Unique applications of Terahertz radiation in various fields such as biology and medical sciences, remote sensing, and chemical detection have motivated researchers to develop compact and coherent sources for this least touched region of electromagnetic spectrum. Of the many techniques for generating terahertz signals, difference-
frequency generation (DFG) in various crystals is one of the mostly explored methods. Various phase matching methodologies, including phase matching in bulk crystals based on birefringence, and quasi-phase matching have been proposed for this purpose. Although GaAs has an order of magnitude higher second-order nonlinear
coefficient in comparison with other crystals, it is one of the least employed crystals for DFG due to phase-matching difficulties. First, it does not provide birefringence in the bulk crystal for birefringence phase matching. Second, GaAs quasi-phase matching has been shown only in few works because patterning the nonlinear susceptibilities in semiconductors is not easily achieved.
In this thesis, integration of a GaAs optical waveguide and a terahertz waveguide is proposed as a wide-band phase matching technique for DFG to generate high power coherent terahertz radiation. Using waveguides for both optical and terahertz
waves allows for tailoring the phase matching and increasing the interaction length to
get high conversion efficiency. Using pump wavelengths between 1.5-1.6 um, where
low cost and high optical powers are available, we obtained phase matching for terahertz generation in the range of 0-3.5 THz. We exploit the differences between
the GaAs dielectric constant in optical and terahertz range, a high second order
nonlinear coefficient, and low terahertz absorption. Simulation results show the appropriate behavior of the proposed devices for both optical and terahertz waves. The
proposed waveguide phase matching can be useful for other types of devices using
similar nonlinear phenomena, such as coherent detection, electro-optic modulation, and ultra-short pulse generation.
| Identifer | oai:union.ndltd.org:uvic.ca/oai:dspace.library.uvic.ca:1828/334 |
| Date | 08 April 2008 |
| Creators | Marandi, Alireza |
| Contributors | So, Poman P.M., Darcie, Thomas E. |
| Source Sets | University of Victoria |
| Language | English, English |
| Detected Language | English |
| Type | Thesis |
| Rights | Available to the World Wide Web |
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