Study On Characteristics Of High-birefringent Photonic Crystal Fiber And Its Polarizing Device

Photonic crystal fibers have many excellent performance characteristics.Among them,high-birefringence characteristics can keep the polarization state stable of the fiber,and have a good development prospect,has received extensive attention in recent years.The photonic crystal fiber has adjustable parameters and flexible structure.By changing the symmetrical structure of the air holes and adding asymmetry factors such as ellipse or other materials such as metal,can achieve high-birefringence characteristics of the photonic crystal fiber,and many new fiber polarization devices with good performance are designed with this.The photonic crystal fiber is applied to coherent optical communication,fiber optic gyroscopes,fiber optic sensors,harmonizable fiber lasers and so on,and has great potential in the fields of industrial manufacturing technology and communications.We mainly studies the high-birefringence of the photonic crystal fiber formed by structural changes and applies it to optical devices to design two kinds of polarization devices.The main innovations obtained are as follows:Firstly,the square structure photonic crystal fiber structure model of quartz substrate is designed,and the asymmetry factor of ellipse is introduced in the core region to destroy the symmetry of the structure.The simulation shows the birefringence intensity of the fiber reached 2.1×10-3 at the communication wavelength of 1.55 ?m,exhibiting the high-birefringence characteristics.And when we analyze the influence of fiber structure parameter changes on the birefringence characteristics,it is proved that the symmetry of the fracture structure plays an important role in achieving high-birefringence characteristics.Secondly,we use the high-birefringence characteristics of photonic crystal fiber to design a gold-coated polarizing filter,the surface plasmon resonance phenomenon occurring at a specific wavelength which can leak the core energy to the surface of the gold layer and achieveing the performance of polarization filtering.The polarizing filter is simulated by finite element method and the data shows that at the communication band wavelength of 1.38?m,the loss in the y-polarization direction reachs 403.76 dB/cm,while the loss in the x-polarization direction is only 19.26 dB/cm.The loss ratio of the direction is more than 20 times.Furthermore,a two-core photonic crystal fiber of square-structured is designed,and three elliptical air holes near the core are introduced to achieve high birefringence characteristics.The simulation shows the coupling length of the two polarization directions ratio is 6:5 at the wavelength of 1.55 ?m.When the length of the passing photonic crystal fiber is 755 ?m,the light in the two polarization directions will be separated,and the splitting function of the polarization beam splitter is achieved.The influencing factors of the coupling characteristics are analyzed as well,and the key role of the fiber structure parameters in changing the coupling length ratio of the two polarization directions,which achieves the function of the polarization beam splitter.Finally,the process of preparation the photonic crystal fibers by stacking method is mentioned.We analysis the problems encountered and propose the feasible solutions.