## Low noise optical multi-carrier generation using optical-FIR filter for ASE noise suppression in re-circulating frequency shifter loop |

Optics Express, Vol. 22, Issue 7, pp. 7852-7864 (2014)

http://dx.doi.org/10.1364/OE.22.007852

Acrobat PDF (2414 KB)

### Abstract

In this paper, an improved multi-carrier generation scheme based on single-side-band recirculating frequency shifter with optical finite impulse response (FIR) filter for amplified spontaneous emission (ASE) noise suppression is proposed and experimentally demonstrated. The carrier-to-noise-ratio (CNR) instead of tone-to-noise-ratio (TNR) is introduced to more reasonably and exactly evaluate the signal-to-noise-ratio of a multi-carrier source with non-flat noise floor. We have experimentally attain the worst case CNR of 22.5dB and 19.1dB for generated 50 and 69 flat low noise carriers, which has shown significant improvement than the previous cited works based on recirculating frequency shifter.

© 2014 Optical Society of America

## 1. Introduction

1. F. Tian, X. Zhang, L. Xi, A. Stark, S. E. Ralph, and G. K. Chang, “Experiment of 2.56-Tb/s, polarization division multiplexing return-to-zero 16-ary quadrature amplitude modulation, 25 GHz grid coherent optical wavelength division multiplexing, 800 km transmission based on optical comb in standard single-mode fiber,” Opt. Eng. **52**(11), 116103 (2013). [CrossRef]

2. D. Hillerkuss, R. Schmogrow, M. Meyer, S. Wolf, M. Jordan, P. Kleinow, and J. Leuthold, “Single-laser 32.5 Tbit/s Nyquist WDM transmission,” J. Opt. Commun. Netw. **4**(10), 715–723 (2012). [CrossRef]

3. Y. Ma, Q. Yang, Y. Tang, S. Chen, and W. Shieh, “1-Tb/s single-channel coherent optical OFDM transmission over 600-km SSMF fiber with subwavelength bandwidth access,” Opt. Express **17**(11), 9421–9427 (2009). [CrossRef] [PubMed]

5. X. Liu, S. Chandrasekhar, X. Chen, P. J. Winzer, Y. Pan, T. F. Taunay, B. Zhu, M. Fishteyn, M. F. Yan, J. M. Fini, E. M. Monberg, and F. V. Dimarcello, “1.12-Tb/s 32-QAM-OFDM superchannel with 8.6-b/s/Hz intrachannel spectral efficiency and space-division multiplexed transmission with 60-b/s/Hz aggregate spectral efficiency,” Opt. Express **19**(26), B958–B964 (2011). [CrossRef] [PubMed]

6. G. Bosco, V. Curri, A. Carena, P. Poggiolini, and F. Forghieri, “On the performance of Nyquist-WDM terabit superchannels based on PM-BPSK, PM-QPSK, PM-8QAM or PM-16QAM subcarriers,” J. Lightwave Technol. **29**(1), 53–61 (2011). [CrossRef]

1. F. Tian, X. Zhang, L. Xi, A. Stark, S. E. Ralph, and G. K. Chang, “Experiment of 2.56-Tb/s, polarization division multiplexing return-to-zero 16-ary quadrature amplitude modulation, 25 GHz grid coherent optical wavelength division multiplexing, 800 km transmission based on optical comb in standard single-mode fiber,” Opt. Eng. **52**(11), 116103 (2013). [CrossRef]

5. X. Liu, S. Chandrasekhar, X. Chen, P. J. Winzer, Y. Pan, T. F. Taunay, B. Zhu, M. Fishteyn, M. F. Yan, J. M. Fini, E. M. Monberg, and F. V. Dimarcello, “1.12-Tb/s 32-QAM-OFDM superchannel with 8.6-b/s/Hz intrachannel spectral efficiency and space-division multiplexed transmission with 60-b/s/Hz aggregate spectral efficiency,” Opt. Express **19**(26), B958–B964 (2011). [CrossRef] [PubMed]

