Very high sensitivity optical receiver employing optical feedback

Abstract

An extra degree of freedom is allowed by the optical feedback optical receiver design, since the normal feedback or bias resistor is eliminated from the input node. Johnson noise and resistor parasitic capacitance are thereby absent from the input. Where resistor noise was previously dominant, optical feedback can offer a considerable sensitivity improvement. The magnitude of the improvement is dependent on bit rate and is highest at the lower bit rates where resistor noise is most strongly dominant in typical receivers. This paper describes the first reported optical feedback receiver to use an avalanche photodiode paired with a PIN photodiode as the twin input photodetectors. The sensitivity of the optical feedback receiver is limited mainly by FET channel/shot noise and photodetector shot noise. For the avalanche photodiode receiver there exists an optimum value of multiplied leakage current. Currently Si devices have lower leakage current than InGaAs or Ge devices, and hence Si devices presently offer the best available performance. AT 2.048 Mbit/s primary photocurrents for a bit error rate of 10-9 were of the order of 200 pA, corresponding to 575 photons/bit and the highest reported optical receiver sensitivity of −65.6 dBm.