CHAPTER 3 Experiment setup and result (DQPSK)
3.8 Result & discussion (RZ-DQPSK)
3.8.2 Timing misalignment tolerance
At section 3-4 and, 3-7 the timing misalignment tolerance for 33% case is 44ps (convention DQPSK) and 37ps (dual-drive DQPSK), representatively. Why tolerate degree the two differently? We can know to Fig 3-36 as our pulse should cut away the transition period of signal. When transition periods of signal are larger which timing misalignment tolerances are smaller. The Fig 3-37 shows eye diagram of dual-drive NRZ-DQPSK and convention NRZ-DQPSK. We can find the transition period of convention NRZ-DQPSK bigger than dual-drive NRZ-DQPSK so its timing misalignment tolerances better than dual-drive NRZ-DQPSK
The Fig 3-36transition period influences timing misalignment tolerance
(a) convention NRZ-DPQSK (b) dual-drive NRZ-DPQSK
The Fig 3-37 eye diagram of dual-drive NRZ-DQPSK and convention NRZ-DQPSK (emphasize transition period)
Chapter 4
Experiment setup and result (DQPSK payload/ASK label)
4-1.1 Dual-Drive DQPSK/ASK label experiment setup
DQPSK Payload 20 Gb/s Clock
10GHz Label 622 Mb/s
DQPSK Payload/ ASK Label Transmitter
Delay
DQPSK Payload/ ASK Label Receiver EDFA
The Fig 4-1 dual-drive DQPSK/ASK label signal experiment setup
The experimental setup is shown in the Fig 4-1, which mainly contains three part:
payload transmitter, transmission fiber, and payload receiver. The RZ-DQPSK payload/ASK label transmitter consists of continuously oscillating laser at 1546.96nm, two external dual-drive Mach-Zehnder modulators. The first modulator generates a 20Gbit/s NRZ-DQPSK signal. Biased atVπ/ 2, two independent electrical data streams, which is driven by 10Gbit/s (PRBS27− ) NRZ data stream individually. The second 1 Mach-Zehnder modulator is used to impress the label data and perform pulse carving.
First, the sin waves mix the low bit rate label data (the label information at 622Mbit/s
and PRBS27− ) used mixer into Mach-Zehnder modulator before. A tunable optical 1 delay line is inserted in between the two modulators to synchronize the pulse train and the 20Gbit/s data. There is place boot amplifier before the transmission fiber and control appropriate power.
The RZ-DQPSK payload/ASK label consists of pre-amplifier, the optical band pass filter, the electroabsorption modulator (EAM), two integrated Mach-Zehnder delay interferometer (the phase difference in the arms of the Mach-Zehnder delay-interferometer (DI) is now set to +π/ 4 and−π/ 4), the photo detector, and the BER tester. The labeled signal is split using a 3dB optical coupler. The output of one arm is directly detected by photodiode and thus the optical label is converted into the electrical domain. Form the second output of the coupler the label signal is input to another EAM driven by the inverted label data with suitable delay and amplitude for label erasure. The payload is then input to as integrated Mach-Zehnder delay interferometer to demodulate the RZ-DQPSK signal. The advantage of using the EAM for label erasure is its negligible frequency chirp. The length difference between the two arms of the MZDI is corresponding to 100ps delay. The signal at the output of MZDI is detected by photo detector and input to a 10Gbit/s BER test.
4-2 Sensitivity of dual-drive DQPSK/ASK label
The detected RZ-DQPSK eye diagrams without and with label erasure are shown in Fig 4-2(a) and (B), respectively. It should be noted that the receiver sensitivity of the ASK label improves as the ASK extinction is increased, while the sensitivity of the RZ-DQPSK payload deteriorates owing to the reduced signal power when an ASK ‘0’is transmitted. Therefore, in our experiment a compromise value of 4 dB is selected for the
extinction ratio of the ASK label. The Fig 3-26 shows the BER of dual-drive DQPSK payload/ASK label and pure payload. For DQPSK payload that sensitivity is -21.4dBm signal. The ASK label signal that sensitivity is -21dBm. The pure payload (not add label signal) that sensitivity is -26.7dBm.
