Research On Principle And Structure Design Of Optical Switch Under Subwavelength Structure

Optical switches have great significance for improving the quality of optical communications networks and improving the performance of photonic circuits.Take advantage of the bandgap of photonic crystal,it is possible to realize the control of the transmission state of a particular wavelength of light.Switches basing on this principle have better performance than conventional optical switches.Optical switches based on a ring resonator structure can achieve resonance because it does not require the formation of a reflective surface due to the characteristics of its cavity structure,which makes this structure easy to implement under the existing planar optical waveguide processing technology.In this thesis,we study the characteristics of optical switches composed of waveguide micro-ring structures and optical switch designs based on photonic crystals,and complete the following work.Finite-difference time-domain(FDTD)method is applied to get the relationship between the transmittance of a one-dimensional photonic crystal and the lattice constant of the photonic crystal.Based on this,a photonic crystal-based all-optical switch with sub-wavelength structure was designed in combination with a nonlinear material.The all-optical switch signal light is different with the control light in wavelength,and is incident from the same endpoint.After further simulation,the relationship between the transmittance of the signal light and the intensity of the control light field is obtained,and the switching power of the optical switch is obtained.Simulation results show that the extinction ratio can reach 7.8d B,and the vertical size of the optical switch is not longer than 2?m.The output spectrum of a two-dimensional photonic crystal waveguide is obtained by simulation.There is a stop band at 1.5 ?m in the two-dimensional photonic crystal waveguide.The cavity is further filled with a liquid crystal material,and the voltage provided by the electrodes at both sides of the photonic crystal waveguide drives the director of the liquid crystal molecules to achieve the purpose of regulating the output spectrum of the photonic crystal waveguide.The simulation results show that with the increase of ? and ? of the liquid crystal molecules,the output spectrum of the photonic crystal waveguide shows a red shift phenomenon.The switch has good switching performance for wavelength of 1530 nm and 1574 nm,and the extinction ratios reach 13.8d B and 19.5d B,respectively.The transmission characteristics of waveguide-micro-rings are studied,and an optical switch based on waveguide dual ring structure is proposed.The control light illuminates one of the micro-rings in the switch.Band filling,bandgap shrinkage,and free carrier absorption effect will cause refractive index change.The relationship between the transmissivity of the switch and the refractive index of one of the micro-rings was obtained by simulation.Comparing the output spectrum in the case of changing only the refractive index of one of the micro-rings and the output spectrum of separately exciting the two micro-rings,it was found that they were different.Further analysis shows that two factors contribute for this difference: 1.the change of the output spectrum due to the change of the refractive index of the micro-ring.2.the phase difference between the light coupled from the different micro-ring due to the change of index of the micro-ring.Data got by simulation shows that the extinction ratio of the proposed switch can reach 12.5 dB.The investigation on all-optical switches presented in this thesis can provide certain indicative significance for the design of all-optical components and parts liable to be microminiaturized and integrated in future.