Abstract

This paper describes a coherent optical receiver for demodulating optical quadrature phase-shift keying (QPSK) signals. At the receiver, a phase-diversity homodyne detection scheme is employed without locking the phase of the local oscillator (LO). To handle the carrier phase drift, the carrier phase is estimated with digital signal processing (DSP) on the homodyne-detected signal. Such a scheme presents the following major advantages over the conventional optical differential detection. First, its bit error rate (BER) performance is better than that of differential detection. This higher sensitivity can extend the reach of unrepeated transmission systems and reduce crosstalk between multiwavelength channels. Second, the optoelectronic conversion process is linear, so that the whole optical signal information can be postprocessed in the electrical domain. Third, this scheme is applicable to multilevel modulation formats such as M-array PSK and quadrature amplitude modulation (QAM). The performance of the receiver is evaluated through various simulations and experiments. As a result, an unrepeated transmission over 210 km with a 20-Gb/s optical QPSK signal is achieved. Moreover, in wavelength-division multiplexing (WDM) environment, coherent detection allows the filtering of a desired wavelength channel to reside entirely in the electrical domain, taking advantage of the sharp cutoff characteristics of electrical filters. The experiments show the feasibility to transmit polarization-multiplexed 40-Gb/s QPSK signals over 200 km with channel spacing of 16 GHz, leading to a spectral efficiency as high as 2.5 b/s/Hz.

© 2006 IEEE

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  1. J. Kahn and K.-P. Ho, "Spectral efficiency limits and modulation/detection techniques for DWDM systems", IEEE J. Sel. Topics Quantum Electron., vol. 10, no. 2, pp. 259-272, Mar./Apr. 2004.
  2. C. Xu, X. Liu and X. Wei, "Differential phase-shift keying for high spectral efficiency optical transmissions", IEEE J. Sel. Topics Quantum Electron., vol. 10, no. 2, pp. 281-293, Mar./Apr. 2004.
  3. R. Griffin and A. Carter, "Optical differential quadrature phase-shift key (oDQPSK) for high capacity optical transmission", in Proc. Optical Fiber Communication Conf. (OFC), Anaheim, CA, Mar. 2002,Paper WX6,. pp. 17-22.
  4. J. Proakis, Digital Communications, 4th ed. New York: McGraw-Hill, 2000.
  5. T. Okoshi and K. Kikuchi, Coherent Optical Fiber Communications, Boston, MA: Kluwer, 1988.
  6. R. Noe, "Phase noise tolerant synchronous QPSK receiver concept with digital I&Q baseband processing", in Proc. Opto-Electronics and Communications Conf. (OECC), Yokohama, Japan,Jul. <day>12-16</day> 2004, pp. 818-819.
  7. D. S. Ly-Gagnon, K. Katoh and K. Kikuchi, "Unrepeatered optical transmission of 20 Gb/s quadrature phase-shift keying signals over 210 km using homodyne phase-diversity receiver and digital signal processing", Electron. Lett., vol. 41, no. 4, pp. 59-60, Feb. 2005.
  8. K. Kikuchi, T. Okoshi, M. Nagamatsu and N. Henmi, "Degradation of bit-error rate in coherent optical communications due to spectral spread of the transmitter and the local oscillator", J. Lightw. Technol., vol. LT-2, no. 6, pp. 1024-1033, 1984.

Other (8)

J. Kahn and K.-P. Ho, "Spectral efficiency limits and modulation/detection techniques for DWDM systems", IEEE J. Sel. Topics Quantum Electron., vol. 10, no. 2, pp. 259-272, Mar./Apr. 2004.

C. Xu, X. Liu and X. Wei, "Differential phase-shift keying for high spectral efficiency optical transmissions", IEEE J. Sel. Topics Quantum Electron., vol. 10, no. 2, pp. 281-293, Mar./Apr. 2004.

R. Griffin and A. Carter, "Optical differential quadrature phase-shift key (oDQPSK) for high capacity optical transmission", in Proc. Optical Fiber Communication Conf. (OFC), Anaheim, CA, Mar. 2002,Paper WX6,. pp. 17-22.

J. Proakis, Digital Communications, 4th ed. New York: McGraw-Hill, 2000.

T. Okoshi and K. Kikuchi, Coherent Optical Fiber Communications, Boston, MA: Kluwer, 1988.

R. Noe, "Phase noise tolerant synchronous QPSK receiver concept with digital I&Q baseband processing", in Proc. Opto-Electronics and Communications Conf. (OECC), Yokohama, Japan,Jul. <day>12-16</day> 2004, pp. 818-819.

D. S. Ly-Gagnon, K. Katoh and K. Kikuchi, "Unrepeatered optical transmission of 20 Gb/s quadrature phase-shift keying signals over 210 km using homodyne phase-diversity receiver and digital signal processing", Electron. Lett., vol. 41, no. 4, pp. 59-60, Feb. 2005.

K. Kikuchi, T. Okoshi, M. Nagamatsu and N. Henmi, "Degradation of bit-error rate in coherent optical communications due to spectral spread of the transmitter and the local oscillator", J. Lightw. Technol., vol. LT-2, no. 6, pp. 1024-1033, 1984.

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