A 1550 nm SM digital fibre optical link needs to operate at 565 Mbps over 50 km without repeaters. A single mode InGaAsp laser diode launched an average power of -13 dBm into the fibre. The fibre has a loss of 0.35 dB/km and there is a splice loss of 0.1 dB every km. The coupling loss at the receiver is 0.5 dB and receiver uses InGaAs APD with sensitivity -39 dBm. Excess penalty noises are predicted to be 1.5 dB. Set up the power budget link and system.