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Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 19, Iss. 24 — Nov. 21, 2011
  • pp: 24540–24545
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1.92Tb/s coherent DWDM-OFDMA-PON with no high-speed ONU-side electronics over 100km SSMF and 1:64 passive split

Neda Cvijetic, Ming-Fang Huang, Ezra Ip, Yin Shao, Yue-Kai Huang, Milorad Cvijetic, and Ting Wang  »View Author Affiliations


Optics Express, Vol. 19, Issue 24, pp. 24540-24545 (2011)
http://dx.doi.org/10.1364/OE.19.024540


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Abstract

Record 1.92-Tb/s (40λ × 48Gb/s/λ) coherent DWDM-OFDMA-PON without high-speed ONU-side ADCs/DACs/DSP/RF clock sources is demonstrated over 100km straight SSMF with a 1:64 passive split. Novel optical-domain OFDMA sub-band selection, coherent detection, and simple RF components are exploited. As the first experimental verification of a next-generation optical platform capable of delivering 1Gb/s to 1000+ users over 100km, the new architecture is promising for future optical access/metro systems.

© 2011 OSA

1. Introduction

Next-generation passive optical networks (PON) will feature 40+Gb/s data rates, longer reach (up to 100km), passive optical splits, and higher per-fiber optical network unit (ONU) counts [1

1. N. Cvijetic, M. F. Huang, E. Ip, Y. K. Huang, D. Qian, and T. Wang, “1.2 Tb/s symmetric WDM-OFDMA-PON over 90km straight SSMF and 1:32 passive split with digitally-selective ONUs and coherent receiver OLT,” in Optical Fiber Communication Conference, OSA Technical Digest (Optical Society of America, 2011), paper PDPD7.

4

4. D. Breuer, E. Weis, R. Hülsermann, and M. Kind, “Next generation optical access networks: the OASE view,” http://www.ict-oase.eu/public/files/2_BREUER_OASE_Overview_FTTHConfMilan2011.pdf.

]. By enabling linear dispersion resistance, record data rates, and flexible bandwidth allocation, digital signal processing (DSP)-based Orthogonal Frequency Division Multiple Access (OFDMA)-PON is a promising candidate technology in this space [1

1. N. Cvijetic, M. F. Huang, E. Ip, Y. K. Huang, D. Qian, and T. Wang, “1.2 Tb/s symmetric WDM-OFDMA-PON over 90km straight SSMF and 1:32 passive split with digitally-selective ONUs and coherent receiver OLT,” in Optical Fiber Communication Conference, OSA Technical Digest (Optical Society of America, 2011), paper PDPD7.

,5

5. N. Cvijetic, D. Qian, and J. Hu, “100 Gb/s optical access based on optical orthogonal frequency-division multiplexing,” IEEE Commun. Mag. 48(7), 70–77 (2010). [CrossRef]

7

7. E. Hugues-Salas, R. P. Giddings, X. Q. Jin, J. L. Wei, X. Zheng, Y. Hong, C. Shu, and J. M. Tang, “Real-time experimental demonstration of low-cost VCSEL intensity-modulated 11.25 Gb/s optical OFDM signal transmission over 25 km PON systems,” Opt. Express 19(4), 2979–2988 (2011). [CrossRef] [PubMed]

]. Moreover, coherent detection, which can provide important performance gains via increased receiver sensitivity [8

8. M. Cvijetic, Coherent and Nonlinear Lightwave Communications (Artech House, 1996).

], has also been proposed for future PON systems [1

1. N. Cvijetic, M. F. Huang, E. Ip, Y. K. Huang, D. Qian, and T. Wang, “1.2 Tb/s symmetric WDM-OFDMA-PON over 90km straight SSMF and 1:32 passive split with digitally-selective ONUs and coherent receiver OLT,” in Optical Fiber Communication Conference, OSA Technical Digest (Optical Society of America, 2011), paper PDPD7.

,9

9. S. Y. Kim, N. Sakurai, H. Kimura, and K. Kumozaki, “10-Gbit/s next-generation coherent QPSK-PON with reduced bandwidth requirements employing linear digital equalization with adaptive algorithm,” Optical Fiber Communication Conference, OSA Technical Digest (Optical Society of America, 2009), paper OMN6.

