Splicing And Fabrication Of Grating Based On Research Of Mechnism Of Heat Transfer And Defromation For Photonic Crystal Fibers

Photonic crystal fiber is a new type of optical fiber, also named as microstructure fiber or holey fiber. An periodical or random arrangement of wavelength-scale air holes run along the full length of the fiber in the cladding region, which induces many unique properties such as high nonlinearity, dispersion tailoring, high birefringence, endlessly single-mode and so on. Many fiber devices based on the photonic crystal fibers are developed including fiber sensor, laser, dispersion compensator, gyroscope and so on. However, little or no work on heat transfer property and air-hole collapse under the high temperature distribution of photonic crystal fiber, which are the basical fundament for the development of optical fiber devices. This paper investigates the heat transfer and mechanical model of photonic crystal fiber under the irradiation of CO2 laser, which would be typically applied in the photonic crystal fiber splicing and fabrication of long period grating on photonic crystal fibers.The main contents are as follows:First, three-dimensional transient heat conduction model is established based on the basic heat transfer differential equation to analyze the temperature distribution on the cross-section and the longitudinal length. The air-hole mechanical model and deformation model under different temperature distribution of photonic crystal fiber are established to demonstrate the air-hole collapse under high temperature.Second, the heat transfer differential equation and the air-hole deformation model are applied in fusion splicing. Laser power, heat source offset depends on the structural parameter, and simulations demonstrate laser power and heat source offset as a function of structural parameter. A the quantitative equation is obtained which can help to predict the splicing laser power in practical ex periments. Fusion splicing experiments are conducted to verify the theoretical analysis.Third, the heat transfer differential equation and the air-hole deformation model are applied in long period grating fabrication on the photonic crystal fiber. A nove l fabrication technique is proposed to induce a long period grating in photonic crystal fiber which result from refractive index modulation by twist the fiber principle axis forth and back with small CO2 laser power without air-hole collapse. The coupled-mode theory is used to analyze the transmission characteristics of the new rocking long period grating. Based on the heat transfer and mechanical analysis of photonic crystal fiber under irradiation of CO2 laser, the laser power are predicted to applied in rocking long period grating fabrication to avoid air-hole collapse.Finally, the experimental system is set up, and the rotation stage and CO2 laser are applied to the fiber alternatively to induce the permanent twist automatically. The transmission characteristics of the rocking long period grating are experimental studied and compared with that of conventional long period grating in photonic crystal fiber.