Light-Fidelity (Li-Fi) Receiver Design Explain the basic principle of coherent detection technique inoptical wireless communications with the help of a system block-diagram.[4 Marks) Explain the basic operation of a LED

and the steps involved toachieve the spontaneous emission, discuss the processes usingappropriate diagrams. Name any three properties of an LEDsthatare important for the design of a communication system.(6 Marksl A photodiode has a quantum efficiency (n) of 65 % when photonsof energy 1.5X1019J are incident upon it, calculate the followings: at what wavelength is the photodiode operating? the responsivity of the photodiode at the above wavelength. the incident power required to obtain a photocurrent of 2.5HA at the above wavelength.[3 Marks] E=hf=\frac{hc}{\lambda};R=\frac{nq}{hf}R=\frac{ip}{p^0}