[1] [1] P Russell. Photonic crystal fibers [J]. Science, 2003, 299(5605): 358-362.

[2] [2] Chai Lu, Hu Minglie, Fang Xiaohui, et al.. Advances in femtosecond laser technologies with photonic crystal fiber [J]. Chinese J Lasers, 2013, 40(1): 0101001.

[3] [3] Zhang Yin, Chen Mingyang, Zhang Yongkang. Investigation of a novel large-mode-area photonic crystal fiber transmission system and its transmission characteristics [J]. Chinese J Lasers, 2012, 39(12): 1205001.

[4] [4] M Koshiba, K Saitoh, K Takenaga, et al.. Multi-core fiber design and analysis: coupled-mode theory and coupled-power theory [J]. Opt Express, 2011, 19(26): 102-111.

[5] [5] Sun Bing, Chen Mingyang, Qian Chunlin, et al.. Design of a broadband directional coupler based on an asymmetric three-core photonic crystal fiber [J]. Acta Optica Sinica, 2013, 33(7): 0706010.

[6] [6] P K Choe, A Liu, G G King. A high-brightness laser beam from a phase-locked multicore Yb-doped fiber laser array [J]. IEEE Photon Tech Lett, 2001, 13(5): 439-441.

[7] [7] Chen Ming, Li Jianfeng, Wang Yishan, et al.. Progress of high-order mode-suppression technology in high-power large mode field fiber lasers[J]. Laser & Optoelectronics Progress, 2012, 49(8): 080002.

[8] [8] H Kim, J Kim, U C Paek, et al.. Tunable photonic crystal fiber coupler based on a side-polishing technique [J]. Opt Lett, 2004, 29(11): 1194-1196.

[9] [9] B H Lee, J B Eom, J Kim, et al.. Photonic crystal fiber coupler [J]. Opt Lett, 2002, 27(10): 812-814.

[10] [10] L R Jaroszewicz, A K Stasiewicz, P Mar, et al.. Broadband photonic crystal fiber coupler with polarization selection of coupling ratio [C]. SPIE, 2010, 7653: 76533W.

[11] [11] Zhu Xiaoliang, Yuan Libo, Liu Zhihai, et al.. Coupling approach and mechanism of single-core and twin-core fiber [J]. Chinese J Lasers, 2009, 36(4): 913-917.

[12] [12] Zheng Jingjing, Zheng Kai, Peng Jian, et al.. Analysis of splicing and splicing fusion coupling efficiency between single-core fiber and dual-core fiber [J]. Acta Optica Sinica, 2010, 30(9): 2529-2535.

[13] [13] Y Tottori, T Kobayashi, M Watanabe. Low loss optical connection module for 7-core multi-core fiber and seven single mode fibers [J]. IEEE Photon Tech Lett, 2012, (24): 1926-1928.

[14] [14] J Palais. Fiber Optic Communications [M]. Wang Jiangping, Liu Jie, Wen Chuanhua, Transl.. Beijing: Publishing House of Electronics Industry, 2011.

[15] [15] Zhang Bingyuan, Wang Guoju, He Jingliang, et al.. Passively mode lock of Nd:YVO4 laser with GRIN lens as optical coupler [J]. Acta Optica Sinica, 2011, 31(7): 0714001.

[16] [16] L Yuan, Z Liu, J Yang, et al.. Bitapered fiber coupling characteristics between single-mode single-core fiber and single-mode multicore fiber [J]. Appl Opt, 2008, 47(18): 3307-3312.