Patent ID: 7130496

Claim:
A method of determining a spatial distribution of polarisation properties of an optical waveguide, the method comprising: (a) transmitting pulses of polarised light along the optical waveguide from an end of the optical waveguide; (b) detecting a first polarisation state of light emerging from the end of the optical waveguide due to backscattering in the optical waveguide between the end of the optical waveguide and an element of the optical waveguide; (c) detecting a second polarisation state of light that emerges from the end of the optical waveguide due to backscattering in a first section of the element of the optical waveguide; (d) detecting a third polarisation state of light that emerges from the end of the optical waveguide due to backscattering in a second section of the element of the optical waveguide; (e) deducing, from the first polarisation state, linear retardance δ e and orientation of linear retardance axes q e of a retarder/rotator pair equivalent to a portion e of the optical waveguide between end of the optical waveguide and the element; (f) determining the polarisation properties of the element from the second polarisation state, third polarisation state, deduced linear retardance δ e and deduced orientation of linear retardance axes q e ; and (g) repeating steps (a) to (f) for plural elements of the optical waveguide to collate a spatial distribution of polarisation properties of the optical waveguide, wherein the determination of polarisation properties of the elements includes determination of orientation of linear retardance axes of the elements by: repeating (a), (b), (c) and (d) with pulses of light each having different wavelengths; deducing values of circular retardance of a retarder/rotator pair equivalent to a portion e of the optical waveguide between the end of the optical waveguide and each element minus orientation of the linear retardance axes of the respective element, p e –q, for the pulses of light having different wavelengths; and extrapolating the calculated values, p e –q, as p e tends to zero for increasing wavelength to obtain a value for orientation of the linear retardance axes q of each element.