Experimental Results and Discussions

5.3 Experimental Results and Discussions

The optical power ratio (OPR) of the optical subcarrier to the optical OFDM-modulated subcarrier strongly influences the performance of the optical OFDM signals [4]. One of the advantages of the proposed OFDM transmitter is that the relative intensity between optical subcarrier and OFDM-modulated subcarrier can be easily tuned by adjusting the individual amplitude of the sinusoidal signal and the OFDM signal to optimize the OFDM performance.

Fig. 5-5 illustrates the receiver sensitivity of the OFDM signals versus different OPRs. For OFDM signals without filtering out LSB2, the optimal OPR is 1 dB.

As LSB2 is filtered out, the optimal OPR is 4 dB. As LSB1 is filtered out, the optimal OPR is -3 dB. Fig. 5-6(a) shows the optical spectrum without filtering.

Fig. 5-6(b) and Fig. 5-6(c) show the optical spectrum with filter out LSB2 and LSB1, respectively. At the Base station, the LSB2 subcarrier is filtered out for the upstream data link and the rest of the signal is sent to local users. After fiber bragg grating, the optical spectrum is shown in Fig. 5-6(d). The optical carrier to noise ratio for wavelength reuse is 20dB. And then the LSB2 provides wavelength reuse for uplink via RSOA. After RSOA, the optical spectrum is shown in Fig. 5-6(e). The optical reuse signal to noise ratio is 15dB. Fig. 5-7(a) shows the electrical spectrum after AWG. This driving RF OFDM signal includes vector signal combined with a sinusoidal signal shown in Fig. 5-7(b).

Fig. 5-7(c) shows the electrical spectrum after photo receiver. In order to demodulator the RF OFDM signal, the signal is down-converted to 3.7GHz by a mixer, as shown in Fig. 5-7(d). Fig. 5-8 shows OFDM constellation diagrams before and after the one-tap equalizer in back-to-back (BTB)

and following 25-km SMF transmission cases. After equalizer, a clear constellation can be achieved. Fig. 5-8(a)(b)(c) shows the constellation diagrams without optical filtering. Fig. 5-8(d)(e)(f) and Fig. 5-8(g)(h)(i) show the constellation diagrams with filter out LSB2 and LSB1, respectively. After filtering out LSB2 or LSB1, the generated OFDM signals do not suffer RF periodic fading issue due to fiber dispersion.

Only in-band distortion of the OFDM-encoded subcarrier caused by fiber dispersion is considered. Since the symbol rate of each subcarrier is only 39.0625 MSym/s, the fiber chromatic penalty can be ignored. Fig. 5-9 shows the BER curves of the downstream 5-Gb/s 16-QAM OFDM signal using optimal OPRs and the upstream 1.25-Gb/s OOK signal after transmission over 25 km SMF. For optical downstream signal, when any optical subcarrier is filter out the sensitivity penalties are negligible. If the optical signal without filtering the sensitivity penalties is 0.5dB. We also measure the BER curves of uplink 1.25-Gb/s OOK signal. After transmission over 25 km SMF, the sensitivity penalty is 0.5 dB. And the eye diagrame little change for BTB and after transmission over 25km SMF is shown in inset (i)(ii).

-8 -6 -4 -2 0 2 4 6 8 Filter out LSB2 Filter out LSB1

  Figure 5-5 BER versus different OPRs.

  Figure 5-6 Optical spectra of RF signals.

3.0 3.5 4.0 4.5 Figure 5-7 Electrical spectra of OFDM signals.

(g) (h) (i)

(d) (e) (f)

(a) (b) (c)

  Figure 5-8 Constellations of OFDM signal

-24 -22 -20 -18 -16 -14 -12 -10 -8 11

10 9 8 7 6 5 4 3

-Log (BER)

Power (dBm)

W/O filter, BTB W/O filter, 25km Filter out LSB2 BTB Filter out LSB2, 25km Filter out LSB1 BTB Filter out LSB1, 25km RSOA, BTB

RSOA, 25km

200ps/div, 200mV/div

(i) (ii)

BTB

25km

  Figure 5-9 BER curves of the downstream and the upstream signal.

