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Submitted on: 02 September 2008.
Revised on: 25 September 2008.
Accepted on: 20 October 2008.
___________________IEEE PHOTONICS TECHNOLOGY LETTERS
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Submitted on: 04 March 2011.
Revised on: 23 June 2011.
Accepted on: 21 July 2011.
___________________IEEE PHOTONICS TECHNOLOGY LETTERS