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Optics Express

Optics Express

  • Editor: C. Martijin de Sterke
  • Vol. 15, Iss. 9 — Apr. 30, 2007
  • pp: 5376–5381
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Reflective SOA re-modulated 20 Gbit/s RZ-DQPSK over distributed Raman amplified 80 km long reach PON link

Jesper Bevensee Jensen, Idelfonso Tafur Monroy, Rasmus Kjær, and Palle Jeppesen  »View Author Affiliations


Optics Express, Vol. 15, Issue 9, pp. 5376-5381 (2007)
http://dx.doi.org/10.1364/OE.15.005376


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Abstract

An 80 km bidirectional Raman amplified long reach PON link has been demonstrated. A 20 Gbit/s RZ-DQPSK signal was transmitted downstream, ASK-remodulated at 1.25 Gbit/s by an RSOA and transmitted upstream in the same fiber. Both signals were detected error free without use of EDFAs.

© 2007 Optical Society of America

1. Introduction

2. Experimental setup

A schematic of the setup used in the experiments is shown in Fig. 1. The DQPSK transmitter is composed of a distributed feedback (DFB) laser emitting continuous wave (CW) light at 1551.3 nm, two Mach-Zehnder modulators (MZM) and a phase modulator (PM) (The modulators have been omitted in the figure for simplicity). The first MZM is driven by a 10 GHz clock, and carves the CW light into a pulse-train with a 10 GHz repetition rate. The other MZM and the PM provide the data modulation. They are both driven by a 27-1 bits long pseudo random bit sequence (PRBS). The MZM was driven between two transmission maxima, thereby giving a π phase shift, and the PM was driven to give a π/2 phase shift. Decorrelation was ensured by the difference in optical and electrical delay between the data modulators. The 27 - 1 word length was chosen for simplicity in the programming of the error detector. Moreover, because of the pattern independent power level of the RZ-DQPSK modulation format, no severe performance degradation would be expected from pattern effects.

After downstream transmission, out of band spontaneous emission noise was filtered away using an optical bandpass filter with a 3 dB bandwidth of 1.3 nm. The 20 Gbit/s RZ-DQPSK signal was split by a 10 dB fiber coupler and the 90% output was detected by a SOA based pre-amplified receiver. This receiver design was chosen for its suitability for integration. The gain of the SOA was measured to be 10 dB. The phase modulation was converted to amplitude modulation by a fiber based one-symbol delay interferometer before direct detection by a pair of balanced photodiodes. A 20 Gbit/s RZ-DQPSK signal consists of two independent 10 Gbit/s tributaries. In a real system implementation, two receivers would be needed to detect both tributaries simultaneously. In the experiment they were measured one after the other. The error performance of the signal was analyzed by a programmable 10 Gbit/s error detector. Since no hardware precoding was utilized, the error detector was programmed with the expected DQPSK tributary.

After upstream propagation, the ASK signal was led to a receiver via a circulator, out of band spontaneous emission noise was supressed by an optical band pass filter with a 3 dB bandwidth of 0.3 nm, and the signal was detected by a photodiode. After detection, the 10 GHz tone from the pulse carving was supressed using a 4th order low pass Bessel filter with a cut-off frequency of 1.8 GHz. Error performance is evaluated by a 1.25 Gbit/s error detector.

Fig. 1. Schematic of the setup used in the experiments.

3. Results

Fig. 2. BER of the 1.25 Gbit/s remodulated upstream signal.
Fig. 3. Eye diagrams of the RSOA remodulated RZ-DQPSK signal before (left) and after (right) transmission.

The bit error ratio (BER) of the ASK signal was measured directly at the output of the RSOA (back to back) with CW light into the RSOA, as well as with the 10 Gbaud RZ-DQPSK signal into the RSOA in order to investigate the effect of the RZ-carving on the performance of the 1.25 Gbit/s ASK signal. The results are plotted in Fig. 2 along with the BER of the upstream transmitted ASK-remodulated RZ-DQPSK signal. Very little difference between the two back to back cases is observed. At a BER of 10-9, the receiver sensitivity was -22.4 dBm for the CW, and -22.1 dBm for the RZ-DQPSK input. After transmission, the receiver sensitivity was -20.8 dBm, corresponding to a penalty of 1.3 dB. The low penalty is confirmed by the eye diagrams in Fig. 3, where only a slight degradation of the signal is observed.

