V. P. Mahadevan Pillai

University of Kerala, Tiruvananantapuram, Kerala, India

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Publications (104)85.86 Total impact

  • Sensors and Actuators B Chemical 10/2013; 187:611-621. · 3.54 Impact Factor
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    ABSTRACT: ZnO thin films are grown on quartz substrates at various substrate temperatures (ranging from 573 to 973K) under an oxygen ambience of 0.02mbar by using pulsed laser ablation. Influence of substrate temperature on the structural, morphological, optical and electrical properties of the ZnO thin films are investigated. The XRD and micro-Raman spectra reveal the presence of hexagonal wurtzite structure of ZnO with preferred orientation (002). The particle size is calculated using Debye-Scherer equation and the average size of the crystallites are found to be in the range 17-29nm. The AFM study reveals that the surface morphology of the film depends strongly on the substrate temperature. UV-Visible transmittance spectra show highly transparent nature of the films in visible region. The calculated optical band gap energy is found to be decrease with increase in substrate temperatures. The complex dielectric constant, the loss factor and the distribution of the volume and surface energy loss of the ZnO thin films prepared at different substrate temperatures are calculated. All the films are found to be highly porous in nature. The PL spectra show very strong emission in the blue region for all the films. The dc electrical resistivity of the film decreases with increase in substrate temperature. The temperature dependent electrical measurements done on the film prepared at substrate temperature 573K reveals that the electric conduction is thermally activated and the activation energy is found to be 0.03911eV which is less than the reported values for ZnO films.
    Spectrochimica Acta Part A Molecular and Biomolecular Spectroscopy 09/2013; 118C:724-732. · 1.98 Impact Factor
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    ABSTRACT: A novel ZnO incorporated MoO3 nanostructured thin film system exhibiting high sensitivity and selectivity to ethanol has been developed. The MoO3:ZnO nanostructures exhibit enhanced ethanol sensing performance in non-humid and humid (75% r.H. at 21 °C) atmospheres compared to the pure MoO3 layer; with increase in ZnO concentrations, the sensitivity and stability increased, and the response/recovery time decreased. The response (Gethanol/Gair) of the 25% MoO3:ZnO sensor at an operating temperature of 300 °C against 500 ppm ethanol is up to 171 under non-humid and 117 under humid (75% r.H.) conditions. By comparing the response of the 25% ZnO added MoO3 sensor toward various gases (H2, CO, C3H6, CH4 and C2H5OH), distinctive selectivity to ethanol is observed. The ethanol sensitivity action over MoO3 nanostructures can be ascribed to the catalytic oxidation of ethanol to acetaldehyde, and the enhancement of gas sensing response of the MoO3:ZnO system can be attributed to more active centers that are obtained from the enhanced oxygen vacancy defects induced by ZnO. The presence of a humid atmosphere has a dramatic influence on the sensor performance towards ethanol; the sensitivity diminishes drastically due to the partial site precluding nature of the adsorbed hydroxyl groups to the analyte. The ZnO incorporated MoO3 nanostructure based sensing layers in the present work show significantly superior ethanol sensing performance to the works previously reported for various metal oxide systems.
    J. Mater. Chem. C. 06/2013; 1(25):3976-3984.
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    ABSTRACT: OBJECTIVES: A quantitative volumetric analysis of caudate nucleus can provide valuable information in early diagnosis and prognosis of patients with Alzheimer's diseases (AD). Purpose of the study is to estimate the volume of segmented caudate nucleus from MR images and to correlate the variation in the segmented volume with respect to the total brain volume. We have also tried to evaluate the caudate nucleus atrophy with the age related atrophy of white matter (WM), gray matter (GM) and cerebrospinal fluid (CSF) in a group of Alzheimer's disease patients. METHODS: 3D fast low angle shot (3D FLASH) brain MR images of 15 AD patients, 15 normal volunteers and 15 patients who had normally diagnosed MR images were included in the study. Brain tissue and caudate nuclei were segmented using the statistical parametric mapping package and a semi-automatic tool, respectively and the volumes were estimated. Volume of segmented caudate nucleus is correlated with respect to the total brain volume. Further, the caudate nucleus atrophy is estimated with the age related atrophy of WM, GM and CSF in a group of AD patients. RESULTS: Significant reduction in the caudate volume of AD patients was observed compared to that of the normal volunteers. Statistical analysis also showed significant variation in the volume of GM and CSF of AD patients. Among the patients who had normal appearing brain, 33% showed significant changes in the caudate volume. We hypothesize that these changes can be considered as an indication of early AD. CONCLUSION: The method of volumetric analysis of brain structures is simple and effective way of early diagnosis of neurological disorders like Alzheimer's disease. We have illustrated this with the observed changes in the volume of caudate nucleus in a group of patients. A detailed study with more subjects will be useful in correlating these results for early diagnosis of AD.