11

11. S. Smolorz, H. Rohde, E. Gottwald, D. W. Smith, and A. Poustie, “Demonstration of a coherent UDWDM-PON with real-time processing,” in Optical Fiber Communication Conference, OSA Technical Digest (Optical Society of America, 2011), paper PDPD4.

]. Due to cost considerations, only upstream 40+Gb/s PON transmission with optical line terminal (OLT)-side coherent detection has previously been demonstrated [1

1. N. Cvijetic, M. F. Huang, E. Ip, Y. K. Huang, D. Qian, and T. Wang, “1.2 Tb/s symmetric WDM-OFDMA-PON over 90km straight SSMF and 1:32 passive split with digitally-selective ONUs and coherent receiver OLT,” in Optical Fiber Communication Conference, OSA Technical Digest (Optical Society of America, 2011), paper PDPD7.

,10

10. D. Qian, N. Cvijetic, Y. K. Huang, J. Hu, T. Wang, J. Hu, and T. Wang, “Single-wavelength 108 Gb/s upstream OFDMA-PON,” in 35th European Conference and Exposition on Optical Communications, OSA Technical Digest (Optical Society of America, 2009), paper PD 3.3.

]. However, if R&D advances enable low-cost optical network unit (ONU)-side components, coherent PON can become attractive, particularly for high-performance mobile backhaul or enterprise applications.

To achieve network consolidation and high aggregate speeds, a 1.2Tb/s (25λ × 48Gb/s/λ) hybrid Wavelength Division Multiplexed (WDM)-OFDMA-PON with 90km straight standard single mode fiber (SSMF) reach and 1:32 split featuring multi-band OFDMA and downstream direct detection has been demonstrated [1

1. N. Cvijetic, M. F. Huang, E. Ip, Y. K. Huang, D. Qian, and T. Wang, “1.2 Tb/s symmetric WDM-OFDMA-PON over 90km straight SSMF and 1:32 passive split with digitally-selective ONUs and coherent receiver OLT,” in Optical Fiber Communication Conference, OSA Technical Digest (Optical Society of America, 2011), paper PDPD7.

]. However, high optical signal to noise ratio (OSNR) requirements limited downstream performance, and high-speed (40+GS/s) ONU-side analog-to-digital and digital-to-analog converters (ADCs/DACs) and expensive 10+GHz radio frequency (RF) clock sources were respectively required for digital selection and RF up-conversion of individual OFDMA sub-bands. In this paper, coherent ONU-side detection, combined with low-speed ADCs/DACs/DSP and off-the-shelf RF components, is proposed to address both the OSNR and high-speed electronics challenges. In the proposed architecture, downstream OFDMA sub-band selection is achieved optically, by tuning the ONU-side local oscillator (LO) laser to the OFDMA sub-band(s) of interest. Following coherent detection, target sub-bands can be digitized directly in the baseband by low-speed (<5GHz) ADCs and DSP. In the upstream, off-the-shelf RF clock sources for mobile devices and/or software defined radio [12

12. Universal Software Radio Peripheral (USRP) N200 Series, http://www.ettus.com/.

] followed by simple RF multipliers can be used in lieu of exotic, high-speed clocks to up-convert OFDMA signals from low-speed DACs. Since mass-produced RF clocks exist for several center frequencies [12

12. Universal Software Radio Peripheral (USRP) N200 Series, http://www.ettus.com/.

], flexible designs can be realized.

To the best of our knowledge, we experimentally demonstrate the first coherent dense WDM (DWDM)-OFDMA-PON with no high-speed ONU-side electronics at a record 1.92Tb/s (40λ × 48Gb/s/λ) aggregate rate over 100km straight SSMF and a 1:64 passive split. Novel optical-domain OFDMA sub-band selection, coherent detection, a flexible downstream/upstream wavelength plan with 50GHz channel spacing, and simple RF components are exploited. This is also the first experimental verification of a next-generation optical platform capable of delivering 1Gb/s to 1000+ users over 100km [4

4. D. Breuer, E. Weis, R. Hülsermann, and M. Kind, “Next generation optical access networks: the OASE view,” http://www.ict-oase.eu/public/files/2_BREUER_OASE_Overview_FTTHConfMilan2011.pdf.

