Faculty Publications
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Item Synthesis and characterization of a new NLO-active donor-acceptor-type conjugated polymer derived from 3,4-diphenylthiophene(2010) Manjunatha, M.G.; Vasudeva Adhikari, A.V.; Hegde, P.K.; Suchand Sandeep, C.S.; Philip, R.A new donor-acceptor-type conjugated polymer (P1) carrying 3,4-diphenylthiophene, 2,5-dihexyloxybenzene, and 1,3,4-oxadiazole units was synthesized through multistep reactions. The polymer was prepared using a polyhydrazide precursor route. The polymer has a well-defined structure and exhibits good thermal stability, with a decomposition onset temperature in nitrogen of 300 °C. Cyclic voltammetry experiments revealed that the polymer has low-lying LUMO (-3.68 eV) and high-lying HOMO (-5.78 eV) energy levels. The electrochemical band gap was found to be 2.10 eV. The UV-visible absorption spectrum of the polymer presented a maximum at 373 nm, and it displayed bluish-green fluorescence in dilute chloroform solution. The nonlinear optical properties of the new polymer were investigated at 532 nm using the Z-scan technique with nanosecond laser pulses. The polymer exhibited strong optical limiting behavior due to excited state absorption, which was phenomenologically similar to a three-photon absorption (3PA) process. The 3PA coefficient ? was found to be 7×10-22 m3/W2. The studies show that the new polymer (P1) is a promising material for developing efficient photonic devices.Item Study of third-order nonlinear optical and all-optical switching properties of palladium metal-organic complex(Elsevier B.V., 2013) Manjunatha, K.B.; Ramakrishna, R.; Umesh, G.; Badekai Ramachandra, B.We report the results of studies on third-order nonlinear optical properties of a newly synthesized palladium metal-organic complex [PdLPPh 3] (L = N-(2-pyridyl)-N?-(5-chlorosalicylidene)hydrazine) both in film and solution form using Z-scan and degenerate four wave mixing (DFWM) techniques. Experiments were performed using Q-switched Nd: YAG laser with nanosecond pulses at 532 nm. Investigations revealed that the palladium metal-organic complex possesses nonlinear absorption coefficient ?eff which is of the order of 10-9 m/W due to reverse saturable absorption (RSA) and negative nonlinear refractive index (self-defocusing) n2 which is of the order of 10-9 esu. The real and imaginary parts of the third-order nonlinear optical susceptibility (?(3)) were found to be of the order of 10-11 esu. The second-order hyperpolarizability (?h) was estimated to be of the order of 10-30 esu. The results of pump-probe experiments show that the switch-on and switch-off times of the palladium metal-organic complex were in ?s for different pump intensities and the energy dependent transmission studies reveal better limiting property of the compound at nanosecond regime. Thus the nonlinear response of the material suggests that it has a potential application for high sensitive photonic devices. © 2013 Elsevier B.V. All rights reserved.Item Influence of annealing on the linear and nonlinear optical properties of Mn doped ZnO thin films examined by z-scan technique in CW regime(Elsevier B.V., 2016) Nagaraja, K.K.; Pramodini, S.; Poornesh, P.; Rao, A.; Nagaraja, H.S.We present the studies on the influence of annealing on the third-order nonlinear optical properties of RF magnetron sputtered manganese doped zinc oxide (MZO) thin films with different doping concentration. It is revealed that the incorporation of Mn into ZnO and annealing lead to prominent changes in the third order nonlinearity. Nonlinear optical measurements were carried out by employing the z-scan technique using a continuous wave (CW) He-Ne laser of 633 nm. The z-scan results reveal that the films exhibit self-defocusing thermal nonlinearity. The third-order nonlinear optical susceptibility ?(3) was found to be of the order of 10-3 esu and 10-2 esu for annealed MZO thin films at 200 °C and 400 °C respectively. The dependence of grain size on the observed nonlinearity was revealed by atomic force microscopy analysis. Optical limiting studies were carried out for a range of input power levels and an optical limiting of about ?8 mW was observed indicating the possible application for photonic devices. © 2016 Elsevier B.V. All rights reserved.Item An investigation on photophysical and third–order nonlinear optical properties of novel thermally–stable thiophene–imidazo [2,1-b][1,3,4] thiadiazole based azomethines(Elsevier Ltd, 2019) Kakekochi, V.; Udayakumar, U.; Nikhil, N.P.; Chandrasekharan, K.The use of ?