7. N. K. Fontaine, “Spectrally-sliced coherent receivers for THz bandwidth optical communications.” European Conference on Optical Communications, paper Mo.3.C.1, London, UK (2012). [CrossRef]

8. M. A. Mirza and G. Stewart, “Multi-wavelength operation of erbiumdoped fiber lasers by periodic filtering and phase modulation,” J. Lightwave Technol. **27**(8), 1034–1044 (2009). [CrossRef]

5. X. Liu, S. Chandrasekhar, X. Chen, P. J. Winzer, Y. Pan, T. F. Taunay, B. Zhu, M. Fishteyn, M. F. Yan, J. M. Fini, E. M. Monberg, and F. V. Dimarcello, “1.12-Tb/s 32-QAM-OFDM superchannel with 8.6-b/s/Hz intrachannel spectral efficiency and space-division multiplexed transmission with 60-b/s/Hz aggregate spectral efficiency,” Opt. Express **19**(26), B958–B964 (2011). [CrossRef] [PubMed]

9. J. Zhang, J. Yu, N. Chi, Z. Dong, X. Li, Y. Shao, J. Yu, and L. Tao, “Flattened comb generation using only phase modulators driven by fundamental frequency sinusoidal sources with small frequency offset,” Opt. Lett. **38**(4), 552–554 (2013). [CrossRef] [PubMed]

11. J. Zhang, N. Chi, J. Yu, Y. Shao, J. Zhu, B. Huang, and L. Tao, “Generation of coherent and frequency-lock multi-carriers using cascaded phase modulators and recirculating frequency shifter for Tb/s optical communication,” Opt. Express **19**(14), 12891–12902 (2011). [CrossRef] [PubMed]

3. Y. Ma, Q. Yang, Y. Tang, S. Chen, and W. Shieh, “1-Tb/s single-channel coherent optical OFDM transmission over 600-km SSMF fiber with subwavelength bandwidth access,” Opt. Express **17**(11), 9421–9427 (2009). [CrossRef] [PubMed]

11. J. Zhang, N. Chi, J. Yu, Y. Shao, J. Zhu, B. Huang, and L. Tao, “Generation of coherent and frequency-lock multi-carriers using cascaded phase modulators and recirculating frequency shifter for Tb/s optical communication,” Opt. Express **19**(14), 12891–12902 (2011). [CrossRef] [PubMed]

13. F. Tian, X. Zhang, J. Li, and L. Xi, “Generation of 50 stable frequency-locked optical carriers for Tb/s multicarrier optical transmission using a recirculating frequency shifter,” J. Lightwave Technol. **29**(8), 1085–1091 (2011). [CrossRef]

1. F. Tian, X. Zhang, L. Xi, A. Stark, S. E. Ralph, and G. K. Chang, “Experiment of 2.56-Tb/s, polarization division multiplexing return-to-zero 16-ary quadrature amplitude modulation, 25 GHz grid coherent optical wavelength division multiplexing, 800 km transmission based on optical comb in standard single-mode fiber,” Opt. Eng. **52**(11), 116103 (2013). [CrossRef]

3. Y. Ma, Q. Yang, Y. Tang, S. Chen, and W. Shieh, “1-Tb/s single-channel coherent optical OFDM transmission over 600-km SSMF fiber with subwavelength bandwidth access,” Opt. Express **17**(11), 9421–9427 (2009). [CrossRef] [PubMed]

14. J. Zhang, J. Yu, N. Chi, Z. Dong, Y. Shao, L. Tao, and X. Li, “Theoretical and experimental study on improved frequency-locked multi-carrier generation by using recirculating loop based on multi-frequency shifting single-side band modulation,” IEEE Photon. J. **4**(6), 2249–2261 (2012). [CrossRef]

15. J. Zhang, J. Yu, N. Chi, Y. Shao, L. Tao, J. Zhu, and Y. Wang, “Stable Optical Frequency-Locked Multicarriers Generation by Double Recirculating Frequency Shifter Loops for Tb/s Communication,” J. Lightwave Technol. **30**(24), 3938–3945 (2012). [CrossRef]