], and is thus promising for future optical access/metro systems.

2. Proposed coherent DWDM-OFDMA-PON architecture with no high-speed ONU-side electronics

Figure 1
Fig. 1 Proposed coherent DWDM-OFDMA-PON architecture with no high-speed ONU-side electronics. Tx = transmitter; Rx = receiver.
illustrates the proposed coherent DWDM-OFDMA-PON architecture with 50GHz downstream/upstream (DS/US) wavelength spacing and no high-speed ONU-side electronics, enabled by the novel coherent ONU approach. Specifically, at each ONU DS receiver, the frequency of LO1 (Fig. 1) is tuned such that LO1 is centered at the OFDMA sub-band(s) of interest, facilitating direct sub-band downconversion via coherent photodetection. For example, to select and process the high-frequency OFDMA sub-bands 3 and 4 of Fig. 1(a), LO1 of ONU1 can be tuned between them, such that, following coherent detection, they are digitized in the baseband by low-speed ADCs as shown in Fig. 1(b); similarly, LO1 of ONUN can be tuned to target sub-band(s) 1 and/or 2, as in Fig. 1(d). Both the ADCs and post-detection DSP can now operate in the 0-5GHz range, while still enabling both high peak rates (e.g.10Gb/s per OFDMA sub-band) and OFDMA-based statistical bandwidth sharing.

For US transmission, a controller first is used to set the frequency of a tunable, off-the-shelf RF clock source, fc,n, n = 1,2, …, N. In this way, fc,n does not have to be pre-determined as in [4

4. D. Breuer, E. Weis, R. Hülsermann, and M. Kind, “Next generation optical access networks: the OASE view,” http://www.ict-oase.eu/public/files/2_BREUER_OASE_Overview_FTTHConfMilan2011.pdf.

], enabling RF-colorlessness. Currently, 700MHz—6GHz off-the-shelf clock sources are commercially available from the mobile and software-defined radio markets, featuring an approximate 1GHz center frequency tunability [12

12. Universal Software Radio Peripheral (USRP) N200 Series, http://www.ettus.com/.

]. Simple frequency multipliers can then be used to cost-efficiently produce the desired high-speed clock signal, fRF,n = M × fc,n, where M is the frequency multiplication factor. As a result, upstream OFDMA sub-band(s) can first be produced by a baseband DSP Tx and low-speed DACs, enabling fully low-speed ONU-side electronics, and then RF upconverted to fRF,n, as illustrated in Fig. 1(c) and Fig. 1(e). To create the US wavelength map, a controller is used to tune LO2 frequency by 50GHz with respect to the DS wavelength, λi,DS.

For fine tuning, the controller can exploit the frequency differential information between λi,DS and LO1, such that if λi,DS drifts, λ i,US,i = 1, 2, …, 40, generated by LO2, can be adjusted to maintain 50GHz DS/US spacing and avoid DS/US OFDMA sub-band overlap. Following ONU-side intensity modulation, the US optical OFDMA signal is circulated upstream; the dotted sub-bands in the DS/US wavelength plan of Fig. 1 indicate that the signal on λi,US is optical double sideband at this point; the OLT-side interleaver (IL) is subsequently used to produce an optical single sideband (OSSB) signal prior to OLT-side coherent detection. Similarly, the OLT-side IL in Fig. 1 is also used for downstream OSSB signal generation.

