[1] Zhou R, Zhao S Y, Cai Z Q et al 2005 Chin. Phys.
Lett. 13 10115

[2] R Zhou, E B Li, H F Li et al 2006 Opt. Lett. 31
1869

[3] J Gao, X Yu, J B Peng et al 2007 Conference on Laser and
Electro-Optics (Baltimore, USA, 6--11 May 2007) paper CFA1

[4] J Gao, J Speiser and A Giesen 2005 Advanced Solid-State
Photonics (Vienna, Austria, 6--9 February 2005) paper TuB34

[5] J Gao, M Larionov, J Speiser et al 2002 Conference on Laser
and Electro-Optics (Long Beach, USA, 19--24 May 2002) p 175

[6] J W Dawson, R Beach, A Drobshoff et al 2004 Advanced
Solid-State Photonics (Santa Fe, USA, 1--4 February 2004) paper MD8

[7] T J Kane, G Keaton, M A Arbore et al 2004 Advanced
Solid-State Photonics (Santa Fe, USA, 1--4 February 2004) paper MD7

[8] T Y Fan and R L Byer 1987 IEEE J. Quantum Electron.
23 605

[9] P Zeller and P Peuser 2000 Opt. Lett. 25 35