Abstract: A method and apparatus sense attributes of reflected signals in an optical sensing system. In one embodiment, a method for sensing in an optical sensing system comprising an interrogator coupled to a Bragg grating sensor by an optical cable includes the steps of producing a first optical signal, coupling the first optical signal to an optical cable, receiving a first reflected signal from a Bragg grating sensor within the optical cable, resolving a wavelength of first reflected signal, producing a second optical signal, coupling the second optical signal to the optical cable, receiving a second reflected signal caused by Brillouin backscattering within the optical cable, and resolving a difference in frequencies between the second optical signal and second reflected signal. Embodiments of the method and apparatus are particularly useful for sensing temperature and strain in hazardous locations such as down hole gas and oil field applications and the like.

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 sense attributes of reflected signals in an optical sensing system. In one embodiment, a method for sensing in an optical sensing system comprising an interrogator coupled to a Bragg grating sensor by an optical cable includes the steps of producing a first optical signal, coupling the first optical signal to an optical cable, receiving a first reflected signal from a Bragg grating sensor within the optical cable, resolving a wavelength of first reflected signal, producing a second optical signal, coupling the second optical signal to the optical cable, receiving a second reflected signal caused by Brillouin backscattering within the optical cable, and resolving a difference in frequencies between the second optical signal and second reflected signal. Embodiments of the method and apparatus are particularly useful for sensing temperature and strain in hazardous locations such as down hole gas and oil field applications and the like.

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: Embodiments of the present invention provide various methods to fabricate optical fibers with reduced radiation sensitivity. Optical fibers are treated to one or more secondary or post-processing “conditioning” steps to create and anneal residual defects in the glass for improved radiation insensitivity.

Abstract: Disclosed herein is an optical sensor design and method for continually interrogating that sensor to produce an accurate representation of a dynamic event (such as a change in strain, pressure or temperature) being monitored by the sensor. The sensor design preferably constitutes continuous wave optical source/detection equipment coupled in series to a first fiber Bragg grating (FBG), a long period grating (LPG), and a second FBG formed in an optical waveguide. The LPG broadly attenuates light in the vicinity of the Bragg reflection wavelength ?2B of the second FBG, and this attenuation profile shifts in wavelength in accordance with the dynamic event being monitored. Perturbation of the attenuation profile thus attenuates the intensity of the light reflected from the second FBG, i.e., I(?B2), because such reflected light must pass (twice) through the LPG. Accordingly, continually monitoring I(?B2) as a function of time allows the dynamic event to be recreated and processed accordingly.

Abstract: The present invention provides a new and unique method for increasing the photosensitivity of a large diameter optical waveguide having a cross-section of at least about 0.3 millimeters. The method features loading the large diameter optical waveguide with a photosensitizing gas at a pressure at least about 4000 pounds per square inch (PSI) at a temperature of at least about 250° Celsius. The photosensitizing gas may be hydrogen, Deuterium or other suitable gas. The method also includes the step of using a particular large diameter optical waveguide having a core more than 1000 microns from the surface thereof. The method may be used as part of a process for writing a Bragg grating in an inner core or a cladding of the large diameter optical waveguide.

Abstract: A method and apparatus for sensing temperature using optical fiber is provided. In one embodiment, a method for sensing temperature using optical fiber includes launching a polarized optical signal having sufficient intensity to produce Brillouin scattering of the signal into a polarization maintaining optical fiber, receiving a first signal reflected from the launched signal, receiving a second signal reflected from the launched signal; and resolving a metric indicative of temperature from the first and second received signals. The method is particularly useful for sensing temperature in hazardous locations such as down hole gas and oil field applications or other applications where minimization of strain effects to signal transmission is desired.

Abstract: A method and apparatus for sensing temperature using optical fiber is provided. In one embodiment, a method for sensing temperature using optical fiber includes launching a polarized optical signal having sufficient intensity to produce Brillouin scattering of the signal into a polarization maintaining optical fiber, receiving a first signal reflected from the launched signal, receiving a second signal reflected from the launched signal; and resolving a metric indicative of temperature from the first and second received signals. The method is particularly useful for sensing temperature in hazardous locations such as down hole gas and oil field applications or other applications where minimization of strain effects to signal transmission is desired.

Abstract: Disclosed herein is an accelerometer and/or displacement device that uses a mass coupled to a rhomboidal flexure to provide compression to an optical sensing element preferably having a fiber Bragg grating (FBG). The transducer includes a precompressed optical sensor disposed along a first axis between sides of the flexure. The top portion of the flexure connects to the mass which intersects the flexure along a second axis perpendicular to the first axis. When the mass experiences a force due to acceleration or displacement, the flexure will expand or contract along the second axis, which respectively compresses or relieves the compression of the FBG in the optical sensing element along the first axis. Perturbing the force presented to the FBG changes its Bragg reflection wavelength, which is interrogated to quantify the dynamic or constant force.

