光纤型梳状滤波器的研究和设计毕业设计论文

1、毕业设计（论文）外文文献翻译毕业设计（论文）题目光纤型梳状滤波器的研究和设计翻译（1）题目基于一个高双折射光纤双sagnac环的可调谐多波长光纤激光器翻译（2）题目可调谐全光纤双折射梳状滤波器学 院通信工程专 业通信工程姓 名班 级学 号指导教师译文一：基于一个高双折射光纤双sagnac环的可调谐多波长光纤激光器王天枢,缪雪峰,周雪芳，钱胜杭州电子科技大学通信工程学院，中国杭州，310018作者通讯：tianshuw2011年12月12日接受；2012年2月21日校订；2012年2月21日完成；2012年2月22日通告（doc. id：159647）；2012年3月28日出版我们提出并证明了一

2、个基于双光纤sagnac环的可调谐多波长光纤激光器。使用琼斯矩阵分析了单个和两个sagnac环梳状滤波器的特性。模拟结果显示两个sagnac环的可调谐性和可控性比单个环的更好，这个结论也被实验结果所确认。通过调整偏振控制器和保偏光纤的长度，可实现波长范围、波长间隔和激光线宽的调谐。实验结果表明多波长光纤激光器输出激光的线宽为0.0187nm和光学边模抑制比为50db。©美国光学学会 2012ocis 编码：060.3510, 140.3600, 060.2420, 120.57901引言工作在波长1550nm附近的多波长光纤激光器已经吸引了许多人的兴趣，它可以应用于密集波分复用（dw

3、dm）系统，精细光谱学，光纤传感和微波（rf）光电1-4等领域。多波长光纤激光器可以通过布拉格光纤光栅阵列5，锁模技术6-7，光学参量振荡器8，四波混频效应9，受激布里渊散射效应实现10-12。掺铒光纤（edf）环形激光器可以提供大输出功率，高斜度效率和大可调谐波长范围。例如，作为一种可调谐edf激光器，带有单个高双折射光纤sagnac环的多波长光纤激光器已经提出13-15。输出波长可以通过调整偏振控制器（pc）进行调谐，波长间隔可以通过改变保偏光纤（pmf）的长度进行调谐。然而，对于单个sagnac环光纤激光器来说，波长间隔和线宽都不能独立调谐16。密集波分复用（dwdm）系统要求激光波长调

4、谐更灵活，否则会限制这些激光器的应用。一个双sagnac环的多波长光纤激光器能提供更好的可调谐性和可控性。采用这种结构，可以实现保持线宽不变的波长间隔可调谐，以及保持波长间隔不变的线宽调谐。本文提出和证明了一种双sagnac环可调谐多波长掺铒光纤环形激光器。多波长选择由两个sagnac环实现，而每个环由一个3db耦合器，一个pc，和一段高双折射pmf组成。本文模拟分析了单个和两个sagnac环的梳状滤波器的特征。实验中，得到输出激光的半峰全宽（fwhm）是0.0187nm，边模抑制比（smsr）是50db。通过调整两个pc可以实现多波长激光器输出的大范围调谐。与单环结构相比，改变pmf长度可以

5、独立调谐波长间隔和激光线宽。本文中提出的双sagnac环光纤激光器是先前单sagnac环多段pmf多波长光纤激光器工作的延伸，其在dwdm系统，传感和仪表测试中具有潜在应用。2实验装置和操作原则提出的多波长光纤激光器的实验装置示意图如图1（a）中所示。一个980nm的泵浦激光二极管（ld）通过一个980/1550nm波分复用（wdm）耦合到一段edf中。用一个能提供10%反馈功率的90/10光纤耦合器耦合出激光输出。多波长光纤激光器通过双sagnac环进行调谐。如图1（b）所示，高双折射sagnac环由一个3db耦合器，一段pmf，一个pc组成。端口3和端口4通过一个pc和一段pmf连接起来。

