Chromatic dispersion estimation methods using polynomial fitting in PDM-QPSK or other multilevel-format coherent optical systems

Optical Fiber Technology, Volume 19, Issue 2, March 2013, Pages 162-168.
Junyi Wang, Xin Jiang, Xuan He, Yi Weng, Zhongqi Pan

 

Department of Electrical and Computer Engineering, University of Louisiana at Lafayette, Lafayette, LA 70504, United States

Department of Engineering Science and Physics, College of Staten Island, New York, NY 10314, United States

 

 

Abstract

We propose a polynomial fitting algorithm based method for non-data-aided chromatic dispersion (CD) estimation in single carrier (SC) coherent optical systems with arbitrary modulation formats, and compare it with our previously proposed CD estimation method which is also based on the polynomial fitting algorithm but requires special modulation formats thus is a data-aided CD estimation method for systems with PDM-QPSK or other multilevel modulation formats. For the data-aided CD estimation method, an extra chirp-free OOK signal is transmitted. The curve of the average phase at the frequency ± f as a function of the frequency f is measured at the coherent receiver. The accumulated CD is then estimated with a polynomial fitting algorithm. In the simulation of a 50 Gbaud 50%-RZ OOK system through 12.5 × 80 km standard single mode fiber (SSMF), the estimation errors are within ± 50 ps/nm in 20 tests when the launch power is from −5 dBm to −1 dBm. Non-data-aided CD estimation for arbitrary modulation formats is achieved by measuring the differential phase between frequency f ± fs/2 (fs is the symbol rate) in digital coherent receivers. The estimation errors are within ± 200 ps/nm, in a 50 Gbaud PDM-QPSK system through 10 × 80 km SSMF with the launch power from −3 dBm to −1 dBm. The estimation accuracy can be potentially improved by averaging multiple results. The data-aided CD estimation method has an inherently bigger estimation range than that of the newly proposed non-data-aided method, while the newly proposed non-data-aided method can tolerate a much larger frequency offset between the transmitter and the local oscillator. These methods are promising for future optical fiber networks with dynamic optical routing and coherent detection.

 

 

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