Variant fractional Fourier transformer for optical pulses

We demonstrate that it is possible to perform a fractional Fourier transfor m of an incident pulse with a continuously variable degree of fractionality , using a dispersive and nonlinear Ken: medium. This medium acts as a linea r waveguide for the optical pulse if its intensity is small and if the refr active index is nonlinearly time-dependently modified by a simultaneously l aunched bright soliton. For optical pulses the dispersive and nonlinear med ium is perfectly equivalent to a graded-index refractive medium for optical beams. (C) 1999 Optical Society of America OCIS codes: 070.2580, 070.6020, 230.7370, 190.4360, 320.5550.