| Terahertz (THz) technology has been rapid development in the past ten years, which has become mature. The researches on the sources, detectors, sensors, and imaging have made great progress. But, there are still a lot of difficulties in THz fiber device, which is important to the transmission. The main reason is that THz ranges between microwave and infrared radiation and most of the materials have strong absorption on it. After several years of research and study, we have done many attempt and exploration in this area. Based on the low loss THz fiber, we design a variety of devices, such as switch, polarization, and splitter and so on.We first introduce the THz characteristics and the latest research results in this paper. Then, the domestic and international research situations about THz devices are demonstrated. At last, we analyze the transmission characteristics and structure features of some THz fiber functional devices designed by ourselves. The main contents as follows:1. A highly birefringent polymer THz fiber is proposed in this paper, which is formed with honeycomb cladding and some elliptical air holes in the fiber core. The losses and mode birefringence of the fiber are investigated by finite-different time-domain method. The results show that the fiber can achieve both high birefringence and low confinement loss in a wide THz frequency range. Moreover, compared with a traditional solid-core fiber, guiding loss of the THz porous fiber caused by the material absorption can be reduced effectively as a part of the mode power is trapped in the air holes.2. A novel dual-core single-polarization single-mode THz fiber based on resonant coupling is analyzed. Its coupling principle is different from the solid core SPSM fiber. The confinement loss of the index-matched polarization state is increased small while that of the other polarization state is enhanced by nearly2orders of magnitude. In particular, the confinement loss of the index-matched polarization state is only0.004. 3. A theoretical study of liquid crystal filled photonic crystal fiber is proposed. The effects of electric birefringence of liquid crystal in the photonic crystal fiber and the transmitting properties of photonic crystal fiber are investigated by using the full vector plane wave expansion and beam propagation methods. At the same time, we use finite different time domain method to calculate the change of liquid crystal molecules with the external electric field. The simulation results show that the electrically controlled liquid crystal filled photonic crystal fiber can act as a THz switch with about0.55THz bandwidth. It also has low coupling loss and high extinction ratio which is more than30.78dB. Furthermore, when the frequency of the incident THz wave meets some conditions, the device can control the polarization state of the incident THz wave better.4. Based on index-matching coupling principle, a novel THz polarization splitter in hollow core fiber is designed. Using beam propagation and time domain finite methods, we study the separation process. The simulation results show that the minimum extinction for the x and y poalrization states reach on-28dB and-13dB, which is as goog as the devices base on two dimentional photonic crystal waveguides. Furthermore, since the device enables polarization splitting through two hollow cores, the absorption loss of substrate material is much lower than traditional polarization splitters. The proposed polarization splitting scheme would be of great significance for potential applications in the fields of THz communications and related sensors.5. We test the transmission characters of the THz fiber and hollow core waveguide by using the time-domain THz spectroscopy system. In the same time, we make a theoretical analysis by using finite element method. Compared the two caculation results, we find that they are coincide with each other, which verifies the accuracy of our design method. |
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