Research On Fabricating And Characteristics Of Long-period Fiber Grating

Since A. M. Vengsarkar et al. wrote successfully Long-Period Fiber Gratings (LPG) in optical fibers in 1996, LPG have become increasingly popular as fiber-optic devices for optical fiber communication and sensing. LPG have been demonstrated as band-rejection and gain-flattening filters for improving Er-doped fiber amplifier systems, and also used as temperature/strain sensors, as well as sensing demodulators. One of their unique characteristicistics is the sensitivity to the refractive index of the cladding, which can be used as biochemical sensor.In this thesis, it is brief introduction to the history of Long-period Fiber Gratings (LPG), reseach on the fabrication and characteristic of LPG by the numbers from theoretical and experimental work, provided theorey and data support for the application in technique of optical communication and optical sensor.in the future.In the theoretical aspect, I deduced the general equations for the couple modes from Maxwell equations;acquired the particular mode-coupled theory for Long-period fiber gratings (LPG). These theories are often used to analysis optical spectra of LPG.In the experimental aspect, using ordinary communication fiber and photosensitive fiber the two kinds of fiber to fabricate LPG respectively;we tried out a lots of conditions of fabrication, then researched on the influence of the gratings spectra characteristic by length, period of the gratings and the order of couple mode. At present, we not only fabricated the LPG of which the resonance loss is to -20~ -30dB, but also found the optimum way of facturing LPG on different type of fiber in dissimilar experimental condition, provided data support for the further research on LPG manufacture.Comparing the data of Anneal with that no Anneal, we selected some LPGs to carry out Package experiment in the derection of theory analysis. Because we adopt four kinds of Package methods, we got different result when did temperature experiment, thus we seived a better package method.In terms of the sensitivity ratio of LPG higher than that of FBG, it is studied a kind of method that can advance the temperature sensitivity ratio of LPG That is used high thermal thermo-optic coefficient, achived a very high sensitivity 19.2nm/°C in a short temperature range, enhanced more than 10 times than other means. We can make LPG temperature sensor with a high sensitivity ratio in this way.It is tested and verified the LPG bending experiment with the good spectral characteristicistic. It is confirmed the bending specialty of LPG, that bending cause resonance amplitude let up, similar with the efficiency of opposite course of LPG fabrication. Different bending direction cause different change of spectra, while the direction where the most variation of spectral amplitude happened is the right orientation in which ultraviolet light fabricate gratings. So, it is the best way of make bending sensor in this direction.It is done the temperature and sress experiment and found the same result as the the theory analysis in this thesis. That is temperature sensitivity of LPG is higher two order of magnitude than FBG, poles apart, the stress sensitivity of LPGlower order of magnitude than FBG.For the further research on the attenuation of LPG, this thesis fabricated a wide-band white light resource of which output power is o.5uw with automobile bomb. It can read the spectra better than LED resource of which band is narrow.Now, we have mastered the technique of LPG fabrication with ultraviolet light in our lab. LPG is to the reach the request of utility after temperature compensatation.