Khem B. Thapa

OMNI-DIRECTION REFLECTION IN ONE DIMENSIONAL PHOTONIC CRYSTAL

It is well known that under certain conditions, one dimensional photonic crystal (1D-PC) displays total omni-directional reflection (ODR) band gaps. The enhancement of total omnidirectional reflection band gap in 1D-PC is calculated theoretically. Using Transfer Matrix Method (TMM) and Bloch theorem, the reflectivity of one dimensional periodic structure for TE and TM-modes at different angles of incidence has been calculated. 134 Srivastava et al.

STRUCTURAL PARAMETERS IN THE FORMATION OF OMNIDIRECTIONAL HIGH REFLECTORS

We investigate the structural parameters for the formation of omnidirectional photonic band gap in one dimensional photonic crystal. Simple transfer matrix method is used for calculations. The effect of two parameters, namely, refractive index contrast and filling fraction on omnidirectional reflection is investigated. We find from our study that when nL, ni, ns and d are fixed, omnidirectional bandgap increases with increasing nH/nL i.e., with increasing nH . Therefore, omnidirectional bandgap can be increased by using the material of high refractive index nH when the low index material nL is fixed. We

General Regression Neural Network and Radial Basis Neural Network for the Estimation of Crop Variables of Lady Finger

Estimation of crop variables is necessary for crop type monitoring as well as crop yield forecast. At the present era artificial neural network methodology are widely used to the remote sensing domain for numerous applications like crop yield forecasting and crop type classification. In the present work, two neural network models namely general regression neural network (GRNN) and radial basis function neural network (RBFNN) are used to estimate crop variables: leaf area index (LAI), biomass (BM), plant height (PH) and soil moisture (SM) by using ground based X-band scatterometer data. The both networks are trained and tested with X-band scatterometer data. The performance of the GRNN and RBFNN networks are found that the radial basis approach is more suitable for crop variable estimation in comparison to the GRNN approach. This work presents the applicability of neural network as an estimator and method employed could be useful to estimate the crop variables of other crops.

ENHANCED ABSORPTION IN PERIODIC ONE- DIMENSIONAL METALLIC-ORGANIC PERIODIC STRUCTURE

We show theoretically that the absorption of one dimensional metal-organic periodic structure (1D MOPS) can be enhanced due to organic constituents. We have used simple transfer matrix method to calculate the absorption, transmittance and reflectance of the 1D MOPS systems. The absorption, transmittance and reflectance of 1D MOPS containing 3.5 periodic of Ag/N,N′-bis-(1naphthyl)-N,N′diphenyl-1, 1biphenyl-4, 4diamine (NPB) structure are calculated taking optical constant of NPB [1] and Ag [2]. The enhanced absorption of the considered structure is obtained in the visible and near infrared regions. Besides this, we have also studied the absorption, transmittance and reflectance of the 1D MOPS with air and glass substrates. We find that the absorption is enhanced with variation of thickness of organic layer (NPB). Such absorption enhancement in 1D MOPS could allow many potential applications in photothermal technology, thermo photo-voltaic and blackbody emission.

Omni-directional bands in multilayer structure containing exponentially graded materials

The omni-directional reflection (ODR) in a one-dimensional multilayered structure containing exponentially graded material is studied theoretically using the transfer matrix method. We propose a periodic multiplayer structure containing alternate layers of the exponentially graded refractive index and layers of constant refractive index. The reflectance for TE- and TM-modes of the structure are studied for different angles of incidence. We obtained two ODR bands, one in the visible and the other in the infrared region for both polarizations. The behavior of the ODR band in the infrared region is different from the usual Bragg ODR band in the visible region. The width of the ODR band for the TM-mode is larger that for the TE-mode in the wavelength range 850 nm–1050 nm. Such a structure with a large ODR band may be useful in the design of a broad infrared reflector.

Photonic and omnidirectional band gap engineering in stack of exponential graded index material and negative index material

We have investigated the photonic band gaps (PBG) and omnidirectional band gaps in one-dimensional photonic crystals made up of alternate layer of exponential graded index material and negative index material. We have considered the influence of material properties, geometrical parameters and material composition on the PBG and omnidirectional band gap. Results show that the parameters of exponential graded index material and negative index material can change the photonic and omnidirectional band structures remarkably. Number and bandwidth of PBG increases with increasing the negative index material layer thicknesses while thicknesses of graded index layer only have an effect on the bandwidth of PBGs. The bandwidth of PBG also depends on grading profile parameter of exponential graded index layers and bandwidth can be tuned with increase the value of grading profile parameter. This work can facilitate the design of filters and reflectors, and provide the basic understanding of the influence of graded index materials and metamaterials on the PBG properties.

Reflectance properties of one-dimensional metal-dielectric ternary photonic crystal

Metallic photonic crystal has a very important application in absorption enhancement in solar cells. It has been found that an ultra-thin metallic layer becomes transparent due to internal scattering of light through the each interface of the dielectric and metal surfaces. The metal has absorption due to their surface plasmon and the plasmon has important parameters for changing optical properties of the metal. We consider ternary metallic-dielectric photonic crystal (MDPC) for having large probabilities to change the optical properties of the MDPC and the photonic crystals may be changed by changing dimensionality, symmetry, lattice parameters, Filling fraction and effective refractive index refractive index contrast. In this present communication, we try to show that the photonic band gap in ternary metal-dielectric photonic crystal can be significantly enlarged when air dielectric constant is considered. All the theoretical analyses are made based on the transfer matrix method together with the Drude m...