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Optics Express

Optics Express

  • Editor: Andrew M. Weiner
  • Vol. 21, Iss. 20 — Oct. 7, 2013
  • pp: 23433–23440
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Intermodulation distortion suppression for intensity-modulated analog fiber-optic link incorporating optical carrier band processing

Yan Cui, Yitang Dai, Feifei Yin, Jian Dai, Kun Xu, Jianqiang Li, and Jintong Lin  »View Author Affiliations


Optics Express, Vol. 21, Issue 20, pp. 23433-23440 (2013)
http://dx.doi.org/10.1364/OE.21.023433


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Abstract

An intermodulation distortion suppression method based on the optical carrier band processing is demonstrated. A systematic analysis of the main optical spectrum contributors for the third-order intermodulation distortion in the nonlinear system is presented. Theoretical analysis shows that the third-order intermodulation distortion terms can cancel each other if a proper phase shifting is imposed to the optical carrier band. We experimentally demonstrate the approach with a two-tone test and a suppression of about 33 dB in the third-order intermodulation distortion is obtained. Experimental results show that an overall fundamental to third-order intermodulation distortion ratio of up to 64 dB is achieved and the link dynamic range is improved by 14.7 dB, compared with the conventional link without the proposed optical carrier band processing.

© 2013 OSA

1. Introduction

2. Operation principle

Applying the Bessel functions expression and ignoring the higher order harmonic and intermodulation terms, we can further express the envelope in Eq. (1) by
E(t)=Ecejωct[sin(φ2)(Jo2(m2)±2J12(m2)cos(ω1±ω2)t+2Jo(m2)J2(m2)cos2ω1,2t+...)cos(φ2)(2Jo(m2)J1(m2)sinω1,2t±2J1(m2)J2(m2)sin(2ω1,2±ω2,1)t+...)].
(2)
wherem=πVRF/Vπ is the modulation depth of the MZM.Jn(x) donates the nth order Bessel function of the first kind.

The output optical field of the MZM is shown in Fig. 1(a)
Fig. 1 (a) The optical spectrum after the MZM ; (b) Detected RF spectrum in system without OCB processing; (c) Detected RF spectrum in system with the proposed OCB processing.
, including the OCB, the 1st order optical upper/lower sideband (1-USB/1-LSB) and the 2nd order upper/lower sideband (2-USB/2-LSB). The higher optical sidebands are not shown in Fig. 1 as they are with negligible amplitude due to the small signal input. The OCB is composed of the optical carrier and the even-order nonlinear components. The 1-USB/1-LSB contains the fundamental and odd-order distortion components, while the 2-USB/2-LSB is composed of the even-order nonlinear components. The double-headed arrows in Fig. 1(a) mark the three main optical spectrum contributors to the IMD3 components. The output optical signal is then distributed to the photo-detector (PD) for the square law detection. The optical carrier and its sidebands are mixed, and the beating products of the fundamental and IMD3 components are shown in Fig. 1(b). There are three pairs of the main contributors for the IMD3. The beating of the optical carrier ωc and ωc + 2ω1,22,1c-2ω1,2 + ω2,1) generates IMD3 with detected photocurrent donates as I01’. The IMD3 induced by the 1-USB/1-LSB of ωc + ω1,2c1,2) and 2nd sideband of ωc + 2ω2,1c-2ω2,1) is represented by I12. I0’1 is the photocurrent coefficient generated by the beating of the spectrum at the angle frequency of ωc + ω2,11,2c2,1 + ω1,2) and ωc + ω1,2c1,2). The sum of all the beating products of the aforementioned optical spectrum contributors builds the amplitude of the detected RF components.

When the signal expressed in Eq. (2) is sent to a square law PD for detection, the generated photo-current containing the fundamental and IMD3 components can be mathematically given as
I(t)=2Posin(φ)Jo(m2)J1(m2)sin(ω1,2t)2Posin(φ)(J1(m2)J2(m2)¯+J1(m2)J2(m2)¯+J13(m2)¯)sin[(2ω1,2ω2,1)t].I01'I12I0'1
(3)
where is the responsivity of the PD, Po = Eo2 is used to represent the received optical power. By adopting small signal approximation, we can derive that I01’ = I12 = 2I0’1.

As has been analyzed above, the induced IMD3s are all with the same sign and are constructively combined at the PD. By properly shifting the phase of the OCB by θ, the envelop of optical filed at the output of the MZM can then be given as

E(t)=Ecejωct[sin(φ2)(ejθ(Jo2(m2)-2J12(m2)cos(ω1-ω2)t)+2Jo(m2)J2(m2)cos2ω1,2t+...)+cos(φ2)(2Jo(m2)J1(m2)sin(ω1,2t)±2J1(m2)J2(m2)sin(2ω1,2±ω2,1)t+...)].
(4)

By taking the phase shifting of the OCB into consideration, we can mathematically evaluated the detected photocurrent including the fundamental and IMD3 components as

I'(t)=2Pocos(θ)sin(φ)Jo(m2)J1(m2)sin(ω1,2t)2Posin(φ)(cosθI01'+I12+cosθI0'1)sin[(2ω1,2ω2,1)t].
(5)