    European journal of radiology 05/2013; · 2.65 Impact Factor
  • B. Soumya, S.K. Sudheer, V.P. Mahadevan Pillai
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    ABSTRACT: Photonic Crystal Fibers (PCFs) are a new class of optical waveguides which offer exceptional light guiding mechanism and deliver significantly improved performance compared to conventional optical fibers. In the present investigation, we propose an solid core PCF for three different values of air filling fraction. The proposed PCF is simulated by using COMSOL Multiphysics. The nonlinearity of proposed PCF is found to be varying with respect to its air filling fraction and a nonlinear coefficient of 148 W-1Km-1 is obtained for PCF with air filling fraction of 0.7. The variation of other parameters like effective refractive index, confinement loss and effective area with respect to wavelength and air filling fraction is also investigated. The supercontinuum spectrum is generated using the designed highly nonlinear fiber and the effect of pump power on the generated output spectrum is studied and results shows that the bandwidth of output spectrum increases with pump power provided its pulse width remains constant.
    Fiber Optics in Access Network (FOAN), 2013 4th International Workshop on; 01/2013
  • N. Anand, S.K. Sudheer, V.P. Mahadevan Pillai
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    ABSTRACT: Design and analysis of a Nonlinear Photonic Crystal Fiber having low confinement loss, low birefringence and low effective mode area has been presented using COMSOL Multiphysics software. The suggested design has a central hole filled with Nematic Liquid Crystal (NLC) surrounded by air holes and a Perfectly Matched Layer (PML). Results show that by using circular holes of small diameter and materials with considerable refractive index difference, the nonlinearity and confinement increases, but the effective area and birefringence properties of the fiber decreases.
    Fiber Optics in Access Network (FOAN), 2013 4th International Workshop on; 01/2013
  • B. Soumya, S.K. Sudheer, V.P. Mahadevan Pillai
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    ABSTRACT: Here, we designed a highly nonlinear and low loss Photonic Crystal Fiber (PCF) structure with square lattice using COMSOL multiphysics. Propagation properties of proposed PCF has been analysed. The analysis has been carried out using finite element method. The proposed fiber obtained low confinement loss, minimum dispersion for wide range of wavelength. Results shows that the proposed PCF gives large negative dispersion for a wide range of wavelength and this makes it suitable for dispersion compensating applications and also it gives high nonlinear coefficient of 117 W-1Km-1. The square lattice PCF structure with elliptical holes is also designed and its birefringence property is compared with PCF with circular holes. Results shows that PCF with elliptical holes shows high birefringence as compared to other and such high birefringent PCF can be used for polarization maintaining applications.
    Fiber Optics in Access Network (FOAN), 2013 4th International Workshop on; 01/2013
  • S. Karpagam, S.K. Sudheer, V.P.M. Pillai
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    ABSTRACT: A new method for Discrete Gyrator Transform (DGT) based image encryption and decryption using Double Random Phase Mask (RPM) is proposed. In the present work encryption and decryption has been done using Gyrator Transform (GT) a kind of discrete algorithm using convolution operation. The proposed method uses DGT to reduce the computational load. The robustness of the proposed algorithm to blind decryption in terms of different key values has been calculated. Numerical simulations and some analysis for security have been presented to verify its validity and efficiency.