–conjugated semiconducting materials in flexible and large–area optoelectronic devices is proliferated worldwide owing to the easy structural modifications and solution processability possible, leading to the change in opto–electronic properties. In this context, new class of thiophene and imidazo [2,1-b][1,3,4] thiadiazole (ITD) based conjugated azomethines (TI1–TI3) were designed and synthesized. The photophysical and electrochemical properties of the synthesized azomethines (TI1–TI3) were investigated experimentally, which were further validated with the aid of theoretical calculations. Further, the azomethines TI1 and TI2 were subjected to Z–scan analysis to study the nonlinear optical (NLO) properties. The molecules exhibited effective two photon absorption (TPA) with the large nonlinear absorption coefficient (?eff) of the order of 10?10 m W?1. The planar structure of TI1 furnished a better interaction between donor and acceptor moieties and extended the ?–conjugation, providing an improved ?eff (0.81 × 10?10 m W?1) to TI1 compared to that of TI2 (0.55 × 10?10 m W?1). From the results it is inferred that the molecules could be of potential materials to be used in efficient photonic devices. © 2019 Elsevier LtdItem Review - A Review of 2D Perovskites and Carbon-Based Nanomaterials for Applications in Solar Cells and Photodetectors(IOP Publishing Ltd, 2021) Omprakash, P.; Viswesh, P.; Bhat Panemangalore, D.B.Photonic devices such as solar cells and photodetectors that produce electricity play a vital role in our daily life for applications such as fibre optic communication systems, process control, and also in defence related applications. Today, two-dimensional perovskites that belong to the class of emerging materials show promising energy applications. 2D perovskites have been investigated for their exceptional properties such as high optical absorption coefficients, structural diversity and tuneable bandgaps which allow their application as active light absorbing materials to develop solar cells and photodetectors. Carbon-based nanomaterials have also found applications as transparent electrodes, charge acceptors and photosensitive layers in solar cells and photodetectors due to properties such as excellent electrical conductivity, high optical transparency, high surface area and remarkable mechanical strength. There has been growing interest in research on devices using these materials to improve their feasibility, ease of production and performance. With the growing urgency of switching to alternate sources of energy and increasing demands for highly accurate and fast sensors, the development and application of such novel materials are essential. Hence, the current state of understanding of these materials and their applications in the field of solar cells and photodetectors are summarized in this review article. © 2021 The Author(s). Published on behalf of The Electrochemical Society by IOP Publishing Limited.Item All-Optical Diode Action through Enhanced Nonlinear Response from Polymeric Photonic Crystal Microcavity(American Chemical Society, 2022) Puthiya Purayil, N.; Kakekochi, V.; Udayakumar, U.K.; Chandrasekharan, C.The search for materials for nanophotonic devices needs a way to overcome the limitations of weak nonlinear optical response due to reduced size. The requirement of a high-power excitation source for inducing nonlinear effects in the active medium poses a hurdle in realizing all-optical and integrated optoelectronic systems. Nanosized optical materials can be embedded in photonic cavities to enhance its optical nonlinear responses through confinement effects. This report systematically investigates the linear and nonlinear optical properties of polymeric 1D-photonic crystals (PhC) with a defect layer incorporated with an imidazo-thiadiazole derivative small molecule. The nonlinear optical studies were carried out by means of a z-scan technique under nanosecond pulse using a Q-switched Nd:YAG laser operating at 532 nm. The resonant excitation creates strong confinement of light in the photonic microcavity and facilitates strong light-matter interaction that induces nonlinear response at low input intensities. A giant enhancement in the nonlinear absorption and optical limiting action was observed for PhC comparing to the bare sample. The significant enhancement in the absorptive nonlinearity is utilized for realizing a practical, on-chip, passive, all-optical diode with a PhC/Au hybrid structure. The asymmetrical nonlinear absorption of the hybrid structure exhibits non-reciprocal light transmission in the nonlinear regime. The high transmittance contrast ratio for forward/reverse bias operation and cost-effective fabrication methods makes our system a potential candidate toward the realization of compact photonic integrated devices. © 2021 American Chemical Society.Item Nanoscale Tapered Hybrid Plasmonic Waveguide for On-Chip Silicon Photonics(Springer