Fig. 1. Structures of hollow-core microstructure optical fiber. (a) Hollow-core photonic bandgap fiber^[1]; (b) hollow-core anti-resonant fiber^[2]

Fig. 2. Schematic of scattering loss caused by roughness of inner wall of air hole

Fig. 3. Surface topography^[19]. (a) Isotropic surface; (b) anisotropic surface

Fig. 4. (a) Topography and (b) roughness PSD of surface with sinusoidal distributed roughness^[20]

Fig. 5. (a) Topography and (b) roughness PSD of surface with central symmetry distributed roughness^[20]

Fig. 6. Measured roughness PSD obtained by breaking HC-PBGF (solid line) and roughness PSD calculated from Eq. (4) with three different values of surface tension (dotted lines). Inset: scanning electron microscope (SEM) image of end face of 19-cell HC-PBGF^[15]

Fig. 7. Roughness PSD measured on external surface of micro-structured optical fiber (white dots), roughness PSD measured on surface of outermost air holes (black dots), and roughness PSD calculated from Eq. (4) when optical fiber is in thermodynamic equilibrium (solid line)^[27]

Fig. 8. Schematic of selective filling HC-PBGF^[28]

Fig. 9. Roughness PSD of inner wall of fiber core obtained by selective filling HC-PBGF^[28]

Fig. 10. Surface topography of the same position of fiber preform (bottom left) and fiber (upper right) ^[19]

Fig. 11. Measured roughness PSD (solid lines) and calculated roughness PSD (dotted lines) of fiber preform and fiber^[19]

Fig. 12. Roughness RMS of inner wall of air hole of fibers using different drawing stresses^[19]

Fig. 13. Influence of optimizing drawing process on inner wall roughness of air hole and fiber loss^[11]. (a) Surface topography, (b) measured RMS roughness, and (c) fiber loss spectra before (G#1) and after (G#2) optimizing drawing process