Study On Characteristics Of Ultra Long Period Fiber Grating

Ultra long period fiber gratings which have much longer periods than that of ordinary long period gratings and are induced by high frequency CO₂ laser pulses are studied by the author here under the supervision of Prof. Rao and teacher Zhu Tao, and these researches have much significance in extending the research which have been done for several years by Prof Yunjiang Rao and his students on long period fiber gratings with periods of several hundred micrometers and are also induced by high frequency CO₂ laser pulses.The studies mainly include:1. Researches on ultra long period fiber gratings written in ordinary single-mode fiber, and its temperature, refractive index, strain and twist characteristics.2. Researches on ultra long period fiber gratings written in panda polarization maintain fiber and its polarization, temperature, strain and twist characteristics.3. Researches on ultra long period fiber gratings written in bend-insensitive fiber and its temperature strain and twist characteristics.The researches show that different resonant peaks of ultra long period gratings written in ordinary single mode fiber have different temperature and refractive index sensitivities, and using this characteristic, a new high sensitivity refractive index sensor with temperature self-compensating is proposed in this thesis. This refractive index sensor can not only sensitively measure the refractive index of the outside environments, but can also compensate the measuring errors brought by the temperature changes of them. The researches also show that the torsion sensitivities of some resonant peaks of ultra long period gratings written in ordinary single mode fiber arrive 4 times of that of ordinary long period fiber gratings, and a highly sensitivity twist sensor is also proposed in this thesis based on this characteristic. The sensitivity of this twist sensor arrives 0.4394dB/(rad/m).The researches on ultra long period gratings written in panda polarization maintain fiber show that the amplitudes of two resonant peaks on two vertical polarization directions of ultra long period gratings changed periodically with a period ofπwhen the polarization angle of incident elliptical polarization light varied from ? 2πto 2π. The phase difference of amplitude changes of them isπ, and the amplitude difference of them in the same incident polarization angle varied periodically as a zigzag wave also...