Science and Business Media B.V., 2022) Reddy, S.K.; Singh, M.Plasmonic waveguides which deploy surface plasmon-polariton (SPP) waves are of colossal interest to the researchers with their ability to realize and integrate nanophotonic circuits beyond the diffraction limit. In order to subjugate the demerits of plasmonic and dielectric waveguides, the light guided by plasmonic and dielectric waveguides are coupled to form hybrid plasmonic waveguide (HPWG). In this work, we have simulated a nanoscale tapered plasmonic waveguide (Au-SiO2-Si) using COMSOL Multiphysics software in the telecommunication C-band. The proposed waveguide shows better normalized effective mode area (Aeff/A= 0.056), enhanced electric field confinement, and long propagation length (Lp = 101.55 μm) with h= 350 nm, WAu = 100 nm, WSlot=20 nm, WSi = 220 nm, and ht=150 nm. The finite element method based approach shows that this enounced waveguide is a feasible choice for the future on-chip nanophotonic devices. © 2021, Springer Nature B.V.Item A low loss hexagonal six-port optical circulator using silicon photonic crystal(Springer, 2023) Sangeetha, S.; Vani, D.; Gupta, P.; Krishnan, P.A 6-port optical circulator using silicon photonic crystals has been designed and proposed in this paper as an essential component of an optical communication system. The proposed 6-port circulator has greater isolation values between the input and isolated ports and lower insertion loss values between the input and output ports. The proposed circulator achieves maximum isolation of 38.7 dB and minimum insertion loss of 0.0029 dB. The proposed designs are extremely useful in the telecommunications industry, wavelength division multiplexing and photonic integrated circuits applications due to their low insertion and high isolations. © 2023, The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.Item Unveiling the Potential of Bismuth Oxy-Iodide (BiOI)-Based Photovoltaic Device for Indoor Light Harvesting(Institute of Electrical and Electronics Engineers Inc., 2023) Manjhi, S.; Siddharth, G.; Pandey, S.K.; Sengar, B.S.; Dwivedi, P.; Garg, V.Indoor photovoltaics (IPVs) have piqued the interest of many because of their potential to power small and portable electronics and photonic devices. This work investigates one of the exemplary perovskite inspired materials (PIMs), bismuth oxy-iodide (BiOI). In order to explore the potential of BiOI in the indoor environment, the baseline model of BiOI device [indium tin oxide (ITO)/NiOx/BiOI/ZnO/Contact] is developed using the experimental results of a recent study with a power conversion efficiency (PCE) of 4%. The performance of the proposed device is fine-tuned by investigating the effect of: 1) absorber thickness and defect density and 2) valence band offset (VBO) between the hole transport layer (HTL) and absorber interface (NiOx/BiOI) along with the interface defect density. Furthermore, the series and shunt resistance of the device is optimized. Additionally, the performance of the optimized device is investigated under different WLED light intensities. Finally, after optimizing the device under WLED illumination, the best performance parameters achieved are Jsc : 1.83 mA/cm2, Voc : 1.33 V, FF: 85.91%, and PCE: 40%. Moreover, the optimized device performance under different indoor light sources: WLED, halogen, and compact fluorescent lamps (CFLs), has been performed to estimate the performance under widely utilized lighting sources. © 1963-2012 IEEE.Item Temperature Detection Using Plasmonic Waveguide Ring Resonator: Design and Analysis(Institute of Electrical and Electronics Engineers Inc., 2024) Nausheen, T.A.; Nikhilesh Kumar, C.; Khanna, A.; Singh, M.A 3-D-hybrid plasmonic waveguide (HPWG) cascaded ring resonator-based temperature sensor is studied in the infrared (IR) spectral regime. The proposed design achieves high sensitivity and precision in temperature measurements by integrating the unique properties of plasmonic and photonics. The HPWG enhances the interaction between the optical field and the surrounding environment, while the cascaded ring resonators provide a compact and efficient means of modulating the optical signal in response to temperature changes. Our theoretical analysis and numerical simulations demonstrate that the device exhibits a significant shift in resonance wavelength with temperature variations, leading to an enhanced sensitivity (0.37 nm/K) compared to traditional photonic sensors. The potential applications of this temperature sensor span various fields, including environmental monitoring, biomedical diagnostics, and industrial process control. It offers a promising solution for advanced temperature sensing with improved performance and miniaturization. © 1973-2012 IEEE.