Abstract: A pressure sensing apparatus has a light source for transmitting pulses of light along a monomode optical fibre. The polarisation of light backscattered from the light pulses in the optical fibre is detected by a polarisation processing unit (PPU) and a photo detector. The optical fibre 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 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 is such that the birefringence beat length of the optical fibre at the wavelength of light propagated by the fibre remains more than twice the spatial length of the light pulses transmitted along the optical fibre.