An optical fibre communication link 5 km long is to be constructed with an analogue modulation bandwidth of 1.0 MHz. The proposed system uses multimode step index fibre with a core refractive index of 1.48 and a numerical aperture of 0.24. The fibre exhibits an attenuation of 2.5 dB/km at the operating wavelength. The emitter is a light emitting diode that has a rise time of 10 ns and can launch 20 mW of optical power into the fibre. No splices are required, but a loss of 1 dB is expected both where the fibre is coupled to the source and to the detector. Determine, giving a clear explanation of your reasoning, both the sensitivity and the bandwidth required of the detector in order to ensure that the link will operate satisfactorily.

An optical fibre communication link 5 km long is to be constructed with an analogue modulation bandwidth of 1.0 MHz. The proposed system uses multimode step index fibre with a core refractive index of 1.48 and a numerical aperture of 0.24. The fibre exhibits an attenuation of 2.5 dB/km at the operating wavelength. The emitter is a light emitting diode that has a rise time of 10 ns and can launch 20 mW of optical power into the fibre. No splices are required, but a loss of 1 dB is expected both where the fibre is coupled to the source and to the detector. Determine, giving a clear explanation of your reasoning, both the sensitivity and the bandwidth required of the detector in order to ensure that the link will operate satisfactorily.