Research of the polarity characteristic for an optical fiber accelerometer demodulated by phase generated carrier technology

For an accelerometer, it is necessary to distinguish the plus/minus axis rightly before use. Demodulated by phase generated carrier (PGC) technology, a definition of the polarity characteristic for a double-arms optical fiber accelerometer is proposed. It was found that, when the selected modulation depth C > 0, the demodulated result by PGC technology is equal to the optical phase shift in the long arm subtracting the one in the short arm, while opposite result would be obtained when C < 0. Then, a simple model is presented to discuss relations between the output of the accelerometer and relative positions of the two arms and the sound source. We demonstrate that, when C > 0, the response of the accelerometer is coincident with the signal when the long arm is placed pointing to the source, while opposite once the relative positions of the two arms were exchanged. On this condition, the long arm is defined as the plus axis and the short arm to be the minus axis. However, when C < 0, the polarity definition should be opposite. Based on this polarity definition, a combination method is offered to fabricate a three-dimensional optical fiber vector hydrophone (OFVH). Finally, these conclusions are proved by experiments.