Studies on Electromagnetic Wave Propagation in Optical Bragg Fiber Waveguide having a Defect Layer and its Applications for Filtering and Sensing

Abstract

We are familiar with the conventional optical fiber (COF) in which the light is guided through the well-known optical phenomena i.e. total internal reflection. To satisfy this optical phenomenon, the refractive index of core material of COF must be kept higher than the cladding material. These fiber waveguides have many advantages over other waveguides like two wire transmission line and microwave devices as it has larger bandwidth, low power losses (i.e. minimum attenuation), immunity to electromagnetic interference, lighter weight, flexible, safe and secure etc. In spite of these advantages, these COF waveguides have many disadvantages like fundamental modes are doubly degenerate, presence of undesirable polarization and birefringence effect, cladding and material losses, unidirectional light propagation, high nonlinearity, presence of material and geometrical dispersions etc., due to their high refractive index of core material. So, a hollow/air core fiber waveguide may overcome these major shortcomings of COF. The publication of the pioneer work of Yeh and Yariv in 1976 have started the intensive studies on Bragg fiber waveguide (BFW) and sparked the modern interest in this field. The BFW is nothing but a periodic arrangement of high and low refractive index based concentric cylinders, where the light is guided in the waveguide through multiple Bragg reflection. Due to this Bragg reflection, it is possible to propagate the light in a hollow/air core waveguide. Therefore, these waveguides have low non linarites because more than 98% of the mode is confined in air rather than high refractive index silica material, free from polarization and birefringence effect as usually present in COF, no Fresnel reflections at open fiber end due to free space coupling in air, free from material and cladding losses. Due to being hollow core in BFW some biological solution or chemical gases can be put or flow into the hollow core which is much needed for a bio or chemical sensor platform.