光纤光栅用作匹配光滤波器的研究
摘要
本文在利用耦合模理论对均匀及线性啁啾变迹光纤光栅(OFBG：Optical Fiber Bragg Grating)的反射谱进行分析的基础上，发现弱耦合条件下(耦合系数κ＜1)，均匀OFBG的反射谱具有类似与Sa~2(x)函数的分布特性，从而创新提出利用OFBG对光纤通信系统中光放大器的ASE噪声进行匹配光滤波的设想。
论文计算了通信系统中矩形光脉冲信号经强、弱OFBG、匹配光滤波器、F-P滤波器的输出光脉冲波形，经分析比较后发现：弱OFBG和理想匹配光滤波器的输出信号波形极其相似，不存在码间干扰，而F-P滤波器的输出波形存在比较严重的码间干扰。另外用计算机模拟计算了光信噪比的改善情况，研究发现：一个相同的噪声信号经弱OFBG后的光信噪比较经过F-P滤波器后的光信噪比高，由此认为，OFBG用作光滤波器对接收端前置光放大器的噪声进行滤波，比常用F-P光滤波器具有更大的优越性。
同时，建立了OFBG调谐测试装置，实现了OFBG的高精度线性调谐，两根光栅分别实现调谐范围6.320nm和5.762nm，调谐装置具有很好的重复性。
文中相关的研究成果已整理成多篇文章在相关刊物上发表。
Based on the coupled mode theory, the reflect spectrum of OFBG is derived. The influenced of grating length, coupling coefficient and chirp coefficient to the maxium reflectivity and reflection bandwidth of OFBG are discussed in details. We find that under weak couple conditions (the couple coefficient K < 1), the reflect spectrum of an OFBG approximately has a characteristic of sa2(x) shape, which matched to the power spectrum of an optical communication signal. According to the above considerations, we proposed an idea to use weak OFBG as matched optical filter to filter the ASE noise of optical amplifier before the signal is detected in optical fiber communication system. The goal of the filter is to improve the sensitivity of an optical receiver by optimally filtering a communication signal.
In this paper we calculated the temporal response of the matched filter, the commonly used F-P filter, as well as the matched weak OFBG filter. We find that the reflected pulse of weak OFBG closely resembles the triangular shape characteristic of a perfectly matched filter. It almost has no intersymbol interference. Whereas the pulse from a F-P transmission filter has a long decaying tail, this will lead to errors in detection. Secondly, we simulate the transmission process in computer, calculate the Optical-Signal-to-Noise-Ratio(OSNR) of output signal with the same input signal filtered by the OFBG, matched filter and F-P filter, analyze the improvement of the OSNR after filtered by them. We find it also has advantage over F-P filter. Taking the two reasons into account, we believe that the weak OFBG is superior to the widely used F-P filter.
Additionally, the tuning characteristics of the OFBG are analyzed. By use of a micro-displacement set we realized a very high precision tuning. The experimental results verified the theoretical predication. The realized tuning ranges of the two OFBG are 6.320nm and 5.762nm respectively.
论文计算了通信系统中矩形光脉冲信号经强、弱OFBG、匹配光滤波器、F-P滤波器的输出光脉冲波形，经分析比较后发现：弱OFBG和理想匹配光滤波器的输出信号波形极其相似，不存在码间干扰，而F-P滤波器的输出波形存在比较严重的码间干扰。另外用计算机模拟计算了光信噪比的改善情况，研究发现：一个相同的噪声信号经弱OFBG后的光信噪比较经过F-P滤波器后的光信噪比高，由此认为，OFBG用作光滤波器对接收端前置光放大器的噪声进行滤波，比常用F-P光滤波器具有更大的优越性。
同时，建立了OFBG调谐测试装置，实现了OFBG的高精度线性调谐，两根光栅分别实现调谐范围6.320nm和5.762nm，调谐装置具有很好的重复性。
文中相关的研究成果已整理成多篇文章在相关刊物上发表。
Based on the coupled mode theory, the reflect spectrum of OFBG is derived. The influenced of grating length, coupling coefficient and chirp coefficient to the maxium reflectivity and reflection bandwidth of OFBG are discussed in details. We find that under weak couple conditions (the couple coefficient K < 1), the reflect spectrum of an OFBG approximately has a characteristic of sa2(x) shape, which matched to the power spectrum of an optical communication signal. According to the above considerations, we proposed an idea to use weak OFBG as matched optical filter to filter the ASE noise of optical amplifier before the signal is detected in optical fiber communication system. The goal of the filter is to improve the sensitivity of an optical receiver by optimally filtering a communication signal.
