Photonic Analog-to-Digital Conversion of Microwave Signals Using Spectral-Interval Estimation

Implementation of photonic analog-to-digital convertor (ADC) using an optimal way of information parallelizing at the level of circuit solutions can significantly improve the performance of the total system (signal source - ADC - computing device). Traditional approach for fast photonic ADC uses processing every time-neighbor sample of input signal by its own channel. For the input signals with limited bandwidth, another approach can be used, in which every input signal spectral interval is processed by its own channel, and the width of the spectral interval is adjusted with the performance of an electronic ADC used for digitizing. In many cases, output signals of electronic ADCs are sufficient for obtaining necessary information from the input signal without joint processing of the output signals of all channels; otherwise, outputs of all channels can be Fourier-processed and concatenated to get complete spectrum of a wideband microwave input signal. For realization of this scheme, a mode locked stable laser together with an amplitude modulator and two combs of narrow band optical filters can be used. Alternatively, a mode locked laser can be replaced with a continuous wave (CW) laser together with a number of optical modulators. Performance capabilities for signal ADC using spectral intervals are estimated. Parameters for optimal system operation are derived. It is shown that, for modern optical elements, 8-10 effective bits can be achieved in the digitized signal.