Fabrication Of Long-period Fiber Gratings And Sampled Fiber Gratings And Their Application In Fiber Gyroscopes And EDFA

At the present information and communication time, the amount of the continuously required information indicates the national civilization and national power and becomes the international rivalry focus. Various communication businesses continuously increase and the especially fast development of Internet induces rapid increase of communication capacity. Thus, it is necessary to establish large-capacity and high-speed optical fiber communication system. UV-written fiber gratings developed since 1990 provide possibilities for the further development of large-capacity and high-speed optical fiber communication system. UV-written fiber gratings possess simple fabrication, excellent property and low-cost, and its application has entered into the area of optical fiber communication. The structure and performance of many devices in optical fiber communication can be improved when fiber gratings are put in. In this thesis, it is brief introduction to the development of the fiber communication and the extensive applications of fiber gratings in this field firstly. And then I introduce my theoretical and experimental work. In the theoretical aspect, I deduced the general equations for the couple modes from Maxwell equations; obtained the brief theory of Bragg fiber gratings; acquired the particular mode-coupled theory for Long-period fiber gratings (LPGs); proposed and demonstrated an idea of the equalization for EDFA using quantum coherence and interference. In the experimental aspect, we studied the effect of the experimental factors on the spectra feature of LPGs; mastered the fabrication method of high quality LPGs; analyzed the thermal-decay rules of LPGs; completed the temperature-compensating package for the sampled fiber Bragg gratings. The above work will become the basis of the application of Long-period fiber gratings and sampled fiber gratings. The inventional results of this thesis are summarized as follows: 1. The theory of waveguide modes is deduced based on Maxwell's equations. It is briefly deduced for the field distribution of Bragg fiber gratings using couple mode theory. The strictly couple mode theory of LPGs is obtained using weak waveguide approximation. The relation between the optical spectra of LPGs and their wavelengthes, grating periods and refractive indexes was acquired. In the process of the fabrication of LPGs, the experimental results approach theoretical analyses. 2. Based on the above theories, we designed and fabricated some amplitude masks with different length and period by use of amplitude masks and scanning exposure methods. During the fabrications, we summarized factors of affecting spectra of LPGs including the length of LPGs, grating period, order of couple modes, refractive-index changes of fiber. We realized the fabrication of LPGs with transmission losses in the range of –1 to –20dB, and the bandwidth of resonance peaks arraging from 5 nm to 30 nm. We also realized the fabrication of sampled gratings by use of phase masks. We propose our own view on choosing annel temperature and time in the experiments of thermal-decay of the LPGs. We systematically studied the feature of strain and temperature of LPGs. It is found that the shift of resonance peaks of LPGs is linear with strain and temperature. This provides possibility for the applications of fiber grating sensor. We calculated theoretically the feature of temperature and strain of LPGs in order to obtain continuous distributions of resonance peaks with changes of temperature and strain. The experimental results meet the theoretical prediction. 3. We measured the characteristics of strain and temperature of sampled fiber Bragg gratings and found that the wavelength of the reflected peak is linearly changed with strain and temperature (temperature shift coefficient is equal to 0.01 nm/oC). The shift rules for the different wavelength is the same, which means the channel span keeps identical when the strain and temperature changed. Therefore, we proposed a method for the first time to package fiber Bragg gratings by thematerials with negative temperature coefficients. The temperature coefficients of the optical fiber gratings packaged in this way are about 0.004nm/oC. This reaches the requirements for the applications. We realize simultaneous measurement of strain (0~1800με) and temperature (20~100oC) using the response characteristics of Bragg grating and long period grating, which is that the shift of the transmitted peaks for Bragg grating and long period grating are linear with strain and temperature with the different values of strain and temperature coefficients. 4. The resonant wavelength and transmitted intensity can be adjusted by HF erosive method. It meets the actual requirements with the wavelength range of 10~200nm, which is obtained by choosing erosive time and order of couple modes. This method can increase the wavelength and intensity of LPGs. We carried out the calculation and experimental fabrication to use LPGs to filter the fiber sources of the fiber gyroscopes and flatten EDFA gain. Based on the theoretical calculations, we fabricated LPG with a peak at 1531.8nm, bandwidth of 4.6nm and peak value loss of -15.1dB, using scanning exposure method. The further experiments are still continuous. Additionally, we proposed ourselves views on the key technologies required during practical applications. It reaches the design requirements to filter the fiber gyroscopes sources and flatten ASE spectra of EDFA. 5. We propose and demonstrate a scheme of gain leveling for erbium-doped fiber amplifier (EDFA) by applying a strong coherent field to a three level amplified system using quantum coherence and interference. Considering the effect of this coupling field on the Stark-splitting sublevels and choosing a proper intensity and frequency for the coherent field, this scheme can be realized a flat gain operating in the 1530-1560 nm. The next step is continuous to carry out the further experiments. VIUV-written LPGs and sampled Bragg gratings are developed as new kinds of fiber grating devices after 1995. Its application areas should be further developed because they merged recently. At present, UV-written sampled Bragg gratings and LPGs in our laboratory have obtained: Sampled Bragg gratings meet the applicable requirements after using our package technology. For the LPGs:...