Signal Spectral-Interval Estimation in Fast Photonic Analog-to-digital Converters

Traditional architectures of fast electronic analog-to-digital conversion (ADC) are typically based on interleaving several lower sample rate digitizers, by combining which it is possible to realize high sample rate ADC. This approach requires high-precision timing and adds noises and harmonic distortions. Traditional architecture of fast photonic ADC is based on processing every time-neighbour sample of input signal by its own channel, however, this method typically requires high precision and expensive photonic components: femtosecond pulse source (mode-locked laser) with ultra-low timing jitter, optical fibers with high precision lengths, balanced photodetectors and others, which together form very unstable and bulky device. For the input signals with limited bandwidth, another approach for photonic ADC 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, joint processing of the output signals of all channels is not necessary; 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, two combs of narrow band optical filters can be used. Performance capabilities for signal ADC using spectral intervals are derived with numerical simulation and compared with experimental results. Parameters for optimal system operation are studied. It is shown that, for modern photonic components, 8–10 effective bits can be achieved in the digitized signal [1].