Semiconductor optical amplifier used as an in-line detector with the signal DC-component conservation

We present in this paper a dc-coupled in-line optical detector based on a multisection semiconductor optical amplifier (SOA). The key principle is to use a voltage reference correlated with the bias voltage level by the way of a two-section or a three-section SOA. So, by means of the differential detection, the signal dc-component is kept with reduced sensitivity to temperature and bias current fluctuations. Experimental and theoretical results are presented when a two-section SOA is used and performance predictions when a three-section is employed. The obtained responsivity is -63 VNV at 40 mA and over -110 VNV at 50 mA when the input optical power, measured within the fiber, is -13 dBm. When the SOA is biased at 40 mA, the detection bandwidth is over 1 GHz when the input optical power is -4 dBm.