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Rajib Chakraborty

Bio: Rajib Chakraborty is an academic researcher from University of Calcutta. The author has contributed to research in topic(s): Lithium niobate & Coating. The author has an hindex of 10, co-authored 62 publication(s) receiving 288 citation(s). Previous affiliations of Rajib Chakraborty include Indian Institute of Technology Kharagpur.
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Journal ArticleDOI
Abstract: In order to improve the surface biocompatibility, a composite coating of hydroxyapatite and calcium hydrogen phosphate was synthesized over 316 L grade of stainless steel through pulsed electro deposition. It was observed that relative phase composition and corresponding crystallinity vary with the deposition current density. Thus a detailed study with the help of simulated body fluid and MG63 cell line was carried out in order to compare their respective biocompatibility in terms osteoconduction and cytocompatibility. A detailed electrochemical behavior study was carried out to assess the corrosion behavior under contact with body fluid. Cell proliferation studies indicate that the coating deposited with a current density of 10 mA/cm2, which is having the highest weight percentage and crystallinity of hydroxyapatite phase, is the most preferable one for continuous, faster and interconnected cell growth. Also cell cytoskeletons spread in bigger areas around their nucleus with a strong interconnection between each other. The bio-mineralization study shows that on immersion of these coatings in simulated body fluid, coating obtained through 10 mA/cm2, trends to build up hydroxyapatite on its surface with 200 nm pores at initial 1–3 days. After 14 days of immersion, hydroxyapatite deposition trends to form a spherical shape of around 2 micron in radius which can accommodate larger surface area for tissue growth vis-a-vis better bonding, as compared to other coating surfaces. The polarization resistance of 10 mA/cm2 coating is almost 10 times higher than the others and thus indicates its slower rate of corrosion under contact with simulated body fluid.

25 citations

Journal ArticleDOI
Abstract: A 1D binary periodic structure with defect has been analysed using Transfer Matrix Method. For a particular nine layered structure of SiO 2 and InP, a number of full stop bands (in other words, zero passbands or forbidden bands) at different regions of the spectrum under investigation are observed. Introducing a central spatial defect in the system by adjusting the layer width, it is possible to achieve an extremely narrow passband centred on 1554.9 nm in the 7th forbidden band. Moreover by varying the defect width, the number of passbands can be increased. These passbands have flat and 100% stopband and hence can be better candidate to drop single or multiple frequencies in WDM systems. It is further observed that with increase in the number of layers and/or defect width, the number of mini pass bands outside the original forbidden band also increases. Also by FDTD simulation it is seen that the field is localised within the defect for the passband frequency.

23 citations

Journal ArticleDOI
Abstract: Inconsistent growth of tissues and poor osteoconduction performance on the metallic implant surfaces due to variation of surface energy are major contributing factors for failure of most metallic implant on account of lack of stronger attachment with surrounding bone or tissues. In this study, composite coating of hydroxyapatite, calcium hydrogen phosphate and MWCNT was developed on SS316 surface with varying amount of calcium phosphate-hydroxyapatite phase and crystallinity by pulsed electrodeposition. TEM study revealed that the MWCNTs were bonded strongly with the in situ deposition phases and thus act as reinforcement in the deposited coating similar to the collagen fiber in natural bone structure. Presence of MWCNT reinforcement increased the overall coating modulus of elasticity in the range of 6–10 GPa similar to that of natural bone. Different coating surfaces with varied amount of phase and crystallinity exhibits altogether different phenomena and growth geometry of apatite formation during osteoconduction period under contact with SBF. Coatings with highest amount of hydroxyapatite phase exhibit formation of porous spherical (~ 1 μm) and rod like (~ 600 nm) scaffold structure along with presence of nanopores (~ 100 nm) all along the contact surfaces. Cell proliferation study indicated uniform and fast spreading of cells over the coating surfaces as compared to bare metallic implant. EIS study illustrated five times high corrosion resistance capability along with formation of passivation layer under contact with SBF for coating comes with 66% of hydroxyapatite phase.

22 citations

Journal ArticleDOI
Abstract: Graded-index optical channel waveguides like Ti-indiffused LiNbO 3 waveguides have been modelled by effective refractive index profile along the lateral direction, discretising the profile and then using the matrix method. This effective-index-based matrix method, which was earlier used to compute the modal propagation constants of Ti:LiNbO 3 channel waveguides and directional couplers [Fib. Integrat. Opt. 17 (1998) 139] and the bending loss [J. Opt. Commun. 155 (1998) 125], has been established in this paper as a computationally fast, analytical method to compute electric field and modal intensity profiles in single and coupled waveguides. In order to handle coupled waveguides consisting of three waveguides, the concept of overlap integral has been used to analyse power coupling to the middle waveguide for applications in power splitting. Some of the computed intensity profiles have been compared with experimental data obtained by the authors. Although computation has been performed only for TE and TM polarisations, the method has the inherent capability of handling arbitrary polarisation.

21 citations

Journal ArticleDOI
Abstract: The effective-index-based matrix method (EIMM) has been used to simulate the characteristics of integrated-optic directional coupler switch (both the uniform-Δ β and reversed-Δ β types) based on electro-optic (EO) effect. The characteristics are derived from the distributions of optical power and electrical modulating field within the device. The analysis was focused on directional coupler switching devices made by the diffusion of titanium in lithium niobate (Ti:LiNbO 3 ) substrates and incorporation of suitable electrodes. The simulated results are found to match well with available experimental results and other numerical simulation results obtained from the literatures. Although the computations are performed for Ti:LiNbO 3 waveguides, the model is applicable to arbitrary graded-index waveguides with the known refractive index profile and electro-optic coefficient. EIMM is found computationally well efficient and considerably faster than beam propagation method (BPM).

