ABSTRACT
The technique of time-to-wavelength mapping followed by spectral domain
processing represents a unique and powerful method for detection, gener-
ation, and processing of ultrawideband waveforms. This chapter presents the
fundamentals of time-wavelength signal processing by a comprehensive
analysis of its important applications, the ultrawideband time-stretched
analog-to-digital conversion. By reducing the signal bandwidth prior to digit-
ization, this technique offers revolutionary enhancements in the performance
of electronic converters. The chapter starts with a fundamental-physics
analysis of the time-wavelength transformation including both continuous-
time and discrete-time implementations, and the implication of time-dilation
on the signal-to-noise ratio (SNR). A detailed mathematical description of the
time-stretch process is then constructed. It elucidates the influence of optical
dispersion and nonlinearity on the fidelity of the electrical signal. Two
techniques for ultrawideband operation, single-sideband (SSB) modulation
and phase diversity, are examined. Further, problems arising from the nonuni-
form optical power-spectral-density are explained, and two methods for
overcoming them are described. Finally, design issues and performance
features of a time-stretch analog-to-digital converter array are discussed.
