光纖型梳狀濾波器的研究和設(shè)計(jì)畢業(yè)設(shè)計(jì)論文

1、畢業(yè)設(shè)計(jì)（論文）外文文獻(xiàn)翻譯畢業(yè)設(shè)計(jì)（論文）題目光纖型梳狀濾波器的研究和設(shè)計(jì)翻譯（1）題目基于一個(gè)高雙折射光纖雙sagnac環(huán)的可調(diào)諧多波長光纖激光器翻譯（2）題目可調(diào)諧全光纖雙折射梳狀濾波器學(xué) 院通信工程專 業(yè)通信工程姓 名班 級(jí)學(xué) 號(hào)指導(dǎo)教師譯文一：基于一個(gè)高雙折射光纖雙sagnac環(huán)的可調(diào)諧多波長光纖激光器王天樞,繆雪峰,周雪芳，錢勝杭州電子科技大學(xué)通信工程學(xué)院，中國杭州，310018作者通訊：tianshuw2011年12月12日接受；2012年2月21日校訂；2012年2月21日完成；2012年2月22日通告（doc. id：159647）；2012年3月28日出版我們提出并證明了一

2、個(gè)基于雙光纖sagnac環(huán)的可調(diào)諧多波長光纖激光器。使用瓊斯矩陣分析了單個(gè)和兩個(gè)sagnac環(huán)梳狀濾波器的特性。模擬結(jié)果顯示兩個(gè)sagnac環(huán)的可調(diào)諧性和可控性比單個(gè)環(huán)的更好，這個(gè)結(jié)論也被實(shí)驗(yàn)結(jié)果所確認(rèn)。通過調(diào)整偏振控制器和保偏光纖的長度，可實(shí)現(xiàn)波長范圍、波長間隔和激光線寬的調(diào)諧。實(shí)驗(yàn)結(jié)果表明多波長光纖激光器輸出激光的線寬為0.0187nm和光學(xué)邊模抑制比為50db。©美國光學(xué)學(xué)會(huì) 2012ocis 編碼：060.3510, 140.3600, 060.2420, 120.57901引言工作在波長1550nm附近的多波長光纖激光器已經(jīng)吸引了許多人的興趣，它可以應(yīng)用于密集波分復(fù)用（dw

3、dm）系統(tǒng)，精細(xì)光譜學(xué)，光纖傳感和微波（rf）光電1-4等領(lǐng)域。多波長光纖激光器可以通過布拉格光纖光柵陣列5，鎖模技術(shù)6-7，光學(xué)參量振蕩器8，四波混頻效應(yīng)9，受激布里淵散射效應(yīng)實(shí)現(xiàn)10-12。摻鉺光纖（edf）環(huán)形激光器可以提供大輸出功率，高斜度效率和大可調(diào)諧波長范圍。例如，作為一種可調(diào)諧edf激光器，帶有單個(gè)高雙折射光纖sagnac環(huán)的多波長光纖激光器已經(jīng)提出13-15。輸出波長可以通過調(diào)整偏振控制器（pc）進(jìn)行調(diào)諧，波長間隔可以通過改變保偏光纖（pmf）的長度進(jìn)行調(diào)諧。然而，對(duì)于單個(gè)sagnac環(huán)光纖激光器來說，波長間隔和線寬都不能獨(dú)立調(diào)諧16。密集波分復(fù)用（dwdm）系統(tǒng)要求激光波長調(diào)

4、諧更靈活，否則會(huì)限制這些激光器的應(yīng)用。一個(gè)雙sagnac環(huán)的多波長光纖激光器能提供更好的可調(diào)諧性和可控性。采用這種結(jié)構(gòu)，可以實(shí)現(xiàn)保持線寬不變的波長間隔可調(diào)諧，以及保持波長間隔不變的線寬調(diào)諧。本文提出和證明了一種雙sagnac環(huán)可調(diào)諧多波長摻鉺光纖環(huán)形激光器。多波長選擇由兩個(gè)sagnac環(huán)實(shí)現(xiàn)，而每個(gè)環(huán)由一個(gè)3db耦合器，一個(gè)pc，和一段高雙折射pmf組成。本文模擬分析了單個(gè)和兩個(gè)sagnac環(huán)的梳狀濾波器的特征。實(shí)驗(yàn)中，得到輸出激光的半峰全寬（fwhm）是0.0187nm，邊模抑制比（smsr）是50db。通過調(diào)整兩個(gè)pc可以實(shí)現(xiàn)多波長激光器輸出的大范圍調(diào)諧。與單環(huán)結(jié)構(gòu)相比，改變pmf長度可以

