Transverse load sensing based on a dual-frequency optoelectronic oscillator.

We propose and experimentally demonstrate a fiber-optic sensor implemented based on a dual-frequency optoelectronic oscillator (OEO) for transverse load sensing. In the OEO loop, a phase-shifted fiber Bragg grating (PS-FBG) is employed to which a transverse load is applied to introduce a birefringence to create two orthogonally polarized notches, which leads to the generation of two oscillating frequencies. The beat frequency between the two oscillating frequencies is a function of the load force applied to the PS-FBG. The proposed sensor is experimentally demonstrated. The sensitivity and the minimal detectable load are measured to be as high as ~9.73 GHz/(N/mm) and 2.06×10(-4) N/mm, respectively. The high-frequency purity and stability of the generated microwave signal by the OEO permit extremely reliable and high-accuracy measurement. The frequency interrogation allows the system to operate at an ultra-high speed. In addition, the sensing signal is insensitive to the variations of both the environmental temperature and the optical carrier wavelength.