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Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 20, Iss. 9 — Apr. 23, 2012
  • pp: 9919–9924
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10m/500Mbps WDM visible light communication systems

Wen-Yi Lin, Chia-Yi Chen, Hai-Han Lu, Ching-Hung Chang, Ying-Pyng Lin, Huang-Chang Lin, and Hsiao-Wen Wu  »View Author Affiliations


Optics Express, Vol. 20, Issue 9, pp. 9919-9924 (2012)
http://dx.doi.org/10.1364/OE.20.009919


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Abstract

A wavelength-division-multiplexing (WDM) visible light communiction (VLC) system employing red and green laser pointer lasers (LPLs) with directly modulating data signals is proposed and experimentally demonstrated. With the assistance of preamplifier and adaptive filter at the receiving sites, low bit error rate (BER) at 10m/500Mbps operation is obtained for each wavelength. The use of preamplifier and adaptive filter offer significant improvements for free-space transmission performance. Improved performance of BER of <10−9, as well as better and clear eye diagram were achieved in our proposed WDM VLC systems. LPL features create a new category of good performance with high-speed data rate, long transmission length (>5m), as well as easy handling and installation. This proposed WDM VLC system reveals a prominent one to present its advancement in simplicity and convenience to be installed.

© 2012 OSA

1. Introduction

2. Experimental setup

3. Experimental results and discussions

A schematic diagram of the preamplifier, in which a push-pull amplifier with bandwidth of 600 MHz, is illustrated in the Fig. 2
Fig. 2 A schematic diagram of the preamplifier (push-pull amplifier).
. Since the even-order harmonic distortions of systems can be eliminated dramatically by the push-pull amplifier, the preamplifier output can be given by
vo=a1vi+a3vi3+a5vi5
(1)
where vo is the preamplifier output voltage, vi is the preamplifier input voltage, and a1, a3, a5 are the amplitude coefficients (a3 and a5 are coefficients characterize nonlinearities). A VLC system with high order nonlinear distortions is expressed as
q=b1m+b3m3+b5m5
(2)
where q is system’s output voltage detected from PIN-PD, m is system’s input voltage, and b1, b3, b5 are the amplitude coefficients (b3 and b5 are coefficients characterize nonlinearities). It is clear that q is equal to vi, substituting Eq. (2) into Eq. (1) and neglecting higher order nonlinear terms, then yields

vo=(a1b1)m+(a1b3+a3b13)m3+(a1b5+a5b15)m5
(3)

While achieving linearity means cancelling out the nonlinear terms, an amplifier would have to cancel out the third-order nonlinear term. Setting the appropriate nonlinear coefficient to eliminate the third-order nonlinear term:

a1b3=a3b13
(4)

Then Eq. (3) can be changed as

vo=(a1b1)m+(a1b5+a5b15)m5
(5)

It is obvious that, from Eq. (5), third-order nonlinear distortion can be eliminated by proper adjusting the nonlinear coefficient. Furthermore, the amplitude of harmonic distortion decreases with the increasing of the harmonic. Thus, the 5th harmonic distortion has a very small amplitude, so it will not induce any distortion in the VLC systems.

A functional block of the adaptive filter is illustrated in the Fig. 3
Fig. 3 A functional block of the adaptive filter, in which including an amplitude/phase comparator.
, in which including an amplitude/phase comparator. In implementing the adaptive filter, first the transmitter send a data pattern with an arbitrary data length as a protocol; and at the receiving site, the adaptive filter has a stored copy of data signal in the adaptive filter before starting communication. The output of the adaptive filter scheme with amplitude and phase without any nonlinear distortion is transmitted. Let d(n) has an amplitude a(n) and phase θ(n):

d(n)=a(n)ejθ(n)
(6)

After transmission through free-space links, the received signal der(n) has a distorted amplitude aer(n) and phase error θer(n):

der(n)=aer(n)ejθer(n)
(7)

The power of a transmitted symbol is P(n), and a received symbol is Pr(n):

P(n)=a2(n)/2
(8)
Pr(n)=ar2(n)/2
(9)

The adaptive filter has to estimate d(n) from der(n) by error feedback. For amplitude compensation, the output of the amplitude compensator is compared with a stored copy of a(n) to create an amplitude error. For phase compensation, the output of the phase compensator is compared with a stored copy of θ(n) to create a phase error. An adaptive algorithm updates amplitude and phase errors every time so that the errors are minimized. Amplitude and phase errors compensation are crucial for ensuring maximum nonlinear distortion suppression, the use of adaptive filter offers significant amplitude and phase errors compensation.

