  We present the full implementation of a room-temperature gravitational wave
bar detector equipped with an opto-mechanical readout. The mechanical
vibrations are read by a Fabry--Perot interferometer whose length changes are
compared with a stable reference optical cavity by means of a resonant laser.
The detector performance is completely characterized in terms of spectral
sensitivity and statistical properties of the fluctuations in the system output
signal. The new kind of readout technique allows for wide-band detection
sensitivity and we can accurately test the model of the coupled oscillators for
thermal noise. Our results are very promising in view of cryogenic operation
and represent an important step towards significant improvements in the
performance of massive gravitational wave detectors.
