Heterodyne autocorrelation method for characterizing 1.55 μm optical pulse train and for measuring dispersion and nonlinearity in optical fibers

Heterodyne autocorrelation measurement of 1.55 μm optical pulses from an actively mode-locked external cavity diode laser is performed before and after transmission through an optical fiber. In heterodyne autocorrelation, optical spectrum is resolved electronically. This method is suitable for measurement of optical pulses with a spectral width of less than 100 GHz, and it gives not only the pulse width and chirp of the pulses, but also it is useful for determining the dispersion and optical Kerr constant of an optical fiber. Analytical formalism for deducing these quantities is given for Gaussian pulses. Principal measurement is performed using a mode-locked diode laser. Dispersion is measured for a conventional-dispersion fiber of 35 km. Also, self-phase modulation (SPM) is measured for a dispersion-shifted fiber of 15.83 km