5、獨(dú)立調(diào)諧波長間隔和激光線寬。本文中提出的雙sagnac環(huán)光纖激光器是先前單sagnac環(huán)多段pmf多波長光纖激光器工作的延伸，其在dwdm系統(tǒng)，傳感和儀表測(cè)試中具有潛在應(yīng)用。2實(shí)驗(yàn)裝置和操作原則提出的多波長光纖激光器的實(shí)驗(yàn)裝置示意圖如圖1（a）中所示。一個(gè)980nm的泵浦激光二極管（ld）通過一個(gè)980/1550nm波分復(fù)用（wdm）耦合到一段edf中。用一個(gè)能提供10%反饋功率的90/10光纖耦合器耦合出激光輸出。多波長光纖激光器通過雙sagnac環(huán)進(jìn)行調(diào)諧。如圖1（b）所示，高雙折射sagnac環(huán)由一個(gè)3db耦合器，一段pmf，一個(gè)pc組成。端口3和端口4通過一個(gè)pc和一段pmf連接起來。

6、光束從端口1進(jìn)入耦合器并被耦合器平均分成兩束。這兩束反向傳播的光束在環(huán)中重新耦合。由于pmf的高雙折射影響，光束在兩個(gè)軸（快軸和慢軸）上出現(xiàn)相位差。因此，當(dāng)光通過pmf時(shí)會(huì)產(chǎn)生一個(gè)角度偏差，通過pc時(shí)會(huì)產(chǎn)生另一個(gè)角度偏差。當(dāng)反向傳播過一個(gè)光纖環(huán)后，兩束光束在耦合器上干涉。sagnac環(huán)的輸出特性可以用jones矩陣分析。pmf的jones傳播矩陣可以描述為： （1）這里的是光在快軸和慢軸傳播相同距離所產(chǎn)生的相位差，l是pmf的有效長度，是波長，是兩個(gè)軸的有效折射率差。還有，和是快軸和慢軸的有效折射率指數(shù)。因?yàn)楫?dāng)光傳播通過一個(gè)pc時(shí)偏振角偏轉(zhuǎn)為，通過pc的透射光束的jones矩陣可以描述為：（2

7、）端口1的入射光電矢量為，端口2的入射光電矢量為（=0）。被耦合器分成和。設(shè)為通過pc和pmf的光學(xué)矢量，為通過pc和pmf的光學(xué)矢量。因此，和相干疊加后在端口1反射，在端口2透過： （3）端口1的入射功率為，反射功率為。端口2的反射功率為。透射率為： （4）這個(gè)說明單sagnac環(huán)的透射率與偏振偏轉(zhuǎn)角度和兩個(gè)軸的相位差有關(guān)。正如圖2的模擬結(jié)果所示，pmf長度越大，濾波周期越短和濾波帶寬越窄。但是，周期和帶寬不能單獨(dú)調(diào)諧。另外，pmf雙折射率越高，濾波周期越短和濾波帶寬越窄。對(duì)雙sagnac環(huán)來說，在兩個(gè)sagnac環(huán)之間安裝一個(gè)光纖隔離器可以消除反射光。因此，雙環(huán)的透射率可以描述為： （5）

8、很明顯，雙sagnac環(huán)的透射率與長度或者基于eq（5）兩段pmf的折射率差有關(guān)。其次，濾波周期和帶寬分別由一段較短的pmf和一段較長的pmf決定，輸出激光可以通過單獨(dú)調(diào)整pc狀態(tài)和pmf長度進(jìn)行調(diào)諧。在雙sagnac環(huán)結(jié)構(gòu)中，兩段pmf長度分別為2m和1m，模擬結(jié)果如圖3（a）所示。圖中我們能看到濾波周期在變而濾波帶寬不變。保持一個(gè)sagnac環(huán)中的pmf為2m長不變，圖3（b）表明改變另一個(gè)sagnac環(huán)中較長pmf（>2m）的長度可以改變?yōu)V波帶寬但使濾波周期不變。因此，使用雙sagnac環(huán)光纖激光器可以實(shí)現(xiàn)波長間隔和帶寬獨(dú)立調(diào)諧。圖1 （a）基于雙sagnac高雙折射光纖環(huán)干涉儀的

9、可調(diào)諧多波長光纖激光器（b）sagnac干涉環(huán)圖2 （彩色線）單sagnac環(huán)的透射率譜圖3 （彩色線）雙sagnac環(huán)的透射率譜 （a）線寬不變時(shí)的可調(diào)諧濾波器的周期（b）周期不變時(shí)的可調(diào)諧濾波器的線寬3實(shí)驗(yàn)及結(jié)果在實(shí)驗(yàn)中，隔離器1的作用是確保光單向傳播和降低噪聲。摻鉺光纖的長度，截至波長，數(shù)值孔徑和在1530nm附近的峰值吸收分別為12m，960nm，0.23，7db/m。pmf的長度為5m和2m，雙折射拍長小于5.0mm。泵浦光功率為300mw，我們使用一種光譜分析儀（aq6370b）監(jiān)視輸出激光。根據(jù)模擬結(jié)果可以得出改變短pmf長度可以調(diào)諧濾波周期，濾波器中所有的傳播光會(huì)產(chǎn)生多個(gè)激光。

