1. Calculate the transmission distance over which the optical power will attenuate by a factor of 10 for three fibres with losses of 0.2, 20, and 2000dB/km. Assuming that the optical power decreases as exp( – α L), calculateα (in cm − 1) for the three fibres.

2.  A 1.55 μm digital communication system operating at 1 Gb/s receives an average power of – 40 dBm at the detector. Assuming that 1 and 0 bits are equally likely to occur, calculate the number of photons received within each 1 bit.

3.  An analog voice signal that can vary over the range 0.50 mA is digitized by sampling it at 8 kHz. The first four sample values are 10, 21, 36, and 16mA. Write the corresponding digital signal (a string of 1 and 0 bits) by using a 4-bit representation for each sample.

4. Sketch the variation of optical power with time for a digital NRZ bitstream 010111101110 by assuming a bit rate of 2.5 Gb/s. What is the duration of the shortest and widest optical pulse?

5. A 1.55-μm fiber-optic communication system is transmitting digital signals over 100 km at 2 Gb/s. The transmitter launches 2 mW of average power into the fiber cable, having a net loss of 0.3 dB/km. How many photons are incident on the receiver during a single 1 bit? Assume that 0 bitscarry no power, while 1 bits are in the form of a rectangular pulse occupying the entire bit slot (NRZ format).

6.  A 0.8-μm optical receiver needs at least 1000 photons to detect the 1 bits accurately. What is the maximum possible length of the fiber link for a 100-Mb/s optical communication system designed to transmit –10 dBm of average power? The fiber loss is 2 dB/km at 0.8 mm. Assume the NRZ format and a rectangular pulse shape.

7. A 1.3-μm optical transmitter is used to obtain a digital bit stream at a bit rate of 2 Gb/s. Calculate the number of photons contained in a single 1 bit when the average power emitted by the transmitter is 4 mW. Assume that the 0 bits carry no energy.