16. J. Li and Z. Li, “Frequency-locked multicarrier generator based on a complementary frequency shifter with double recirculating frequency-shifting loops,” Opt. Lett. **38**(3), 359–361 (2013). [CrossRef] [PubMed]

17. J. Li, C. Yu, and Z. Li, “Complementary frequency shifter based on polarization modulator used for generation of a high-quality frequency-locked multicarrier,” Opt. Lett. **39**(6), 1513–1516 (2014). [CrossRef]

## 2. Proposed scheme and noise characteristic analysis

### 2.1 Proposed ASE noise suppression scheme

**17**(11), 9421–9427 (2009). [CrossRef] [PubMed]

12. J. Li, X. Zhang, F. Tian, and L. Xi, “Theoretical and experimental study on generation of stable and high-quality multi-carrier source based on re-circulating frequency shifter used for Tb/s optical transmission,” Opt. Express **19**(2), 848–860 (2011). [CrossRef] [PubMed]

13. F. Tian, X. Zhang, J. Li, and L. Xi, “Generation of 50 stable frequency-locked optical carriers for Tb/s multicarrier optical transmission using a recirculating frequency shifter,” J. Lightwave Technol. **29**(8), 1085–1091 (2011). [CrossRef]

*f*is provided by CW laser, and an I/Q modulator driven by two RF signals of frequency

_{0}*f*is used to implement carrier frequency shift. The exact polarization alignments are ensured by the polarization controllers (PCs) and the number of generated carriers is controlled by a band pass filter (BPF). The role of EDFA is to compensate the total loss suffered in one round trip (RT) with inevitable ASE noise accumulation that could result in a great system performance degradation. In our proposed scheme, an N-tap optical FIR structured notch filter is placed after EDFA to further reduce accumulated ASE noise, which ensures a significant improvement in overall system performance.

_{s}### 2.2 Analysis of noise accumulation and CNR definition

*n*th (

*n*= 1,2,…N) RT.

*n*th RT. A stable and flat output is always ensured by EDFA condition of

*n*th RT induced random ASE noise

*N*th channel can be calculated by Eq. (6).

*N*th channel is represented by Eq. (7).Equation (7) indicates that ASE noise power accumulation in each channel seems linear with required circulating time

*N*. Where,

*N*times noise power accumulated on

*N*th generated carrier tone compared to first tone, would result in a great degradation on signal loading process. In this work, carrier-to-noise ratio (CNR) is defined and used to have a quick and accurate evaluation on noise characteristic of each channel instead of tone-to-noise ratio (TNR, defined as

13. F. Tian, X. Zhang, J. Li, and L. Xi, “Generation of 50 stable frequency-locked optical carriers for Tb/s multicarrier optical transmission using a recirculating frequency shifter,” J. Lightwave Technol. **29**(8), 1085–1091 (2011). [CrossRef]

*n*th channel with 0.1nm reference noise bandwidth likewise OSNR is defined as Eq. (8).where

*n*th channel within channel spacing

### 2.3 Analysis of ASE noise power reduction

#### CASE I: Parallel FIR implementation

#### CASE II Serial FIR implementation

*m*th tap coefficient equals

### 2.4 System performance improvements with the proposed ASE noise suppression scheme

#### CNR improvement

*N*RTs could be denoted by Eq. (15).

*N*th channel can be represented by Eq. (16).There are two observations can be inferred from Eq. (16), which are: 1) total noise in

*N*th channel has been overlapped

*N*times and 2) ASE noise induced in

*m*th trip has passed FIR filter

*N*-

*m +*1 times. Therefore, the power of residual ASE noise after FIR filtering in

*N*th channel can be represented byAccording to the above definition, the CNR of

*N*th channel with 0.1nm equivalent reference noise bandwidth isIt is hard to find analytic solution from Eq. (18) since

