All-optical recognition of spectrally coded optical pulses using periodically poled lithium niobate second-harmonic waveguides for ultrashort pulse optical code division multiple-access

Summary form only given.There been increasing interest in realizing optical signal processing functions in optical communication systems based on nonlinear optical parametric processes. In the proposed ultrashort pulse optical code-division multiple access (CDMA) systems, in order to realize multiplexing and demultiplexing for multichannel operation, a nonlinear element is needed to distinguish between correctly decoded signals and incorrectly decoded multiaccess interference, which have comparable average optical power but carry different spectral information. It had been proposed to realize all-optical recognition of optical phase-coded ultrashort waveforms by using second-harmonic generation in long nonlinear crystals, which could have advantages in contrast ratio, operating power and detection efficiency over other proposed schemes. While high contrast ratios have been demonstrated based on such a scheme using bulk periodically poled lithium niobate (PPLN) crystals, the high efficiency has not yet been demonstrated. We use a simple combination of PPLN SHG waveguides and conventional photodetectors to realize all-optical recognition of spectrally phase coded optical pulses, which shows the potential of much higher conversion efficiency compared to previous bulk experiments, which is crucial for real-time operation with a high signal to noise ratio.