Method and apparatus for determining scattering parameters of a scattering matrix of an optical device. A method according to the present invention comprises applying an optical stimulus to a plurality of ports of the optical device, measuring optical fields emerging from the plurality of ports in amplitude and phase, and calculating the scattering parameters using the measured optical fields. The applying step includes applying the optical stimulus to the plurality of ports simultaneously. The method ensures a consistent phase reference for measurement of all of the scattering parameters so that all measurable characteristics of the device can be calculated directly from the scattering parameters.