[1] J. G. Endriz, M. Vakili, G. S. Bowder, M. DeVito, J. M. Haden, G. L. Harnagel, W. E. Plano, M. Sakamato, D. F. Welch, S. Willing, D. P. Vorland, and H. C. Yao, IEEE J. Quantum Electron. 28, 952 (1992).
[2] F. Dorsch, V. Blumel, M. Schroder, D. Lorenzen, P. Hennig, and D. Wolff, Proc. SPIE 3945, 42 (2000).
[3] W. A. Clarkson and D. C. Hanna, Opt. Lett. 21, 375 (1996).
[4] F. Dorsch, P. Hennig, and M. Nickel, Proc. SPIE 3285, 192 (1998).
[5] S. Yamaguchi, T. Kobayashi, Y. Saito, and K. Chiba, Appl. Opt. 36, 1875 (1997).
[6] X. Wang, G. Fang, X. Ma, X. Feng, H. Sun, Y. Liu, B. Liu, and J. Xiao, Chin. J. Semicondctors (in Chinese) 25, 579 (2004).
[7] X. W. Wang, G. Fang, W. Ying, H. Sun, X. Feng, Y. Liu, X. Ma, and J. Xiao, Chin. High Technology Lett. (in Chinese) 155, 35 (2003).
[8] X. Wang, X. Ma, J. Xiao, G. Fang, X. Feng, Y. Liu, and B. Liu, Chin. Opt. Lett. 1, 96 (2003).