An optical device (10) for determining a physical parameter includes: a laser diode (11) for emitting a beam toward a target; an element for detecting (13) an interferometric signal SM(t) which includes the information on the physical parameter to be determined, and which is generated by an interference between the emitted beam and a light beam reflected by the target; element for converting (15) the signal SM(t) obtained by the detection element (13) into a measurement of the physical parameter, the conversion element (15) including: first element (17) for suppressing a continuous component Off(t) of the interferometric signal SM(t); second element (18) for determining interferometric peaks in the interferometric signal SM(t) obtained from the signal obtained at the output of the first element (17). An associated method, particularly suitable for speckle interferometric signals is also described.