Answer Happy

2. Photodetector and active device. (a) Different photodetectors are used to measure an incident optical pulse as shown in Figure 2 (a). The electrical pulses detected by the photodetectors are shown in Figure 2(b)-(d) in which w is the thickness of the active layer, as is the absorption coefficient of the active material and Cj is the capacitance of the photodetectors. Explain the shapes of the detected pulses. (11 marks)

(optical) Rectangular input pulse w >> Ifa Small () Slow w>> 1/a, component Large C Fast components Diffusion component W<10 Small (c) Figure 2, (a) The optical pulse and (b)-(d) the detected electrical pulse pulses by different photodetectors. (b) Describe the angular distribution of light emitted from a planar light emitting diode with the schematic diagram. State the relationship of light coupling efficiency. (5 marks) () Show the device structure and describe operation condition of laser, optical amplifier and modulator. (9 marks)