Investigation of evanescent scattering for low-distortion submicron vibration sensing using ferromagnetic cantilevers

In this study, we investigate the dynamic performance of a previously reported evanescent-scattering platform for submicron vibration sensing with low distortions. The platform consists of self-assembled ferromagnetic cantilevers located above a liquid-cladded optical waveguide. Theoretical analyses show enhancement of sensitivity and dynamic sensing range by reducing the waveguide core-cladding index difference. Moreover, a careful tradeoff between sensitivity and linearity is required, which is determined by the bias position of the cantilever tip. Experimental results confirm that our platform can offer low total-harmonic-distortions (THD) of < 3.00% with a submicron displacement of 0.40 µm over the frequency range from 80 Hz to 750 Hz. The measured THD value is very close to our theoretical prediction. Thus, our platform can be employed in submicron vibration sensing with high-precision requirements.