Design And Sensing Characteristics On Photonic Crystal Fibers

Photonic crystal fiber(PCF), a new waveguiding material, appeared in recentyears as an alternative of the traditional fiber. It has a different guiding principlefrom the traditional fiber and shows superior performance to traditional fiber byproperly design such as the endless single-mode transmission, the adjustabledispersion, a remarkable nonlinear effects, the extremely low confine loss. The fibersensor made of PCF attracts a lot of research attention for its simple structure,common preparation and excellent characteristics. This paper is mainly about thedesign of a novel photonic crystal fiber and the preparation of a new photoniccrystal fiber sensor.First, the designed "8"-shaped core photonic crystal fiber was simulated by thefinite element method. The transmission of different wavelength were calculatedand many properties were found, such as dual-mode transmission, highbirefringence, near zero flattened dispersion and low confine loss. Further studyrevealed the influence of the hole spacing and the diameter of the air holes on theabove properties. The calculations found that the properties improvements were leadby the mode field distribution of a transmission mode, and the limiting effect of thehole spacing is much greater diameter than some of the air holes diameter. Inaddition, fine-tuning the position of the inner layer of the air holes would bringsome special phenomenon, for example, the fundamental mode and the second-ordermode splitting; octagonal outer layers instead of hexagonal outer layersthe modefield will be good limit in the core region even in the long wavelength region, andthis photonic crystal fiber design would produce a higher birefringence, a wider flatdispersion and lower confine loss.Second, the non-adiabatic photonic crystal fiber taper sensor and S-typephotonic crystal fiber taper sensor were studied. In this paper, the taper sensor’spreparation, sensing mechanism, sensing tests were carried out. The non-adiabatictapering process caused the collapse of the air holes in photonic crystal fiber, notonly stimulate higher order modes, but also transfer the modes to the surface of thetaper. The propagation constant of this part of the modes would be impacted byoutside environmental. When the interference occurs between modes, theinterference spectrum would carry the information of the external environment. TheS-type photonic crystal fiber optic taper utilized the advantages of the shape toexcite higher order mode and transmit them to the surface. Therefore long taperlength and slim waist diameter are not needed to bring the better interference spectrum. The S-type photonic crystal fiber tapers are superior to non-adiabaticphotonic crystal fiber cone in durability.In addition, the application of the two sensors are very extensive, especially inthe refractive index of the test of micro area. The environmental refractive indexbring the exponential redshift response. The axial tensile stress test made the non-adiabatic photonic crystal fiber tapers linear blueshift and S photonic crystal fibertapers exponential redshift, which are caused by the deformation in stretching of theS-shaped taper. In the temperature sensing test, the temperature raising make thespectrum linear redshift, but this linear change is segmented, and above100°Credshift were accelerated.