6、光束从端口1进入耦合器并被耦合器平均分成两束。这两束反向传播的光束在环中重新耦合。由于pmf的高双折射影响，光束在两个轴（快轴和慢轴）上出现相位差。因此，当光通过pmf时会产生一个角度偏差，通过pc时会产生另一个角度偏差。当反向传播过一个光纤环后，两束光束在耦合器上干涉。sagnac环的输出特性可以用jones矩阵分析。pmf的jones传播矩阵可以描述为： （1）这里的是光在快轴和慢轴传播相同距离所产生的相位差，l是pmf的有效长度，是波长，是两个轴的有效折射率差。还有，和是快轴和慢轴的有效折射率指数。因为当光传播通过一个pc时偏振角偏转为，通过pc的透射光束的jones矩阵可以描述为：（2

7、）端口1的入射光电矢量为，端口2的入射光电矢量为（=0）。被耦合器分成和。设为通过pc和pmf的光学矢量，为通过pc和pmf的光学矢量。因此，和相干叠加后在端口1反射，在端口2透过： （3）端口1的入射功率为，反射功率为。端口2的反射功率为。透射率为： （4）这个说明单sagnac环的透射率与偏振偏转角度和两个轴的相位差有关。正如图2的模拟结果所示，pmf长度越大，滤波周期越短和滤波带宽越窄。但是，周期和带宽不能单独调谐。另外，pmf双折射率越高，滤波周期越短和滤波带宽越窄。对双sagnac环来说，在两个sagnac环之间安装一个光纤隔离器可以消除反射光。因此，双环的透射率可以描述为： （5）

8、很明显，双sagnac环的透射率与长度或者基于eq（5）两段pmf的折射率差有关。其次，滤波周期和带宽分别由一段较短的pmf和一段较长的pmf决定，输出激光可以通过单独调整pc状态和pmf长度进行调谐。在双sagnac环结构中，两段pmf长度分别为2m和1m，模拟结果如图3（a）所示。图中我们能看到滤波周期在变而滤波带宽不变。保持一个sagnac环中的pmf为2m长不变，图3（b）表明改变另一个sagnac环中较长pmf（>2m）的长度可以改变滤波带宽但使滤波周期不变。因此，使用双sagnac环光纤激光器可以实现波长间隔和带宽独立调谐。图1 （a）基于双sagnac高双折射光纤环干涉仪的

9、可调谐多波长光纤激光器（b）sagnac干涉环图2 （彩色线）单sagnac环的透射率谱图3 （彩色线）双sagnac环的透射率谱 （a）线宽不变时的可调谐滤波器的周期（b）周期不变时的可调谐滤波器的线宽3实验及结果在实验中，隔离器1的作用是确保光单向传播和降低噪声。掺铒光纤的长度，截至波长，数值孔径和在1530nm附近的峰值吸收分别为12m，960nm，0.23，7db/m。pmf的长度为5m和2m，双折射拍长小于5.0mm。泵浦光功率为300mw，我们使用一种光谱分析仪（aq6370b）监视输出激光。根据模拟结果可以得出改变短pmf长度可以调谐滤波周期，滤波器中所有的传播光会产生多个激光。

10、由于增益谱平坦度和偏振衰减的限制，滤波带宽的部分光将被抑制。激射波长的数量对pc状态敏感。中心波长在1549.6nm的三波长激光运行如图4中所示，激光器的smsr大于50db。多波激光器不规则的输出频谱主要由不精确的pmf折射率差，不精确的pmf长度和接头损耗引起。图4（b）显示了超过10分钟周期，每隔2分钟重新扫描得到的激光输出光谱，其激光波长在1544.9、1549.6和1554.3nm，可以观察到稳定的输出功率和波长。对三波长激光光功率的测量表明最大的功率起伏小于0.2db，波长起伏小于0.02nm。偏振偏转角度可以通过调整pc1和pc2进行调谐，因此输出激光的波长和波长间隔也可以调谐。