(a) Eye diagrams for payload without label erasure (b) Eye diagrams for payload with label erasure The Fig 4-2 Eye diagrams of dual-drive DQPSK for payload without and with label erasure
The Fig 4-3 BER of dual-drive DQPSK payload/ASK label and pure payload 20ps/div
4-3 Convention DQPSK/ASK label experiment setup
DQPSK Payload/ ASK Label Transmitter
Delay
DQPSK Payload/ ASK Label Receiver EDFA
The Fig 4-4 convention DQPSK/ASK label signal experiment setup
The experimental setup is shown in the Fig 4-4, which mainly contains three part:
payload transmitter, transmission fiber, and payload receiver. The RZ-DQPSK payload/ASK label transmitter consists of continuously oscillating laser at 1546.96nm, two external dual-drive Mach-Zehnder modulators. The first and second modulator generates a 10Gbit/s NRZ-DPSK signal
{ }
0,π which is driven by 10Gbit/s (PRBS27− ) NRZ data stream individually and phase of the second modulator 1rotate / 2π ,
2 2
π π
⎧ − ⎫
⎨ ⎬
⎩ ⎭. Two DPSK signal combine to become DQPSK signal. The second Mach-Zehnder modulator is used to impress the label data and perform pulse carving. First, the sin waves mix the low bit rate label data (the label information at 622Mbit/s and PRBS27− ) used mixer into Mach-Zehnder modulator before. A 1 tunable optical delay line is inserted in between the two modulators to synchronize the
pulse train and the 20Gbit/s data. There is place boot amplifier before the transmission fiber and control appropriate power.
The RZ-DQPSK payload/ASK label consists of pre-amplifier, the optical band pass filter, the electroabsorption modulator (EAM), two integrated Mach-Zehnder delay interferometer (the phase difference in the arms of the Mach-Zehnder delay-interferometer (DI) is now set to +π/ 4 and−π/ 4), the photo detector, and the BER tester. The labeled signal is split using a 3dB optical coupler. The output of one arm is directly detected by photodiode and thus the optical label is converted into the electrical domain. Form the second output of the coupler the label signal is input to another EAM driven by the inverted label data with suitable delay and amplitude for label erasure. The payload is then input to as integrated Mach-Zehnder delay interferometer to demodulate the RZ-DQPSK signal. The advantage of using the EAM for label erasure is its negligible frequency chirp. The length difference between the two arms of the MZDI is corresponding to 100ps delay. The signal at the output of MZDI is detected by photo detector and input to a 10Gbit/s BER test.
4-4 Sensitivity of convention DQPSK/ASK label
The detected RZ-DQPSK eye diagrams without and with label erasure are shown in Fig 4-5(a) and (B), respectively. It should be noted that the receiver sensitivity of the ASK label improves as the ASK extinction is increased, while the sensitivity of the RZ-DQPSK payload deteriorates owing to the reduced signal power when an ASK ‘0’is transmitted. Therefore, in our experiment a compromise value of 4 dB is selected for the extinction ratio of the ASK label. The Fig 4-6 shows the BER of dual-drive DQPSK payload/ASK label and pure payload. For DQPSK payload that sensitivity is -26.1dBm
signal. The ASK label signal that sensitivity is -25.5dBm. The pure payload (not add label signal) that sensitivity is -30.3dBm.
(a) Eye diagrams for payload without label erasure (b) Eye diagrams for payload with label erasure The Fig 4-5 Eye diagrams of convention DQPSK for payload without and with label erasure
20ps/div
The Fig 4-6 BER of convention DQPSK payload/ASK label and pure payload
4-5 Result & discussion (DQPSK payload/ASK label)
Using two kinds of method (dual-drive DQPSK and convention DQPSK) to generated DQPSK payload and ASK label which the performance differ too much (dual-drive DQPSK payload -21.4 dBm label -21dBm and convention DQPSK payload -26.1 dBm label -25.5dBm), but the second modulator (pulse carver and ASK label modulator) that were the same way to generated RZ pulse and ASK label. When amplitude jiter of NRZ-DQPSK is larger, which amplitude jiter influence more serious to add label after the second modulator. Therefore, we used label eraser to erase label that can not .complete clearly. The section 3-8.1 has discussed amplitude jiter influence the performance of NRZ-DQPSK. That is the reason to cause two kinds of method to generated DQPSK payload and ASK label which the performance differ too much. The fig 4-7 shows EAM can not erase label complete clearly.
