As an important member of optical fiber sensor, fiber optic Extrinsic Fabry-Perot Interferometric (EFPI) sensor has
prospects for a wide range of industrial applications due to its small size, compact configuration, good reliability and
flexibility. In a white light based fiber optic EFPI sensor system, which has the advantages of large dynamic range and
high resolution, spectral analysis equipment is the most important part which takes the major cost of the system.
Therefore, multiplexing spectral analysis equipment to measure multiple sensors simultaneously is an effective and
necessary way that can save the cost of the whole sensor system. In this paper, a scheme based on the frequency division
multiplexing of EFPI optical fiber sensors is proposed. Two EFPI sensors with different gap lengths are parallely
connected through the optical fiber coupler. The overlapped interference spectrum of the two EFPI sensors is measured
by using an optical spectrum analyzer, which is separated into two individual interference spectrums with a Finite
Impuse Response (FIR) band-pass filter. Their envelope components are extracted with Hilbert transform, and then the
interference spectrums are normalized by the envelope components. The respective gap lengths of the two EFPI sensors
are achieved with the cross correlation calculation. Using this frequency division spectral analysis method, a two-channel
multiplexing EFPI sensor system is implemented in the laboratory. The deployment of this frequency division
multiplexing technology can greatly reduce the cost of the whole system which has extensive potential applications for
distributed fiber optic EFPI sensor system.