Photonics and Optoelectronics (P&O) Volume 2 Issue 1, January 2013 www.jpo-journal.org/ 17 Defect Mode Properties and Origin in one Dimensional Photonic Crystal Vipin Kumar 1 *, B. Suthar 2 , J. V. Malik 3 , Arun Kumar 4 , Kh. S. Singh 5 , T.P. Singh 6 , A. Bhargva 7 1,5 Department of Physics, Digamber Jain College, Baraut-250611, India 2 Department of Physics, Govt. College of Engineering & Technology, Bikaner 334004, India. 3,6 Department of Physics, Janta Vedic College, Baraut-250611, India 4 AITTM, Amity University, NOIDA, India 7 Nanophysics Laboratory, Department of Physics, Govt. Dungar College, Bikaner 334001 India 1* vrpcommon@gmail.com; 2 bhuvneshwer@gmail.com; 3 vk_ccsum@rediffmail.com; 4 arun_mtech@yahoo.co.in; 5 khundrakpam.ss@gmail.com; 6 vrpcommon@indiatimes.com; 7 anamib6@gmail.com; Abstract The properties and origin of defect modes in the one dimensional photonic crystal (PC) with a central defect has been studied. Two types of photonic crystals, each having single defect, namely, symmetric and asymmetric PCs are considered. It is found that a defect mode arise at central wavelength for asymmetric PC, whereas two defect modes arise in the vicinity of central wavelength for symmetric PC. These two defect modes can be fixed to a single central defect by increasing the width of the defect layer. But the intensities of these defect modes are found to be different from the intensities of defect modes for asymmetric case. The origin of these defect modes can be explained using impedance matching condition. The propagation characteristics of the proposed structure are analyzed by using the transfer matrix method. Keywords Defects; Transfer Matrix Method; Symmetric and Asymmetric PCs; Impedance Matching; Transmittance Introduction Photonic crystals (PCs) which are artificial structures with periodically modulated dielectric constants have been attracting a great deal of interest among the researchers particularly for the study of their electromagnetic properties [1-7]. It was observed that periodic modulation of the dielectric functions significantly modifies the spectral properties of the electromagnetic waves. The electromagnetic spectrum in such structures is characterized by the presence of allowed and forbidden photonic energy bands similar to the electronic band structure of periodic potentials. For this reason, such a new class of artificial optical material with periodic dielectric modulation is known as photonic band gap (PBG) material [8]. Fundamental optical properties like band structure, reflectance, group velocity and rate of spontaneous emission, etc. can be controlled effectively by changing the spatial distribution of the dielectric function [4, 5]. Photonic crystal structure has many interesting applications in the field of photonics and optical engineering. PCs can guide the flow of light inside them, and they have many applications such as localization of the light wave [9], inhibition spontaneous emission [10], lasers [11-13], waveguides [14], splitters [15], antennas [16], optical fibres [17], ultrafast optical switches [18], optical circuits [19], tuneable optical filters [20] and absolute omni-directional PBGs [21-25]. These applications can be realized using pure PCs, but doped or defective PCs may be more useful, just as semiconductor doped by impurities are more important than the pure ones for various applications. The idea of doped PCs comes from the consideration of the analogy between electromagnetism and solid state physics, which lead to the study of band structures of periodic materials and further to the possibility of the occurrence of localized modes in the band gap when a defect is introduced in the lattice. These defect-enhanced structures are called doped photonic crystals and present some resonant transmittance peaks in the band gap corresponding to the occurrence of the localized states [26], due to the change of the interference behaviour of the incident waves. Defect(s) can be introduced into perfect PCs by changing the thickness of the layer [27], inserting another dielectric into the structure [28], or removing a layer from it [29, 30].