Fig. 1. Schematic of (left) three-dimensional structure and (right) cross section of TB-PCF. The number of rings in the three-dimensional sketch is reduced for clarity. The simulation is carried out for the cross section shown in the right panel. The dashed lines are a square with the side length of 2Λ. The inside area is used to calculate the Poynting vector in the core.

Fig. 2. (Top left) neff and B and (top right) Lpol and αpol as functions of dside, and (bottom) neff as a function of the twisting rate.

Fig. 3. Optical power in the core of TB-PCFs as a function of propagation distance for different values of dside. Input modes are (left) LCP and (right) RCP modes. α=0.006  rad/μm.

Fig. 4. (Left) Stokes parameters of TB-PCF for dside=2.0  μm and α=0.006  rad/μm and (right) S3 of TB-PCF for different values of dside calculated by BPM.

Fig. 5. (Left) Stokes parameters of TB-PCF for dside=2.0  μm and α=0.006  rad/μm and (right) S3 of TB-PCF for different values of dside calculated by the analytical method.

Fig. 6. S3 as a function of propagation distance for dside=2.5  μm with α=0.006  rad/μm.

Fig. 7. S3 as a function of propagation distance for α=0.006  rad/μm and different values of dside. Ey mode is launched.

Fig. 8. (Left) Optical power in the core of TB-PCFs and (right) S3 as a function of propagation distance for different values of α. dside=2.5  μm.

Fig. 9. (Left) Transmission spectra of TB-PCFs for α=0.006  rad/μm and different values of dside. Ex mode is launched, and the fiber length is 30,000 μm. (Center) S3 as a function of propagation distance for different wavelength and (right) enlarged view of the center panel.

Fig. 10. Stokes parameters of periodically inverted TB-PCF calculated by (left) the analytical method and (right) BPM. dside=2.0  μm and α=0.0024  rad/μm. Dashed vertical lines show the distance of integer multiples of Λtwist/4.

Fig. 11. Poincaré sphere plots of the polarization state in TB-PCF with dside=2.0  μm. (Left) α=0.0024  rad/μm with constant twisting, (center) α=0.0024  rad/μm with periodically inverted twisting, and (right) α=0.006  rad/μm with periodically inverted twisting.

Fig. 12. Stokes parameters of periodically inverted TB-PCF calculated by BPM. dside=1.25  μm and α=0.000314  rad/μm. Dashed vertical lines show the distance of integer multiples of Λtwist/4.

Fig. 13. Schematic of a multimode TB-PCF and its NFPs.

Fig. 14. Overlap powers (blue solid lines) and total Poynting vectors (black dashed lines) as functions of propagation distance for (left) LP11bx and (right) LP21bx mode input. The inset shows mixed FFIP at the distance marked by red circles.

Fig. 15. Overlap powers (green and blue) and total Poynting vectors (black) as functions of periodically inverted multimode TB-PCF for (top) LP11bx and (bottom) LP21bx mode input. The right panels show NFP and mixed FFIP at the distances marked by red circles.

Fig. 16. Schematic of a twisted waveguide and rotated frame.