Terahertz bandwidth waveform spectrum analysis

We review the recent demonstrations of the waveform power spectrum (WPS) analysis of high-speed optical signals based on using the ultra-fast Kerr effect in an optical medium. Experiments with highly nonlinear planar waveguides have highlighted the technique's capability to achieve a multi-terahertz measurement bandwidth that far surpasses the limits of electronics by over an order of magnitude. This has enabled the WPS measurement of pulses as short as 260 fs, and for signals with bit-rates as high as 1.28 Tb/s. Furthermore, the broadband WPS of high bit-rate signals has been effectively used to retrieve the signal autocorrelation waveform via an inverse Fourier Transform operation. This in turn has provided a novel approach for characterizing the signal in terms of quantifying distortions such as dispersion, timing jitter and noise. The critical design features of the nonlinear waveguide for application to short pulses and high-speed signals are discussed.