High pressure discrimination based on optical fiber microsphere cavity Fizeau interferometer

Abstract

ABSTRACT Ahigh pressure sensor based on an optical fiber micro sphere cavity Fizeau interfer ometer (MSC-FI) is presented in this paper.The sensorwas fabricated by use of a fusion splicer. Th e achieved pressure sensitivity of MSC-FI sensor was in the range of 500 to 7000pi to be 4×10 -4 nm/psi. With a 10 pm resolution for the wavelength shift detection, the resolution of the device at room temperature for pressure measurement is to be 25 psi. This sensor can be used as a high pressure sensor in downhole application. Keywords: optical fiber sensor, Mi cro sphere cavity, Fizeau interferometer, pressure. 1. INTRODUCTION Efficient and complete recovery of petroleum reserves is difficult in part due to lack of robust instrumentation for characterization of physical conditions in the downhole environment. Accurate evaluation of pressure, temperature and volumetric flow would permit optimization of oil recovery processes.This parameters were traditionally measured by electrical gauges based on electrical gauge [1,2].They are al so sensitive to electromagnetic noise and have low potential for multiplexing application. The use of optical fiber sensors for measurement of physical parameters such as temperature, pressure and flow plays an important role in in dustry and engineering sciences [2]. Optical fibersensorsdue to thecompact size, potential low cost,immunity to electromagnetic interference and the ab ilityof multiplexing, arevery important.Many different optical fiber pressure sensors have been reported, including those based on fiber bragg gratings, highly birefringent (Hi-Bi) microstructure and photonic crystal fiber fibers [3-4], Fabry-Perot interferometers (FPIs) [2], FPI based on capillary micro cavity[5], hollow core fiber [6]. For many practical application of interfe rometry small sensor heads is required. Fizeau interfero meters with short optical cavity are specially attractive as they have the advantages of being simple, compact, low cost with minimum cross sensitivity to temperature [7]. Enbang Li et al reported a strain sensor based on Fizeau interferometer in-fiber spherical micro cavity, in their work an air bubble was cr eated in splice mechanism by fusion splicing.[8] In this paper, we report a novel pressure sensor based on a spherical micro cavity extrin sic Fizaue interferometerc. The sensor was made by melting the capillary at the tip to form a micro sphere with fusing, and then putting a single mode fiber into the capillary tube. The sensor has a compact size and good mechanic strength and it can be used for high pressure applications.