Analysis of the sign reversal of the photodetected signal response in a multielectrode semiconductor optical amplifier

We present a theoretical analysis and experimental results for a two-electrode (200 /spl mu/m/spl times/300 /spl mu/m) 1.5-/spl mu/m semiconductor optical amplifier (SOA) used in photodetection. The experimental results show that at a particular operating point regarding current and optical input power, a sign reversal of the photodetected signal response, and a frequency bandwidth shape modification are obtained at the SOA front contact. These results are confirmed by simulation and explained by the developed theoretical photodetection expression obtained by small signal analysis from the rate equation.