A hybrid photonic crystal fiber was proposed in

A hybrid photonic crystal fiber was proposed in [27] which show birefringence of 3.79×10−2 and high nonlinearity of 40.1 W−1km−1 at the wavelength of 1.55μm. In [13], hybrid cladding PCF was proposed where the holes of the cladding wherein different shapes and used for dispersion, a nonlinear effect, birefringence and effective area. High birefringent PCFs can easily be realized for design flexibility and high Index contrast. There are lots of significant applications of high birefringent PCFs such as- fiber sensors, fiber filters, fiber communication etc. By depicting an asymmetric solid fiber core which is surrounded by air holes having double/triple defect core of PCF can be shaped for achieving high birefringence [28]. On the other hand, several papers show that ultrahigh birefringence can be gained by applying elliptical holes [28]. It is not easy to fabricate PCFs with elliptical holes accurately [29]. In addition, birefringence study in PCFs is growing interest day by day. The design of PCFs with high nonlinear coefficients due to its small effective area is more challenging [30]. Besides, in the field of telecommunication and supercontinuum applications nonlinearity with high birefringence derived a massive interest [31]. In this epothilone paper, a microstructure core based photonic crystal fiber is proposed that shows high birefringence, high relative sensitivity and lower confinement loss at the same time. The proposed PCF contains five rings of air holes in the cladding where the core contains elliptical air holes. The air holes of cladding are kept same to avoid design complexities. The proposed PCF shows 53.07% relative sensitivity as a gas sensor. Besides, the PCF shows high birefringence of 6.9×10 and lower confinement loss of 3.21×10, the high nonlinearity of 15.67Wkm at the wavelength of 1.33μm. V parameters show the proposed PCF is a single mode fiber with a large effective area 3.88μm2 at the wavelength 1.33μm. In addition, splice loss and beat length are also analyzed. A large number of analyses of the guiding and optical properties of PCF take place in this paper which makes our research unique one.
Geometries of the proposed E-PCF Fig. 1 shows the transverse cross-sectional view of the proposed E-PCF. The cladding contains five rings of air holes in hexagonal manner. This method was introduced by [25] where the cladding was hexagonal with six missing holes in the edges of the outermost cladding. The diameters of two outermost ring and the three innermost rings were not same in the work. In our proposed E-PCF the diameters of all the five rings of cladding were kept same to match the proper fabrication tolerance and assumed as d. The concept of microstructure core was introduced by [24]. In [26] elliptical holes were used to get high birefringence. In the proposed E-PCF the core is organized with an array of 8 elliptical air holes which is horizontally arranged. The major and minor axis of the elliptical air holes is defined as da and db respectively. The hole to hole distance of two adjacent air holes is called pitch. The pitch between the holes of core and the holes of cladding is defined as Λ1 and Λ respectively. By article [25], the diameters of the innermost ring are responsible for high sensitivity and the diameters of outermost rings are responsible for lower confinement loss. In our proposed E-PCF the cladding air holes are optimized bigger to attain the low confinement loss and make the proper interaction of light through the core. All the parameters of both core and cladding were optimized by varying as a function of wavelength. By using perfectly matched layer (PML) boundary condition the optical properties and propagation characteristics of leaky mode can be measured. The PML is set 10% of the total diameter of the proposed E-PCF to meet the boundary condition.
Synopsis of the simulation method A finite element method (FEM) is used for solving Maxwell\'s Equation to simulate the guiding properties of the proposed PCF. It can solve very complex structures and can provide full vector analysis of different PCF structure [32].