To overcome the accuracy limits of fringe counting method for a F-P interferometer and the complexity of a higher
resolution demodulation system such as phase generated carrier (PGC), where a residual amplitude modulation always
exists in frequency modulation, this paper presents a fiber F-P displacement sensor based on double-interferometer phase
demodulation, which eliminates the modulation of lightsource. Comparing to the reported double-fiber F-P structure, our
design has no strict requirement for a specific phase difference between the two optical paths. Experimental results
demonstrate a good linearity of 1.1% and a resolution of ±3 μm within a measuring range of 0-0.5 mm.
This paper presents a liquid level sensor with a double-fiber Fabry-Perot (F-P) cavity and a diaphragm serving as the
sensing element. The end surfaces of the two fibers that integrated in a ferrule serve as the front surfaces of the F-P cavities,
and the diaphragm (one of the standard components of a manometer) as the rear surface. The random difference in position
between the two fiber ends makes a phase difference between the two F-P interferometers, and is used to interpret the
direction of the pattern shifts with the variation of the F-P cavity length, which leads to a much lower technological
requirement for the cavity manufacture and a more stable sensor. A prototype is fabricated to demonstrate the design, and
the experimental results show a system accuracy of 1/2 fringe, refer to a height-resolution of 1mm.