Fiber-optic extrinsic Fabry-Perot interferometer strain sensor with <50 pm displacement resolution using three-wavelength digital phase demodulation

Abstract

A fiber-optic extrinsic Fabry-Perot interferometer strain sensor (EFPI-S) of ls = 2.5 cm sensor length using three-wavelength digital phase demodulation is demonstrated to exhibit <50 pm displacement resolution (<2nm/m strain resolution) when measuring the cross expansion of a PZT-ceramic plate. The sensing (single-mode downlead-) and reflecting fibers are fused into a 150/360 microm capillary fiber where the fusion points define the sensor length. Readout is performed using an improved version of the previously described three-wavelength digital phase demodulation method employing an arctan-phase stepping algorithm. In the resent experiments the strain sensitivity was varied via the mapping of the arctan - lookup table to the 16-Bit DA-converter range from 188.25 k /V (6 Volt range 1130 k ) to 11.7 k /Volt (range 70 k ).

Geotechnical pressure cell using a long-term reliable high-precision fiber optic sensor head

“…The most interesting solutions, which solve these problems, are: a) the current of the laser diode is driven by a feedback of the interferometric signal; a Serrodyn characteristics of the output signal is created from which the shift direction of the sensing interferometer arm can be detected unambiguously [1]; b) several defined laser wavelengths are used. An absolute measurement of distance changes is then possible by using the beat wavelength [2]. The cited methods suffer from two problems: either the signal resolution respectively the accuracy is not sufficiently high for some measurement tasks, or a reliable detection of absolute measurement signals is not really possible if the device or components of it have to be renewed.…”

Lightning-safe diaphragm pressure gauge for geotechnical applications using a long-term reliable absolute EFPI sensor

“…The most interesting solutions, which solve these problems are: a) the current ofthe laser diode is driven by a feedback of the interferometric signal; a Serrodyn characteristics of the output signal is created from which the shift direction of the sensing interferometer arm can be detected unambiguously [1]; b) several defined laser wavelengths are used. An absolute measurement of distance changes is then possible by using the beat wavelength [2]. The cited methods suffer from two problems: either the signal resolution respectively the accuracy is not sufficiently high for some measurement tasks, or a reliable detection of absolute measurement signals is not really possible if the device or components of it have to be renewed.…”

Tunable Fabry–Perot filter in cobalt doped fiber formed by optically heated fiber Bragg gratings pair

“…The most popular way in forming a tunable fiber F-P cavity is to change its cavity length mechanically, such as driven by a piezoelectric transducer (PZT) [10,11]. Although the mechanical way is popular for its high speed and high resolution, it also has its deficiencies: one is the hysteresis due to which the wavelength-voltage relationship of an F-P filter is nonreciprocal when driven by a PZT actuator [12,13], another one is the relatively short life time of a mechanical structure. Instead of mechanically controlling, in this paper we managed to design a tunable fiber F-P filter by all-optical heating.…”