Integrated non-linear waveguide optics for high-efficiency THz sources

Summary form only given. We present a novel concept for THz generation based on non-linear integrated waveguide optics leading to compact, coherent and room-temperature stable THz sources. Our concept is based on non-linear frequency down conversion of near infrared modes in a silicon waveguide with organic electro-optic polymer cladding. Organic electro-optic polymers have an engineered ultra-high non-linearity [1] and can be well combined with the silicon photonic platform [2]. The challenge for THz generation based on optical down conversion lies in the dramatic wavelength mismatch of the optical and THz modes making it difficult to achieve phase matching and sufficient mode overlap of the optical and THz waves [3, 4]. We show how the large wavelength mismatch can be exploited, thereby introducing a paradigm change in device design strategy: By folding optical waveguides on sub-wavelength THz scale we can exploit interference of THz waves emitted from different waveguide sections. By adjusting the separation between the optical waveguides, the interference pattern is engineered in order to achieve directed THz emission from the device. Phase matching of the optical fields and emitted THz mode is achieved in a Cherenkov-scheme employing a high-index THz coupling material such as high-resistivity silicon which features a low loss in the THz regime.