Research On Terahertz Functional Devices Based On Photonic Crystal Waveguides Formed By Dielectric Rods

Nowadays terahertz (THz) applications mainly depended on free space systems, but with the development of THz solid-state system, functional devices are expected to play an important role. In this thesis, based on photonic crystal waveguide structures formed by dielectric rods, several THz functional devices are researched.First, comparing with commonly used THz time domain spectroscopy (THz-TDS) system with focused beam, THz-TDS system with parallel beam is more suitable for the measurement of waveguide type devices. So a THz parallel beam TDS system is set up. Through optimizing each component, the signal to noise ratio of the system reaches128.9and the dynamic range reaches147.3. The diameter of the THz beam at different positions is about the same, which is3.89cm. The fluctuation of the diameter along the propagation direction is smaller than0.17%/cm, thus the depth of parallelism is satisfying.Second, based on photonic crystal theory, an all-rod THz solid core photnic crystal fiber (PCF) and an all-rod THz air core PCF are designed and fabricated. The solid core PCF is composed of61dielectric rods. Experimental results show the sample relative transmission is2.5times as larger as that of the air reference with same apertures in a large frequency range and the insertion loss (including the coupling loss and the transmission loss) of the PCF with the length of3.5cm is as low as2.45dB, displaying the wave guiding function. The air core PCF is formed by60dielectric rods. Obvious photonic bandgap property is observed and in transmission bands the insertion loss of the PCF with the length of3.5cm is as low as6.65dB.Third, based on proposed THz PCF, the surface plasmon polaritons effect on metal wires is introduced. After sysmetrically inserting metal wires into the PCF, the coupling effect between waveguide mode and surface plasmon mode is studied. The influence brought by the size and the location of the metal wires is analized. The single polarization operation of the modified PCF is experimentally tried. In agreement with the simulation, single polarization working is observed around specific frequency and the extinction ratio reaches7.8dB. At last, non-reciprocal waveguide devices based on two-dimensional magneto-optical photonic crystals are designed, including isolator, circulator and crossing waveguide. The isolator uses several Yttrium Iron Garnet (YIG) rods to gain a continual one-way pass band. If the working band is defined as the band where the transmittance larger than0.5at transmission port and smaller than0.1at isolation port, the relative bandwidth is defined as the ratio of the bandwidth and center frequency, the bandwidth can reach10.6%with highest isolation of115dB. Based on the isolator, the first kind of circulators uses five YIG rods to obtain a usable circulation bandwidth of4.7%with isolation reaching35dB. Through simplification, another kind of waveguide cross structure circulators uses four YIG rods to gain a circulation bandwidth of2.5%with isolation reaching31dB. A derivative low-crosstalk crossing waveguide uses twelve YIG rods to achieve a large usable bandwidth of16.6%and has low crosstalk.