Abstract: A method implemented by computer for simulating an optical system includes the steps consisting in: a) defining a set of light rays or beams at the input (e) of the optical system, each the light ray or beam being represented by a first vector of parameters; and b) calculating, for each the light ray or beam at the input of the optical system, a light ray or beams at the output (s) of the optical system, represented by a second vector of parameters by applying, to each the light ray or beam at the input of the optical system, one and the same nonlinear function, termed the transmission function, representative of the optical system as a whole. A computer program product for the implementation of such a method is also provided.