Optimized Design And Permormance Analysis Of Polarization Device Based On High Birefringence Photonic Crystal Fiber

Photonic crystal fiber,who has the characteristics of flexible structure and high birefringence,can be utilized to develop the new polarization devices.The new polarization devices can overcome the defects of traditional optical fiber polarization devices,such as long device length and narrow working bandwidth.In this paper,the finite element method is used to simulate the mode field distributions,loss and birefringence,when the light transmits in photonic crystal fiber.Combining with the modes coupling theory,the structures of photonic crystal fiber are optimized,and the performances of the photonic crystal fiber polarization filters and polarization beam splitters are analyzed.The main research contents are as follows:First,the gold layers are added near the core of photonic crystal fiber with rhombus structure,of which the hole pitch in the y-direction is compressed.It is investigated that the effects of changing the hole pitch and the thickness of gold layer on the surface plasmon resonance wavelength of two orthogonal polarization directions.By changing the hole pitch and the thickness of gold layer,the resonance wavelength of the y-direction is adjusted to the communication window of 1550 nm,and a single-mode single-polarization filter near 1550 nm is realized.Second,the structure parameters of photonic crystal fiber with square structure arranged vertically by two sizes of air holes are changed,and the influence of changing the diameters on the loss curve is studied.Comparing the transmission characteristics of four groups optical fibers with different apertures,a 1550 nm low-loss photonic crystal fiber polarization filter is obtained,by the rational selection of the optical fiber parameters.Third,the structural parameters of the gold-filled dual-core photonic crystal fiber are changed,including the diameters,hole pitch and gold layer thickness.The effects on the coupling lengths in two orthogonal polarization directions and on their ratio are investigated.According to the simulation results,three structures of photonic crystal fiber are optimized.Different polarization beam splitters are repectively obtained: a broadband polarization beam splitter based on the rhombus structure photonic crystal fiber for 1550 nm,a narrowband polarization beam splitter based on D-type photonic crystal fiber for 1310 nm,and a narrowband polarization beam splitter based on rectangular structure photonic crystal fiber for 1550 nm.Finally,two oval air holes are arranged between two cores of rectangular structure dualcore photonic crystal fiber.The lengths of minor axis of elliptical pores are changed.The effects on the polarization coupling lengths of x and y directions and the ratio of two coupling lengths are investigated.The ratio of two coupling lengths is modulated by changing the minor axis length of elliptic pores between two cores.Low-loss photonic crystal fiber polarization beam splitters at the wavelengths of 1310 nm and 1550 nm are obtained,respectively.