[1] [1] F. Castro, A. D. S′anchez, and H. S. Wio, Phys. Rev. Lett. 75, 1691 (1995).

[2] [2] M. O. Magnasco, Phys. Rev. Lett. 71, 1477 (1993).

[3] [3] A. J. R. Madureira, P. Hˇanggi, and H. S. Wio, Phys. Lett. A 217, 248 (1996).

[4] [4] M. I. Dykman, R. Mannella, P. V. E. McClintock, and N. G. Stocks, Phys. Rev. Lett. 65, 2606 (1990).

[5] [5] L. Zhang, L. Cao, and D.Wu, Chin. Phys. 12, 33 (2003).

[6] [6] A. Fuli′nski and T. Telejko, Phys. Lett. A 152, 11 (1991).

[7] [7] S. Zhu, Phys. Rev. A 45, 3210 (1992).

[8] [8] S. Zhu, Phys. Rev. A 47, 2405 (1993).

[9] [9] L. Cao and D. J. Wu, Phys. Lett. A 185, 59 (1994).

[10] [10] J. Wang and S. Zhu, Phys. Lett. A 207, 47 (1995).

[11] [11] Y. Jia, X. Zheng, X. Hu, and J. Li, Phys. Rev. E 63, 031107 (2001).

[12] [12] B. Wang, S. Dai, and S. P. Ge, Chin. Opt. Lett. 4, 397 (2006).

[13] [13] B. Wang and X. Wu, Chin. Opt. Lett. 5, 288 (2007).

[14] [14] R. Bartussek, P. H¨anggi, and P. Jung, Phys. Rev. E 49, 3930 (1994).

[15] [15] D. Mei, C. Xie, and L. Zhang, Phys. Rev. E 68, 051102 (2003).

[16] [16] X. Luo and S. Zhu, Phys. Rev. E 67, 021104 (2003).

[17] [17] Q. Cheng, L. Cao, and D. Wu, Chin. Opt. Lett. 2, 331 (2004).

[18] [18] L. Ning and W. Xu, Chin. Phys. Lett. 23, 3180 (2006).

[19] [19] R. Bonifacio and L. A. Lugiato, Phys. Rev. A 18, 1129 (1978).

[20] [20] C. M. Bowden, M. Ciftan, and H. R. Robl, Optical Bistability (Plenum Press, New York, 1981).

[21] [21] A. Hern′andez-Machado, M. S. Miguel, and J. M. Sancho, Phys. Rev. A 29, 3388 (1984).