In the thesis, we investigated the fundamental linear and nonlinear system limitations of multichannel SSB/SCM/DWDM systems through theoretical analysis, numerical calculations, and computer simulations. We have presented general analytical tools, which can be used in either wireless or metro optical systems, which transport multiple SSB/SCM narrowband digital signals on a single or multiple wavelengths. These analytical tools include: (2.11) and Table 2.1 for MZI modulator-induced CTB; (2.12) and Table 2.2 for CSOs caused by linear fiber dispersion; (2.13) – (2.15) for CTBs caused by linear fiber dispersion; (2.21) – (2.24) for XPM-induced XT. To predict XPM-induced XT precisely and without the limitation of wavelength spacing or modulation frequency range, (2.20) was derived for numerical calculations.
Through case studies of 64 or 32 channels of 155 Msymbol/s n-QAM signals, several system considerations for SSB/SCM/DWDM transmission were discovered.
The MZI modulator nonlinear transfer curve-induced CTB is the very basic SSB/SCM system limitation even when all fiber dispersion has been completely compensated.
Although an SSB/SCM system does not have the same distance-dependent carrier suppression problem as in a conventional double-sided SCM system, its transmission distance is still severely limited by linear fiber dispersion-induced CSOs when the multiple modulation signals occupy more than an octave of frequency range.
The main optical fiber nonlinearity-induced impairment in a DWDM SSB/SCM system is caused by XPM. To avoid this XPM-induced XT, the launched optical power per wavelength should be kept below a certain level.
Two case studies of 20 Gb/s per wavelength over an 80 km DWDM system
without dispersion compensation were carried out. We found that both are theoretically achievable but with little margin left, especially when wavelength channel spacing is small. We did notice that, however, it is possible to transport 10 Gb/s (e.g., 32-ch 155 Msymbol/s QPSK signals with traditional FEC and within an octave) per wavelength using SSB/SCM in a DWDM system, even at 25-GHz wavelength spacing, over a transmission distance of many hundreds of kilometers without dispersion compensation. The key point in achieving this superior transmission performance is to keep all the modulation frequencies within an octave so that the dominant transmission impairment is linear-dispersion-induced CTB.
We also proposed a new HFC network architecture in the thesis, whose feasibility has been experimentally verified. This architecture incorporates a smooth transition from a single-wavelength narrowcast laser to DWDM narrowcast lasers. For a 64-QAM channel loading of 50 per wavelength, and using dual-receiver fiber nodes, the coverage range can be up to ~100 km when using a single laser, and can be up to ~70 km when using 16 wavelengths. Therefore, this architecture can meet the demand of an HFC network economically and gracefully with both light and heavy narrowcast traffic demands.
References
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[2] G. H. Smith and D. Novak, “Broad-band millimeter-wave (38 GHz) fiber-wireless transmission system using electrical and optical SSB modulation to overcome dispersion effects,” IEEE Photon. Technol. Lett., vol. 10, pp. 141–143, Jan. 1998.
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[5] Ming-Chia Wu, Pi-Yang Chiang and Winston I. Way, “On the validity of using CW tones to test the linearity of multichannel M-QAM subcarrier multiplexed lightwave systems,” IEEE Photon. Technol. Lett., vol. 12, no. 4, pp. 413–415, April 2000.
[6] H. Schmuck, “Comparison of optical millimetre-wave system concepts with regard to chromatic dispersion,” Electron. Lett., vol. 31, no.21, pp. 1848–1849, Oct. 1995.
[7] A. Cartaxo, “Impact of modulation frequency on cross-phase modulation effect in intensity modulation-direct detection WDM systems,” IEEE Photon. Technol. Lett., vol. 10, pp. 1268–1270, Sept. 1998.
[8] A. Cartaxo, “Cross-phase modulation in intensity Modulation-direct Detection WDM systems with multiple optical amplifiers and dispersion compensators,” J. Lightwave Technol., vol. 17, no. 2, pp. 178–190, Feb. 1999.
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839–850, May. 1996.
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30, no.2, pp. 152–153, Jan. 1994.
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17, no. 10, pp. 1806–1813, Oct. 1999.
[14] F. Ramos and J. Marti, “Frequency transfer function of dispersive and nonlinear single-mode optical fibers in microwave optical systems,” IEEE Photon. Technol.
