Continuously phase-matched terahertz difference frequency generation in an embedded-waveguide structure supporting only fundamental modes

We demonstrate an all-single mode structure which enables continuous phase matching of difference frequency generated THz light from the near-IR. This structure provides a long interaction length by way of well-confined collinear propagation of pumps and product without diffraction, resulting in high conversion efficiency. A LiNbO3 version of this structure achieved a power-normalized conversion efficiency of 1.3×10-7 W-1 - some 23 times larger than the largest previously reported results.