A method and apparatus for measuring the pulse width of a narrow optical
pulse, particularly in a multi-mode optical fiber. A spectrograph and
streak camera are combined to record optical intensity data in a
2-dimensional array resolving both wavelength and temporal dependence of
the optical pulse. The data is analyzed to calculate the chromatic
dispersion and then to remove it. For example, the data in different
wavelength windows are time shifted relative to each other by the amount
of the chromatic dispersion so that all windows have approximately the
same temporal dependence. The correction may numerically establish time
offsets producing the maximum cross-correlation between wavelength
windows. The corrected data may then be summed over optical wavelength,
and the corrected time-dependent data is further analyzed to establish
optical pulse width and impulse response of the fiber. Thereby, a laser
diode with relatively large spectral width can characterize a
high-bandwidth fiber.