    Fiber Optics in Access Network (FOAN), 2013 4th International Workshop on; 01/2013
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    ABSTRACT: Silver incorporated tungsten oxide thin films are prepared by RF magnetron sputtering technique. The effect of silver incorporation in micro structure evolution, phase enhancement, band gap tuning and other optical properties are investigated using techniques such as x-ray diffraction, micro-Raman spectroscopy, atomic force microscopy, scanning electron microscopy, energy dispersive x-ray spectroscopy, and UV-Visible spectroscopy. Effect of silver addition in phase formation and band gap tuning of tungsten oxide thin films are investigated. It is found that the texturing and phase formation improves with enhancement in silver content. It is also found that as the silver incorporation enhances the thickness of the films increases at the same time the strain in the film decreases. Even without annealing the desired phase can be achieved by doping with silver. A broad band centered at the wavelength 437 nm is observed in the absorption spectra of tungsten oxide films of higher silver incorporation and this can be attributed to surface plasmon resonance of silver atoms present in the tungsten oxide matrix. The transmittance of the films is decreased with increase in silver content which can be due to increase in film thickness, enhancement of scattering, and absorption of light caused by the increase of grain size, surface roughness and porosity of films and enhanced absorption due to surface plasmon resonance of silver. It is found that silver can act as the seed for the growth of tungsten oxide grains and found that the grain size increases with silver content which in turn decreases the band gap of tungsten oxide from 3.14 eV to 2.70 eV.
    Journal of Applied Physics 12/2012; 112(11). · 2.21 Impact Factor
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    Dataset: 05676474
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    ABSTRACT: In this paper we have demonstrated a simple and secure method to encrypt and decrypt a color image. In the proposed method, the color image is initially encrypted with jigsaw transform and followed by double random phase encryption. The jigsaw transform is employed at the input plane and random phase masks (RPMs) are placed at the Fourier planes. The jigsaw transformed image is Fourier transformed and multiplied with the RPM1. Inverse transform of this image is performed and multiplied with the RPM2 gives the encrypted image. The jigsaw transform indices of the transformed image and the random phase code of the encrypted image form the keys for the successful retrieval of the data. Encrypting with this technique makes it almost impossible to retrieve the image without using both the right keys. Results of the computer simulation have been presented in support of the proposed idea. Mean square error (MSE) between the decrypted and the original image has also been calculated in support of the technique.
  • S. R. Chalana, R. Vinodkumar, I. Navas, V. Ganesan, V. P. Mahadevan Pillai
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    ABSTRACT: Nanostructured zinc suplhide thin films are successfully deposited on quartz substrates using pulsed laser deposition (PLD) under different argon pressures (0, 5, 10, 15 and 20Pa). The influence of argon ambience on the microstructural, optical and luminescence properties of zinc sulphide (ZnS) thin films is systematically investigated. The GIXRD data suggests rhombohedral structure for ZnS films prepared under different argon ambience. Self assembly of grains into well-defined patterns along the y direction is observed in the AFM image of the film deposited under argon pressure 20Pa. All the films show a blue shift in optical band gap. This can be due to the quantum confinement effect and less widening of conduction and valence band for the films with less thickness and smaller grain size. The PL spectra of the different films are recorded at excitation wavelengths 250nm and 325nm and the spectra are interpreted. The PL spectra of the films recorded at excitation wavelength 325nm show intense yellow emission. The film deposited under an argon pressure of 15Pa shows the highest PL intensity for excitation wavelength 325nm. For the PL spectra (excitation at 250nm), the highest PL intensity is observed for the film prepared under argon free ambience. In our study, 15Pa is the optimum argon pressure for better crystallinity and intense yellow emission when excited at 325nm.
    Journal of Luminescence 04/2012; · 2.14 Impact Factor
  • Journal of Nanoscience Letters. 01/2012;
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    ABSTRACT: We report all optical Integrator based on FBGs and FP_FBGs which has been analyzed to determine the impulse response for various impulse pulse excitations.
    Fiber Optics and Photonics (PHOTONICS), 2012 International Conference on; 01/2012
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    ABSTRACT: Fabry-Perot filters based on fiber Bragg gratings are widely used as optical narrowband filters and as sensors. Here we propose and demonstrate all optical clock recovery (10Gbit/s, 40Gbit/s & 100Gbit/s) with Fabry-Perot filters made up of fiber Bragg gratings.
