[1] Li T Y. Lightwave telecommunication[J]. Physics Today, 38, 24-31(1985).

[2] Saitoh K, Matsuo S. Multicore fiber technology[J]. Journal of Lightwave Technology, 34, 55-66(2016).

[3] Essiambre R J, Kramer G, Winzer P J et al. Capacity limits of optical fiber networks[J]. Journal of Lightwave Technology, 28, 662-701(2010).

[4] Wang J, Gray S, Walton D et al. Fiber fuse in high power optical fiber[J]. Proceedings of SPIE, 7134, 71342E(2008).

[5] Desurvire E B. Capacity demand and technology challenges for lightwave systems in the next two decades[J]. Journal of Lightwave Technology, 24, 4697-4710(2006).

[6] MoriokaT. New generation optical infrastructure technologies: “EXAT initiative” towards 2020 and beyond[C]∥2009 14th OptoElectronics and Communications Conference, July 13-17, 2009, Vienna, Austria. New York: IEEE Press, 2009: 1- 2.

[7] Richardson D J, Fini J M, Nelson L E. Space-division multiplexing in optical fibres[J]. Nature Photonics, 7, 354-362(2013).

[8] Li G F, Bai N, Zhao N B et al. Space-division multiplexing: the next frontier in optical communication[J]. Advances in Optics and Photonics, 6, 413-487(2014). http://www.opticsinfobase.org/abstract.cfm?uri=aop-6-4-413

[9] Mizuno T, Miyamoto Y. High-capacity dense space division multiplexing transmission[J]. Optical Fiber Technology, 35, 108-117(2017).

[11] Winzer P J. Making spatial multiplexing a reality[J]. Nature Photonics, 8, 345-348(2014). http://www.nature.com/nphoton/journal/v8/n5/abs/nphoton.2014.58.html

[12] Pei L, Wang J S, Zheng J J et al. Research on specialty and application of space-division-multiplexing fiber[J]. Infrared and Laser Engineering, 47, 1002001(2018).

[13] Saitoh K, Matsuo S. Multicore fibers for large capacity transmission[J]. Nanophotonics, 2, 441-454(2013). http://www.degruyter.com/view/j/nanoph.2013.2.issue-5-6/nanoph-2013-0037/nanoph-2013-0037.xml?format=INT

[14] Sillard P, Bigot-Astruc M, Molin D. Few-mode fibers for mode-division-multiplexed systems[J]. Journal of Lightwave Technology, 32, 2824-2829(2014). http://smartsearch.nstl.gov.cn/paper_detail.html?id=556079d4a2b47510da8ca793454eebd3

[15] Sasaki Y, Takenaga K, Matsuo S et al. Few-mode multicore fibers for long-haul transmission line[J]. Optical Fiber Technology, 35, 19-27(2017).

[16] Saitoh K, Koshiba M, Takenaga K et al. Crosstalk and core density in uncoupled multicore fibers[J]. IEEE Photonics Technology Letters, 24, 1898-1901(2012).

[17] Saitoh K, Koshiba M, Takenaga K et al. Homogeneous and heterogeneous multi-core fibers[C]∥2012 IEEE Photonics Society Summer Topical Meeting Series, July 9-11, 2012, Seattle, WA, USA., 210-211(2012).

[18] Koshiba M, Saitoh K, Kokubun Y. Heterogeneous multi-core fibers: proposal and design principle[J]. IEICE Electronics Express, 6, 98-103(2009).

[19] Tu J, Saitoh K, Koshiba M et al. Design and analysis of large-effective-area heterogeneous trench-assisted multi-core fiber[J]. Optics Express, 20, 15157-15170(2012).

[20] Hayashi T. Multi-core fibers for space division multiplexing[M]. ∥Handbook of Optical Fibers. Singapore: Springer Singapore, 1-47(2019).

[21] Tu J J, Saitoh K, Koshiba M et al. Optimized design method for bend-insensitive heterogeneous trench-assisted multi-core fiber with ultra-low crosstalk and high core density[J]. Journal of Lightwave Technology, 31, 2590-2598(2013).

