This application described methods and apparatus for distributed fibre optic sensing. A sensing apparatus has a modulator which modulates radiation from an optical source to interrogate a sensing optical fibre with a first interrogation pulse at a first frequency (F1) and a second interrogation pulse at a second, different, frequency (F2), both different in frequency from a local oscillator (LO). A mixer mixes backscatter from the sensing optical fibre with the local oscillator and supplies the mixed signal to a detector that provides a corresponding digital signal. A processor processes the digital signal (DX, DY) in a first and second processing channels to demodulate respective first and second phase signals based on the respective frequency difference between the first and second frequency and the local oscillator and determines a temporal difference between the first and second phase signals.

This application described methods and apparatus for distributed fibre optic sensing. A sensing apparatus has a modulator which modulates radiation from an optical source to interrogate a sensing optical fibre with a first interrogation pulse at a first frequency (F1) and a second interrogation pulse at a second, different, frequency (F2), both different in frequency from a local oscillator (LO). A mixer mixes backscatter from the sensing optical fibre with the local oscillator and supplies the mixed signal to a detector that provides a corresponding digital signal. A processor processes the digital signal (DX, DY) in a first and second processing channels to demodulate respective first and second phase signals based on the respective frequency difference between the first and second frequency and the local oscillator and determines a temporal difference between the first and second phase signals.

Methods and systems for characterizing fractures in a subterranean formation are provided. The method includes introducing an encapsulated explosive unit into a casing located in a wellbore within the subterranean formation and maintaining the encapsulated explosive unit in a stage of the casing. The method also includes detonating the encapsulated explosive unit within the stage to generate a pressure wave that passes through a group of perforations and into the fractures and measuring a reflected pressure wave using a pressure sensor coupled to the bridge plug to produce a pressure measurement. The method further includes converting the pressure measurement into an acoustic signal correlated with the pressure measurement by an acoustic signal generator contained in the bridge plug and transmitting the acoustic signal to apply acoustic pressure on a fiber optic cable coupled to an exterior surface of the casing.

Methods and systems for characterizing fractures in a subterranean formation are provided. The method includes introducing an encapsulated explosive unit into a casing located in a wellbore within the subterranean formation and maintaining the encapsulated explosive unit in a stage of the casing. The method also includes detonating the encapsulated explosive unit within the stage to generate a pressure wave that passes through a group of perforations and into the fractures and measuring a reflected pressure wave using a pressure sensor coupled to the bridge plug to produce a pressure measurement. The method further includes converting the pressure measurement into an acoustic signal correlated with the pressure measurement by an acoustic signal generator contained in the bridge plug and transmitting the acoustic signal to apply acoustic pressure on a fiber optic cable coupled to an exterior surface of the casing.

A plasma processing chamber optical temperature sensor is disclosed. The plasma processing chamber optical temperature sensor includes a light source, a light detector, and a means for transmitting light through a wall of a plasma processing chamber. An optical temperature sensing element is thermally coupled to a plasma processing chamber component within the plasma processing chamber. The optical temperature sensing element includes a monolithic crystalline phosphor element configured to be excited by light from the light source and to emit light back to the light detector indicative of a temperature of the monolithic crystalline phosphor element.

A plasma processing chamber optical temperature sensor is disclosed. The plasma processing chamber optical temperature sensor includes a light source, a light detector, and a means for transmitting light through a wall of a plasma processing chamber. An optical temperature sensing element is thermally coupled to a plasma processing chamber component within the plasma processing chamber. The optical temperature sensing element includes a monolithic crystalline phosphor element configured to be excited by light from the light source and to emit light back to the light detector indicative of a temperature of the monolithic crystalline phosphor element.

A temperature sensor used in a molding machine is provided. The temperature sensor comprises a cylindrical fiber probe through which an optical fiber is inserted; an outer housing having a shaft, into which the fiber probe is inserted to be displaceable in an axial direction; a protective window disposed on a tip end side of the fiber probe and configured to protect a tip end of the fiber probe; and an elastic member that presses the fiber probe toward the protective window.

A temperature sensor used in a molding machine is provided. The temperature sensor comprises a cylindrical fiber probe through which an optical fiber is inserted; an outer housing having a shaft, into which the fiber probe is inserted to be displaceable in an axial direction; a protective window disposed on a tip end side of the fiber probe and configured to protect a tip end of the fiber probe; and an elastic member that presses the fiber probe toward the protective window.

Example embodiments include an optical assembly for an optical interrogation system having a single core or a multicore sensing fiber, a measurement fiber to couple light into the sensing fiber, and a reference fiber arranged with the measurement fiber as part of an optical interferometer. A beam splitter combines light from the sensing fiber and with light from the reference fiber. A polarization beam splitting prism separates the combined light into first polarized light and second polarized light that is orthogonal to the first polarized light. The optical assembly can substantially reduce the size, complexity, or cost associated with the traditional optical components in an optical interrogation system that it replaces. Other example optical assemblies are described. Embodiments describe optical interrogation systems using the example optical assemblies.

An optical fiber sensing system, method and apparatus for simultaneously measuring temperature, strain, and pressure are provided and belong to the field of optical fiber sensors. A distributed optical fiber temperature sensor is configured to monitor the temperature, and transmit the monitored temperature to a fiber grating strain and pressure sensor; the fiber grating strain and pressure sensor performs self temperature compensation based on received temperature; and the fiber grating strain and pressure sensor monitors the strain and the pressure. The distributed optical fiber temperature sensor is used to replace a temperature compensation function of the fiber grating strain sensor, and sense temperature distribution of each point along a route. Further, the fiber grating strain and pressure sensor is simplified inside, temperature demodulation is no longer required and speed of obtaining values of the strain and the pressure has been accelerated.