The measured BER curves of red light LPL channel as a function of the free-space transmission distance are plotted in the Fig. 4
Fig. 4 The measured BER curves of red light LPL channel as a function of the free-space transmission distance.
. At a free-space transmission distance of 10 m; without employing the preamplifier and the adaptive filter, the BER is around 10−5; with employing the preamplifier and the adaptive filter, the BER is reached to 10−9. It is clear that as the preamplifier and the adaptive filter are employed simultaneously, large BER performance improvement (104 order) can be achieved. In order to know how much BER performance improvement is based on each scheme, VLC systems employing the preamplifier alone have been used to evaluate the BER performance. At a free-space transmission distance of 10 m, the measured BER is about 10−7. And VLC systems employing the adaptive filter alone have been used to measure the BER value. At a free-space transmission distance of 10 m, the measured BER is also about 10−7. It means that the VLC systems employing the preamplifier alone or the adaptive filter alone to improve the BER performance, the BER performance improvement is limited. The results indicate that the preamplifier and the adaptive filter play important roles for error correction functions, and they can further improve systems’ signal-to-noise ratio and BER performance.

4. Conclusions

We proposed and demonstrated a WDM VLC system using red and green LPLs with directly modulating data signals. With the help of preamplifier and adaptive filter t the receiving sites, low BER of <10−9 at 10m/500Mbps operation is obtained for each wavelength. The use of preamplifier and adaptive filter offer significant improvements for free-space transmission performance. Improved performance of BER of <10−9, as well as better and clear eye diagram were achieved in our proposed WDM VLC systems. Employing LPLs in VLC systems is a promising option, an attractive feature that could accelerate the VLC deployment. This proposed that such a WDM VLC system has been successfully demonstrated, which can inter-operate with free-space lightwave transport applications.

Acknowledgment

The authors would like to thank the financial support from the National Science Council of the Republic of China under Grant NSC 100-2221-E-027-067-MY3.

References and links

1.

D. C. O'Brien, “Visible light communications: challenges and potential,” IEEE Photon. Conf. 365–366 (2011).

2.

B. Bai, Z. Xu, and Y. Fan, “Joint LED dimming and high capacity visible light communication by overlapping PPM,” Wireless and Opt. Commun. Conf. (WOCC), 1–5(2010).

3.

Y. H. Son, S. C. An, H. S. Kim, Y. Y. Won, and S. K. Han, “Visible light wireless transmission based on optical access network using white light-emitting diode and electroabsorption transceiver,” Microw. Opt. Technol. Lett. 52(4), 790–793 (2010). [CrossRef]

4.

S. Okada, T. Yendo, T. Yamazato, T. Fujii, M. Tanimoto, and Y. Kimura, “On-vehicle receiver for distant visible light road-to-vehicle communication,” IEEE Intelligent Vehicles Symposium, 1033–1038 (2009).

5.

H. Le Minh, D. O’Brien, G. Faulkner, L. Zeng, K. Lee, D. Jung, and Y. Oh, “High-speed visible light communications using multiple-resonant equalization,” IEEE Photon. Technol. Lett. 20(14), 1243–1245 (2008). [CrossRef]

6.

T. Komine and M. Nakagawa, “Fundamental analysis for visible-light communication system using LED lights,” IEEE Trans. Consum. Electron. 50(1), 100–107 (2004). [CrossRef]

7.

J. Vucic, C. Kottke, S. Nerreter, A. Buttner, K.-D. Langer, and J. W. Walewski, “White light wireless transmission at 200+ Mb/s net data rate by use of discrete-multitone modulation,” IEEE Photon. Technol. Lett. 21(20), 1511–1513 (2009). [CrossRef]

8.

