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Contact analysis of transversally loaded Bragg grating strain sensors

Wavelength tuning of fiber Bragg gratings (FBGs) by virtue of a lateral or transverse load is attractive for a variety of applications in the field of optical sensing. The wavelength response characteristic of the FBG upon application of a transverse load is highly dependent on the pressurizing media and the contact conditions. In this paper, we evaluate the effect of contact friction and contact angle of the pressurizing media on the lateral pressure tuning of FBGs. Our results showed that pressurizing media with a lower value of stiffness is favorable for greater contact areas and for distributing the lateral load. Thus, the sensing load becomes more hydrostatic in nature, which enhances the lateral pressure sensitivity and tuning range while reducing birefringence. Also, a higher contact friction is favorable for effective transfer of the load through the contact area and improved sensitivities accordingly. The present study is thus useful in better utilization of lateral pressure tuning of FBGs for sensing applications.