Perfluorinated graded-index plastic optical fiber Bragg gratings: Observation and theoretical analysis of unique dependence on pressure

The pressure dependence of a fiber Bragg grating (FBG) inscribed in a perfluorinated graded-index plastic optical fiber (POF) is investigated at 1550 nm. As pressure is applied, the Bragg wavelength shifts with a relatively long time constant (several tens of minutes) with a coefficient of 1.3 nm/MPa, which is over 5 times the highest value previously reported in other POF-FBGs). After the Bragg wavelength becomes constant at 0.5 MPa, the pressure-dependence coefficient is quickly measured to be −0.13 nm/MPa, the sign of which is opposite to those of other POF-FBGs. These unique behaviors are theoretically analyzed.