Low-power spectral phase correlator using periodically poled LiNbO3 waveguides

We report a novel optical spectral phase correlation scheme for coded ultrashort pulses based on the use of long periodically poled lithium niobate second harmonic generation waveguides. Second harmonic efficiency as high as 50%/pJ was obtained, which allowed us to demonstrate nonlinear detection of individual pulses at 0.25 pJ input energies over a 500-MHz detection bandwidth with >50:1 signal-to-noise ratio. These results offer the possibility of sub-pJ real-time operation of such devices as nonlinear receivers in ultrashort-pulse optical code-division multiple-access (CDMA) networks.