論文中，我們分別利用
<1> Back-to-Back
、<2>
摻鉺光纖放大器 加上25km
的LEAF
光纖、<3> 25km
的LEAF
光纖的拉曼放大器、<4> 25km
的單模光纖的拉曼放大器以及<5>
長距離80km
的LEAF
光 纖加上摻鉺光纖放大器與分佈式拉曼光放大器這五種不同的架構於 類比的CATV
系統中來探討拉曼光放大器在其上之性能表現與其適 用性，並且與以往在系統上作為放大信號的摻鉺光纖放大器作一比 較。同時也討論不同光纖的特性在拉曼放大器上的性能之差異與經過 長距離的傳輸情形。結果發現，在類比的
CATV
系統中加入分佈式拉曼放大器其CNR
會有較嚴重之劣化情況，相較於同樣系統下改用EDFA
放大器，其性 能也較差，我們發現影響其CNR
劣化的原因主要為拉曼自發性輻射在
1510~1600 nm
的波長範圍間累積較高的雜訊與信號本身的光源自發性輻射
( Source Spontaneous Emission, SSE )
所致。而對於分別使用 不同的光纖( SMF/LEAF )
的系統下，我們也發現其光纖所產生的色散 量將對CSO
將產生較大的影響，色散量越大將對CSO
劣化越嚴重。長距離的傳輸系統中，搭配了
EDFA
與拉曼光放大器一起使用的結 果，致使兩種放大器的雜訊在系統中相互的累積而明顯的造成系統的 性能劣化了。我們發現，在此研究的結果中，分佈式拉曼光纖放大器 在於類比的CATV
系統中相較於EDFA
在相同之類比系統架構而言，其性能較差，原因為它將造成系統上
CNR
較嚴重之劣化。至於是否 可實用，仍待進一步對系統需求之評估。
參考文獻
[1] F. W. Willems, W. Muys, and J. S. Leong, “Simultaneous suppression of stimulated Brillouin scattering and interferometric noise in externally modulated lightwave AM-SCM systems,” IEEE Photon. Technol. Lett., vol. 6, no. 12, pp.
1476-1478, 1994.
[2] T. H. Wood, A. K. Srivastava, J. L. Zyskind, J. W. Sulhoff, “Two-wavelength WDM analog CATV transmission with low crosstalk,” in Technical Digest, OFC’97, paper THP2, 1997.
[3] Y. K. Chen, Y. L. Liu and C. C. Lee, “Directly modulation 1.55µm AM-VSB video EDFA-repeatered supertrunking system over 110km standard singlemode-fiber using split-band and wavelength division multiplexing techniques,” Electron. Lett., vol. 33, no. 16, pp. 1400-1401, 1997.
[4] C. H. Chang and Y. K. Chen, “Experimental demonstration of bi-directional lightwave CATV 100km transmission system using SMF and LEAF links,”
Electron. Lett., vol. 36, no. 3, pp. 243-244, 2000.
[5] M. Yan, J. Chen, W. Jiang, J. Li, J. Chen and X. Li, “Automatic design scheme for optical-fiber Raman amplifiers backward-pumped with multiple laser diode pumps,” IEEE Photon. Technol. Lett., vol. 13, no. 9, pp. 948-950, 2001.
[6] M. Nissov, K. Rottwitt, H. D. Kidorf and M. X. Ma, “Rayleigh crosstalk in long cascades of distributed unsaturated Raman amplifier,” Electron. Lett., vol. 35, no. 12, pp. 997-998, 1999.
[7] A. Berntson, S. Propov, E. Vanin, G. Jacobsen and J. Karlsson, “Polarisation dependence and gain tilt of Raman amplifiers for WDM systems,” Optical Fiber Communication (OFC), vol. 1, paper MI2, 2000.
[8] H. Kim, K. H. Han, Y. C. Chung, “Performance limitation of hybrid WDM systems due to stimulated Raman scattering,” IEEE Photon. Technol. Lett., vol.
13, no. 10, pp. 1118-1120, 2001.
[9] M. E. Marhic, F. S. Yang, Y. Akasaka and L. G. Kazovsky, “Suppression of fiber nonlinearities in HFC systems by distributed fiber Raman amplification,” Tech.
Dig. IEEE Laser and Electro-Optics Society Topical Meeting (LEOS’99), pp.
53-54, 1999.
[10] W. I. Way, Broadband hybrid fiber/coax access system technologies, Chapter 5 , 1999.
[11] 張嘉雄, “光纖調幅視訊傳輸與網路監控技術之研究, ” 國立中山大學光電 工程研究所碩士論文, 1998 年 6 月.
