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Optics Express

Optics Express

  • Editor: Andrew M. Weiner
  • Vol. 22, Iss. 15 — Jul. 28, 2014
  • pp: 18246–18253
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Optical beat interference noise reduction by using out-of-band RF clipping tone signal in remotely fed OFDMA-PON link

Sang-Min Jung, Seung-Min Yang, Kyung-Hak Mun, and Sang-Kook Han  »View Author Affiliations


Optics Express, Vol. 22, Issue 15, pp. 18246-18253 (2014)
http://dx.doi.org/10.1364/OE.22.018246


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Abstract

A novel technique for mitigating the optical beat interference (OBI) noise in an optical orthogonal frequency division multiple access passive optical network (OFDMA-PON) uplink transmission is presented. By using an out of signal band RF clipping tone to the optical seed carrier, the OBI noise has been reduced and the resulting throughput and spectral efficiency has been improved. As an experimental verification, we demonstrate that the spectral efficiency of 23 km and 50 km have been doubled in the OFDMA-PON uplink transmission.

© 2014 Optical Society of America

1. Introduction

In recent years, the network resource management of optical networks has become important with the advent of next-generation network services such as software-defined networking (SDN) and the Internet of Things (IoT). To support these advanced network services effectively, the advancement of next-generation access networks will need the flexible network resource management to deal with complex network functionality [1

1. L. G. Kazovsky, W. T. Shaw, D. Gutierrez, N. Cheng, and S.-W. Wong, “Next-generation optical access networks,” J. Lightwave Technol. 25(11), 3428–3442 (2007). [CrossRef]

]. Not only improve the data capacity, but it will should provide resource management functions such as flexible data rate and efficient multiple access. The orthogonal frequency division multiple access passive optical network (OFDMA-PON) has been spotlighted as the next-generation optical access networks with various merits of orthogonal frequency-division multiplexing (OFDM) such as high spectral efficiency, the transparency of subcarriers and adaptive modulation for each subcarrier, it can also provide dynamic bandwidth allocation for efficient multiple access and strong scalability with wavelength-division multiplexing (WDM) [2

2. N. Cvijetic, “OFDM for next-generation optical access networks,” J. Lightwave Technol. 30(4), 384–398 (2012). [CrossRef]

].

2. Schematics

3. Experiments and results

Figure 3 shows the experimental setup for the proposed scheme.
Fig. 3 Experimental setup.
A distributed feedback laser (DFB) with a center wavelength of 1554.348 nm was used as a CW light source for the OLT.

In the experiments, we used DMT as a modulation format to transmit a real-valued baseband version of an OFDM signal under the IM/DD-based transmission system. The calculated DMT signal was loaded into a 6.4 Gs/s arbitrary waveform generator (AWG: Tektronix 7122B). The number of FFT size was 512 with Hermitian symmetry. So, the number of effective subcarriers was 256 ranging from DC to 3.2 GHz. And the cyclic prefix was 8 samples per each DMT frame. The signal bandwidth was also optimized to maximize the data throughput with adaptive modulation based on a water-filling algorithm.

Figure 7 shows the variations of the achievable data rate as a function of the input optical power of the preamplifier in the OLT.
Fig. 7 Total data throughput and spectral efficiency for input optical power of preamplifier in the case of a b2b, 23 km, 50 km transmission.
In this figure, total throughput includes the redundancy of the DMT frame like cyclic prefix. Without the OBI noise reduction, the maximum achievable data rate was only 3.8 Gbits/s even in the case of the optical back-to-back transmission with adaptive modulation on DMT signals. By applying the out-of-band clipping tone signal, the achievable data rate improved from 3.8 Gb/s to 9.8 Gb/s, when the input optical power was higher than −3 dBm in the optical back-to-back transmission. In the 20 km transmission and 50 km transmission, the achievable data rates improved from 3 Gb/s to 8.1 Gb/s and 2.8 Gb/s to 6.4 Gb/s, when the input optical powers were higher than −8 dBm and −11 dBm, respectively. In 23km and 50km transmission, we didn’t use additional optical amplifier to meet same optical power with the case of optical back-to-back, because we want to avoid the additional noise figure comes from the optical amplifier. In each case, the spectral efficiency was enhanced by more than two times. Consequently, the proposed technique was able to provide the reliable 8 Gb/s and 6 Gb/s DMT transmission in 23 km and 50 km, respectively. And the total throughput could be improved with the enough optical power in each transmission.

