High-performance analog photonic links are discussed and the prevalent modulation formats are highlighted. Because of
its multi-octave and millimeter-wave potential, special attention is given to intensity modulation with direct detection
(IMDD) employing an external Mach-Zehnder modulator (MZM). The theory for IMDD is reviewed and some
experimental results are discussed. Two limiting factors in multi-octave IMDD implementations are quantified. The
MZM bias requirements in order to remain third-order limited are shown to be very stringent in high-performance links.
Photodiode nonlinearities, perhaps the most inhibiting factor in present-day wideband analog photonics, are cast in terms
of output intercept points and tied to the IMDD link performance.
Femtosecond pulse shaping for generating nearly arbitrarily shaped ultrafast optical pulses is now a well-established technology and has been widely adopted for applications ranging from high-speed communications to coherent laser control of chemical reactions. Arbitrary waveform generation (AWG) capabilities for millimeter-wave, microwave and THz electromagnetic signals, however, are quite limited. Commercial radio frequency AWG instrumentation is currently limited to ~2 GHz bandwidth. In this talk we review work at Purdue in which shaped optical pulses are used to drive an optical-to-electrical (O/E) converter. This leverages our femtosecond optical AWG technology to achieve cycle-by-cycle synthesis of arbitrary voltage waveforms in the range between a few GHz and ~1 THz. Such capabilities could open new possibilities for applications in areas such as wireless communications, electronic countermeasures, sensing, and pulsed radar.
Recently our work has focused on the range from GHz to tens of GHz. A particular focus has been on the generation of signals appropriate for ultrawideband (UWB) wireless communications using "monocycle" pulses with very large fractional bandwidths. UWB technology provides high immunity to multipath interference, low probability of intercept, and high spatial resolution (for position location). Potential defense applications include tactical sensor networks and RFIF tags for inventory control. Our experiments demonstrate the ability to generate programmable monocycles with spectra that can be tailored to match emission limits and with durations and bandwidths that improve on the mainstream electronic technology. Additional potential applications include predistortion of transmit waveforms in order to precompensate distortions associated with broadband antennas and waveform optimization for enhanced target discrimination in pulsed radar.