11、如图5所示，调整两个pc可以观察到多波长输出激光在c波段内的（a）短波长和（b）长波长。图5（c）整个c波段可以观察到多波长输出激光，并且激光器稳定性随着振荡模式的增加而降低。在实验中，我们观察到输出波长间隔可以通过调整两个pc进行调谐。如图6所示，多波长光纤激光器的波长间隔从2.82（a）降到1.76（b）nm。调整pc，滤波器带宽中的部分光不会达到阈值。其次波长大小和波长间隔可以通过pc调谐。通过调整pc，我们观察到能够实现稳定输出峰值的波长最大数目是6个。波长间隔可以通过改变基于eq（5）的短pmf长度进行调谐。在实验中，如图7（a）所示，我们可以观察到用5m长的长pmf和1m长的短pm

12、f时波长间隔为2.81nm。另外，如图7（b）所示，我们可以观察到用2m长的短pmf时波长间隔为1.79nm。根据模拟和实验的结果，波长间隔随着短pmf长度增大而变小但带宽保持不变。根据模拟结果，激光器线宽可以通过改变长pmf的长度进行调谐。如图8（a）所示，当两段pmf长度为1m时能观察到0.036nm的3db线宽；如图8（b）所示，当长pmf为5m时能观察到0.0187nm的3db线宽。实验结果表明了激光线宽随着长pmf长度增大而变小但波长间隔保持不变。因此，模拟结果图3（b）已经用实验结果证实。峰值线宽越小，光纤激光器的抗环境干扰能力越弱，但抖动起伏小于0.02nm。图4 （彩色线）多波

13、长光纤激光器的输出光谱 （a）三波长激光光谱 （b）10分钟内重复检测输出光谱图5 多波长激光输出光谱 （a）短波长带 （b）长波长带（c）整个c波段图6 可调谐波长间隔在输出激光光谱 （a）波长间隔为2.82nm （b）波长间隔为1.76n m图7 改变短pmf长度的输出多波长激光器光谱 （a）1m长的短pmf（b）2m长的短pmf图8 改变长pmf长度的输出多波长激光器光谱 （a）1m长的长pmf （b）2m长的长pmf4结论我们提出并证明了基于双sagnac环的可调谐多波长环型edf激光器。通过jones矩阵分析了单个和两个sagnac环梳状滤波器的特性。模拟结果表明双sagnac环比单

14、sagnac环具有更好的可调谐性和可控性。3db的输出激光的线宽测量为0.0187nm，smsr为50db。通过调整两个pc可以观察到大范围可调谐多波长光纤激光器的输出，能够实现稳定输出峰值的波长最大数目是6个。改变短pmf长度可以调谐波长间隔而不改变线宽；改变长pmf长度可以独立调谐激光线宽。我们由衷地感谢中国自然科学基金的支持（项目号6907020）。5、参考文献1. a. e. h. oehler, s. c. zeller, k. j. weingarten, and u. keller,“ broad multiwavelength source with 50 ghz channe

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25、amilla, and e. a. kuzin, “switchable and tuneable multisavelength er-doped fibre ring laser using sagnac filters,” laser phys. 20, 720725 (2010).外文原文一：tunable multiwavelength fiber laser basedon a double sagnac hibi fiber looptianshu wang,* xuefeng miao, xuefang zhou, and sheng qiancollege of commun

26、ication engineering, hangzhou dianzi university, hangzhou 310018, china*corresponding author: tianshuwreceived 12 december 2011; revised 21 february 2012; accepted 21 february 2012;posted 22 february 2012 (doc. id 159647); published 28 march 2012a tunable multiwavelength fiber laser based on double

27、sagnac loops is pro-posed and demonstrated. comb filter characteristics of single and double sag-nac loops are analyzed by jones matrix. simulated results show that thereare better tunability and controllability with double loops than with a singleloop, and this also has been confirmed by experiment

