Photonic synthesis and hardware correlations of ultrabroadband radio -frequency waveforms and power spectra via optical pulse shaping

Interest has rapidly increased in the area of microwave photonics. Current interest in ultrawideband (UWB) communication wireless system also motivates novel techniques for arbitrary electrical waveform generation. Within the Federal Communications Commission (FCC)-specified frequency band of 3.1-10.6 GHz, UWB systems employ short bursts of radiation to achieve material penetration as well as to mitigate multipath interference in communications applications. We presented an open-loop reflection-mode dispersive Fourier Transform (FT) optical pulse shaping technique for generation of broadband sinusoidal and ultra-broadband impulsive radio-frequency (RF) waveforms in the ranges of 1-10 GHz aiming at applications in UWB wireless communication. This open-loop technique provides the means to rapidly prototype UWB wireless systems by providing real-time waveform design capability—an ability not offered by current electronic techniques. Through appropriate optical waveform design, we showed direct control over the shape of the RF spectrum which enables us to tailor our RF waveforms to conform to the low-power UWB spectral criteria. In addition, we also investigated RF power spectrum design by using the Gerchberg-Saxton (GS) algorithm. This optimization scheme calculates the temporal waveforms associated with the target spectral shapes, which are implemented by synthesizing these waveforms via our optical pulse shaping techniques. Photonic techniques for generation and correlation processing of UWB RF waveforms may serve as enablers for novel wireless UWB schemes including laboratory tests of wireless Ultrawideband- Code Division Multiple Access (UWB-CDMA), which have recently been theoretically analyzed but not been implemented due to lack of waveform generation and processing hardware capable of covering a large fraction of the UWB band. To illustrate the capability of ultrawideband correlation detection, we demonstrate hardware auto/cross- correlation measurements of photonically generated ultrawideband RF burst waveforms in the 3-10 GHz range. Full delay dependent correlation studies with matched waveform pairs reveal correlation peaks ∼ 15dB above those obtained with non-matching sets of waveforms. The possibility of real-time correlation detection is also explored, as are correlation measurements of waveforms that are transmitted over a short line-of-sight wireless link. With waveforms modified to precompensate for antenna dispersion, 7 dB correlation contrast between matched and non-matched waveform pairs is obtained. Our results suggest hardware correlation detection as a possibility for processing of arbitrary waveforms in an UWB receiver