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建立BOSA发射端的耦合模型,即实现SMF与LD的高精度耦合,首先需对光束的模场、束腰半径及数值孔径进行计算和研究。SMF芯径很小,只有8μm~10μm左右,只能传输一种模式的光,其模间色散小,适用于远程通讯,SMF模场高斯分布是旋转对称的,其数学表达式如下式所示[14]:
$ \psi \left( r \right) = A\exp \left[ { - {{\left( {\frac{r}{{{w_0}}}} \right)}^2}} \right] $
(1) 式中,A代表振幅,r代表光纤的径向长度,w0代表单模光纤的模场半径。
采用国产G652.B单模光纤(中心波长为1310nm, 模场直径为9μm~10μm)为研究对象,其束腰半径定义为4.6μm,数值孔径为0.14。模场仿真分布如图 3所示,基本为标准的圆形。
BOSA发射端内部结构如图 4所示。通过设置光源类型可以模拟单模激光器光束,其光束分布可以近似看作高斯分布[15],LD发出的光束经透镜汇聚后与SMF进行耦合,耦合前经透镜整形后在光纤端面形成的光斑如图 5所示。选用的激光器类型为(InGa)(AsP)/InP双异质结小纵横比激光器,其具体参量如下:标准功率P0=6mW,加载电流30mA,工作中心波长λ=1310nm,发散角θ//=25°, θ⊥=38.27°。激光器的数值孔径由以下两式求出[16], 分别为:dNA, //=0.363,dNA, ⊥=0.537。
$ {d_{NA, //}} = {\rm{sin}}(0.85 \times {\theta _{//}}) $
(2) $ {d_{NA, \bot }} = {\rm{sin}}(0.85 \times {\theta _ \bot }) $
(3) 高斯函数中,发散角与光束强度为1/e2时的半角的比值为0.84932,通常取0.85[14]。dNA, //表示水平方向的数值孔径,dNA, ⊥表示垂直方向的数值孔径。得出激光器光束的束腰半径[17]:w//=1.911μm,w⊥=3.6755μm。
建立仿真模型后,设置仿真工艺参量,如表 1所示。
Table 1. The value of specific parameters
dNA, // dNA, ⊥ w///μm w⊥/μm r/μm SMF 0.14 0.14 4.6 4.6 — LD 0.363 0.537 1.911 3.6755 — lens — — — — 2000 -
在光学仿真软件中,首先设置LD、透镜以及SMF的参量,通过物理光线轨迹追踪的方法,调整SMF与LD的相对位置和角度位置,使LD与SMF的模场的达到最佳匹配,从而获得最佳耦合效率。仿真耦合效率利用下式进行计算:
$ \begin{array}{*{20}{c}} {T = }\\ {\frac{{{{\left| {\smallint \smallint {F_{\rm{r}}}\left( {x,y} \right)W\prime \left( {x,y} \right){\rm{d\mathit{x}d\mathit{y}}}} \right|}^2}}}{{\smallint \smallint {F_{\rm{r}}}\left( {x,y} \right){F_{\rm{r}}}\left( {x,y} \right){\rm{d\mathit{x}d\mathit{y}}}\smallint \smallint W\left( {x,y} \right)W\prime \left( {x,y} \right){\rm{d\mathit{x}d\mathit{y}}}}}} \end{array} $
(4) 式中, Fr(x, y)是描述接收光纤复振幅的函数,W(x, y)是描述耦合到光纤中的光束的复振幅的函数,上标′表示复共轭。当光束模式的幅度和相位在所有点处完全匹配光纤模式时,实现最大接收器效率T=1.0;模式形状或相位的任何偏差都会对T的值产生较大影响,使其减小到小于1.0。
在SMF与LD的耦合过程中,忽略光的吸收以及散射等其它情况,经过透镜汇聚的光斑模场与SMF的模场匹配程度越高,则耦合效率越大[18],选用小纵横比的半导体激光器其模场分布更加接近于圆形,在经过球透镜聚焦后,其光斑模场与光纤模场的匹配程度更高,有利于总的耦合效率的提高。
