Rajib Chakraborty

Bio: Rajib Chakraborty is an academic researcher from University of Calcutta. The author has contributed to research in topics: Lithium niobate & Coating. The author has an hindex of 10, co-authored 62 publications receiving 288 citations. Previous affiliations of Rajib Chakraborty include Indian Institute of Technology Kharagpur.

Integrated optical waveguides in LiNbO3: modeling and experimental analysis

Abstract: Graded-index optical channel waveguides rare fabricated by diffusion of Ti in LiNbO 3 . A model has been developed for calculating the mode profiles of the same, by first finding the effective refractive index profile along the lateral direction, and then discretizing the profile and applying the matrix method. This effective-index-based matrix method has been presented in this paper and established as a computationally fast, analytical method to computer modal electric field and intensity profiles in single and coupled graded-index channel waveguides. The method can be used in coupled systems consisting of three or more waveguides where the input power may be launched to any of the waveguides. Some of the computed intensity profiles have been compared with experimental data. Although computation and measurements have been performed only for TE and TM polarizations, the method has the inherent capability of handling arbitrary polarization.

Zinc-indium-oxide sol-gel thin film: surface patterning, morphology and photocatalytic activity

Abstract: We report the fabrication of surface patterned zinc indium oxide thin films by pressure assisted capillary force lithography from the precursor solutions of varying indium content 55 maximum. The presence of various morphologies spherical, hexagonal plate, cotton ball, flower and islandlike of hexagonal ZnO together with the formation of light surface patterns was observed from electron microscopes field emission scanning electron microscope, TEM for the films deposited from the precursors of 45 indium. However, at 55 indium ZI55, the development of high fidelity surface patterns average periodicity 15m peak height 15nm was observed from atomic force microscopy (AFM) study. A gradual increase in photocatalytic activity PA of the films towards decomposition of rhodamine 6G dye under UV 254nm was found on increasing indium content. Moreover, an improvement of the PA over 13 times was noticed by nanoAu coating on ZI55. This fabrication strategy could be used for PA improvement of metal oxide semicond...

Further enhancement of light extraction efficiency from light emitting diode using triangular surface grating and thin interface layer

Abstract: Analysis has been done of improvement of forward directional light extraction efficiency of light emitting diodes (LEDs) by surface patterning of different types of one-dimensional profiles on indium-zinc-oxide films developed recently by our group using sol–gel technique. Finite-difference time-domain simulations by MEEP software have been used for this purpose. From the analysis, it is found that the patterned film is suitable for near-infrared LED. The optimized structure, which gives maximum improvement at around 1.040 μm wavelength, is determined and fabricated using soft lithography. Further enhancement of the light output of the LED with the fabricated gratings is possible by introducing an interlayer within the top contact layer. The mathematical formulation of the coupling of light in structured/multilayered surfaces is also discussed.

Transmission Filters Utilizing Cavity Resonances in Bandgap-Engineered Monomaterials

Abstract: A monomaterial-based resonator structure is proposed here, which can replace the multilayer-based narrowband transmission filter. This new concept of introducing the effect of multilayered structures of different materials into a single material is based on etching out repeatable structures of two different dimensions on the same material. As the etched-out repeatable structures are of different dimensions, it is possible to obtain periodic layers of two different-effective refractive indices. This type of monomaterial-based optical filters avoids the challenges generally faced while fabricating multilayer structures of different heterogeneous materials having different refractive indices. The dependence of the filter action on the number of bilayers of two different-effective refractive-index materials formed by etching and on the cavity region thicknesses is studied. Although the study is done mainly on lithium niobate on insulator, but it is seen that similar effects occur for materials of varying refractive indices.

Realization of mode independent multichannel transmission filter by controlling the photon localization in symmetric cavities

Abstract: Modern optical communication system requires multiple channel transmission in different spectral band for different applications. Here we are proposing a microresonator structure for closely spaced, mode independent multiple channel transmission in 3rd transmission window by controlling the localization of photons in its cavity. To design the proposed structure, the spectral filtering properties of a single cavity planar microresonator are studied initially. In conventional multilayer dielectric filter, the localization of light in the microcavity is generally controlled by controlling the number of layers. Here we have shown that application of electric field across the structure, designed with suitable materials can also affect the localization of light in the cavity as well as the Q values of the transmission spectra. The mode independent characteristic of the structure is found from the study of its transmittance characteristics at different angle of incidence of light. It is found that the results of single cavity structure hold well for multicavity resonator structure also, in the regime of optical communication wavelength range. A method to increase the number of transmission channels is also proposed here keeping the fabrication perspective in mind.

Photonic crystals

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.

Integrated optical components utilizing long-range surface plasmon polaritons

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.

Cationic Substitutions in Hydroxyapatite: Current Status of the Derived Biofunctional Effects and Their In Vitro Interrogation Methods.

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.

Recent Advances and Tendency in Fiber Bragg Grating-Based Vibration Sensor: A Review

Abstract: Vibration sensing is critical to monitor and ultimately preserve the health state of engineering systems. These systems with a large structure are typically working in some harsh environments including strong magnetic fields. However, traditional electrical sensors are difficult to accurately measure the vibration under harsh environments. Besides these instinct advantages of normal fiber optic sensors (FOS) sensors such as compact size, passive sensing, resistance to electromagnetic interference, etc., fiber Bragg grating (FBG) sensors have a capability of distributed sensing based on wavelength demodulation and resistance to light intensity fluctuation and unwanted fiber bending losses. Such merits lead them to be a hot topic in FOS field and excellent candidates for vibration sensing. Three types of FBG-based vibration sensors have been classified based on the difference of vibration-strain coupling way to FBG in this survey, which are pasted FBG-based, axial property of FBG-based and transverse property of FBG-based, respectively. FBG-based vibration sensors' principles and designs have been introduced and discussed. Recent advances in the applications of FBG-based vibration sensors have been investigated. The limitations and prospects of the FBG-based vibration sensing technologies have been analyzed and discussed.

Coating Techniques for Functional Enhancement of Metal Implants for Bone Replacement: A Review

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.