In interferometric Bragg cell-type spectrum analysers with a reference Bragg cell, the reference light generated by this Bragg cell generates an interfering background which should be avoided. For this purpose, a device (RE) for mutually separated generation of reference light rays (Ri) and separated superposition of light (S) deflected by the signal Bragg cell (BZ) on the reference light rays (Ri) is used instead of the conventional reference Bragg cell. Used for spectrum analysis of radio-frequency signals. <IMAGE>
