Optical Spatial Quantization for Higher Performance Analog-to-Digital Conversion

A novel optical spatial quantized analog-to-digital conversion scheme for real-time conversion at ultrahigh sampling frequencies is presented. At each sampling instant, the analog input voltage deflects an optical sampling pulse onto an array of photodetectors. The output code is derived from the output voltages of the photodetectors on which the optical beam lands. Particular benefits of the proposed architecture are significant reduction in jitter through the use of a mode-locked laser to generate the sampling pulses, high quantization bandwidth through a fully optical quantization scheme, and the system simplicity through the use of just one phase modulator and an embedded binary encoder in the binary-connected photodetector arrays. We experimentally demonstrate an eight-level quantization consuming only 7.2 pJ per quantization with 18-GHz bandwidth, projected to an estimated bandwidth of 30 GHz. Measured 8-ps full-width half-maximum photodetector output voltages promise the potential of realizing a 3-bit 125-GS/s analog-to-digital converter.