Chirp Multiplication by Four Wave Mixing for Wideband Swept-Frequency Sources for High Resolution Imaging

We present an analysis and demonstration of the doubling of the chirp rate and total chirp bandwidth of a frequency chirped optical signal by the process of four-wave mixing in a non-linear optical medium. The effects of chromatic dispersion and input power on the maximum achievable output bandwidth are analyzed, and a dispersion compensation technique for phase matching is described. The doubling of an input linear frequency sweep of 100 GHz/1 ms in a highly nonlinear optical fiber is experimentally demonstrated. Further, it is proposed that a cascaded implementation of the four-wave mixing process leads to a geometric increase in the bandwidth of the frequency chirp. With an electronically tuned chirped laser at the input stage, this process can be used to generate extremely wideband swept frequency sources with no moving parts, for applications in high-speed and high-resolution optical imaging and spectroscopy.