Fig. 4. BER of the 20 Gbit/s RZ-DQPSK downstream signal. a and b denote the two RZ-DQPSK tributaries.
Fig. 5. Eye diagrams of the RZ-DQPSK signal back to back (left), after transmission without remodulation (middle), and after transmission with the remodulated upstream signal on (right).

Results of the BER measurements of the 20 Gbit/s RZ-DQPSK downstream signal are plotted in Fig. 4. Back to back performance was measured, as well as performance after transmission, both with the ASK-remodulated upstream signal on and with the RSOA disconnected. The back to back receiver sensitivity at a BER of 10-9 was -18.7 dBm and after transmission it was -17.7 dBm without the RSOA and -17.2 with the RSOA. No significant difference between the two DQPSK tributaries was observed. Eye diagrams of the 20 Gbit/s RZ-DQPSK signal is shown in Fig. 5. The good dispersion tolerance of the RZ-DQPSK modulation format is illustrated by the very limited pulse broadening after transmission. The pulse broadening undergone by a binary modulation format at 20 Gbit/s after 370 ps/nm total dispersion would have been considerably larger. For 20 Gbit/s NRZ on-off keying (OOK), the 1 dB eye closure limit is 250 ps/nm, corresponding to 55 km of NZ-DSF. Therefore, the long reach transmission could not have been achieved using 20 Gbit/s OOK without incorporating further dispersion compensation. [7

7. L. Nelson and B. Zhu “40 Gbit/s Raman-Amplified Transmission,” in M. N. Islam (editor) Raman amplifiers for trelecommunication (Springer, 2003), pp. 676–677.

]. Also, the very similar performance with- and without the counterpropagating ASK modulated signal is confirmed.

In order to estimate the end user capacity of the proposed system, a crude power budget calculation can be performed. Taking into account the loss of two arrayed waveguide gratings (AWGs), and assuming said loss to be 4 dB each, the power margin is approximately 19 dB for the downstream signal and 16 dB for the upstream signal. These power margins can be used fr dimensioning the system, for example assuming a maximum distance of 20 km from the passive splitting point to the end user, and 0.2 dB/km propagation loss, 25 end users can be reached within the margin of the upstream signal. For the downstream signal, this leaves an additional 3 dB margin, allowing for further simplification of the system by single ended detection of the DQPSK signal.

4. Conclusion

The presented bidirectional link, employing a single fiber with distributed Raman amplification and carrier remodulation at the customer premises, offers advantageous features for applications in long reach PONs, such as reduced complexity in the fiber link, downstream bit rates up to 20 Gbit/s, and easy upgradability of the upstream bit-rate.

Acknowledgments

References and links

1.

D. B. Payne and R. P. Daveyet.al. “The Future of Fiber Access Systems?” BT Technol. J. 20.4, 104–114 (2002). [CrossRef]

2.

D. P. Shea and J. E. Mitchell, “Operating Penalties in Single-Fiber Operation 10-Gb/s, 1024-Way Split, 110-km Long-Reach Optical AccesNetworks,” IEEE Photon. Technol. Lett. 18, 2463–2465 (2006). [CrossRef]

3.

H. S. Chung, B. K. Kim, H. Park, S. H. Chang, M. J. Chu, and K. J. Kim, “Effects of Inverse-RZ and Manchester Code a Wavelength Re-used WDM-PON,” in Proc. LEOS 2006, Paper TuP3, 298–299 (2006).

4.

R. Kjӕr, I. T. Monroy, L. K. Oxenloewe, and P. Jeppesen, “Bi-birectional 120 km Long-Reach PON Link Based on Distributed Raman Amplification,” in Proc. LEOS 2006, paper WEE3, 703–704 (2006)

5.

A. Garreau, J. Decobert, C. Kazmierski, M. C. Cuisin, J. G. Provost, H. Sillard, F. Blache, D. Carpentier, J. Landreau, and P. Chanclou, “ 10 Gbit/s Amplified Reflective Electroabsobtion Modulator for Colorless Access Networks,” Workshop on Optical Components for Broadband Communication 2006, Paper TuA2.3, 168–170 (2006)

6.

