Analog-to-Digital Conversion Based on Modular Blocks Exploiting Cross-Gain Modulation in Semiconductor Optical Amplifiers

A new approach based on modular blocks to implement all-optical analog-to-digital conversion is presented. The basic blocks exploit cross-gain modulation in semiconductor optical amplifiers. A four-level signal at 20 Gsamples/s is successfully quantized and coded onto 2 bits. The output extinction ratio of the encoded bits is higher than 3.6 dB. The extinction ratio can be improved by means of a thresholder, e.g., a saturable absorber, at each output port.