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[16] A. Cartaxo, B. Wedding, and W. Idler, “Influence of fiber nonlinearity on the phase noise to intensity noise conversion in fiber transmission: theoretical and experimental analysis,” J. Lightwave Technol., vol. 16, pp. 1187–1194, July. 1998.
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fiber links with multiple optical amplifiers and dispersion compensators,” J.
Lightwave Technol., vol. 14, pp. 249–260, Mar. 1996.
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748–750, May. 2003.
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[22] S. Mysore, “Twenty-wavelength, dual-receiver DWDM system: modeling and experiments,” Technical Digest, IEEE LEOS Summer Topical Meeting, pp. 5-6, paper WC2.3, July 1999.
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[24] W. H. Chen, J. K. Wong and W. I. Way, “Experimental verification of an evolutionary HFC network architecture for adding narrowcast services,” in OFC2000 Technical Digest, pp. 157-159, paper WJ5.
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Tables
Table 2.1 Analytic expressions for the individual third order distortions due to SSB/SCM Modulation, Ωi, Ωjand Ω , are three arbitrarily k chosen distinct subcarrier frequencies.
Ωd
Distortion Type Distortion Frequency ( ) Formula
Third Harmonic 3Ωi
Third-Order Intermodulation 2Ωi ±Ωj
4
Table 2.2 Analytic expressions for SSB/SCM 2nd order NLDs due to linear fiber dispersion. ρ =1 2⋅β2⋅z.
Distortion Type Distortion Frequency (Ωd) Formula
Second Harmonic 2Ωi
( )
2Table 2.3 Parameters for a 20 Gb/s SSB/SCM systems
Number of subcarrier channels on pump wavelength 64 Bandwidth Efficient Modulation (BEM) scheme QPSK
Symbol rate per channel 155 Msymbol/s
Bandwidth excess factor 0.2
Channel spacing 1.2×155 MHz
Channel frequency plan 0.93 ~ 12.648 GHz
Optical modulation scheme USB/SCM
Number of wavelengths 2 (Fig. 2.8), 4 (Fig. 2.9–Fig. 2.13)
Wavelength separation 25, 50, and 100 GHz
Probe Wavelength (λ3) 1550 nm
Fiber dispersion coefficient at λ3 (D) 17 ps/nm/km Fiber dispersion slope at λ3 (S) 0.044 ps/nm2/km Fiber nonlinear index coefficient (n2) 2.6×10-20 m2/W Fiber effective core area (Aeff) 80 µm2
Fiber nonlinearity coefficient at λ3 (γ=2πn2/λ/Aeff) 1.32 W-1km-1 Fiber power attenuation coefficient (α) 0.21 dB/km
Fiber length 80 km
Receiver equivalent thermal noise 10 pA/√Hz
Table 2.4 For the system given in Table 2.3, a summary of the optimum optical power, RMS OMI/ch and the corresponding worst-case NSR in a transmission system with four multiplexed wavelengths. Three wavelength spacings are given: 25, 50 and 100 GHz. The required coding gains to reach a BER of 10-12 are also shown.
25 GHz (0.2 nm) 50 GHz (0.4 nm) 100 GHz (0.8 nm)
Optimum optical power per wavelength (dBm) 2.24 4.48 6.81
Optimum RMS OMI per channel (%) 1.78 1.55 1.36
Worst-channel NSR (dB) –14.66 –15.72 –16.88
Coding gain required to reach BER = 10-12 (dB) in practice* 5.34 4.28 3.12
* For QPSK, NSR < ~ –16.95 dB in theory and –20 dB in practice is required to obtain a BER = 10-12
Table 2.5 For 32 channels of 16-QAM signals equally distributed between 6.882 and 12.648 GHz (same transport capacity as that given in Table 2.3), a summary of the optimum optical power, RMS OMI/ch and the corresponding worst-case NSR in a transmission system with four multiplexed wavelengths. Three wavelength spacings are studied: 25, 50 and 100 GHz. The required coding gains to reach a BER of 10-12 for QPSK and 16-QAM are also shown.
