Experimental Method of Temperature and Strain Discrimination in Polymer Composite Material by Embedded Fiber-Optic Sensors Based on Femtosecond-Inscribed FBGs

Experimental method of temperature and strain discrimination with fiber Bragg gratings (FBGs) sensors embedded in carbon fiber-reinforced plastic is proposed. The method is based on two-fiber technique, when two FBGs inscribed in different fibers with different sensitivities to strain and/or temperature are placed close to each other and act as a single sensing element. The nonlinear polynomial approximation of Bragg wavelength shift as a function of temperature and strain is presented for this method. The FBGs were inscribed with femtosecond laser by point-by-point inscription technique through polymer cladding of the fiber. The comparison of linear and nonlinear approximation accuracies for array of embedded sensors is performed. It is shown that the use of nonlinear approximation gives 1.5–2 times better accuracy. The obtained accuracies of temperature and strain measurements are 2.6–3.8°C and 50–83 με in temperature and strain range of 30–120°C and 0–400 με, respectively

Efficiency of energy deposition by fundamental and second harmonics in femtosecond laser inscription

We present the results of numerical modelling of energy deposition in single-shot femtosecond laser inscription for fundamental and second harmonics, which shows that second harmonic is more efficient considering the amount of absorbed energ

A study of bending effect on the femtosecond-pulse inscribed fiber Bragg gratings in a dual-core fiber

Fiber Bragg gratings with different reflection wavelengths have been inscribed in different cores of a dual-core fiber section. The effect of fiber bending on the FBG reflection spectra has been studied. Various interrogation schemes are presented, including a single-end scheme based on a cross-talk between the cores that uses only standard optical components. Simultaneous interrogation of the FBGs in both cores allows to achieve a bending sensitivity of 12.8 pm/m−1, being free of temperature and strain influence. The technology enables the development of real-time bending sensors with high spatial resolution based on series of FBGs with different wavelength inscribed along the multi-core fiber