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Study Of A New-style Liquid Refractive Index Sensor Based On Polymer Optical Fiber With Micro-holes

Posted on:2013-11-19Degree:MasterType:Thesis
Country:ChinaCandidate:G P XinFull Text:PDF
GTID:2248330371484004Subject:Optics
Abstract/Summary:PDF Full Text Request
The liquid refractive index (RI) sensors based on silica fiber have been widelyinvestigated because of their higher resolution and sensitivity. However, they usuallyhave a bad linear characteristic and small operation range of RI, and are further limitedby high cost of the processing equipment and sensing device for extensive application. Inour knowledge of range, a new-style liquid RI sensor is presented that is based on stepindex multimode polymer optical fiber with micro-holes created by miniature numericalcontrol machine. The RI sensor developed in this work exhibits many advantages, suchas easy fabrication, easy operation, good linearity, wide RI sensing range, low-costsensing device, low thermal sensitivity, low fabrication cost, potential for massproduction, etc.This paper focuses mainly on two parts.1. Theoretical analysis of the sensing mechanism of the designed liquid RI sensorbased on step index polymer optical fiber with a micro-hole.The transmission properties of this sensor with a hole have been investigated withray optics theory, and find that the optical fiber transmission power increased as the RI inthe hole increases.We also analyze the transmission properties of the sensor with a hole of differentsize with a series of logical deduction, and demonstrate that the relationship between thetransmission power in fiber and the RI in the hole is critically dependent on the hole’sdiameter and depth. With RI increment in the hole keeping constant, the fiber outputpower increases larger as the diameter or depth of the hole increases,. That is to say: thesensitivity of this kind of sensor is related to the size of the hole. So it can be optimizedby choosing the proper size of the hole. We can also increase the number of the holesalong the fiber axis, the interval of the holes along the fiber axis, or changing therelations of the holes’ axis in order to improve the sensitivity of this kind of sensors.. 2. Prove the operability of the designed liquid RI sensor in the experiment.1) The characteristic of the liquid RI sensor based on polymer optical fiber with acertain hole.The experiment results show that the transmission power of the sensor based onpolymer optical fiber with a hole increases as the liquid RI in the hole increases, and theyexhibit a good linear relationship, lager operation range of liquid RI (1.335~1.475) and amaximum sensitivity of12.56dB/RIU. The fitted curve of the experimental datum is in agood agreement with the above theoretical analysis.2) The characteristics of the proposed sensors based on polymer optical fiber withdifferent size, number, interval, axis relationship of the holes,respectively.In the experiment, different sensing heads with one or more holes are used to do therelated tests. Many results obtained is as follow:(a) The diameter of the hole changes, but other parameter keeps constant: in the caseof keeping the liquid RI increment in the hole constant, the greater the diameter of thehole is, the greater of the transmission power in polymer optical fiber increases. So thesensitivities of the group liquid RI sensing heads with holes gradually increase as thediameter of the holes increases.(b) The depth of the hole changes, but other parameters keep constant: when thedepth of the hole increases, the transmission loss will decrease in the case of the liquid RIincrement in the hole being kept constant. So, the sensitivities of this group micro-holebased step index multimode polymer optical fiber sensing heads increase rapidly as thedepth of the hole increases.(c) Different number of the axis parallel holes with same size and interval: when thenumber of the parallel holes in the polymer optical fiber changes, the transmission powerof all the sensors increases as the liquid RI in the hole increases, but the sensitivity foreach of them increases as the number of the holes in the sensing head increases.(d) Different interval of the axis parallel holes with same size and number: when theinterval of the holes in the polymer optical fiber changes, the transmission power of allthe sensing heads increases as the liquid RI in the hole increases, and the sensitivity ofeach of the sensors increases as the interval of the holes in the sensing head increases. (e) The same size of the axis perpendicular holes with same interval and number:when the axis relation of the holes in the polymer optical fiber changes, the transmissionpower of all the sensing heads increases as the liquid RI in the hole increases, and thesensitivity of the sensing head with the axis perpendicular holes is larger than that of thesensing head with the axis parallel holes.Except considering the above five methods to improving the sensitivity of the liquidRI sensor based on step index polymer optical fiber with holes, the robustness of thesensing head should be also guaranteed by limiting the holes’ depth and diameter in thecore region in order to get the high quality liquid RI sensor based on step index polymeroptical fiber with holes.3) The temperature characteristics of the new-style sensor.By the experimental analysis, we find that the transmission power of the sensornearly keeps constant within the whole temperature variation range between20oC and55oC. So, it confirms that the capability of the sensor based on step index multimodepolymer optical fiber with micro-holes for nearly temperature-independent liquid RImeasurement.In a word, the liquid RI sensor based on step index multimode polymer optical fiberwith micro-holes proposed in this paper exhibits many advantages, and has very highvalue to research and application.
Keywords/Search Tags:Fiber sensor, Polymer optical fiber, Micro-hole, Refractive index sensing
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