28、al results. by adjusting the polarization controller and the length of the polarization maintaining fiber the wavelength range, wavelength spacing, and laser linewidth can be tuned. experimental results indicate that the linewidth of the multiwavelength fiber laser was 0.0187 nm and the optical side

29、mode suppression ratio was 50 db. © 2012 optical society of americaocis codes: 060.3510, 140.3600, 060.2420, 120.5790.1. introductionmultiwavelength fiber lasers operating on the wavelength around 1550 nm have attracted much interest, such as sources for dense wavelength division multiplexing (

30、dwdm) systems, precise spectroscopy, optical fiber sensing and rf photonics 14. amultiwavelength fiber laser can be realized by a fiber bragg grating array 5, the mode-locked technique 6,7, an optical parametric oscillator 8, the fourwave mixing effect 9, or the stimulated brillouin scattering effec

31、t 1012. ring erbium-doped fiber (edf) lasers can provide large output power, high slope efficiency, and a wide tunable wavelength range. as a kind of tunable edf lasers, multiwavelength fiber lasers with single high birefringence (hibi) fiber sagnac loop have been highlighted 1315. the output wavele

32、ngth can be tuned by adjusting the polarization controller (pc), and the wavelength spacing can be tuned by changingthe length of polarization maintaining fiber (pmf). however, neither the wavelength spacing nor the linewidth can be tuned independently for single sagnac loop fiber lasers 16. dwdm sy

33、stems require that tuning of the laser wavelength be more flexible, or the applications of these lasers will be limited. however, a multiwavelength fiber laser with double sagnac loops can provides better tenability and controllability. for this structure, wavelength spacing can be tuned while keepi

34、ng the linewidth unchanged, and linewidth can be tuned while keeping wavelength spacing unchanged. in this paper, a tunable multiwavelength ring edf laser with double sagnac loops is proposed and demonstrated. the multiwavelength selection is performed by two sagnac loops, and each loop is composed

35、of a 3 db coupler, a pc, and a segment of hibi pmf. the comb filter characteristics of single and double sagnac loops are simulated and analyzed. in experiment, thefwhm of the output laser is measured as 0.0187 nm, and the sidemode suppression ratio (smsr) is 50 db. by adjusting two pcs, the multiwa

36、velength laser can be widely tuned. by changing the length of the pmf, the wavelength spacing and the linewidth can be tuned independently, compared with a single loop structure. the double-sagnac-loop fiber laser proposed in this work is an extension of previous works on multiwavelength fiber laser

37、s with multiple sections of pmfs in the single sagnac loop, and it has potential applications in dwdm systems, sensing, and instrument testing.2. experimental setup and operation principlethe experimental setup of the proposed multiwavelength fiber laser is shown in fig. 1(a). a 980 nm pump laser di

38、ode (ld) is coupled into a segment of edf through a 9801550 nm wavelength division multiplexer (wdm). the laser output is coupled out with a 90/10 fiber coupler, which provides 10% power for feedback. the multiwavelength fiber laser is tuned by the double sagnac loops. as shown in fig. 1(b), the hib

39、i sagnac loop is composed of a 3 db coupler, a segment of pmf, and a pc. port 3 and port 4 are connected together through a pc and a segment of pmf. the beam enters into the coupler from port 1, and is divided into two beams by the coupler averager. these two counterpropagating beams recombine in th

40、e loop. due tohibi effect of the pmf, there is a phase difference of the lights on two axes (fast axis and slow axis). hence, when the light passes through the pmf, there is an angle deflection, and there is another angle deflection when the light passes through the pc. after traveling through a fib

41、er loop oppositely, the two beams interfere in the coupler. the output characteristics of the sagnac loop can be analyzed by a jones matrix. the jones transmission matrix of the pmf can be described as （1）where is the phase difference between the light on the fast axis and that on the slow axis in t

42、he same transmission distance, is the effective length of the pmf, is the wavelength, and is the effective refractive difference between two axes. then, and are the effective refractive indices of the fast axis and the slow axis. since the polarization angle deflection of the light is when the light