3. Experimental setup and results

The experimental setup is shown in Fig. 2
Fig. 2 Experimental coherent DWDM-OFDMA-PON setup with signal spectra: (b,d,i,j) at 0.01nm resolution, (c,h) at 0.1nm resolution.
. At the DS transmitter, the outputs of two 12GS/s arbitrary waveform generators were up-converted with in-phase/quadrature (IQ) mixers to 9.25GHz and 16.75GHz, respectively, and combined to form the multi-band OFDMA signal shown in Fig. 2(a). To generate the OFDMA sub-bands, Fast Fourier Transform (FFT) size of 256 was used with 64 data-bearing subcarriers, 16-QAM symbol mapping, 13% cyclic prefix and training sequence overhead, and 7% FEC overhead. The net data rate of the 4 × 12Gb/s = 48Gb/s/λ multi-band OFDMA signal was thus 40Gbs/λ. For DS transmission, 40 carriers with 100GHz channel spacing, λ1, DS to λ40,DS, were generated by DFB lasers (1532.29-1563.45nm), combined by an arrayed waveguide grating (AWG), and input to a 40GHz intensity modulator (IM) biased at null. Due to equipment availability, the presence of 39 neighboring DWDM channels was thus emulated using DFB lasers, while the DFB laser on the target channel was swapped with a tunable external cavity laser (ECL) with 100kHz linewidth to perform BER measurements. This swapping was subsequently repeated for all 40 channels, to satisfy the narrow laser linewidth requirements for coherent detection. A 25 GHz optical interleaver (IL) was used to produce the downstream OSSB WDM-OFDMA signal of Fig. 2(b), launched at −6dBm/λ launch power over 80km straight SSMF.

Figure 3(a)
Fig. 3 (a) DS sub-band BER comparison for λ21,DS. (b) DS/US BER for coherent DWDM-OFDMA-PON.
plots the DS BER results for the distinct OFDMA sub-band groups of channel 21 (λ21,DS), showing virtually identical performance between the higher and lower frequency sub-bands. Unlike in [1

1. N. Cvijetic, M. F. Huang, E. Ip, Y. K. Huang, D. Qian, and T. Wang, “1.2 Tb/s symmetric WDM-OFDMA-PON over 90km straight SSMF and 1:32 passive split with digitally-selective ONUs and coherent receiver OLT,” in Optical Fiber Communication Conference, OSA Technical Digest (Optical Society of America, 2011), paper PDPD7.

], where the higher sub-bands suffered a penalty due to response degradations in high-speed electronics, novel optical-domain sub-band selection enabled favorable low-frequency ADC operation in this case. Moreover, as shown in Fig. 3(b), all 40 DS channels satisfied the FEC limit (BER = 1.1 × 10−3) after 100km and 1:64 split. It is noted that in addition to reach, split, and WDM capacity gains, the coherent approach also benefits from a lower 7% FEC limit BER compared to WDM-OFDMA with direct detection (FEC limit = 3.8 × 10−3) [1

1. N. Cvijetic, M. F. Huang, E. Ip, Y. K. Huang, D. Qian, and T. Wang, “1.2 Tb/s symmetric WDM-OFDMA-PON over 90km straight SSMF and 1:32 passive split with digitally-selective ONUs and coherent receiver OLT,” in Optical Fiber Communication Conference, OSA Technical Digest (Optical Society of America, 2011), paper PDPD7.

], enabling a much simpler FEC implementation. To enable this comparison, the system in [1

1. N. Cvijetic, M. F. Huang, E. Ip, Y. K. Huang, D. Qian, and T. Wang, “1.2 Tb/s symmetric WDM-OFDMA-PON over 90km straight SSMF and 1:32 passive split with digitally-selective ONUs and coherent receiver OLT,” in Optical Fiber Communication Conference, OSA Technical Digest (Optical Society of America, 2011), paper PDPD7.

] and the proposed coherent approach exploited an identical set of underlying optical and electrical/RF components, wherever this was not precluded by fundamental architectural differences. The DS/US BER symmetry was also confirmed by the 8 representative US channels in Fig. 3(b), indicating that high-frequency clock generation by simple multiplication of a lower-frequency signal is a viable approach for cost-effective US transmission.

4. Conclusions

The first coherent 1.92Tb/s (40λ × 48Gb/s/λ) DWDM-OFDMA-PON was proposed and verified over 100km SSMF with a 1:64 passive split. Novel optical-domain OFDMA sub-band selection, coherent detection, a flexible downstream/upstream wavelength plan with 50GHz channel spacing, and simple RF components were exploited to eliminate high-speed ONU-side electronics. The demonstrated architecture is also the first experimental verification of a next-generation optical platform capable of delivering 1Gb/s to 1000+ users over 100km which is an attractive option for future converged optical access/metro networks.