[12] H. Ono, M. Yamada, T. Kanamori, S. Sudo and Y. Ohishi, “1.58-µm band gain-flattened Erbium-doped fiber amplifiers for WDM transmission systems, ” IEEE Journal of Lightwave Tech., vol. 17, no. 3, pp. 490-496, March 1999.
[13] J. F. Massicott, R. Wyatt, B. J. Ainslie and S. P. Craig-Ryan, “Efficient, high power, high gain, Er3+ dope silica fiber amplifier,” Electron. Lett., vol. 26, pp.
1038-1039, 1990.
[14] S. Namiki and Y. Emori, “Ultrabroad-band Raman amplifiers pumped and gain-equalized by wavelength-division-multiplexed high-power laser diodes,”
IEEE Journal Quantum Eiectronics vol. 7, no. 1, pp. 3-16, 2001.
[15] J. A. Yeung and A. Yariv, “Spontaneous and stimulated Raman scattering in long loss fibers,” IEEE J. Quantum Electron. QE-14, pp. 347-350, 1978.
[16] S. B. Papernyi, V.I. Karpov, W. R. L. Clements, “Efficient dual-wavelength Raman fiber laser,” Conference on OFC, paper WDD15, 2000.
[17] G. P. Agrawal, Fiber-optic communication system, Chapter 8, John Wiley &
Sons, New York, 1997.
表
2-1
摻鉺光纖放大器(EDFA)與拉曼放大器(DRA)之比較( Erbium Doped Fiber Amplifier, EDFA ) ( Distributed Raman Amplifier, DRA ) Amplification Band Depends on dopant Depends on pump wavelength
Gain
Depends on：
1. ion concentration 2. fiber length
3. pumping configuration
Depends on：
1. effective fiber area 2. fiber length
3. pumping configuration
Pump Wavelength 980 nm or 1480 nm 13 THz higher than signal frequency at peak gain
Pump Power Gain threshold depends on doping Gain depends on power intensity
Crosstalk Very low Strong
表
2-2
拉曼幫激雷射合波器之生產廠商與規格廠商 #Ports Channel spacing(nm) I.L.(dB) PDL(dB) Iso.(dB) Directivity(dB) R.L.(dB) △λ(nm) Handling Power(W)
Wavesplitter 2 7~60 ≦ 0.3
www.wavesplitter.com 3&4 7~25 ≦ 0.6 Dicon Fiberoptics
www.diconfiberoptics.com U-Conn
www.uconn.com.tw
Laser 2000 2 ≦ 0.4
www.laser2000.co.uk 3&4 ≦ 0.8
1420~1433
Oplink communication.Inc 2 6.4 < 0.6 < 0.2
www.oplink.com 4 7.5 < 0.8 < 0.2
BROWave 2 5~20 ≦ 0.4
www.browave.com 3&4 5~20 ≦ 0.8 ≦0.2 ≧ 15 ≦ -55 ≧ 55 1420~1490 5
1455~1498 N/A
N/A > 55 > 55 1465/1472.5/1480/1487.5 0.5
N/A N/A 55 55
表 3-1.Ortel TX (Model 3960A) characteristics
RF Input power ：+22dBmV/ch Transmitter Output Power：+6.12dBm
Received Optical Power：0dBm
CNR (dB) CSO (dBc) CTB (dBc) Carrier frequency (MHz)
Ch.2 50.8 78.4 65.6 55.25
Ch.6 50.9 77.8 63.9 83.25
Ch.7 50.6 77.7 64.4 175.25 Ch.13 51.9 78.2 64.5 211.25
Ch.24 51.9 76 64.6 223.25
Ch.36 53.1 77.5 62.2 295.25 Ch.40 53.3 74.4 64.4 319.25 Ch.45 53.2 70.9 62.2 349.25 Ch.56 52.1 65.5 64.6 415.25 Ch.60 52.5 63.2 61.7 439.25 Ch.66 52.4 65.7 60.9 475.25 Ch.78 53.3 65.3 55.3 547.25
圖2-1 CNR 的分佈與量測圖[10]
Frequency (MHz)
圖2.2 CSO 對不同頻率時之分佈情形[10]
4 MHz
Frequency (MHz)
圖2.3 CTB 對不同頻率時之分佈情形[10]
圖 2-4 CSO 之分佈與量測圖
0.75 MHz 1.25 MHz
影像載波
彩色副載波
聲音載波
f
0圖2-5 CTB 之分佈與量測圖
圖 2.6 摻鉺光纖放大器(EDFA)之基本架構
P
inPump LD1 Pump LD2
ISO2
P
outISO1 WDM1 WDM2
EDF
影像載波
聲音載波
CTB
三次合成拍差
彩色副載波
圖2.7 鉺離子(E3+)的能階分佈圖[12]
Intermediate state
hνi
hνi hνs
hνs
＜c＞
hνs
＜b＞
＜a＞
圖2.9 激發性拉曼散射能階變化[15]
Intermediate state
hνi
hνi hνs
hνs
＜c＞
hνcb
＜b＞
＜a＞
(a) Stokes transition
Intermediate state
hνi
hνi hνs
hνs
＜c＞
＜b＞
hνba
＜a＞
(b) Anti-stokes transition
圖2.8 自發性拉曼散射能階分佈變化情形[15]
圖2-10 拉曼增益頻譜[17].
