We demonstrate ultrasensitive intensity autocorrelation measurements of subpicosecond optical pulses in the telecommunication band by using aperiodically poled lithium niobate (A-PPLN) waveguides. The tightly confined optical beam in the waveguides and the chirped poling period facilitate simultaneous high second-harmonic generation (SHG) efficiency and broad phase-matching (PM) bandwidth. The resulting measurement sensitivity is 3.2×10<sup>-7</sup> mW<sup>2</sup>, ~500 times better than the previous record for intensity autocorrelations. We also show that chirped A-PPLN waveguides retain nearly the same SHG efficiency as the unchirped guide as long as the PM bandwidth is not significantly broader than the input spectrum.
© 2004 Optical Society of America
(120.3180) Instrumentation, measurement, and metrology : Interferometry
(130.3730) Integrated optics : Lithium niobate
(320.7100) Ultrafast optics : Ultrafast measurements
(320.7110) Ultrafast optics : Ultrafast nonlinear optics
Shang-Da Yang, Andrew M. Weiner, Krishnan R. Parameswaran, and Martin M. Fejer, "400-photon-per-pulse ultrashort pulse autocorrelation measurement with aperiodically poled lithium niobate waveguides at 1.55 μm," Opt. Lett. 29, 2070-2072 (2004)