In this paper we calculated the temporal response of the matched filter, the commonly used F-P filter, as well as the matched weak OFBG filter. We find that the reflected pulse of weak OFBG closely resembles the triangular shape characteristic of a perfectly matched filter. It almost has no intersymbol interference. Whereas the pulse from a F-P transmission filter has a long decaying tail, this will lead to errors in detection. Secondly, we simulate the transmission process in computer, calculate the Optical-Signal-to-Noise-Ratio(OSNR) of output signal with the same input signal filtered by the OFBG, matched filter and F-P filter, analyze the improvement of the OSNR after filtered by them. We find it also has advantage over F-P filter. Taking the two reasons into account, we believe that the weak OFBG is superior to the widely used F-P filter.
Additionally, the tuning characteristics of the OFBG are analyzed. By use of a micro-displacement set we realized a very high precision tuning. The experimental results verified the theoretical predication. The realized tuning ranges of the two OFBG are 6.320nm and 5.762nm respectively.
引文
1. K.Hill, Y.Fujii, D.Johnson et al. Photosensitivity in optical fiber waveguides: Application to reflection filter fabrication. App. Phy. Lett. Vol.32, 1978:647-649
2. G.Meltz, W. Morey, and W.Glenn. Formation of Bragg gratings in optical fibers by a transverse holographic method. Opt. Lett. Vol. 14, 1989:823-825
3. K.Hill, G.Meltz. Fiber Bragg Grating Technology Fundamentals and Overview. Journal of Lighwave Technoloyy. Vol.14, 1997(6): 1265-1274
4. K.Hill, B.Malo, F.Bilodeau et al. Bragg gratings fabrication in monomode photosensitivity optical fiber by UV exposure through a phase mask. App. Phy. Lett. Vol.62, 1993:1035-1037
5. K.Hill, B.Malo, K.A.Vineberg et al. Efficent mode conversion in telecommunication fiber using externally writing gratings. Electron Lett. Vol.26, 1990: 1270-1272
6. Q.Zhang, D.A.Brown, J.L.Reinhart et al. Linearly and nonlinearly chirp Bragg grating fabrication on curved fibers. Opt.Lett.Vol.21, 1995:1122-1124
7. D.Taverner, D.J.Richardson, S.Barcelos et al. Dispersion compensation of step-index fiber using cascaded chirp fiber gratings. Electron. Lett. Vol.31, 1995: 1004-1005
8. M.J.Cole, W.H.Loh, R.I.Laming et al. Moving fiber-phase mask-scanning beam technique for enhanced flexibility in producing fiber gratings with uniform phase mask. Electron. Lett. Vol.31, 1995:1488-1490
9. C.Byron, K.Sugden, T.Bricheno et al. Fabrication of chirp Bragg gratings in photosensitive fiber. Electron. Lett. Vol.29, 1993: 1659-1660
10. M.Farries, K.Sugden,D.C.Reid et al. Very broad reflection bandwidth(44nm)chirp fiber gratings and narrow bandpass filters produced by the use of an amplitude mask. Electron. Lett. Vol.30, 1994:891-892
11. K.Hill, F.Bilodeau, B.Malo et al. Chirp in fiber-gratings for compensation of optical-fiber dispersion. Opt. Lett, Vol. 19, 1994(17): 1314-1316
12. Y.Painchaud, A.Chandommet, J.Lauzon. Chirp fiber gratings produced by tilting the fiber. Electron. Lett, Vol.31, 1995:171-172
13. F.Ouellette, Dispersion cancellation using linearly chirp Bragg filter in optical waveguides. Opt.Lea. Vol. 12, 1987:847-849
14. W.Loh, R. Laming, X Gu, et al. 10cm chirped fiber Bragg grating for dispersion compensation at 10Gbit/s over 400km of non-dispersion shifted fiber. Electron. Lett,
Vol.31, 1995(25):2203-2204.