[22] Takara H, Sano A, Kobayashi T, 12 SDM/222 WDM/456 Gb/s et al. European Conference on Optical Communication, September 16-20, 2012, Amsterdam, Netherlands. Washington, D.C.: Optical Society of America, 2012: Th.3.C., 1(2012).

[23] Sano A, Takara H, Kobayashi T et al. 409-Tb/s+409-Tb/s crosstalk suppressed bidirectional MCF transmission over 450 km using propagation-direction interleaving[J]. Optics Express, 21, 16777-16783(2013).

[24] Sakaguchi J, Puttnam B J, Klaus W et al. 19-core fiber transmission of 19×100×172-Gb/s SDM-WDM-PDM-QPSK signals at 305 Tb/s. [C]∥ 2012 Optical Fiber Communication Conference, March 4-8, 2012, Los Angeles, California, USA. Washington, D.C.: Optical Society of America, PDP5C, 1(2012).

[25] Puttnam B J, Luís R S, Klaus W et al. 2.15 Pb/s transmission using a 22 core homogeneous single-mode multi-core fiber and wideband optical comb[C]∥2015 European Conference on Optical Communication (ECOC), September 27 - October 1, 2015, V, 1-3(2015).

[26] Amma Y, Sasaki Y, Takenaga K et al. High-density multi-core fiber with heterogeneous core arrangement. [C]∥ 2015 Optical Fiber Communication Conference, March 9-14, 2015, San Francisco, California, USA. Washington, D.C.: Optical Society of America, Th4C, 4(2015).

[27] Mizuno T, Shibahara K, Ono H et al. 32-core dense SDM unidirectional transmission of PDM-16QAM signals over 1600 km using crosstalk-managed single-mode heterogeneous multicore transmission line. [C]∥2016 Optical Fiber Communications Conference and Exhibition (OFC), March 20-24, 2016, Anaheim, CA, USA. Washington, D.C.: Optical Society of America, Th5C, 3(2016).

[28] Xia C, Bai N, Ozdur I et al. Supermodes for optical transmission[J]. Optics Express, 19, 16653-16664(2011).

[29] Ho K P, Kahn J M. Statistics of group delays in multimode fiber with strong mode coupling[J]. Journal of Lightwave Technology, 29, 3119-3128(2011).

[30] Arik S O, Kahn J M, Ho K P. MIMO signal processing for mode-division multiplexing: an overview of channel models and signal processing architectures[J]. IEEE Signal Processing Magazine, 31, 25-34(2014).

[31] Ryf R, Sierra A, Essiambre R J et al. -km 6 × 6 MIMO mode-multiplexed transmission over 3-core microstructured fiber. [C]∥ 2011 European Conference on Optical Communication and Exhibition, September 18-22, 2011, Geneva, Switzerland. Washington, D.C.: Optical Society of America, 2011: Th.13.C., 1(1200).

[32] Ryf R, Essiambre R J, Gnauck A H et al. Space-division multiplexed transmission over 4200-km 3-core microstructured fiber. [C]∥OFC/NFOEC, March 4-8, 2012, Los Angeles, CA, USA. Washington, D.C.: Optical Society of America, PDP5C, 2(2012).

[33] Ryf R, Fontaine N K, Guan B et al. 1705-km transmission over coupled-core fibre supporting 6 spatial modes[C]∥2014 The European Conference on Optical Communication (ECOC), September 21-25, 2014, Cannes, France., 1-3(2014).

[34] Hayashi T, Taru T, Shimakawa O et al. Design and fabrication of ultra-low crosstalk and low-loss multi-core fiber[J]. Optics Express, 19, 16576-16592(2011).

[35] Koshiba M, Saitoh K, Takenaga K et al. Multi-core fiber design and analysis: coupled-mode theory and coupled-power theory[J]. Optics Express, 19, B102-B111(2011).

[36] Takenaga K, Arakawa Y, Tanigawa S et al. An investigation on crosstalk in multi-core fibers by introducing random fluctuation along longitudinal direction[J]. IEICE Transactions on Communications, 94, 409-416(2011).

[37] Koshiba M, Saitoh K, Takenaga K et al. Analytical expression of average power-coupling coefficients for estimating intercore crosstalk in multicore fibers[J]. IEEE Photonics Journal, 4, 1987-1995(2012).

