Low-power ultrashort optical pulse characterization using linear dispersion

We demonstrate a new technique to characterize short optical pulses, which is both simple and capable of yielding pulse characteristics in near-real time (greater than once a second). The optical pulse to be characterized is spectrally dispersed until it is long enough to be easily measured by a fast detector and electronic oscilloscope. The phase of this dispersed pulse is then determined, in our case by means of an optical delay-line discriminator. Once the phase and intensity of the dispersed pulse is known, and knowing the linear dispersion, one can use a simple linear transform to obtain the phase and intensity of the original input pulse. We have applied this technique to the characterization of subpicosecond and picosecond pulses from various fiber lasers. In one set of experiments a fiber ring laser provided roughly transform-limited pulses of 0.63 ps width at an 11-MHz repetition rate. The pulses were attenuated to 10 /spl mu/W, to eliminate any nonlinear effects, and coupled into 6 km of standard telecommunications fiber. The output of the 6 km fiber was coupled into the discriminator and the output detected using a fast detector and oscilloscope.