Chapter 6 Conclusion

This work presents a new modulation approach to generate optical vector signals by frequency multiplication based on a DSBCS scheme. Compared with conventional DSBCS modulation using MZM which can support vector signals, the proposed modulation using single-electrode MZM needs lower bandwidth requirement and also support vector signal.

First, we provide the theoretical calculations, including optical nonlinear distortion, electrical nonlinear distortion and optical power ratio. When the modulation index increased, optical and electrical nonlinear distortion of the results is become worse. When the optical signal without filtering, the optimal optical power ratio is 0dB. When the optical signal filters out LSB1 and LSB2 the optimal power ratio is 3dB and -3dB, respectively. Second, we experimental demonstrate three different modulation formats of 1.25-Gb/s OOK, 1.25-Gb/s BPSK and 625-MSym/s QPSK signals are adopted to determine the system performance. For RF signal generation without filtering out any subcarrier, the optimal SOPR of both BPSK and OOK RF signals is 0 dB. When LSB2 is filtered out, the optimal SOPR of both BPSK and OOK RF signals is 3 dB. When LSB1 is filtered out, the optimal SOPR is shifted to -3 dB. After transmission over 50 km SMF, the power penalty of all three modulation formats is less than 0.2 dB. QPSK format has twice the spectral efficiency and approximately 2-dB better receiving sensitivity than the OOK format. Final, we apply this system to transmit OFDM signal. ROF systems supporting OFDM signals that have been widely utilized in RF-wireless communication are of utmost importance to extent transmission distance over

fiber and air links. The data rate of 16-QAM OFDM signal is 5-Gb/s and the center frequency is about 3.7Ghz and the sinusoidal signal frequency is 16.3GHz. For the downstream OFDM signal after transmission over 25km SMF, the sensitivity penalty is less than 0.1 dB. We also demonstrate wavelength reuse via reflective semiconductor optical amplifier for 1.25-Gb/s OOK signal upstream data link. After transmission over 25 km SMF, the sensitivity penalty is 0.5 dB.

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Publications

International journals (SCI journal paper)

1. P. C. Peng, C. T. Lin, W. J. Jiang, J. Chen, F. M. Wu, P. T. Shih, and S.

Chi, “Improvement of Transmission in Fiber Wireless System Using Semiconductor Laser Amplifier,” IEE Electronics Letters, vol. 44, no. 4, pp. 298-299, Feb 2008.

2. C. T. Lin, P. T. Shih, J. Chen, P. C. Peng, S. P. Dai, W. J. Jiang, W. Q.

Xue, and S. Chi, “Cost-Effective Multi-Services Hybrid Access Networks with no Optical Filter at Remote Nodes,” IEEE Photonics Technology Letters, vol. 20, issue 10, pp. 812-814, May 15, 2008.

3. P. C. Peng, F. M. Wu, C. T. Lin, J. H. Chen, W. C. Kao, P. T. Shih, W. J.

Jiang, H. C. Kuo, and S. Chi, “40 GHz Phase Shifter based on Semiconductor Laser,” Accepted by IEE Electronics Letters.

4. Chun-Ting Lin, Wen-Jr Jiang, Jason (Jyehong) Chen, Peng-Chun Peng, Er-Zih Wong, and Sien Chi, “Novel Optical Vector Signal Generation with Carrier Suppression and Frequency Multiplication Based on Single-Electrode Mach-Zehnder Modulator,” Accepted by IEEE Photonics Technology Letters.

