Noise performance of optical receivers: comparison of directional coupler and resistive feedback based front ends

Noise properties of a directional-coupler-based optical receiver (DCOR) and the resistive-feedback optical receiver (RFOR) topologies are compared. For the DCOR the authors have both simulated and subsequently measured an input equivalent noise current of 3 pA/ square root (Hz) for a bandwidth of up to 2.5 GHz. By using the same noise modelling approach the simulation results for the RFOR topology gave a noise current of 10 pA/ square root (Hz) over the same bandwidth thus verifying the superiority of the DCOR over the resistive feedback optical receiver.