14. J. Zhang, J. Yu, N. Chi, Z. Dong, Y. Shao, L. Tao, and X. Li, “Theoretical and experimental study on improved frequency-locked multi-carrier generation by using recirculating loop based on multi-frequency shifting single-side band modulation,” IEEE Photon. J. **4**(6), 2249–2261 (2012). [CrossRef]

#### EVM improvement of loaded signals

#### Amplification efficiency improvement of EDFA

12. J. Li, X. Zhang, F. Tian, and L. Xi, “Theoretical and experimental study on generation of stable and high-quality multi-carrier source based on re-circulating frequency shifter used for Tb/s optical transmission,” Opt. Express **19**(2), 848–860 (2011). [CrossRef] [PubMed]

## 3. Experimental setup and results

12. J. Li, X. Zhang, F. Tian, and L. Xi, “Theoretical and experimental study on generation of stable and high-quality multi-carrier source based on re-circulating frequency shifter used for Tb/s optical transmission,” Opt. Express **19**(2), 848–860 (2011). [CrossRef] [PubMed]

*n*th channel and is read from Fig. 3. Moreover, in our previous experiment results of 50 carrier tones with 12.5GHz spacing having a worst TNR of 20dB observed with a resolution of 0.02nm OSA [13

**29**(8), 1085–1091 (2011). [CrossRef]

*B*= 12.5GHz), EDFA saturation output power is about 29dBm while in this work only 25dBm output power is needed to generate 50 flat carriers but with much higher CNR. It is consistent with theoretical analysis above that, not only ASE noise power is reduced by 2-tap optical FIR filter but also the EDFA amplification efficiency is improved.

_{r}## 4. Conclusion

## Acknowledgments

## References and links

1. | F. Tian, X. Zhang, L. Xi, A. Stark, S. E. Ralph, and G. K. Chang, “Experiment of 2.56-Tb/s, polarization division multiplexing return-to-zero 16-ary quadrature amplitude modulation, 25 GHz grid coherent optical wavelength division multiplexing, 800 km transmission based on optical comb in standard single-mode fiber,” Opt. Eng. |

2. | D. Hillerkuss, R. Schmogrow, M. Meyer, S. Wolf, M. Jordan, P. Kleinow, and J. Leuthold, “Single-laser 32.5 Tbit/s Nyquist WDM transmission,” J. Opt. Commun. Netw. |

3. | Y. Ma, Q. Yang, Y. Tang, S. Chen, and W. Shieh, “1-Tb/s single-channel coherent optical OFDM transmission over 600-km SSMF fiber with subwavelength bandwidth access,” Opt. Express |

4. | 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,” European Conference on Optical Communications, paper PD2.6, Vienna, Austria (2009). |

5. | X. Liu, S. Chandrasekhar, X. Chen, P. J. Winzer, Y. Pan, T. F. Taunay, B. Zhu, M. Fishteyn, M. F. Yan, J. M. Fini, E. M. Monberg, and F. V. Dimarcello, “1.12-Tb/s 32-QAM-OFDM superchannel with 8.6-b/s/Hz intrachannel spectral efficiency and space-division multiplexed transmission with 60-b/s/Hz aggregate spectral efficiency,” Opt. Express |

6. | G. Bosco, V. Curri, A. Carena, P. Poggiolini, and F. Forghieri, “On the performance of Nyquist-WDM terabit superchannels based on PM-BPSK, PM-QPSK, PM-8QAM or PM-16QAM subcarriers,” J. Lightwave Technol. |

7. | N. K. Fontaine, “Spectrally-sliced coherent receivers for THz bandwidth optical communications.” European Conference on Optical Communications, paper Mo.3.C.1, London, UK (2012). [CrossRef] |

8. | M. A. Mirza and G. Stewart, “Multi-wavelength operation of erbiumdoped fiber lasers by periodic filtering and phase modulation,” J. Lightwave Technol. |

9. | J. Zhang, J. Yu, N. Chi, Z. Dong, X. Li, Y. Shao, J. Yu, and L. Tao, “Flattened comb generation using only phase modulators driven by fundamental frequency sinusoidal sources with small frequency offset,” Opt. Lett. |