[38] Okamoto K. Fundamentals of optical waveguides[M]. 2nd ed. London: Elsevier Inc(2006).

[39] Ye F H, Tu J J, Saitoh K et al. Design of homogeneous trench-assisted multi-core fibers based on analytical model[J]. Journal of Lightwave Technology, 34, 4406-4416(2016).

[40] Ye F H, Tu J J, Saitoh K et al. Wavelength-dependence of inter-core crosstalk in homogeneous multi-core fibers[J]. IEEE Photonics Technology Letters, 28, 27-30(2016). http://ieeexplore.ieee.org/document/7268865/references

[41] Ye F, Tu J, Saitoh K et al. Simple analytical expression for crosstalk estimation in homogeneous trench-assisted multi-core fibers[J]. Optics Express, 22, 23007-23018(2014).

[42] Tu J J, Long K P, Saitoh K. An efficient core selection method for heterogeneous trench-assisted multi-core fiber[J]. IEEE Photonics Technology Letters, 28, 810-813(2016). http://ieeexplore.ieee.org/xpls/icp.jsp?arnumber=7370880

[43] Xie X Q, Tu J J, Zhou X et al. Design and optimization of 32-core rod/trench assisted square-lattice structured single-mode multi-core fiber[J]. Optics Express, 25, 5119-5132(2017).

[44] Takenaga K, Arakawa Y, Sasaki Y et al. A large effective area multi-core fiber with an optimized cladding thickness[J]. Optics Express, 19, B543-B550(2011).

[45] Matsuo S, Takenaga K, Arakawa Y et al. Large-effective-area ten-core fiber with cladding diameter of about 200 μm[J]. Optics Letters, 36, 4626-4628(2011).

[46] Zhang W D, Huang L G, Wei K Y et al. Cylindrical vector beam generation in fiber with mode selectivity and wavelength tunability over broadband by acoustic flexural wave[J]. Optics Express, 24, 10376-10384(2016).

[47] Han Y, Liu Y G, Wang Z et al. Controllable all-fiber generation/conversion of circularly polarized orbital angular momentum beams using long period fiber gratings[J]. Nanophotonics, 7, 287-293(2018). http://www.degruyter.com/view/j/nanoph.2018.7.issue-1/nanoph-2017-0047/nanoph-2017-0047.xml?rskey=hZKIl5&result=9

[48] Han Y, Liu Y G, Huang W et al. Generation of linearly polarized orbital angular momentum modes in a side-hole ring fiber with tunable topology numbers[J]. Optics Express, 24, 17272-17284(2016).

[49] Bigot-Astruc M, Trinel J B, Maerten H et al. Weakly-coupled 6-LP-mode fiber with low differential mode attenuation. [C]∥Optical Fiber Communication Conference (OFC) 2019, San Diego, California. Washington, D.C.: Optical Society of America, M1E, 3(2019).

[50] Bigot A M, Molin D, Jongh K D et al. Next-generation multimode fibers for space division multiplexing. [C]∥ 2017 Advanced Photonics Congress, July 24-27, 2017, Zurich, Switzerland. Washington, D.C.: Optical Society of America, NeM3B, 4(2017).

[51] Ma L, Jiang S L, Du J B et al. Ring-assisted 7-LP-mode fiber with ultra-low Inter-mode crosstalk. [C]∥Asia Communications and Photonics Conference, November 2-5, 2016, Wuhan, China. Washington, D.C.: Optical Society of America, AS4A, 5(2016).

[52] Ge D W, Li J H, Zhu J L et al. Design of a weakly-coupled ring-core FMF and demonstration of 6-mode 10-km IM/DD transmission. [C]∥2018 Optical Fiber Communications Conference and Exposition (OFC), March 11-15, 2018, San Diego, CA, USA. Washington, D.C.: Optical Society of America, W4K, 3(2018).

[53] Tu J, Saitoh K, Takenaga K et al. Heterogeneous trench-assisted few-mode multi-core fiber with low differential mode delay[J]. Optics Express, 22, 4329-4341(2014).

