Laser bias effect on the receiver sensitivity of passive fibre optic star bus networks

Abstract

We examine in this paper the reduction in receiver sensitivity in passive fibre optic star bus networks due to the laser bias power transmitted by every terminal. Both transimpedance and high impedance preamplifier configurations using PIN and avalanche photodiodes are considered. The penalty in receiver sensitivity is examined as a function of bit rate, number of terminals, amplifier noise and the ratio of the launched laser bias power to average launched signal power. For PIN receivers the penalty has a maximum at low bit rates and falls off rapidly on either side of the maximum. In an example quoted in the paper the PIN receiver sensitivity penalty for networks with less than 50 terminals is less than 1 dB for all bit rates. The penalty for APD receivers increases with bit rate, and, in a further example, is shown to be less than 1 dB for networks with less than 50 terminals operating at bit rates lower than approximately 20 Mbit s⁻¹. Techniques for reducing the penalty to negligible levels are also examined.