Underwater Pressure and Temperature Sensor Based on a Special Dual-Mode Optical Fiber

Abstract

In this paper, an all fiber optic sensor based on a Mach-Zehnder interferometer (MZI) has been proposed for the simultaneous measurement of underwater pressure and temperature, utilizing a dualmode fiber (DMF) which has been specially designed, and supporting only the LP01 and LP02 modes propagating in the fiber. In this design, an in-line MZI sensor that was constructed by splicing a DMF between two pieces of single mode fibers, shows a critical wavelength (CWL) which exists in the transmission spectrum of the LP01-LP02 mode interference. Since the two peaks, located closest to the CWL (and from both lower and higher wavelengths), shift in opposite directions and show different sensitivities under temperature and water pressure variations, the DMF-MZI sensor is capable of measuring both the water pressure and the temperature simultaneously. The CWL-based interference spectrum is stable with the variation of underwater salinity or impurities seen around the fiber surface and independent of the polarization states of the transmission light. As a result, in the operation of the DMF-MZI sensor, underwater pressure and temperature sensitivities increase significantly, when the peak wavelengths are close to that of the CWL. A theoretical analysis has been developed and used to predict that the sensitivities of this specific DMF-MZI structure which can be further improved by increasing the physical length of the DMF and by adjusting the position of the first left/right peak to be closer to the critical wavelength. This co-located, multi-parameter all-fiber sensor developed in this way and showing relatively high sensitivity is easy to implement in the underwater environment. It does not require a complex shell design and the peaks nearest to a CWL are convenient, allowing easy identification and detection, thereby providing a large measurement range to satisfy the requirements of practical marine and fresh water measurements. INDEX TERMS fiber sensor, temperature, pressure, dual mode fiber, Mach-Zehnder interferometer.

Simultaneous Measurement of Temperature and Pressure Based on Fabry-Perot Interferometry for Marine Monitoring

“…Over the last couple of years, various types of optical fiber pressure and temperature sensors have been extensively investigated and developed. Most of them are on the basis of Mach-Zehnder interferometer (MZI) [5][6][7], fiber Bragg gratings (FBG) [8][9][10], Sagnac interferometer (SI) [11,12], and the Fabry-Pérot interferometer (FPI) [13][14][15][16][17][18][19][20], etc. Among these sensing structures, the FPI-based sensors have attracted increasing attention due to simple structure, compact size and high accuracy.…”

Strain and Temperature Discrimination Based on a Mach-Zehnder Interferometer With Cascaded Single Mode Fibers

“…In-fiber Mach-Zehnder interferometers (MZIs) have been studied recently for various sensing applications such as the sensing of strain [1][2][3][4][5], temperature [6], pH [7,8], pressure [9,10], curvature [11,12], humidity [13], refractive index [14][15][16], and magnetic field [17,18]. An in-fiber MZI can be manufactured with multiple methods, for instance, using down-tapering structures [3], up-tapering structures [1], core-offset splicing structures [14] or simply splicing fibers with mismatched cores [4].…”

“…The second category is the single fiber structure which applies a single fiber, usually a special fiber, as the sensing fiber. Recently, an optical MZI sensor based on a homemade few mode fiber (FMF) is proposed for strain and temperature sensing [2] as well as for the measurement of underwater pressure and temperature [10]. Special fibers such as a side-polished fiber [16], a microfiber [9], and a ring-core fiber [12] are utilized in the MZI to discriminate temperature from the refractive index, pressure, and curvature, respectively.…”

Detection of Refractive Index With a Temperature-Compensated MZI-Based Optical Sensor Using Few-Mode Fiber

“…Over the years, measurement of surround refractive index (SRI) is increasingly essential in many fields, such as medical biology, environmental monitoring, aerospace, construction industry and meteorological services [1][2][3][4]. Fiber-optic sensors possess good application prospects in SRI measuring, and have drawn a great deal of attention due to several inherently distinctive features, such as low weight, compact size, anti-erosion, chemical and biological inert, immunity to electromagnetic interference and remote operation [5][6][7].…”