Broadband arbitrary waveform generation based on microwave frequency upshifting in optical fibers

An interesting method for broadband arbitrary waveform generation is based on the frequency upshifting of a narrowband microwave signal. In this technique, the original microwave signal is imaged into a temporally compressed replica using a simple and practical fiber-based system. Recently, it has been shown that the conventional limitations of this approach (e.g., bandwidth limitations) can be overcome by exploiting a temporal self-imaging (Talbot) effect in fiber. This effect can be used whenever the signal to be imaged is a quasi-periodic waveform (e.g., microwave tones or any arbitrary periodic waveform). This paper provides a comprehensive study of the microwave frequency upshifting technique with special focus on the Talbot-based approach. Following a theoretical analysis of the design constraints of the conventional approach, the Talbot-based solution is theoretically investigated in detail. In particular, the design specifications of a Talbot-based microwave upshifting system are derived, and the practical capabilities and constraints of these systems (e.g., in terms of achievable bandwidth) are stated and examined. The theoretical findings are confirmed by means of numerical simulations. Moreover, a numerical study of the influence of higher-order (second-order) dispersion terms on system performance is presented, and some additional design rules to minimize the associated detrimental effects are given. The results show that microwave frequencies up to a few hundreds of gigahertz over nanosecond temporal windows can be easily obtained with the described technique using input optical bandwidths in the terahertz range. This has been experimentally confirmed.