THE DEMODULATION ALGORITHM OF OPTICAL FIBER FABRY–PEROT SENSOR USING THE NONLINEAR DYNAMIC CHARACTERISTICS OF THE OPTICAL FIBER BROADBAND LIGHT SOURCE

Abstract

The purpose is to optimize the optical fiber Fabry–Perot (F-P) sensor’s performances to provide a realistic basis for the optical fiber’s development. First, the classification of the optical fiber F-P sensors is summarized. The optical fiber F-P sensors’ fundamental principles are analyzed, focusing on the phase demodulation method that converts the optical fiber F-P sensing system’s input light source into a broadband light source. The broadband light source’s lightwave changes are analyzed, and the Fourier transform method and the fringe counting method are proposed to optimize the phase demodulation method’s function and analyze the light source’s nonlinear dynamic characteristics. According to the proposed demodulation method, the optical fiber F-P sensor with a cavity length change of [Formula: see text][Formula: see text][Formula: see text]m is simulated, and the cavity length selected for the simulation spectrum is the change range’s center value, 185[Formula: see text]um. The wavelength division multiplexer (WDM) decomposes the two optical signals, and an equation directly calculates the wavelength value orthogonal to its phase. The results show that the light intensity’s initial value of the actual spectrum is 0.04, and that of the standard function is 0.06. The light intensities for the maximum peak values are the same, 0.12, with the wavelength in [Formula: see text]–[Formula: see text][Formula: see text]m. When the wavelength exceeds [Formula: see text][Formula: see text]m before the next peak, the light intensity difference between them is large. The two orthogonal optical signals’ peaks change between the cavity length 0.18[Formula: see text]nm and 0.19[Formula: see text]nm after the wavelength selected, and the two signals’ peak values are orthogonal with the cavity length changes. The two signals’ initial and end peak values are different. The curve obtained by the two signals division calculation shows a tangent trend with the highest peak value of 87 and the lowest of [Formula: see text]. The peak curve changes obtained by the two signals’ arctangent calculation are in an orthogonal state, with the maximum peak value of 1.3 and the minimum of [Formula: see text]. The reflected light peak value changes of the optical fiber F-P sensor are in an orthogonal state, with the highest value of [Formula: see text] and the lowest [Formula: see text], and the adjacent peak changes in the wavelengths of 1500–1580 are the same. The curve’s fitting linearity is 1, and the linearity in the dynamic demodulation is 0.9776. The sampling frequency in the phase demodulation is [Formula: see text][Formula: see text]Hz, and the sampling frequency in the dynamic demodulation is [Formula: see text][Formula: see text]Hz, showing that upgrading the interface can increase the dynamic sampling frequency continuously to improve the device performance.