Research On Structure Design And Sensing Characteirstics Of New Hase-shifted Grating

As a novel optic passive device, Phase-shifted fiber grating has inspired theinterests of internal and overseas investors because of its many natural merits such asnarrow bandwidth, multiple channels and flexible combination etc. By changing themagnitude, position or value of phase shift, the index distribution of Phase-shiftedfiber grating will become more complex than the general cases, which consequentlyresults in special spectrum and widely applications. With the further investigation ofgrating writing method and the development of grating writing technology, manyspecial structural phase shifted fiber grating with novel application are designed.Moreover, some of them recently receive more and more attentions in the novel opticdevice.Following the study of written methods and applications about Phase-shiftedfiber grating, we consider the formative principle, special structural design andapplications of Phase-shifted fiber grating. In our research, we design some novelPhase-shifted fiber gratings, and expound their applications in the filed of sensor andcommerce. The design method we proposed affords a new approach for gratingstructure design and achieve excellent optic trait. The main contents and results ofthis dissertation include are list as follows:1. We systematically summarize the written technology, spectrum properties and development of fiber grating. We particularly analyze the written method, specialspectrum characteristics and typical application of Phase-shifted fiber grating. Wemake some conclusions about the method to form Phase-shifted fiber gratingincluding their corresponding advantages and disadvantages.2. The spectrum and sensor characteristics of Phase shifted-ultra long period grating（PS-LPFG） formed by changing one written step is studied. Then we obtain therelationship of phase shift and fiber grating structural parameters. Theexperiments show that the phase shift value is dependence not only on the stepchange but also on the diffraction order. Based on the results, we propose a newmethod to identify the diffraction order.3. Based on a PS-ULPFG, we propose and demonstrate a temperature-and strain-insensitive torsion. We theoretically and experimentally show that by measuringthe spacing between the two phase shifted resonance peaks, the sensor could beeliminating the influence of temperature and axial sensor effectively. In addition,the sensor could be measure the twist oration if twist at first.4. We propose a novel Phase shifted long period grating （PSLPFG） formed byadding a modulated grating. By transfer matrix method and CO₂laser writtensystem, we establish and demonstrate its structural model and its phase shiftedvalue function. The experiments show that the phase shift value of the novelPSLPFG is dependent on the length and resonance peaks of the modulated grating. Based on the formed method, we obtain a temperature insentive strain sensor.5. We proposed a novel PSLPFG by adding an embedded modulated grating. Whenthe second modulated grating has the same structures with the original grating, thewhole grating was two phase shift PSLPFG. When the second modulated gratinghas the different structures with the original grating, the whole grating was singlePSLPFG and the phase shifted value is the sum of that brings by the twomodulated fiber grating.6. Based on the results of5, we proposed a tunable two wavelength filters based on anovel Phase Shifted fiber Bragg grating （PSFBG）. The grating is formed by twomodulated method CO₂laser exposure and the temperature arises. Since it onlyneeds one temperature device, thus it will not have the problem of temperaturedisturb ion.