Abstract

The generation of terahertz (THz) radiation in a compact geometry is crucial for the implementation of on-chip, coherent THz radiation sources. Here, via numerical time-domain simulations, we show that ${\mathrm{LiNbO}}_3$ (LN) waveguides having sub-wavelength core widths can provide highly efficient optical-to-THz radiation frequency conversion over short lengths. By exploiting the nonlinear susceptibility, ${\mathit{\chi }}_{33}^{(2)}$, enhancement of LN near its phonon reststrahlen band and utilizing THz leaky-mode guidance to minimize reststrahlen band absorption and improve phase matching, we show that broadband (0.2–11.6 THz) electric field pulses of 3.4 kV/cm can be generated at an optical-to-THz conversion efficiency of $2.5\times {10}^{-4}$. These sub-wavelength leaky-mode waveguides provide a compact platform for wideband, coherent THz radiation sources.

© 2018 Optical Society of America

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