## Simultaneous transmission of 20x2 WDM/SCM-QKD and 4 bidirectional classical channels over a PON |

Optics Express, Vol. 20, Issue 15, pp. 16358-16365 (2012)

http://dx.doi.org/10.1364/OE.20.016358

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### Abstract

We report the transmission of 40 quantum-key channels using WDM/SCM-QKD technology and 4 bidirectional classical channels over a PON. To our knowledge the highest number of quantum key channels simultaneously transmitted that has ever been reported. The quantum signal coexists with classical reference channel which is employed to process the qbits, but it has enough low power to avoid Raman crosstalk and achieving a high number of WDM-QKD channels. The experimental results allow us to determine the minimum rejection ratio required by the filtering devices employed to select each quantum channel and maximize the quantum key rate. These results open the path towards high-count QKD channel transmission over optical fiber infrastructures.

© 2012 OSA

## 1. Introduction

**ti**onal assumptions [1

1. N. Gisin, G. Ribordy, W. Tittel, and H. Zbinden, “Quantum criptography,” Rev. Mod. Phys. **74**(1), 145–195 (2002). [CrossRef]

2. V. Scarani, H. Bechmann-Pasquinucci, N. J. Cerf, M. Dušek, N. Lütkenhaus, and M. Peev, “The security of practical quantum key distribution,” Rev. Mod. Phys. **81**(3), 1301–1350 (2009). [CrossRef]

3. J. Capmany and D. Novak, “Microwave photonics combines two worlds,” Nat. Photonics **1**(6), 319–330 (2007). [CrossRef]

4. J. Chen, G. Wu, L. Xu, X. Gu, E. Wu, and H. Zeng, “Stable quantum key distribution with active polarization control based on time-division multiplexing,” New J. Phys. **11**(6), 065004 (2009). [CrossRef]

5. K. Yoshino, M. Fujiwara, A. Tanaka, S. Takahashi, Y. Nambu, A. Tomita, S. Miki, T. Yamashita, Z. Wang, M. Sasaki, and A. Tajima, “A high-speed wavelength-division multiplexing quantum key distribution system,” Opt. Lett. **37**(2), 223–225 (2012). [CrossRef]

6. J. Mora, A. Ruiz-Alba, W. Amaya, A. Martínez, V. García-Muñoz, D. Calvo, and J. Capmany, “Experimental demonstration of subcarrier multiplexed quantum key distribution system,” Opt. Lett. **37**(11), 2031–2033 (2012). [CrossRef] [PubMed]

7. P. Townsend, “Simultaneous quantum cryptographic key distribution and conventional data transmission over installed fibre using wavelength-division multiplexing,” Electron. Lett. **33**(3), 188–190 (1997). [CrossRef]

8. A. Tanaka, M. Fujiwara, K. Yoshino, S. Takahashi, Y. Nambu, A. Tomita, S. Miki, T. Yamashita, Z. Wang, M. Sasaki, and A. Tajima, “A scalable full quantum key distribution system based on colourless interferometric technique and hardware key distillation,” in Proc. 37th European Conference on Optical Communication, paper Mo.1.B.3, 1–3 (2011).

9. I. Choi, R. J. Young, and P. D. Townsend, “Quantum key distribution on a 10Gb/s WDM-PON,” Opt. Express **18**(9), 9600–9612 (2010). [CrossRef] [PubMed]

5. K. Yoshino, M. Fujiwara, A. Tanaka, S. Takahashi, Y. Nambu, A. Tomita, S. Miki, T. Yamashita, Z. Wang, M. Sasaki, and A. Tajima, “A high-speed wavelength-division multiplexing quantum key distribution system,” Opt. Lett. **37**(2), 223–225 (2012). [CrossRef]

6. J. Mora, A. Ruiz-Alba, W. Amaya, A. Martínez, V. García-Muñoz, D. Calvo, and J. Capmany, “Experimental demonstration of subcarrier multiplexed quantum key distribution system,” Opt. Lett. **37**(11), 2031–2033 (2012). [CrossRef] [PubMed]

## 2. Description of the hybrid DWDM quantum and classical transmission

10. B. Ortega, J. Mora, G. Puerto, and J. Capmany, “Symmetric reconfigurable capacity assignment in a bidirectional DWDM access network,” Opt. Express **15**(25), 16781–16786 (2007). [CrossRef] [PubMed]

## 3. Experimental setup

6. J. Mora, A. Ruiz-Alba, W. Amaya, A. Martínez, V. García-Muñoz, D. Calvo, and J. Capmany, “Experimental demonstration of subcarrier multiplexed quantum key distribution system,” Opt. Lett. **37**(11), 2031–2033 (2012). [CrossRef] [PubMed]

