Studies of temperature-insensitive dynamic pressure sensing using elliptical-core side-hole fibers

Abstract

We present a new idea for minimizing temperature sensitivity of a fiber-optic interferometric sensor based on highly birefringent side-hole fibers. The sensing part is composed of a side-hole fiber characterized by a very high pressure-to-temperature sensitivity ratio equal to 25°C/bar, which is about two orders of magnitude higher than in the case of other highly birefringent fibers. We took advantage of this unique property to assure good insensitivity to temperature effects, which are always associated with fast pressure changes. The presented sensor requires no additional temperature-compensating fiber, which has been a normal procedure until now for all fiber-optic pressure sensors. We used a digital demodulation system based on the coherence-addressing principle to decode a differential phase shift introduced by the sensing fiber and the quartz plates, which compensate an optical path delay of the fiber. The demodulation system allows unambiguous measurement of a phase shift with a resolution of 1/8 interference fringe in a range of 40 fringes. In this paper we also show that the side-hole fibers can be applied for measurements of high dynamic pressures at an operating range of 110 bar. We compared the dynamic characteristics of the fiber-optic sensor to the responses of a calibrated and temperature-compensated piezoelectric sensor with a sampling rate up to 200 kHz. The dynamic characteristics of the fiber-optic sensor are in good agreement with the reference piezoelectric sensor, which shows the great utility of the side-hole fibers in accurate measurements of high dynamic pressures.