A distributed acoustic system (DAS) with an interrogator, an umbilical line attached at one end to the interrogator, and a downhole fiber attached to the umbilical line at the end opposite the interrogator. A method for optimizing a sampling frequency may begin with identifying a length of a fiber optic cable connected to an interrogator, identifying one or more regions on the fiber optic cable in which a backscatter is received, and optimizing a sampling frequency of a distributed acoustic system (DAS) by identifying a minimum time interval that is between an emission of a light pulse such that at no point in time the backscatter arrives back at the interrogator that corresponds to more than one spatial location along a sensing portion of the fiber optic cable.

Example embodiments add an optical amplifier to an multi-channel, continuously swept OFDR measurement system, adjust amplified swept laser output power between rising and falling laser sweeps, and/or utilize portions of a laser sweep in which OFDR measurements are not typically performed to enhance the integrity of the OFDR measurement system, improve the performance and quality of OFDR measurements, and perform additional measurements and tests.

A high-speed interrogation system is provided for interferometric sensors, one example of which is an EFPI sensor, that operates based on spectral interference. The system uses a two mode operation that includes a lower speed, accurate absolute measurement mode and a higher speed, relative measurement mode. The system achieves greater overall measurement accuracy and speed than known sensor interrogation approaches.

An optomechanical system including a guide structure, to guide a light beam; and two waveguide segments. Each guide structure include beams that together form two combs partially nested one in the other. At least one beam is free to move in translation along an axis orthogonal to the long axis of the guide structure. A displacement into an optical phase shift, while limiting additional effects on the intensity.

The present invention provides novel apparatus and methods for fast quantitative measurement of perturbation of optical fields transmitted, reflected and/or scattered along a length of an optical fibre. The present invention can be used for point sensors as well as distributed sensors or the combination of both. In particular this technique can be applied to distributed sensors while extending dramatically the speed and sensitivity to allow the detection of acoustic perturbations anywhere along a length of an optical fibre while achieving fine spatial resolution. The present invention offers unique advantages in a broad range of acoustic sensing and imaging applications. Typical uses are for monitoring oil and gas wells such as for distributed flow metering and/or imaging, seismic imaging, monitoring long cables and pipelines, imaging within large vessel as well as for security applications.

The present invention provides novel apparatus and methods for fast quantitative measurement of perturbation of optical fields transmitted, reflected and/or scattered along a length of an optical fibre. The present invention can be used for point sensors as well as distributed sensors or the combination of both. In particular this technique can be applied to distributed sensors while extending dramatically the speed and sensitivity to allow the detection of acoustic perturbations anywhere along a length of an optical fibre while achieving fine spatial resolution. The present invention offers unique advantages in a broad range of acoustic sensing and imaging applications. Typical uses are for monitoring oil and gas wells such as for distributed flow metering and/or imaging, seismic imaging, monitoring long cables and pipelines, imaging within large vessel as well as for security applications.

A fibre optic sensing device is provided. The fibre optic sensing device comprises a plurality of optical fibre portions, wherein each optical fibre portion is arranged to receive laser light from a common laser and reflect the laser light to a common detector, wherein each optical fibre portion comprises a first reflector spaced from a distal end of the optical fibre portion and a second reflector at the distal end, wherein each optical fibre portion comprises a sensor provided at the respective distal end of the optical fibre portion, the sensor comprising a third reflector the position of which varies depending on a value of a property being sensed, wherein a distance between the first and second reflectors is different for each of the optical fibre portions.

Example embodiments add an optical amplifier to an multi-channel, continuously swept OFDR measurement system, adjust amplified swept laser output power between rising and falling laser sweeps, and/or utilize portions of a laser sweep in which OFDR measurements are not typically performed to enhance the integrity of the OFDR measurement system, improve the performance and quality of OFDR measurements, and perform additional measurements and tests.

Various embodiments of sensors are described that exhibit several spectral features that together offer coverage of a wavelength range corresponding to the desired strain dynamic range (or temperature range) of a system. The spectral features arise from a Fabry-Perot interferometer formed by two overlapping chirped FBGs, the free-spectral range (FSR) of which varies with wavelength. The spectral features may be differentiated due to a combination of spacing and slope of the overlapped, chirped gratings.

The disclosure discloses a phase delay extraction and compensation method in a PGC phase demodulation technology. The sinusoidal phase modulation interference signal is converted into a digital interference signal by an analog-to-digital converter after amplification and filtering, and the digital interference signal is subjected to orthogonal downmixing of first-order, second-order, and fourth-order harmonics simultaneously to obtain three pairs of orthogonal harmonic amplitude signals. The three pairs of orthogonal harmonic amplitude signals are used to extract phase delay, and the result is used to calculate the corresponding phase delay correction coefficients, and the phase delay correction coefficient are multiplied by the corresponding absolute harmonic amplitude signal equal to the sum of the absolute value of the orthogonal harmonic amplitude signals to obtain a new harmonic amplitude signal that is not affected by the phase delay, then the phase to be measured is obtained through the arc tangent operation.