OSA's Digital Library

Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 17, Iss. 24 — Nov. 23, 2009
  • pp: 21350–21361

Experimental investigation on the performance of closely spaced multi-carrier PDM-QPSK with digital coherent detection

S. Chandrasekhar and Xiang Liu  »View Author Affiliations

Optics Express, Vol. 17, Issue 24, pp. 21350-21361 (2009)

View Full Text Article

Enhanced HTML    Acrobat PDF (1213 KB)

Browse Journals / Lookup Meetings

Browse by Journal and Year


Lookup Conference Papers

Close Browse Journals / Lookup Meetings

Article Tools



We experimentally investigate the performance of a spectrally efficient multi-carrier channel consisting of two or more optical carriers spaced around the baud rate, with each carrier modulated with polarization division multiplexed (PDM) quadrature phase shift keyed (QPSK) format. We first study the performance of a 100-Gb/s 2-carrier PDM-QPSK channel with each carrier modulated at 12.5 Gbaud as a function of various design parameters such as the time alignment between the modulated carriers, the frequency separation between the carriers, the oversampling factor at the receiver, and the bandwidth of the digital pre-filter used for carrier separation. While the measurements confirm the previously reported observations, they also reveal some interesting additional features. The coherent crosstalk between the modulated carriers is found to be minimized when these carriers are symbol aligned. Spacing the carriers at the baud rate, corresponding to the orthogonal frequency-division multiplexing (OFDM) condition, leads to a local maximum in performance only for some specific cases where large oversampling (>2 × ) is applied. It is found that 4 × oversampling, together with a constant modulus algorithm (CMA) based digital equalizer having multiple quarter-symbol (T/4) spaced taps, gives much better overall performance than 2 × oversampling with a CMA-based equalizer having T/2 spaced taps. In addition, using a T/4-delay-and-add filter (DAF) as a pre-filter for assist carrier separation is found to give better performance than the commonly used T/2-DAF. In addition, it is possible to set the carrier spacing to be as small as 80% of the baud rate while incurring negligible penalty at BER≈10−3. 3-carrier and 5-carrier PDM-QPSK channels at 12.5-Gbaud with frequency-locked carriers spaced at 12.5 GHz and 4 × oversampling are also studied, and shown to perform reasonably well with small relative penalties. Finally, increasing the baud rate of the 2-carrier PDM-QPSK to 25 Gbaud and 28 Gbaud is investigated. It is found that with a fixed sampling speed of 50 Gsamples/s, scaling from 12.5 Gbaud to 25 and 28 Gbaud causes excess crosstalk penalties of about 2.8 dB and 4.8 dB, respectively, indicating the need to increase the sampling speed and transmitter bandwidth in order to support these high-data-rate channels without excessive coherent crosstalk.

© 2009 OSA

OCIS Codes
(060.1660) Fiber optics and optical communications : Coherent communications
(060.2330) Fiber optics and optical communications : Fiber optics communications
(060.5060) Fiber optics and optical communications : Phase modulation

ToC Category:
Fiber Optics and Optical Communications

Original Manuscript: August 5, 2009
Revised Manuscript: September 26, 2009
Manuscript Accepted: October 26, 2009
Published: November 9, 2009

S. Chandrasekhar and Xiang Liu, "Experimental investigation on the performance of closely spaced multi-carrier PDM-QPSK with digital coherent detection," Opt. Express 17, 21350-21361 (2009)

