Polarization-maintaining terahertz anti-resonant fibers based on mode couplings between core and cladding

Influence of cladding tube structure on transmission characteristics of negative curvature terahertz fiber

“…This is attributed to the gradual decrease in the gap between cladding tubes, which results in less terahertz wave leakage from the cladding tube gap. The cladding tube not only reduces the terahertz wave leakage, but also compresses the fiber core inwards at a higher rate in the oblique direction, leading to an elliptical and asymmetric core structure [9]. This results in a stronger asymmetric distribution of effective refractive index [16] and suppression of the coupling effect, leading to higher birefringence in the Type3 fiber.…”

“…In 2021, Liu et al designed a negative curvature polarization fiber composed of double semicircles with different radii in the horizontal and vertical directions, achieving birefringence above 10 −4 in the range of 1490 nm-1550 nm [8]. In the same year, Sun et al reported the study of mode coupling mechanisms based on the three negative curvature fiber structures, where the cladding tubes of negative curvature polarization fiber were composed of four semicircle tubes and vertical semicircle nested structure [9]. When the fiber was in the y-bending direction with a large bending radius, the birefringence remained around 10 −4 .…”

The design of polarization-maintaining and polarization-filtering hollow core with nested anti-resonance nodeless fiber for THz guidance

“…With an intention to propose a high birefringence hollow-core anti-resonant fiber, we implemented the approach of breaking the core symmetry to the proposed fiber by introducing unequal sizes of the nested tubes. This concept is similar to other works that introduce the birefringence and induce the phase match between the core mode and cladding mode by breaking the symmetry in the fiber structure [22]. This model was done by keeping the diameter of the nested tubes in the horizontal direction fixed while decreasing the diameter of the nested tubes in the vertical direction.…”

“…The effective indexes correspond to LP lm mode can be approximated by the modified Marcatili-Schmeltzer model which is [22]…”

“…The simulated birefringence was found to be above 10 −4 . Lastly, in 2021, S Sun et al [22] numerically investigated the polarization-maintaining THz ARF based on index-induced mode coupling. The highest birefringence was found to exceed 4×10 −4 when elliptical core and bi-thickening approaches were implemented.…”