10、由于增益譜平坦度和偏振衰減的限制，濾波帶寬的部分光將被抑制。激射波長的數(shù)量對(duì)pc狀態(tài)敏感。中心波長在1549.6nm的三波長激光運(yùn)行如圖4中所示，激光器的smsr大于50db。多波激光器不規(guī)則的輸出頻譜主要由不精確的pmf折射率差，不精確的pmf長度和接頭損耗引起。圖4（b）顯示了超過10分鐘周期，每隔2分鐘重新掃描得到的激光輸出光譜，其激光波長在1544.9、1549.6和1554.3nm，可以觀察到穩(wěn)定的輸出功率和波長。對(duì)三波長激光光功率的測(cè)量表明最大的功率起伏小于0.2db，波長起伏小于0.02nm。偏振偏轉(zhuǎn)角度可以通過調(diào)整pc1和pc2進(jìn)行調(diào)諧，因此輸出激光的波長和波長間隔也可以調(diào)諧。

11、如圖5所示，調(diào)整兩個(gè)pc可以觀察到多波長輸出激光在c波段內(nèi)的（a）短波長和（b）長波長。圖5（c）整個(gè)c波段可以觀察到多波長輸出激光，并且激光器穩(wěn)定性隨著振蕩模式的增加而降低。在實(shí)驗(yàn)中，我們觀察到輸出波長間隔可以通過調(diào)整兩個(gè)pc進(jìn)行調(diào)諧。如圖6所示，多波長光纖激光器的波長間隔從2.82（a）降到1.76（b）nm。調(diào)整pc，濾波器帶寬中的部分光不會(huì)達(dá)到閾值。其次波長大小和波長間隔可以通過pc調(diào)諧。通過調(diào)整pc，我們觀察到能夠?qū)崿F(xiàn)穩(wěn)定輸出峰值的波長最大數(shù)目是6個(gè)。波長間隔可以通過改變基于eq（5）的短pmf長度進(jìn)行調(diào)諧。在實(shí)驗(yàn)中，如圖7（a）所示，我們可以觀察到用5m長的長pmf和1m長的短pm

12、f時(shí)波長間隔為2.81nm。另外，如圖7（b）所示，我們可以觀察到用2m長的短pmf時(shí)波長間隔為1.79nm。根據(jù)模擬和實(shí)驗(yàn)的結(jié)果，波長間隔隨著短pmf長度增大而變小但帶寬保持不變。根據(jù)模擬結(jié)果，激光器線寬可以通過改變長pmf的長度進(jìn)行調(diào)諧。如圖8（a）所示，當(dāng)兩段pmf長度為1m時(shí)能觀察到0.036nm的3db線寬；如圖8（b）所示，當(dāng)長pmf為5m時(shí)能觀察到0.0187nm的3db線寬。實(shí)驗(yàn)結(jié)果表明了激光線寬隨著長pmf長度增大而變小但波長間隔保持不變。因此，模擬結(jié)果圖3（b）已經(jīng)用實(shí)驗(yàn)結(jié)果證實(shí)。峰值線寬越小，光纖激光器的抗環(huán)境干擾能力越弱，但抖動(dòng)起伏小于0.02nm。圖4 （彩色線）多波

13、長光纖激光器的輸出光譜 （a）三波長激光光譜 （b）10分鐘內(nèi)重復(fù)檢測(cè)輸出光譜圖5 多波長激光輸出光譜 （a）短波長帶 （b）長波長帶（c）整個(gè)c波段圖6 可調(diào)諧波長間隔在輸出激光光譜 （a）波長間隔為2.82nm （b）波長間隔為1.76n m圖7 改變短pmf長度的輸出多波長激光器光譜 （a）1m長的短pmf（b）2m長的短pmf圖8 改變長pmf長度的輸出多波長激光器光譜 （a）1m長的長pmf （b）2m長的長pmf4結(jié)論我們提出并證明了基于雙sagnac環(huán)的可調(diào)諧多波長環(huán)型edf激光器。通過jones矩陣分析了單個(gè)和兩個(gè)sagnac環(huán)梳狀濾波器的特性。模擬結(jié)果表明雙sagnac環(huán)比單

14、sagnac環(huán)具有更好的可調(diào)諧性和可控性。3db的輸出激光的線寬測(cè)量為0.0187nm，smsr為50db。通過調(diào)整兩個(gè)pc可以觀察到大范圍可調(diào)諧多波長光纖激光器的輸出，能夠?qū)崿F(xiàn)穩(wěn)定輸出峰值的波長最大數(shù)目是6個(gè)。改變短pmf長度可以調(diào)諧波長間隔而不改變線寬；改變長pmf長度可以獨(dú)立調(diào)諧激光線寬。我們由衷地感謝中國自然科學(xué)基金的支持（項(xiàng)目號(hào)6907020）。5、參考文獻(xiàn)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,