Slow Light Characteristics And Sensing Research Of Photonic Crystal Waveguide

Slow light is defined as the light propagating in the medium with a smaller group velocity than that in vacuum.Slow light can enhance light-matter interaction,which makes it a good prospect in the fields such as nonlinear optics,optical communication,optical sensing etc.There are plenty of ways to achieve slow light effect.Among these methods,photonic crystal waveguide(PCW)with strong parameter controllability,easy integration with optical system and good nonlinear effect has become an important method to achieve slow light.This paper studies the slow light characteristics and sensing applications of one-dimensional(1D)and two-dimensional(2D)photonic crystal waveguides.As a typical representative of 1D-PCW,the transmission characteristics of fiber Bragg grating(FBG)based on the coupled mode theory are analyzed.The slow light effect is achieved and optimized by adjusting the structure parameters of grating.And the sensing research is performed by using the customized FBG.The 2D photonic crystal slow light waveguide is studied based on plane wave expansion(PWE)and supercell theory.Slow light characteristic is optimized by adjusting the location of dielectric cylinders on both sides of the defect based on the line defect PCW,which obtains lower group velocity.Then the refractive index sensing research is performed by using the optimized 2D-PCW.The main contents of this paper are as follows:1.For 1D-PCW,the coupled mode theory and slow light mechanism of uniform FBG are analyzed.For 2D-PCW,the band structure,guided mode characteristics of defect waveguide and slow light mechanism are analyzed.Then the theoretical basis of sensing using the slow light effect in FBG and PCW is introduced,which shows that the larger time delay is,the higher sensing sensitivity is.2.The influences of index modulation depth,grating length and period on slow light effect in FBG are simulated.The theoretical value of sensitivity is also calculated.According to the results,the deeper modulation depth and the longer grating length are,the greater maximum group time delay and sensitivity are.The period mainly decides the location of center wavelength and has little effect on group time delay.The experiment of slow light time delay for a customized FBG is conducted.The greatest group time delay is about 273.84 ps with a corresponding wavelength at 1552.56 nm.Then the sensing experiment using slow light effect in FBG is conducted.The FBG exhibits good linearity with a minimum detectable strain of 0.0145 με when the strain range is from 0 to 12.8 με.3.The band structure of perfect two-dimensional square lattice photonic crystal with silicon cylinder is analyzed.By adjusting the radius of cylinder,a larger bandgap is obtained.A new type of photonic crystal slow light waveguide is designed based on the line defect PCW.The group velocity can be reduced to 0.00142 c by changing the location of some cylinders on the both sides of the line defect channel.Then the optimized photonic crystal slow light waveguide is used for refractive index sensing.The sensitivity is more than 2 μm/RIU with a very good linearity,which can distinguish some gases and liquids efficiently.The result provides a reference for the application of slow light waveguide in sensing field.