Nonlinear spatio-temporal processing

To meet the speed requirements of ultra-high bandwidth optical communications, devices need to be operated in real time, i.e., as fast as the time window of the time-multiplexed pulse packet. Nonlinear optical processes such as nondegenerate wave mixing can achieve such real-time operation. We describe our real-time spatio-temporal processing techniques by wave mixing; time-to-space conversion using three-wave mixing in a second-order nonlinear crystal and space-to-time conversion by a four-wave mixing arrangement employing cascaded second-order nonlinearities (CSN) for enhanced conversion efficiency. The ultrafast waveform imager performs serial-to-parallel demultiplexing of the shaped pulse train into parallel spatial channels for electronic detection. Our pulse image converter (PIC) system is capable of real-time conversion of a femtosecond pulse sequence into its spatial images. The approach employs spectral domain nonlinear 3-wave mixing in a LiB₃O₅ (LBO) crystal, where the spectral decomposition waves (SDW) of a shaped femtosecond pulse are mixed with those of a transform limited pulse to generate a quasi-monochromatic second harmonic field