10. | X. Zhou, X. Zheng, H. Wen, H. Zhang, and B. Zhou, “Generation of broadband optical frequency comb with rectangular envelope using cascaded intensity and dual-parallel modulators,” Opt. Commun. |

11. | J. Zhang, N. Chi, J. Yu, Y. Shao, J. Zhu, B. Huang, and L. Tao, “Generation of coherent and frequency-lock multi-carriers using cascaded phase modulators and recirculating frequency shifter for Tb/s optical communication,” Opt. Express |

12. | J. Li, X. Zhang, F. Tian, and L. Xi, “Theoretical and experimental study on generation of stable and high-quality multi-carrier source based on re-circulating frequency shifter used for Tb/s optical transmission,” Opt. Express |

13. | F. Tian, X. Zhang, J. Li, and L. Xi, “Generation of 50 stable frequency-locked optical carriers for Tb/s multicarrier optical transmission using a recirculating frequency shifter,” J. Lightwave Technol. |

14. | J. Zhang, J. Yu, N. Chi, Z. Dong, Y. Shao, L. Tao, and X. Li, “Theoretical and experimental study on improved frequency-locked multi-carrier generation by using recirculating loop based on multi-frequency shifting single-side band modulation,” IEEE Photon. J. |

15. | J. Zhang, J. Yu, N. Chi, Y. Shao, L. Tao, J. Zhu, and Y. Wang, “Stable Optical Frequency-Locked Multicarriers Generation by Double Recirculating Frequency Shifter Loops for Tb/s Communication,” J. Lightwave Technol. |

16. | J. Li and Z. Li, “Frequency-locked multicarrier generator based on a complementary frequency shifter with double recirculating frequency-shifting loops,” Opt. Lett. |

17. | J. Li, C. Yu, and Z. Li, “Complementary frequency shifter based on polarization modulator used for generation of a high-quality frequency-locked multicarrier,” Opt. Lett. |

18. | G. P. Agrawal, |

**OCIS Codes**

(060.0060) Fiber optics and optical communications : Fiber optics and optical communications

(060.2630) Fiber optics and optical communications : Frequency modulation

**ToC Category:**

Optical Communications

**History**

Original Manuscript: January 27, 2014

Revised Manuscript: March 16, 2014

Manuscript Accepted: March 17, 2014

Published: March 27, 2014

**Citation**

Jiachuan Lin, Lixia Xi, Jianrui Li, Xiaoguang Zhang, Xia Zhang, and Shahab Ahmad Niazi, "Low noise optical multi-carrier generation using optical-FIR filter for ASE noise suppression in re-circulating frequency shifter loop," Opt. Express **22**, 7852-7864 (2014)

