Design Of A Novel Complex Structure Gaas Waveguide Thz Emitter

To improve the conversion efficiency of the THz, a hybrid GaAs waveguide emitter for the generation of terahertz radiation was proposed based on a phase-matched optical rectification process pumped by 1550nm fiber lasers. In the waveguide structure proposed, the phase-matching condition for the optical rectification pumping with 1.55μm optical pulses can be satisfied. However, the energy conversion efficiency from optical pulse to THz pulse and the optical at 1.55μm are very small (i.e., about 10-5 ~ 10-4).That means that the energy of an incident optical pulse is consumed relatively little for one trip in the device. Therefore we could recycle the pump pulse to scale up the power of the THz radiation.Because GVD in the medium of GaAs cannot be avoided and its effect is quite severe in the optical band, the ultra-short optical pulses cannot propagate over long distances with significant broadening of the pulse durations(100fs to 143fs). The key to overcome this obstacle is to find out a proper way to compress the exiting pulse to an ultra-short pulse with duration close to its initial one.In this paper, a scheme is presented to compress the broadening pulse with a semiconductor laser as the chirp compensation, which is coupled with the waveguide structure by a GRIN lens. The main research work and key ideas of the dissertation are listed as follows:1 Analyse the dispersion effect as the pump pulse propagating in the GaAs waveguide THz emitter based on the dispersion theory.2 In order to improve the conversion efficiency of the THz further, a semiconductor laser is proposed for compressing the broadening pulse in thescheme.3 Based on analyzing the function of ray trace in GRIN rod lens and comparingthe GRIN lens placed along transverse direction and the GRIN lens placed along paraxial direction, the one placed along transverse direction is chosen as the bidirectional coupler between the waveguide structure (thickness of the core layer is about 145μm) and the conventional semiconductor.