All-Optical Ultrafast Signal Processors Based on Long-Period Fiber Gratings

A simple and practical all-fiber approach for realizing ultrafast optical differentiators is proposed and numerically tested. In particular, it is demonstrated that first-order and second-order temporal differentiation of an arbitrary optical waveform can be realized by simply propagating the waveform through a suitable uniform longperiod grating photoinscribed in the core of an optical fiber (LPFG structure). An alternative design based on a π phaseshifted LPFG is shown to be especially advantageous in terms of stability and robustness against variations in the grating parameters. Our results have confirmed the feasibility of the proposed approach for processing optical signals with temporal features in the sub-picosecond range (corresponding bandwidths of as much as a few terahertz).