Design, fabrication, and characterization of novel waveguide structures for high-power and compact THz sources based on a novel concept

In the proposed work we will investigate the THz properties of a slab waveguide made from a GaP or ZnGeP2 wafer. We plan to investigate how the width of a slab waveguide will affect the output power of the THz waves and normalized conversion efficiencies. We are particularly interested in the exploration of how the multi-modes supported by the waveguide will affect the THz parametric conversion due to the interference among the multi-modes. We expect that the normalized conversion efficiencies will be significantly increased by using a slab waveguide. Following our results, we are going to design, fabricate, and characterize a novel coupled-waveguide structure in which a slab GaP or ZnGeP2 waveguide is coupled to an adjacent waveguide made from a polymer material by a thin polymer layer. The idea behind this is to couple the THz wave from an electro-optic crystal to a polymer waveguide before it is absorbed by the electro-optic crystal. According to our previous theory, this is equivalent to the increase of the interaction length among the three parametric waves within the electro-optic crystal, and therefore, the output power and conversion efficiencies for the THz generation can be increased by one order of magnitude. The coupling layer can be fabricated in such a way that it serves as a confinement layer for the two waveguides and it is used to achieve the phase-matching for the parametric conversion. We will use the method of diffusion-bonding technique to bond the electro-optic crystal and polymer wafers together. We will experimentally determine the condition for fabricating such a high-quality waveguide structure by using this technique. Since in such a case the polymer plate does not have to be poled, we could just use any low-loss polymer such as polyethylene. We will use our ultrafast laser pulses to characterize such a novel structure by measuring the THz output characteristics such as the central wavelength, linewidith, conversion efficiencies, and coupling efficiencies. Following our result, we will optimize our coupled-waveguide structure in order to further improve the normalized conversion efficiencies. We also plan to carry out comprehensive study and design for a prototype device which can produce an output power of more than 10 W. In addition, we are going to identify key sub-components for the device with a tuning range of 0.3-10 THz. Furthermore, we will complete a feasibility study on the increase of a conversion efficiency to about 1%.