I. T. Monroy, F. hman, K. Yvind, R. Kjӕr, C. Peucheret, A. M. J. Koonen, and P. Jeppesen, “85 km Long reach PON System using a Reflective SOA-EA Modulator and Distributed Raman Fiber Amplification,” in Proc. LEOS 2006, paper WEE4, 705–706 (2006).

7.

L. Nelson and B. Zhu “40 Gbit/s Raman-Amplified Transmission,” in M. N. Islam (editor) Raman amplifiers for trelecommunication (Springer, 2003), pp. 676–677.

8.

W. Lee, M. Y. Park, S. H. Cho, J. Lee, C. Kim, G. Jeong, and B. Kim “Bidirectional WDM-PON base on Gain- Saturated Reflective Semiconductor Optical Amplifiers,” IEEE Photon. Technol. Letters 8, 2460–2462 (2005).

OCIS Codes
(060.2360) Fiber optics and optical communications : Fiber optics links and subsystems
(060.4250) Fiber optics and optical communications : Networks
(060.5060) Fiber optics and optical communications : Phase modulation

ToC Category:
Fiber Optics and Optical Communications

History
Original Manuscript: January 5, 2007
Revised Manuscript: April 3, 2007
Manuscript Accepted: April 9, 2007
Published: April 18, 2007

Citation
Jesper Bevensee Jensen, Idelfonso Tafur Monroy, Rasmus Kjær, and Palle Jeppesen, "Reflective SOA re-modulated 20 Gbit/s RZ-DQPSK over distributed Raman amplified 80 km long reach PON link," Opt. Express 15, 5376-5381 (2007)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-15-9-5376


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References

  1. D. B. Payne, R. P. Daveyet.al. “The Future of Fiber Access Systems?” BT Technol. J. 20.4, 104–114 (2002). [CrossRef]
  2. D. P. Shea, J. E. Mitchell, “Operating Penalties in Single-Fiber Operation 10-Gb/s, 1024-Way Split, 110-km Long-Reach Optical AccesNetworks,” IEEE Photon. Technol. Lett. 18, 2463–2465 (2006). [CrossRef]
  3. H. S. Chung, B. K. Kim, H. Park, S. H. Chang, M. J. Chu, K. J. Kim, “Effects of Inverse-RZ and Manchester Code a Wavelength Re-used WDM-PON,” in Proc. LEOS 2006, Paper TuP3, 298–299 (2006).
  4. R. Kjӕr, I. T. Monroy, L. K. Oxenloewe, P. Jeppesen, “Bi-birectional 120 km Long-Reach PON Link Based on Distributed Raman Amplification,” in Proc. LEOS 2006, paper WEE3, 703–704 (2006)
  5. A. Garreau, J. Decobert, C. Kazmierski, M. C. Cuisin, J. G. Provost, H. Sillard, F. Blache, D. Carpentier, J. Landreau, P. Chanclou, “ 10 Gbit/s Amplified Reflective Electroabsobtion Modulator for Colorless Access Networks,” Workshop on Optical Components for Broadband Communication 2006, Paper TuA2.3, 168–170 (2006)
  6. I. T. Monroy, F. hman, K. Yvind, R. Kjӕr, C. Peucheret, A. M. J. Koonen, P. Jeppesen, “85 km Long reach PON System using a Reflective SOA-EA Modulator and Distributed Raman Fiber Amplification,” in Proc. LEOS 2006, paper WEE4, 705–706 (2006).
  7. L. Nelson, B. Zhu “40 Gbit/s Raman-Amplified Transmission,” in M. N. Islam (editor) Raman amplifiers for trelecommunication (Springer, 2003), pp. 676–677.
  8. W. Lee, M. Y. Park, S. H. Cho, J. Lee, C. Kim, G. Jeong, B. Kim “Bidirectional WDM-PON base on Gain- Saturated Reflective Semiconductor Optical Amplifiers,” IEEE Photon. Technol. Letters 8, 2460–2462 (2005).

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