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BOSA激光器端与光纤的耦合精度达到0.1μm量级,因此在实验平台搭建过程中,需要选取高精密的运动平台来实现LD和SMF的相对运动,并结合全局最优搜索算法,才能达到最大的耦合效率。目前国内生产厂家合格器件通常选择在最大耦合效率处波动3%~5%为可接受范围,结合仿真结果,x, y运动方向选用日本骏河生产的型号为KYG06020-C的运动平台,该平台的重复定位精度为0.1μm,z运动方向选用型号为KYL06050-N1-C运动平台,重复定位精度为0.5μm;x′, y′运动方向(表示绕x, y旋转)的平台选用型号为KAWO6100-LA,旋转中心为100mm;可以满足本次激光器与光纤耦合试验的要求。运用实验室自行研发的LD自动耦合系统可实现LD和SMF的自动耦合对准,其基本原理为:上夹具夹持SMF保持竖直,LD插入其管座并且放入下夹具中夹紧,z轴运动平台保证光纤与LD的纵向距离,x, y运动平台保证SMF与LD的横向距离,x′, y′运动平台保证LD分别绕x, y轴旋转,将激光二极管插座和光纤尾端分别通过导线和探头连入光功率计即可对耦合功率的变化情况进行实时监测。耦合平台实物图如图 6所示。
小纵横比光电器件发射端耦合工艺研究及优化
Research and optimization of coupling of small aspect ratio optoelectronic devices
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摘要: 为了系统研究影响耦合效率的因素,采用仿真和实验的方法建立了半导体激光器与单模光纤的耦合模型,并搭建自动耦合平台,进行了理论分析和实验验证,得到了模型的耦合效率与各个方向位移敏感度的关系以及实际耦合过程中耦合效率与各个方向容忍度的关系。结果表明,耦合效率对水平方向位移最为敏感,其后依次是角度旋转和纵向位移; 仿真与实验最大耦合效率分别为64.29%与51.46%,误差在合理范围之内,结果具有较高可信度。这一结果对实际光电器件封装耦合效率的提高是有帮助的。Abstract: In order to systematically research the factors affecting coupling efficiency, the coupling model of semiconductor laser and single-mode fiber was established and an automatic coupling platform was built by means of simulation and experiment. Theoretical analysis and experimental verification were carried out, and the relationship between coupling efficiency of the model and displacement sensitivity of each direction and the relationship between coupling efficiency and tolerance of each direction in the actual coupling process were obtained. The results show that, coupling efficiency is most sensitive to horizontal displacement, followed by angular rotation and longitudinal displacement. The maximum coupling efficiency of simulation and experiment is 64.29% and 51.46% respectively. The error of simulation and experiment is within a reasonable range, thus the results are highly credible. The results are helpful to improve the packaging coupling efficiency of practical photoelectric devices.
