Conjugation of space and time variables in optics

A review of the main landmarks which proceed the fundamentals of space‐time optics is given. It includes a comparison of the roles of space and time variables in optics as far as information transfer is concerned. Illustrations deal with interference and diffraction phenomena, the light beam being considered as a carrier whose capacity is linked to the width of the spectral band. Experimental examples are reported in metrology, information processing, spectral analysis and wavelength coding, holography, transmission by spectral modulation, etc.