Research On Blazed Fiber Bragg Grating And The Demodulation Technology Of Fiber Bragg Grating

As novel passive optical components, fiber gratings have a comprehensive prospect in optical communication and sensing systems, due to their excellent optical properties. Blazed fiber Bragg grating, an important member of fiber gratings, because of its special structure, not only has all properties of fiber Bragg grating, but also has its own unique properties. With the fiber sensitivity enhanced and the technology of fabrication fiber grating improved, blazed fiber Bragg grating with an excellent character comes true. Now a group of researchers have made their best effort on its applications and it have been used in the area of gain flatten, sensing system and wavelength demodulation.Gas cell is a standard referenc material using the special gas molecular vibration-rotatoin aborption lines which unsesitive with the environment temperature and pressure. Therefore the stabilization of the FBG demodulation system with the gas cell will be improved a lot.The objective of this thesis is to investigate and develop techniques of blazed fiber Bragg grating and the FBG demodulation system with the gas cell.The thesis is supported by the National High-Tech Research and Development Program of China (863 program), the National Basic Research and Development Program of China (973 program), Technological Tackle Key Problem Project of Tianjin, Open Project Foundation of Key Laboratory of Opto-electronic Information Science and Technology, Ministry of Education in Nankai University. In the thesis, the theoretical model of blazed fiber Bragg grating has been made; the experimental research on its sensing and demodulation characteristic has been taken; the application of the gas cell in FBG demodulation system has been made.The contents are listed as follows:1. A brief introduction of history, research significance is presented. Three mature technologies of wavelength demodulation, their own characteristic have been recommended and the history of blazed fiber Bragg grating, its sensing characteristic and wavelength demodulation characteristic have been presented here.2. Using coupled mode theory and volume current method analysed the mode transmissive characteristic in blazed fiber Bragg grating. The wave equations, modes coupled coefficient and Poynting vector have been got here. 3. The sensing theory of blazed fiber Bragg grating is presented here. Theoretical and Experimental research on its temperature sensing characteristic, strain sensing characteristic and refractivity sensing characteristic have been taken. The blazed fiber Bragg grating has the same temperature sensing and strain sensing characteristic as fiber Bragg grating. The transmission power of the blazed fiber Bragg grating decreased linearly with the environment refractive changed and the sensitivity came to 1.718μW/ (10-3 index changed).4. The demodulation characteristic of blazed fiber Bragg grating is presented using edge filter linear demodulation method and side detection of strong radiation-mode method. Theroecally analysis the principle of edge filtering of BFBG dumped in glycerite which is used as edge filterer. It has been proved in the experiment that the demodulation system with BFBG has a good property of wavelength linearly. There are different positions pointing to the differnet wavelengths of theincident light which comes into BFBG and it has been proved in the experiments. The FBG demodulation system with such method has the ability of simple, stable and repeatble.5. Gas cell is applied in the FBG demodulation system. It has been proved that compared with the reference FBG which was usually use, the system with gas cell is more stablility and the precision of the system improved about 10 percent of the former system.