Qualification: 
Ph.D
viswassnair@am.amrita.edu

Dr. Viswas S. Nair serves as Assistant Professor at Amrita Vishwa Vidyapeetham. He received his B.Tech in Electronics and Communication Engineering from Rajiv Gandhi Institute of Technology, Kottayam (2006). His higher education includes M.E. Communication Engineering from BITS Pilani (2009) and Ph.D. in Electrical Engineering from IIT Kanpur (2017). He also spent some time with VSNL Mumbai, Intel Technology India Pvt. Ltd., and CSIR-CEERI-Pilani. Viswas is currently involved in teaching/research related to optoelectronics, solid-state devices, and optical communication.

Degree Name of the University Year of Passing
PhD. IIT Kanpur 2017

Publications

Publication Type: Journal Article

Year of Publication Title

2021

Viswas Sadasivan, “Circular Optical Arrays Using Waveguide Fed 45° Angled Mirrors”, IEEE Journal of Selected Topics in Quantum Electronics, vol. 27, no. 1, pp. 1 - 8, 2021.[Abstract]


An array of optical waveguide fed 45° metal-coated mirrors are proposed and validated by simulation, for generating optical scalar and vector vortices. Subwavelength element-to-element spacings are achieved, which is not possible in traditional grating-based phased arrays. This vortex source can be superior over other methods like phase masks which are not planar process integrable with lasers and phase modulators. A simple plane wave reflection model is used to analyze the mirror and the results are matched with reasonable tolerance against simulation results. The spin and orbital angular momentum charges are directly calculated from the field values for quantifying the performance. Four- and eight-element arrays are studied. The matching of prediction with simulation has been good for linear, azimuthal and radial polarization. Good angular momentum conversion efficiencies are obtained for up to orbital angular momentum charges ${l}$ = ±2. Important aspects of generating vortices with circular polarization are brought out. Directional beams with >10 dB gains are achieved. This is the first report in which a planar dielectric optical waveguide array with subwavelength spacing has achieved good angular momentum control for linearly, azimuthally, radially and circularly polarized beams, in the same geometry.

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2019

Viswas Sadasivan, Paliwal, A., and Mathew, M., “Strain and threshold reduction for a multi-wavelength blue–green laser-triad”, Laser Physics, vol. 29, no. 8, p. 085802, 2019.[Abstract]


Ocean water has a varying transmission around a blue–green window with maximum shifting from blue to green based on chlorophyll and other contained impurities. Here, heterostructure strain accommodation methods necessary to make a three-wavelength InGaN-AlGaN-GaN laser-triad have been studied using simulations. The effect of the GaN/AlGaN doped superlattice (SL) on strain accommodation at the GaN-AlGaN interface has been studied, and Al% twice the bulk layer has been found to be sufficient. InGaN/GaN SL has also been studied to reduce the strain in the InGaN/GaN multi-quantum well active layer and thereby allowing greater In%. Further, a 7 times reduction in the green laser threshold has been obtained by using a superlattice barrier for the quantum well (QW), which also creates asymmetry in the QW. The laser triad is potentially useful in making underwater communication links that can adapt to the optical transmission of the water.

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2018

Viswas Sadasivan and Das, U., “Nonlinear tuning in InGaAsP Embedded Rings”, Optical and Quantum Electronics, vol. 50, no. 2, p. 76, 2018.[Abstract]


Embedded Rings (ER) have been fabricated on InGaAsP/InP multi-quantum wells (MQW) using electron beam lithography and methane + hydrogen reactive ion etching through Cr/SiO2 etched mask. The ER showed a spectrum with interfering resonance modes which has been positively compared with simulation. The device has been used to demonstrate low speed nonlinear tuning of 2 nm with 10 mW input optical power.

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2016

Viswas Sadasivan, Dagar, S., and Bhowmick, T., “InGaAsP/InP integrated waveguide photodetector pair using quantum well intermixing”, Optical and Quantum Electronics, vol. 48, 2016.[Abstract]


Quantum well intermixing using single layer ZrO2 capped annealing on InGaAsP/InP MQW has been used to achieve integrated two wavelength photodiode pair. The selective solubility of In and Ga in ZrO2 has been used for bandgap engineering. The top layers of the hetrostructure is chosen by lithography and etching into the same hetrostructure. The regions with lower desired bandgaps are chosen to be of lower Ga content. Comparison of different top layer and anneal conditions with respect to wavelength shift and surface quality is also shown. A uniform F ion implantation performed before the annealing has shown an increase of differential blue shift. Regions with up to a minimum of 60 nm InGaAs top layer have been shown to produce a differential bandgap change of 10 nm with no F ion implantation, and 30 nm with uniform F ion implantation (when annealed at 750 °C for 10 s with 300 nm ZrO2 cap).

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2015

Viswas Sadasivan, Dagar, S., and Das, U., “Fabrication of low grass, smooth sidewall InGaAsP by methane–hydrogen inductively coupled plasma RIE through a metal lift-off mask patterned by e-beam lithography”, Journal of vacuum science & technology. B, Microelectronics and nanometer structures: processing, measurement, and phenomena: an official journal of the American Vacuum Society, vol. 33, p. 051210, 2015.[Abstract]


An optimized CH4+H2 inductively coupled-plasma reactive-ion-etching process for fabrication of high quality nanophotonic InGaAsP/InP waveguide device has been developed. Important parameters that influence e-beam lithography and etching have been optimized for a simple metal lift-off masked process. Smooth sidewalls with low grass content has been demonstrated for >3 μm etch depths in InGaAsP/InP using an Al lift-off etch mask.

