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(b) A basic, two-wavelength WDM uni-directional link operating over one fibre is implemented in Figure Q2(b). A 99/1 wavelength dependent optical coupler is used as the demultiplexer, with the 1310 nm signal destined for Rx-a and the 1550 nm signal for Rx-b. 99% Rx-a 1310 nm 1550 nm 1% 1% 99% Rx-b Figure Q2(b) If the link is 8.3 km long calculate the worst-case signal to noise ratio due to crosstalk at each of the of the receivers for the following specifications. Clearly state any assumption made. Fibre attenuation = 0.35 dB/km @1310 nm Fibre attenuation = 0.22 dB/km @ 1550 nm Total splice loss = 2.7 dB Transmitter output power 1310 nm -4 dBm Transmitter output power 1550 nm -5 dBm Coupler insertion loss at 1% port = 21.0 dB at 99% port = 0.4 dB [12 Marks]