  The paper presents an experimental study of the temporal behaviour of a
bistable vertical cavity surface emitting laser (VCSEL) under the effect of
optical feedback coming from vibrating diffusely-reflecting surface. We
demonstrate that a VCSEL operating in the regime of polarization switchings
caused by self-mixing effects can greatly enhance a responsivity of the
detection of microvibrations. For small amplitudes of microvibrations (less
than $\lambda$/2, where $\lambda$ is the operating wavelength of the laser),
which cause only harmonic (or close to harmonic) oscillations in the laser
output outside of the bistability region, the use of polarization switching can
increase the responsivity up to 45 times. For the amplitudes larger then
$\lambda$/2 the response of a bistable VCSEL well reproduces a fine temporal
structure of the self-mixing signal. A procedure of the data processing in the
switching regime for the correct determination of the direction of the
displacement and for the reconstruction of the waveform of surface vibrations
with a basic resolution of $\lambda$/2 is also shown.