[54] Sasaki Y, Amma Y, Takenaga K et al. Few-mode multicore fiber with 36 spatial modes (three modes (LP01, LP11a, LP11b)×12 cores)[J]. Journal of Lightwave Technology, 33, 964-970(2015). http://ieeexplore.ieee.org/document/6971082/references

[55] Sillard P, Molin D, Bigot A M et al. Low-differential-mode-group-delay 9-LP-mode fiber[J]. Journal of Lightwave Technology, 34, 425-430(2016).

[56] Tu J, Saitoh K, Amma Y et al. Heterogeneous trench-assisted few-mode multi-core fiber with graded-index profile and square-lattice layout for low differential mode delay[J]. Optics Express, 23, 17783-17792(2015).

[57] Maruyama R, Kuwaki N, Matsuo S et al. Two mode optical fibers with low and flattened differential modal delay suitable for WDM-MIMO combined system[J]. Optics Express, 22, 14311-14321(2014).

[58] Sakamoto T, Mori T, Yamamoto T et al. Differential mode delay managed transmission line for wide-band WDM-MIMO system. [C]∥Optical Fiber Communication Conference, Los Angeles, California. Washington, D.C.: Optical Society of America, OM2D, 1(2012).

[59] Gregg P, Kristensen P. -12-03)[2020-08-24]. https:∥arxiv., org/abs/1412, 1397(2014).

[60] Brunet C, Vaity P, Messaddeq Y et al. Design, fabrication and validation of an OAM fiber supporting 36 states[J]. Optics Express, 22, 26117-26127(2014). http://www.ncbi.nlm.nih.gov/pubmed/25401644

[61] Ung B, Vaity P, Wang L et al. Few-mode fiber with inverse-parabolic graded-index profile for transmission of OAM-carrying modes[J]. Optics Express, 22, 18044-18055(2014). http://www.ncbi.nlm.nih.gov/pubmed/25089424

[62] Tu J, Liu Z, Gao S et al. Ring-core fiber with negative curvature structure supporting orbital angular momentum modes[J]. Optics Express, 27, 20358-20372(2019). http://www.ncbi.nlm.nih.gov/pubmed/31510131

[63] Tandjè A, Yammine J, Dossou M et al. Ring-core photonic crystal fiber for propagation of OAM modes[J]. Optics Letters, 44, 1611-1614(2019). http://www.ncbi.nlm.nih.gov/pubmed/30933103

[64] Tu J J, Gao S C, Wang Z et al. Bend-insensitive grapefruit-type holey ring-core fiber for weakly-coupled OAM mode division multiplexing transmission[J]. Journal of Lightwave Technology, 38, 4497-4503(2020). http://ieeexplore.ieee.org/document/9072547/

[65] Zhang J W, Liu J Y, Shen L et al. Mode-division multiplexed transmission of wavelength-division multiplexing signals over a 100-km single-span orbital angular momentum fiber[J]. Photonics Research, 8, 1236-1242(2020). http://www.opticsjournal.net/Articles/Abstract?aid=OJ84da69e489f50d0b

[66] Zhu L, Wang A, Chen S et al. Orbital angular momentum mode groups multiplexing transmission over 2.6-km conventional multi-mode fiber[J]. Optics Express, 25, 25637-25645(2017).

[67] Chen S, Li S, Fang L et al. OAM mode multiplexing in weakly guiding ring-core fiber with simplified MIMO-DSP[J]. Optics Express, 27, 38049-38060(2019). http://www.ncbi.nlm.nih.gov/pubmed/31878577

[68] Kasahara M, Saitoh K, Sakamoto T et al. Design of three-spatial-mode ring-core fiber[J]. Journal of Lightwave Technology, 32, 1337-1343(2014).

[69] May A R, Zervas M N. Few-mode fibers with improved mode spacing[C]∥2015 European Conference on Optical Communication (ECOC), September 27 - October 1, 2015, Valencia, Spain., 1-3(2015).

[70] Snyder A W, Love J D. Optical waveguide theory[M]. Arrowsmith W J, Transl. 1 ^st ed. London: Chapman and Hall Ltd, 312-313(1983).