International conferences papers

1. Chun-Ting Lin, Wen- Jr Jiang, Jason(Jyehong) Chen, Er-Zih Wong, Sheng-Peng Dai, Yu-Min Lin, Po Tsung Shih, Peng-Chun Peng, and Sien Chi,“Experimental Demonstration of Optical 5-Gb/s 16-QAM OFDM Signal Generation and Wavelength Reuse for 1.25-Gbit/s Uplink Signal”

34nd European Conference and Exhibition on Optical Communication Conference (ECOC 2008), Mo.3.E.1, Brussels, Belgium, September 21-25, 2008.

2. Chun-Ting Lin, Sheng-Peng Dai, Wen- Jr Jiang, Jason(Jyehong) Chen, Yu-Min Lin, Po Tsung Shih, Peng-Chun Peng, and Sien Chi,

“Experimental Demonstration of Optical Colorless Direct-Detection OFDM Signals with 16- and 64-QAM Formats beyond 15 Gb/s” 34nd European Conference and Exhibition on Optical Communication Conference (ECOC 2008), We.1.F.3, Brussels, Belgium, September 21-25, 2008.

3. P. C. Peng, F. M. Wu, W. J. Jiang, C. T. Lin, J. H. Chen, P. T. Shih, W. C.

Kao, S.Chi, “Slow Light in Distributed Feedback Laser for All-Optical Inverter” 2008 OSA Slow and Fast Light Topical Meeting (SL 2008), JMB29, Boston, Massachusetts, July 13-16, 2008.

4. C. T. Lin, W. J. Jiang, E. Z. Wong, J. Chen, P. T. Shih, P. C. Peng, and S.

Chi, “Optical Vector Signal Generation Using Double Sideband with Carrier Suppression and Frequency Multiplication,” IEEE/OSA Conference on Lasers and Electro-Optics (CLEO/QELS 2008), CThR5, San Jose, California, May 4-9, 2008.

5. P. C. Peng, F. M. Wu, C. T. Lin, J. Chen, P. T. Shih, W. C. Kao, W. J.

Jiang, H. C. Kuo, and S. Chi, “Tunable Slow Light in Quantum Well Vertical-Cavity Surface-Emitting Laser at 40 GHz,” IEEE/OSA Conference on Lasers and Electro-Optics (CLEO/QELS 2008), JThA2, San Jose, California, May 4-9, 2008.

6. P. C. Peng, C. T. Lin, W. J. Jiang, J. Chen, P. T. Shih, F. M. Wu, and S.

Chi, “Transmission Improvement in Fiber Radio Links Using Semiconductor Laser,” 2008 Optical Fiber Communication Conference (OFC 2008), JThA68, San Diego, California, Feb. 24-28, 2008.

Local conference papers

1. Wen-Jr Jiang, Peng-Chun Peng, Chun-Ting Lin, Jason (Jyehong) Chen, Po Tsung Shih,Fang-Ming Wu, Sien Chi, “PERFORMANCE IMPROVEMENT IN RADIO-OVER-FIBER SYSTEM BY USING SEMICONDUCTOR LASER AMPLIFER,” BO-043, presented at OPT2007 (Optics and Photonics Taiwan), Nov. 30-Dec.1, 2007, Taichung, Taiwan.

2. Ching-Wei Chen, Wen-Jr Jiang and Ci-Ling Pan, “Phase Retrieval Of Ultrafast Optical Pulses From Interferometric Autocorrelation Measurement By Population-Split Genetic Algorithm (PSGA) ,”

C-FR-V2-7, presented at OPT2005 (Optics and Photonics Taiwan), Dec.

9-10, 2005, Tainan, Taiwan.(2005 年光電科技研討會學生論文獎)

3. Wen-Jr Jiang, Ching-Wei Chen , and Ci-Ling Pan, “Pulse Reconstruction From Frequency-Resolved Optical Gating Measurement By Use Of Population-Split Genetic Algorithm (PSGA),” PC-FR2-05, presented at OPT2005 (Optics and Photonics Taiwan), Dec. 9-10, 2005, Tainan, Taiwan.

Patents

1. “一種光調變系統(An Optical Modulation System) ,” 台灣與美國專利申 請中