15. J.Williams, I.Bennion, L.Zhang, The compression of optical pulses using self-phase-modulation and linearly chirped Bragg-gratings in fibers. IEEE Photon. Technol. Lett. Vol.7, 1995:491-493
16. K.Hill, et al. Narrow-bandwidth optical wave guide transmission filter. Electron. Lett. Vol.23, 1987:64-466
17. Fallon R W, Zhang L, Gloag A, et al. Identical broadband chirped grating interrogation technique for temperature and strain sensing. Electron Lett, Vol.33, 1997(8):705-707
18. Xu M G, Dong L, Reekie L, et al. Temperature-independent strain sensor using a chirp Bragg grating in a tapered optical fiber. Electron Lett. Vol.31, 1995(10):823-825
19．张培琨，李育林，刘家英等．线性啁啾光栅结果参数优化的定量研究方法．光子学报，1998(6)：499—503
20. Leonid Kazovsky, Sergio Benedtto, Alan Willner. Optical Fiber Communication System, Artech House, 1996
21. Djafar K. Mynbaev, Lowell L.Scheiner. Fiber-Optic Communications Technology. Prentice Hall. Inc, 2000
22. PeytonZ. Peables. Jr. Digital Communication System. Perentice-Hall, Englewood Ciffs, NJ. 1987
23. Steel, R.C., G.R. Walker, and N.G.Walker. Sensitivity of Optically Preamplified Receivers With Optical Filtering. IEEE Photonics Technology Letter. Vol.31,1991(4): 545-547
24. Mao Jin-li. Data Traffic System. Beijing: Journal of Beijing University of Posts and Telecommunications Publishing Company, 2001:48-51
25．王秉钧，窦晋江，张广森等编．通信原理及其应用．天津：天津大学出版社，2000：185—186
26．沈振元等．通信系统原理．西安：西安电子科技大学出版社，1999
27. S. Chinn. Error-rate performance of optical amplifiers with Fabry-Perot filters. Electron Letters. Vol.31, 1995(9):756-757
28. Iocco A,Limberger H G,Salathe R P. Bragg grating fast tunable filter. Electron. Lett. Vol.33, 1997(25):2147-2148
29. Kim S Y, Lee S B,Kwon S W et al..Channel-switching active add/drop multiplexer with tunable gratings. Electron. Lett. Vol.34, 1998(1):104-105
30. Cruz J L,Diez A,Andres M V et al.. Fiber Bragg gratings tuned and chiped using magnetic fields. Electron.Lett. Vol.33, 1997(3):235-236
31. Cruz J L,Dong L,Reekie L. Improved thermal sensitivity of fiber Bragg gratings using a polymer overlayer. Electron.Lett. Vol.32, 1996(4):385-386
32．杜卫冲，郑建成．一种测定光纤光栅布拉格波长位移的简单方法．光学学报．1996(1)：1636-1639
33. Kenneth O Hju, Gerald M. Fiber Bragg grating technology fundamentally and overview. J.Lithtwave technol. Vol.15, 1997(8):1263
2. G.Meltz, W. Morey, and W.Glenn. Formation of Bragg gratings in optical fibers by a transverse holographic method. Opt. Lett. Vol. 14, 1989:823-825
3. K.Hill, G.Meltz. Fiber Bragg Grating Technology Fundamentals and Overview. Journal of Lighwave Technoloyy. Vol.14, 1997(6): 1265-1274
4. K.Hill, B.Malo, F.Bilodeau et al. Bragg gratings fabrication in monomode photosensitivity optical fiber by UV exposure through a phase mask. App. Phy. Lett. Vol.62, 1993:1035-1037
5. K.Hill, B.Malo, K.A.Vineberg et al. Efficent mode conversion in telecommunication fiber using externally writing gratings. Electron Lett. Vol.26, 1990: 1270-1272
6. Q.Zhang, D.A.Brown, J.L.Reinhart et al. Linearly and nonlinearly chirp Bragg grating fabrication on curved fibers. Opt.Lett.Vol.21, 1995:1122-1124
7. D.Taverner, D.J.Richardson, S.Barcelos et al. Dispersion compensation of step-index fiber using cascaded chirp fiber gratings. Electron. Lett. Vol.31, 1995: 1004-1005
8. M.J.Cole, W.H.Loh, R.I.Laming et al. Moving fiber-phase mask-scanning beam technique for enhanced flexibility in producing fiber gratings with uniform phase mask. Electron. Lett. Vol.31, 1995:1488-1490
9. C.Byron, K.Sugden, T.Bricheno et al. Fabrication of chirp Bragg gratings in photosensitive fiber. Electron. Lett. Vol.29, 1993: 1659-1660
10. M.Farries, K.Sugden,D.C.Reid et al. Very broad reflection bandwidth(44nm)chirp fiber gratings and narrow bandpass filters produced by the use of an amplitude mask. Electron. Lett. Vol.30, 1994:891-892
11. K.Hill, F.Bilodeau, B.Malo et al. Chirp in fiber-gratings for compensation of optical-fiber dispersion. Opt. Lett, Vol. 19, 1994(17): 1314-1316
12. Y.Painchaud, A.Chandommet, J.Lauzon. Chirp fiber gratings produced by tilting the fiber. Electron. Lett, Vol.31, 1995:171-172
13. F.Ouellette, Dispersion cancellation using linearly chirp Bragg filter in optical waveguides. Opt.Lea. Vol. 12, 1987:847-849
14. W.Loh, R. Laming, X Gu, et al. 10cm chirped fiber Bragg grating for dispersion compensation at 10Gbit/s over 400km of non-dispersion shifted fiber. Electron. Lett,
Vol.31, 1995(25):2203-2204.
