[1] Pierce J R[J]. J. Appl. Phys., 25, 179(1954).

[2] Gould R W[J]. IRE Trans. Electron Devices, PGED-2, 37(1955).

[3] Louisell W H[J]. Coupled-Mode and Parametric Electronics, 148-225(1960).

[4] Miller S E[J]. Bell Syst. Tech. J., 33, 661(1954).

[5] Miller S E[J]. Bell Syst. Tech. J., 47, 1801(1968).

[6] Miller S E[J]. Bell Syst. Tech. J., 48, 2189(1969).

[7] Tang C C H[J]. Advances in Microwaves, 4, 301(1969).

[8] Schelkunoff S A[J]. Bell Syst. Tech. J., 34, 995(1955).

[9] Haus H A[J]. Electron Beam Waves in Microwave Tubes, 115-130(1958).

[10] Marcuse D[J]. Bell Syst. Tech. J., 50, 1791(1971).

[11] Marcuse D[J]. Bell Syst. Tech. J., 52, 817(1973).

[12] Snyder A W[J]. J. Opt. Soc. Am., 62, 1267(1972).

[13] Snyder A W[J]. IEEE Trans. Microwave Theory Tech., 18, 383(1970).

[14] Yariv A[J]. IEEE J. Quantum Electron., 9, 919(1973).

[15] Taylor H F, Yariv A[J]. Proc. IEEE, 62, 1044(1974).

[16] Kogelnik H[J]. Bell Syst. Tech. J., 48, 2909(1969).

[17] McIntyre P D, Snyder A W[J]. J. Opt. Soc. Am., 63, 1518(1973).

[18] Yeh C, Manshadi F, Casey K F, Johnston A[J]. J. Opt. Soc. Am., 68, 1079(1978).

[19] Dionnet M J F, Shaw H J[J]. IEEE Trans. Microwave Theory Tech., 30, 592(1982).

[20] Thyagarajan K, Tewari R[J]. J. Lightwave Technol., 3, 59(1985).

[21] Zhang M, Garmire E[J]. J. Lightwave Technol., 5, 260(1987).

[22] Elechi C, Yeh C[J]. Opt. Commun., 7, 201(1973).

[23] Stoll H, Yariv A[J]. Opt. Commun., 8, 5(1973).

[24] Yeh P, Taylor H F[J]. Appl. Opt., 19, 2848(1980).

[25] Syms R R A[J]. Appl. Opt., 24, 717(1985).

[26] Marcuse D[J]. J. Lightwave Technol., 5, 268(1987).

[27] Hardy A, Streifer W[J]. J. Lightwave Technol., 3, 1135(1985).

[28] Haus H A, Huang W P, Kawakami S, Whitaker N A[J]. J. Lightwave Technol., 5, 16(1987).

[29] Chuang S L[J]. J. Lightwave Technol., 5, 5(1987).

[30] El-Ganainy R, Makris K G, Christodoulides D N, Musslimani Z H[J]. Opt. Lett., 32, 2632(2007).

[31] Golshani M, Weimann S, Jafari Kh, Khazaei Nezhad M, Langari A, Bahrampour A R, Eichelkraut T, Mahdavi S M, Szameit A[J]. Phys. Rev. Lett., 113, 123903(2014).

[32] Klaiman S, Gunther U, Moiseyev N[J]. Phys. Rev. Lett., 101, 080402(2008).

[33] Feng L, Xu Y L, Fegadolli W S, Lu M H, Oliveira J E B, Almeida V R, Chen Y F, Scherer A[J]. Nat. Mater., 12, 108(2013).

[34] Zhu X, Ramezani H, Shi C, Zhu J, Zhang X[J]. Phys. Rev. X, 4, 031042(2014).

[35] Lin Z, Ramezani H, Eichelkraut T, Kottos T, Cao H, Christodoulides D N[J]. Phys. Rev. Lett., 106, 213901(2011).

[36] Shi Y, Yu Z F, Fan S H[J]. Nat. Photonics, 9, 388(2015).

[37] Wang X Z[J]. Opt. Lett., 43, 5623(2018).

[38] Ruter C E, Makris K G, El-Ganainy R, Christodoulides D N, Segev M, Kip D[J]. Nat. Phys., 6, 192(2010).

[39] Hodaei H, Miri M A, Heinrich M, Christodoulides D N, Khajavikhan M[J]. Science, 346, 975(2014).