**37**(11), 2031–2033 (2012). [CrossRef] [PubMed]

_{o}which is externally modulated by using an Amplitude Modulator (AM) which is fed employing independent electrical subcarriers. For parallel key distribution, each subcarrier transmits a different key which is generated by a voltage controlled oscillator (VCO) randomly phase-modulated among four possible values 0, π and π/2, 3π/2 which form a pair of conjugate bases required to implement the BB84 protocol. In our experimental setup, two subcarriers are considered coming from VCOs of frequencies f

_{1}= 10 and f

*= 15 GHz. To encode the binary secret key in each subcarrier, Alice introduces a random and independent phase shift Φ*

_{2}_{1A}and Φ

_{2A}for each subcarrier. The amplitude modulation generates different optical sidebands corresponding to each electrical subcarrier. Each one corresponds in the time domain to a faint pulse with a given average photon number, μ. In this way, the SCM-QKD system is a scheme which encodes the bits by means of the optical sidebands generated in the modulation. As example, Fig. 2(a) shows the probability distribution for a scenario where Alice transmits 2 keys in parallel. In this case, 2 lower and 2 upper sidebands appear around the optical carrier ω

_{o}which are named LSB and USB, respectively. The receiver (Bob) has a similar configuration as transmitter (Alice) but in this case the optical signal after propagating through the fiber link is modulated by means of a Phase Modulator (PM). Bob selects the basis for each subcarrier to realize the measurement of the transmitted qubit by synchronously inserting independent random phase shifts Φ1B and Φ2B (now randomly phase-modulated among values 0 and π/2). After filtering, the photon detection was realized by placing a Single Photon Avalanche Detector (SPAD) for each optical sideband. The SPADs worked with a detection gate width of 2.5 ns, an efficiency

*ρ*close to 10% and the dark count probability was 1.2x10

^{−5}.

_{1}and f

_{2}, respectively.

14. Z. L. Yuan, B. E. Kardynal, A. W. Sharpe, and A. J. Shields, “High speed single photon detection in the near infrared,” Appl. Phys. Lett. **91**(4), 041114 (2007). [CrossRef]

## 4. Conclusion

## Acknowledgments

## References and links

1. | N. Gisin, G. Ribordy, W. Tittel, and H. Zbinden, “Quantum criptography,” Rev. Mod. Phys. |

2. | V. Scarani, H. Bechmann-Pasquinucci, N. J. Cerf, M. Dušek, N. Lütkenhaus, and M. Peev, “The security of practical quantum key distribution,” Rev. Mod. Phys. |

3. | J. Capmany and D. Novak, “Microwave photonics combines two worlds,” Nat. Photonics |

4. | J. Chen, G. Wu, L. Xu, X. Gu, E. Wu, and H. Zeng, “Stable quantum key distribution with active polarization control based on time-division multiplexing,” New J. Phys. |

5. | K. Yoshino, M. Fujiwara, A. Tanaka, S. Takahashi, Y. Nambu, A. Tomita, S. Miki, T. Yamashita, Z. Wang, M. Sasaki, and A. Tajima, “A high-speed wavelength-division multiplexing quantum key distribution system,” Opt. Lett. |

6. | J. Mora, A. Ruiz-Alba, W. Amaya, A. Martínez, V. García-Muñoz, D. Calvo, and J. Capmany, “Experimental demonstration of subcarrier multiplexed quantum key distribution system,” Opt. Lett. |

7. | P. Townsend, “Simultaneous quantum cryptographic key distribution and conventional data transmission over installed fibre using wavelength-division multiplexing,” Electron. Lett. |

8. | A. Tanaka, M. Fujiwara, K. Yoshino, S. Takahashi, Y. Nambu, A. Tomita, S. Miki, T. Yamashita, Z. Wang, M. Sasaki, and A. Tajima, “A scalable full quantum key distribution system based on colourless interferometric technique and hardware key distillation,” in Proc. 37th European Conference on Optical Communication, paper Mo.1.B.3, 1–3 (2011). |

9. | I. Choi, R. J. Young, and P. D. Townsend, “Quantum key distribution on a 10Gb/s WDM-PON,” Opt. Express |

10. | B. Ortega, J. Mora, G. Puerto, and J. Capmany, “Symmetric reconfigurable capacity assignment in a bidirectional DWDM access network,” Opt. Express |

11. | J. Mora, A. Ruiz-Alba, W. Amaya, V. Garcia-Muñoz, A. Martínez, and J. Capmany, “Microwave photonic filtering scheme for BB84 subcarrier multiplexed quantum key distribution,” in IEEE Topical Meeting on Microwave Photonics, pp. 286–289 (2007). |

12. | O. Guerreau, F. J. Malassenet, S. W. McLaughlin, and J. M. Merolla, “Quantum key distribution without a single-photon source using a strong reference,” IEEE Photon. Technol. Lett. |

