Studies On Waveguide Terahertz Radiation Sources Excited By 1.55μm Optical Pulses

As the basis of terahertz technology, terahertz radiation sources are always being the focus people concerning. Because its single-photon energy is only 0.8 eV, using 1.55μm ultra-short fiber laser as the excitiong source to generate terahertz radiation by optical rectification is the most useful and simplest method. However, phase-matching conditions cannot be satisfied because of the lack of appropriate crystals.So the efficiency of the radiation is smaller. In this paper, we studied terahertz modes in dielectric and metal waveguides and designed waveguide geometry of terahertz radiation by optical rectification to improve its phase-matching condition. At the same time using of air dielectric layer in the waveguide structure reduced the propagation power loss of terahertz wave.The main research work and key ideas of the dissertation are listed as follows:1 Different terahertz radiation sources were introduced ,especially the sources using the ultra-short pulse lasers. The method based on 1.55μm fiber lasers were analyzed and the applications of waveguide structures in terahertz technology are summarized.2 The refractive indexes of terahertz radiation and optical pulses in different crystals were discussed and calculated and GaAs crystal were identified to be the nonlinear optical crystal by optical rectification using 1.55μm fiber lasers.3 In order to enhance the coherent length, the dielectric waveguide structures were used to regulate the transmission factor thereby increasing the non-linear coherent length.With detailed studies of three different waveguides, the coherence length can be improved from 0.78 mm to 4 mm.4 For the further consideration, a more complex five layer planar dielectric waveguide was designed and phase-matching conditions were achieved by optimization in the optical rectification process.5 Finally, phase-matching condition in different dielectric filled metal planar was discussed. Complete phase-matched waveguide structure parameters under 2THz were given .