Method and apparatus for detecting pressure distribution in fluids

A pressure sensing apparatus (100) has a light source (102) for transmitting pulses of light along a monomode optical fibre (110). The polarisation of light backscattered from the light pulses in the optical fibre (110) is detected by a polarisation processing unit (PPU) (104) and a photo detector (16). The optical fibre (110) is adapted to deform asymmetrically under the influence of applied external isotropic pressure, e.g. from a fluid. The deformation causes the birefringence of the optical fibre (110) to change proportionally to the applied pressure. The change in birefringence can be determined from the detected polarisation of the backscattered light, allowing detection of pressure distribution in the fluid. Importantly, the construction of the optical fibre (110) is such that the birefringence beat length of the optical fibre (110) at the wavelength of light propagated by the fibre (110) remains more than twice the spatial length of the light pulses transmitted along the optical fibre (110). Applications of the invention include detection of fluid flow; location of an interface between two fluids of different density; and tsunami detection.