Photonic Analog-to-Digital Conversion

280 INTRODUCTION Accurate collection and processing of electromagnetic information is critical to a wide variety of applications. Present day RF and microwave sensor systems must cover many frequency bands, detect and identify a large range of signal powers, and analyze the signal information on an ever-decreasing time scale. Simultaneously achieving these attributes typically requires multiple hardware systems, stressing even the most accommodating platforms and requiring the elimination of functionality on some. The power of digital signal processing to deliver increased functionality and improved system performance has long been recognized. The resulting preference for digital representation of signals as the format for receiver system outputs has elevated the importance of the analog-to-digital converter (ADC), which serves as the interface between the received analog signals and the digital domain. With this move to the digital domain, the ADC is and will continue to be a major bottleneck for many systems.1 The aim of the authors’ current research is to leverage the unique benefits of photonic technology to build ADC systems capable of far greater speed, bandwidth, and accuracy. In this article we describe novel sampling techniques developed and implemented at APL that he analog-to-digital converter (ADC) performs the crucial transformation of physical electromagnetic signals into ones and zeros that can be processed by computers. As such, it is of great importance to a vast number of electronic systems and is often a limiting component for the performance of such systems. Photonic technology is capable of overcoming many of the limitations in traditional electronic ADCs and is therefore the subject of much experimental investigation. In this article we provide a brief overview of ADCs within the context of receiver systems and of the advantages that photonic technology has to offer, as well as a discussion of recent developments in research performed at APL that promise to extend the functionality of photonic ADCs. Finally, we present the results of experiments implementing nonuniform photonic sampling techniques to unambiguously identify signals separated by many traditional Nyquist zones. Photonic Analog-to-Digital Conversion