Ultrasensitive nonlinear optical pulse characterizations by chirped quasi-phase matched lithium niobate waveguides.

摘要

We have realized ultra-sensitive self-referenced nonlinear measurements of subpicosecond optical pulses in the lightwave communication band by using chirped quasi-phase matched (QPM) lithium niobate waveguides. The tightly confined optical beam in the long waveguides and the chirped QPM grating period simultaneously enable high second-harmonic generation (SHG) efficiency and broad SHG phase-matching bandwidth, which are essential for sensitive and accurate pulse measurements. Our experiments of intensity autocorrelation measurement achieve a record sensitivity of 0.32 microwatt square , about 500 times better than the previous record. We also employed the SHG frequency-resolved optical gating (FROG) technique to completely retrieve intensity and phase of the unknown pulses. The resulting sensitivity is 2.7 microwatt square, greatly improving on the previous record for FROG schemes by 75,000 times. Our work significantly contributes to system monitoring in ultrafast lightwave communications, nonlinear optical material characterizations, and other experiments using shaped ultrashort optical pulses.