25 GHz (0.2 nm) 50 GHz (0.4 nm) 100 GHz (0.8 nm) Optimum optical power per wavelength (dBm) –1.49 0.75 3.01
Optimum RMS OMI per channel (%) 5.94 5.45 5
Worst-channel NSR (dB) –22.39 –23.88 –25.39
Coding gain required to reach BER= 10-12 (dB)*
for QPSK 0 0 0
Coding gain required to reach BER= 10-12 (dB)**
for 16-QAM 4.61 3.12 1.61
* For QPSK, NSR < ~ –16.95 dB in theory and –20 dB in practice is required to obtain a BER= 10-12
** For 16-QAM, NSR < ~ –23.88 dB in theory and –27 dB in practice is required to obtain BER= 10-12
Figures
Fig. 2.1 An SSB/SCM/DWDM system.
Ω
0 2Ω
−2Ω
−3Ω −Ω 3Ω
0dB
−17.5dB (−45ο)
(180ο) (45ο)
(0ο)
−33.8dB
0 1 (m) 2 (m)
10log( J ) = 11.5dB J
Fig. 2.2 Optical spectrum of a single channel SSB/SCM signal with m=0.1 (note that ω0 is subtracted from all frequency components).
0 0
0 1
(m) (m) 2 (m) (m)
J J
10log( ) = 11.5dB
J J
(45ο)
(180ο)
0dB Ω1+Ω2
−14.5dB (−45ο)
Ω2−Ω1
−14.5dB (−135ο)
2Ω1−Ω2, 2Ω2−Ω1
−29dB (0ο)
2Ω1, 2Ω2
−17.5dB (−45ο) 2Ω1+Ω2, 2Ω2+Ω1
−29dB (0ο)
3Ω1, 3Ω2
−33.8dB (0ο)
Fig. 2.3 Optical spectrum of a 2-ch SSB/SCM signal with m=0.1 (note that ω0 is subtracted from all frequency components).
0 5 10 15 20 25 30 -50
-45 -40 -35 -30 -25 -20 -15 -10
64 channels (0.93 ~ 12.648GHz)
CTBSSB/SCM,MZI
CSOSSB/SCM,D
NSR [dBc]
Frequency [GHz]
NSR (80km) NSR (0km)
Fig. 2.4 Noise-to-signal ratio (NSR) versus frequency in an SSB/SCM optical transmission system with 64 QPSK channels (ranging from 0.93 to 12.648 GHz), for fiber lengths of 0 and 80 km. Dashed line and upper triangular symbols are the theoretical and simulation results for the case of no fiber transmission, respectively. Solid lines and circular symbols are the theoretical and simulation results after 80 km fiber transmission, respectively. RMS OMI per channel is around 4%.
Fig. 2.5 Linear fiber dispersion-induced CSO versus transmission distance in a SSB/SCM system with 64 QPSK channels. Dashed and solid lines are the results of channel 32 and worst-case channel, respectively. RMS OMI per channel is 4%.
0 100 200 300 400 500 600
-25 -20 -15 -10 -5
Ch32 worst-case
CSO [dBc]
Transmission Length [km]
6 8 10 12 14 -54
-52 -50 -48 -46 -44 -42
CTBSSB/SCM,MZI
CTBSSB/SCM,D
NSR (0km) NSR (30km) NSR (80km)
NSR [dBc]
Channel Frequency [GHz]
Fig. 2.6 Noise-to-signal ratio (NSR) versus frequency in an SSB/SCM optical transmission system with 32 16-QAM channels (ranged from 6.882 to 12.648 GHz), for fiber lengths of 0, 30 and 80 km. Dashed line and upper triangular symbols are the theoretical and simulation results for the case of no fiber transmission, respectively. Square and circle symbols are the simulation results after 30 and 80km fiber transmissions, respectively. Solid lines are the theoretical results. RMS OMI per channel is around 1.8%.
0 100 200 300 400 500 600 -53
-52 -51 -50 -49 -48 -47 -46 -45 -44
CTBSSB/SCM,D(Ch16) CTBSSB/SCM,D(worst-case) CTBMZI(Ch16)
CTB [dBc]
Transmission Length [km]
Fig. 2.7 Linear fiber dispersion-induced CTB versus transmission distance in an SSB/SCM system with 32 16-QAM channels. Dashed and solid lines are the results of channel 16 and worst-case channel, respectively. Dotted line is the intrinsic MZI-induced CTB at channel 16. RMS OMI per channel is 1.8%.
