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研究采用的实验结构如图1所示,一个980 nm泵浦源通过980/1550 nm波分复用器(Wavelength Division Multiplexer, WDM)泵浦0.9 m长高掺铒光纤,二阶色散为−0.02001 ps2/m。腔中的两个偏振控制器 (Polarization Controller, PC) 和一个偏振相关隔离器 (Polarization Dependent Isolator, PD-ISO) 作为一种类饱和吸收体结构实现激光器在腔中的锁模。色散补偿光纤长度为1 m,二阶色散为1.848 ps2/m。其他器件的尾纤均为标准单模光纤 (Singe Mode Fiber, SMF),长度为5 m,二阶色散为−0.02294 ps2/m。谐振腔内10%的光通过光纤耦合器1 (Optical Coupler, OC) 从腔中输出,其余90%的光反馈回环形腔中。输出的激光通过耦合器2的20%端口输出,并通过频谱分析仪 (FSA, Agilent N1996 A) 显示和记录频谱信息。光纤耦合器2的80%端口输出激光的脉冲宽度通过单模光纤压缩,然后通过掺铒光纤放大器 (Erbium-Doped Fiber Amplifier, EDFA) 进行放大。
图 1 锁模光纤激光器结构。WDM:波分复用器;EDF:掺铒光纤;PC:偏振控制器;PD-ISO:偏振无关隔离器;DCF:色散补偿光纤;OC:光耦合器;SMF:单模光纤;EDFA:掺铒光纤放大器;HNLF:高非线性光纤
Figure 1. Structure of mode-locked fiber laser. WDM: wavelength division multiplexer; EDF: erbium-doped fiber; PC: polarization controller; PD-ISO: polarization-dependent isolator; DCF: dispersion compensation fiber; OC: optical coupler; SMF: single-mode fiber; EDFA: Erbium-doped fiber amplifier; HNLF: high nonlinear fiber
放大的脉冲光注入进一段经过拉锥的10 m长高非线性光纤(High Nonlinear Fiber, HNLF),如图2所示。实验中使用的HNLF的数值孔径为0.35,传输损耗小于1.5 dB/km。经光谱分析仪(OSA, YOKOGAWA AQ6375)对输出的各种光谱进行观察和数据记录,光谱仪最高分辨率为0.05 nm。锁模激光的脉冲序列由10 GHz高速光电探测器探测,并通过高速示波器观测相应的波形(Oscilloscope, Agilent D S 09254 A),脉冲的自相关曲线由自相关仪(Auto-correlator, FR-103 XL)测量。
拉锥后的高非线性光纤直径为10 μm,相比于普通高非线性光纤,根据公式(1)和(2),它的非线性效应更强。
$$ {A_{{\rm{eff}}}} = \dfrac{{{{\left( {\mathop { \displaystyle\iint \displaystyle\iint }\nolimits_{ - \infty }^\infty |F(x,y){|^2}{\rm{d}}x{\rm{d}}y} \right)}^2}}}{{\mathop {\displaystyle\iint \displaystyle\iint }\nolimits_{ - \infty }^\infty |F(x,y){|^4}{\rm{d}}x{\rm{d}}y}} $$ (1) 式中:
${A_{\rm eff}}$ 为光纤的有效模场面积;$ F\left( {x,y} \right) $ 代表光纤中基模的模分布。$$ \gamma \left( {{\omega _0}} \right) = \dfrac{{{\omega _0}{n_2}}}{{c{A_{{\rm{eff }}}}}},{n_2} = \dfrac{{2{n_2}}}{{{_0}nc}} $$ (2) 式中:
$ \gamma $ 为非线性参量;$ {\varepsilon _0} $ 为介电常数;$ {\omega _0} $ 为中心频率;$ {n_2} $ 为非线性克尔参量;$ c $ 为光速;$ {\bar n_2} $ 为非线性折射率系数。
Supercontinuum generation assisted by dissipative and bound state pulse switchable
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摘要: 当超短脉冲进入高非线性光纤时,在色散和非线性效应的共同作用下,脉冲频谱中会产生一些新的频率分量,使得输出频谱比输入频谱宽得多。这种光谱被称为超连续谱。超连续谱光源具有光谱范围宽、方向性好、亮度高、空间相干性好等优点。在锁模激光器中,传统孤子、耗散孤子和类噪声脉冲可以作为种子源产生超连续谱。文中,笔者建立了一个NPR被动锁模光纤激光器来产生脉冲激光。然后,添加一段DCF以补偿腔中的色散,从而产生耗散孤子。同时,通过调节腔内PC,可以实现束缚态和耗散孤子的状态切换。输出脉冲经10 m单模光纤压缩后注入部分拉锥后的高非线性光纤以产生超连续谱。实验中,我们得到了脉宽为5.6 ps、重复频率为32 MHz、信噪比为52 dB的耗散孤子锁模脉冲,压缩后的脉冲宽度为868 fs,用作超连续谱产生。超连续谱的覆盖范围约为1200~2200 nm,其20 dB谱宽为357 nm。通过调节偏振控制器,实现耗散孤子脉冲与束缚态脉冲之间的切换,束缚态脉冲持续时间为1.4 ps,脉冲间隔为14 ps,信噪比为51 dB,产生1600~1870 nm的超连续光谱,20 dB的光谱宽度为135 nm。