Round the feature of the ultrafast speed, make the detailed description of phase noise, receiver noise figure, launch power, threshold level of system.

Based on the equivalent circuit model of a two-port optical receiver front-end, the relationship between the equivalent input noise current spectral density and the noise figure is analyzed.

For the requirement of high gain and low noise figure (NF) of the receiver RF destination, two LNAs most be cascaded, which is determined by each noise calculation of the two different LNAs.