Lithium Niobate Waveguides for Continuous Wave Terahertz Generation

In this work, a device is proposed which is capable of operating as an Electromagnetic (EM) wave emitter between 2 and 5 Terahertz (THz) in Continuous Wave (CW) operation. Very few widely tunable EM sources currently exist in this frequency range. The proposed THz source would be tunable and able to produce monochromatic emission over a broad spectral range at room temperature.
The proposed device employs a rib waveguide, fabricated from a thin film Lithium Niobate (LN) substrate. By phase matching the Near Infra-Red (NIR) and THz waves using cladding materials, Difference Frequency Generation (DFG) of two NIR pump beams is attempted in order to generate THz radiation.
Modelling of the device is presented, detailing the influence of geometry on phase matching and mode confinement. Calculations are then presented to estimate the expected power. The upper bound on emission power is given by the quality of the phase matching, which determines the length of the waveguide in which frequency conversion occurs. The results suggest that a realistic device operating at 2 THz could generate 2 μW of THz power.
Techniques to fabricate the proposed device are investigated and fabrication of LN rib waveguides is described. These test ribs are then characterised in an experimental setup.
An alternative approach to phase matching, using a Cherenkov angle, is presented near the end of the thesis as a route towards efficient THz generation with less stringent phase matching and simplified fabrication. The fabrication and experimental testing of this emitter is discussed.