    Fiber Optics and Photonics (PHOTONICS), 2012 International Conference on; 01/2012
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    ABSTRACT: Nanostructured Eu2O3 doped Barium tungstate (BaWO4) crystallites are successfully synthesized using pulsed laser deposition (PLD) technique. The influence of different Eu2O3 doping concentrations (1,2,3 & 5 wt.%) on the structural, surface morphological and optical properties are systematically studied using XRD, micro-Raman, SEM, AFM, UV–vis and photoluminescence spectroscopy. All the films are polycrystalline with tetragonal scheelite structure. The vibrational analysis of the atoms in BaWO4 is studied by micro-Raman spectra using factor group analysis. The surface morphological analysis by SEM and AFM reveals the presence of fine nanoparticles with distinct grain boundaries in all the films. The band gap energy variation in the Eu2O3 doped BaWO4 films is in accordance with the variation of the sizes of nano particles in the films. The films with higher Eu3+ doping concentrations (≥2 wt.%) show a PL emission peak centered around 614 nm when excited at 394 nm which can be attributed to the 5D0 → 7F2 (0–2) transition of Eu3+ ion.Research highlights▶ Study on the influence europium oxide doping on the structural and optical properties of laser ablated barium tungstate thin films is new. ▶ The surface morphological analysis by SEM and AFM reveals the presence of fine nanoparticles with distinct grain boundaries in all the films. ▶ The films with higher Eu3+ doping concentrations (≥2 wt.%) show a PL emission peak centered around 614 nm when excited at 394 nm which can be attributed to the 5D0 → 7F2 (0–2) transition of Eu3+ ion ▶ The observation of PL emission in these films is a new result which can have large practical applications and also it shows that BaWO4 can act as host material for europium ion. ▶ Detailed analysis of the Raman spectra of BaWO4 films are presented.
    Journal of Alloys and Compounds 01/2011; 509(6):2745-2752. · 2.39 Impact Factor
  • M. Ratheesh Kumar, V. P. Mahadevan Pillai, K. G. Gopchandran
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    ABSTRACT: This paper reports the design and simulation of a 10Gbps optical communication system with dispersion managed RZ pulse. The return-to-zero (RZ) format is very efficient for long haul, high bit rate, low power and wavelength division multiplexed (WDM) optical communication system. In RZ format, the power is transmitted only for a fraction of bit length. The effect of altering dispersion parameter of a single mode fiber on the optical communication link has been reported. The analysis has been performed in terms of bit error rate, Q-factor, optical spectrum analysis and average eye opening. It is observed that as the value of dispersion parameter is increases, the Q-factor and the average eye opening also increases. It is also observed that the timing jitters decreases with the increase in dispersion parameter. It is also shown that by reducing the duty cycle, performance of the system is enhanced.
    3rd International Congress on Ultra Modern Telecommunications and Control Systems and Workshops, ICUMT 2011, Budapest, Hungary, October 5-7, 2011; 01/2011
  • M. Ratheesh Kumar, V. P. Mahadevan Pillai, K. G. Gopchandran
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    ABSTRACT: This paper reports the design, implementation and the performance analysis of a lossless and dispersion managed soliton transmission system for long haul fiber optic communication. The soliton pulses are so stable that their shape and velocity are preserved while travelling long distances along a medium. This means that soliton pulses do not spread in optical fibre after propagating thousands of kilometres. Thus solitons are useful for data communication over several kilometres of distance. In an optical fibre, solitons pulses are generated by counter balancing the effect of the dispersion with the Self-Phase Modulation (SPM). A soliton has to retain its power between specified levels to preserve its dispersion resilient nature in an optical link. To achieve the lossless and dispersion managed soliton, dispersion compensated fiber and periodic amplification is used. Eye diagram, dispersion map and optical spectrum are used for the performance analysis.
    3rd International Congress on Ultra Modern Telecommunications and Control Systems and Workshops, ICUMT 2011, Budapest, Hungary, October 5-7, 2011; 01/2011
  • International Journal of Nanoscience 01/2011; 10.
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    Materials Science and Engineering: C. 01/2011; 31(7):1618-1618.