In this research, we present the design, fabrication and experimental validation of 3D printed mux/demux elements for terahertz frequencies. The devices consist of a set of in-line polystyrene (PS) rectangular waveguides, separated by 100 μm, 200 μm and 400 μm air gaps. The principle of operation for the proposed elements resides in coupled-mode theory. Q-factors of up to 3.4 are observed, and additionally, the experimental evidence demonstrates that adding fibers to the design improves the Q-factor by up to 0.62 per fiber added. Using two independent THz broadband channels, we demonstrate the first mux/demux device based on 3D printed in-line filters for the THz range. This approach represents a fast, robust and low-cost solution for the next generation of THz devices for communications.
We use a Monte-Carlo model to simulate semi-classical photo-carrier dynamics on bulk InAs, InGaAs and GaAs that leads to terahertz emission after ultrafast photoexcitation. This detailed model has allowed us to understand various aspects of the THz emission process, including the near-field distribution which has been experimentally observed, the role of the excess excitation photon energy, and the relative importance of the surface field driven, diffusive (photo-Dember) and ballistic currents.
In order to understand the near-field emission we coupled a finite-difference time-domain routine to the carrier dynamics simulation, by doing this, we were able to analyse the near terahertz field emission caused by the motion of such carriers even when the excitation is performed at normal incidence. We found that both the current parallel, which has traditionally been assumed not to take part in the emission, and normal to the interface take a relevant role in the terahertz generation. We performed another set of simulations for different bandgaps and excitation-photon energies in order to compare the emission power of all three semiconductors as function of excitation photon energy finding that the carrier excess excitation energy is more relevant to explain their performance difference than their motilities. We conclude that ballistic transport after photoexcitation is the dominant mechanism for terahertz emission instead of diffusion driven or surface field driven charge separation, which were traditionally considered the most relevant mechanisms.
The design, fabrication and characterization of space-variant Pancharatnam-Berry phase optical elements is presented for the terahertz regime (THz). These PBOEs are made out of polystyrene and were fabricated by commercially available three-dimensional printers, providing a simple and inexpensive solution for the generation of THz vector beams. The polarization structure was characterized by using a THz time-domain imaging system. These devices can find applications in future THz technologies and provide new tools for the study of polarization morphologies
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