[8] Liu A, Song J, Kametani K, and Ueda K. Rectangular double-clad fibre laser with two-end-bundled pump[J]. Electron. Lett., 1996, 32(18):1673~1674.
[9] Kishi N and Yamashita E. Model and coupling filed analysis of optical fibers circularly with distributed multiple cores and a central core[J]. J.Lightwave Technol., 1986, 4(8):991~996.