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Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 15, Iss. 11 — May. 28, 2007
  • pp: 6790–6797

Quantum limit of optimum four-level ASK signals with direct detection optically preamplified receivers

Wei-Ren Peng and Sien Chi  »View Author Affiliations

Optics Express, Vol. 15, Issue 11, pp. 6790-6797 (2007)

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We analytically obtain the exact fundamental limit of 4-level amplitude shifted keying formats (4ASK) with direct detection optically preamplified receivers. The optimum multilevel spacing and the corresponding decision thresholds, which depend both on the signal to noise ratio and optical bandwidth, are obtained numerically considering the Chi-squared distribution of each level. The quantum limit under the optimum level spacing is 127.5 photons/bit, which is about 0.2 dB smaller than the results by the Gaussian approximation. Over a broad range of the signal to noise ratio and the optical bandwidth, we have found that not only the bit error rate but also the optimum level spacing are well predicted by Gaussian method, although the three decision thresholds are all underestimated.

© 2007 Optical Society of America

OCIS Codes
(060.2330) Fiber optics and optical communications : Fiber optics communications
(060.4510) Fiber optics and optical communications : Optical communications

ToC Category:
Fiber Optics and Optical Communications

Original Manuscript: January 29, 2007
Revised Manuscript: March 16, 2007
Manuscript Accepted: March 21, 2007
Published: May 18, 2007

Wei-Ren Peng and Sien Chi, "Quantum limit of optimum four-level ASK signals with direct detection optically preamplified receivers," Opt. Express 15, 6790-6797 (2007)

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