Optical Properties of Asymmetrical Bragg Fiber: With Defect

In the previous chapter, it was observed that the hollow-core high-refractive index contrast of cladding BFs shows high order PPBG along with FWHM at the considered visible design wavelength window 632.8 nm supporting communication as well sensing technology. We have also observed a considerable shift in LBE, RBE, and the whole PPBG with the shift in incidence angle, no. of bilayer periodicity as well as core refractive index. Hence, it also opens the necessity of studying low refractive index contrast cladding BFs for lowering significantly the width of PPBG for considering the obtained lobes as sensing signals. It also suggests on behalf of lowering FWHM of the signal that we can also opt for modification in the present BFs structure. The present chapter will discuss the comparative study between low and high refractive index contrast BFs and explore the interesting result obtained. Along with this, introducing the defect layer either by breaking the symmetry of periodic bilayers in BFs or adding an additional layer in between the periodic cladding layers. So, the present chapter deals with the design mechanism of hollow-core BFs with defects and matching the electric and magnetic fields at various interfaces and cylindrical slabs, the optical relation has been stabilized to obtain interesting features of such multilayer asymmetrical structure. The defect layer within the cylindrical periodic structure exhibits a peak in the ideal photonic band gap region. The width of the defect peak at half of its maximum intensity is determined by the periodicity of the cladding layers. Additionally, the spectral location and displacement of the defect’s peak are contingent upon the light’s angle of incidence, the refractive index of the core material, and the structure’s designated wavelength. Thus, it is more suitable to regard the peak due to the defect to be a sensing signal rather than taking the entire photonic band gap as a signal for sensing.