Enhanced pressure and thermal sensitivity of polymer optical fiber Bragg grating sensors

One of the features of reliable polymer optical fiber (POF) Bragg grating sensors is high sensitivity. Towards this, we have investigated a method to enhance the intrinsic pressure and thermal sensitivity of fiber Bragg grating (FBG) sensors inscribed in POFs. By pre-straining the FBG we demonstrated that: (1) the pressure induced mechanical contraction of the fiber can be suppressed, resulting in an increase in the pressure sensitivity of the grating by a factor of 5; and (2) the temperature induced strain can be suppressed, resulting in an increase in the thermal response by more than a factor of 10. The pressure sensitivity enhancement was found to be independent of the amount of pre-strain for levels ranging from 0.07 to 0.33%. The enhancement of the temperature sensitivity was also found to be independent of the amount of pre-strain, but only for temperatures up to when the thermal expansion cancels the pre-strain.