[1] Cheng L, Liao L, Luo X et al. Design of multi-core photonic crystal fiber for space-division multiplexing[C](2014).

[2] Sillard P. Few-mode fibers for space division multiplexing[C](2016).

[3] Li S, Wang J. A compact trench-assisted multi-orbital-angular-momentum multi-ring fiber for ultrahigh-density space-division multiplexing (19 rings × 22 modes)[J]. Scientific Reports, 4, 3853(2014).

[4] Xia C, Correa R A, Bai N et al. Low-crosstalk few-mode multi-core fiber for high-mode-density space-division multiplexing[C](2012).

[5] von Huene J H, Ryf R, Winzer P et al. LCoS-based mode shaper for few-mode fiber[J]. Optics Express, 21, 18097-18110(2013).

[6] Feng Y H, Luo J W, Li Y R et al. Mode multiplexing and high efficient switching in few-mode fiber based on modeled blazed grating[J]. IEEE Photonics Journal, 8, 1-7(2016).

[7] Melati D, Alippi A, Melloni A et al. Integrated spatial division (de)multiplexer for few-mode fiber transmission[C], 1-3(2016).

[8] Dai D X, Mao M. Mode converter based on an inverse taper for multimode silicon nanophotonic integrated circuits[J]. Optics Express, 23, 28376-28388(2015).

[9] Huang Q D, Wu Y F, Jin W et al. Mode multiplexer with cascaded vertical asymmetric waveguide directional couplers[J]. Journal of Lightwave Technology, 36, 2903-2911(2018).

[10] Ismaeel R, Lee T, Oduro B et al. All-fiber fused directional coupler for highly efficient spatial mode conversion[J]. Optics Express, 22, 11610-11619(2014).

[11] Li J, Liu J T, Hu H F et al. Tunable orbital angular momentum mode conversion in asymmetric long period fiber gratings[J]. IEEE Photonics Technology Letters, 29, 2103-2106(2017).

[12] Zhao Y H, Liu Y Q, Zhang C Y et al. All-fiber mode converter based on long-period fiber gratings written in few-mode fiber[J]. Optics Letters, 42, 4708-4711(2017).

[13] Xue Y R, Tian P F, Jin W et al. Superimposed long period gratings based mode converter in few-mode fiber[J]. Acta Physica Sinica, 68, 054204(2019).

[14] Jung Y, Alam S U, Richardson D J et al. Compact higher-order mode converter based on all-fiber phase plate segment[C], 1-3(2015).

[15] Yin G L, Wang C L, Zhao Y H et al. Multi-channel mode converter based on a modal interferometer in a two-mode fiber[J]. Optics Letters, 42, 3757-3760(2017).

[16] Gavrilov A V, Pavelyev V S. Integrated fiber-based transverse mode converter[J]. Computer Optics, 41, 510-514(2017).

[17] Zhao Y H, Liu Y Q, Zhang L et al. Mode converter based on the long-period fiber gratings written in the two-mode fiber[J]. Optics Express, 24, 6186-6195(2016).

[18] Zhang X H, Liu Y G, Wang Z et al. LP01-LP11a mode converters based on long-period fiber gratings in a two-mode polarization-maintaining photonic crystal fiber[J]. Optics Express, 26, 7013-7021(2018).

[19] Xiao G L, Zhang K F, Yang H Y et al. Refractive index sensor with double resonance peaks for D-type symmetric two-core photonic crystal fiber[J]. Acta Optica Sinica, 40, 1206001(2020).

[20] Yu C L, Wang M, Feng S Y et al. Research progress on ytterbium-doped large mode area photonic crystal fibers[J]. Laser & Optoelectronics Progress, 56, 170602(2019).

[21] Liu H, Bai B B, Zhang Y Z et al. High-sensitivity temperature measurement based on SPR in gold-PDMS-coated photonic crystal fiber[J]. Chinese Journal of Lasers, 47, 0404003(2020).