Sort:  Author  |  Year  |  Journal  |  Reset  


  1. M. O’Sullivan, “Expanding network applications with coherent detection”, in Proc. Optical Fiber Commun. Conf. (OFC) 2008, San Diego, CA, February 2008, tutorial paper NWC3 (2008).
  2. K. Roberts, “Digital Compensation of the Optical Line: Pre-distortion Tx & Coherent Rx”, in Proc. IEEE LEOS Summer Topicals, Mexico, July 2008, paper WD2.2 (2008).
  3. E. Yamada, A. Sano, H. Masuda, T. Kobayashi, E. Yoshida, Y. Miyamoto, Y. Hibino, K. Ishihara, K. Takatori, K. Okada, K. Hagimoto, T. Yamada, and H. Yamazaki, “Novel no-guard-interval PDM CO-OFDM transmission in 4.1 Tb/s (50 x 88.8-Gb/s) DWDM link over 800 km SMF including 50-GHz spaced ROADM nodes”, in Proc. Optical Fiber Commun. Conf. (OFC) 2008, San Diego, CA, February 2008, post-deadline paper PDP8 (2008).
  4. K. Yonenaga, A. Sano, E. Yamazaki, F. inuzuka, Y. Miyamoto, A. Takada, and T. Yamada, “100 Gbit/s All-Optical OFDM Transmission Using 4 x 25 Gbit/s Optical Duobinary Signals with Phase-Controlled Optical Sub-Carriers”, in Proc. Optical Fiber Commun. Conf. (OFC) 2008, San Diego, CA, February 2008, Paper JThA48 (2008).
  5. A. Sano, E. Yamada, H. Masuda, E. Yamazaki, T. Kobayashi, E. Yoshida, Y. Miyamoto, S. Matsuoka, R. Kudo, K. Ishihara, Y. Takatori, M, Mizoguchi, K. Okada, K. Hagimoto, H. Yamazaki, S. Kamei, and H. Ishii, “13.4-Tb/s (134 x 111-Gb/s/ch) No-Guard-Interval Coherent OFDM Transmission over 3,600 km of SMF with 19-ps average PMD”, in Proc. European Conf. Optical Commun. 2008., Brussels, Belgium, post-deadline paper Th3E1 (2008).
  6. H. Masuda, E. Yamazaki, A. Sano, T. Yoshimatsu, T. Kobayashi, E. Yoshida, Y. Miyamoto, S. Matsuoka, Y. Takatori, M. Mizoguchi, K. Okada, K. Hagimoto, T. Yamada, S. Kamei, “13.5-Tb/s (135 × 111-Gb/s/ch) no-guard-interval coherent OFDM transmission over 6,248 km using SNR maximized second-order DRA in the extended L-band,” OFC’09, post-deadline paper PDPB5 (2009).
  7. G. Goldfarb, G. Li, and M. G. Taylor, “Orthogonal wavelength-division multiplexing using coherent detection,” IEEE Photon. Technol. Lett. 19(24), 2015–2017 (2007). [CrossRef]
  8. H. Yamazaki, T. Yamada, K. Suzuki, T. Goh, A. Kaneko, A. Sano, E. Yamada, and Y. Miyamoto, “Integrated 100-Gb/s PDM-QPSK modulator using a hybrid assembly technique with silica-based PLCs and LiNbO3 phase modulators”, in Proc. European Conf. Optical Commun. 2008., Brussels, Belgium, paper Mo3C1 (2008).
  9. F. Derr, “Coherent optical QPSK intradyne system concept and digital receiver realization,” J. Lightwave Technol. 10(9), 1290–1296 (1992). [CrossRef]
  10. S. J. Savory, “Digital filters for coherent optical receivers,” Opt. Express 16(2), 804–817 (2008). [CrossRef] [PubMed]
  11. X. Liu, S. Chandrasekhar, and A. Leven, “Self-coherent optical transport systems” (Chap. 4) in Optical Fiber Telecommunications V B, edited by I. P. Kaminow, T. Li, and A. E. Willner (Academic Press, 2008).
  12. A. Ellis and F. C. G. Gunning, “Spectral density enhancement using coherent WDM,” IEEE Photon. Technol. Lett. 17(2), 504–506 (2005). [CrossRef]
  13. Y. Ma, Q. Yang, Y. Tang, S. Chen, and W. Shieh, “1-Tb/s per channel coherent optical OFDM transmission with subwavelength bandwidth access,” OFC’09, post-deadline paper PDP1.
  14. R. Dischler and F. Buchali, “Transmission of 1.2 Tb/s continuous waveband PDM-OFDM-FDM signal with spectral efficiency of 3.3 but/s/Hz over 400 km of SSMF,” OFC’09, post-deadline paper PDP2.
  15. S. Chandrasekhar, X. Liu, B. Zhu, and D. W. Peckham, “Transmission of a 1.2-Tb/s 24-carrier no-guard-interval coherent OFDM superchannel over 7200-km of ultra-large-area fiber,” ECOC’09, post-deadline paper PD2.6.

Cited By

Alert me when this paper is cited

OSA is able to provide readers links to articles that cite this paper by participating in CrossRef's Cited-By Linking service. CrossRef includes content from more than 3000 publishers and societies. In addition to listing OSA journal articles that cite this paper, citing articles from other participating publishers will also be listed.

« Previous Article  |  Next Article »

OSA is a member of CrossRef.

CrossCheck Deposited