The Research Of Sensing Characteristics Of Liquid Crystal Photonic Crystal Fibers

Photonic crystal fiber which has many advantages to attract the attention of many scholars and researchers is a new type of microstructure optical fiber. There are periodic arrangements of air holes existing in the cross-section of photonic crystal fiber. A flexible design space is provided for photonic crystal fiber by the existence of these air holes. The transmission characteristics can be changed by changing the arrangement, size or holes spacing of air holes. Later, the air holes began to be filled with other substances to change the transmission characteristics of photonic crystal fiber. Because of the high temperature and voltage sensitivity of liquid crystal, it has been increasingly applied to the photonic crystal fiber sensing studies in recent years. In this paper, the sensing properties of photonic crystal fiber filled with liquid crystal in the infrared and terahertz wave band are analyzed theoretically.This paper includes the following:The nature and the concept of photonic crystals and photonic crystal fiber are introduced first. The photonic crystal fiber of optical refractive index type and optical band-gap type are described respectively. Then the research progress in recent years of photonic crystal fibers sensing is analyzed.The optical properties of liquid crystal are introducted briefly. And the nematic liquid crystal is highlighted. Nematic liquid crystal is equivalent to uniaxial crystal, and its optical axis direction is the long axis of liquid crystal molecules. In this paper, the arrangement of liquid crystal molecules is the arrangement that is parallel to the fiber axis. The liquid crystal refractive index can be affected by temperature and voltage. The refractive index of anisotropic liquid crystal is expressed by tensor in this paper.Finite element method and plane wave expansion method which are the theoretical numerical calculation method in this paper are introduced.The temperature and voltage characteristics of refractive index of liquid crystal E7in the infrared wave band are analyzed. The temperature and voltage characteristics of photonic crystal fiber which is the type of refractive index guide filled with liquid crystal in the infrared wave band are analyzed by the finite element software:Comsol. The degrees of temperature and voltage modulation under the different core radius are compared. Temperature sensing properties of bandgap photonic crystal fiber is analyzed based on the whole plane expansion method by the software:Rsoft.Temperature sensing of photonic crystal fiber in the terahertz is made a numerical simulation. Temperature characteristics of the terahertz refractive index of liquid crystal5CB are analyzed. Then temperature sensing properties of photonic crystal fiber of refractive index guide type which is filled with liquid crystal is simulated by Comsol. The situations of different core radius are compared. Temperature sensing mechanism of bandgap photonic crystal fiber is interpreted by anti-resonance model.