圖 2-11 不同幫激功率所對應之拉曼增益分佈情形[17].
圖 3-1 Back-to-Back 架構圖.
EDFA ASE Spectrum
-40 -35 -30 -25 -20 -15 -10
1520 1530 1540 1550 1560 1570
Wavelength(nm)
(d B )
ASE Spectrum
圖 3.2 摻鉺光纖放大器頻譜圖
VOA1 20.0 dBm
80 CHs
CATV EM-TX
EDFA RX RF-BPF
6.0 dBm 2 dBm
CATV-ESA
DMUX CH2 Passband
1544 1546 1548 1550 1552 1554
Wavelength(nm)
圖
3-7. 25km LEAF 光纖拉曼增益量測頻譜圖(9.25dB )
. (w/i w/o Raman) DMUX input Spectrum-60 -50 -40 -30 -20 -10 0 10
1547 1548 1549 1550 1551 1552
Wavelength(nm)
(dBm) (w/o) Raman)Spectrum
(w/i Raman)Spectrum
9.25dB
W/O Raman W/I Raman
圖 3-8 EDFA+80km LEAF Raman amplifier 架構圖
CATVEM-TX
EDFA 1*8
DMUX RX RF-BPF CATV-ESA 1460nm FP-LD
1470nm FP-LD 1480nm FP-LD 1490nm FP-LD LEAF
(50km)
LEAF (30km) OBPF
6.0 dBm 20 dBm 15.65 dBm 6.1 dBm 2 dBm
20.98 dBm VOA2 80
CHs
w/i EDFA 25km LEAF
1539 1544 1549 1554 1559
Wavelength(nm)
1499 1519 1539 1559 1579 1599
Wavelength(nm)
(dBm)
w/i EDFA
w/i Pump & Signal
1460 1480 1500 1520 1540 1560 1580 1600 Wavelength(nm)
w/i Pump & Signal (DMUX right)
-80
1460 1480 1500 1520 1540 1560 1580 1600
Wavelength(nm)
(dBm)
w/i Signal & Pump
1. w/o Iso. 25km LEAF Raman 2. w/i Iso. 25km LEAF Raman
55.25 121.25 223.25 307.25 331.25 415.25 475.25 547.25
(MHz)
55.25 121.25 223.25 307.25 331.25 415.25 475.25 547.25
(MHz)
w/o Signal w/i Pump
1460 1480 1500 1520 1540 1560 1580 1600
Wavelength(nm)
1545 1547 1549 1551 1553 1555
Wavelength(nm)
圖
3-15
1460 nm
幫激雷射(on/off)電訊號頻譜圖( average mode )圖
3-16. 1460 nm
幫激雷射(on/off)電訊號頻譜圖( real time mode )
圖
3-17 1460 nm
幫激雷射(on/off)電訊號頻譜圖( Max & hold mode )
CNR
40 42 44 46 48 50 52 54
55.25 121.25 223.25 307.25 331.25 415.25 475.25 547.25
(MHz)
(dB)
B-B
EDFA+25km LEAF
25km LEAF Raman (1460nm pump off) 25km SMF Raman
EDFA+80km LEAF Raman
圖
3-18
各架構之CNR 比較
CSO
70 71 72 73 74 75 76 77 78 79 80
55.25 121.25 223.25 307.25 331.25 415.25 475.25 547.25
(MHz)
(dBc)
B-B
EDFA+25km LEAF
25km LEAF Raman (1460nm pump off) 25km SMF Raman
圖
3-19
各架構之CSO 比較
CTB
60 62 64 66 68 70 72 74 76 78 80
55.25 121.25 223.25 307.25 331.25 415.25 475.25 547.25
(MHz)
(dBc)
B-B
EDFA+25km LEAF
25km LEAF Raman(1460nm pump off) 25km SMF Raman
EDFA+80km LEAF Raman
圖