Abstract
This paper reviews over 30 years of work on photonic analog-to-digital converters. The review is limited to systems in which the input is a radio-frequency (RF) signal in the electronic domain and the output is a digital version of that signal also in the electronic domain, and thus the review excludes photonic systems directed towards digitizing images or optical communication signals. The state of the art in electronic ADCs, basic properties of ADCs and properties of analog optical links, which are found in many photonic ADCs, are reviewed as background information for understanding photonic ADCs. Then four classes of photonic ADCs are reviewed: 1) photonic assisted ADC in which a photonic device is added to an electronic ADC to improve performance, 2) photonic sampling and electronic quantizing ADC, 3) electronic sampling and photonic quantizing ADC, and 4) photonic sampling and quantizing ADC. It is noted, however, that all 4 classes of "photonic ADC" require some electronic sampling and quantization. After reviewing all known photonic ADCs in the four classes, the review concludes with a discussion of the potential for photonic ADCs in the future.
Highlights
The use of photonic components to make or improve an analog-to-digital converter (ADC) has attracted interest since the early 1970s, and today one can assemble more than 100 references on “photonic ADCs”
The purpose of this review is to describe all known ways in which photonics has been used or proposed for use in ADCs that digitize radio-frequency signals, to put these technologies in well-defined classes, and to identify those technologies that offer promise for dramatic improvement over electronics
This work is fascinating for the breadth of optical processes that researchers have investigated for possible application to analog-to-digital conversion, but it is frustrating because so few publications report full operation of an ADC, which makes it very hard to compare different schemes on an equal basis similar to the evaluation the Walden has performed for electronic ADCs [2, 6]
Summary
The use of photonic components to make or improve an analog-to-digital converter (ADC) has attracted interest since the early 1970s, and today one can assemble more than 100 references on “photonic ADCs”. During this period, lasers and optical components have improved and matured remarkably, but photonics is still not used in any commercial or special purpose ADC to the best of my knowledge. Lasers and optical components have improved and matured remarkably, but photonics is still not used in any commercial or special purpose ADC to the best of my knowledge One reason for this may be the rapid advance in electronics since the early 1970s, but as discussed by Walden (1999, 2006), electronic ADCs improve somewhat slower than digital electronics. I have used the following sources for this review paper: IEEE Xplore, SPIE online journals and proceedings, OSA online journals, Optics Communications online, other references found in journal articles and several books
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