Design and experiment of cyclic olefin copolymer based 2.5 THz hollow-core photonic crystal fiber

Efficient transmission of terahertz (THz) wave is an important research direction in development of THz technology. Polymeric photonic crystal fiber (PCF) is ideal in THz waveguide transmission because of the advantages of low loss, low dispersion and fine flexibility to bend. Based on the full vector finite element method (FEM), a hollow-core PCF with operating frequency of 2.5 THz is designed. Some samples made of cyclic olefin copolymer (COC) are fabricated. The fiber transmission performance of THz wave is measured by using the CO2 pump laser THz source. The measured minimum loss is 0.17 dB/cm and the average loss is about 0.5 dB/cm. The fluctuation of transmission loss is less than 5% after the fiber is bent 90, showing good flexibility to bend. The measured mode field distribution results of the output port show that the optical fiber transmits signals through the main mode, so the THz energy is well bound in the core of optical fiber.