Fig. 1. Few-mode fiber[24]. (a) Transverse mode field intensity and effective refractive index in scalar mode; (b) transverse mode field intensity, polarization and effective refractive index in vector mode

Fig. 2. Numerical simulation results of vortex light field generation by superposition of three strict degenerate high-order vector modes[24]. (a) HE21even/odd; (b) HE31even/odd; (c) EH11even/odd

Fig. 3. Fiber-based cylindrical vector light field generated by free space vector light field coupling. (a) Experimental setup; (b) transverse mode field intensity and polarization distributions

Fig. 4. (a) Optical image of cross section and refractive index distribution of materials for air-core optical fiber; (b) effective refractive index difference between adjacent high-order vector modes of air-core optical fiber; (c) experimental setup for fiber-based vortex light field generation by free-space vortex light field coupling; (d) detection results of spiral phase distribution of fiber-based high-order vortex light field[27]

Fig. 5. (a) Experimental setup for cylindrical vector beams and first-order vortex beams via a micro-bend long period fiber grating; (b) transmission spectra of micro-bend long period fiber grating; (c) fiber-based cylindrical vector light field generation and detection results of polarization distribution; (d) fiber-based vortex light field generation and detection results of spiral phase distribution[29]

Fig. 6. (a) Principle of first-order vortex light field generation by micro-bend long period fiber grating; (b)(c) mode field intensity distributions of ±1-order vortex light fields; (d)(e) spiral interference fringes generated by coaxial interference between ±1-order vortex light fields and Gaussian light[31]

Fig. 7. (a) Schematic of transmission of mode F11 in fiber; (b) transverse mode field intensity distribution of mode F11; (c) transverse mode field intensity distribution of mode HE11; (d) included angle ? between polarization directions of modes HE11 and F11 on cross section of optical fiber; (e)-(h) coupling coefficient κ between mode HE11 and first group high-order vector modes (TE01, HE21even/odd, TM01) versus ?[32]

Fig. 8. Polarization vector light field generation and detection results of polarization of (a1)-(a5), (c1)-(c5), (e1)-(e5) radial/(b1)-(b5), (d1)-(d5), (f1)-(f5) azimuthal fiber-based vector fields at wavelengths of 632.8, 532, 1550 nm[33]

Fig. 9. (a1)-(e1), (a3)-(e3) Mode field intensity distributions of fiber-based ±1-order vortex light fields and (a2)-(e2), (a4)-(e4) spiral interference fringes generated by coaxial interference between ±1-order vortex light fields and Gaussian light at wavelengths of 1540,1545,1550,1555,1560 nm[32]

Fig. 10. Fiber-based high-order vortex light field generation by cascaded vector mode coupling of AIFG[24]. (a)(b) Schematic diagrams; (c)(d) mode field intensity distributions and spiral interference fringes

Fig. 11. (a) Autocorrelation curve of femtosecond pulse; (b) spectrum of femtosecond pulse and transmission spectrum of AIFG; (c) phase matching relationship between fundamental vector mode and first group high-order vector mode coupling achieved by AIFG; (d)(e) numerical calculation results of intensity and linear polarization characteristics of femtosecond vortex light field; (f)(g) calculation results of spiral phase distribution of femtosecond vortex light field[34]

Fig. 12. (a)(b) Transverse mode field intensity distributions of ±1-order femtosecond vortex light fields; (c)(d) horizontal intensity curves through centers of Fig. 12 (a) and Fig. 12 (b); (e)(f) fork-shaped interference fringes generated by off-axis interference between femtosecond vortex light field and Gaussian light; (g) detection results of linear polarization characteristics of 1-order femtosecond vortex light field[34]

Fig. 13. (a) Scanning electron microscope (SEM) image of spiral phase plate patterned on a fiber core; (b) local amplification image of spiral phase plate; (c) SEM image of fork-shaped grating patterned on a fiber core; (d) local amplification image of fork-shaped grating; (e)(f) intensity distributions of vortex light field generated by spiral phase plate and fork-shaped grating; (g)(h) fork-shaped interference fringes generated by off-axis interference between Gaussian light and vortex light field gene

Fig. 14. (a) Experimental setup for chiral fiber grating construction and vortex light field generation; (b) mode field intensity distribution of vortex light field; (c)(d) spiral interference fringes generated by coaxial interference between ±1-order vortex light field and linearly polarized Gaussian light[39]

Fig. 15. (a) Experimental setup for chiral fiber grating generation by superposition of two perpendicularly polarized acoustic flexural waves; (b)-(e) transverse mode field intensity and phase distributions of fiber-based vortex acoustic field; (f)-(i) detection results of mode field intensity distribution and spiral phase of fiber-based vortex light field

Fig. 16. (a) Detection results of fiber-based radial/angular polarization vector light field generation and polarization state; (b) structural diagram of tilted long-period fiber grating; (c) detection results of fiber-based vortex light field generation and spiral phase distribution[45-46]

Fig. 17. (a) Experimental setup for cylindrical vector light field generation by fiber coupler; (b)(c) detection results of transverse mode field intensity distribution and polarization state of fiber-based radial/angular polarization vector light field[48]

Fig. 18. (a) Fiber-based STED fluorescence microscopic imaging system; (b) 3D plots of the focal spot achieved by the overlapping of the excitation and depletion beams in the focal region; (c)(d) image and cross-section of the focal spot of the excitation beam; (e)(f) image and cross-section of a doughnut shaped focal spot of the depletion beam; (g) STED imaging of nanofluorescence microspheres[54]

Fig. 19. (a) OAM as new degree of freedom for data multiplexing; (b) optical microscopic image of vortex fiber; (c) experimental configuration of fiber OAM communication; (d) block diagram of 20×4 Gbit/s 16-QAM signal transmission over 10 wavelengths carrying two vortex modes in vortex fiber

Fig. 20. (a) Structural diagram of metal-coated optical fiber tip excited by radially polarized vector light field; (b) relationship between effective refractive index of optical radial polarization vector mode and SPP radial polarization vector mode with tip diameter; (c) SEM image of metal-coated optical fiber tip; (d) local enlargement of tip; (e) generation of nanofocusing light source at tip of metal-coated optical fiber by excitation in radial polarization vector mode of optical fiber; (f) schemati

Fig. 21. (a) Fiber-based radially polarized vector field generation and SRS measurement setup; (b) SRS spectra at different pumping powers; spectra and polarization state detection results of transverse mode field intensity distributions of (c) pumping light, (d) first-order and (e) second-order Stokes lines[67]

Table 1. Field direction functions of fiber-based vector modes