H. Le Minh, D. O’Brien, G. Faulkner, L. Zeng, K. Lee, D. Jung, Y. Oh, and E. T. Won, “100-Mb/s NRZ visible light communications using a postequalized white LED,” IEEE Photon. Technol. Lett. 21(15), 1063–1065 (2009). [CrossRef]

9.

Y. F. Liu, Y. C. Chang, C. W. Chow, and C. H. Yeh, “Equalization and pre-distorted schemes for increasing data rate in-door visible light communication system,” Conf. on Opt. Fiber Commun. (OFC) JWA83 (2011).

10.

J. Vucic, C. Kottke, S. Nerreter, K.-D. Langer, and J. W. Walewski, “513 Mbit/s visible light communications link based on DMT-modulation of a white LED,” J. Lightwave Technol. 28(24), 3512–3518 (2010).

OCIS Codes
(060.4510) Fiber optics and optical communications : Optical communications
(140.7300) Lasers and laser optics : Visible lasers
(060.2605) Fiber optics and optical communications : Free-space optical communication

ToC Category:
Fiber Optics and Optical Communications

History
Original Manuscript: March 7, 2012
Revised Manuscript: April 2, 2012
Manuscript Accepted: April 3, 2012
Published: April 16, 2012

Citation
Wen-Yi Lin, Chia-Yi Chen, Hai-Han Lu, Ching-Hung Chang, Ying-Pyng Lin, Huang-Chang Lin, and Hsiao-Wen Wu, "10m/500Mbps WDM visible light communication systems," Opt. Express 20, 9919-9924 (2012)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-20-9-9919


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References

  1. D. C. O'Brien, “Visible light communications: challenges and potential,” IEEE Photon. Conf. 365–366 (2011).
  2. B. Bai, Z. Xu, and Y. Fan, “Joint LED dimming and high capacity visible light communication by overlapping PPM,” Wireless and Opt. Commun. Conf. (WOCC), 1–5(2010).
  3. Y. H. Son, S. C. An, H. S. Kim, Y. Y. Won, and S. K. Han, “Visible light wireless transmission based on optical access network using white light-emitting diode and electroabsorption transceiver,” Microw. Opt. Technol. Lett.52(4), 790–793 (2010). [CrossRef]
  4. S. Okada, T. Yendo, T. Yamazato, T. Fujii, M. Tanimoto, and Y. Kimura, “On-vehicle receiver for distant visible light road-to-vehicle communication,” IEEE Intelligent Vehicles Symposium, 1033–1038 (2009).
  5. H. Le Minh, D. O’Brien, G. Faulkner, L. Zeng, K. Lee, D. Jung, and Y. Oh, “High-speed visible light communications using multiple-resonant equalization,” IEEE Photon. Technol. Lett.20(14), 1243–1245 (2008). [CrossRef]
  6. T. Komine and M. Nakagawa, “Fundamental analysis for visible-light communication system using LED lights,” IEEE Trans. Consum. Electron.50(1), 100–107 (2004). [CrossRef]
  7. J. Vucic, C. Kottke, S. Nerreter, A. Buttner, K.-D. Langer, and J. W. Walewski, “White light wireless transmission at 200+ Mb/s net data rate by use of discrete-multitone modulation,” IEEE Photon. Technol. Lett.21(20), 1511–1513 (2009). [CrossRef]
  8. H. Le Minh, D. O’Brien, G. Faulkner, L. Zeng, K. Lee, D. Jung, Y. Oh, and E. T. Won, “100-Mb/s NRZ visible light communications using a postequalized white LED,” IEEE Photon. Technol. Lett.21(15), 1063–1065 (2009). [CrossRef]
  9. Y. F. Liu, Y. C. Chang, C. W. Chow, and C. H. Yeh, “Equalization and pre-distorted schemes for increasing data rate in-door visible light communication system,” Conf. on Opt. Fiber Commun. (OFC) JWA83 (2011).
  10. J. Vucic, C. Kottke, S. Nerreter, K.-D. Langer, and J. W. Walewski, “513 Mbit/s visible light communications link based on DMT-modulation of a white LED,” J. Lightwave Technol.28(24), 3512–3518 (2010).

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