Figures 8(a) and 8(b) show the bit/power loading profile and its estimated SNR for each subcarrier.
Fig. 8 Bit/Power-loading Profile and SNR for each subcarrier in case of best transmission performance (a) without RF clipping tone and (b) with RF clipping tone.
All the profiles were measured for the maximum transmission performance in each transmission length. In the loading process, a probe signal, which contained uniform bits (4 QAM) and power among the entire DMT subcarriers, was first transmitted to evaluate the channel response before the loading process, and the number of bits and power were allocated to every DMT subcarrier based on the evaluated channel response. It was verified that more bits were allocated to subcarriers which had high SNR performance in the loading process. On the other hands, relatively lower bits were loaded to subcarriers which had lower SNR performance in the loading process. The power level was allocated to optimize the signal performance in every OFDM subcarrier with a given bit number. The average BER among the entire DMT frame was less than 10−3. This means that it was able to transmit the adaptively loaded DMT signal in the proposed scheme, which satisfied the forward error correction (FEC) limit. In both with/without RF clipping tone cases, some of subcarriers at high frequency region had no bit in the transmission. This is because, as represented in the SNR evaluation, it had not enough SNR to allocate even a single bit into these subcarriers. In the view of the OBI noise effect, Fig. 8(a) shows that the maximum allocated bits for subcarrier were only 2 bits for each transmission length in the case of without RF clipping tone. This is because the OBI noise degrades the SNR severely in the signal bandwidth. However, in the case of with the RF clipping tone (Fig. 8(b)), the maximum allocated bits for subcarrier was 6 bits for each transmission length by the virtue of the OBI noise reduction effect.

In view of the optical spectral efficiency, RF clipping tone may decrease the spectral efficiency because of its spectral broadening effect. But in the access network, especially at the ONU, it is important to maximize the transmission efficiency with the cost effective device which has limited RF frequency response. Therefore, in the proposed system, the OBI noise reduction with RF clipping tone provides advantage in view of transmission throughput, even with sacrificing of optical spectral efficiency.

4. Conclusion

Acknowledgments

This work was supported by the Industrial Strategic Technology Development Program of KEIT (10041775) funded by the Ministry of Trade, Industry & Energy, Korea.

References and links

1.

L. G. Kazovsky, W. T. Shaw, D. Gutierrez, N. Cheng, and S.-W. Wong, “Next-generation optical access networks,” J. Lightwave Technol. 25(11), 3428–3442 (2007). [CrossRef]

2.

N. Cvijetic, “OFDM for next-generation optical access networks,” J. Lightwave Technol. 30(4), 384–398 (2012). [CrossRef]

3.

C. Desem, “Optical interference in subcarrier multiplexed systems with multiple optical carriers,” IEEE J. Sel. Areas Comm. 8(7), 1290–1295 (1990). [CrossRef]

4.

N. Cvijetic, D. Qian, J. Hu, and T. Wang, “Orthogonal frequency division multiple access PON (OFDMA-PON) for colorless upstream transmission beyond 10Gb/s,” IEEE J. Sel. Areas Comm. 28(6), 781–790 (2010). [CrossRef]

5.

L. A. Neto, G. B. de Farias, N. Genay, S. Menezo, B. Charbonnier, and P. Chanclou, “ On the Limitations of IM/DD WDM-FDMA-OFDM PON with Single Photodiode for Upstream Transmission” in Proc. Opt. Fiber Commun. Conf. (OFC) (Los Angeles, USA, 2012), paper OM4B.1. [CrossRef]

6.