0 2 4 6 8 10 12 14 -60
-50 -40 -30 -20 -10 0
6dBm
0dBm 10dBm
simu.(∆λbp= -0.2) simu.(∆λbp= +0.2) theory(Θ
p=0) theory numerical
2WDM XT [dBc]
Channel Frequency [GHz]
Fig. 2.8 Two wavelengths XT versus pump modulation frequency for an average optical power per wavelength of 0, 6 or 10 dBm. Circular (∆λbp= –0.2 nm) and triangular (∆λbp= +0.2 nm) symbols are simulation results; dashed (Θ = 0) and dotted (p Θ ≠ 0) lines show p the theoretical predictions; solid lines are numerical results. The pump wave is modulated with 64 QPSK channels between 0.93 and 12.648 GHz using USB/SCM.
0 2 4 6 8 10 12 14 -60
-50 -40 -30 -20 -10
λ1 λ2 λ3 λ4 100G
50G
probe 25G
simulation theory numerical
4WDM (P 0=6dBm) XT [dBc]
Channel Frequency [GHz]
Fig. 2.9 Four wavelengths XT versus pump modulation frequency for wavelength separations of 25, 50 and 100 GHz (with the probe channel in the center (λ3). Circular, dotted and solid lines show the simulation, theoretical and numerical results, respectively. Three pump wavelengths are simultaneously modulated by three uncorrelated 64 QPSK channels (between 0.93 and 12.648 GHz) using USB/SCM. The average optical power per wavelength is 6 dBm.
0.5 1.0 1.5 2.0 2.5 3.0 -24
-22 -20 -18 -16 -14 -12 -10 -8 -6
baseline due to
linear dispersion-induced CSO 10dBm
4dBm
-2dBm
single wavelength 4WDM (inculde XPM)
worst-case NSR [dBc]
RMS OMI per channel [%]
Fig. 2.10 Theoretical results of the worst channel NSR versus the RMS OMI/ch for an average optical power per wavelength of -2, 4 and 10 dBm, for the system given in Table 2.3. Dotted lines are for single wavelength, while solid lines are for four wavelengths. The wavelength separation is 50 GHz. Dashed line is due to linear fiber dispersion-induced CSO.
0 2 4 6 8 10 12 14 -30
-25 -20 -15
-10 10dBm
4dBm
baseline due to
linear dispersion-induced CSO -2dBm
NSR [dBc]
Channel Frequency [GHz]
simulation theory numerical
Fig. 2.11 NSR versus channel frequency in the case of four wavelengths for the system given in Table 2.3. Average optical power per wavelength is -2, 4 or 10 dBm. Circular symbols are simulation results; dotted lines are theoretical results; and solid lines are numerical results. The wavelength separation is 50 GHz and RMS OMI per channel is 1.8%.
2 3 4 5 6 7 8 9 10 -34
-32 -30 -28 -26 -24 -22 -20 -18 -16
baseline due to
linear dispersion-induced CTB 6dBm
0dBm
-6dBm
single wavelength 4WDM (inculde XPM)
The worst-case NSR [dBc]
RMS OMI per channel [%]
Fig. 2.12 Theoretical results of the worst channel NSR versus the RMS OMI/ch for an average optical power per wavelength of -6, 0 and 6 dBm.
Dotted lines are for the case of single wavelength, while solid lines are for the case of four wavelengths. The wavelength separation is 50 GHz. Dashed line is due to linear fiber dispersion-induced CTB.
6 8 10 12 14 -34
-32 -30 -28 -26 -24 -22 -20 -18 -16
-6dBm
6dBm
baseline due to linear dispersion-induced CTB 0dBm
NSR [dBc]
Channel Frequency [GHz]
simulation theory numerical
Fig. 2.13 NSR versus the channel frequency in the case of four wavelengths. Average optical power per wavelength is -6, 0 or 6 dBm.
Circular symbols are simulation results; dotted lines are theoretical results; and solid lines are numerical results. The wavelength separation is 50 GHz and RMS OMI per channel is 5.5%.
Broadcast Video
Fig. 3.1 Proposed HFC Network architecture for adding narrowcast services to broadcast services.
1.2 1.3 1.4 1.5 1.6 1.7 1.8 11
12 13 14 15 16 17
SBS Threshold [dBm]
OMI/ch [%]
Fig. 3.2 Measured SBS threshold versus OMI/ch for 81 km conventional SMF.
1 2 3 4 5 6 7 25
30 35 40 45 50 55
analysis C/(CTB+N)
C/CTB
C/CTB or C/(CTB+N) [dB]
OMI/ch [%]
Fig. 3.3 Measured C/CTB (●) and C/(CTB+N) (■) of Ch.50 (centered@ f = 745.25 MHz, Bandwidth = 6 MHz) versus OMI/ch. Dashed and solid lines are analytical results.
