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Wigner distribution and spectral dynamics of laser diodes.

The Wigner distribution is a simultaneous representation of a signal in both time and frequency domains. We discuss the Wigner distribution as an instrument-independent method of displaying the time–frequency response of a laser transmitter. This is important in long-haul communication systems that use semiconductor lasers, which exhibit chirp. If the type of spectrometer for measuring the spectrum as a function of time is known, so that the instrument's impulse response is known, then the Wigner distribution can be recovered. This distribution is then identical to that obtained with a different instrument with a different resolution. Examples of the calculated time-resolved spectra, obtained with two different instruments, are shown for a gain-switched laser. They are compared with the Wigner distribution obtained by deconvolution.