Highly birefringent hollow-core anti-resonant terahertz fiber with a thin strut microstructure

A novel highly birefringent and low transmission loss hollow-core anti-resonant (HC-AR) fiber with a central strut is proposed for terahertz waveguiding. To the best of our knowledge, it is the first time that a design of a highly birefringent terahertz fiber based on the hybrid guidance mechanism of the anti-resonant mechanism and the total internal reflection mechanism is provided. Several HC-AR fibers with both ultra-low transmission loss and ultra-low birefringence have been achieved in the near-infrared optical communication band. We propose a HC-AR fiber design in terahertz band by introducing a microstructure in the fiber core which leads to tremendous improvement in birefringence. Calculated results indicate that the proposed HC-AR fiber achieves a birefringence higher than 10-2 in a wide wavelength range. In addition, low relative absorption loss of 0.8% (8.6%) and negligible confinement loss of 1.69×10-4 dB/cm (9.14×10-3 dB/cm) for x-polarization (y-polarization) mode at 1THz are obtained. Furthermore, the main parameters of the fiber structure are evaluated and discussed, proving that the HC-AR fiber possesses great design and fabrication tolerance. Further investigation of the proposed HC-AR fiber also suggests a good balance between birefringence and transmission loss which can be achieved by changing strut thickness to cater numerous applications ideally.