abstract: A method and apparatus for mitigating the effects of polarization on wavelength determinations is disclosed. An optical source produces light across an optical spectrum, while a polarization element changes the polarization of the light at a first rate. The resulting light is applied to an optical element that produces a spectral response with a feature of interest from the polarization changed light. The optical element and the polarization element are such that the bandwidth of the feature of interest of the optical element is significantly greater than the first rate. A receiver network produces received signals from the received spectrum; and a data processing unit calculates a wavelength that is insensitive to ripple in the received signal and/or the received signals are low-pass filtered to reduce the ripple resulting from the polarization change.