1. Describe the type of light emission and the output characteristics of Semiconductor lasers. [7] 2. Calculate the resp

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1. Describe the type of light emission and the output characteristics of Semiconductor lasers. [7] 2. Calculate the responsivity of a p-i-n photodiode at 1.3 um and 1.55 um if the quantum efficiency is 80%. (Planck constant h=6.626x10-34 m?kg/s, the speed of light in vacuum c =3x108 m/s, the elementary charge on the electron = 1.6x10-1° C). [9] 3. Attenuation in fibre optics, also known as transmission loss, is the reduction in intensity of the signal as it travels through the optical fibre. (a)Explain the cause of attenuation. [13] (b) 10 mW of power is launched into an optical fibre that has an attenuation of =0.18 dB/km. What is the received power after traveling a distance of 50 km? [5] 4. The material gain of an optical amplifier has a full width at half maximum (FWHM) bandwidth of 500 GHz. Neglecting gain saturation effect for simplicity, please find the amplifier bandwidths when the peak gains of the amplifier are 20 dB, and 30 dB, respectively. (AVA= Avg[ln2/In(G,/2)]"2, Ava is optical bandwidth, Avg is the material gain bandwidth and Go is the amplifier's peak optical gain) [6] 5. A signal modulator is an important component of a transmitter. a) Draw simple diagrams to define i) direct modulation and ii) external modulation. [8] b) Explain the limitations of direct modulation. [4] 6. Wavelength-division multiplexing (WDM) is a popular technique in optical communication systems. a) With the aid of a diagram, explain what WDM is. [7] b) Describe and explain four benefits of WDM. [8] c) Nam 5 main components required in the implementation of WDM technology (excluding transmitters, receivers, and amplifiers) and define their function, [10] 7. (a) With the aid of simple diagrams, describe the basic principle of coherent optical detection, [7] (b) Explain why coherent optical detection can improve receiver sensitivity and achieve much higher capacity in the same bandwidth compared to intensity modulation and direct detection. [16]