Complete Characterization of Optical Pulses in the Picosecond Regime for Ultrafast Communication Systems

Ultrashort optical pulses have a variety of applications, one of which is the development of optical time-devision multiplexing (OTDM) networks. Data is encoded in these short optical pulses (typically a few picoseconds in length) which are then interleaved in time to provide very high data rates on a single wavelength. Wavelengthdivision multiplexing (WDM) uses multiple channels by interleaving pulses in frequency in order to achieve high data rates. Typical pulse lengths in WDM are on the order of hundreds of picoseconds. OTDM networks have some advantages over WDM networks, but in order to take advantage of these characteristics, a better understanding of short optical pulse characterization needs to be reached. Such investigation requires accurate pulse characterization in the form of amplitude and phase measurements. Traditional methods of measurement such as nonlinear optical autocorrelation and spectral analysis cannot accurately measure pulse shape and phase. Two new methods of accurate characterization of amplitude and phase are frequency-resolved optical gating (FROG) developed by Rick Trebino, and a spectral interferometric method developed by Jean Debeau. The second-harmonic generation FROG method is highly sensitive but works best for femtosecond pulse lengths, due to the need for large spectrum. The spectral interferometric method is straightforward to implement using common fiber-coupled components, but suffers from a need for high pulse-to-pulse coherency, which implies that it is less practical for actual communication networks. Thesis Supervisor: Erich P. Ippen Title: Elihu Thomson Professor of Electrical Engineering Thesis Supervisor: Scott A. Hamilton Title: MIT Lincoln Laboratory Staff Member