Study Of Long Period Fiber Gratings And High Order Waveguided Bragg Gratings

Fiber Grating is one of the passive fiber devices that have been developed most quickly in recent years. It's an important milestone in the history of Fiber Technology. The appearance of Fiber Grating make it possible that the all-fiber devices, such as fiber laser, fiber filter, fiber Multi/Demultiplexer, etc.gained quickly progress.Long Period Fiber Gratings(LPFG) have been paid much attention to on both its theory and applications in the sensors, filters , mode converters for it's easy to be made, convenient to connect and compact structure etc.The study of transmission spectra of LPFG is the theoretical foundation for the study of its application. The transmission spectra of cascaded long period grating are analyzed by a transfer matrix method. The effects of the length, position and loss coefficient of the fiber that connects the LPGs on the cascaded LPG spectral characteristics are discussed. Through numerical analysis, we draw conclusion that the spectra of cascaded LPG and phase shifted LPG will show great consistency when the length of the cascading fiber is small or the cascading position is near the end of the cascaded LPG The amount of Transmission Loss keeps constant no matter how the length of the cascading fiber changes, if other losses are not considered. The calculation and analysis results also show that if the loss coefficient of the cascading fiber's cladding mode is large enough, the spectra of cascaded LPG can be dealt as non-interrelated cascaded LPG, which provides an efficient way to the optimization and design of LPG Gain Equalizer.The spectra of cascaded LPFG of different period have been study for the first time in the thesis.The grating's cladding mode loss was considered for the first time. By adding a loss factor in the coupled mode equation, the spectra of uniform LPFG as well as the transfer matrix of non-uniform LPFG when considering the grating's cladding mode loss was deduced.The Amplitude mask of LPFGs will bear the advantage of easy to be made, high precision and good agility if fabricated by MEMS technique. By using the Inductivity Coupled Plasma (ICP) etching technique and KOH etching and other MEMS technique, the amplitude mask of LPFG was made on the Si material. With these maskes, Several LPFGs were made by UV writing method. The spectra of ASE were flattened by LPFGs we made with a maximum 2.5dB undulation over the wavelength from 1525nm to 1550nm and less than 1 dB undulation over the wavelength from 1525nm to 1540nm.Highorder Waveguided Bragg gratings(WBG) also has the character of big line-width. To fabricate the highorder WBG by standard MEMS technique is a possible way to make it massive produced. High-order WBG was designed and fabricated in this thesis.The high-order Bragg Grating's reflective peak is observed, which proved the feasibility of this method. The design in our thesis is based on the fabrication condition of our lab(with a minimum line width of 2 um). If a better fabrication condition with smaller minimum line width is available, better result could be expected by designing and fabricating less high order WBG...