Design of the proposed FP-PCF
Fig. 1 shows the end-faced of proposed FP-PCF. It is a PCF with microstructure porous shaped infiltrated with aqueous analysts ethanol (n=1.354). Circular five layer air hole surrounded by the core acts as cladding region. The core region exists two layers microstructure holes where the radius of the core is homogenous. The core holes radius are rc=0.18nμm. The hole to hole distance is called pitch and denoted by Ʌ. For the core the pitch is denoted by Ʌc=0.4nμm. For the cladding region five layers are hole diameter are d3=1.48nμm, d2=d4=1.05d3μm, d1=d5=1.10d3μm and pitch distance are Ʌ1=1.81nμm, Ʌ2=Ʌ3=Ʌ4=Ʌ5=0.98Ʌ1μm. As the cladding region much air holes are existed and the core is infiltrated with chemical so the refractive index of core is greater than cladding region. As a result, the light propagating mechanism of this FP-PCF is TIR. The host material of the proposed PCF is silica which is highly uses to manufacture the optical fiber. Anisotropic perfectly matched layers are used to reduce undesirable electromagnetic reflection acting as absorbing boundary condition. The depth of PML boundary is 10% of the total cladding. Among various photonic crystal fibers manufacturing technique sol-gel technique is most suitable to make the fiber successfully. The numerical investigation is run over the parameter and shown details in below.
The host material of the proposed PCF is pure silica. Silica has a refractive index dependency on wavelength followed by Sellmeier Eq. .where B1=0.6961663, B2=0.4079426, B3=0.8974794, C1=0.0684043, C2=0.1162414, C3=98.96161 and n (λ) is the refractive index for corresponding operating wavelength λ in μm.
A most powerful numerical simulation tool is full vectorial finite rotenone method. This method has the greater efficiency for any kind of complex geometry structure to calculate. Various photonic waveguide devices are numerically analyzed by FEM [28,29]. FEM processes complex structure PCF in homogenous subspaces and then computed with Maxwell\’s vector equation.where, [s] is the PML matrix; inclusion with PML parameter Sx and Sy, E is the electric field vector, the wave number k0 which is a function of wavelength (λ) followed by the equation,
Running time of simulation, COMSOL solve Maxwell\’s equation internally, and simulation outcomes provide the propagation constant of the operating wavelength. The propagation constant of corresponding mode may complex numbers. PCF characteristics effective mode index and confinement loss are calculated from this. The real part produces the effective mode index and imaginary produces confinement loss. These are calculated by using the following equations,
When the power flow through the fiber some power penetrates into cladding region of the fiber, this causes confinement loss or leakage loss,
The effective mode area of the proposed PCF structure can be calculated the propagating mode area by given equation,where, E is the transverse electric field. Computation of nonlinear coefficient γ(λ) is fully dependent on two parameter n2 and Aeff. The n2 is the nonlinear coefficient of PCF forming material. Here PCF formation material silica has a nonlinear coefficient n2=3.0×10m2W. The nonlinearity of the PCF can be calculated by following relation,
Numerical aperture is the properties of the fiber can be calculated by the following equation,
For the purpose of sensing applicant it is needed to evaluate the relative sensitivity coefficient,
The relative sensitivity coefficient r is closely associated with f. Calculating sensitivity and the f is represented bywhere Ex, Ey and Hx, Hy are the transverse electric fields and magnetic fields of the mode respectively.
Effective refractive index is a function of wavelength λ. Fig. 2 demonstrates the relationship of effective refractive index verses wavelength of the proposed FP-PCF at the operating wavelength band E+S+C+L+U for x polarization. The wavelength increment lowers the effective refractive index linearly. The proposed FP-PCF is propagating light on the basis of TIR. From Fig. 2, it is nicely acquitted that the light is tightly confined with larger area through the core region for both x and y polarization. So the leakage loss of proposed FP-PCF will be very low. Besides, in case of sensor design higher the sensitivity is highly demanded. Not only to gain higher sensitivity and lower confinement loss simultaneously but also to identify fiber characteristics it must be needed to be perfectly optimized. A simple optimization technique is followed here. This process is divided into three modules. Modules are done step by step, discussed below.
Design of the proposed FP-PCF