Prof. Limin Tong’s group from Zhejiang University made significant achievement on non-linear optics and publisher their work on Nano Letters.

Ultrashort optical pulses have broad applications spanning from optical communication, fluorescence microscopy to biological medicine. A variety of technologies, such as standard aotucorrelators, frequency-resolved optical gating (FROG), spectral phase interferometry for direct electric-field reconstruction (SPIDER), have been developed to characterize ultrashort pulses. While most of them are typically based on optical nonlinear effects in bulk crystal and require a fair amount of space. To develop integrable and energy-efficient photonic circuitry, nanoscale photonic components and devices are highly desired. Transverse second harmonic generation (TSHG) in subwavelength-scale waveguide has been proved to be an efficient approach to characterize ultrashort optical pulses within ultracompact footprints.

The paper reported a single CdTe nanowire optical correlator for femtojoule pulses. A beam of optical pulses was firstly split into two and coupled into a subwavelength-diameter CdTe nanowire from both ends using two fiber tapers. As long as the counterpropagating pulses meet each other within the nanowire, TSHG happens and second harmonic light emits perpendicularly to the axis of the nanowire resulting from wave-vector matching. The temporal profile of input pusles can be readily retrieved from the second harmonic spatial image. Benefitting from the high nonlinearity and larger refractive index of CdTe, the minimum input energy goes down to a few femtojoules (e.g., 2 fJ/pulse at 1064 nm). This correlator may find applications in on-chip ultrafast optical signal processing and ultracompact laser spectroscopy.

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