When square law detection is implemented, the phase shift of OCB can be mapped directly to the generated RF signals. It is obvious that the detected IMD3 can be completely suppressed in theory if the introduced phase shift meets the following expression

cosθ=I12I01'+I0'10.33.
(6)

3. Experiment

The OCB processor used in this paper is a waveshaper (Finisar 4000s) that can be considered as a filter bank which can finely and independently processing the different photonic spectrum bands. By properly setting the processing filter bandwidth and the respective band information of the waveshaper, both the phase and the amplitude of the spectral components in the respective band can be assigned with the desired value independently. A band-pass filter, whose center frequency is set to be in accordance with the optical carrier, is assigned with a 3-dB bandwidth of 18 GHz and is used to process the OCB in the proposed approach. The phase of the OCB is shifted by approximately acos(−0.33) as has been analyzed in the second part, while the amplitude and phase of the 1-SB and 2-SB are leaving unchanged. The managed optical spectrum is then imposed to the following PD (EM4, EM169-03), at which square law detection is implemented. The electrical output is analyzed by the following electrical signal analyzer (ESA, Agilent N9030A).

4. Conclusion

Acknowledgments

This work was supported in part by 973 Program (2012CB315705), National 863 Program (2011AA010306), NSFC Program (61271042, 61107058 and 61120106001), the Fundamental Research Funds for the Central Universities, and the Fund of State Key Laboratory of Information Photonics and Optical Communications.

References and links

1.

C. Cox, E. Ackerman, G. Betts, and J. Prince, “Limits on the performance of RF-over-fiber links and their impact on device design,” IEEE Trans. Microw. Theory Tech. 54(2), 906–920 (2006). [CrossRef]

2.

J. Yao, “Microwave photonics,” J. Lightwave Technol. 27(3), 314–335 (2009). [CrossRef]

3.

V. Urick, “Long-haul analog links tutorial,” in Optical Fiber Communication (OFC), collocated National Fiber Optic Engineers Conference, 2010 Conference on OFC/NFOEC (San Diego, Calif., USA, 2010), pp. 1–39.

4.

B. Masella, B. Hraimel, and X. Zhang, “Enhanced spurious-free dynamic range using mixed polarization in optical single sideband Mach–Zehnder modulator,” J. Lightwave Technol. 27(15), 3034–3041 (2009). [CrossRef]

5.

V. Urick, M. Rogge, P. Knapp, L. Swingen, and F. Bucholtz, “Wide-band predistortion linearization for externally modulated long-haul analog fiber-optic links,” IEEE Trans. Microw. Theory Tech. 54(4), 1458–1463 (2006). [CrossRef]

6.

T. Ismail, C. Liu, J. Mitchell, and A. Seeds, “High-dynamic-range wireless-over-fiber link using feedforward linearization,” J. Lightwave Technol. 25(11), 3274–3282 (2007). [CrossRef]

7.

J. Dai, K. Xu, R. Duan, Y. Cui, J. Wu, and J. Lin, “Optical linearization for intensity-modulated analog links employing equivalent incoherent combination technique,” in Proceedings of International Topical Meeting on Microwave Photonics, (Singapore, 2011), pp. 230–233. [CrossRef]

8.

A. Karim and J. Devenport, “High dynamic range microwave photonic links for RF signal transport and RF-IF conversion,” J. Lightwave Technol. 26(15), 2718–2724 (2008). [CrossRef]

9.

S. Li, X. Zheng, H. Zhang, and B. Zhou, “Highly linear radio-over-fiber system incorporating a single-drive dual parallel Mach-Zehnder modulator,” IEEE Photon. Technol. Lett. 22(24), 1775–1777 (2010). [CrossRef]

10.

S. K. Kim, W. Liu, Q. Pei, L. R. Dalton, and H. R. Fetterman, “Nonlinear intermodulation distortion suppression in coherent analog fiber optic link using electro-optic polymeric dual parallel Mach-Zehnder modulator,” Opt. Express 19(8), 7865–7871 (2011). [CrossRef] [PubMed]

11.

C. Lim, A. T. Nirmalathas, K. L. Lee, D. Novak, and R. Waterhouse, “Intermodulation distortion improvement for fiber–radio applications incorporating OSSB+C modulation in an optical integrated-access environment,” J. Lightwave Technol. 25(6), 1602–1612 (2007). [CrossRef]

12.

M. H. Huang, J. B. Fu, and S. L. Pan, “Linearized analog photonic links based on a dual-parallel polarization modulator,” Opt. Lett. 37(11), 1823–1825 (2012). [CrossRef] [PubMed]

13.

G. Zhu, W. Liu, and H. R. Fetterman, “A broadband linearized coherent analog fiber-optic link employing dual parallel Mach–Zehnder modulators,” IEEE Photon. Technol. Lett. 21(21), 1627–1629 (2009). [CrossRef]

14.

G. Zhang, S. Li, X. Zheng, H. Zhang, B. K. Zhou, and P. Xiang, “Dynamic range improvement strategy for Mach-Zehnder modulators in microwave/millimeterwave ROF links,” Opt. Express 20(15), 17214–17219 (2012). [CrossRef]

15.

