Study on the high birefringence and low confinement loss terahertz fiber based on the combination of double negative curvature and nested claddings

A novel double negative curvature nested fiber structure is designed by adding extra circular cladding tubes to enhance the birefringence and reduce the confinement loss. The fiber structure is composed of eight circular cladding tubes and two semi-elliptical nested tubes. The transmission performances of terahertz fiber, including birefringence, confinement loss, dispersion and effective mode field area, are studied by changing the parameters of cladding tubes. In the frequency range of 1.75-2.6 THz, the broad bandwidth of 850 GHz with high birefringence (above 10(-4)) can be achieved. The confinement loss of y-polarization mode with the frequency of 2.575 THz can be as low as 0.00231 dB cm(-1). The waveguide dispersion coefficient is between +/- 0.188 ps (THz cm)(-1) in the frequency range of 2.0-2.475 THz. The maximum effective mode field area of x-polarization mode is 2.618 x 10(-6) m(2) at 2.6 THz.