18 citations

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Proceedings Article
01 Jan 1999
Abstract: The term photonic crystals appears because of the analogy between electron waves in crystals and the light waves in artificial periodic dielectric structures. During the recent years the investigation of one-, two-and three-dimensional periodic structures has attracted a widespread attention of the world optics community because of great potentiality of such structures in advanced applied optical fields. The interest in periodic structures has been stimulated by the fast development of semiconductor technology that now allows the fabrication of artificial structures, whose period is comparable with the wavelength of light in the visible and infrared ranges.

2,639 citations

Journal ArticleDOI
Abstract: New optical waveguide technology for integrated optics, based on propagation of long-range surface plasmon polaritons (LR-SPPs) along metal stripes embedded in dielectric, is presented. Guiding and routing of electromagnetic radiation along nanometer-thin and micrometer-wide gold stripes embedded in polymer via excitation of LR-SPPs is investigated in the wavelength range of 1250-1650 nm. LR-SPP guiding properties, such as the propagation loss and mode-field diameter, are investigated for different stripe widths and thicknesses. A propagation loss of /spl sim/6 dB/cm, a coupling loss of /spl sim/0.5 dB (per facet), and a bend loss of /spl sim/5 dB for a bend radius of 15 mm are evaluated for 15-nm-thick and 8-/spl mu/m-wide stripes at the wavelength of 1550 nm. LR-SPP-based 3-dB power Y-splitters, multimode interference waveguides, and directional couplers are demonstrated and investigated. At 1570 nm, coupling lengths of 1.9 and 0.8 mm are found for directional couplers with, respectively, 4- and 0-/spl mu/m-separated waveguides formed by 15-nm-thick and 8-/spl mu/m-wide gold stripes. LR-SPP-based waveguides and waveguide components are modeled using the effective-refractive-index method, and good agreement with experimental results is obtained.

401 citations

Journal ArticleDOI
TL;DR: A comprehensive inventory of the progresses achieved so far is gathered, to allow fellow researchers to compare with ease and filter the best solutions for the cation substitution of HA-based materials and enable the development of multi-functional biomedical designs.
Abstract: High-performance bioceramics are required for preventing failure and prolonging the life-time of bone grafting scaffolds and osseous implants. The proper identification and development of materials with extended functionalities addressing socio-economic needs and health problems constitute important and critical steps at the heart of clinical research. Recent findings in the realm of ion-substituted hydroxyapatite (HA) could pave the road towards significant developments in biomedicine, with an emphasis on a new generation of orthopaedic and dentistry applications, since such bioceramics are able to mimic the structural, compositional and mechanical properties of the bone mineral phase. In fact, the fascinating ability of the HA crystalline lattice to allow for the substitution of calcium ions with a plethora of cationic species has been widely explored in the recent period, with consequent modifications of its physical and chemical features, as well as its functional mechanical and in vitro and in vivo biological performance. A comprehensive inventory of the progresses achieved so far is both opportune and of paramount importance, in order to not only gather and summarize information, but to also allow fellow researchers to compare with ease and filter the best solutions for the cation substitution of HA-based materials and enable the development of multi-functional biomedical designs. The review surveys preparation and synthesis methods, pinpoints all the explored cation dopants, and discloses the full application range of substituted HA. Special attention is dedicated to the antimicrobial efficiency spectrum and cytotoxic trade-off concentration values for various cell lines, highlighting new prophylactic routes for the prevention of implant failure. Importantly, the current in vitro biological tests (widely employed to unveil the biological performance of HA-based materials), and their ability to mimic the in vivo biological interactions, are also critically assessed. Future perspectives are discussed, and a series of recommendations are underlined.

106 citations

Journal Article
Abstract: A new type of wave front shearing interferometer is described in which two images of the wave front under test which are of different sizes are made to interfere. When the centres of the two images coincide, this results effectively in shear along the radial direction. It is shown that the interpretation of the resulting interferogram is comparatively easy. In addition, the instrument is extremely convenient to handle, since all the adjustments can be made with a white light source.

68 citations

Journal ArticleDOI
TL;DR: A significant reduction in patient healing time with less loss of mechanical strength of implants has been achieved after coating with hydroxyapatite (HA), and a comparative study of these techniques is presented.
Abstract: To facilitate patient healing in injuries and bone fractures, metallic implants have been in use for a long time. As metallic biomaterials have offered desirable mechanical strength higher than the stiffness of human bone, they have maintained their place. However, in many case studies, it has been observed that these metallic biomaterials undergo a series of corrosion reactions in human body fluid. The products of these reactions are released metallic ions, which are toxic in high dosages. On the other hand, as these metallic implants have different material structures and compositions than that of human bone, the process of healing takes a longer time and bone/implant interface forms slower. To resolve this issue, researchers have proposed depositing coatings, such as hydroxyapatite (HA), polycaprolactone (PCL), metallic oxides (e.g., TiO2, Al2O3), etc., on implant substrates in order to enhance bone/implant interaction while covering the substrate from corrosion. Due to many useful HA characteristics, the outcome of various studies has proved that after coating with HA, the implants enjoy enhanced corrosion resistance and less metallic ion release while the bone ingrowth has been increased. As a result, a significant reduction in patient healing time with less loss of mechanical strength of implants has been achieved. Some of the most reliable coating processes for biomaterials, to date, capable of depositing HA on implant substrate are known as sol-gel, high-velocity oxy-fuel-based deposition, plasma spraying, and electrochemical coatings. In this article, all these coating methods are categorized and investigated, and a comparative study of these techniques is presented.

55 citations

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Author's H-index: 10

No. of papers from the Author in previous years