Compare the construction, principles of operation and characteristics of photomultiplier tube and avalanche photodiode detectors.
What are the relative advantages and disadvantages of each type of detector?
An analogue optical link is to be set up between two points 2 km apart. The required link bandwidth and signal-to-noise ratio are 100 MHz and 60 dB respectively. The source can emit 0.5 m W peak optical power at 0.83 J.Lm into the fibre, whose loss is 1.5 dB /km at this wavelength. Assuming 100% modulation depth, calculate the average photocurrent generated in a PIN detector placed at the output end of the fibre. Assume the detector quantum efficiency is 70%. Does the shot noise in the signal current allow the SNR specification to be met? What is the system margin, ignoring any other noise sources?