Prof. Sathisha Ramachandrapura Nagaraju Profile

Prof. Sathisha Ramachandrapura Nagaraju

at Indian Institute Of Science Bengaluru

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Author

Publications (3)

Proceedings Article | 8 March 2024 Presentation + Paper

Demonstration of gigabits-per-second two-user NOMA using laser-based indoor optical wireless communication

Sathisha Ramachandrapura Nagaraju, Faheem Ahmad, Varun Raghunathan

Proceedings Volume 12894, 128940J (2024) https://doi.org/10.1117/12.3002196

KEYWORDS: Receivers, Visible light communication, Simulations, Transmitters, Wireless communications, Laser optics, MATLAB, Forward error correction, Orthogonal frequency division multiplexing, Modulation

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Proceedings Article | 4 March 2022 Presentation + Paper

Lighting fixture compatible NIR laser-based 16QAM-OFDM modulated visible light communication

Faheem Ahmad, Sathisha Ramachandrapura Nagaraju, Jyothsna K. M. , Varun Raghunathan

Proceedings Volume 12027, 120270V (2022) https://doi.org/10.1117/12.2609498

KEYWORDS: Near infrared, Light emitting diodes, Transmitters, Receivers, Diffusers, Semiconductor lasers, Modulation, Orthogonal frequency division multiplexing, Signal to noise ratio, Visible radiation

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Proceedings Article | 2 March 2020 Paper

Lens design-based optimization of path loss in a high data-rate indoor visible light communication link

Faheem Ahmad, Sathisha Ramachandrapura Nagaraju, Jyothsna K. M., Rabindra Biswas, Varun Raghunathan

Proceedings Volume 11272, 1127218 (2020) https://doi.org/10.1117/12.2545939

KEYWORDS: Transmitters, Receivers, Telecommunications, Semiconductor lasers, Lens design, Visible radiation, Modulation, Light emitting diodes, Optical communications, Sensors

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In this paper, lens design-based optimization of the optical system for a blue laser diode downconverted with remote phosphor based indoor visible light communication link is studied using optical raytracing and experimentally characterized for illumination/ communication performance. Data modulated 450nm blue laser-diode is used to excite a remote-phosphor to down-convert the blue spectrum to white which is transmitted over a direct line-of-sight free-space link and detected using an amplified p-i-n detector. The combination of transmit and receive lenses are optimized in Zemax ray-tracing software with the objective of minimizing the path loss or maximizing the light collection efficiency within the detector area when placed at different transmitter-to-receiver separation distance. It is found that contrary to the typical 1/d² dependence typically used in VLC system models, the path loss can be minimized at the required link distance by choosing the lens to phosphor and p-i-n detector distance at the transmitter and receiver side respectively. At the optimized location, the VLC link is experimentally characterized by transmitting digital data at a maximum rate of 700 Mbps and bit error rates (BER) obtained is much below 10^-3 . BER versus distance is also found to follow the inverse relation of the path-loss versus distance indicating that the optimized lens positions help in achieving improved data through-put due to minimization of the path losses. Optical spectra and color content measurements indicate that the optimized lens positioning results in enhanced blue content at the receive side due to efficient collection of the data modulated blue components at the expense of the green and red components of the down-converted white light. Further improvements to this link can be achieved by simultaneously optimizing performance at multiple wavelengths spanning blue, green and red wavelengths or using lower color temperature phosphors to improve illumination performance, albeit at the expense of some deterioration to the communication performance.

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