Enhanced sensing and accessing capabilities of an FBG sensor using fiber loop mirror

Abstract

Novel implementations of fiber Bragg gratings (FBG) and phase shifter in loop mirror configurations enable monitoring of environmental conditions at both terminals of the loop. These implementations allow accessing the sensed signals in both directions (east and west) at locations far from the sensing position using regular fiber transmission schemes. Optical light of a 1550 nm wideband LED diode (100nm) is launched into the fiber loop that has the FBG and phase shifter. The center wavelength of the FBG varies with changes of conditions affecting the grating such as temperature, pressure, stress and strain. As a result, the center wavelength of the generated continuous wave (CW) optical signal in the fiber loop mirror sensor shifts based on these conditions at the sensing location. Controlling the phase of the phase shifter determines the direction of the generated CW sensed signal to the transmission path or reflection path of the optical loop mirror. Numerical simulations were conducted, which demonstrated the operation of the fiber sensor design.