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2014

Viswas Sadasivan and Das, U., “QCSE tuned embedded ring modulator”, Lightwave Technology, Journal of, vol. 32, pp. 107-114, 2014.[Abstract]


A micro embedded ring resonator modulator using quantum confined stark effect (QCSE) has been modeled and studied in this paper. Semi analytical design methods for various components like bend, coupler, and the whole embedded ring have been used here. Time domain and frequency domain analysis methods have been developed and studied. Using these methods a 50 Gbps, 11 dB extinction ratio, 5 μm outer radius embedded ring, QCSE tuned optical modulator design has been proposed.

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Publication Type: Conference Proceedings

Year of Publication Title

2019

M. P. A. Das, P. Arjun, A. S. Bhaskaran, P. S. Aravind, T. R. Aswin, and Viswas Sadasivan, “Estimation of maximum range for underwater optical communication using PIN and avalanche photodetectors”, 2019 International Conference on Advances in Computing and Communication Engineering (ICACCE). pp. 1-6, 2019.[Abstract]


This paper presents an estimate of underwater optical communication (UWOC) range, using PIN and avalanche photodetectors (APDs). In this simulation-based study, the maximum range while transmitting high-quality video at 6Mbps speed is estimated as 520m in Pure Sea water, 65m in Clear Ocean and 44m in Coastal waters, when using a 100mW laser and APD. The channel here is modeled to include the effect of attenuation and noise. This work quantifies the benefits of using an adaptive system where the wavelength (blue, blue-green and green) of transmission and modulation scheme is changed based on water transmission. Wavelength adaptation according to varying water transmission was found to provide 16 to 40dB advantage in SNR, compared to a system with fixed wavelength, in different waters. A recommendation for wavelength adaptable transmitter design is made based on this. This study assumes the current state of the art in commercially available components.

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2019

Viswas Sadasivan and Mathew, M., “Direct Epitaxial Lateral Overgrowth of GaN on Sapphire”, The Physics of Semiconductor Devices, Proceedings of International Workshop on the Physics of Semiconductor and Devices. Springer International Publishing, Cham, pp. 263-267, 2019.[Abstract]


A regrowth-free direct epitaxial lateral overgrowth method for MOCVD GaN on Sapphire is demonstrated here. The mask used is 2 μm thick SiO2 stripes with 5 μm separation and 19 μm period, formed on c-plane sapphire substrate. An uninterrupted two step growth process has been developed to obtain appropriate growth rates in vertical and horizontal directions. Coalescence has been achieved when the stripes were aligned perpendicular to the primary cut. The AFM image revealed \textasciitilde1.4° surface tilt in the regrown regions. Photoluminescence study showed uniformity in the central region of the wafer and slight broadening of the spectrum, possibly due to defects in the coalescence region.

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2016

Viswas Sadasivan and Das, U., “Embedded ring resonator in InGaAsP multi-quantum wells”, 13th International Conference on Fiber Optics and Photonics. Optical Society of America, Kanpur India, 2016.[Abstract]


Embedded ring (ER) is fabricated on InGaAsP/InP multi-quantum wells using electron beam lithography and methane hydrogen reactive ion etchinG.Experimental findings of this ER are also compared with the theoretical study.

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2014

Viswas Sadasivan and Das, U., “Parameter variation in QCSE tuned embedded ring resonator”, IEEE Region 10 Symposium (TENSYMP-14). IEEE, Kuala Lumpur, Malaysia, 2014.[Abstract]


Micro embedded ring resonator using Quantum Confined Stark Effect (QCSE) is studied for its parameter variations with respect to spectral shape and modulation speed. The effects of number of quantum wells, coupling coefficient, ring detuning, symmetry of the structure and temperature on the spectrum are studied here.

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2014

Viswas Sadasivan and Das, U., “Optical switching in InGaAsP/InP Embedded Ring Resonators”, International Conference on Fibre Optics and Photonics, 2014. 2014.[Abstract]


A simulation of embedded ring resonators for intensity dependent nonlinearity in InGaAsP/InP hetrostructure has been carried out. A narrow band all-optical switching of 14dB is obtained for an input power of 100mW.

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Publication Type: Patent

Year of Publication Title

2016

Viswas Sadasivan and Das, U., “Low loss fast electro-optically or all-optically tuned embedded ring modulator or filter”, 2016.[Abstract]


Application Number:1519/DEL/2014 (Indian patent)

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Publication Type: Conference Paper

Year of Publication Title

2015

Viswas Sadasivan and Das, U., “Embedded ring high speed modulators and switches”, in International Conference on Computers and Devices for Communication(CODEC-15), Kolkata, India, 2015.

2015

Viswas Sadasivan and Das, U., “Fabrication of InGaAsP/InP nano-photonic ridge waveguides using CH4+H2 ICP RIE and Al lift-off mask”, in International Workshop on the Physics of Semiconductor Devices 2015 (IWPSD-15), Bangalore, 2015.