Augmentation of sensitivity of FBG strain sensor for biomedical operation.

The performance of a highly sensitive strain sensor based on nonlinear four wave mixing (FWM) using two uniform fiber Bragg gratings (FBGs) is investigated. Strain is measured by the proposed setup with high resolution and precision. It is observed that the wavelength shift induced by very small strain over the FBG is significantly magnified by the higher-order FWM process. The sensitivity is enhanced by a factor of nine based on a wavelength shift of the eighth-order FWM product. Strain sensitivity of 11.23 pm/μϵ is achieved against initial strain sensitivity of 1.23 pm/μϵ. The proposed scheme can provide a strain measurement range of about 3500 μϵ. Application of the proposed setup in the cardiac and respiratory systems is also studied, and the results are found to be reliable and accurate, even if the applied strain on the FBG is of the order of 0.1 μϵ.