Abstract: When an ultrashort pulse bursts into a highly nonlinear fiber, some new frequency components are generated in the pulse spectrum under the combined action of dispersion and nonlinear effects, which makes the output spectrum much broader than the input spectrum. The spectrum is called the supercontinuum. Supercontinuum light sources have the advantages of a wide spectral range, good directivity, high brightness, and good spatial coherence. In mode-locked lasers, traditional solitons, dissipative solitons, and noise-like pulses can be used as seed sources to generate a supercontinuum spectrum. In this paper, we build an NPR passively mode-locked fiber laser to generate pulsed laser. Then, a section of DCF is added to compensate for the dispersion in the cavity to produce dissipative solitons. Meanwhile, the states of bound states and dissipative solitons can be switched by carefully adjusting the paddles of PC in the cavity. The output pulse is compressed by a 10 m single-mode fiber before being injected into a tapered highly nonlinear fiber to generate a supercontinuum. In the experiment, we obtain a dissipative soliton mode-locked pulse with a pulse duration of 5.6 ps, a repetition frequency of 32 MHz, and a signal-to-noise ratio of 52 dB. The compressed pulse duration is 808 fs, which is used as the seed to generate a supercontinuum. The cover range of the supercontinuum is approximately 1200 nm to 2200 nm, and its 20 dB spectrum width is 357 nm. By tuning the polarization controller, the switch between the dissipative soliton pulse and the bound state pulse is realized. The pulse duration of the bound state is 1.4 ps, the pulse separation is 14 ps, and the signal-to-noise ratio is 51 dB, which produces a supercontinuum spectrum of 1600-1870 nm with a 20 dB spectral width of 135 nm.
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Key words:
- ultrafast lasers /
- passively mode-locked /
- supercontinuum /
- dissipative soliton /
- bound state soliton
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图 1 锁模光纤激光器结构。WDM:波分复用器;EDF:掺铒光纤;PC:偏振控制器;PD-ISO:偏振无关隔离器;DCF:色散补偿光纤;OC:光耦合器;SMF:单模光纤;EDFA:掺铒光纤放大器;HNLF:高非线性光纤
Figure 1. Structure of mode-locked fiber laser. WDM: wavelength division multiplexer; EDF: erbium-doped fiber; PC: polarization controller; PD-ISO: polarization-dependent isolator; DCF: dispersion compensation fiber; OC: optical coupler; SMF: single-mode fiber; EDFA: Erbium-doped fiber amplifier; HNLF: high nonlinear fiber
图 6 束缚态孤子的超连续谱产生耗散孤子工作图。(a) 光谱图;(b) 自相关;(c)和(d)射频谱;(e) 位于第三窗口的超连续谱
Figure 6. Working diagram of dissipative generated by the supercontinuum of bound state soliton. (a) Optical spectrum; (b) Autocorrelation trace; (c), (d) Radio-frequency spectrum; (e) Supercontinuum spectrum located in the third window