13. | J. Capmany and C. R. Fernandez-Pousa, “Impact of third-order intermodulation on the performance of subcarrier multiplexed quantum key distribution,” J. Lightwave Technol. |

14. | Z. L. Yuan, B. E. Kardynal, A. W. Sharpe, and A. J. Shields, “High speed single photon detection in the near infrared,” Appl. Phys. Lett. |

**OCIS Codes**

(060.4230) Fiber optics and optical communications : Multiplexing

(270.5568) Quantum optics : Quantum cryptography

**ToC Category:**

Fiber Optics and Optical Communications

**History**

Original Manuscript: May 1, 2012

Revised Manuscript: June 13, 2012

Manuscript Accepted: June 25, 2012

Published: July 3, 2012

**Citation**

J. Mora, W. Amaya, A. Ruiz-Alba, A. Martinez, D. Calvo, V. García Muñoz, and J. Capmany, "Simultaneous transmission of 20x2 WDM/SCM-QKD and 4 bidirectional classical channels over a PON," Opt. Express **20**, 16358-16365 (2012)

http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-20-15-16358

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### References

- N. Gisin, G. Ribordy, W. Tittel, and H. Zbinden, “Quantum criptography,” Rev. Mod. Phys. 74(1), 145–195 (2002). [CrossRef]
- V. Scarani, H. Bechmann-Pasquinucci, N. J. Cerf, M. Dušek, N. Lütkenhaus, and M. Peev, “The security of practical quantum key distribution,” Rev. Mod. Phys. 81(3), 1301–1350 (2009). [CrossRef]
- J. Capmany and D. Novak, “Microwave photonics combines two worlds,” Nat. Photonics 1(6), 319–330 (2007). [CrossRef]
- J. Chen, G. Wu, L. Xu, X. Gu, E. Wu, and H. Zeng, “Stable quantum key distribution with active polarization control based on time-division multiplexing,” New J. Phys. 11(6), 065004 (2009). [CrossRef]
- K. Yoshino, M. Fujiwara, A. Tanaka, S. Takahashi, Y. Nambu, A. Tomita, S. Miki, T. Yamashita, Z. Wang, M. Sasaki, and A. Tajima, “A high-speed wavelength-division multiplexing quantum key distribution system,” Opt. Lett. 37(2), 223–225 (2012). [CrossRef]
- J. Mora, A. Ruiz-Alba, W. Amaya, A. Martínez, V. García-Muñoz, D. Calvo, and J. Capmany, “Experimental demonstration of subcarrier multiplexed quantum key distribution system,” Opt. Lett. 37(11), 2031–2033 (2012). [CrossRef] [PubMed]
- P. Townsend, “Simultaneous quantum cryptographic key distribution and conventional data transmission over installed fibre using wavelength-division multiplexing,” Electron. Lett. 33(3), 188–190 (1997). [CrossRef]
- A. Tanaka, M. Fujiwara, K. Yoshino, S. Takahashi, Y. Nambu, A. Tomita, S. Miki, T. Yamashita, Z. Wang, M. Sasaki, and A. Tajima, “A scalable full quantum key distribution system based on colourless interferometric technique and hardware key distillation,” in Proc. 37th European Conference on Optical Communication, paper Mo.1.B.3, 1–3 (2011).
- I. Choi, R. J. Young, and P. D. Townsend, “Quantum key distribution on a 10Gb/s WDM-PON,” Opt. Express 18(9), 9600–9612 (2010). [CrossRef] [PubMed]
- B. Ortega, J. Mora, G. Puerto, and J. Capmany, “Symmetric reconfigurable capacity assignment in a bidirectional DWDM access network,” Opt. Express 15(25), 16781–16786 (2007). [CrossRef] [PubMed]
- J. Mora, A. Ruiz-Alba, W. Amaya, V. Garcia-Muñoz, A. Martínez, and J. Capmany, “Microwave photonic filtering scheme for BB84 subcarrier multiplexed quantum key distribution,” in IEEE Topical Meeting on Microwave Photonics, pp. 286–289 (2007).
- O. Guerreau, F. J. Malassenet, S. W. McLaughlin, and J. M. Merolla, “Quantum key distribution without a single-photon source using a strong reference,” IEEE Photon. Technol. Lett. 17(8), 1755–1757 (2005). [CrossRef]
- J. Capmany and C. R. Fernandez-Pousa, “Impact of third-order intermodulation on the performance of subcarrier multiplexed quantum key distribution,” J. Lightwave Technol. 29(20), 3061–3069 (2011). [CrossRef]
- Z. L. Yuan, B. E. Kardynal, A. W. Sharpe, and A. J. Shields, “High speed single photon detection in the near infrared,” Appl. Phys. Lett. 91(4), 041114 (2007). [CrossRef]

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