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Key words:
- optical communication /
- tolerability /
- simulation optimization /
- coupling model /
- laser diode /
- coupling efficiency
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Table 1. The value of specific parameters
dNA, // dNA, ⊥ w///μm w⊥/μm r/μm SMF 0.14 0.14 4.6 4.6 — LD 0.363 0.537 1.911 3.6755 — lens — — — — 2000 -
[1] GERD K. Fiber optic communication[M].Beijing:Electronic Industry Press, 2016:71-73(in Chinese). doi: 10.1002/(SICI)1098-2337(1997)23:2<81::AID-AB1>3.0.CO;2-W [2] AMMON Y, POCHI Y. Photonics-modern communication optoelectronics[M]. Beijing:Electronic Industry Press, 2009:105-108(in Chinese). [3] LU Sh Q, ZHEN Y. Comparative investigation of spherical lensed fiber and cylindrical lensed fiber for coupling to laser diode[J]. Journal of Central South University, 2014, 45(1):72-76(in Chinese). [4] JIANG J H, LI Y Q, LV H Zh, et al. Coupling structure of truncated wedge-shaped optical microlens based on DFB laser[J]. Laser Technology, 2019, 43(5):655-659 (in Chinese). [5] WANG W L, WANG J, XU L W, et al. Tunable fiber lasers based on semiconductor saturable absorber mirrors[J]. Laser Technology, 2019, 43(5):672-675(in Chinese). [6] WANG H L, ZHANG D Y. The design for coupling system of semiconductor laser and single mode fiber based on ZEMAX[J]. Acta Photonica Sinica, 2011, 40(s1):82-84(in Chinese). [7] YU J H, GUO L H, WU H L, et al. High brightness laser-diode device emitting 500W from a 200μm/0.22nm fiber [J]. Optics & Laser Technology, 2016, 80(s1):92-97. [8] SAMI D A. Single-mode fiber-to-single-mode fiber coupling efficiency and tolerance analysis:Comparative study for ball, conic and grin rod lens coupling schemes using Zemax Huygen's integration and physical optics calculations[J]. Optik, 2015, 126(30):5923-5927. [9] LAI L P, WANG W F, ZHAUNG Q R. Design of LED Fresnel lens fiber bundle coupler[J]. Laser & Optoelectronics Progress, 2018, 55(2):022201(in Chinese). [10] NIE G, LI B H. Efficient coupling of semiconductor lasers to single-mode optical fibers[J]. Optical Communication Technology, 1996, 20(2):161-165(in Chinese). [11] CHEN S L, JEN M T, CHEN K S, et al. The design and application of an automatic optical inspection system for the advanced fiber coupler assembly manufacturing process[J]. International Journal of Precision Engineering and Manufacturing, 2014, 15(9):1847-1854. doi: 10.1007/s12541-014-0538-z [12] PARASKEVI C D. Coupling characteristics of laser diodes to high numerical aperture thermally expanded core fibers[J]. Materials in Electronics, 2009, 20(1):59-62. [13] NING Ch Ch, CHEN T L. Research on fiber coupling technology of high power semiconductor laser[J]. Lasers & Infrared, 2007, 37(10):1041-1043(in Chinese). [14] LIU W T, LIU J Y, SHEN Q N. Integrated modeling and filtering of fiber optic gyroscope's random errors[J]. Opto-Electronic Engineering, 2018, 45(10):180082(in Chinese). [15] HUANG Sh H, LI Y J. Progress and prospect of novel specialty fibers for fiber optic sensing[J]. Opto-Electronic Engineering, 2018, 45(9):170684(in Chinese). [16] LIU L N, GAO X. Design of fiber coupling module based on multi-wavelength beam combining technology[J]. Journal of Changchun University of Science and Technology, 2018, 41(1):5-7. [17] MIAO P P, ZHU Y Q, WANG J, et al. Simulation and experimental study of drawing process of fused fiber couper[J]. Acta Photonica Sinica, 2015, 44(9):0923003 (in Chinese). doi: 10.3788/gzxb20154409.0923003 [18] WANG X. Optical fiber coupling technology for semiconductor laser diodes[J]. Electro-Optic Technology Application, 2010, 25(3):26-32(in Chinese). [19] TOYOSHIMA M. Maximum fiber coupling efficiency and optimum beam size in the presence of random angular jitter for free-space laser systems and their applications[J]. Journal of the Optical Society of America, 2006, A23(9):2246-2250. [20] LIU W, SHI W X, YAO K N, et al. Fiber coupling efficiency analysis of free space optical communication systems with holographic modal wave-front sensor[J]. Optics and Laser Technology, 2014, 60:116-123. doi: 10.1016/j.optlastec.2014.01.013 [21] SHEN H. Study of key technology of automatic packaging for butterfly laser diode module[D]. Harbin: Harbin University of Engineering, 2010: 17-19(in Chinese). [22] YU H Y. Study on high efficiency coupling of semiconductor laser and fiber[D]. Beijing: Beijing University of Technology, 2006: 23-25(in Chinese).