High-sensitivity microfiber strain and force sensors

A microfiber biconically tapered from a standard optical fiber shows obvious sinusoidal oscillatory transmission spectrum due to the multimode interference, with evident blue-shifted peak wavelength when applying an axial force. Based on this force-induced spectral shift, here we experimentally demonstrate compact microfiber strain and force sensors with low optical power and high sensitivity. With a 1.5-μW probing light, measured sensitivity of a 2.5-μm-diameter microfiber for the strain and elongation sensing are 4.84 pm/με and 404 pm/μm respectively, with a force detection limit down to 50 μN.