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[1] Zhang Z X, Xu Z W, Zhang L. Tunable and switchable dual-wavelength dissipative soliton generation in an all-normal-dispersion Yb-doped fiber laser with birefringence fiber filter [J]. Opt Express, 2012, 20: 26736-26742. [2] Pan Wei, Jin Liang, Wang Jiazhu, et al. All-normal-dispersion dissipative soliton fiber laser using an offset-splicing graded-index-multimode-fiber-based saturable absorber [J]. Appl Opt, 2021, 60: 923-928. [3] Aghayari E, Ghaleh K J. High-power supercontinuum generation by noise-like pulse amplification in Yb-doped fiber amplifier operating in a nonlinear regime [J]. Appl Opt, 2019, 58: 4020-4024. [4] 于峰, 孙畅, 高静, 匡鸿深, 张晶, 高鹏坤, 葛廷武, 王智勇. 全光纤结构超短脉冲超连续谱的产生及其特性研究[J]. 红外与激光工程, 2014, 43(11): 3555-3558. doi: 10.3969/j.issn.1007-2276.2014.11.009 Yu Feng, Sun Chang, Gao Jing, et al. All-fiber ultra-short super-continuum generation and characters [J]. Infrared and Laser Engineering, 2014, 43(11): 3555-3558. (in Chinese) doi: 10.3969/j.issn.1007-2276.2014.11.009 [5] 胡孔云, 肖光宗, 张莹, 陈鑫麟, 谢元平. 采用超连续谱激光的双光束光纤光阱实验[J]. 中国光学, 2017, 10(3): 370-375. doi: 10.3788/co.20171003.0370 Hu Kongyun, Xiao Guangzong, Zhang Ying, et al. Double-beam fiber optical trap experiments based on supercontinuum laser [J]. Chinese Optics, 2017, 10(3): 370-375. (in Chinese) doi: 10.3788/co.20171003.0370 [6] 王瀚霄, 李雷, 赵鹭明. 色散管理光纤激光器中束缚态孤子动力学演化特性[J]. 红外与激光工程, 2018, 47(8): 803008-0803008(5). doi: 10.3788/IRLA201847.0803008 Wang Hanxiao, Li Lei, Zhao Luming. Dynamics evolution characteristics of bound state solitons in dispersion-managed fiber laser [J]. Infrared and Laser Engineering, 2018, 47(8): 0803008. (in Chinese) doi: 10.3788/IRLA201847.0803008 [7] Hernández-Escobarl E, Bello-Jiménez1 M , Pottiez O, et al. Flat supercontinuum generation pumped by amplified noise-like pulses from a figure-eight erbium-doped fiber laser [J]. Laser Physics Letters, 2017, 14(10): 105104. doi: 10.1088/1612-202x/aa829c [8] 高静. 可调谐锁模光纤激光器泵浦的超连续谱光源[J]. 光学精密工程, 2018, 26(1): 25-30. doi: 10.3788/OPE.20182601.0025 Gao Jing. Tunable mode-locked fiber laser pumped super-continuum source [J]. Optics and Prescion Engineering, 2018, 26(1): 25-30. (in Chinese) doi: 10.3788/OPE.20182601.0025 [9] 王凱杰, 王航, 杜团结, 等. 腔内滤波带宽对正色散束缚态孤子形成的影响[J]. 中国激光, 2019, 46(8): 0806004. Wang Kaijie, Wang Hang, Du Tuanjie, et al. Effect of intracavity filtering bandwidth on bound-state soliton generation in normal dispersion regime [J]. Chinese Journal of Lasers, 2019, 46(8): 0806004. (in Chinese) [10] 邹宝英, 戴佳男, 洪伟毅. 光纤中飞秒双脉冲束缚态产生超连续谱的研究[J]. 中国激光, 2020, 47(7): 0706003. doi: 10.3788/CJL202047.0706003 Zou Baoying, Dai Jianan, Hong Weiyi. Study on supercontinuum generation of femtosecond double pulses bound-state in optical fiber [J]. Chinese Journal of Lasers, 2020, 47(7): 0706003. (in Chinese) doi: 10.3788/CJL202047.0706003 [11] 纪海莹, 王天枢, 熊浩, 等. 位于第三近红外窗口的平坦光纤超连续谱产生[J]. 应用光学, 2021, 42(3): 565-570. doi: 10.5768/JAO202142.0308002 Ji Haiying, Wang Tianshu, Xiong Hao, et al. Flat fiber super-continuum spectrum generation in the third near-infrared window [J]. Journal of Applied Optics, 2021, 42(3): 565-570. (in Chinese) doi: 10.5768/JAO202142.0308002