| As an important part of photonic integrated circuits,polarization control devices need to meet the characteristics of high integration,compactness and large capacity.Unlike conventional optical components and conventional optical fiber devices,photonic crystal fibers are popular for designing polarization devices because of their good nonlinearity,flexible structural design and high integration.In addition,due to the special porous structure of photonic crystal fibers,polarization devices with different properties obtained by filling the inside of photonic crystal fibers with different materials have emerged.Many optical materials that we are familiar with exhibit attractive optical properties under external environment or excitation,and these properties pave the way for tunable polarization devices.In order to solve the shortcomings of the current photonic crystal fiber polarization devices such as complex structure,poor working performance and uncontrollable performance,this thesis designs three different functional selectively filled photonic crystal fiber polarization devices based on mode coupling theory and surface plasmon resonance theory,respectively,using the finite element method simulation software COMSOL,the specific studies are as follows:(1)A voltage-modulated high-performance polarization rotator based on a flat-type photonic crystal fiber is proposed.The core of the fiber is filled with liquid crystal to realize the polarization rotation of the fiber,and the electronically controlled birefringence effect of the liquid crystal is used to realize the voltage regulation of the polarization rotator performance.The simulation results show that the magnitude of the modulation voltage is closely related to the thickness of the flat fiber.When the fiber thickness is 20μm,only an applied voltage of 100 V is required to obtain the highest polarization rotation performance.In the 1.45～1.65 μm band,only 3.99 μm of fiber is required to achieve conversion efficiency close to 100% with a minimum crosstalk value of-26.2 d B.This device with controlled performance and good polarization rotation has promising applications in communication systems and photonic integrated circuits.(2)A voltage-modulated high-performance polarization beam splitter based on a flat-type photonic crystal fiber is proposed.In this structure,high birefringence is achieved by filling the central air hole of the fiber with liquid crystal while achieving voltage modulation of the fiber birefringence.The simulation results show that the fiber can achieve beam splitting in the 1.235～1.4 μm band with a splitting length of 355 μm when there is no applied voltage,and in the 1.45～1.61 μm band with an operating bandwidth of160 nm and a splitting length of 300 μm at 2000 V.This high-performance,photonic crystal fiber polarization beam splitter that can be adjusted for performance without structural changes has very high potential for applications in photonic integrated circuits and optical communication systems.(3)An ultra-wideband silicon core single-polarization photonic crystal fiber based on surface plasmon effect is proposed.In this structure,the left and right air holes of the silicon core are filled with gold nanospheres to excite the surface plasmon mode,and the coupling of the surface plasmon mode and the fiber transmission mode is used to achieve single polarization transmission.The simulation results show that the limiting losses of x-polarization and y-polarization are 1400 d B/m and 15 d B/m,respectively,at 1.55 μm wavelength.With a fiber length of 2 cm,the extinction ratio of both polarization modes is less than-20 d B at 1.51 μm wavelength,while the y-polarization power is still greater than0.5 at 2.24 μm wavelength,achieving an ultra-wide bandwidth of 730 nm for single-polarization transmission.This simple structure of ultra-broadband single polarization fiber has great potential for applications in polarization-preserving systems and photonic integrated circuits. |