Acknowledgments

The authors would like to thank Dr. Sang-Yeup Kim and Dr. Naoto Yoshimoto of NTT AS Laboratories, Japan, for valuable technical discussions.

References and links

1.

N. Cvijetic, M. F. Huang, E. Ip, Y. K. Huang, D. Qian, and T. Wang, “1.2 Tb/s symmetric WDM-OFDMA-PON over 90km straight SSMF and 1:32 passive split with digitally-selective ONUs and coherent receiver OLT,” in Optical Fiber Communication Conference, OSA Technical Digest (Optical Society of America, 2011), paper PDPD7.

2.

P. Chanclou, F. Bourgart, B. Landousies, S. Gosselin, B. Charbonnier, N. Genay, A. Pizzinat, F. Saliou, B. Le Guyader, B. Capelle, Q. T. Le, F. Raharimanitra, A. Gharba, L. Anet Neto, J. Guillory, Q. Deniel, and S. Deniel, “Technical options for NGPON2 beyond 10G PON,” in 37th European Conference and Exposition on Optical Communications, OSA Technical Digest (Optical Society of America, 2011), paper We.9.C.3.

3.

P. Iannone and K. Reichmann, “Optical access beyond 10Gb/s PON,” in 2010 36th European Conference and Exhibition on Optical Communication (ECOC) (IEEE, 2010), paper Tu.B.3.1.

4.

D. Breuer, E. Weis, R. Hülsermann, and M. Kind, “Next generation optical access networks: the OASE view,” http://www.ict-oase.eu/public/files/2_BREUER_OASE_Overview_FTTHConfMilan2011.pdf.

5.

N. Cvijetic, D. Qian, and J. Hu, “100 Gb/s optical access based on optical orthogonal frequency-division multiplexing,” IEEE Commun. Mag. 48(7), 70–77 (2010). [CrossRef]

6.

D. Qian, J. Hu, J. Yu, P. N. Ji, L. Xu, T. Wang, M. Cvijetic, and T. Kusano, “Experimental demonstration of a novel OFDM-A based 10 Gb/s PON architecture,” in 33th European Conference and Exposition on Optical Communications, OSA Technical Digest (Optical Society of America, 2007), paper 5.4.2.

7.

E. Hugues-Salas, R. P. Giddings, X. Q. Jin, J. L. Wei, X. Zheng, Y. Hong, C. Shu, and J. M. Tang, “Real-time experimental demonstration of low-cost VCSEL intensity-modulated 11.25 Gb/s optical OFDM signal transmission over 25 km PON systems,” Opt. Express 19(4), 2979–2988 (2011). [CrossRef] [PubMed]

8.

M. Cvijetic, Coherent and Nonlinear Lightwave Communications (Artech House, 1996).

9.

S. Y. Kim, N. Sakurai, H. Kimura, and K. Kumozaki, “10-Gbit/s next-generation coherent QPSK-PON with reduced bandwidth requirements employing linear digital equalization with adaptive algorithm,” Optical Fiber Communication Conference, OSA Technical Digest (Optical Society of America, 2009), paper OMN6.

10.

D. Qian, N. Cvijetic, Y. K. Huang, J. Hu, T. Wang, J. Hu, and T. Wang, “Single-wavelength 108 Gb/s upstream OFDMA-PON,” in 35th European Conference and Exposition on Optical Communications, OSA Technical Digest (Optical Society of America, 2009), paper PD 3.3.

11.

S. Smolorz, H. Rohde, E. Gottwald, D. W. Smith, and A. Poustie, “Demonstration of a coherent UDWDM-PON with real-time processing,” in Optical Fiber Communication Conference, OSA Technical Digest (Optical Society of America, 2011), paper PDPD4.

12.

Universal Software Radio Peripheral (USRP) N200 Series, http://www.ettus.com/.