L. Xu, H. Miao, and A. M. Weiner, “All-order polarization-mode-dispersion (PMD) compensation at 40 Gb/s via hyperfine resolution optical pulse shaping,” IEEE Photon. Technol. Lett. 22(15), 1078–1080 (2010). [CrossRef]

OCIS Codes
(060.0060) Fiber optics and optical communications : Fiber optics and optical communications
(060.5625) Fiber optics and optical communications : Radio frequency photonics

ToC Category:
Fiber Optics and Optical Communications

History
Original Manuscript: August 5, 2013
Revised Manuscript: September 17, 2013
Manuscript Accepted: September 17, 2013
Published: September 25, 2013

Citation
Yan Cui, Yitang Dai, Feifei Yin, Jian Dai, Kun Xu, Jianqiang Li, and Jintong Lin, "Intermodulation distortion suppression for intensity-modulated analog fiber-optic link incorporating optical carrier band processing," Opt. Express 21, 23433-23440 (2013)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-21-20-23433


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References

  1. C. Cox, E. Ackerman, G. Betts, and J. Prince, “Limits on the performance of RF-over-fiber links and their impact on device design,” IEEE Trans. Microw. Theory Tech.54(2), 906–920 (2006). [CrossRef]
  2. J. Yao, “Microwave photonics,” J. Lightwave Technol.27(3), 314–335 (2009). [CrossRef]
  3. V. Urick, “Long-haul analog links tutorial,” in Optical Fiber Communication (OFC), collocated National Fiber Optic Engineers Conference, 2010 Conference on OFC/NFOEC (San Diego, Calif., USA, 2010), pp. 1–39.
  4. B. Masella, B. Hraimel, and X. Zhang, “Enhanced spurious-free dynamic range using mixed polarization in optical single sideband Mach–Zehnder modulator,” J. Lightwave Technol.27(15), 3034–3041 (2009). [CrossRef]
  5. V. Urick, M. Rogge, P. Knapp, L. Swingen, and F. Bucholtz, “Wide-band predistortion linearization for externally modulated long-haul analog fiber-optic links,” IEEE Trans. Microw. Theory Tech.54(4), 1458–1463 (2006). [CrossRef]
  6. T. Ismail, C. Liu, J. Mitchell, and A. Seeds, “High-dynamic-range wireless-over-fiber link using feedforward linearization,” J. Lightwave Technol.25(11), 3274–3282 (2007). [CrossRef]
  7. J. Dai, K. Xu, R. Duan, Y. Cui, J. Wu, and J. Lin, “Optical linearization for intensity-modulated analog links employing equivalent incoherent combination technique,” in Proceedings of International Topical Meeting on Microwave Photonics, (Singapore, 2011), pp. 230–233. [CrossRef]
  8. A. Karim and J. Devenport, “High dynamic range microwave photonic links for RF signal transport and RF-IF conversion,” J. Lightwave Technol.26(15), 2718–2724 (2008). [CrossRef]
  9. S. Li, X. Zheng, H. Zhang, and B. Zhou, “Highly linear radio-over-fiber system incorporating a single-drive dual parallel Mach-Zehnder modulator,” IEEE Photon. Technol. Lett.22(24), 1775–1777 (2010). [CrossRef]
  10. S. K. Kim, W. Liu, Q. Pei, L. R. Dalton, and H. R. Fetterman, “Nonlinear intermodulation distortion suppression in coherent analog fiber optic link using electro-optic polymeric dual parallel Mach-Zehnder modulator,” Opt. Express19(8), 7865–7871 (2011). [CrossRef] [PubMed]
  11. C. Lim, A. T. Nirmalathas, K. L. Lee, D. Novak, and R. Waterhouse, “Intermodulation distortion improvement for fiber–radio applications incorporating OSSB+C modulation in an optical integrated-access environment,” J. Lightwave Technol.25(6), 1602–1612 (2007). [CrossRef]
  12. M. H. Huang, J. B. Fu, and S. L. Pan, “Linearized analog photonic links based on a dual-parallel polarization modulator,” Opt. Lett.37(11), 1823–1825 (2012). [CrossRef] [PubMed]
  13. G. Zhu, W. Liu, and H. R. Fetterman, “A broadband linearized coherent analog fiber-optic link employing dual parallel Mach–Zehnder modulators,” IEEE Photon. Technol. Lett.21(21), 1627–1629 (2009). [CrossRef]
  14. G. Zhang, S. Li, X. Zheng, H. Zhang, B. K. Zhou, and P. Xiang, “Dynamic range improvement strategy for Mach-Zehnder modulators in microwave/millimeterwave ROF links,” Opt. Express20(15), 17214–17219 (2012). [CrossRef]
  15. L. Xu, H. Miao, and A. M. Weiner, “All-order polarization-mode-dispersion (PMD) compensation at 40 Gb/s via hyperfine resolution optical pulse shaping,” IEEE Photon. Technol. Lett.22(15), 1078–1080 (2010). [CrossRef]

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