Research On Fiber Interferometer Sensor Base On Core-offset For Simultaneous Measurement Of Dual Parameters

With the development of technology, sensor technology in various fields plays anincreasingly important role. In recent years, fiber sensor has become a hot topic because of itsadvantages such as high sensitivity, wide range of measurement objects. With thedevelopment of the fiber optics, optical fiber sensors are developing forward the direction ofminiaturization low-cost, high-precision. After a long time optimized, fiber sensor is more andmore important in civil and research field.In this paper, a core-offset way is presented to improve the traditional fiber sensor. Thismethod is using fiber spliced with another fiber in core-offset way to excite cladding mode.And two different kinds of interference dip is made. Using the different sensitivities of thedips, two parameters can be measured simultaneously, The main work consists the followingparts;1) The history of development and classification of optical fiber are described. Theprinciples and the classification of the fiber sensor are also described. Several classic fibersensors are listed. The advantages and the problem should be deal with are describedpreliminary.2) Several interferometric fiber sensors’ principles are described. Especially some popularsingle-arm fiber sensors’ principles are introduced. Some common ways to achievemulti-mode interference are presented too. The causes and solutions for cross-sensitivity arealso elaborated.3) The theory of MMF spliced in core-offset way is described. A novel fiberinterferometer sensor based on core offset for simultaneous measure temperature and liquidlevel is proposed. It makes a multimode fiber spliced with another multimode fiber left whichhas a same core diameter and length in core-offset way, and weld with a third multimode fiberright which has a larger core diameter to be the sensor head. By observating the wavelengthshifts of the interference dips, temperature and refraction index can be measuredsimultaneously since the core modes and the cladding modes have different sensitivities to thetwo parameters. Experiments indicate that the temperature sensitivity is0.105nm/oC at most,the RI sensitivity is32.2nm/RIU.4) The theory of SMF spliced in core-offset way is described. A fiber sensor based oncore-offset SMS interferometer for simultaneous measurement of temperature and liquid levelis proposed. The sensor is fabricated by a SMS interferometer spliced with a single modefiber (SMF) in core-offset way. Since the cladding mode of SMF is excited in the core-offsetSMS, two different kinds of interference dips which are formed by the SMF and the SMSinterferometer respectively are obtained. Using the difference sensitivities to the twoparameters of the selected dips, temperature and liquid level can be measured simultaneously. Experiments indicate that The temperature sensitivity is0.0815nm/oC at most.. When theliquid is water (n=1.33), the sensitivity of the liquid level is0.14nm/mm. When the liquid issodium chloride solution (n=1.38), the sensitivity of the liquid level is0.29nm/mm.