A method for use in controlling light transmission through a medium, the method comprising the steps of: (i) transmitting light corresponding to a selected spatial portion of an input optical field and a selected input polarisation state through the medium to create a corresponding output optical field; (ii) superposing the corresponding output optical field with a reference optical field to create a corresponding optical interference field; (iii) detecting an intensity of a spatial portion of a selected polarisation component of the corresponding optical interference field; (iv) using the detected intensity to determine a value of an optical field amplitude and a value of an optical field phase corresponding to the selected spatial portion of the input optical field and the selected input polarisation state; and (v) repeating steps (i) to (iv) for each selected spatial portion of a plurality of spatial portions of the input optical field and for each selected input polarisation state of first and second orthogonal input polarisation states, wherein each iteration of steps (i) to (iii) is performed sequentially so that each iteration of steps (i) to (iii) provides the detected intensity corresponding to a selected one of the plurality of spatial portions of the input optical field in combination with a corresponding selected one of the first and second orthogonal input polarisation states, wherein step (iii) comprises detecting a variation in the intensity of the spatial portion of the selected polarisation component of the corresponding optical interference field for the selected spatial portion of the input optical field and for the selected input polarisation state whilst varying a phase applied to the selected spatial portion of the input optical field, and wherein step (iv) comprises determining the optical field amplitude value and the optical field phase value for the selected spatial portion of the input optical field and for the selected input polarisation state from the detected variation in the intensity of the spatial portion of the selected polarisation component of the corresponding optical interference field as a function of the phase applied to the selected spatial portion of the input optical field. (i) transmitting light corresponding to a selected spatial portion of an input optical field and a selected input polarisation state through the medium to create a corresponding output optical field; (ii) superposing the corresponding output optical field with a reference optical field to create a corresponding optical interference field; (iii) detecting an intensity of a spatial portion of a selected polarisation component of the corresponding optical interference field; (iv) using the detected intensity to determine a value of an optical field amplitude and a value of an optical field phase corresponding to the selected spatial portion of the input optical field and the selected input polarisation state; and (v) repeating steps (i) to (iv) for each selected spatial portion of a plurality of spatial portions of the input optical field and for each selected input polarisation state of first and second orthogonal input polarisation states, wherein each iteration of steps (i) to (iii) is performed sequentially so that each iteration of steps (i) to (iii) provides the detected intensity corresponding to a selected one of the plurality of spatial portions of the input optical field in combination with a corresponding selected one of the first and second orthogonal input polarisation states, wherein step (iii) comprises detecting a variation in the intensity of the spatial portion of the selected polarisation component of the corresponding optical interference field for the selected spatial portion of the input optical field and for the selected input polarisation state whilst varying a phase applied to the selected spatial portion of the input optical field, and wherein step (iv) comprises determining the optical field amplitude value and the optical field phase value for the selected spatial portion of the input optical field and for the selected input polarisation state from the detected variation in the intensity of the spatial portion of the selected polarisation component of the corresponding optical interference field as a function of the phase applied to the selected spatial portion of the input optical field.