S. P. Ojha

ENHANCEMENT OF OMNIDIRECTIONAL REFLECTION BANDS IN ONE-DIMENSIONAL PHOTONIC CRYSTALS WITH LEFT-HANDED MATERIALS

In this paper we show, theoretically, that total omnidirec- tional reflected frequency band is enlarged considerably by using one- dimensional photonic crystal (PC) structure composed of alternate lay- ers of ordinary material (OM) and left handed material (LHM). From the analysis it is found that the proposed structure has very wide range of omnidirectional total frequency bands for both polarizations in com- parison to the normal PC structure, which consists of alternate layers of ordinary material having positive index of refraction. The proposed structure also has an absolute band gap that can be exploited to trap the light.

OMNIDIRECTIONAL REFLECTION BANDS IN ONE-DIMENSIONAL PHOTONIC CRYSTAL STRUCTURE USING FULLERENE FILMS

We study the omnidirectional reflection (ODR) in onedimensional photonic crystal (PC) structures consisting of alternate layers of fullerene-gallium arsenide (GaAs), fullerene-germanium (Ge) and fullerene-telurium (Te). The proposed structures give 100% reflection within a very wide range of wavelength in the visible and in a very narrow portion of near IR region of the EM spectrum. Fullerene (C60) in the form thin film structure is a suitable candidate for the designing the PC structure because alkali-metal doped thin film of fullerene acts as conductor and have almost zero absorption in the wavelength range > 530 nm and near IR region. Also, in this region its dielectric constant has very small dependence on the frequency and can be ignored. Thus being a metallic counter part as well as almost frequency independent dielectric constant and easier fabrication technique it is useful in designing the PC structure. The investigation has also been made for the study the role of ambient medium and effect of number of layers in the formation of ODR.

Analysis of the guidance of electromagnetic waves by a deformed planar waveguide with parabolic cylindrical boundaries

An analytical study of a waveguide with two parabolic cylindrical surfaces separating the guiding region of refractive index n1 from two cladding regions of common refractive index n2 with n1≳n2 is presented. The cutoff conditions for modes are derived as equations containing trigonometric functions. The modes show a bunching tendency instead of well‐defined discreteness, and several mode bunches occur because the distance of separation between the two interfaces does not remain constant but continues to increase as one moves away from the region near the vertices of the parabolas. Unlike the planar waveguide, a nonzero cutoff is deduced which may be attributed to the curvature of the boundaries, and the flare.

DESIGN OF A TUNABLE OPTICAL FILTER BY USING A ONE-DIMENSIONAL TERNARY PHOTONIC BAND GAP MATERIAL

A band pass filter with a linearly periodic refractive index profile is discussed in analogy with Kroning Penney model in band theory of solids. The suggested filter is a one-dimensional ternary periodic structure and provides better control in dispersion relation as compared to a binary structure because it has two more controlling parameters relative to those of the binary one. Since three layers are involved in the formation of band gaps a much broader range of dispersion control is obtained. Both refractive index modulation and optical thickness modulation are considered. A mathematical analysis is presented to predict allowed and forbidden bands of wavelength with variation of angle of incidence. It is also possible to get desired ranges of the electromagnetic spectrum filtered with this structure by manipulating the value of the lattice parameters.

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.

A Mathematically Rigorous Cutoff Analysis of Parabolic Cylindrical Waveguides

We present a rigorous study of a planar waveguide which, under the influence of unintentional or deliberate effects, takes the form of a parabolic cylindrical waveguide. Extending our earlier study on this problem, where some physically plausible assumptions were made, we now develop the characteristics and the cutoff condition equations for such a waveguide under mathematically rigorous conditions. It is found that results again show a bunching tendency of modal cutoff confirming the validity of our earlier results. Mode-bunching is thus found to be a fundamental characteristic of parabolically bent slab waveguides.

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

Modal Analysis and Waveguide Dispersion of an Optical Waveguide Having a cross-section of the Shape of a Cardioid

In this paper, we choose a simple and practical analytical method based on scalar wave approximation to study the modal behaviour, cutoff condition of an unconventional optical waveguide having a cross section of the shape of a cardioid. We take the appropriate orthogonal coordinates for the proposed structure and impose the boundary conditions under the weak guidance approximation to get the modal eigen value equation. Using this equation we obtain numerical results in the form of dispersion curves and cutoff frequencies. Also the dependence, d(Vb′)/dV on V has been obtained and shown graphically, where V stands for normalized frequency parameter and b′ stands for normalized propagation constant. An attempt has been made to estimate how the modal behaviour and waveguide dispersion change as circular shape is changed to the shape of a cardioid.

Modal cutoff condition for an optical waveguide with a hypocycloidal cross section

The characteristic equation for an optical waveguide with a hypocycloidal cross section is obtained. This cross section can be thought of as having the shape of a distorted square and leads to a tolerance analysis for deformation in a square waveguide. The complex geometry makes the analysis of modes difficult. With some simplifications the cutoff condition under the weak-guidance condition is obtained. A brief comparison is then made with the cutoff condition for the conventional fiber and also that of a waveguide with a square cross section.

Glass fibers of triangular cross-sections with metal loading on one or more sides: a comparative modal study

Using the point-matching method a comparative study has been made of the propagation characteristics of a triangular-cored glass fiber waveguide which is loaded on one or two sides with a highly conducting substance, the remaining side/sides being adjacent to a dielectric material of lower refractive index than that of the core.