X. Q. Jin, E. Hugues-Salas, R. P. Giddings, J. L. Wei, J. Groenewald, and J. M. Tang, “First real-time experimental demonstrations of 11.25Gb/s optical OFDMA PONs with adaptive dynamic bandwidth allocation,” Opt. Express 19(21), 20557–20570 (2011). [CrossRef] [PubMed]

7.

A. Zadok, H. Shalom, M. Tur, W. D. Cornwell, and I. Andonovic, “Spectral shift and broadening of DFB lasers under direct modulation,” IEEE Photon. Technol. Lett. 10(12), 1709–1711 (1998). [CrossRef]

8.

M. M. Banat and M. Kavehrad, “Reduction of optical beat interference in SCM/WDMA networks using pseudorandom phase modulation,” J. Lightwave Technol. 12(10), 1863–1868 (1994). [CrossRef]

9.

S. L. Woodward, X. Lu, T. E. Darcie, and G. E. Bodeep, “Reduction of optical beat interference in subcarrier networks,” IEEE Photon. Technol. Lett. 8(5), 694–696 (1996). [CrossRef]

OCIS Codes
(060.2330) Fiber optics and optical communications : Fiber optics communications
(060.2360) Fiber optics and optical communications : Fiber optics links and subsystems

ToC Category:
Optical Communications

History
Original Manuscript: May 27, 2014
Revised Manuscript: July 3, 2014
Manuscript Accepted: July 7, 2014
Published: July 21, 2014

Citation
Sang-Min Jung, Seung-Min Yang, Kyung-Hak Mun, and Sang-Kook Han, "Optical beat interference noise reduction by using out-of-band RF clipping tone signal in remotely fed OFDMA-PON link," Opt. Express 22, 18246-18253 (2014)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-22-15-18246


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References

  1. L. G. Kazovsky, W. T. Shaw, D. Gutierrez, N. Cheng, and S.-W. Wong, “Next-generation optical access networks,” J. Lightwave Technol.25(11), 3428–3442 (2007). [CrossRef]
  2. N. Cvijetic, “OFDM for next-generation optical access networks,” J. Lightwave Technol.30(4), 384–398 (2012). [CrossRef]
  3. C. Desem, “Optical interference in subcarrier multiplexed systems with multiple optical carriers,” IEEE J. Sel. Areas Comm.8(7), 1290–1295 (1990). [CrossRef]
  4. N. Cvijetic, D. Qian, J. Hu, and T. Wang, “Orthogonal frequency division multiple access PON (OFDMA-PON) for colorless upstream transmission beyond 10Gb/s,” IEEE J. Sel. Areas Comm.28(6), 781–790 (2010). [CrossRef]
  5. L. A. Neto, G. B. de Farias, N. Genay, S. Menezo, B. Charbonnier, and P. Chanclou, “ On the Limitations of IM/DD WDM-FDMA-OFDM PON with Single Photodiode for Upstream Transmission” in Proc. Opt. Fiber Commun. Conf. (OFC) (Los Angeles, USA, 2012), paper OM4B.1. [CrossRef]
  6. X. Q. Jin, E. Hugues-Salas, R. P. Giddings, J. L. Wei, J. Groenewald, and J. M. Tang, “First real-time experimental demonstrations of 11.25Gb/s optical OFDMA PONs with adaptive dynamic bandwidth allocation,” Opt. Express19(21), 20557–20570 (2011). [CrossRef] [PubMed]
  7. A. Zadok, H. Shalom, M. Tur, W. D. Cornwell, and I. Andonovic, “Spectral shift and broadening of DFB lasers under direct modulation,” IEEE Photon. Technol. Lett.10(12), 1709–1711 (1998). [CrossRef]
  8. M. M. Banat and M. Kavehrad, “Reduction of optical beat interference in SCM/WDMA networks using pseudorandom phase modulation,” J. Lightwave Technol.12(10), 1863–1868 (1994). [CrossRef]
  9. S. L. Woodward, X. Lu, T. E. Darcie, and G. E. Bodeep, “Reduction of optical beat interference in subcarrier networks,” IEEE Photon. Technol. Lett.8(5), 694–696 (1996). [CrossRef]

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