[71] Zhang Z, Gan J, Heng X et al. Optical fiber design with orbital angular momentum light purity higher than 99.9[J]. Optics Express, 23, 29331-29341(2015).

[72] Gregg P, Kristensen P, Rubano A et al. Enhanced spin orbit interaction of light in highly confining optical fibers for mode division multiplexing[J]. Nature Communications, 10, 4707(2019). http://www.ncbi.nlm.nih.gov/pubmed/31624247

[73] Watanabe T, Kokubun Y. Ultra-large number of transmission channels in space division multiplexing using few-mode multi-core fiber with optimized air-hole-assisted double-cladding structure[J]. Optics Express, 22, 8309-8319(2014).

[74] Tu J J, Long K P, Saitoh K. Design and optimization of 3-mode×12-core dual-ring structured few-mode multi-core fiber[J]. Optics Communications, 381, 30-36(2016).

[75] Mizuno T, Kobayashi T, Takara H et al. 12-core×3-mode dense space division multiplexed transmission over 40 km employing multi-carrier signals with parallel MIMO equalization. [C]∥ 2014 Optical Fiber Communication Conference, March 9-13, 2014, San Diego, California, USA. Washington, D.C.: Optical Society of America, Th5B, 2(2014).

[76] Sakaguchi J, Klaus W. Mendinueta J M D, et al. Realizing a 36-core, 3-mode fiber with 108 spatial channels. [C]∥2015 Optical Fiber Communications Conference and Exhibition (OFC), March 22-26, 2015, Los Angeles, CA, USA. Washington, D.C.: Optical Society of America, Th5C, 2(2015).

[77] Uden R, Correa R A, Lopez E A et al. European Conference on Optical Communication and Exhibition, September 22-24, 2014, Cannes, France. New York: IEEE, 2014: Mo.3., 3, 4(2014).

[78] Sakamoto T, Matsui T, Saitoh K et al. Low-loss and low-DMD few-mode multi-core fiber with highest core multiplicity factor. [C]∥2016 Optical Fiber Communications Conference and Exhibition (OFC), March 20-24, 2016, Anaheim, CA, USA. Washington, D.C.: Optical Society of America, Th5A, 2(2016).

[79] Soma D, Wakayama Y, Beppu S et al. 10.16-peta-B/s dense SDM/WDM transmission over 6-mode 19-core fiber across the C+L band[J]. Journal of Lightwave Technology, 36, 1362-1368(2018).

[80] Rademacher G, Puttnam B J, Luís R S et al. 10.66 peta-bit/s transmission over a 38-core-three-mode fiber. [C]∥2020 Optical Fiber Communications Conference and Exhibition (OFC), March 8-12, 2020, San Diego, CA, USA. Washington, D.C.: Optical Society of America, Th3H, 1(2020).

[81] Yang C, Li B R, application [EB/OL]. -06-15) [2017-06-15]. https:∥www.yofc.com/view/1548.html.(2017).

[82] Shen L, Chen S, Sun X T et al[J]. Analysis of YOFC few-mode fibers Telecommunications Technology, 2017, 30-32.

[83] Chen W C, Hu G J, Liu F et al. Measurement of mode coupling at a splice point between few-mode fiber[J]. Acta Optica Sinica, 37, 1206005(2017).

[84] Zhang Z Z, Guo C, Zhang Y C et al. Gain-equalized remotely pumped few-mode fiber amplifier[J]. Acta Optica Sinica, 39, 1006004(2019).

[85] Lai J S, Tang R, Wu B B et al. Analysis on the research progress of space division multiplexing in optical fiber communication[J]. Telecommunications Science, 33, 118-135(2017).

[86] Wang Y H, Wu B J, Wan F et al. Analysis of compensation for inter-mode nonlinear phase modulation in few-mode optical fiber communication systems[J]. Acta Optica Sinica, 39, 1206006(2019).

[87] Shi C M, Shen L, Zhang J W et al. Ultra-low inter-mode-group crosstalk ring-core fiber optimized using neural networks and genetic algorithm[C]∥2020 Optical Fiber Communications Conference and Exhibition (OFC), March 8-12, 2020, San D, W1B, 3(2020).