US 2021/0278255 A1 · Method and Apparatus for Optical Sensing

Abstract

Embodiments of the invention provide an improved optical fiber distributed acoustic sensor system that makes use of an optical fiber having reflector portions distributed along its length in at least a first portion. In particular, in order to increase the spatial resolution of the sensor system to the maximum, the reflector portions are positioned along the fiber separated by a distance that is equivalent to twice the distance an optical pulse travels along the fiber in a single sampling period of the data acquisition opto-electronics within the sensor system. As such, no oversampling of the reflections of the optical pulses from the reflector portions is undertaken, which means that it is important that the sampling points for data acquisition in the sensor system are aligned with the reflections that arrive at the sensor system from along the sensing fiber. In order to ensure such alignment, adaptive delay componentry may be used to adaptively align the reflected optical signals (or their electrical analogues) with the sampling points. Alternatively, control over the sampling points can also be undertaken to re-synchronise the sampling points with the returning reflections. In addition, in order to allow higher speed sampling to be undertaken, reflection equalisation componentry may also be used to reduce the dynamic range of the returning reflections.

Claims14

Dependent claims

A distributed sensing system, comprising:

an optical fiber deployable in an environment to be sensed, the optical fiber having reflector portions regularly distributed in at least a first region thereof and having a first fixed and known spacing therebetween;
an optical signal source arranged in use to input optical pulses into the optical fiber;
and
sensing apparatus arranged in use to detect light from the optical pulses reflected back along the optical fiber from the reflector portions and to determine any one or more of an acoustic, vibration, strain, temperature or other parameter that perturbs the path length of the optical fiber in dependence on the reflected light, the sensing apparatus comprising opto-electronic componentry that samples the reflected light or light derived therefrom at temporally discrete sampling points at a first sampling rate;
wherein the first sampling rate is of a value that is at or near to the Nyquist limit for the fixed and known spacing between the reflector portions in the at least first region of the optical fiber such that no oversampling occurs, and
the sensing apparatus further comprises signal level adjustment circuitry arranged to equalise the amplitude of the reflected light from the reflector portions received at the sensing apparatus.

3 more elements

A distributed sensing system, comprising:

an optical fiber deployable in an environment to be sensed, the optical fiber having reflector portions regularly distributed in at least a first region thereof and having a first spacing therebetween;
an optical signal source arranged in use to input optical pulses into the optical fiber;
and
sensing apparatus arranged in use to detect light from the optical pulses reflected back along the optical fiber from the reflector portions and to determine any one or more of an acoustic, vibration, strain, temperature or other parameter that perturbs the path length of the optical fiber in dependence on the reflected light, the sensing apparatus comprising opto-electronic componentry that samples the reflected light or light derived therefrom at temporally discrete sampling points at a first known sampling rate that gives a first known sampling period;
wherein the first spacing between each of the reflector portions in the at least first region of the optical fiber is of a size that is at least twice the distance travelled by the optical pulses along the fiber in one of the first known sampling periods, such that the first sampling rate is at or near to the Nyquist limit and no oversampling occurs;
and
the sensing apparatus further comprises signal level adjustment circuitry arranged to equalise the amplitude of the reflected light from the reflector portions received at the sensing apparatus.

4 more elements

Dependencies are inferred from the claim text.

Method and Apparatus for Optical Sensing

Life of this patent

Method and Apparatus for Optical Sensing

Life of this patent

Abstract

Claims14