Crosstalk and phase-noise reduction in time-division multiplexing of polarization-insensitive fiber optic Michelson interferometric sensors

• The Time-division multiplexing of polarization-insensitive fiber optic Michelson interferometric sensors (TDM-PIFOMI) can solve the polarization induced signal fading by using Faraday rotator mirror.
• The TDM of the fiber optic interferometric sensors suffers the crosstalk and noise between the sensors and degrades the performance of the sensor system. Thus, crosstalk and noise suppression is important.
• The emission time difference of each interference term of TDM-PIFOMI system is a key parameter to reduce the crosstalk and noise by using laser diode high frequency modulation.
• The laser diode high frequency modulation is a compact and cheap method which is very efficient to reduce the crosstalk and noise of the TDM-PIFOMI system.

The multiplexing system of fiber optic interferometric sensors suffers from crosstalk and noise, and the performance degrades. The crosstalk of TDM of the fiber optic interferometric sensor includes lead fiber crosstalk, sensor crosstalk for optical gate with finite extinction ratio (ER) and delay fiber crosstalk. In this paper, the laser emission time difference of each interference term of the TDM-PIFOMI system was utilized to reduce the crosstalk and noise by using laser diode high frequency modulation. The temporal characteristics of the crosstalk and the noise of the TDM-PIFOMI system were analyzed, and the theoretical sensor crosstalk, Asensor, is −4 ER(dB) by using laser diode high frequency modulation. According to the PGC demodulation process, the minimum frequency of the laser diode modulation was estimated to be larger than nine times of the carrier frequency of the PGC demodulator.In our experimental results, the improvements of the sensor crosstalk were from 8.3 to 15.5 dB, and the improvements of the delay fiber crosstalk were 15.7 and 14.6 dB by using laser diode high frequency modulation. The phase noise was reduced from 2 dB to 3.9 dB. Using laser diode high frequency modulation to decrease the crosstalk and the noise of the TDM-PIFOMI system is effective and cheap.