43、 transmits through a pc, the jones matrix of the positive transmitting light beam through the pc can be described as （2）the electric vector of the incident beam is at port 1, and the electric vector of the incident beam is at port 2 (=0). is split into and by the coupler. let be the optical vector o

44、f the through the pc and the pmf, and be the optical vector of the through the pc and the pmf. thus, and are reflected at port 1 and transmitted at port 2 after coherent superimposition: （3）the incident power at port 1 is , and the reflective power is . the reflective power at port 2 is . the transm

45、issivity is（4） this shows that single-sagnac-loop transmissivity is related to the polarization deflection angle and the phase difference between two axes. as shown in the simulated results in fig. 2, the filter period is shorter and the filter bandwidth is narrower when the length of the pmf is inc

46、reased. however, the period and bandwidth cannot be tuned independently. in addition, with the pmf birefringences higher, the filter period is shorter and the filter bandwidth is narrower. for the double sagnac loops, a fiber isolator is mounted between two sagnac loops for eliminating the reflectiv

47、e light. so, the transmissivity of double loops can be described as （5）obviously, the transmissivity of double sagnac loopsis related to the length or the refraction difference of two segments of pmfs based on eq. (5). then, the filter period and bandwidth are determined by a shorter pmf and a longe

48、r pmf, respectively, and the output laser can be tuned by adjusting the pcs and the lengths of the pmfs. in a double-sagnac-loop structure, two segments of pmf were 2 m long and 1 m long. figure 3(a) shows the simulated result. from the figure we can see that the filter period can be changed while t

49、he filter bandwidth is unchanged. keeping a 2 m long pmf in one sagnac loop, fig. 3(b) shows that the filter bandwidth can be changed while the filter period is unchanged by changing the length of a longer pmf (>2 m) in another sagnac loop. thus, by using double sagnac loops in the fiber laser, b

50、oth the wavelength spacing and the bandwidth can be tuned independently.fig. 1. (a) tunable multiwavelength fiber laser based on a double sagnac hibi fiber loop interferometer. (b) sagnac interference loop.fig. 2. (color online) transmissivity spectrum of single sagnac loop.fig. 3. (color online) tr

51、ansmissivity spectrum of double sagnac loop. (a) tunable filter period without changing filter bandwidth.(b) tunable filter bandwidth without changing filter period.3. experiments and resultsin experiments, isolator 1 was used to ensure the unidirectional propagation of the light and decrease the no

52、ise. the length, cutoff wavelength, numerical aperture, and peak absorption near 1530 nm of the edf are 12 m, 960 nm, 0.23, and 7 dbm, respectively. lengths of pmfs are 5 and 2 m, and the birefringence beat length is less than 5.0 mm. to be pumped at 300 mw, we used an optical spectrum analyzer (aq6

53、370b) to monitor the output laser. based on simulated results, the filter period can be tuned by changing the length of the short pmf, and multiple lasers will be produced by all the transmitted light of the filter. since gain spectrumflatness and polarization attenuation are limited, part of the li

54、ght in the filter bandwidth will be suppressed. the number of lasing wavelengths was sensitive to the pc. the operation of three wavelengths with the center wavelength at 1549.6 nm is illustrated in fig. 4, and the smsr of the laser is greater than 50 db. the irregular output spectrum of the multiwa

55、velength laser was mainly caused by inaccurate refractive difference of pmfs, inaccurate length of pmfs, and the splicing loss. fig. 4(b) shows the repeated scans of the output spectrum with 1544.9, 1549.6, and 1554.3 nm at 2 min intervals over a 10 min period. stable output power and wavelength can

56、 be observed. a measurement of the optical powers at three wavelengths showed that the maximum power fluctuation was less than 0.2 db and the wavelength fluctuation was less than 0.02 nm. the polarization deflection angle can be tuned by adjusting pc1 and pc2. then the wavelength and the wavelength spacing of the output laser can be tuned. as shown in fig. 5,