The Fig 4-7 EAM incomplete to dispel label EAM
Label Eraser Delay
Chapter 5 Conclusion
IN this thesis, we provide a simple and cost effective method to generate DQPSK payload/ASK label signal which only needs two dual-drive Mach-Zehnder modulator (DD-MZM). First, we use bias position (bias=Vπ/2) and drive signal of dual-drive Mach-Zehnder modulator to generated DQPSK signal which replaced two Mach-Zehnder modulator. Second, we also used mixer to mix the sinwave and the low bit rate label data into Mach-Zehnder modulator replace pulse carver and ASK modulator.
This thesis also tries to contract performances with two kinds of method (dual-drive DQPSK and convention DQPSK) shown the Table5-1. The performance of dual-drive DQPSK signal will be improved when MZM drive are promoted in the future.
DD DQPSK
Table 5-1 Performance evaluation of Dual-Drive DQPSK and Convention DQPSK transmitters
References
[1]. D. J. Blumenthal, A. Carena, L. Rau, V. Curri, and S. Humpries, “All-optical label swapping networks and technologies,” J. Lightwave Technol., vol. 18, pp.
2058-2075, Dec. 2000.
[2]. C. Wree, N. Hecker-Denschlag, E. Gottwald, P. Krummrich, J. Leibrich, E-D.
Schmidt and B. L. W. Rosenkranz, “High spectral efficiency 1.6-b/s/Hz transmission (8x40Gb/s with a 25-GHz grid) over 200-km SSMF using RZ-DQPSK and polarization multiplexing”, IEEE Photon. Technol. Lett., vol. 15, no. 9, pp. 1303-1305,Sep 2003
[3]. P. Cho, Y. Achiam, G. Levy-Yurista, M. Margalit, Y. Gross and J. B. Khurgin,
“Investigation of SOA nonlinearities on the amplification of DWDM channels with spectral efficiency up to 2.5 b/s/Hz”, IEEE Photon. Technol. Lett., vol. 16, no. 3, pp918-920, Mar. 2004
[4]. K. P. Ho and Han-Wei Cuei, “Generation of arbitrary quadrature signals using one dual-drive modulator”, J. Lightwave Technol., vol. 23, no. 2, pp. 764-770, Feb 2005.
[5]. N. Chi, C. Mikkelsen, L. Xu, J. Zhang, P. V. Holm-Nielsen, H. Ou, J. Seoane, C.
Peucheret, and P. Jeppesen, “Transmission and label encoding/erasure of orthogonally labeled signal using 40Gb/s RZ-DPSK payload and 2.5Gb/s IM label,” Electron. Lett., vol. 93, no. 18, pp. 1335-1337, Sep 2003.
[6]. Wei-Ren Peng, Yu-Chang Lu, Jye-Hong Chen, Sien Chi, “Encoding ASK Labeled CSRZ-DPSK Payload by Using Only One Dual-Drive Mach-Zehnder Modulator with Enhanced Label Performance”, IEEE Photon. Technol. Lett., vol. 17, no. 10 pp.
2227-2229, Oct 2005
[7]. N. Chi, J. Zhang, P. V. Holm-Nielsen, C. Peucheret, and P. Jeppesen,
“Transmission and transparent wavelength conversion of an optically labeled signal using ASK/DPSK orthogonal modulation,” IEEE Photon. Technol. Lett., vol. 15, no. 5, pp.
760-762, May 2003
[8]. A. H. Gnauck, P.J. Winzer, “Optical Phass-Shift-Keyed transmission”, J.
Lightwave Technol., vol. 23, no. 1, pp. 115-130, Jan 2005.
[9]. Chris Xu, Xiang Liu, Xing Wei, “Differentail Phase-Shift Keying for high spectral efficiency optical transmission”, J of Selected Topics in Quantum Electronics, vol. 10, no. 2, pp. 281-293, Mar/Apr 2004.
[10]. Takahide Sakamoto, Tetsuya Kawanishi, Tetsuya Miyazaki, Masayuki Izutsu,
“10-Gb/s external modulation in optical CPFSK format”, IEEE Photon. Technol. Lett, vol. 18, no. 8, pp. 968-970, Apr 2006.