Experimental Characterization of a Vernier Strain Sensor Using Cascaded Fiber Rings

A highly sensitive strain sensor consisting of two cascaded fiber ring resonators based on the Vernier effect is proposed. Each fiber ring resonator, composed of an input optical coupler, an output optical coupler, and a polarization controller, has a comb-like transmission spectrum with peaks at its resonance wavelengths. As a result, the Vernier effect will be generated, due to the displacement of the two transmission spectra. Using this technique, strain measurements can be achieved by measuring the free spectral range of the cascaded fiber ring resonators. The experimental results show that the sensing setup can operate in large strain range with a sensitivity of 0.0129 nm^-1/με. The new generation of Vernier strain sensor can also be useful for micro-displacement measurement.