http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-22-7-7852

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### References

- F. Tian, X. Zhang, L. Xi, A. Stark, S. E. Ralph, G. K. Chang, “Experiment of 2.56-Tb/s, polarization division multiplexing return-to-zero 16-ary quadrature amplitude modulation, 25 GHz grid coherent optical wavelength division multiplexing, 800 km transmission based on optical comb in standard single-mode fiber,” Opt. Eng. 52(11), 116103 (2013). [CrossRef]
- D. Hillerkuss, R. Schmogrow, M. Meyer, S. Wolf, M. Jordan, P. Kleinow, J. Leuthold, “Single-laser 32.5 Tbit/s Nyquist WDM transmission,” J. Opt. Commun. Netw. 4(10), 715–723 (2012). [CrossRef]
- Y. Ma, Q. Yang, Y. Tang, S. Chen, W. Shieh, “1-Tb/s single-channel coherent optical OFDM transmission over 600-km SSMF fiber with subwavelength bandwidth access,” Opt. Express 17(11), 9421–9427 (2009). [CrossRef] [PubMed]
- 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,” European Conference on Optical Communications, paper PD2.6, Vienna, Austria (2009).
- X. Liu, S. Chandrasekhar, X. Chen, P. J. Winzer, Y. Pan, T. F. Taunay, B. Zhu, M. Fishteyn, M. F. Yan, J. M. Fini, E. M. Monberg, F. V. Dimarcello, “1.12-Tb/s 32-QAM-OFDM superchannel with 8.6-b/s/Hz intrachannel spectral efficiency and space-division multiplexed transmission with 60-b/s/Hz aggregate spectral efficiency,” Opt. Express 19(26), B958–B964 (2011). [CrossRef] [PubMed]
- G. Bosco, V. Curri, A. Carena, P. Poggiolini, F. Forghieri, “On the performance of Nyquist-WDM terabit superchannels based on PM-BPSK, PM-QPSK, PM-8QAM or PM-16QAM subcarriers,” J. Lightwave Technol. 29(1), 53–61 (2011). [CrossRef]
- N. K. Fontaine, “Spectrally-sliced coherent receivers for THz bandwidth optical communications.” European Conference on Optical Communications, paper Mo.3.C.1, London, UK (2012). [CrossRef]
- M. A. Mirza, G. Stewart, “Multi-wavelength operation of erbiumdoped fiber lasers by periodic filtering and phase modulation,” J. Lightwave Technol. 27(8), 1034–1044 (2009). [CrossRef]
- J. Zhang, J. Yu, N. Chi, Z. Dong, X. Li, Y. Shao, J. Yu, L. Tao, “Flattened comb generation using only phase modulators driven by fundamental frequency sinusoidal sources with small frequency offset,” Opt. Lett. 38(4), 552–554 (2013). [CrossRef] [PubMed]
- X. Zhou, X. Zheng, H. Wen, H. Zhang, B. Zhou, “Generation of broadband optical frequency comb with rectangular envelope using cascaded intensity and dual-parallel modulators,” Opt. Commun. 313, 356–359 (2014). [CrossRef]
- J. Zhang, N. Chi, J. Yu, Y. Shao, J. Zhu, B. Huang, L. Tao, “Generation of coherent and frequency-lock multi-carriers using cascaded phase modulators and recirculating frequency shifter for Tb/s optical communication,” Opt. Express 19(14), 12891–12902 (2011). [CrossRef] [PubMed]
- J. Li, X. Zhang, F. Tian, L. Xi, “Theoretical and experimental study on generation of stable and high-quality multi-carrier source based on re-circulating frequency shifter used for Tb/s optical transmission,” Opt. Express 19(2), 848–860 (2011). [CrossRef] [PubMed]
- F. Tian, X. Zhang, J. Li, L. Xi, “Generation of 50 stable frequency-locked optical carriers for Tb/s multicarrier optical transmission using a recirculating frequency shifter,” J. Lightwave Technol. 29(8), 1085–1091 (2011). [CrossRef]
- J. Zhang, J. Yu, N. Chi, Z. Dong, Y. Shao, L. Tao, X. Li, “Theoretical and experimental study on improved frequency-locked multi-carrier generation by using recirculating loop based on multi-frequency shifting single-side band modulation,” IEEE Photon. J. 4(6), 2249–2261 (2012). [CrossRef]
- J. Zhang, J. Yu, N. Chi, Y. Shao, L. Tao, J. Zhu, Y. Wang, “Stable Optical Frequency-Locked Multicarriers Generation by Double Recirculating Frequency Shifter Loops for Tb/s Communication,” J. Lightwave Technol. 30(24), 3938–3945 (2012). [CrossRef]
- J. Li, Z. Li, “Frequency-locked multicarrier generator based on a complementary frequency shifter with double recirculating frequency-shifting loops,” Opt. Lett. 38(3), 359–361 (2013). [CrossRef] [PubMed]
- J. Li, C. Yu, Z. Li, “Complementary frequency shifter based on polarization modulator used for generation of a high-quality frequency-locked multicarrier,” Opt. Lett. 39(6), 1513–1516 (2014). [CrossRef]
- G. P. Agrawal, Applications of Nonlinear Fiber Optics (Academic Press, 2001), Chap. 4.

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