The invention relates to a Doppler frequency shift measuring device of the
optical type comprising an optical signal channel delivering, through a
polarization-splitting coupler, through a bidirectional signal port of
the coupler, a signal light beam illuminating a reference medium, the
coupler receiving, through said bidirectional port, a backscattered light
beam returned by the reference medium; a reference channel providing a
reference light beam for detection of the Doppler frequency shift, the
frequency shift being determined by the frequency shift between the light
signal illuminating the reference medium and the light beam returned by
the reference medium. The reference light beam is applied to a reference
port of the polarization-splitting coupler, said coupler delivering, at a
port, a beat signal between the frequency of the reference light beam
applied to the port and the frequency of the backscattered light beam
applied to the port, possibly containing the Doppler shift.