Theoretical suppression of cavity interferences in a fiber Bragg grating array interrogated with coherent optical frequency domain reflectometry

A theoretical method for the suppression of cavity interference is described that suppresses the cavity interference in a fiber Bragg grating array (FBGA) interrogated using the coherent optical frequency domain reflectometry (C-OFDR) technique. In C-OFDR, a tunable laser source is used to scan an interferometer, composed of a FBGA and a broadband reference reflector, as a function of wavelength. The interference between the FBGA and the reference reflector results in a composite modulated interferometric signal. A Fourier transform of this signal is then made to spatially separate out each fiber Bragg grating (FBG) in the array. In this work, the undesirable cavity interference component of this signal is simultaneously suppressed by directly subtracting the cavity interference signal from the overall interference signal. This method is simulated with polarization optics and a circularly polarized tunable laser source. The cavity suppression method allows the C-OFDR/FBGA to operate at half the bandwidth of the downshifting method, potentially saving optical fiber material, and at a higher return signal than the FBG reflectance reduction method. In addition, the detection system is polarization insensitive.