Optical Properties of Symmetrical Bragg Fiber: Periodic Structures

This chapter provides a comprehensive presentation of theoretical concepts about the propagation of electromagnetic waves in a chalcogenide (As2Se3)-polymeric (PEI) Bragg Fiber (CPBF). The connection between two polarization modes, E and H-polarization, is also addressed. We have presented initial numerical results for two model configurations: the single cylindrical interface and the single cylindrical slab, considering both chalcogenides (with a high refractive index) and polymeric materials (with a low refractive index). The CPBF was specifically engineered to operate within the optimal visible wavelength range of 632.8 nm. This was achieved by the utilization of advanced techniques such as the Transfer Matrix Technique (TMT) and Hankel Formalism (HF), which were applied in cylindrical coordinates. Subsequently, the characteristics of propagation and dispersion in Bragg fiber, which is composed of cladding materials with a strong refractive index contrast, are investigated for the specific wavelength range of 632.8 nm in the visible spectrum. The boundary matching approach was employed to establish a correlation between the incoming and departing light waves using TMT. A Brewster initial radius has been found where the maximum transmittance is consistently reached for both photonic materials in CPBF. The polymeric interface exhibits a lower reflectance compared to chalcogenides for the basic mode (m = 0). Even for higher-order modes, a rapid decrease in reflectance from 100% is observed for the polymeric contact. The reflectance response of both materials in the cylindrical unit slab exhibits both oscillating and non-oscillating components as the wavelength varies. This indicates that the initial radius of the slab significantly influences the optical characteristics, assuming a constant slab thickness. As the initial radius rises, the oscillatory reflectance becomes more squizzing. Additionally, the optical parameter exhibits an oscillating pattern in relation to the thickness of the slab, particularly for smaller mode numbers. It reaches its maximum value and remains constant for the mode number (m = 4). In addition, the observed photonic band gap (PBG) is significant in high refractive index contrast cladding BFs, and fewer periodic cladding layers are needed to obtain a perfect photonic bandgap (PPBG). The spectrum range and spectral position of PBG are significantly influenced by the angle at which the electromagnetic beam is incident. The dispersion properties have been evaluated in this chapter as well. These discoveries pave the path for many applications in the field of optoelectronic devices and sensors.