Start: 0 Hz Stop: 800 Hz -62.7
dBm 6dB /div -2.7 dBm
Center: 601.25 MHz -88.7
dBm 10dB /div 11.3 dBm
Span: 100 MHz
Fig. 3.4 Received RF spectrum after 102.5 km conventional SMF transmission and 14 dB splitting loss.
450 500 550 600 650 700 750 38
40 42 44 46 48 50 52
analysis C/CTB
C/(CTB+N)
C/CTB or C/(CTB+N) [dB]
Channel Frequency [MHz]
Fig. 3.5 C/CTB (●) and C/(CTB+N) (■) as a function of channel frequency. The dashed and solid lines are analytical results.
λ
11x16 MUX
Freq. Syn. 1
λ
2Freq. Syn. 2
λ
3Freq. Syn. 3 CW Laser
λ
probeSpectrum Analyzer Polarization
controler
Rx
WDM-EDFA
Tunable Attenuator
Tunable filter SMF
λ
1λ
2λ
3λ
probeCrosstalk RF Power on λ
probeRF Power on λ
i (i=1,2,3)Fig. 3.6 4-wavelength experimental setup for measuring DWDM crosstalk. Wavelength spacing was 3.2 nm.
550 600 650 700 750 -58
-56 -54 -52 -50 -48 -46 -44 -42
predicted in λ
2 or λ
3
total XT
XT due to λ
1
XT due to λ
2
XT due to λ3
4 WDM Crosstalk [dB]
Channel Frequency [MHz]
Fig. 3.7 Measured crosstalk in the probe wavelength due to λ1 (▼), λ2 (■), λ3 (▲) and total crosstalk (●) as a function of channel frequency. All broken lines are analytical results. Solid line is the predicted crosstalk at the middle (worst case) wavelength.
Transmission distance is 80 km.
0.8 1.6 2.4 3.2 48
50 52 54 56 58 60
4
λ8
λ16
λMax. Transmission Dist. [km]
Wavelength Spacing [nm]
Fig. 3.8 Predicted maximum transmission distance between primary and secondary hub versus wavelength spacing for 4 (■), 8 (●) and 16 (▲) wavelengths. The transmission distance between secondary hub and optical nodes is fixed at 20 km.
Publication List
A. 期刊論文(journal papers)
1. W. H. Chen, J. K. Wong and Winston. I. Way, "An Evolutionary HFC Network Architecture for Adding Narrowcast Services," J. Opt.
Commun., vol. 22, pp. 74-77, March 2001.
2. W. H. Chen and Winston. I. Way, “Multi-Channel Single-Sideband SCM/DWDM Transmission System,” J. Lightwave Technol., vol. 22, no. 7, July 2004. (JLT #6532).
B. 研討會論文(conference papers)
1. Wei Hong Chen, MingChia Wu, Ching Ten Chang, Winston I. Way,
“Self-phase-modulation-limited transmission distance of repeaterless 1.55 µm multichannel AM-VSB external modulation systems,”
Proceedings of SPIE, pp. 138-145, Jun 1998.
2. W. H. Chen, J. K. Wong and W. I. Way, "Experimental Verification of an Evolutionary HFC Network Architecture for Adding Narrowcast Service," OFC2000 Technical Digest, pp. 157-159, paper WJ-5.
C. 專利(patents)
1. “An Optical Fiber Transmitter Using Chirped Fiber Grating and Pre-distortion Circuit For Long Distance Subcarrier Multiplexed Lightwave Systems,” U.S. Patent No. 6,559,994, May 6, 2003.
簡 歷
姓 名 ： 陳威宏 性 別 ： 男
出生年月日 ： 民國 62 年 1 月 25 日
籍 貫 ： 嘉義縣民雄鄉豐收村好收 133-12 號 住 址 ： 嘉義市民生南路 111 巷 13 號
電 話 ： (05) 2283-528
Email ： [email protected]
學 歷 ： 國立交通大學電信工程研究所 博士 (87 年 9 月 ~ 93 年 7 月)
國立交通大學電信工程研究所 碩士 (85 年 9 月 ~ 87 年 9 月)
國立交通大學電信工程學系 學士 (81 年 9 月 ~ 85 年 9 月)