Kh. S. Singh

To compare CSF adenosine deaminase levels and CSF-PCR for tuberculous meningitis

This study was planned to compare the adenosine deaminase (ADA) levels and polymerase chain reaction (PCR) in cerebrospinal fluid (CSF) as a rapid method to diagnose tuberculosis meningitis (TBM). Fifty-four adult patients with suspected TBM and 37 controls were included in this study. The median ADA level was 21U/L of most likely TBM, 14U/L of unconfirmed TBM and 5U/L of controls. PCR for Mycobacterium tuberculosis was positive in 12 out of 27 most likely TBM cases, 5 out of 27 unconfirmed TBM cases and 3 out of 37 controls. Using a cut off level of >10U/L, CSF-ADA had a sensitivity of 92.5% and specificity of 97% for the diagnosis of TBM. PCR for M. tuberculosis had a sensitivity of 44.5% and specificity 92% in the most likely TBM cases. This study shows that CSF-ADA is a more sensitive indicator than PCR for the diagnosis of M. tuberculosis.

Wide Range Temperature Sensors Based on One-Dimensional Photonic Crystal with a Single Defect

Transmission characteristics of one-dimensional photonic crystal structure with a defect have been studied. Transfer matrix method has been employed to find the transmission spectra of the proposed structure. We consider a Si/air multilayer system and refractive index of Si layer has been taken as temperature dependent. As the refractive index of Si layer is a function of temperature of medium, so the central wavelength of the defect mode is a function of temperature. Variation in temperature causes the shifting of defect modes. It is found that the average change or shift in central wavelength of defect modes is 0.064 nm/K. This property can be exploited in the design of a temperature sensor.

Trapping of Light in Nonlinear 1-D Photonic Crystal

Theoretical studies on the group velocity of light wave in 1-D polystyrene/SiO2 nonlinear photonic crystal is investigated. The speed of light wave through these multilayered structures is calculated in the absence as well as in the presence of a high intensity controlling wave by using the transfer matrix method. This letter shows that we can trap a light wave inside the nonlinear 1-D photonic crystal by switching off the controlling wave.

Silicon Based One-Dimensional Photonic Crystal as a TM-Mode Filter

The effect of temperature and angle of incidence on the transmission spectra of a one dimensional photonic crystal for TE and TM polarizations has been studied. For a range of angle of incidence from 0° to 60°, the proposed structure works as an omni-directional reflector. For other angles of incidence more than 60°, the structure works as a selective TM-polarization filter i.e. a filter which completely blocks TE-polarized waves but allows certain frequencies of TM-polarized waves. At an angle of incidence of 89°, the structure works as a multi channel optical filter without introducing any defect in the geometry. Also, this multi-channel filter can work as a tunable filter by varying the temperature of the structure and the number of layers in the geometry. Only for two bi-layers the proposed structure works as a single channel filter. Therefore, such types of structure are easier to fabricate and may be cost effective as compared to defect one-dimensional photonic crystals.

TM polarized filter using 1D photonic crystal

The present communication deals with the transmission of electromagnetic waves through a one-dimensional photonic crystal based on Si/air multilayer system. The structure can work as a selective TM-polarization filter i.e. a filter which completely blocks TE-polarized waves but allows certain wavelengths of TM-polarized waves. At the angles of incidence of 87° to 89°, the structure can work as a single or multi-channel optical filter by varying the number of unit cells. Only for one unit cell the structure can work as single channel filter without introducing any defect in the geometry. Therefore, such types of structure easier to fabricate and may be cost effective as compared to one-dimensional photonic crystals with defect.

Enhanced ODR range using exponentially graded refractive index profile of 1D binary photonic crystal

A simple design of broadband one dimensional dielectric/semiconductor multilayer structure having refractive index profile of exponentially graded material has been proposed. The theoretical analysis shows that the proposed structure works as a perfect mirror within a certain wavelength range (1550 nm). In order to calculate the reflection properties a transfer matrix method (TMM) has been used. This property shows that binary graded photonic crystal structures have widened omnidirectional reflector (ODR) bandgap. Hence a exponentially graded photonic crystal structure can be used as a broadband optical reflector and the range of reflection can be tuned to any wavelength region by varying the refractive index profile of exponentially graded photonic crystal structure.

Gap soliton in nonlinear-plasma 1D photonic crystal

Theoretical studies of propagation of electromagnetic wave through one-dimensional nonlinear/plasma 1D photonic crystal have been investigated. Maxwell’s electromagnetic equations and modified transfer matrix method has been used for this purpose. The study shows that gap soliton exist at high intensities and this property can be exploited in the design of an optical switch, which can be used in optical computing.

Design of a transmission TM mode filter using one-dimensional ternary photonic crystal

Omni-directional photonic bandgaps (PBG) has been presented in the one-dimensional ternary photonic crystals formed by sandwiching the superconductor layer (GaAs) between two dielectric materials (MgO) & (SiO2) in the unit cell. The existence of total Omni-directional reflection band gap in 1D-PC is predicted theoretically. Reflectivity of one dimensional periodic structure for TE and TM-modes at a particular angle of incidence has been calculated by using Transfer Matrix Method (TMM). It is found that the mirror designed with these materials has a ODR range which covers the window of 1550nm used in optical communications.

Design of an omni-directional reflector using 1D ge-based photonic crystal

A simple design of an omni-directional reflector based on Ge/Sio2 has been presented. The photonic band gap (PBG) of this photonic crystal for TE and TM mode at different angles of incidence is calculated numerically using transfer matrix method. It is found that this type of photonic crystal has omni-direction reflection in near infrared region, which can be used in various application such as deformable mirror, high resolution InAs camera etc.

Effect of Temperature on Photonic Band Gaps in Semiconductor-Based One-Dimensional Photonic Crystal

The effect of the temperature and angle of incidence on the photonic band gap (PBG) for semiconductor-based photonic crystals has been investigated. The refractive index of semiconductor layers is taken as a function of temperature and wavelength. Three structures have been analyzed by choosing a semiconductor material for one of the two materials in a bilayer structure. The semiconductor material is taken to be ZnS, Si, and Ge with air in first, second, and third structures respectively. The shifting of band gaps with temperature is more pronounced in the third structure than in the first two structures because the change in the refractive index of Ge layers with temperature is more than the change of refractive index of both ZnS and Si layers with temperature. The propagation characteristics of the proposed structures are analyzed by transfer matrix method.