[40] Alaeian H, Dionne J A[J]. Phys. Rev. B, 89, 075136(2014).

[41] Alaeian H, Dionne J A[J]. Phys. Rev. A, 89, 033829(2014).

[42] Shen Y, Deng X H, Chen L[J]. Opt. Express, 22, 19440(2014).

[43] Liu Z Z, Zhang Q, Liu X L, Yao Y, Xiao J J[J]. Sci. Rep., 6, 22711(2016).

[44] Ke S L, Zhao D, Liu J X, Liu Q J, Liao Q, Wang B, Lu P X[J]. Opt. Express, 27, 13858(2019).

[45] Peng B, Őzdemir S K, Lei F, Monifi F, Gianfreda M, Long G L, Fan S, Nori F, M.Bender C, Yang L[J]. Nat. Phys., 10, 394(2014).

[46] Xu J, Chen Y[J]. Opt. Express, 23, 22619(2015).

[47] Wu B, Xu J, Xiao J, Chen Y[J]. Opt. Express, 24, 16566(2016).

[48] Liu Z Z, Zhang Q, Chen Y, Xiao J J[J]. Photonics Res., 5, 57(2017).

[49] Wu B, Wang J, Xiao M, Xu J, Chen Y[J]. Opt. Express, 25, 1040(2017).

[50] Xiong Z F, Chen W J, Wang P, Chen Y T[J]. Opt. Express, 25, 29822(2017).

[51] Chen W, Xiong Z, Xu J, Chen Y[J]. Phys. Rev. B, 99, 195307(2019).

[52] Zhang X Q, Chen R S, Zhou Y, Ming H, Wang A T[J]. Chin. Phys. Lett., 33, 084201(2016).

[53] Li L, Liu G Q, Chen Y H[J]. Acta Opt. Sin., 33, 0123002(2013).

[54] Wu L H, Wang M H[J]. Acta Opt. Sin., 35, 0923003(2015).

[55] Cai Y J, Li M, Xiong X, Yu L, Ren X F, Guo G P, Guo G C[J]. Chin. Phys. Lett., 32, 107305(2015).

[56] Zhang Z D, Zhao Y N, Lu D, Xiong Z H, Zhang Z Y[J]. Acta Phys. Sin., 61, 187301(2012).

[57] Wang L W, Lou S Q, Chen W G, Lu W L, Wang X[J]. Acta Phys. Sin., 61, 154207(2012).

[58] Xu J, Wu B, Chen Y T[J]. Opt. Express, 23, 11566(2015).

[59] Sakurai J J, Tuan S F[J]. Modern Quantum Mechanics Rev.Ed., 71-73(1994).

[60] Rumsey V H[J]. Phys. Rev., 94, 1483(1954).

[61] Moiseyev N[J]. Non-Hermitian Quantum Mechanics, 174-210(2011).

[62] Collin R E[J]. Field Theory of Guided Waves, 231(1960).

[63] McIsaac P R[J]. IEEE Trans. Microwave Theory Tech., 39, 1808(1991).

[64] Villeneuve A T[J]. IEEE Trans. Microwave Theory Tech., 7, 441(1959).

[65] Silvestre E, Abián M A, Gimeno B, Ferrando A, Andrés M V, Boria V E[J]. IEEE Trans. Microwave Theory Tech., 48, 589(2000).

[66] Snyder A W, Love J D[J]. Optical Waveguide Theory, 214-216(1983).

[67] Zhu Y, Cangellaris A C[J]. Multigrid Finite Element Methods for Electromagnetic Field Modeling, 244-249(2006).

[68] Qian J R[J]. Acta Opt. Sin., 29, 1188(2009).

[69] Liu H, Lalanne P[J]. Nature, 452, 728(2008).

[70] Chen Y T, Zhang R Y, Xiong Z F, Hang Z H, Li J S, Shen J Q, Chan C T[J]. Nat. Commun., 10, 3125(2019).

[71] Shi H K, Xiong Z F, Chen W J, Xu J, Wang S B, Chen Y T[J]. Opt. Express, 27, 28114(2019).

[72] Bender C M, Boettcher S, Meisinger P N[J]. J. Math. Phys., 40, 2201(1999).

[73] Bernevig B A, Hughes T L[J]. Topological Insulators and Topological Superconductors, 30-40(2013).