Noise in an FM-Converted Self-Mixing Interferometer

We measure the noise of the converted frequency-modulated (cFM) signal in a self-mixing interferometer (SMI) and confirm the theoretical prediction of a dependence of rms noise from ( 1+ C)-1 , where C is the Acket feedback factor, up to a high value (i.e., C=30 ) in region III of Tkach and Chraplyvy feedback diagram. We also verify the minor dependence of noise from the phase factor 2ks + atan α. Finally, we show that the cFM SMI easily attains an unprecedented limit of small-signal detection, with amplitudes down to 0.25 pm surd Hz.