Abstract: A fluid diffusion resistant tube-encased fiber grating pressure sensor includes an optical fiber 10 having a Bragg grating 12 impressed therein which is encased within a sensing element, such as a glass capillary shell 20. A fluid blocking coating 30 is disposed on the outside surface of the capillary shell to prevent the diffusion of fluids, such as water molecules from diffusing into the shell. The fluid diffusion resistant fiber optic sensor reduces errors caused by the diffusion of water into the shell when the sensor is exposed to harsh conditions.

Abstract: A method and apparatus for sensing temperature using optical fiber is provided. In one embodiment, a method for sensing temperature using optical fiber includes launching a polarized optical signal having sufficient intensity to produce Brillouin scattering of the signal into a polarization maintaining optical fiber, receiving a first signal reflected from the launched signal, receiving a second signal reflected from the launched signal; and resolving a metric indicative of temperature from the first and second received signals. The method is particularly useful for sensing temperature in hazardous locations such as down hole gas and oil field applications or other applications where minimization of strain effects to signal transmission is desired.

Abstract: A method and apparatus for sensing attributes of reflected signals in an optical fiber sensing system is provided. In one embodiment, a method for sensing in an optical fiber sensing system comprising an interrogator coupled to a Bragg grating sensor by an optical cable includes the steps of producing a first optical signal, coupling the first optical signal to an optical cable, receiving a first reflected signal from a Bragg grating sensor within the optical cable, resolving a wavelength of first reflected signal, producing a second optical signal, coupling the second optical signal to the optical cable, receiving a second reflected signal caused by Brillouin backscattering within the optical cable, and resolving a difference in frequencies between the second optical signal and second reflected signal. Embodiments of the method and apparatus are particularly useful for sensing temperature and strain in hazardous locations such as down hole gas and oil field applications and the like.

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: A method and apparatus for removing optical noise from an optical system. A light source produces optical signals applied to a remote optical element that produces reflected optical signals and is subject to optical background noise such as reflections from splices and optical connections. Part of the reflected optical signals and at least some of the background noise is applied to a receiver. The receiver output is analyzed to determine either the amount of noise (if broadband) or the frequency components of the noise. If broadband, the noise is subtracted from the composite signal, thus increasing the signal to noise ratio. If periodic, the frequency components of the noise are gated out of the receiver output.

Abstract: Disclosed herein is an optical sensor design and method for continually interrogating that sensor to produce an accurate representation of a dynamic event (such as a change in strain, pressure or temperature) being monitored by the sensor. The sensor design preferably constitutes continuous wave optical source/detection equipment coupled in series to a first fiber Bragg grating (FBG), a long period grating (LPG), and a second FBG formed in an optical waveguide. The LPG broadly attenuates light in the vicinity of the Bragg reflection wavelength &lgr;2B of the second FBG, and this attenuation profile shifts in wavelength in accordance with the dynamic event being monitored. Perturbation of the attenuation profile thus attenuates the intensity of the light reflected from the second FBG, i.e., I(&lgr;B2), because such reflected light must pass (twice) through the LPG. Accordingly, continually monitoring I(&lgr;B2) as a function of time allows the dynamic event to be recreated and processed accordingly.

Abstract: Disclosed herein is an accelerometer and/or displacement device that uses a mass coupled to a rhomboidal flexure to provide compression to an optical sensing element preferably having a fiber Bragg grating (FBG). The transducer includes a precompressed optical sensor disposed along a first axis between sides of the flexure. The top portion of the flexure connects to the mass which intersects the flexure along a second axis perpendicular to the first axis. When the mass experiences a force due to acceleration or displacement, the flexure will expand or contract along the second axis, which respectively compresses or relieves the compression of the FBG in the optical sensing element along the first axis. Perturbing the force presented to the FBG changes its Bragg reflection wavelength, which is interrogated to quantify the dynamic or constant force.

Abstract: A method and apparatus for sensing temperature using optical fiber is provided. In one embodiment, a method for sensing temperature using optical fiber includes launching a polarized optical signal having sufficient intensity to produce Brillouin scattering of the signal into a polarization maintaining optical fiber, receiving a first signal reflected from the launched signal, receiving a second signal reflected from the launched signal; and resolving a metric indicative of temperature from the first and second received signals. The method is particularly useful for sensing temperature in hazardous locations such as down hole gas and oil field applications or other applications where minimization of strain effects to signal transmission is desired.

Abstract: A temperature compensated optical device includes a compression-tuned glass element 10 having a Bragg grating 12 therein, a compensating material spacer 26 and an end cap 28 all held within an outer shell 30. The element 10, end cap 28 and shell 30 are made of a material having a low coefficient of thermal expansion (CTE), e.g., silica, quartz, etc. and the spacer 26 is made of a material having a higher CTE, e.g., metal, Pyrex®, ceramic, etc. The material and length L5 of the spacer 26 is selected to offset the upward grating wavelength shift due to temperature. As temperature rises, the spacer 26 expands faster than the silica structure causing a compressive strain to be exerted on the element 10, which shifts the wavelength of the grating 12 down to balance the intrinsic temperature induces wavelength shift up. As a result, the grating 12 wavelength is substantially unchanged over a wide temperature range.