Microwave signal generation by mixing of modulated optical carriers in saturated semiconductor optical amplifiers

The gain-crossed property of semiconductor optical amplifiers for generation of microwave carriers after photodetection is experimentally investigated. It was observed that cascaded saturated amplifiers were able to offer up to 10 dB gain to two 8-nm-apart modulated optical carriers. However, due to the saturation, the amplifier gain mechanism was also altered, leading to a mixing effect that causes the frequency components of the optical signals to be exchanged at the cascaded amplifier output. For optical carriers modulated at 700 MHz and 1 GHz it was possible to produce, after photodetection, up and down-converted electronic components at 1.7 GHz and 300 MHz respectively.