15. J.Williams, I.Bennion, L.Zhang, The compression of optical pulses using self-phase-modulation and linearly chirped Bragg-gratings in fibers. IEEE Photon. Technol. Lett. Vol.7, 1995:491-493
16. K.Hill, et al. Narrow-bandwidth optical wave guide transmission filter. Electron. Lett. Vol.23, 1987:64-466
17. Fallon R W, Zhang L, Gloag A, et al. Identical broadband chirped grating interrogation technique for temperature and strain sensing. Electron Lett, Vol.33, 1997(8):705-707
18. Xu M G, Dong L, Reekie L, et al. Temperature-independent strain sensor using a chirp Bragg grating in a tapered optical fiber. Electron Lett. Vol.31, 1995(10):823-825
19．张培琨，李育林，刘家英等．线性啁啾光栅结果参数优化的定量研究方法．光子学报，1998(6)：499—503
20. Leonid Kazovsky, Sergio Benedtto, Alan Willner. Optical Fiber Communication System, Artech House, 1996
21. Djafar K. Mynbaev, Lowell L.Scheiner. Fiber-Optic Communications Technology. Prentice Hall. Inc, 2000
22. PeytonZ. Peables. Jr. Digital Communication System. Perentice-Hall, Englewood Ciffs, NJ. 1987
23. Steel, R.C., G.R. Walker, and N.G.Walker. Sensitivity of Optically Preamplified Receivers With Optical Filtering. IEEE Photonics Technology Letter. Vol.31,1991(4): 545-547
24. Mao Jin-li. Data Traffic System. Beijing: Journal of Beijing University of Posts and Telecommunications Publishing Company, 2001:48-51
25．王秉钧，窦晋江，张广森等编．通信原理及其应用．天津：天津大学出版社，2000：185—186
26．沈振元等．通信系统原理．西安：西安电子科技大学出版社，1999
27. S. Chinn. Error-rate performance of optical amplifiers with Fabry-Perot filters. Electron Letters. Vol.31, 1995(9):756-757
28. Iocco A,Limberger H G,Salathe R P. Bragg grating fast tunable filter. Electron. Lett. Vol.33, 1997(25):2147-2148
29. Kim S Y, Lee S B,Kwon S W et al..Channel-switching active add/drop multiplexer with tunable gratings. Electron. Lett. Vol.34, 1998(1):104-105
30. Cruz J L,Diez A,Andres M V et al.. Fiber Bragg gratings tuned and chiped using magnetic fields. Electron.Lett. Vol.33, 1997(3):235-236
31. Cruz J L,Dong L,Reekie L. Improved thermal sensitivity of fiber Bragg gratings using a polymer overlayer. Electron.Lett. Vol.32, 1996(4):385-386
32．杜卫冲，郑建成．一种测定光纤光栅布拉格波长位移的简单方法．光学学报．1996(1)：1636-1639
33. Kenneth O Hju, Gerald M. Fiber Bragg grating technology fundamentally and overview. J.Lithtwave technol. Vol.15, 1997(8):1263