OCIS Codes
(060.2330) Fiber optics and optical communications : Fiber optics communications
(060.4230) Fiber optics and optical communications : Multiplexing

ToC Category:
Fiber Optics and Optical Communications

History
Original Manuscript: October 6, 2011
Revised Manuscript: November 4, 2011
Manuscript Accepted: November 5, 2011
Published: November 15, 2011

Citation
Neda Cvijetic, Ming-Fang Huang, Ezra Ip, Yin Shao, Yue-Kai Huang, Milorad Cvijetic, and Ting Wang, "1.92Tb/s coherent DWDM-OFDMA-PON with no high-speed ONU-side electronics over 100km SSMF and 1:64 passive split," Opt. Express 19, 24540-24545 (2011)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-19-24-24540


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References

  1. N. Cvijetic, M. F. Huang, E. Ip, Y. K. Huang, D. Qian, and T. Wang, “1.2 Tb/s symmetric WDM-OFDMA-PON over 90km straight SSMF and 1:32 passive split with digitally-selective ONUs and coherent receiver OLT,” in Optical Fiber Communication Conference, OSA Technical Digest (Optical Society of America, 2011), paper PDPD7.
  2. P. Chanclou, F. Bourgart, B. Landousies, S. Gosselin, B. Charbonnier, N. Genay, A. Pizzinat, F. Saliou, B. Le Guyader, B. Capelle, Q. T. Le, F. Raharimanitra, A. Gharba, L. Anet Neto, J. Guillory, Q. Deniel, and S. Deniel, “Technical options for NGPON2 beyond 10G PON,” in 37th European Conference and Exposition on Optical Communications, OSA Technical Digest (Optical Society of America, 2011), paper We.9.C.3.
  3. P. Iannone and K. Reichmann, “Optical access beyond 10Gb/s PON,” in 2010 36th European Conference and Exhibition on Optical Communication (ECOC) (IEEE, 2010), paper Tu.B.3.1.
  4. D. Breuer, E. Weis, R. Hülsermann, and M. Kind, “Next generation optical access networks: the OASE view,” http://www.ict-oase.eu/public/files/2_BREUER_OASE_Overview_FTTHConfMilan2011.pdf .
  5. N. Cvijetic, D. Qian, and J. Hu, “100 Gb/s optical access based on optical orthogonal frequency-division multiplexing,” IEEE Commun. Mag.48(7), 70–77 (2010). [CrossRef]
  6. D. Qian, J. Hu, J. Yu, P. N. Ji, L. Xu, T. Wang, M. Cvijetic, and T. Kusano, “Experimental demonstration of a novel OFDM-A based 10 Gb/s PON architecture,” in 33th European Conference and Exposition on Optical Communications, OSA Technical Digest (Optical Society of America, 2007), paper 5.4.2.
  7. E. Hugues-Salas, R. P. Giddings, X. Q. Jin, J. L. Wei, X. Zheng, Y. Hong, C. Shu, and J. M. Tang, “Real-time experimental demonstration of low-cost VCSEL intensity-modulated 11.25 Gb/s optical OFDM signal transmission over 25 km PON systems,” Opt. Express19(4), 2979–2988 (2011). [CrossRef] [PubMed]
  8. M. Cvijetic, Coherent and Nonlinear Lightwave Communications (Artech House, 1996).
  9. S. Y. Kim, N. Sakurai, H. Kimura, and K. Kumozaki, “10-Gbit/s next-generation coherent QPSK-PON with reduced bandwidth requirements employing linear digital equalization with adaptive algorithm,” Optical Fiber Communication Conference, OSA Technical Digest (Optical Society of America, 2009), paper OMN6.
  10. D. Qian, N. Cvijetic, Y. K. Huang, J. Hu, T. Wang, J. Hu, and T. Wang, “Single-wavelength 108 Gb/s upstream OFDMA-PON,” in 35th European Conference and Exposition on Optical Communications, OSA Technical Digest (Optical Society of America, 2009), paper PD 3.3.
  11. S. Smolorz, H. Rohde, E. Gottwald, D. W. Smith, and A. Poustie, “Demonstration of a coherent UDWDM-PON with real-time processing,” in Optical Fiber Communication Conference, OSA Technical Digest (Optical Society of America, 2011), paper PDPD4.
  12. Universal Software Radio Peripheral (USRP) N200 Series, http://www.ettus.com/ .

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