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Study On Partial Characteristics And Applications Of Novel Long-Period Fiber Gratings

Posted on:2005-09-24Degree:MasterType:Thesis
Country:ChinaCandidate:A Z HuFull Text:PDF
GTID:2168360125963872Subject:Optical Engineering
Abstract/Summary:PDF Full Text Request
In this thesis, some characteristics of novel long-period fiber gratings (LPFGs) induced by focused high-frequency CO2 laser pulses are studied. The main work is provided as follows:1. The characteristics of dynamic transverse load of the LPFGs induced by high-frequency CO2 laser pulses is studied, for the first time, to our knowledge. The peak amplitude of the LPFG has a good linear relationship with the transverse load. A new measurement system consisting of a narrowband light source and a photodetector is proposed to measure the dynamic transverse load directly. As the measurement is realized by detecting the peak amplitude change of the LPFG directly, this sensor system is simple and fast. The experimental results show that such a system could be a practical approach to realize dynamic transverse load measurement for large engineering structures, such as bridges, highways, et al.2. Etching characteristics of the LPFGs written by high-frequency CO2 laser pulses are studied. The experimental results show that the resonant wavelength of the LPFGs floats 'red' linearly with the etching time growing whereas its resonant peak amplitude varied little. Furthermore, the basal characteristics of etched LPFGs are demonstrated in this paper for the first time. It came out that the characteristics of temperature,strain and distortion change little when comparing both un-etched and etched cases except that the bending become less sensitive for the ethched LPFG. So that we draw a conclusion that such an etching method could be used to adjust the resonant wavelength of the LPFG without change in its characteristics. Also we used it in the process of the LPFG filters. 3. The characteristics of LPFGs fabricated in bend insensitive fiber (BIF) or photosensitive fiber by high-frequency CO2 laser pulses are studied for the first time. Regarding the temperature,strain and torsion, the characteristics are similar for LPFGs written in the three type of optical fibers, i.e common fiber , bend insensitive fiber and optosensitive fiber. But their sensitivities are dissimilar. The bending characteristic of the LPFG in a bend insensitive fiber is special. The experimental results show that the resonant peak amplitude of the LPFG written in a bend insensitive fiber has a higher sensitivity than that written in a standard telecommunication fiber, further more they have different bending characteristics at circular orientation i.e. the resonant peak amplitude of the LPFG is the most sensitive to bending but the resonant wavelength of the LPFG is insensitive at some circular orientations. Based on this finding, a gain equalizer is proposed to flat the gain of an EDFA by bending directly. The experimental results show that such a system would be a practical and simple approach to realize gain flattening of an EDFA with high precision for gain control.
Keywords/Search Tags:high frequency CO2 laser pulses, long-period fiber grating, transverse load, etching, temperature, strain, torsion, bending, special fiber, gain equalizer, optical fiber sensors
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